A friend of mine has an aluminum jon boat he uses for ducking in saltwater, and he used a piece of modern pressure-treated wood in it (I think to put the battery box on) and got holes in the aluminum under the PT wood. Apparently they changed the chemicals used in PT wood, banning arsenic compounds and using copper compounds instead, and the copper next to the aluminum with saltwater in-between = bad juju.
You've got to be really careful with copper around aluminum in boats. A tiny piece of copper wire left in the bilge will eat right through aluminum like alien blood. They say that if you use Kopper-Kote gasket cement in an outboard motor where it's in contact with saltwater, it'll eat up the aluminum faster than you can spit.