Effect of Interrupted Ageing and Retrogression-Reageing Treatments on Fatigue Crack Growth with a Single Applied Overload in 7050 Aluminum Alloy

The influences of interrupted ageing and retrogression and re-ageing heat treatments on fatigue crack growth with a single applied overload in 7050 aluminum alloy were investigated. The main aims were: to evaluate the influence of these heat treatment conditions on tensile properties, mainly fatigue crack growth rate and fracture process in the low-moderate ΔK region; to determine how both ageing treatments generate bimodal microstructure features as a contribution of the two conditions on the crack closure phenomenon; and the influence of the single applied overload to fatigue crack growth retardation. The results show that by using the RRA heat treatment condition it is possible to enhance the ductility without detrimental effects on the yield stress. T6I4-65 and RRA conditions contributed to enhancement of the crack closure phenomenon in the low-moderate ΔK region, and, accordingly, produced a lower fatigue crack growth rate in relation to the traditional T7451 condition.