Why paint aluminium?

[Low Gear Guy]

My 'turbo' bike is unpainted aluminium. I thought it would be ok unpainted just sat in the garage on my turbo, but oil & grease marks don't shift too easy & it's starting to look a little messy Reckon once summer is here & I'm not on the turbo so much I'll strip the bike back down, clean the frame up & give it a coat or 2 of paint, just to keep it looking a bit cleaner

I hadn't considered the effect of grease on unpainted aluminum. This is a good reason for painting the frame.

The paint doesn't seem to have bonded as well to the aluminum in comparison to a steel frame but this may be down to frame preparation.

 

[boydj]

I seem to remember from high school chemistry that aluminium is chemically very active, but forms a tightly bonded oxide coat as soon as it's exposed to air and thereafter won't corrode in normal conditions.

 

[Venod]

I had a Genesis Core 5 that was raw Aluminium just a clear coat lacquer, I always thought it was a good looking frame, I am a big fan of raw titanium frames, no lacquer required.

 

[rogerzilla]

Chlorides such as road salt make rather a mess of aluminium. It's ok lacquered.

 

[Beebo]

What about the classic Airstream caravans. They appear to be bare aluminium

 

[silva]

Depends on the Aluminium alloy, some alloys oxidize quickly and you'll be covered in black oxidized aluminium every time you touch the frame.

Which chemical reaction / reaction product, is that "black oxidized"?

 

[Rusty Nails]

I've got a 25 year old unpainted aluminium Merlin mtb. It does require a polish with autosol at the end of every winter but that only takes a half hour and it still looks good.

 

[the_mikey]

Which chemical reaction / reaction product, is that "black oxidized"?

Amazingly, I was referring to aluminium oxide, and the apparent colour of the oxidised aluminium, it can appear to be dark, perhaps subjectively it could be described as black, much like the colour of Iron oxide is often described as red, when it could perhaps also be described as brown or orange or yellow.

At this point I feel I don't need to be scientifically accurate, I was simply making a point that unpainted aluminium freely gives up it's oxidized particles to any passing material, including clothes and skin, which isn't necessarily a desirable quality in a bicycle frame, but it's also likely that a bicycle frame will be alloyed with another material which may change the way the material reacts.

 

[silva]

The aluminium "oxidation" creates a thin dense layer that prevents the underlying material remainder to oxidize further.
So that "freely gives up its oxidized particles" is not exactly true.
And this is the "natural" layer.
Human invented anodisation, which grows the thickness of that "natural" layer to hundredsfolds.
The protection that paint offers, is far inferior to anodisation, hence aluminium is painted only for cosmetical purposes.

 

[midlife]

https://www.aopa.org/go-fly/aircraft-and-ownership/maintenance-and-inspections/aircraft-corrosion

This is an interesting read..

 

[Tenkaykev]

https://www.aopa.org/go-fly/aircraft-and-ownership/maintenance-and-inspections/aircraft-corrosion

This is an interesting read..

It's random technical stuff like this that I find fascinating, thanks for the link

 

[midlife]

It's random technical stuff like this that I find fascinating, thanks for the link

I was looking for the blurb as to why they had to paint the EE lightning at my local airdrome (Crosby on Eden) in order to stop it corroding

 

[keithmac]

https://www.aopa.org/go-fly/aircraft-and-ownership/maintenance-and-inspections/aircraft-corrosion

This is an interesting read..

We sell ACF-50 for use on motorcycles (a must if you run one through winter imho), nice to find out where it came from!.