Characterization of single- and multilayer cold-spray coating of Zn on AZ31B

Zinc, a soft material with a low melting point and high corrosion resistance, was coated onto AZ31B Mg alloy using different cold spraying process parameters. The physical and mechanical properties of the resulting Zn/AZ31B samples were then investigated to explore the effect of the process parameters on the microstructural and mechanical characteristics. The results obtained via X-ray diffraction show the formation of an intermetallic material at the interface of Zn/AZ31B even at low process temperatures. In addition, spherical droplets of Zn were observed at the surface, confirming the partial melting of Zn particles during the impact. This partial melting is believed to lead to the formation of intermetallic compounds during solidification. To engineer the residual stress induced in the cold spraying process, a thin layer of dense Zn was then used as an intermediate layer before coating with Al7075, forming a multilayered surface of Al7075/Zn/AZ31B. Because of the higher thermal expansion coefficient of Zn compared with those of Al7075 and AZ31B, beneficial compressive residual stress could be created in all three layers of this novel multilayer deposition. Without the Zn interlayer, Al7075/AZ31B under the same coating parameters exhibited undesirable tensile residual stress in the substrate.