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Cleaning flux from welded aluminum joints

2003

We're a small vintage automobile restoration shop. We are having trouble thoroughly cleaning flux from gas welded joints on sheet aluminum on the bodywork of a vintage automobile. The aluminum is 1100, as is the welding rod. The flux is a private labeled product for gas welding aluminum. We are told it is the proper flux to use. I do not have an MSDS, but am told it is the equivalent of ABC #8. It does seem to perform very well. Several long welds, totaling nearly 8 feet were made, butt-joining two aluminum panels using oxy/acetylene. The welds were washed with clean water and scrubbed with a stainless steel brush. A water/ baking soda [on eBay or Amazon] solution, scrubbed with a stainless brush followed. The welds were then sanded & filed to shape. A lacquer thinner [on eBay or Amazon] wash followed Water/soda wash with brush again. At this point some parts were polished and some parts were treated with an aluminum conditioner and then primed, sealed, painted, polished to a show finish. The painted parts begin to show tiny blisters along the long weld after a couple months. The polished parts also showed tiny white, powdery pinholes. We believe we are not cleaning out the flux thoroughly. How can we improve our methods?

Tom Rasmussen
Vintage Automobile Restoration - Spring Lake Park, Minnesota, USA

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If you have access to an ultrasonic cleaning unit it should greatly speed up and improve the cleaning process. Lacking that, try pumice [on eBay or Amazon] and detergent instead of baking soda with the scrub brush [on eBay or Amazon]. That's the standard method to get a surface "assumed clean" 2hen we are trying to isolate whether a problem is in the cleaning or later in the process.

But I don't share your belief that the problem is necessarily failure to clean the flux. The fact is that aluminum corrodes if left bare, and paint will not help much either. It really needs a chromate conversion coating.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey