Influence of anodization on the fatigue strength of 7050‐T7451 aluminium alloy

Abstract

A B S T R A C T In recent years, with higher demand for improved quality and corrosion resistance, recovered substrates have been extensively used. Consequently residual stresses originated from these coatings reduce the fatigue strength of a component. Due to this negative influence occasioned by corrosion resistance protective coatings, an effective process like shot peening must be considered to improve the fatigue strength. The shot peening treatment pushes the crack sources beneath the surface in most of medium and high cycle cases due to the compressive residual stress field (CRSF) induced. The aim of this study was to evaluate the influence on the fatigue life of anodic films grown on 7050-T7451 aluminium alloy by sulphuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on the rotating and reverse bending fatigue strength of anodic films grown on the aluminium alloy is to degrade the stress life fatigue performance of the base material.A consistent gain in fatigue life in relation to the base material was obtained through the shot peening process in coated specimens, associated to a residual stress field compressive near the surface, useful to avoid fatigue crack nucleation and delay or even stop crack propagation.

A predictive fatigue life model for anodized 7050 aluminium alloy

“…On another hand, from experimental SEM observations of tested specimens, there was no evidence of coating crack initiating from external surface so that it was assumed that fatigue cracks initiated from pickling pits. As it is generally assumed oxide layer has a brittle behavior and so is subjected to quite instantaneously cracking [4,6,7]. Such behavior leads to instantaneous increase of the lengths of the cracks which nucleate from pits, and thus affects short crack propagation stage.…”

“…The benefits obtained for wear and corrosion resistance is obtained at the expense of fatigue resistance [2][3][4][5]. Numerous researchers have attributed the fatigue resistance decrease to the brittle and porous nature of the oxide layer and equally to the tensile residual stress induced during anodizing process [4,[6][7][8]. Some others have shown that surface degradation was responsible too [9][10][11][12].…”

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

“…Often, the wear and corrosion protection requirements of Al alloys are further enhanced by employing traditional anodizing and hard anodizing processes . However, the applications including landing gear components of aerospace sector often demand an additional property namely the fatigue resistance . The current state‐of‐art can only provide adequate wear and corrosion protection of Al alloys even when the advanced technologies such as micro arc oxidation (MAO) are deployed thereby leaving a clear space for developing the materials and processes that can simultaneously provide resistance against wear, corrosion and fatigue …”

“…[4][5][6] However, the applications including landing gear components of aerospace sector often demand an additional property namely the fatigue resistance. 2,[7][8][9][10] The current state-ofart can only provide adequate wear and corrosion protection of Al alloys even when the advanced technologies such as micro arc oxidation (MAO) are deployed thereby leaving a clear space for developing the materials and processes that can simultaneously provide resistance against wear, corrosion and fatigue. [11][12][13] It is very well documented that the anodized, hard anodized (HA) and MAO coatings in general degrade the fatigue life (number of cycles before failure) up to 75% than that of corresponding Al alloy.…”

A Study on Surface Modification of Al7075-T6 Alloy against Fretting Fatigue Phenomenon

“…Aluminum alloys with high silicon or copper content are prone to not being very hard and porous. Table 2 lists some of the alloys that are difficult to be coated and should be practically avoided [80][81][82][83]. Pure aluminum coating via magnetron sputtered Al7075-T6 alloy may facilitate substrate hard anodizing.…”