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After doing some reading, it is common to read that aluminum is corroded by oxygen, but that the thin layer of aluminum oxide protects the internal metal from further damage. How much does this layer of aluminum oxide protect the underlying layers? Does it completely seal off the aluminum or is there still a slow degradation compared to a metal like iron?

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    $\begingroup$ It passivates, so reaction stops with very thin layer. $\endgroup$
    – Mithoron
    Dec 27 '19 at 20:51
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Yes, the aluminum oxide coating is generally protective, but not always. For example, in the presence of $\ce{NaCl}$ (like in spray from ocean water), it is reported that aluminum alloys in coastal communities undergo significant corrosion.

Here is a reference to quote:

When salt air and salt water come into contact with aluminum they can cause both the chalky, white coating of aluminum oxide and unpleasant pitting. Fortunately, there’s an easy way to protect aluminum from salt water and prevent unsightly corrosion: a powder coating.

A more precise discussion of chemical intermediates is outlined in a paper by Foley and Nguyen [1]. I also recall a comment on the slow removal of the passive $\ce{Al2O3}$ layer in the presence of vinegar.

So, I do not recommend leaving a salt and vinegar dressing in contact with an aluminum foil-wrapped sandwich for days before eating.

References

  1. Foley, R. T.; Nguyen, T. H. The Chemical Nature of Aluminum Corrosion V . Energy Transfer in Aluminum Dissolution. J. Electrochem. Soc. 1982, 129 (3), 464–467. DOI: 10.1149/1.2123881.
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No. Aluminium stops corroding once a strong oxide layer is formed.

Aluminium is a fairly reactive metal. The reason why it usually survives in air and water under normal conditions is because the aluminium oxide layer on the surface is very strong and normally protects the metal from further attack. Even if the layer is disrupted, it reforms quickly preventing any further reaction. Aluminium oxide is a very strong compound and impervious to water and oxygen. In bulk form it is known as corundum and appears in nature as ruby and sapphire, just about the hardest non-diamond minerals.

But there are substances that can disrupt that layer and expose aluminium to attack from air and water. Mercury and its salts and gallium metal both do this. Once they penetrate the surface layer, aluminium will be destroyed fairly rapidly and will crumble to a weak bulky mess. See examples on youtube from NurdRage and NileRed.

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