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Selecting an aircraft aluminum alloy means balancing three competing demands: strength-to-weight ratio for airframe performance, fatigue life for inspection intervals, and damage tolerance for safety margins. A wrong grade choice — or an overlooked temper specification — can add structural weight, increase crack growth rates under cyclic loading, or create corrosion risks that shorten service life.
This guide covers the main alloy families used in aerospace structures: 2xxx series (2024-T3), 7xxx series (7075-T6 / 7075-T73), and the 6xxx series (6061-T6 and 6063-T6) for secondary structures. Each section explains what the alloy is actually good for, where the limits are, and what to check before specifying or ordering.
Primary Aircraft Alloy Families
2xxx Series: 2024-T3 — Fatigue-Driven Airframe Alloy
2024 aluminiumlegering is the baseline airframe material. Its copper content provides high tensile strength (approximately 470 MPa) and excellent fatigue crack growth resistance — particularly important in tension-dominated lower wing skins where cracks grow under repeated load cycles before detection.
2024-T3 uses natural aging at room temperature after solution heat treatment and cold working. This temper provides a strong balance of strength and damage tolerance without the stress corrosion cracking risk associated with some 7xxx tempers.
The main trade-off: 2024 offers better fatigue crack growth behavior than 7075 in tension applications, but its general corrosion resistance is poor. Exterior applications require Alclad — a thin layer of pure aluminum roll-bonded to the surface — for protection. Fusion welding is strongly discouraged; the heat-affected zone loses significant strength and the copper-rich chemistry makes sound welds difficult to achieve.
Typical applications: fuselage skins, lower wing skins (tension-dominated), bulkhead webs, and rib structures.
7xxx Series: 7075-T6 and 7075-T73 — Peak-Strength Structural Alloys
7075 aluminiumlegering provides the highest strength commercially available in aluminum — approximately 572 MPa tensile and 503 MPa yield in the T6 temper. Its zinc-based chemistry makes it the default choice for compression-dominated structures and high-stress components where weight savings justify higher material cost.
Tempers matter significantly for 7075:
- 7075-T6: Solution heat treated and artificially aged for maximum strength. The main risk is stress corrosion cracking (SCC) in the short-transverse direction of thick sections. Use for parts where SCC exposure is controlled or where the service environment allows it.
- 7075-T73: Solution heat treated and overaged to improve SCC resistance. Tensile strength drops approximately 10-15% from T6 levels, but SCC resistance increases significantly. This temper is standard for thick-section forgings and parts exposed to sustained tensile stress in corrosive environments.
7075 has poor weldability — similar to 2024 in this respect — and should not be fusion-welded in primary structural applications. Its corrosion resistance is moderate; anodizing or protective coatings are standard practice for exterior exposure.
Typical applications: upper wing skins (compression-dominated), fuselage frames, wing spars, landing gear components, and high-stress machined fittings.
6xxx Series: 6061-T6 and 6063-T6 — Weldable Secondary-Structure Alloys
6061 aluminiumlegering en 6063 aluminiumlegering are magnesium-silicon alloys with good weldability and corrosion resistance — the opposite trade-off from 2024 and 7075. They are not primary-structure grades in commercial aerospace, but they appear widely in secondary brackets, interior fittings, instrument mounts, and non-load-bearing components where weldability or anodizing quality matters more than peak strength.
| Eigendom | 6061-T6 | 6063-T6 |
|---|---|---|
| Treksterkte | 290 MPa (42 ksi) min | 241 MPa (35 ksi) min |
| Opbrengststerkte | 276 MPa (40 ksi) min | 207 MPa (30 ksi) min |
| Rek | 12% min (50 mm) | 8% min (50 mm) |
| Bewerkbaarheid | Goed | Uitstekend |
| Lasbaarheid | Good — standard TIG/MIG procedures | Excellent — commonly extruded and welded |
| Anodiseerrespons | Good — clear, black, color anodizing | Excellent — superior surface finish after anodizing |
| Aerospace Role | Secondary brackets, fittings, interior structures | Interior trim, non-structural extrusions, cabin components |
6063-T6 is easier to extrude into complex profiles and produces a smoother anodized surface, making it the standard choice for visible interior components. 6061-T6 is stronger and is preferred when the secondary part carries moderate structural load.
