An eco-friendly one-step pretreatment method for the synthesis of electroless coating on magnesium alloy

Using a one-step pretreatment process, this study synthesized an environmentally friendly and cost-effective electroless Ni-W-P coating on the AZ31 magnesium alloy. Aqueous iron (II) sulfate treatment was used as a replacement for conventional pretreatment in the electroless coating on magnesium alloy. Using ammonia solution in the plating bath results in micro-pits in the coating, and cracks appear on the surface after a certain time of deposition. The deposition rate of the coatings was around 10 and 7 μmh from plating baths with and without ammonia, respectively. Coatings from baths without ammonia (T2), on the other hand, have no pits and can develop thick coatings, whereas coatings from baths with ammonia (T1) can only form deposits up to 10 μm thick. The atomic structure of both coatings exhibits a mixture of microcrystalline and amorphous phases. The coatings T1 and T2 showed an adhesion strength of 6 ± 0.24 and 8.1 ± 0.15 MPa, respectively. Both T1 and T2 coatings have significantly higher corrosion resistance and microhardness than the base alloy.