Nice video on polishing Al from major corrosion to mirror smooth:
wire brush - sand blaster - 200 - wet 400 - wet 1000 - polish
YouTube
video: polishing aluminum
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At my university, I can get some 2500 wet grit, it is so so nice to use, also 1 micron diamond polish gives the best mirror finish I know of. Source, I'm a materials science student and have to polish samples to make them suitable for microscopy haven't tried any old bike parts yet but I bet the microstructures would look pretty cool in some parts
Awesome! Then you can do TEM on your crank arms, and impress everyone here (not sure how good sample prep is for the crank arms, though...)