There is the posibility of corosion on the surface, that is easy to spot, but with the alloyed aluminum, there is also the posibility of intergranular corosion, which can go deep into the material.
An example of an alloy that might suffer badly from intergranular corosion is 2024. In this case You have a galvanic cell form between the aluminum and the copper it is alloyed with in the presence of an electrolite [the salt water]. It can just eat itself away.
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