Influence of melt superheating on microstructures of Mg-3.5Si-1Al alloys

The influence of melt superheating treatment on the microstructures of Mg-3.5Si-1Al alloys unmodified and modified with 0.2% Sr-Sb (mass fraction) was investigated. The results show that when the melt superheating temperature increases from 750 to 900 °C, the average size of primary Mg2Si in the unmodified alloys decreases progressively from about 27 to about 19 μm, while that in Sr-Sb-modified alloys is refined considerably from about 14 to about 7 μm when the temperature increases from 750 to 850 °C, and then slightly increases to about 9 μm with temperature further increasing to 900 °C, which might be attributed to the burning loss of Sr and Sb in melts. However, the superheating temperature only has a slight effect on the morphologies of both primary and eutectic Mg2Si phases in unmodified and Sr-Sb-modified alloys.