Comparison of Dissimilar Aluminum Alloys Joined by Friction Stir Welding with Conventional and Bobbin Tools

Dissimilar aluminum alloys 2024-T351 and 7075-T651 were friction stir welded utilizing a conventional tool and a bobbin-style tool. The welds produced with the conventional tool yielded higher mechanical properties than those produced with the bobbin tool, and fracture of all tensile specimens occurred on the 2024 side of theweld regardless of the tool or weld configuration. Temperature data and modeling demonstrated that the temperature distribution from either tool skews toward the advancing side. Ultimately, the mechanical properties and hardness profiles across the welds correlated with the temperature distribution and the associated precipitation behavior of the alloys. Optical microscopy revealed distinct layers of the alloys interwoven within the stir zone and identical grain sizes in both alloys. Grain boundary orientations from the stir zone followed the Mackenzie plot, suggesting complete recrystallization and a lack of texture within this zone.