Corrosion-fatigue behaviour of 7075-T651 aluminum alloy subjected to periodic overloads (original) (raw)
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Corrosion Fatigue of Aluminum Alloys
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Corrosion fatigue on 2024T3 and 6056T4 aluminum alloys
Surface and Interface Analysis, 2010
Fatigue corrosion phenomenon is a form of degradation that is because of the combined occurrence of a mechanical cyclical stress and a corrosive environment. Fatigue corrosion can be an issue in commercial and military aircraft, and has the potential to affect the structural integrity and the useful life of an aerostructure. Although the distinct consequences of both fatigue and corrosion have been extensively documented for aluminum alloys, their synergistic action is not completely understood and continues to be an area of considerable scientific and industrial interest. In this paper, a novel approach is proposed and applied for monitoring the electrochemical behavior of different types of aluminum alloy samples while they are subjected to fatigue loading. Cyclic load experiments were conducted on bare 2024T3 and 6056T4 aluminum alloy samples in the presence of an aggressive aerated solution of 3.5% NaCl over a range of frequencies. The R-ratio was 0. Two different aluminum alloys have been tested in both high- and low-cycle fatigue. In the former case, the maximum stress experienced by the specimen is lower than the material yield strength, which means that the average expected number of cycles to failure is high; in the latter case, the maximum stress experienced by the specimen during the test is higher than the material yield strength, which means that the average expected number of cycles to failure is low. The open circuit potential(OCP) was monitored versus time during the tests described above. The observed OCP variations are interpreted as the occurrence of corrosion during crack initiation and propagation at the air formed oxide/solution interface film. As expected, there is a more pronounced influence of corrosion at lower fatigue frequencies. Crack propagation allows bulk material to be progressively more exposed to the aggressive environment, which stimulates accelerated crack propagation, resulting in a lower fatigue resistance. Copyright © 2010 John Wiley & Sons, Ltd.
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This work studies the influence of the saline atmospheric corrosion on the fatigue strength of 6061-T6 aluminum alloy. For this purpose, this alloy was subjected to tests in a salt spray corrosion chamber at different exposure times (1, 2, and 3 months) according to ASTM B117 standard. The morphological study of the pits was carried out by confocal microscopy. Subsequently, fatigue tests were performed at variable stresses whose maximum stress (Smax) was between 30% and 95% of the yield strength (S0) in order to keep them within the zone of elastic behavior of the material. Data were analyzed using the Basquin equation and the maximum likelihood function method. The results show a similar decrease in the conventional fatigue limit (2 × 106 cycles) after one month (98 MPa) and two months (91 MPa) of corrosion. After three months of corrosion, the material showed a very important reduction in the fatigue limit (68 MPa) with respect to the uncorroded material (131 MPa). The data of Se/...
Elevated Temperature Corrosion of Mechanical Properties and Fatigue Life of 7025 Aluminum Alloy
Engineering and Technology Journal, 2022
• All mechanical and fatigue properties were reduced due to corrosion-elevated temperature interaction for AA 7025. • The experimental results showed that the Ultimate Tensile Strength (UTS) and Yield stress (YS) of AA 7025 reduced by 8.7% and 19.35% respectively when subjected to tensile and corrosion-elevated temperature test. • Fatigue life and strength of AA 7025 significantly reduced under the application of corrosion and elevated temperature together. Aluminum alloys are widely used in aircraft industry where good corrosion resistance, light weight and high strength are the primary requirements. In the present study, attempts have been made to extend the application of mechanical and fatigue properties of AA7025 in laboratory with corrosive environment of media and combined corrosive at elevated temperature (ET) 150⁰C. The experimental results and analysis of corrosion and corrosionelevated temperature mechanical and fatigue behavior of the samples showed that the 3.5%NaCl corrosive media and corrosion-elevated temperature (ET) greatly decrease the properties mentioned. The Ultimate Tensile Strength (UTS) and Yield stress YS of AA 7025 reduced by 5.3% and 14.83% respectively due to combine corrosion and elevated temperature but these properties reduce by 8.7% and 19.35% respectively due to combined actions corrosion (ET). The Brinell hardness also reduced by 4.2% and 11.26% due to corrosion only and corrosion and (ET). Ductility was increased by 10.5% and 16.25% for corrosion and corrosion (ET). The environment and elevated temperaturecorrosion have significant effect on reduction the fatigue life and strength of AA 7025. It's clear that the combine corrosion and (ET) combination reduce safely of the mechanical properties compared with the corrosion only and room temperature conditions.
Fatigue Behavior of Aluminum Alloys Requested by a Simple Overload: Environment Influence
Lecture Notes in Mechanical Engineering, 2013
In this study we were interested in the behavior of two aluminum alloys (2024 T351 and 7075 T7351) requested by a simple overload with an aim of determining the number of cycles of delay of each one and of comparing their behavior various environments (air and vacuum).For that, we carried out fatigue tests stopped by a simple overload with a rate of overload τ = 2 and reports/ratios of loads R=0,1 and R=0,5.The results obtained show that the number of cycles of delay of alloy 2024 T351 is higher than that of the alloy 7075 T7351 and that the number of cycles of delay is more significant in the vacuum than with the air for two materials.This observation will lead us to make a judicious choice as for the industrial use (aeronautical) of two materials.
