Processing-property correlation in friction stir welds

Friction Stir Welding (FSW) is a relatively new process for joining of metals. The process was invented in 1992 at The Welding Institute, Cambridge, UK. FSW is particularly well suited to use in highly alloyed aluminum because it is a solid state process; therefore, no undesirable, brittle, low-melting eutectic phases are formed during the welding process. The microstructure of a typical friction stir weld is that of a wrought product. The details of the weld formation mechanism have been the subject of some debate. Previous work on elucidation of flow patterns in friction stir welds indicated that the process may be described as an in-situ extrusion. Material flow in two friction stir welds produced using different welding parameters was visualized using embedded marker materials and the fidelity of the visualization technique was demonstrated. Flow of material in the friction stir welds was observed to depend strongly on the temperature of the weld. In this paper, welding temperature measurements are combined with tensile test data to further promote understanding of the process in 2XXX, 5XXX, 6XXX, and 7XXX series aluminum alloys. Weld parameters (spindle rotation rate and welding speed) and time-temperature histories are correlated with the global and local tensile properties, and microstructure of the resulting welds.