Author: Hesham Y. Saleh Mraied
Publisher:
ISBN:
Category : Aluminum-manganese alloys
Languages : en
Pages : 162
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Book Description
Magnetron-sputtered aluminum (Al) and aluminummanganese (Al-Mn) films with structures ranging from nanocrystalline to amorphous were obtained by tuning the Mn% up to 20.5 at.%. Corrosion behavior of the films was investigated in 0.6 M and 0.01 M NaCl aqueous solutions by potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS). Pitting corrosion was found to be strongly affected by alloy composition. The amorphous Al20.5 at.% Mn exhibited the best pitting resistance during short term exposure. However, over longer immersion in 0.01 M NaCl up to 108 hrs, nanocrystalline Al5.2 at.% Mn showed the highest corrosion resistance. The dual-phase Al-11.5 at % Mn alloy was found to have higher nominal corrosion rate compared to its nanocrystalline or amorphous counterparts.
Author: G.-L. Song
Publisher: Elsevier Inc. Chapters
ISBN: 0128089407
Category : Technology & Engineering
Languages : en
Pages : 42
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Book Description
Magnesium (Mg) alloys have low corrosion resistance and exhibit unusual corrosion behavior in aqueous environments. Because of this unique corrosion performance, some special corrosion prevention techniques have to be employed for Mg alloys in their applications. This chapter briefly summarizes the corrosion characteristics of Mg alloys, and also presents a strategy and methodologies to mitigate the corrosion damage of Mg alloys in applications.
Author: L. A. Neumeier
Publisher:
ISBN:
Category : Aluminum-zinc alloys
Languages : en
Pages : 42
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Author: Liang Wu
Publisher: Frontiers Media SA
ISBN: 2832515614
Category : Technology & Engineering
Languages : en
Pages : 111
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Book Description
Magnesium (Mg) alloys, possessing good thermal and electrical conductivity, low density, recyclability, high specific strength, and excellent damping capacity, are regarded as one of the most promising light metallic materials. Mg alloys are also known as the “inexhaustible green light engineering material” compared with steel, aluminum, copper, and engineering plastics, providing some important applications in communications, automotive, defense, aerospace, and biomedical industries. However, the low electrode potential causes poor corrosion resistance in the environment of moist air, sulfur, and marine atmosphere. And thus, the corrosion and protection technology of Mg and its alloys is listed as an important research topic in this field. In this Research Topic, the latest research papers on corrosion and protection of Mg and its alloys are collected to provide a platform for researchers and readers to understand the recent developments in this field. Good use of this platform could improve the international research level in corrosion and protection of Mg and its alloys and promote the “green, safe, life-extending and smart” anti-corrosion technology and expand the application range of Mg and its alloys. High-quality Original Research and Review articles in this field are all welcome for submission to this Research Topic. Research interests include but are not limited to the following areas: • Corrosion behaviors and mechanisms • Surface treatment technology • Biodegradable medical applications • High-temperature oxidation • Inhibitors for Mg and its alloys • New monitoring, evaluation, simulation, and prediction methods
Author: Maria del Rosario Silva Campos
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The role of intermetallic phases in the corrosion of Mg-RE alloys A new concept to develop a RE based Mg alloy with improved corrosion resistance was followed in the current work. Based on subsequent characterisation steps to eliminate less suitable RE elements the best microstructure for improved corrosion resistance was identified. At first, the corrosion properties of selected RE elements were determined. Based on these results RE elements that have a potential to enhance the corrosion resistance of Mg-RE alloys were selected. Two aspects of RE elements were important for the selection: the electrochemical properties and the solid solubility in Mg. If the solubility limit of RE elements in the Mg matrix is exceeded, they form intermetallic phases with Mg. By performing galvanic coupling measurements the compatibility between Mg matrix and intermetallic phases were estimated. At that point three binary Mg-RE alloys systems remained (Mg-Ce, Mg-La, and Mg-Gd). To evaluate the influence of composition (amount of intermetallic phases) on the corrosion behaviour, four concentrations were cast with 1, 5, 10 and 15 wt. % of RE. Ce and La have a lower solid solubility in Mg matrix generating higher volume fraction of the secondary phases, thus higher dissolution rates in the binary Mg-RE alloys. While Gd with higher solid solubility shows a different behaviour. Additions of up to 10 wt. % Gd resulted in similar behaviour compared to 1 wt. % Gd addition. The most promising results were obtained for the Mg-Gd system with 10 wt. % Gd. Thus, the microstructure of this alloy was further modified by heat treatments to understand the influence of microstructural changes on corrosion behaviour. A ternary element was used to attempt further optimisation of the corrosion performance. Additions of Al, Zn, Ga and Y did not show any improvement in the corrosion resistance of Mg10Gd. This is due to increasing volume fractions of critical more noble phases and the microstructure dominated by eutectic phase formation. Thus galvanic effects became much stronger due to the increased amount of cathodic phases in the eutectic regions. Mn was the only suitable ternary alloying element as it did not lead to the formation of Mn-rich intermetallics. It was found in solid solution in the intermetallics and to a lesser extent in the matrix without modifying the microstructure but increasing the corrosion resistance. The results of this work allow the design of new corrosion resistant Mg-Gd-Mn alloys by electrochemical evaluation and understanding of the basic corrosion mechanisms and interactions of the different phases. Better performance was predicted for reduced Gd contents and was finally experimentally verified.
