It has been shown that high power welding hardly affects the quality of the seam welds and brings out many defects such as porosities in the material. The aim of the study is to investigate and model the porosities forming and trapping at the end of a laser pulse, in the case of tantalum Nd:YAG laser spot welding. So we focused on the solidification stage of single spot welds and we developped a simple model that helps to understand how little porosities can be trapped in the welded zone. The results are in good agreement with the experimental data observed on tantalum and stainless steel.

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