Function and selection of flux
Release time:
2021-11-09 10:27
The functional parts of flux include: substrate, defilm agent and interface active agent.
The matrix is the main component of the flux, which controls the melting point of the flux, which is covered on the surface of the solder joint after melting, and plays the role of isolating air, at the same time, it is the solvent of other functional components.
The film removal agent is a physical and chemical process to remove, break or loosen the surface oxide film of the base metal, so that the molten filler metal can wet the surface of the fresh base metal.
The interfacial tension between the molten filler metal and the base metal can be further reduced by the surfactant, and the molten filler metal can be spread better on the surface of the base metal.
Function and selection of flux
Main functions of flux:
(1) The oxide on the surface of the base metal and liquid solder is removed during brazing to create conditions for the spreading of the liquid solder.
(2) Cover the surface of the base metal and filler metal with a thin layer of liquid to isolate the air and play a protective role.
(3) It plays an interface active role to improve the wetting and spreading performance of liquid filler metal on the base metal surface.
Selection of flux
(1) Match the melting point of the filler metal used
In order to cooperate with the use of solder, the melting point of the selected flux should be lower than the melting point of solder 10-30℃. If the melting point of the flux is too lower than the melting point of the solder, it is easy to melt prematurely and lead to premature failure of the active component of the flux.
(2) Select the appropriate flux according to the characteristics of the oxide film on the surface of the material to be welded
For alkaline oxide film, acidic flux should be selected; For the more acidic oxide film, the more alkaline flux should be selected.
(3) Select according to the brazing process used
According to the specific process to choose different forms of flux, such as wave welding to choose liquid flux, high frequency or medium frequency induction brazing to choose paste flux, flame brazing to choose powder flux or paste flux and so on.
(4) Select the corresponding flux according to the characteristics of the substrate of the material to be welded and the main alloy components in it
Due to the different oxide film on the surface of different matrix materials, there are also great differences in the types of flux selected, especially some difficult-to-weld metals, such as magnesium aluminum alloy, stainless steel, cemented carbide and so on. In order to ensure the weldability of aluminum alloys containing magnesium, a highly active flux is usually selected.
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