High-pressure die-casting (HPDC) AZ91 tensile specimens were used to investigate characteristics of gas pores and their effects on mechanical properties of HPDC AZ91 magnesium (Mg) alloy. Combining the stereoscopic morphology of gas pores obtained from a three-dimensional (3D) reconstruction technique with the experimental data from uniaxial tensile testing, we worked on finite element simulation to find the relationship between gas pores and the mechanical properties of HPDC AZ91 Mg alloy. Results indicate that the 2D metallography images have one-sidedness. Moreover, gas pores >100 µm in the center region have a remarkable negative influence on the ultimate tensile strength (UTS) and elongation. With an increase in the size of large gas pores in the center region, the UTS and elongation of the material decreases. In addition, the distribution of gas pores in the specimens and the areal fraction of gas pores >100 µm on cross sections can also affect the UTS and elongation to some extent.

The effects of trace La additions on the microstructures and mechanical properties of Cu–0.2 wt% Zr alloy have been investigated. Traditional thermo-mechanical processing was applied to the Cu–Zr alloys. Isochronal aging and isothermal aging were used to optimize the aging conditions. According to the hardness and conductivity tests, the optimized aging condition should be 150 min isothermal holding at 400 °C following 85% cold-rolling. If the as-cast sample is subjected to aging, the addition of La obviously refines the microstructures. After cold-rolling, however, the La addition has no significant effects on the grain size of the aged sample. SEM and TEM are combined to observe the distribution and morphology of the precipitates, which are identified to be Cu5Zr. The addition of La can improve the hardness and conductivity simultaneously in the as-cast samples after aging, while it improves the hardness and strength and decreases the conductivity slightly in the cold-rolled samples after aging. XRD and TEM results show that the lattice parameter and the dislocation density are increased by the addition of La.