Effects of welding parameters on micro-junction structure and fracture behavior of refill friction stir spot welded joints for 2060 aluminum alloys

Abstract

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.