Structure and decomposition behavior of rapidly solidified Mg-Al-Zn-Nd

Microstructural changes in a rapidly solidified Mg-Al-Zn-Nd alloy during heat treatment at 100°C, 250°C, 350°C for 1hr and 24hrs have been investigated by using TEM, EDS, DSC, and X-ray diffraction analysis and hardness measurements. Asextruded Mg-Al-Zn-Nd alloy consists of 1 approx. 2 μm size fine grains, 10 approx. 50nm size Al₂Nd particles and 0.1 approx. 0.3 μm size quasicrystal-related particles. No microstructural changes occur during heat treatment at 100°C and 250°C for 1hour and 24 hours. After heat treatment at 350°C, the Al₂Nd particles are still stable, but the quasicrystal-related particles are replaced with Al₁₁Nd₃-related particles. The amount of hardness decrease after heat treatment at 350°C for 24 hours is only 10% of the hardness of the as-extruded material, which suggests the high thermal stability of the rapidly solidified Mg-Al-Zn-Nd alloy due to the relatively fine grain size and, particularly, due to the presence of thermally stable 50nm size Al₂Nd particles.