Enhancing high-temperature tensile properties of Al-20Si alloy via in-situ Al₂O₃ reinforcement and its influences on microstructural stability

In this work, the high-temperature tensile properties of in-situ Al₂O₃ reinforced Al-20Si alloy fabricated by powder metallurgy were systematically investigated. Two types of powders, coarse and fine, were used as variables for comparative study. The results indicate that both particle sizes exhibit an excellent combination of high strength and superior elongation at room temperature, with an ultimate tensile strength (UTS) of approximately 325 MPa and elongation ranging from ∼8.1 % to ∼11.6 %. At an increased test temperature of 200 ℃, the alloy with finer particle size demonstrated a UTS of 207 MPa and an elongation of 14.1 %, whereas the coarser particle size alloy showed a UTS of 137 MPa and an elongation of 19.6 %. The enhanced strength of the alloy with finer particles at elevated temperatures can be attributed to the presence of highly thermally stable in-situ Al₂O₃. The ultrafine Si particles, enveloped by a dense Al₂O₃ film, resist Ostwald ripening, while the fine Al grain boundaries are pinned by the in-situ Al₂O₃ particles, which hinders their migration. These factors contribute to stabilizing the microstructure at elevated temperatures, resulting in high strength. This work provides an effective approach to achieving excellent high-temperature tensile properties in Al-Si alloys.