This study was undertaken to evaluate the effect of extrusion ratio on the microstructure and mechanical properties of Mg–8Li–3Al–2Zn–0.5Y (wt%) alloy, which was prepared by casting and then deformed by hot extrusion at 200 ℃ with four different ratios of 4:1, 9:1, 16:1 and 25:1, respectively. It was identified that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy is composed of α-Mg, β-Li, AlLi, MgLi2Al and Al2Y phases. After hot extrusion with all four ratios, the microstructure was significantly refined. The mechanical properties of Mg–8Li–3Al–2Zn–0.5Y alloy at room temperature were improved, mainly caused by grain refinement and precipitation strengthening. As the extrusion ratio increases from 4 to 25, the grains of the alloy become elongated and refined, and the tensile properties first increase and then decline. Among all the tested alloys, the alloy with the extrusion ratio of 16 exhibits the highest yield strength, ultimate tensile strength and elongation of 214 MPa, 243 MPa and 41%. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically.

The tensile properties, impact toughness and plane-strain fracture toughness of sand-cast Mg-6Gd-3Y-0.5Zr magnesium alloy were studied in different thermal conditions, including as-cast, as-quenched and isothermal aging states. The results show that optimum heat treatment is solutionized at 490℃ for 12 h, and then aged at 212℃ for 100 h. Tensile test exhibits that as-quenched GW63 alloy shows high elongation but low tensile strength, nevertheless, aged alloy shows higher strength but worse ductility. Impact values of GW63 alloy are 34.6, 50.9 and 20.3 J/cm2 in the as-cast, as-quenched and aged states, respectively. Room temperature impact toughness is more closely related to material ductility than strength for the studied alloy. The plane-strain fracture toughness values of the as-cast, as-quenched and aged alloy are 16.2, 17.7 and 19.5 MPa m½, respectively, i.e., the improvement of 20.4% has been achieved by aging precipitation strengthening in contrast with slight improvement of 9.3% by solid solution strengthening. In addition, fractured characteristics after impact and fracture toughness tests were also investigated by fracture analysis.

In this study, the microstructure evolution and mechanical properties of as-cast Mg–8Li–3Al–2Zn–0.5Y alloy during solid solution treatment from 300 °C to 450 °C were firstly investigated, and then the effect of Y content (from 0.5 wt% to 1.5 wt%) on the age softening of solid solution treated Mg–8Li–3Al–2Zn alloy was also analyzed. The results show that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy mainly consists of α-Mg, β-Li, Al2Y and AlLi phases. With the increase of solid solution temperature from 300 °C to 450 °C for as-cast Mg–8Li–3Al–2Zn–0.5Y alloy, the AlLi phase is decomposed and the atoms of Al and Li dissolve into the matrix gradually. The hardness, yield strength and ultimate tensile strength of the tested alloy are increased dramatically; however, the ductility is relatively decreased. Meanwhile, the room temperature aging treated Mg–8Li–3Al–2Zn–0.5Y has age hardening during initial time, and the addition of Y is helpful to the thermal stability of Mg–8Li–3Al–2Zn alloy. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically.

In this study, the compositional dependence of the age hardening response and high temperature tensile properties of the Mg–xGd–3Y–0.5Zr (x=3, 6, 10, and 12 wt%) alloys are investigated. The amount of cuboid-shaped phases and β′ precipitates increased significantly with increasing the Gd content. The Mg–10Gd–3Y–0.5Zr alloy exhibited the maximum ultimate tensile strength at room temperature, while at higher temperatures the Mg–12Gd–3Y–0.5Zr alloy exhibited the maximum yield strength and ultimate tensile strength. The yield strength and ultimate tensile strength of the Mg–12Gd–3Y–0.5Zr alloy increased with the test temperature and showed its maximum at 150 °C, and then decreased as the temperature increased further. The Mg–12Gd–3Y–0.5Zr alloy maintained a high ultimate tensile strength of more than 300 MPa up to 250 °C. The superior high temperature tensile strength of the tested alloy is mainly associated with solution strengthening and precipitation hardening of the cuboid-shaped phases and β′ precipitates in Mg matrix. Especially, β′ precipitates can hinder the dislocation movement at high temperature.

