A new technique of filling friction stir welding (FFSW) relying on a semiconsumable joining tool has been developed to repair the keyhole left at the end of friction stir welding (FSW) seam. The conventional nonconsumable tool of FSW was transformed, and a semiconsumable joining tool consisting of alloy steel shoulder and aluminium alloy joining bit was designed to create a solid state joint. Using the combined plastic deformation and flow of the consumable joining bit and the wall of the keyhole, the FFSW process is able to repair the keyhole with both metallurgical and mechanical bonding characteristics, and the FSW seam can be achieved without keyhole or other defects. The relative tensile strength and elongation of the FFSW joint are 84?3 and 98?9% of the base weld without defects respectively.
Dissimilar alloys of Ti-6Al-4V and 5A06 Al were butt joined by Al based fillers using a novel TIG welding process, referred to as keyhole arc welding-brazing. The flow behaviour of weld pool was introduced, which was characterised by the formation of a keyhole under the tungsten electrode. It was found that porosity tended to be produced in the middle of the fusion line, while adding elements prevented its formation. At brazing interface, interfacial reaction at root face was enhanced, and a uniform serrated layer, identified as TiAl 3 , was obtained by pure Al fillers. When Al-Cu-La fillers were used, block Ti 2 Al 20 La phases appeared at the interface between the TiAl 3 layer and the brazed seam. Compared to joints brazed by pure Al fillers, the formation of Ti 2 Al 20 La reduced the hardness of the interfacial layer by more than half, while Al 2 Cu increased that of the brazed seam by y50%. The tensile strength of Ti/Al joints reached 270 MPa.
In the present work, 7?8 mm thick AA 2219 rolled plates were successfully joined without keyholes using semiconsumable tools by filling friction stir welding (FFSW). The shoulder further effect was performed to enhance mechanical stir, and mechanical properties were enhanced effectively. The results showed that the bonding interface of AA 2219 bit and keyhole is defect free. The softened region on the advanced side is the weakest part of FFSW joint rather than the bonding interface of the keyhole. The average ultimate tensile strength and elongation are 172 MPa and 11?2%, equal to 90 and 82% of the base weld without defects respectively. Excellent bonding interface and mechanical properties of FFSW joints have been exhibited.
In the present work, we design a novel tool called self-support FSW (SSFSW) with adjustable dip angle to join the aluminium hollow extrusion. This tool consists of a big concave upper shoulder and a small convex lower shoulder. Compared with conventional FSW, it eliminates root flaws and does not need backing bars during operation. In particular, the SSFSW can adapt to variation of thickness and does not need predrilled pilot holes, resulting in simplifying the welding process compared with the bobbin tool FSW tool. Significant changes are observed at the cross-section of the SSFSW joint, which looks like a 'waist'. The average tensile strength and elongation of 6005A aluminium alloy joint with a thickness of 5 mm is 190 MPa and 6?86% respectively. Furthermore, the failure of specimen presents a ductile fracture in the typical joint.
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