Thermography analysis and porosity formation during laser beam welding of AA5083-H111 aluminum alloy

Abstract

In this work, the thermal characteristics of the weld pool during Yb:YAG laser welding of the AA5083-H111 aluminum alloy were captured using an infrared thermal imaging camera and a numerical model was developed to predict the temperature fields using COMSOL Multiphysics software. On comparing the measured and predicted temperature of the weld pool surface, the deviation was below 10 °C and the average experimental error was not more than 1%. It shows the reliability of IR camera used in this investigation. Also, it was apparent from the thermal images that at a higher beam power, an erratic molten pool was created due to the instability of keyhole and spatters were ejected from the molten pool. The higher recoil pressure built at the walls of keyhole due to the high intensity of the laser beam and instigation of the ejected fluid flow mechanism was responsible for this occurrence. Also, the formation and floating mechanisms of process-induced porosities were analyzed. Porosities were identified in the weldments processed with longer shielding gas blown distance (30 mm), whereas other welds had no porosities. Since the gas blown distance was more, gas pressure over the molten pool was not sufficient to suppress the plasma plume and, thereby, results in porosity formation. Interestingly, a high number of porosities were evident at the toe of the weld bead and it was assumed to be caused by the high thermal gradient-induced Marangoni flow. This study provides a better understanding of molten pool behavior, porosity formation and its floating mechanism.