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Abstract: In the present study, AZ91 magnesium matrix composites reinforced with six volume fractions (0.5, 1, 1.5, 2, 3 and 5vol.%) of submicron-SiC particulates (0.2μm) were fabricated by stir casting. The as-cast ingots were forged at 420°C with 50% reduction, and then extruded at 370°C with the ratio of 16 at a constant ram speed of 15mm/s. The microstructure of the composites was investigated by optical microscopy, scanning electron microscope and X-ray diffractometer. Microstructure characterization of the composites showed relative uniform reinforcement distribution, significant grain refinement and presence of minimal porosity. The X-ray diffractometer analysis showed that a strong basal plane texture was formed in both AZ91 alloy and SiCp/AZ91 composites during extrusion and the addition of submicron-SiC particulates could weaken the basal plane texture. The presence of submicron-SiC particulates assisted in improving the thermal stability, micro-hardness, elastic modulus and 0.2% yield strength. Both of the 0.2% yield strength and ultimate tensile strength increased with the increasing of submicron-SiC particulate content, however, decreased as the SiC particulate content overrun 2vol.%. [ABSTRACT FROM AUTHOR]

Abstract: Equal channel angular pressing (ECAP) of the in situ Mg2Si reinforced Mg composite was performed with route Bc up to 8 passes using a 90° die. Refinement and re-distribution of the reinforced phase Mg2Si was investigated. Bulk texture development during ECAP was characterized by neutron radiation. Results showed that only the eutectic Mg2Si (Type-II) was proposed to be effective for preparing the in situ Mg2Si/Mg composite. Neutrons texture analysis briefly illustrated that a 〈00.2〉 basal fiber with the obtainment of less shear effect was formed. But the asymmetry of basal fiber around the ECAP direction was also observed. Both uniform texture and homogeneity distribution of Mg2Si particles played an important role in the tensile behavior of ECAPed composite. [Copyright &y& Elsevier]

Abstract: The hot deformation behavior of ZK60 magnesium alloy reinforced with 20vol.% of Al18B4O33 whisker was investigated by compression testing in temperature range of 523–723K and strain rate range of 0.001–10s−1. The deformation behavior was mainly dependent on strain rate and temperature on certain strain condition. Variations of flow behavior with deformation temperature as well as strain rate were analyzed. The microstructural evolution at different temperatures and strain rates are mainly characterized by twinning, dislocation slip and dynamic recrystallization (DRX) during the hot compression. They were observed by transmission electronic microscope (TEM). It is shown that twinning occurred at lower temperature and earlier deformation stage. Twinning is the main reason for the high strain hardening rate at relatively low temperature. The material showed DRX at higher temperature and moderate strain rate, which is the reason for flow softening at relatively high temperature. Al18B4O33 whiskers promote nucleation of DRX. A fine dislocation substructure forms upon hot deformation, leading to subgrain formation. [Copyright &y& Elsevier]

Abstract: The effect of Si content on low frequency damping capacities and mechanical properties of as-cast Mg–Si alloys were investigated. Both hypoeutectic alloys with 0.3wt.%Si, 0.8wt.%Si and hypereutectic alloy with 2.3wt.%Si exhibit high damping capacities since these Mg–Si alloys possess large size α-Mg phase with very small amount of soluble atoms in it. The amount of the in situ formed Mg2Si determines the dislocation density and then influences the damping capacity of these Mg–Si alloys. The Mg–0.3wt.%Si alloy exhibits the lowest damping value at small strain region but the highest damping value at large strain region among these Mg–Si alloys. Two damping peaks were found in Mg–Si alloys at 80 and 230°C, respectively. But the addition of Al in Mg–Si alloy impeded the appearance of these two damping peaks since the soluble Al atoms hindered the movement of dislocations and the slide of grain boundaries. The presence of large size, brittle primary Mg2Si particles decreases the tensile strength and ductility of the hypereutectic Mg–Si alloy. [Copyright &y& Elsevier]

Abstract: Mechanical properties of coated AZ91 Mg alloy, Al18B4O33w/AZ91 and SiCw/AZ91 composites by microarc oxidation (MAO) surface treatment technique were measured and effects of MAO treatment on the mechanical properties were investigated. Tensile test shows that MAO treatment just slightly decreases ultimate tensile strength (UTS) and elongation of the Mg-based materials, while enhances their elastic modulus to some extent. But the effects of MAO treatment on the mechanical properties will be influenced by the energy parameters applied during surface treatment. The three materials coated under the same process conditions have exhibited differential surface morphology and fracture after tensile test, which indirectly indicates that the qualities of MAO coatings are also related with the substrate materials. [Copyright &y& Elsevier]

