The influence of Zn addition on the microstructure and mechanical and corrosion properties of warm rolled AlMg alloys containing Er and Zr

The effects of a minor Zn addition on the mechanical and corrosion properties and microstructure of a high Mg content AlMg alloy containing Er and Zr in the warm-rolled state were studied using tensile test, nitric acid mass loss test (NAMLT), exfoliation corrosion susceptibility test (ASSET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The tensile test results showed that the 0.58 wt% Zn addition to the Al-Mg-Er-Zr alloy increased the yield strength from 297 to 351 MPa and tensile strength from 416 to 445 MPa, but decreased the elongation from 13.3 % to 12.5 %. The NAMLT and ASSET results showed that the two warm rolled alloys were initially in the stabilization state, but the Al-Mg-Er-Zr alloy without Zn added became sensitized severely after the accelerated sensitization annealing (ASA) at 100 °C. The Zn addition improved the intergranular corrosion (IGC) resistance and exfoliation corrosion (EC) resistance significantly. The TEM results showed that, for the Al-Mg-Er-Zr alloy, there were Al₃(Er,Zr) phase particles in the matrix and β (Al₃Mg₂) phase particles separated from each other at the grain boundary. After the ASA treatment, more β phase particles were precipitated and covered the grain boundary completely. For the Al-Mg-Zn-Er- Zr alloy, another nanoscale T (Al₃₂(Mg, Zn)₄₉) phase was precipitated in the matrix, and there were no grain boundary phase particles observed at the grain boundary, because the precipitation of T phase consumed the supersaturated Mg in the matrix, thus suppressing the formation of grain boundary phase particles during the ASA treatment and resulting in a good corrosion resistance. The strengthening effect of the Zn addition was mainly due to the formation of T phase particles during the warm rolling process.