When brazing, only when the molten liquid brazing material wets the surface of the base metal well can the fillet be filled. The measure of the wettability of the solder to the base metal can be expressed by the contact angle between the solder (liquid phase) and the base metal (solid phase). The main factors affecting the wetting of the base metal by the solder are:

1. Composition of solder and base material

If there is no physical and chemical interaction between the solder and the base material in both solid and liquid states, the wetting effect between them is very poor, such as lead and iron. If the solder and the base material can dissolve or form a compound with each other, the solder is considered to be able to wet the base material well, such as silver to copper.

2. Brazing temperature

升高 The increase of brazing heating temperature will improve the wettability of the brazing material to the base metal due to the decrease of the surface tension of the brazing material.

3. Surface oxide of base material

. If there is an oxide on the metal surface of the base metal, the liquid solder tends to condense into a sphere and does not wet with the base metal. Therefore, the oxide must be fully removed before brazing to ensure good wetting.

4. Surface roughness of base material

When the effect between the solder and the base metal is weak, the rough grooves on the surface of the base metal play a special capillary role, which can improve the wetting and spreading of the solder on the base metal.