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Significant progress has been made in magnesium-based composites during recent decades, especially for the appearance of magnesium matrix composite reinforced by nanoparticles. The nanoparticles added not only exhibit a good strengthening effect, but also maintain the initial toughness of the matrix, effectively balancing the contradiction between the strength and plasticity in the traditional magnesium matrix composites. The magnesium matrix nanocomposites with excellent mechanical properties have pushed the development of magnesium matrix composites to a new stage. However, it is very difficult to disperse the nanoparticles in metal melt especially in magnesium melt which is different from other metal melts and dangerous during the cast processing. This means that the preparation of magnesium matrix nanocomposite is extremely challenging. Further, the magnesium matrix nanocomposites possess a distinctive characteristic in deformation behavior, strengthening and toughening mechanism due to their special size effect of nanoparticles. Accordingly, this review will focus on the new preparation technologies, deformation behavior, mechanical properties and strengthening and toughening mechanisms. The potential applications, development trends and future research ideas of magnesium matrix nanocomposite are also prospected. [ABSTRACT FROM AUTHOR]

Copper matrix composites were fabricated through mixing fixed amount of reduced graphene oxide and the different amounts of titanium. The dried copper/titanium/reduced graphene oxide mixture powders were firstly obtained by the wet‐mixing process, and then the spark plasma sintering process realized their faster densification. In the as‐sintered bulk composites, the layered reduced graphene oxide network, uniform titanium particles and copper‐titanium solid solution are observed in copper matrix. Investigations on mechanical properties show that the as‐prepared bulk composites exhibit the hardness and compressive yield strength compared with single reduced graphene oxide added composites. Increased titanium addition resulted into higher hardness and strength. The relevant formation and failure mechanisms of the composites and their influence on mechanical properties were discussed. [ABSTRACT FROM AUTHOR]

In the present study, magnesium-based composites with three different volume percentages of nano-sized SiC particulates (SiCp) reinforcement were fabricated using a simple and inexpensive technique followed by hot extrusion. Microstructural characterization of the materials revealed uniform distribution of nano-size SiCp and obvious grain refinement. The tensile test result indicates a remarkable improvement on the strength for the as-extruded SiCp/AZ31B nanocomposite, while the elongation to fracture was decreased by comparing with the AZ31B alloy. Although, compared with the as-extruded AZ31B alloy, the ductility of the SiCp-reinforced AZ31B nanocomposite is decreased, but the ductility of the present SiCp-reinforced AZ31B nanocomposite is far higher than that of the conventional micron or submicron SiCp-reinforced magnesium matrix composites. It is concluded that, compared with the larger sized (micron or submicron) particles, the addition of nano SiCp in the AZ31B alloy resulted in the best combination of the strength and ductility. An attempt is made in the present study to correlate the effect of presence of nano-SiCp as reinforcement and its increasing amount with the microstructural and mechanical properties of magnesium. [ABSTRACT FROM AUTHOR]

In the present study, AZ31B magnesium matrix composites reinforced with two volume fractions (3 and 5 vol.%) of micron-SiC particles(1 μm) were fabricated by semisolid stirring assisted ultrasonic vibration method. The as-cast ingots were extruded at 350 °C with the extrusion ratio of 15:1 at a constant ram speed of 15 mm/s. The microstructure of the composites was investigated by optical microscopy, scanning electron microscope and transmission electron microscope. Microstructure characterization of the composites showed relative uniform reinforcement distribution and significant grain refinement. The presence of 1 μm-SiC particles assisted in improving the elastic modulus and tensile strength. The ultimate tensile strength and yield strength of the 5 vol.% SiCp/AZ31B composites were simultaneously improved. [ABSTRACT FROM AUTHOR]

Abstract: The Mg/Al laminated composite was fabricated by the accumulative roll bonding (ARB) using the pure magnesium and Al5052 alloy at 400°C. Tensile properties along rolling direction and the transverse direction and the microhardness were evaluated at the ambient temperature. The tensile strength of the laminated Mg/Al composite along both directions increased gradually till two ARB cycles, but then decreased after the third ARB cycles. Optical microscopy and scanning electron microscopy (SEM) were utilized to reveal the microstructure evolution and the failure mechanism. Grain refinement of Mg layers was not obvious during the ARB process due to the high temperature and interval reheating. The obvious crack at the coarse intermetallic compounds and rupture of the Al layer after the third cycle led to the premature failure of the sample along the rolling direction during the tensile test. [Copyright &y& Elsevier]

