Role of Beam Manipulation on Keyhole Stability and Defect Formation during the Laser Welding of Aluminum Alloys

During high power laser welding, laser beam energy densities above 10⁵ W/cm² result in the evaporation of alloying elements and the formation of a deep and narrow vapor cavity, known as a keyhole. The prevalence of keyhole collapse defects in laser welding has largely been material dependent, with aluminum alloys and austenitic stainless steels displaying a particular propensity for keyhole collapse porosity, impacting the structural integrity of these welds. In order to achieve defect free single pass welds with high process efficiencies, an improved understanding and control of this keyhole stability is needed. Improvements in the mitigation of the formation of keyhole collapse porosity in electron beam welding have also been achieved through the manipulation of the electron beam energy source. Manipulation of the beam in this manner primarily impacts the shape and size of the molten pool and the predominant convective fluid flows generated by the large thermal gradients formed during the welding process. The dynamics of keyhole formation with beam manipulation become more complex when considering the combination of flow of molten metal in the weld pool and two-phase mushy zone, melting, solidification and heat transfer in the weldment, and the solid state phase transformations. A combined experimental and numerical modeling approach was used to develop an improved means for controlling keyhole stability during the laser welding of aluminum alloys.