Influence of a Zn Interlayer on the Interfacial Microstructures and Mechanical Properties of Arc-Sprayed Al/AZ91D...

A novel technique combining solid-liquid compound casting (SLCC) with arc spraying was designed to manufacture the arc-sprayed Al/AZ91D bimetals with a Zn interlayer. The Al/Mg bimetal was produced by pouring the AZ91D melt into the molds sprayed with Al/Zn double-deck coating, during which the arc-sprayed Zn coating acted as the interlayer. The effect of the Zn interlayer on microstructures, properties, and fracture behaviors of arc-sprayed Al/AZ91D bimetals by SLCC was investigated and discussed in this study. The optimal process parameter was acquired by analyzing the results from different combinations between the arc-spraying time of the Zn coating (10, 18, and 30 s) and the preheat time of the Al/Zn double-deck coating (6 and 12 h). The interfacial microstructures of the arc-sprayed Al/AZ91D bimetals with a Zn interlayer could be approximately divided into two categories: One was mainly composed of (α-Mg + Al₅Mg₁₁Zn₄) and (α-Al + Mg₃₂(Al, Zn)₄₉) structures, and the other primarily consisted of (α-Mg + Al₅Mg₁₁Zn₄), (MgZn₂ (main) + β-Zn), and (β-Zn (main) + MgZn₂) structures. In the interface zone, the (α-Mg + Al₅Mg₁₁Zn₄) structure was the most abundant structure, and the MgZn₂ intermetallic compound had the highest microhardness of 327 HV. When the arc-spraying time of the Zn coating was 30 s and the preheat time of the Al/Zn double-deck coating was 6 h, the shear strength of the arc-sprayed Al/AZ91D bimetal reached 31.73 MPa. Most rupture of the arc-sprayed Al/AZ91D bimetals with a Zn interlayer occurred at the (α-Mg + Al₅Mg₁₁Zn₄) structure and presented some typical features of brittle fracture.