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Mechanical vibration was utilized to enhance the mechanical properties of the WAAM 2319 aluminum alloy and address issues related to coarse grains and porosity in this paper. The research aims to investigate the impact of varying vibration accelerations on the microstructure and mechanical properties of the specimens. The mechanism of solutes transfer caused by vibration has been described in this paper, which significantly improved elongation. The dendrites during growth were broken by vibration, which led to microstructure refinement. The solutes located in the interstices of the dendrites were transferred to the liquid phase by vibration, reducing the concentration of solutes in the interstices of the dendrites. The continuous coarse precipitation phase becomes intermittent and fine; resulting in increased matrix plasticity. With the increase of vibration acceleration, the elongation was significantly enhanced. The longitudinal elongation was enhanced more significantly because of the alternating distribution of INZ and ITZ, with longitudinal elongation showing a 29.3% increase and transverse elongation a 52.5% increase, while the UTS and YS was not changed significantly in the presence of multiple factors. • Mechanical vibration increases the elongation without affecting the UTS and YS. • Mechanical vibration applies reciprocating force to the dendrite, causing the fracture of the dendrite and the refinement of the grain. • Mechanical vibration induces solutes located in the dendrite interstices toliquid phase, reducing the solute concentration in the INZ. • Intermittent precipitation phases and fewer intragranular precipitation phasesin the INZ lead to increased elongation. [ABSTRACT FROM AUTHOR]

To improve the performance of probeless friction stir spot welded (P-FSSW) joints, a fast electric pulse treatment (EPT) method was proposed firstly, and the microstructure evolution and mechanical properties of the joints after EPT was investigated in this study. Results show that the tensile and shear strength decreases slightly by about 10%, but the joint plasticity increases by about 23.7% after three electric pulse treatments. As the number of electric pulse treatments increases, the joint lap interface undergoes dynamic recrystallization and atomic diffusion, so microcracks are closed and interface bonding is improved. However, due to the different recrystallization degree in different characteristic zones of welded joints after electric pulse treatment, the plastic deformation gradient in the transition zone of welded joints increases. The incongruity of plastic deformation compatibility in the transition region would cause stress concentration. Therefore, the interface on both sides of the joint is favorable for crack propagation, which makes the shear fracture mode change into the plug fracture mode. • In this paper, AA2198-T8 probeless friction stir spot welded joints are used as a research object. • A fast EPT method is proposed firstly to improve the spot welded joint performance. • This paper elucidates the macroscopic interfacial morphological changes and microstructural evolution before and after the EPT. • This paper describes the microscopic mechanism of fracture morphology transformation of joints under the EPT. [ABSTRACT FROM AUTHOR]

In this paper, the effects of cooling rate after casting and stirring process on γ' phase, γ / γ' eutectic phase, MC type carbide morphology and grain structure of K447A alloy turbine blisk were studied systematically. The quantitative relationships between cooling rate, stirring process and γ' phase, γ / γ' eutectic phase, MC type carbide and grain size were described in detail. The results show that with the increase of cooling rate, the distribution region of γ / γ 'eutectic phase from the center of blisk to blade decreases gradually and MC type carbide changes from skeleton to block due to the shorter formation time of eutectic and carbide in the later stage of solidification. Besides, with the decrease of cooling rate, the size of γ' phase increases under the influence of interfacial strain energy and elastic strain energy, and the morphology of γ' phase gradually evolves from cuboid to concave cuboid, octet and dendritic. At the same time, due to the synergistic effect of cooling rate and stirring process, the blade part is columnar grain and the central part of the blisk is equiaxed grains. In this paper, the evolution mechanism of γ 'phase, γ / γ' eutectic phase, MC type carbide and grain size with cooling rate and stirring process was proposed. The research results would play a key supporting role in precise control during solidification for microstructures and properties of dual-performance superalloy blisk. [Display omitted] • The precipitation phase and grain are affected by the cooling rate and stirring process. • The effects of cooling rate after casting and stirring process on γ' phase, γ / γ' eutectic phase, MC type carbide morphology and grain structure of K447A alloy turbine blisk were studied systematically. • The blade part is columnar grain and the central part of the blisk is equiaxed grains. • The evolution mechanism of γ 'phase, γ / γ' eutectic phase, MC type carbide and grain size with cooling rate and stirring process was proposed. [ABSTRACT FROM AUTHOR]

In this paper, continuous SiC fiber-reinforced Ti60 (SiC f /Ti60) composites were fabricated by preparing SiC f /Ti60 precursor wires from matrix-coated fibers and hot isostatic pressing (HIP) consolidation. The microstructures of the precursor wires and composites were investigated using XRD, SEM, EPMA, EBSD, and TEM, which led to the microstructure evolution of the composites. The conclusions of this study are as follows. 1. A reaction layer (RL) with a thickness of approximately 0.1 μm already exists at the interface of the precursor wires during the preparation. The HIP process accelerates the diffusion of the carbon coating with the Ti60 matrix, resulting in an increase in the thickness of the RL to approximately 0.5 μm. This layer is primarily composed of fine-grained TiC layer || discontinuous silicides || coarse-grained TiC layer. 2. The matrix of SiC f /Ti60 precursor wires contains α-Ti (∼ 1.9 μm), S2 (∼ 50 nm), and β-Ti (∼ 50 nm), in the matrix, β-Ti is precipitated from α-Ti, and HIP makes α-Ti, S2, and β-Ti grow to ∼ 2.4 μm, ∼ 200 nm, and ∼ 300 nm, respectively. 3. There are 〈0001〉//axial direction (AD) and 〈10−10〉//AD fiber textures in the matrix of the precursor wires, and HIP makes the matrix undergo a plastic deformation dominated by dislocation slip, and the pole density of the two kinds of textures are both increased. • Detailed study of precursor wires to SiC f /Ti60 composites interface and matrix microstructure evolution during hot isostatic pressing. • Sample preparation and characterization using advanced techniques such as FIB, EBSD, TKD, and TEM, etc. • During hot isostatic pressing, the reaction layer is transformed from fine-grained TiC to fine-grained TiC layer || discontinuous silicides||coarse-grained TiC layer. • During hot isostatic pressing, β-Ti and S2 silicides are precipitated from the Ti60 matrix, and the pole density of α-Ti changes. [ABSTRACT FROM AUTHOR]

In this paper, high-temperature impact fatigue (HTIF) was carried out on a Co-based surface layer cladded by TIG welding, and cracks emerged at 400-cycle condition. The reasons for cracking were investigated from three aspects: microstructure, stress distribution, and crystal orientation. Crack generation was induced by high stress distribution in eutectic carbides at grain boundaries and the great disparity in orientations between grains on two sides of the crack path. The microstructural advantage for cracking behavior played a key role in emergence of cracks, which was verified by the investigation and comparison of three distances from the weld interface. Moreover, the interface microstructure of Co-based layer and FB2 substrate was characterized by transmission electron microscopy, and the phase composition of the weld interface comprised Fe Co and M 23 C 6. The results presented that the addition of Ni-based transition layer caused the acquisition of the crack-free surface layer after HTIF. Finally, microhardness test was conducted on samples with and without a transition layer. The hardness of Co-based surface layer without the transition layer was mainly affected by the transformation of carbides, dilution of Fe, and work hardening during HTIF. The hardness of Co-based surface layer with the transition layer showed minimal change during HTIF, and this finding was attributed to the slight variation in the microstructure. • The microstructural evolution of Stellite 6 layer was revealed. • Mechanisms of cracks generation during HTIF were illustrated. • Crack problem was solved by the addition of Inconel 625 transition layer. • The phase composition of interfacial layer was determined. • Reasons for hardness variation during HTIF was explained. [ABSTRACT FROM AUTHOR]

This paper introduced spherical and non-spherical TiC ceramic particles into 4Cr5MoSiV1 steel through laser cladding technology, employing various TiC volume fractions to produce ceramic matrix composites. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to examine TiC-reinforced composites' microstructure. The results reveal that the two ceramic matrix composites with different TiC geometries have the same phases: martensite and TiC. Because of the superior fluidity of the spherical TiC particles in the molten pool, which is distributed more evenly in the composite layer than the non-spherical TiC particles. Additionally, spherical TiC exhibits a lower dissolution rate in the laser-molten pool and has a noticeable grain refinement for the microstructure of 4Cr5MoSiV1 steel, attributed to the increase in the proportion of high-angle grain boundaries. Therefore, under the action of grain refinement, the hardness of the composite material increases. • The microstructure of the composite coatings reinforced with TiC particles of different geometry were studied in detail. • The spherical TiC-reinforced composite layer displays a more even surface and sufficient compactness and ductility. • Spherical TiC particles have a more significant grain refinement effect on the matrix, contributing the higher strength and hardness of composites. [ABSTRACT FROM AUTHOR]

laser shock forming (LSF) is a high strain rate forming process, which can significantly improve the formability of materials. Nevertheless, there is a lack of research on the microstructure evolution and improving mechanical properties of parts deformed by LSF. In this paper, pure copper sheet are formed into flat bottom parts under one- and two-shot LSF. The deformation topography, surface morphology and thickness distribution of the deformed parts are tested. The surface micro morphology of the mould can be additionally printed in the formed parts, and the sheet forming accuracy improved continuously and lower thickness thinning with the increase of the shock number. Transmission electron microscopy (TEM) showed that the microstructure on the surface of the formed specimens was composed of nanocrystalline arrays elongated in the direction of the transverse flow of the workpiece material. The dislocation density decreased and the twinned structures gradually disappeared with an increasing depth from the treated surface. More laser shocking can refine the metal material grain and improve material mechanical property of the formed part further. Eventually, the underlying improvement mechanism of mechanical properties induced by LSF-induced microstructure evolution on pure copper was systematically revealed. • The effect of laser shock number on the morphology, thickness and microhardness of the copper was investigated. • The microstructure evolution of sheet shocked by laser with shots was characterized and the evolution model was proposed. • The strengthening mechanism of the copper part formed by two-shot laser shock was analyzed. [ABSTRACT FROM AUTHOR]

