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Galvanic corrision - Aluminum worns

 
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Simon Whitaker



Joined: 21 Nov 2004
Posts: 486
Location: Giggleswick, North Yorkshire

PostPosted: Fri Sep 09, 2005 4:54 pm    Post subject: Galvanic corrision - Aluminum worns Reply with quote

Hi
We all suffer from this Sad - galvanic corrosion, electrolytic corrosion - what ever you want to call it it's a pain ! My 50th has a fair bit of this so am looking into why it occurs and how to prevent or cure it. It occurs when two metals react with each other when an electrolite gets between them - ie water with salt in it ! Electrolysis takes place and the least noble metal is eaten away - in our case the ali ! Apparently stainless steel can be worse than mild steel - so fitting stainless bolts might be a bad idea !

I am getting loads of stuff off the net - James how can this be posted as a Word doc/pdf for all to have access to ? - it will have links on it specialist web sites for the more technically minded.

I have so far found a product called Duralac which is a jointing compound - which if it does what it says could be the answer see -
www.llewellyn-ryland.co.uk/durala.html.
This is a product is made for the aviation and marine industries who often have to join materials of a different type and the sea is huge electolyte ! I bought a 115ml on line from:
www.lightaero.co.uk
with p&p cost 8.80 in vat - they do 250, 500ml and 1 can if I recall.

Cathodic protection is often used on boats (annodes of less noble metals acting as 'scarifice blocks' are attached to the aluminium ) - but in our case it argued this is a waste of time as we would need so many as the vehicle is not immersed in a chloride solution - ie salt water.

With recards a cure prior to painting - anyone got any clues ? I believe Phosphoric acid does the trick and that it is the active agent in ali wheel cleaner - anyone got any info on this ?

Cheers
Simon #149
Sad
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Simon Whitaker



Joined: 21 Nov 2004
Posts: 486
Location: Giggleswick, North Yorkshire

PostPosted: Fri Sep 09, 2005 4:56 pm    Post subject: Reply with quote

Embarassed sorry aluminium is spelt wrong - what a wally Rolling Eyes
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Simon Whitaker



Joined: 21 Nov 2004
Posts: 486
Location: Giggleswick, North Yorkshire

PostPosted: Fri Sep 09, 2005 5:09 pm    Post subject: Reply with quote

Embarassed Embarassed Embarassed

even corrosion is spelt wrong - end the week Exclamation Rolling Eyes

200 lines for me tonight Exclamation
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defender50th
Site Admin


Joined: 14 Nov 2004
Posts: 1481
Location: Hampshire

PostPosted: Fri Sep 09, 2005 7:57 pm    Post subject: Reply with quote

Hi Simon,

What you will need to do to get the word document on here is to have it on the net and then post a link to it. If you want you can email it to me and i can host it as i have lots of space on my account for this site.

I do have to agree, this electrolytic corrosion is a real pain. I luckally only have one bad spot which is on the back door, so have bought a mint door off a 50th owner who upgraded his door to the new type, so will fit that sometime. But before i fit it i'm going to slip something between the frame and panel so it does not happen again.

Fixing it is a real problem. As you say you need a barrier between the two metals. This can be done in some places but not everywere unless you take the car apart Laughing

I dont think there is a cure before paining. If you rub it down and paint its only going to come back, unless you take the panel off and put a barrier between the surfaces first.

Why didnt land rover ever address this issue Exclamation Mad

Best regards

James
GB 002
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Ads90



Joined: 02 Feb 2005
Posts: 290
Location: Gloucestershire

PostPosted: Sat Sep 10, 2005 8:25 am    Post subject: Reply with quote

Simon - I have the stainless steel bolt set to put on some time - would this Duralac be any use in this case - or would the threads just bite through it anyway do you think?

Also, I do remember reading somewhere that there is a company who makes replacement LR panels (is it PRB or something?) and they have come up with a technique of putting a plastic layer between the ali & steel - ie in doors between the frame and skin... so if you are replacing any body parts, it may be worth checking them out...

Also, I wonder how Audi get around this problem with their A2 & A8s - and Jaguar for that matter with the XJ - I'm sure they are steel framed, with the ali panels 'bonded' on - i.e. no rivets - whatever they use as 'glue' must have the non-elecrolytic properties that you speak of...?
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