Composition design and as-cast microstructure of Al-Si-Mg-Sc-Zr-Sb alloy

Al-Si-Mg-Sc-Zr alloys are prepared through phase diagram design and the smelting process. The effect of elemental addition levels on solidification parameters is investigated. Additionally，the room-temperature tensile properties and microstructure of the as-cast alloys are thoroughly analyzed.The results reveal that the as-cast microstructure consists of α-Al matrix， Al-Si eutectic phase， Mg₂Si phase， Al₃Zr phase， and Al₃（Sc， Zr） phase. Silicon has the most pronounced effect on the tensile strength， whereas magnesium primarily influences the secondary dendrite arm spacing（SDAS）. The liquidus temperature gradually decreases with an increase in silicon content， and the solidus temperature continuously drops as the magnesium content rises.With the addition of the Sb element， the morphology of the eutectic silicon phase transforms from needle-like and long-striped shapes to short rod-shaped or worm-shaped forms， and its aspect ratio decreases from 8.19 to 3.31. The fine-sized Al₃Zr and Al₃（Sc， Zr） phases refine the grain size from 272 μm to 224 μm. As a result， the ultimate tensile strength and yield strength reach 211 MPa and 125 MPa， respectively， with an elongation of approximately 5.1%. The enhancement of mechanical properties is attributed to the fine-grained strengthening of the Al₃Zr and Al₃（Sc， Zr） phases， as well as the second-phase strengthening effect of the eutectic silicon phase. As the addition of silicon and magnesium elements increases， the fracture mechanism shifts from a combination of intergranular and dimple fractures to purely intergranular fractures.