Improving the strength and SCC resistance of an Al-5Mg-3Zn alloy with low-angle grain boundary structure

Abstract

The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening. Adding a third component to form precipitation can improve their strength, but it usually leads to high-stress corrosion cracking (SCC) sensitivity due to the formation of high-density precipitates at grain boundaries (GBs). So far, it is still challenging to improve the strength of Al-Mg alloys without reducing SCC resistance. Herein, a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced. By dynamic plastic deformation and appropriate annealing treatment, near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion (71%) of the low-angle grain boundary. TEM statistical investigations show that the precipitation of active T' phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions, and the area fraction of GB precipitates is reduced from 72% to 21%, which significantly decreases the SCC susceptibility. This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.