Promoting of metallurgical bonding by ultrasonic insert process in steel-aluminum bimetallic castings

It is challenging to efficiently prepare bimetallic composites with excellent metallurgical bonding. Here, we present a strategy, the ultrasonic insert casting (UIC) process, to solve this problem. The ultrasound cavitation effectively destroys the oxide film and promotes diffusion in the UIC-prepared steel/aluminum bimetallic castings, resulting in a uniform reaction layer between steel and aluminum. The reaction layer contains FeAl3, Al8Fe2Si, and Al4.5FeSi, and has a higher microhardness than the steel/aluminum matrix, with an average thickness of 8 mu m. Moreover, the thickness of the reaction layer increases with the improvement of pouring temperature but the thicker reaction layer (approximately 12 mu m) does not bring higher strength. The highest shear strength, about 70 MPa, is approximately three times higher than that without ultrasonic treatment. These results indicate a useful strategy for the low cost and high-efficiency preparation of metallurgical boding bimetallic casting.