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Herein, to improve the service life of die steels, many methods are used to improve their properties. However, some properties may be weakened after different heat treatments. In this study, a novel method of nanoparticle treatment is used to improve the service performance of high‐Cr steel (HCS), and the effect of nano‐TiC ceramic particles on its microstructures and properties under different heat‐treatment conditions is investigated. After forging and isothermal spheroidization, the nano‐TiC ceramic particles treatment HCS has a mixed grain with equiaxed grain and striated grain. Under different heat‐treatment conditions, the nano‐TiC reinforced HCS has refined martensite laths, carbides, and a higher content of retained austenite. In contrast, the nano‐TiC ceramic‐particles‐reinforced HCS that have higher strength and strain, the yield strength (σ0.2), tensile strength (σb), fracture strain, product of strength and strain, and impact toughness of HCS‐51 with nano‐TiC (HCSN‐51) are 1349 MPa (1531 MPa), 1662 MPa (1770 MPa), 9.4% (12.1%), 12 405 MPa% (18 766 MPa%), and 266 J cm−2 (445 J cm−2), which is 13.5%, 6.5%, 28.7%, 51.3%, and 67.3% higher, respectively. The primary strengthening mechanisms included fine‐grain strengthening and precipitation strengthening. The main toughness mechanism was fine‐grain and transformation‐induced plasticity. [ABSTRACT FROM AUTHOR]

In the present work, the tensile properties at 77 K of the 0.3 wt% nano‐sized TiCp/Al–Cu composite is investigated to explore its potential application at cryogenic temperature. The TiCp/Al–Cu composite exhibits superior ultimate tensile strength (620 MPa), yield strength (531 MPa), and fracture strain (7.2%) at 77 K. The addition of TiCp leads to the refinement of θ′ precipitates and enhanced dislocation strengthening effect, contributing to the improved tensile strength. [ABSTRACT FROM AUTHOR]

A sandwich structure laminate composed of a ductile 2014Al inter-layer and two nanoscale SiC reinforced 2014Al (SiC/2014Al) composite outer layers was successfully fabricated through the combination of powder metallurgy and hot rolling. The ductile 2014Al inter-layer effectively improved the processability of the sandwiched laminates. Tensile test revealed that the yield strength and ultimate tensile strength of the sandwiched laminate were 287 and 470 MPa, respectively, compared with 235 and 425 MPa for monolithic 2014Al. The good performance of the sandwiched laminate results from the strong bonding between the SiC/2014Al composites layer and the ductile 2014Al layer. Thus, the sandwich structure with a composite surface and ductile core is effective for increasing the strength and toughness of composite laminates. [ABSTRACT FROM AUTHOR]

Nano-SiC particulates (n-SiC) reinforced Mg-8Al-1Sn (AT81) composites with different volume fractions (0, 0.25, 0.5 and 1.0 vol.%) were fabricated by powder metallurgy process (P/M) combined with hot extrusion. The mechanical properties of the composite increased as the n-SiC content increased until the n-SiC content exceeded 0.5 vol.%, at which point they began to decrease. For this reason, the 0.5 vol.% n-SiC/AT81 composite was considered optimal. The 0.2% offset yield strength (YS), ultimate tensile strength (UTS) and elongation (ε) of 0.5 vol.% n-SiC/AT81 composites increased from 175, 318 MPa and 4.5% to 239, 381 MPa and 8.3%, respectively, compared to AT81. Both, the strength and plasticity of the 0.5 vol.% n-SiC/AT81 composites were improved as well. The improvement in mechanical properties can be attributed to the progressively refined matrix grain size, relatively uniform distribution of n-SiC and the well-bonded interfaces between n-SiC and the matrix. [ABSTRACT FROM AUTHOR]

Since the aluminum matrix composites prepared by additive manufacturing are prone to defects such as pores and cracks, the properties of the formed composites cannot be further improved. Therefore, the preparation of SiC/AlSi10Mg composites with high modulus and high strength by selective laser melting technology is of great significance for the wide application of aluminum matrix composites. This work will further investigate the defect formation, microstructure evolution, and solidification mechanism of the composites. The matrix microstructure of the composites can be efficiently refined by adding SiC. In addition, the 5 wt.% SiC/AlSi10Mg composites showed improvements in the tensile yield strength, microhardness, bending strength, elastic modulus, and ultimate tensile strength as compared to the AlSi10Mg alloy. These increases were 21.1 %, 18 %, 8.7 %, 23.2 % and 9.2 % respectively. The strengthening mechanisms at room temperature include fine grain strengthening, thermal mismatch strengthening, solid solution strengthening and precipitation strengthening. It is also mentioned that the primary causes of the decrease in toughness are stress concentration and the existence of the brittle precipitation phase (Al 4 C 3). The increase in high-temperature strength is attributed to the pinning role of SiC and precipitate phases relative to grain boundary and dislocation climbing. [ABSTRACT FROM AUTHOR]

