Use of Magnesium Alloys - Essay Example

an alloy is a mixture of a metal to or some of the other metals to obtain different chemical and physical properties. Magnesium, being the lightest structural metal in the modern periodic table often forms alloy with the metals like Aluminum, zinc, manganese, silicon, copper and zirconium. Introduction Over the past few years, use of Magnesium alloys has been increased on a much faster rate, mainly in automobile industry. This all has happened because of the introduction of new air pollution regulations and fuel economy attainment (mainly in the western world and Japan). Magnesium alloys like Mg ZK60 and Mg AK80 have occupied the essential demands for automotive Mg parts. Car structural parts are essentially produced from energy absorption materials with reasonable elongation, high yield strength and most importantly high impact energy. A type of alloys called Wrought Mg alloys have the potential to serve these needs better then the die cast Mg alloys. 1 more benefit of using alloys is “The use of Wrought Mg parts in vehicles will cause weight saving up to an average of 30% compared to Aluminum and 70% compared to steel. Magnesium alloys are in demand now days for the properties like low density, high melting and boiling point, high specific strength, good electromagnetic shielding characteristics, excellent castability and machinability. Magnesium AZ80 Structure Magnesium ZK60 Structure Types of Alloys Magnesium alloys are divided mainly in 2 types. First type is Cast Alloys. Magnesium casting proof stress is mainly 75-200 MPa, tensile strength is between 135-285 MPa and elongation 2-10%. Common density is 1800 kg/m3 and Young's modulus is 42 GPa. Some of the most popular and common alloys are AZ63, AZ81, AZ91, ZK51, ZK61, Elektron 21. Second is Wrought Alloys. Magnesium wrought alloy proof stress mainly coincides between 160 and 240 MPa, tensile strength is 180-440 MPa and elongation remains 7-40%. Some of the examples of these kinds of alloys are AZ31, AZ61, AZ80, ZK60, and HM21 Code System if we look at the names of the alloys of magnesium, we’ll find that these names have a different kind of pattern. The name includes 2 letters followed by 2 digits. The first two letters in the names indicates towards the main composing elements. Like (A= aluminum, Z= Zinc, M= Manganese, S= Silicon) and remaining the two digits after the letters indicates towards the percent composition respectively. For an example – If the given alloy is AZ63, we can predict that the two elements, Aluminum and Zink are present in the alloy and the percent composition of both the metals is 6% and 3% respectively. Specification Physical properties of Alloys Magnesium and its alloys mainly have silvery and white shades. As discussed above, Magnesium is the lightest structural metal present. So the alloys of magnesium are used to build structures like automobiles and massive buildings. As magnesium being reactive in nature, the alloy of magnesium is used for the building purposes. Magnesium and its alloys can be fabricated very easily. Pieces of Magnesium’s alloys can be welded, molded, cut and shaped according to requirement. Magnesium is the 6th most found element in nature, consisting of 2.1% of the earth’s crust. Common density of Magnesium alloys is 1800 Kg/m3. Relative Intensity of Magnesium Chemical properties of Alloys: - Magnesium is present in 2nd group and 3rd period of the periodic table, having atomic no as 12. Its average atomic mass is 24.035 gm. The boiling point of magnesium in standard conditions is 1090 degree Celsius or 1994 degree Fahrenheit. Magnesium is one of the most reactive metals present in the periodic table that is why; generally magnesium is not present in Free State on the earth. This is 1 of the need to form the alloys. The alloys of Magnesium like AZ80 and ZK60 have high melting and boiling points as compared to Magnesium. Alloys have higher stable condition and can be kept freely in the atmosphere. Uses of the given alloys Variety of the stock for subsequent working is mainly produced by the direct chill process but, compared with advances in other metals; the process has seen almost nil development for magnesium in the past decade. A well described American work on atomized powder-compacted alloys which later resulted in the extrusion alloy ZK60B (Mg-6Zn-0.6Zr) was described recently. The suppression of grain growth, ascribed partly to the cored structure of the powder and partly to the oxide coating on the particles, leads to high tensile strength coupled with high compressive strength, a combination difficult to achieve with more conventional wrought magnesium alloys. Applications of the alloys Structural Engineering Applications In the past decade, variety of applications of magnesium was declined