Cu/Al composites have the excellent properties of both Cu and Al, and have the properties of light weight and high conductivity, so they have been widely concerned. In this paper, 5-mm-thick Cu/Al composites prepared by the cast-rolling process are used as experimental materials. To reveal the strengthening and toughening mechanisms of the Cu/Al composites, the interfacial structure, micro-morphology, stress-strain condition, and GND distribution of Cu/Al composites before and after deformation were characterized utilizing TEM, TKD, and EBSD. The results show that the submicron intermetallic compounds Al 2 Cu and Al 4 Cu 9 are formed from the casting-rolling Cu/Al composites. After 15% tensile deformation, many gaps occurred in the interface layer, but at the gaps, there was no crack spreading to the Cu and Al layers. Meanwhile, the deformation in different directions occurs in the Cu grains near the interface, forming a dislocation wall, and the entanglement of the dislocation occurs in the Cu layer near the interface, which contributes to the improvement of tensile strength. The Al layer near the interface layer produces kink bands, which helps to improve the ductility of the composites. Besides, due to the action of the hard intermetallic compound layer, with the increase in tensile deformation, a large number of GND are gradually accumulated in the Cu and Al layers near the interface, resulting in remote back stress, which makes the softer Cu and Al layers obtain higher strength. At the same time, the back stress caused by GND will induce strain hardening, which helps to maintain ductility, so that Cu/Al composites have higher plastic deformation ability while improving mechanical properties. • The effect of the interfacial layer on the strengthening and toughening of Cu/Al composites during deformation was studied. • The Cu/Al composites could induce dislocation pile-up in the Cu side, after tensile deformation. • The deformation in different directions is generated in the Cu layer grain and the dislocation wall is formed. • GND accumulates gradually at the interface, with the progress of tensile deformation. [ABSTRACT FROM AUTHOR]

TiAl-based alloys are known for their exceptional high-temperature properties but suffer from low hot workability. The emergence of additive manufacturing (AM) technology significantly decreases the workability requirement, while the microstructure heterogeneities in AMed TiAl are troublesome. This paper explores the hot deformation behavior and microstructure evolution of a layered heterogeneous microstructure TiAl alloy prepared by selective electron beam melting. The Arrhenius constitutive model with strain compensation was established, and hot processing maps were constructed. The microstructure showed that at the initial stage of deformation, a large number of dislocation slips occur preferentially in the soft coarse-grained layers. With the increase of strain, dislocation accumulation in heterogeneous interfaces, and dynamic recrystallization (DRX) occurs. Eventually, the coarse-grained region is constantly occupied by fine DRX grains. A high density of deformation twins at high strain rates further promotes the formation of tiny DRX grains. When the hot compression temperature reaches 1200 °C, the initial alternative fine-grained and coarse-grained hetero-structure transforms into duplex (DP) and near-lamellar (NL) microstructure, and microstructure heterogeneity is eliminated. The results enhance understanding of the hot deformation behavior of heterogeneous microstructure TiAl alloys. • Constitutive equation and processing map of heterogeneous TiAl alloy are established. • Thermal plastic deformation promoted the elimination of microstructure heterogeneity. • Coarse-grained and fine-grained layer exhibit different deformation mechanisms. [ABSTRACT FROM AUTHOR]

WAAM-LDM hybrid additive manufacturing can achieve high efficiency and high precision preparation of Ti-6Al-4V alloy. However, the inhomogeneous microstructure of WAAM-LDMed Ti-6Al-4V samples results in overall poor tensile properties. Therefore, this paper attempts to ameliorate the inhomogeneous microstructure of the hybrid sample by STA, and simultaneously improve the strength and plasticity. The results showed that the WAAM zone and HAZ were composed of α colonies, the RZ and LDM zone were distributed with fine basketweave structure of the AD samples. With the introduction of STA, the microstructure of each zone of the hybrid sample changes and transformed into a 'dual-phase' structure with bi-modal α p and β t. With the increase of aging temperature, the volume fraction of β t increased and the volume fraction of α p phase decreased, accompanied by the formation of bulk α phase and the coarsening of α s phase. It is worth noting that the strength of WAAM zone was obviously improved by STA, and the fracture positions of the STA samples were randomly distributed in the WAAM and LDM zones. Additionally, with the aging temperature increased, the strength of WAAM-LDMed samples was weakened, and the ductility was improved because the coarsened bulk α played a role of coordinating deformation in the tensile process. The excellent strength and ductility (UTS = 976 MPa, YS = 876 MPa, EL = 13.57%) of WAAM-LDMed samples was achieved at aging temperature 750 °C, compared with the AD samples (UTS = 860 MPa, YS = 767 MPa, EL = 12.5%). Finally, by optimizing the STA (940 °C/1 h/WQ + 750 °C/4 h/AC), the amelioration of the microstructure and the improvement of the strength-ductility of the hybrid samples were achieved. • The microstructure of WAAM-LDM sample is homogenized into α p + β t by STA. • STA treatment makes the strength of WAAM zone comparable to that of LDM zone. • The WAAM-LDM sample prepared by STA obtain excellent strength and ductility. [ABSTRACT FROM AUTHOR]

This paper proposes a new stretch bending approach for aluminum alloy extrusion profiles based on a novel pre-hardening forming (PHF) process. Tensile tests were carried out to examine the flow behavior and mechanical responses of a 7A09 extrusion profile in PHF process. Microstructure evolution was investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and small angle X-ray scattering (SAXS). It is interesting to find that the yield stress at 200 °C was higher than that at 185 °C. The quantitative analysis revealed that the higher volume fraction of precipitates (200 °C) played a greater role than the refinement of precipitate sizes (185 °C) in precipitation strengthening mechanism, thereby causing an enhanced hardening effect. This phenomenon indicated that there was a preferred temperature zone for the precipitation behavior in PHF process, and it also explained the lower yield stress at 185 °C than that at 200 °C. Additionally, similar results were also observed in strength of the warm-deformed alloys. The optimal strength (σ / σ 0.2 =589/517 MPa) can be achieved at 200 °C without subsequent heat treatment, which exceeded the typical strength of 7A09-T6 extrusion. The primary strengthening mechanisms in PHF process were strain hardening and precipitation strengthening, and the warm forming procedure caused a hardening effect, rather than a softening impact as in traditional warm/hot forming procedures. [Display omitted] • The yield stress and warm-deformed strength initially increased and then dropped with the increasing forming temperature. • An optimal warm-deformed strength superior to typical 7A09-T6 was obtained at 200 °C without subsequent heat treatment. • The higher volume fraction played a greater role than refinement of precipitate sizes in precipitation strengthening. • The warm forming procedure caused a hardening effect, rather than a softening effect during traditional warm/hot forming. [ABSTRACT FROM AUTHOR]

In this paper, uniaxial hot compression tests of β-quenched Zr-1Nb-1Sn-0.1Fe alloy under a strain of 0.91 were conducted at various temperatures ranging from 600 °C to 750 °C. The microstructure, texture evolution, deformation mode and dynamic recrystallization (DRX) mechanism were investigated using electron backscatter diffraction (EBSD). The results of the In-Grain Misorientation Axis (IGMA) method showed that the prismatic was the dominant deformation mode when the temperature was 600 °C. The prismatic and pyramidal were the dominant deformation modes during hot compression between 650 and 750 °C. To study the mechanism of DRX, the geometrically necessary dislocation (GND) density, grain orientation spread (GOS) and grain reference orientation deviation (GROD) maps were calculated. The results showed that both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during hot compression. When deformed at 600 °C, the recrystallization mechanism was mainly DDRX, while it was mainly CDRX above 600 °C. The change in the DRX mechanism can be attributed to the activation fraction of different slip systems and the resulting development of misorientation. • The effects of the temperatures on microstructure evolution and deformation mode were analyzed. • Different DRX mechanisms and their effects on texture are discussed in detail. • The DRX mechanism changed due to the activation of different slip systems and the resulting development of misorientation. [ABSTRACT FROM AUTHOR]

One effective method for fabricating liquid rocket engine thrust chambers involves using laser directed energy deposition (LDED) to produce Cu/Ni bimetals by depositing Ni-based superalloys onto a High Strength and High Conductivity (HSHC) copper alloy. However, it is difficult to fabricate strengthening layer to the surface of HSHC Cu alloy due to its extremely high thermal conductivity. This paper investigates the influence of states of the HSHC CuCuCr0.8 substrate e.g., as-built of LPBF, rolled and annealed, and direct age after LPBF at 480 °C for 4 h, on the formability of In718 single track by LDED. The results indicate that the thermal conductivity is significantly influenced by the state of the HSHC CuCuCr0.8 substrate. At room temperature and 300 °C, the order of the thermal conductivity from low to high is as-built of LPBF, rolled and annealed, and direct age after LPBF at 480 °C for 4 h, while at 500 °C, the as-built of LPBF substrate has the lowest thermal conductivity, while the rolled and annealed substrate has the largest thermal conductivity. Thermal conductivity has a significant effect on the formability of LDED. The LPBF-ed substrate has the best formability, with a minimum Ra value of 9.72 ± 0.12 μm, a maximum deposition depth of 193.00 ± 4.32 μm, and a minimum grain size of 5.2 ± 2.6 μm because of its smallest thermal conductivity. These findings demonstrate that using an as-built LPBF-ed substrate can improve the LDED formability of the In718 single track compared with the other two substrates. This paper presents a new approach for LDED on alloy surfaces with high thermal conductivity. [Display omitted] • In718 single tracks were fabricated on CuCr0.8 substrates in three different states of LPBF-ed, RA, and LPBF-DA by LDED. • The morphology, geometric characteristics, microstructure, and the element distribution of LDED In718 single track on different CuCr0.8 substrate states were mainly investigated. Meanwhile, the influence mechanism of the substrate state on the molten pool was discussed. • The LPBF-ed substrate reduces the influence of CuCr0.8 thermal conductivity on LDED and improves the LDED formability of the In718 single track. • This paper presents a novel approach to mitigate the challenges for LDED on surfaces associated with high thermal conductivity substrate. [ABSTRACT FROM AUTHOR]

