Effect of testing frequency on the corrosion fatigue of a squeeze-cast aluminum alloy
The corrosion fatigue crack propagation behavior of a squeeze-cast Al-Si-Mg-Cu aluminum alloy (AC8A-T6), which had been precracked in air, was investigated at testing frequencies of 0.1, 1, 5, and 10 Hz under a stress ration (R) of 0.1. Compact-toughness specimens were precracked about t mm in air prior to the corrosion fatigue test in a 3 pct saline solution. At some near-threshold conditions, these cracks propagated faster than would be predicted by the mechanical driving force. This anomalous corrosion fatigue crack growth was affected by the initial stress-intensity-factor range ({Delta}K{sub i}), the precracking conditions, and the testing frequency. The initial crack propagation rate was as much as one order of magnitude higher than the rate for the same conditions in air. This rapid rate was associated with preferential propagation along the interphase interface in the eutectic structure. It is believed that a chemical reaction at the crack tip and/or hydrogen-assisted cracking produced the phenomenon. Eventual retardation and complete arrest of crack growth after this initial rapid growth occurred within a short period at low {Delta}K values, when the testing frequency was low (0.1 and 1 Hz). This retardation was accompanied by corrosion product-induced crack closure and could be better explained by the contributory stress-intensity-factor range ({Delta}K{sub cont}) than by the effective stress-intensity-factor range ({Delta}k{sub eff}).
- Research Organization:
- Toyama Univ. (JP)
- OSTI ID:
- 20050547
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 31, Issue 4; Other Information: PBD: Apr 2000; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
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