A cooling rate analysis in the gas tungsten arc aluminum alloy welding

Abstract

This work presents an analysis of the heat transfer by convection and radiation during a GTA (Gas Tungsten Arc) aluminum welding process. The authors in-house C++ previous developed code was modified to calculate the amount of heat transfer by convection and radiation. In this software, an iterative Broydon-Fletcher-Goldfarb-Shanno (BFGS) inverse method was applied to minimize the amount of heat delivered to the plate when the appropriate sensitivity criteria were defined. In the software, the thermal properties were considered temperature-dependent. The methodology was validated by accomplishing lab controlled experiments. In order to improve the study, four positive polarities conditions were tested during the lab experiments. Due to some experimental singularities, the forced thermal convection induced by electromagnetic field and thermal-capillarity force could be disregarded. Significant examples of these singularities are the relatively small weld bead when compared to the sample size and the reduced time of welding process. In order to evaluate the local Nusselt number, empirical correlations for flat plates was used. The Nusselt number was applied to estimate the local heat transfer coefficient h. The presented method solved the thermal problem satisfactorily. The numerical cooling rate analysis presented the same pattern for all experimental conditions. The Free Convection proves to be the dominant effect in the cooling rate after the welding torch is turned off. However, the thermal radiation emission plays a major role on the cooling process while the GTA torch is on. The thermal radiation emissivity reaches this peak at the end of the welding process. The study also found that the heat losses by convection and radiation of the weld pool do not affects significantly the cooling process.