A high extrusion ratio of 166:1 was applied to commercial AZ61 alloy in one step with an extrusion speed of 2.1 m·min−1. The effects of DA (direct aging) treatment on the microstructure and tensile properties of extruded alloy were investigated. The extruded alloy exhibits fine DRXed grains and the average grain size is ~11 μm. After DA treatment at 170 °C, the tensile strength and 0.2% offset yield strength is enhanced from 314 to 336 MPa and from 169 to 191 MPa respectively, sacrificing elongation from 26.5% to 23.3%. The grain size and texture distribution of extruded AZ61 scarcely evolve during the post aging treatment. However, the enhanced strength in peak-aged alloy is mainly caused by the high-density elliptical Mg17Al12 precipitates distributing uniformly along the grain boundaries or within the grains, by precipitation and dispersion hardening. Furthermore, the nano-sized precipitates effectively inhibit grains from coarsening by triggering pinning effects along the grain boundaries at elevated temperature. As a result, the peak-aged alloy exhibits a better superplasticity of 306.5% compared with that of 231.8% of extruded sample. This work provides a practical one-step method for mass-producing Mg alloy sheets with excellent tensile strength and ductility compared with those fabricated by conventional extrusion methods. [ABSTRACT FROM AUTHOR]

Abstract Relatively high strength and good ductility are rarely obtained simultaneously in aluminum matrix composites. In the present work, dual-phased TiC n -Al 3 Ti m (n: nanosized TiC particles and m: micron-sized Al 3 Ti particles) particles were in situ synthesized in an Al-Ti-C system via the combustion synthesis method. Subsequently, (TiC n -Al 3 Ti m)/Al hybrid composites were readily fabricated at high addition levels (0, 1, 3, 5 and 7 vol%) via the re-melting and diluting method assisted ultrasonic vibration. Then, the isolated influences of the dual-phased TiC n -Al 3 Ti m particles on the solidification behaviors, microstructure evolution and mechanical properties, at both ambient- and elevated-temperatures, of aluminum alloys were systematically investigated. The experimental results revealed that the α-Al dendrites were substantially refined with a reduction of up to 4 times when compared with that of the unreinforced base alloy. Furthermore, at ambient temperature, 5 vol% (TiC n -Al 3 Ti m)/Al exhibited the optimum comprehensive mechanical properties, and the yield and ultimate tensile strength were 124.3% and 165.2% higher than those of the unreinforced base alloy, whilst the fracture strain was not sacrificed. Theoretical calculations suggest that thermal-mismatch and Orowan strengthening effects contributed most to the yield strength increment, whereas the favourable fracture strain was achieved mainly due to grain refinement. Moreover, at elevated temperature (453 K), the yield strength and ultimate tensile strength were improved by 327.8% and 236.1%, respectively, whilst the fracture strain was still at a relatively high level of 29.2%. The improved thermal resistance primarily resulted from the pinning effects of the TiC n -Al 3 Ti m particles on the grain boundaries and dislocations. Highlights • Novel dual-phased TiC n -Al 3 Ti m particles were in situ synthesized. • TiC n -Al 3 Ti m exerted refinement by heterogeneous nucleation and inhibited growth. • TiC n -Al 3 Ti m enhanced strength at 298 K by thermal mismatch and Orowan effects. • TiC n -Al 3 Ti m enhanced strength at 453 K by pinning and retarding effects. [ABSTRACT FROM AUTHOR]

Abstract A novel Mg-8Al-2Sn-1Zn alloy with a bimodal structure prepared by hard-pate-rolling (HPR) exhibits both higher tensile strength and ductility than its fine-grained counterparts prepared by conventional rolling. By delicate electron back-scatter diffraction (EBSD) analysis, we found fine grains with weak basal texture is beneficial for basal slip and favors initial deformation. Meanwhile, coarse grains with a strong basal texture could accommodate abundant newly generated dislocations, promoting work hardening after fine grains are saturated with dislocations. For the first time, individual roles of fine and coarse grains and their synergy effect on enhancing ductility in bimodal structured Mg alloys is clarified. Graphical abstract Image 1 Highlights • A bimodal grain-structured Mg alloy is fabricated by hard-pate-rolling. • The bimodal sample has higher strength and ductility than fine-grained samples. • The synergy effect of fine and coarse grains on enhancing ductility is clarified. [ABSTRACT FROM AUTHOR]

Abstract In situ TiC p /Al-Cu-Mg-Si nanocomposites were prepared in Al-Ti-C systems with different carbon sources (pure carbon black, mixed carbon source (50 wt% CNTs + 50 wt% carbon black) and pure CNTs) via a combination of the combustion synthesis, hot press and hot extrusion methods. The in situ TiC p /Al-Cu-Mg-Si nanocomposites synthesized by the mixed carbon source obtained the most uniform distribution of nanosized TiC p , highest yield strength (σ 0.2) and tensile strength (σ UTS) and best fracture strain (ε f). The 30 vol% TiC p /Al-Cu-Mg-Si nanocomposite synthesized by the mixed carbon source showed superior σ 0.2 (217 MPa), σ UTS (251 MPa), and ε f (17.7%) at 533 K, which were respectively 4.3%, 4.1% and 136% higher than those of the nanocomposite synthesized by pure C black (208 MPa, 241 MPa and 7.5%) and respectively 3.8%, 1.6% and 88.3% higher than those of the nanocomposite synthesized by pure CNTs (209 MPa, 247 MPa and 9.4%). The superior high-temperature tensile strength and ductility of the nanocomposites prepared by the mixed carbon source were attributed to the homogeneous distribution of nanosized TiC p. The strengthening of the nanosized TiC p and θ′ precipitates was the main strengthening mechanism of the in situ TiC p /Al-Cu-Mg-Si nanocomposites at high temperatures. Highlights • In situ TiC p /Al nanocomposites are prepared in Al-Ti-C systems with various carbon sources. • Nanocomposites prepared by mixed C/CNTs show the best dispersion of nanosized TiC p. • Nanocomposites prepared by mixed C/CNTs show the best strength and ductility at 493 K and 533 K. [ABSTRACT FROM AUTHOR]

