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In this study, concurrent enhancements in both strength and ductility of the Al-2Li-2Cu-0.5Mg-0.2Zr cast alloy (hereafter referred to as Al-Li) were achieved through an optimized forming process comprising ultrasonic treatment followed by squeeze casting, coupled with the incorporation of Sc. Initially, the variations in the microstructure and mechanical properties of the Sc-free Al-Li cast alloy (i.e., alloy A) during various forming processes were investigated. The results revealed that the grain size in the UT+SC (ultrasonic treatment + squeeze casting) alloy was reduced by 76.3% and 57.7%, respectively, compared to those of the GC (gravity casting) or SC alloys. Additionally, significant improvements were observed in its compositional segregation and porosity reduction. After UT+SC, the ultimate tensile strength (UTS), yield strength (YS), and elongation reached 235 MPa, 135 MPa, and 15%, respectively, which were 113.6%, 28.6%, and 1150% higher than those of the GC alloy. Subsequently, the Al-Li cast alloy containing 0.2 wt.% Sc (referred to as alloy B) exhibited even finer grains under the UT+SC process, resulting in simultaneous enhancements in its UTS, YS, and elongation. Interestingly, the product of ultimate tensile strength and elongation (i.e., UTS × EL) for both alloys reached 36 GPa•% and 42 GPa•%, respectively, which is much higher than that of other Al-Li cast alloys reported in the available literature. [ABSTRACT FROM AUTHOR]

In this study, a high-strength and high-toughness Mg–5Sn–1Ca (i.e., TX51) alloy was produced through a continuous squeeze casting-extrusion (CSCE) process without billet homogenization or secondary preheating for the first time. Effects of extrusion temperature and extrusion ratio on the microstructure and mechanical properties of extruded TX51 alloy were investigated. The results show that the CaMgSn eutectic in the as-cast billet was crushed during the CSCE process and exerted the particle stimulated nucleation (PSN) effect, which stimulated dynamic recrystallization of α-Mg. Improper extrusion temperature and extrusion ratio will lead to incomplete recrystallization or grain growth in the extruded alloy, whereas the average grain size of CSCE TX51 alloys can be as small as 2 μm under appropriate process parameters. Interestingly, the TX51 alloy prepared by the CSCE process achieved an excellent strength-toughness match, with optimal ultimate tensile strength, yield strength and elongation of 277.1 MPa, 233.2 MPa and 23.27%, at an extrusion ratio of 16:1 and an intermittent time of 60s (i.e., extrusion temperature is 246 °C). Based on quantitative calculations, the high strength and plasticity are attributed to four strengthening mechanisms, among which grain boundary strengthening and geometric strengthening are the most important contributors. [ABSTRACT FROM AUTHOR]

Abstract Nano-sized SiC particles (SiC np for short) reinforced Al-5Cu-0.5Mn-0.15Ti composites have been successfully fabricated by a process consisting of high energy ball milling, mechanical stirring and ultrasonic treatment for composite slurry and squeeze casting. The variation of microstructure and mechanical properties with SiC np levels in x SiC np /AlCuMnTi (x = 0.5, 1, 1.5, 2 wt%) composites is investigated for the first time. The SiC np are uniformly distributed in the SiC np /Al-5Cu composites made with the process. With the increase of SiC np content from 0.5 to 2.0 wt%, the primary α-Al and Al 2 Cu phases are refined significantly up to 1.5 wt% but then become coarser at 2.0 wt%. The optimal mechanical properties are obtained in 1.5 wt% SiC np /AlCuMnTi composites, which exhibit 298 MPa in ultimate tensile strength (UTS), 178 MPa in yield strength (YS) and 12.9% in elongation. These properties are increased by 18.7%, 11.3% and 25.3%, respectively, compared with the AlCuMnTi matrix alloy. The enhancement of strength is attributed to four strengthening mechanisms, among which the Δ σ C T E and Δ σ O r o w a n are the most important contributors. It is noteworthy that with more SiC np in the present composites, the strength increases while elongation increases as well. Highlights • The SiC np are uniformly distributed in the SiC np /Al-5Cu composites with ultrasonic treatment. • The primary α-Al and Al 2 Cu phases are refined in the composites with the addition of SiC np. • With increase of SiC np content in composites, the strength increases while elongation increases as well. • The contributions of SiC np content and various strengthening mechanisms are analyzed. [ABSTRACT FROM AUTHOR]

Effects of semisolid squeeze casting (SSC) process on microstructures and mechanical properties of the LPSO structure reinforced Mg 97 Zn 1 Y 2 alloy were studied by optical microscopy, SEM equipped with EDS, TEM, XRD and Nanoscale indentation for the first time. The LPSO structure and α-Mg grains in the Mg 97 Zn 1 Y 2 alloy can be refined significantly by SSC. The gran size of α-Mg was decreased from 170 µm to 109 µm, and the LPSO structure could be distributed uniformly in the alloy under the combined action of ultrasonic vibration (UV, preparation for semisolid slurry) and squeeze casting (SC). The type of LPSO structure was remained as the initial 18R-type structure after SSC, but a strip YZn 3 phase precipitated out inner the block LPSO structure, which has never been found in the LPSO-containing Mg 97 Zn 1 Y 2 alloy. With the increase of squeeze pressure, the amount of YZn 3 phase was increased and the tensile strength and elongation of the alloy were increased at first and then maintained nearly constant. When the pressure was 100 MPa, the optimum mechanical properties were obtained. The yield strength, ultimate tensile strength and elongation were 141 MPa, 234 MPa and 11.6%, which were enhanced by 28.2%, 11.1% and 45.1%, respectively, compared with those of the alloy without SSC. [ABSTRACT FROM AUTHOR]

The evolution of structural characteristics and mechanical properties of Cu-Zr metallic glasses during multiple recovery annealing process was investigated via molecular dynamics simulation. Firstly, the aged and rejuvenated samples were prepared after the first recovery annealing by varying the annealing temperature. Then, these samples were subsequently treated with the following annealing process. It is found that when reheating the firstly aged sample (annealing at 900 K) to a higher annealing temperatures of 1100 K at the second annealing, the degree of rejuvenation was even higher than that of the initially rejuvenated sample (annealing at 1100 K) at the same temperature. Microstructural analysis shows that the degree of rejuvenation shows a strong correlation with Cu-centered clusters, around a 4% difference in < 0, 0, 12, 0 > (high local fivefold symmetry) content between the most aged and most rejuvenated samples. Moreover, the volume variation of different atomic clusters in the rejuvenated samples is more obvious. It is noted that the initial aged samples can be rejuvenated to an even higher degree when compared with initial rejuvenated ones. The more icosahedral clusters in the aged sample contributes to such phenomenon since they are more easily modified to other types with low local fivefold symmetry at high annealing temperature during the second annealing. The present study demonstrates that the appropriate multiple recovery annealing can rejuvenate the sample to a higher degree. • Multiple recovery annealing can adjust the degree of ageing or rejuvenation. • Firstly aged sample can rejuvenate to a higher degree after multiple annealing. • More icosahedral structures with high local atomic symmetry in firstly aged sample. • The icosahedral clusters are more easily to be modified when annealed again. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration (UV) treatment has been successfully applied to improve the particles distribution of nano-sized SiC particles (SiC p ) reinforced Al-5Cu alloy matrix composites which were prepared by combined processes of dry high energy ball milling and squeeze casting. When UV treatment is applied, the distribution of nano-sized SiC p has been greatly improved. After UV for 1 min, large particles aggregates are broken up into small aggregates due to effects of cavitation and the acoustic streaming. After UV for 5 min, all the particles aggregates are dispersed and the particles are uniformly distributed in the composites. Compared with the Al-5Cu matrix alloy, the ultimate tensile strength, yield strength and elongation of the 1 wt% nano-sized SiC p /Al-5Cu composites treated by UV for 5 min are 270 MPa, 173 MPa and 13.3%, which are increased by 7.6%, 6.8% and 29%, respectively. The improvements of mechanical properties after UV are attributed to the uniform distribution of nano particles, grain refinement of aluminum matrix alloy and reduction of porosity in the composites. [ABSTRACT FROM AUTHOR]

