Abstract: Effects of different solid solution treatments and aging processes on the microstructure and mechanical properties of die-cast Al-Si-Mg alloy containing Er were studied by using tensile test, optical metallographic microscope, scanning electron microscope (SEM), energy spectrum (EDS) and transmission electron microscope (TEM) analyses and quantitative statistics. The results show that the two-stage solid solution treatment is beneficial for the primary phase to dissolve back into the matrix and improve the plasticity of the alloy. The increase of solution treatment temperature and time can increase the number of solute atoms and primary phases dissolved in the matrix. In the alloy, the main strengthening phases during peak aging are β″ and β′, and the β′ phase mainly exhibits strip shape and T-shape. When the heat treatment process is (280 ℃×3 h+530 ℃×3 h) solid solution treatment +170 ℃×3 h aging, the alloy has the elongation of 8.5% and shows high plasticity. When the heat treatment process is (280 ℃×3 h+540 ℃×10 h) solid solution treatment +170 ℃×10 h aging, the alloy has high strengths of which the tensile strength is 344 MPa and the yield strength is 312 MPa.

Key words: die-casting Al-Si-Mg alloy, two-stage solid solution treatment, aging precipitated phase, mechanical properties