Abstract: The ceramic coatings were synthesized on AZ91 Mg alloy, Al18B4O33w/AZ91 and SiCw/AZ91 Mg matrix composites by microarc oxidation (MAO) technique in an alkali–silicate electrolyte solution. The microarc discharge phenomena of the three substrates during MAO process were described. SEM and XRD were employed to characterize microstructure and phase composition of the coatings. The corrosion resistance of the coatings was evaluated by electrochemical method. The results show that the three substrates have different voltage span of microarc discharge and different voltage evolution trend with increasing period during MAO. As a consequence, mass gain after oxidation and microstructure of coatings are also different for the three substrates. These MAO behaviors are believed to be attributed to the addition of reinforcement phases with different properties. The reinforcement phases in the composites have no influence on the phase composition of MAO coatings. MAO treatment could improve the corrosion resistance of Mg alloy and composites to different extent. [Copyright &y& Elsevier]

Abstract: As-cast hypoeutectic Mg–Si alloy showed a high damping capacity at room temperature. This resulted from the co-effect of damping peaks P 0 and P 1 which were detected at 0°C and 100°C, respectively. P 0 and P 1 were considered to possess similar properties and they were caused by the interaction between dislocations and impurity atoms or vacancies. Heat treatment strongly influenced the damping capacity of this Mg–Si alloy. [Copyright &y& Elsevier]

The effect of high temperature exposure on the interface and tensile properties of Al18B4O33w/AZ91 magnesium matrix composite fabricated by squeeze casting was studied. The interfaces of the composites were examined using transmission electron microscopy, and the mechanical properties were evaluated by tensile tests. The interfacial region was composed of MgO which was formed by the reaction between the Al18B4O33 whisker and the Mg matrix. An thin and uniform interfacial reaction layer with a thickness of 10–20 nm formed during squeeze casting could act as a barrier to prevent the further reaction between Al18B4O33 whisker and Mg alloys. The interfacial reaction rate was very low during thermal exposure below the liquidus temperature of AZ91 matrix alloy. Only after exposure above the liquidus temperature of the AZ91 matrix alloy for a long period, the thickness of the interfacial layer increased obviously. However, the interfacial reaction rate was much slower than that in the Al18B4O33w/Al–Mg composites. The interfacial reaction kinetics was controlled by the seepage of Mg and release of Al and B along the narrow diffusion channels between the fine MgO particle. The composite did not show a degradation in the tensile properties after exposure below the solidus temperature of AZ91 for long periods, suggesting that the Al18B4O33w/AZ91 magnesium matrix composite could be subjected to long-term service at elevated temperature. [Copyright &y& Elsevier]

SiC particles reinforced AZ91D Mg matrix composites with different particle contents fabricated by a ultrasonic method were extruded at 350 °C. Hot extrusion eliminated the “island” particle distribution, and evidently improved SiC particles distribution of the composites. However, hot extrusion induced particle cracking besides the improvement of SiC particles distribution. There existed more cracked particles in the particle-rich zones. During extrusion, SiC particles stimulated the nucleation of dynamic recrystallization in the matrix. Dynamic recrystallization is also sensitive to the particle content on a local scale in the composites. As SiC contents increased, the yield strength of the composites increased. However, the ultimate tensile strength increases of the composites were small as the SiC contents increased from 10% to 20%, because the improvement of ultimate tensile strength caused by the strengthen effects of SiC particles was offset by extrusion-induced particle cracking. [ABSTRACT FROM AUTHOR]

Abstract: Ageing treatment at 200°C and 225°C for various periods of time was introduced to the Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt.%) alloy, the age-hardening behaviour and phase transformation were analysed systematically. The alloy aged at 225°C exhibits accelerated ageing progress compared with that aged at 200°C. The precipitation sequences of the alloy aged at both 200°C and 225°C are supersaturated solid solution (SSSS)→β′′ (D019)→β′ (bco). Stacking faults and 14H LPSO phase formed in the alloy over-aged at 200°C and 225°C, respectively. The equilibrium β phase precipitated at the grain boundaries with the formation of precipitate free zone (PFZ) at the peak-aged stage, after further ageing treatment, the β phase got coarsened, which was accompanied with the widening of the PFZ. [Copyright &y& Elsevier]

