Aerospace aluminium alloys

The materials used for aircraft manufacture must meet a demanding set of property requirements. Aircraft structures must be lightweight, durable and damage tolerant.

Furthermore, these properties must be attained at as low a cost as possible.

High strength aluminium alloys are able to meet the property challenges in a cost effective way and aluminium therefore remains the predominant choice for the construction of civil aircraft, although competition from other materials is increasingly intense.

Aluminium Alloys in Aerospace are used for three aerospace applications:

Fuselage skin

Upper wing skin

Lower wing skin

These three applications all have different property requirements, and this leads to different alloy selection choices.

Fuselage Skin

The materials used for the fuselage skin are determined by the loading (e.g. compressive or tensile, static or dynamic).

The fuselage will experience different loads depending on whether the aeroplane is in flight, or on the ground.

Materials selection for the wing skins.

The upper and lower wing skins are subject to different loading conditions in flight. This influences the choice of materials in each case. There are important differences in property requirements.

The fuselage requires a material that is both strong and has a high fracture toughness.

Upper Wing Skin Material must have

Compressive strength

Stiffness

Fatigue resistance

Fracture toughness

Compressive strength is the key property for upper wing skin.

Lower Wing Skin Material must have

Tensile strength

Fatigue resistance

Fracture toughness

Also, which alloys have the best resistance to fatigue crack growth?

There are a number of age hardenable alloys that do exceed the minimum strength and fracture toughness requirements. However, it is also critical that the lower wing skin is damage tolerant and is able to resist failure by fatigue crack growth.

The properties required for fuselage and wing-skins of aeroplanes all require strong, lightweight (low density) materials.

However, a different balance of properties is required for the fuselage, upper wing skin and lower wing skin. To meet these different requirements, different aluminium alloys are chosen.