In this study, both AZ91 alloy and nano-SiCp/AZ91 composite were subjected to multi-pass forging under varying passes and temperatures. The microstructure and mechanical properties of the alloy were compared with its composite. After six passes of multi-pass forging at a constant temperature of 400 ℃, complete recrystallization occurred in both the AZ91 alloy and composite. The decrease of temperature and the increase of passes for the multi-pass forging led to further refinement of dynamic recrystallized grains and dynamic precipitation of second phases. The grain size of the nano-SiCp/AZ91 composite was smaller than that of the AZ91 alloy under the same multi-pass forging condition, which indicated that the addition of SiC nanoparticles were beneficial to grain refinement by pinning the grain boundaries. The texture intensity for the 12 passes of multi-pass forging with varying temperatures was increased compared with that after nine passes. The ultimate tensile strength is slightly decreased while the yield strength was increased unobviously for the AZ91 alloy with the decrease of temperature and the increase of the passes for the multi-pass forging. Under the same condition of multi-pass forging, the yield strength of the composite was higher than that of the AZ91 alloy due to the Orowan strengthening effect and grain refinement strengthening resulting from externally applied SiC nanoparticles and internally precipitated second phases. By comparing the microstructure and mechanical properties between the AZ91 alloy and nano-SiCp/AZ91 composite, the strength-toughness properties of the composites at room temperature were affected by the matrix grain size, texture evolution, SiC nanoparticles distribution and the precipitated second phases. [ABSTRACT FROM AUTHOR]

Abstract: The extruded Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy were subjected to large-strain hot rolling with different final rolling temperatures. The microstructural evolution and mechanical properties of the sheets were investigated. The microstructure became homogeneous after hot rolling process and long period stacking ordered (LPSO) phase distributed at grain boundaries along rolling direction. The sheet rolled at 300°C was composed of deformed grains, substructures and excessive dislocations. With increasing final rolling temperatures from 300°C to 400°C, the volume fraction of recrystallized grains with relatively random orientations increased significantly. The strength of the rolled sheets was improved while the ductility was deteriorated with decreasing final rolling temperatures. The tensile yield strength and ultimate tensile strength of the sheet rolled at 300°C reached 320MPa and 416MPa, respectively with the elongation to failure of 5.3%. The mechanical anisotropy of the rolling sheet became unity when rolled at higher temperature of 400°C due to the formation of weaker basal texture. [Copyright &y& Elsevier]

Abstract: Different cooling processes, such as quenching in warm water and cooling in furnace, were introduced to homogenize Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy. Microstructure evolution and mechanical properties of the homogenized alloy were investigated. The as-quenched sample was comprised of α-Mg matrix, Mg5RE phase and 18R LPSO phase distributed at the grain boundaries and a few of RE-rich particles distributed randomly. During the process of cooling in furnace, Mg5RE and 18R LPSO phases were transformed into block-shaped 14H LPSO phase and lamellar-shaped 14H LPSO phase, respectively, due to the diffusion of solute atoms into the α-Mg matrix. Furthermore, the lamellar-shaped 14H LPSO phase grew and ran through the whole grains. The as-quenched sample exhibits tensile yield strength of 130MPa, ultimate tensile strength of 206MPa and elongation to failure of 5.5%, while the sample cooled in the furnace exhibits higher tensile yield strength but lower ultimate tensile strength and ductility due to the coarse grains and formation of block-shaped 14H LPSO phase. [Copyright &y& Elsevier]

Abstract: The Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt.%) alloy was hot rolled with different final rolling reductions at 400°C. The microstructure evolution and texture of the sheets were analyzed, and their effect on the mechanical properties was discussed. All of the rolled sheets consist of fine dynamically recrystallized grains with almost random orientation, large deformed grains with strong basal texture. In addition, bent lamellar-shaped long period stacking ordered (LPSO) phases due to kink deformation were observed in the deformed grains. The volume fraction of the dynamic recrystallization increased with increasing final rolling reduction and the basal texture weakened gradually. The strength of the alloy sheets changed a little with increasing final rolling reduction, while the yield anisotropy and the ductility were significantly improved. The sheet final-rolled with thickness reduction of 60% exhibits tensile yield strength of 306MPa, ultimate tensile strength of 393MPa and elongation to failure of 14.6% at ambient temperature, and tensile yield strength of 264MPa, ultimate tensile strength of 345MPa and elongation to failure of 19.4% at 250°C. [Copyright &y& Elsevier]

Abstract: The pure Mg sheets were processed by ARB at 400°C and 300°C up to 8 cycles and 4 cycles, respectively. The microstructure was refined during the first cycle and only homogenized during the following ARB process due to the high deformation temperature, intermediate reheating and air-cooling. The ARB process did not show an obvious effect on the tensile properties of the as-ARBed pure Mg sheet due to the stable grain size and dominant basal plane texture during ARB. Further deformation should be introduced to improve the bonding quality of the as-ARBed sheet. [ABSTRACT FROM AUTHOR]

