Evaluation of an Al-Zn-Mg-Li alloy/potential candidate as Al-sacrificial anode

This paper forms part of an overall effort to develop Al-sacrificial In/Hg free anodes; our research has been directed toward developing Al alloys appropriate for cathodic protection. The Al-Zn-Mg system has been particularly selected due to the presence of precipitates in the α-Al matrix, which are capable of breaking down passive films while presenting good electrochemical efficiencies. At the same time, the effect of Li additions on superficial activation of the anode by means of precipitation of AlLi-type compounds was examined. The microstructure was characterized in the as-cast and as-aged ingots, showing the presence of α-Al dendrites as well as eutectic of Al₂Mg₃Zn₃ and precipitates of Mg₇Zn₃ in interdendritic regions. Electron microscopic observations performed on specimens with and without heat treatments showed in the α-Al matrix the presence of a uniform distribution of precipitates of (τ-Al₂Zn₃Mg₃, Mg₇Zn₃, and δ-AlLi type. The electrochemical behavior of the alloy was investigated in a 3% NaCl solution simulating seawater at room temperature. After evaluation of the electrochemical efficiency, values up to 67% were obtained. The relationship between microstructure and electrochemical efficiency is discussed in this work and suggestions of future research are given in order to improve the electrochemical behavior of Al anodes in the field.