Effect of Drying on the Corrosion of Carbon Steel, Zinc, Aluminium and AZ31B Magnesium Alloy During Cyclic Accelerated Corrosion Tests

In cyclic atmospheric accelerated corrosion tests used in the automotive industry, drying is usually simulated by reducing the relative humidity (RH) to 50% or 70%, which is significantly higher than during real vehicle operation. This study investigated the effect of RH in dry phases of a cyclic corrosion test on the corrosion of carbon steel, zinc, aluminium and AZ31B magnesium alloy. Three modifications of a test with the drying RH of 30%, 50% and 70% were carried out, and average and real-time corrosion rates, corrosion morphologies and composition of corrosion products were evaluated. The drying RH had a specific effect on the corrosion of each metal. The corrosion rate of carbon steel was the highest in the test with the highest drying RH while zinc and aluminium showed a decrease in corrosion rates with increasing drying RH. The mechanism of magnesium alloy corrosion was influenced by electrolyte distribution with the highest corrosion rate in the test with drying at 50% RH. Drying at 30% RH was found to provide the best correlation to the real-world performance of the metals.