Abstract
This work systematically investigates the interface behavior and impact properties of the keyhole-free friction stir spot welding (FSSW) of a dissimilar metal AA6082-T4 Al alloy and DP600 galvanized steel. The keyhole is eliminated by pin retraction technology. The welding process is in accordance with the welding temperature curve and the maximum temperature of the periphery of the shoulder, measured at about 500 °C. The transition layers were formed at the interface, in which the Al, Fe, and Zn elements form an inhomogeneous diffusion. A cloud cluster-like mechanical mixing of the Al and steel components is formed in the stirring zone. The impact toughness of the specimen with a welding parameter of 1000 rpm is the best. To a certain extent, the factors affecting the impact energy are not the maximum impact load but the maximum impact deformation. The maximum impact deformation directly reflects the post-crack propagation energy, which significantly affects its impact toughness. In addition, the impact fracture showed a mixed ductile and brittle fracture mode with a brittle–ductile transition zone. Most of the impact energy was absorbed by the ductile fracture.
Highlights
Friction stir spot welding (FSSW) is a type of solid-state welding process that combines friction stir welding (FSW) and spot welding
Compared with solid state welding, it is easier to produce gas pockets and intermetallic compounds (IMCs) in dissimilar Al/steel joints during fusion welding, which results in a decline in the mechanical properties of joints
The joints of the dissimilar 6082 Al alloy and the DP600 galvanized steel were welded by a retractile keyhole-free FSSW machine
Summary
Friction stir spot welding (FSSW) is a type of solid-state welding process that combines friction stir welding (FSW) and spot welding. Hsieh et al [11] obtained dissimilar lap joints for a low carbon steel (SS400) sheet on a 6061-T6 Al alloy sheet, which were achieved by FSSW with a welding tool that had an independent tool pin and shoulder They found that two IMC layers, Fe2 Al5 and Fe4 Al13 , were formed at this surface, and the failure load was related to the thickness of the IMC layer. Dong et al [13] studied dissimilar lap joints of a Novelist AC 170 PX Al alloy and 1.2 mm thick ST06 Z galvanized steel sheets with RFSSW They found that the IMC layer of ZnO, which was as thin as 0.68 μm in the sleeve-plunging zone, was the weakest part of the structure. In order to determine the relationship between the microstructure and the mechanical properties of the keyhole-free FSSW joints, an impact test was carried out on the dissimilar Al/steel keyhole-free FSSW joint
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