Aluminum in Marine Environments

usualy suppliers have such data,

I would probably lean toward anodizing (you can get a heavy coat version, too), that is what beach chairs do, but why not pick up the phone and call a number of marine shops and ask the owners what works and what doesn't?

Second, maybe go to a marine store and look at the products they sell and what they are made of.

Even aluminum will corrode over time, but chances are you can learn something from other manufactures in the marine business that will give you a jump start.

As the first answer stated, check with the aluminum supplier for information. They should have technicians that can answer that question.

Personally, I would consider using steel or aluminum coated with a heavy vinyl plastic layer to prevent contact of the surface with damp saly air.

Why aluminum over stainless? Huntco sells stainless, and the company I work for installs these in the marine construction we do. http://huntco.com/mercantool/mtool.pl?command=productpage_list&category=2

That is a very good question.

The biggest reason for the aluminum is that I want to use an extrusion in the design.

The application is a bike rack.

Montie

I don't think it will last very long on a beach...think sand blasting and salt spray.
I wouldn't touch it with a barge pole...
If it needs coating then it's the wrong material!
I'll wager 100 Quatlous that Oak or Teak would outlast aluminium, and probably look just as good.... hmm maybe cost more tho'

Del

I agree that Teak, etc. may be a better product. BUT! Mass production, cost, reliability, production ease, resistance to salt, resistance to sand, resistance to sand fleas, mosquitoes, old hags, raucus kids that want to hang on to them, perverts that want to use them for ulterior purposes, etc., etc. dictates a definite lean toward the aluminuminuminm that poster suggests.

Besides, who, in their right(?) mind would use a beautiful piece of teak for a bike rack? Absurd!

I have been told aluminum windows do not do well in coastal area with a lot of salt spray. Salt water acts as an electrolite to speed corrosion. The paint starts to peel off at the cut ends as the aluminum corrodes out from under it. Salt crystallizes in the corroded aluminum under painted surface forcing the paint to peel back. Anodizing and painting will help. A epoxy base paint that can with stand the abuse of use is needed. Any scoring of the paint leaving exposed aluminum will start the corroding process and the paint peeling.

Using an epoxy-based paint seems to be a common theme. From what I am reading, aluminum boat hulls use epoxy paints.

Thanks for the feedback.

Montie

I would probably go with powder coating versus anodizing. Anything that will be bolted to the rack may cause galvanic corrosion. Some of the work we did with NOAA for bouys required powder coating vs. any other coating. If you have to drill the aluminum to bolt or fasten the rack to another item (bumper) you should try to isolate from other metals to increase the life of the rack.

Talk to your extruder about the suitability of alloys 5083, 5086, 6061 and 6063. He may have other suggestions also. Clear anodizing is common on polished aluminum such as tuna towers. Any paint or coating is going to extend the service life of your product over the same product unpainted or uncoated. It's wise to make sure you get the entire product coated such as by dipping. I've seen some products dipped in a vinyl type of coating that gave it a soft surface that was very resistant to normal abrasion and chipping. Hope this helps.

Look into powder coating, but be sure the powdercoater knows what he is doing. Aluminum should be chem filmed before powdercoat. Anodize is good, but you still must protect end cuts, and rivet and screw holes where the anodize has been cut through.

In my humble opinion. If you are fabricating a small batch of these bike racks, stainless steel will not change the TOTAL cost for you to manufacture them drastically. But if you plan to sell hundreds of them, The additional cost saving of powder coating will probably be required to have a marketable product. Good luck.

Thanks for the feedback.

Montie

Try designing one out of PVC water pipe (the thick one) I have made furniture, hose brackets (wall mount) and several other items with it. It's easy to work with, not to expensive and no rust. Support the bike in areas where heavier pipe can be used.

The plastic is an excellent idea. I have been buying some mounting products that are made from plastic. Some kind of polyethylene. Not as stiff as metal, but absolutely weatherproof.

Maybe a heavy cross section molded from recycled plastic.

I have been sailing catamarans (Hobie Cats) for years and I also live on the beach. My boat (When not in the water) sits behind my house, on the beach in Newport Beach, Ca. U.S.A. The mast is extruded 6061T6 Alum. and does get a little oxadation but has lasted for years.

Have you considered a fiberglass pultrusion with stainless joiner plates? Relatively lightweight and should withstand the environment for years without any maintenance and you can maintain the use of a common profile.

Any suggestions for vendors for the fiberglass pultrusions?

Montie

I've used GlassForms in the past. F.B. Wright also has a good reputation.

Thanks.

Montie

In industry we have used racks made from steel cold rolled sections.They are powder coated for longer life. Paint mfrs have special paints for sea corrosion. Also these sections have punched holes so you can change the compartment size in future. They are assembled with galvanised fastners which are corrosion proof. Advantage of such racks will be cost benefit, and stronger material. There are many mfrs. of such racks through out the world.

I believe you should have a serious look at aluminum - reasonably hard - 6061 tops and have it hard anodised up to 70 microns - will be expensive - virtually scratch proof.

The catch is that its colour varies between olive drab (light and dark) and shades of grey.

It will be quite dark between the 50 o 70 micron range.

Make sure that you have done all the drilling, threading and machining you want done before the anodising takes place, minimising spot and places open to the atmosphere.

Make sure that when you assemble use nylon and tuffnol washers and have the bolts and nuts anodised as well.

This approach will ensure a very hardy and long lasting surface in the marine environment. Just or very close to as good as stainless steel.

Make a prototype, sort out all the small little glitches and problems before starting with mass production so that you can do a good costing exercise before venturing on the real thing.

Good luck

sias

First thought that comes to mind is WHAT KIND of Aluminum. I would guess that less than 5% of aluminum used is pure aluminum. It comes in various alloys depending on requirements such as strength, corrosion resistance, weldability, machinability, ability to anodize, etc. You might want to Wiki "aluminum alloys" to get an idea of what is available, and these are standard well defined alloys. The "Mag wheels" which we ran on our cars as youngsters were actually aluminum with a high degree of magnesium in the mix. You can imagine the environment which they went through. I can't tell you the alloy number though.

We use alloy 6061 for radio antennas which are out in the weather, with no protection from the weather. I have heard of no problems with any of these in a marine environment.

I think that with the right alloy, you might be able to get away with little or no protection and save on steps in the manufacturing process. Also, if feasible, I think I would anodize. It is the forced oxidation of the outer molecules of the aluminum, and I believe I read that it is actually harder than the aluminum itself. I know it is harder than paint.

Have fun!!

Bill