The Development Of Brazing Flux Of Aluminium With Low Point And No Corrosion

Aluminum and its alloys are more widely used in various industries due to the excellent performance, especially in the aviation and aerospace field. Aluminum brazing connection is an important method of welding deformation with small size and high precision. Brazing flux is often used in brazing to clean the oxide film on the surface of aluminum alloys and reduce the molten solder and the interfacial tension between the base metal. Potassium aluminum fluoride flux is nonhygroscopic and no corrosion, it is widely used as aluminium and aluminium alloy brazing.However, the scope of its use has been limited because of its high melting point. In this study, the aim is to decrease the melting point by adding a third component to KF-AlF₃ flux. The results reveal that the brazing flux of the low melting point and non-corrosiveness can be obtained through increase the content of KBr. Besides, DSC, XRD analysis and a group of experiments of brazing performance show that the flux reached the lowest melting point 522.1℃when KBr is 20wt%, consisting of KAlF₄, K3AlF₆, KAlBr₄. A principal reason of the low melting point may attribute to the ternary eutectic of KAlF₄-K3AlF₆-KAlBr₄. Owing to the excellent spreadability and clearance fillability, improved ability of striping the flux can be used in aluminum alloy braze welding of low melting point.X-ray analysis of the clearance mechanism on surface of pure aluminum to AlF₃-KF flux and new AlF₃-KF-KBr flux indicate that AlF₃-KF-KBr flux resulted in the oxide film loosen, broken and completely been destroyed with reacting to the flux. And the product is a layer of uniform, dense KAl₅O₈ and Al₅O₇Br membrane, which prevented the exposed aluminum from a further re-oxidation. It also deliver that the clearance of oxide film with AlF₃-KF flux reined by the K₃AlF₆ reacting with Al₂O₃ instead of KAlF₄ to ensure mobility of the flux. Brazing on surface of 6063 aluminum alloy with AlF₃-KF-KBr flux demonstrates that the new AlF₃-KF-KBr flux is difficult to clean MgO film, which leaded to a poor brazing property of 6063 aluminum alloy. However, the property can be improved with the oxidation film well cleaned by adding CsF to AlF₃-KF-KBr flux.