Abstract: Equal channel angular pressing (ECAP) has been conducted on as-cast Mg–4.3 wt.%Zn–0.7 wt.%Y Mg alloy containing quasicrystal phase at a temperature of 623 K. After 8 ECAP passes, the grain size of the as-cast alloy is decreased from ∼120 to ∼3.5 μm, and the coarse eutectic quasicrystal phases are broken and dispersed in the alloy. Tensile testing has been performed on the ECAPed Mg–Zn–Y alloy at temperatures of 523 K and 623 K with initial strain rates from 1.5×10−3 to 1.5×10−4 s−1. The ECAPed alloy exhibits a maximum elongation of about 600% when testing at 623 K using an initial strain rate of 1.5×10−4 s−1. Grain boundary sliding is considered to be the dominant deformation mechanism of the Mg–Zn–Y alloy in the temperature and strain-rate range investigated. [Copyright &y& Elsevier]

Grain boundary (GB) engineering via alloying opens a pathway to design the interfaces in alloys for tuning their mechanical properties, thus it is quite critical to determine the optimum addition of alloying element. Here, we prepared immiscible Cu-Cr alloyed thin films by non-equilibrium magnetron sputtering deposition to study Cr alloying effects on the microstructure and mechanical properties of Cu thin films. It is found that Cr doping can notably refine the grains and promote the formation of fully nanotwinned columnar grains at low Cr volume concentrations (≤∼3.7 at.%) associated with the average GB Cr concentrations ≤ ∼15 at.%, beyond which the formation of nanotwins is significantly suppressed. The role of Cr atoms/clusters played in the twinning process is rationalized in terms of dislocation rebound-promotion mechanism. Importantly, a maximum hardness is discovered at the optimum Cr addition of ∼2.0 at.%. The Cr concentration-dependent hardness of Cu-Cr alloyed films was quantified by a combined strengthening model. The achievement of the maximum hardness was related to the greatest GB solute segregation-induced strength contribution. It is further uncovered that the Cu-Cr system exhibits strain rate sensitivity (SRS, m ) monotonically reduced with increasing the Cr concentration, ranging from a positive m of 0.0314 (for pure Cu) to a negative m of −0.0245, which is attributed to a competition between the dislocation-boundary interactions (increasing m ) and the dislocation-solute atoms interactions (decreasing m ). These findings provide valuable insights into tuning the composition of alloyed thin films to achieve optimized mechanical performance. [ABSTRACT FROM AUTHOR]

This study investigates the precipitation behavior in the graphene nanoplatelets (GNPs) reinforced bimodal structural Mg-6Zn (wt%) matrix composite. The GNPs with an increasing content progressively accelerate the age-hardening response in the local regions of the composite. The composite takes only half the time that the Mg-6Zn alloy needs to reach the peak strength when aging at 200 °C. The observation reveals that the planar and wrinkled GNPs in the composite act as the effective trigger of dislocations and collector of solute atoms to accelerate the precipitation. It is concluded that GNPs have a pronounced effect on the development of matrix microstructure. Moreover, the orientation relationship between the aligned GNPs towards the extrusion direction and the matrix grains with a fiber type texture makes the GNPs and [0001] Mg precipitate rods constitute a hybrid strengthening architecture in the composite. As a result, the synergistic strengthening effect of the GNPs and the precipitates is realized. [ABSTRACT FROM AUTHOR]

Tuning the microstructure to optimize the mechanical performance of nanocrystalline Cu thin films via the alloying strategy is quite important for their application in microdevices. In this work, we prepared nanocrystalline miscible Cu-Ti and immiscible Cu-Mo alloyed thin films to investigate alloying effects on the microstructure and mechanical properties of Cu thin films in terms of mixing enthalpies. It is found that the dopants of both Ti and Mo can notably refine the grains, and in particular promote the formation of nanotwins below a critical content of solute, beyond which the formation of nanotwins is notably suppressed. The nonmonotonic solute concentration-dependent twinning behavior observed in Cu-Ti and Cu-Mo alloyed thin films is explained by the coupling effects between grain size and grain boundary segregated dopants that affects the stimulated slip process of partials. The increased hardness of both Cu-Ti and Cu-Mo systems with increasing the solute contents are quantitatively explained by combining several strengthening mechanisms, including solid solution strengthening, grain/twin boundary (GB/TB) strengthening, solute segregation-induced strengthening. It unexpectedly appears that with increasing the solute contents, the Cu-Ti system exhibits monotonically reduced positive strain rate sensitivity (SRS, m ), whereas the Cu-Mo system manifests almost constant negative SRS. The fundamental difference in SRS m between Cu-Ti and Cu-Mo is rationalized in terms of the interactions between solute atomic clusters and dislocations based on the cross-core diffusion mechanism. [ABSTRACT FROM AUTHOR]

