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 τ 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 τ phase is much easier than that of β phase (Al 3 Mg 2 ), somehow replacing β phase and reducing the possibility of β 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.