Friction stir welding of thin 1050 aluminum sheet by heat assisted tool

Abstract

The objective of the present study is to relieve the friction stir welding (FSW) tool from one of its main role: to generate heat by friction. 1-mm-thick 1050-H24 aluminum sheets were friction stir welded using a heater-embedded FSW tool. It is demonstrated that butt welding of the sheets becomes successful even at a low rotational speed of 60 rpm under the assist-heating of the FSW tool. The fact indicates that it is possible to weld without frictional heat. Sound joints with the highest average fracture strength, which is equivalent to that of the base metal, was obtained under the welding speed of 0.5 mm/s and the tool rotational speed of 60 rpm. The temperature of the sheet does not exceed 400 K throughout the welding under this condition. This temperature is 60 K lower than the ordinary FSW in which assist-heating is not used. One of the microstructural features in heat-assisted FSW is that the widths of heat affected zone (HAZ) and thermo-mechanically affected zone are suppressed, compared to the ordinary FSW. Particularly, HAZ becomes almost negligible. The hardness profile shows the maximum at the stir zone without revealing HAZ softening.