日本金属学会誌

J. Japan Inst. Metals, Vol. 52, No. 3 (1988),
pp. 272-278

Effect of Bending Strain on Stress Corrosion Cracking of 7475 Aluminium Alloy

Kunio Nagaoka1, Toshio Nasu1, Toyojiro Isano2 and Keisuke Ikeda3

1Section of Technology, Faculty of Education, Yamagata University, Yamagata
2Department of Chemistry, Faculty of Science, Yamagata University, Yamagata
3Institute for Materials Research, Tohoku University, Sendai

Abstract:

Stress corrosion cracking (SCC) processes of 7475 aluminium alloy in 3%NaCl aqueous solution at constant temperature, 348 K, under several degrees of strain were recorded using a time-lapse video tape recorder (VTR). The strain were loaded to the sample by the bending method. The crack initiation time, relationship between crack length and time, SCC propagation velocity, SCC initiation point and type of crack propagation route were analyzed by observing the VTR images.
The effect of hydrogen charging on mechanical properties of 7475 alloy by cathode charge method was studied, and the relation between SCC and hydrogen was discussed.
The crack initiation time of SCC became shorter with increasing strain. The propagation velocity was increased with increasing strain. The crack initiation points were not distributed only in the front area of notch but also in the active area of corrosion. The ductility of 7475 alloy was decreased by hydrogen charging. The crack initiation points and the propagation routes of SCC in this alloy were sorted into four types. However, the propagation velocities were almost the same in these four types, suggesting analogous mechanisms of crack propagation. The hydrogen embrittlement and reaction of anodic dissolution were deemed to be related to the SCC propagation of this alloy.


(Received 1987/9/19)

Keywords:

7475 aluminium alloy, stress corrosion cracking, crack initiation, crack propagation, bending stress, sodium chloride solution, time lapse video tape recorder, strain


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