Fengyuan Shu

FEM modeling of softened base metal in narrow-gap joint by CMT+P MIX welding procedure

Abstract 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.

Prediction of vulnerable zones based on residual stress and microstructure in CMT welded aluminum alloy joint

Abstract 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.

Effects of Different Filler Metals on the Mechanical Behaviors of GTA Welded AA7A52(T6)

ER4043, ER5356, and AA7A52 on behalf of the Al-Si, Al-Mg, and Al-Zn-Mg-based welding material, respectively, were chosen as the filler metal to weld AA7A52(T6) plates by GTAW. The variance in mechanical performances of the joints caused by the various filler materials was investigated with reference to the SEM and EDS test results for the weld seam and the fracture surface. Failure was found in the seam for all the welded joints. With regard to the joint obtained with ER4043 welding wire, the total elongation was limited by the brittle intergranular compound Mg2Si of which Mg was introduced by convection mass transfer. As for the other two welds, the content ratio of Zn and Mg was found to play the dominant role in deciding the mechanical properties of the intergranular Mg-Zn compounds which were responsible for the tensile behavior of the joints. The content ratio (wt.%) of beyond 2:1 gave birth to the strengthening phase MgZn2 leading to a ductile fracture. Cr in the seam obtained with AA7A52 filler metal was found to enhance the strength of the joint through isolated particles.