Corrosion fatigue of an extruded 7046 alloy
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The corrosion fatigue properties of a 7046 alloy were investigated and compared to previously reported work by SINTEF on the same alloy tested in air. To establish the corrosion fatigue properties, samples were either fatigue tested in a 5 wt% NaCl solution or pre-corroded in the same solution and subsequently tested in laboratory air. For the fatigue testing in 5 wt% NaCl solution, both T6 and T7 tempered samples were considered. To better understand how the corrosive environment influences the samples, SEM was used. The simultaneous effect of corrosion and fatigue was found to have a detrimental effect on fatigue life for this alloy, with a clearly reduced lifetime at all tested stress amplitudes. Additional heat treatment to T7 condition did not yield any lifetime differences compared to T6, suggesting a similar crack initiation mechanism for both temper states. For pre-corroded samples, lifetime differences were only found at longer exposure times (1 week and more). For the samples tested in 5 wt% NaCl, an initiation mechanism caused by oxide film rupture is proposed. For the samples pre-corroded for longer times (1 week and more), corrosion pits are thought to be the site for crack initiation.