Effects of minor Zn content on microstructure and corrosion properties of Al-Mg alloy

The effects of different Zn contents in Al-Mg alloy on the microstructure characterizations were observed by advanced electron microscopy and the corrosion properties were investigated by the inter-granular corrosion tests, the exfoliation corrosion tests, and the Potentiodynamic polarizaion tests. The tau phase (Mg-32 (Al, Zn)(49) ) forms on the pre-existing Mn-rich particles and at the grain boundaries. According to the theory of binding energy, the formation of t phase is much easier than that of beta phase (Al3Mg2), somehow replacing beta phase and reducing the possibility of beta phase precipitation. This change dramatically decreases the susceptibility of corrosion. The Zn addition increases the corrosion resistance of Al-Mg alloy with an optimal value of 0.31%. When the Zn addition is increased to 0.78%, however, the corrosion resistance of alloy decreases once again but it is still better than that of the alloy without Zn addition.