The d0-distribution in Al-2024 friction stir welds

Neutron and synchrotron radiation have been employed to create 2D maps of the variation of strains and the unstrained lattice spacing d0 in longitudinal and transverse direction over a cross-section of a friction stir weld (FSW) of an aluminium alloy AA-2024. Strains have been measured directly in the FSW using neutrons. The variation of the unstrained lattice parameter has been measured with synchrotrons on specially prepared stress-relaxed ‘combs’ of the original weld. The variation of d0 across the weld varies on the same scale as the strains on a magnitude of ~1000 µ;epsilon; thus influencing greatly the magnitude of inferred residual stresses in the sample. Both the d0 variation and strain map show detailed features reflecting the characteristic microstructure generated during the welding process. In particular, they are asymmetric about the weld centre-line. The dominant longitudinal residual stress field is tensile beneath the edge of the tool and compressive in the weld centre-line. Transverse stresses are smaller by a factor of 3 and tend to be compressive. Stresses measured by diffraction agree well with results from conventional holedrilling performed in the same sample. © 2001 OPA (Overseas Publishers Association).