MetalsAlloy5251 Aluminum
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5251 Aluminum (AA 5251) is a wrought aluminum–magnesium alloy in the 5000 series, internationally cross-referenced as AlMg2. Its 1.7–2.4% magnesium content provides medium strength, rapid work hardening, and useful ductility for formed sheet and plate components. The alloy is especially valued for corrosion resistance, including marine exposure, together with ready weldability. Unlike heat-treatable 6xxx alloys, 5251 develops strength principally through cold work; the selected O or H temper therefore has a major effect on finished-part strength and formability. It is commonly considered where corrosion-resistant, fabricated sheet is needed without the higher magnesium level of 5754 or 5083.
| Chemical Composition wt.% | ||
|---|---|---|
| Element | Min | Max |
| Silicon | — | 0.40 |
| Iron | — | 0.50 |
| Copper | — | 0.15 |
| Manganese | 0.10 | 0.50 |
| Magnesium | 1.7 | 2.4 |
| Chromium | — | 0.15 |
| Zinc | — | 0.15 |
| Titanium | — | 0.15 |
| Others, each | — | 0.05 |
| Others, total | — | 0.15 |
| Aluminum | Remainder | |
Registered wrought composition limits in mass percent. Values shown as a single number are maximum limits unless stated as a range. Aluminum is the remainder; the registered limits also specify 0.05% maximum for each other element and 0.15% maximum for others total.
Physical-property values and sheet/plate mechanical-property values are reported by AZoM. Mechanical figures are temper- and thickness-specific minimums or ranges, not universal values for all 5251 products.
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| Physical Properties | Metric |
|---|---|
| Density | 2.69 g/cm³2.69 g/cm³ |
| Mechanical Properties | Metric |
| Modulus of Elasticity | 70 GPa |
| Proof Stress (O, sheet and plate 0.2–50.00 mm) | ≥60 MPa |
| Tensile Strength (O, sheet and plate 0.2–50.00 mm) | 160–200 MPa |
| Brinell Hardness (O) | 44 HB |
| Proof Stress (H22, sheet and plate 0.2–25 mm) | ≥120 MPa |
| Tensile Strength (H22, sheet and plate 0.2–25 mm) | 190–230 MPa |
| Brinell Hardness (H22) | 56 HB |
| Proof Stress (H24, sheet and plate 0.2–12.5 mm) | ≥140 MPa |
| Tensile Strength (H24, sheet and plate 0.2–12.5 mm) | 210–250 MPa |
| Brinell Hardness (H24) | 62 HB |
| Proof Stress (H26, sheet and plate 0.2–4 mm) | ≥170 MPa |
| Tensile Strength (H26, sheet and plate 0.2–4 mm) | 230–270 MPa |
| Brinell Hardness (H26) | 69 HB |
| Thermal Properties | Metric |
| Melting Point | 625 °C |
| Thermal Conductivity | 134 W/(m·K) |
| Thermal Expansion | 25 × 10⁻⁶ /K |
| Electrical Properties | Metric |
| Electrical Resistivity | 0.44 × 10⁻⁶ Ω·m |
Test conditions & data notes
- Density: Typical reported value
- Melting Point: Typical reported value
- Modulus of Elasticity: Typical reported value
- Thermal Conductivity: Typical reported value
- Thermal Expansion: Typical reported value
- Electrical Resistivity: Typical reported value
- Proof Stress (O, sheet and plate 0.2–50.00 mm): Soft O condition; BS EN 485-2:2008.
- Tensile Strength (O, sheet and plate 0.2–50.00 mm): Soft O condition; BS EN 485-2:2008.
- Brinell Hardness (O): Soft O condition; sheet and plate 0.2–50.00 mm.
- Proof Stress (H22, sheet and plate 0.2–25 mm): H22 condition; BS EN 485-2:2008.
- Tensile Strength (H22, sheet and plate 0.2–25 mm): H22 condition; BS EN 485-2:2008.
- Brinell Hardness (H22): H22 condition; sheet and plate 0.2–25 mm.
- Proof Stress (H24, sheet and plate 0.2–12.5 mm): H24 condition; BS EN 485-2:2008.
- Tensile Strength (H24, sheet and plate 0.2–12.5 mm): H24 condition; BS EN 485-2:2008.
- Brinell Hardness (H24): H24 condition; sheet and plate 0.2–12.5 mm.
- Proof Stress (H26, sheet and plate 0.2–4 mm): H26 condition; BS EN 485-2:2008.
- Tensile Strength (H26, sheet and plate 0.2–4 mm): H26 condition; BS EN 485-2:2008.
- Brinell Hardness (H26): H26 condition; sheet and plate 0.2–4 mm.
