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Novel bio-inspired ZL205A/SiC composites with a lamellar-interpenetrated structure were successfully fabricated via gas-pressure infiltration of a commercial ZL205A alloy into freeze-cast porous SiC scaffolds. The influences of initial ceramic content (20, 30 and 40 vol%) on the microstructure and damage-tolerance behavior of the resultant composites as well as their toughening mechanism were investigated. With an increase in the ceramic content in the composite, the flexural strength and fracture toughness in the longitudinal direction gradually decreased; whereas, in the transverse direction they showed a first increase and then decrease but their elastic modulus increased. The composites displayed significant damage-tolerance anisotropy, with higher strength and toughness in the longitudinal direction (parallel to the lamellae) than that in the transverse direction (perpendicular to the lamellae). In the longitudinal bending, the ZL205A/20 vol%SiC composite exhibited the maximum flexural strength (760 MPa) and the largest fracture toughness (33.0 MPa m 1/2 ). The excellent damage tolerance of the composites was attributed to multiple toughening mechanisms such as plastic deformation in the matrix alloy, crack blunting, deflection and branching, and uncracked-ligament bridging of the ductile alloy layers. However, in the transverse bending, the crack propagated along the ceramic layer in the composites and thus greatly weakened their damage-tolerance capability. [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]

The present work investigates the microstructure and tensile properties of a hot rolled 6061 alloy quenched by cold rolls (RQ) at different preheating temperatures. The preheating temperature strongly affects microstructure evolution and mechanical properties. Low preheating temperature (490 °C) resulted in both low strength and low elongation. The RQ alloy preheated at 540 °C exhibited improved ductility compared to those subjected to T6 and T8 temper, and comparable strength to that after T8 temper. The dynamic recovery during hot rolling contributed to the improved tensile elongation and retained work hardening. High preheating temperature also led to pronounced ageing hardening during short-term ageing. [ABSTRACT FROM AUTHOR]

The cast aluminum alloys with light weight and good castability show great potential in aerospace and automotive applications. Due to their poor weldability and the low strength of welded joints, these alloys are difficult to fuse using conventional fusion welding techniques. Here, through friction stir welding (FSW) for cast Al-Si 7 -Cu 4 -Mg 0.3 alloy manipulated by in-situ nanocrystals, a novel method to realize the automatic solid-state joining of cast aluminum alloys was proposed, along with the guarantee of high strength-plasticity combination of the joints. The microstructure of cast Al-Si 7 -Cu 4 -Mg 0.3 alloy comprehensively manipulated by in-situ nanocrystals ensured the complete globalization of eutectic silicon and comprehensive mechanical performances of base materials to fulfill FSW. The microstructure evolution across various welded regions of the joints was revealed. The dendritic grains with a certain degree of coarsening and short needle-like eutectic silicon were formed in the heat affected zone (HAZ), and the mechanism of microstructure evolution was mainly dynamic recovery (DRV). The dynamic recrystallization (DRX) of grains in the nugget zone (NZ) resulted in regular fine equiaxed grains, and nearly spherical eutectic silicon distributed uniformly in the matrix. The optimal yield strength (YS) and ultimate tensile strength (UTS) of friction stir welded joints were 280 MPa and 400 MPa, which achieved 84.8% and 83.3% of the base material respectively (330 MPa and 480 MPa). This study contributes to producing friction stir joint of cast aluminum alloys with complex structures, as an alternative to traditional stamping-welding process of deformed aluminum alloys. Keywords • A novel method to realize the automatic solid-state joining of cast aluminum alloys was proposed. • The overall microstructure of base materials was refined by in-situ nanocrystals. • The microstructure evolution behavior of friction stir joints in different regions was revealed. • The friction stir joints exhibited excellent strength-plasticity combination. [ABSTRACT FROM AUTHOR]

