Corrosion Resistance of Hybrid Films with Chromium Plating and Silicone Compound

For a hybrid chromium plating film produced by impregnation and polycondensation of silicon compounds, formation and corrosion resistance of cracks expanded by anodic etching of chromium plating were investigated. During anodic electrolytic etching of chromium plating film, crack widths and numbers increased along with the electrolysis time. The plateau area decreased after electrolysis duration of 600 s. The entire surface became porous after electrolysis duration of more than 900 s. The amount of silicon compound impregnated into the expanded cracks increased from a crack width of 0.3 μm. The hybrid chromium plating film was a gradient film in which the silicon compound decreased from the surface side to the substrate. Its maximum thickness was inferred as ca. 30 μm. The order of corrosion resistance in the CASS test results was as follows: hybrid chromium plating >> nickel undercoat plating / chromium plating >> nickel plating > chromium plating. The hybrid chromium plating which had been optimized by controlling the expanded crack showed no sign of pitting, corrosion or discoloration after 336 h during the CASS test.