Abstract: Al-Cu-Mg-Sc alloy with different Cu contents (4%-6%, mass fraction, similarly hereinafter) was prepared by gravity die casting process, and a two-stage solution treatment(500 ℃×4 h＋520 ℃×6 h) with water cooling was carried out, subsequently aged at 175 ℃ for 5 h.Effect of Cu content on microstructure and mechanical properties of the tested alloy was investigated by means of Vickers hardness test, room temperature tensile test, scan electron microscope observation. Then, the optimized composition of Al-Cu-Mg-Sc alloy was obtained. The results show that when the Cu content increases from 4.26% to 5.58%, the precipitation content of Al₂Cu phase increases continuously after heat treatment, and the yield strength and tensile strength of the alloy increase from 191 MPa and 323 MPa to 216 MPa and 355 MPa, respectively, and the elongation is maintained around 13%. While the Cu content is higher (6.13%), the volume fraction of Al₂Cu phase in the microstructure is relatively high, and the amount of Al₂Cu phases dissolved into the matrix after solution treatment is limited, and a large amount of residual Al₂Cu phases remain at the grain boundary. After aging, the strengthening effect of the high-Cu alloy cannot continue to increase as the Cu content increases. Therefore, on the whole, with the increase of Cu content, the hardness and tensile strength of the alloys with high Cu content increase firstly and then stabilize, the elongation of the alloys first increases and then decreases. The cast Al-Cu-Mg-Sc alloy with Cu content of 5.58% after aging can achieve the best overall properties, of which the hardness is 117 HV, tensile strength and yield strength are 355 MPa and 216 MPa, respectively, and the elongation is maintained in 13.5%.

Key words: Al-Cu-Mg-Sc alloy, Cu content, precipitation strengthening, mechanical properties