Microstructures And Properties Of Friction Stir Welds Of 40mm-thick 6082-T6 Aluminum Alloy

Aluminum alloy material has good comprehensive performance,and is widely used in the field of rail transportation vehicles to realize the lightweight of the car body.Compare to the traditional fusion welding method,friction stir welding(FSW)as a new type of solid-state welding technology has many advantages,and gradually began to engineering application on the aluminum alloy car body of the rail vehicle in recent years.However,the current application mainly focuses on the welding of small thickness aluminum alloy.For the medium thickness and thickness of aluminum alloy,the friction stir welding is still in engineering stage.This study is a system research on the microstructure and mechanical properties of welded joints about friction stir welding of 40mm thick 6082-T6 aluminum alloy,this has practical value for promoting the application of the friction stir welding technology in the welding of the aluminum alloy of rail vehicles.This research made use of microstructure observation and micro area composition analysis method such as OM,SEM,SEM-EBSD,SEM-EDS,TEM,micro hardness and tensile test,revealing the relationship between the microstructure and the properties of the friction stir welded joint.The main results were as follows:1.The dynamic recrystallization occurs in the weld nugget zone,and the grains are tiny isometric crystal;The grains occurs deformation and recovery or incomplete recrystallization in the thermo mechanically influence zone,the grains are deformation microstructure along the rheological direction;The grain of the heat affected zone is obviously growing,and the fibrous tissue of the parent material is still retained;2.Duo to the shaft shoulder thermal effects,the temperature gradually reduced from the surface of the bead to the center,thus leading to gradually refine of grains of from the top to the bottom in the welded nugget zone;3.The micro hardness of the weld cross section was high-low-higher-high,similar to W distribution.On both sides of the base metal grains distributed acicular ?" phase,the hardness is highest.The heat affected zone distribution coarse ?" phase,the hardness decreased significantly,forming obvious softening zone.The hardness of the thermo mechanically affected zone and the welded zone was picked up,which was duo to the dissolution and re-precipitation of the large of precipitated phase in the welded zone.4.The tensile strength of FSW was 227MPa,and the elongation reached 11.35%.The location of the fracture is located in the heat affected zone of the back side of the joint.5.The tensile samples of the delamination in the welded zone were not broken at Z line,and the Z line was not the weak area of the mechanical properties of the welded nugget region.