Şişe kapağı üretiminde kullanılan 8011 alüminyum alaşımının üretim süreci parametrelerinin mekanik özelliklere etkisi
Başlık çevirisi mevcut değil.
- Tez No: 46266
- Danışmanlar: PROF.DR. E. SABRİ KAYALİ
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 60
Özet
ÖZET Bu çalışmada şişe kapağı malzemesi olarak kullanılan ve özel bir alaşım türü olan 801 1 Alüminyum Alaşımının üretim süreci parametrelerinin mekanik özelliklere etkisi incelenmiştir. Bu üretim sürecinde 10mm olarak dökülen levha halindeki alüminyum alaşımı malzeme, homojenleştirme ve yeniden kristalleşme ara tavları uygulanarak, kapak üretiminin hammaddesi olan 0.22mm kalınlığında sac haline soğuk olarak haddelenmektedir. Sürecin her kademesinden sonra alınan numuneler üzerinde çeşitli mekanik testler yapılmıştır. Bu mekanik testler sonucunda soğuk işlem miktarı arttıkça çekme ve akma mukavemetinde artışlar, süneklikte ise düşüşler gözlenmiştir. Sürecin tav kademesinde ise, soğuk işlem ile artmış olan akma ve çekme mukavemetleri düşmüş, süneklik artmıştır. Standart bileşim sınırları içerisinde olan fakat farklı iki bileşimdeki malzemeler için sabit kalınlık ve sürede oda sıcaklığı ile 450°C aralığı ndaki tav sıcaklıklarında yapılan ısıl işlemler sonucunda mekanik özellikler incelenerek yeniden kristalleşme eğrisi çıkarılmış, alaşımdaki silisyum miktarı yeniden kristalleşme sıcaklığını düşürdüğü gözlenmiştir. Yine aynı ısıl işlem şartlarında Erichsen derinlikleri incelenerek maksimum Erichsen derinliğine 350°C'da 3 saat tav sonucunda erişildiği, bu sıcaklığın üzerindeki sıcaklıklarda ise tane büyümesi sonucunda Erichsen derinliğinde düşüşler meydana geldiği tespit edilmiştir. 350°C civarında 3 saat ısıl işleme maruz bırakılmış 0,5mm kalınlığındaki malzemelerin, dikey ve düzlemsel anizotropi katsayıları tespit edilmiş, en iyi biçimlenebilirlik 350°C'da 3 saat tav sonucunda, en az kulaklarıma ise 300°C'da 3 saat tav sonucunda meydana gelmiştir. Son olarak, optik ve taramalı elektron mikroskoplarıyla yapılan metalografik incelemelerden, malzemelerin tanelerinin hadde yönünde uzadığı ve malzeme içerisinde metaller arası bileşiklerin bulunduğu tespit edilmiştir.
Özet (Çeviri)
EFFECTS OF THE PRODUCTION PROCESS PARAMETERS ON THE MECHANICAL PROPERTIES OF THE SPECIAL 8011 ALUMINUM ALLOY BEING USED AS A BOTTLE LID MATERIAL SUMMARY In this study, the effects of the production process parameters of the special 8011 Aluminum alloy being used as a bottle lid material on the mechanical properties have been investigated. The production process used in this study, begins with continuous casting of strip in the thickness of 10 mm. After continuous casting, cold-rolling operation begins to get the desired thickness and mechanical properties. Cold-rolling is used to procedure sheet and strip with superior surface finish and dimensional tolerances compared to hot-rolled strip. In addition, the strain hardening resulting from the cold reduction may be used to obtain higher strength. A greater percentage of rolled metals is finished by cold-rolling in nonferrous materials compared to rolled-steel products. The starting material condition for cold-rolling of aluminum sheet is cast state. The cold-worked state is a condition of higher internal energy than the undeformed metal. Although the cold-worked dislocation cell structure is mechanically stable, it is not thermodynamically stable. The cold-worked state becomes more and more unstable with increasing temperature. Eventually the metal softens and reverts to a strain- free condition. The overall process by which this occurs is known as annealing. Annealing is very important because it restores the ductility of a metal that has been severely strain- hardened. Therefore, by interposing annealing operation after severe deformation, It is possible to deform most metals to a very great extent. The process of annealing can be divided into three fairly distinct processes: recovery, recrystallization and grain growth. Recovery is usually defined as the restoration of the physical properties of the cold-worked metal without any observable change in microstructure. Recrystallization is the replacement of the cold-worked vistructure by a new set of strain- free grains. Recrystallization is readily detected by metallographic methods and is evidenced by a decrease in hardness or strength and an increase in ductility. The density of dislocations decreases considerably on recystallization, and all effects of strain hardening are eliminated. The stored energy of cold-work is the driving force for grain growth is the decrease in free energy resulting from a decreased grain-boundary area due to an increase in grain size. Six main variables influence recrystallization behavior. They are amount of prior deformation, temperature, time, initial grain size, composition and amount of recovery or polygon! zat ion prior to the start of recrystallization. 