Study of friction stir welded butt joint of aluminium and stainless steel

Abstract

For application purposes, conventional welding involving liquid state joining of two dissimilar materials is undesirable due to poor weldability caused by differences in chemical, mechanical, and thermal properties of the welded materials, as well as the formation of large quantities of hard and brittle intermetallic phases, resulting in a reduction in the welded joint's mechanical strength. Friction stir welding (FSW), an energy efficient and environmentally benign solid state joining procedure pioneered by The Welding Institute (TWI) of Cambridge, England in 1991, has been developed to address this issue. FSW seems to have a number of benefits over traditional fusion welding processes, including the lack of expensive consumable filler materials, the result is strong mechanical and metallurgical qualities of resultant joint and the lack of contamination. Friction stir welding has been used to make a butt joint between plates of AA 6061-T6 aluminium alloy and AISI 304 stainless steel. Different combination of rotational speed and welding speed has been used in order to achieve optimum weld. Welding speed of 40 mm/min, rotational speed of 700 RPM, tool offset of 0 mm, and tilt angle of 2° produced the best weld. The ultimate tensile strength of the optimal weld was 80 percent of the 6061 aluminium alloy weld material. According to microscopic examination, the best weld interface was free of intermetallic and had a serrated profile, resulting in a very high mechanical strength when compared to other weld specimens. The weld was also discovered to be cracked at the heat affected zone, which had the lowest hardness value. The fracture surface of a tensile specimen exhibits bimodal fracture behavior.