Improving the Weld Formation and Mechanical Properties of the AA-5A06 Friction Pull Plug Welds by Axial Force Control

In the present study, the weld formation and mechanical properties of the AA-5A06 friction pull plug welded (FPPW) joints were improved by controlling the axial force history. Several defect-free FPPW joints were made successfully by using the welding parameters of 15–20 kN/s axial loading rate, 20–30 kN axial welding force and 6–7 mm axial feeding displacement. The results indicated that using higher axial loading rate and axial welding force produced more stable heat generation and shorter frictional heating time between the frictional interface. In this case, the plastic flow of the materials around the hole could be further improved since the axial feeding displacement of the plug was increased. The maximum ultimate tensile strength (UTS) and elongation of the FPPW 5A06 joints were 314 MPa and 4.8%, respectively. The thermal mechanically affect zone (TMAZ) had the lowest hardness value throughout the joint and was found as the fracture location to all the tensile samples. The softening of TMAZ was mainly caused by the weakening of the cold work hardening and the coarsening of grains.