Aluminum 5083-H321

5083-H321 is the marine-grade Al-Mg plate alloy in its strain-hardened then thermally stabilized temper. The 5083 alloy carries about 4 to 4.9 percent magnesium and is non-heat-treatable, so strength comes only from work hardening. H321 means strain-hardened to roughly quarter-hard then given a low-temperature stabilization soak that locks the dislocation structure and prevents service softening, giving about 215 MPa minimum yield and 305 MPa tensile with good corrosion resistance in seawater. It is the standard hull and superstructure plate for high-speed craft, patrol boats, and aluminum catamarans; the related H116 temper targets the same strength with controlled exfoliation resistance.