Effect of Submillimeter Variation in Plunge Depth on Microstructure and Mechanical Properties of FSLW 2A12 Aluminum Alloy Joints

Abstract

Friction stir lap welding was conducted on 2 mm + 2 mm sheets of aluminum alloy 2A12-T4. The plunge depth (PLD) was designed as 2.45-2.58 mm, which was varied in submillimeters as 2.45, 2.50, 2.53, 2.55, and 2.58 mm, and the axial force was recorded in the welding process. The results show that the PLD fluctuation in submillimeters causes significant variation in the axial force and affects the voids (i.e., Void I and Void II), hook, and effective sheet thickness (EST), among which Void I is the main factor that affects the EST. The fracture load-PLD function in the tensile shear test of the joints follows the rule of the EST-PLD function. An optimized PLD is approximately 2.55 mm, at which the EST reaches 1.71 mm, corresponding to a peak fracture load of 11.03 kN. Thus, a PLD of 2.55 mm is suggested with a tolerance of 0.02 mm, corresponding to a fracture load of 9.6-11.0 kN, i.e., within a fluctuation of 12%.

Dissimilar Friction Stir Lap Welding of Al to Mg: Characteristic Signal, Microstructure and Mechanical Properties

“…During the plunging stage (Stage I), the tool started to rotate and was pressed down until it plunged into the parent material to the specified depth. In this stage, the tool continued to be pressed into the yet-to-be-softened metal material, and the axial force (F z ) increased sharply with time [28], while the lateral force (F x ) and the feed force (F y ) increased slightly. Forcellese et al [22] claimed that the axial force quickly risen owing to the strength of the deforming material to the pin penetration that prevailed on the softening due to the heat generated by the stirring action of the rotating pin.…”

EBSD Characterization of the Microstructure of 7A52 Aluminum Alloy Joints Welded by Friction Stir Welding

“…W.F. Xu et al [ 14 ] found that in microstructure evolution during the conventional single-side friction stir welding (SS-FSW), significant grain refinement and a larger percentage of high-angle grain boundaries (HAGBs) exist in the SZ and TMAZ; the fracture location is TMAZ. In summary, the microstructure of friction stir-welded joints in different zones is different, and the cracking behavior and mechanical properties of welded joints are distinct [ 15 , 16 , 17 , 18 ].…”