Liquidus in the pseudo-ternary system AlF3-KF-KCl was investigated by thermal analysis. The aim of the study is to modify and improve the Nocolok flux used in aluminum brazing. The mentioned ternary system is divided into three sub-systems: K3Cl3-K3F3-K3AlF6, K3Cl3-K3AlF6-KAlF4 and K3Cl3-KAlF4-AlF3. Ternary eutectics were observed in each sub-system: E-1 located at 2.5 mol% AlF3, 44.7 mol% K3F3 and 52.8 mol% K3Cl3 at 584degreesC; E-2 at 61.7 mol% AlF3, 26.5 mol% K3F3 and 11.8 mol% K3Cl3 at 534degreesC; E-3 at 63.7 mol% AlF3, 20.7 mol% K3F3 and 15.6 mol% K3Cl3 at 541degreesC. A mixture with the composition of point E-2 seems to be a good substrate for aluminum brazing flux since this lowered the melting temperature of the Nocolok flux from 558 to 534degreesC. (C) 2003 Elsevier Science B.V. All rights reserved.