Abstract The effects of a small addition of nanosized TiC particles (TiC p) on the microstructure evolution of the Al-Mg-Si (6061) alloy throughout the entire fabrication process including casting, cold rolling and heat treatments were investigated. TiC p impeded the recrystallization and grain growth, refined the grain structure, and evidently increased the tensile strength without obvious decrease on ductility. The ultimate tensile strength and yield strength of the 1.0 wt% TiC p /6061 composite were 330 MPa and 275 MPa in T6 state and 438 MPa and 426 MPa in the as-rolled state, an increase of 42 MPa and 38 MPa, 41 MPa and 52 MPa, respectively, compared to the matrix 6061 alloy. The strength increase is attributed to strengthening effect of TiC p , dislocation accumulation and precipitate strengthening. [ABSTRACT FROM AUTHOR]

In this paper, the 4 vol% SiC p /Al-Cu-Mg-Si-Mn composites were prepared by method of stirring casting. The effects of SiC p surface modifications (oxidization and Ti-coating) and particle sizes (5 μm, 10 μm and 15 μm) on the microstructure and tensile properties of the composites were analyzed. The effects of SiC p sizes on the distribution of SiC p in the pre-oxidized SiC p /Al-Cu-Mg-Si-Mn composites were larger than those in Ti-coated SiC p /Al-Cu-Mg-Si-Mn composites. The Al-Cu-Mg-Si-Mn composites reinforced with Ti-coated SiC p exhibited more uniform SiC p distributions and higher tensile mechanical properties than those reinforced with the pre-oxidized SiC p . When the SiC p size was 15 μm, the Ti-coated SiC p /Al-Cu-Mg-Si-Mn composite showed the best yield strength (σ 0.2 ), ultimate tensile strength (σ UTS ) and fracture strain (ε f ) of 410 MPa, 548 MPa and 7.6% with the increase of 10.2%, 2.6% and 5.6% than that of reinforced by pre-oxidized SiC p . The more uniformly dispersed particles and better tensile properties of the Ti-coated SiC p /Al-Cu-Mg-Si-Mn composites could be attributed to the better wetting between Ti-coated SiC p and molten Al. [ABSTRACT FROM AUTHOR]

The Al-Cu-Mg-Si matrix composites reinforced with in situ hybrid-sized TiC x -TiB 2 particles with sizes ranging from 20 nm to 1.3 µm were successfully synthesized using the Al-Ti-B 4 C reaction system via a method that combined the combustion synthesis and the hot press assisted with hot extrusion. The sizes of the fabricated TiC x and TiB 2 particles increased with increasing TiC x -TiB 2 content. The hybrid-sized TiC x -TiB 2 particles improved the elevated-temperature yield strength ( σ .2 ), the tensile strength ( σ UTS ), and the fracture ductility ( ε f ) of the composites at both 493 K and 573 K. The 40 wt% (TiC x -TiB 2 )/Al-Cu-Mg-Si composite exhibited superior σ .2 (141 MPa), σ UTS (164 MPa), and ε f (31.2%) at 573 K, with enhancements of 60.2%, 72.6%, and 22.4% compared to the Al-Cu-Mg-Si matrix alloy (88 MPa, 95 MPa, and 25.5%). The improvement of the elevated-temperature mechanical properties for the in situ (TiC x -TiB 2 )/Al-Cu-Mg-Si composites was attributed primarily to the strengthening effects induced by the hybrid-sized TiC x -TiB 2 particles and the θ′ precipitation strengthening. [ABSTRACT FROM AUTHOR]

In the present work, Mg-9Al-1Zn-0.4Sn (AZT910) magnesium alloy sheets with a fine-grained structure (∼5 μm) and tilting basal texture were prepared by a 16-passes rolling process. Effect of tensile directions on properties and microstructural evolutions of the AZT910 alloy sheet at different temperatures, i.e. room temperature, 200 and 300 °C, respectively, were investigated by using three kinds of tensile specimens (rolling direction (RD), transverse direction (TD) and 45° towards RD). Experimental results showed that tensile properties exhibited a strong dependence on tensile directions at room temperature and 200 °C, while a negligible dependence at 300 °C. The anisotropic tensile properties imply that the deformation system of rolled AZT910 sheet consists of basal and non-basal slips at room temperature, and is a combination of basal slip, non-basal slip and grain boundary sliding/rotation (GBS) at 200 °C. The decrease of intensity and spreading of basal poles during tensile test and isotropic tensile properties indicates that GBS becomes the dominate deformation mechanism at 300 °C. The present work provides reference for the study of deformation behavior of novel superplastic magnesium alloy, and hence is of great significance for further application of wrought magnesium alloy. [ABSTRACT FROM AUTHOR]

