Technology for Electroless Bright Nickel-Phosphorous Alloy Plating on Aluminum and Aluminum Alloy

Pretreatment technology suitable for electroless Ni-P alloy plating on Al alloy was selected.A novel process of all bright electroless Ni-P alloy plating was established by adding Ni plating intermediate and inorganic salts into conventional electroless Ni-P plating bath.The effects of composition of the plating bath and plating conditions on the deposition rate,corrosion resistance and appearance of the coating were analyzed.It was found that the optimized plating bath consisted of 25~35 g/L nickel sulfate,25~40 g/L sodium hypophosphite,15~25 mL/L lactic acid,8~12 g/L sodium citrate,15 g/L sodium acetate,10 mg/L 2-ethyl hexyl sodium sulfate,0.4 g/L saccharin,5~10 mg/L PPS,5~10 mg/L DEP and 40~50 mg/L inorganic salt.The optimized pH value and temperature were determined as 4.4～4.8 and 80~90 ℃ respectively.The Ni-P alloy coating obtained under the optimized plating condition was fine and bright,and had good adhesion to Al substrate and good corrosion resistance,showing promising application in decoration of Al and Al alloy.