Influence of corrosion on the fatigue properties of Al 7075-T6

Chloride ion attack on Al 7075-76 in aqueous hydrochloric acid leads to localized corrosion and subsequent initiation of fatigue cracks on the surface. Fitting is observed when the specimen is exposed to a corrosive environment. Microcracks, voids, extrusions, and intrusions are then formed during the fatigue process. From a global viewpoint, all of the corrosion and fatigue damage appears to be randomly oriented, resulting in a change in the surface roughness. The Laser Speckle Sensor technique is used to detect the minute surface texture change, associated with the damage caused by corrosion and fatigue. Nonuniform surface roughness is observed due to corrosion. The corrosion pits tend to coalesce along the rolling direction. The change in surface roughness is significant around the crack tip during the fatigue process. As a result there are synergistic activities; the surface roughness caused by corrosion and fatigue leads to crack initiation, and the crack growth further increases surface roughness.