The Effect of Cyclic Closed Die Forging (CCDF) Process on Fatigue Crack Growth Behavior of Precipitation-Hardened Al ۷۰۷۵ Alloy

In this study, the effect of the cyclic closed die forging (CCDF) process on the fatigue crack growth rate (da/dN) of aluminum alloy ۷۰۷۵ in the peak-aged (T۶) condition was experimentally investigated. Specimens were prepared in three different conditions: base T۶, T۶ with one pass of CCDF, and T۶ with two passes of CCDF. Fatigue crack growth tests were conducted in accordance with the ISO ۱۲۱۰۸ standard using compact tension (CT) specimens. Key parameters, including the stress intensity factor range (ΔK) and crack growth rate (da/dN), were calculated and compared. The results indicated that CCDF-processed specimens exhibited about ۳۳% improvement in resistance to fatigue crack initiation. They also tolerated more than ۱ mm greater fatigue crack growth compared to the T۶ specimen. Finally, the crack growth rate of CCDF-processed specimens decreased by up to ۱۸% compared to the T۶ specimen. Furthermore, no significant difference was observed between the performance of specimens subjected to one pass and two passes of CCDF. This improvement can be attributed to the refined microstructure, increased dislocation density, and better distribution of precipitates resulting from the CCDF process. The findings of this research represent an effective step towards optimizing hybrid processes for improving the fatigue life of aluminum components in engineering applications.

کلیدواژه ها:

Aluminum Alloy ۷۰۷۵ ، Cyclic Closed Die Forging (CCDF) ، fatigue crack growth ، Crack Growth Rate (da/dN) ، Stress Intensity Factor Range (ΔK)