Influence of water cooling on microstructure and mechanical properties of friction stir welded 2014Al-T6 joints

6 mm thick 2014Al-T6 alloy plates were friction stir welded under both normal air cooling (AC) and submerged water cooling (WC) conditions at welding speeds of 100-800 mm/min and a constant rotational rate of 800 rpm. While sound FSW joints could be produced under the investigated welding speeds of 100-800 mm/min for the AC condition, defect-free joint was only obtained under the low welding speed of 100 mm/min and higher welding speeds of 400-800 mm/min led to void defects or breakdown of welding tools for the WC condition. The FSW thermal cycle resulted in the formation of a low hardness zone (LHZ) on both retreating side and advancing side of the FSW 2014Al-T6 joints for both welding conditions. The LHZs were located at the heat affected zone and the thermo-mechanically affected zone adjacent to the nugget zone for the AC and WC joints, respectively. The tensile strength of the AC joints increased as the welding speed increased from 100 to 800 mm/min. Water cooling did not enhance the hardness of LHZs and tensile strength of FSW 2014Al-T6 joints.