Containerless rapid solidification and microscopic mechanical properties of hypoperitectic Mg-6.5 at.%La alloy

The rapid solidification mechanism of hypoperitectic Mg-6.5 at.% La alloy was investigated by containerless processing via drop tube technique. Typical peritectic solidification prevailed at liquid undercoolings lower than the critical value of 40 K. Once alloy undercooling exceeded 40 K, the nucleation and growth of primary Mg₁₇La₂ phase were suppressed, leading to the direct nucleation of peritectic Mg₁₂La phase. The volume fraction of Mg₁₂La compound increased and its actual La content decreased with alloy undercooling, which was accompanied with remarkable dendritic structure refinement. Almost segregationless solidification took place at the maximum liquid undercooling of 182 K (0.19 T_L). Mg₁₂La dendrites exhibited great nano-hardness and elastic modulus at various liquid undercoolings. In particular, a maximum average Vickers hardness of 210.7 HV was achieved at 124 K undercooling, representing a 34% enhancement over master alloy.