This paper proposes a method involving low-temperature SPS for preparing ZrTi/GH4169 alloy blanks. The addition of GH4169 alloy significantly reduces the sintering temperature of ZrTi alloy. The Zr30-Ti62-Ni8 ratio was used to obtain equiaxed grains of ZrTi alloy through sintering at 1000 °C, and billets with excellent strength and plasticity under high-temperature deformation were obtained by sintering at 1100 °C. In the sintering temperature range from 1000 °C to 1200 °C, while both α-phase and Zr 2 (Fe,Ni) phase size increased with the sintering temperature, the amount of increase was different. Specifically, the α-phase in the alloy blanks sintered at 1100 °C was fine and reticulated, whereas that sintered at 1200 °C developed into a slatted structure. Strengthening mechanism analysis showed that the strength and plasticity of the 1100 °C sintered blanks were excellent, especially because of the effect of the reticulated α-phase and Zr 2 (Fe,Ni) phase. Furthermore, the high density of the phase interface hindered dislocation movement and inhibited stress concentration. In particular, the Zr 2 (Fe,Ni) phase distributed along the β-phase grain boundaries and around the α-phase in the grain acted as a nail, and it could inhibit grain growth and increase resistance to dislocation motion. The weaker β-phase weave and lower defect density also contributed to the superior material properties of the 1100 °C sintered blanks. • This paper proposes a method involving low-temperature SPS for preparing ZrTi/GH4169 alloy blanks. • Zr30-Ti62-Ni8 blanks with excellent strength and plasticity under high temperature deformation were obtained by sintering at 1000°C–1200 °C. • 4) The weaker β-phase weave and lower defect density were also responsible for the superior material properties in the case of sintering at 1100 °C. [ABSTRACT FROM AUTHOR]

To achieve superior damage tolerance and fatigue properties, it is desirable for the microstructure of Ti-6Al-4V ELI (Extra Low Interstitial) titanium alloy to consist of equiaxed grains with a homogeneous lamellar structure. However, traditional forging and single additive manufacturing techniques require extreme processes such as quasi β heat treatment and hot isostatic pressing. In this paper, a hybrid directed energy deposition method that integrates in-situ rolling with simple annealing is proposed to simultaneously achieve these microstructures. The results indicate that the initial microstructures produced by hybrid directed energy deposition consist of fine equiaxed prior-β grains, inconspicuous interpass bright bands, randomly oriented lamellar structure and numerous small substructures at the TEM scale. Due to the plastic deformation caused by in-situ rolling, the primary β grains underwent significant refinement with a reduction in grain diameter from over 2000 μm to 113.8 μm. Besides, the unique microstructures and thickness of α laths are influenced by coarsening and dissolution mechanisms that are controlled by diffusion during phase transformation. Furthermore, a uniform microstructure without bright bands and excellent comprehensive properties can be achieved through heating at 880 °C for 2 h and natural cooling. These findings validate that hybrid directed energy deposition coupled with simple annealing present a novel and cost-effective approach for the direct manufacturing of uniform titanium alloy forgings. • Microstructure evolution in DED with in-situ rolling and annealing was studied in detail. • Uniform microstructure realized with fine equiaxed grains. • Driving forces and mechanisms of α lamellae evolution were summarized. • Optimal comprehensive properties were analyzed. [ABSTRACT FROM AUTHOR]

In this paper, the influence of electrical pulse treatment (EPT) on the evolution of microstructure and texture and the resultant magnetic and mechanical properties of a cold rolled Nb-alloyed non-oriented silicon steel (NOSS) was investigated carefully. When the temperature rise caused by Joule heat is higher than the starting temperature of dissolution, more precipitates are dissolved in the EPT specimens than those subjected to the conventional heat treatment (CHT) at the same temperature, and higher current density resulted in Laves precipitates dissolved at lower temperature. The permeability of all the EPT and CHT specimens increase first and then decrease with the increasing temperature, and it reaches the maximum at the temperature for nearly the complete recrystallization. B 50 is higher for the EPT specimen than CHT before the completion of recrystallization due to enhanced recrystallization, but lower than CHT after the completion because the athermal effect of pulsed current promotes the growth of γ-fiber grains, disfavoring the permeability. Moreover, the EPT specimen has the lower iron loss and lower yield strength than the CHT one at the same annealing temperature, because the dissolution of precipitates, recrystallization and grain growth in cold rolled matrix are all enhanced due to the athermal effect of pulsed current. [Display omitted] • Higher current density leads to Laves precipitates in NOSS dissolved at lower temperature. • The maximum B 50 in EPT samples appeared at lower temperature than that of CHT ones. • Athermal effect of pulsed current resulted in the lower iron loss and lower yield strength. [ABSTRACT FROM AUTHOR]

In the paper, the disc sheet of 2024 aluminum alloy was shaped precisely into a flat-bottom cup by two stage laser shocking, and its microstructure evolution was studied by Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) in detail. The investigations show that the grains are elongated and continuously refined by continuous dynamic recrystallization during two stage laser shock sheet forming (TSLSSF). With the increase of strain of metal sheet, the transformation from low-angle grain boundaries and high dislocation densities to high-angle grain boundaries and low dislocation densities occurs, which improves the strength and plasticity of the processed material in comparison with the untreated material. The impact affects significantly the texture evolution process of aluminum alloy sheet under two stage forming. After laser shocking, the textures of the aluminum alloy sheet tend to be stabilized at the β-Fiber and a strong P texture is also formed. Due to the combined effect of grain size and dislocation density, the hardness of the second impact material increases less than that of the first impact. The research provides a reference for the application and development of laser shock forming. • The microstructure evolution of the material after laser shocks was characterized. • The proportion of low-angle grain boundaries first rises and then falls. • The ratio of dislocation density first enhances and then drops after laser shocks. • The textures of the sheet are inclined to be stabilized at β-Fiber and P component. • The hardness increase after the second impact is less than that after the first. [ABSTRACT FROM AUTHOR]

This paper presents the microstructure of quartz fiber reinforced SiO 2 matrix (SiO 2f /SiO 2) wave-transparent composites characterized by X-ray computed tomography (XCT) and the impregnation of silica sol by conducting permeability and pore network model analyses. Results show that in 2.5D woven structural preform silica gel mainly flowed along the extension direction of weft yarns during impregnation, and the permeability rate in this direction reached 368.49μm2. Attributing to the large pore size, large throat radius and good pore connectivity, impregnation of this preform was more uniform, resulting in a small final porosity of the composite (2.32%). Comparatively speaking, in stitched structural preform silica sol flowed primarily between the layers of fiber cloths, achieving a maximum permeability rate of 36.47μm2, but along the direction of stitching fiber yarns permeability rate was only 5.23μm2. Small throat radius and pore size of fiber preform led to poor impregnation effect and a total porosity of 11.85%. Preform structure plays a crucial role in the densification process of SiO 2f /SiO 2 composites prepared by sol-gel method. • Morphology characteristics and phase distribution of two types of SiO 2f /SiO 2 composites were observed. • Permeability and pore characteristics of fiber preforms were discussed. • Preform structure plays a crucial role in the densification process of SiO 2f /SiO 2 composites prepared by sol-gel method. • XCT has significant advantages in exploring the microstructure and anisotropy of fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

In this paper, we designed a new L1 2 nanoparticles-strengthened fcc-structured (Co 2 Ni 2 Cr) 85 Al 7.5 Ti 7.5 MEA. The high-density L1 2 nanoparticles with an average size of ∼57 nm are uniformly distributed in the grain with an average size of ∼37 μm. The volume fraction of L1 2 nanoparticles is up to ∼45%. The L1 2 nanoparticles can be identified as the (Ni,Co,Cr) 3 (Ti,Al) multi-component phase. Compared to the single-phase Co 2 Ni 2 Cr base alloy with a yield strength of ∼208 MPa and an ultimate tensile strength of ∼660 MPa, (Co 2 Ni 2 Cr) 85 Al 7.5 Ti 7.5 MEA possesses a much higher yield strength of ∼1125 MPa and an ultimate tensile strength of ∼1540 MPa while retaining an excellent ductility of ∼38%. The precipitation strengthening by L1 2 nanoparticles takes the largest contribution to the yield strength, and the contribution value is up to ∼712 MPa. The deformation mode is dominated by mechanical twins for Co 2 Ni 2 Cr base alloy and (Co 2 Ni 2 Cr) 85 Al 7.5 Ti 7.5 MEA, and the mechanical twins are more prevalent in the Co 2 Ni 2 Cr base alloy. • A new L1 2 nanoparticles-strengthened (Co 2 Ni 2 Cr) 85 Al 7.5 Ti 7.5 MEA is well designed. • The volume fraction of L1 2 nanoparticles with a mean size of ∼57 nm is up to ∼45%. • (Co 2 Ni 2 Cr) 85 Al 7.5 Ti 7.5 MEA has an excellent property (σ s ∼ 1125 MPa, σ b ∼ 1540 MPa, δ ∼ 38%). • L1 2 nanoparticles precipitation strengthening takes the largest contribution to strength. • The deformation mode is dominated by mechanical twins for (Co 2 Ni 2 Cr) 85 Al 7.5 Ti 7.5 MEA. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effects of In and aging treatment on the microstructure, mechanical properties and electrochemical corrosion behavior of Sn 2Cu solder alloy. It is found that In could refine the β-Sn grains, resulting in an improved microstructure and enhanced microhardness and tensile properties. Moreover, adding In lowered the undercooling of the Sn 2Cu solder alloy, with a maximum reduction of 5.97 °C. The corrosion resistance of the alloy was also dramatically improved by In addition, as evidenced by: (1) a lower corrosion current density compared to the matrix alloy; (2) a smaller surface roughness and pit depth after corrosion; (3) an increased ratio of SnO 2 in the corrosion product layer. On the other hand, aging treatment had an adverse impact on the mechanical properties, but a beneficial influence on corrosion resistance of solder alloy. • In and aging treatment effectively changed the mechanical and electrochemical properties of Sn 2Cu solder alloys. • In significantly increased the ratio of SnO 2 in the corrosion product layer of solder alloys • In dramatically reduced the undercooling and pasty range temperature range of Sn-2Cu solder alloys [ABSTRACT FROM AUTHOR]

