Effects of zinc coating on interfacial microstructures and mechanical properties of aluminum/steel bimetallic composites

In the present work, the effects of zinc coating on interfacial microstructures and mechanical properties of the aluminum/steel bimetallic composites prepared by a solid-liquid diffusion method were investigated, and the formation mechanism of intermetallic compounds at the interface between the aluminum and the steel were also discussed. The results show that a relatively uniform and compact interface between the aluminum and the steel was formed with the application of the zinc coating. The reaction layer that was mainly composed of τ6-Al4.5FeSi, α-Al rich, α + η eutectoid, η-Zn and eutectic silicon phases, between the aluminum and the steel, had an average thickness of approximately 650 μm. The microhardnesses at the interface between the aluminum and the steel gradually decreased from the steel insert side to the aluminum base side, where the microhardnesses were obviously higher than those of the aluminum base metal. Moreover, the shear stress of the aluminum/steel bimetallic composite with the zinc coating increased by 71% compared to that of the one without the zinc coating. The zinc coating played important roles in the removal of oxidation of the steel insert and the improvement of the wettability between the aluminum and the steel, which promoted the metallurgical reaction of the aluminum with steel, resulting in a significant improvement of the bonding between the aluminum and the steel.