The influence of Ti and Zr on electrochemical properties of aluminum sacrificial anodes

The electrochemical behavior of Al–5% Zn–0.02% In sacrificial anode was studied in 3 wt.% sodium chloride solution. The experiments focused on the influence of Ti and Zr as additional alloying elements on the electrochemical behavior of aluminum sacrificial anodes. For this purpose Ti and Zr were added in different levels from 0.01 to 0.2 wt.%. NACE efficiency and polarization tests were used. It was found that by using 0.03–0.05 wt.% Ti and 0.05 wt.% Zr as the alloying elements; incremental homogeneous dissolution could be achieved resulting in improved electrochemical properties of aluminum sacrificial anodes, such as current capacity and anode efficiency. The results suggest that corrosion behavior seems to be strongly related to the presence of bifilms (doubled-over oxide films) suspended in the liquid alloy. Higher levels of Ti and Zr additions precipitate on the bifilms and cause them to sediment out from the liquid alloy prior to casting, thus depleting the cast alloy of a useful dispersion of corrosion centers, and impairing the uniform distribution of dissolution of the cast alloy.