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.
SS400 steel studs were joined to 5052 aluminum alloy plates by solid-state stud welding at charged voltages of 300 to 475 V. Effects of joining conditions on the interfacial microstructures and tensile fracture load of the joints were evaluated. Thin intermediate layers (Al5Fe2 and Al3Fe) approximately 1 µm thick in total were observed along the joint interface at a distance of 150 µm from both ends of the interface respectively. The tensile fracture surfaces on the stud after tensile test were covered with dimpled structures, indicating ductile fracture, with the exception of the stud tip. This indicates that the stud and plate were joined strongly enough for the base material to partially fracture during the tensile test. The fracture load increased with charged voltage up to 450 V but decreased gradually thereafter. The maximum temperature reached during joining could be also estimated by the presence of martensite near the joint interface.