In this paper, the NbTa 0.5 TiZr X series refractory high entropy alloys(RHEAs) were processed by selective laser melting (SLM). NbTa 0.5 TiZr X alloy are observed with BCC crystal structures.The effect of Zr content on microstructure and properties of NbTa 0.5 TiZr X alloys was studied, as the Zr content increases, the main defects of NbTa 0.5 TiZr X alloy changed from lack of fusion defects to solidification cracks. Due to the different melting points of alloying elements, the elements with high melting point are enriched in the dendrite and the elements with low melting point are enriched in the inter-dendrite. As the Zr content increases, the number of cellular subgrain increases, and the number of columnar subgrain decreases. The fine equiaxed grain at the boundary of the molten pool and the coarse grain in the molten pool make the grain of the NbTa 0.5 TiZr X alloy with bimodal size distribution. The compressive yield strength increases with the increase of Zr content. Due to the effects of solid solution strengthening, precipitation strengthening and fine crystal strengthening, the alloy has the highest yield strength of 1320 MPa. When Zr content reaches 10 wt%, and the Compressive strain of NbTa 0.5 TiZr X alloy exceeds 75% at room temperature. • We designed and prepared a NbTa 0.5 TiZr X RHEA. • The novel alloy shows high ductility at RT. • compressive strength increased with increasing Zr content. • The NbTa 0.5 TiZrx alloy was fabricated by SLM using elemental mixed powders. [ABSTRACT FROM AUTHOR]

In this paper, a novel Al-Zn-Mg-Cu alloy with Si-Zr-Er addition was prepared by selective laser melting (SLM) technology. Effects of aging temperature and aging time on the microstructure, mechanical properties and corrosion resistance of the alloy were systematically studied. Results show that unique bimodal grain structure is formed in the as-printed and direct aging treated alloys, which is composed of fine equiaxed grains at the molten pool boundary and coarse columnar grains in the molten pool. Mechanical properties of the alloy can be improved by direct aging treatment, and the highest tensile strength reached 465 MPa. The precipitated Mg 2 Si and Al 3 (Er,Zr) with L1 2 structure play an important role in improving the mechanical properties. The precipitates and fraction of high-angle grain boundaries are important to evaluate the corrosion resistance of the investigated alloy. Considering the mechanical properties and corrosion resistance, the optimal aging process of the alloy studied in this paper is 150 °C × 4 h. • A novel Al-Zn-Mg-Cu alloy with Si-Zr-Er addition was prepared by SLM. • Direct aging treatment can improve the alloy's tensile strength to 465 MPa. • Precipitates and fraction of HAGBs are important to evaluate the corrosion resistance. [ABSTRACT FROM AUTHOR]

In this paper, the rolled TiB whisker (TiBw)/Ti65 composites with different rolling reductions were obtained by high temperature (HT) rolling in the β single-phase region. The changes in TiBw, silicide and grain size after rolling deformation were analyzed by microstructure characterization. Based on this, the strengthening mechanism and HT deformation behavior of rolled composites were analyzed in combination with room temperature and HT tensile experiments. The results show that TiBw fractured after rolling deformation, leading to a decrease in the aspect ratio and an increase in matrix connectivity. Silicide with an average diameter of 80 nm appeared in the rolled composites. The grain was continuously refined as the rolling reduction increased. A T-type texture with the crystal C-axis parallel to the transverse direction appeared at 40% rolling reduction. The strength and plasticity of sintered TiBw/Ti65 composites were increased after rolling. With an increase of rolling reduction, the composites exhibited fine-grain strengthening below 650 °C. When tensile above 700 °C, a softening effect occurred with the decrease of grain size, that is, the yield strength decreased for grain size <3.6 μm. The strengthening mechanisms of rolled TiBw/Ti65 composites include fine grain strengthening, load transfer strengthening of TiBw, Orowan strengthening of silicide, and dislocation density strengthening. Among them, fine grain strengthening and load transfer strengthening predominated and increased as the rolling reduction increased. After tensile at 750 °C, many recrystallized grains with large misorientation appeared around the initial coarse grains and TiBw. • The strength and plasticity of sintered TiBw/Ti65 composites were increased by HT rolling. • The effects of rolling reductions on microstructure and mechanical properties were studied. • The strengthening mechanism of rolled TiBw/Ti65 composites was analyzed. • The effect mechanisms of silicide on mechanical properties and DRX were investigated. [ABSTRACT FROM AUTHOR]

The formation of interfacial intermetallic compounds (IMCs) such as Cu 6 Sn 5 , Cu 3 Sn or platelet-shaped Ag 3 Sn which are formed in reflow soldering process will directly destroy the soldering reliability. Magnetic pulse welding (MPW), as a solid state welding technique can effectively restrain or even impede the formation of interfacial IMCs. In this paper, Cu and Sn dissimilar metals were welded by MPW under the discharge energy from 17 to 31 kJ. The typical wavy interface and metal jet flow were found in all samples. When the discharge energy reached 31 kJ, a typical gradient nanograined (GNG) interface has been observed to undergo an evolution from a sub-micron secondary solid solution of Cu 6.26 Sn 5 IMCs to a nanoscale secondary solid solution of Cu 81 Sn 22 IMCs, followed by the formation of nanoscale equiaxed α-Cu grains, and ultimately leading to the deformed elongated nanoscale α-Cu grains. This discontinuous distribution of the aforementioned phases occurs specifically at the interface of the 23 kJ_1.5 mm sample. In contrast, when subjected to a discharge energy of 17 kJ, there were no indications of a secondary solid solution of Cu 6.26 Sn 5 IMCs or elongated nanoscale α-Cu grains. However, a discontinuous secondary solid solution of Cu 81 Sn 22 IMCs was observed to form at the Cu/Sn interface under these conditions. Based on these findings, the utilization of microprojection welding (MPW) techniques involving Cu and Sn-based solder in the microscale is anticipated to serve as a highly efficient and automated technology within the field of electronic micropackaging. [Display omitted] • The wavy interface and metal jet were formed at the Cu/Sn interface. • The gradient nanograined interface has been observed. [ABSTRACT FROM AUTHOR]

In this paper, in-situ nanoparticles ZrB 2 were introduced to improve the mechanical properties of Friction Stir Welding (FSW) joints in 7N01 matrix composites. The recrystallization driving force was increased induced by ZrB 2 particles. Modified by ZrB 2 nanoparticles, the grains in the SZ (stir zone) were refined from 4.8 μm (7N01) to 3.7 μm (ZrB 2 /7N01), and the recrystallization proportion was increased from 75.1% (7N01) to 85.4% (ZrB 2 /7N01). Compared with the 7N01 matrix, the ultimate tensile strength (UTS) of friction stir welding joints in ZrB 2 /7N01 composites was enhanced from 283.3 to 395.6 MPa, the yield strength (YS) was enhanced from 250.8 to 361.4 MPa, elongation was enhanced from 12.7% to 16.2%. The strengthening effect was mainly achieved through the Orowan mechanism. The MgZn 2 precipitates grew up under the influence of heat input, the inhibiting effect of precipitates on dislocations movement was weakened. Nanosized ZrB 2 particles with superior coarsening resistance can still maintain its morphology and size at high temperature, playing a good strengthening role during the FSW. • High temperature stable phase ZrB 2 particles can still play a good strengthening role during the FSW welding. • ZrB 2 particles can promote and hinder recrystalization, which driving force was larger than restraining force. • The semi-coherent interface between ZrB 2 and α-Al promote precipitation of MgZn 2. [ABSTRACT FROM AUTHOR]

A novel LPSO containing Mg-5Y-2n-2Li-0.5Al alloy with superior mechanical behaviors and damping capacities was first developed in this paper. The microstructure evolution, mechanical and damping properties of Mg-5Y-2n-2Li-0.5Al alloy were analyzed and compared with those of Mg-5Y-2Zn-2Li alloy. The results indicated the extruded Mg-5Y-2n-2Li-0.5Al alloy exhibited bimodal grain structure, including fine dynamically recrystallized grains (DRXed grains) and coarse un-dynamically recrystallized (unDRXed) grains, accompanied by the produce of the 14H LPSO phase, Al 3 (Y, Zn) particle and nano-precipitates AlLi phase. Due to the strengthening effects of grain boundary, residual dislocation and precipitation, the ultimate tensile strength (UTS), tension yield strength (TYS) and elongation (EL) of the extruded Mg-5Y-2Zn-2Li-0.5Al alloy were 312 MPa, 229 MPa and 10.9%, respectively, which were higher than that those of the extruded Mg-5Y-2Zn-2Li alloy. In addition, the extruded Mg-5Y-2Zn-2Li-0.5Al alloy displayed good damping capacities at both room and high temperature (RT and HT), and its RT damping value (Q−1) at 5 × 10−4 strain amplitude exceeded 0.01, which associated with a high density of movable dislocation. With rising the temperature, the extruded Mg-5Y-2n-2Li-0.5Al alloy possessed superior damping properties than the Al-free alloy, which derived from the grain boundary slide (GBS) and the activation of the incoherent interface between the Al 3 (Y, Zn) and α-Mg phase after adding Al element. [Display omitted] • The addition of trace Al element significantly changed the microstructure of the Mg-5Y-2Zn-2Li alloy. • The mechanical properties and damping capacities were simultaneously improved in the extruded Mg-5Y-2n-2Li-0.5Al alloy. • It was a major breakthrough in balancing the relationship between strength and damping of Mg alloys. [ABSTRACT FROM AUTHOR]

