Magnesium poisoning of NOCOLOK{sup}TM (K{sub}3AlF{sub}6-KAlF{sub}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 thattreating 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 mostcases, equal to the Mg-free materials.
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