Synthesis And Melting Properties Of No-corrosive Moderate Temperature Aluminum Brazing Flux

The overburning temperatures of most of the treatable aluminum alloy are below 550℃, so the brazing temperature should between 450 to 550℃. No-corrosive aluminum brazing is a commenly used technique. The typical no-corrosive aluminum brazing is KF-AlF₃ eutectic flux, which is also called Nocolok. Its melting temperature is up to 558℃, this may cause overburning of weldments, so it is necessary to develop no-corrosive moderate temperature aluminum brazing flux.Wet synthesis is adoped to prepare a series of fluorate flux with different melting point. Material analysis methods such as XRD,SEM,DSC are adopted to analyse the chemical reactions in solution synthesis of aluminum alloy brazing fluorate flux. from quantities of Component selection experiment, two sorts of typical ternary eutectic aluminum alloy brazing flux that can be used in moderate temperature.From the study, in solution synthesis of KF-AlF₃ binary flux, K2AlF5 was first generated, then in the process of boiling down, spare AlF4- turn to the form of precipitation AlF₃. Solid state reaction was occurred between K2AlF5 and AlF₃, KAlF4 can be finally generated.For the KF-AlF₃ binary flux, separation process and pH value should match each other in order to accept precise flux. If pH value is 2-6, precise flux can be obtained by using the boiling method. By increasing the pH value up to 6, precise flux can be obtained by filtering.By analysing the melting characteristic of many groups of typical region in KF-CsF-AlF₃ ternary phase diagram, we acquire two different parts of ternary flux, they are a31(AlF₃ CsF KF)= (46 51.5 2.5),with melting interval 431.7⁴48.9℃and a31(AlF₃ CsF KF)= (41 18 41), with melting interval 496.2⁵10.6℃.The ternaty moderate temperature aluminum brazing fluxs don't absorb moist, the melting experiment and spreading experiment show that they are fit for brazing in the temperature 500℃and 550℃, and they can fully wipe out oxidation film.