Strength and fracture behavior of AA2A14-T6 aluminum alloy friction stir welded joints

The formations and fracture behavior of the AA2A14-T6 aluminum alloy friction stir welded (FSWed) joints are investigated under different ratios of rotational speed to welding speed (n/v). The relationship between the viscous layer (δ) and the rheological layer (ξ) is the key factor to determine the welding quality of joints. When δ < ξ, loose microstructure, needle-like, dispersive, or through void is generated in the joint as the n/v decreases. When δ ≥ ξ, the defect-free joints can be obtained. The through void greatly weakens the tensile properties, and the tensile specimens fracture in the stir zone (SZ). Other defects mainly influence the ultimate strength and the elongation, and the joints fracture at the SZ/thermo-mechanically affected zone or the base material/heat-affected zone (BM/HAZ). The defect-free joints have the largest tensile properties and fracture at the BM/HAZ. Based on the above analysis, the reasonable quality assessment criteria of the FSWed joint need to combine with four aspects: internal formation, strength, plasticity, and fracture behavior. Meanwhile, according to the reasonable matching relationship between δ and ξ, the critical conditions of FSW process parameters for the 2A14-T6 aluminum alloy can be obtained.