Unraveling Microstructure Evolution Induced Mechanical Responses in Coaxial Fiber-Diode Laser Hybrid Welded Fe-36ni Invar Alloy

Abstract

Invar alloys, renowned for its ultra-low coefficient of thermal expansion, are qualified for widespread use in aerospace applications. This study explores the utilization of fiber-diode laser hybrid welding in Fe-36Ni Invar alloy, specifically focusing on addressing the undesirable microstructure and properties arising from unstable molten pool and high-temperature gradient encountered during single fiber laser welding. Experimental and simulation analyses were conducted to systematically explore the influence of diode laser power on the microstructure evolution and mechanical responses of fiber-diode hybrid laser welded Invar alloy joints. Results indicate that the addition of diode laser could notably widen the keyhole opening and improve the molten pool stability. An acceleration of dynamic recrystallization is observed in the weld seam, with a significant increase in high-angle grain boundaries. Moreover, with increasing diode laser power, temperature gradient decreases, leading to the formation of numerous equiaxed grains. Electron backscatter diffraction (EBSD) results demonstrate a considerable enhancement in the intensity of the γ texture, particularly the {111}<110> texture. Comparatively, fiber-diode laser hybrid welding exhibits superior plasticity and tensile strength over single fiber laser welding. This research can improve Fe-36Ni Invar alloy quality and performance through fiber-diode laser hybrid welding, making it more suitable for aerospace applications.

Keywords: Fiber-diode laser hybrid welding, Fe-36Ni Invar alloy, numerical simulation, Microstructure, mechanical properties