ESTIMATION OF CORROSION RESISTANCE OF Zn-0〜30%AL HOT-DIP COATINGS ON STEEL

概要

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A recently developed Zn-Al hot-dip coating on steel has a higher corrosion resistance than that of the Zn hot-dip coating. For estimating the corrosion rate for the hot-dip coating on steel, the polarization resistance(R_p) was measured using a coulostatic method. The cross-section of the Zn-Al hot-dip coating was analyzed by X-ray and EPMA. The results showed a tendency in which the Al concentration increased from the surface of the coating toward the base steel side. Based on the R_p values of five kinds of Zn-Al coatings hot-dip coated in a bath with 5, 10, 15, 20 and 30%Al, the coating obtained in the 15%Al bath showed the highest R_p value. In other words, this indicated that the corrosion resistance of the coating from the 15%Al bath was superior. Electrochemical impedance spectroscopy(EIS) with a frequency response analyzer(FRA) was used to obtain further inoformation about the interface of the Zn-Al hot-dip coating and a 5% NaCl aqueous solution of pH 8. The measurement results showed two capacitive semicircles on the hih-frequency side and a diffusion curve on the low-frequency side, which are considered to be formed by a typical Randles-type equivalent circuit. This results the fact that the corrosion reaction is rate limited by both the charge and material transfer processes.
社団法人日本材料学会の論文
1998-03-15