2024 aluminium alloy

2024 aluminium alloy is an aluminium alloy, with copper as the primary alloying element. It is used in applications requiring high strength-to-weight ratio, as well as good fatigue resistance. It is weldable only through friction welding, and has average machinability. Due to poor corrosion resistance, it is often clad with aluminium or Al-1Zn for protection, although this may reduce the fatigue strength. In older systems of terminology, 2XXX series alloys were known as duralumin, and this alloy was named 24ST.

2024 is commonly extruded, and also available in alclad sheet and plate forms. It is not commonly forged (the related 2014 aluminium alloy is, though).

Basic properties
Aluminium alloy 2024 has a density of 2.78 g/cm3 (0.1 lb/in3), electrical conductivity of 30% IACS, Young's Modulus of 73 GPa (10.6 Msi) across all tempers, and begins to melt at 500 C.

2024 aluminium alloy's composition roughly includes 4.3–4.5% copper, 0.5–0.6% manganese, 1.3–1.5% magnesium and less than half a percent of silicon, zinc, nickel, chromium, lead and bismuth.

Chemical composition
The alloy composition of 2024 is:
 * Aluminium (90.7–94.7%)
 * Silicon no minimum, maximum 0.5% by weight
 * Iron no minimum, maximum 0.5%
 * Copper minimum 3.8%, maximum 4.9%
 * Manganese minimum 0.3%, maximum 0.9%
 * Magnesium minimum 1.2%, maximum 1.8%
 * Chromium no minimum, maximum 0.1%
 * Zinc no minimum, maximum 0.25%
 * Titanium no minimum, maximum 0.15%
 * Other elements no more than 0.05% each, 0.15% total

Mechanical properties
The mechanical properties of 2024 depend greatly on the temper of the material.

2024-O
2024-O temper aluminium has no heat treating. It has an ultimate tensile strength of 21 - 30 ksi, and maximum yield strength of no more than 14000 psi. The material has elongation (stretch before ultimate failure) of 10–25%, this is the allowable range per applicable AMS specifications.

2024-T3
T3 temper 2024 sheet has an ultimate tensile strength of 58 - 62 ksi and yield strength of at least 39 - 40 ksi. It has an elongation of 10–15%.

2024-T4
Solution treated at foundry and naturally aged.

2024-T5
Cooled from hot working and artificially aged (at elevated temperature)

2024-T351
T351 temper 2024 plate has an ultimate tensile strength of 68 ksi and yield strength of 41 ksi. It has elongation of 20%.

Uses
Due to its high strength and fatigue resistance, 2024 is widely used in aircraft, especially wing and fuselage structures under tension. Additionally, since the material is susceptible to thermal shock, 2024 is used in qualification of liquid penetrant tests outside of normal temperature ranges.