Abstract
In this work, three types of probeless tools (archimedes, involute, and concave tools) were designed. A 7075-T651 sheet of 1.0 mm thickness was welded using the designed probeless tools. It was found that the stir zone and hook defect varied a lot for different joints. Plunge depth was the dominant process parameter for joint property. The joint’s maximum failure load (5.73 kN) was obtained with the concave tool when the target plunge depth was 0.55 mm. Two typical joint fracture modes (shear fracture and plug fracture) were found using three designed tools with different plunge depths, rotation speeds, and dwell times. Shoulder geometry presented little influence on heat generation. Compared with involute grooves, archimedes grooves showed to be more effective on the material flow. The properties of the joints with the archimedes tool were more sensitive to welding parameters. Compared with the flat tool, the concave tool decreased the escape of plasticized material, improved the forge force, and optimized the metallurgical bond at the interface.
Highlights
High-strength aluminum alloys are increasingly applied in the transportation and aerospace industries for their high specific strength character
friction stir spot welding (FSSW) is a variant of friction stir welding (FSW), which is suitable for lap joining of lightweight alloy sheets [7]
Several variants of FSSW have been applied for eliminating the keyhole defect, such as refill friction stir spot welding (RFSSW) and probeless friction stir spot welding (P-FSSW)
Summary
High-strength aluminum alloys are increasingly applied in the transportation and aerospace industries for their high specific strength character. FSSW is a variant of friction stir welding (FSW), which is suitable for lap joining of lightweight alloy sheets [7] This process involves the plunge, dwell, and retract stages [8]. A greatly simplified welding technique named P-FSSW was proposed by Bakavos [13] In their studies, optimum joints were produced using a short probe or a probeless. Li et al [12] employed an involute grooves tool for P-FSSW and investigated the effects of processing parameters on joint mechanical properties, microstructure, and morphology evolution. Three types of new probeless tools were designed for welding, which were two flat tools with archimedes grooves and involute grooves and one concave tool with involute grooves By using these tools, the P-FSSW processes were conducted on sheets of 7075-T651 alloy. Based on the experimental results, the influences and mechanisms of shoulder geometry were discussed and revealed
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