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

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.