The application of magnesium alloys is hindered by the inherent contradiction between mechanical performance and thermal conductivity. Achieving simultaneous enhancement of both properties is crucial for broadening their applications. In this study, Mg-5Zn-xCu-0.5Zr (x = 0, 0.5, 1, 2) alloys were fabricated using semi-solid rheo-diecasting (RDC). The microstructure was characterized via OM, SEM, XRD, TEM and EBSD, and its influence on mechanical properties and thermal conductivity was analyzed. The results show that adding Cu refines the grain size, induces the formation of the MgZnCu phase, and reduces solidification shrinkage defects. The RDC Mg-5Zn-xCu-0.5Zr alloy features a heterogeneous microstructure comprising primary α-Mg (α1) with low solute content, secondary α-Mg (α2) with high solute atom content, and intergranular second phases. This heterogeneous structure synergistically enhances both mechanical properties and thermal conductivity. Specifically, α1 grains and the MgZnCu phase reduce lattice distortion, thereby improving thermal conductivity, while α2 generates more dislocations during tensile deformation, contributing to enhanced mechanical properties. Additionally, a small amount of MgZnCu phase contributes to simultaneous improvements in both properties. However, excessive MgZnCu phase can lead to stress concentration due to dislocation pile-up, causing fracture and degrading mechanical properties. Among the alloys studied, the Mg-5Zn-1Cu-0.5Zr alloy exhibits the best combination of mechanical and thermal properties, with a tensile strength of 221 MPa, yield strength of 109 MPa, elongation of 5.72%, and thermal conductivity of 113.8 W/(m·K). This demonstrates the successful simultaneous enhancement of both mechanical and thermal properties in magnesium alloys.

In this study, the twinning–detwinning behavior and slip behavior of rolled AZ31 magnesium-alloy plates during a three-step intermittent dynamic compression process along the rolling direction (RD) and normal direction (ND), are investigated via quasi-in situ electron backscatter diffraction, and the causes of the twinning and detwinning behavior are explained according to Schmid law, local strain coordination, and slip trajectories. It is found that the twins are first nucleated and grow at a compressive strain of 3% along the RD. In addition to the Schmid factor (SF), the strain coordination factor (m’) also influences the selection of the twin variants during the twinning process, resulting in the nucleation of twins with a low SF. During the second and third steps of the application of continuous compressive strains with magnitudes and directions of 3%RD+3%ND and 3%RD+3%ND+2.5%ND, detwinning occurs to different extents. The observation of the detwinning behavior reveals that the order in which multiple twins within the same grain undergo complete detwinning is related to Schmid law and the strain concentration, with a low SF and a high strain concentration promoting complete detwinning. The interaction between slip dislocations and twin boundaries in the deformed grains as well as the pinning of dislocations at the tips of the {1012} tensile twins with a special structure result in incomplete detwinning. Understanding the microstructural evolution and twinning behavior of magnesium alloys under different deformation geometries is important for the development of high-strength and high-toughness magnesium alloys.

In order to solve the issues concerning high hot tearing susceptibility (HTS) of Mg-Al-Ca series alloys, a rotating magnetic field (RMF) was applied during their solidification. The effect of RMF at different excitation current intensities (50 A, 100 A, and 150 A) on the solidification and hot tearing behavior of AXJ530 (Mg-5Al-3Ca-0.17Sr) alloy was investigated. The results indicated that the HTS of AXJ530 alloy decreased with the increase of excitation current intensity. This aspect can be attributed to significant grain refinement under the action of RMF, which improved the intergranular bonding and relieved the stress concentration. On the other hand, the stirring effect of the electromagnetic force on the melt could break up the developed dendrites and delay the dendrite coherence, as well as optimize the feeding channels and improve the feeding drive of the residual liquid at the end of solidification. Therefore, under the action of RMF, the hot tearing initiation of the alloy was suppressed and the feeding efficiency of the liquid was greatly improved, which led to a noticeable reduction of the HTS of the alloy. Moreover, no significant hot tearing was detected in castings at the excitation current parameters of 150 A and 10 Hz.

The effects of addition of minor amount of (0.5 wt.%) antimony (Sb) or gadolinium (Gd) and combined addition of Sb and Gd (0.5 wt.%, respectively) on the hot tearing susceptibility (HTS) of Mg-5Al-3Ca alloy were investigated experimentally using a “T-shaped” hot tearing measuring system. Various solidification parameters of the alloys were measured and calculated through thermal analysis experiments. The microstructure, grain size, and morphology of the crack zone were characterized by scanning electron microscopy and electron backscatter diffraction, and the crystal phases of the alloys were analyzed by X-ray diffraction and energy-dispersive X-ray spectroscopy. The results showed that the addition of 0.5 wt.% Gd resulted in the increase in the vulnerable temperature range (T_v) and reduced the eutectic structure content that could participate in feeding, thereby improving the HTS of the alloy. However, addition of 0.5 wt.% Sb or combined addition of Gd and Sb (0.5 wt.%, respectively) to the Mg-5Al-3Ca alloy shortened the T_v and improved the skeleton strength of the alloy, thereby reducing HTS. Moreover, significantly refined structure of Mg-5Al-3Ca-0.5Gd-0.5Sb alloy improved the feeding ability of the eutectic structure, thus the alloy exhibited the lowest HTS.