Influence of alloying elements and microstructure on aluminium sacrificial anode performance: case of Al-Zn

The electrochemical behaviour of Al-x%Zn alloys (1 wt% < = x < = 80 wt%) was studied in 0.5 M sodium chloride solution. The experiments focused on the influence of casting conditions on sacrificial anode performance. The influence of casting conditions, solidification structure, polarization behaviour and attack morphology on the anode efficiency and operating potential was analysed. For alloys with low Zn content (1-5 wt%), the interdendritic zones or grain boundaries were the initial sites of attack and self corrosion was the principal cause of efficiency loss. Particularly, for Zn contents below 3 wt% the operating potential was strongly affected by the solidification macrostructure. Casting conditions that produced better alloying element distribution (chill structures) promoted higher anode efficiency. For Zn content higher than 5 wt% the operating potential and the anode efficiency were defined by the alpha / beta phases area relationship.