Due to different filling modes of the material in sleeve-affected zone (SAZ), probe-affected zone (PAZ), and thermo-mechanically affected zone (TMAZ), the micro-junction structure is formed at the bottom of the SAZ of the refill FSSW joint for 3.2-mm-thick 2060 aluminum alloys. The plasticized degree of the filling material and refilling time greatly affect the morphologies of micro-junction structure. Thus, the welding defects such as void with different sizes, kissing bond, and crack are easily formed in the micro-junction structure. Besides, the tensile-shear properties are related to the micro-junction structure and bonding strength of the lap interface. The increase of the plunge depth or rotation speed within a certain range enhances the flow of material in the stir zone and increases the atomic diffusion capacity of the lap interface, which is beneficial to increasing the tensile-shear load. The maximum tensile-shear load was obtained when the rotation speed of 2500 rpm and the plunge depth of 4 mm are used, and the tensile-shear specimen fractures along the bottom of the SAZ. Other fracture paths are also obtained under different welding parameters combinations, first along the lap interface, and second, not only along the lap interface but along the SAZ bottom.

由于套管影响区（SAZ），探针影响区（PAZ）和热机械影响区（TMAZ）中材料的填充方式不同，因此，微结结构形成在外壳的SAZ底部为3.2mm厚的2060铝合金填充FSSW接头。填充材料的塑化程度和重新填充时间极大地影响了微结结构的形貌。因此，在微结结构中容易形成焊接缺陷，例如具有不同尺寸的空隙，亲吻结合和裂纹。此外，拉伸剪切性能还与搭接界面的微结结构和粘结强度有关。切入深度或旋转速度在一定范围内的增加会增加搅拌区内的物料流动，并提高搭接界面的原子扩散能力，这有利于增加拉伸剪切负荷。当使用2500 rpm的转速和4 mm的切入深度时，获得最大的拉伸剪切载荷，并且拉伸剪切试样沿SAZ底部断裂。还可以在不同的焊接参数组合下获得其他断裂路径，首先是沿着搭接界面，其次是不仅沿着搭接界面而且沿着SAZ底部。