Machining
Soft Al-Mg alloys can form long, stringy chips and built-up edge. Use sharp, polished carbide or HSS tools with high positive rake, generous chip clearance and plenty of coolant. H112 machines more cleanly than O.
Marine bar stock
5A02 Marine Grade Aluminium Hexagonal Bar
5A02 is a non-heat-treatable aluminium-magnesium alloy with about 2.5 % magnesium, specified in the Chinese GB/T 3190 standard and close in character to Russian AMg2 and to 5052 / 5251. As an extruded hexagonal bar in O or H112 temper it gives seawater-resistant, weldable stock for nuts, couplings, spacers and fittings on boats and offshore equipment. Metline supplies 5A02 hex bar cut to length, with mill certificates, to buyers worldwide.
- Alloy family
- Al-Mg (5xxx), about 2.5 % Mg
- Tempers
- O, H112
- Across flats
- about 10 – 200 mm
- Standards
- GB/T 3190 · GB/T 3191
What is 5A02 hexagonal bar and why is it used at sea?
A hexagonal bar is the natural starting stock for any part that will end up with six flats: nuts, union bodies, hose fittings, threaded spacers, bushes and turned connectors. Starting from hex rather than round saves a milling operation and a lot of swarf. When those parts go on a vessel, the alloy has to cope with salt spray, condensation and contact with seawater, and that is where the 5xxx family earns its place.
5A02 is the Chinese national designation for a medium-magnesium aluminium alloy. Its magnesium content of 2.0 – 2.8 % sits between the 5052 and 5154 grades familiar to Western buyers, and a small manganese (or chromium) addition refines the grain and supports corrosion resistance. Like every 5xxx alloy it gains strength from magnesium in solid solution and from cold work, not from heat treatment, so welding does not destroy a heat-treated condition the way it does with 6061 or 6082.
For marine hex bar the practical result is a material that machines into fittings without special tooling, can be welded with ordinary 5xxx filler wire, keeps a stable oxide film in salt air and is unlikely to suffer the intergranular or exfoliation attack that troubles high-magnesium grades kept warm for long periods. It is not a high-strength alloy; if your fitting carries heavy structural load, 6082-T6 or 5083 bar is the better starting point.
5A02 chemical composition (wt %)
Limits below follow GB/T 3190. Some older supplier sheets print a 4 – 5 % magnesium figure under the 5A02 heading; that range belongs to the higher-magnesium grades such as 5A05 and 5083, not to 5A02. The mill certificate with each lot shows the actual analysis.
| Element | Limit | Why it matters |
|---|---|---|
| Magnesium (Mg) | 2.0 – 2.8 | Main strengthening element; also the source of good seawater resistance |
| Manganese (Mn) or chromium (Cr) | 0.15 – 0.40 | Grain refinement and a small strength gain |
| Silicon (Si) | ≤ 0.40 | Impurity |
| Iron (Fe) | ≤ 0.40 | Impurity; kept low for ductility and surface quality |
| Copper (Cu) | ≤ 0.10 | Held low because copper harms corrosion resistance |
| Titanium (Ti) | ≤ 0.15 | Grain refiner added at casting |
| Others, each / total | ≤ 0.05 / ≤ 0.15 | |
| Aluminium (Al) | Remainder | About 96 – 97.5 % |
Because copper is capped at 0.10 % and magnesium stays below 3 %, 5A02 is not susceptible to the sensitisation (grain-boundary precipitation of the Al3Mg2 beta phase) that limits 5083 and 5A06 in service above about 65 °C. That makes it a comfortable choice for parts near engines, exhausts or sun-heated decks.
Mechanical and physical properties of 5A02 bar
GB/T 3191 sets 5A02 bar in O and H112 with a maximum tensile strength rather than a minimum, plus a minimum elongation. That reflects how the alloy is used: soft, ductile stock that is machined, headed or formed. Typical values below are guidance from production experience with comparable Al-Mg2.5 alloys; design to the certificate.
| Condition | Tensile strength Rm | Proof strength Rp0.2 | Elongation | Brinell hardness |
|---|---|---|---|---|
| O / H112, GB/T 3191 requirement (25 – 150 mm) | ≤ 225 MPa | not specified | ≥ 10 % | — |
| O, typical | 170 – 200 MPa | 70 – 90 MPa | 20 – 25 % | about 45 HB |
| H112, typical | 180 – 220 MPa | 80 – 110 MPa | 15 – 22 % | about 50 HB |
Physical properties (typical)
- Density
- 2.68 g/cm³
- Modulus of elasticity
- about 70 GPa
- Thermal conductivity
- about 140 W/m·K
- Electrical conductivity
- about 35 % IACS
- Coefficient of thermal expansion
- about 23.8 µm/m·°C (20 – 100 °C)
- Melting range
- about 605 – 650 °C
5A02 standards and nearest international grades
5A02 has no exact twin in ASTM or EN. Engineers outside China usually treat it as interchangeable with one of the grades below after checking the drawing requirement, because magnesium content and corrosion behaviour are close.
