A predictive fatigue life model for anodized 7050 aluminium alloy

Abstract

International audienceThe objective of this study is to predict fatigue life of anodized 7050 aluminum alloy specimens. In the case of anodized 7050-T7451 alloy, fractographic observations of fatigue tested specimens showed that pickling pits were the predominant sites for crack nucleation and subsequent failure. It has been shown that fatigue failure was favored by the presence of multiple cracks. From these experimental results, a fatigue life predictive model has been developed including multi-site crack consideration, coalescence between neighboring cracks, a short crack growth stage and a long crack propagation stage. In this model, all pickling pits are considered as potential initial flaws from which short cracks could nucleate if stress conditions allow. This model is built from experimental topography measurements of pickled surfaces which allowed to detect the pits and to characterize their sizes (depth, length, width). From depth crack propagation point of view, the pickling pits are considered as stress concentrator during the only short crack growth stage. From surface crack propagation point of view, machining roughness is equally considered as stress concentrator and its influence is taken into account during the all propagation stage. The predictive model results have been compared to experimental fatigue data obtained for anodized 7050-T7451 specimens. Predictions and experimental results are in good agreement

A study on corrosion‐fatigue behavior of AA7075‐T651 subjected to different surface modification treatments

“…When using the NaCl solution, formation of pits is likewise feasible during the corrosion‐fatigue testing. This is mainly ascribed to the different electrochemical potential among the intermetallic compounds and the Al‐matrix, hence leading to localized corrosion and formation of pits . Nevertheless, the duration of the experiments was rather limited.…”

“…This is mainly ascribed to the different electrochemical potential among the intermetallic compounds and the Almatrix, hence leading to localized corrosion and formation of pits. [24][25][26] Nevertheless, the duration of the experiments was rather limited. Consequently, there was brief period for pits to be created and adversely influence corrosion-fatigue durability.…”

Effects of Cryogenic Forging and Anodization on the Mechanical Properties of AA 7075-T73 Aluminum Alloys

“…The pretreatment could produce pits through the dissolution of intermetallic particles at the surface. These pits acted as the stress concentration sites and enhanced crack initiation ( Ref 9,10). The disparities in the strength reported in these studies might have been partly caused by the polishing process that was used.…”

Corrosion rate of AA 7050 in 3.5% NaCl environment with sodium chromate (Na2CrO4) inhibitor variation

“…The aluminium oxide layer developed naturally on aluminium alloy surface is able to provide good corrosion resistance characteristics. However, when the airplane is operated and exposed in a corrosive environment, the natural oxide layer of aluminium alloy is not thick enough to ensure corrosion protection [3,4]. Therefore, researchers have to concern to improving the level of corrosion protection for aerospace components and structures [5].…”