Ally corrosion ??

What little knowledge of aluminium corrosion I know is posted below.

Aluminium which is an oily metal requires "etch priming" to provide a suitable key to promote paint adhesion. Acid etch is a corrosion preventive phosphoric acid that can be applied by spray or roller it is not a substance that can be successfully applied by brush mainly because it is a rapid drying alcohol base formulated to spread thinly and therefore very evenly over the surface.

Aluminium (or the Birmabright used on series Land Rovers) is classed as a reactive metal and like iron it reacts with oxygen causing surface corrosion. Aluminium left in its bare metal state corrodes producing "aluminium oxide" which is a form of corrosion that will completely cover the surface and yet to some degree actually protects it from further corrosion. This white "aluminium oxide powder" formed on bare aluminium is naturally weak having little or no strength and can easily be scraped off leading to further corrosion. The oxide forming process is called anodising.

Anodising aluminium by an electro chemical process physically alters the metal surface and produces a really tough dense layer of oxide offering maximum protection to bare aluminium. Because the chemical structure is different on aluminium as opposed to steel the anodising process can be used as an anti-corrosion advantage leaving the finished aluminium absolutely bare with no need for paint protection. Although a similar process exists for steel the surface corrosion must be protected by paint.

To put it simply in your case its the paint that has failed allowing the aluminium to become unprotected and oxidise which now requires re-etching and re-painting.

The preparation is easy enough to do and you might find this: "

Mines exactly the same, it beats Land Rover too, you have to keep the two metals apart (bulkhead is steel) to prevent this type of thing. The screen surround is seperated from the bulkhead by a rubber screen seal but the hinges (also alloy) fit direct to the bulkhead & the screen surround. The way it looks on mine is the corrosion has crept up the hinges bypassing the sealing strip. This is hat causes it I believe.

What can be done about it is another matter I have not yet looked into!!

Nige

-- Subaru WRX (Annabel)

Landrover 110 County Station Wagon (Tyson)

'"Say hello to my little friend"

While etch priming is the most important part of securing the paint to the outside, there is another problem. The steel studs that secure the aluminium blocks (used to be hinges) are screwed straight in the back. There is also the possibility that tightening the inside nuts has damaged the paint on the bulkhead and there is now a direct path between aluminium and steel and electrolytic corrosion is happening. There are some exotic assembly pastes that minimise this sort of thing. "Titanine" is the name of one that springs to mind. It was used mainly on things like aeroplanes, so I'm not sure where you might buy it for domestic use. I have used a Shell product called "Ensis" with some success. This is the brown stuff that comes smeared all over new bearings etc. to stop them corroding. It comes in a spray can, as liquid or even a grease (for electric motor sealing I think). The corner garage probably will not have it but a specialist outlet should be able to order it.

Regards,

Nick Webster

Isn't it enough to electrically insulate steel from aluminium? In which case some kind of plastic/rubber spacer should do the trick. Inner tube springs to mind in that case. Or even tape?

Fred

True. In the case of the Defender front screen the hinges (dummy or real) should have gaskets to keep things apart.

Richard

Yes, indeed, but my point was that not only do you have to insulate the block but also the studs that fasten it on - that literally short circuits the hinge insulation through the bulkhead.

I was also miserably looking at another well known trouble area on my Landy today. The rear body corners (the bit where the rear lights fasten). They are painted steel and look fine but the paint is lifting off the aluminium either side of them. It has never been the same since L-R stopped galvanising them. In order to do a good remedial job, I figure the corner plate ought to be taken off. They look like they tuck under the capping around the top of the body tub. If I drill out the rivets, does anyone know whether the corner will pull away easily?

Nick

In theory - yes, there is no "top" to prevent it being pulled down, but whether it would work in practice....

Richard

Having recently waved goodbye to my old 1988 Landy 110 csw with astonishing corrosion around the cappings, this is an interesting thread, since I dread the same thing happening again. After the briefest of studies on the net, I think that the best thing for the new(ish) Defender is to take off all the painted steel bits I can and hunt out galvanised replacements. The following links make quite interesting reading.

I discovered a bit of rust around one of the rivets holding the right rear angle steel bit. I applied waxoyl to it a few months ago, but clearly this was not enough. I'm gonna remove the rivet, paint the steel (hammerite) and then re-rivet with waxoyl everywhere in the hole. I'll see what that does.

Fred

Trying to achieve the same, which involves loads of hammerite, waxoyl and time...