Experimental analysis and modelling of natural aging in AA7xxx Al alloys

•Microstructural characteristics of naturally aged AA7xxx alloys are investigated.•The natural aging kinetics of different AA7xxx alloys are analyzed.•Compositional similarities in AA7xxx alloys result in similar rates of natural aging.•A reverse yield strength modeling methodology is provided to analyze the kinetics of natural aging in AA7xxx alloys. The effect of natural aging on the strengthening behavior and microstructural characteristics of AA7xxx alloys is investigated using a combination of hardness measurement, tensile testing, differential scanning calorimetry (DSC), and atom probe tomography (APT). Compositional similarities in copper-containing AA7xxx alloys result in a parallel logarithmic trend in their yield strength evolution and similar rates of natural aging. Through microstructural analysis, three types of precipitates are identified in the microstructure of the as-quenched and naturally-aged conditions of AA7075. Nucleation of Zn-Mg precipitates is the main precipitation phenomenon during natural aging of the as-quenched AA7075 alloy, while the precipitates formed during quenching remain unchanged. The kinetics of natural aging for two different AA7xxx alloys is analyzed through a reverse yield strength modelling methodology. Following validation, the methodology is used to investigate the natural aging kinetics of four different AA7xxx alloys. It is concluded that compositional similarities cause similar kinetics of precipitation during natural aging of AA7xxx alloys. The calculated parameters are used to model the yield strength evolution during natural aging of AA7xxx alloys. The model predictions are found to agree well with the experimental results reported in the literature.