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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: 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: 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]

Pure molybdenum (PM) and La 2 O 3 dispersion strengthened Mo alloy (ODS-Mo) were prepared by powder metallurgy through two different mixing method (solid-solid or SS mixing and solid-liquid or SL mixing). After annealed at 1050 °C for 1 h, the PM, SS-Mo and SL-Mo were compared in microstructure and mechanical properties. The microstructural examinations showed that the PM was mostly recrystallized with rather coarse grains, but the ODS-Mo alloys remained fine elongated grains. This discrepancy is due to a higher recrystallization temperature held in the ODS-Mo alloys. The uniaxial testing results showed that the ODS-Mo had higher tensile mechanical properties compared to the PM, which are attributed to the remarkable strengthening and ductilizing effect induced by the La 2 O 3 particles. The low cycle fatigue (LCF) testing results revealed that the PM experienced cyclic hardening behaviors, while the ODS-Mo alloys exhibited cyclic softening behaviors. The Basquin-Manson-Coffin analyses results demonstrated that the ODS-Mo possessed a higher fatigue ductility and longer fatigue life than the PM. Two kinds of cracks, i.e., cleavage cracks and intergranular cracks, were experimentally observed to coexist on the fracture surface. In particular in the SL-Mo alloy, the two crack interacted and propagated forward until final fracture, leading to a step-like crack growth path and concomitantly enhanced fatigue ductility. In addition, different cycling dislocation structures were revealed between the PM and ODS-Mo alloys. Cycle fatigue mechanisms responsible for the fatigue behaviors and microstructure evolution during LCF testing were discussed. The best LCF resistance combined with superior uniaxial tensile mechanical properties found in the SL-Mo alloy were rationalized. [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]

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]

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: 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 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: 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]