Abstract
Al₂O₃ hollow spheres were implanted in cast Al-Si-Cu-Mg alloy to prepare Al-matrix syntactic foams by gravity infiltration casting. The effects of hollow sphere size and heat treatment on microstructure, quasi-static compressive properties, and energy absorption properties of the Al-matrix syntactic foams were investigated. The results show that hollow sphere size is the most critical factor affecting the compressive and energy absorption properties. The plateau strength and specific energy absorption of the syntactic foam increase with the decrease of the hollow sphere size. The as-cast syntactic foams with a sphere size of 0.5–1 mm have the highest plateau strength and specific energy absorption, reaching 66.55 MPa and 20.38 kJ kg^–1, respectively. The compressive properties of all heat-treated syntactic foams are significantly improved compared with the as-cast. The maximum plateau strength and specific energy absorption are 87.71 MPa and 30.45 kJ m^-3, respectively. The fundamental reason why small hollow spheres are more conducive to improving compression performance is that small spheres in the syntactic foam are subject to less leverage torque and are not accessible to damage; they can withstand more significant compressive stress. The improvement of the compressive properties of the heat-treated syntactic foam is mainly attributed to the release of residual compressive stress.

Key words
Al-matrix syntactic foam, hollow sphere size, heat treatment process, compression performance, energy absorption ability

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