Cleaning aluminum wheels

My alloy wheels are covered with patches of “stuff” and it won’t come off. It seems to be some kind of whitish-gray corrosion, but it’s incredibly hard (sandpaper abrades the good aluminum but leaves the corrosion intact, and a wire brush is just useless). The wheels were originally uncoated, but I intend to shine them up as best I can and then use a spray-on lacquer to seal them.

Anyone know how to get the corrosion off with the least damage to the rims?

some kinds of oven cleaner. ammonia based (spot check first).

I’ve heard rhubarb works on aluminium-hulled assault boats, but I’ve never tried it myself. Its got oxalic acid in it.

Never seen rhubarb here but you might be able to get oxalic acid.

I’d be tempted to rub them with aluminium foil/sunflower oil (works a treat on steel) but I doubt it’d be pretty enough on alloy wheels.

EDIT: People use steel wool on aluminium (sandpaper is usually aluminium oxide, so essentially the same as the stuff you are trying to take off, which is similarly hard).

I’d have some theoretical reservations about this because you could end up with lots of tiny particles of steel embedded in the alloy, and which could lead to sacrificial corrosion of the alloy. Protected it might be OK.

Alloy wheels are a bit daft, though. Coulld you perhaps score a set of steel wheels from a scrappy, and keep the alloys for when you sell the car?

ENDEDIT.

Thanks. I have a feeling that ammonia will also attack the uncorroded aluminum and I would end up with even uglier wheels than I have now.

I did some research online and found out that aluminum oxide is used to make grinding wheels, which is why the sandpaper won’t budge it. It is amazingly hard stuff.

Silicon carbide is a little harder (9.3 on Mohs scale, vs 9.0 for aluminum oxide), so that MIGHT work if I can find a suitable carbide sandpaper or polishing disk.

The other option appears to be diamond paste. I can use an angle grinder and polishing pad, though I think this would be prohibitively expensive.

About 100 years ago I did a short MIG welding course which included some aluminium welding. Surface prep used stainless steel wire brushes (which hadn’t been used for anything else) to remove the thin layer of oxide that all aluminium has.

Stainless steel is quite a bit harder than “ordinary” steel wire brushes, though probably it was specified to reduce the weld contamination.

These were “clean” aluminium test pieces. I asked what would be required in a marine environment where aluminium is often contaminated with hydroxides. IIRC degreasing with detergent or acetone, wire brushing and/or wet sanding, and/or acid etching (vinegar, phosporic, oxalic and very dilute hydrochloric ) were all mentioned as possibilities.

I’m not sure its actually necessary to use something harder than the material you’re removing, (water wears away stone, after all) and if you do, you’re probably more lkely to abrade the “intact” aluminium.

Have you tried wet sanding? I find it much better for this sort of thing than dry.

For rust-treating steel, I use short lengths of aluminium tubing (old TV ariel or arrow shaft packed with rolled up beercan and/or aluminium foil, in a drill chuck. It gives you quite good control/localised action, and it would be fairly easy to include an abrasive (eg valve grinding paste, or toothpaste) in the tube (or just spot it onto the corrosion) to increase its agressiveness.

You might also try an aluminium roofing nail in a drill or Dremel. I’m thinking the chuck would grip the nail at the pointy end and the head form a little grinding disk. I can’t try that here because I don’t know where to get them, but IIRC B+Q (and probably builders merchants) had them loose in the UK. You could apply a bit of grinding paste to the “wheel” like copper-wheel engraving. No copper, though. That’d be an electrochemical disaster.

Water doesn’t wear away rock - it leaches minerals and carries abrasive particles. I can assure you that water pipes don’t “wear out.”

The patches of corrosion on the wheels are not normal surface oxidation, it’s more like a gray “rust” that sticks out 0.5mm and is maybe 0.55 mm deep. I can actually chisel grain-sized chunks out if i try hard enough and it leaves the metal surface pitted quite badly.

I got some silicon carbide sanding disks for my angle grinder (they come in flat and conical forms) plus something that looks like a circular brillo pad made from silicon carbide. It’s so sharp that it hurts just to hold it firmly. I got hold of some high-temperature spray clearcoat also at B&Q.

How this is gonna turn out I have no idea… :s

I know the stuff you mean, and it’s very hard and quite crystalline: large chunks can be flaked out of the surface, leaving pits and holes. You’re never going to get rid of it: live with it, or get new wheels.

Ammonium oven cleaners can remove the anodised surface of the whole wheel, as well as the hard gunk, and allow you to polish the whole wheel but you’d lose a lot of metal getting it all smooth. Mild acids like oxalic can do the same but they’re better for rust on steel than oxide on aluminium. Other aluminium cleaners like aluminium window frame refurbishers are also based on ammonia rather than the phosphoric acid used in steel corrosion reversing agents.

prevention of the corrosion, by cleaning your wheels and removing all surface gunk that will retain corrosion promoting moisture is the only way to deal with that kind of corrosion, before it begins. Polishes often have a wax that will protect the wheel. The corrosion is more than just aluminium oxide; it also contains hydroxides and sulfates and a whole range of complex mixtures of the above.

Interesting thread, and enjoyably prejudice-confirming, as was the disintegration of an alloy wheel on James May’s Volvo in Top Gears Africa Challenge the other night. Steel rules.

Oh Yeh?

(The explanation of that example of cavitation seems to be a bit wrong in detail, but then they’re apparently German.)

http://www.rsime.com/CHcavitation.asp

Back On Topic-ish, up to you of course, but your proposed abrasive treatment sounds (to me) a bit brutal and likely to make a bigger mess which’ll be rather labour/skill intensive to clean up, and might cause structurally relevant damage.

If you end up “living with it” I’d seriously suggest you consider the abrade-with-aluminium/bond-with-oil approach. Its essentially painting the surface with a metallic paint, but, since you’re using the aluminium as an abrasive, its forced into more intimate contact with the metal surface. Its to some extent self-configuring, since more aluminium rubs onto the rougher corroded parts of the surface.

I’ve never tried it on alloy, where you’d loose the galvanic protection element that (perhaps) you get on steel. The sunflower oil I’ve used takes a while to set and collects dust unless protected.

You might be able to speed it up by adding an oxidising agent like potassium permangenate or hydrogen peroxide, or using an alternative binder like superglue or laquer, but I havn’t tested those mods, not having needed to.

Or just buy some aluminium paint, if you don’t want to re-invent the wheel covering. Whatever you try, you could test on the inside first.

The correct approach would be to have them resurfaced on a lathe and then re-sealed, but the expense and hassle of it is just too much for me.

Painting them is certainly one option but I have never seen this done with any success. Usually the wheels end up looking like they were taken off a piece of farm machinery.

I’m gonna attack the spare first. If I screw up, at least I can hide it. :s

[quote=“monkey”]The correct approach would be to have them resurfaced on a lathe and then re-sealed, but the expense and hassle of it is just too much for me.

Painting them is certainly one option but I have never seen this done with any success. Usually the wheels end up looking like they were taken off a piece of farm machinery.

I’m gonna attack the spare first. If I screw up, at least I can hide it. :s[/quote]

Just FYI, he’s running a Rodeo…and they have really nice factory aluminum rims. In the states would probably bead blast with non metallic shot and then powdercoat…

Yeah, they are (were) pretty nice snowflakes.

Beading or sandblasting will shine them up for sure, but it won’t restore a flat surface, as there is pitting under the corrosion. I’ll try to take some photos.