Although reinforced by quasicrystal I-phase, Mg-Zn-Y castings with low contents of Zn and Y exhibits still inadequate strength at elevated temperature. In this study, different contents of low-cost misch metal (Mm, the mixture of Ce and La) were added to ZW61 (Mg-6Zn-1.4Y) alloy to develop a new series of Mg alloys simultaneously containing multiple rare earth elements. The effects of Mm content on the microstructure, mechanical properties and fracture mechanisms both at room and elevated temperatures were systematically investigated. The results showed that the addition of Mm contributed to the grain refinement and the formation of T-phase. Besides, the precipitation behaviors of I-phase and W-phase were also changed due to the variation of Mm content. The yield and tensile strengths at room temperature firstly increased with 1 wt% Mm addition, but then deteriorated slightly when adding more Mm. In contrast, the strengths at 200 °C kept a continually increasing trend and the yield strength and ultimate tensile strength of ZW61-3Mm alloy were respectively increased by 20.9% and 28.0% compared with the corresponding strengths of ZW61 alloy, which were mainly attributed to the reduction in grain size and the high volume fraction of thermally-stable T-phase and W-phase. [ABSTRACT FROM AUTHOR]

In this study, in-situ 3 wt% Mg 2 Si/Al–Cu composites have been prepared by a novel continuous squeeze casting-extrusion (CSCE) process assisted with ultrasonic treatment (UT) for the first time. Different from the traditional semi-continuous hot extrusion process, the new method eliminates billet homogenization annealing and preheating. After UT + CSCE, the fine Al 2 Cu and eutectic Mg 2 Si phases in the UT + SC (squeeze casting) billet are further crushed to form a fibrous microstructure distributed along the extrusion direction (ED). Moreover, the α-Al grains are elongated along the extrusion direction, and the proportions of LAGBs (low-angle grain boundaries) and HAGBs (high-angle grain boundaries) are 72.3% and 27.7%, respectively. Meanwhile, fiber textures with orientations <111>//ED and <100>//ED are formed, and the ratios of the two textures are 60.9% and 30.5%, respectively. After UT + CSCE, the ultimate tensile strength (UTS), yield strength (YS) and elongation of the in-situ 3 wt% Mg 2 Si/Al–Cu composite are 330 MPa, 250 MPa and 11%, and its YS and elongation are 23.2% and 69.2% higher than those of the UT + SC billet, respectively. Compared with the Al–Cu alloy prepared by UT + CSCE, its UTS and YS are increased by 11.9% and 38.9%, respectively. [ABSTRACT FROM AUTHOR]

The content of alloying elements in most thermally conductive magnesium alloys is as low as possible, and this will lead to lack of alloying effect. In this paper, a Mg-xZn-xCu(x = 1,3,5, wt%) alloy was studied with comparatively high alloying element contents. The thermal conductivity of this alloy declines very slowly with the increment of element concentration. Even with the additive amount of 10 wt% of alloying elements, this alloy can attain a high thermal conductivity of 136.5 W/(m·K). After T6 treatment, the thermal conductivity of Mg-5Zn-5Cu alloy increases to 141.6 W/(m·K). The CuMgZn intermetallic compound are specially prepared to study the thermal conduction mechanism. The results show that the formation of CuMgZn ternary compound in Mg-Zn-Cu alloy consumes massive solute atoms, which makes the thermal conductivity of the alloy insensitive to alloy composition changes. • The Mg-xZn-xCu alloy possesses high thermal conductivity with relatively high element content. • The CuMgZn ternary compound was prepared and its thermal conductivity was investigated. • The Mg-Zn-Cu alloy has a broad range of composition regulation due to the formation of CuMgZn. [ABSTRACT FROM AUTHOR]

Due to a monolithic body-centered cubic solid solution structure, refractory high-entropy alloys (HEA) always exhibit high strength and good softening resistance at both ambient and elevated temperatures. However, high density and low plasticity at ambient temperature limit their widespread applications as one kind of potential structural materials. The present study investigated the microstructure and mechanical properties of MoNbVTa x HEA with various Ta conent at both ambient and elevated temperatures. The sample of MoNbVTa x (x = 0, 0.3, 0.5, 0.7, 1) all shows a monolithic BCC solid solution phase with a dendritic microstructure. The micro-segregation of constituent elements was caused by the non-equilibrium solidification. The alloys exhibit superior high temperature performance at 1000 °C and 1200 °C, with a certain degree of plasticity at ambient temperature. The MoNbVTa 0.5 alloy possesses both excellent high temperature performance (σ 0.2 =697 MPa, ε p = 35.4% at 1200 °C) and relatively low density (∼9.65 g/cm3), which is attributed to the solid solution strengthening effects and excellent thermal stability of constituent phase. Compared with commercial superalloys, the present MoNbVTa HEAs possess the advantages of high temperature performance, making it a potential engineering material for structural application. • The microstructure and mechanical properties at both ambient and elevated temperatures of MoNbVTa x HEAs are investigated. • The degree of elemental micro-segregation can be quantitatively analyzed, more severe with more Ta. • All MoNbVTa x alloys exhibit excellent strengths and plasticity at ambient temperature and elevated temperatures. • MoNbVTa 0.5 shows the best high temperature mechanical property, yielding at near 700 MPa at 1200 °C. • The yield strength of different alloys could be described by the solid solution strengthening mechanism. [ABSTRACT FROM AUTHOR]

The refinement of the microstructure and uniform distribution of RE-rich intermetallic compounds are beneficial for strengthening and toughening the rare earth (RE) containing Mg alloy castings. A novel Mg–3RE–6Zn–1.4Y alloy was designed, and fabricated by rheo-squeeze casting (RSC) in this research. The semi-solid slurry used in the process was treated by direct ultrasonic vibration (DUV) and then casted with squeeze casting. The microstructure evolution and mechanical properties of the RSC alloy with different pressures were investigated. The RE-rich intermetallic compounds were analysed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). The results indicate that the increase of the pressure not only contributes to the refinement of α-Mg grains but also results in the increasing solid solubility in the matrix and uniform distribution of RE-rich intermetallic compounds along the grain boundary. The tensile properties increase continuously with the increase of applied pressure. The yield strength (YS), ultimate tensile strength (UTS) and elongation of RSC sample under 200 MPa pressure are 110 MPa, 180 MPa and 8.6%, which are improved by 17.0%, 19.2% and 81.7% respectively than the corresponding values of the samples without pressure. [ABSTRACT FROM AUTHOR]

