Mechanisms Controlling the Microstructure Evolution and Mechanical Property in Al-7Si-0.3Mg Alloy via Semisolid Rheological Die Casting and Short-Term T6 Heat Treatment

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发表日期：

2025年9月24日

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Wentao Xiong,
Yichao Ding,
Kaiwen Wei,
Kunming Wang,
Xiangwei Lu,
Shihao Wang,
Zhihua Hu,
Zhaofei Huang

摘要

This study proposes a process that integrates the metal melt instantaneous undercooling-induced nucleation technique with rheological die casting. It systematically investigates the effects of this process, along with a subsequent short-term T6 heat treatment (consisting of solution treatment at 535 °C for 2 hours followed by artificial aging at 165 °C for durations ranging from 3 to 12 hours), on the microstructure, the development of Fe-rich intermetallic compounds, and the mechanical properties of the Al-7Si-0.3Mg alloy. The results indicate that, in samples quenched in water after cooling to 250 °C in the mold, a sandwich-structured, metastable flake-like Fe-rich intermetallic compound forms. Although after a 2 hour solution treatment at 535 °C and 6 to 12 hours of artificial aging at 165 °C, the metastable flake-like Fe-rich intermetallic compounds gradually decompose, and this process promotes the growth of the detrimental β-Al₅FeSi phase. In contrast, rheological die castings subjected to short-term mold retention followed by immediate water quenching exhibit a notable rounding of the eutectic Si phase after the short-duration T6 heat treatment, with uniform distribution near the π-Al₈FeMg₃Si₆ and β-Al₅FeSi phases. As artificial aging time increases, a distinct phenomenon of prior dissolution followed by precipitation of the π-Al₈FeMg₃Si₆ and β-Al₅FeSi phases occurs. After a 535 °C solution treatment for 2 hours and 165 °C artificial aging for 6 hours, the sample exhibits the best overall properties, with a tensile strength of 265.69 MPa, a yield strength of 221.12 MPa, and an elongation of 11.60%. This study elucidates the mechanisms of Fe and Mg enrichment at the grain boundaries, as well as the dissolution and precipitation behaviors of the π-Al₈FeMg₃Si₆ and β-Al₅FeSi phases. It confirms the efficacy of short-term T6 heat treatment in suppressing the formation of harmful Fe-rich phases and achieves the balance of high strength and ductility in Al-7Si-0.3Mg alloy.