The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

Winter, Lisa; Morgenstern, R; Hockauf, Kristin; Lampke, Thomas

doi:10.1088/1757-899x/118/1/012033

Cited by 9 publications

(5 citation statements)

References 13 publications

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“…As a common point of observation to both the Al alloys, multiple predominant cracks can be noticed in the case of plain MAO coated fracture surface and fewer dominant cracks in the case of SP + MAO coatings . Furthermore, upon examination of a cross section for a fatigue test interrupted at 80% of experimentally measured life, the fatigue crack propagates almost like a straight line in the case of plain MAO coating (Figure ), while major crack deflection in the substrate region beneath the substrate‐coating interface as shown in Figure accompanied by multiple crack deflections of relatively smaller magnitude and crack‐branching as shown in Figure leads to major energy absorption and significantly increased fatigue life can be clearly noticed in the case of SP + MAO coatings . It may be noted that the SP induced compressive residual stresses beneath the substrate‐coating interface region of SP + MAO coating are the primary reason behind the deflection and branching of cracks as shown in Figures .…”

Section: Resultsmentioning

confidence: 99%

Enhancing the high cycle fatigue life of high strength aluminum alloys for aerospace applications

Krishna

Madhavi

Sahithi

et al. 2018

Fatigue Fract Eng Mat Struct

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Hard anodized (HA) and micro arc oxidation (MAO) coatings of identical thickness were deposited on two different high strength aluminum (Al) alloys namely, 2024‐T3 and 7075‐T6. Further, as received Al alloys were also subjected to shot peening (SP) to induce subsurface compressive residual stresses followed by the MAO coating deposition (SP + MAO). The average velocity of particle‐in‐flight during the SP process was measured and utilized to calculate the kinetic energy of the peening particles. The bare and coated alloys were subjected to completely reversed stress (R = −1) rotating beam high cycle fatigue tests at five different stress levels. In addition, the bare and coated alloys were also evaluated for their tensile properties, elemental composition, phase constituents, surface, and cross‐sectional morphologies including the surface roughness (Ra, Rz) and correlated the same with the corresponding fatigue behavior. Irrespective of substrate alloy composition and stress levels investigated, the duplex SP + MAO treatment resulted in significant fatigue life enhancement over and above the fatigue life of corresponding bare (not shot peened) Al alloy, while the hard anodized and plain MAO (both without prior shot peening) continue to exhibit significant fatigue debit. Driven by the compressive residual stresses present beneath the subsurface region of SP + MAO coating interface, fractured surface examination of SP + MAO coatings clearly highlights the crack‐branching associated multiple crack deflection as the predominant operative mechanism responsible for diminishing the crack growth rate and therefore enhance the fatigue life as compared with the near linear crack extension without significant deflections leading to relative premature failure of plain MAO coated alloys.

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Section: Resultsmentioning

confidence: 99%

Enhancing the high cycle fatigue life of high strength aluminum alloys for aerospace applications

Krishna

Madhavi

Sahithi

et al. 2018

Fatigue Fract Eng Mat Struct

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“…There are certainly reports [96][97][98][99][100] of significant impairment of fatigue life, for both Al and Mg alloys. There have been very few indications of any improvement, although it has been reported [101] that no change occurs with the Ti-6Al-4V alloy.…”

Section: Resistance To Fatigue Loadingmentioning

confidence: 99%

A review of recent work on discharge characteristics during plasma electrolytic oxidation of various metals

Clyne

Troughton

2018

International Materials Reviews

416

225

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The review describes recent progress on understanding and quantification of the various phenomena that take place during plasma electrolytic oxidation, which is in increasing industrial use for production of protective coatings and other surface treatment purposes. A general overview of the process and some information about usage of these coatings are provided in the first part of the review. The focus is then on the dielectric breakdown that repeatedly occurs over the surface of the work-piece. These discharges are central to the process, since it is largely via the associated plasmas that oxidation of the substrate takes place and the coating is created. The details are complex, since the discharge characteristics are affected by a number of processing variables. The interrelationships between electrical conditions, electrolyte composition, coating microstructure and rates of growth, which are linked via the characteristics of the discharges, have become clearer over recent years and these improvements in understanding are summarised here. There is considerable scope for more effective process control, with specific objectives in terms of coating performance and energy efficiency, and an attempt is made to identify key points that are likely to assist this.

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“…The testing frequency was approximately 100 Hz for the uncoated and anodized specimens. An alternating tension-compression loading (R = −1) was applied, as a previous study showed that this load ratio results in a more pronounced shattering of the coating and is therefore more critical when compared to a tension-tension loading [34]. The stopping criteria for the fatigue tests were an endurance limit of N D = 10 7 (specimen is a run-out) or a drop in resonant frequency of 1 Hz or more, which indicates a crack (specimen failed).…”

Section: High Cycle Fatigue Testingmentioning

confidence: 99%

Influence of Hydrothermal Sealing on the High Cycle Fatigue Behavior of the Anodized 6082 Aluminum Alloy

Winter

Lampke

2022

Coatings

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For aluminum alloys, anodizing is a common electrochemical surface treatment to allow for protection against corrosion and wear. The produced conversion layers are first sealed in industrial processes to further enhance the corrosion protection by closing the coating surface pores. In their lifetime, anodized components often undergo cyclic loadings. However, despite the relevance of a sealing treatment, there is a lack of systematic studies regarding its influence on the fatigue behavior of anodized aluminum components. In this work, a 6082-aluminum alloy was anodized in sulphuric acid and the effect of the anodizing treatment with and without further hydrothermal sealing on the fatigue strength was investigated. The thickness and Martens hardness of the coatings were determined and the coating appearance in non-sealed and sealed conditions was analyzed by scanning electron microscopy prior to and after cyclically loading at R = −1. The fatigue strength was significantly decreased by the anodizing treatment, when compared to the bare substrate. However, hydrothermal sealing had a positive influence as the anodized and sealed condition attained a fatigue strength in the range of the bare aluminum. Distinct differences regarding the coating appearances, thickness, and hardness were not observed when comparing the non-sealed and the sealed conditions. After fatigue loading, numerous pronounced radial cracks were present in the anodic coating, but the number of cracks were significantly lower for the hydrothermally sealed coating. Fatigue failure occurred due to propagation of one crack from the coating towards the substrate, resulting in single-point crack initiation, which was similar to the fatigue fracture behavior of the bare aluminum substrate.

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The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

Cited by 9 publications

References 13 publications

Enhancing the high cycle fatigue life of high strength aluminum alloys for aerospace applications

Enhancing the high cycle fatigue life of high strength aluminum alloys for aerospace applications

A review of recent work on discharge characteristics during plasma electrolytic oxidation of various metals

Influence of Hydrothermal Sealing on the High Cycle Fatigue Behavior of the Anodized 6082 Aluminum Alloy

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