Material aluminium alloy selection guide for strength, forming and corrosion
Quick answer for choosing an aluminium alloy material
When selecting a material aluminium alloy, start with four practical questions: how strong does the part need to be, how will it be formed or machined, what corrosion environment will it face, and what surface finish is required? For general machined parts and structural hardware, 6061-T6 is often the balanced starting point. For bent sheet, housings and marine-adjacent panels, 5052-H32 is usually easier to form and more corrosion resistant. For architectural extrusions and anodized profiles, 6063-T5 is common. For high static strength, 7075-T6 or stress-corrosion-resistant 7075-T73 may be considered, but welding and corrosion limits become more important. The grade number alone is not enough; the temper after the dash can change strength, ductility and fabrication behavior as much as the alloy family itself.
What the alloy number tells you
Most wrought aluminium alloys use a four-digit designation system administered by the Aluminum Association and reflected in widely used standards and handbooks. The first digit identifies the main alloy family, giving a quick indication of chemistry, strengthening method and typical use. It is not a substitute for a product specification, but it is a useful first screen when comparing candidate materials.
| Series | Main alloying idea | Typical selection meaning |
|---|---|---|
| 1xxx | Commercially pure aluminium, generally 99.00% aluminium or higher | High conductivity and corrosion resistance, low strength |
| 2xxx | Copper | High strength, often aerospace-related, usually lower corrosion resistance unless protected |
| 3xxx | Manganese | Moderate strength, good workability, common in sheet and general fabrication |
| 4xxx | Silicon | Often used where lower melting range, wear behavior or filler alloy function matters |
| 5xxx | Magnesium | Good corrosion resistance, good sheet forming and many marine or transport uses |
| 6xxx | Magnesium and silicon | Heat-treatable, versatile, widely used for extrusions and general structural parts |
| 7xxx | Zinc, often with magnesium and copper | Very high strength potential, but corrosion and stress-corrosion behavior require care |
| 8xxx | Other elements | Special-purpose alloys, including some foil and conductor applications |
As a broad rule, 1xxx, 3xxx and 5xxx wrought alloys are strengthened mainly by strain hardening, while 2xxx, 6xxx and 7xxx alloys are commonly strengthened by heat treatment and ageing. The 4xxx family is mixed, so it should be checked alloy by alloy. This distinction matters in fabrication. Heat-treatable alloys can lose properties in welded heat-affected zones, while strain-hardened sheet can soften if it sees enough heat during forming, welding or service.
Why temper may matter more than the grade name
The temper designation follows the alloy number, as in 6061-T6 or 5052-H32. It describes the processing condition, not just a label. Two products with the same alloy number can behave very differently if one is annealed and the other is strain hardened or artificially aged.
- O temper means annealed. It generally provides maximum softness and formability, but lower strength.
- H temper applies to strain-hardened non-heat-treatable alloys, often seen in 5xxx sheet such as 5052-H32.
- T temper applies to thermally treated conditions. T5, T6 and T73 are common examples, but they are not interchangeable.
- F temper means as fabricated. It may describe the process condition, but it is usually less precise for engineering properties.
For purchasing, always specify both alloy and temper. Ordering “6061 aluminium” without “T6,” “T651,” “O” or another temper leaves room for ambiguity. For engineered parts, the specification should also include product form, thickness or section size, applicable standard, surface condition and any certification requirements.
Common aluminium alloys compared
The table below summarizes typical reference values and practical trade-offs for frequently selected wrought alloys. Values vary by product form, thickness, standard and producer data sheet, so they should be used as selection guidance rather than design allowables. For safety-critical parts, use the governing standard, certified mill test report or accepted design database.
| Alloy and temper | Typical density | Typical tensile strength range or value | Where it fits | Main limitation |
|---|---|---|---|---|
| 5052-H32 | About 2.68 g/cm³ | About 228 MPa typical ultimate tensile strength | Formed sheet, panels, tanks, brackets, marine-adjacent hardware | Lower strength than 6061-T6 or 7075-T6 |
| 6061-T6 | About 2.70 g/cm³ | About 310 MPa typical ultimate tensile strength | General machining, frames, fixtures, fittings and structural components | Not as formable as softer sheet alloys; welding can reduce local strength |
| 6063-T5 | About 2.70 g/cm³ | About 186 MPa typical ultimate tensile strength | Extrusions, architectural profiles, trim and anodized shapes | Lower strength than 6061-T6 |
| 2024-T3 | About 2.77 g/cm³ | Often listed around 480 MPa ultimate tensile strength | High-strength sheet and aerospace-style applications where fatigue performance is important | Corrosion protection is usually more important than with 5xxx or 6xxx alloys |
| 7075-T6 | About 2.81 g/cm³ | Often listed around 570 MPa ultimate tensile strength | High-strength machined parts, aerospace fittings, molds and highly loaded components | More difficult to weld and more sensitive to corrosion or stress-corrosion concerns |
This comparison shows why “aluminium alloy” is not a single material choice. 7075-T6 can have much higher static strength than 6061-T6, but that does not automatically make it better. If the part must be welded, bent tightly, used in a chloride-rich environment or anodized for appearance, a lower-strength alloy may give the more reliable overall result.
Selection criteria that should drive the decision
Strength and stiffness
Aluminium alloys vary widely in strength, but their elastic modulus is relatively close compared with steel. Changing from 6061-T6 to 7075-T6 can raise yield and tensile strength, yet it will not increase stiffness in the same proportion. If a bracket deflects too much, geometry may solve the problem more effectively than switching to a stronger alloy. Increasing section depth, adding ribs or changing the profile should be considered before assuming a high-strength 7xxx alloy is the answer.
