Gravity casting of aluminum-Al₂O₃ hollow sphere syntactic foams for improved compressive properties

Alumina hollow spheres with a diameter range of 1–2 mm were filled in 6061 Al alloy by gravity infiltration casting to synthesize Al-matrix syntactic foams. The effects of infiltration temperature and heat treatment on microstructure, compressive properties, and energy absorption properties of the syntactic foams were studied. The results show that high quality syntactic foams could be synthesized in the infiltration temperature range 770–830 °C and the particles seamlessly bonded with the matrix. The average density and porosity of the syntactic foams were around 1.66 g/cm³ and 37.47%, respectively. The highest energy absorption capacity and specific energy absorption of the as-cast syntactic foams occurred at infiltration temperature 770 °C, reaching 41.11 MJ/m³ and 23.63 kJ/kg, respectively, while these parameters for the heat-treated samples showed the maximum values for the solution-aging treated samples, reaching 48.92 MJ/m³ and 31.36 kJ/kg respectively. Extensive literature survey is presented in this work by extracting the compressive properties of a variety of Al-matrix syntactic foams and comparing them with the results obtained in the present work. It is observed that the syntactic foams synthesized by gravity infiltration method equal or exceed the properties demonstrated by many Al-matrix syntactic foams synthesized by other methods reported in recent years. As a major advantage, the gravity infiltration method can be scaled up to industrial production level.