The corrosion layer forms an oxide barrier. So when you get alloy parts anodized, that's exactly what it is. However a newly exposed scratch, cut etc. will quickly form an oxidized surface and be resistant to further corrosion.
With aluminium alloy the real danger is what we called "inter-crysterline" corrosion. that's when the corrosion goes deep and corrodes around the alloy crystals. Then the metal comes apart in slithers, or just breaks away.
Seen it in boats and aircraft.
That's just a bit of useless information you didn't want to know!