Friction Stir Welding and Hybrid Laser Welding Applied to 6056 Alloy

Abstract

Innovative welding processes are continuously gaining industrial interest. Both friction stir welding (FSW) and hybrid laser welding (HLW) are automated welding processes which allow achieving high quality joints in aluminium alloys, in combination with a high productivity. The EN AW-6056-T4 alloy is a relatively recent high strength weldable AlMgSiCu alloy, which is used in aviation. This alloy was subjected to FSW and HLW. The optimisation procedures which were used for FSW and HLW to assess the most appropriate welding parameters are discussed. A comparison is made between the mechanical properties in the as-welded and in the T78 post-weld heat treated (PWHT) temper. Concerning the friction stir welds, the PWHT only caused a decrease of the elongation after fracture; the thermal treatment had no effect on the minimal hardness zones of the weld, hence the tensile strength did not change. The hybrid laser welds however showed a significantly higher tensile strength after PWHT, but this was also accompanied by a ductility loss. Fatigue testing was performed on the PWHT welds. Friction stir welds clearly possessed better fatigue properties than hybrid laser welds.