Abstract: Liquid diffusion welding method was used to prepare metallurgical bonding aluminum foam sandwich. The bonding interfacial microstructure was observed by optical microscope (OM) and SEM. Under the effect of ultrasonic vibration, the bonding seam is uniform and continuous. The ZnAl eutectic dendrite structure forms on the surfaces of Al foam core and Al sheet substrates. Furthermore, obvious erosion behavior can be seen on the bonding surfaces as ZnAl alloy filler melted. EDS line scan results show that the mutual diffusion of the main elements Zn and Al across the interface is extensive. All these characteristics imply that the oxide film on the substrates is destroyed and sound bonding achieves. Three point bending fatigue test was employed to the sandwich structure fatigue behavior. Comparing with the adhesive aluminum foam sandwich, the fatigue life (S-N) curves indicate that the metallurgical bonding samples have a better fatigue performance, and their fatigue limits are 3 058 N and 2 829 N respectively. Under the same load, the metallurgical bonding sample has much longer fatigue life than the adhesive sample. And the fatigue fracture mode for these two types samples are completely different in two ways, the failure mode for adhesive sample is shear debonding, but no debonding occurred for metallurgical bonding sample, which indicates that failure mode of metallurgical bonding sample due to foam core shear.