Mg-matrix syntactic foam filled with alumina hollow spheres coated by MgO synthesized with solution coating-sintering

For a long time, the extremely high chemical activity of magnesium melt with ceramics at high temperatures makes it challenging to synthesize Mg-matrix syntactic foams (MgSFs) by casting. In this work, for the first time, high porosity of AZ31B magnesium alloy matrix syntactic foams containing Al₂O₃ hollow spheres (Al₂O_3-HS) were successfully synthesized by gravity infiltration casting. The Al₂O_3-HS were coated with MgO using MgCl₂ solution after high-temperature calcination to prevent the interfacial reaction. The results show that the concentration of the MgCl₂ solution strongly influences the porosity of the syntactic foams because it determines the coverage of Al₂O_3-HS with the MgO coating and the survival of particles. The maximum porosity of the syntactic foam was 41.64 vol%, and the corresponding density was 1.17 g/cm³. At the MgCl₂ solution coating concentration of 0.15 g/ml, the plateau stress of the syntactic foam reaches the maximum value of 55.96 MPa, the energy absorption capacity was 39.27 MJ/m³, and the maximum energy absorption was 26.06 kJ/kg. These properties are comparable to some MgSFs prepared by other methods in recent years.