In the present study, the application of hard–plate rolling (HPR) on the hard-to-deform Mg–7Al–5Zn (AZ75) alloy resulted in a homogeneous fine grained (∼6 μm) microstructure, where numerous micron/nano Mg 17 (Al, Zn) 12 precipitates with spherical morphology uniformly dispersed both at grain boundaries and within grain interiors. More importantly, the HPRed AZ75 alloy exhibited superior mechanical properties with a simultaneous high strength and ductility at room temperature, i.e. yield strength (YS) of ∼218 MPa, ultimate tensile strength (UTS) of ∼345 MPa and elongation of ∼19%, which was comparable to the commercial wrought magnesium alloys. According to the contribution from the several strengthening mechanisms estimated by simplified models, the grain boundary strengthening is the predominant mechanism for the high YS of the alloy. The high ductility is benefited from the strong work-hardening capacity resulted from Zn solid solutes and the presence of numerous well-dispersed nanosized precipitates as well as weakened texture. Moreover, the fine grained AZ75 alloy exhibits an optimum superplasticity of ∼615% at 300 °C at 1 × 10 −3 s −1 . It is attributed to the enhanced grain boundary slip (GBS) promoted by a well maintained fine grain structure resulted from the pining effect by numerous Mg 17 (Al, Zn) 12 particles segregating along grain boundaries during tension. The results will be helpful for the development and processing of high alloying element content Mg alloys with high strength and ductility as well as enhanced formability. [ABSTRACT FROM AUTHOR]

The coarse segregative eutectic phases, emerged in the twin roll casting (TRC) process of Mg strips, which cannot be resolved solely by controlling the processing variables or post heat treatment, are detrimental to the subsequent rolling deformation. Considering it, we introduce the pre-rolling steps on the TRC Mg-4Al-2Sn-1Zn (ATZ421) alloys, which is expected to facilitate the dissolution of these segregative phases by increasing distortion of crystal lattices and rolling stress, and further investigate the effect of a single pass or two passes pre-rolling on the microstructure evolution and tensile properties. It indicates that the pre-rolled alloy with two passes presents more uniform precipitates and higher twinning density in comparison with that using a single pass. The uniform distribution of precipitates in two passes pre-rolling is due to the increase in density of dislocations and deformed twins, which results in more distortion of crystal lattices with more stored energy, facilitating the diffusion of solutes. Moreover, the pre-rolling of two passes introduces more rolling stress into Mg matrix, which is beneficial for the crush of coarse eutectic phases, and further accelerates the sufficient dissolution of second phases. After the subsequent rolling and annealing processes, the sheet with pre-rolling deformation of two passes shows finer microstructure, which mainly benefits from the pinning effects of uniform nano-sized precipitates. As a result, the annealed sheet with two-pass pre-rolling deformation exhibits an advantageous combination of high strength and high ductility with fine microstructure, showing an ultimate tensile strength of ~297 MPa, a yield strength of ~ 205 MPa and an elongation of 25.0%. This work provides an effective method of dissolving the coarse segregative phases in the TRC Mg alloys with significant potential for industrial production. [ABSTRACT FROM AUTHOR]

Different dendritic grain morphology of an Al-Cu alloy was obtained by adjusting the casting parameters. Compared to the equiaxed dendritic grains, the tortuous dendritic grains led to increased tensile elongation (from 10.4% to 16.8%) and work of fracture (from 11.2 J/mm 2 to 17.2 J/mm 2 ) by more than 50%, respectively. Meanwhile, the high tensile strength (∼540 MPa) and grain size (∼80 μm) were unchanged. The intergranular fracture crack zigzagged along tortuous grain boundaries, reducing the stress concentration at the crack tip and increasing the propagation resistance and path, leading to increased toughness and elongation. The zigzag morphology of grain boundaries was attributed to tortuous dendritic grains. [ABSTRACT FROM AUTHOR]

Adding various amounts of nano-sized TiC p (0.1–0.7 wt%) made a simultaneous improvement in high-temperature strength and ductility of the Al-Cu matrix alloy. The influences of temperature and strain rate on the high-temperature tensile properties and θ′ precipitate sizes in the Al-Cu matrix alloy and the nano-sized TiC p /Al-Cu composites were investigated. Theoretical calculations suggest that the yield strength increment of the composites at 453 K was primarily attributed to the strengthening effect of both the refined θ′ precipitates and TiC p , while at 493 K only the strengthening effect of TiC p was predominant due to the significant coarsening of θ′ precipitates at this temperature. [ABSTRACT FROM AUTHOR]

