Flux forming an insoluble brazing residue

摘要

Aluminum parts, e.g., heat exchangers, with improved resistance towards corrosion caused by contact with stationary water or aqueous compositions such as cooling water can be obtained by addition of Li compounds in specific amounts to the flux used for brazing the parts. LiF and especially Li fluoroaluminates are very suitable. The flux and the Li salt can be dispersed in water or an aqueous composition separately.

主权项

1. A modified flux for aluminum brazing, consisting of:
a basic flux consisting of K2AlF5; mixtures of KAlF4 and K2AlF5; mixtures of K2AlF5, cesium fluoroaluminate, and optionally KAlF4; or mixtures thereof; or a precursor of K2AlF5 which forms K2AlF5 during brazing selected from the group consisting of potassium fluorozincates and K2SiF6; and a Li salt in an amount which corresponds to from 80% to 120% of the amount which is stoichiometrically needed to convert all K2AlF5 to K2LiAlF6 during brazing; and optionally a brazing metal or brazing metal precursor selected from the group consisting of silicon, copper and germanium; and which contains less than 1% by weight of K3AlF6.