Mechanisms of combined GP zone and θ' precipitation in an Al-Cu alloy

摘要

Al-Cu alloys with copper contents of around 3-4.5 wt% Cu form the basis of an important class of heat treatable aluminium alloys. The full precipitation sequence of binary Al-Cu alloys is [1, 2]: Solid solution → GPI → GPII → θ'→θ where GP stands for Guinier-Preston zone, 6' (Al2Cu) is a semi-coherent metastable phase, and 9 (AI2C11) is the equilibrium phase. Precipitation hardening in commercial Al-Cu alloys is mostly carried out at temperatures around 150-180 °C, at which both GP zones and 9' phase form. Al-Cu alloys have been studied extensively, and the structures of the GP zones and the 0 and 6' phases have been identified [1, 3-9]. Generally, GPI zones are considered to be planes of copper along {10 0} planes, while GPII zones are clusters of two or more parallel planes of copper separated by three planes of Al [9, 10]. On the other hand, the kinetics of GP zones and 0' phase formation have received less attention, and little is known about the kinetics of precipitation in the temperature range where both phases occur.