Magnesium poisoning of NOCOLOK™ (K_3AlF_6-KAlF_4) flux is a well known problem that limits material post-braze strength of aluminum heat exchangers to about 55 MPa (8 ksi). Two approaches were taken to increase Mg tolerance. First, it was discovered that filler metals containing between about 0.01% and 0.1% calcium which were clad to 0.5% Mg core alloys developed fillets that were about 300% larger than Mg-free control materials similarly brazed. Second, it was found that treating heat exchanger components in a heated bath of dilute aqueous NaF or KF solutions promoted joint formation without flux. Combining Ca-filler metals and immersion into KF or NaF solutions resulted in braze quality of 0.5% alloys that was, in most cases, equal to the Mg-free materials.
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