Two Tempers, Two Different Purposes
5083-H111 and 5083-H116 are both Al-Mg-Mn plate made to the same ASTM B209/B209M composition range, and both are common in shipyards, but they are qualified against different rules. H111 is a formability temper: strain hardened and partially annealed so that panels can be rolled and pressed after delivery. H116 is a marine service temper, defined in ASTM B928/B928M for high-magnesium alloys containing 3% or more magnesium, and it is accepted only when the material also passes a corrosion test rather than merely a tensile test.
The difference that matters to a naval architect is not the label but what happens at the grain boundaries during long exposure to seawater and warm weather.
Why H116 Resists Corrosion Better
In 5xxx alloys, corrosion performance is decided by the distribution of the Mg2Al3 beta phase. If that phase forms a continuous network along grain boundaries, the alloy becomes sensitive to intergranular attack and, under sustained stress, to stress corrosion cracking. The metallurgical task in producing H116 is to keep the beta phase discontinuous.
H116 is achieved by a carefully controlled strain-hardening schedule combined with thermal treatment of the cast and hot-rolled product. The final cold reduction and the temperature history are chosen so that beta phase precipitates as discrete particles rather than a continuous film. The result is a plate that retains the strength of a work-hardened 5083 while keeping grain-boundary chemistry stable in marine atmospheres. This is the specific advantage of H116 over H111, which is designed around ductility and does not carry the same corrosion qualification.
Standards, Testing and Mechanical Values
ASTM B928/B928M governs the marine tempers: it sets mechanical property minima and requires demonstrated corrosion resistance. ASTM G67, the nitric acid mass loss test, is the acceptance measure for sensitisation, and a mass loss of 15 mg/cm² or less is the accepted limit for H116 and H321 plate. ASTM G66, the ASSET visual test, is used to rate exfoliation resistance. Mechanical testing is carried out per lot, and ultrasonic inspection is available for thick plate.
| Property | 5083-H111 | 5083-H116 |
|---|---|---|
| Governing specification | ASTM B209/B209M | ASTM B928/B928M |
| Tensile strength min, MPa | 275 | 305 |
| 0.2% proof stress min, MPa | 125 | 215 |
| Elongation min, % | 12 | 12 |
| Corrosion qualification | Not required | ASTM G67 mass loss, ASTM G66 rating |
| Formability | Best in the H1x group | Restricted to moderate forming |
Both tempers share the same composition: magnesium 4.0-4.9%, manganese 0.40-1.00%, chromium 0.05-0.25%, with silicon and iron each limited to 0.40% maximum and copper to 0.10% maximum.
Where Each Temper Is Specified
H116: hull plating and stiffeners, deck plating, sea water ballast tank internals, superstructures, fishing vessel hulls, offshore walkways and splash-zone structures.
H111: interior bulkheads, deckhouse linings, ventilation trunking, non-structural partition panels and formed components welded on land.
Both: truck and trailer panels, rail wagon cladding, chemical tank shells and general fabrication where weight saving matters.
A common specification practice is to use H116 for all seawater-wetted structure and H111 for dry-side or highly formed items, which keeps the corrosion-critical areas compliant while avoiding the extra forming cost of the stronger temper.
Fabrication and Quality Control Notes
H116 plate is stiffer and less forgiving than H111. Minimum bend radii are larger, springback is greater and press brake tooling often needs compensation. Welding is routine with ER5183 or ER5356 filler to AWS A5.10, and joint efficiency is high, but heat input should be kept within qualified ranges because excess heat both softens the heat-affected zone and alters beta phase distribution.
Sustained service temperature above roughly 65 °C is the exposure limit for H116; where higher temperature is unavoidable, H321 is the stabilised temper normally specified because it holds exfoliation resistance under thermal exposure. Users should also avoid leaving heavy forming strain in H116 parts intended for permanent seawater immersion.
Verification of composition per heat against ASTM B209/B209M.
Tensile and proof stress testing per lot, in the rolling direction.
ASTM G67 mass loss results reported for marine service lots.
Thickness and flatness checked against ASTM B209 tolerances, with ultrasonic testing on request.
EN 10204 3.1 mill test certificate with heat number and full test data.
Frequently Asked Questions
Q: Is H116 simply a stronger version of H111?
A: Not only stronger. H116 is also a separately qualified marine temper with higher minima of about 305 MPa tensile and 215 MPa proof stress, and it must pass intergranular corrosion testing.
Q: Which standard defines 5083-H116?
A: ASTM B928/B928M, which covers high-magnesium aluminium sheet and plate for marine service and requires corrosion testing in addition to mechanical testing.
Q: How is sensitisation measured on H116 plate?
A: By the ASTM G67 nitric acid mass loss test, with a mass loss of 15 mg/cm² or less accepted for marine service tempers.
Q: Can H116 be formed to tight radii like H111?
A: No. H116 has less elongation available in practice, so minimum bend radii are larger and springback has to be compensated in tooling.
Q: What is the maximum service temperature for H116?
A: About 65 °C for continuous exposure. Above that, H321 is normally specified because it is stabilised against beta phase precipitation.
Q: Does H116 require a different welding procedure?
A: The consumables are the same as for H111, ER5183 or ER5356 to AWS A5.10, but heat input must be controlled within qualified ranges to protect both HAZ strength and corrosion resistance.