In this paper, the strength and ductility of Al–Cu–Mn–Ti alloy prepared by squeeze casting have been simultaneously increased after heat treatment. The effects of solution and aging treatment on the microstructure evolution and mechanical properties of squeeze cast Al–Cu alloy are investigated to discuss its micro-mechanism using various methods, including SEM, XRD, EBSD and TEM. The results show that the Al 2 Cu phase disappeared completely after solution treatment at 530 °C for 10h. During aging, nano-sized or submicron-sized Al 12 Mn 2 Cu precipitates and much smaller nano-sized θ'' phase were uniformly distributed throughout the alloy, and the interface between the two phases and the matrix was coherent. After solution + aging treatment (i.e., T6 treatment) the ultimate tensile strength, yield strength and elongation of the alloy were 445 MPa, 265 MPa and 17.9%, which were increased by 71.2%, 65.6% and 70.5%, respectively, compared with the as-cast alloy. The precipitation strengthening caused by the two kinds of precipitates θ'' and Al 12 Mn 2 Cu is the most important factor for the simultaneous increase in the strength and elongation. [ABSTRACT FROM AUTHOR]

Abstract: The semisolid slurry of A356 Al alloy was prepared by indirect ultrasonic vibration (IUV) method and then formed by direct squeeze casting (SC). The effects of squeeze pressure and T6 heat treatment on the microstructure and mechanical properties of rheo-squeeze casting (RSC) A356 Al alloy were investigated. The results indicate that with the increase of squeeze pressure, the average diameter of primary α-Al particles decreased, while the densities and mechanical properties of the samples increased. The effect of T6 heat treatment on the mechanical properties is more significant in RSC samples than in conventional SC samples. The tensile strength and elongation of T6 heat treated RSC samples under 100MPa pressure are 338MPa and 8%, respectively. [Copyright &y& Elsevier]

Abstract: This paper reports a new slurry-making process with indirect ultrasonic vibration (IUV), in which the horn is vibrated under the outside of the metallic cup containing alloy melt. Semisolid slurry of A356 Al alloy was prepared by this process, and the effects of IUV treatment time on the morphology of the primary α-Al phase and mechanical properties of rheo-diecasting samples were studied. The results indicate that excellent semisolid slurry of A356 Al alloy could be obtained within 50s by applying IUV near its liquidus temperature. The sample rheocasted with the slurry made by IUV for 50s had the maximum tensile strength and elongation, which were 254MPa and 7.5% respectively. [Copyright &y& Elsevier]

Abstract: The indirect ultrasonic vibration (IUV) method, in which the horn was vibrated under the outside of the metallic cup containing alloy melt, was employed for preparing semisolid slurry of 5083 Al alloy in this work. The effect of IUV on the microstructure of semisolid slurry and mechanical properties of rheo-diecasting samples were studied. The results indicate that good semisolid slurry could be obtained when the melt treated by IUV for 50s, and the average diameter and shape coefficient of primary α-Al particles were 60μm and 0.54 respectively. Apart from preparing semisolid slurry with fine microstructure, IUV had degassing effect on semisolid slurry of 5083 Al alloy. The tensile strength and elongation of the rheo-diecasting samples were 283MPa and 9% respectively, which were increased by 11.4% and 32.4% respectively compared to conventional liquid die-casting samples. [Copyright &y& Elsevier]

In this study, through the comparison of the microstructure evolution between composites and matrix alloy, the effects of nano-sized SiC particles (i.e. nano-SiC p) on solution behavior and properties of 1 wt.% nano-SiC p /Al-Cu composites were investigated for the first time. Results indicate that different from the traditional solution treatment process of Al-Cu matrix alloy, due to the hindering effect of nano-SiC p on the solution behavior of Al 2 Cu phase, the composites need higher solution temperature to show better mechanical properties. The T6 treated composites exhibit excellent hardness and tensile properties after solution treatment at 540 °C for 10 h. Its hardness, ultimate tensile strength and yield strength are 150 HV, 500 MPa and 350 MPa, which are increased by 120 %, 82 % and 106 % than that of the as-cast composites respectively. Compared with the T6 treated Al-Cu matrix alloy, the UTS and YS of nano-SiC p /Al-Cu composites are elevated by 16.3 % and 34.6 %, respectively. [ABSTRACT FROM AUTHOR]

A novel continuous squeeze casting-extrusion (CSCE) process was proposed to prepare high strength and toughness AZ31 alloy. The average grain size of AZ31 alloy after CSCE was reduced to 2.43 μm. An excellent combination of the ultimate tensile strength of 321 MPa and the elongation of 14.7% was achieved. [ABSTRACT FROM AUTHOR]

The in-situ porous Ti particle reinforced Mg-based bulk metallic glass matrix composites have been successfully prepared via dealloying reaction in metallic melt. The microstructure, thermal properties and mechanical properties of the composites containing various volume fraction of porous Ti particles were investigated in detail. It is shown that with higher content of porous Ti particles, the glass-forming ability of the composites degrades gradually with the precipitation of fine crystalline phases among the glassy matrix. When the volume fraction of porous Ti particle is 26.3 vol%, the composite shows an fracture strength of 1125 MPa, 14.1 % higher than the monolithic glassy base alloy. Furthermore, the composite also exhibit an improved plastic strain of 0.94 %. The in-situ porous Ti particle and the submicron crystalline phase can hinder the rapid propagation of the main shear bands, causing the generation of multiple shear bands. It is found that abundant shear bands are formed around the porous Ti particle. The present synthesis strategy of in-situ porous reinforcing phase will contribute to the breakthrough in designing novel metal matrix composites. • Porous Ti particles were induced in Mg-based BMG matrix via dealloying reaction. • Pores are fulfilled with the matrix and good bonding are formed between them. • Mechanical properties were improved in the composites compared with the base alloy. • Strength and plasticity were higher in samples with more porous particles. [ABSTRACT FROM AUTHOR]

The viscosity of high Fe-containing hypereutectic Al–Si alloys was studied by using a high-temperature Searle-type rheometer. The results show that the steady-state viscosity of Al–17Si–(2,3,4) Fe alloy melts increases with the increase of iron content. During the continuous cooling of Al–17Si–(2,3,4) Fe alloy melts, the transient viscosity increases slowly at the initial stage of cooling. When the temperature decreases to a critical value, the transient viscosity increases abruptly. In the cooling process of Al–17Si–2Fe–(0,0.4,0.8)Mn alloy melts, the steady-state viscosity continues to increase and reach the maximum value firstly, then decreases abruptly, and then continues to increase again. The steady-state viscosity of Al–17Si–2Fe, Al–17Si–2Fe–0.4Mn and Al–17Si–2Fe–0.8Mn alloy melts experiences a sudden decrease at 630°C, 640°C and 670°C respectively due to the settlement of Fe-rich phases. The maximum value of viscosity of the Al–17Si–2Fe–(0,0.4,0.8)Mn alloy melts is increased with the increase of Mn content. [ABSTRACT FROM AUTHOR]

