Keyhole formation and thermal fluid flow-induced porosity during laser fusion welding in titanium alloys: Experimental and modelling

By C. Perumal, B A. Ward, M. Turner, Chinnapat Panwisawas, B. Perumal, Mark Ward, Nathanael Turner, R. Turner, J. Brooks, Hector Basoalto. 2017

241 citations recorded by the source corpus.

High energy-density beam welding, such as electron beam or laser welding, has found a number of industrial applications for clean, high-integrity welds. The deeply penetrating nature of the joints is enabled by the formation of metal vapour which creates a narrow fusion zone known as a “keyhole”. However the formation of the keyhole and the associated keyhole dynamics, when using a moving laser heat source, requires further research as they are not fully understood. Porosity, which is one of a number of process induced phenomena related to the thermal fluid dynamics, can form during beam welding processes. The presence of porosity within a welded structure, inherited from the fusion welding operation, degrades the mechanical properties of components during service such as fatigue life. In this study, a physics-based model for keyhole welding including heat transfer, fluid flow and interfacial interactions has been used to simulate keyhole and porosity formation during laser welding of Ti-6Al-4V titanium alloy. The modelling suggests that keyhole formation and the time taken to achieve keyhole penetration can be predicted, and it is important to consider the thermal fluid flow at the melting front as this dictates the evolution of the fusion zone. Processing induced porosity is significant when the fusion zone is only partially penetrating through the thickness of the material. The modelling results are compared with high speed camera imaging and measurements of porosity from welded samples using X-ray computed tomography, radiography and optical micrographs. These are used to provide a better understanding of the relationship between process parameters, component microstructure and weld integrity.

Subfields: Computational Mechanics, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/0a4c5fbb9c71ccf85e45a397a0fea1f4dc393a1c

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Citations in the corpus

Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation (2019, background): “This figure not only shows the significant increase of fluid motion, but also demonstrates how unstable the keyhole regime is [29,30].”
Numerical analysis of heat transfer and fluid flow in multilayer deposition of PAW-based wire and arc additive manufacturing (2018, unknown): “Property, (unit) Value Solidus temperature, (K) 1878 [40] Liquidus temperature, (K) 1928 [40-41] Density at ambient temperature, (kg m) 4420 [41] Specific heat of solid metal, (J kg K) temperature-dependent[41] Thermal conductivity of solid metal, (W m K ) temperature-dependent[41] Viscosity, (Pa·s)”
X-Ray Microcomputed Tomography in Additive Manufacturing: A Review of the Current Technology and Applications (2018, unknown): “33 In another study, keyhole mode porosity was analyzed by sectioning and microCT.”
Modeling of solidification microstructure evolution in laser powder bed fusion fabricated 316L stainless steel using combined computational fluid dynamics and cellular automata (2019, methodology): “For the conventional welding simulations that involve melt pool flow, the laser power is usually represented by a volumetric heat source since it can take into account the effect of laser penetration in metals[18].”
Effect of Laser-Matter Interaction on Molten Pool Flow and Keyhole Dynamics (2019, methodology): “In the more recent multiphysics modeling of keyhole dynamics [27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39], the ray tracing model is coupled with a computational thermofluidic dynamics model and a free surface tracking model (based on level-set, volume-of-fluid, or arbitrary Lagrangian-Euleri”