GB802483A - Improvements in or relating to method of dip brazing aluminous metal - Google Patents

Abstract

A molten salt bath for brazing comprises 2-70 per cent total of at least one of the following salts: beryllium chloride, magnesium chloride, calcium chloride, strontium chloride and barium chloride, and 30-80 per cent total of at least one of the salts, potassium chloride and sodium chloride, the total of all the said chlorides constituting the major portion, preferably at least 90 per cent, of the bath, and the bath is activated by at least periodically passing a direct current therethrough to liberate nascent chlorine. Calcium chloride preferably forms 20-40 per cent, strontium chloride preferably forms 2-15 per cent, and beryllium, magnesium or barium chloride preferably form 10-30 per cent total, with the total of these chlorides being preferably 20-70 per cent. The total of the salts potassium and sodium chloride is preferably 50-80 per cent. Lithium chloride up to 25 per cent, preferably 0.2-2 per cent, may be included as may 0.5-10, preferably 2-5, per cent of at least one of beryllium fluoride, magnesium fluoride, aluminium fluoride and the double fluorides of aluminium and alkali metal or alkali metal fluoride and aluminium fluoride in the proportions necessary to form the double fluoride. Examples of the baths has the following percentage compositions: (a) 35 NaCl, 65 CaCl2; (b) 15 NaCl, 41 KCl, 30 CaCl2, 6 SrCl2, 8 Na3AlF6; (c) 0.5 LiCl, 22 NaCl, 46 KCl, 29 CaCl2, 2.5 Na3AlF6. The bath may be treated with gaseous hydrohalide, viz. hydrogen fluoride and/or chloride, before or at the same time as the application of current. The hydrohalide may be bubbled through the bath, possibly diluted with helium, argon or nitrogen or may be added as a decomposable halide, e.g. ammonium chloride. Specifications 539,337 [Group XXII], 744,862, and U.S.A. Specification 2,602,413 are referred to.