The effects of high pressure rheo-squeeze casting (HPRC) on Fe-containing intermetallic compounds (FIMCs) and mechanical properties of Al-17Si-2Fe-(0, 0.8)V alloys were studied. The melt of alloys was treated by ultrasonic vibration (UV), then the melt was formed by high pressure squeeze casting (HPSC). The results show that irregular polygonal AlFeVSi phase is formed when 0.8%V is added into the Al-17Si-2Fe alloy. When the pressure is 0 MPa, the FIMCs in HPSC alloy are coarse plate-like or long needle-like. The coarse FIMCs are fractured as the pressure is increased to 100 MPa. The degree of fragmentation is enhanced with the increase of pressure from 100 MPa to 300 MPa. When the pressure is 0 MPa, the FIMCs in HPRC alloys are refined significantly, and the size of block-like δ phase and short needle-like β phase are decreased furtherly as the increase of pressure. For the alloy with the same composition, the ultimate tensile strength (UTS) of HPRC sample is higher than that of the HPSC sample under the same pressure. The UTS is increased with the increase of the pressure irrespective of whether there is UV or not. With HPSC, the UTS of Al-17Si-2Fe-0.8 V alloy samples is increased by 4.6%, 7.1%, 7.4% and 7.3% respectively compared with that of Al-17Si-2Fe-0V alloy samples under 0, 100, 200 and 300 MPa. With HPRC, the UTS of Al-17Si-2Fe-0.8 V alloy samples is increased by 5.4%, 4.3%, 6.3% and 6.2% respectively compared with that of Al-17Si-2Fe-0V alloy samples under 0, 100, 200 and 300 MPa. [ABSTRACT FROM AUTHOR]

Effect of ultrasonic treatment (UT) on the microstructures and mechanical properties of Mg 99.0−x Ni x Y 1.0 (x = 0.5, 1.0, 1.5, at.%) alloys was investigated. With the increase of Ni content, the amount of eutectic structure, consisting of Mg, Mg 2 Ni phase and LPSO structure, increased while the mechanical properties decreased in as-cast alloys. After introducing UT to the melt, the secondary phases in these alloys were refined significantly and distributed uniformly, especially for long period stacking ordered (LPSO) structure. In Mg 98.5 Ni 0.5 Y 1.0 alloy, the formation of MgNi 4 Y phase, which was distributed adjacent to the LPSO structure at the grain boundaries, was stimulated by UT. In Mg 97.5 Ni 1.5 Y 1.0 alloy with UT, not only the width of grain boundaries were reduced, but also both the width of LPSO structure and that of eutectic structure were reduced. The optimal mechanical properties were obtained in Mg 98.5 Ni 0.5 Y 1.0 alloy, which exhibited 206 MPa in ultimate tensile stress and 7.96% in elongation, respectively. After UT, these properties were enhanced to 231 MPa and 14.56%, respectively. The other alloys’ mechanical properties were also enhanced significantly by UT. [ABSTRACT FROM AUTHOR]

The evolution of phase constituent of Mg 99.0-x Ni x Y 1.0 (x = 0.2, 0.5, 0.8, 1.0, 1.5, at.%) alloys was investigated by OM, SEM/EDS, TEM and XRD. Apart from the α-Mg phase, the secondary phases in these ternary alloys mainly consist of LPSO (long period stacking ordered) structure, Mg 24 Y 5 phase or Mg 2 Ni phase, which depend on the atomic ratio of Ni and Y. The amount of LPSO structure in the alloys increases firstly and then decreases with the increase of Ni level, but the change in the amount of LPSO structure is not proportional to that of Ni level. In the as-cast alloys containing excessive Ni, there exist two forms of LPSO structures with different characteristics of bulk and lamellar shapes, respectively. During solidification process, part of the bulk 18R-type LPSO structure formed firstly is transformed to the lamellar 14H-type LPSO structure. The tensile properties of different alloys are tested and the changing trend of strength is similar to that of the amount of LPSO structure. When the Ni content is 0.5 at.%, the ultimate tensile strength, yield stress and elongation are 208 MPa, 93 MPa and 8.0%, respectively, which are the optimal properties among these alloys. [ABSTRACT FROM AUTHOR]

Ternary Mg 94 Ni 2 Y 4 (at%) alloy was prepared by conventional gravity casting or direct squeezing casting and then subjected to T6 heat treatment. The influence of squeeze casting pressure and heat treatment on microstructure evolution and mechanical properties of Mg 94 Ni 2 Y 4 alloy containing long period stacking ordered (LPSO) structure was studied. The results show that gravity cast Mg 94 Ni 2 Y 4 alloy consisted of primary α-Mg, 18 R LPSO and eutectic structure containing α-Mg, LPSO and Mg 2 Ni phases. The application of pressure cannot change phase constituents and the type of LPSO phase. With the increase of squeeze casting pressure, microstructure was refined, the volume fraction of LPSO was decreased while that of eutectic structure was increased. Under the highest pressure of 320 MPa, kinking of LPSO phase was induced and the best mechanical properties were obtained, with the ultimate tensile strength of 250 MPa, the yield strength of 140 MPa and the elongation of 8%. They were improved by 20.2%, 22.8% and 45.5%, respectively, than those of gravity cast Mg 94 Ni 2 Y 4 . After heat treatment, bulk-shaped LPSO phase transformed into rod-shaped one, but no lamellar 14 H LPSO was precipitated in the matrix. Besides, the application of squeeze casting pressure prevented LPSO from delaminating during heat treatment. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration treatment is successfully applied in preparation of in-situ 5 vol% TiB 2 particulates reinforced Al-4.5Cu alloy matrix composites with salt-metal reaction route. Formation of TiB 2 phase is confirmed by X-ray diffraction analysis, and intermediate phases such as Al 3 Ti are not detected. Agglomerations of particles in the melt are effectively eliminated by the cavitation and acoustic streaming affects in the melt with ultrasonic vibration. TiB 2 particles are uniformly distributed throughout the bulk melt after treated by ultrasonic vibration for 240 s. The tiny agglomerations formed by TiB 2 particles smaller than 100 nm are also broken by ultrasonic vibration. Some TiB 2 particles smaller than 400 nm are observed to dispersed near grain boundary in the matrix after solidification. The optimal improvements of yield strength and ultimate tensile strength are 114% and 50%, respectively, when composite treated by ultrasonic vibration for 240 s. [ABSTRACT FROM AUTHOR]

The ultrasonic vibration treatment is successfully applied to improve the particles distribution of in-situ 2.5 vol% TiB 2 particles reinforced Al-4.5Cu alloy matrix composites fabricated by salt-metal reaction process. Large particles aggregates are eliminated by effects of the cavitation and the acoustic streaming of ultrasonic vibration for 30 s. All the particles aggregates are eliminated and the particles are uniformly distributed in the melt after treated by ultrasonic vibration for 120 s. TiB 2 particles are identified by X-ray diffraction and transmission electron microscope analysis. Some TiB 2 particles are dispersively distributed in the matrix after solidification. The composite treated by ultrasonic vibration for 120 s has the optimal improvements of yield strength and ultimate tensile strength, which increased by are 84% and 39% respectively. The strengthening mechanisms are discussed, the improved particles distribution brings enhancements on Orowan strengthening, Thermal expansion mismatch strengthening, grain refinement, etc., which are responsible for the improvements of mechanical properties. [ABSTRACT FROM AUTHOR]

