Stress corrosion cracking resistant nanostructured Al-Mg alloy with low angle grain boundaries

Abstract

For decades, high susceptibility to intergranular corrosion and stress corrosion cracking is the Achilles's heel for the 5xxx series Al alloys with high Mg (> 3 wt%) owing to precipitation of electrochemically active Mg-rich β phase at grain boundaries (GBs) at moderately elevated temperatures. Herein, nanostructured Al-5Mg alloy with a high proportion of low angle grain boundary equiaxed grains were generated by dynamic plastic deformation and appropriate annealing treatment. Electron back-scattered diffraction discloses that the fraction of low angle boundaries reaches 70%, which has been demonstrated to greatly suppress the precipitation of β phase at GBs. The nanostructured Al-5Mg alloy exhibits excellent intergranular corrosion resistance and stress corrosion cracking resistance after being sensitized at 150 °C for 100 h. Moreover, its strength and ductility are much higher than the corresponding coarse-grained alloys, thus solving the classic problem that has existed for decades. The introduction of a high fraction of low angle grain boundaries by dynamic plastic deformation and appropriate annealing provides a novel strategy for the development of advanced nanostructured Al alloys.