forms a whitish powdery substance underneath the paint
. It will eventually push the paint off, because the corrosion
products take up more room than the plain aluminum alloy.
Cure is to remove the paint and all
the powdery stuff, prime with aluminum primer, and repaint. (You'll still be able to see the pits that are left behind, but if you try and fair it out, the oxidization will return, which it may do, any way.) If you have the money
, and you know of a good aluminum yacht painter, I'd discuss it with him or her, or hire them.