Friction stir welding is an advanced solid state welding technology, which has been widely used in aerospace and other fields. However, the large tensile residual stress developed in such joints will significantly affect mechanical properties. Cold spraying, as a new method to reduce residual stress of welded joints, can also improve the mechanical properties of the joints. In this paper, the correlation between microstructure and mechanical properties and residual stress of 2219 aluminum alloy joints prior and after coated with cold spraying was studied with experiments and numerical simulation for a 4 mm thick joint. The primary mechanism of stress relief of the joint was identified. Results show the refinement of grain size, with grain size decreasing from 2.1 μm in welded joints to 0.7 μm of cold sprayed joints, while high angle grain boundaries increase from 38.0% in the welded joint to 62.7% in cold sprayed ones. The ratio of recrystallized grains in the joints increases from 19.1% to 46.9%, while the joint strengthening phases θ″ and θ' increase, which increases tensile strength of the joints from 343 MPa to 398 MPa. The elongation is increased from 4.5% to 10.2%, and the average hardness of the joint is increased by 35 HV. The " shot peening effect " of cold spraying is found to be the primary factor to reduce residual stresses, while the " heat flow effect " has negligible effect on stress reduction. The mechanism of reducing residual stresses is provided by the macroscopic stress-strain theory and the microscopic dislocation theory. • Residual stresses can be significantly reduced by cold spraying. • The SPE and HFE play different roles in improving the mechanical properties. • The primary mechanism of stress relief of the joint is identified. [ABSTRACT FROM AUTHOR]

Fe 50 Mn 30 Co 10 Cr 10 high entropy alloy (HEA) can be considered as a candidate structural and functional material, but the early failure during friction with heavy load can limit its more extensive applications. In this paper, a series of tungsten carbide particle reinforced Fe 50 Mn 30 Co 10 Cr 10 HEAs were fabricated by laser cladding technique, the influence of tungsten carbide content on microstructure, mechanical properties and tribological behaviors were explored systematically. The results indicated that the dissolution and diffusion of tungsten carbide could contribute to a wettability between tungsten carbide and HEA matrix, and grain refinement was caused by increasing tungsten carbide. The UTS and EL of the P10 sample are increased by simultaneously by 26.8% and 31.1% compared with UTS of 696 MPa and EL of 15.1% for P5 sample. UTS and EL were enhanced simultaneously owing to fine-grained strengthening and nanoscale precipitate strengthening. But higher content of tungsten carbide could cause lower elongation owing to the embrittlement of the materials. Just as this, Rockwell hardness and friction coefficient has an increasing trend with increasing tungsten carbide when an opposite trend exists in volume wear rate. It can indicate that hardness is a more important factor for wear resistance, and excellent wear resistance with 1.25 × 10−5 mm3/(N·m) appear in higher-content WCp reinforced HEA composite. Furthermore, wear mechanism is transformed from abrasive wear in low-content tungsten carbide to adhesive wear in high-content tungsten carbide. • A series of Metastable FeCrMnCo HEAs with the reinforcement of tungsten carbide fabricated by laser melting. • Microstructural evolution and its influence on mechanical properties and wear resistance are explored. • Strengthening mechanisms in mechanical properties are discussed. • Tribological behaviors and wear mechanism are explained. [ABSTRACT FROM AUTHOR]

In recent years, closed-cell foam has drawn increasing attention in applications ranging from energy absorption devices to serving as the core material of light-weight structures. Although closed-cell foams are critical in many applications, the microstructural characteristics and mechanical properties of these foams are not fully understood. In this paper, we performed a comprehensive study on the commercially available ALPORAS closed-cell aluminium foam by means of experiment. First, inspection of the foam microstructure was systematically performed. Based on this inspection, the geometric features of the foam were characterised. Crushing experiments were subsequently conducted on specimens under various conditions to examine the effect of each of the testing parameters such as the specimen size and geometry as well as the loading direction, on the mechanical response of closed-cell foam. We found that the cells were irregular polyhedra with approximately 14 faces and that each face had approximately 5 sides. The cell wall was thinnest in the middle section, became increasingly thicker towards the edges, and eventually formed circular fillets as it intersected with neighbouring walls. The foam was geometrically and mechanically anisotropic. The factors that most influenced the mechanical properties were the loading direction and relative density. In this paper, we also compare the experimental results on the foam mechanical properties with existing equations from the literature. [ABSTRACT FROM AUTHOR]

Al-Zn-Mg-Cu alloys are traditional lightweight materials with extraordinary mechanical properties. Nevertheless, the manufacturing of Al-Zn-Mg-Cu alloys by directed energy deposition (DED) technique is still a tough problem since these alloys are prone to hot-cracking during the rapid solidification process of DED. In this paper, the co-incorporation of Si and ZrO 2 into the Al-Zn-Mg-Cu alloy was adopted for alleviating solidification shrinkage and enhancing mechanical properties. After the addition of Si, cracks are completely eliminated and the microstructure is refined due to the formation of Si rich eutectic phases. The average grain size is further decreased when ZrO 2 was added and the elevation of ZrO 2 amount facilitates the declination. The combined effects of Si and ZrO 2 induce the enhanced tensile properties (241 MPa in tensile strength, 160 MPa in yield strength and 4.1% in elongation) of the Al-Zn-Mg-Cu alloy modified with 2.9 wt% Si and 1.5 wt% ZrO 2 , which are further improved after T6 treatment (304 MPa in tensile strength, 225 MPa in yield strength and 4.3% in elongation). This paper indicates that the present approach can enable the manufacturing of crack free hard-to-weld Al-Zn-Mg-Cu alloys with ultrafine grains by DED through adding appropriate ceramic inoculants. • Si and ZrO 2 were added for crack elimination and mechanical property enhancement. • Columnar grains are transformed into equiaxed grains after adding ZrO 2. • The tensile strength is increased to 304 MPa after T6 treatment. [ABSTRACT FROM AUTHOR]

Hydroforming (HF) is a traditional sheet metal forming method with high forming efficiency and reliability. However, under HF, the material at room temperature is easy to crack due to the low strain rate. Electromagnetic hydraulic forming (EMHF) is a high-speed forming process, which can significantly improve the forming limit of materials. Nevertheless, there is a lack of research on the performance and microstructure of parts deformed under EMHF. In this paper, AA5052 sheets are formed into flat bottom parts under the HF and EMHF processes. The tensile properties and hardness of the deformed parts are tested. The yield strength and tensile strength of the EMHF samples were higher by 7.5% and 9.0%, respectively, compared to those of the HF samples. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) showed that the EMHF samples had higher internal dislocation density, smaller grain size, higher proportion of small-angle grain boundaries, and higher texture intensity compared to those of the HF samples. This corresponds to the higher strength and hardness observations. Finite element models of the EMHF and HF configurations were developed. The deformation velocity of the EMHF sample exceeded 200 m/s and the strain rate exceeded 600 s−1, while the maximum local liquid pressure reached 211 MPa. The comparison of the thickness distribution obtained by simulation and experimentally indicated that the simulation results were in good agreement with the experimental ones. Moreover, the reasons for the improvement of strength and hardness are discussed, and the strength evolution mechanism is elaborated. [Display omitted] • The parts strength and hardness were improved by EMHF compared with HF. • High strain rate and high liquid pressure is responsible for high strength and hardness. • The deformation velocity exceeds 200 m/s and liquid pressure reached 211 MPa in EMHF. • The texture types have been changed and average grain size was small in EMHF samples. [ABSTRACT FROM AUTHOR]

In this study, the Inconel 718 foil with a thickness of 0.05 mm and an average grain size of 1.78 ⁓ 2.68 μm was prepared by multi-pass rolling and annealing. In the annealing process after rolling, two kinds of multistage heat treatments were designed to improve the plasticity and strength of the foil respectively by regulating precipitation phase. The RT process for plasticity enhancement (900 °C × 4 h + 960 °C × 1 h) provides a better elongation of 12.8% and a tensile strength of 1305 MPa. The sufficient pre-precipitation of the fine δ phase promotes nucleation and growth of recrystallized grain to refine the equiaxed grains and improve the strength of the alloy. Fine grains inhibit crack initiation and delay crack propagation to improve the toughness of the foil. Furthermore, the dispersed δ phase balances the stress at the grain boundaries and within the grain, resulting in uniform deformation of the grains to enhance the plasticity of the foil. Based on RT process, strength enhancement process (RT + DA process, RT process +720 °C × 8 h + 620 °C × 8 h) increases the tensile strength of the foil to 1480 MPa and reaches a suitable elongation of 8.52%. The improved tensile strength indicates a significant contribution of intensive γ" precipitation to impede the movement of dislocations. This paper is anticipated to provide as a reference for foil preparation regarding microstructure and property adjustment. • The 0.05 mm foil is prepared by sizeable plastic deformation and intermediate annealing treatment. • The high consistency of grain size and δ phase evolution in multistage annealing are illustrated. • The dispersed δ phase has good deformation compatibility and prevents crack propagation. • The strengthening and toughening mechanism of the foil are discussed. [ABSTRACT FROM AUTHOR]

