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My bike has been sitting out in the open for a few months due to lack of space. When I finally decided to strip it down and bring it inside, a lot of water came out of the frame. It could have been sitting there for a few months. The chain and the cables have started to rust but that's an easy fix. I'm worried if the frame could have began to rust from the inside and should I expect it to break unexpectedly in the future?

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    Here is some good information on aluminum & corrosion: lytron.com/Tools-and-Technical-Reference/Application-Notes/… – radiocontrolled Jan 20 '16 at 20:49
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    What will rust, more than anything else, is the bottom bracket cartridge, if it's plain steel and not stainless steel. If you had a lot of water in the frame I'd lay odds the cartridge is looking pretty bad. Aluminum will corrode, but the rate of such corrosion is low so long as you're dealing with plain rainwater and not,eg, some sort of smog/rain combo. – Daniel R Hicks Jan 20 '16 at 20:56
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    Easy fix for the future - "Don't do that" Seriously a bike should be stored inside a garage or house, not left exposed to rain and weather. – Criggie Jan 21 '16 at 0:05
  • @Criggie that's all very well but not everyone is lucky enough to have the sort of home they can keep a bike inside. Any shelter is beneficial though, especially in heavy /driving reason. – Chris H Jan 21 '16 at 7:42
  • @chrish I know - but if you've put time and effort and money into a bike, its worth looking after. There's got to be a solution, even by thinking outside the box. A Tarpaulin is slightly better than nothing, then a lean-to roof against a fence or wall, then a carport or covered porch, then a shed, a garage, etc. – Criggie Jan 21 '16 at 9:00
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While the aluminum frame itself will be relatively ok, the problem will be your bottom bracket (almost certainly made in part of steel) which was most probably sitting in a big puddle of water. Even if the water didn't cause the bearings to rust, a freezing/melting cycle can cause damage to the bearings themselves, force lubricants out, and otherwise mess-up the bottom bracket.

Your seat stem might also have corrosion problems caused by galling between the metal seat tube and seat post to the point where it'll be impossible to remove or adjust the seat height. You will want to remove it and put some grease or other anti-seize lubricant on it.

tl;dr: You should have your bottom bracket checked out, make sure your seat post can actually still move, and clear your drain holes (if you have any).

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Technically rust is limited to iron. What is bad is the rust starts and continues. The water / oxidizing agent is not consumed.

Aluminum will oxidize but it forms a protective coating. An aluminum frame will not "oxidize out".

Some iron alloys such as stainless steel prevent rust. I don't know why you don't seem to see stainless in bicycles.

  • You do see stainless steel in bicycles. Just Google stainless steel manufacturers and you will see many manufacturers of SS bikes. But they tend to be pretty pricey. A well cared for chromoly steel bike will last decades, so there isn't really much demand for a bike with the added cost associated with purchasing a stainless steel bike. Plus, stainless can still rust if it isn't cared for correctly. If you want a true corrosion free bike, you should be looking at something like titanium. – Kibbee Jan 20 '16 at 21:34
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    Stainless steel is weaker than other steels, so it works out heavier for the same overall strength. Its also harder to weld and produces some pretty noxious fumes when being welded. Finally, stainless steel does rust, albeit much slower than normal steel. – Criggie Jan 21 '16 at 0:31
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Is the frame pure aluminium? Aluminium does not rust. If the frame is an alloy you would need to check whether or not the other materials are susceptible to rust.

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    You are mixing metaphors. Aluminum will oxidize. – paparazzo Jan 20 '16 at 20:58
  • Pure aluminium is never used for bicycle frames, which are typically 6000- or 7000-series alloys. – Emyr Jan 25 '16 at 14:02

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