Analysis of residual stress in metal-inert-gas-welded Al-2024 using neutron and synchrotron X-ray diffraction

A combination of neutron and synchrotron X-ray diffraction was used to measure and map the full three-dimensional state of residual stress across the cross-section in coupon samples of metal-inert-gas (MIG)-welded 2024 aluminium alloy. Samples were analysed both as-welded and following a post-welding skim which served to remove the weld flash and reduce the plate thickness. The profile of the residual stress and its evolution following skimming has been accurately characterized. The longitudinal direction shows the highest residual stress, approaching 300 MPa in tension. The skimming treatment did not change the peak stress, but the overall profile of stress was altered: this is slightly unexpected as machining away stressed material would generally be expected to reduce the peak residual stress. The results are discussed in terms of the generation of stress during welding and its evolution during skimming. Finally a comparison is made with the stress generated in the as-welded and skimmed conditions of a variable polarity plasma arc (VPPA)-welded specimen of similar dimensions, to show the effects of different weld processes on the residual stress generated. The stress measurement in the VPPA sample was carried out under near identical experimental conditions.