5052, 5083, 5086 and 5454 all carry marine credentials and their datasheets look interchangeable. Service temperature, strength after welding and sensitisation risk are what actually separate them - and one of those has caused real failures at sea.
Aluminium alloys are grouped by their principal alloying element. The 5000 series is alloyed with magnesium, and magnesium is what gives these alloys their resistance to seawater. They are non-heat-treatable, which means their strength comes from work hardening rather than precipitation, and they retain that strength after welding better than any other family. For hulls, superstructures, tanks and deck plate, that combination is decisive.
The complication is that four alloys — 5052, 5083, 5086 and 5454 — all carry marine credentials, and their datasheets look similar. The right choice depends on three questions: how much strength do you need, how hot will it get, and how much forming is involved.
| Alloy | Mg content | Tensile (H32/H116) | Best at | Watch out for |
|---|---|---|---|---|
| 5052 | 2.2 – 2.8% | ~230 MPa | Forming, fuel tanks, trim, small craft | Lowest strength of the four |
| 5083 | 4.0 – 4.9% | ~305 MPa | Hull plate, structural, cryogenic | Sensitisation above 65 °C |
| 5086 | 3.5 – 4.5% | ~275 MPa | Hull and deck plate, general marine | Slightly below 5083 in strength |
| 5454 | 2.4 – 3.0% | ~250 MPa | Elevated temperature service to 200 °C | Lower strength than 5083/5086 |
This is the point most selection guides skip, and it is the one that causes real failures. Aluminium-magnesium alloys with more than about 3% magnesium can precipitate a magnesium-rich beta phase (Mg2Al3) along the grain boundaries when held above roughly 65 °C for extended periods. That phase is anodic to the surrounding metal. In a chloride environment it corrodes preferentially, producing intergranular attack and, under stress, stress corrosion cracking.
5083 has the highest magnesium of the four and is therefore the most susceptible. This is not a theoretical concern — it has caused cracking in fast ferries and in deck structures exposed to sustained solar heating in hot climates.
If the component will sit continuously above 65 °C in a marine atmosphere, do not specify 5083. Specify 5454, which was designed for exactly this duty.
Where 5083 is the right structural choice, specify the H116 or H321 temper rather than plain H32. These tempers are produced under controlled thermomechanical processing and are qualified against ASTM G66 (ASSET) and ASTM G67 (NAMLT) exfoliation and intergranular corrosion tests. The certificate should carry those test results.
5083-H116 or 5086-H116. Choose 5083 where the strength is needed to save weight and service temperature is genuinely ambient. Choose 5086 where you want a slightly more forgiving alloy with excellent weld performance and marginally lower sensitisation risk, at a small strength penalty.
5086 or 5052 depending on load. 5052 forms beautifully and takes a good finish, which matters for visible panels and for anything with tight bend radii.
5052-H32. Its formability lets you press complex tank shapes without cracking, and the corrosion resistance is more than adequate for the contents and for a wet bilge environment.
5454-H32. This alloy is specifically qualified for continuous service up to about 200 °C because its magnesium content sits below the sensitisation threshold. It is the correct answer wherever heat and chlorides coexist.
5083-O. Aluminium has no ductile-to-brittle transition, and 5083 in the annealed condition retains excellent toughness down to −196 °C.
Alloy and temper together (5083-H116, not just 5083), thickness and plate size, the governing standard (ASTM B209 or EN 485), whether ASTM G66 and G67 test results are required on the certificate, and any class society approval — DNV, Lloyd's Register, ABS or IRS — that the project demands. Class approval is arranged at mill level and cannot be added later.
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