in aerospace industry because of several reasons. The main reasons for this were “the possible effects of the corrosion in the airframe and the increasing and unacceptable cost of the preventive maintenance of the magnesium parts”. Also, the modern engines, having higher capacity, have limited the need of reduced weight of various parts in the body of automobile or aircraft (1). Products and applications in Chemical and metallurgical treatment This is a vast category, where magnesium is used as a chemical (like in the production of zirconium, as flares for production of life, titanium etc,), also for its electrochemical characteristics (Cathodic protection, primary batteries), last but not the least, for metallurgical treatment such as in nodular iron, steel desulphurization etc. A large number of products have been developed using magnesium in this category. Powder and granulated forms A large composition of magnesium powder is produced by mechanical procedure, usually with a milling cutter. The initial product may be milled to produce a finer or more rounded particle. Magnesium powder can also be obtained by gas jet or centrifugal disintegration of melted magnesium metal. Additives for treatment of ferrous metals Adding magnesium to melted cast iron, to produce nodular iron, has been a routine practice for over two decades. The majority of such iron is made by treatment with ferrosilicon containing 5-10% of magnesium. Since the last decade, a lot of interest has developed in the use of magnesium for desulphurising blast furnace iron. The increased number of operations and decrease on the composition of the additive has required special developments. Primary Battery Anodes A great example of the application of Magnesium alloy is “Magnesium alloys are used in seawater-activated primary batteries; the batteries usually have silver chloride cathodes. This system was developed to use the magnesium alloy AZ61. Although the theoretical open circuit electromagnetic force for this type of cell is 2.6 V practical working voltage are of the order of 1.1 volt. Used in Cathodic Projection Cast magnesium anodes are usually supplied in AZ63 and extruded shapes in AZ61 alloys. AM503 is used for higher performance requirements. Alloys in Manufacture and Fabrication Industry For years, the automobile industry has touted the use of and need for steel in trucks, cars and sports utilities vehicles. Then, the public began to asking for a more fuel efficient, less emissive and cheaper vehicles, comparatively. Newer, more environmentally sound cars are answering this call; they have accomplished this without the use of the industry’s beloved steel. The kicker is that consumers dint notices the material switch. The alloy wasn’t actually new. It had been discovered in 1755 by Joseph Black and isolated in 1808. The search for a more efficient and abundant material was led researchers to experiment with magnesium alloys in the place of the more traditional materials like steel that doesn’t perform as expected and hence, magnesium got it’s platform to get launched. The aforementioned factors have made the alloy a newfangled contraption in the auto industry. The alloy was thus a step above steel, without a sacrifice in safety. One of the most common misconceptions is that cars made from magnesium alloy as opposed to steel are less safe. You now know that the opposite is true. Magnesium alloys may just replace steel completely in the future. Processing of the Magnesium alloys the magnesium alloy with refined grains and fine magnesium silicides (Mg2Si) dispersions (MgSiX®) is developed via repeated plastic working process in solid-state, and thus it indicates a high strength. For the synthesis of Mg2Si, in-house wastes or scraps of SiO2 glasses with a high purity could be employed as input raw materials instead of silicon particles. A Brief on the Fatigue Behavior of Magnesium Alloy AZ80 the fatigue performance of the high-strength magnesium alloy AZ 80 is studied in air as well as in aqueous 0.5 and 3.5% NaCl solutions. The effect of mechanical surface treatments, specifically mechanical polishing, shot preening, and roller burnishing on the S-N curves, is investigated using an electro polished surface as a reference. While mechanical polishing as well as shot preening improves fatigue performance in air, no improvement is observed in NaCl solutions. However, roller burnishing, which combines a smooth surface finish with residual compressive stresses in sufficient depths, leads to outstanding fatigue performance even in 3.5% NaCl solution (2).    