Mg-10Zn-6Y-0.5Zr (wt%) alloy and Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy with medium RE content have been fabricated by conventional casting and indirect extrusion. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy shows a bimodal microstructure containing dynamic recrystallized (DRXed) grains with average grain size of 2 μm and deformed regions. In addition to the fragmented W phase particle bands distributing along the extrusion direction, large amount of nano W phase and small amount of nano β 2 ′ phase are precipitated in the matrix. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy exhibits completely dynamic recrystallized microstructure with average grain size of 3 μm. The broken W phase particles are distributed homogeneously in the matrix. Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy exhibits yield strength of 341 MPa, ultimate tensile strength of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy shows lower yield strength of 247 MPa, ultimate tensile strength of 330 MPa and higher elongation to failure of 19.8%. The higher strength in the as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy is mainly attributed to higher area fraction of unDRXed regions with strong texture and the precipitation of nano W and β 2 ′ phase. The fully recrystallized microstructure with weak texture and the formation of icosahedral quasicrystal phases with good coherent bond with α-Mg contribute to the good ductility of the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. [ABSTRACT FROM AUTHOR]

In this study, low volume fraction SiCp/AZ91 magnesium matrix nanocomposites billets intended for structural applications were synthesized using semisolid stirring assisted ultrasonic vibration, leading to the dispersion of SiC nanoparticles. Both the AZ91 alloy and nanocomposite billets were then subjected to isothermal multidirectional forging (IMDF). Micrographic observations illustrated that the mean grain size of the developed nanocomposite showed an initial increase after 3 IMDF passes, followed by a decrease after 6 IMDF passes compared to the AZ91 alloy. This indicated that the effect of dispersed SiC nanoparticles on the inhibition of the dynamic recrystallization grains growth was impaired due to the present high IMDF temperature. The improved yield strength of the nanocomposite could be attributed to Orowan strengthening effect related to the dispersed SiC nanoparticles as well as the second phases precipitated far from the dynamic recrystallization grains. [ABSTRACT FROM AUTHOR]

The effect of Ca/Al ratio on microstructure and mechanical properties of the as-cast and as-extruded Mg-Al-Ca-Mn alloys were investigated. The as-cast Mg-Al-Ca-Mn alloys with Ca/Al mass ratios less than 0.50 contain divorced and lamellar eutectic (Mg,Al) 2 Ca. When Ca/Al ratio is greater than 0.90, fine lamellar Mg 2 Ca phase is formed in the as-cast Mg-Al-Ca-Mn alloys. After extrusion, the second phases are broken and dispersed along the extrusion direction. The area fraction of DRXed regions decrease with increasing Ca/Al ratio, the microstructure changes from an almost fully recrystallized structure to a bimodal structure consisting of fine dynamically recrystallized (DRXed) grains and coarse deformed regions. With increasing Ca/Al ratio, the DRXed grains and dispersed second phases are refined. The as-extruded alloys exhibit a strong basal fiber texture, the intensity of which is increased with increasing Ca/Al ratio. With increasing Ca/Al ratio, the {0002}<11-20> texture component in the DRXed regions is suppressed, and shifted to a {0002}<10-10> texture component. The strength of the as-extruded Mg-Al-Ca-Mn alloys increases significantly with increasing Ca/Al ratio. The as-extruded Mg-2.7Al-3.5Ca-0.4Mn (wt%) alloy exhibits a tensile proof strength of 438 MPa and an ultimate tensile strength of 457 MPa. The extraordinary high strengths are attributed to the ultrafine DRXed grains pinned by fragmented secondary phases, strong basal texture and dense nano-scale precipitates. The present research indicates that the Mg-Al-Ca-Mn alloys have a great potential as next generation low-cost ultrahigh-strength wrought Mg alloys. [ABSTRACT FROM AUTHOR]

The (micron[m]+submicron[s]+nano[n]) SiC particles (SiCp) reinforced AZ31B magnesium matrix composites (AZ31B/SiCp/m + s + n composites) were fabricated by stirring casting technology followed by hot extrusion. This method has successfully solved the homodisperse problem of SiCp/m + s + n in the magnesium matrix composites. The influence of SiCp/m + s + n on the dynamic recrystallization (DRX) behavior of the magnesium matrix was investigated by researching the TEM microstructures of composites. The results indicated that the addition of SiCp/m + s + n was helpful to increase the ratio of DRXed nucleation and reduce the average grain size of matrix. The particle deformation zone (PDZ) can be formed in the vicinity of micron SiCp, while the region with high dislocation density can be created around submicron SiCp owing to pin dislocation and deformation mismatch between matrix and particles. These regions are ideal sites for the formation of recrystallization nucleus. Meanwhile, the addition of fine SiCp(nano and submicron) may delay or hinder the growth of matrix grain through the pinning effect on the grain boundaries during hot extrusion. The tensile test indicates that the strength of the AZ31B/SiCp/m + s + n composites has a significant improvement. Compared with the single sized or bimodal sized particles reinforced magnesium matrix composites, the tensile strength of the AZ31B/SiCp/m + s + n composites were highlighted. [ABSTRACT FROM AUTHOR]

