NOCOLOK flux aluminium brazing technology have been the first choice for more than 25 years in the production of aluminium heat exchangers and other components. NOCOLOK is more than just a flux. This page gives you access to details you need for successful aluminium brazing. To find out all you need to know to achieve successful aluminium brazing visit www.nocolok.com, the Aluminium Brazing Blog or go to our download section.

Successful Aluminium Brazing – a Guide

This guide sets out how to best select and use materials, temperatures, markers, flux, solder and filler alloy. The most competent way of joining aluminium components together is brazing with flux and solder.

Solvay Fluor is proud to be the market leader of long standing: we have collected our many years of experience with NOCOLOK flux into a single file.

"7 Steps to Successful Aluminium Brazing"

1. Select the right alloy at controlled atmosphere conditions

You can download a table of suitable and classified aluminium alloys here. Alloys of 2xxx, 5xxx, 7xxx and 8xxx are not suitable for brazing with non-corrosive fluxes. The only exception is alloy 7072.

2. Clean the surfaces

Dust and dirt, condensates, lubricants and oils must be thoroughly removed. If the metal work pieces are poorly prepared, the flux will not spread evenly and the flow of filler alloy will be haphazard: it will either not spread properly or will discolour. The consequence would be an incomplete joint. The first step is therefore: always clean the components of all oil and grease. The surfaces can be cleaned using either chemical, water-based or thermal cleaning techniques and substances.
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3. Remove the oxide layer

Successful aluminium bonding requires prior removal of the oxide layer. NOCOLOK Flux in the molten stage partially dissolves and removes oxide layer from the metal surface. The metal surface is therefore cleaned by the flux itself, leaving the surface ideally prepared for the filler alloy to join the metal work pieces. Therefore it is of primary importance to provide flux to the brazed joints.

4. Choose the right flux and the right filler alloy

When brazing with NOCOLOK Flux, a typical filler alloy is a fusible alloy of aluminium and silicon. There are many different filler alloys available: furnace brazing uses mainly filler alloys with 6.8 to 8.2 per cent Si (AA4343) and also 9 to 11 per cent Si (AA4045). For further applications

5. Select capillary size (gap)

Making a perfect joint requires the components to have the right capillary gap. Only if the gap is correct will the filler alloy spread when molten, by capillary action. Filler alloy, but not an excessive amount, must be available to fill the joint. It is necessary to have intimate contact between the two components to be joined and the filler metal at some point along the joint. A common phrase to emphasize this point is that "filler metal can run, but it cannot jump". This contact point is what initiates the capillary flow of the filler metal.
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6. Apply sufficient amounts of flux

In practice the recommended loading for fluxing is 5 g/m2, uniformly distributed on all active brazing surfaces. To visualize what 5 g/m2 flux loading might look like, think of a very dusty car. As the heat exchange manufacturer gains experience with his products, he may find that a little more is required for consistent brazing or that he can get away with a little less flux. Find out exactly how much solder you need either from the detail PDF or by talking to our experts.

7. Heat metal components evenly

Achieving an even temperature distribution of 600°C throughout the work pieces is an important factor in controlled atmosphere brazing. Slow heating ensures even temperature distribution and a consistent bond. Caution: Heating too slowly can dry out the flux, which reduces its effectiveness. There must be sufficient molten flux present when the solder reaches its melting point. As a rule, the heating cycle should be as fast as possible to achieve stable temperature distribution.

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