多层铝箔回填式搅拌摩擦点焊接头显微组织特征

Microstructure Characteristics of Refill Friction Stir Spot Welded Multilayered Aluminum Foils Joint

围绕新能源汽车锂离子电池集流体多层铝箔与极耳铝片的连接工艺,以80层0.012 mm厚工业纯铝箔和上、下各1层0.8 mm厚6061铝板组成的夹层结构的回填式搅拌摩擦点焊(Refill friction stir spot welding,RFSSW)接头为研究对象,采用电子背散射衍射等技术,研究了接头各区组织特征及其演变机制。结果表明:6061铝合金板材与多层铝箔夹层结构的RFSSW接头可分为搅拌区-1(SZ-1),搅拌区-2(SZ-2),热力影响区(TMAZ),热影响区(HAZ)以及母材区(BM)。接头上层铝合金板材变形抗力较高,中间层箔材变形抗力较低,在焊接过程剪切力的作用下,箔材流动程度更剧烈,导致搅拌区不同区域的晶粒取向和尺寸存在差异。位于中间铝箔层和套筒作用区外侧的SZ-1,晶粒取向都以(101)为主,均由等轴晶粒组成,平均晶粒尺寸在3.46~4.14μm。位于上层铝板的SZ-2内不同区域平均晶粒尺寸在4.07~4.35μm,晶粒取向、形态明显不同。靠近搅拌针的上层区域晶粒主要呈(111)取向,其余区域晶粒以(101)取向为主。远离搅拌针靠近中间铝箔层区域,由等轴晶粒和部分长条状晶粒组成,其余区域均为等轴晶粒。连续动态再结晶是多层铝箔RFSSW的主要再结晶机制,在高温和剧烈塑性变形作用下,小角度晶界持续吸收位错形成大角度晶界。搅拌区由于持续的剪切和挤压作用,再结晶晶粒经历多次塑性变形,发生反复的动态再结晶行为。

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 3.46-4.14μm.The average grain size in different positions of the SZ-2 in the upper aluminum plate is 4.07-4.35μm,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.