Al–Al2O3 syntactic foams – Part I: Effect of matrix strength and hollow sphere size on the quasi-static properties of Al-A206/Al2O3 syntactic foams

The microstructure and quasi-static compressive mechanical properties of Al-A206/Al2O3 hollow sphere syntactic foams were investigated for foams with three different hollow sphere size ranges (0.106–0.212 mm, 0.212–0.425 mm, 0.425–0.500 mm) and three different conditions including As cast (F), T4 and T7. The peak strength, plateau strength and toughness of the foams were found to increase with increasing wall thickness to diameter (t/D) ratio. Since the t/D ratio was found to increase with decreasing sphere diameter, the foams produced with the smallest hollow spheres (0.106–0.212 mm) showed superior performance for the peak strength (F: 226 MPa, T4: 312 MPa, T7: 342 MPa), plateau strength (F: 190 MPa, T4: 269 MPa, T7: 269 MPa), and toughness (F: 59 J/cm3, T4: 78 J/cm3, T7: 88 J/cm3). These properties were also found to generally increase with increasing matrix yield strength. The 0.212–0.425 mm T7 heat treated syntactic foams in this study exhibit the highest specific plateau strength (102 MPa-cm3/g) and the second highest specific energy absorption (41 J/g) of aluminum syntactic foams reported in literature for which comparable data is available.