Zn-Mg-Al coatings (ZMA) on steel can provide enhanced corrosion resistance compared to zinc coating (GI) and are often used in applications that require shaping processes. This study investigates the effect of deformation-induced cracking on the corrosion of ZMA coatings of different weights (310 and 80 g m-2) benchmarked against GI. Cracks were more prevalent and of greater depth in ZMA coatings due to the presence of MgZn2 in the eutectic. ZMA with 310 g m-2 weight (ZMA310), exhibited a ~ 3 times greater crack area than 80 g m-2 weight (ZMA80) through an increased eutectic volume fraction. This caused an increase in corrosion rate of 3.8 times for ZMA310 relative to its undeformed condition over 24 h, with increases between 1.5 and 1.7 times for ZMA80 and GI. Two phenomena cause this increase: deformation-accelerated corrosion due to differential aeration-induced anodic activation in non-through-coating cracks, and cathodic activation in through-coating cracks resulting from galvanic coupling with the steel.
Malla et al. (Mon,) studied this question.