Influence of Frequency on Corrosion Fatigue Crack Propagation in Squeeze-Cast Al-Si Aluminum Alloy.

Abstract

Corrosion fatigue crack propagation tests of squeeze-cast Al-Si aluminum alloy, AC 8 A-T 6, were performed under the conditions of the stress ratio of 0.1, triangular waveform and testing frequency, f, of 0.1, 1 and 5 Hz in 3.0% saline solution using compact tension specimens with side grooves. The experimental results obtained in this investigation were compared with those reported previously under the tests of f=10Hz. Corrosion fatigue crack propagation behavior under f=0.1 and 1 Hz was also affected by the initial stress intensity factor range, ΔKi, as the test was started, the same as that under f=10 Hz. It was observed that the retardation and complete arrest of crack propagation occur within a short period in low ΔK, due to the wedge effect induced by the corrosion products. This behavior was explained uniquely by the contributory stress intensity factor range, ΔKcont, considering the viscoelasticity of the corrosion products formed within a crack. The enhancement in da/dN occurred immediately after starting the test because the preferential dissolution around the eutectic spheroidal silicon was not dependent on ΔKi, or f. Corrosion fatigue cracks were apt to propagate along eutectic spheroidal silicon, as compared with that in air, and this behavior was independent of f.