Effects of Prior Corrosion and Stress in Corrosion Fatigue of Aluminum Alloy 7075-T6

Abstract

The nucleation of fatigue cracks from corrosion pits was investigated by evaluating the effects of two variables on the fatigue life of dog-bone specimens of aluminum alloy 7075-T6 (UNS A97075). The specimens were exposed to different levels of corrosion in an acidified saline solution of 3.5% sodium chloride (NaCl). In addition, the specimens were exposed to concomitant fatigue and corrosion exposure during fatigue until failure by fracture occurred. Scanning electron microscopy (SEM) analysis indicated that fatigue cracks formed/nucleated from each pit, and subsurface mechanisms of degradation were identified associated with the pitting nucleation sites including subsurface pitting, cracking, tunneling, and intergranular attack. Failure data was analyzed using analysis of variance (ANOVA) methods, and three transformations were evaluated to minimize the variance, including natural log, inverse square root, and power with a lambda of 1/3. Contour and surface plots were developed to show how these variables impact the response of cycles to failure for the conditions evaluated. Results indicate that p values for these models are statistically significant. The effect of stress appears to be more detrimental than corrosion time on the fatigue life of the specimens for the values previously defined by the matrix.

Experimental investigation on damage evolution in pre-corroded aluminum alloy 7075-T7651 under fatigue loading

“…The phenomena that fatigue cracks originate from localized corrosion, accompanied with typical quasicleavage fracture characteristics, is consistent with previous work reported [14,[29][30][31], which reveals that stress concentration at localized corrosion accelerates crack initiation. In the present work, the methodology using a combination of damage severity curves, DIC-measured strain maps, and detailed SEM fracture morphology, provides a quantitative and qualitative characterisation of the entire corrosion-nucleated fatigue failure process, under a range of loading conditions.…”

Corrosion fatigue crack propagation behavior of A7N01P‐T4 aluminum alloy welded joints from high‐speed train underframe after 1.8 million km operation

“…As the “high‐density dislocation area” near the second phase or slag inclusion is dissolved, the second phase or inclusions fall off automatically due to the adhesion loss, thus leading to the stress concentration and secondary cracks in the area. [ 28,29 ]…”

“…As the "high-density dislocation area" near the second phase or slag inclusion is dissolved, the second phase or inclusions fall off automatically due to the adhesion loss, thus leading to the stress concentration and secondary cracks in the area. [28,29] 5 | CONCLUSION In this study, the corrosion fatigue crack propagation behavior of the A7N01P-T4 aluminum alloy welded joints from a high-speed train was studied in a 3.5 wt% NaCl solution. On the basis of the obtained findings, the following conclusions can be drawn:…”

Fatigue damage evolution and failure of pre‐corroded aluminum alloy 7075‐T651 under air and corrosion environments

“…The coupling of corrosion damage and fatigue loading causes premature failure of structural material, which is one of the most common and dangerous damage mechanisms for aircraft components. 1,2 Once localized corrosion exists, fatigue cracks tend to initiate at these corrosion pits, 3,4 and the aggressive environment can also affect corrosion and cracking behavior. [5][6][7] Given the complex environmental spectrum experienced by aircraft structures during service, it is important to understand the fatigue damage evolution characteristics and corresponding failure mechanisms of precorroded aluminum alloys in both air and corrosion environments.…”