電着塗装における鋼板の耐クレータリング性能に及ぼすりん酸塩処理皮膜の影響

概要

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Effects of zinc phosphating on the cratering phenomena during cathodic electrodeposition coating were studied. Cold rolled(CR), electrogalvanized(EG), double-layer zinc-iron electroplated (Zn-Fe) and galvannealed sheet(GA) were used as test materials. The voltage applied between the anode and the cathode in a plating solution was increased at a constant rate from zero to a certain value (200 to 400V), and then kept constant. Two peaks were observed in the change of the current with time in the coating process. The peak current ratio, i_B(second peak)/i_A(first peak), correlated to the crater density. Phosphate treatment increased the crater density and brought about a high peak current ratio. This tendency was the most remarkable on GA. For all kinds of steel sheets both the value of i_A and i_A/V(voltage) were decreased by phosphating. The electric resistance calculated from the current-time relation did not depend on the materials.
1987-06-01