Flux Activity
Flux activity is the temperature-dependent ability of a flux to reduce oxides and lower the surface tension of the liquid solder. It determines the time window for a successful brazing process.
Physico-chemical mechanism of action
Flux activity describes how well a flux reduces oxides at a given temperature and lowers the surface tension of the liquid solder. This happens through chemical reactions between the flux and the oxides on the surface of the material to be joined.
Metallurgical relevance & risks during welding
High flux activity leads to faster reduction of oxides and lower surface tension. This improves solderability and prevents porosity. However, too low an activity level can cause oxides to be reduced ineffectively, leading to poor brazing results and possible cracks.
Workshop practice & instructions
To use flux activity optimally, choose a flux with the correct chemical composition for the material to be joined. Make sure the solder temperature is within the specific activity range. If the activity level is too high, the liquid solder may evaporate too quickly, leading to insufficient sealing. If the level is too low, oxide formation may not be sufficiently inhibited, leading to porosity and cracks.