Fatigue strength of the alloys R.R. Moore type tests  at 5 x 108 cycles: AZ80 (F temper): 97 MPa (14 ksi) at 1 x 108 cycles: ZK60: 80-95 MPa (12 to 14 ksi). Corrosions And Coating For Them If galvanic corrosion is the issue in the application then one of the most important things to consider in the prevention of a galvanic cell is the elimination of FE on or embedded in the surface of the magnesium alloy. The purer the alloy the better it should perform. As far as a coating is concerned, there are several on the market all suitable depending on the application. There are alodine and powder coat solutions and ceramic type electrolytic surface finishes that can be produced. One of the ceramic type finishes is Keronite. The application it is being used for is an important consideration as a lot of Companies can tend to go OTT with some internal magnesium applications when it does not actually require anything as there is no electrolytic bridge formed to create the galvanic cell. Tensile Behavior of the Alloys of Magnesium Several magnesium alloys have been developed especially for the manufacture of wrought products. The most important are M1A, AZ80, AZ6IA, AZ80A, and ZK60A. As in the case of the casting alloys, the principal added elements in the wrought compositions are aluminum, manganese, and zinc (3). M1A is used for various wrought manufactures including sheet, forgings, and extrusions. In any form, the strength of M1A is relatively low. AZ3lB is employed for sheet and extrusions. AZ6lA and AZ80A find use for extrusions. Of the extrusion alloys, only AZ80A is not extruded into hollow shapes or tubing. T A54A is employed exclusively for forgings and ZK60A for extrusions. Magnesium alloys for wrought products are classified as non-heat treatable and heat treatable. AZ80A and ZK60A are heat treated by aging the material as fabricated. The strengths are increased substantially but with loss of elongation on aging. M1A and AZ31B sheet are supplied as hot rolled, as cold rolled, and annealed. The principal wrought manufactures which are commercially available in magnesium alloys include sheet and other flat rolled products, extrusions (bars, rods, solid shapes, hollow shapes, and tubing), forgings, screw-machine stock, and impact extrusions. Development of the Microstructure of Severelyplastically Deformed Mg Alloy, ZK60 Mg alloys are of interest for lightweight structural materials with applications in the automotive and aircraft industries. The deformation mechanisms for hexagonal structures, such as Mg, are not fully understood, especially with respect to the crystallographic texture. The mechanical twinning, as deformation mode of an Mg alloy, AZ31, was the focus of recent studies. Twinning can induce major change in texture, if the initial texture contains a significant fraction of grains oriented with their c-axis nearly perpendicular to the compression direction. This arrangement has a peculiar twinning effect, which operates in certain hexagonal materials with c/a < v3 (e.g., Mg), for which the twinning on the 10.2 plane in the 10.1 direction will lengthen the grain along the original basal direction and shorten the grain perpendicular to it. Our prime goal was to investigate texture changes induced by twinning in Mg alloy, ZK60, under compression, and track the possible twinning contributions in a severe deformation mode, such as equal-channel-angular processing (ECAP). ECAP technology has been successfully used for refining grains down to 100 nm or less in many metallic alloys and composites. For ZK60, deformed at 2600C, the grain refinement is not very pronounced (7 - 10 ?m). However, previous studies showed a significant increase of the ductility, at relatively low temperatures (4). The texture evolution during ECAP can impact the mechanical behavior of the materials. Some experimental results concerning the texture Generated after multipass ECAP of ZK60 have been reported, as well as polycrystalplasticity Simulations designed to discriminate the relative activities of different deformation Mechanisms .Here we examine more closely the texture evolutions during one pass of ECAP by mapping the texture of a partially ECAP-ed specimen, and contrast the ECAP and uniaxial Compression textures. When mapping the ECAP texture, the amount of the shear-strain at each sampling point of the ECAP-ed specimen was known from the experiment on scribed billets, and Calculated based on the slip-line theory using a recently reported method. Magnesium Alloys, in relation to Safety and Environmental Consideration Magnesium alloys are very bio compatible and show promise for use in orthopedic implant. Significant progress of research on bioabsorbable magnesium stents and orthopedic bones has been achieved in recent years. The issues on degradation, hydrogen evolution, and corrosion fatigue and erosion corrosion of magnesium alloys and various influencing factors in simulated body fluid (SBF) are discussed. The research progress on magnesium and its alloys as biomaterials and