Heat Treatment and Temper Selection
Temper designation is as important as alloy choice — the same base chemistry produces fundamentally different properties depending on processing. In aerospace, three temper families dominate:
- T3 (2024-T3): Solution heat treated, cold worked, and naturally aged at room temperature. Provides good strength with high damage tolerance. Common for fuselage and lower wing skins.
- T6 (7075-T6, 6061-T6): Solution heat treated and artificially aged for peak strength. Shorter aging time than T73. Use where maximum tensile and yield values are required and SCC risk is managed.
- T73 (7075-T73): Solution heat treated and overaged beyond peak strength. Sacrifices approximately 10-15% of tensile strength for substantial improvement in stress corrosion cracking resistance. Standard for thick-section 7075 forgings in corrosive environments.
The aging step — whether at room temperature (natural aging) or elevated temperature (artificial aging) — controls the precipitation hardening that gives these alloys their final strength. Skipping or shortening aging to save production time creates parts that do not meet specification values.
Aircraft Aluminum Grade Comparison
| Eigendom | 2024-T3 | 7075-T6 | 6061-T6 | 6063-T6 |
|---|---|---|---|---|
| Treksterkte | ~470 MPa | ~572 MPa | ~ 310 MPa | ~241 MPa |
| Opbrengststerkte | ~345 MPa | ~503 MPa | ~276 MPa | ~207 MPa |
| Weerstand tegen vermoeiing | Uitstekend | Goed | Matig | Laag |
| Corrosiebestendigheid | Poor — requires Alclad for exterior | Moderate — anodizing standard | Goed | Uitstekend |
| Lasbaarheid | Not weldable for primary structure | Not weldable | Good — TIG/MIG | Uitstekend |
| SCC Resistance | Moderate (T3 temper) | T6: Low | T73: High | Hoog | Hoog |
| Primary Aerospace Role | Fuselage skins, lower wing, bulkheads | Upper wing, frames, spars, landing gear | Secondary brackets, fittings, interiors | Interior trim, non-structural extrusions |
Go/No-Go Selection Logic
Use the criteria below to narrow the alloy choice before checking temper, form, and document requirements. Each entry states the condition first — so the decision follows from the engineering requirement, not from the alloy name.
Go — Use This Alloy When
- Fatigue crack growth resistance and damage tolerance drive the decision: 2024-T3 is the standard. Typical scenario: fuselage skins and lower wing skins where crack propagation under cyclic tension is the primary design limit.
- Peak strength and minimum weight are the main requirements: 7075-T6 fits when compression or high tensile loads dominate and the part geometry limits alternative materials. Typical scenario: upper wing skins, landing gear beams, high-stress machined fittings.
- Stress corrosion cracking resistance is critical and the part is a thick-section forging: 7075-T73 provides a safer temper for applications with sustained tensile stress in corrosive environments. Typical scenario: wing spar forgings, bulkhead forgings with short-transverse tensile loading.
- Welding is required and strength is moderate: 6061-T6 is the default for secondary brackets and fittings that need to be welded in place. Typical scenario: interior support brackets, instrument mounting plates, repair parts.
- Surface finish and extrudability matter more than strength: 6063-T6 is the standard for visible non-structural profiles. Typical scenario: cabin trim, seat tracks, decorative extrusions.
No-Go — Do Not Use This Alloy When
- The part requires fusion welding in primary structure: 2024-T3 and 7075-T6 are not suitable — the heat-affected zone loses temper strength, and crack-sensitive chemistry makes weld quality unreliable.
- Exterior exposure without cladding or coating is required: 2024-T3 without Alclad will corrode rapidly in moisture — specify Alclad or switch to a more corrosion-resistant alloy if protection is not possible.
