Fatigue properties of a modified 7075 aluminum alloy containing scandium

Fatigue properties such as the fatigue strength, fatigue notch sensitivity, and fatigue crack propagation rate, of a modified Al-7075 + Sc aluminum alloy were investigated in this study. The effects of solution treatment on the fatigue performance of this alloy were also investigated. The ultimate tensile strength of the as-extruded sample was 705.5 MPa. The ultimate tensile strength decreased by 12% after solution treatment. The fatigue limit σe of the as-extruded sample decreased from 201.2 to 154.4 MPa after solution treatment. The fatigue notch sensitivity for the as-extruded and solution-treated (ST) samples was 0.97 and 0.64, respectively. The crack growth rate in the as-extruded sample with fine precipitates was clearly lower than that of the ST sample that had coarse precipitates at R = 0.1 when ΔK < 15 MPa\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \sqrt m $$\end{document}. However, the growth rates of both the samples were approximately the same when ΔK > 15 MPa\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \sqrt m $$\end{document}. The higher yield strength of the as-extruded sample led to a lower crack growth rate when compared to the ST sample.