The Effect of Aluminum Cold Spray Coating on Corrosion Protection and Corrosion Fatigue Life Enhancement of Magnesium Alloy, AZ31B PDF Download
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Author: Mohammad Waheeb Diab
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 113
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Book Description
Magnesium alloys are of a recent interest for the transportation industry due to their excellent properties such as high strength and low density which will save energy and reduce gas emission and it will also improve the vehicle performance. However due to their high chemical activity, magnesium and magnesium alloys have unsatisfactory corrosion resistance and high tendency to corrode in humid and aqueous environments. Although alloying elements provides some improvement in magnesium against corrosion, further protection for these alloys is needed against the corrosion in different corrosive environments. Aluminum powder cold spray is a new coating technology with very promising results in corrosion protection of magnesium alloys. The effect of applying pure aluminum cold spray coating on wrought AZ31B Mg alloy from the corrosion and corrosion fatigue point of view is studied. This research comprises two parts. The first part is studying the corrosion behavior of AZ31B cold spray coated and uncoated coupons by performing an accelerated corrosion testing in a corrosion chamber. The results for both types of coupons have been compared to each other. The second part of this research is to study the fatigue strength by rotating bending machine of stress relieved and stress relieved/coated specimens in salt water environment. S-N curves for the two groups of specimens were plotted. After the analysis and comparison of all the testing results, it was revealed that pure Al cold spray coating considerably improved the corrosion resistance of Mg alloy AZ31B in 5% NaCl fog environment. The microstructural analysis revealed the presence of some secondary phases which act as a cathode and accelerate the corrosion of the anode, Mg alloy. Comparison of corrosion-fatigue S-N curves of stress relieved and stress relieved/coated specimens show fatigue life reduction after cold spray coating to a maximum percentage of 87.6%. The reason for that is the fact that the pure Al powder has much lower ultimate tensile strength than Mg alloy AZ31B. This fact will lead to an earlier crack on the Al coating surface during the fatigue cycles, from which the electrolyte will penetrate to the Mg substrate and cause a localize corrosion and failure.
Author: Mohammad Waheeb Diab
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 113
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Book Description
Magnesium alloys are of a recent interest for the transportation industry due to their excellent properties such as high strength and low density which will save energy and reduce gas emission and it will also improve the vehicle performance. However due to their high chemical activity, magnesium and magnesium alloys have unsatisfactory corrosion resistance and high tendency to corrode in humid and aqueous environments. Although alloying elements provides some improvement in magnesium against corrosion, further protection for these alloys is needed against the corrosion in different corrosive environments. Aluminum powder cold spray is a new coating technology with very promising results in corrosion protection of magnesium alloys. The effect of applying pure aluminum cold spray coating on wrought AZ31B Mg alloy from the corrosion and corrosion fatigue point of view is studied. This research comprises two parts. The first part is studying the corrosion behavior of AZ31B cold spray coated and uncoated coupons by performing an accelerated corrosion testing in a corrosion chamber. The results for both types of coupons have been compared to each other. The second part of this research is to study the fatigue strength by rotating bending machine of stress relieved and stress relieved/coated specimens in salt water environment. S-N curves for the two groups of specimens were plotted. After the analysis and comparison of all the testing results, it was revealed that pure Al cold spray coating considerably improved the corrosion resistance of Mg alloy AZ31B in 5% NaCl fog environment. The microstructural analysis revealed the presence of some secondary phases which act as a cathode and accelerate the corrosion of the anode, Mg alloy. Comparison of corrosion-fatigue S-N curves of stress relieved and stress relieved/coated specimens show fatigue life reduction after cold spray coating to a maximum percentage of 87.6%. The reason for that is the fact that the pure Al powder has much lower ultimate tensile strength than Mg alloy AZ31B. This fact will lead to an earlier crack on the Al coating surface during the fatigue cycles, from which the electrolyte will penetrate to the Mg substrate and cause a localize corrosion and failure.
