TWI

Electron backscattering diffraction (EBSD) was employed to examine the grain refinement during rapid cooling friction stir welding of commercially pure copper sheets (thickness 2 mm) and the application of a liquid CO₂ cooling technique to reduce the post-annealing effect was investigated. Experiments were conducted using a WC-based tool with a concave shoulder and rapid cooling equipment placed behind the rotating tool with a movement speed the same as the welding speed. Welding was performed at a traverse speed of 150 mm/min and a tool rotational speed of 800 rpm. EBSD analysis of plan-view sections near the keyhole was undertaken to reveal the grain structure evolution surrounding the rotating probe. The formation of high dislocation density ultrafine grains in the stir zone and their freezing by liquid CO₂ cooling are discussed.

10th International Symposium, 20-22 May 2014, Session 10B: High Temperature, Paper 03