Grain refining mechanism of cast magnesium alloy AZ91 by superheat treatment

Abstract

To clarify the grain-refining mechanisms of a commercial AZ91E magnesium alloy by superheat treatment, the molten alloy was quenched by using two chilled copper blocks. The superheat treatment was performed at 1123 K for 900 s, then cooled at 2.5 K/s. The quenching temperatures were 1023, 973, 923 and 873 K. In the superheat-treated samples particle-like substances as nucleants could be observed in the center of dendrite crystals. The samples quenched at 1023 K reveals that the particle-like substances consisted of Al, C and O. However, different types of substances were observed in the sample quenched at 973 K. They were consisted of Al, Mn, Fe, Si, C and O elements. It is concluded that the compound consisting Al, C and O is obviously heterogeneous nucleation substance in the superheat-treated AZ91E magnesium alloys.