hihi2u2

Hi there,

Just picked up a second-hand Giant Defy 3 Composite and just took the wheel off the bike and I've noticed that the drop out is flaking with white powder.
I'm guessing this might be the alumnium oxidizing and have caused the paint to peel off, creating the white powder?

The geometry of the dropout seems to be intact, I assume it's still safe to use, albeit strip the oxidising bits off the aluminium part (if it is aluminium and not the actual carbon fibre). Coat it to protect it and I can continue to use it? Or the oxidising has compromised the carbon fibre and aluminium bonding? Or it's not aluminium at all, Giant Defy 3 Composite don't have aluminium in the dropout?

Apart from this problem, the bike looks brand new and immaculate, quite amazing for the age.

Crankycrank

I hesitate to make a judgement on the complete health of the dropout/carbon fiber bond but I looks fine to me from the photos and the corrosion can just be lightly sanded off and dabbed with some paint on the area that had the corrosion. That's not uncommon with aluminum dropouts to have the metal start to corrode slightly where the paint inevitably gets chipped from wheel changes. I recommend taking it to a shop so someone can see it in the flesh if you're unsure.

sch

Completely agree with cranky: cosmetic superficial corrosion of the aluminum fork end, of no significance by itself.

Ironfish653

Agree with the above posters. Surface oxidation on the exposed aluminum. Aluminum oxidation is not the same as rust
The bike also looks like it was stored with the wheel removed, and the fork tips resting on the ground.

​​​​​​​If it bothers you, you can touch up the paint on the fork tips, and you could put some anti-seize paste in the fork notch (although that would be kinda overkill). The QR clamping surfaces are always going to look like that, unless you never put the front wheel back on.

hihi2u2

Thanks, guys, that is such a relief. It's the second second-hand bike I bought in two weeks. The first Bianchi ML3 had cracks all over the frame, only found out after I took it to the shop. I will take it to the shop for a flesh assessment, but it sounds like simple sand and paint to protect it.

Sy Reene

I am curious how just by viewing these photos, that it's able to be told that the corrosion is only superficial? IOW, if it wasn't superficial, what difference would one look for?

Mr. 66

Oh, I would not want to find puffing paint at the the union point of the Carbon fiber to the alloy tip, or the alloy flaking away so much that it is visable cratering.

For the pictures above I'd just wipe some oil on the area, that will soak in enough to halt corrosion, call it good.

vane171

Don't sand it off as suggested, I'd try to dab on CLR (buy in any house cleaning shop section) and wash with water or maybe dab on the exposed aluminum rust remover, like what you buy in automotive section of just about any shop to remove rust from chrome surfaces but it works on aluminum type of oxidation too. Just read the label and maybe don't put it much on the paint.

I had aluminum shifters (those you have on TT style handlebars) corroded from sweat dripping on them and over years it developed what looked like corrosion, after few applications of rust remover, it is clean and healthy looking, even if a little pitted. I wipe some oil on it once in a while to keep it protected.
As pointed out above, likely the bike was without wheels, fork tips probably resting on a concrete garage floor from which dampness might have been rising a bit causing the oxidation.

Crankycrank

A light sanding is better in this case as the oxidation is minimal and any paint applied will adhere much better to a sanded surface. No need to paint the inner dropout groove or the axle clamping surface either as the paint will just chip off again in short order, paint the tips is all you need.

Feelgood1

Thanks for the comments as I too have aluminum oxidation on my carbon Ridley from the bottle cage mounts. I'll use a fine sand paper and the oxidation chemical as suggested.

cyccommute 

Gonna have to disagree. Oxidation of aluminum (or any other reduced metal) is exactly the same as “rust” or iron oxidation. It’s caused by the metal reacting with oxygen to form an oxidized metal. Aluminum oxidation can be beneficial since it passivates the surface of a far more reactive metal than steel but under the right conditions it can be just as devastating as iron oxidation.

Before you proceed, look into other removal methods than sanding. There are aluminum oxide removers out there. It’s better to try to remove the oxide chemically than mechanically. Mechanical methods will remove too much material. I probably wouldn’t use CLR because of it’s acidic nature. Nor would I use any other acid treatment.

To me, it looks like the fork tips have had some road salt exposure which is what caused the corrosion. It’s not bad but if salt is left on aluminum too long (steel as well), it can catalyze further corrosion. At the very least rinse the tips well.