The Mg-6 mass%Zn alloys microalloyed with different amounts of Ca were cast and extruded. The second phase in the as-cast Mg-6Zn alloy is Mg 4 Zn 7 , which is replaced by Ca 2 Mg 6 Zn 3 with an increase of Ca addition. Microalloying by Ca affects the grain size, dynamic recrystallization, and dynamic precipitation of Mg-6Zn alloys during extrusion. The Ca addition inhibits dynamic recrystallization and grain growth due to the pinning effect of fine precipitates, giving rise to fine dynamic recrystallized grains. A large amount of precipitates is observed in the Ca containing alloys after extrusion. Ca effectively improves strength of the as-extruded Mg-6Zn alloy, which is mainly attributed to refined dynamic recrystallized grains, dense precipitates, and deformed regions with high-density dislocations and strong basal texture. [ABSTRACT FROM AUTHOR]

High strong magnesium matrix composites can be obtained by refining grain size, heat treatment and severe plastic deformation methods. However, most of the composite enhancing approaches result in the disappointingly poor tensile ductility. Thus, the designing and fabricating of composites with simultaneously good ductility and high strength have become burning issues for the application of light metals/alloys. Simply adding particles or changing particle parameters can not solve the problem of combination of high strength and good ductility. A new method has been developed, wherein the bimodal size grained microstructure formed by adding the bimodal sized SiC particles (SiCp) was selected as favorable microstructure for achieving good ductility and high strength in present work. The fine grains (grain size: <1 μm) were obtained through the particle stimulate of nucleation (PSN) and pin grain boundary effect. However, the coarse grains (grain size: ∼4 μm) were obtained through forming SiCp free zones in the present magnesium matrix composites. The tensile test indicates a significant improvement in the ductility (∼8.3%) and strength (UTS: ∼402 MPa, YS: ∼323 MPa) of the composites. Compared with the conventional single-sized particles (micron or nano) reinforced magnesium matrix composites, the tensile ductility and strength of present composite (AZ31B/SiCp/1n + 9m composite) were highlighted in the current literature. [ABSTRACT FROM AUTHOR]

AZ91 alloy was subjected to multidirectional forging (MDF) and the relationship between microstructures and mechanical properties generated by MDF were investigated. The results showed that after 1 MDF pass grain size of the alloy decreased compared with as-cast alloy, and the amount of recrystallization grains increased when the MDF temperature increased from 250 °C to 400 °C. With increasing the MDF passes at 350 °C, grains of the alloy were gradually refined. A typical basal texture was obtained after 1 MDF pass, and then the basal pole scattered with the increase of MDF passes. Mg 17 Al 12 phases were precipitated along grain boundaries during MDF, which could hinder the growth of recrystallization grains. Both tensile strength and elongation to failure of the alloy were significantly enhanced till 3 MDF passes with increasing the MDF passes. [ABSTRACT FROM AUTHOR]

The present study dealt with the AZ91 alloy subjected to multidirectional forging (MDF) under decreasing temperature conditions with emphasizing on relationship between microstructures and mechanical properties generated by MDF. The obtained results showed that grains of the alloy were gradually refined while the amount of the second phase precipitated along the grain boundaries was increased with increasing the MDF passes and decreasing the MDF temperature. Compared with the as-cast alloy, yield strength, ultimate tensile strength and elongation of the AZ91 alloy after MDF under decreasing temperature conditions were simultaneously increased. As the numbers of MDF passes were gradually increased and the MDF temperature was gradually decreased, the yield strength was gradually decreased, suggesting that texture softening may overwhelm the strengthening due to the grain refinement as well as the homogeneous distribution of precipitates. [ABSTRACT FROM AUTHOR]

The hardness, tensile ductility and fatigue lifetime of nanostructured (NC) Cu-Zr alloyed thin films have been systematically measured at different Zr additions (0, 0.5, 2.0, 4.0, 8.0at.%). Experimental results showed that the Cu-0.5at.% Zr film exhibited the highest hardness, largest ductility and longest fatigue lifetime, which are increased by 120%, 80%, and above an order of magnitude, respectively, in comparison with its pure Cu counterpart. The simultaneous improvements of mechanical properties are rationalized with respect to microstructural evolutions related to Zr segregation at grain boundaries (GBs). Besides refinement in NC grains and enhancement in nanotwins, grain orientation was apparently modified by the GB Zr segregation. (110) grains were promoted and layer-like microstructure was formed with coexistence of three orientation of grains at the upper layer, facilitating Cu grain growth at room temperature. GB doping strengthening worked as an additional strengthening mechanism and mechanically driven grain growth became the predominant deformation mechanism and fatigue mechanism, which accounted for the optimal combination of mechanical properties achieved in the Cu-0.5at.% Zr film. When the Zr content was >2.0at.%, however, amorphous phases were formed at the GBs due to locally increased Zr concentration. The GB doping strengthening effect was concomitantly weakened and strength was gradually decreased. In addition, stress/strain localization occurred readily at the amorphous phase regions, triggering intergranular fracture and reducing ductility. During cyclic testing in the low stress range, GB amorphous phases strengthened rather impaired the GBs, which gave the Cu-Zr films a fatigue lifetime greater than that of the pure NC Cu film. The present results clearly indicate that, once solute content is suitably explored, the solute segregation at GBs in NC metals can not only retain NC grains in loading-free conditions, but also impart enhanced mechanical properties when exposed to applied stress. [ABSTRACT FROM AUTHOR]

