An aluminum alloy material having an excellent sea water corrosion resistance comprises an aluminum alloy substrate whose ten-points average surface roughness Rz, which is the average of five greatest peak-to-valley separations on the surface, is controlled at 0.3 μm or over, an organic phosphonic primer film formed on a surface of the aluminum alloy substrate, and a fluorine resin paint film formed on the primer film and having a dry average thickness of 1 to 100 μm. A plate heat exchanger having an excellent sea water corrosion resistance is also provided wherein the aluminum alloy material is used as a heat transfer unit using sea water as cooling water.