Abstract: Effect of aging treatment (single aging and two-step aging) on the microstructure, mechanical properties and corrosion resistance of Al-Si-Cu-Mg cast alloy was studied. The results show that the microstructure of the Al-Si-Cu-Mg cast alloy after aging is composed of α-Al matrix and eutectic Si phase. After single aging at 170 ℃ for 10 h, the peak hardness of the alloy is 151.8 HV0.1, the tensile strength and yield strength are 287 MPa and 252 MPa, respectively, and the elongation is 10.6%. However, the corrosion resistance is poor, and the maximum intergranular corrosion depth reaches 113.3 μm. As compared with that after the single aging, after the optimized two-step aging at 90 ℃ for 3 h and 170 ℃ for 4 h, the mechanical properties and corrosion resistance of the tested alloy are greatly improved. The peak hardness is increased by 5.7%, and the tensile strength and yield strength are increased by 4.5% and 6%, respectively. Moreover, the elongation is increased more than twice. The corrosion resistance improves, and the maximum intergranular corrosion depth is reduced to 60.0 μm. The fine and uniform Si phase and relatively less gray-black acicular β phase and black block structure are responsible for the improvement of mechanical properties and corrosion resistance of the tested alloy.

Key words: Al-Si-Cu-Mg cast alloy, two-step aging, mechanical properties, corrosion resistance