Freeze casting has been widely used in the preparation of nacre-inspired composites because of its prominent advantages in controlling the fine structure of ceramic scaffolds. However, the ceramic-phase content in composites prepared by this method is much lower than that in nacre due to the limitations of the dispersion and viscosity of the ceramic slurry. In this work, we combined the ideas of freeze casting and in-situ reaction to prepare nacre-inspired lamellar composites with high hard-phase contents. We first prepared the TiO 2 -−SiO 2 porous scaffold with an initial solid loading of 20 vol% via unidirectional freeze casting and then infiltrated it with a 6061Al alloy. During the reaction process, the TiO 2 -SiO 2 layers were progressively transformed into Al 2 O 3 layers, and the Al layers were transformed into Al 3 Ti. Composites with different hard-phase volume fractions (approx. 29%, 38%, 52% and 65%) and different interfacial bonding strengths could be obtained by altering the infiltration temperature. Increases in the hard-phase content and the interfacial bonding strength substantially enhanced the bending and compressive strengths of the composites, with maximum values of 350 MPa and 854 MPa, respectively, achieved in the composites with approx. 65 vol% hard phases. However, the highest fracture toughness of 42.9 MPa m1/2 and maximum fracture work of 3.6 kJ/m2 appeared when the hard-phase content in the composite was approx. 38 vol%, sharing an appropriate interfacial bonding strength. A robust interface favors stress transfer but impedes crack deflection, while a weak interface fails to bear loads, even though it is conducive to crack deflection. A moderately-strong interface together with a considerable amount of layered soft phase contributes to the generation of multiple-cracking, and thereby greatly toughens the metal−ceramic composite. [ABSTRACT FROM AUTHOR]

Abstract The strength and toughness of a material are generally two mutually exclusive properties. Optimization of these properties can be realized by regulating microstructures based on a bio-inspired idea. Herein, we used gelatin as a pore-regulating agent to investigate the effect of microstructural transition from "nacre-like" lamellae to "honeycomb-like" reticulae on the mechanical properties of metal–ceramic composites. By introducing different quantities of gelatin into SiC slurries during freeze casting and infiltrating the sintered SiC scaffolds with pure molten Al, we prepared the Al/SiC (88/12 in volume) composites with variable yet controllable microstructures and further demonstrated that the desired properties could be achieved by tailoring their microstructures. Specifically, the Al/SiC composites with a fully laminated structure exhibited optimal fracture toughness (K Jc) of 51.9 ± 2.9 MPa m1/2 while those with a three-dimensional reticular structure displayed peak three-point flexural strength of 371 ± 6 MPa. The relationship between the microstructures and mechanical properties of the composites was addressed based on material strengthening and toughening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract The performances of particulate–reinforced aluminum matrix composites are strongly dependent on alloying elements, precipitates and added particulates. To reveal the sole influence mechanisms of high volume fraction of nanosized particulates on the solidification behavior, microstructure and mechanical properties of aluminum alloys, nanosized SiC P (60 nm) was incorporated into commercial pure Al at different volume fractions (i.e., 0, 1, 3, 5, 7 and 9 vol%) by stir–casting assisted ultrasonic vibration. The results reveal that a fairly uniform dispersion of nanosized SiC P throughout the matrix was achieved at a volume fraction as high as 7 vol%. Average α–Al dendritic sizes were significantly refined from 270 µm for the matrix to 90 µm in the solidified microstructure of nanocomposites. Thermal analysis during solidification indicates that the presence of nanosized SiC P increased the nucleation temperature of α–Al, whilst recalescence during solidification process disappeared. Additionally, the yield and ultimate tensile strength of the nanosized SiC P /Al composites at both ambient temperature and 453 K were remarkably improved, whilst remaining suitable fracture strain. Theoretical analysis suggests that the significant strength increments induced by nanosized SiC P at ambient temperature could be attributed to thermal mismatch strengthening, Orowan strengthening and grain refinement strengthening, while the pinning effect of nanosized SiC P could predominantly account for the strengthening effect at 453 K. Highlights • Nanosized SiC P refined the microstructure via heterogeneous nucleation and inhibited growth. • SiC P enhanced strengths at 298 K mainly due to thermal mismatch and Orowan strengthening. • Pinning effects of SiC P on grain boundaries and dislocation climbing enhanced strengths at 453 K. [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 bimodal-sized (micron+nano) TiC p /Al-Cu composites were successfully fabricated by adding the in situ micron-sized and nano-sized TiC p -Al master alloys into the molten Al-Cu alloy. The composites reinforced with bimodal-sized TiC p exhibited finer α-Al grains and smaller θ′ precipitates, and possessed enhanced room- and high-temperature strength and relatively high ductility compared with the Al-Cu matrix alloy and their counterparts reinforced with monomodal-sized TiC p . The improved tensile properties may be attributed to the more significant precipitation strengthening due to the smaller θ′ precipitates, grain refinement and strengthening effects of the nano-sized and micron-sized TiC p . [ABSTRACT FROM AUTHOR]