The effects of solid solution and aging treatments on the microstructure evolution and mechanical property of the as-cast Mg–14Gd–3Y–1.8Zn–0.5Zr alloy are investigated in this study. The microstructures of the 14H type long period stacking ordered (LPSO) structure and RE precipitates in the conditioned alloys are observed and analyzed by XRD, SEM and TEM. The mechanical properties of the alloys are evaluated Vickers hardness and ambient-temperature tensile tests. The results show that the volume fraction of 14H-LPSO structure in the alloy increased gradually with continued solution. The maximum volume fraction of RE precipitates is obtained when the alloy is solid-solution-treated at 793 K for 10 h and subsequently aged at 498 K for 16 h, under this optimum condition the mechanical properties (ultimate tensile strength: 366 MPa, yield strength: 230 MPa, elongation: 2.8%) at ambient temperature are achieved. The good performance of the studied GWZK alloy results from the dense precipitation of 14H-LPSO structure and RE precipitates in the matrix during the solid solution and aging process.Highlights► Effect of heat treatment on microstructure and mechanical property of GWZK alloy is investigated. ► Volume fraction and distribution of RE precipitates is modulated by controlling formation of 14H-LPSO structure. ► The best mechanical property is obtained from the alloy treated at 793 K × 10 h + 498 K × 16 h. ► The performance is affected by optimization for combination between 14H-LPSO structure and RE precipitates.

Magnesium alloy GW103 samples were heat treated to different ageing conditions and then shot peened using process parameters that deliver optimized high cycle fatigue (HCF) life. Significant HCF life improvements were observed in all samples, with a peak-aged sample showing the biggest increase. In order to simulate the effect and evolution of residual stresses during low cycle fatigue (LCF), a Finite Element (FE) model was employed, taking into account both the shot-peening-induced plastic strains and the influence of hardening on subsequent deformation. Experimental and modelling results offer a basis for explaining the observed fatigue performance improvement due to shot peening.

This paper studies the fatigue properties and fracture behavior of as-extruded Mg–6Zn–0.5Zr and Mg–10Gd–3Y–0.5Zr alloys before and after shot peening. Compared to Mg–6Zn–0.5Zr alloy, Mg–10Gd–3Y–0.5Zr alloy shows higher optimal Almen intensity, and possesses a broader process window. The stress-controlled rotating bending fatigue property improvement for Mg–10Gd–3Y–0.5Zr alloy by shot peening is significantly superior to that of Mg–6Zn–0.5Zr alloy. With the increase in peening (Almen) intensity, the fatigue crack nucleation site of Mg–6Zn–0.5Zr alloy under stress control shifted from the surface to subsurface, and then back to the surface again. Meanwhile, a significantly higher number of fatigue crack initiation sites can be seen as a consequence of overpeening. However, the fatigue cracks of the peened Mg–10Gd–3Y–0.5Zr alloy initiated subsurface at all Almen intensities, showing unchanged crack initiation location with the increase in Almen intensity. The observed phenomenon is related to differences between the two alloys both in the deformation mechanisms during shot peening and the residual stress relaxation mechanisms during subsequent fatigue process. Namely, at present test conditions such as Almen intensity range and high cycle fatigue stress, in the Mg–6Zn–0.5Zr alloy twinning dominates deformation during shot peening and detwinning during fatigue. Comparatively, dislocation slip dominates deformation in both shot peening and fatigue process in the Mg–10Gd–3Y–0.5Zr alloy.Highlights• The as-extruded Mg–6Zn–0.5Zr alloy exhibits a strong twinning and detwinning phenomenon. • Mechanical twinning dominates deformation in Mg–6Zn–0.5Zr alloy during shot peening. • Dislocation slip dominates deformation in Mg–10Gd–3Y–0.5Zr alloy during shot peening. • The two alloys exhibit different fatigue strengthening mechanisms by shot peening.