1991-02-01

Evaluation of Anti-Cratering Properties of Precoated Steel Sheets Using Current-time Profile and Mechanism of Cathodic Electrocoat Primer Cratering 910763

A new method of evaluating the anti-cratering properties of precoated steels has been developed which detects minute differences among materials. The anti-cratering properties of precoated steel sheets are evaluated by measuring the variation of current with electrodeposition time (current-time profile) at the initial stage of cathodic electrocoat deposition. Although some current peaks were observed in the current-time profiles, the slight differences of anti-cratering properties in precoated steel sheets were able to be evaluated by measuring the last current peak height. In the case of cratering at high applied voltage, the peak height of the last current peak was high and the variation of the current was vigorous. On the other hand, when few craters were generated, the last current peak height was low.
Furthermore, our results were: variation in resistance which is calculated by means of measured current and voltage from the relation “V=IR”, optical microscopic study of uncured film in the course of electrodeposition, and no electric discharges occurrence in the case of cratering. These results led to the conclusion that electro-deposited films are ruptured by local hydrogen gas generation and these defects cause cratering.

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