Anodizing Aluminum to Protect Against Corrosion

Hello Francis

Try a sulphuric acid based solution, with a chromate passivate such as "anochrome" or equivalent. Any surface treatment chemical supplier should be able to help.

Todd

I agree sulphuric treatment then finish with a chromic solution.

post anodising, for resistance against sea water corrosion, a bathing in hot ptfe seals microscopic cracks in the anodised surface. Although i think the resultant finish is green!

Hi,

there are some naturally seawater resistant Al-alloys, for example aluminum with 3% magnesium.

If you want to stay with anodising its best to avoid copper and zinc contents in the aluminum.

The anodising bath will be either sulfuric or oxalic acid. The former cheaper the latter less dangerous and ready to use also in private trials. Temperature and current density are vital for success.

There are many many many different anodising solutions, there is a voluminous book on this but I forgot the title.

Never start with a fresh solution, ever add some 15% used solution.

Cooling is often useful, especially if hardness is to be achieved.

Very important: sealing is required: with steam, or with cobalt-acetate, or with impregnatings of molten wax, polyethylene or other plastics also with any type of glue to be sprayed on and then wiped off (mostly) again.

Have success

RHABE

I am a amateur in this subject. I would like to know a complete receipice. Witch voltage or witch current, witch liquid solution. I am interrest by 2 way. First corrosion resistant. second is harden alluminium.

Thanks for your help

I'm not an expert on this, but you may want to check out the alodine process for corrosion protection against seawater. It leaves the aluminum with a yellow/green coating you've probably seen on a lot of aircraft and marine products. I know that our company used it for a military contract on trim vane stiffners. It wasn't too difficult a process and I get the impression it is even easier now as I've seen some comments about brushing it on. We used a series of dip tanks. Check it out by doing a web search with just the word "alodine". Good luck.

Here are some sites with more details. For in-depth information you might have to visit the library at a college or university with an engineering school.

http://en.wikipedia.org/wiki/Anodizing

Do-it-yourself home anodizing:

http://astro.neutral.org/anodise.shtml

-Bill

What about an expoxy-based coating (speciality paint) to protect it instead?

Why use aluminium at all: would a substitute material that is not attacked by seawater be a better choice? Among the substitute metals that could be considered are CuNi alloys, Monel and Naval Brass.

What about substituting plastics? ABS and PVC are widely used for pipework containing seawater.

What about galvanic protection? Marine outboard motors are protected by a magnesium block, which forms a sacrificial anode that corrodes preferentially to the lightweight alloy (containing aluminium) from which the downshaft and propeller are often made.

A visit to a boat chandlery store may provide more options.