Effect of Pull-Speed on Microstructures of Unidirectionally Solidified Mg-Ga Alloy

We experimentally addressed the microstructures of Mg-Ga alloys, exemplified by Mg-12.85 Gd-1.25 Zn-0.45 Y, fabricated by unidirectional solidification.The influence of the pull-speed on the microstructures and preferential growth orientation of primary α-Mg grains was investigated with X-ray diffraction and electron backscattered diffraction (EBSD).The results show that the pull-speed has a major impact.For example, α and Mg₅Gd phases co-exist independent of the solidification conditions;as the pull-speed increased, fairly smooth grains formed in Mg-matrix and the dendrite spacing decreases;a small number of grain boundary indicated that the preferential grain-growth orientations were highly consistent, with an orientation deviation within 15°;moreover, the deviation changed in an decrease-increase manner, minimizing at a pull-speed of 100 mμ/s.0001plane oriented in the solidification heat-flow direction, 1010and1120planes formed almost identical polar diagrams.