Microstructure and properties of 6082 aluminum alloy ultra-thick plate preparated by friction stir weld

The double-sided of friction stir butt welding was carried out on the 6082-T4 aluminum alloys with thickness of 84 mm, and artificial aging (180℃×5 h) was applied after welding. The microstructure and mechanical properties of welded joints along the thickness direction were studied. The results indicate that the microstructure of the Welding Nugget Zone (WNZ) is fine equiaxed grains. From the surface of the plate to the center of welding seam, the grain sizes are 16 μm, 13 μm, and 5 μm, respectively, and the proportions of high angle grain boundaries are 77.2%, 76.3%, and 72.5%, respectively. The strengthening phase of WNZ is mainly "GP zone" and β″. The grain of the Thermo-Mechanically Affected Zone (TMAZ) is elongated and there is a high density dislocation. The microhardness in the thickness direction indicates that the hardness curve of the center overlap area of the weld is "V" type, the lowest hardness value appears in the double-sided welding overlap area, while the hardness curve of the other area is "W" type,. The samples are all broken in the area where TMAZ and Heat Affected Zone (HAZ) meet. The tensile strengths from the surface to the center overlap in the thickness direction are 211 MPa, 201 MPa, and 180 MPa, which gradually decrease. The center overlap zone has the lowest tensile strength, but its elongation is the highest, which is about 69% of the base metal. The fracture surfaces were distributed with dimples of different sizes, and fractures in all tensile specimens were ductile fracture. © 2020, Jilin University Press. All right reserved.