Laser surface treatment of Ti6Al4V alloy: finite element prediction of melt pool morphology and microstructure evolution

Researchers from the University of Calabria, University of Salento, and LUM University in Italy have reported on the progress of finite element prediction research on laser surface treatment of Ti6Al4V alloy: melt pool morphology and microstructure evolution. The related research was published in The International Journal of Advanced Manufacturing Technology under the title "Laser surface treatment of Ti6Al4V alloy: finite element analysis for predicting mole pool geometry and microstructure modifications".

This study systematically investigated the effect of laser surface treatment on Ti6Al4V titanium alloy through a combination of experiments and finite element analysis. The experiment used a fixed pulse frequency and average power, and process parameters with varying laser scanning speeds (30, 45, and 60 mm/s). The heat exchange coefficient of the numerical model was calibrated by real-time monitoring of the temperature field. Metallographic analysis shows a significant increase in hardness in the remelted zone, and X-ray diffraction confirms the formation of α - phase martensite (particularly evident during low-speed scanning). After experimental data calibration, the established 3D finite element model can accurately predict geometric features such as melt pool width and depth, and effectively characterize the influence mechanism of laser treatment on microstructure and mechanical properties. Research has shown that scanning speed is a key parameter in regulating the size of the melt pool and the behavior of phase transformation, which can significantly improve the hardness and wear resistance of alloys.

Figure 1 Metallographic analysis of laser treated surface cross-section (scanning speed 45mm/s)

Figure 2 Finite Element Modeling: Trajectory of Heat Source Movement and Subsurface Heat Field Distribution in the Cross Section of the Workpiece

Figure 3a) Gaussian heat source model b) DEFORM heat exchange window c) Calibration of heat source model parameters metallographic (30mm/s)

Figure 4 Calibration process for trial and error of heat exchange coefficient

Figure 5 Numerical simulation and experimental verification of laser surface heat treatment (45mm/s)

Figure 6 Finite element prediction of molten pool morphology (45mm/s)

Figure 7 Temperature gradient and remelting layer prediction (60mm/s)

Figure 8 XRD phase analysis (60mm/s)

Figure 9 Finite Element Thermal Gradient Prediction

Figure 11: The Influence of Scanning Speed on the Geometric Dimensions of the Molten Pool

This study comprehensively explores the effect of laser surface treatment on Ti6Al4V titanium alloy, with a focus on the influence of different laser scanning speeds on the microstructure and mechanical properties of the treated surface. This study reveals the regulatory mechanism of laser scanning speed on the surface microstructure and mechanical properties of Ti6Al4V titanium alloy:

1. Control of melt pool morphology: When the scanning speed increases from 30 to 60 mm/s, the melt depth decreases by about 65%, the melt width decreases by 30%, and the thickness of the remelted layer changes relatively smoothly. This is attributed to the fact that high-speed scanning shortens the laser material interaction time and limits energy input.

2. Hardness strengthening mechanism: The nano hardness in the remelted zone is increased by 24-30% compared to the matrix, and XRD confirms that the formation of α - phase martensite is the main cause. The supersaturated phase originates from the high-temperature quenching characteristics of laser treatment, and the surface Ti oxide layer further strengthens the hardening effect.

3. Model validation: The finite element model based on SFTC DEFORM-3D is highly consistent with experimental data in predicting the geometric dimensions of the melt pool, melt depth, and remelted layer thickness, successfully reproducing the temperature gradient and phase transformation behavior during the processing.

The experimental numerical joint analysis method established in this study provides a reliable tool for optimizing laser surface treatment processes, which helps to improve the mechanical properties and corrosion resistance of Ti6Al4V alloy in industrial applications. The research results have deepened the understanding of laser surface modification technology and have guiding significance for improving the performance of titanium alloy components in aerospace, biomedicine and other fields.

Source: Yangtze River Delta Laser Alliance