Achieving excellent strength-ductility in Al-Si-Cu-Mg cast alloy via effective work hardening

The synergistic improvement of strength and ductility in Al-Si-Cu-Mg cast alloys is an important issue for their engineering applications. Aging treatment can effectively improve the strength of the alloy, but inevitably sacrifice the ductility of the alloy. In this paper, work hardening caused by multiple solute-atoms is designed to achieve the high strength-ductility of the alloy. The multiple Cu, Mg and Si solute-atoms results in the high proportions of low angle grain boundaries, the dislocation tangles with high density and fine dislocation cells in solution-treated Al-7%Si-2/3%Cu-0.5%Mg alloys after plastic deformation. The higher Cu level can promote work hardening effect, resulting in the improvement of ultimate tensile strength. The solution-treated Al-7% Si-3%Cu-0.5%Mg alloy shows the ultimate tensile strength of 440 MPa with an excellent elongation of 16.58% by effective work hardening. The in-situ EBSD tensile results show that dislocation accumulation extends from high angle grain boundaries and Si particles to intragranular areas, which weakens excessive stress accumulation on high angle grain boundaries and effectively promotes the synergistic improvement of strength and ductility. The contribution of dislocation strengthening at various strain levels was estimated, which implies that dislocation accumulation is dominated to working hardening during plastic deformation stage. This study proposed a new design idea for the synergistic improvement of strength and ductility in Al-Si-Cu-Mg cast alloys.