Effect of Cu and Sn additions on the thermal stability of Al–Mg–Si alloy

Age-hardening aluminum alloys generally exhibit poor thermal stability, making them unsuitable for prolonged use at temperatures around the aging range. This study investigated the effect of 0.08 wt% Cu and 0.05 wt% Sn on the thermal stability of peak-aging Al–0.9Mg–1.1Si (wt.%) alloy. After an exposure of 150 °C for 1000 h, the combined effects of Cu and Sn result in a higher yield strength (∼322 MPa) than that of the Cu/Sn-free alloy (∼311 MPa). This improvement is mainly attributed to the Sn-induced fine precipitate morphology. Specifically, precipitates with higher aspect ratios exhibit rapid coarsening rates, significantly promoting the response of experimental alloys to thermal exposure. In contrast, precipitates with lower aspect ratios coarsen at a slower rate and maintain a higher level of strengthening during thermal exposure. Furthermore, Sn atoms may also contribute to the formation of the thermostable Cu-containing phases (L phase). On the one hand, the Sn-induced higher precipitate density will increase the amount of L phase. On the other hand, the special Sn-containing sub-units may serve as heterogeneous nucleation sites to promote the formation of L phase. In summary, the combined effects of Cu and Sn enhance the thermal stability of the experimental alloys near the aging temperature range. The present study provides a straightforward and feasible approach to enhancing the thermal stability of Al–Mg–Si alloys.