Solidification of GTA aluminum weld metal: Part 2 - Thermal conditions and model for columnar-to-equiaxed transition

In this study, the influence of solute content and heat input on microstructure was investigated for gas tungsten arc (GTA) bead-on-plate welding of the aluminum alloys 1050A (Al 99.5) and 6082 (Al SilMgMn). Temperature measurements in the solidifying weld pool showed that parameters such as solidification growth rate, cooling rate, local thermal gradient, and solidification time vary significantly along the solidification front (between weld centerline and weld interface). As a result, the obtained thermal data were used to explain the corresponding grain morphology from the first part of this study. On the basis of this comparison, an analytical approach was used to model the transition from columnar-to-equiaxed grain growth (CET). This model allows the prediction of critical values for both solidification growth rate and thermal gradient, at which the CET occurs.