Corrosion behaviour of weathering steel in diluted Qinghai salt lake water in a laboratory accelerated test that involved cyclic wet/dry conditions

The corrosion behaviour of CortenA weathering steel has been investigated using a laboratory accelerated test that involved cyclic wet/dry conditions in Qinghai salt lake water diluted 30 times. The characteristics of the rust layers on tested samples were observed by SEM and EPMA, analyzed by IRS and XRD, and studied by polarization and EIS measurements. The weight loss was almost linear, indicating that the rust layer had no retarding effect on the corrosion process. The crystalline components of the rust layers consisted primarily of β-FeOOH, magnetite (Fe3O4) and γ-FeOOH. As the corrosion proceeded, the amount of β-FeOOH decreased while that of magnetite and γ-FeOOH increased. XRD, EDAX and EPMA indicated that the complex corrosion products magnesioferrite (MgFe2O4) and iowaite (Mg4Fe(OH)8OCl·4H2O) probably existed in the rust layer, in which case they will have had an important influence on the protectiveness of the rust layer. The results of electrochemical measurements showed that the rust layer exhibited high reduction reactivity, which facilitated the corrosion of weathering steel in the wetting process. The large rust capacitance and small rust resistance indicated that the rust layer had a loose and porous structure which provided poor protection.