In-situ observation of the wetting behavior during pw-cw-laser beam brazing

In flux-free laser beam brazing, the surface oxides of the base material and the filler wire have a significant influence on the wetting behavior. In order to achieve optimal wetting results, the surface oxides must be removed. One approach is to use a ns-pulsed laser beam source to remove them prior to the cw-laser beam brazing process. To further improve wetting, the oxides on the filler wire also need to be removed. Therefore, the pw-beam source is now also used to remove the wire oxides during brazing in a combined pw-cw-laser beam brazing process. The ns-pulsed laser beam is applied in a line and a circle across the filler wire.
The novel brazing process is observed using a high-speed camera. The camera's built-in illumination laser enables it to see through the bright process light, allowing in-situ observations of the wetting process. The experiments are conducted using a bead-on-plate brazing technique with aluminum AlSi12 filler wire and a copper Cu-OF base material. The position of the ns-pulsed laser beam is adjusted throughout the process zone, with the pulse energy varying from 120 μJ to 300 μJ. It can be observed that the ns-pulsed laser beam ablates the surface of the molten filler wire and exerts a pressure on the surface of the melt, thereby inducing a forced wetting behavior. The aim of the study is to understand the differences in wetting behavior and to obtain suitable parameters for future flux-free brazing experiments using this novel method.