Degradation of precipitation hardening in 7075 alloy subject to thermal exposure: A Cs-corrected STEM study

Abstract Thermal exposure can cause severe damages to aluminum alloys in service. The present paper, using advanced Cs-corrected scanning transmission electron microscopy (STEM), reports on a study on the degradation of precipitation hardening in peak-aged 7075 alloy subject to thermal exposure. During the thermal exposure at 300°C, nano-scale fine precipitates in peak-aged 7075 dissolve and form coarse Mg(Zn, Cu) 2 on the surface of Al 18 Mg 3 Cr 2 dispersoid particles, which are several hundred nanometers in size, leading to the loss of precipitation strengthening. The interface between Mg(Zn, Cu) 2 and Al 18 Mg 3 Cr 2 is fully coherent and thus facilitates the heterogeneous nucleation of Mg(Zn, Cu) 2 . Therefore, the Cr content should be paid attention to for 7075 alloys that may undergo thermal exposure.