Electrically conductive and corrosion resistant coating on Mg-Li alloy, part II: electroless nickel plating coating with a cut-off design for the galvanic corrosion

Electroless nickel (EN) plating could simultaneously offer protectiveness and electrical conductivity to Mg alloys, but micro-galvanic corrosion is the most detrimental factor that needs to be alleviated. In this work, various intermediate coatings, including electrically conductive conversion coating (EC-PCC), conventional phosphate chemical conversion coating (PCC) and plasma electrolytic oxidation coatings (PEO), were prepared before the EN process. Results show that, compared with Mg-Li alloys being coated with intermediate layers, the corrosion resistance of Mg-Li alloys after the EN process was severely deteriorated. This deterioration was ascribed to the futile design of cutting off the micro-galvanic corrosion. After sealing the pores in the PEO coating, a cut-off design of the galvanic corrosion was successfully designed, and the EN composite layer demonstrates a significant increase in corrosion resistance.