Achievement of high-strength 2219 aluminum alloy joint in a broad process window by ultrasonic enhanced friction stir welding

Abstract

High-strength joints are required to suit a more and more wide industrial application of friction stir welding (FSW). However, the achievement of high-strength joints is generally confined within a narrow process window due to the significant dependence of material plastic deformation on welding parameters. In the present study, ultrasonic enhanced friction stir welding (UFSW) was proposed as a strategy to broaden the process widow for achieving high-strength joints. The results indicated that the tensile strength of UFSW joint only slightly fluctuated around 355–361 MPa, indicating a stable joint efficiency of 81%–82%, even though the welding speed was increased from 300 mm/min to 600 mm/min at a constant rotation speed of 800 rpm. Acoustoplastic effect of the ultrasonic contributes to sufficient plastic deformation of the materials in the stir zone (SZ) and thus welding defects were successfully avoided. With the welding speed increasing, the widths of SZ can stabilize at 4.7 mm in the middle and 3.3 mm in the bottom, respectively. Furthermore, ultrasonic improved the SZ strength by enhancing precipitation strengthening and thus the fracture position was located in the TMAZ. Coarsening of precipitates in the TMAZ cannot make prominent contributions to the resultant strength, leading to a stable joint efficiency of 81%–82%.