Micro-mechanism of simultaneous improvement of strength and ductility of squeeze-cast Al–Cu alloy

In this paper, the strength and ductility of Al–Cu–Mn–Ti alloy prepared by squeeze casting have been simultaneously increased after heat treatment. The effects of solution and aging treatment on the microstructure evolution and mechanical properties of squeeze cast Al–Cu alloy are investigated to discuss its micro-mechanism using various methods, including SEM, XRD, EBSD and TEM. The results show that the Al2Cu phase disappeared completely after solution treatment at 530 °C for 10h. During aging, nano-sized or submicron-sized Al12Mn2Cu precipitates and much smaller nano-sized θ'' phase were uniformly distributed throughout the alloy, and the interface between the two phases and the matrix was coherent. After solution + aging treatment (i.e., T6 treatment) the ultimate tensile strength, yield strength and elongation of the alloy were 445 MPa, 265 MPa and 17.9%, which were increased by 71.2%, 65.6% and 70.5%, respectively, compared with the as-cast alloy. The precipitation strengthening caused by the two kinds of precipitates θ'' and Al12Mn2Cu is the most important factor for the simultaneous increase in the strength and elongation.