Enhanced fatigue performance of tandem MIG 5083 aluminium alloy weld joints by heat sink and static thermal tensioning

In this work, tandem metal inert gas (MIG) welding using double torches with each torch contained a single wire feed was conducted to join AA5083 aluminium alloy plates. In order to minimise excessive welding distortion and residual stress and hence fatigue crack propagation rate due to high heat input, two methods for minimisation of welding distortion and residual stress, namely heat sink and static thermal tensioning (STT) treatments were applied during welding. The tandem MIG processes were conducted by locating two torches at a distance of 100 mm from each other with and without the treatments. Furthermore, welding distortion, residual stress, microstructure, hardness distribution, tensile strength and fatigue crack propagation were characterised and evaluated. Results showed that the use of heat sink effectively reduced fatigue crack propagation rate of the tandem weld, especially at low ΔK below 6 MPa√m. This fatigue crack propagation inhibition in the heat sink treated weld could be linked to its fine grained equiaxed structure and compressive residual stress. However, in term of welding distortion reduction, heat sink treatment seemed to be less effective compared to STT treatment. The beneficial effect of heat sink and STT in minimising welding distortion and residual stress was attributed to thermal tensioning due to temperature gradient and it is discussed in the present study