[Closed] corrosion on an ALU frame

Cosmetic. Aluminium forms an oxide which protects the base metal underneath. Don't rub it off !

Interesting read up on this matter [url= http://www.snelsons.co.uk/aluminium_corrosion.html ]http://www.snelsons.co.uk/aluminium_corrosion.html[/url]

My mates heckler swing arm started to corrode it was a bin job(swing arm was replaced) warranty I think

I work on classic cars, and I have seen this before on Alu panels where the white powdery dots actually go through when you strip off the paint. It is very unusual though.

I had a Verlicchi MTB frame that corroded badly before cracking.

Cheers for the reply. It does seem to go beneath the clear coat but not much. I have to rub it off as it seems to be spreading and it looks nasty. I was either going to lacquer over the rub down or have it repainted. I guess I am trying to make sure the frame is structurally sound especially around the bb.

Many years ago a mates seat stays on a Cannondale mtb developed 1cm diameter holes, one on each side at tyre height. He had been winter commuting on it and never washed it, I think road salt was to blame.

Nitromors is quite good at stripping corrosion of Aluminium but I'd be cautious about leaving it on too long.

If it were me I'd pay more attention to rinsing road muck off after you've ridden - it'll be the salts in there that are causing the problems.

Crevice and Pitting corrosion are more likely on Al. Extruded Al is more susceptible to something call stress-corrosion cracking - but this would be highly unlikely in bikes. If the bike is made from a 6000 grade Al alloys then it should have better corrosion resistance (Mg and Si added).

Chlorine from road salt (NaCl), some cleaning agents etc. it particularly nasty when it mixes with water and forms HCl - although the passivating oxide layer on Al is very good - Cl ions can degrade it.

For nerdy people - use SiC paper on some Al and then measure the electrical resistance....... then wait 30 seconds and look at the resistance..... thats the Al2O3 film forming 🙂

I can remember a chemistry lesson where the oxide layer was removed using acid and left. You could see the oxide layer reforming while you watched!

One of my M2 frames has quite a bit of bubbling - especially around the bottle boss inserts. Mind you it's a 1998 frame, so I'm not that bothered! the other M2 frame - same year - has a bit less, less salt or corrosion exposure I guess.

it is most frequent at stress points and 'lean' chips i.e. it looks like if the clear coat has been damaged then something has got in and started working

what I am hearing (though correct me if I am wrong)is that it is just cosmetic and not structural so if I repainted that should fix the problem (or buy a new bike?)

Cheers again:)

Extruded Al is more susceptible to something call stress-corrosion cracking - but this would be highly unlikely in bikes

Bike frames I agree, but I've stress corrosion cracked a rear rim on my winter road bike. White corrosion product around where the nipple screwed into the rim, then cracks running around the rim either side of the nipple. All cracks appeared in the rim, but only at the drive side spokes. It was a Rigida rim can't remember the model.

If it's just surface corrosion it won't cause any structural problems if you catch it early. Just make sure you clean it thoroughly with coarse scotchbrite or similar (avoid metal scourers and wire brushes). Clean until you get back to bright metal ( the early stages of corrosion looks black in colour )and repaint. Should keep it at bay for a couple more years.

Ok, hopefully this works...

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Enhance!

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Gosh it looks worse now!