Nanosized silver (nano-Ag) has been proposed as a flip-chip interconnection material owing to its low sintering temperature and impressive working performance. With ever-shrinking size of electronic devices, electromigration (EM) becomes an important reliability issue. However, the EM behavior of nano-Ag joints has rarely been investigated before. In this study, a flip-chip structured nano-Ag joint was examined at a current density of 1.0 × 104 A/cm2 at 150 °C and its microstructural change at different experimental times was analyzed. Severe delamination between the Cu substrate and sintered Ag occurred at the cathode, and the extent of delamination increased with increasing EM time. Fractured surfaces revealed the presence of a large number of whiskers on the opposite side of the cathode owing to stress release during the EM process. For comparison, a Sn-3Ag-0.5Cu solder joint was examined under identical experimental conditions. Although failure in both samples originated from the cathode, the failure mechanism was different. The root cause for the difference in the EM phenomenon observed in the two types of materials was determined in this study. • This is the first paper to report the electromigration behavior of nano-Ag joints. • The diffusivities of nano-Ag joint have been calculated to explain failure mechanism. • The electromigration resistivity comparison between nano-Ag and Sn-based joints. [ABSTRACT FROM AUTHOR]

To overcome the brittleness of high‑carbon steels, it is necessary to develop the strategy to remove the carbides on the grain boundaries and strengthen grain boundaries. In this paper, we achieved them by simply controlling the heat treatment conditions and the microstructure before heat treatment. It was found the dissolution behavior of the θ-cementite particles is changed greatly with and without Cr in the high‑carbon steels. In the Cr-free hypereutectoid steel, dissolution of θ particles at high temperatures is remarkably fast, but the dissolution behavior is greatly affected by the microstructure in the Cr-containing hypereutectoid steel. In the Cr-containing hypereutectoid steel, the dissolution of θ particles into the γ-austenite phase was rapid in steel with smaller θ particles in fine α grains, but slow in steel with larger θ particles in coarse α grains. The θ particles on the grain boundaries preferentially dissolved and rapidly disappeared in the initial stage of the dissolution treatment owing to the contribution of grain boundary diffusion, since the grain boundary diffusion of Cr is fast as comparable to C. However, the θ particles inside the grains slowly dissolved and then remained until the later stage, owing to slow dissolution via the partition local equilibrium (PLE) mode controlled by the lattice diffusion of Cr. Owing to the preferential dissolution of θ particles on the grain boundaries in the initial stage, large amounts of Cr atoms dissociated from the θ particles diffused along the grain boundaries with grain boundary diffusion, forming Cr-enriched grain boundaries. Such grain boundary microstructure control is expected to lead to the suppression of intergranular fracture, resulting in the improvement of fracture toughness. • The dissolution behavior of cementite particles into austenite phase was examined. • The θ particles on the grain boundaries preferentially dissolved, forming Cr-enriched grain boundaries. • The dissolution mode of the θ particles changed from the NPLE mode to the PLE mode. • The control of dissolution behavior is expected to improve the mechanical properties of hypereutectoid steels. [ABSTRACT FROM AUTHOR]

The novel Ti 3 AlC 2 /Inconel 718 composites were fabricated by in-situ hot press reaction to improve the thermostability and strength of the In718 alloy. In this paper, the effect of Ti 3 AlC 2 content on the microstructure and high-temperature properties of composites were investigated. Microstructures and mechanical properties were evaluated using scanning electron microscopy and tensile testing. The phase diagram and time-temperature-transformation curve of γ'-γ"-δ phases were simulated by JMatPro6.0 software. The results reveal that Ti 3 AlC 2 has an obvious refining effect on Inconel 718 grain, and the dominant strengthening phase in composites is γ' phase. The tensile results demonstrate that the addition of Ti 3 AlC 2 to the Inconel 718 significantly improves the mechanical properties at elevated temperatures. The 15 vol% Ti 3 AlC 2 /Inconel 718 sample showed a higher tensile strength of 1241 ± 13 MPa with a noticeable elongation of 5.2 ± 0.4% at 650°C compared to the pure Inconel 718 (tensile strength = 852 ± 12 MPa, elongation = 7.9 ± 1.1%). At 750°C, 850°C and 900°C, the tensile strength of 15 vol% Ti 3 AlC 2 /Inconel 718 composite can reach 911 ± 11 MPa, 459 ± 15 MPa, 283 ± 10 MPa, increased by 35.2%, 61.1% and 68.5%, respectively. The superior strength of the Ti 3 AlC 2 /Inconel 718 composites is attributed to the dispersive second phases strengthening, grain refinement strengthening, and load transfer strengthening. • A novel Ti 3 AlC 2 /Inconel 718 composite was prepared by in-situ hot pressing sintering. • Al element strongly promotes the precipitation of γ' phase in composites. • The γ' phase replaces the γ" phase as the strengthening phase in composites. • The tensile strength of composites increases significantly compared with Inconel 718. • The improved strength is attributed to the combined effect of three mechanisms. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure evolution of two as-cast CoNiCrAl bond coat alloys after various isothermal heat treatments were investigated. The CoNiCrAl bond coat alloys were prepared by vacuum induction melting and casting process. The as-cast alloys were subjected to heat treatments from 550 °C to 1300 °C for periods up to 100 h to study the effects of temperature on the microstructure and phase distribution. The microstructure of heat treated CoNiCrAl bond coat alloys was characterised by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The CoNiCrAl alloys exhibited a two phase γ + β structure, with the β phase acting as the primary phase. It was shown that the precipitation of needle-like secondary γ phase was slow at temperatures below 600 °C but became rapid above 900 °C. It was found that the morphology of the secondary γ phase changed from needle-like to rod-like at 1100 °C. A homogeneous γ + β two phase structure was obtained at 1300 °C even after 2 h heat treatment. It was revealed that the heat treatment temperature had a significant influence on the formation and distribution of the secondary γ phase. In addition, the precipitation of sub-micron Cr-rich particles occurred at 1300 °C in both CoNiCrAl alloys, which was due to the low solubility of Cr in the β phase and rapid coalescence of γ phase at elevated temperatures. • Needle-like secondary γ phase was formed after heat treatment at 900 °C. • The transition from needle-like to rod-like morphology occurred at 1100 °C. • A homogeneous γ + β two phase structure was obtained at 1300 °C. • Cr-rich precipitates were formed within the β phase at elevated temperatures. [ABSTRACT FROM AUTHOR]

Regarding the light-weight welding application, the strategy of non-tool penetration into lower hard sheet is considered as a promising dissimilar friction stir lap welding (FSLW) process for restriction of tool wear and reduction of welding force. In order to further improve the mechanical properties of the lap joint for such a case, AlCoCrFeNi high-entropy alloy (HEA) particles were selected as reinforcement for the Al-Cu dissimilar FSLW. A novel approach to incorporating HEA particles into lap weld, where a HEA particle-reinforced Al matrix was pre-prepared by FSLW, was proposed to prevent the overflow of particles from weld effectively during Al-Cu FSLW. The strengthening characteristic and mechanism of the HEA particles were systematically explored in this paper. Microstructural analyses indicate that the spherical HEA particles with large size contribute to the grain refinement via particle-stimulated nucleation mechanism, furthermore, nanoscale particles (Al 3 Ni and Al 13 Fe 4) are formed adjacent to the HEA particles in the Al matrix. The induced grain refinement strengthening and secondary phase strengthening by the HEA particles are responsible for the significant improvement in the mechanical properties of Al-Cu lap joint. This study provides a technological approach and a theoretical foundation for the high-quality dissimilar FSLW used in light-weight manufacturing field. • Pre-incorporation of HEA particles into Al through FSLW is proposed for Al-Cu FSLW. • Incorporation of HEA particles leads to strength improvement of Al-Cu FSLW joint. • Large-size HEA particles contribute to grain refinement of Al-Cu FSLW joint. • Nanoscale particles are formed in the lap joint due to addition of HEA particles. [ABSTRACT FROM AUTHOR]

