Intergranular stress corrosion cracking of friction stir welded nugget on a 2050-T8 aluminum alloy

Intergranular corrosion sensitivity is studied for the friction stir weld nugget of aluminum alloy 2050-T8. The weld nugget consists of fine equiaxed grains having average sizes from 4 to 20 μm, the grain size increases with decreasing of the distance from the weld surface. The weld nugget contains a particular microstructure called "onion rings" due to crystallographic orientations. The effect of the "onion rings" on stress corrosion cracks initiation is studied for stress corrosion cracking tests at a strain rate of 2.10^-6 s^-1. EBSD cartographies allow showing that the initiation site of the biggest cracks is located at boundaries between the texture bands. Corrosion and stress corrosion tests in 1.0 M NaCl are performed in order to show stress effect on intergranular corrosion. Pitting corrosion is observed during corrosion tests, whereas intergranular cracks appear during stress corrosion tests. The medium crack length is 20 μm and 168 cracks per mm² can be located. In these severe laboratory conditions, the order of magnitude of long crack growth rate is 5.10^-8 m.s^-1.