Freeze casting has been proven to be a versatile processing approach for the design of biomimetic composites that exhibit unique combinations of strength and toughness. However, to date, most studies have focused on polymer–ceramic composites, and very limited work has examined metal–ceramic composites, even though the latter possess much superior mechanical properties. In this work, we prepared nacre-like Al/Al 2 O 3 –ZrO 2 composites using freeze casting and pressure infiltration techniques and then investigated the influences of the ceramic lamellae compactness and interface reaction on the mechanical properties and fracture behavior of the composites. The results show that the compactness of the ceramic lamellae greatly influences the Al penetration and subsequent interfacial reaction with ZrO 2 . The presence of Al 3 Zr reaction product layers facilitates crack initiation and interface debonding, weakening the fracture toughness of the composites. The ceramic lamellae can be densified by using fine ceramic particles and increasing the ceramic loading and sintering temperature, thus greatly reducing the extent of the interfacial reaction and improving the strength and toughness of the materials. [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 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]

Al–Zn–Mg–Cu alloys that are prone to segregation and hot cracks always encounter difficulty in manufacturing large-size workpiece with desirable strength-plasticity synergy, especially when the tonnage of the extruder exceeds 6000 tons. This work puts forward a novel idea to address this challenge by joining extruded profiles of Al–Zn–Mg–Cu-based composite reinforced by trace in-situ TiC–TiB 2 nanoparticles through friction stir welding (FSW). The extruded profiles of Al–Zn–Mg–Cu-based composite along transverse direction (TD) achieved superior yield strength (σ Y) of 827 MPa and large plastic strain (ε p) of 10.2%. The σ Y of FSW-ed joint along TD reached 847 MPa, and the ε p was maintained at 2.8%. It was found that trace nanoparticles can weaken the grain boundary segregation of the composite ingot significantly, effectively avoiding the hot cracking that may occur during hot extrusion and FSW. In extruded profiles, nanoparticles promoted the nucleation of η′ precipitates, promoted the dislocation multiplication, and increased the proportions of low-angle grain boundaries (LAGBs) within 2°–15° and high-angle grain boundaries (HAGBs), thereby enhancing the strength. Meanwhile, nanoparticles increased the density of LAGBs and facilitated the precipitation of Guinier–Preston (GP) zones, which facilitated to maintain high plasticity of the extruded profiles of composite. Additionally, nanoparticles can effectively inhibit the abnormal grain growth in nugget zone (NZ) during post-weld heat treatment (PWHT), which strengthened the FSW-ed joint. This work elaborated the multiscale microstructure evolution mechanisms, offering guidance to fabricate Al–Zn–Mg–Cu workpieces with infinitely extensive size as required in actual manufacturing and fantastic mechanical performances. [Display omitted] • Trace in-situ TiC–TiB 2 enhanced performance of large-size Al–Zn–Mg–Cu composite. • TiC–TiB 2 optimized segregation, recrystallization and precipitation behavior. • TiC–TiB 2 inhibited the abnormal grain growth during post-weld heat treatment. • Microstructure evolution and performance improvement mechanisms were revealed. [ABSTRACT FROM AUTHOR]

Inspired by nacre, we designed biomimetic metal–ceramic composites in which hard and ductile phases were alternately arranged. We first prepared lamellar-structured TiC scaffolds with 25, 30 and 35 vol% solid loadings using a unidirectional freeze casting technique and then measured wetting and infiltration dynamics for a commercial Al cast alloy, ZL107, with the main composition of Al–7Si–5Cu on the porous TiC scaffold using a modified sessile drop method at 850 °C. The wetting was affected by liquid spreading at horizontal surface and infiltration in depth, while the latter played a dominant role in the decrease in contact angle. On the basis of the wetting results, the lamellar ZL107/TiC composites were successfully fabricated by pressure infiltration of the molten ZL107 alloy into porous TiC scaffolds and their mechanical properties were evaluated. The compressive strength and elastic modulus increased while bending strength decreased with increasing TiC content, giving maximum values of 1166 ± 20 MPa, 205 ± 2 GPa and 363 ± 5 MPa, respectively. Formation of (Al m ,Si 1 − m ) 3 Ti, Al 3 Ti and Al 4 C 3 phases in the composites was presumed to deteriorate the toughness of the composites, leading to brittle fracture under loading. [ABSTRACT FROM AUTHOR]

