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 app ropriate for cathodic protection. The Al-Zn-Mg system has been particularly selected due to the presence of precipitates in the alpha -Al matrix, whic h are capable of breaking down passive films while presenting good electroc hemical efficiencies. At the same time, the effect of Li additions on super ficial activation of the anode by means of precipitation of AlLi-type compo unds was examined. The microstructure was characterized in the as-cast and as-aged ingots, showing the presence of alpha -Al dendrites as well as eute ctic of Al2Mg3Zn3 and precipitates Of Mg7Zn3 in interdendritic regions. Ele ctron microscopic observations performed on specimens with and without heat treatments showed in the alpha -Al matrix the presence of a uniform distri bution of precipitates of (tau -Al2Zn3Mg3, Mg7Zn3, and delta -AlLi type. Th e electrochemical behavior of the alloy was investigated in a 3% NaCl solut ion simulating seawater at room temperature. After evaluation of the electr ochemical efficiency, values up to 67% were obtained. The relationship betw een microstructure and electrochemical efficiency is discussed in this work and suggestions of future research are given in order to improve the elect rochemical behavior of Al anodes in the field.