Fabricating magnesium alloy sheets exhibiting superplasticity >500% by conventional rolling remains a challenge due to the difficulty in achieving fine-grained structure. Even more puzzling is the role of softened Mg 17 Al 12 particles locating at grain boundaries, which play a promoting or retarding effect on superplasticity at elevated temperatures, has not been understood so far. Here, fine-grained (∼3.0 μm) Mg–9Al–1Zn (AZ91) alloy with a high volume fraction of spherical Mg 17 Al 12 particles was prepared by conventional rolling. The rolled AZ91 alloy exhibits a high tensile strength of ∼370 MPa and ductility of ∼13% at room temperature. More importantly, high superplasticity of ∼563% and ∼735% is achieved at 250 and 300 °C, respectively. It is recognized that the deformation mechanisms of the Mg–Al–Zn alloys at elevated temperatures depend significantly on the amount of Mg 17 Al 12 particles. This work highlights the prominent role of a high volume fraction of Mg 17 Al 12 particles segregating along grain boundaries at elevated temperatures, which on one hand can effectively pin grain boundaries to retard grain coarsening, and on the other hand, are beneficial to relax the intergranular stress incompatibility, and hence significantly facilitate GBS behavior. The current study promotes significantly the industry application of high superplastic rolled AZ91 alloy sheets. [ABSTRACT FROM AUTHOR]

The overall microstructure-manipulated Al-13Si-5Cu-0.6 Mg alloy was successfully fabricated via introducing 0.1 wt% Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator with short time of 60 s, to determine its suitability for applications at room and higher temperatures. The microstructure manipulation mechanism, mechanical properties and strengthening mechanism in manipulated Al-13Si-5Cu-0.6 Mg alloy were discussed. The Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator provides more nucleation sites in the formation of primary Si, Al Si eutectic and Al 2 Cu. As a result, the optimal microstructure is composed of finer α-Al grains, Al 2 Cu and more rounded primary and eutectic Si, with sizes decreased to ∼52%, 13%, 73% and 42%, respectively. The yield strength, tensile strength, elongation and fracture strain of manipulated Al-13Si-5Cu-0.6 Mg alloy are improved by 22.9%, 16.8%, 58.2% and 47.7% at room temperature than those of the unmanipulated Al-13Si-5Cu-0.6 Mg alloy, respectively. The improved tensile properties at room temperature are attributed to the significant strengthening effect of smaller precipitates and grain refinement while the excellent plasticity is derived from finer α-Al grain, round-corner primary Si and eutectic Si spheroidization. The yield strength and tensile strength are increased by 28.1% and 15.3% at 250 °C, and 28.3% and 10.8% at 300 °C, respectively. The strengthening mechanism at high temperature is mainly the second phase strengthening and the effect of finer eutectic Si on the pinning grain boundary. The overall microstructure manipulation in this work provides better comprehensive mechanical properties and a practicable method to fabricate the Al-Si-Cu-Mg alloy with superior strength and ductility, especially for die-casting alloy with short-time and high-efficiency. [Display omitted] • Fully microstructure-manipulated alloy was made via adding trace nanoparticles. • Nanosized ZrCu(B2) and Zr 2 Cu have ideal lattice mismatch with Si, α-Al and Al 2 Cu. • The sizes of primary Si, α-Al, eutectic Si and Al 2 Cu decreased simultaneously. • The tensile strength and elongation of manipulated alloy are greatly improved. [ABSTRACT FROM AUTHOR]

Effects of Zn addition on the microstructure and tensile properties of as-extruded Mg-8Al-2Sn (AT82) alloy were investigated in the present work. All the extruded AT82 alloys exhibited a fully dynamically recrystallized (DRXed) microstructure, while the grains were slightly refined with Zn addition. Moreover, second phase particles (Mg 2 Sn and Mg 17 Al 12 ) increased significantly in amount with increasing Zn content. It was found the ultimate tensile strength (UTS) and yield strength (YS) gradually increased with increasing Zn content from 0 to 1.5 wt%, meanwhile the elongation maintained unchanged at a high level, i.e. ~17–19%. In particular, the as-extruded AT82-1.0Zn alloy exhibited both a high strength and high ductility at room temperature, e.g. UTS of ~357 MPa and elongation of ~19%. The superior combination of strength and ductility is mainly benefited from the enhanced work-hardening ability resulted from Zn solid solutes and the presence of more well-dispersed fine particles in AT82-1.0Zn alloy. [ABSTRACT FROM AUTHOR]

In the present study, Mg-6Zn-1Zr (ZK60) alloy with a homogeneous fine-grained structure (~5 µm) was produced by hot extrusion. The influence of temperature on tensile properties anisotropy and the associated change in deformation mechanisms in the range of 25–275 °C of the fine-grained ZK60 alloy were investigated. Under room temperature, the fine-grained ZK60 alloy exhibited a high tensile strength of ~269–327 MPa and high ductility of ~15–39% when tested at three different directions, indicating a high anisotropy. With increasing testing temperature to 150 °C and further to 275 °C, the alloy showed a gradual decrease in anisotropy. Especially, the fine-grained ZK60 alloy exhibited superplasticity of ~376–434% when tested at 275 °C, which should be due to the increasing role of grain boundary sliding (GBS), as the strong basal texture associated with room temperature deformation became almost random at elevated temperatures. Moreover, the abrupt decrease in tensile anisotropy and associated change in texture with increasing temperature correlates closely to the transformation of deformation mode from a dislocation-dominated behavior to a GBS-mediated one. [ABSTRACT FROM AUTHOR]