Abstract: Magnesium matrix nanocomposites reinforced by SiC nanoparticles were fabricated by ultrasonic vibration with SiC nanoparticle size of 60nm and volume fractions of 0.5%, 1% and 2%, respectively. With increasing the volume fraction of the SiC nanoparticles, grain size of matrix in the SiCp/AZ91 nanocomposites was gradually decreased and morphology of the phase Mg17Al12 was refined compared with as-cast AZ91 alloy. Most of the SiC nanoparticles exhibited a homogeneous distribution in the 0.5 and 1vol.% SiCp/AZ91 nanocomposites. The ultimate tensile strength, yield strength and elongation to fracture of the 0.5 and 1vol.% SiCp/AZ91 nanocomposites were simultaneously improved. However, agglomerates of SiC nanoparticles along the grain boundaries were evidently increased when the volume fraction of nanoparticles was increased to 2, which caused the decrease of ultimate tensile strength and elongation to fracture. [Copyright &y& Elsevier]

Abstract: Magnesium matrix composites reinforced with micro-SiC particles were fabricated by semisolid stirring assisted ultrasonic vibration with SiC particle size of 1μm and volume fractions of 3% and 5%, respectively. Compared with as-cast AZ91 alloy, with the addition of the micro-SiC particles grain size of matrix was decreased while most of the phase Mg17Al12 varied from coarse plates to lamellar precipitates in 3vol.% SiCp/AZ91 composite. Although some dispersed micro-SiC particles were found within the grains, most of the micro-SiC particles were located along grain boundaries in both 3vol.% and 5vol.% SiCp/AZ91 composites. The study of the interface between the micro-SiC particle and the alloy matrix suggested that micro-SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength and yield strength of the 3vol.% SiCp/AZ91 composite were improved while elongation to fracture was almost kept. [Copyright &y& Elsevier]

Abstract: Ultrasonic vibration with frequency of about 20kHz and power of 350W was introduced into molten AZ91 alloy. After ultrasonic vibration, morphology of the phase Mg17Al12 formed during the cooling and solidification varied from coarse plates to lamellar precipitates. With application of solution heat treatment, the phase Mg17Al12 was mostly dissolved in both the alloy with ultrasonic vibration and without ultrasonic vibration. The ultimate tensile strength and the elongation to fracture of the alloy were significantly increased after ultrasonic vibration. After solution heat treatment the tensile strength of the alloy without ultrasonic vibration increased remarkably while the alloy with ultrasonic vibration increased slightly. [Copyright &y& Elsevier]

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]

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]

High quality WE43 magnesium alloy ingots with diameter of 500 mm are successfully fabricated by direct-chill (DC) casting. The alloying elements distributed almost homogeneously across the large ingot. With the average grain size decreasing from the center to the edge of the ingot, the mechanical properties are improved gradually. After solution treatment at 525 °C for 8 h, the Mg 14 Nd 2 Y phases distributing along the grain boundaries are well dissolved into matrix. The direct-chill (DC) casting ingot exhibits remarkable age-hardening response from 85 Hv to 117 Hv after T6 treatment at 250 °C. The T6 peak-aged sample exhibits ultimate tensile strength of 274 MPa, yield strength of 215 MPa and elongation to failure of 3.4%, which are higher than those of sand-cast and permanent mold cast WE43 alloys. The large amount of nano prismatic β ′ and β 1 phases precipitated during T6 treatment contribute to improved strength of the WE43 alloy. [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]

Nano-SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were extruded at 350 °C, then processed by equal channel angular pressing (ECAP) at various temperatures (250 °C, 300 °C and 350 °C). Grains are significantly refined after the extrusion and the ECAP. A basal fibre texture was detected by neutron diffraction after the extrusion, which inclines about 45° to the extrusion direction (ED) after the ECAP. Nano-scaled SiC particles agglomerate in the as-cast composite. After the extrusion, the agglomeration tends to form continuous or discontinuous strips along the extrusion direction. By application of the ECAP, the agglomerated SiC particles are partly dispersed and the strips formed during the extrusion tend to be thinner and broken with the increasing pass number. The yield tensile strength (YTS) and the ultimate tensile strength (UTS) of the composite are dramatically increased after the extrusion. ECAP for one pass at various temperatures further increases the strength, however, the YTS decreases with the increasing ECAP temperature and the pass number. The Orowan equations predict the maximum YTS of the composite may be up to 400 MPa providing SiC particles are homogenously distributed in the matrix. [ABSTRACT FROM AUTHOR]