In this paper, the low-temperature hot rolling was conducted on air-cooled medium manganese martensitic steel, utilizing a finishing rolling temperature (FRT) that was significantly lower than the conventional used temperature. The effect of FRT on the microstructure, mechanical properties and wear resistance was systematically investigated. The results revealed that the pancaked austenite grain formed after low-temperature hot rolling could still be completely transformed into martensite structure under air-cooled condition. The lower FRT significantly refined the martensite multi-level microstructures, increased the grain boundaries density and dislocations density, and promoted the nano-scaled V(C, N) precipitation. These resulted in enhanced refinement strengthening, dislocation strengthening and precipitation strengthening. Compared to the FRT-900 sample, the FRT-700 sample exhibited increased yield strength, tensile strength, and Brinell hardness, with values rising from 973 MPa, 1526 MPa, and 454 HB to 1174 MPa, 1701 MPa, and 482 HB, respectively. In addition, the refined microstructure effectively increased the dimple region in the fractography of impact samples, preventing the propagation of crack and thereby enhancing the impact absorbing energy. Consequently, the impact absorbed energy at −40 °C of experimental steel was increased from 28 J to 38 J, while also increasing strength. Moreover, the low-temperature hot rolling effectively increased the surface hardness of the experimental steel, inhibited abrasive embedding and improved impact wear resistance. The mass loss rates of low-temperature hot rolling samples were 0.052 mg/s and 0.063 mg/s under the impact energy of 1 J and 2.5 J, respectively. • The low-temperature hot rolling was conducted on air-cooled medium manganese martensitic steel, and its finishing rolling temperature was substantially lower than the temperature commonly used. The pancaked austenite grain formed after low-temperature hot rolling could still be completely transformed into martensite structure under air cooling condition. • The low-temperature hot rolling significantly can refine the martensite multi-level microstructures, increase the grain boundaries density and dislocations density. Meanwhile, it can promote the nano-scaled V(C, N) precipitation and inhibit Fe 2 C carbides. • The low temperature hot rolling can improve impact absorbed energy (−40 °C) while increasing the strength and hardness of the experimental steel. And The effect of finishing rolling temperature on the strengthening, toughening mechanism and wear resistance was systematically investigated. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys, owing to their superior resistance against mechanical and chemical degradation, have been widely applied in the aerospace, turbine engine, nuclear reactor, and chemical industries. The microstructure recognition plays a key role in the characterization and design of new superalloys. Although deep learning techniques have achieved satisfactory performance in the microstructure recognition, these methods usually suffer from generalization when the alloy composition or process changed, especially in the high-throughput experiments. In this paper, we propose a semi-supervised deep transfer learning framework for the microstructure recognition of nickel-based superalloys with different compositions and heat treatment procedures. To be specific, we achieve the knowledge transfer of recognition models from one condition (source domain) to another (target domain) by feature distribution alignment (FDA). To avoid the over-fitting, we design a dynamic alignment strategy to achieve the feature alignment based on the label guidance. Additionally, we effectively utilize the unlabeled samples in the target domain and achieve the distribution alignment between the two domains by adversarial training. The experimental results show that our method is superior to the commonly used deep transfer learning methods. In spite of few labeled samples, it can also approach the satisfactory accuracy. Codes are available at: https://github.com/yangchuanwu/FDA. • A semi-supervised deep transfer learning framework for high throughput characterization was developed. • For labeled and unlabeled samples, the feature distribution alignment method is used to transfer knowledge from the source domain to the target. • By learning from small samples, our method can approach the accuracy obtained by training a large number of samples. [ABSTRACT FROM AUTHOR]

The additive manufacturing (AM) shows a great market prospect in the closed-impeller for the centrifugal compressor. In the paper, the precipitation hardened martensitic stainless steel (PHMSS) deposition with different heat input parameters by the selective laser melting (SLM) and the micro-Vickers hardness, tensile strength and impact toughness were detected respectively. The evolution laws of microstructure were analyzed by the SEM, TEM, EDS and EBSD. The tensile strength of the deposition with heat input of the 4.21 J/cm were best and the strength along the build surface direction (X and Y) and the build height direction (Z) were 1193.3 MPa、1222.1 MPa、1159.8 MPa respectively. The impact toughness of the deposition were lower than that of base metas and the tonghness between the sureface direction and the bulid heght direction was anisotropy. The crystals showed a conlumanr pattern along the Z direction and with the increase the heat input, the preferred orientation along the Z changed from the preferred crystal plane and crystal orientation to the pure preferred crystal orientation. A large amount of Cr 3 C 2 phase is precipitated and its size increased with the increase of heat input. The above research results normalize the influence of each parameter during the AM on the microstructure and mechanical properties of the deposition to the heat input, which is helpful to simplify the optimization of the procedure specification and promote its industrial application. • The maximum tensile strength of the 17–4PH deposition is higher than that of base metal. • The maximum impact toughness with heat input 3.52 J/cm is the 22.38 J but lower than that of base metal. • Cr 3 C 2 were found in the fracture and cross-section and the its size increased as the heat input increased. • With the increase of heat input, the preferred orientation of grains in the deposition becomes weaker. [ABSTRACT FROM AUTHOR]

Dual heat treatment, the combination of near-β heat treatment and two-phase field heat treatment, provides an effective approach for near-α titanium alloy to obtain a tri-modal microstructure with excellent comprehensive performance. In this paper, the three-dimensional morphology of a tri-modal microstructure in TA15 Ti-alloy and the evolution mechanisms of equiaxed α and lamellar α were revealed by means of interrupted quenching experiments and three-dimensional reconstruction experiments. It is found that the equiaxed α and the lamellar α showed irregular shapes in three-dimensional space, and the α phases were in contact with each other except for some small and fine lamellar α. During the near-β heat treatment, the decomposition of equiaxed α was caused by β phase wedging at grooves. Grooves formed on the surface of the equiaxed α, extending inwards and further the equiaxed α being separated. In addition, a prediction model of equiaxed α decomposition was proposed in this paper. During two-phase field heat treatment, the increase of equiaxed α size was caused by the merging of adjacent α grains or the adhering growth of fine lamellar α. Some lamellar α decomposed through the mechanism of deflection fracture proposed in this paper, i.e., grooves formed at the substructures of the lamellar α and expanded inwards. The lamellar α on both sides of the grooves deflected at small angles to reduce the interface energy and finally the fracture occurred. • Real three-dimensional morphology of tri-modal microstructure is obtained. • Evolution mechanisms of constitute phases during dual heat treatment are revealed. • Decomposition of equiaxed α grain is caused by β phase wedging at grooves. • A decomposition prediction model of equiaxed α is proposed. • A lamellar α decomposition mechanism of deflection fracture is proposed. [ABSTRACT FROM AUTHOR]

This paper describes the experiment of joining of the Ti-6Al-4V alloy with a freestanding Ti/Al multilayer foil used as a filler material. The joining process relied on an exothermic reaction of Ti/Al multilayers backed with a resistive heating. The DC electric current (1.6 kA/cm2) was maintained for 2 to 6 min in order to determine the effect of the bonding time on microstructure and mechanical strength of the obtained connection. Visual observations and measurements of the temperature of the joint indicated that the reaction accompanied by emission of light starts already after few tens of seconds of the current heating (thermocouple read-out: ~250 °C). The microstructure investigations showed that, independently of applied resistive heating times, their central parts are built of randomly oriented equiaxed crystallites, confirming that the Ti/Al multilayer foil had undergone self-propagating high temperature synthesis (SHS). The sides of the joints were separated from the filler material with layers of Ti 3 Al intermetallic phase of the thickness increasing with the processing time. The hardness of the Ti-6Al-4V alloy near the TiAl filler material after 2 min and 4 min of joining process time is still comparable with that measured for as-supplied material. It slightly decreases after 6 min indicating that the latter time is a threshold for the base material overheated during such experiments. The shear tests of Ti-6Al-4V/(Ti/Al)/Ti-6Al-4V joints helped to estimate their strength at ~300 MPa for all processing times, proving it as fast and reliable method for joining parts of Ti-6Al-4V alloy. • SHS reaction of Ti/Al multilayer was successfully used for joining Ti-6Al-4V parts. • Resistive heating backing Ti/Al reaction needed only for a short time. • Produced joint shows fine crystalline microstructure void of any major porosity. • Shear strength of Ti-6Al-4V/(Ti/Al)/Ti-6Al-4V joints approached 300 MPa. [ABSTRACT FROM AUTHOR]

There are number of works describing microstructural and mechanical properties of asymmetrically rolled polycrystalline metals. However, in industrial practice the rolled metals are generally annealed and recrystallized before final applications. Therefore, the influence of recrystallization on the properties of asymmetrically rolled metallic materials has to be studied. In the present paper such properties are studied for polycrystalline copper grade M1E rolled symmetrically and asymmetrically and then recrystallized. The microstructure characteristics, texture, hardness and mechanical anisotropy were examined using EBSD, X-ray diffraction and mechanical tests. The activation energy and released heat during recrystallization were determined using the differential scanning calorimetry tests. In general, the examined microstructural and mechanical properties of the recrystallized polycrystalline copper exhibit a pronounced dependence on the asymmetry ratio of the prior rolling deformation. • In recrystallized material grain size decreases but GAM and KAM increase with rolling asymmetry ratio. • Maxima of thermograms of asymmetrically rolled samples are shifted towards lower temperatures. • Released heat and recrystallization activation energy increase with rolling asymmetry ratio. • Content of Cube component in asymmetrically rolled and recrystallized samples strongly depends on annealing temperature. • Plastic anisotropy after recrystallization is affected in some degree by rolling asymmetry. [ABSTRACT FROM AUTHOR]

