Effect of static magnetic field and laser parameters on microstructure and tensile properties of laser-deposited GH4169 alloy

Laser Metal Deposition (LMD) has shown significant potential for manufacturing aeroengine components. However, defects such as microporosity and inhomogeneous microstructures—resulting from ultra-high temperature gradients within the molten pool—restrict the mechanical properties of the components. This study investigates the combined effects of processing parameters and a static magnetic field (SMF) on the microstructure and tensile properties of laser-deposited GH4169 alloy, utilizing both experimental and numerical simulation approaches. Numerical simulations indicate that SMF can significantly suppress Marangoni convection by virtue of the Lorentz force. This suppression in turn enhances the temperature gradient between the middle and bottom regions of the molten pool, while effectively reducing the maximum melt flow velocity at the top of the molten pool—ultimately creating a favorable environment for the epitaxial growth of columnar crystals. Experimental results show that it significantly reduces porosity at higher energy densities by weakening molten pool convection through Lorentz forces, while potentially increasing porosity at lower energy densities. The presence of the SMF also promotes the epitaxial growth of columnar dendrites, resulting in increased primary dendrite spacing, grain size, and aspect ratio. Tensile tests demonstrate that the SMF reduces the room-temperature yield strength but enhances elongation, shifting the fracture mode from a mixed failure mode of “microvoid coalescence ductile fracture + intergranular fracture” to predominantly microvoid coalescence ductile fracture. This study highlights the optimization of material defects and mechanical properties through magnetic field regulation, providing valuable guidance for high-quality metal additive manufacturing of hot-end components.