5083-H116 vs H321 Aluminum Plate: Marine Temper Selection

Quick answer: 5083-H116 and 5083-H321 can both be specified for marine plate, but H321 is not simply a “harder” or universally better version of H116. The two tempers describe different processing routes and must meet the mechanical and corrosion-resistance requirements of the governing material specification. Select the temper from the vessel design, product thickness, fabrication plan, class requirements and the exact edition of the purchase specification.

Selection point	5083-H116	5083-H321
Temper concept	Strain hardened with controls for mechanical properties and resistance to exfoliation corrosion	Strain hardened and stabilized, with controls for mechanical properties and resistance to exfoliation corrosion
Marine use	Commonly specified for hull and marine structures where the design standard permits it	Also used for marine structures, often where the approved drawing or specification calls for H321
Strength ranking	Do not rank by the temper name alone; compare the minimum properties for the actual thickness and specification
Purchase decision	Follow the drawing, class rule, ASTM/EN requirement and approved welding procedure

What H116 means

H116 is a special temper designation used for certain high-magnesium 5xxx-series wrought aluminum products. It indicates strain hardening combined with defined limits for mechanical properties and resistance to exfoliation corrosion. It is not a coating or a separate “anti-corrosion treatment.” The alloy chemistry remains 5083; the temper identifies how the product was processed and qualified.

What H321 means

H321 identifies material that has been strain hardened and then stabilized. For high-magnesium marine products, the applicable specification also controls mechanical properties and corrosion performance. Stabilization changes the processing history, but the designation does not prove that every H321 plate is harder, stronger or more corrosion resistant than every H116 plate.

Why thickness and specification matter

Minimum tensile and yield properties can vary with plate thickness and the material standard. ASTM B928 is commonly referenced for high-magnesium aluminum-alloy sheet and plate intended for marine service, while EN standards and classification-society rules may use different property tables, test requirements or temper acceptance. A quotation should therefore identify the complete requirement—for example, alloy, temper, product form, thickness range, dimensions and specification edition.

Do not substitute H116 for H321, or the reverse, only because both appear in marine applications. The designer or class-approved documentation may require one specific temper. If substitution is proposed, compare the specified mechanical values, corrosion tests, dimensional tolerances, inspection documents and welding qualification before obtaining design approval.

Corrosion resistance in marine plate

5083 is an Al-Mg alloy valued for strength, weldability and seawater service. Its performance still depends on metallurgical condition, long-term temperature exposure, fabrication and the local environment. High-magnesium 5xxx alloys can become susceptible to intergranular corrosion when an unsuitable microstructure develops during prolonged exposure to elevated temperature. The correct temper and corrosion qualification help manage this risk but do not remove the need for sound design and service-temperature control.

Crevices, dissimilar-metal contact, stagnant seawater, deposits and coating damage can create localized attack. Isolate aluminum from more noble metals where required, design for drainage, follow the specified surface-protection system and repair fabrication damage before service.

Welding and fabrication

5083 plate is widely welded, but there is no universal laser power or travel speed that applies to all thicknesses and joint designs. The old fixed “5–6 kW at 6–9 m/min” instruction should not be used as a production procedure. Welding parameters must be qualified for the process, plate thickness, joint geometry, filler metal, shielding gas, equipment and required acceptance criteria.

Also account for the lower strength of the heat-affected zone when the design code requires it. Control fit-up, contamination, heat input and distortion; then inspect the welds to the drawing or class requirement. If the finished assembly will be classed, confirm approval of the plate source, consumables, welder and procedure before production.

How to choose between H116 and H321

• Use the temper stated on the approved drawing or bill of materials.
• Confirm that the governing material standard covers the requested alloy, temper, thickness and plate form.
• Compare guaranteed properties for the actual thickness—not generic internet values.
• Check class-society approval and any corrosion-testing requirement for marine construction.
• Review forming, welding, heat exposure, inspection and surface-protection requirements.
• For a substitution, obtain written approval from the responsible designer or class authority.

RFQ checklist for 5083 marine plate

For an accurate technical and commercial review, provide the alloy and temper, specification and edition, class requirement, thickness, width, length, quantity, dimensional tolerances, flatness, surface finish, inspection document, ultrasonic or corrosion testing, edge preparation and delivery destination.

Frequently asked questions

Is 5083-H321 always stronger than 5083-H116?

No. The temper name alone does not establish a universal ranking. Use the minimum mechanical properties in the applicable specification for the requested thickness.

Can H116 and H321 be used interchangeably?

Not automatically. Both may be used in marine structures, but the approved design, material standard or class rule can require a specific temper.

Does H116 mean the plate has received a corrosion coating?

No. H116 is a metallurgical temper designation. Coating, anodizing or painting requirements are separate purchase and fabrication controls.

Request a specification-based quotation

Send your plate schedule, governing standard, class requirement and inspection-document needs to [email protected]. We will review the requested 5083-H116 or H321 condition against the stated product form and dimensions before quoting.