Although the icosahedral quasicrystal phase found in Mg-Zn-Y alloys has some outstanding characteristics, the coarse α-Mg dendrites and the agglomeration of the secondary phases in as-cast microstructure restrict the improvements in the mechanical properties. In this study, the semisolid slurry of Mg-6Zn-1.4Y alloy was obtained with ultrasonic vibration (UV) treatment and then formed by rheo-squeeze casting (RSC) process. The effects of UV on the microstructure evolution and mechanical properties were systematically investigated. With UV, primary α-Mg grains and the agglomerated Mg-Zn-Y compounds were significantly refined. Notably, a large mass of fine and granular quasicrystal I-phase particles precipitate in the grains at the later stage of solidification. The RSC alloy subjected to 6 W/mL UV exhibited the optimal mechanical properties, with the yield strength of 129 MPa, the ultimate tensile strength of 231 MPa and the elongation of 18.5%. Compared with the samples without UV, they are increased by 18.3%, 14.9% and 55.5%, respectively. [ABSTRACT FROM AUTHOR]

Ultrafine-grained AZ31 alloy was successfully fabricated by the novel continuous squeeze casting-extrusion process with different extrusion ratios (ER). The average grain size (AGS) reduced first and then grew as the extrusion ratio increased from 4 to 36. Increasing the extrusion ratio cannot ensure the refinement of AGS. The dynamic recrystallization behavior was successively promoted by the increase of ER. But the average grain size reached the minimum with ER of 25, since the size of recrystallized grains increased in large extrusion ratio. The rise of extrusion temperature contributed to the growth of recrystallized grains. The texture evolution resulted in some extruded rods with different ERs exhibiting distinct mechanical property characteristics, despite similar AGS. The ultrafine-grained AZ31 alloy with ER of 16 presented a strong texture, and the AGS of 1.90 µm is achieved. It displayed a high ultimate tensile strength of 332.08 MPa, yield strength of 221.04 MPa, and elongation of 16.9 %. When ER increased to 25, the finest microstructure was obtained with the AGS of 1.85 µm. Its elongation reached maximum of 20.9 % due to the weak texture and ultrafine-grained microstructure, although the ultimate tensile strength and yield strength slightly reduced. Microstructure distribution, dynamic recrystallization behavior, and texture evolution were investigated and discussed in this study. [ABSTRACT FROM AUTHOR]

In this study, the combined use of grain refinement and modification was studied on a hypoeutectic Al–Si–Mg–Ti–Be cast alloy. The primary α-Al grains were transformed from columnar dendrites in the as-received alloy into fine equiaxed dendrites. Meanwhile, the eutectic Si with irregular morphologies were modified to fine fibrous. The room-temperature ultimate tensile strength is increased by ∼14% from 145 MPa to 165 MPa, while the elongation to fracture is increased from 3% to 5%. The comprehensive enhancement of mechanical properties is due to the synergistic effect of microstructural refinement and isotropic improvement by α-Al grain refinement and eutectic Si modification. [ABSTRACT FROM AUTHOR]

In this paper, the refinement effect of Al-5Ti-0.2C refiner on Al-Zn-Mg-Cu alloys was first investigated, and then the effects of three forming processes, i.e., Gravity Casting (GC), Squeeze Casting (SC), and Squeeze Casting after Ultrasonic Treatment (UT-SC), on microstructure and properties of Al-Zn-Mg-Cu alloys were studied. The results show that the refining effect of Al-5Ti-0.2C refiner is obvious; first, the average grain size of the alloy decreases and then increases with the increase in Ti content from 0.15 wt.% to 0.3 wt.%. The optimal amount of added Al-5Ti-0.2C is 0.2 wt.% Ti content. The good refining effect is attributed to the formation of TiC particles and Al3Ti compounds by the refiner, which can all be the nucleus of solidification. The poor refining effect when the Ti content was more than 0.2 wt.% is due to the formation of coarse Al3Ti particles. The results of three forming processes that cast Al-Zn-Mg-Cu alloys under the addition of Al-5Ti-0.2C with 0.2 wt.% Ti content show that the mechanical properties under the UT-SC process are the best; the tensile strength in the as-cast state reaches 367 MPa, and the elongation is 3.84%. The effect of tiny TiC particles in the refiner on the microstructure and properties of Al-Zn-Mg-Cu alloys is also discussed. [ABSTRACT FROM AUTHOR]

In-situ 5 vol% TiB 2 /Al–4.5Cu composites are successfully prepared by the salt–metal reactions assisted by improved mechanical stirring. The X-ray diffraction confirms the formation of TiB 2 particles, and no cluster or large precipitate of intermediate phases Al 3 Ti and AlB 2 can be traced. Mechanical stirring can reduce the large agglomerations and finally eliminate them when the speed rises to 540 rpm. Most of TiB 2 particles are uniformly distributed along the grain boundary in the matrix, and lots of dispersed particles with a size under 0.4 μm are also found. Yield stress and ultimate tensile strength of the composite are improved by 85% and 46%, respectively. [ABSTRACT FROM AUTHOR]

The in-situ (TiB 2 +Mg 2 Si)/Al composite is successfully fabricated by the combination of salt-metal reaction route and ingot metallurgy. The presence of Mg 2 Si phase solves the problem that the particulate volume fraction of TiB 2 /Al composite processed by salt-metal reaction route is low. X-ray diffraction confirms the formation of TiB 2 and Mg 2 Si phases, no other intermediate phases are traced. TiB 2 and Mg 2 Si particles are relative uniformly distributed in the matrix. TiB 2 particles are sub-micron in size, and Mg 2 Si phase is refined from Chinese script morphology to short dispersed sticks by TiB 2 particles. The refined Mg 2 Si phase are under 10 μm in size and the whole reinforcements volume fraction is about 14∼15%. The grains are effectively refined. The mechanism of mutual refinement between TiB 2 particles and Mg 2 Si phase is discussed. The yield stress and ultimate tensile strength of TiB 2 +Mg 2 Si/Al composite are improved by 244% and 229% compared with Al matrix, respectively. [ABSTRACT FROM AUTHOR]

Development of magnesium alloys with exceptional mechanical properties and high thermal conductivity is a prominent subject in the field of thermal conductive magnesium alloys. Rare-earth containing magnesium alloys are known for their ability to achieve higher strength. However, they often exhibit higher density and higher cost. This study developed a high-strength and high-conductivity magnesium alloy without the need for rare earth elements through considered composition design. By utilizing the pinning effect of Mg 2 Si and solute drag effects of Zn and Cu, a fine-grained magnesium alloy with an average grain size of merely 4.5 μm was achieved. The simultaneous introduction of hard Mg 2 Si particles and ductile Cu-rich particles allow Mg-1.38Si-0.5Zn-0.5Cu alloy (SZC100) to attain a desirable combination of strength and plasticity. Althogh free of rare-earth elements, this magnesium alloy demonstrates a thermal conductivity of 141.5 W/(m·K), a yield strength of 238 MPa, and an elongation of 16.2 %. [ABSTRACT FROM AUTHOR]

