Numerical analysis of magnetic-controlled periodic solidification pattern in deeppenetration laser beam welding of aluminium alloys

• Applicant: Dr.-Ing. Marcel Bachmann
• Subject Area: Joining and Separation Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551161340

In this project, a multi-physical coupled numerical model will be developed to describe the influence of an external magnetic field on the periodic solidification pattern in high-power laser beam welding of 10 mm thick AlMg3. Since it is impossible to eliminate all reasons for the detrimental periodic solidification pattern to achieve a stable equilibrium, a new strategy, in which the magnetohydrodynamic (MHD) technology will be implemented to control the periodic solidification pattern in the weld to realize a refinement and homogenization of the grain distribution and to improving weld performance, is proposed in this project. A computational fluid dynamics (CFD) model that comprehensively considers the relevant factors affecting periodic solidification will be established in this project for the first time. Two novel models regarding the influence from the vapor plume and the metallurgical influence from the mushy zone will be developed and integrated into an existing well experimentally validated multi-physics model. A model of the metal vapor plume effect related to the welding parameters and the magnetic field parameters will be established to describe the periodic effect of metal vapor on the laser source, so that the periodic oscillation of the molten pool originating from the keyhole is expected to be realized in the CFD model. Based on the calculation results of dendritic growth in a phase field method (PFM) model at different characteristic positions, a relationship function between the mushy zone parameters and the distance from the solidus will be established and used in the LBW CFD model for the first time, and the influence of the thermal electromagnetic Lorentz force on this relationship will be considered with applying a magnetic field. With the accompanying welding tests (magnetic flux density up to 500 mT and frequency up to 5 kHz), the temperature measurements, the microstructure characterization and the mechanical testing, the proposed model will be validated and the hypothesized factors that lead to the periodic solidification mode, i.e., uneven heat source and recoil pressure, thermal capillary effect, the effect of periodic metal vapor plume, and instability of the solidification process will be quantitatively calculated and evaluated. Combined with the numerical simulation results, the effects of different periodic driving forces (recoil pressure and Lorentz force), capillary effect (Marangoni force) the effect of plume, and mushy zone parameters (solidification rate difference at different stages) in the LBW process of improving the mechanical properties of the joint by controlling the periodic solidification mode will be analyzed. The effects of different welding parameters (laser power and welding speed) and magnetic parameters (frequency, magnetic flux density and rotation angle) on the mechanical properties of the joint will be summarized to give guidance for proper welding parameter selection.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Michael Rethmeier