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

1989; Japan Institute of Metals; Volume: 30; Issue: 8 Linguagem: Inglês

10.2320/matertrans1989.30.601

2432-471X

Tadakazu OHNISHI, Yoshiaki Ibaraki, Taichiro Ito,

Aluminum Alloys Composites Properties

In order to improve fracture toughness and SCC properties with retention of the high strength of T6 level, a three-step aging process (RRA) was investigated for the 7475 aluminum alloy. To keep the strength 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 retention of high strength and the improvements in fracture toughness and SCC resistance can be simultaneously effected by an optimum RRA process, and that the conventional over-aged treatments such as T76 and T73 which accompany a loss of strength may be replaced by the RRA process.