Highlights: [•] Corrosion resistance of die cast AlMg5Si2Mn is superior to that of permanent mold sample. [•] Corrosion and pitting potential of AlMg5Si2Mn is around −1220mV and −690mV. [•] The application potential of die cast AlMg5Si2Mn in marine industry is confirmed. [•] Fine size microstructure and defects are responsible for the different mechanical properties. [•] Fe-rich particles deteriorate the tensile and fatigue strengths of permanent mold specimens. [ABSTRACT FROM AUTHOR]

Highlights: [•] The δ-Al4(Fe,Mn)Si2 phase is refined in the alloy produced by rheo-diecasting (RDC). [•] The mechanical properties of the RDC samples are increased obviously. [•] The optimum temperature range of USV treatment is 665–645°C. [•] The α phase keeps invariant in both morphology and composition after T6 treatment. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ultrasonic vibration (USV) on the microstructure and mechanical properties of Al–17Si–2Fe–2Cu–1Ni (mass %) alloys with 0.4% or 0.8% Mn were studied. The results show that the average grain size of primary Si in the alloys treated by USV could be refined to 21–24 μm, whether with or without P modification. The P addition has no further refinement effect on the primary Si in the case of the combined use of USV with P addition. Without USV, the alloy with 0.4%Mn contains a large amount of long needle-like β-Al5(Fe,Mn)Si phase and coarse plate-like δ-Al4(Fe,Mn)Si2 phase. Besides, the alloy with 0.8% Mn contains a small amount of coarse dendritic α-Al15(Fe,Mn)3Si2 phase. With USV treatment, the Fe-containing compounds in the alloys are refined and exist mainly as δ-Al4(Fe,Mn)Si2 particles with average grain size of about 18 μm, and only a small amount of β-Al5(Fe,Mn)Si phase is remained. With USV treatment and without P modification, the ultimate tensile strengths (UTS) of the alloys containing 0.4% and 0.8% Mn are 271 MPa and 289 MPa respectively at room temperature, and the UTS are 127 MPa and 132 MPa at 350 °C. The Brinell hardness of the alloys are 131 HB and 139 HB respectively. It is considered that the modified morphology and uniform distribution of the Fe-containing intermetallic compounds and the primary Si phases, which are caused by USV process, are the main reasons for the increase of the tensile strength and hardness of these two alloys. [Copyright &y& Elsevier]

Abstract: The semisolid slurry of AlCu5MnTi alloy was prepared by indirect ultrasonic vibration (IUV), in which the horn was vibrated under the outside of the metallic cup containing alloy melt, then the slurry was formed by direct squeeze casting (SC). The effects of applied pressure, mould temperature and heat treatment on microstructure and mechanical properties of rheo-squeeze casting (RSC) AlCu5MnTi alloy were studied. The results show that with the increase of pressure, the average diameter of grain decreased continuously, while the average shape factor increased. With the increase of mould temperature, mechanical properties of RSC samples increased firstly and decreased afterward. When the pressure was 100MPa and the mould temperature was 270°C samples achieved the best mechanical properties after T5 heat treatment. The tensile strength and elongation were 326.5MPa and 11% respectively, which were improved by 6.5% and 47% respectively compared with conventional squeeze casting samples. [Copyright &y& Elsevier]

In this paper, a new type of Al-8Si-1.5Cu-1Ni-0.5Mg-0.5Mn-0.2Ti-0.2Zr-0.2V-0.06Sr alloy (Al-Si-Cu-Ni alloy for short) was prepared by combining micro-alloying and squeeze casting (SC) forming technology, and its microstructure and mechanical properties were investigated. The results show that the average diameter and secondary dendritic arm spacing of α-Al grains in Al-Si-Cu-Ni alloy prepared by SC are 63 µm and 12.8 µm respectively, and the internal pores of the alloy are basically eliminated. Moreover, the eutectic Si and complex second phases (i.e., AlSiMnFe, Al 3 CuNi and (Al,Si) 3 (Zr,Ti,V)) are greatly refined and more uniformly distributed in the SC alloy. In particular, the eutectic Si can even be refined to sub-micron or nanoscale, and its average F value (i.e., average shape factor) for eutectic Si in the SC alloy is 0.57, which is 29.5 % higher than that of GC alloy. The as-cast ultimate tensile strength (UTS), yield strength (YS) and elongation of the SC Al-Si-Cu-Ni alloy are 310 MPa, 169 MPa and 3.8 %, respectively. Interestingly, its UTS and ductility are much higher than those of most other Al-Si alloys formed by same method, especially its UTS can even be comparable to that of some T6 heat-treated alloys. The increase in strength and elongation is mainly attributed to a reduction in porosity, grain refinement and improvement in the morphology of the second phases. • Development of a novel Al-Si-Cu-Ni alloy through micro-alloying and SC. • The Al-Si-Cu-Ni alloy exhibits high strength and some ductility in as-cast state. • The SC alloy has fine grains and second phases (e.g., nanoscale eutectic Si). • Clarifying the mechanism for high strength of Al-Si-Cu-Ni alloy under SC. [ABSTRACT FROM AUTHOR]

In this study, a new squeeze-cast Al-5Cu- x Li-0.5Mn-0.3Mg-0.15Ti (x = 0.3, 0.6, 0.9, 1.2 wt%) alloy (Al-5Cu- x Li alloy for short) was prepared with ultrasonic treatment (UT), and the effects of UT and Li content on the microstructure evolution and mechanical properties of Al-5Cu- x Li alloy were investigated. Unlike other aluminum alloys, UT applied to aluminum-lithium alloys can bring about significant degassing effects in addition to grain refinement and homogenization, which is beneficial for the high strength and toughness of Al-5Cu- x Li alloy. With the increase of Li content from 0.3 wt% to 1.2 wt%, the average grain size remains unchanged at first, and then increases significantly. Interestingly, the average size of α-Al grains is 30% smaller than that of Al-5Cu-0Li alloy (without Li element) after adding only 0.3 wt% of Li element, while the ultimate tensile strength (UTS), yield strength (YS) and elongation are increased by 11.3%, 15.6% and 26.9%, respectively. The optimal comprehensive mechanical properties are obtained in Al-5Cu-0.6Li alloy, which exhibits 300 MPa in UTS, 190 MPa in YS and 16.7% in elongation. However, by further increasing the Li content, the strength of the Al-5Cu- x Li alloy remains almost unchanged, while its elongation decreases significantly (but still more than 13.5%), due to grain coarsening and slight compositional segregation. • Development of a novel Al-5Cu- x Li alloy through UT+SC for the first time. • The role of UT and SC on the solidification microstructure was investigated. • Effect of Li content on microstructure evolution and properties was explored. • The Al-5Cu- x Li alloy exhibited high strength and ductility in the as-cast state. • Clarifying the mechanism for the change of microstructure and properties. [ABSTRACT FROM AUTHOR]

