Effect of Humidity on Fatigue Strength of Extruded and Age-Hardened Al Alloy under Rotating Bending
Kohji KARIYA, Norio KAWAGOISHI, Takuro FUKUDOME, Yuzo NAKAMURA and Eiji KONDO
Abstract:In order to investigate the effect of humidity on fatigue strength of an extruded and age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out using plain specimens in environments of controlled relative humidity of 25% and 85%. Both of initiation and propagation of a crack were accelerated by high humidity, causing the decrease in fatigue strength. In high humidity, a crack tended to propagate in a shear mode macroscopically and it was ductile accompanied with glide plane decohesion and void formation microscopically, though the propagation was a tensile mode with striations in low humidity. The shear mode propagation inclined about 35 to the extruded direction due to the marked texture of the alloy. Key Words:Fatigue, Extruded 7075-T6, Rotating bending, Humidity, Texture, Crack initiation, Crack propagation, Fracture mechanism