Highlights: [•] The solidification rates significantly affect the CNTs distribution. [•] Uniform CNTs distribution was achieved in the composites. [•] The tensile properties of the composites follow the Kelly–Tyson formula well. [Copyright &y& Elsevier]

Abstract: Bimodal sized (Micro-particles: m and Nano-particles: n) SiC particulates (SiCp) reinforced magnesium matrix composites with different volume fractions of micro-particles (1n+4p, 1n+9p and 1n+14p) were prepared by a semisolid stirring assisted ultrasonic vibration method. Both the as-cast SiCp/AZ31B composites and the AZ31B alloy were extruded at 350°C with the extrusion ratio of 12:1 at a constant ram speed of 15mm/s. The microstructure investigation was carried out by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the distribution of bimodal size SiCp and the mechanical properties of the AZ31B alloy were significantly improved after hot extrusion. When the volume fraction of nano SiCp is 1vol%, both the yield strength and ultimate tensile strength of the AZ31B/SiC/1n+14p composite are stronger than that of the AZ31B/SiC/1n+4p and AZ31B/SiC/1n+9p composites, while the elongation to fracture was decreased comparing with the AZ31B/SiC/1n+4p and AZ31B/SiC/1n+9p composites. [Copyright &y& Elsevier]

Abstract: Carbon nanotube (CNTs) reinforced Mg matrix composites were successfully fabricated by a novel approach. After hot extrusion, the influence of CNTs on microstructure and mechanical properties of Mg–6Zn matrix was investigated. The results showed that most CNTs distributed uniformly and individually in the composites, and good interfacial bonding was achieved. CNTs significantly refined the grains of Mg–6Zn matrix, and the CNTs evidently improved the ultimate tensile strength (UTS), yield strength (YS) and Young's modulus. Grain refinement, load transfer mechanism and Orowan strengthening mechanism play important roles on the increase of the yield strength. [Copyright &y& Elsevier]

Highlights: [•] Submicron-SiCp/AZ31B composites were fabricated.. [•] The influence of submicron SiCp for matrix alloy was determined. [•] Mechanical properties of submicron SiCp/AZ31B composite were enhanced significantly. [Copyright &y& Elsevier]

Highlights: [•] Bimodal size SiCp/AZ31B composites were fabricated. [•] The influence of bimodal size SiCp for matrix alloy was determined. [•] Mechanical properties of bimodal size SiCp/AZ31B composite were enhanced significantly. [ABSTRACT FROM AUTHOR]

The Mg–4.50Zn–1.13Ca (wt%) alloy was subjected to double extrusion, and the microstructure and mechanical properties of the extruded alloys were investigated. Double extrusion refined the microstructure significantly, resulting in the enhancement of mechanical properties of the double-extruded alloys compared with the single-extruded alloy. The yield strength of the single-extruded alloy was 173MPa, while the value was increased to 320MPa and 370MPa after subsequent second extrusion at 300°C and 250°C, respectively. The second extrusion ratio had little effect on the microstructure and mechanical properties of the double-extruded alloys, while grain size was decreased and strength was increased with the decrease of double extrusion temperature. The double-extruded Mg–Zn–Ca alloy exhibited superior elevated temperature mechanical properties, which was attributed to the fine stable Ca2Mg6Zn3 intermetallic compound particles dispersed in the alloy. [ABSTRACT FROM AUTHOR]

Abstract: The microstructures and mechanical properties of Mg–5.3Zn–0.2Ca–0.5Ce (wt%) alloy fabricated by semi-continuous casting were investigated. The as-cast alloy consists of α-Mg, Ca2Mg6Zn3 and T′1 phase with orthorhombic structure (a=0.57nm, b=0.75nm and c=1.00nm). T′1 phase mainly distributes at the triple conjunctions while the Ca2Mg6Zn3 at the grain boundaries. The as-cast alloy exhibits high strength retention due to the stable Ca2Mg6Zn3 and T′1 phase at the grain boundaries. [Copyright &y& Elsevier]

Abstract: Extruded Mg–8.2Gd–3.8Y–1Zn–0.4Zr (wt%) alloy was subjected to ageing treatment at 200°C. The microstructures, textures and mechanical properties of the as-extruded and peak-aged alloys were investigated. Recrystallization occurred during ageing treatment. A large number of β′ phases were observed in the peak-aged alloy, accompanied with the decrease of the volume fraction of LPSO phases. A basal fiber texture and an unusual texture component with basal planes perpendicular to the extrusion direction were found in the as-extruded alloy, and the basal fiber texture was strengthened after ageing treatment. The peak-aged alloy exhibited a tensile yield strength (TYS), an ultimate tensile strength (UTS) and an elongation to failure of 395MPa, 470MPa and 8%, respectively, at ambient temperature, and 271MPa, 311MPa and 19%, respectively, at 300°C. The superior strength of the peak-aged alloy was mainly attributed to the precipitation of fine β′ phases, the remaining LPSO phases and the texture modification. [Copyright &y& Elsevier]

