Effect of Tool Pin Thread Forms on Friction Stir Weldability of Different Aluminum Alloys

The primary objective of this study is to investigate parametric effects of pin features on material flow and friction stir weldability of two different aluminum alloys. A series of bead on plate friction stir welds were made on two different aluminum alloys (AA 7050 and AA6061) with cylindrical tool pin having four thread pitches (1.02 mm, 1.41 mm, 2.12 mm & 3.18 mm) including smooth/unthreaded pin attached to an unvarying single scrolled shoulder geometry. Welds were performed under a range of process parameters (welding & rotational speed). It was observed that thread forms are obviously beneficial for improving tool performance and reducing in-plane reactions (X & Y forces) forces on tool. Wormhole defects in the weld nugget were eliminated or minimized by employing threaded pins as a consequence of effective material transportation near the weld root. Tool pins having intermediate thread pitches (1.41 mm and 2.12 mm) perform better than either extreme over the range of attempted parameters. Defects are far more prevalent in 7050 welds than in 6061. In-plane reaction forces on pin are significantly larger in AA7050 welds than in AA 6061 and torque- peak temperature values are of similar order in both welded materials.