An investigation of the reduction in tensile strength and fatigue life of pre-corroded 7075-T6 aluminum alloy

In aging aircraft, the synergetic interaction between corrosion and fatigue has been shown to reduce the life expectancy of aluminum alloys. The objec tive of this study was to quantify the effects of corrosion, in terms of ma ss loss per unit area, on the static strength and fatigue life of 7075-T6 a luminum alloy. This was an experimental study in which test specimens were corroded in a laboratory environment. The corrosion process was accelerated by use of a corrosion cell. Test specimens were cut from flat sheets of al uminum and covered with masking material to restrict corrosion to a confine d area, After testing, the fatigue life, ultimate tensile strength (UTS), a nd hardness of the specimens were observed to drop significantly with small amounts of corrosion. After the initial decrease, the UTS was observed to decrease linearly with increasing corrosion levels. The fatigue life of the specimens decreased in an inverse exponential fashion as mass loss per uni t area increased, The hardness values of the corroded surfaces were also ob served to drop. The topology of the pits and the related subsurface damage produced areas of high stress concentration resulting in the immediate redu ction of UTS and fatigue life of the specimens. Subsurface corrosion damage was responsible for the reduction in hardness.