Microstructure and mechanical properties of friction stir welded 6082 AA in as welded and post weld heat treated conditions

Friction stir welding of 6082 AA-T651 was performed using three different combinations of feed rates (90, 140 and 224 mm/min) and tool rotational speeds (850, 1070 and 1350 rpm). Mechanical properties of the weldments were evaluated by hardness measurements on the transverse section and tensile testing, while microstructure evaluation was done by optical microscopy and electron back scattered diffraction (EBSD). Irrespective to welding parameters the dynamically recrystallized grains in the stir zone were measured to be in the range of 2-3 mu m for different feeds rates and rotational speeds. A considerable loss in hardness in the stir zone and more severely in the thermo-mechanically affected zone was noted due to dissolution of beta' and beta '' second phase particles. A post weld heat treatment (PWHT) of 175 degrees C for 5 and 12 h was given to the weldments for all welding conditions and the mechanical properties and microstructure were re-evaluated. The hardness and strength were partially recovered and this was attributed to the possible re-precipitation of the beta '' precipitates. The grain size barely exhibited a change, whereas the texture displayed a significant diminish in the Goss orientation after PWHT. (C) 2012 Elsevier Ltd. All rights reserved.