Influence of the depth of scroll grooves of the shoulder and welding pressure on temperature distribution and material mixing during FSW of AA6063 aluminum alloy sheets

The aim of the work was to investigate the effect of the scroll groove depth and welding pressure on the temperature distribution and material mixing in pinless friction stir butt welding of AA6063 aluminum alloy sheets using the method of mathematical modeling. The tool was a shoulder with two scroll grooves, the depth of which varied from 0 to 0.5 mm with a step of 0.1 mm. Modeling showed a significant effect of the groove depth on the temperature distribution and the formation of surface defects. The maximum temperature and the largest area of strong heating were observed at a groove depth of 0.2 mm, which ensured a complete connection of sheets at a welding pressure of 12.5 MPa. The effect of the groove depth on the magnitude and distribution of temperature was explained based on the concepts of the action of two material heating mechanisms: 1) frictional heating and 2) heating from plastic deformation of the material volume. Strong and uniform heating at a groove depth of 0.2 mm was achieved by summing the heat from frictional heating and heat from plastic deformation. A full-scale experiment using a shoulder with a scroll groove depth of 0.2 mm showed good agreement with the simulation results.