aluminum hand rail coating

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I'm starting an aluminum handrail for a house boat. The old one was all mangled. The customer asked if there was a way to prevent the black residue from getting on the dock fenders, his hands, and other things. Aside from painting (too much maintenance) and anodizing (too expensive), are there any other alternatives? The material is 6063 aluminum square tubing and it will be tig welded. I'll post pictures as I progress.Man invented metal, he can do whatever he wants with it.KMAC
Reply:Powder coat. Other than that, the best fix is an alloy with some chromium and nickel, like 304......... If you paint it, use zinc chromate primer, and then use a one part urethane by Interlux. It is much better paint than anything you will ever get at home depot, or Dunn Edwards.
Reply:Why not stainless steel?  The savings from no coating (initial and maintenance) might pay for it.
Reply:Hey KMAC,I faced a similar problem about 15 years back; the aluminum hand rail running around the bow of my newly purchased used boat was scratched, pitted, salt water corroded, etc. along with the chrome plated zinc fittings.  I replaced the fittings with new ones and then went to work on the aluminum hand rail.Home made anodization - worked for me.PreparationThe aluminum tubing was about 3/4 inch diameter, maybe 10 to 12 feet long in a big loop.  First, I used dry sandpaper #120 my hand and a twisting motion to scratch up and remove the old anodizing.  I think I then switched to wet paper #220 and did it again.  I likely went as low as #600 eventually.   OK - then I switched to a metal shinning paste (something like Chrome Brite from Canadian Tire Store).  By the time I was done, the aluminum handrail looked like a mirror - perfect.Except - if you handled it, your hands became black!Anodization   I read about the process. Basically you usually need to immerse the piece in a bath of dilute sulphuric acid and run direct current through the piece - the piece being the +ve anode (hence anodization).Practical Application:  I went to Canadian Tire and got about a pint of fresh battery acid (sulphuric); they got the acid around for car batteries.  I diluted that about 4 or 5 to one.  I wasn't about to immerse my big loop rail!  I used a plastic trough that folks use when applying wall paper - trough was about two feet long and 4 inches deep.  I half filled that with diluted acid.For a power source, I used a power supply I had built years before - metered volts and amps, 0 - 30 volts and 0 - 1.5 amps.  Note: You don't need a lot of amps for what follows - too many amps and you get a milky, not clear, finish.  Try to stay below 1 amp for the brush technique.  In your case, you could use a 12 volt battery or a battery charger - just be certain to add a resistor to limited the current to about 1 amp or so.  I placed a battery charger clamp (+ve) around one end of the handrail.Brush TechniqueThe cathode (-ve) is a foam brush!  You know those foam brushes they sell for painting?  In my case, I think I used a 1.5 or 2 inch wide one.  I opened the back of the split foam and worked out the plastic form attached to the wooden handle.  It looks like an open 'D' with some barbs on it.  I duplicated that form and handle (without the open hole) in aluminum sheet.  I replaced the wooden handle and plastic form with my aluminum sheet one.  I connected the -ve of my power supply to the end of my aluminum foam brush.To anodize, I would have the aluminum rail loop sitting in the tray/trough and I would dip the foam brush in the acid and paint the portions of the aluminum handrail that were not submerged in the acid in the tray.  The tray was only serving as a basin and to catch acid drips.  I had to manipulated the loop around as I went.  It is better to to 'paint' the whole thing a few times than to try and stay in one region to long.  It is weird because it is like you are painting with invisible paint!  There a few, if any bubbles visible (else your current is too high).  As I recall, the process took about 40 minutes.Tips: At first I had too high a current and got milky appearance.  I had to start over - yes redoing the wet sanding and polish - so don't use too much current.  Anyway, with patience, the end result should look exactly like what you started with!   except it won't blacked your hands!   In my case, I retained a factory-look, mirror-like finish that does not blacken hands.  15 years later, the handrail looks like the day I put it back on the boat.  Oh yeah, make certain you wear rubber gloves and wear safety glasses!  (Wear old clothes too - acid drips.)Note: Anodization is like a clear coat - your base has to be perfect.  Any visible imperfection (scratches, etc) will show. Anodization is not like paint; it will not cover up imperfections.Welds:  Here is where you may have a problems.  I am not certain if different alum alloys touching side-by-side especially like in a weld will anodize the same way.  You might want to run a test.I hope that helps - good technique/capability to have in your tool bag! Rick V
Reply:Thanks guys. I'll run it past the customer and see if he wants the extra protection. I've never done acid before, I look forward to testing it out!Man invented metal, he can do whatever he wants with it.KMAC
Reply:be aware if you are going to anodize, use 5356 for better color matching. Silicon based fillers, like 4043, will darken.