Process for brazing of aluminum alloys and a flux

Abstract

A process for brazing of aluminium magnesium alloys is described applying a flux which comprises KAlF 4 or CsAlF 4 or both as major constituent. The flux further comprises at least one alkaline or alkaline earth metal compound selected from the group consisting of KAlF 4 , CsAlF 4 , Li 3 AlF 6 , CaF 2 , CaCO 3 , MgF 2 , MgCO 3 , SrF 2 , SrCO 3 , BaF 2 , and BaCO 3 . Preferably the flux comprises or consists of KAlF 4 , CsAlF 4 , and Li 3 AlF 6 and optionally contains also BaF 2 .

1 .- 10 . (canceled) 
     
     
         11 . A brazing flux comprising, relative to the total weight of the brazing flux, equal to or more than 80% by weight of KAlF 4  and equal to or more than 1% by weight of CsAlF 4 , and equal to or more than 2% by weight of a second component selected from the group consisting of Li 3 AlF 6 , CaF 2 , CaCO 3 , MgF 2 , MgCO 3 , SrF 2 , SrCO 3 , BaF 2 , BaCO 3 , and mixtures of two or more of said second components. 
     
     
         12 . The brazing flux of  claim 11  comprising, relative to the total weight of the brazing flux, equal to or more than 80% by weight of KAlF 4 , equal to or more than 1% by weight of CsAlF 4 , and equal to or more than 3% by weight of a second component selected from the group consisting of Li 3 AlF 6 , CaF 2 , MgF 2 , SrF 2 , BaF 2 , and mixtures of two or more of said second components. 
     
     
         13 . The brazing flux of  claim 11  comprising or consisting of, relative to the total weight of the brazing flux, equal to or more than 80% by weight of KAlF 4 , equal to or more than 1% by weight of CsAlF 4 , and wherein the second component is selected from the group consisting of Li 3 AlF 6 , BaF 2 , and mixtures thereof. 
     
     
         14 . The brazing flux of  claim 11  consisting essentially of KAlF 4 , CsAlF 4  and Li 3 AlF 6  and optionally BaF 2 . 
     
     
         15 . A brazing flux composition comprising a brazing flux according to  claim 11  and at least one brazing additive. 
     
     
         16 . Coated parts of aluminum or aluminum-magnesium alloys, coated with a flux according to  claim 11 . 
     
     
         17 . Coated parts of aluminum or aluminum-magnesium alloys, coated with a brazing flux composition according to  claim 15 . 
     
     
         18 . The brazing flux according to  claim 11 , wherein a content of free KF is lower than 0.1% by weight, relative to the total weight of the brazing flux if at least one compound selected from the group consisting of LiF, NaF and CaF 2  is comprised in the flux.