I didn't know aluminum oxidized within minutes so I did a test.

Part of a piece of aluminum was scraped removing any oxidation and making
the scraped part bright and shiny. Two hours later the scraped part was
still just as bright and shiny. Eighteen hours later the scraped part was
not as bright and shiny. Part of the surface which had been scraped the
day before was rescraped and the difference was noticeable, the newly
scraped surface was brighter than the surface scraped the day before, but
both scraped surfaces were still a lot brighter than the part of the
surface which had not been scraped at all.

I would conclude that there is some oxidation in the first 24 hours.



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