Effect of sealed anodic film on fatigue performance of 2214-T6 aluminum alloy

Abstract

The aim of present study is to investigate the influence of anodic film, grown by sulfuric acid anodizing and sealed in nickel-acetate solution, on fatigue strength of aluminum alloy 2214-T6 by conducting axial fatigue tests at stress ratio 'R' of 0.1 and − 1. The influence of sealed anodic film is to degrade the stress-life (S-N) fatigue performance of the base material at all stress levels. Effects of pre-treatments like degreasing and pickling employed prior to anodizing were also studied and no influence of these pre-treatments was observed on fatigue life. The surface and cross-section observations of anodic film were made by scanning electron microscope (SEM) before and after fatigue tests. The surface observations have revealed cavities which resulted from dissolution of coarse Al 2 Cu particles during anodization and network of micro-cracks on anodic film surface which were initiated as a result of sealing process. Some of these micro-cracks were found to penetrate up-to substrate and have detrimental effect on subsequent fatigue strength. The decrease in fatigue life for anodized-sealed specimens as compared to bare condition has been attributed to decrease in initiation period and multi-site crack initiations. Multi-site crack initiation has resulted in rougher fractured surfaces for the anodized specimens as compared to bare specimens tested at same stress levels.

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

“…The anodized specimen demonstrates a number of pits as verified by means of confocal microscopy which can be proven detrimental because they can act as stress concentration sites and facilitate the crack initiation, resulting thus to lower fatigue strength 6,7 Fractographs of anodized specimens showing a jagged texture (see Figure 5) support this assumption. The separated propagation zones of the various cracks (as signified by the several fracture steps) indicate that the fracture of anodized specimens occurred as a consequence of the nucleation and simultaneous propagation of a number of cracks.…”

“…Despite that fact, the porous outer layer is brittle and can cause the effortless formation and propagation of cracks into the substrate. Therefore, the fatigue strength of the metal can dramatically be reduced …”

“…The fatigue strength and crack propagation of several types of aluminum alloy are well documented in literature . However, the synergistic effects, between cyclic alternating mechanical loads and chemical degradation, remain still elusive.…”

“…Therefore, the fatigue strength of the metal can dramatically be reduced. [5][6][7] Micro-arc deposition of ceramic coatings, plasma electrolytic oxidation (PEO), and hard anodized ceramic coatings have been used in the past on light materials (including aluminum alloys) to enhance tribological properties and improve corrosion resistance. During the last decade, it has been shown that by using appropriate sealing processes and better quality of coatings surfaces, these hard oxides do not deteriorate the fatigue durability of aluminum Nomenclature: AA, Aluminum Alloy; EDM, Electrical Discharge Machining; FEM, Finite Element Method; MAO, Microarc Oxidation; OCP, Open Circuit Potential; PEO, Plasma Electrolytic Oxidation; SCE, Saturated Calomel Electrode alloys.…”

“…14,15 The fatigue strength and crack propagation of several types of aluminum alloy are well documented in literature. 4,[6][7][8][9][10][11][12][13][14][15] However, the synergistic effects, between cyclic alternating mechanical loads and chemical degradation, remain still elusive. High strength Al-alloys find many uses in aerospace and automotive applications for fatigueoriented applications such as components, subjected to severe safety requirements.…”