Short Communication: Influence of Hypophosphite on Efficiency and Coating Qualities of Electroless Ni-P Deposits on Magnesium Alloy AZ91D

The effect of reducing agent (sodium hypophosphite) on plating rate, reduction efficiency of sodium hypophosphite, properties of baths and coatings in electroless Ni-P plating on magnesium alloys were studied. The results showed that the concentration of sodium hypophosphite in the bath had impact on properties of bath and coatings. Low concentration of sodium hypophosphite would reduce the reactivity of the bath and form incompact coatings with poor corrosion resistance. Exorbitant concentration of sodium hypophosphite would lower reduction efficiency and efficiency of nickel deposition in electroless Ni-P plating process and coatings adhesion. The specific phosphorus content of coatings with high corrosion resistance was obtained by controlling the concentration of sodium hypophosphite. High stability of bath was established based on high reduction efficiency and efficiency of nickel deposition. The effect of concentration of sodium hypophosphite provided a route for controlling properties of coatings and monitoring bath stability. When the concentration of sodium hypophosphite in the bath was controlled to 25-30 g.dm-3, the compact Ni-P coatings with strong adhesion and good corrosion resistance were obtained and the electroless bath possessed high stability.