Effects of Cu content on microstructure and properties of super-high-strength Al-9.3Zn-2.4Mg-xCu-Zr alloy

Abstract

A high-Zn-Mg-content super-high-strength Al-9.3Zn-2.4 Mg-xCu-Zr alloy was fabricated by the ingot metallurgy method. The effects of the Cu content (0.8–2.2 wt%) of the alloy on its microstructure and properties were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile tests, and intergranular corrosion, exfoliation corrosion, and stress corrosion cracking resistance measurements. The results showed that with a decrease in the Cu content over a certain range (2.2 wt% to 1.8 wt%), the mechanical properties of the alloy improved and its exfoliation corrosion resistance increased. The reason is that a decrease in the Cu content in this range leads to a decrease in the volume fraction of the residual eutectic phase, with the Cu content of the grain boundary precipitates remaining unchanged. The optimal properties of the Al-9.3Zn-2.4 Mg-xCu-0.16Zr alloy were obtained for a Cu content of 1.5 wt% and were as follows: σb, σ0.2, and δ of 753 MPa, 725 MPa, and,8.4%, respectively.