Study of trivalent chromium iridescent passivation technology producing high corrosion resistance for electroplated zinc coatings

The bath composition of trivalent chromium iridescent passivation for Zn plating coatings was optimized by orthogonal test. The effects of process parameters on the appearance and corrosion resistance of passivation film were studied. The optimal process conditions are 20 g/L CrCl3, 7 g/L NaNO3, 3 g/L NiSO4, 8 g/L CH3COOH, 6 g/L ammonium complexing agent, temperature 25-30 °C, pH 2.5-3.0 and time 50-60 s. Bright and flamboyant passivation films with uniform color and good adhesion strength were obtained. No white rust was observed on the passivated Zn coating after exposure in neutral salt spray for 144 h.