Author: Hassan Mahmoudi-Asl
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Hassan Mahmoudi-Asl
Publisher:
ISBN:
Category :
Languages : en
Pages : 90
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Book Description
Wrought magnesium alloys are considered attractive candidates for structural members in automotive and aerospace industries due to their high specific strength. Although new processes have helped to produce high purity magnesium alloys with higher resistance to corrosion, these alloys still need protection against corrosion when they are used in aggressive environments. Cold spray coating is one of the protective methods that are employed for this purpose. The similarity between cold spray coating and shot peening process poses the question whether cold spray coating can improve the fatigue strength in addition to providing corrosion protection. The objective of this research is to answer this question for the specific case of the coating of wrought magnesium alloy AZ31B with aluminum powder. This study comprises two parts. The first part characterises the residual stress induced by cold spray coating. This investigation employs both numerical and experimental methods. For the numerical study, the cold spray coating process has been simulated via ANSYS software classic package. The numerical results have been compared to experimental results from X-Ray Diffraction (XRD) stress measurement of a coated sample. For the second part of this research, the fatigue strength of as received, stress relieved, and stress relieved/coated specimens have been compared. Three groups of AZ31B specimens have been prepared and tested by rotating bending machine and their S-N curves have been prepared. Comparison of the results reveals that there is a considerable loss in fatigue strength of as received specimens after stress relief. This is due to the removal of compressive residual stress in the raw material induced by the extrusion process. Also, comparison of S-N curves of stress relieved and stress relieved/coated specimens shows fatigue life improvement after cold spray coating. The maximum improvement is 49 percent in the load of 120 MPa and the endurance limit has improved 9 percent.
Author: Siavash Borhan Dayani
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 80
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Book Description
Recent advancements in manufacturing of light-weight structures have caused high interest in industries toward magnesium alloys because of its excellent properties such as specific strength, low density, and fatigue strength. Application of magnesium in the vehicle structure saves energy and reduces gas emission which consequently improves the performance of the vehicle. Magnesium alloys have low corrosion resistance and high tendency to corrode in humid and aqueous environments. The results of recent research show that cold spray coating of pure aluminum powder results in significant improvement in magnesium corrosion. However when tested under cyclic loads, the coated samples developed surface cracks and delamination. Which lead to highly localized corrosion damages underneath of the cracks or any discontinuity in the components. The early cracking was attributed to the low fatigue resistance of pure aluminum. The results of two new approaches in enhancing the corrosion fatigue life of coated magnesium are presented in this thesis. First, an aluminium alloy coating powder with the higher fatigue strength was selected for coating. Al-7075 powder, with average particle size of twenty microns have successfully been coated on AZ31B samples with highly densed, low porosity coated layer. The coating was performed using nitrogen gas at 400oC temperature, and gas pressure of 200 psi. Electrostatic painting was then applied. Result of tests in the corrosive atmosphere of 3.5 % of NaCl solution as well as rotating fatigue test in corrosive environment will be presented. Improvement of fatigue resistance of cold spray coated samples and corrosion-fatigue resistance of cold spray coated, e-painted samples are studied in this thesis.
Author: The Minerals, Metals & Materials Society
Publisher: Springer
ISBN: 3319725262
Category : Technology & Engineering
Languages : en
Pages : 898
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Book Description
This collection features papers presented at the 147th Annual Meeting & Exhibition of The Minerals, Metals & Materials Society.
