塩水噴霧試験における55%Al-Zn合金めっき鋼板の切断端面部近傍の腐食挙動(表面処理・腐食)

概要

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Hot-dip 55%Al-Zn alloy coated steel sheet has superior corrosion resistance in various atmospheric environments. However, the corrosion often occurs near the shear cut edge in continuous wet environments, for example, salt spray test (SST, JIS Z2371), whose behavior is different from in cyclic corrosion tests including dry process (CCT, ISO 14993). To make clear the behavior and the mechanisms of the corrosion of 55%Al-Zn alloy coated steel sheet near the cut edge in SST, cross-sectional observations after the corrosion tests by SEM and polarization measurements in addition to the corrosion tests were conducted. The time to the red rust occurrence near the cut edge of 55%Al-Zn coated steel sheet was made longer with increasing the coating weight and decreasing the steel thickness in SST. The corrosion near the cut edge in SST is caused by a galvanic attack between the coating as an anode and the steel exposed at the edge as a cathode. Moreover, in the case of SST, which has no drying process, the corrosion products almost never formed near the edge, while they were observed to be adhered on the surface in CCT. These differences can be explained by whether these tests have the drying process or not.
2005-09-01