The Effect of Microstructure on Local Corrosion Product Formation during Initial SO2-Induced Atmospheric Corrosion of ZnAlMg Coating Studied by FTIR-ATR FPA Chemical Imaging

Corrosion and Materials Degradation Pub Date : 2023-09-08 DOI:10.3390/cmd4030026

Dan Persson, Dominique Thierry, N. LeBozec

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Abstract

The initial atmospheric corrosion of ZM (ZnAlMg)-coated steel in humid air (85% RH) and humid argon (85% RH) containing 320 ppb SO2 was studied using in situ infrared reflection absorption spectroscopy (IRRAS), FTIR-ATR focal plane array (FPA) imaging and SEM-EDS. The corrosion products formed in humid air containing SO2 are mainly composed of magnesium sulphites and sulphates, with sulphite-containing corrosion products formed initially while the contribution from sulphates increased with exposure time. The results from FTIR-FPA imaging and SEM-EDS showed that the magnesium sulphite and sulphate are formed mainly on eutectic phases with a higher quantity of corrosion products formed on the binary eutectic (Zn-MgZn2) phases. This is due to presence of microgalvanic elements with the zinc-rich phases as the main sites for the cathodic oxygen reduction while the anodic reactions take place on the eutectic areas. Sulphate content is the highest on the binary eutectic phases, due to the microgalvanic effects and the production of oxidants by the cathodic reaction, which increases the oxidation of sulphite to sulphate.

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FTIR-ATR FPA化学成像研究了so2诱导ZnAlMg涂层大气腐蚀过程中微观结构对局部腐蚀产物形成的影响

采用原位红外反射吸收光谱(IRRAS)、FTIR-ATR焦平面阵列(FPA)成像和SEM-EDS研究了ZM (ZnAlMg)涂层钢在含320 ppb SO2的潮湿空气(85% RH)和潮湿氩气(85% RH)中的初始大气腐蚀。在含SO2的潮湿空气中形成的腐蚀产物主要由亚硫酸镁和硫酸盐组成，含亚硫酸盐的腐蚀产物最初形成，硫酸盐的贡献随着暴露时间的增加而增加。FTIR-FPA成像和SEM-EDS分析结果表明，亚硫酸镁和硫酸镁主要在共晶相上形成，在二元共晶(Zn-MgZn2)相上形成的腐蚀产物较多。这是由于富锌相的微电元素的存在作为阴极氧还原的主要部位，而阳极反应发生在共晶区域。硫酸盐含量在二元共晶相中最高，这是由于微电效应和阴极反应产生的氧化剂，这增加了亚硫酸盐氧化成硫酸盐。

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来源期刊

Corrosion and Materials Degradation

CiteScore

4.50

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0.00%

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