Semi-solid thixoforming, microstructure, and mechanical properties of Al-6wt%Si alloy via liquid reaction sintering of elemental powders

Abstract. Al-6wt%Si semi-solid alloy billets were prepared via the liquid phase reaction sintering process by using elemental Al and Si powders as starting materials. Cup-shaped components were fabricated by direct semi-solid thixoforming at 685-595℃ with the liquid phase fraction in the range of 0.141-0.196. By microstructure observation and mechanical testing, the influence of the liquid phase sintering and subsequent thixoforming conditions on the microstructure evolution and mechanical properties of the final components was investigated. The results show that, when the liquid phase fraction of the alloy billet is in the range of 0.141-0.167, cup-shaped components with uniform microstructure and no forming defects can be obtained by direct thixoforming. Due to the strengthening effect of the fine Al grains and the Si particles and precipitates, the component thixoformed by using billet with a liquid phase fraction of 0.167 presented the best mechanical properties, with yield strength, ultimate tensile strength and elongation achieving 115MPa, 220MPa and 38%, respectively. It is evident that the semi-solid thixoforming process proposed in the present study turns out to be a practical way to fabricate high-performance Al-Si alloy components.