Improving high-temperature creep resistance in Al-Si cast alloy by trace Sn-induced high number density dispersoids

As an important precipitation-strengthening phases in Al-Si cast aluminum alloys, submicron dispersoids still lack effective methods to sufficiently refine them and increase their number density. In this study, we introduce the trace Sn into an Al-7%Si-0.5%Mn cast alloy and employ non-isothermal heat treatment to simultaneously refine both Si and Mn-containing dispersoids. This approach reduces their average size by 28% and markedly increases the total number density of dispersoids by 2.4 times, thereby achieving a minimum secondary creep rate that is 74.1 % lower than that of the Sn-free alloy at 300 °C/25 MPa condition. The trace Sn produces more nucleation sites for the Si precipitates by combining more vacancies, and the high number-density Si precipitates promote the precipitation of Mn-containing dispersoids at high temperature. Moreover, after holding at 500 °C for 6 hours, the coarsening of Mn-containing dispersoids in the Sn-containing alloy is only 4.9 %. This study elucidates the mechanism by which the trace Sn enhances the dispersoid precipitation in the Al-Si cast alloy and provides a novel design strategy for high-temperature creep-resistant cast aluminum alloy.