The solution quenching process is a critical heat treatment process for aluminum alloy aiming at obtaining better strength and homogeneous super solid solution. In this paper, the mechanical properties of Al-5%Cu-0.4%Mn (which is labled as ZL205 in China standard with similar chemical content of 2XXX series aluminum alloy) in as-quenched state, which is used for constructing large thin wall components. are tested. ZL205A shows good performance under loading at room temperature, while losing its toughness and exhibiting tensile brittleness, which is unexpected, at elevated temperature (especially at 300°C). After observing the fracture sections of ZL2O5A at room temperature and 300°C, it may be concluded that one possible reason leading to this phenomena may be the formation of T phase at grain boundaries. Such a hypothesis is validated and discussed with the help of SEM observations.