Coil-coated Zn-Mg and Zn-Al-Mg: Effect of climatic parameters on the corrosion at cut edges

We studied the effect of temperature, wet/dry cycling, pH, and the type and concentration of the corrosion activator on cut edge corrosion of painted Zn-15Mg and Zn-1.5Al-1.5Mg coated steel. In most accelerated tests, paint delamination and red rust formation were reduced compared to hot dip galvanised steel (HDG), and Zn-15Mg outperformed Zn-1.5Al-1.5Mg; however, Zn-1.5Al-1.5Mg showed better results when exposed outdoors. The alloyed materials were particularly resistant when HDG was prone to elevated corrosion, i.e. under permanent wetness, at higher temperatures, with high chloride loadings and in the presence of sulphate. Oxygen reduction on steel cut edges was inhibited by the alloying elements.