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

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 Al18Mg3Cr2 dispersoid particles, which are several hundred nanometers in size, leading to the loss of precipitation strengthening. The interface between Mg(Zn, Cu)2 and Al18Mg3Cr2 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. [Display omitted] •The degradation mechanism of peak-aged 7075 during thermal exposures revealed.•The effect induced by dispersoid on precipitation hardenings discussed.•The interface between the precipitate/dispersoid interface is fully coherent.•Cr content should be considered when designing 7075 that may undergo thermal exposure.