The authoritative public forum
  for Metal Finishing since 1989
-----

Torch brazing of aluminum, removal of white (flux) residues

 

This problem relates to torch (flame) brazing of aluminum assemblies (6061) and post braze residues. The brazing process yields a thin white residue around the fluxed areas. This is present after boiling off the flux and the subsequent clean in nitric acid. It is a side effect of using the flux but I understand not particular to this brand of flux. I have referred this matter to the makers of the flux who said it was just one of those unfortunate side effects. Ultrasonics will not remove the residue (a timescale that will not damage the part), nor will very lengthy immersion in nitric acid. The only method so far is to do a mechanical action, either wiping or shot/bead blasting which is obviously very inefficient. I am looking for a cost effective cleaning method, ideally a quick and simple chemical dip.

If anyone has any suitable ideas I would be extremely grateful.

Ian Walker
- UK

---

March 25, 2009

Dear Ian Walker,

There are two basic types of flux for aluminum brazing, corrosive and non-corrosive. Residues from the non-corrosive type are insoluble in most substances and are removed mechanically. Residues from most of the corrosive type fluxes are water soluble and will certainly come off in diluted nitric acid. HTH

Roger Barker

Roger Barker
- Willoughby, Ohio, USA