装飾クロムメッキの耐食性に及ぼすクロムメッキの影響

Abstract

The effects of chromium layer on the corrosion protection of decorative chromium plated steel panels were investigated. In this series of corrosion study the Sargent type chromium plating baths were used with varied chromic acid concentrations.Accelerrated corrosion test of the nickel-chromium plated steel panels showed that the effect of increasing chromium thickness is greatly changed with the type of underlying nickel layer. Thus the plated panel with underlayer of Ni-Cr alloy of relatively rich ductility but high internal tensile stress loses corrosion resistance with increasing chromium thickness. This is clearly due to the crazing of nickel layer along the cracks of outer chromium layer, although the tendancy decreases with an increase of chromic acid concentration in the chromium plating bath.On the contrary, the plated panels with the underlayer of levelling bright nickel showed little deterioration with chromium thickness increase, even in the low concentrated chromium bath.Furthermore in this case, increase of chromium thickness by using high concentrated chromium plating bath increases corrosion resistance.Then, the corrosion resistance test of copper-nickel-chromium layer of the same thickness as the above nickel chromium plating was carried out, and is found that in the case of Ni-Cr alloy as intermediate layer, the presence of copper layer depresses deteriorating effect caused by the increase of chromium thickness.