Effect of Al Addition on Grain Refinement and Phase Transformation of the Mg-Gd-Y-Zn-Mn Alloy Containing LPSO Phase

The effect of 0–1.0 at.% Al additions on grain refinement and phase transformation of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy containing a long period stacking ordered (LPSO) phase was investigated in this work. The addition of Al promoted the formation of the Al₂ RE phase in the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy, and the dominant secondary phases in the as-cast Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn-1.0Al (at.%) alloy were the Mg₃ RE phase, LPSO phase, and Al₂ RE phase. With increased Al addition, the area fraction of the Al₂ RE phase increased monotonously, while the area fraction of LPSO phase and Mg₃ RE phase decreased gradually. The orientation relationship between the Al₂ RE phase and the α-Mg matrix was determined to be <112>_Al2RE/ /<1120>_α-Mg, {101}_Al2RE/ /{1010}_α-Mg, which was not affected by Zn and Mn concentrations in the Al₂ RE phase. Since the Al₂ RE particles with a size more than 6 µm located at the center of grains could act as nucleants for α-Mg grains, the average grain size of the as-cast alloys decreased from 276 µm to 49 µm after 1.0% Al addition. The effect of the Al addition on the grain refinement of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn alloy was comparable to that of the Zr refined counterpart.