TWI

Friction stir welding experiments were undertaken on rolled plates (thickness 25.4 mm) of AA 6061-T6 aluminium alloys to investigate the role of backing plate material on thermal gradient changes in the through-thickness direction. Welding was performed using an hydraulically powered MTS process development system using forge force control. Bead-on-plate welds were produced at a rotational speed of 480 rpm and a welding speed of 3.4 mm/s on ceramic tile, titanium, steel and aluminium backing plate materials with widely varying thermal diffusivity. Thermocouples were employed to measure stir zone temperature during welding at the midplane height and near the probe tip corresponding to the weld root. Optical microscopy was used to observe microstructure and grain size. Microhardness tests were conducted using a Vickers hardness indenter on naturally aged and heat treated samples. The performance of a "composite" backing plate, comprising a longitudinal strip of steel and two side plates of aluminium, is discussed.

9th International Symposium, 15-17 May 2012, Session 3A: Weld Performance, Paper 04