| System | Nearest grade | Comment |
|---|---|---|
| China (GB/T 3190) | 5A02 (formerly LF2) | Bar to GB/T 3191; tolerances to GB/T 14846 |
| Russia (GOST 4784) | AMg2 (1520) | Very close in magnesium and manganese |
| Aluminum Association / ASTM | 5052 | Mg 2.2 – 2.8 % with Cr; ASTM B211 or B221 bar |
| European (EN 573-3) | EN AW-5251 / EN AW-5052 | 5251 (AlMg2Mn0.3) is the closest chemistry; bar to EN 755-2 |
| Japan (JIS) | A5052 | JIS H4040 bar |
If your specification names 5052 or 5251, we supply that grade directly rather than substituting 5A02, so the certificate matches the drawing.
5A02 hex bar sizes and weights
Supply range
- Across flats
- About 10 – 200 mm; larger sizes on request
- Temper
- O, H112
- Length
- Random or fixed lengths, typically 2 – 6 m; cut pieces to order
- Corners
- Sharp or radiused corners per the standard; chamfered ends on request
- Surface
- As-extruded mill finish; peeled or turned surface on request
A hexagon of across-flats size s has a cross-section of 0.866 × s². At a density of 2.68 g/cm³ the weights are:
| Across flats (mm) | kg per metre | kg per 3 m bar | kg per 6 m bar |
|---|---|---|---|
| 10 | 0.232 | 0.70 | 1.4 |
| 13 | 0.392 | 1.18 | 2.4 |
| 17 | 0.671 | 2.01 | 4.0 |
| 19 | 0.838 | 2.51 | 5.0 |
| 22 | 1.12 | 3.37 | 6.7 |
| 24 | 1.34 | 4.01 | 8.0 |
| 27 | 1.69 | 5.08 | 10.2 |
| 30 | 2.09 | 6.27 | 12.5 |
| 32 | 2.38 | 7.13 | 14.3 |
| 36 | 3.01 | 9.02 | 18.0 |
| 41 | 3.90 | 11.70 | 23.4 |
| 46 | 4.91 | 14.73 | 29.5 |
| 50 | 5.80 | 17.41 | 34.8 |
| 55 | 7.02 | 21.06 | 42.1 |
| 60 | 8.36 | 25.07 | 50.1 |
| 70 | 11.37 | 34.12 | 68.2 |
| 80 | 14.85 | 44.56 | 89.1 |
| 100 | 23.21 | 69.63 | 139.3 |
Dimensional tolerances for extruded hex bar
With magnesium below 3 %, 5A02 falls in the easier-to-extrude tolerance group of GB/T 14846 and EN 755-6. The across-flats tolerances most often applied are shown below; straightness is normally held within about 0.8 mm over any 300 mm for sizes up to 80 mm, and twist within roughly 1 – 1.5 mm per metre for smaller sections.
| Across flats (mm) | Permitted deviation (mm) |
|---|---|
| over 8 to 18 | ±0.22 |
| over 18 to 25 | ±0.25 |
| over 25 to 40 | ±0.30 |
| over 40 to 50 | ±0.35 |
| over 50 to 65 | ±0.40 |
| over 65 to 80 | ±0.45 |
| over 80 to 100 | ±0.55 |
| over 100 to 120 | ±0.65 |
| over 120 to 150 | ±0.80 |
| over 150 to 180 | ±1.00 |
| over 180 to 220 | ±1.15 |
Inspection and documents
- Chemistry
- Spectrometer analysis per cast, reported on the certificate
- Mechanical test
- Tensile and elongation per lot to the order standard
- Dimensions
- Across-flats, corner radius, straightness, twist and length checked
- Certificate
- EN 10204 3.1 mill test certificate; class-surveyor or third-party witness where the order requires it
Machining, welding and finishing 5A02 hex bar
Threading
Roll threads where possible: the alloy cold-works well and rolled threads resist galling better than cut threads. Use an anti-seize compound on stainless fasteners.
Welding
MIG or TIG with ER5356 or ER5183 filler. The weld zone keeps close to annealed strength, which is already the condition of O-temper bar, so there is little loss to design around.
