TWI Industrial Member Report Summary 692/1999
W M Thomas and M F Gittos
Friction stir welding (FSW) tools and conditions have been developed to allow the butt welding of 25mm thick 6082 and 7075 aluminium alloy plate.
Friction stir welding was invented and patented by TWI in 1991. A rotating tool with a central probe is pressed into the components to be welded and traversed along the joint line forming a solid phase weld.
Although FSW can be applied to a number of metals - including Pb, Zn, Mg alloys, Cu, Ti and steel - it has been applied to-date predominantly for the welding of Al alloy sheet and plate. The latter has been facilitated by a TWI Group Sponsored Project which has developed tools and procedures for welding 1.5-12mm thick aluminium alloy sheets and plate at speeds of up to 6.6 mm/sec (400 mm/min) for 6.4mm plate.
Only limited work has been conducted on the welding of thicker aluminium alloy plate (>12mm). Results for FSW of 50 and 75mm thick 6082 (T6) Al alloy plate were first presented by TWI in 1998. Welds were made in one and two passes at ~1 mm/sec (60 mm/min) using two tools - a slender TrifluteTM and a more robust WhorlTM tool. Both tools incorporated threaded probes with re-entrant shoulder scoops. Because of the limited scope of this work, further work has been conducted to establish welding tools and conditions for these thicker materials.
To develop further the WhorlTM and TrifluteTM family of tools and to establish high speed welding conditions to give one pass butt welds of acceptable quality in 25mm thick 6082 (T6 condition) and 7075 (T73511 condition) aluminium (the former being easier to weld by FSW than the latter).