镀锌层破损汽车钢板在含NaCl溶液和泥浆中的腐蚀行为与EIS研究

CORROSION PROPERTIES OF GALVANIZED AUTO STEEL SHEET WITH BREAKAGES OF ZINC COATING IN NaCl CONTAINING SOLUTION AND MUD

采用镀锌层破损面积不同的热镀锌汽车钢板试样,在含相同3.5%Cl-浓度的鹰潭泥浆和NaCl水溶液中进行了浸泡和浸没腐蚀实验,研究了镀锌板、基板和镀锌层不同程度破损试样在两种介质中的腐蚀规律.结果表明:完整镀锌层的腐蚀速率高于基板;镀锌层破损试样的腐蚀失重随镀锌层破损面积的增加而增大;在泥浆中的腐蚀速率比在溶液中大,且腐蚀速率随时间的变化不同.EIS分析结果表明,镀锌层破损试样的锌层在两种介质中的电荷转移电阻都比基材小得多,镀锌层的腐蚀对腐蚀失重结果起主要贡献.泥浆溶氧高和pH值低是造成镀锌层破损试样在两种介质中腐蚀行为明显不同的主要因素.

The corrosion properties of the galvanized steel sheets for autos with various broken areas of their zinc coating were evaluated and compared by immersion tests in a mud of Yingtan soil containing 3.5% NaC1 and a solution with the same concentration of NaC1. The results show that corrosion weightloss rate of the sheet with intact zinc coating was higher than that of the substrate ; the corrosion rate increased with the broken area increasing, and was higher in the mud than in the solution. In the two cases, the variations of corrosion rate with time were also different. The analysis of EIS diagrams show that the electric charge transfer resistances of the specimens with broken zinc coating were much lower than that of the steel substrate, so the corrosion of zinc coating played a major important role in the weight loss. Higher oxygen concentration and lower pH value in the mud were two key factors to give rise to the corrosion behavior of specimens with broken zinc coating in the mud different from that in the NaC1 solution.