Influence of Pretreatment on Zinc Dipped Coating of AZ91D Magnesium Alloy

Zinc dipping is an important process before electroless platingor electroplating of magnesium. The quality of zinc coating affected the properties of electroless or electroplating coatings directly. The effects of picking and activating processes on the properties of zinc coating were investigated by SEM and potentio-dynamic polarization test. The results show that the best pickling process is pickling 20 s at ambient temperature in 30 ml/L 65% HNO3 + 0.5 g/L thiourea. The best activating process is activating 10 minutes at ambient temperature in HF (40%) 375 ml/L. Fine zinc coating can be obtained in optimization process. The zinc coating combined well with magnesium matrix and had good corrosion resistance.