Microstructure Evolution and Strengthening Mechanisms of Cast Al–Cu–Mn Alloy via Ti–Zr-Synergistic Micro-alloying

Synergistic micro-alloying with Ti–Zr effectively enhances the mechanical properties of cast Al–Cu–Mn alloys. In this study, the connection between microstructure evolution and mechanical properties of Al–Cu–Mn alloy through gravity casting was investigated with synergistic addition of Ti and Zr elements, aiming to promote the strength and toughness of Al–Cu–Mn alloy. The results showed that synergistic addition of 0.15 wt%Ti and 0.2 wt%Zr refined grains owing to the constitutional supercooling caused by Ti and Zr. A large number of Al₃(Ti,Zr)-L1₂ dispersoids with core–shell structure uniformly precipitated within the grains during the solution process. The Al₃(Ti,Zr) dispersoids served as heterogeneous nucleation sites for θ′(Al₂Cu) precipitates during aging. As confirmed by quantitative analysis, Ti–Zr-modified alloys (with 0.15 wt%Ti and 0.2 wt%Zr) exhibited finer and more densely populated θ′ precipitates than unmodified alloys, resulting in superior mechanical properties. In the peak-aged state, the ultimate tensile strength, yield strength and elongation of Ti–Zr-modified alloy were 530.5 MPa, 462.8 MPa and 7.6%, respectively, which were mainly ascribed to grain boundaries strengthening, solution strengthening and precipitation strengthening. This work is expected to provide reliable theoretical guidance for the successful preparation of high-strength and high toughness Ti–Zr-modified aluminum alloys.