Grain refining mechanism of Mg-Al base alloys by carbon addition

Abstract

This study is aimed at investigating the grain refining mechanism of Mg-Al base alloys by carbon addition. In AZ91 alloys, the morphology of Al-Mn particles were modified from rod to globular-type by inoculating C2Cl6 to AZ91 alloy melt. These particles were identified as Al-8(Mn,Fe)(5) phase and formed in the melt before the formation of alpha-Mg, resulting in grain refinement by heterogeneous nucleation. However, no grain refinement was found in Mn-free Mg-Al binary alloys with an addition of C2Cl6, because most of Al carbides and Al-Fe compounds existed in eutectic region, indicating that they are not effective nucleants for Mg grains. Therefore, Al-8(Mn, Fe)(5) is considered as the most effective nucleant in Mg-Al base alloys. In this study, it is suggested that the grain refinement in Mg-Al base alloys is achieved by the sequences that Al carbides formed by carbon addition are surrounded by Al-8(Mn,Fe)(5), which in turn are surrounded by alpha-Mg.