Synchrotron X-ray observation of flow evolution during fusion welding.

Joining materials together is an integral part of the chemical, energy, and automotive industries. Fusion welding with Tungsten inert gas (TIG) process normally uses a non-expendable electrode to weld materials and is widely adopted in modern design due to its stability and versatility. The molten metal flow in the weld pool has an immediate impact on the performance of the welded part by affecting the heat transfer, chemical element distribution, and defect formation. The prediction accuracy of the final microstructure and properties can be improved by understanding the evolution of flow in the melt pool. However, the complexity of the process as well as the limited real-time experimental data availability with comprehensive internal flow behavior considerably hinders accurate modeling and predications of the weld pool. To overcome this issue, we demonstrate the quantitative mapping of the weld pool flow using high-energy synchrotron X-ray imaging. Our X-ray imaging approach with the tracking particles allowed us to visualize the flow evaluation across the weld pool over the solid-liquid-solid transformation. Experimental results indicated the flow patterns are progressively becoming complicated with the expansion of the melt pool. Our flow analysis in conjunction with the variation of the driving forces suggests that gravity-derived buoyancy has a significant effect on fluid flow at the melt pool boundary.