The composites reinforced with Ti 5 Si 3 -coated SiC P showed higher relative densities and mechanical properties than those of uncoated ones. It is mainly due to the translation of Ti 5 Si 3 coating layer into Al 3 Ti interfacial layer during the sintering process, increasing the interfacial bonding strength between α-Al and SiC P . [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]

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]

Solution heat treatment (SHT), immediately followed by water quenching, can significantly improve the strength of precipitation-hardenable metallic materials, but frequently compromises the well-defined dimensional design of the geometrically complex or thin-wall engineering components. Here, to avoid this catastrophic high-temperature scheme, we introduce an alternative conceptual strategy to design a novel hypoeutectic Al–10Si–Mg alloy especially for "as-cast" services, i.e., extraordinarily high Mg addition and trace co-incorporation of innovative in situ TiCN–TiB 2 particles coupled with a direct post-solidification isothermal low-temperature stabilization treatment (LTST). The performance was carefully characterized by multi-scale characterization techniques. Solidification kinetics and the resultant microstructural arrangement response to the TiCN–TiB 2 particle additions were systematically investigated. Results demonstrated that both α-Al dendrites and eutectic Si structures were substantially refined by the TiCN–TiB 2 particles. In the absence of conventional SHT, the precipitation kinetics associated with the customized LTST was also thoroughly studied. Interestingly, an extremely fine dispersion and high number density of perfectly coherent GP zones and pre- β'' nanoprecipitates were found coexisting after LTST. As a result, well-combined strength and ductility were therefore achieved by the synergistic effects of trace TiCN–TiB 2 particles and LTST in this Al–10Si-2.0 Mg system. • In situ TiCN–TiB 2 particles enabled significant microstructure refinement. • More highly supersaturated solid solutions were obtained by TiCN–TiB 2 particles. • GP zones and pre- β'' coexisted after low-temperature stabilization treatment. • Excellent strength-ductility was yielded after direct thermal exposure at 150 °C. [ABSTRACT FROM AUTHOR]

TiAl-5wt.%Ti 2 AlC-3wt.%Mn composites reinforced by the addition of Mn and in situ synthesized Ti 2 AlC nanoparticles with a novel microstructure were fabricated. The microstructure and compressive properties of the fabricated composites were thoroughly investigated. The interface between the nanoparticles and the TiAl matrix maintained a very small mismatch and exhibited a stable combination, leading to noticeable grain refinement in the fabricated composites. Furthermore, the yield strength, maximum compressive strength, fracture strain, and strength-ductility balance of the TiAl-5wt.%Ti 2 AlC-3wt.%Mn composites increased by 30.7%, 10.1%, 5.5%, and 9.9%, respectively, compared with those of the TiAl alloy. The mechanisms by which the properties of the composites were improved mainly thermal mismatch strengthening, Orowan strengthening, grain refinement strengthening, and solid solution strengthening. • In-situ Ti 2 AlC particles and Mn evolved TiAl alloy into a refined microstructure. • The interface between the TiAl matrix and nanoparticles exhibited a stable combination. • Toughness and strength of TiAl composites were significantly elevated by 9.9% and 30.7%. • The dominant ones were the thermal mismatch and the Orowan strengthening mechanism. [ABSTRACT FROM AUTHOR]

