Electrochemical Behaviors Of Segregations In Series Of Al-Zn-In-Sn Anode

Five kinds of Al-Zn-In-Sn anode materials had been melted, in which the contents of Sn were 0, 0.05%, 0.10%, 0.15%, 0.20% separately. The electrochemical performances and the hydrogen evolutions of five anodes had been tested in the 3% NaCl solution; the micro-structures of these five anodes and the compositions of segregations had been investigated by the electron probe microanalysis (EPMA) and energy spectrum; The electrochemical behaviours of grain boundaries and segregations were investigated in 3% sodium chloride solution by electrochemical impedance spectroscopy (EIS), galvanostatic polarization techniques and galvanic corrosion. The experiments focused on the influence of element Sn on the micro-structures and macro-electrochemical performances of alloys and the effect of segregations in the Al-Zn-In-Sn anodes activation process.With the content of Sn increasing, the crystal particle of Al-Zn-In-Sn alloy electrodes was smaller and smaller, when the content of Sn was 0.20%, the crystal particle was much bigger accidentally. The segregation shapes riching in In and Sn were concentrated in the crystal boundary unevenly. With element Sn, the crystal boundaries of Al-Zn-In-Sn alloys were wider and the quantity of segregations falls off obviously.Element Sn can improve the component of segregations noticeably, Sn had discriminated against In and Zn, it would be cut down for In and Zn to segregate on the crystal boundary with Sn joined, thus the solubility for In and Zn in the aluminum solid solution would been increased.The simulated segregation and simulated crystal boundary alloys were developed according to the average elements distribution in Al-Zn-In-Sn alloy. The simulated segregation exhibited preferential dissolution because of its more cathodic corrosion potential, more extrusive current density and less impedance. By the means of researching on the galvanic corrosion between the segregations and the crystal boundary, it would be believed that the Sn, In segregation in Al-Zn-In-Sn alloy can be attributed to the formation of local galvanic cells as coupled with alloy base, which lead to the preferential dissolution of active site and disruption of the oxide film.Contrasting micro-structures pictures after corroded with the micro-structures pictures before corroded, It can be proved that there were two places for the aluminum alloy sacrifice anode to start activating. One is the casting defects, such as blowhole, loose, where hole eclipse was easily happened. The other is the segragated shape appearanced along the crystal boundary.