Material Guide

Aluminum Alloys for Aerospace: 6061 vs 7075 vs 2024 — Complete Selection Guide

By YKWiki Engineering Team · Published 2026-07-22

Quick Comparison: Aerospace Aluminum Alloys

Property6061-T67075-T62024-T3
Series6xxx (Al-Mg-Si)7xxx (Al-Zn-Mg-Cu)2xxx (Al-Cu-Mg)
Yield Strength (MPa)276503345
Tensile Strength (MPa)310572483
Elongation (%)121118
Density (g/cm³)2.702.812.78
Fatigue Strength (MPa)97159138
Corrosion ResistanceExcellentPoorFair
WeldabilityExcellentPoorFair
Relative Cost$$$$$$

6061-T6: The General-Purpose Aerospace Structural Alloy

6061-T6 is the most versatile aluminum alloy in aerospace, providing an optimal balance of strength, corrosion resistance, weldability, and machinability at the lowest cost. Its magnesium-silicide precipitation hardening (Mg₂Si) delivers 276 MPa yield strength — sufficient for non-primary structural components, interior panels, brackets, and hydraulic manifolds where extreme loading is not anticipated.

The standout property of 6061-T6 is its weldability. Unlike 7xxx and 2xxx series alloys, 6061 can be joined by all conventional fusion processes — MIG, TIG, resistance welding, and friction stir welding — without hot cracking or significant loss of strength in the heat-affected zone. This makes it the default choice for welded airframe assemblies, fuel tank structures, and repair of field-damaged components.

Corrosion resistance is excellent, with the 6xxx series forming a stable, protective oxide layer that tolerates atmospheric exposure, freshwater, and mild marine conditions without anodizing. In aerospace service, 6061-T6 is used for wing fairings, cockpit components, passenger cabin structures, and non-pressurized fuselage skins where its 2.70 g/cm³ density and moderate strength provide adequate performance with minimal weight penalty.

See 6061-T6 vs 7075-T6 for a detailed head-to-head comparison.

7075-T6: The High-Strength Aerospace Grade

7075-T6 is the strongest commonly available aluminum alloy, delivering 503 MPa yield strength — nearly double that of 6061-T6. Developed for military aircraft during World War II, 7075 remains the primary structural alloy for high-stress airframe components: wing spars, fuselage frames, bulkheads, and landing gear forgings. Its zinc-magnesium-copper precipitation hardening (primarily η' MgZn₂ precipitates) provides the exceptional strength-to-weight ratio that makes aluminum competitive with titanium in many aerospace applications.

The critical limitations of 7075-T6 are its poor corrosion resistance and weldability. The copper-bearing 7xxx alloys are susceptible to stress corrosion cracking (SCC) and exfoliation corrosion, particularly in the short-transverse direction of thick plate and forgings. All 7075-T6 aerospace components require protective anodizing, chromate conversion coating, or organic coating systems for environmental protection. The T73 overaged temper sacrifices approximately 15% of T6 yield strength to dramatically improve SCC resistance — a common trade-off for thick-section structural forgings.

7075 cannot be reliably welded by fusion processes. The high zinc and copper content causes hot cracking and severe property degradation in the HAZ. All 7075 structural joints must use mechanical fasteners (rivets, bolts, Hi-Loks) or adhesive bonding. This design constraint drives significant manufacturing cost, as every joint requires precision hole drilling, cold-working, and interference-fit fastener installation per military specifications.

See 6061-T6 vs 7075-T6 for cost and weldability trade-offs, and Ti-6Al-4V vs 7075-T6 for the aluminum-vs-titanium decision.

2024-T3: The Fatigue-Resistant Classic

2024-T3 is the original Duralumin alloy — the material that made all-metal aircraft possible in the 1930s. Its copper-magnesium precipitation hardening delivers 345 MPa yield strength with an exceptional fatigue endurance limit of 138 MPa, making it the preferred alloy for fatigue-critical structures: lower wing skins, fuselage skins under cyclic pressurization, and rotorcraft dynamic components.