A new ultrahigh-strength W phase (Mg 3 Y 2 Zn 3 ) containing Mg–10.3Zn–6.4Y–0.4Zr–0.5Ca (wt.%) alloy with medium RE content has been fabricated through conventional casting and indirect extrusion. The as-extruded alloy exhibits ultimate tensile strength of 466 MPa, tensile yield stress of 447 MPa and elongation to failure of 4.7%. The as-cast Mg–10.3Zn–6.4Y–0.4Zr–0.5Ca (wt.%) alloy is mainly composed of α-Mg and lamellar eutectic α-Mg and W phase distributed at grain boundaries. After extrusion, the coarse lamellar W phases in the as-cast alloy are broken into fine particles of about 0.5 μm, dispersing in the particle bands along the extrusion direction. The as-extruded alloy exhibits a bimodal microstructure consisting of ultrafine dynamic recrystallized (DRXed) grains with fine broken W phase particles at the DRXed grain boundaries and coarse un-DRXed regions. Large number of nano W phase and small amount of nano β 2 ′ phase are dynamically precipitated in the coarse unDRXed regions during extrusion, which contribute to the ultrahigh strength of the as-extruded alloy. [ABSTRACT FROM AUTHOR]

The effect of fly ash cenospheres (FACs) on the electromagnetic interference (EMI) shielding effectiveness (SE) of the magnesium matrix was investigated. Raw FACs and FACs modified by Ca(OH) 2 were employed as reinforcements. The two kinds of FACs dispersed uniformly in the matrix. Most unmodified FACs were severely broken in the composites, but the majority of FACs kept complete integrated in the composites reinforced by modified FACs. In the range of the testing frequency, raw FACs did not evidently improve the EMI SE of matrix. However, the modified FACs with better ball structure improved the EMI SE of matrix to 75–90 dB. This improvement is attributed to the reflection loss occurred at the outer face (R), absorption at interior place (A) of the composites as well as multiple reflection (B) between different modified FACs. [ABSTRACT FROM AUTHOR]

A high-strength low-cost Mg-2.5Zn-0.3Ca-0.4La (mass%) alloywas fabricated by hot extrusion following directchill casting. Yield strength (YS), ultimate tensile strength (UTS) and elongation to failure of the alloy are 325 MPa, 341 MPa and 15%, respectively. The high strength of the extruded Mg-2.5Zn-0.3Ca-0.4La alloy is mainly due to grain refinement, dense precipitation and high density of dislocations. The extruded alloy exhibits a bimodal microstructure containing fine dynamic recrystallized (DRXed) grains and deformed regions. High density of dislocations is stored in the deformed regionswhile dense precipitates are homogeneously distributed in both the DRXed grains and the deformed regions. However, precipitates in the DRXed regions show in spherical shape only, while they are in rod-like shape and spherical shape in the deformed regions. [ABSTRACT FROM AUTHOR]

Multidirectional forging (MDF) under decreasing temperature conditions was adopted to process SiC nanoparticles reinforced magnesium matrix composite. The results showed that grains of the nanocomposite were effectively refined while the amount of precipitated phases was significantly increased after MDF under decreasing temperature conditions. The precipitated phases as well as dispersed SiC nanoparticles could hinder the growth of dynamic recrystallization. The yield strength and ultimate tensile strength of the nanocomposites were increased compared with that of as-cast nanocomposite. This improvement could be attributed to obvious grain refinement as well as Orowan strengthening effect introduced by the dispersed SiC nanoparticles and the precipitated phases. Microcrack could initiate within the SiC nanoparticle dense zones during tensile test at room temperature, resulting in decrease of the elongation. [ABSTRACT FROM AUTHOR]

A particulate reinforced magnesium matrix nanocomposite was subjected to multidirectional forging (MDF). The results showed that the microstructure of the nanocomposite mainly consisted of some large initial grains and fine recrystallized grains along initial grain boundaries after 1 MDF pass. With increasing the MDF passes, the degree of dynamic recrystallization increased and ultrafine grains with average size of about 20 nm were observed in the nanocomposites after 6 MDF passes. The distribution of SiC nanoparticles in the nanocomposite was homogeneous outside some SiC nanoparticle dense zones after different MDF passes. Compared with typical basal texture obtained for 1 MDF pass, the basal pole intensity decreased firstly for 3 MDF pass and then increased for 6 MDF passes. Both ultimate tensile strength and elongation to fracture of the nanocomposite were enhanced with increasing the MDF passes, while yield strength decreased after 3 MDF passes and then increased slightly after 6 MDF passes. [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]

