Coupled Effects of Sc-Zr Microalloying and Casting Conditions on the Microstructural Evolution and Mechanical Properties of Al-Ce-Mg Alloys

The effects of Sc-Zr microalloying and casting conditions on the microstructure, precipitation behavior, and mechanical properties of Al-Ce-Mg alloys were investigated. Sc-Zr addition refined the grains, suppressed coarse primary Al11Ce3, and changed the eutectic Al11Ce3 from a Chinese-script morphology to a fishbone-like structure. STEM-EDS analysis showed that both Sc and Zr were incorporated into primary Al11Ce3, suggesting that they participated in its formation and growth during solidification. Compared with permanent mold casting (PMC), squeeze casting (SC) produced a finer solidification structure, owing to enhanced heat extraction under pressure. The faster solidification is also expected to retain more Sc and Zr in supersaturated solid solution, thereby promoting the formation of finer and denser Al3(Sc, Zr) precipitates after ageing at 350 °C for 24 h. At room temperature, Sc-Zr addition increased the compressive yield strength from 176.7 to 224.0 MPa under PMC and from 185.0 to 258.3 MPa under SC. At 300 °C, the ACMSZ-SC alloy exhibited an ultimate tensile strength of 125.5 MPa, a yield strength of 123.0 MPa, and an elongation of 11.3%, showing a better strength–ductility balance than its PMC counterpart. These improvements arise from the concurrent contributions of grain refinement, Al11Ce3 modification, and Al3(Sc, Zr) precipitation strengthening.