The present paper reports an effect of ECAP on the microstructure of the AZ31 magnesium alloy prepared in two conditions: conventionally cast and twin-roll cast. Subsequently, the thermal stability of fine-grained conditions was investigated with a special regard to microhardness, grain structure and dislocation density changes. Similar processing conditions of ECAP resulted in achieving similar average grain size for both initial conditions regardless differences in the initial microstructure. The only difference in the microstructure of a fine-grained condition was a distribution of β-Al 12 Mg 17 secondary phase particles. Isochronal annealing in the temperature range 160–500 °C showed differences in the response of individual fine-grained samples to the temperature increase. It was proven that these differences primarily originated from the different distribution of secondary phase particles, which significantly affected static recovery and grain growth. Consequently, the thermal stability of fine-grained structure was much better in twin-roll cast samples in the temperature range 220–340 °C. Exceeding 340 °C, accelerated dissolution of β-Al 12 Mg 17 phase resulted in a similar evolution of all studied parameters showing that distribution of secondary phase particles is a crucial parameter of thermal stability of fine-grained AZ31 magnesium alloy. • After ECAP, comparable grain size, hardness and dislocation density • Different distribution of beta-phase after ECAP due to initial microstructure • Differences in recovery and grain growth during isochronal annealing up to 500 °C • TRC-8P, higher thermal stability of fine-grained microstructure between 220 and 340 °C [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of two new aerospace Al-6.00 Mg-0.40Mn-0.12Zr (wt%) alloy sheets, containing 0.10 wt% Sc (low content) and 0.25 wt% Er(cheap), respectively, were investigated by tensile tests and electron microscopy methods. The results showed that microalloying elements were present in the form of core-shell-structured secondary Al 3 (Sc 1−x Zr x) and Al 3 (Er 1−x Zr x) nanoparticles, whose cores were enriched in Sc and Er, respectively. Stable core-shell structured nanoparticles enabled the annealed sheets to retain a completely non-recrystallized structure and strong β-fiber rolling textures. The ultimate tensile strength (UTS), yield strength (YS) and elongation to failure (El f) of the annealed sheets reached 422 ± 1 MPa, 312 ± 6 MPa, and 20.7 ± 1.5% in the Al-Mg-Mn-Sc-Zr alloy, and 404 ± 5 MPa, 283 ± 7 MPa, and 24.2 ± 0.9% in the Al-Mg-Mn-Er-Zr alloy, respectively, both exhibiting high strength and superior ductility. The mean diameters of the spheroidal Al 3 (Sc 1−x Zr x) and Al 3 (Er 1−x Zr x) particles were 12.1 ± 4.2 nm and 20.2 ± 8.4 nm, respectively, meantime, the number densities of the Al 3 (Sc 1−x Zr x) and Al 3 (Er 1−x Zr x) precipitates were (7.7 ± 3.2) × 1013 m2 and (6.4 ± 1.9) × 1012 m2. The higher number density and the smaller particle sizes of the Al 3 (Sc 1−x Zr x) leaded to the higher strength of the Al-Mg-Mn-Sc-Zr alloy. The main strengthening mechanisms from the secondary Al 3 (Sc 1−x Zr x)/Al 3 (Er 1−x Zr x) nanoparticles were associated with the direct Orowan precipitation strengthening and sub-structure strengthening. Based on the results of this paper, enhanced mechanical properties and a reduced cost can be simultaneously achieved with the new Al-Mg-Mn-Zr alloys with low Sc contents or inexpensive Er addition, offering great potential for the development of new high-strength micro-alloyed Al Mg alloys in industrial applications. Unlabelled Image • Successfully prepare two new Al-Mg-Mn alloys with secondary Al 3 (Sc 1−x Zr x) and Al 3 (Er 1−x Zr x) nanoparticles • Characterize the microstructure evolution of new alloy sheets during their preparations • Clarify the existing forms of the combined additions of low-content Sc and Zr or Er and Zr • Discuss the potential for developing new cost competitive Al-Mg-Mn-Sc-Zr/ Al-Mg-Mn-Er-Zr alloys [ABSTRACT FROM AUTHOR]

In this paper, the evolution of precipitate phases in 9CrMoCoB (CB2) steel after tempering at 650 °C for different times has been investigated using transmission electron microscopy. As the tempering time prolonged from 0 to 100 h, four types of secondary phases consisting of M 3 C, M 2 X, M 7 C 3 and M 23 C 6 were identified in the experimental steel. It was found that the needle-like M 3 C carbides could be precipitated during both the air cooling process after austenization and the early stage of tempering. After tempering for 15 to 120 min, fine M 2 X particles were observed. The precipitation and growth of M 2 X were derived from the partially consumption of M 3 C carbides. After tempering for 50 h, M 2 X disappeared, while the rod-like M 7 C 3 carbides were observed to be precipitated independent of the early formed M 3 C precipitates. After tempering for 100 h, only M 23 C 6 carbides persisted, of which the number density and size kept increasing throughout 30 min to 100 h owing to their high thermostability. In addition, the precipitation mechanisms of the four types of precipitates were explained, and the relationship between the measured hardness values and microstructure was discussed. • Precipitates evolution in 9CrMoCoB (CB2) steel during tempering has been investigated. • M 3 C precipitated during both the air cooling process after austenization and the early stage of tempering. • The precipitation sequence can be given as follows: M 3 C → M 2 X → M 7 C 3 → M 23 C 6. • Hardness reduction rate of specimens decreased with the tempering time increasing. [ABSTRACT FROM AUTHOR]

The gradient microstructure occurring adjacent to fusion interface of dissimilar metal between high Cr steel and nickel-based Alloy 617 was characterized in detail, and its formation mechanism was discussed in this paper. The island-like and peninsula-like structures present various characters due to difference in elements mixing during welding process. It is found that an unmixed zone (UMZ), a partial mixed zone (PMZ) with lamellar structure and a transition zone (TZ) together make up island-like gradient microstructures. In UMZ, the tempered martensite with much finer equiaxed grains was the main microstructure. In PMZ, nickel-deficient ferrite as the dendritic core, which is separated by nickel-rich fresh lath martensite in interdendritic region, lead to the lamellar structure. The formation of fresh martensite showed phase transition happened under post weld heat treatment (PWHT), which is also verified by the higher nanohardness. In TZ, the occurrence of carbide-free ferrite indicates the carbon diffusion was inhibited by the reaustenitization of TZ. It is also found that the formation of gradient microstructure has close relationship with the angle (θ) between tangents of fusion line and the interface of multi-layer, it is easier to form gradient microstructure as θ > 0 due to complex fluid flow of steel. So, suitable design of multi-layer in weld could help in controlling the formation of this kind of gradient microstructure. Unlabelled Image • Gradient microstructure was clarified at the fusion interface between steel-Ni metals. • UMZ, PMZ with lamellar structure and TZ together make up the island structure. • The shape of fusion line and the multi-layer interface determines this microstructure. • The diffusion path of carbon was found at the interface of PMZ next to TZ. [ABSTRACT FROM AUTHOR]

In this paper, relatively lightweight AlCoCrFeNi HEA ingots with different initial microstructures were fabricated by utilizing the cooling rate effect. The associated mechanical properties and strengthening response are also reported. The body-centered cubic (BCC) AlCoCrFeNi HEAs solidified dendritically, and the dendrite (DR) regions were surrounded by the inter-dendrite (ID) regions. The volume fraction of the DR regions of the alloy formed via arc-melting was higher than those of their counterparts produced via levitation melting, which is considered to have a strong dependence on the cooling rate effect. In addition, the compressive properties were significantly influenced by the ratio of volume fraction of ID and DR regions, as well as the morphologies of the disordered body-centered cubic (A2) and ordered body-centered cubic (B2) phases. The alloy formulated via levitation melting exhibited higher hardness and compressive yield strength (YS) than the arc-melting alloy, at the expense of plasticity. The strengthening effects including grain boundary strengthening, dislocation strengthening, solid solution strengthening, and precipitation strengthening were estimated and compared with the experimental measurements. • The AlCoCrFeNi HEA ingots with different microstructure were designed and fabricated. • Microstructure and mechanical properties evolution with cooling rate were analyzed. • The strengthening mechanisms were estimated and compared with the experimental value. [ABSTRACT FROM AUTHOR]

Thin-walled and hollow profiles of magnesium alloys have more light-weight advantages. However, longitudinal welds exist inevitably in hollow profiles produced by porthole die extrusion. The welding qualities of the welds have a critical impact on mechanical properties of the profiles. In this paper, hot extrusion experiments of an asymmetrical hollow magnesium alloy profile extruded at different ram speeds were carried out. The effects of extrusion speed on grain structure, second phase particles, texture and mechanical properties of longitudinal welds in hollow profiles were systematically studied. The effects of microstructure and texture on mechanical properties of longitudinal welds were revealed. The fracture morphology and fracture mode of the welds extruded at different ram speeds were analyzed. A method based on K criterion for evaluating the welding quality of magnesium alloy profile in three-dimensional space was proposed. The values of three-dimensional welding quality factor K 3D and non-dimensional welding quality factor K ⁎ of the hollow magnesium alloy profile were determined respectively. Finally, the welding qualities of longitudinal welds in the hollow magnesium alloy profiles extruded at different ram speeds were evaluated. Unlabelled Image • Microstructure and mechanical properties evolution at welding area were revealed. • The grain structure on the weld is finer than that of the reference area. • The extruded profile at welding area exhibits a split and tilted basal texture. • Higher extrusion speeds lead to better welding quality and mechanical properties. • The three-dimensional welding quality evaluation method shows high accuracy. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization to a large extent determines the microstructure of near-α titanium alloys during the thermo-mechanical processing in α + β two phases zone. And the initial microstructure has a dramatic effect on the recrystallization behavior. Therefore, this paper deals with the recrystallization behavior of a near-α TA15 titanium alloy sheet with substantial prior deformed substructures during the annealing and hot tension at 800 °C. Undeformed and deformed regions of tensile samples, viz., static recrystallization and dynamic recrystallization, were studied respectively through EBSD observation. It was found that, the unusual intragranular nucleation of discontinuous recrystallization was observed in the relatively coarse grains, which was formed by the enclosed low angle grain boundaries rearranged by the thermally activated recovery. And most of the recrystallized grains manifested as three types of special grain boundaries, namely [0001]30°, 11 2 ¯ 0 75 ° and 13 8 ¯ 5 ¯ 3 90 ° , which showed the cusps in grain boundary energy and can stabilize the recrystallized grain embryo. The substantial prior deformed substructures of the employed TA15 sheet, viz., low angle grain boundaries and dislocations, can facilitate the formation of subgrains and nucleation, which brought about a mixture of continuous and discontinuous recrystallization, regardless of dynamic or static. During the hot tension, the activation of dislocations would accelerate the annihilation and rearrangement of dislocations, thus, recrystallization can take place more frequently, which finally leads to an equiaxed microstructure. • Quasi-in-situ annealing treatment of the initial TA15 sheet was carried out. • A mixture of continuous and discontinuous recrystallization was observed during annealing and hot tension. • Effect of substantial prior deformed substructure on the recrystallization behavior was investigated. [ABSTRACT FROM AUTHOR]