Study on Microstructure and Mechanical Properties of Mg9AlZnGdY Magnesium Alloy after T6 in Lost Foam Casting

摘要

The microstructures and mechanical properties of Mg9AlZnGdY alloy after T6 heat treatment in lost foam casting (LFC) are compared with that of AZ91D magnesium alloy. The results show that the microstructures of Mg9AlZnGdY alloy after T6 heat treatment consist of the α-Mg solid solution, β-Mg_(17)Al_(12) precipitation phase, a small amount of rod Al_2Y and block Al_2Gd phases, which are distributed over grain boundaries of the α-Mg phase. The thermal stability of Al_2Y and Al_2Gd phases offers the pinning effect on the grain boundary under high temperature, and therefore, the grain boundary sliding is eliminated and the high-temperature strength is increased. After the T6 heat treatment, the tensile strength of Mg9AlZnGdY alloy was 235MPa at room temperature, and 156MPa at 200°C. Compared with that of AZ91D alloy, the tensile strength was increased by 19.3% and 38.1% respectively.