Research on the Mechanical Properties and Microstructural Evolution of Al-Si Alloy for Automotive Rear Floors Based on Simulation-Assisted Casting

Al-Si alloys are essential in manufacturing automotive body structural components due to their superior casting properties, high specific strength, and excellent corrosion resistance. The microstructural evolution and mechanical properties of Al-Si alloy used in rear floors were systematically investigated based on a casting simulation. The results indicate that the alloy microstructure consists of α-Al, an Al-Si eutectic, and the Al₁₅(Mn,Fe)₃Si₂ intermetallic phases. The accumulation of Al₁₅(Mn, Fe)₃Si₂ intermetallic compounds increases toward the end of the filling process, leading to a reduction in mechanical properties. The optimal filling distance of the alloy ranges from 210 mm to 450 mm, while the optimal thickness ranges from 3.36 mm to 4.14 mm. With a filling distance and thickness increase, the yield strength, tensile strength, and elongation of the alloy initially increase and then decrease. The optimal properties are achieved when the filling distance is 210 mm and the thickness is 4.14 mm, with a yield strength of 122.35 MPa, a tensile strength of 258.43 MPa, and an elongation of 11.60%. At the same filling distance, near the gate position, when the thickness increases from 4.1 mm to 5.3 mm, the alloy's tensile strength and elongation decrease. However, at positions farther from the gate, when the thickness increases from 2.94 mm to 4.93 mm, both the tensile strength and elongation of the alloy increase. This study provides a theoretical basis for the process design of large integrated die-casting components for new energy vehicles and supports the development of a high-strength ductile Al-Si alloy material system.