Corrosion environment
For outdoor, marine, food-equipment-adjacent or chemically exposed parts, corrosion resistance and coating compatibility should be evaluated early. 5xxx alloys are commonly chosen for corrosion resistance, especially where sheet forming is needed. 6xxx alloys also offer useful general corrosion resistance and are widely anodized. Copper-rich 2xxx alloys and high-strength 7xxx alloys may need cladding, anodizing, conversion coating, painting or careful isolation from dissimilar metals.
Forming and bending
If the part is a bent sheet component, formability can matter more than headline tensile strength. 5052-H32 is often selected because it forms well compared with many heat-treated 6xxx and 7xxx options. Annealed tempers are easier to form but weaker, so a production route may involve forming first and then finishing or heat treating where applicable. Minimum bend radius should come from the material supplier or design standard, not from alloy family alone.
Machining and dimensional stability
6061-T6 is popular in CNC work because it machines predictably, accepts many finishes and is widely available. 7075-T6 can also machine well and offers higher strength, but cost, availability, corrosion protection and stress-corrosion behavior must be considered. For precision machining from plate, stress-relieved tempers such as T651 may be specified to reduce movement after material removal.
Welding and heat-affected zones
Weldability is a major separator between alloy choices. Many 5xxx and 6xxx alloys are weldable with proper filler selection and procedure. High-strength 2xxx and 7xxx alloys are often avoided for fusion welding unless a qualified procedure and application-specific justification exist. Even when 6061 is weldable, the heat-affected zone can lose T6 strength locally. Designers should size welded joints using post-weld properties rather than parent-metal values.
Surface finish and anodizing
Alloy chemistry affects anodized appearance. 6063 is widely used for architectural anodized extrusions because it can provide attractive finish quality. 6061 can anodize well for many industrial parts, although appearance may vary. Alloys with higher copper or zinc content can be less predictable visually and may need a finish trial if appearance is critical. For decorative surfaces, specify alloy, temper, extrusion quality, pretreatment and acceptable color variation. See also: Bolts & Fasteners.
Practical matching guide by application
- General machined aluminium parts: Start with 6061-T6 or 6061-T651 if strength, machinability, availability and cost all matter.
- Formed sheet enclosures and covers: Consider 5052-H32 where bending, corrosion resistance and moderate strength are more important than maximum strength.
- Architectural or trim extrusions: Consider 6063-T5 or related 6xxx extrusion alloys when surface finish and profile complexity matter.
- Marine-adjacent sheet and panels: Consider 5xxx alloys such as 5052 or 5083, then verify service temperature, joining method and coating system.
- High-strength non-welded components: Consider 7075-T6 or other 7xxx options only after reviewing corrosion protection, stress direction and certification needs.
- Aerospace-style high-strength sheet: 2024 and 7075 families may be relevant, but application rules, fatigue data and approved material specifications should control the final choice.
For additional metal selection explainers and surface-treatment context, visit the Metals & Surfaces section.
Common specification mistakes to avoid
The most common error is specifying only the alloy number. A drawing that says “aluminium 6061” is incomplete because 6061-O, 6061-T4, 6061-T6 and 6061-T651 do not have the same strength or dimensional behavior. Another frequent error is using catalog values without checking product form. Sheet, plate, bar, tube and extrusion can have different allowable values even under the same alloy-temper label.
Corrosion is also often treated too late in the design process. Aluminium forms a protective oxide naturally, but real service conditions may include chlorides, trapped moisture, galvanic contact, cleaning chemicals, coating damage and crevices. Stainless fasteners, carbon steel frames and copper-containing alloys can create galvanic issues if the joint design allows an electrolyte to remain in place.
A final mistake is selecting for maximum strength when the part is more likely to fail by deflection, fatigue, buckling, wear, thread pullout or poor surface finish. Material selection should start with the failure mode. If the load is low but appearance is important, 6063 may be better than 7075. If the part is welded, a lower parent-metal strength with predictable joint properties may be safer than a high-strength alloy that loses performance at the weld.
Frequently asked questions
Is 6061-T6 the best all-purpose aluminium alloy?
6061-T6 is a useful general-purpose starting point because it balances strength, machinability, corrosion resistance, availability and finishing options. However, it is not automatically the right choice for tight bending, decorative extrusions, marine sheet or very high-strength non-welded parts. The application should decide the alloy.
What is the difference between 5052 and 6061?
5052 is a 5xxx aluminium-magnesium alloy commonly selected for formed sheet and corrosion resistance. 6061 is a 6xxx magnesium-silicon alloy that is heat treatable and usually stronger in T6 temper. In simple terms, 5052 is often easier for sheet bending, while 6061-T6 is often stronger and more common for machined structural parts.
Why is 7075 stronger but not always preferred?
7075 can reach very high strength, especially in T6 temper, but it brings trade-offs in corrosion behavior, welding suitability, cost and stress-corrosion considerations. It is most attractive when high strength-to-weight ratio is essential and the design can control surface protection and joining method.
Can aluminium alloy parts be welded without losing strength?
Some aluminium alloys weld well, but welding can change local microstructure and properties. Heat-treatable alloys such as 6061-T6 may lose strength in the heat-affected zone. Welded designs should use appropriate filler, qualified procedures and post-weld strength assumptions rather than relying only on parent-metal data.
Should I use aluminium or steel for hardware?
Use aluminium when weight reduction, corrosion resistance, thermal conductivity or nonmagnetic behavior is important. Use steel when stiffness, wear resistance, high-temperature strength, low material cost or compact threaded strength is more important. Many assemblies use both, but galvanic isolation and coating details should be planned when dissimilar metals are joined.