The Al2014 composites reinforced with uncoated and Ti 5 Si 3 -coated SiC P were fabricated by stir-casting. The results suggested that the Ti 5 Si 3 -coated SiC P /Al2014 composites exhibited more uniform dispersion of SiC P , higher elastic modulus and tensile properties than uncoated ones. Additionally, the nano-sized Ti 3 AlC 2 interfacial layer was detected between the Ti 5 Si 3 -coated SiC P and α-Al. [ABSTRACT FROM AUTHOR]

The morphology evolution of primary Mg 2 Si particles in a Al-20Mg 2 Si-4.5Cu alloy both unmodified and modified with 0.5 wt% Ca-Sb prepared by hot-extrusion followed by T6 heat treatment was investigated in the present study. Interestingly, we found that the combination of hot-extrusion and T6 heat treatment was efficient in transforming truncated octahedral primary Mg 2 Si into sphere in the modified alloy. In contrast, the primary Mg 2 Si particles still kept dentritic in the unmodified alloy. It suggested that the formation of truncated octahedral primary Mg 2 Si particles in as-cast state, the fragmentation of particles by hot-extrusion and the enhanced solid-state diffusion of Si and/or Mg atoms during heat treatment were responsible for the spheroidization of primary Mg 2 Si. Moreover, the existence of fine (~10–20 µm) spherical primary Mg 2 Si played an important role in strengthening the alloy, i.e., the ultimate tensile strength (UTS) increased from ~227 MPa in the unmodified alloy to ~303 MPa in the modified one. It is because the fine spherical primary Mg 2 Si particles can provide a higher fracture stress and strength of the matrix/particle interface. Our study offered a simple methodology to prepare spherical primary Mg 2 Si in an Al-high Mg 2 Si alloy, which is beneficial to design novel light-weight Al-Mg-Si alloys with improved mechanical properties. [ABSTRACT FROM AUTHOR]

Cast-rolling AZ31 Mg alloy sheets were manufactured at four rolling speed ratios of 0.8, 1.0, 1.2 and 1.3. The results show that the basal texture can be weakened by differential speed rolling (DSR). The AZ31 alloy sheet manufactured at a speed ratio of 1.2 exhibits a fine microstructure with an average grain size of 10.3 μm. The yield strength, ultimate tensile strength and elongation-to-failure at this speed ratio are 145 MPa, 240 MPa and 28.5% at room temperature, respectively. These parameters mainly benefit from the fine grains and weakened basal texture. The AZ31 alloy sheets processed by the DSR exhibit a remarkable improvement in elongation-to-failure compared with the AZ31 alloy sheets processed by equal speed rolling (ESR) primarily due to the weakened basal texture at room temperature. However, the difference in elongation-to-failure of the AZ31 alloy sheets processed by the ESR and DSR decreases at elevated temperatures, which can be attributed to the weakening of the influence of basal texture, with probable activation of non-basal slips and grain boundary sliding (GBS). The results obtained here will shed light on some DSR methods, which is critical to the development of Mg alloys with high mechanical properties. [ABSTRACT FROM AUTHOR]

Forging and welding are common necessary procedures for AA6××× alloys, and recrystallization is an inevitable process. However, it is still difficult to realize the control of the recrystallization behavior, while realizing the strengthening of mechanical properties of the base metal and welded joint. In this study, we overcome this problem through 0.5 wt% TiC–TiB 2 nanoparticles, and fully reveal the influence of the nanoparticles on the recrystallization behavior of the base metal and nugget zone of a friction-stir-welded (FSW)-ed joint from the perspectives of dislocation rearrangement and grain boundary motion. The strengthening mechanisms of the base metal and FSW-ed joint are clarified. The recrystallization driving force of the base metal and nugget zone was increased. Dislocations with a higher density rearranged and formed more grain boundaries in the nugget zone. Besides, nanoparticles distributed on the grain boundaries restrained the vanishing of low-angle grain boundaries. The nugget zone microstructures were refined from 3.1 to 2.3 μm, and the recrystallization ratio was increased from 7.2% to 10.4% at 800 rpm. The grains in the nugget zone were refined from 2.2 to 1.9 μm, and the recrystallization ratio was increased from 16.1% to 18.4% at 1200 rpm. The promoted recrystallization in the nugget zone accelerated the release of stress. Nanoparticles weakened the precipitate coarsening in the nugget zone. After strengthening, the ultimate tensile strength and plastic strain of the FSW-ed joint at 800 rpm were increased by 4.7% and 18.8%, respectively. This study provides new approaches for a systematic microstructure evolution control in FSW-ed 6061 Al alloys. • Trace nanoparticles double the recrystallization driving force of base metal. • More dislocation tangles promoted recrystallization of nugget zone. • Nanoparticle also inhibited grain coarsening of nugget zone. • Precipitate coarsening in the nugget zone was weakened. • FSW-ed joint softening was alleviated and the mechanical properties were enhanced. [ABSTRACT FROM AUTHOR]