Author: G.-L. Song
Publisher: Elsevier Inc. Chapters
ISBN: 012808944X
Category : Technology & Engineering
Languages : en
Pages : 32
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Book Description
Corrosion is a surface degradation process determined by an alloy’s surface state, composition and microstructure. This chapter presents an overview of surface processing and alloying techniques that can improve the corrosion resistance of Mg alloys. It is found that some surface engineering processes can significantly change the surface state, composition and microstructure of Mg alloys. For example, surface mechanical and chemical cleaning can effectively remove surface contaminations; burnishing can modify the surface layer’s microstructure including grain size and grain orientation; surface alloying can produce a metallic layer on top of the Mg alloy base material. All these surface engineering processes lead to enhanced corrosion resistance of Mg alloys without affecting their bulk properties.
Author: B.L. Jiang
Publisher: Elsevier Inc. Chapters
ISBN: 0128089466
Category : Technology & Engineering
Languages : en
Pages : 43
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Book Description
Micro-arc oxidation (MAO) is a novel and attractive surface engineering process for magnesium (Mg) alloys. In an electrolytic bath with high electric energy, the surface of a magnesium alloy can be converted into a dense and hard ceramic oxide coating. The MAO process can be used in diverse applications as a corrosion control technique. Due to its simplified pre-treatment, superior corrosion resistance performance and environmentally safe coating process, MAO technology has emerged as an important alternative to anodizing techniques in certain areas. This chapter presents a review of MAO techniques for Mg alloys from the scientific, technological and application points of view.
Author: J. S. Dunning
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 28
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Author: Darren Samuel Gandel
Publisher:
ISBN:
Category :
Languages : en
Pages : 324
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Manganese (Mn) and zirconium (Zr) are two common alloying additions in magnesium (Mg) alloys. Both of these elements, while having low solubilities in Mg, each serve a specific purpose when added to Mg. Mn is often added to improve the extrudability and formability of Mg alloys and in aluminium (Al) containing Mg alloys to produce the Al8(Mn,Fe)5 phase which is able to remove iron (Fe) impurities to dramatically improve the corrosion resistance. Zr is incorporated in Mg mainly due to its unique ability to act as a grain refiner to greatly reduce the grain size and hence improve the mechanical properties of Mg.The effect of Mn alone on the corrosion of Mg and subsequent Fe impurity levels in the absence of any Al alloying addition is not well documented. Furthermore, the independent role that Zr has on the corrosion of Mg and Mg alloys has also not been reported thoroughly. In this study, Mg alloys containing various levels of Mn, Zr and Fe alloying additions in binary, ternary and quaternary combinations were produced and examined via SEM, EDX and EBSD techniques. The corrosion rates and morphologies of Mg alloy samples were examined via electrochemical polarisation and immersion testing.It was discovered that Zr additions, while beneficial in being able to remove Fe impurities, has a negative impact on the corrosion rates of Mg. Zr is able to increase both the anodic and cathodic reaction kinetics of Mg, thereby increasing the corrosion rate. Zr dissolved in the Mg solid solution was shown to act as an 'anodic activator', increasing the anodic reaction kinetics and the rate of Mg dissolution. Zr not dissolved in solid solution was present as Zr particles embedded in the Mg matrix. These Zr particles were efficient local cathodes, enhancing the cathodic reaction. The difference in electrochemical potential between these, essentially pure Zr, particles and the surrounding Mg matrix lead to the formation of micro-galvanic couples at open circuit, which increased corrosion rate.Mn was observed to slightly decrease the cathodic reaction kinetics of Mg when included as an alloying addition. This is rationalised on the basis that Mn will interact with Fe, and not on the basis that Mn can support reduction reactions at lower rates than Mg. This notion also appreciates that there is no Mg metal that has 0% Fe. However, beyond Mn additions of ~2 wt.%, Mn particles which formed in the Mg matrix increased the corrosion rate through the formation of micro-galvanic couples with the Mg matrix. While Mn additions in this study were ineffective at removing Fe from the alloy system, Mn was found to be capable of rendering Fe impurities less detrimental to Mg. Mn additions were found to increase the tolerance limit of Fe in Mg. As such, higher levels of Fe were necessary to increase the cathodic reaction kinetics required for increased corrosion rates. It was observed that the Mn additions form an intermetallic phase with the Fe impurities. At low Fe levels these phases appeared to be Mn particles with Fe dissolved in solid solution within these particles. At higher Fe levels, there were large Fe particles encapsulated by a layer of Mn. It is proposed that this interaction between Mn and Fe decreases the electrochemical potential difference between the Fe impurities and the Mg matrix in a similar manner to the Al8(Mn,Fe)5 phase observed in Al-containing Mg alloys, thereby, decreasing the driving force to increase the cathodic reaction kinetics through micro-galvanic coupling.This work has elucidated the interactions and effects of Mn and Zr additions on Mg and has shown that Zr is inherently detrimental to the corrosion resistance of Mg and that Mn can interact with Fe in Mg to reduce the impact that Fe impurities have on Mg alloys in the absence of Al.
Author: Henri S. Sack
Publisher:
ISBN:
Category : Corrosion and anti-corrosives
Languages : en
Pages : 172
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