Neutron Diffraction Analysis of Residual Stress in Double-Acting Friction Stir Welded Aluminum Alloy AA1100

Friction Stir Welding (FSW) is a solid-state joining process widely used for aluminium alloys due to its ability to produce high-quality welds with minimal defects. However, welding thick plates remains a challenge for conventional FSW due to limited heat input and insufficient material mixing. Double-Acting Friction Stir Welding (DA-FSW) addresses these issues by using two opposing tools to enhance heat generation and material flow through the full plate thickness. This configuration creates a complex thermo-mechanical environment that can significantly affect residual stress—key to dimensional stability, distortion, and fatigue life. Despite growing interest in DA-FSW for thick-section welding, studies on residual stress are still limited. This research investigates residual stress distribution in AA1100 aluminium joints welded by DA-FSW using neutron diffraction on the ENGIN-X beamline at ISIS. Plates (8 mm thick) are welded with varying tool offsets (0 mm and 2 mm) and rotation directions (clockwise–clockwise and clockwise–counterclockwise). Residual stress is measured in three orthogonal directions at 18 points per sample using a 2×2×2 mm³ gauge volume. Neutron radiography on the IMAT instrument further visualises post-weld material flow to correlate with residual stress patterns.