Influence of Mg and Al alloying additions on the corrosion mechanisms of Hot-dipped Zn-Mg-Al coatings: role of microstructure and phase distribution
Amar Malla, G. Williams, Daniel Britton, Frank Goodwin, Ana Paula Domingos Cardoso, T. Richards, David Penney, James Sullivan
Abstract
Abstract Systematic investigations into the individual effects of increasing alloying additions of Mg and Al on the corrosion mechanisms of Zn-Mg-Al coatings have demonstrated that microstructural phases and their surface distribution determine the anodic and cathodic behaviour of the coating. Increasing either Al and/or Mg from 1 to 3 wt.% improved the surface corrosion performance of the coating, with a greater effect observed for Al additions due to anodic deactivation. Mg additions led to cathodic deactivation due to a significant reduction in Zn dendrites at the surface. The corrosion rate was minimised by maximising the ternary eutectic area fraction at the coating surface. A 52% and 32% decrease in SVET-derived metal loss is achieved at 3 wt.% increase in Al and Mg, respectively.