Abstract:This study systematically investigated the influence of cerium (Ce) additions on the microstructure and mechanical properties of Al-Cu-Mn-Mg alloys through multi-scale characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results reveal that the addition of Ce leads to the formation of two distinct Ce-containing intermetallic compounds. The first is the primary Al20Ti2Ce phase formed during solidification, which has caused the grain coarsening due to consumption of the effective grain-refining element Ti in Al melt. The second Ce-containing phase is Al16Cu4Mn2Ce, which forms through a eutectic reaction at the final stage of the solidification process. This phase is unstable at high temperatures and undergoes a phase transformation into Al24Ce3Cu8Mn and Al20Cu2Mn3 during heat treatment, it means that Al16Cu4Mn2Ce can not dissolve like Al2Cu, which prevents an increase in the concentration of Cu and Mn in the Al matrix, thereby leading to a low degree of supersaturation. Furthermore, the addition of minor Ce can retard the phase transformaiton from θ"" to θ" in the Al matrix. Therefore, the main strengthening phase is still the θ"" phase in the Ce-containing alloy while θ" phase in 0Ce alloy after the same heat treatment. Changes in the microstructure and phase composition directly affect the mechanical properties of alloys, the ultimate tensile strength and yield strength decrease by 87 MPa and 42 MPa respectively when the Ce content increases from 0 to 0.3 wt%, and the elongation decreases by 50% compared with 0Ce alloy.