The Study On Corrosion Morphology And Residual Fatigue Life Of Corroded Aluminium Alloy

Corrosion is the environmental damage which aerospace structures can not avoid in service, inwhich pitting and exfoliation are the most important corrosion forms of aluminum alloy. Corrosionpromotes the initiation and propagation of cracks, severely reducing the residual fatigue life. Theresearch on residual life of pre-corroded structures is of great significance for life extension of agingaircrafts.The main method to predict residual life of pre-corroded structures is equaling pit as an initialcrack currently, of which the analysis of corrosion morphology is the basis. First, this paper gives areview on research progress of three corrosion fatigue modes (corrosion fatigue simultaneously,corrosion fatigue alternately and pre-corrosion fatigue), and summarizes the parameters characterizingthe condition of the pit damage. Then, the pre-corrosion test of LC4CS aluminum alloy is performedin EXCO solution, fatigue and static tensile tests of pre-corroded specimens are followed to get theS-N cures and residual strength. Next, a program is developed in this section to identify corrosion pitsfrom cross-sectional profiles and calculate the damage parameters of pit (such as depth, width, aspectratio etc) automatically, which avoids the subjectivity when measures manually. Finally, the pit isequaled as an initial crack with the damage parameters calculated in the last chapter, and residual lifeis calculated using the fracture mechanics method. Several equivalence methods are compared in thissection, which indicates that equaling pit as an initial crack is an effective method to predict residuallife of pre-corroded structure no matter the surface crack equaled is semi-elliptical or semi-circular,and depth and cross-sectional area of pit are the effective parameters for pit equivalence. However, itis of great difference between the prediction results based on the maximum or average value of themeasured damage parameters. The average value of depth or cross-sectional area should be used whenequaling pit as a semi-elliptical surface crack, while the maximum value should be used whenequaling pit as a semi-circular surface crack.