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i thought aluminum didnt corrode?(14 posts)

i thought aluminum didnt corrode?ishmael
Aug 3, 2002 3:40 PM
I was putting new tape on my bars and noticed a lot of rough brown spots where the shine of the aluminum has disapeared. Im assuming its from sweat. The bars are only a year and a half old (cinelli nerve).
Sure doespeloton
Aug 3, 2002 3:56 PM
Aluminum does corrode, just not as quickly as say steel. That doesn't mean that it doesn't happen though. A year and a half of sweat and moisture being locked in by bar tape could do it. That is one reason to change your bar tape every now and again. Also, depending on your yearly mileage it may be a good idea to change your bars every season, or every other season. I do this more for the fatigue life of aluminum and the consequences of a bar failure. Better safe than sorry is my opinion. The corrosion you speak of might be a good reason to find a new set as well.
Tear a can in half and leave it overnight. nmonespeed
Aug 3, 2002 3:58 PM
re: more along the lines of oxidation...Akirasho
Aug 3, 2002 4:07 PM
... and in some forms, this is a good thing cuz it forms a protective "blister"...

Indeed, under similar conditions, an aluminium frame will not oxidize at the same rate or in the same way as steel (rust is a much more aggressive form of oxidation that weakens the very molecular structure of steel)... even titanium can be oxidized under the proper conditions.

We abide.

Remain In Light.
rust & oxidation... same thingTig
Aug 3, 2002 7:40 PM
Rapid oxidation is also known as fire, and slow oxidation is known as corrosion or rust. A smoldering compost pile sits somewhere in between. I had to attend a fire academy to learn that! ;o)
Tear a can in half and leave it overnight. nmonespeed
Aug 3, 2002 4:53 PM
Could it be rust from the brake lever clamp? (nm)OffTheBack
Aug 3, 2002 6:00 PM
Steel Rusts (bad) Al Oxidizes (good)jose_Tex_mex
Aug 3, 2002 10:37 PM
Yeah, Yeah, Yeah rusting and oxidation are the same. However, rusting is bad and oxidation is not necessarily - it's often a form of protection such as in Silver. Oxidation helps increase corrosion resistance in the case of Al.

Steel rusts more as more rust forms. Eventually, the rust eats through and you are left with Iron Oxide.

Aluminum rusts to form aluminum oxide, but this coats the metal and retards further rusting. This oxidation looks almost white in color. The brownish color you sounds more like steel. As someone else asked - was it around your shifters?

Unless of course your bars are not Al and some alloy...
Tell that to an aviation engineer and you'll get laughed at! -nmTig
Aug 4, 2002 12:32 PM
Are we talking about planes or bikes?jose_Tex_mex
Aug 4, 2002 1:20 PM
Actually I learned this in my Strength of Materials which I had to take while pursuing my degree in Aerospace Engineer - which I later changed to a minor in order to double up in Math and Physics.

If you disagree with something I have said, state it, provide your proof, and we'll discuss it further.

:-)
Primarily aluminum in aircraft. This is fundamental stuff.Tig
Aug 4, 2002 3:37 PM
At no time is corrosion acceptable in an airframe. Spending most of my career in NASA, which included working directly with orbiter flight hardware, tends to provide me with such fundamental knowledge. An FAA airframe maintenance license and the education it took to achieve it completes the knowledge. Sorry, but corrosion in aircraft is not an option! A little on an aluminum bike doesn't amount to much.
Sorry about my previous tone...jose_Tex_mex
Aug 4, 2002 6:14 PM
I just re-read my response and I think it sounded a bit nasty - not my intention. Sometimes you just write and respond without thinking about what your intentions may look like. I tend to forget you can't tell via the computer when I am not trying to be combative. With that said I am sorry if I sounded nasty.

However, I still stand by what I said with the following clarifications/elaborations. When steel rusts it is a bad thing because rust begets rust. The rust will go right through the metal. There's really nothing good to be said about rusting.

When Al oxidizes, the area oxidized does not continue through the entire piece as the top most layer does form a sort of barrier. I never said that allowing Al to oxidize was a better alternative than say painting raw Al.

I agree with what you have to say wrt aircraft. The forces undergone by tubes vs sheets of metal are quite different. My original reply was wrt Al applied in cycling.

Lastly, are rusting and oxidation really the same thing? Al oxidizes as a reaction to "oxygen." However, doesn't rusting require moist air - water in oxygen?
Tex is correctskibert
Aug 4, 2002 9:31 PM
Aluminum is one of the most reactive metals, much more so than steel but the aluminum oxide formed when Al corrodes is one of the strongest ceramics and protects the Al from any further corrosion. When exposed to air AL will oxidize completly almost instantly, that is why AL powder is highly explosive. I just took a class on this last Quarter.
so I guess I have nothing to worry aboutishmael
Aug 5, 2002 8:13 AM
And it wasnt rust from the lever clamps (which show no sign of corrosion).