Fabrication, microstructure and property of AZ31/7075 composites with Zn intermediate layer

Abstract

AZ31/7075 composite with the addition of Zn foil (about 100 μm in thickness) in the dissimilar material interface was successfully fabricated by pre-extrusion+caliber rolling composite process. The microstructure evolution especially for the composite interface was characterized by optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) and the microhardness test was also performed. The effect of the Zn intermediate layer on the product during the extrusion and caliber rolling was explored. The results show the hard 7075 Al alloy as the core can refine the grain size of AZ31 alloy. In addition, introducing Zn intermediate layer can reduce or completely avoid the formation of Mg-Al intermetallic compounds. The temperature increased by extrusion and deformation results in the remelting of eutectic Mg-Zn phase, and the diffusion of both elements from the solid to the liquid phase are accelerated. However, discontinuous cracks can be observed in the Mg-Zn diffusion layer but will be healed after caliber rolling. The MgZn2 intermetallic compound generated at Mg-Zn diffusion layer has high hardness (161HV), but the overall hardness of bonding layer is not changed a lot due to thinner thickness of the Mg-Zn diffusion layer after deformation.

Keywords

• mg/al alloy
• zn intermediate layer
• compound forming
• microstructure
• microhardness