RELATIVE TESTS ON FATIGUE PROPERTIES OF ALUMINUM ALLOYS IN 3.5% NaCl CORROSION ENVIRONMENT

Fatigue properties in typical corrosion environments are the preconditions of fatigue life design for metallic structures in aircrafts. Fatigue tests were performed on smooth and notched specimens subjected to constant amplitude loading in two environments of dry air and 3.5% NaCl sodium chloride solution respectively to determine the pure and corrosion fatigue properties of two categories of aluminum alloys 2E12-T3 and 7050-T7451. Corrosion fatigue properties in the two environments were analyzed and compared with each other. The interaction mechanisms between corrosion and fatigue were deduced from fractographical studies by using scanning election microscope (SEM). The results show that the 3.5% NaCl sodium chloride solution has a detrimental influence on fatigue properties of both aluminum alloys. The interaction between corrosion and fatigue loading increases with the decreasing of stress level, and ultimately decreases the fatigue strength. The effect of 3.5% NaCl sodium chloride solution on fatigue behavior is more significant for the notched specimen of aluminum alloy 2E12-T3 than for the smooth specimen, but it is insignificant for the notched specimen of aluminum alloy 7050-T7451 as against for the smooth specimen. The crack closure is prevented by the corrosion products produced from the electrochemical attack at the crack tip in corrosion environment. Furthermore, the hydrogen embrittlement effect resulted from the electrochemical attack enhances the crack propagation to cause the degradation of fatigue properties.