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.It is often clad with aluminium or Al-1Zn for protection, although this may reduce the fatigue strength. 2024 is commonly extruded, and also available in alclad sheet and plate forms.