Corrosion -Fatigue Characteristics of 4043 Aluminium Alloy
International Journal for Research in Applied Science and Engineering Technology IJRASET, 2020
The paper provides the information of corrosion-fatigue characteristics of aluminium alloy 4043 (AA4043). Casted aluminium alloy 4043 was used for tensile and fatigue test with and without corrosion. The ultimate tensile strength obtained from tensile test and was used to conduct fatigue test on rotating bending fatigue testing machine as per RR Moore rotating bending fatigue test for un-corroded specimens for different stress values and compared the results with that of corroded specimens. The S-N curves were plotted. It is found that the corroded specimen became weak due to formation of oxides on its surface which resulted in early failure. Keywords: Aluminium Alloy 4043, Corrosion-fatigue test, Weight loss method, Rotating bending type fatigue test I. INTRODUCTION Corrosion1is a phenomena1in which1pure metal1is modified into1irreversible form to its1hydroxide, sulphide1or1oxide. It1is the1slow destruction of1metal by electrochemical1reaction (1). Study on effect1of grain width during corrosion1for various1alloy highlight the compound interrelation between1grain width, processing rate,1environment relating that1both structural1&1chemical changes influence the corrosion1susceptibility (2). Some metal-environment1combination irrespective of1the electrochemical modification or1solute alteration, the grain1refinement will lead to lower corrosion rates. Alloy of aluminum, silicon and magnesium provides resistance to corrosion when dipped in sample sea water for about 40-45 days. In partial desert areas, the lakes have high concentration of salt in its environment and it is common in several places on universe (3-10). Aluminum is used more when compared to steel in aerospace and automobile sector due to its light weight and reduced cost. These parts are exposed to different loading and climatic conditions, i.e they are subjected to corrosion and fatigue at a time. This gives rise to interest in evaluating fatigue characteristics to the scientists. Fatigue1crack usually start on surface of1the materials and its behavior depends strongly on the mechanical and geometrical properties. Let us consider a crack on surface, it widens if the tensile stresses are applied and contracts with the compressive stresses. The compressive stress is favorable since it reduces crack opening. The surface roughness and stress concentration factor also influence the fatigue characteristics of a material (11-15). A fatigue check allows us to assess the material's ability to sustain cyclic1loading. The1material is chosen1for fatigue1testing applications1 to1meet1or exceed1duty1loads. Fatigue test consists of applying tensile and compressive loads, twisting, bending1 or merging1of1these loads continuously. Very limited research is done on fatigue properties of materials and it1is essential to understand properties of fatigue of a material and1plot the results on S-N1curves (stress v/s no of cycles to failure) by conducting tests on un-notched polished specimen and the fatigue crack can originate in a1classical way through localized slip1 on1surface of1the specimen. The1fatigue test results on aluminum alloy castings are in complement with the steel and cast iron where the fatigue crack initiated from casting defect and deep study has not been done on effects of heat treatment (16).
Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy
Surface and Coatings Technology, 2007
The tendency of the aircraft industry is to enhance customer value by improving performance and reducing environmental impact. In view of availability, aluminum alloys have a historically tendency to faster insertion due to their lower manufacturing and operated production infrastructure. In landing gear components, wear and corrosion control of many components is accomplished by surface treatments of chrome electroplating on steel or anodizing of aluminum. One of the most interesting environmentally safer and cleaner alternatives for the replacement of hard chrome plating or anodizing is tungsten carbide thermal spray coating, applied by the high velocity oxy fuel (HVOF) process. However, it was observed that residual stresses originating from these coatings reduce the fatigue strength of a component. An effective process as shot peening treatment, considered to improve the fatigue strength, pushes the crack sources beneath the surface in most of medium and high cycle cases, due to the compressive residual stress field induced. The objective of this research is to evaluate a tungsten carbide cobalt (WC-Co) coating applied by the high velocity oxy fuel (HVOF) process, used to replace anodizing. Anodic films were grown on 7050-T7451 aluminum alloy by sulfuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on axial fatigue strength of anodic films grown on the aluminum alloy surface is to degrade the stress-life performance of the base material. Three groups of specimens were prepared and tested in axial fatigue to obtain S-N curves: base material, base material coated by HVOF and base material shot peened and coated. Experimental results revealed increase in the fatigue strength of Al 7050-T7451 alloy associated with the WC 17% Co coating. On the other hand, a reduction in fatigue life occurred in the shot peened and coated condition. Scanning electron microscopy technique and optical microscopy were used to observe crack origin sites, thickness and coating/substrate adhesion.
This paper introduces a systematic methodology providing insights to the corrosion fatigue behavior of untreated, anodized and blasted 7075-T651 aluminum alloy C-ring specimens. A 3.5% NaCl solution and distilled water was used as corrosive medium for the purposed of this investigation, for both treated and untreated specimens, as to quantify the effect of the processes on their fatigue response. An appropriate, fully automated, corrosion fatigue device capable of producing cyclic loading in the corrosive solution was used. The experimental process was simulated through Finite Element Modelling (FEM) to determine in-situ stress fields and elucidate crack propagation. The applied blasting process facilitated a prolongation of the corrosion fatigue for both corrosive medium when compared to the uncoated samples under identical conditions. On the contrary anodizing resulting in a considerably decrease of corrosion fatigue life in every case tested. The fracture surfaces of the specimen...
The Interaction of Corrosion and Fatigue in Aircraft Structures
Corrosion and fatigue present risks to aircraft structural integrity and can lead to increased aircraft life cycle costs and reduced aircraft availability. The two processes can interact in a variety of ways, such as the nucleation and growth of fatigue cracks from corrosion damage.