Effect of pickling processes on the microstructure and properties of electroless Ni–P coating on Mg–7.5Li–2Zn–1Y alloy

Abstract

The electroless plating Ni–P is prepared on the surface of Mg–7.5Li–2Zn–1Y alloys with different pickling processes. The microstructure and properties of Ni–P coating are investigated. The results show that the Ni–P coatings deposited using the different pickling processes have a different high phosphorus content amorphous Ni–P solid solution structure, and the Ni–P coatings exhibit higher hardness. There is higher phosphorus content of Ni–P amorphous coating using 125g/L CrO3 and 110ml/L HNO3 (w=68%) than using 180g/L CrO3 and 1g/L KF during pre-treatment, and the coating structure is more compact, and the Ni–P coatings exhibit more excellent adhesion with substrate (Fc up to 22N). The corrosion potential of Ni–P coating is improved and exhibits good corrosion resistance. As a result, Mg-7.5Li-2Zn-1Y alloy is remarkably protected by the Ni–P coating.