Effect of semi-solid isothermal heat treatment on the microstructure of Mg–6A1–1Zn–0.7Si alloy

In this paper, the effect of semi-solid isothermal heat treatment on the microstructure of Mg–6A1–1Zn–0.7Si alloy, especially on the semi-solid microstructural evolution and the modification of Chinese script shaped Mg2Si phase, are first investigated. The research results indicate that it is possible to produce the Mg–6A1–1Zn–0.7Si alloy with non-dendritic microstructure by the semi-solid isothermal heat treatment. After treated at 575–585 °C for 120 min, the experimental alloy can obtain a non-dendritic microstructure with a 12–21% liquid content and an average size range of 48–67 μm of the unmelted primary solid particles. In addition, the semi-solid isothermal heat treatment can modify the Chinese script shaped Mg2Si phases in experimental alloy. After treated at 580 °C or 585 °C for 120 min, the morphology of Mg2Si phases in the experimental alloy changes from the initial Chinese script shape to granule and/or polygon shapes.