Abstract
In this work, the tensile-shear mechanical behaviors of friction stir spot weld and adhesive hybrid joint were performed from both numerical and experimental viewpoints. Weld through (WT) and flow in (FI) processes were studied in this research. The focus was to evaluate joint defects, tensile-shear failure load (TSFL), failure energy, failure mode and stress distribution of the joint. In FI joints, keyhole and hook defects appeared in the weld zone and the areas of material removed from the base metal were filled with adhesive. In the WT joints, the adhesive layer close to the weld zone was carbonized due to the welding heat. Meanwhile, under the rotating movement of welding tool, the adhesive impurities entered the stirring zone (SZ) and heat affected zone (HAZ) of the weld, which decreased mechanical performances of WT joints. Compared to the friction stir spot welding (FSSW) joint, the TSFL value, stiffness and failure energy of FI joint were increased by 2.7, 1.1 and 8.14 times, respectively. In order to study the stress distribution of the joints, a finite element (FE) model, which considered the weld structure and mechanical properties of weld regions, was implemented. Moreover, the adhesive layer was simplified by the cohesive zone model (CZM). FE results show that the FI process effectively decreases the stress concentration of the weld edge from 243.09 to 15.5 MPa, under the 2 kN tensile load. The weld can block the adhesive crack propagation, and the adhesive optimized the stress distribution of FI joints through a synergistic effect. So, the use of FI process for aluminum alloy connection is strongly recommended, especially in crucial structure areas.
Highlights
As a result of the huge consumption of natural resources and global warming, many countries have enacted legislation to reduce fuel consumption and greenhouse gas emissions [1,2]
Failure modes of friction stir spot welding (FSSW), Adhesive bonding (AB), flow in (FI) and WT joints were determined by observing the morphology of fracture surfaces
The nugget of the weld was diagonally split into two parts and a mixed failure mode appeared in the adhesive area of the FI joint
Summary
As a result of the huge consumption of natural resources and global warming, many countries have enacted legislation to reduce fuel consumption and greenhouse gas emissions [1,2]. Friction stir spot welding (FSSW) has been developed as a derivative of FSW for joining automobile body structures [14]. Adhesive bonding (AB) is one of the most common joining techniques used in advanced structures (e.g., aerospace, racing and automobile bodies, marine) This joining technique has some special advantages compared to traditional joining methods, (like riveting, bolting and welding). AB joints have a higher load-bearing capacity by reducing stress concentrations [23] This method can be combined with other joining processes to benefit from the advantages of them, such as spot welding and riveting. The FSSW process requires a certain residence time in order to adequately plasticize the material This inevitably results in burn-up of the adhesive layer, which decreases performances of the hybrid joint [29]. From [30], with permission from Springer Nature, 2020
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