Effect of retrogression and reaging heat treatment on corrosion fatigue crack growth behavior of AA7050 alloy

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2004

Öğrenci: NEVZAT AKGÜN

Danışman: RIZA GÜRBÜZ

Özet:

The effect of retrogression and reaging heat treatment on corrosion fatigue crack growth behavior on AA7050 T73651 aluminum alloy is investigated. CT (Compact Tension) specimens are prepared in LS direction for fatigue crack growth tests . Samples are solution heat treated at 477 °C and aged at 120 °C for 24 h (T6 condition). After that, samples are retrogressed at 200 °C for times of 1, 5, 30, 55 and 80 minutes in a circulating oil bath. Then, samples are re-aged at 120 °C for 24 h (T6 condition). Hardness measurements are taken at different retrogression times and at the end of the heat treatment. Fatigue crack growth tests are performed at as received condition and at different retrogression times with sinusoidal loading of R=0.1 and f=1 in both laboratory air and corrosive environment of 3.5% NaCl solution. The highest fatigue crack growth resistance is observed for 30 min. and 5 min. retrogression for laboratory air and corrosive environment respectively. It is concluded that RRA can successfully be used to improve fatigue performance of this alloy.