Optimisation of Nocolok(TM) Brazing Conditions for Higher Strength Brazing Sheet 971861

In non-corrosive flux brazing the flux contains a eutectic mixture of K3AIF6, and KAIF4, which starts to melt at around 560°C. The melted flux disrupts the existing oxide film on aluminium alloys and suppresses further oxidation thus maintaining fluidity of the AI-Si based brazing alloy.
To facilitate downgauging there is a drive to develop higher strength core alloys. Using alloys with an increased level of magnesium will readily achieve significant improvements in post-brazed strength, however, the brazeability of alloys containing high levels of magnesium deteriorates as a result of magnesium reacting with the flux to form a higher melting point compound, which inhibits fluidity of the molten cladding alloy.
This paper discusses the influence of brazing conditions to increase tolerance to magnesium in core alloys. Once the optimum brazing conditions are established for varying levels of magnesium, the use of high strength magnesium containing alloys can be exploited for specific components, eg side supports and headers.


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