热浸镀层在青岛站的海水腐蚀行为对比(Ⅱ)——潮差区

Seawater corrosion behavior of hot dip coatings at Qingdao test station(II)-Tidal zone

测试了热浸镀锌(GI)、锌-5%铝-稀土(GF)和锌-55%铝-1.6%硅(GL)镀层钢板在青岛站的潮差区海水腐蚀行为,并利用腐蚀质量损失测试和显微结构分析,首次研究了3种镀层钢板的海水潮差区腐蚀行为。结果表明:3种镀层在潮差区均出现不同程度的生物污损,与全浸区相比其腐蚀速度明显降低;GI镀层溶解速度最快,氧化膜保护效果不佳,耐腐蚀性能最差;GF镀层的耐蚀性明显提高,潮差区的充气条件又促进了镀层的钝化,表现出较为优异的耐腐蚀性能;由于保护性的锌的腐蚀产物被滞留在富铝的枝晶网络中,比较充分的充气条件又促进了镀层富铝相的钝化,GL镀层在海水潮差区表现出最佳的腐蚀性能。对位于海水潮差区的钢材基体提供1 a保护期所需的镀层最小厚度分别为:GI镀层25μm;GF镀层12μm;GL镀层3μm;GF和GL镀层在潮差区的耐蚀性分别是厚度相当的GI的3倍和5倍。

The corrosion behavior of hot dip Galvanized （GI）, Galfan （GF） and Galvalume （GL） coated steels exposed to seawater tidal zone of Qingdao site was investigated with seawater corrosion test and microscopy morphology analysis. Biofouling takes place on the coupons in this zone to some extend and may result in partial protection of coating surface and lower corrosion rate. The poor performance of GI coating is mainly attributed to its largest dissolution rate and less protective oxidation product layer. The better performance of GF coating is ascribed to its lower dissolution rate and more resistant oxidation film formed on the coating surface in contact with well-aerated seawater. The protective zinc corrosion products retained in the Al-rich dendritic network slows down further attack, and well-aerated condition promotes passivity of Al-rich phase, GL coating thus shows the best performance in tidal zone. The minimum coating thickness requirement for one year protection afforded to steel structures that is exposed to tidal zone is then calculated as： GI, 25 μm ; GF, 12 μm; GL, 3 μm. The corrosion resistance of GL and GF are five and three fold as that of GI exposed to tidal zone.