A new design method of Al-Si-Mg alloy manipulated by in situ nanosized crystals was proposed. Starting from source design of the microstructure manipulation agent with a high crystallographic matching relationship with the α-Al, eutectic Si and Mg 2 Si phases in Al-Si-Mg alloy, the interatomic misfit (f r) between NiTi(B2) and α-Al or Mg 2 Si is 5.0% or 5.3%, respectively, and that between NiTi(B2) and Si is 9.9%, corresponding to good crystallographic matching. Based on calculations, in situ nanosized crystals could be considered as heterogeneous nucleation sites of α-Al, eutectic Si and Mg 2 Si, thus, uniformly fine α-Al grains, near-spherical eutectic Si and fine precipitated Mg 2 Si were obtained. The solidification behavior analysis also highly corresponded to the E2EM calculations. In the alloy manipulated by 0.05 wt% NiNbTi manipulation agent, the average sizes of α-Al, eutectic Si and Mg 2 Si were greatly decreased by nearly 8, 2 and 20 times, respectively, thus achieving comprehensive multiscale manipulation of the microstructure of the alloy in one step. Specially, the huge energy stemmed from the B2 to B19' phase transformation will generate a large number of crystal defects, which provides nucleation sites and driving force for the formation of Mg 2 Si and greatly refines the Mg 2 Si.Moreover, the yield stress, tensile stress and fracture strain of the manipulated alloy were simultaneously improved by 34.1%, 20.4% and 35.0%, respectively. The excellent strength and plasticity could be ascribed to grain-refinement strengthening, Orowan strengthening and eutectic Si refinement and spheroidization, which reduced the stress concentration during deformation. The comprehensive microstructure manipulation of Al-Si-Mg alloy using nanosized crystals formed by in situ physical crystallization, especially the manipulation of the precipitated phase, is an innovative work that not only avoids the "poisoning" effect between multiple manipulation agents but also realizes comprehensive manipulation of the overall microstructure, consequently broadening further industrial applications. • The low fr shows good mismatch between Al, Si, Mg 2 Si and NiTi. • The new method achieves multiscale manipulation of the alloy in one step. • The mean sizes of α-Al, eutectic Si and Mg 2 Si were decreased by nearly 8, 2 and 20 times. • The yield strength and plasticity were simultaneously improved by 34.1% and 35.0%. [ABSTRACT FROM AUTHOR]

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]

Al Cu alloys inoculated by in-situ nano-sized particles crystallized from Ni-Nb-Ti amorphous alloys were prepared by casting method in this work. Different compositions of Ni-Nb-Ti amorphous alloys significantly enhanced heterogeneous nucleation for α-Al and promoted obvious grain refinement of the Al Cu alloys. It was found that 0.05 wt% Ni-Nb-Ti amorphous alloys addition caused a significant and efficient refinement on α-Al (from 200 μm to 39 μm) and θ′ phase (from 146.4 nm to 37.6 nm). The strength and ductility of the inoculated alloy were improved significantly at high temperature. The tensile strength and fracture strain of the alloy inoculated by 0.05 wt% Ni-Nb-Ti amorphous alloy for 20 min at 533 K under the strain rates of 10−1 s−1 were increased by 32.63% and 90.35% respectively, compared to those of the uninoculated alloy. The nano-sized NiTi particles contributed to the grain refinement of α-Al, and grain refinement shortened the solute atomic diffusion distance and refined θ′ phase during heat treatment, resulting in higher strength and plasticity at high temperature. The model developed for this new type Al Cu alloy is found to be efficient in predicting the stress at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. • In-situ nano-sized NiTi can serve as efficient heterogeneous nuclei of α-Al. • Inoculation caused a significant refinement on α-Al and precipitation θ′ phase. • The tensile strength and fracture strain were increased by 32.63% and 90.35% respectively at 533 K with 10−1 s−1. • The enhanced tensile property was due to the finer θ′ phase which impeded dislocation motion. • A stress prediction model was presented at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. [ABSTRACT FROM AUTHOR]

Ni-coated SiC p /Al–Cu nanocomposites with different addition levels (0, 1, 2 and 3 wt% Ni-coated SiC p nanoparticulates) were successfully fabricated by semisolid stir casting combined with hot extrusion. The microstructures of the as-cast and hot-extruded nanocomposites showed that the grain size could be substantially refined. The dispersion mechanism of the SiC p nanoparticulates was discussed. Because the Al 3 Ni that was formed on the SiC p surface improved the wettability, more Ni-coated SiC p nanoparticulates were captured as the solid/liquid interface advanced, causing the Ni-coated SiC p to enter the α-Al interior and reduce agglomeration in the grain boundaries. The strengthening mechanism of the SiC p nanoparticulates at room temperature and high temperatures was studied. At 298 K, the strengthening was attributed to the hindrance of dislocation movement by the uniformly distributed SiC p nanoparticulates, grain size refinement and thermal mismatch strengthening. At 453 K and 493 K, the strengthening effect was ascribed to the impeded dislocation climb by the SiC p nanoparticulates distributed in the grain interior and the pinning effect of nanoparticulates on the grain boundaries. [ABSTRACT FROM AUTHOR]