Author: Bahareh Marzbanrad
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Global warming, dwindling fossil fuels, and the low efficiency of alternative energy sources such as batteries and solar panels compared to traditional carbon-based energy sources, have shifted the industrial design paradigm towards minimizing structural weight. In this scenario, employing low density grade metals is inevitable. Magnesium (Mg) alloys, such as AZ31B, are one of the lightest structural materials, and have been able to gain strong foothold in the industrial world due to their high "strength to weight ratio". However, the long-term performance of parts manufactured from Mg alloys are required for reliable structural applications. Hence, research on the methods to enhance the fatigue properties of Mg alloys is crucial. Surface treatment, particularly surface coating of manufactured parts with a thin layer of high fatigue strength material is considered a versatile approach to address fatigue shortcomings of Mg alloys. Cold gas dynamic spray is an emerging technology that deposit metal powder with a supersonic velocity on substrate in a solid-state. The nature of this technology (peening) promotes compressive residual stress and results in a refined grain structure, which reinforces a material's surface and prolong crack initiation, thus enhancing the fatigue performance of materials like AZ31B alloy. Among all potential candidates for coating Mg parts, aluminum alloys are one of the best, due to their low density and strong fatigue performance. Hence, in this research, cold spraying is employed to deposit a thin layer of Al7075 on AZ31B-H24 Mg substrates in order to improve their fatigue performance. The complexity of the cold spray process requires some in-depth study through in situ measurements. For this, fiber Bragg grating (FBG) sensors is employed for monitoring and assessing the thermo-mechanical behaviour of Mg alloy during cold-spray coating. Furthermore, the hole drilling, X-ray diffraction and in situ FBG sensors residual stress measurement techniques are used to explore the effect of processing parameters and thermal mismatch on the residual stress distribution of coated Mg samples. In addition, SEM, TEM, CT scanning tomography, micro indentation hardness, surface topography and roughness measurements are utilized to identify the physical and microstructural characteristics of the coating, interface and substrate. Based on the findings of this research, the common understanding that cold spray induced residual stresses are compressive is questioned. It is shown that the heat associated with the spraying, although much lower than melting temperature, can wash out the peening effect and result in tensile residual stress in the substrate. Hence, to customize the residual stress and for inducing compressive residual in the Mg substrate, the cold spray coating parameters were tuned to decrease the heat input to the substrate. Moreover, a cooling system was designed that increased heat transfer from the substrate during the coating process. Another major factor affecting the state of the residual stress is the thermal mismatch of the coating and the substrate materials. The detrimental effect of thermal mismatch between the Al7075 coating and AZ31B substrate on the residual stress of substrate and coating was addressed by adding an interlayer of zinc, which has a higher thermal expansion coefficient than the substrate and coating material. Zinc is successfully deposited, and its coating parameters were selected in a way that resulted in inducing compressive residual stress in the substrate, coating and the zinc interlayer. However, detail characterization of the zinc and AZ31B substrate reveals that intermetallic phases have formed at the interface. Therefore, despite the induced compressive residual stress, cracking at the zinc magnesium interface restricts the application of this interlayer. Two extreme coating conditions that lead to induced tensile and compressive residual stress in the Mg substrate have been selected for the rest of this research. The quality of the coating is examined by CT-scan, which demonstrates that the compressive samples have less porosity than the tensile samples, although the densities of both samples are above 99%. The physical and mechanical properties of the compressive samples, including hardness and surface roughness, have also been significantly improved compared to tensile samples. Finally, the fatigue performance of the two types of coated samples (tensile and compressive) is investigated revealing that the compressive samples demonstrate exceptional fatigue life in high cycle regime compared to the bare AZ31B samples with 130% life enhancement.
Author: V.K. Champagne
Publisher: Elsevier Inc. Chapters
ISBN: 0128089547
Category : Technology & Engineering
Languages : en
Pages : 42
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Book Description
Magnesium alloys are widely used in aircraft and automotive components because of their inherent light weight compared to other engineering metals. However, premature corrosion is one of the challenges associated with magnesium. In the aerospace industry, many expensive castings cannot be reclaimed adequately because current methods are often inappropriate due to excessive porosity, oxidation and thermal damage. Cold spray is a solid-state coating process that uses a supersonic gas jet to accelerate small particles against a substrate to produce metal bonding by rapid plastic deformation of the impacting particles. Significantly, magnesium components can be repaired, restored and protected by cold spray deposition of pure aluminum which has thus already been specified by some aerospace users as a standard technique for magnesium repair. In this chapter, the state of the art of commercial cold spray technologies for magnesium repair will be discussed, as well as their advantages and limitations compared to traditional thermal processes.
