Corrosion Behavior Of Friction Stir Welded Joint Of 6082-T6 Aluminum Alloy

Corrosion and fatigue are the main reasons of failure of the aluminum alloy welded structure.A large amount of economic losses and disasters are caused each year.During the process of friction stir welding,the joint of the aluminum alloy undergoes different degrees of plastic deformation and welding thermal cycling,resulting in different degrees change of the microstructure including the second-phase particles and ?-Al matrix.So the joint of the aluminum has different corrosion sensitivity in the corrosion environment.In this paper,a systematic study of the microstructure and corrosion behavior of 6082-T6 aluminum alloy FSW joint for high-speed train was carried out to reveal the key factors that affect corrosion.This is of great significance in formulating an effective anti-corrosion measure and corrosion evaluation criteria for aluminum alloy FSW joint.In this paper,the susceptibility to intergranular corrosion of friction stir welded 6082-T6 aluminum alloy was investigated by intergranular corrosion testing.The results show that the characteristics of precipitates are the decisive factors affecting the susceptibility of intergranular corrosion.A large amount of?" phase spread around the base metal,PFZ width is 100 nm.So the intergranular corrosion sensitivity of base metal is high.Affected by the heat of welding,the precipitates from the stir zone to the heat-affected zone has different degree remelting,growing and transformation.The precipitated phase density decreased,resulting in the stir zone,the heat affected heat-affected zone closing to seam(HAZ1)and the heat affected zone closing to base metal(HAZ3)are not susceptible to intergranular corrosion.The HAZ2 zone between the HAZ1 and HAZ3 is intermittently distributed with Cu-rich phase grains,so,the area is more sensitive to intergranular corrosion.In addition,the stress corrosion cracking behavior of 6082-T6 aluminum alloy FSW joint is studied by the method of slow strain rate tensile stress corrosion testing and four-point bending stress corrosion testing.In slow strain rate tensile stress corrosion testing,the ISSRT values of all samples are distributed in the range of 0.01-0.05,and the stress sensitivity corrosion index of the joint is lower.Compared with the strain rate of 10-6 s-1,the joint ISSRT value show an increasing tendency under the strain rate of 4×10-7 s-1.In the four-point bending stress corrosion experiment,no stress corrosion cracking is observed in all the specimen cross-sections and only a large number of pitting corrosion are observed on the tensile stress surface.The characteristics of crystalline phase have an important influence on the size and density of pitting corrosion.Due to the high temperature and severe plastic deformation,the particles in the stir zone is fragmented and dispersed.During the four-point bending stress corrosion experiment,the density of pitting corrosion in the stir zone is larger.The stir zone of the center layer sample undergo two times plastic deformation,the crystal phase particles are more fine,so the degree of pitting corrosion is more serious than stir zone of the upper and lower surface samples.Based on the results of tensile strain stress at slow strain rate and four-point bending stress corrosion testing,the stress-corrosion propensity of 6082-T6 aluminum alloy FSW joint is not found.The characteristics of the second phase particles and the microstructure of the ?-Al matrix are important factors affecting the corrosion behavior of the FSW joints in the 6082-T6 aluminum alloy.Among them,the characteristics of the second phase particles are the decisive factors.