jlat

hello people: Has anyone just made an unpainted AF? With this new to me, Hardrock had some ugly-looking scratches in areas so I filled the paint and just left the plane alum. I kinda like it. Also then if you scratch it up you could take down the flaw with sandpaper or a file.
IBBY

Rolla

There have been lots of raw aluminum frames over the years, especially BMX and mountain bikes. In the 90s, GT made the Avalanche in raw aluminum. Might have ben polished, though.

indyfabz

alcjphil

Raw untreated aluminum will corrode. How much will depend on environmental conditions. I owned a Mercury Zephyr(Ford Fairmont clone) that had 1\4" thick cast aluminum bumpers. they were very strong. One time I was hit from behind at a stoplight, a pretty good whack and no damage was done. However, after about 5 years the bumpers had holes from corrosion at the points where the bumpers were bolted to the steel mounting points. Aluminum may be rustproof, but it isn't corrosion proof

wolfchild

Clear coated aluminum looks very nice depending on who did the preparation and painting. Plus clear coat will protect raw aluminum form corrosion.

jlat

hello people: I have raw alum. on my motorcycle and I just hit it scotch bright if I want it to look nice. It sits in my shed over the winter and come spring all I have to do is what I say and it's all good.
IBBY

jlat

hello people: Didn't Merlin frames come raw? Maybe just not painted? I think they were made in Somerville Mass. at one time
IBBY

dedhed

Merlin frames are titanium

alcjphil

Most Merlins were titanium, not aluminum

base2 

Raw aluminum oxidizes pretty quickly. The trick is to passivate the surface so that the atoms are happier to not react with any other passing elements.

Various grades of Chromium Phosphate are used throughout the aerospace industry. This creates a very strong bond with the aluminum atoms such that even oxygen does very little to convince them to recombine.

The difficulty is proper preparation. But it's totally do-able & Chromium Phosphate is readily available online. Bond-Rite is one such brand name. As with all chemicals, it will cause cancer in California.

jlat

hello people: I don't think Merlins were painted so maybe that's why I thought they were alum. wow, titanium.
IBBY

Rolla

I believe all Merlins were titanium.

jlat

hello people: At work just about all alum. is chromated after welding to help stop oxidation. But a lot is painted.
IBBY

koala logs

You might end up sanding the whole frame to oblivion.

jlat

hello and hello people: You could be right as the tubing wall thickness can't be too great. Maybe not a good idea.
IBBY

Ironfish653

There have been more than a few bikes available with polished (unpainted) aluminum frames; notably 1990’s bikes like the aforementioned GT’s, and similar vintage Cannondale models. A handful of the SoftRide Power-V ‘wing’ bikes were polished as well.

Factory polished frames are usually clear-coated, but for DIY, you may be better off leaving it unsealed. If the clearcoat has any ‘thin spots’ or gets scratches in it, moisture or other contaminants can get between it and the polished surfaces, leading to cloudiness or “chrome worm”. The only way to fix it is to strip the clearcoat off.
A lot of hot-rodders will wax polished parts after polishing, as it’s a lot easier to touch-up the shine over time

indyfabz

In ‘99 I rode across the U.S. with a guy who rode a full suspension GT. (He had a bad back from riding a motorcycle as a CHiP for 30 years.) The finish looked a lot like that. Same color decals as well.

He was 60 at the time and was the overall strongest rider in our group of 13.

wolfchild

Use a chemical paint stripper or have it sandblasted.

cyccommute 

If exposed to just air and water, untreated aluminum is fairly impervious to corrosion. Think of an aluminum rim that is used for braking. The aluminum is always “bare”. It doesn’t corrode any faster than the rest of the rim that isn’t constantly scrubbed by the brake pads. Aluminum is a reactive metal that quickly becomes covered with a thin layer of aluminum oxide whenever the bare metal is exposed. Other parts on a bicycle are also bare aluminum although they may have be anodized (purposely oxidized).

Add chloride ions from various road salts (not just sodium chloride) into the mix with a bit of water, and even the anodization can be plucked off. Add in a contact between steel and aluminum along with the chloride and you have a recipe for accelerated corrosion.

But, bare aluminum used in a dry environment or even a wet environment without much salt should be fairly impervious to corrosion.

indyfabz

I think I mentioned this a long time ago, but my red anodized CK headset spacers “became one” with the steel steerer tube of my Colnago carbon fork thanks to my caustic sweat, riding in the rain and poor maintenance habits. After days of experimenting with ways to free them, the shop finally had to cut through them with a Dremel and pry them off. Wish I had saved the spacers for visual effect.

terrymorse 

On an aluminum frame, you might be surprised at how thick the tube walls are.

They need to be substantially thicker than steel or titanium tubes, to avoid the "beer can dent" buckling. Also, aluminum needs to be thicker to avoid fatigue failure.

t2p

many lightweight aluminum frames use oversize / large diameter tubing to add strength when the wall thickness is (very) thin

( I believe this was the subject of the project / thesis Gary Klein worked on back in his days at MIT )

https://en.wikipedia.org/wiki/Klein_Bicycle_Corporation

I had an early 90's Cannondale 2.8 frame that had large diameter butted tubing with thin walls - in some areas I believe the wall thickness was .6 mm

this frame was defective - we cut to inspect - but this was in the mid-90's so I cannot be certain on the dimensions

a relatively strong hand could get a little 'oil can' effect from the middle of the top tube on that frame

Camilo

Any commercially produced "raw" aluminum frames you see are painted with clear coat. I do like the looks - my wife had that kind of a Cannondale cross frame that I built up for her first "gravel" bike and I really liked the looks of it. It didn't really show minor grease grime, was easy to clean and looked brand new with no visible scuffs and scrapes. I bought her a new gravel bike, Litespeed titanium Watia and i sincerely believe I could have "snuck" it into the garage with her thinking it was another clear coated aluminum frame. But since she pays the credit card bills, I didn't bother.

indyfabz

Just buy a ti frame and color it with Cerakote.

terrymorse 

The Klein bikes had oversized tubing for stiffness, not particularly for strength.

0.6 mm thick aluminum seems extremely thin. That's about 20 mils, and the thinnest commonly available Al tubing is ~25 mils. A thin steel tube is about 28 mils.

BTW, I had a Klein Navigator, which weighed in at about 25 lbs. V-brakes, bar end sifters, triple chainrings, 3 water bottle cages.

I rode the cols of France on it, during the 2003 Tour. Here I am, proving that I have some upper body strength:



Water stop somewhere in the Pyrenees.