TWI

The effects of multiple overlapping friction stir weld runs (with 100% overlap) on the welding parameters and weld properties during the repair of high-strength AlCuMgZn alloy were investigated. Square butt welds were made in 7050-T7451 alloy (Al, 6.2%Zn, 2.3%Mg, 2.3%Cu, 0.12%Zr, 6.4 mm thickness), with welds overlapped to produce material that had been welded between one and seven times. Process parameters were constant for runs 1-5; tool rotation speed and traverse speed were decreased for run 6 and 7. Welds were allowed to cool for one hour between runs. Following 2 weeks of natural aging, each weldment was heat treated at 121 deg.C for 24 h. The microstructure, hardness, transverse and longitudinal tensile strength, ductility and fracture path of the stir zone and welded joint were determined. Peak temperature during welding was assessed using a K-type thermocouple spot welded into the probe of the welding tool. Modification of the morphology of the intermetallic phases and restoration of the stir zone ductility resulting from the use of lower weld power is discussed.

8th International Symposium, 18-20 May 2010, Session 7B: Aluminium and Repair, Paper 02