Abstract
The fatigue crack growth (FCG) behavior and fatigue strength of 7020 aluminum alloy in an over aged treatment and two retrogression and re-aging (RRA) treatments were investigated. The microstructures and fractographies were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The result showed that RRA-treated alloys have faster FCG rate than over aged alloy at lower ΔK region due to the dense non-shearable precipitates. And the RRA120 alloy re-aged at 120 °C/24 h has a relatively faster FCG rate than RRA150 alloy re-aged at 150 °C/12 h. RRA-treated alloys have higher fatigue strength than over aged alloy. The fatigue strength corresponding to 107 cycles of over aged, RRA120 and RRA150 conditions are 114, 129 and 118 MPa, respectively. The effect of RRA treatment on the fatigue property is mainly caused by its finer and more dispersed precipitates and narrower precipitate free zone (PFZ).
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