Al.Fe.Si. ve Al.Fe.Si.Mn. alaşımlı alüminyum folyoların mekanik performans özelliklerinin karşılaştırılması
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- Tez No: 75245
- Danışmanlar: PROF. DR. EYÜP SABRİ KAYALI
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji Eğitimi Ana Bilim Dalı
- Bilim Dalı: Malzeme Bilim Dalı
- Sayfa Sayısı: 85
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Özet (Çeviri)
SUMMARY MECHANICAL PERFORMANS OF ALUMINIUM FOILS OF AlFeSi AND AlFeSiMn ALLOYS In this study..mechanical performans of aluminium foils of Al.Fe.Si. and Al.Fe.Si.Mn alloys have been investigated. The ability to produce a variety of shapes from flat shapes from flat sheet of metal at high rates of production has been one of the real technological advances of the twentieth century. This transition from hand - forming operation to mass -production methods has been important factor in the great improvement in the standart of living which an occured during the period. Because of the complexity of sheet forming operations,simple mechanical property measurments made from the tension test are of limited value.Over the years a number of laboratory tests have been developed to evaluate the formability of sheet materials.The Swift flat -bottom cup test is a standardized test for deep drawing.The drawability is expressed in terms of the limiting draw ratio.In the Olsen test and Erichsen tests the sheet is clamped between two ring dies while a punch, usually a ball, is forced against the sheet untill it fractures.The depth of the bulge before the sheet fracture is measured.These tests subject the sheet primarily to streching, while the Swift test provides nearly pure deep drawing. Howewer,most practical sheet forming operations provide a combination of both biaxial stretching and deep drawing.The Fukui test, which produce a conical cup using a hemispherical punch, provide a combination of both streching and drawing. A useful technique for controlling failure in sheet -metal forming is the forming limit diagram.The surface of the sheet is covered by a grid of circles, produced by electrochemical marking.When the sheet is deformed, the circles distord into ellipses.The major and minor axes of an ellipse XIthese two directions is measured by the percentage change in the lenghts of the major and minor axes.These strains,at any point on the surface,are then compared with Keeler Goodwin diagram for the material. Strain states above the curve represent failure, those below do not cause failure. The failure curve tension-tension was determined by Keeler and tension -compression region was first determined by Goodwin. Another approach to predicting sheet formability is the stretch -draw shape analysis. The forming limit of the material is established with the Olsen test and the Swift cupping test. Then the part is broken down into simple shapes and the percentage of draw and strech are calculeted from the geometry. This places the part on the forming limit diagram ( FLD ) and the degree of severity of the part can be established. FLD can be predicted theoretically,but the best way is to obtain it experimentally by performing tension test,deep darwing test, Erichsen test and bulge tests. Represantation of fracture data as a plot of major versus minor strains at the fracture gives the limit curve. Fracture occurs when the strain state at the end of the process is above the limit curve. The direction and the magnitude of maximum strain are easily determined by a grid pattern of small diameter circles on the surface of the blank.The grid pattern can be produced by electro-chemical marking, serigraph techniques or fotochemical etching. During deformation, grid circles are deformed into ellipses.The major and minor axes of ellipses represent the two principal strain directions in the test specimen.The strain in these two directions are measured by the percentage change in the lengts of the major and minor axes.The tension -compression region of the FLD is determined by the strain values obtained from tension and deep drawing tests at the instant of fracture.For deep drawing stampings,the strain state is tension-compression,and the major axes of circles elongate and minor axes are shortened.In tension- tension (stretching ) region both major and minor XIIaxes are greater than the initial circle diameter. This region of the FLD is determined from fracture strain values obtained from Erichsen and Bulge tests. Trough a complete analysis of the FLD and the actual deformations, die tryout and modification can be simplified, selection of optimum materials and lubricants can be made easier, and breakage of stampings in the production can be minimized. Formability is a function of both materials properties ( strain hardening exponent“n”, strain rate sensitivity exponent“m”, plastic anisotropy“r”, thickness,grain size ) and process variables ( die design lubrication,workpiece geometry ).FLD offers a graphical method for the representation of material influences in formability. Material effects are embodied in the limit curve, the shape of which depends on microstructural features and composition.FLD is independent of the process variables such as lubrication and die design but the process variables affect the formability because of their effects on the uniformity of strain distribution in the stamping operation The aim of this study is to compare the formability of two Al alloys (AlFeSi and AlFeSiMn alloys ) in the