Numerical simulation and experimental results were employed for the identification of the most vulnerable zones in three-pass cold-metal-transferring （CMT） welded joint. The residual stress distribution in the joint was predicted by finite element （FE） method, while the structural morphology of distinctive zones was obtained through metallographic experiments. The highest principal stress made the symmetric face of the joint most sensitive to tensile cracks under service conditions. Whereas, the boundaries between the weld seam and the base plates were sensitive to cracks because the equivalent von Mises stress was the highest when the first interpass cooling was finished. The third weld pass and the inter-pass remelted zones exhibited the modest mechanical performances as a result of the coarse grain and coarse grain boundary, respectively. The most vulnerable zones were regarded to be the crossed parts between the zones identified by numerical and experimental methods.
A required finite element method（FEM） model applicable for narrow gap CMT and CMT＋P MIX welding was established based on the interactions between arc,base metal and filler metal.A novel method of simplifying wire feeding pulses and heat input pulses was supposed under the conduction of equivalent input.The method together with composed double-ellipse heat sources was included in the model.The model was employed in the investigation of thermal cycling and the identification of the softened zone of AA7A52 base plates.Low-frequency behavior emerged in the form of low-cooling rate sects,which were not expected under experimental conditions.The softened zone including the quenched zone and averaging zone of the base plate was much wider internal the base plate than that close to the surfaces.The reliability of the predictions in thermal cycling was supported by infrared imaging test results of the thermal cycle process.