Ironfish653

I'm familiar with what can happen to aluminum, especially when in the presence of other metals, in a conductive environment, but we're talking about bicycles here, not subsea assets. ( I've never seen a bike down here)
If it was such an issue, aluminum bikes would have anodes on them, or they'd be dissolving away to nothing. Could also be that I don't have any bikes that get ridden in Midwestern Winter

WizardOfBoz

Uhhh. So pure aluminum in air forms an oxide layer almost immediately. As pointed out by cycommute, this layer is a pretty strong barrier to further oxidation. Chemicals (e.g salt air near the sea does this nicely) can strip the old aluminum oxide but then you get new oxide layer formation and the aluminum can corrode away. Repeatedly removing and replacing the wheel will scuff of some of the protective oxide later, allowing more oxide to form. But, unless you live on the beach near the ocean and ride in salt air, probably won't be an issue. In short, I'm not sure that you have to do anything to the fork tips. For me, I'd use an old nylon bristled toothbrush to knock most powder off, wipe it with a damp rag, make sure its dry, replace the wheel and then I'd ride...

If you must remove the white powder do not use a metal brush or sandpaper or harsh abrasives. If you want to use chemical means, vinegar in distilled water should work. CLR may or may not work as well (others may have direct experience) but the same company makes something called CLR Metal Clear, which specifically touts its use on aluminum. I'd probably try that.

There are many ways to protect aluminum. In an ideal (not realistic) world, the aluminum oxide coating would be thick and strong and would resist abrasion. Rubies and sapphires are, after all, aluminum oxide. As are the grains on a lot of sandpaper. It's hard! But, given we have a very hard, very think layer on top of a soft substrate (if you're with me, think of the hard caramelized sugar coating on creme brulee), any pressure will crack that coating. So other means (anodizing, chromate conversion coating, powder coating, or painting) will be needed. Unfortunately all of these surfaces will, in the end, surrender to the force of the quick release after repeated wheel mountings. Of these, painting (after scrupulously cleaning off the existing oxide) is probably easiest.

Use a self-etching primer, then paint formulated for metal (get exterior grade, I guess), and then two coats of enamel sealer.

And then prepare to have the QR remove that paint over the course of a couple weeks of riding.

Good luck.

cyccommute 

There are now hundreds of pictures on Facebook of handlebars that are crumbling white aluminum oxide rather than aluminum from people sweating on them…usually on trainers.

Paint covers most aluminum frames but handlebars and rims and some components are exposed metal and are subject to corrosion. The chloride ion in salts…sodium chloride and magnesium chloride for road salt and just sodium chloride in sweat…can catalyze a corrosion cycle that can cause a lot of damage depending on the ambient humidity. The salt absorbs water from the air which helps mobilize the chloride. The chloride has an affinity for aluminum forming aluminum chloride. The aluminum chloride will give up the chloride to oxygen which releases the chloride to go back an pick up more aluminum. The process goes on until there no more aluminum or until the water is no longer available.

The same happens with iron but it’s slightly less energetic.

In this case, the tips have probably had a little salt exposure and corrosion because the paint has been scraped away. It’s probably not that bad but removing it chemically would be a better way to go than physically.

hihi2u2

Hi all, thanks for all the suggestions. The fork is full carbon fibre, would sanding be better than chemical in case it affects the carbon fibre that joins onto the aluminium drop out?

Crankycrank

This discussion has gotten far too complicated for the issue at hand. You have a minimal amount of corrosion from what I can see in the photos and I'll say it again. painting will protect it from further corrosion and also shouldn't be much of an issue even if left bare as long as you wipe it off every so often to keep the corrosive road junk from sitting on the alu. Lightly sanding will create a surface that will bond to the paint better and we're not talking about going Michelangelo and re-shaping your forks. Simple.

WizardOfBoz

Yes, stop with the sanding discussion already. Sanding will remove metal and damage carbon. Sanding will do much more damage to your fork than the normal, minimal amount of oxidation on the fork tips.

"Hey, I have some butter and honey droplets on my mahogany dining room table - would it be best to use a chain saw. or a chisel, to remove it?"

No more talk of sandpaper or of metal brushes.

BTW, the epoxy in CF composite is notoriously hard to attack chemically. Neither diluted vinegar nor CLR will affect it.

Stop worrying about the non-issue on your fork tips. Wipe em off with a damp rag, put your wheel on, and enjoy riding the bike. You're bike (at least the fork tips) are in much better shape than you thought.

cyccommute 

+1 Ketones aren’t good for epoxy and a few other really exotic and, frankly, very dangerous chemicals. But, for the most part, the resin in carbon fiber is robust and chemically inert.

Just ride it.