抄録
Cosmetic corrosion performance of Zn-Fe, Zn-Ni alloy and Zn electroplated steel sheets was evaluated by paint creepage behavior at the scratch where both of substrate steel and the plated layer were exposed to corrosive environment.
On the other hand, galvanic corrosion behavior of the plated layer at the scratch was investigated by electrochemical measurement.
Since the Zn plated layer corrodes under cathodic control ; that is, corrosion current density is proportional to the ratio of exposed area of substrate steel to that of the plated layer (C/A ratio), the decreace of the value by increasing the plated coating weight retards blister formation.
The Zn-Fe alloy plated layer corrodes by 'preferentially dissolution mechanism' when C/A ratio is rather high. In such a case, paint blister appears to be formed earlier.
The high corrosion resistance of Zn-Ni alloy layer is effective for retarding cosmetic corrosion. The only problem, the loss of cathodic protection' ability, may be occured in the case of fairly high C/A ratio.
In this work, the new cyclic corrosion test that mainly consists of humidity test at room temperature was devised.