Adding alloying elements to increase precipitation is a common method to strengthen aluminum (Al) alloys, but an excessively high alloying element content causes segregation and a reduction in plasticity. In this work, the tradeoff between alloying element content and segregation was explored along with the simultaneous increase in precipitation and dislocation density under the action of trace TiB 2 +TiC particles with the aim of giving a full play to the strengthening effect of dislocation and precipitation and maximizing the strength and toughness of the alloy. The cast Al–Zn–Mg–Cu alloys contained various alloying elements (Zn, Mg), and the alloys were reinforced with 0.5 wt% TiB 2 +TiC particles via in-situ reaction in the Al melt. The TiB 2 +TiC particles blocked the diffusion of the alloying elements and inhibited segregation, promoting solution of alloying elements and yielding dispersed and finer precipitates after solution and aging. Meanwhile, owing to the difference in the thermal expansion coefficients of the matrix and particles, the dislocation density of the alloy doubled. Therefore, the yield strength, elongation, and the product of the tensile strength and elongation of the Al-6.60Zn-3.15Mg-1.60Cu alloy with particles reinforcement were 562 MPa, 4.5%, and 3163 MPa·%, respectively, representing increases of 31.6%, 108.9%, and 186.0%, respectively, compared with the cast 7075 alloy. This study is significant for the successful preparation of high-strength and high-toughness cast aluminum alloys with high alloying-element content. [ABSTRACT FROM AUTHOR]

The nano-sized TiC p /Al-Cu composites were fabricated using the self-propagating high-temperature synthesis (SHS) reaction of Al-Ti-CNT master alloys in molten aluminum alloys. The tensile strength and ductility of the alloys were simultaneously improved by the addition of nano-sized TiC particles. The yield strength, ultimate tensile strength and fracture strain of the 0.3 wt% nano-sized TiC particles reinforced Al-Cu matrix composite increased to 350 MPa, 554 MPa and 14.75%, improved by 15.5%, 14.2% and 123.5%, respectively, compared with the unreinforced Al-Cu alloy (303 MPa, 485 MPa and 6.6%). The enhanced mechanical properties are attributed to the refined α-Al dendrites, a larger amount of smaller θ′ precipitates and the dispersed nano-sized TiC particulates. This study provides a feasible method to fabricate the nano-sized TiC p /Al-Cu composites with superior strength and ductility. [ABSTRACT FROM AUTHOR]

This work was carried out to investigate the relationship between microstructures and mechanical properties of extruded Al–20Mg 2 Si–4Cu alloys unmodified and modified with 0.5 wt% Sb addition at room and high temperatures. Various techniques including metallography, field emission scanning electron microscope, differential thermal analysis and scanning electron microscopy were used to characterize the microstructure, tensile behavior and fracture mechanism of the alloys. It was found that 0.5 wt% Sb additions were highly effective in refining microstructures by changing the morphology of primary Mg 2 Si from coarse dendrite into smaller polyhedral shape with average size less than 20 µm. Tensile test showed that ultimate tensile strength (UTS) of the modified alloy increased dramatically to 283 MPa at room temperature and 213 MPa at 150 °C, evidently higher than the 220 MPa and 185 MPa for the unmodified alloy, respectively. Fracture surface examinations revealed a transition from particle fracture of primary Mg 2 Si in the unmodified alloy to particle–matrix interface debonding in the modified alloy. The transformation of primary Mg 2 Si from coarse dendrites to refined polygonal shapes contributes to the enhanced strength and ductility of the modified alloy, since the polygonal primary Mg 2 Si particles dispersed uniformly in modified alloy, impeding dislocation motions and freeing stress concentrations. A schematic map was established to further elucidate the mechanisms of fracture behavior during stretching process. [ABSTRACT FROM AUTHOR]

It is challenging to concurrently control the microstructure evolutions after undergoing casting, sheet forming and welding. This study successfully addressed this challenge via trace TiC–TiB 2 nanoparticles in the amelioration of solidification-rolling-welding microstructural evolution. Nanoparticles refined the solidified microstructures and significantly increased the net driving force for recrystallization, promoting the precipitation of nanoscale Guinier–Preston zones and β'' phases. The coarsening of the fusion and heat-affected zones was also effectively suppressed. The yield strength (YS) and ultimate tensile strength (UTS) of the rolled plates were enhanced by 31.3% and 16.3%, respectively, without significantly sacrificing ductility. Additionally, the YS and UTS of the as-welded welding joints were enhanced by 30.2% and 7.8%, respectively. The amelioration mechanism of TiC–TiB 2 throughout the microstructural evolution and strengthening process was systematically investigated. This study provides a typical model for the complete amelioration of microstructural evolution in aluminum alloys under multiple processing conditions. • The nucleation of solidified phases is promoted, and their growth is hindered. • Recrystallization and formation of coherent nanoscale precipitates are promoted. • Coarsening of fusion zone and heat affected zone is suppressed. • Building better microstructure configuration for improved properties. [ABSTRACT FROM AUTHOR]

