Effect of low temperature on fatigue crack formation and microstructure-scale propagation in legacy and modern Al–Zn–Mg–Cu alloys

• Fracture surface measurement techniques enhance microstructure scale characterization of cracking.
• Low temperature and high alloy purity increase fatigue resistance in 7xxx-series alloys.
• Fatigue behavior reflects the effect of low temperature on the hydrogen embrittlement process.

Temperature dependence of fatigue crack formation and microstructure-scale growth from constituent particles in 7075-T651 and 7050-T7451 is quantified via load induced fracture surface marker-bands. Larger and more abundant particles in 7075-T651 lead to increased crack formation frequency and decreased life. Crack growth rates are similar between alloys and decreased with decreasing temperature, paralleling crack formation behavior. The temperature dependence is attributed to hydrogen environment embrittlement, but is not sufficiently understood to fully model the observed behavior.