Forming and heading
O temper takes cold heading, flaring and bending readily, which is why the same grade is also drawn into rivet wire.
Anodising
Takes clear sulphuric anodising for extra salt-spray resistance; colour match is acceptable but slightly duller than 6xxx alloys.
Galvanic contact
Isolate from copper alloys, carbon steel and stainless steel with washers, sleeves or sealant; in submerged service add sacrificial anodes.
Where 5A02 hex bar is used on vessels and offshore
- Pipe and hose fittings: unions, adaptors and nipples for fuel, fresh-water and bilge lines on small craft
- Fasteners and spacers: nuts, stand-offs and threaded bushes where aluminium-to-aluminium contact avoids galvanic cells
- Deck hardware: stanchion bases, cleat and fairlead bodies, awning and canopy fittings
- Cable and electrical: gland bodies and earthing studs on aluminium hulls
- Instrumentation: sensor housings and connector bodies on buoys and survey equipment
- Repair work: replacement fittings on older vessels built to GB or GOST specifications
For large structural members such as frames, girders or masts, rolled 5083 plate and 6082 or 6005A extrusions are the usual class-approved choices; hex bar is mainly for turned components.
5A02 compared with 5083 and 6082 hex bar
| Property | 5A02 (O / H112) | 5083 (O / H112) | 6082-T6 |
|---|---|---|---|
| Strengthening | Solid solution, cold work | Solid solution, cold work | Precipitation heat treatment |
| Typical tensile strength | 170 – 220 MPa | 270 – 300 MPa | 310 – 340 MPa |
| Seawater corrosion | Very good | Excellent | Good |
| Machinability | Fair (gummy in O) | Fair | Very good |
| Strength after welding | Little change | Little change | Falls to about half in the weld zone |
| Service above 65 °C | No sensitisation concern | Sensitisation risk | No sensitisation concern |
Choose 5A02 for lightly loaded fittings that need excellent corrosion resistance and ductility. Move up to 5083 when strength matters and the part stays cool, or to 6082-T6 when machinability and strength matter more than weld-zone strength.
How to order 5A02 hex bar from Metline
- SpecifyGrade 5A02 (or the equivalent named on your drawing), temper, across-flats size, length, quantity and governing standard.
- QuoteWe confirm availability, tolerance, certification and delivery terms (EXW, FOB, CIF or DAP).
- Cut and checkBars are cut to length, inspected for size, straightness and surface, and identified by cast.
- DocumentEN 10204 3.1 certificate and packing list; class or third-party inspection on request.
- ShipBundled and wrapped in moisture-resistant film in wooden cases for sea or air freight.
References and standards
- GB/T 3190-2020 – Chemical composition of wrought aluminium and aluminium alloys
- GB/T 3191 – Aluminium and aluminium alloy extruded bars
- GOST 4784-2019 – Aluminium and wrought aluminium alloys: grades
- EN 755-2 and EN 755-6 – Extruded rod/bar, tube and profiles: mechanical properties; hexagonal bar tolerances
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
5A02 marine aluminium hex bar: frequently asked questions
What is 5A02 aluminium equivalent to?
There is no exact match, but the closest grades are Russian AMg2, EN AW-5251 and 5052 (A5052 in JIS). All are aluminium-magnesium alloys with roughly 2 – 2.8 % magnesium and similar corrosion behaviour.
Is 5A02 suitable for seawater?
Yes. Its magnesium content and low copper give very good resistance to seawater and salt spray, and it does not suffer the sensitisation that affects high-magnesium alloys kept above about 65 °C. Isolate it from stainless steel and copper alloys to avoid galvanic corrosion.
Can 5A02 be heat treated to increase strength?
No. It is a non-heat-treatable alloy; strength comes from magnesium in solid solution and from cold work. Heating only anneals it to the soft O condition.
What is the difference between O and H112 temper hex bar?
O is fully annealed for maximum ductility, suited to heading and forming. H112 is the as-extruded condition with slightly higher strength and is the usual choice for machined fittings.
How much does a 5A02 hex bar weigh?
Multiply 0.866 × across-flats² (mm) × 2.68 and divide by 1,000 for kg per metre. A 30 mm hex weighs about 2.09 kg/m, and a 50 mm hex about 5.80 kg/m.
Which filler wire should I use to weld 5A02?
ER5356 is the common choice; ER5183 gives a little more weld strength. Both match the corrosion behaviour of the parent metal.
Need 5A02 hex bar for marine fittings?
Send the size, temper, length, quantity and destination. We will reply with availability, certification and a delivered price.
