Temperature‐Dependent Compressive Behaviors and Energy Absorption of Magnesium‐Modified Aluminum‐Cenosphere Syntactic Foams

Aluminum‐fly ash cenosphere (Al‐FAC) syntactic foams with magnesium (Mg) additions are fabricated via vacuum‐assisted infiltration, and their compressive behaviors and energy absorption capacity are investigated over the temperature ranged from room temperature to 650 °C. Compared to Mg‐free Al‐FAC foam, modified foams exhibit pronounced stress drops attributed to brittle phase fracture and shear band formation. In addition, the compressive strength and energy absorption are up to 148.0 MPa and 54.6 J cm −3 , corresponding to significant enhancements of 99.2% and 45.6%, respectively, for modified foams. Syntactic foams exhibit higher yield stress than the matrix at 300 °C despite progressive strength degradation at elevated temperatures, accompanied by increasing critical strain for stress drops. Above 300 °C, matrix softening induces a brittle‐to‐ductile transition that reduces stress fluctuations, while hollow spheres retain brittle fracture and interfacial coatings suppress debonding to preserve structural integrity. At 600 °C, the compressive strength and energy absorption are retained at 24.7 MPa and 8.0 J·cm −3 . A modified Johnson–Cook model captures the exponential decay of yield stress with temperature. Concurrently, energy absorption efficiency rises with temperature due to delayed densification and plateau stress stabilization. Microstructural and fracture characterization confirms the integrity of interfacial coatings at high temperatures, effectively suppressing hollow spheres debonding.