form of foil at 0.2 mm thickness. These two alloys produced Hunter continuous casting machine as strip, then cold rolling operation begins to get desired thickness and annealed to get desired mechanical properties. Since rather high solidification rates are encountered in the twin -roll casting of wrought aluminium alloys, their as-cast microstructures are often not in eguilibrium. The aluminium solid solution is super satureted and the intermetallic phases are often metastable and aluminium -rich. Moreover, in spite of a very fine dendritic structure, both micro and macro segregation patterns are observed in as-cast sheet.Hence, homogenization is an essential step in the production process of such alloys particularly when they are submitted to forming operations in the post production applications. XIIIIn the experimental studies, firstly the chemical compositions of these two aluminium alloys are determined by spectral analysis ( Table -1 ), then tension test, Erichsen test and Swift test have been used to evaluate the formability of these alloys in the form of foil at 0.2 mm thickness. The result of these mechanical test are given in Table -2 Table-1 : The chemical compositions of the alloys studied ( as Weight % ) Table -2 The result of mechanical test of the Al alloys studied When the chemical compositions of these two alloys are compared, the most noticeable difference is Fe contents of these alloys. The other XIVimportant observation in the chemical composition of AlFeSiMn alloy is decreasing Si content while increasing Mn content compared to the chemical composition of AlFeSi alloy. Fe / Si ratio is 7.81 for AlFeSiMn alloy and 1.14 for AlFeSi alloy. During production of these alloys, the Fe/Si ratio is expected to be max 2.5,but the high Fe / Si ratio in AlFeSiMn alloy influences the process of the foil production in a negative way. However the high Fe/Si ratio is also desirable for use of scraps in high amount during Al foil production. Tensile test result show that foils of AlFeSi andAlFeSiMn alloys have similar yield and tensile strength values. Any problem which may occur during forming would be related to the ductility of these materials. The % elongation value which is a measure for ductility in tension, is the most basic data in comparison of forming performance.When the % elongation values of these two alloys given in Table -2 are compared,it has been observed that the AlFeSiMn alloy foil has a better ductility than the AlFeSi alloy foil. Strain hardening exponent“n”and normal plastic anisotropy“r”values for AlFeSi and AlFeSiMn alloy foils have been determined in three dimensions ( 0°,45° and 90° ) from tensile tests. The strain hardening exponent (n) determined by tension test as a measure of strech forming capacity and high value of n is desirable. Increasing n value reduces peak strains and increases the limit strain of the FLD. When the strain hardening exponent values of these two Al alloys given in Table-2 are compared, it has been observed that AlFeSiMn alloy foil has higher“n”value than the AlFeSi alloy foil.The high“n”value means that this material has high uniform plastic deformation,hence better formability. The average plastic anisotropy value, r, is a measure of normal anisotropy which characterizes the resistance to thinning.The r value must xvMajor Strain (%) s 1 Minor Strain (%) s 2 Figure 1. The forming limit diagrams of AlFeSi and AlFeSiMn alloys in the form of foil at 0.2 mm thickness.8 XVIIThe average plastic anisotropy value, r, is a measure of normal anisotropy which characterizes the resistance to thinning.The r value must be larger than one.Deep drawability of the materials increases with the increase of r value. The average plastic anisotropy value r is 0.54 for AlFeSi alloy and 0.76 for AlFeSiMn alloy. Therefore AlFeSiMn alloy has higher resistance to thinning and better deep drawability than AlFeSi alloy. The variation of normal anisotropy r with the plane of sheet is called planar anisotropy, Ar, and is responsible for earing in deep draw cup. The ideal value of Ar is zero.When the planar anisotropy (Ar) values of both alloys given in Table -2 are compared, the AlFeSiMn alloy which has Ar value smaller than the Ar value of AlFeSiMn alloy is indicates less earing during deep drawing,hence better performance in forming of AlFeSiMn alloy is expected. When the results of Swift and Erichsen tests given in Table -2 are compared, Swift and Erichsen values of AlFeSiMn alloy are little higher than the values of AlFeSi alloy. This result also indicates that AlFeSiMn alloy foil has better formability than AlFeSi alloy foil. Tensile, Erichsen and Swift test are mechanical tests which give indirect information about formability.These tests can compare materials in their forming performances, but can not give information what type of sheet has to be used or what has to be done for a succesfull forming operation. To overcome these,the forming limit diagrams of these two alloys are obtained given in Figure 1. The forming limit of AlFeSiMn alloy is above the forming limit of AlFeSi alloy as shown is Figure 1. This means that AlFeSiMn alloy has better formability than AlFeSi alloy. When one takes into account the result of tensile, Erichsen and Swift tests, beside forming limit diagrams of these two alloys, it is concluded that AlFeSiMn alloy foil will show better performance in forming than AlFeSi alloy foil. XVI
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