Effect of Trace Sc Addition on Aging Precipitation and Fatigue Crack Propagation Behavior of 7085 Alloy

ABSTRACT In this work, the effects of Sc‐alloying and aging treatments, including T6 peak‐aging and retrogression with reaging (RRA) on the fatigue crack propagation (FCP) behavior of 7085 alloy, were investigated. The results show that the RRA‐treated alloy exhibits high volume fraction of larger sharable η ′ phases, wider precipitate free zone (PFZ), and high Schmid factor. These microstructures contribute to frequent transgranular propagation, increasement of ΔK th , and higher FCP resistance than T6‐treated alloy. Sc alloying can significantly refine grain structure, inhibit recrystallization, and accelerate the nucleation of η ′ strengthening phase, thus improving the mechanical properties of 7085 alloy. However, Sc alloying also tends to induce the occurrence of intergranular propagation due to presence of microscale AlZnMgCuSc phase and fine grain structure with high grain boundary volume fraction. Therefore, Sc alloying plays a negative role in improving the FCP resistance of 7085 alloy.