Research On The Corrosion Behavior Of Friction Stir Welding Joints For High-strength Aluminum Alloy 6061

The 6061-T6 aluminum alloy specimens were welded by the solid phase welding- the friction stir welding(FSW) technology. Microstructure of the welded joints and the mechanical properties of the joints were researched. Base metal and joints were experimented with intergranular corrosion and stress corrosion test in welded state, solution and aging treatment after welding and stress relief annealing after welding in the corrosive environment. The differences of the corrosion resistance in the base metal and joints were studied by SEM,EDS technology. The main contents were as follows:In the welded state, the 6061-T6 aluminum alloy joints by FSW had a good shape. By analyzing the microstructure it showed that weld nugget(WN) had the small fine grains, no directions; Thermo-mechanically affected zone(TMAZ) appeared the stretched bent and deformed grains; Heat-affected zone(HAZ) appeared coarse grains. The joints of microhardness curve was "W"-shaped distribution. The microhardness of WN was maximum and the maximum value was 82.4, which was higher than the microhardness value of the base metal. Tensile tests showed that when the welding parameter was w = 1080r/min, v=120mm/min, the mechanical properties of joints was the best than others and its tensile strength was 230 MPa, reaching 72.6% of the tensile strength of the base metal.After the intergranular corrosion test, the base metal suffered more shallow corrosion. WN suffered the worst corrosion where appeared some " dendrimers " corrosion cracking extending from the edge of the specimen towards inside along the grain boundaries. TMAZ and HAZ had different degrees of pitting corrosion, pitting obviously. Intergranular corrosion reduced the binding force between the grains so that made the microhardness of welded joints overall decline.After the slow strain rate tensile test, the stress corrosion sensitivity coefficient ISSRT of welded joints was greater than the base metal. When the welding process parameter was w=1080r/min, v=120mm/min, the stress corrosion sensitivity coefficient ISSRT of the welded joints was to a minimum.Compared with the microstructure, mechanical properties and corrosion resistance of the welded joints under the welded state, grain orientation of welded joints had been optimized after the solution and aging treatment. The matrix microstructure had precipitated the black second phase particles Mg2 Si and microstructure evenly distributed. Microhardness of welded joints overall increased and it enhanced resistance to intergranular corrosion. After stress relief annealing, the intergranular corrosion susceptibility of joints has reduced and the stress corrosion susceptibility of the joints has been reduced.