Background: Alloy 5083 and Its Tempers
Alloy 5083 is an aluminum-magnesium alloy with 4.0 to 4.9 percent magnesium, the highest-strength non-heat-treatable aluminum alloy in common structural use. It is the reference material for marine hulls, pressure vessels, and cryogenic equipment because it combines high strength with excellent corrosion resistance and weldability. Plate is supplied in several tempers, most commonly O, H112, H116, H32, and H321. The difference between H32 and H321 is subtle but important for fabricators who weld large structures and need stable properties.
How the Tempers Are Produced
Both H32 and H321 begin with strain hardening of the plate. H32 means the plate was strain hardened to a quarter-hard level and then stabilized. Stabilization is a low-temperature heat treatment that prevents gradual hardening and loss of ductility during service, which is a characteristic concern of magnesium-rich 5xxx alloys. H321 is essentially the same processing but with a specific stabilization treatment that is controlled to satisfy the requirements of marine and pressure vessel standards such as those of classification societies. In practice, H321 is the temper most often quoted for 5083 plates used in shipbuilding, because classification rules recognize it as a stable, weld-friendly condition with guaranteed minimum properties.
Mechanical Property Comparison
| Property | 5083-H32 | 5083-H321 |
|---|---|---|
| Ultimate tensile strength | 290 to 330 MPa | 290 to 330 MPa |
| Yield strength | About 215 MPa | About 215 MPa |
| Elongation | 8 to 12 percent | 8 to 12 percent |
| Stabilization control | General | Per classification requirements |
| Typical use | General fabrication | Shipbuilding and pressure vessels |
The mechanical values overlap because the two tempers aim for the same strength level; the defining difference is the quality and documentation of the stabilization treatment.
Why Stabilization Matters
Aluminum-magnesium alloys with more than about 3 percent magnesium can slowly sensitize at service temperatures, with magnesium migrating to grain boundaries. In aggressive environments, sensitized material may be more susceptible to intergranular corrosion and stress corrosion. The stabilization treatment, typically heating at 120 to 250 degrees Celsius for a controlled time, precipitates the excess magnesium as harmless particles and locks the structure. H321 plate carries the documented guarantee that this treatment was performed, which is why classification societies accept it for hulls without additional qualification.
Application Scenarios
5083-H321 plate is specified for ship hulls, decks, and superstructures; offshore platform topsides; pressure vessels for chemical and cryogenic service; and storage tanks for liquefied gas. 5083-H32 plate serves similar roles where the project does not require classification documentation, including road tankers, transport containers, and general marine fabrication. Both tempers weld with 5183 or 5356 filler and are used bare in most marine atmospheres.
Frequently Asked Questions
Common tempers are O (annealed), H12/H14/H16/H18 with their H2x equivalents for sheet work, and H112 or F for thick plate; the temper is chosen by the forming operation and the final strength required.
EN 573-3 and ISO 209 define the chemical composition, EN 485-2 the mechanical properties of sheet, GB/T 3880.2 the Chinese equivalent, and ASTM B209 the US product standard.
Store dry and off the floor with the protective interleaving in place, keep the bundles separated from steel and other metals, and handle with care so the surface is not scratched or stained.
Yes, but weldability depends on the alloy family: 3xxx and 5xxx alloys weld readily, 6xxx alloys weld with good strength, and 1xxx pure alloys weld easily for non-structural service.
Mill finish is standard; bright, embossed, anodized and color-coated finishes are available for architectural and decorative service, and the finish is specified on the order.
Sheet is typically supplied from 0.2 mm to 6.0 mm and plate from 6 mm upward, with coil widths from 500 mm to about 2000 mm depending on mill capability and the ordered temper.
