Investigation of weld pool in aluminum alloys: Geometry and solidification microstructure

In the present research, weld pool geometry, thermal cycle, temperature and velocity fields during gas tungsten arc welding of aluminum alloys were predicted by solving three-dimensional equations of conservation of mass, energy and momentum under steady-state conditions. Welding experiments were then conducted on several samples with different thicknesses and chemical compositions. The geometries of the weld pools as well as the thermal cycles were measured. It is found that the calculated geometry of the weld fusion zone and the weld thermal cycles are in good agreement with the corresponding experimental results. In addition, the magnitude of the maximum velocities under different conditions were estimated to understand the importance of heat transfer by convection and the roles of various driving forces in the weld pool. It is observed that the molten metal convection strongly affects on the weld pool geometry. A two vortex pattern due to the electromagnetic force and negative surface tension temperature gradient was coexisted in the weld pool. Finally, the predictions make it possible to estimate the morphology and the scale of the solidified structure through solidification parameter such as G/R and GR. The results show that as the welding speed increases, the value of G/R at the weld pool centerline decreases and tendency to develop an equiaxed microstructure increases.