5083 sensitization risk checker
Estimate β-phase sensitization risk from alloy, starting temper, service temperature and time at temperature.
Alloy and temper
Service conditions
Sensitization is magnesium migrating to the grain boundaries as β-phase (Mg2Al3) when 5xxx plate sits in a critical temperature band. The screen combines a base rate, a temper factor and time at temperature.
Risk = base(alloy) × temper factor × temperature factor × time factor
| Temperature band | Effect on 5xxx |
|---|---|
| Below 65 °C | No practical sensitization |
| 65 – 200 °C | Sensitization band — avoid prolonged exposure |
| Above 200 °C | β-phase re-dissolves; not the sensitizing range |
| Peak around 100 – 150 °C | Fastest β-phase precipitation |
- Never let 5083 H116 plate sit in the 65–200 °C band for long. Insulated engine rooms and exhaust-adjacent structure are the usual offenders.
- If a repair needs heating, keep the affected area below the band or re-solution-treat; a torch pass at 120 °C is the classic way to create a problem.
- For LNG and cryogenic service, H116 / H321 are the specified tempers and the mill test reports carry a G67 result.
People also ask
What does sensitization actually do?
Magnesium leaves solution and forms β-phase (Mg2Al3) along grain boundaries. The boundary becomes anodic and the plate loses resistance to intergranular corrosion and stress-corrosion cracking.
Why is 5083 H116 the marine standard?
The H116 temper is specified with a maximum ASTM G67 mass-loss value, so it is proven not sensitized as delivered. H321 has a similar guarantee for heavier plate.
Does welding sensitize the plate?
A normal weld pass is fine — it is above the band and re-dissolves β-phase. The risk is long, slow heating in the 65–200 °C range, not a quick weld.
Can sensitized plate be recovered?
Yes, by a full solution treatment above 400 °C followed by the correct temper. In practice this is a mill operation, not a yard one.
How is sensitization tested?
ASTM G67 nitric acid mass-loss test is the standard for 5xxx plate. A value under 15 mg/cm² generally passes; higher indicates sensitization.
Does 5052 or 5754 sensitize?
Far less. Their magnesium content is lower (about 2.5–3.5%), so there is less solute to precipitate. The issue is concentrated in the 4.5% Mg and above grades.
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