A Closer Look at Aluminum Brazing

May 05, 2017

On a basic level, brazing aluminum is similar to brazing other base metals.  However, aluminum’s low melting temperature, lower melt temperature brazing alloys, and specialized fluxes make brazing aluminum a unique process.

3000 series aluminum is the most frequently brazed aluminum base metal, but certain 6000 series aluminum may also be used.  Very few cast aluminum and 5000 series alloys can be brazed, and extra care must be given during the brazing process to insure success.

Brazing filler metals must have the AWS BAlSi classification.  These brazing alloys are comprised of pure aluminum alloyed with copper and silicon, which lower the melting range of aluminum, and are able to melt below the solidus of brazeable aluminum base metals.  Alloys intended for brazing in vacuum contain magnesium to help break down oxides.

Brazing flux must be used in all brazing processes except in vacuum.  Aluminum fluxes are available in powder or dispensable paste form, in corrosive and non-corrosive formulations.

ChannelFlux® aluminum brazing alloys are designed to present aluminum brazing alloy and non-corrosive flux in a flexible and durable matrix, allowing for the manufacture of preforms without compromising the integrity of the flux in the channel.  Additionally, the flux in ChannelFlux® is non-corrosive; brazed parts need no post-braze cleaning.  ChannelFlux® saves brazing operators time by eliminating the need to flux parts or clean parts after brazing.

Because of the low melting temperature of aluminum base metals, tight process control is necessary to minimize braze failure.  In addition to directing the heat appropriately, a precise amount of flux must be used when brazing.  Because flux is pre-measured and placed in channeled wire, ChannelFlux® also lends itself to the tight process control required for aluminum brazing.

In addition to brazing aluminum to itself, it may also be brazed to dissimilar metals like copper, titanium, and cobalt.  Many other alloys can be pre-coated with nickel to allow for brazing. ChannelFlux® ZA-1, an alloy of zinc and aluminum, is designed to address the challenges presented when brazing copper to aluminum transition joints with different thermal expansion rates.

Learn how to make a repair with ChannelFlux® ZA-1 on our videos page.  Call Bellman-Melcor for technical support and guidance on your upcoming aluminum brazing project, to see which ChannelFlux® alloys are right for you, or click here to get a quote.