Development of low-cost high entropy alloys composite coating with gradient structures on Mg alloys manufactured by supersonic solid-state cold spray

Abstract

This work prepared a composite coating of CoCrFeNi high entropy alloys (HEAs) containing 30 vol% Al₂O₃ on an AZ91 substrate by supersonic solid-state cold spray (CS). The resulting CoCrFeNi/Al₂O₃ composite coating exhibited a gradient-like structure with increased bond strength, and the elements in the coating region were uniformly dispersed. The coating was compact without visible cracks or significant pores, and the average surface roughness (Ra) was 4.28 µm. Additionally, the dynamic recrystallization occurred at the bonding interface of the AZ91 substrate, leading to gradient grain refinement and a rise in hardness from 73±5HV to ~196HV. The surface hardness of the coating was ~363HV, and the wear depth was only 1/10 of that of the AZ91 substrate. Meanwhile, the coating’s E_corr increased from -1599mV to -876mV and the I_P was reduced by five orders of magnitude compared to the substrate, resulting in an anti-corrosion efficiency of 99.92%. The passive film of the coating was primarily composed of oxides, with Al₂O₃ playing a significant role in its formation. In summary, this work achieved the innovative goal of lowering costs and weight while significantly improving the wear and corrosion resistance of Mg alloys.