Mechanistic investigation on the influence of coating weights on the corrosion behaviour of hot-dip-galvanised Zn-Mg-Al coatings

Time-lapse Microscopy, scanning vibrating electrode technique and potentiodynamic methods were used to study the influence of increasing coating weight (80-310 gm-2) on microstructure, cut-edge and surface corrosion of Zn-Mg-Al coatings in 0.17 M NaCl. Cut-edge corrosion was similar for all coatings due to the oxygen reduction reaction becoming diffusion-limited. A 64% reduction in surface corrosion was observed for high coating weights through increases in eutectic volume fraction. Spatial and temporal corrosion mechanisms were controlled by microstructural morphological differences as coating weight varied. 80 g.m-2 coatings demonstrated lateral anodic spreading potentially reducing coating penetration rates despite their higher surface corrosion rate.