Effect of wavelength on fusion-zone geometry, cooling rate, and solidification parameters during keyhole mode laser welding of pure copper

For the laser welding of pure copper, laser wavelength and absorptivity significantly affect keyhole formation and melt pool geometry. Different wavelengths and absorptivity are applied to achieve the desired melt pool geometry and the part’s mechanical properties. Here, we investigate the influence of wavelength on the melt pool geometry, cooling rate, solidification parameters, and keyhole stability during the keyhole mode laser welding of pure copper. A mechanistic model combining heat transfer and fluid flow is tested by experimental data and then applied to calculate the melt pool, cooling rate, and solidification parameters under different process conditions with varying laser wavelengths. We find that under the same laser welding process condition, a short laser wavelength with high absorptivity can generate a large melt pool depth and width with a deep steep and unstable keyhole, a small cooling rate, and a solidification parameter. A long laser wavelength with a low absorptivity can improve the keyhole stability by producing a small size melt pool and a shallow keyhole. In addition, we generate process maps to show the integrated influence of laser wavelength and heat input on the melt pool depth and width. The melt pool depth and width can be increased by reducing laser wavelength or increasing heat input (high ratio of laser power to welding speed). Moreover, this well-tested mechanistic model can capture the complex influence of laser wavelength and power, welding speed, and material properties on the melt pool and keyhole geometry, which can be applied to estimate the fusion zone for other laser welding processes using different alloys.