Expedient protective coating for aluminium?

This topic has 14 replies, 9 voices, and was last updated 10 April 2015 at 12:35 by Mark P..

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9 April 2015 at 20:10 #185938
Ian P
Participant
@ianp
At short notice I have to design, make and finish some aluminium parts for three days hence. Ideally these would be hard anodised because they are going to be used in sea water for a few hours. Once they have served their initial purpose I will have chance to get them back, refinish, and then have them anodised.

Painting is not really suitable because some in places there are close fits against movable parts.

I know its possible to do DIY anodising and I probably have suitable power supplies, but apart from the chemicals I doubt I will have enough time to get everything together and learn how to do it!

Is there some chemical I can dip them in to give at least some short term protection?

Ian P
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9 April 2015 at 20:10 #23808
Ian P
Participant
@ianp
Not enough time for anodising
9 April 2015 at 20:29 #185942
JasonB
Moderator
@jasonb
Will a few hours exposure be worth worrying about?
9 April 2015 at 20:29 #185943
Mike Clarke
Participant
@mikeclarke87958
Hi,

I make lots of aluminium parts that are used in fresh water (lakes). I have used this in an emergency, where like you it's not possible to get parts anodised in time:

It's not great, but might just offer the few days of protection you need. Like a lot of things, cleanliness is key to good coverage. Instructions also mention applying wax post-treatment – which might be good for your application(?).

Regards,

Mike.

Edited By Mike Clarke on 09/04/2015 20:31:02
9 April 2015 at 21:03 #185957
Ian P
Participant
@ianp
Posted by JasonB on 09/04/2015 20:29:00:

Will a few hours exposure be worth worrying about?

I have been surprised just how fast aluminium disappears once corrosion starts. The main problem is that stainless steel fastening are used and those in contact with stainless are just about optimum for galvanic action.

If salt water is washed off immediately after use, refinishing the parts to get them properly anodised later would be OK, in reality though the usage is out of my hands so by the time I get them back some of the machined surfaces have pock marks and cavities that wont clean up without removing more metal is available ('O' ring grooves and the like)

Ian P
9 April 2015 at 21:08 #185958
Ian P
Participant
@ianp
Mike

That looks a possibility so I will try and see if I can get hold of some in time.

Thanks for suggesting it.

Ian P
9 April 2015 at 21:38 #185965
Michael Checkley
Participant
@michaelcheckley34085
We use Alocrom 1200 to give a protective coating on areas of aluminium parts that dont need a more 'tough' finish. Its normally a process we outsource but it is available as a 'touch up' that I have used on parts that have been modified exposing the natural aluminium. No idea how well it would work exposed to sea water but it is a good finish used prior to anodising so you could do a proper job later.
9 April 2015 at 23:21 #185973
jason udall
Participant
@jasonudall57142
not so much a coating but..

if submerged would an anode in this case… magnesism..

(kinky naughty canibals must ask zombies for supper..)

serve?..

bolt on some sacrifical blocks ….if only a few days then might not need too large…

effective ness would depend on alloy of ali used..since some already have high magnesium content…

failing all other attempts.. grease works as barrier..

..even on stainless.. a4(316 s11) which isn't if submerged more than 100 m for 2 weeks….don't ask'…
10 April 2015 at 09:19 #185990
john carruthers
Participant
@johncarruthers46255
Know anyone with an oxygen bottle? fresh ally oxidises really fast to Al2 O3, tough stuff.
10 April 2015 at 11:37 #186003
Speedy Builder5
Participant
@speedybuilder5
Alacrom was good enough for the TSR2, Concorde, VC10 etc. If a small packing piece was fabricated by the 'fitters', it would be dipped / painted with the Alacrom acid and just wiped clean on a cloth some minutes later and then fitted to the aircraft. I don't remember any special washing procedure. It leaves the aluminium with a nice golden finish.
BobH
10 April 2015 at 11:50 #186005
Ian P
Participant
@ianp
Posted by Speedy Builder5 on 10/04/2015 11:37:08:

BobH

'Alacrom was good enough for the TSR2, Concorde, VC10 etc.'

Yes, but look what happened to all those!

Ian
10 April 2015 at 11:57 #186006
Ian P
Participant
@ianp
I have just had a fruitless phone call regarding getting Alocrom 1200 and been told that apart from the fact its too expensive for an individual to purchase, it needs special equipment and a trained person to apply it.

On Monday I will call the anodising company I use as they offer an Alocrom finishing service.

Ian P
10 April 2015 at 12:22 #186007
Neil Wyatt
Moderator
@neilwyatt
Sounds like it contains chromate, even the small amounts in cement are controlled as it is a health hazard.

Neil
10 April 2015 at 12:24 #186008
Michael Checkley
Participant
@michaelcheckley34085
I imagine the proper dipping process is one you would not want to do in your kitchen The brush on stuff used here in the workshop is a bit more practical for small areas, I guess it depends on how much you wish to apply….

If it was me I would get someone else to do it and being a standard process usually has a quick turnaround. Anodising can be slower as it is specific to the customers requirements.

…..yes it is a chromate conversion process.

Edited By Michael Checkley on 10/04/2015 12:26:40
10 April 2015 at 12:35 #186009
Mark P.
Participant
@markp
We used alacrom 1200 on aircraft skins, quite simple to use cover area to be treated with tissue paper brush the liquid onto the paper leave for a short time10-30 mins remove paper job done, must be degreased before hand nice yellow tint to the ally. Don't use on mag alloy use selienium acid.

Mark P.
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