TWI

With regard to the occurrence of residual oxide defects associated with friction stir welding (FSW) of aluminium alloys, an investigation is presented into a possible alternative mechanism for oxide formation within the weld nugget involving enhanced oxidation on interior surfaces at elevated temperatures (above 400 deg.C) during FSW resulting from entrained air entering the seam gap. FSW experiments were performed on AA 2219-T87 aluminium alloy panels (thickness 9.5-15.9 mm). Butt joints were fabricated using a Legio machine at a pinch force of 0.9-2.2 kN and a weld pitch of 6.4-8.72 rev/mm. Macrostructures and microstructures were observed by optical microscopy, field emission SEM and energy dispersive spectroscopy. Tensile tests were conducted in displacement control at room temperature. Issues discussed include liquation at grain boundaries and oxidation rate acceleration in areas of localised liquation.

11th International Symposium, 17-19 May 2016, Session 9B: Microstructure and Dissimilar, Paper 03