Effect of electro-spark deposited ZA12 interlayer on the microstructure and mechanical property of A356/AZ91D by liquid-solid compound casting

Abstract

In this paper, to fabricate high strength Al/Mg bimetallic composite without the formation of Al12Mg17 intermetallic compound at the interface, ZA12 deposited A356/AZ91D bimetal was achieved by liquid-solid compound casting. The combination between electro-spark technology and compound casting was realized. The process parameters of electro-spark deposition were optimized by considering the thickness, quality, and efficiency of the coating. The microstructure, phase composition and mechanical properties of A356/AZ91D bimetal without and with ZA12 coating were investigated. From AZ91D to A356, the main phases formed across the interface region are: Mg17(Al, Zn)12 + α-Mg in diffusion layer I, Al5Mg11Zn4 and Mg32(Al, Zn)49 in diffusion layer II, and Al3Mg2 and Mg2Si in diffusion layer III. The microhardness of the interface is obviously higher than that of the substrate on both sides. The average shear strength of ZA12 coated A356/AZ91D bimetal is 69.2 MPa. The interface microstructure evolution mechanism of ZA12 coated A356/AZ91D by liquid-solid compound casting was analyzed. The result is helpful for further development of high strength Al/Mg bimetallic composites.