High-pressure linear friction welding of dissimilar AA5052-H34 and AA6061-T6 joint

Abstract

Dissimilar linear friction welding (LFW) of AA5052/AA6061 was performed at different applied pressures. A dissimilar joint obtained at a high applied pressure of 200 MPa exhibited a tensile strength equivalent to that of the AA5052 base material, mainly because of the high density of low-angle grain boundaries (LAGB) per unit area at the weld regions. Meanwhile, the joints obtained at low applied pressures of 30 and 100 MPa softened at the weld regions because the LAGB density decreased because of the increased peak welding temperature. Therefore, the joints fractured in the weld regions, and the tensile strength of the joints decreased. Because dissimilar AA5052/AA6061 joints have metallurgical inhomogeneities and strength mismatches, plastic strain constraints near the weld interface of the soft material inevitably occur during tensile testing. Although the Vickers hardness at the weld interface on the AA5052 side had the lowest value, fracture was suppressed owing to the plastic strain constraint. At 100 and 200 MPa, the average grain diameters as a function of Z on the AA5052 side of the dissimilar AA5052/AA6061 joints matched the plot obtained from the similar AA5052 joint. At an applied pressure of 30 MPa, the average grain diameter was much larger than that of similar joints because the dissimilar joints underwent lower strain during LFW compared to similar joints, which resulted in the suppression of grain refinement during continuous dynamic recrystallization (CDRX).