Al合金の低サイクル腐食疲労

抄録

Studies have been mede on the influence of no stress time, varying stress time and maximum stress time in 1 cycle on low cycle corrosion fatigue strength of Al alloy. The electrode potential of the specimens has been measured against the saturated calomel electrode during the cycles and the fatigue cracks have been observed through a microscope. The following facts have been made clear.
(1) When the cycle frequency is constant, varying stress time (t_a) and maximum stress time (t_m) have destructive effects which will increase the corrosion fatigue damage. The effect of t_a is greater than the effect of t_m. This results are due to the difference of recovery of the corrosion potential on the specimen surface.
(2) When the cycle frequency gets slower owing to the increase of varying stress time (t_a), destructive effects appear. When the cycle frequency gets slower by the increase of no stress time (t₀) or maximum stress time (t_m), protective effects appear which decrease the corrosion fatigue damage. The protective effects are due to the recovery of the corrosion potential in the crack initiation period. In the crack propagation period the effects are due to the decrease of crack propagation rate caused by the lowering of stress concentration according to the branching or the thickening of the crack tip, or to the pit formation from the cracks.