Electron Beam Welding Procedure Of6082-T6Aluminum Alloy And Microstructure And Properties Of Welded Joints

6082-T6aluminum alloy belongs to the Al-Mg-Si series alloys that can be hardened through heattreatment. Due to its light weight and high strength, good extrudability and excellent corrosionresistance etc., recently,6082-T6aluminum alloy has been widely used in the rail transportation fieldespecially in high-speed train body. Because6082-T6aluminum alloy is usually used as weldstructure in practical application, weld defects such as coarse grains in weld metal, high weld porosityand hot crack will appear when the conventional welding methods such as TIG, MIG welding are usedto weld this type of aluminum alloy. The welded joints with high quality are difficult to be obtianedand the application of6082-T6aluminum alloy is limited to a certain extent.Compared to traditionalwelding process, vacuum electron beam welding （EBW） has many advantages such as high energydensity, low weld heat input and small welding deformation, therefore, it is superior to weld6082-T6aluminum alloy. Based on these, this paper focuses investigation on the electron beam weldingprocess of6082-T6aluminum alloy with8mm and15mm thickness respectively, and themicrostructure and properties of welded joints are analyzed. In addition, the microstructure andproperties of EBW joint are compared with that of MIG joint, and the difference of microstructure,mechanical properties and corrosion resistance properties between the two types of welded joints isinvestigated under different welding conditions.The microstructure observation shows that the weldment microstructure of EBW joint iscomposed of fine equiaxed grains and dendrites, and it has the obvious secondary dendrites. A largenumber of eutectic structure uniformly distribute along the grain boundaries. Moreover, the adding ofcircular scanning during welding can effectively stir the molten pool to improve the fluidity of soluteelements and reduce the segregation of alloying elements, so it can greatly refine the grain. Theweldment microstructure of MIG joint is composed of coarse equiaxed grains and dendrites, and noobvious secondary dendrites exsits. The XRD analysis of phase constituent indicates that the weldmetal of welded joints mainly consists of α-Al matrix phase, β （Mg₂Si） strengthening phase andSi-phase, so the phase constituent of the weld metal of EBW and MIG joints is basically same. Andfurther analysis by transmission electron microscopy （TEM） verifies that β （Mg₂Si） is the mainstrengthening phase in the joints.The test of microhardness distribution shows that the microhardness of weld zone with EBW islower than that of heat-affected zone（HAZ）and base metal.The width of HAZ is narrow, which indicates the extent of softening is lower. Moreover, the hardness value of weld zone of EBW jointwith the pattern of circular scanning is the highest, followed by linear scanning and without scanningis the lowest. Compared with EBW joint，the HAZ width of MIG joint is bigger and there is anobvious soften zone in the HAZ, where is the weakest region of welded joint.The tensile strength test indicates that all of the welded joints have good mechanical properties,which can satisfy the engineering application. The highest tensile strength of EBW joint reaches about84.1%of that of base metal. But the strength of MIG joint is lower, which can only reach68.6%ofthat of base metal. SEM observation shows that the fractograph of welded joint presents the obviouscharacteristic of ductile fracture, and there are a large number of dimples which have different sizeand depth on the fracture surface. Moreover, it can be clearly observed some second phase particles atthe bottom of dimples, and further analysis by energy diffraction spectrum （EDS） demonstrates thatthe second phase particles are mainly β （Mg₂Si） phase.Static weight loss experiment and electrochemical test are used respectively to evaluate corrosionresistance of weld metal. Reasults show that for8mm-thick EBW joints of6082-T6aluminum alloy,the joint A5obtained by circular scanning has the best corrosion resistance, while the corrosionresistance of MIG joint is the worst.In a word, under such experiment conditions, the overall performance of8mm-thick EBW jointsis better than that of MIG joint, and the optimized welding parameters are: I=105mA, U=50kV,Ï…=1500mm·min^-1with circular scanning pattern, and for the15mm-thick plate are: I=205mA,U=50kV, V=1500mm/min with circular scanning pattern.