Influence of Heat Treatment on Tensile Properties of High Vacuum Die Casted AlSi10MnMg Alloy

High vacuum die casted AlSi10MnMg alloy was treated by T5 (180 ℃×2 h), T6 (515 ℃×1 h air cooling +175 ℃×2 h) and T7 (460 ℃×1 h water cooling +175 ℃×2.5 h) heat treatment, respectively. The microstructure and tensile properties of the alloy under different heat treatment conditions were studied. The results show that the aluminum matrix phase of the as-cast alloy grew after T5 heat treatment, the roundness was high, and the grain size was mainly concentrated in the range of 20-80 μm. The Si phase after T5 heat treatment was still a slender shap. Compared with those of the as-cast test alloy, the tensile strength of the test alloy increased by 8.9% and the percentage elongation after fracture was reduced by 9.1% after T5 heat treatment. After the heat treatment of T6 and T7, the irregular degree of aluminum matrix phase shape decreased, the grain size was 2-50,2-30 μm, respectively, and the microstructure was relatively uniform and dense. The Si phase changed from a slender shape in the cast state to a regular round shape. Compared with those of the as-cast test alloy, the tensile strength of the test alloy after T6 and T7 heat treatment was reduced by 26.0% and 23.9%, and the percentage elongation after fracture increased by 54.5% and 72.7%, respectively. The tensile fracture modes of the as-cast and T5 heat-treated test alloys were both tough-brittle mixed fracture. The fracture mode of the test alloys in T6 and T7 states were mainly ductile fracture, while the tough dimple in the tensile fracture of the T7 heat-treated test alloy was fine and deep, indicating better plasticity.