日本金属学会誌

J. Japan Inst. Metals, Vol. 52, No. 9 (1988),
pp. 872-877

Improvement in Fracture Toughness of 7475 Aluminum Alloy by Applying the RRA (Retrogression and Re-Aging) Process

Tadakazu Ohnishi1, Yoshiaki Ibaraki2 and Taichiro Ito1

1Department of Metallurgical Engineering, Faculty of Engineering, University of Osaka Prefecture, Sakai
2Graduate Student, University of Osaka Prefecture, Sakai

Abstract:

In order to improve fracture toughness and SCC properties and to keep high strength of the T6 level, a three-step aging process (RRA) was investigated for 7475 aluminum alloy. To keep the strength of the T6 level and simultaneously to improve both properties, the usual T6 condition was suitable for the first step aging. For the second step aging (retrogression), the improvement of the properties became more remarkable with increasing temperature and time. However, the strength decreased in the case of over-aging of the retrogression. For the final step aging (re-aging), it was preferable to increase the aging temperature and time to an extent within the permissible range of loss in strength. In conclusion, the present results suggest that the maintenance of high strength and improvements in fracture toughness and SCC properties can be simultaneously effected by the optimum RRA process, and the conventional over-aged treatments, accompanying a loss of strength, such as T76 and T73 may be replaced by the RRA process.


(Received 1988/3/4)

Keywords:

heat treatment, retrogression and re-aging process, aluminum-zinc-magnesium-copper alloy, strength, fracture toughness, stress corrosion cracking


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