Abstract: The microstructure and mechanical properties of Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy sheets produced by combined processes of extrusion, large-strain hot rolling and ageing treatment were investigated. The sheet rolled at 300°C was mainly composed of deformed grains while that rolled at 400°C was fully recrystallized, and the LPSO phase distributed at the grain boundaries in both sheets. The sheet rolled at 300°C and then peak-aged at 200°C exhibits 0.2% proof stress (PS) of 454MPa, ultimate tensile strength (UTS) of 469MPa and elongation to failure of 1.3% at ambient temperature, and 0.2% PS of 413MPa, UTS of 457MPa and elongation to failure of 6.8% at 200°C, respectively. While the sheet rolled at 400°C and peak aged at 200°C had lower 0.2% PS and superior ductility. The improvement of strength is ascribed to the fine β′ phase precipitated within the grains, the LPSO phase and dispersed cuboid Mg–Gd–Y containing phase located at the grain boundaries. [Copyright &y& Elsevier]

Abstract: Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy ingot with diameter of 280mm and length of 2940mm was successfully fabricated by semi-continuous casting. The microstructure and mechanical properties of the large ingot at different locations were investigated. The concentration of the RE and Zn elements distributed almost homogeneously through the whole alloy ingot. The average grain size decreased from the center to the surface of the alloy ingot, while the strength and ductility were improved gradually. The main eutectic compounds located at the grain boundaries were (Mg,Zn)3(Gd,Y) phase, adjacent to these eutectic compounds the 14H-type long period stacking ordered (LPSO) phase formed. Furthermore, some block-shaped Mg24(Gd,Y)5 phase and isolated Zr cores can be recognized in the interior of the grains. [Copyright &y& Elsevier]

Abstract: In this research, the as-cast and as-homogenized Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr alloy were subjected to the hot rolling with the same processing parameters. The microstructure and mechanical properties of the two kinds of as-rolled sheets were investigated. The sheet rolled from the as-cast alloy was mainly composed of recrystallized α-Mg grains surrounded by Mg3(Gd,Y) eutectic compounds. While the sheet rolled from the as-homogenized alloy was composed of large deformed grains with long-period stacking ordered (LPSO) phase inside and fewer recrystallized α-Mg grains, and exhibited higher strength due to the deformed grains with stronger basal texture and larger volume fraction of long-period stacking ordered (LPSO) phase. [Copyright &y& Elsevier]

Abstract: Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr alloy sheets containing long period stacking ordered (LPSO) phase were prepared by hot rolling at 400°C with total reduction of 96%. Microstructure evolution of the sheets during hot rolling was investigated, and its influence on mechanical properties was discussed. Twinning occurred during the early stage of hot rolling, and disappeared after total reduction higher than 89%. Average grain size was gradually refined, microstructure became much more homogeneous and volume fraction of LPSO phase decreased with increasing rolling reduction. Furthermore, the type of LPSO phases far from and near the block shaped phases were identified to be different. Basal texture was obtained during rolling process, but the intensity declined with the further rolling, which is mainly due to the dynamic recrystallization and the addition of RE elements. The as-rolled sheet with 96% reduction shows excellent mechanical properties: yield strength of 318MPa, ultimate tensile strength of 403MPa and elongation to failure of 13.7% at ambient temperature along the rolling direction. [Copyright &y& Elsevier]

sAbstract: The Mg/Al laminated composites were fabricated by the accumulative roll bonding (ARB) at ambient temperature using the pure magnesium and commercial pure Al sheets. Mg grains were refined after the primary sandwich preparation and then homogenized during the following ARB process while the grain size of Al layer decreased with increasing of the accumulated strains. Both the yield strength and ultimate strength along rolling direction and transverse direction increased gradually while the elongation to failure along both directions decreased with increasing of the ARB cycles. Formation of the Mg17Al12 phase indicated that the ARB process at ambient temperature could lead to a metallurgic bonding of the Mg/Al interface. [Copyright &y& Elsevier]

Abstract: In this paper, three kinds of magnesium matrix composites reinforced by SiCp with the sizes of 0.2, 5 and 10μm, respectively, were fabricated by stir casting technology. Then the as-cast ingots were deformed by the combination of forging and extrusion process. Typical microstructures were obtained in the composites reinforced by different particle sizes. For the composites with lower volume fraction of particles (2%), submicron SiCp had significant influence on grain refinement and strengthening effect, which resulted in better mechanical properties of submicron SiCp/AZ91 composite. However, mechanical properties reduced owing to the obvious agglomerated submicron SiC particles as the volume fraction increased to 5% and 10%. On the contrary, for micron SiCp/AZ91 composite, the grain size was refined and the strengthening effect was enhanced with the increasing of volume fraction. Although particle size has no influence on the texture type, it has different effects on weakening the intensity of texture. [Copyright &y& Elsevier]

