welding aluminum

By jwright650 (*****)

Date 01-22-2004 18:32

Hi Pete,
Did you remove the anodized finish before welding?
John Wright

By pfortin (*)

Date 01-22-2004 18:55

Thanks for the quick reply John,

Yes, the weld was stripped back a little bit, but just enough to give a small gap to fill... How far back from the weld does it have to be stripped? Is there anything else I should or can do to make the welding cleaner / easier?

Some info I maybe should have posted earlier: The material is 0.080" thick 6063 in case it helps. The weld is about 3" long.

Also, is there anything that can be done to protect the weld area from corosion? I've tried some cold galvanize sprays, but they discolor too much. It will probably be okay as-is, but I'd like to further educate myself if there are options.

Thanks,
Pete

By jwright650 (*****)

Date 01-22-2004 19:21

http://aws.org/cgi-bin/mwf/topic_show.pl?id=2529#8291
Above is a link to some other discussions on weld prep of aluminum and also machine settings to achieve a better arc for a cleaning action. Read over some of the posts and see if this is the type of info you are looking for. You may have to scroll to the top of the page to get to the first post and then read on down from there. If this doesn't help post back and someone will try and help you further.

Aluminum is a funny animal when welding, gotta get it clean and use dedicated tools that have seen only aluminum. Like a stainless steel brush used only on aluminum and then clean with acetone. Any oxidation from the anodizing needs to be completely removed from the weld prep areas.
Hope this helps,
John Wright

By pfortin (*)

Date 01-23-2004 01:36

Thanks, this is all very educational - especially the line from that last posting: "You will find with aluminum (especially castings) that "visually" clean means nothing!"

As for the process of stripping - I assume we're talking about mechanically removing the treated layer rather than chemically yes? It sounds like the acetone is strictly a cleaner, and does nothing to actually strip the anodize.

I had used a belt sander to grind away a little. Maybe this wasn't the best choice... I'll try a stainless steel brush and acetone clean tommorrow as you suggest.

Thanks again,
Pete

By LarryL

Date 01-23-2004 05:05

Getting brown areas around your welds indicates that there may have been some contamination of the weld area. Anodizing consists of the electrochemical application of 0.002" to 0.003" thickness of aluminum oxide on top of the base aluminum. Anodizing can be mechanically abraded away with a stainless steel brush but it takes a great deal of elbow grease and considerable time. Sanding or grinding off the anodizing does a faster and more thorough job but always leaves some residue of the abrasive, which in most cases is aluminum oxide. Since all aluminum oxide, whether deposited by natural weathering or by a belt sander, must be removed before TIG welding, it's best to give all areas a final brushing with a stainless steel brush before wiping clean with alcohol or acetone.

By ssbn727 (*****)

Date 01-23-2004 20:34

Hi Pfortin!
Just curious, what filler grade aluminum are you using?

By pfortin (*)

Date 01-27-2004 00:33

Hi all... I had some great success today, and I thought I'd share with you. I have a friend in forensics, but his degree is in chemistry. He gave me this tip... Dipping the end in Sodium Hydroxide (aka Lye; aka Caustic Soda), commonly found as a powdered drain cleaner, mixed with water will chemically strip the anodize. Worked awsome, first try.

Anodizing treats the aluminum with acid, so a caustic solution removed the oxidized layer.

SSBN727, I'm using 4043 as the filler.

Thanks for all you help! As a novice welder you can be sure I'll be back, this place is a great resource.

-Pete

By dee

Date 01-27-2004 02:22

Hello Pete,
Let me see how well I recall the details...
Anodizing involves the formation of of an aluminum oxide matrix on the surface of the aluminum, which matrix is naturally pourous. These pores are optionally dyed with a decorative color if desired, then sealed, which protects the substrate with a thin film of what is technically a ceramic. I believe the soda bath acts on the substrate, a detail upon which I would welcome correction. In any event, the anodized surface, I recall, is an excellent base for paint- although I am not recalling with total clarity. There are pretreatments and additives available for certain organic coatings (paint) to improve adhesion for use on aluminum, according to the coating system selected... You should be able to achieve excellent results with any variety of pigmented colors, and I suspect results would be quite acceptable if you were to strip the entire anodize film, polish and clearcoat with an appropriate coating formula. Such finishes are providing outstanding finishes and durability on brass door hardware exposed to direct sunlight and weather, as well as plumbing fittings.
Technical information on professional coatings is usually quite easily obtained from the manufacturers (eg: DuPont) but surprisingly you can learn all you need to know with the help of a local Sherwyn-Williams representative. You want a "professional coatings catalog", and not all of the coatings are available for sale in all states or to the general public. My guess is you will be selecting some kind of polyurethane based coating.

I thought that follow-up was a nice thought for all of us, and perhaps the information I have given will provide some food for conversation with your chemist friend and perhaps lead to the color solution you wanted.

It's inappropriate to apply a cold galvanizing, zinc-rich paint to the surface of aluminum. Zinc works on the surface of steel to inhibit corrosion by combining with the oxygen before the iron in the steel. It corrodes- thats what oxidation is, after all- sacrificing itself to preserve the substrate.. indeed it's classified as a sacrificial coating (as is cadmium). Aluminum on the other hand combines very readily with oxygen to form an oxide layer which, conveniently for mankind, serves as a barrier to prevent oxygen from coming in contact with the "pure" (or at least unoxidized) aluminum below. The rapid formation of this handy oxide is one of the phenomenon which makes aluminum difficult to weld.

Sorry I didnt spot this post earlier, but I hope I helped you find a more attractive coating to protect your work.
Unfortunately Ive been distracted. I had some bad news at home and the kids were quite disrought. While working on a piano restoration project our pet canary escaped, flew into a closed windowpane and fell, unconcious, into an open can of paint. Although it was a tragic loss and we'll miss him terribly, at least he had a fine finish.

Regards
d