Microstructures, wear resistance and corrosion resistance of CoCrFeNi high entropy alloys coating on AZ91 Mg alloy prepared by cold spray

In this work, a fully dense CoCrFeNi high entropy alloys (HEAs) coating with homogeneous microstructure was successfully prepared on AZ91 alloy by cold spray. It is innovative to cross-integrate HEAs with Mg alloys using cold spray to break through the "bottleneck" of Mg alloys. The average microhardness of the coating was 5 times higher than Mg alloys. The weight loss of the coating in wear test was 2 orders of magnitude lower than Mg alloys. The E-corr of the coating was noticeably improved to be similar to - 290 mV(SCE) and the i(coor) of the coating was significantly decreased by 4-5 orders of magnitude. The coating exhibited significantly spontaneous passivation due to the multi-layer passive film composed of FeO, Cr2O3 and NiO. The weight loss of CoCrFeNi coated AZ91 plates was below 1% after 28 days immersion. Lots of tiny micropits in size less than 1 mu m were distributed on the corroded coating surface because the formation of large pitting pits was restricted. Unique corrosion mechanisms of the coatings were found: the repeatedly repassivation effect and the competing effect triggered by the rapid initiations of new pittings. The stable passive film and uniform microstructure of the coating resulted in the significant decrease of corrosion rate. The shielding effect of the coating can bring outstanding surface protection for Mg alloys. (C) 2022 Elsevier B.V. All rights reserved.