- 7075-T6 is specified for a thick-section part exposed to sustained tension and corrosive conditions: Check whether 7075-T73 is required instead — the SCC risk difference is significant.
- 6061-T6 is proposed for primary airframe structure where 2024 or 7075 is the specification: 6061-T6 does not meet the strength or fatigue requirements — it is a secondary-structure alloy in aerospace.
Corrosion, Fatigue, and Operational Limits
Understanding failure modes is as important as knowing alloy properties. The three most relevant limits in aerospace aluminum structures are:
Exfoliation corrosion: 2xxx and 7xxx series alloys are susceptible due to their grain structure. Corrosion attacks grain boundaries parallel to the rolling direction, causing layers of metal to separate. Alclad on 2024 and anodizing or coatings on 7075 are the standard countermeasures. Inspection intervals must account for the risk.
Stress corrosion cracking: 7075-T6 develops SCC when sustained tensile stress acts in the short-transverse direction in a corrosive environment. The primary mitigation is switching to 7075-T73 for affected parts, or redesigning to avoid short-transverse tensile loading.
Fatigue crack initiation vs. propagation: 2024-T3 has better crack growth resistance (slower propagation once a crack starts) while 7075-T6 has higher initiation resistance (takes more cycles to start a crack). This distinction drives alloy assignment: 2024 for tension-dominated skins where cracks must grow slowly enough for inspection to catch them, and 7075 for compression structures where initiation resistance matters more.
For any aerospace aluminum order, the material certificate should confirm the alloy, temper, and mechanical properties against the governing specification — typically AMS, ASTM, or an internal OEM standard. If the part geometry involves thick sections, check whether ultrasonic testing is required.
Conclusie
2024-T3, 7075-T6, 6061-T6, and 6063-T6 cover the main aircraft aluminum alloy families. The real risk is not choosing the wrong alloy family — it is overlooking temper, ignoring form-specific limits, or using a weldable alloy where the specification requires a non-weldable aerospace grade.
Linsy Aluminum stocks 2024, 7075, 6061, and 6063 aluminum in plate, sheet, bar, and tube forms. Every order ships with a full MTC documenting alloy chemistry and mechanical properties. Custom dimensions and low-MOQ orders are supported when standard stock does not match the part geometry. SGS test reports — including chemical composition, mechanical properties, and ultrasonic inspection — are available on request.
If the project involves tight temper, thickness, or document requirements, send the drawing or specification for a grade-fit review.
FAQ
Can 2024-T3 aluminum be welded?
For primary aircraft structure — no. 2024-T3 is fusion-weldable only with specialized filler materials and process controls, and the heat-affected zone loses significant strength. Mechanical fastening is the standard joining method. If welding is required, consider 6061-T6 for secondary applications instead.
What is the difference between 7075-T6 and 7075-T73?
7075-T73 is overaged beyond peak strength to improve stress corrosion cracking resistance. Tensile strength drops approximately 10-15% compared to T6, but SCC resistance increases significantly. T73 is standard for thick-section forgings and parts exposed to sustained tensile stress in corrosive environments.
Is 6061-T6 suitable for primary aircraft structure?
No. 6061-T6 has approximately 310 MPa tensile strength — well below 2024-T3 and 7075-T6. It is used for secondary brackets, fittings, interior structures, and welded assemblies where the load is lower and weldability or corrosion resistance matters more than peak strength.
What is Alclad and when is it required?
Alclad is a thin layer of high-purity aluminum roll-bonded to 2024 sheet and plate surfaces during manufacturing. It provides galvanic corrosion protection for the copper-rich alloy underneath. Alclad 2024 is required for any exterior aircraft skin application where moisture exposure is expected.
How is temper verified before accepting an aluminum shipment?
The material test certificate (MTC) should list the alloy, temper, and measured mechanical properties against the governing specification. Hardness testing and conductivity testing are practical field verification methods: 2024-T3 has a typical conductivity of 30-33% IACS, while 7075-T6 is approximately 32-35% IACS. Tensile testing on a sample coupon from the actual lot provides definitive confirmation.
