Abstract
In welding processes, solidification is very specific. This phenomenon leads to high grain growth rates, in presence of high temperature gradients and strong fluid flows in the liquid, that can change the solidification mechanisms.This work investigates the coupling between fluid flows and solidification mechanisms, related to welding parameters, at weld pool scale (macroscale) and at grains scale (microscale).An experimental study is carried out, based on in-situ observations of a fully penetrated weld pool, generated on a thin Cu30Ni plate with a GTAW torch in two configurations :a static configuration generating an antisymmetric weld pool and a translating configuration generating a weld bead.For each configuration, the solidification morphology and the fluid flows in the solidification front area are observed at microscopic scale, with a high speed camera coupled with a high magnification lens.At macroscopic scale, the whole weld poll is observed with an infra-red camera and two cameras in visible range.We can then obtain on one hand the temperature field on the bottom of the plate and on the other hand the weld pool boundaries on the top and the bottom of the plate.The synchronised observations give access to an important quantity of data allowing the discussion of the interactions between solidification mechanisms and fluid flows for several welding conditions.Finally, the experimental results are compared to theoretical results obtained from analytical and numerical simulations, in order to discuss the possible limitations of models and try to better understand the analysis.