Corrosion on an aluminum frame? How?

That's impressive pressure-retention. I've never much liked air shocks for that reason, among others. Coil springs don't leak and that's the way I like it

Corrosion on an aluminum frame? How?

That's impressive pressure-retention. I've never much liked air shocks for that reason, among others. Coil springs don't leak and that's the way I like it

i dont know,there are suspicious looking bubbles under the paint....perhaps its not corrsion but just the paint film itself

there is a patch of bubbling paint about 2 or 3 inches along the top tube and the top and front of the swingarm has a lotsmall bubbles.Some of the nice yellow paint has flaked of the top aluminium caps on the girvin

Brilliant! We've diverted Kiwi's post into a techie anorak discussion on corrosion! I love this forum! <GRIN>

I agree, Aluminium oxidation is a form of passivation, but as it's a corrosive form, I used the term corrosion to differentiate from the other methods of passivation which create a thin layer of another substance over the Aluminium, e.g. Anodizing or Chrome coating.

So relating to that, are our bikes made of Pure Aluminium or an Aluminium Alloy? I've heard the various Aluminium type numbers bandied about on here and have even heard that the top end bikes were made in the USA (rather than Taiwan) out of a superior Aluminium (alloy?)

Good Stuff!

Col

I thought passivation was the opposite of motivation. You get it every time you pass by your bicycle.

I agree, Aluminium oxidation is a form of passivation, but as it's a corrosive form, I used the term corrosion to differentiate from the other methods of passivation which create a thin layer of another substance over the Aluminium, e.g. Anodizing or Chrome coating.

Oxidation and corrosion are not interchangeable terms like you're using them. Corrosion and passivation are both forms of oxidation, but passivation is oxidation that doesn't corrode the metal. The oxide layer remains at the surface and doesn't penetrate further into the metal, so its strength is not compromised.

Anodizing is just artificially-enhanced oxidation, produced by exposing the metal to pure oxygen by using the metal as the positive electrode in an electrolysis bath. (hence "anode-izing".) The anodizing is actually just a super-thick oxide layer, and in the case of aluminum it has a honeycomb structure that allows it to absorb dyes, which people use to produce those pretty colors. Plating and vapor-deposition are not forms of passivation, they are just plating and vapor-deposition -- same end result for engineering purposes, but scientifically different processes.

As an interesting aside, some metals can be passivated by reacting them with nitrogen instead of oxygen, producing a nitride layer instead of an oxide layer. (however, the chemical reaction is still called "oxidation" because "oxidation" just refers to an exchange of electrons between two atoms.) Titanium nitride has a pretty gold color and is far more durable than titanium dioxide, hence its use on cutting tools. Normally, nitrogen just wants to be bonded to itself, and it will do just about anything (including exploding) to escape from other atomic bonds to revert to its normal triple-bonded diatomic state, but raw titanium is so stupendously reactive that titanium powder can spontaneously combust in a pure nitrogen atmosphere -- nitrogen would actually rather be bonded to titanium than to itself, though the conditions for that to occur almost never arise in nature.

So relating to that, are our bikes made of Pure Aluminium or an Aluminium Alloy? I've heard the various Aluminium type numbers bandied about on here and have even heard that the top end bikes were made in the USA (rather than Taiwan) out of a superior Aluminium (alloy?)

Pure aluminum is pretty much useless; it's very weak and malleable. All aluminum intended for long-term load-bearing use is alloyed to make it stronger. Pure metals of any sort are rarely used for commercial purposes, actually; pretty much the only ones are cast iron for brake discs and copper for wires, and that's only because metallurgists haven't figured out how to enhance the thermal conductivity of cast iron and the electrical conductivity of copper without using extremely expensive additives. But for aluminum bike frames, mixing some zinc and/or magnesium into the aluminum makes it much more useful at a reasonable cost.

You can get that by taking a vac-ation.