Mg–5.3 wt%Zn alloy microalloyed with 0.2 wt%Ca and 0.5 wt%Ce was extruded, and the microstructure, texture and mechanical properties of the as-extruded alloy were investigated. The undissolved coarse T 1 ′during homogenization treatment stimulated nucleation of dynamic recrystallization (DRX) grains during extrusion. The double microalloying with Ca and Ce promoted the dynamic precipitation, resulting in high density precipitates after hot extrusion. Fine Ca 2 Mg 6 Zn 3 particles precipitated dynamically at the grain boundaries (GBs) could effectively hinder the grain growth during hot extrusion. A weaker texture in DRXed grains was attributed to the coarse-particle stimulated nucleation (PSN) and pinning of the grain boundaries by fine precipitates. The fine DRXed grains, high density of dislocation in the unDRXed region, and fine dense precipitates gave rise to the improved strength of the as-extruded Mg–Zn–Ca–Ce alloy. [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]

Highlights: [•] Novel stir casting assisted by ultrasonic treatment was developed. [•] Ultrasonic treatment significantly improved the stir casting. [•] Ultrasonic treatment improved the mechanical properties. [Copyright &y& Elsevier]

Highlights: [•] Friction stir processing (FSP) was applied to Mg–Gd–Y–Zn–Zr casting. [•] The grain boundary Mg3RE and LPSO phases in the casting dissolved after FSP. [•] Fine grains with LPSO phase distributed only within the grains was achieved. [•] High mechanical properties were obtained in FSP Mg–Gd–Y–Zn–Zr. [ABSTRACT FROM AUTHOR]

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: A large Mg-4.50Zn-1.13Ca (wt%) alloy ingot 350mm in diameter and 1730mm long was successfully fabricated by semi-continuous casting. The microstructures and mechanical properties of the as-cast and as-extruded alloys were investigated. The as-cast alloy exhibits uniform chemical composition and microstructure from the centre to the surface of the ingot and mainly consists of α-Mg and Ca2Mg6Zn3. The coarse grains and network-like second phases that are distributed at the grain boundaries result in poor mechanical properties for the as-cast alloy. The mechanical properties of the as-extruded alloys are significantly enhanced. The high yield strengths of the as-extruded alloys mainly result from the fine DRXed grain and the stronger basal texture. [Copyright &y& Elsevier]

Abstract: In this paper, 0.2μm SiCp/AZ91 composite was fabricated by stir casting technology. The influence of fine (<1μm) particles on the dynamic recrystallization (DRX) behavior of AZ91 matrix was investigated by researching the microstructure evolution of 0.2μm 1vol% SiCp/AZ91 composite during the hot extrusion process. Results showed that the DRXed ratio of AZ91 matrix increased as well as the average size of DRXed grains reduced due to the addition of fine particles. The SiCp could not only pin dislocation, but also was helpful to generate dislocations owing to the deformation mismatch between matrix and particles, thus causing the increase of dislocation density around SiCp, which was benefit to stimulate DRX nucleation. Meanwhile, the growth of DRXed grains was suppressed in the following deformation process due to the pinning effect of fine particles on grain boundaries. Thus, the fine particles had significant effect on stimulating DRXed nucleation and refining grain size. The yield strength and ultimate tensile strength of the as-deformed 0.2μm 1vol% SiCp/AZ91 composite are 275 and 335MPa, respectively, which are mainly attributed to the grain refinement, basal plane texture and uniform particle distribution induced by hot deformation. [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 study, equal channel angular pressing (ECAP) was applied to a hot-extruded Mg–5.00Zn–0.92Y–0.16Zr (wt.%) alloy to produce an ultrafine-grained a-Mg structure of 0.6μm with uniformly distributed fine quasicrystal Mg3YZn6 particles. The basal planes in the as-ECAPed alloy were inclined approximately 45° to the ECAP direction (EPD); thus, a high Schmid factor of 0.36 for basal slip along EPD was obtained. Then, the superplastic behavior at low temperatures of 150–250°C and initial strain rates of 1.67×10−3 s−1–1.67×10−1 s−1 of the as-ECAPed alloy was investigated and compared with that of the as-extruded alloy. The microstructural development, texture evolution and cracking behavior during tensile tests were systemically investigated by electron backscattered diffraction (EBSD) analysis. During the tensile test along the EPD, the basal planes in the as-ECAPed alloy specimen were tilted approximately 15° away from the original position; thus, the basal planes were still in a position favorable for the basal slip along the EPD. As a result, a maximum elongation of 865% was obtained at 200°C and a strain rate of 1.67×10−3 s−1, as a result of this favored basal texture and the excellent thermal stability of the ultrafine-grained structure. This optimum superplastic temperature of 200°C is much lower than that obtained for other Mg–Zn–Y–(Zr) alloys. In contrast, for the as-extruded alloy specimen, superplastic behavior did not occur until the critical condition of 250°C and a strain rate of 1.67×10−3 s−1. Below this temperature and strain rate, the strong extrusion basal texture was maintained, and the cracks in the hot-worked coarse region (or un-DRXed region) were observed nucleating mainly associated with the formation of a 38° double twin. At this temperature and strain rate, the hot-worked coarse regions were significantly refined by the dynamic recovery and the following recrystallization process. In the case, the formation of a double twin was prevented and the facture was delayed. [Copyright &y& Elsevier]

