Investigation on effect of anodic oxidation on fatigue behavior of 7075-T6 aluminum alloy

Key Words: 7075-T6, Pitting Corrosion, Fatigue, Anodic Oxidation The effect of pre-corrosion and anodic oxide coating on the bending fatigue performance of high-strength aluminum alloy has been investigated by conducting a series of rotary bending fatigue tests at 95 Hz. From pre-corrosion studies including 6, 48, 96 and 240 h duration in 3,5 % NaCl solution, it was observed that coarse constituent particles play the main role in the pitting process. The results obtained from fatigue tests revealed that the fatigue strength, based on a fatigue life of 107 cycles, was dramatically reduced by the presence of pitting. The reduction in fatigue life depended on the severity of pitting; an approximately 60% decrease in fatigue strength was obtained. The results from coated specimen indicated that oxidation has a tendency to decrease the fatigue performance, and degradation was accelerated as the coating thickness increased. However, application of the oxidation mitigates pitting corrosion. An improvement of 47% in fatigue strength based on a fatigue life of 107 cycles was obtained as compared to uncoated pre-corroded specimens. Beneficial effect of anodic coating can be attained at high cycle region for the maximum 240 h of pre-corrosion length of times. Care should be taken, however, for a prolonged pre-corrosion times.