Parameter optimization for electroless Ni–W–P coating

• Optimized plating parameters for ternary Ni–W–P coating were determined.
• Parameters influence W deposition analogously for electro- and electroless methods.
• Parameters influence P deposition analogously between binary and ternary coating.
• The influence of W apposition on P deposition was evaluated.
• Stabilizers were found to have dramatic influence on W content in deposits.

Ternary Ni–W–P coatings were electrolessly plated on an Al alloy substrate. The influence of the main parameters including: the concentrations of sodium hypophosphite and sodium citrate; bath temperature; bath pH; and selected bath stabilizers on the composition of coatings was investigated by an orthogonal experimental method. The results indicated that by controlling the bath composition and process parameters, the percentage of W and P in the coating could be optimized while using a constant amount of sodium tungstate. Furthermore, the presence of stabilizers in the bath had a significant influence on the W and P content of the coatings. The parameters controlling the deposition of W by electroless method were found to be similar with those affecting W deposition in electroplating. Induced co-deposition of W on catalytic Ni surface was suggested to explain the experimental results.