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A new family of Al-Si filler metals that contain low levels of Li has been developed for use in both vacuum and NOCOLOK™ brazing processes. The use of Li in the filler metal makes it possible to use the same core-clad combinations for both brazing processes; specifically, higher strength core alloys that contain up to 0.5% Mg. When a Mg-containing core alloy has been clad with the new Li filler metal and is controlled atmosphere brazed, it develops fillets that are equal to or larger than those obtained with conventional Mg-free CAB alloys. No flux penalty was observed when NOCOLOK brazing core alloys that contained about 0.5% Mg. Vacuum brazing the Li-containing filler metals clad to a 0.5% Mg-containing core alloy resulted in fillets that were 200% to 400% larger than typically observed in conventional vacuum brazing sheet that contained 0.25% Mg in the liner.

Kaiser Aluminum & Chemical Corporation, in cooperation with Ravenswood Aluminum Corporation, conducted a program to determine the optimum Mg level in aluminum-silicon vacuum brazing filler alloys. Most users of vacuum brazing sheet operate at one extreme or the other, i.e., Mg levels around 0.2% or near 1.5%. Both alloy families have problems. We fabricated and brazed several brazing sheet materials with K319 cores (similar to AA3005) and 4045 type filler metals with Mg levels ranging from 0.2% up to 2.0%. The optimum magnesium level in Al-10Si filler metals typically used in vacuum brazing applications was determined to be in the range from 0.6% to 1.0%. Filler metal Mg levels outside the optimum range result in smaller fillet sizes. Empirical data suggest that for filler metal Mg levels about 1.00%, fillet sizes are about twice those for filler metals containing approximately 0.2% Mg.