Aluminium Oxidation

I today bought a cannondale, with a more detailed inspection upon getting it home there seems to be oxidation on a few places (nothing too serious)

But the rear stay near the axle has a large section of oxidation under the paint.

After a quick google it seems like this may just be a protective barrier formed by the aluminium but I was wondering if anyone had any more expertise on it.

Is it something I should be worried about and can it eat away the metal in that location?

Will post a picture tomorrow morning.

The reason aluminium doesn't corrode is that bare aluminium reacts with oxygen in the air to form a layer of aluminium oxide, one molecule thick on the surface. The oxide is highly impermeable and protects the underlying metal. On unpainted aluminium, all you see is a dullness of the metal. There are other ways of protecting aluminium including painting and anodising.

In your case, it's difficult to say without seeing it what the problem is. It may be that some of the paint layer is damaged, allowing air (and/or water) to get under the paint and react with the aluminium. If the oxide accumulates, it forms a white powder which can cause the paint to bubble. Usually cleaning away the damaged paint and accumulation of oxide is enough, and touching up the paint if desired.

That's for the awnser.

That is the worst area the other places are just small amount of bubbling.

I scraped away this peice of the paint.

Seems a shame to strip all the paint from the areas but happy to.

I just want to insure that there is nothing else under that area, cracks or dents or anything.

The seller is helpful but seems to have just covered up all the corroded areas. I doubt that helped maybe.

Providing the frame is not cracked, you can either leave it alone and hope for the best or remove all the bubbled paint and underlying oxide with emery paper or similar, then repaint the bare areas with a metal primer and a suitable colour.

Short of a full sandblast and repaint, of course.

What did yon buy mate? caad 3?

@yoav

Thanks, I think this will be what I do. Strip the sections back to the metal and try and match the paint. It was just a little disappointing when I got the bike home as these parts had been covered with a red protective tape and I had missed them.

The previous owner has been quite good and seemed to genuinely not know about it but who knows.

@Thrasher yep yep

Gears and this problem need sorting but it's in great condition otherwise.

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