Even though the Mg-based bulk metallic glasses (BMGs) have shown superior anti-corrosion properties compared with their crystalline counterparts, the brittleness of them limits the widespread application of these materials. In the present study, we have firstly introduced porous NiTi shape memory alloy particles into an Mg-Zn-Ca BMG by the direct adding method. This composite showed both improved compressive strength and corrosion resistance in Hank's solutions than its monolithic glassy counterpart. The NiTi dispersoids among the matrix were likely to hinder the main shear band propagation, and also acted as the corrosion barriers. Furthermore, the porous nature of present added particle could further increase the interface areas, which should enhance the reinforcing effects compared with solid ones. This low-cost, high-anticorrosive composite was a good candidate as an engineering material. [ABSTRACT FROM AUTHOR]

In this paper, the rejuvenation of Zr-Cu-Al-Ni-Ta bulk metallic glasses (BMGs) upon deep cryogenic cycling treatment (DCT) has been studied. The samples show rejuvenation upon DCT with an increased enthalpy of relaxation (ΔH relax) and a decreased density. With more Ta addition, the BMGs can be rejuvenated to a higher energy state, that is, the increment in both ΔH relax and reduced free volume is larger for the BMGs with a higher Ta content. The fracture strength and plastic strain under compression increase with Ta content due to the evolution of intrinsic heterogeneous microstructures. Furthermore, the DCT treated samples show even better plasticity than the as-cast counterparts for the more induced free volume, which contribute to the generation of multiple shear bands. This study proves the universality of DCT on rejuvenating Zr-based BMGs and explains the effect of composition on rejuvenation and plasticization behavior. • BMGs containing Ta can be rejuvenated upon DCT with a higher enthalpy of relaxation. • With increasing Ta content, the rejuvenation can be achieved to a higher degree. • A higher Ta content induces a higher fracture strength and larger plastic strain. • DCT can plasticize the BMGs because of more induced free volume. • Ta causes the evolution of local heterogeneity and contributes to the rejuvenation. [ABSTRACT FROM AUTHOR]

• In-situ BMGMCs can be rejuvenated upon DCT with a higher enthalpy of relaxation. • Higher volume fraction of Ta-rich phase induces a more rejuvenated state. • Internal stress caused by heterogeneity contributes to the rejuvenation. • 4 times higher stress can be generated for the BMGMC compared with BMG counterpart. • Rejuvenated BMGMCs show improved plasticity, the highest plastic strain is ∼51%. The rejuvenation behavior of Ta-rich particle reinforced Zr-based bulk metallic glass matrix composites upon deep cryogenic cycling treatment has been studied. The composite can be rejuvenated resulting in a higher enthalpy of relaxation and lower density. The internal stress generated from both the intrinsic heterogeneity in amorphous matrix and the interfaces between the matrix and Ta-rich phase should contribute to the rejuvenation behavior. The composite structure can generate a 4 times higher internal stress than that from the intrinsic heterogeneity, which causes the more rejuvenated state of the composites compared with the monolithic counterpart. With a higher volume fraction of Ta-rich phase, both the increment in enthalpy of relaxation and free volume between as-cast and thermal treated state increases almost linearly. The rejuvenated samples show better plasticity compared with as-cast counterparts because of more induced free volume. [ABSTRACT FROM AUTHOR]

Abstract The nano-SiC p /A356 Al-matrix composites containing 2 wt.% nano-SiC p were synthesized with solid-liquid mixed casting method. The effects of ultrasonic vibration (UV) treatment and squeeze casting on refinement were studied and the role of nano-SiC p distribution on refinement was focused. Results show that both of the secondary dendritic arm spacing (SDAS) of α-Al grains and the size of eutectic Si phase decrease with the increase of the UV time and the applied pressure of squeeze casting. When UV is applied for 3 min, the SDAS of α-Al in composites is 8.1 μm, which is reduced by 49% than that of A356 matrix alloy. The mean diameter and aspect ratio of eutectic Si phase in composites are 0.92 μm and 2.33, and they are reduced by 42% and 32% respectively than those of A356 matrix alloy. When the applied pressure of squeeze casting is 400 MPa, SDAS of α-Al in composites is 6.9 μm, which is reduced by 55% than that of A356 matrix alloy. Both the processes of UV and squeeze casting can affect the refining effects by regulating the distribution of nano-SiC p. The better the dispersion of nano-SiC p is, the better the refinement of α-Al and eutectic Si phase can be achieved. The mechanical properties of 2 wt.% AMNCs are improved with the increase of UV time and applied pressure, which is consistent with the refinement of the composites' microstructure. [ABSTRACT FROM AUTHOR]

The rejuvenation behavior of a Pd-based bulk metallic glass (BMG) upon deep cryogenic cycling treatment (DCT) has been investigated in the present study. Unlike the obvious rejuvenation phenomenon of Zr-based BMGs, unconspicuous rejuvenation can be observed for the Pd-based samples. The enthalpy of relaxation, hardness and mechanical properties maintained almost unchanged after thermal cycling. The free volume in Pd-based BMG is very difficult to be induced by DCT or eliminated by relaxation annealing, which may relate with the high rigidity of cage structures and subsequently high stability of free volume. In addition, once the free volume is eliminated by annealing for Zr-based BMG, similar unconspicuous rejuvenation upon DCT occurs, which indicates the importance of free volume in the rejuvenation mechanism. These findings provide a deeper understanding between the intrinsic amorphous structures and cryogenic thermal cycling induced rejuvenation behaviors. [ABSTRACT FROM AUTHOR]

The effects of ultrasonic treatment (UT) on the microstructure and mechanical properties of 10 wt% Mg 2 Si+1 wt% nano-sized SiC particles (SiC np for short) hybrid reinforced Al-Cu alloy matrix composites were investigated for first time. The existence of Mg 2 Si phase solves the problem effectively that the particle content of SiC np /Al-Cu composites cannot be high by the external addition of SiC np and casting method. The results show that after UT, the big eutectic Mg 2 Si phase was remarkably refined, from coarse Chinese characters (about 50 μm) to fine strips or dots (about 0.5–2 μm). Meanwhile SiC np agglomerations were also eliminated, and both Mg 2 Si phase and SiC np were uniformly distributed in the composites. The interaction between Mg 2 Si and SiC np was discussed to analyze this behavior that SiC np could act as heterogeneous nucleus of Mg 2 Si phase, or be captured by the Mg 2 Si solid front during solidification, leading to the refinement of eutectic Mg 2 Si phase. It was also found that the effects of UT could be even improved by using squeeze casting (SC), instead of gravity casting (GC). The as-cast ultimate tensile strength (UTS) and elongation of hybrid Mg 2 Si + SiC np /Al-Cu composites fabricated by combining UT and SC were enhanced to 336 MPa and 3.0%, which were increased by 31.3% and 130.8%, respectively, compared with the composites without UT. The UTS of the hybrid Mg 2 Si + SiC np /Al-Cu composites was also 33.5% higher than that of the Al-Cu matrix alloy and 23.5% higher than that of 1 wt% SiC np /Al-Cu composites prepared by the same process. • Hybrid Mg 2 Si + SiC np /Al-Cu composites treated by ultrasonics are investigated for first time. • Ultrasonics can refine and homogenize the big eutectic Mg 2 Si phases in the composites. • Ultrasonics can promote uniform distribution of SiC np in Mg 2 Si + SiC np /Al-Cu composites. • SiC np can act as nucleus of Mg 2 Si, leading to reduction of the size of Mg 2 Si phase. • Mechanical properties of composites can be enhanced significantly by ultrasonics. [ABSTRACT FROM AUTHOR]