Abstract: Ultra high-strength Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr alloy sheet was prepared by large-strain hot rolling and subsequent ageing process. The sheet exhibits excellent tensile properties at ambient temperature with ultimate tensile strength of 517MPa, 0.2% proof stress of 426MPa and elongation to failure of 4.5%. The notable improvement in strength is attributed to the dense distribution of the fine precipitates inside the grains, scattered precipitates at the grain boundaries, bimodal grain size distribution with fine recrystallized grains and large deformed grains with intense basal texture. [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]

Abstract: In the present study, 10vol.% SiCp/AZ91 magnesium matrix composites are fabricated by stir casting. The as-cast ingots are cut into cylindrical billets, and then forged at 420°C with different deformation amounts (40, 50, 60 and 80%) at a constant RAM speed of 15mm/s. The results illustrate that the addition of SiC particles has significant influence on refining grain size and improving tensile strength of AZ91 matrix, however, weakening basal plane texture. After forging SiCp/AZ91 composites, the intensity of basal plane texture increases as deformation amount increases. The grain size of composite matrix grows up slightly as the deformation amount increased to 60%, and then it was refined obviously as the deformation amount continues to increase to 80%. The smaller deformation amount is propitious to improve particle distribution, while lager deformation amount promotes SiC particle agglomeration. Thus, the tensile strength increases as the deformation amount increases to 50%, however, it decreases as the deformation amount continues to increase to 80%. [Copyright &y& Elsevier]

Abstract: An ultrafine-grained (UFG) Mg–Zn–Y–Zr magnesium alloy with a grain size of about 0.8μm was produced by subjecting the extruded alloy to equal channel angular pressing (ECAP) for eight passes at 473K. Compressive testing was performed on the as-extruded and on the further ECAP-processed Mg–Zn–Y–Zr alloy at a temperature of 423K and under strain rates from 1.67×10−3 to 1.67×10−1 s−1. In the UFG ECAP-processed magnesium alloy, the strain hardening rate was extremely low, in contrast to that of the extruded alloy. The ultrafine grains of the ECAP-processed alloy were stable in compression because of the presence of the dispersion of a fine I-phase and of precipitates in the alloy, which restricted grain growth. The ECAP-processed alloy exhibited a higher strain rate sensitivity exponent than the as-extruded magnesium alloy, which may have contributed to its enhanced ductility. [Copyright &y& Elsevier]

Abstract: The hot working behavior of ZK60 magnesium alloy by squeeze casting has been studied in the temperature range of 523–723K and strain rate range of 0.001–10s−1 by establishing processing maps. The strain rate sensitivity (m), power dissipation efficiency (η) and instability parameter were computed based on the experimental compression data and are plotted in the temperature–strain rate plane to obtain power dissipation and instability maps. The power dissipation map reveals that a domain of dynamic recrystallization (DRX) occurred in the temperature range of 573–648K and strain rate range of 0.001–0.01s−1, with its peak efficiency of 36% at 648K and 0.001s−1, which are the optimum hot working parameters. Analysis of the flow behavior and microstructure observations indicated that dynamic recrystallization occurred at higher temperatures and lower strain rates. Instability map showed flow localization at lower temperatures and higher strain rates. [Copyright &y& Elsevier]