Author: Anatolii Papyrin
Publisher: Elsevier
ISBN: 008046548X
Category : Science
Languages : en
Pages : 341
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Book Description
The topic of this book is Cold Spray technology. Cold Spray is a process of applying coatings by exposing a metallic or dielectric substrate to a high velocity (300 to 1200 m/s) jet of small (1 to 50 μm) particles accelerated by a supersonic jet of compressed gas. This process is based on the selection of the combination of particle temperature, velocity, and size that allows spraying at the lowest temperature possible. In the Cold Spray process, powder particles are accelerated by the supersonic gas jet at a temperature that is always lower than the melting point of the material, resulting in coating formation from particles in the solid state. As a consequence, the deleterious effects of high-temperature oxidation, evaporation, melting, crystallization, residual stresses, gas release, and other common problems for traditional thermal spray methods are minimized or eliminated. This book is the first of its kind on the Cold Spray process. Cold Spray Technology covers a wide spectrum of various aspects of the Cold Spray technology, including gas-dynamics, physics of interaction of high-speed solid particles with a substrate as well as equipment, technologies, and applications. Cold Spray Technology includes the results of more than 20 years of original studies (1984-2005) conducted at the Institute of Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Science, as well as the results of studies conducted at most of the research centres around the world. The authors' goal is threefold. The first goal is to explain basic principles and advantages of the Cold Spray process. The second goal is, to give practical information on technologies and equipment. The third goal is to present the current state of research and development in this field over the world. The book provides coverage and data that will be of interest for users of Cold Spray technology as well as for other coating experts. At the present time the Cold Spray method is recognized by world leading scientists and specialists. A wide spectrum of research is being conducted at many research centres and companies in many countries. New approach to spray coatings Results are exceptionally pure coatings Low spray temperature without degradation of powder and substrate materials High productivity, high deposition efficiency High operational safety because of absence of high temperature gas jets, radiation and explosive gases Excellent thermal and electrical conductivity Wide spectrum of applications because of important advantages of the process
Author: Jin Zhang
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 8
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Book Description
In this study, aluminum coatings were prepared by dc magnetron sputtering on AZ31B magnesium alloy. The influence of sputtering parameters (include sputtering current, argon pressure, and deposition time) on corrosion behavior was investigated by potentiodynamic polarization tests in 3.5 % NaCl solution. The corrosion morphology was examined in detail by scanning electron microscopy and optical microscopy, respectively. It was found that the corrosion current density of magnesium alloy with aluminum coating was 2-3 orders of magnitude less than that of bare alloy. The corrosion potential with aluminum coating had been positive shift. The corrosion resistance of the coatings was strongly affected by its structure and residual stress, which depended on the process condition. Severe corrosion will occur after the aluminum coating is damaged due to the interaction of galvanic corrosion and other corrosion forms.
Author: D. N. Williams
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 22
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Book Description
The effects of environment on fatigue behavior are quite intimately related to such test variables as stress intensity, cyclic frequency, and temperature. The effect of these variables has been shown to be quite complex. However, a consistent pattern of behavior is beginning to emerge which, it is hoped, will lead to a considerably changed understanding of the corrosion-fatigue process. It is considered probable that an increased understanding of the corrosion-fatigue process will also contribute measureably to an improved understanding of general fatigue processes. Material variables such as composition, directionality of properties, and microstructure, have important effects on corrosion-fatigue behavior of aluminum alloys. However, it appears that these variables, at least in gaseous environments, may be important largely because of their effects on the mechanical behavior of aluminum alloys. On the other hand, studies in seawater suggest that these variables become increasingly important as the corrosive nature of the environment increases. This memorandum discusses in detail the effects of both test variables and material variables on corrosion fatigue. In addition, current theories of corrosion-fatigue mechanisms are outlined, and several methods of preventing corrosion fatigue are suggested. (Author).