A fine-grained (∼3.6 μm) Mg–6Al–3Sn (AT63) alloy prepared by a hot rolled method is subjected to uniaxial tensile tests within the temperature range of 25–250 °C. Mg 2 Sn and Mg 17 Al 12 precipitates at grain boundaries effectively retard the growth of dynamically recrystallized (DRXed) grains. Grain boundary sliding (GBS) is activated at 250 °C, which is indicated by the stable DRXed grain size and agglomeration of the precipitates at grain boundaries. Moreover, Mg 2 Sn and Mg 17 Al 12 precipitates promote the formation of dynamic recrystallization (DRX). Both the DRX and GBS result in the high elongation (151.4%) of the AT63 alloy at 250 °C. Results obtained here will shed some light on elevated temperature deformation mechanisms of a new type of Mg–Al–Sn system, which is critical to the development of new Mg alloys with potential for applications at elevated temperatures. [ABSTRACT FROM AUTHOR]

The (micron+nano) bimodal sized SiC p /Al2014 composites fabricated by semi-solid stirring exhibited fine α-Al grains, well-dispersed bimodal sized SiC p and well-bonded interface between SiC p and matrix. The yield and ultimate tensile strength of the extruded bimodal sized SiC p /Al2014 composites were significantly enhanced, compared to the extruded single-sized SiC p /Al2014 composites. [ABSTRACT FROM AUTHOR]

The tensile properties at elevated temperature of nano-SiC p /Al2014 composites have been investigated. The nano-SiC p can remarkably improve the tensile strength at 493 K of Al2014 alloy without sacrificing the ductility. The strengthening effect for the matrix alloy of 0.5 vol% nano-particles is superior to that of 4 vol% micron-particles. [ABSTRACT FROM AUTHOR]

Abstract: Many experimental and theoretical studies indicated that the decrease of the size of the reinforcing particles can lead to substantial improvements in the mechanical performance of the composites. However, the investigations on the addition of the nano particles into conventional metal materials are still rare, especially the nano-TiC p into the Al–Cu alloys. In this study, the Ni coated nano-TiC p reinforced Al–Cu matrix composites were successfully fabricated by a casting route. It was found that the nano-TiC p was in the α-Al grains. The α-Al dendrites became finer and more developed. Moreover, the θ′ precipitates in the Al–Cu matrix were finer and uniformly distributed. The tensile strength and elongation of the composites increased simultaneously. After T6 heat treatment, compared with the unreinforced Al–Cu alloy, the tensile strength and elongation of the 0.8wt.% nano-sized TiC p /Al–Cu composite increased from 485MPa and 6.6% to 573MPa and 12.4%, respectively. [Copyright &y& Elsevier]

A hypoeutectic Al–10Si-2.0 Mg ternary alloy with high strength and high ductility was developed for as-cast service conditions. The effects of eutectic-forming element Mg on the primary α-Al dendrites, eutectic Si structure, Mg 2 Si intermetallic compound, mechanical properties and fracture behavior were systematically investigated via multiscale characterization methods. Interestingly, the results demonstrated that with the increasing Mg content, the secondary dendrite arm spacings of the primary α-Al dendrites were significantly reduced, and the grain size was refined, while the flaky eutectic Si structure was fully modified into a coral-like morphology. Additionally, the size of the Mg 2 Si intermetallic phase sharply decreased, and it was distributed much more uniformly in the interdendritic/intergranular eutectic regions. In contrast with the binary Al–10Si alloy, the yield strength, the ultimate tensile strength and the fracture strain were substantially enhanced to 159.4 MPa, 275.3 MPa and 14.1%, respectively, which correspond to improvements of 131.0%, 70.4% and 27.0%, respectively. The underlying mechanisms that were responsible for the evolution of the microstructure and mechanical properties are explicitly discussed. • Grain size and SDAS were substantially refined by growth restriction effect of Mg. • Eutectic Si phase and Mg2Si intermetallic were highly modified with increasing Mg. • Strength and ductility were increased simultaneously and achieved best at 2.0% Mg. [ABSTRACT FROM AUTHOR]

At high temperatures, the weakened strength and decreased ductility of Al alloys limit their industrial applications. (TiB 2 –TiC)/Al–Cu–Mg–Si composites were synthesized by adding in situ dual-phased and bimodal-sized (TiB 2 –TiC)/Al master alloys to molten Al–Cu–Mg–Si alloys. The addition of minor amounts of TiB 2 and TiC particles (0.05 and 0.1 wt%, respectively) effectively refined the α-Al grains and θ′ and Q′ precipitates and increased the elevated-temperature strength and uniform elongation of the Al–Cu–Mg–Si alloys. The 0.1 wt% (TiB 2 –TiC)/Al–Cu–Mg–Si composite showed the best yield strength (279 MPa), ultimate tensile strength (366 MPa), and uniform elongation (10.6%) at 493 K, with enhancements of 9.4%, 15.1%, and 24.7% compared to the Al–Cu–Mg–Si matrix alloy (255 MPa, 318 MPa, and 8.5%). The simultaneous increases in the elevated temperature strength and ductility of the composites were attributed to the strengthening effects of the bimodal-sized TiB 2 and TiC particles, θ′ and Q′ precipitation strengthening, and the refined partial recrystallization microstructure. [ABSTRACT FROM AUTHOR]