Environmentally friendly and facile Mg(OH)2 film for electroless nickel plating on magnesium alloy for enhanced galvanic corrosion inhibition

Abstract

Electroless amorphous nickel (Ni)–phosphorus (P) (NiP) alloy coatings were successfully achieved on magnesium alloys using an environmentally friendly and facile Mg(OH)2 conversion film, followed by AgNO3 activation. The success of the coating was confirmed through scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction characterizations. Electrochemical tests showed that the charge transfer resistance of the newly developed electroless NiP plating coating, which had a horizontally stacked Mg(OH)2 nanosheet primer (Mg(OH)2/pH 14/ENP), was significantly higher than that with a vertically grown Mg(OH)2 nanosheet underlayer (Mg(OH)2/pH 10/ENP) or that with a phosphate pretreatment (ENP). The measured corrosion current density of the Mg(OH)2/pH 14/ENP coating was 1.08 μA cm−2, one magnitude smaller than that of the ENP coating. Notably, the ENP coating exhibited severe galvanic corrosion, peeling off after only 24 h of the neutral salt spray (NSS) test. In contrast, the Mg(OH)2/pH 14/ENP surface showed no visible corrosion cavities or signs of galvanic corrosion even after 120 h of the NSS test or 21 d of exposure to a NaCl solution. These results indicate that the as-prepared coating possesses a strong inhibition capability against galvanic corrosion between the Ni layer and the magnesium alloy, providing long-lasting corrosion protection.