Abstract: In this study, firstly, dynamic microstructural changes of an as-cast Mg–5.0 Zn–0.9 Y–0.16 Zr (wt.%) alloy (designated ZWK510) during hot extrusion at 350°C and a ram speed of 3.33mms−1 was systematically investigated by electron backscattering diffraction (EBSD) analysis. The dynamic recrystallization (DRX) mechanism during hot extrusion was discussed. Then, the effect of microstructure and texture on the mechanical properties of the as-extruded alloy specimens at room temperature was discussed. The as-cast ZWK510 alloy consists of a-Mg and quasicrystalline I-phase. During hot extrusion at 350°C, the main DRX mechanism is the continuous DRX near the original grain boundaries. The I-phase can accelerate the DRX behavior near these areas by obstructing the slip of dislocations. The deformation twins and massive blocky substructures formed in original grains can coordinate the DRX process near the original grain boundaries, however the DRX seldom occurs inside of these area. After further deformation, these deformation twins and massive blocky substructures are elongated along the material flow and become so-called unDRXed area, then a bimodal “necklace structure” composed of fine DRXed grains of about 2.1μm and unrecrystallized coarse area is formed. The extruded ZWK510 alloy shows a DRX ratio of about 58% and a typical basal fiber texture of extrusion direction (ED). In the DRXed area around the crushed eutectic I-phase a large number of fine I-phase precipitates are observed pinning at the newly formed DRXed grain boundaries. The 0.2% proof strength and the ultimate tensile strength of the extruded ZWK510 alloy specimen are 317 and 363MPa, respectively, with an elongation to failure of 12%, which have been attributed to strong basal fiber texture, refined grain size as well as the existence of fine precipitates formed during the hot extrusion. [Copyright &y& Elsevier]

Abstract: The effect of trace Mn addition on the microstructure, texture and mechanical properties of the as-cast and as-extruded Mg–5.25wt.% Zn–0.6wt.% Ca (ZX51) alloys was investigated in this study. Mn addition had a negligible effect on the grain size of the as-cast ZX51 alloy. However, the addition of Mn led to the obvious decrease of grain size in the as-extruded Mg–5.25wt.% Zn–0.6wt.% Ca–0.3wt.% Mn (ZXM510) alloy, because the Mn addition restricted the grain growth during the hot extrusion process. After the addition of Mn, the basal fiber texture with most of {0002} planes parallel to the extrusion direction (ED) was significantly enhanced in the as-extruded ZXM510 alloy. Both tensile yield strength (TYS) and ultimate tensile strength (UTS) were increased in the as-extruded ZXM510 alloy, while the ductility was slightly decreased, which was ascribed to the grain refinement and texture strengthening. [Copyright &y& Elsevier]

Abstract: Mg–5.25wt.% Zn–0.6wt.% Ca alloy was subjected to equal channel angular pressing (ECAP) at 250°C using route A, Bc and C, respectively, in order to investigate the effect of shearing strain path on microstructure, texture and mechanical properties. Route Bc was the most effective in grain refinement and generating high angle grain boundaries, while route A was the least effective. Different textures were developed when a different ECAP route was applied. After ECAP using route A, the tensile yield strength (TYS) got much higher than those of the as-extruded alloy, which was primarily resulted from the strengthening due to the grain refinement. Because the Schmid factor for basal slip system was changed only a little, the texture soften effect was not obvious. After ECAP using route C, TYS of the Mg alloy was significantly decreased although the grain size was significantly refined, because the texture softening effect was dominant over the strengthening due to the grain refinement. [Copyright &y& Elsevier]

Abstract: An ultrafine-grained (UFG) Mg–5.12wt.% Zn–0.32wt.% Ca alloy with an average grain size of 0.7μm was produced by subjecting the as-extruded alloy to equal channel angular pressing (ECAP) for 4 passes at 250°C. The fine secondary phase restricted the dynamic recrystallized (DRXed) grain growth during the ECAP processing, resulting in a remarkable grain refinement. A new texture was formed in the ECAPed Mg alloy with the {0002} plane inclined at an angle of 58° relative to the extrusion direction. The yield stress (YS) was decreased in the as-ECAPed alloy with finer grains, indicating that the texture softening effect was dominant over the strengthening from grain refinement. The ductility of the as-ECAPed alloy was increased to 18.2%. The grain refinement caused an obvious decrease in work hardening rate in the as-ECAPed alloy during tensile deformation at room temperature. [Copyright &y& Elsevier]