Trace Sn effects on mechanical properties and intergranular corrosion resistance in high-strength Al-Mg-Si-Cu alloy

In high-strength 6XXX-series aluminum alloys, Cu additions readily increase susceptibility to intergranular corrosion. Here, by introducing trace amounts of Sn, the Cu-induced intergranular corrosion is mitigated while maintaining high intensity. When the Sn content is maintained below 0.05 wt%, improved corrosion resistance is achieved, primarily due to the narrowing of the precipitation-free zone. However, excessive Sn additions (>0.05 wt%) increase the intergranular corrosion susceptibility of the alloys because of the formation of cathodic second phases such as Mg2(Si,Sn) phases. Under high Cu conditions, Cu atoms exhibit a higher tendency than Sn atoms to replace Al sites in the β" phases, thereby promoting strengthening of alloys. Meanwhile, Sn additions accelerate the age-hardening process, advancing the peak hardness by approximately 1 h. The mechanical properties exhibit a non-monotonic dependence on Sn level. Among them, the alloy containing 0.025 wt% Sn achieves the optimal property combination, with a yield strength approaching 400 MPa, a tensile strength of ~445 MPa, and a maximum intergranular corrosion depth of only ~110 μm.