時効硬化Al合金の超音波疲労強度に及ぼす大気湿度の影響

概要

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In order to investigate the effect of humidity on fatigue strength of an age-hardened and extruded Al alloy 7075-T6 under ultrasonic frequency, ultrasonic fatigue tests were carried out using plain specimens in 7 kinds of environments of controlled humidity of 25, 50, 65, 75 and 85%, distilled water and oxygen gas. Although fatigue strength was decreased by high humidity, the decrease in fatigue strength was small in humidity below 60%-70% and the strength was largely decreased above that humidity. A crack tended to propagate in tensile mode and then change to shear mode propagation, macroscopically. The direction of the shear mode propagation was about 35° to the extruded one. The tendency to the shear mode propagation was large in high humidity and most of propagation process of a crack was occupied by the propagation of shear mode in the humidity of 75% and 85% and in water. There was no or little effect of environment on fracture mechanism in the shear mode propagation.
2010-07-25