This is exactly why you cant tolerate corrosion on your boat! Corrosion doesn't just eat away the metal like a very slow grinder. It changes the metal that's left behind so that it all becomes JUNK! 'Aluminum' as we know it is highly alloyed. It is far from pure aluminum. Structurally, it's like comparing iron to steel. The downside of this type of alloying is that it's both prone to corrosion (pure aluminum BTW is very corrosion resistant) and succeptible to changes in the crystalline structure so that it becomes weak and brittle when corroded. Beware!

Jimbo