Bicycle Mechanics - Bare aluminum frame - OK?

Hello.

I recently stripped my 1987 Cannondale to the bare aluminum. Originally, I was going to paint it or get it powder coated. I decided against the two for the following reasons - quality and cost, respectively.

The bare aluminum actually looks REALLY cool, so I've decided to keep it this way. I'm concerned, however, that this "really cool" looking frame is going to rust/oxidize/corrode with no protective layer on it.

Will I be OK as is? Should I apply some sort of protective coat? Tips, hints, suggestions? Thanks.

it will oxidize, and that's a bummer because it looks so bad. also, the oxidation is damaging to the integrity of the frame. you can leave it bare temporarily, but you have to do something sooner or later.

for now, spray with spray wax or use mother's mag wheel polish or similar metal polish often.

If you leave it as is aluminum will naturally form a rather strong oxide layer, dulling the surface somewhat. If you're in a dry environment this natural oxide will usually be enough to stop further oxidation. But if you're close to the ocean, significant industrial pollution, insist on riding on salted roads during winters or accidentally happen to trigger some interaction with the other metals bolted to the frameyou can get some serious corrosion going on.
As far as protection goes there are a bunch of options. Clearcoat is one, but doing that well is just borderline easier than an all-out paintjob. Car wax will offer some protection, as will regular applications of pretty much the oil of your choice.

it will oxidize, and that's a bummer because it looks so bad. also, the oxidation is damaging to the integrity of the frame. you can leave it bare temporarily, but you have to do something sooner or later.

for now, spray with spray wax or use mother's mag wheel polish or similar metal polish often.

The formation of the oxide layer on aluminum is nearly instantaneous. Unlike steel, the oxidation process for aluminum is a surface phenomenon and once in place resist further oxidation. Unless you ride in the conditions that dabac pointed out, removal of the layer is relatively slow and it is an excellent protectorant. It may look dull but, from the standpoint of frame integrity, it won't hurt anything to leave the frame bare.

Alright, this all (pretty much) sounds good.

When you mention waxing/oiling the frame, I can't help but wonder: won't it sully up my pants/clothing as I ride and legs rub up against it?

Have several options:

Take it to an auto paint or powder coating shop and have it clear coated. Use a satin clear if you don't want a glossy finish.

Use a protective coating/polish like Sharkhide, Rolite. Nuvite, etc.

Use a good car/marine wax or sealant. Collinite's insulator or fleet wax come to mind, as well as easy to find sealants like Meguiars NXT or Mothers FX Synwax. There's higher end products like Zaino, Klasse, Einszett, etc etc, but may be harder to find locally.

As a professional powder coater I can tell you that you can maintain the finish with a clear powder coat as mentioned above. There are many differant gloss %s available for whatever effect you are seeking, from 25% to 150%, as well as many colors of powder that mimic metal. When I built my H.D Sportster frame after coming back from the blaster it was so shiney and perfect color that I said just clear coat the blasted look. Now we have available a blasted aluminum powder that is the same color and texture. You say cost was a factor , I have heard stories of $600 p/c jobs which is ludicrous, our prices start at $75 and rarely exceed $250 for frames and forks combined with all prep included. The cost of some these bikes today warrant some sort of protection from corrosion so it isnt a constant chore to keep it looking good.

...When you mention waxing/oiling the frame, I can't help but wonder: won't it sully up my pants/clothing as I ride and legs rub up against it?
It's a wipe on, wipe off kind of thing so it's not like the bike will be dribbling with the stuff.
There is a possibility of transfer, sure. But IME not enough to be an issue. Then again, I usually ride in tights anyhow...

Hmm...lots of interesting things to consider here.

Basically this is a great commuter bike, hence my reservations about getting an expensive paint job.

That being said, while the brushed aluminum looks cool, a powder coated job would look infinitely better. I had to strip the frame b/c I got hit by a car and had to make sure there were no cracks in the frame. The driver that hit me was at fault and if all goes well with her insurance company, I'll have enough dough to get a professional PC. Until then, though, looks like I'm gonna be oiling my frame.


Thanks all!

I wouldn't PC an Al frame, PC curing temperature is 200*C is half way to the annealing temp used to relax your frame after welding.

Don't oil the frame! Use aluminum polish on it every couple of months and it will look great and there will be no corrosion.

I've been looking for an old Canondale that I can strip and then polish out to a mirror finish. It should be beautiful with those smooth welds.

I wouldn't PC an Al frame, PC curing temperature is 200*C is half way to the annealing temp used to relax your frame after welding.This is wholly incorrect.

First, being partway toward annealing a metal doesn't damage it.

Second, the annealing temperature of most aluminum alloys is above 600°. 200° is lower than boiling water. That won't anneal anything.

Third, aluminum frames are almost always powdercoated. It's common practice because the finish is so good. They use low-temperature stuff designed specifically for aluminum, to be sure.

