aluminum finishes

[Gold Rock]

Many years ago, I machined some parts out of aluminum for my motorcycle. I had determined that having these parts anodized would be the ideal way to treat them for durability's sake. I called three different anodizing companies, and each of them declined to help me out. No definative reason. Small parts to be chrome plated, galvanized, or powder coated have never been a problem, but anodizing seemed to be different. So now I have a notion to make some boat bits out of aluminum, but assume the shadow of rejection may still be lurking in the anodizing industry. If that's the case, does anyone know of some alternative treatments for aluminum that might suit? Powder coating would possibly work, though the thickness of finish that a proper application represents might be problematic.

Chuck

[tokalou]

I had a friend who also made some aluminum parts and had the same problem as you; no one wanted to anodize just a few parts. So he searched the web and figured out how to anodize at home. I don't remember all the details but it worked out great for him. He even got the color right. A little acid, a little electricity, could be fun. So I recommend searching and trying a DIY method.
-good luck

[Gold Rock]

Good thought. I'd like to try it, but I'm a liveaboard on a thirty foot sailboat, and the thought of setting up a mini lab on the boat is, well,... I try not to think about it.

[pipefitter]

Anodizing aluminum is pretty straightforward. It can be done with a common 12v battery charger and diluted sulphuric acid. After the oxide has grown on the aluminum, it is sealed by immersing in boiling water believe it or not. Coloring is done before it is sealed. The hardest part is the polishing and buffing to a consistent mirror or scratch grained surface before the process and getting it done before it starts to gray off. In some cases, it can be chemically polished or both, depending on the quality of the material you choose initially.

If you need to get parts anodized, find out who is getting parts done and include yours in the run of their parts is how it is most commonly done. Check with motorcycle restorers, mag wheel refinishers etc.

I did some small parts some years ago. I put ping pong balls on the surface to keep the acid from fuming on everything around where I was working. The parts came out excellent. You can vary the voltage and the acid/water solution for varying degrees and brilliance/thickness of coating.

I have some fabricated hardware I want to use as trend setting ideas into some of the things I build for boats.
If you build parts that include welding, don't use 5356 filler metal as it will turn black which I found out the hard way. I think it was 4043 I ended up using.

[P.I. Stazzer-Newt]

Pipefitter is right - this is do-able domestically.

If you're not confident with the chemistry - Caswell do popular kits.
http://www.caswellplating.com/kits/aluminum.htm

[Canoez]

While you can do anodic coatings on aluminum yourself, you may want to consider going to a specialist to have it done for a few reasons.

Dyed/colored anodize can fade in the sun if it isn't done properly. There are special coatings (Type II, hardcoat, sealed, etc.) that improve the resistance of the coating to fading, corrosion, chemical exposure and other environmental attack. It's very often not an expensive process to have done on a one-off basis and the chemicals are not nice to be exposed to. If you're only planning on doing a few parts once, it's probably cheaper to pay the plater for a batch job.

[P.I. Stazzer-Newt]

Aye its cheaper - if you can find a man willing to do the job.

The risk the plating shop takes is that what the customer calls "Alumin(i)um" is undoubtedly going to be an alloy - now which one? - and how might it react?

[Canoez]

True, PISN, but if Gold Rock is going to fabricate the parts himself, I would think he'd know the alloy he was working with. Also, if he approaches the plater BEFORE he selects his alloy, he'll get better results. Some plate better than others.

Platers in our area do a lot of non-industrial work... Mostly for guys doing auto/bike restorations.

[pipefitter]

Typically, when someone chooses aluminum for marine environment, it would be the 60 series of alloys. T4-T6, with the most commonly used and widely available being 6061. 6061finishes and anodizes very well. For that bright, super chrome looking finish, the material has to be manually polished and chemically etched as well. Most aluminum that is handled at common metal distributors, will need a good degree of mechanical finishing because it will have a lot of handling scratches. Not so problematic for common hardware sized pieces but would be for full lengths of tubing say for a bow rail perhaps. Also, some of the alloys don't bend well at all, some bend in only one direction. If you are considering having to hand form parts, be sure to get an alloy that is suitable for bending etc.

[Gold Rock]

Thanks, gentlemen. The material I contemplate producing would be cast. I melt down scrap 6061-T6 plate stock, though there may be the odd bit of other stuff mixed in from time to time. I had always wondered if the specific alloy might not be significant to the plater, as I have been rejected even when I suggested that the parts could be run with anyone else's stuff. Specific appearance, at least so far, has never been a concern for me. That is, colored or not. I've always just been interested in inhibiting corrosion. The potential prorosity of a sand cast surface might be something to consider. Most prorosity is limited to only a few mls. at the surface, but sometimes buffing that out can be, uh, difficult if the part has a highly convoluted surface, which mine would. Hmm.

[P.I. Stazzer-Newt]

Long ago we used to finish sand cast bow handles where the approach was to smooth using abrasives down to about 220 grit then powder coat.

This despite having anodizing facilities and needing to send the job out. - The reason is that there is no point attempting to anodise a porous or deeply pitted surface as there will be substantial gaps in the film.