Micro-electrochemical investigation on the role of Mg in sacrificial corrosion protection of 55mass%Al-Zn-Mg coated steel

The effects of Mg on the anodic dissolution behavior of the 55mass%Al-Zn coating layer were determined by in situ observation during galvanostatic polarization. The Zn-‍rich phases were observed to corrode at lower potentials than the dissolution potential region of the Al-rich matrix phases, and the dissolution duration of the Zn-rich phases was prolonged by Mg addition. Moreover, the corrosion products of the 55mass%Al-Zn-Mg coating layer were suggested to inhibit the oxygen reduction reaction on the steel substrate. The sacrificial corrosion protection mechanisms due to the addition of Mg to the 55mass%Al-‍Zn coating layer were discussed.