Experimental and Numerical Study of Heat Source Modeling for Keyhole Formation in Ti-6Al-4V Single Pass Laser Treatment

Abstract This study analyses the impact of laser surface treatment on Ti-6Al-4V titanium alloy using an air-cooled ytterbium fiber laser system. The alloy’s microstructure, consisting of α and β phases, was processed at different laser powers (80 W, 90 W, 100 W) while maintaining a constant scanning speed. Through microscopic analysis, hardness testing and phase evolution observations, the results revealed notable microstructural changes, particularly the formation of a martensitic Ti-oxide layer. Numerical simulations were conducted using the SFTC DEFORM-3D™ software, which modelled the laser heat source and thermal behaviour, along with a custom subroutine for predicting hardness and phase transformations. The study specifically examined molten pool geometry, Ti-oxide layer thickness and the hardness distribution on the treated surface. Several heat source models were tested, with the Gaussian polynomial curve model providing the most accurate results for simulating keyhole formation, phase transitions and hardness variations. The findings revealed that increasing laser power significantly affected the thermal and mechanical properties of the material, providing crucial insights for selecting the most appropriate thermal heat source model and optimizing laser surface treatment parameters for enhanced performance. Furthermore, the research proposes a new approach for modelling the heat source based on process temperature, as opposed to traditional geometric heat flux models. This study contributes to the broader field of laser-based manufacturing by advancing numerical modelling techniques aimed at improving the mechanical properties and functional behaviour of Ti-6Al-4V components.