TWI

An investigation was made of approaches to tool design for the self reacting pin tool (SRPT) (bobbin tool) to mitigate the effects of friction stir welding owing to enlarged grains that occur in large structural extrusions, in order to yield acceptable mechanical properties. A FSW machine was developed with dual opposed SRPT heads to simultaneously weld both sides of the extrusion. Self reacting friction stir development welds were produced in aluminium alloy 7249-T6511 extruded plate (Al, 0.12-0.18%Cr, 1.3-1.9%Cu, 2.0-2.4%Mg, 7.5-8.2%Zn), 7.36 mm thickness, as part of preliminary process development work in order to establish the approximate process parameters and tool designs that would be utilised in a later project involving FSW of large extruded beams. A design of experiments approach was used to screen performance of each tool design using a pin material MP-159 coated in TiN-ZrN. Welded samples were examined for microstructure and microhardness. Tensile tests were conducted to examine ultimate tensile strength (UTS), yield strength and fracture mechanisms. UTS was examined as a function of tool offset.

8th International Symposium, 18-20 May 2010, Session 4A: Process Development, Paper 03