J - IGH was using degrees C, so 200C is 392F. Whether or not that's hot enough for long enough to significantly affect the strength of an Al frame, I don't know.

200c for heat treated aluminum alloys found on bicycles is not an issue.

100c~200c would be precipitation heat, which is an ageing process

This is wholly incorrect....They use low-temperature stuff designed specifically for aluminum, to be sure.


Hmmm, they use special low temp PC, and I am wholly incorrect...There will be grain growth, I suppose that's why there's special low temp PC solutions. Just because they can PC decorative Al panels without any issue doesn't mean grain growth in a stressed bike frame, beyond what the manufacturer does post welding, is good to have.

Dude, aluminum bike frames are powder coated all the time. It's how it's done. I imagine some places use liquid paint, too, but powder coat on aluminum is extremely common.

From the first hit on Google (emphasis mine):


... A metallurgist friend told me a few years ago that things like aluminum wheel spindles should not be powder coated. He explained that aluminum billet material (6061-T6 ?) changed crystal structure at a critical temperature around 410 degrees F (as I recall). The thrust was that the heating step would adversely affect the strength of the material. Non-structural components would be OK, but not something that "holds the spokes on". The metallurgist is correct. Products like wheel billets, scuba tanks, etc. can be powder coated, but only with powders which cure below peak metal temperature of 300 degrees F. The crystalline realignment at 400 degrees F causes the previous ductile aluminum to become brittle. Imagine the catastrophe when an 80 cu. ft. scuba tank explodes under 3000 psi pressure after an unauthorized powder coat (this actually happened). To my knowledge, all Aluminum wheels and other strength-critical aluminum components are powder coated with these cooler curing powders.

Which manufactureres sell their frames with powdercoating?

downtube, jamis, pedalforce, etc.

... and the inestimable Dr. Deltron doesn't seem to have a problem with it (http://www.bikeforums.net/showthread.php?t=176822) as a custom method, either.

Dropping your Al frame off at a office furniture PC house and running it through with all the steel desks isn't a good idea. Taking an Al frame to a specialty house and having low temp PC coating applied to your Al frame sounds OK.

A general awarness about not temperature curing Al parts has awakened in the last 10 years. Hot rodders don't have their Al mags PC'ed anymore (if they're smart). 400*F for an hour is going to cause grain growth, just not as much as 600*F.

I am a machinist. Check into having it anodizing. Its cheap and it will protect. Find a coating shop (just call around) and ask "if you could just add to one of their batches". They have dip parts all the time and throwing another part in the batch should be much of a hassle. $25? It MUST be nothing but metal. No dirt, grease, water, nothing. an abrasive pad and MEK.

Hmmm, they use special low temp PC, and I am wholly incorrect...There will be grain growth, I suppose that's why there's special low temp PC solutions. Just because they can PC decorative Al panels without any issue doesn't mean grain growth in a stressed bike frame, beyond what the manufacturer does post welding, is good to have.

That's entirely correct. You also want to make sure you don't look at your Aluminum frame wrong either as that can do all sorts of bad things.

if you can get the frame down to just the aluminum, no thread inserts or press fit stuff, I would recommend anodizing to any unique finish you like. you can also polish, mask, and bead blast a subtle pattern into the frame which would be really cool. Anodizing can be clear or in almost any color, there are also teflon impregnated processes which might let road grime fall away more easily. if you want to keep your polished metal finish and just protect it, this is the way to go. I've seen front surface optical mirrors with anodized faces and they looked great.

When annealing or heat treating these metals, the part is subjected to this heat for 1/2 an hour. When powder coating, the part is only at 375-400F degrees for 10 minutes not having any adverse effect on the aluminum. I specialize in powder coating bicycles and have never had an issue with coating aluminum frames and have always used a standard temp powder. I have spoken with metallurgists and was told that while the metal does get soft at these temps, as long as you bring it back down to room temp it will return to its original hardness having no lasting ill effects. I can coat that frame for you when your're ready.www.creativecandy.org (http://www.creativecandy.org)

Hello.

I recently stripped my 1987 Cannondale to the bare aluminum. Originally, I was going to paint it or get it powder coated. I decided against the two for the following reasons - quality and cost, respectively.

The bare aluminum actually looks REALLY cool, so I've decided to keep it this way. I'm concerned, however, that this "really cool" looking frame is going to rust/oxidize/corrode with no protective layer on it.

Will I be OK as is? Should I apply some sort of protective coat? Tips, hints, suggestions? Thanks.

Why do anything to it?

I have a 1987 Rocky Mountain Stratos that has been through h***, and it has been bare aluminium since birth. This is my winter bike/commuter so it has seen -35 C to +30 C with tons of wet/sandy/salty roads to boot (and I get lazy cleaning it in the winter so it's maintenance is also neglected).

I can still use FLITZ metal polish to bring it to a mirror like shine if I want. I then use 100% carnuba wax on it so it holds the shine a little longer before oxidizing.