Environmentally-friendly method for electroless Ni–P plating on magnesium alloy

In this paper, an environmentally-friendly procedure has been introduced for electroless nickel plating on AZ61 magnesium alloy. Magnesium alloy was firstly etched in nitric acid and then treated in a Cerium–lanthanum–permanganate (CLP) conversion coating bath. Finally, the electroless Ni–P deposition was carried out on the conversion coating from a sulfate solution. The microstructure of the CLP conversion coating was observed using Scanning Electron Microscopy (SEM), while the composition was analyzed by Energy Dispersive X-Ray Spectroscopy (EDX). Subsequently, deposited Ni–P coating was also characterized by its chemical composition, crystalline structure, morphology, and corrosion resistance. A uniform and amorphous nickel coating with high phosphorus content was successfully deposited on the pre-applied chemical conversion coating on the AZ61 alloy. An obvious passivation occurred for the nickel coating during the anodic polarization in 3.5 wt.% NaCl solution. Compared with the bare and CLP treated substrates, the Ni–P deposits showed more nobler corrosion potential and also lower corrosion current density. Open circuit potential (OCP) measurements and electrochemical impedance spectroscopy (EIS) experiments were carried out in 3.5 wt.% NaCl to determine the real anticorrosion performance of the Ni–P deposits.

► A novel and green method has been used for electroless Ni–P plating on AZ61 alloy.
► Rare earth-Permanganate conversion coating acts as pretreatment for Ni–P plating.
► A compact and uniform deposit with high phosphorous content was obtained.
► The coating shows very noble corrosion potential and high anti-corrosion performance.