Change of Intergranular Corrosion Behavior along the Thickness in a Friction-Stir-Welded 7N01-T5 Aluminum Alloy

The intergranular corrosion behavior of friction-stir-welded 7N01-T5 aluminum alloy joints was investigated by using sliced samples extract from the top, middle and bottom layers of the joint, with the sliced direction parallel to the welding direction. The relationship between microstructure and local corrosion property of the welded joints was analyzed. The results show that the heat-affected zone (HAZ) of the weld exhibit the highest susceptibility to intergranular corrosion, and the corrosion degree of the top and bottom surface layers were more serious than the central layer in the HAZ, continuously dispersed precipitates on grain boundaries and the grains size may be the main factor which caused the different corrosion severity of HAZ. The thermo-mechanically affected zone (TMAZ) is characterized by a highly deformed structure, and the temperature reached in this local zone during welding is high enough for the strengthening precipitates, especially the precipitates on the grain boundary to be partially re-dissolved. The temperature gradient caused resistance to intergranular corrosion of TMAZ reduced from top to bottom surface. The stirred zone (SZ) experienced heavily plastic deformation and temperature cycling, the sensibility of intergranular corrosion was low, which is attributed to the sufficient re-dissolve of the strengthening precipitates during welding.