Flux powder for brazing aluminum material and process for producing the flux powder

Abstract

A flux powder which has satisfactory spreading properties when used in brazing magnesium-containing aluminum materials. It is noncorrosive, highly safe, relatively inexpensive, highly economical, and generally usable extensively. It is an improved flux powder for use in the brazing of aluminum materials having a magnesium content of 0.1-1.0 wt.%. It comprises KAlF4, K2AlF5, and K2AlF5H2O. It is characterized in that it has composition in which the K / Al molar ratio is 1.00-1.20, the F / Al molar ratio is 3.80-4.10, and the total content of K2AlF5 and K2AlF5H2O is 6.0-40.0 wt.%, with the remainder being KAlF4, and that part or all of the crystal structure of the K2AlF5H2O is at least one of K-deficient type, F-deficient type, and K- and F-deficient type crystal structures.

Description

technical field [0001] The invention relates to a flux powder suitable for brazing magnesium-aluminum base materials and a preparation method of the flux powder. Background technique [0002] For a long time, aluminum-silicon (Al-Si) eutectic alloys, which have a slightly lower melting point than the aluminum-based materials, have been used as solders in the brazing of aluminum-based materials. In order to make the solder and the aluminum-based material bond well, it is necessary to remove the oxide film formed on the surface of the aluminum-based material, so a fluoride-based flux is used to remove the oxide film. Among them, including potassium fluoride (KF) - aluminum fluoride (AlF 3 ) complex (potassium fluoroaluminate) non-corrosive flux, which has the following excellent properties: it can be directly coated or spread on the surface of aluminum-based materials, it can be processed continuously in a nitrogen atmosphere furnace, brazing The flux film is stable after so...

AI Technical Summary

Problems solved by technology

[0004] However, the aforementioned KF-AlF 3 Flux-like fluxes have the disadvantage of not showing sufficient performance when brazing magnesium-containing aluminum-based materials

[0006] Therefore there is the following problem: currently used flux, when brazing the aluminum-based material containing Mg, needs to coat about 5 times the amount of coating when brazing the aluminum-based material that does not contain Mg, otherwise it will not be possible. There is a problem that the oxide film on the surface of the material cannot be removed until the expansion is sufficient

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