Microstructure, mechanical property and bonding mechanism of the repaired mechanical hole out of dimension tolerance of 2024 aluminum alloy by radial-additive friction stir repairing

Repairing mechanical hole out of dimension tolerance of aluminum (Al) alloy has a high potential and function in manufacturing industries. To achieve a reliably repaired hole of 2024 Al alloy, radial-additive friction stir repairing (R-AFSR) was developed, and this technology was divided into the regularizing-defect and repairing stages. Results showed that by adjusting the filling depth of pinless tool at the regularizing-defect stage and the rotating direction of tool with threaded pin at the repairing stage, the sufficient metallurgical bonding was achieved and then the kissing bond defect was eliminated due to not only the enlarged stir zone but also the heightened pressure and temperature. Under the suitable processing parameters, the maximum tensile and compressive shear strengths of the repaired hole by R-AFSR were 281.8 and 206.8 MPa, which were 89.1 % and 95.1 % of those of the standard hole. The fracture mode of repaired hole was decided by the metallurgical bonding effect of interface between filling material (FM) and base material (BM) (the FM/BM interface), and three fracture modes, including tensile fracture, tensile-plug fracture and plug fracture, were obtained. The R-AFSR provides a new approach to acquiring a high-quality repaired mechanical hole of Al alloy.