Material Conditions & Tempers
5251 is non-heat-treatable: O temper provides maximum forming latitude, while strain-hardened H tempers progressively increase proof and tensile strength. Confirm product form, thickness, and the governing procurement specification because guaranteed properties vary with each.
| Condition | Tensile Strength | Yield / Proof Strength | Notes |
|---|---|---|---|
| O | 160–200 MPa | ≥60 MPa | Annealed (soft) sheet and plate condition for demanding forming. Reported for sheet and plate 0.2–50.00 mm. |
| H22 | 190–230 MPa | ≥120 MPa | Strain-hardened and partially annealed condition balancing strength and formability. Reported for sheet and plate 0.2–25 mm. |
| H24 | 210–250 MPa | ≥140 MPa | Higher-strength strain-hardened and partially annealed sheet/plate condition. Reported for sheet and plate 0.2–12.5 mm. |
| H26 | 230–270 MPa | ≥170 MPa | High strain-hardened condition where forming demand is comparatively limited. Reported for sheet and plate 0.2–4 mm. |
Advantages & Limitations
| Advantages | Limitations |
|---|---|
|
|
Processing & Fabrication
| Process | Description |
|---|---|
| Cold forming | 5251 has good ductility and is rated very good for cold workability. Select O temper for the most severe forming; account for rapid work hardening when planning multi-stage operations. |
| Welding | The alloy is readily weldable and is rated very good for gas and arc welding. AZoM identifies 5356 filler for 5251-to-5251 and many 5xxx/6xxx/7xxx joints, while 4043 is identified for joints to 5005, 5020, 1xxx, or 3xxx alloys; qualify the filler and procedure for the specific joint and service environment. |
| Machining | Machinability is described as average. Use sharp tooling, appropriate lubrication, and workholding that limits distortion of thin sheet. |
| Finishing | Clean surfaces before welding, bonding, or coating to remove oxide, lubricant, and contaminants. The alloy’s natural oxide supports corrosion resistance, but finishing and isolation practices should suit the actual exposure and adjoining materials. |
Applications
5251 is suited to fabricated products that combine moderate strength, low mass, formability, weldability, and corrosion resistance. Typical selection centers on sheet and plate assemblies rather than highly machined parts or heat-treated structural members.
- Marine sheet fabrications: Its corrosion resistance in marine environments and ready weldability suit non-critical marine enclosures, fittings, and fabricated panels.
- Vehicle and transport body panels: Low density and good forming response help reduce mass in formed bodywork, covers, and interior or exterior panels.
- Architectural and building sheetwork: The alloy can be bent and fabricated into trims, flashings, cladding details, and enclosures while offering atmospheric corrosion resistance.
- General tanks, cabinets, and enclosures: Moderate strength, good sheet formability, and weldability support light fabricated vessels and protective housings.
- Formed consumer and industrial components: O, H22, and H24 tempers offer practical options where the balance between drawability and finished-part stiffness must be tailored.
Standards & Designations
| Designation | Value | Description |
|---|---|---|
| Aluminum Association / International Alloy Designation System | 5251 (AA 5251) | Active registered wrought aluminum alloy designation; composition limits are listed in the Aluminum Association Teal Sheets. |
| ISO cross-reference | AlMg2 | The Aluminum Association cross-reference table identifies 5251 as AlMg2. |
| BS EN 485-2:2008 | 5251 sheet and plate mechanical-property basis | AZoM reports the cited O, H22, H24, and H26 sheet/plate values on this basis; verify the current edition and applicable dimensional range for procurement. |
Frequently Asked Questions
Is 5251 Aluminum heat treatable?
No. 5251 is a non-heat-treatable 5xxx-series aluminum–magnesium alloy. Its strength is adjusted primarily through strain hardening, which is why O, H22, H24, and H26 conditions have distinctly different mechanical properties.
What is the difference between 5251 O and 5251 H24?
O is the soft annealed condition and provides the greatest forming latitude. H24 is strain hardened and partially annealed; for the cited 0.2–12.5 mm sheet and plate range, it has tensile strength of 210–250 MPa and proof stress of at least 140 MPa, versus 160–200 MPa and at least 60 MPa for cited O material.
Can 5251 Aluminum be welded?
Yes. 5251 is readily weldable and is described as very good for gas and arc welding. Welding can locally soften strain-hardened material, so joint design and post-weld strength requirements should be evaluated for the chosen temper. Filler selection must be qualified for the materials being joined and the intended service.
References & Data Notes
- (n.d.). The Aluminum Association, International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys (Teal Sheets), December 2025. https://www.aluminum.org/sites/default/files/2026-01/Teal%20Sheets%20December%202025.pdf
- (n.d.). AZoM, Aluminium Alloys – Aluminium 5251 Properties, Fabrication and Applications. https://www.azom.com/article.aspx?ArticleID=2805
- (n.d.). Engineer Calculator, Properties and Overview of Aluminium Alloy 5251. https://engineercalculator.com/metal-alloy-properties-and-overview/aluminium-alloy-5251-various-properties-and-overview
Chemical composition is the registered AA 5251 wrought-alloy limit composition. Physical and mechanical values are source-reported reference data; mechanical properties apply only to the stated temper, sheet/plate thickness range, and cited standard basis. Confirm current specification requirements, product form, dimensions, and certified mill test data before design or purchase.