The 18% elongation of 2024-T3 is the highest among the three alloys compared, providing superior damage tolerance and crack growth resistance. In damage-tolerant design philosophy (FAR 25.571), 2024-T3 allows slower crack propagation rates than 7075-T6, giving inspectors more time to detect fatigue cracks before critical length is reached. This makes 2024-T3 the standard for fuselage skins on commercial transport aircraft, where pressurization cycles exceed 60,000 over the airframe life.

Corrosion resistance is intermediate — better than 7075 but inferior to 6061. 2024 requires alclad protection (a thin pure-aluminum surface layer metallurgically bonded during rolling) for atmospheric service. The alclad layer sacrifices ~5% of static strength but provides galvanic protection that prevents pitting and intergranular corrosion of the core alloy. In modern practice, 2024-T3 with alclad remains the standard for commercial transport fuselage skins.

Application-Specific Recommendations

Wing Structures and Primary Load Path

Use 7075-T6 for upper wing skins and spar caps (compressive-dominated, high stress) and 2024-T3 for lower wing skins (tension-dominated, fatigue-critical). This bimetallic wing design is standard practice on commercial and military aircraft worldwide.

Fuselage Skins

Use 2024-T3 alclad for pressurized fuselage skins where damage tolerance and fatigue resistance are paramount. The superior crack growth resistance provides the safety margin required by FAR 25.571 damage tolerance requirements.

Welded Assemblies and Non-Primary Structure

Use 6061-T6 for any component requiring fusion welding: fuel tanks, hydraulic manifolds, welded brackets, and repair patches. Its weldability eliminates the need for costly mechanical fastening in non-critical assemblies.

Landing Gear and Forgings

Use 7075-T73 (overaged) for landing gear components and large forgings where stress corrosion cracking is a concern. The 15% strength penalty versus T6 is acceptable for the dramatically improved SCC resistance in thick sections.

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Frequently Asked Questions

Why is 7075-T6 used for aircraft wings but not fuselage skins?

7075-T6 has the highest static strength (503 MPa yield) which is ideal for upper wing skins under compressive loading. However, its fatigue crack growth rate is 3-5× faster than 2024-T3, making it unsuitable for fuselage skins that undergo thousands of pressurization cycles. 2024-T3's superior damage tolerance and slower crack propagation provide the safety margin required by FAR 25.571 for pressurized structures.

Can 7075 aluminum be welded?

No. 7075 cannot be reliably welded by conventional fusion processes (MIG, TIG). The high zinc and copper content causes hot cracking and severe property loss in the heat-affected zone. All 7075 structural joints use mechanical fasteners (rivets, Hi-Loks, bolts) or adhesive bonding. If welding is required, use 6061-T6 instead.

What is alclad 2024-T3?

Alclad 2024-T3 is 2024-T3 aluminum sheet with a thin (2.5-5% of total thickness) layer of commercially pure aluminum metallurgically bonded to both surfaces. The pure aluminum cladding provides galvanic corrosion protection, preventing pitting and intergranular attack on the core alloy. The clad layer reduces net section strength by approximately 5% — an acceptable trade-off for the dramatically improved corrosion performance.

Which aluminum alloy is best for fatigue resistance?

2024-T3 provides the best fatigue resistance among common aerospace aluminum alloys, with an endurance limit of 138 MPa and the slowest fatigue crack growth rate. Its 18% elongation and damage-tolerant microstructure make it the standard for cyclic-loaded structures like fuselage skins and lower wing caps.

How does the T73 temper improve 7075?

The T73 overaged temper sacrifices approximately 15% of T6 yield strength (dropping from 503 MPa to ~435 MPa) but dramatically improves stress corrosion cracking (SCC) resistance in the short-transverse direction. T73 is specified for thick-section forgings and plate where residual stresses from quenching create SCC risk. For primary structure requiring maximum strength, T6 is used with mandatory protective coatings.

References & Standards