Marine grade aluminium alloy plate (5083 and 5383, H116 and H321)

01

Choose alloy, temper and thickness

BlueScope Distribution's 5083 data sheet states that 5083 H321 or H116, when certified under ASTM B928M, can be sold to marine customers for ship and boat building, and that its plate is ordered to both AS/NZS 1734:1997 and ASTM B928M. For 3–40 mm plate it lists minimum tensile strength of 305 MPa and minimum yield of 215 MPa for both 5083-H321 (with maxima of 385 and 295 MPa) and 5083-H116, with 10% minimum elongation; 5383-H321 and H116 are listed for 3–50 mm at 305 MPa tensile and 220 MPa yield. [1]

The same data sheet gives 5083 chemistry of 4.0–4.9% Mg, 0.40–1.0% Mn and 0.05–0.25% Cr, and lists minimum 90° bend radii for H321 sheet rising from 1t at 1.6 mm to 2½t at 12 mm, with no bend radii given for H116. It names filler alloy 5356, with the choice dependent on the alloys being joined. [1]

Editorial calculation: the data sheet's mass factor of 2.66 kg per millimetre of thickness per square metre means a 6 mm × 2,000 × 6,000 mm plate (12 m²) weighs about 12 × 6 × 2.66 ≈ 192 kg; use it to check quoted weights and lifting plans. [1]

Give the supplier the alloy and temper, thickness, width, length and quantity, the standard (for example ASTM B928M), the classification society and survey required, corrosion test reporting (G66 and G67), flatness and surface requirements, forming and welding plans, protective film and packing, and the mill certificate type.

02

Check corrosion tests and control sensitisation in service

BlueScope's data sheet lists ASTM G66 (ASSET, visual assessment of exfoliation corrosion susceptibility of 5xxx alloys) and ASTM G67 (NAMLT, intergranular corrosion susceptibility by mass loss in nitric acid) among the standards referenced for its B928M plate. [1] A US patent filed through the US Naval Research Laboratory explains why: heat exposure forms magnesium-rich beta phase (Mg₂Al₃) on grain boundaries, which is anodic to the surrounding alloy and raises the risk of intergranular corrosion, stress-corrosion cracking and corrosion fatigue in ship structures; G67 measures the degree of sensitisation by the mass lost when acid attacks the grain boundaries, and is destructive. [2]

Zhang and co-authors (Monash University and others, Scientific Reports 2017) state that AA5083 is susceptible to intergranular corrosion and intergranular stress corrosion cracking after prolonged exposure between 40 °C and 220 °C, and that the driving force for beta-phase precipitation becomes appreciable when Mg exceeds 3.5 wt.%. In their tests, 30 days at 100 °C produced a NAMLT value of about 32.9 mg/cm², and 8 days at 150 °C about 50.8 mg/cm². [3]

The patent notes that hardness falls rapidly with sensitisation but that comparison needs an unsensitised reference sample, and describes etching and image analysis of grain-boundary beta as a non-destructive alternative calibrated against G67. [2] Editorial note: ask the designer and supplier which areas of the vessel may run warm (engine rooms, exhausts, sun-heated decks) and whether in-service sensitisation checks are planned.

03

Class-certified marine plate on the listed site

The supplier reviewed lists marine grade sheet and plate under more than one classification society; for each order ask for the class certificate, the mill test report with G66 and G67 results and the standard the plate is certified to.

04

Read the G67 mass-loss result against ASTM's ranges

ASTM International's summary of G67-18 (NAMLT) says the nitric acid dissolves the aluminium-magnesium intermetallic (β Al-Mg) in preference to the magnesium solid solution in the matrix. Where that phase forms a relatively continuous network along grain boundaries, grains fall out and mass losses are of the order of 25 to 75 mg/cm² (160 to 480 mg/in.²), whereas intergranular-resistant material loses only about 1 to 15 mg/cm² (10 to 100 mg/in.²). Randomly distributed β gives intermediate losses, and metallographic examination is then required to establish whether the loss comes from intergranular attack. The method applies only to wrought 5XXX products, and ASTM links the same grain-boundary precipitate to intergranular corrosion in seacoast atmospheres or sea water, seen as pitting, exfoliation or stress-corrosion cracking. [4]

Editorial comparison: the 32.9 mg/cm² after 30 days at 100 °C and 50.8 mg/cm² after 8 days at 150 °C reported by Zhang and co-authors both fall inside ASTM's 25 to 75 mg/cm² range for a continuous grain-boundary network. [3] [4] Editorial note: ask the mill to state the G67 mass loss on the certificate, and for a result between the two ASTM ranges, the metallographic examination the method calls for.

05

From chemistry to G67: what each certificate line proves

06

Thickness band, yield minimum and corrosion results per plate lot

The strength rows hold only within a thickness band, so give the thickness first; BlueScope's 5083 minimums apply from 3 to 40 mm.

07

Send the alloy, size and certification data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Alloy and temper: [5083 or 5383; H116 or H321]
Sizes: [thickness; width; length; quantity]
Standard: [ASTM B928M; other]
Class: [society; survey]
Tests: [tensile; G66; G67]
Fabrication: [forming; welding; filler]
Packing: [film; interleaving; crates]

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