I have an aluminium frame.
The top tube has become slightly scratched or pitted (by something hard, presumably, I don't know what; maybe while it was parked).
Does it need maintenance (e.g. does the paint job need fixing, will it corrode/weaken without), and if so what?
Aluminium frames do not corrode, no need to worry. My 2006 mountain bike frame has lots of scratches and defects, but it is still stiff enough. Aluminium frames have shorter life expetency than steel frames had, because aluminium has a tendency to tire, but it can be used without worries for 10 years.
If you are really worried, put a sticker over it :)
Really deep dents or cracks are a cause for concern, but not little dimples and such.
Also, the "work hardening" of aluminum is considerably less than industry types would make out....I've worked on numbers of aluminum frames that are at least 20 years old with no sign whatever of any structural problems. Kind of depends what you're doing. The average roadster isn't subject to much in the way of severe shocks; not so with a mountain bike being used to bounce off boulders and do 10-foot vertical drops.
