Durability of Passivation in Zinc Electroplating

The durability of passivation in zinc electroplating has been studied using weak acid zinc bath free from cyanide and ammonia for zinc plating. and yellow and noncolored passivating solutions for passivation process. At the running voltage of 1.1 V, amperage ofl A. pH S-S.4, and at room temperature, best plating results were obtained from the zinc bath. The plated sample was washed in distilled water and then dipped in dilute HN03 for two seconds to make zinc plated surface active toward accepting fmal passivating film. The sample was then dipped in passivating solutions; cllromate film developed on the zinc surface, which protected it against corrosion as well as gave it an attractive appearance. It was found that yellow passivation at dipping time of one minute and at room temperature with the passivating solution composition of cr03 SO gIL, H2S04 1 mIlL, HN03 3 milL gives best corrosion resistance but weak abrasion resistance, while on the other hand colorless passivating solution comprising Cr03 2 g/L, KF 4 g/L and HN03 3 mIlL gives good abrasion resistance with weak corrosion resistance. 

I SADIQ ,I U HAQUE ,N AHMAD ,