Study on the influences of different process temperatures on microstructural evolution of Mg-11%Al-2%Zn-1%Si alloy through isothermal semi-solid treatment

Abstract

Due to the eutectic reaction, the Mg2Si phase is inclined to creating an unfavorable fishbone shape at low solidification rates. This can significantly degrade the mechanical characteristics and become the main barrier to the practical application of Mg-Si based alloy. It is regarded that isothermal semi-solid treatment is an efficient technique to modulate the fishbone-shape eutectic Mg2Si phases in Mg-Si based alloys. In this work, a new type of Mg-11%Al-2%Zn-1%Si alloy is successfully fabricated through isothermal semi-solid treatment, and the influences of different process temperatures on microstructural evolution of Mg-11%Al-2%Zn-1%Si alloy are studied. The findings illustrate that the mean size of the α-Mg grains increases and their trendency of spheroidization becomes more evidently after held for 30 min at different process temperatures from 550 °C to 580 °C. Additionally, through isothermal semi-solid treatment, the eutectic Mg2Si phases in experimental alloy are totally changed from their original fishbone shape into polygon or granule shapes. With increasing the process temperatures, the mean size and morphologies of eutectic Mg2Si phases have no significantly changes. The morphological change theory of eutectic Mg2Si phases through isothermal semi-solid treatment is also studied.