Unraveling the pressure-induced microstructural origin of enhanced corrosion resistance in a high-strength Al-Si-Cu-Mg alloy

This work aims to combine a high-pressure synthesis strategy and heat treatments to enhance corrosion resistance via microstructural regulation in a high-strength Al-Si-Cu-Mg alloy. The results showed that coarse α-Al dendrites, fine α-Al dendrites and equiaxed α-Al phases emerged in the alloys solidified under normal pressure (NP), 4 GPa and 5 GPa, respectively. A complete solid solution alloy was successfully obtained under 6 GPa. The underlying mechanisms of microstructural evolution were discussed based on interfacial stability, crystal growth rate and nucleation rate. The alloys prepared at 6 GPa demonstrated the most favorable corrosion resistance in both as-cast and heat-treated states. The unconventional pressure-induced supersaturation could simultaneously reduce the proportion of cathodic phases and raise the potential of the matrix. Moreover, the multiple supersaturated solutes and dense precipitates could induce a stable corrosion product layer, which serves as an effective shielding barrier to delay the corrosion process. The corresponding corrosion mechanisms of alloys prepared under various conditions were discussed in detail. Our approach may provide a valid option for developing a new generation of high-performance Al-Si-Cu-based alloys.