TWI

Low temperature post weld ageing heat treatment, with and without deep cryogenic pretreatment, was applied to friction stir welded joints of 2024-T351 (Al, 4.3%Cu, 1.6%Mg, 0.7%Mn) alloys, and the microstructure and mechanical properties of the joints were investigated. 2024 alloy sheets (thickness 2 mm) were butt welded using an FSW-3LM-2010 machine at a rotational speed of 1500 rpm and a travel speed of 200 mm/min. The post weld heat treatments comprised low temperature ageing at 120 deg.C for 8 h, deep cryogenic treatment at -196 deg.C for 24 h, or a combination of the two. Microstructures and the evolution of precipitates were examined by optical microscopy, SEM, energy dispersive spectroscopy and differential scanning calorimetry. Mechanical properties were characterised by Vickers microhardness measurements and tensile tests. Fracture surfaces were observed by SEM. The effects of the heat treatments on soft zones, tensile properties and precipitation are discussed.

10th International Symposium, 20-22 May 2014, Session 9A: Techniques III, Paper 02