miscellaneous approaches to enhancement in corrosion resistance is reviewed. Finally the challenges and strategy for their application as orthopedic biomaterials are also proposed. Use of this alloys as a human body part replacement – are they (or any of them) biocompatible to the human body? Metallic materials including stainless steel, titanium alloys, and cobalt-based alloys constitute, due to their high strength, ductibility, and good corrosion resistance, an important class of materials in hard tissue replacement, especially load-bearing implants for the repair or replacement of diseased or damaged bones tissues. But, these metallic materials are not biodegradable in the human body, so a second surgical intervention may be necessary after the tissues have healed. Thus a strong body of research focuses on new biodegradable implants, which dissolves in biological environment after a certain time of functional use. Biodegradable implants constitute an appropriate solution because of cost, convenience and aesthetic reasons favorable to patients. Magnesium is one of the essential elements in the human body and has the advantage to be biodegradable (5). So its corrosion performance can also be envisaged as potential applications for bio absorbable stent implant logy for cardiovascular diseases. Although excellent preliminary results have been achieved, absorbable metal stents (AMS) currently under clinical investigation possess degradation kinetics and mechanical characteristics which are far from being completely optimized for all uses and applications. The purpose of this study is to investigate the Corrosion behaviors of pure magnesium and of a standard Mg-Y-RE WE43 alloys (untreated and anodized) in artificial body fluids. Because of potential use of Magnesium alloys and especially the WE43 for different types of implants, two types of physiology solutions were used, Artificial Plasma (AP) with high carbonate content and a buffered Simulated Blood Fluid (SBF). Due to solid-solution strengthening, the presence of yttrium in the WE43 should not only increase the creep resistance properties but also the corrosion resistance, in addition to favorable high temperature properties. Then, the influence of the Galvan static anodization treatment on the surface on the corrosion behavior was documented. Characterization of the oxide film structure and composition for optimized conditions was performed by different electrochemical (EIS), optical, SEM, and Auger Electron Spectroscopy (AES) measurements. The investigations showed that SBF is significantly more aggressive than AP with regard to the untreated WE43 surface. The anodization process led to a formation of a thin hydroxide layer (few hundred nm) which increases the corrosion resistance of the alloy in both physiological solutions, especially in AP. The final objective is to modify the composition and / or the surface of the alloy with an anodic layer to obtain a suitable material with initial stability for an absorbable implant, followed after a couple of weeks by a full degradation of the implant. Conclusion In fast growing science Industry, Scientists have got an alternative of every possible thing. The chemical components are being used on a larger scale for the betterment of human. Till a few decades back, Magnesium was just a simple reactive metal which was not found in Free State on the earth. But in recent time, Due to the Science’s techniques, so many ways have been implemented and the alloys of magnesium were found, which turned out to be a very useful thing for human and science. From the spare parts of automobiles to the metal rods inside the human body, magnesium has occupied each and everything as a successor. If it would be continue, then one day Magnesium alloys will really be boon for humanity as it will fine some other options to be used at. Sources:- 1. W. Unsworth. Int. J. of Materials and products Technology, 4 (4), 359-378, 1989. http://www.maik.ru/abstract/rjapchem/99/rjapchem0395_abstract.pdf 2. http://www.magnesium.com/w3/forum/read.php?thread=2807 3. http://www.keytometals.com/article138.htm 4. Stoica, G. M.; Chen, L. J.; Payzant, E. A.; Agnew, S. R.; Lu, Y. L.; Han, B. Q.; Langdon, T. G.;Liaw, P.K.; in Modeling the Performance of Engineering Structural Materials II [D.R. Lesuer and T.S. Srivatsan, eds.], pp. 295-306, TMS., Warrendale, PA, 2001. 5. http://www.ecmjournal.org/journal/supplements/vol014supp03/pdf/v014supp03a004.pdf 6. http://Latest-science-articles.com/articles/article-68. Gehrmann, R.; Frommert, M. M.; Gottstein,        G.; Mat. Sci. Eng., A, 2005, 395, 338-349 7. Kallend, J. S.; Kocks, U. F.; Rollett, A. D.; Wenk, H. R., Mat. Sci. & Eng., A, 1991, 132, 1-11. 8. http://chemicalelements.com/elements/mg.html 9. http://www.magnesium-elektron.com Read More