Study On Microstructure And Properties Of Friction Stir Welding Joints Of 5052 And 6061 Dissimilar Aluminum Alloys

The5052-O and6061-T6dissimilar aluminum alloy plates with the thickness of6mm were welded by friction stir welding (FSW), micro structure evolution and fracture characteristics study by optical microscopy (OM)、scanning electron microscopy (SEM)^transmission electron microscopy (TEM) and electron backscatter diffraction technology (EBSD); study phase and conponent by X-ray diffraction (XRD) and spectroscopy (EDS); The mechanical properties of welded joints and corrosion resistance study by micro hardness、cupping machine and electrochemical exprriments.The main research results are as follows:(1)Through metallurgical structure observe, study the macrostructure and microstructure of5052-O/6061-T6dissimilar aluminum alloys by friction stir welding. The result shows that:Onion ring was formed in the weld zone when5052located on the advancing side, it is the result of layered structure stacked, rotational speed and welding speed are not major factor for the onion rings form, tool offset is less affected on the organization structure of welded joints.(2) The result of XRD、SEM and TEM studie showed that:Precipitates presence in the5052-O and6061-T6base material occurs dissolved in the weld zone due to the temperature exceeds the melting of the precipitates.only uniform distribution of the silicon-rich particles keep;6061-T6was sensitive to welding heat, the precipitates occurs coarse in the Thermo-mechanical affected zone of this side, needle-like precipitate turned to rod β’ phase, howerer, in the heat affected zone a number of circular β phase appeared.(3) Friction Stir Welding5052-O and6061-T6dissimilar aluminum alloy made a good welded joints, the maximum ultimate tensile strength is230MPa, elongation is5.77%, the hardness of the heat affected zone on both sides occurs decline.Especially,in the HAZ of6061side hardness sharply decline.Under the low rotational speed and welding speed, fracture occur in the heat affected zone of6061side, while with rotational speed and welding speed increase fracture all located on one side—5052heat-affected zone, fracture mechanisms is ductile and brittle hybrid fracture.(4) Microstructure、grain orientation and texture changes were studied by EBSD. The results showed that:most of the base metal and heat affected zone is low-angle grain boundaries, and a sub-crystal grain boundaries is inside. The low-angle grain boundary continue to absorb dislocations lead to misorientation increases in FSW process, eventually changing to high angle boundary, the mechanism is continuous dynamic recrystallization.The original low-angle grain boundary migration and elimination, the continuous dynamic recrystallization process leads to fine equiaxed nugget zone microstructure. The{100}<001> cube texture,{011}<100> Goss texture and a small amount of S{123}<634> texture present in the parent material, however,in the weld nugget turn into{112}<110> shear texture. (5) Corrosion potential of welded joints positive shift, the radius capacitive arc smaller than base material. Dissimilar aluminum alloy welded joint by friction stir welding exhibits better corrosion resistance.