Non-thermal partial crystallization in a heterogeneous or structurally unstable Zr-Cu-Al metallic glass upon deep cryogenic cycling has been firstly observed, in which the samples are cooled and heated between ambient temperature and 113 K. With the increment of cryogenic cycling number, the volume fraction of nano-ordered clusters increases, which finally results in partial crystallization. Meanwhile, the amorphous phase is rejuvenated into a less relaxed state, which is caused by the internal stress during cycling. The non-thermal partial crystallization is induced by the hopping events of the atoms activated by the internal stress, which causes the less-ordered or matrix atoms to adopt more ordered states. The partial crystallization in samples can greatly plasticize the sample because of the generated composite structure, as well as more free volume in the samples. These findings provide a new method to plasticize metallic glasses, as well as a deeper understanding of microstructure change of metallic glasses upon the cryogenic treatment. [ABSTRACT FROM AUTHOR]

Abstract In this study, a new type of external added nano-sized SiC particles (SiC np for short) and in-situ Mg 2 Si particles reinforced composites, i.e. (1.5 wt% Mg 2 Si+1 wt% SiC np)/Al-Cu composites, has been successfully prepared for the first time, and the microstructure and mechanical properties of the composites are studied. The eutectic Mg 2 Si phase in the Mg 2 Si/Al-Cu composites is refined from short strip with length of about 10 µm to dot shape with diameter of about 2 µm in (Mg 2 Si+SiC np)/Al-Cu composites, which is uniformly distributed inside Al 2 Cu phases precipitated at the grain boundary. The α-Al grains are also significantly refined. It is also first discovered that SiC np can act as nucleus of Mg 2 Si, or be captured by the Mg 2 Si phase during solidification, which promotes the heterogeneous nucleation of the eutectic Mg 2 Si phase to reduce the size of Mg 2 Si phase. The ultimate tensile strength (UTS) and yield strength of (Mg 2 Si+SiC np)/Al-Cu composites are 325 MPa and 210 MPa, which are 3.2% and 28.8% higher than those of Mg 2 Si/Al-Cu composites, respectively. These properties are also improved by 20.4% and 21.4% respectively compared with SiC np /Al-Cu composites, while (Mg 2 Si+SiC np)/Al-Cu composites maintain good ductility. [ABSTRACT FROM AUTHOR]

Abstract In-situ Ta-rich particle reinforced Zr-based bulk metallic glass matrix composite has been successfully fabricated by doping Ta. The dispersion of Ta-rich particles was quite homogenous. The size and inter-particle spacing of the Ta-rich particles were very close to the plastic processing zone size. By varying the doping amount of Ta, the volume fraction of Ta-rich particles can be tailored. Furthermore, the bonding between Ta-rich particle and glassy matrix seemed to be strong for the lack of oxide or compound layer at the interfaces. With more Ta-rich particles, the composites show better mechanical properties, including higher fracture strength and larger plastic strain. The Ta-rich particles can hinder the rapid propagation of main shear band, generating multiple shear bands. Smaller value of average stress drop after yielding for the composites with more Ta doping indicates lower formation energy of shear bands, which links to the better plasticity. The deformation of Ta-rich particle itself also contributes to the plasticity and hardening behavior of the composite. The composite with 10 at.% Ta doping even shows ∼2% plastic strain under tension. Highlights • In-situ Ta reinforced bulk metallic glass composites are fabricated by doping. • The bonding between Ta and glassy matrix are strong without oxide layer. • The composites show better plasticity with more Ta particles. • The composites with more Ta particles possess lower shear plane formation energy. • The highest plastic strain is about 35% under compression and 2% under tension. [ABSTRACT FROM AUTHOR]

A relaxed heterogeneous metallic glass is successfully rejuvenated by using a recovery-annealing technique. It is found that the rejuvenation state is related to the final cooling rate and more nano-clusters are formed in the less rejuvenated heterogeneous metallic glass with a slower final cooling rate. Interestingly, the less rejuvenated heterogeneous metallic glass shows better plasticity than the more rejuvenated glass, which may result from the stress-induced crystallization (SIC) during deformation. The reasons for the SIC in the less rejuvenated sample are considered to be the evolution of nano-clusters, a more unstable glassy phase (easier to crystallize), and the high temperature rise in each shear band. These results suggest that not only the relaxation state of the amorphous phase, but also the heterogeneous microstructures, including nano-clusters, should be considered to improve the mechanical properties of metallic glasses. [ABSTRACT FROM AUTHOR]

In this paper, the aging process of in-situ TiB 2 /Al-4.5Cu composites has been investigated carefully, especially the precipitation behavior in the presence of TiB 2 particles. The mechanism of this particle-assisted precipitation in the composites are also studied systemically. Comparisons of the aging behavior between composites and matrix alloy have been made to investigate the effect of TiB 2 particles. Moreover, attention has also been paid to tensile properties and hardness of TiB 2 /Al-4.5Cu composites and matrix alloy during aging procedure. Results indicate that TiB 2 particles accelerate the aging processes and also induce inhomogeneous distribution of Al 2 Cu precipitates due to the high-density dislocations adjacent to particles. Besides, a rare phenomenon was found that the evolution on mechanical properties of the composites can be divided into two stages and this evolution is in good accordance with the evolution of the Al 2 Cu precipitates. Moreover, the time to peak-aged condition of the composites in mechanical properties comes down from 20 h to 8 h. [ABSTRACT FROM AUTHOR]

In this study, a novel Al–5Cu-0.6Li-0.5Mn-0.3Mg-0.15Ti alloy was developed, in which Li is as low as 0.6 wt% and Ti is added, no Ag, Zn, Zr, RE, etc., and high-performance Al–Cu–Li alloy casting billets were prepared by squeeze casting (SC) with ultrasonic treatment (UT). The results show that compared with traditional gravity casting (GC), the porosity and compositional segregation in the SC billets are significantly reduced, and the grain size is also reduced from 80 μm to 38 μm, especially the microstructure of UT + SC billets is further optimized. After UT + SC, the ultimate tensile strength (UTS), yield strength (YS) and elongation of Al–Cu–Li alloy billets are 300 MPa, 190 MPa and 16.5%, which are 27.1%, 35.7% and 230% higher than those of the GC billets, and these as-cast properties are increased by 13.2%, 15.2% and 37.5%, compared with Li-free Al–5Cu-0.5Mn-0.3Mg-0.15Ti alloy billet prepared by UT + SC, respectively. The improvement of the strength and elongation of Al–Cu–Li alloy billet prepared by UT + SC is attributed to the reduction of porosity, grain refinement and uniform distribution of second phases. [ABSTRACT FROM AUTHOR]