多层铝箔回填式搅拌摩擦点焊接头显微组织特征

The connection process of multi-layer aluminum foil and pole aluminum sheet for collecting fluid in lithium-ion battery of new energy vehicle. A layer of 0.8 mm thick 6061 aluminum plate is placed on the top and bottom of 80 layers of 0.012 mm thick industrial pure aluminum foil, forming a sandwich structure. And the sandwich structure was welded by refill friction stir spot welding. The microstructure characteristics and their evolution mechanism of the weld was investigated by EBSD. The results show that the RFSSWed multilayered aluminum foils joint can be divided into stir zone-1(SZ-1), stir zone-2(SZ-2), thermal-mechanical affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM). During welding, the deformation resistance of the upper aluminum alloy sheet is higher than that of the middle layer foil. Under the shearing force, the flow ability of the foil is more intense, which leads to various grain orientation and size of different positions in stirring zone. In the middle aluminum foil layer and outside of the action zone of the sleeve of SZ-1, the grain orientation near the stirring needle and the sleeve are mainly (101), and grain morphologies are basically equiaxed. The average grain size is 3.46-4.14 μm. The average grain size in different positions of the SZ-2 in the upper aluminum plate is 4.07-4.35 μm, and the grain orientation and morphology are different. The grains in the upper position near the pin are mainly (111) orientation, and the grains in the other position are mainly (101) orientation. The position away from the pin and close to the middle aluminum foil layer is composed of equiaxed grains and some elongated grains, and the rest positions are consisted of equiaxed grains. Continuous dynamic recrystallization is the main recrystallization mechanism of RFSSWed multilayered aluminum foils joint, which means under high temperature and severe plastic deformation, low angle grain boundaries continuously absorb dislocation to form high angle grain boundaries. The recrystallized grains undergo multiple plastic deformation and repeated dynamic recrystallization behavior due to continuous shear and extrusion in the stirred region.