8011 Aluminum alloy sheet material should be formed before using as a bottle lid. Deep drawing is the metal working process used for shaping flat sheets into cup- shaped articles such as bath tubs, shell cases, and automobile fenders. This is done by placing a blank of appropriate size over a shaped die and pressing the metal into the die with a punch. Generally a clamping or hold down pressure is required to press the blank against the die to prevent wrinkling. This is best done by means of a blank holder or hold-down ring in a double-action press. Although the factors which control the deep-drawing process are quite evident, they interact in such a complex way that precise mathematical description of the process is not possible in simple terms. The greatest amount of experimental and analytical work has been done on the deep drawing of a flat-bottom cylindrical cup from a flat circular blank. Formability of a sheet metal can be assessed by some material parameters such as strain hardening exponent (n), plastic anistropy (r), strain rate sensitivity exponent (m). It is well established that the plastic anisotropy which is related to a material's resistance to thinning is very important during deep drawing. The ability, of a material to resist thinning in deep drawing can be described by the r value, which is the ratio of the transverse surface strain to the thickness strain in a tensile-test specimen. The anisotropy parameter r can be obtained for different directions in the sheet. Normally, specimens are removed from the sheet at 90,45,0 degrees to rolling direction. For isotropic materials all the r values would viibe equal to unity. For most materials, however, there is a variation in the values of r with direction. This variation of r within the plane of sheet is called planar anisotropy (Ar) and responsible for earing in deep drawn cups. Earing is the formation of a wavy edge on the top of a drawn cup which necessitates extensive trimming on the preferred orientation in the plane of the sheet. WhenAr approaches to zero, the earing will be seen less, on the contrary it gets greater. The direction of the formation of the ears is in the direction of the greatest r value. In stretching, the ability of a metal to resist strain localization is the most important material property. This depends on the strain-hardening and strain-rate hardening capacity of metal. Strain hardening exponent is shown as n, it determines the increase in stress for each increment of strain. The higher the n value, the more the material will work harden. The mathematical calculations shown that the n value is equal to the true strain at the on set of necking which is the uniform elongation of the material. The higher then n value, the greater resistance to necking. Strain rate sensitivity exponent (m) value is being important as much as strain hardening exponent (n) value during formability. A positive strain- rate sensitivity exponent value indicates that the flow stress increases as the rate of deformation increases. This has two consequences. Higher stresses are required to form parts at higher rates. Also, at a given forming rate, the material resists further deformation in regions that are being strained more rapidly than adjacent regions by increasing the flow stress in these regions. This helps to distribute the strain more uniformly. High n and m values lead to good formability in stretching operations, but have little effect on drawability. In a drawing operation, metal in the flange must be drawn in without causing fracture in the wall. In this instance, high n and m values strengthen the wall, which is beneficial, but they also strengthen the flange and make it harder to drawn in, which is detrimental. The aim of this study is to investigate the effects of the production process parameters of the special 8011 Aluminum alloy being used as a bottle lid material on the mechanical properties. The nominal composition of 8011 Aluminum alloy is Al-0,60 %Si-0,70 %Fe. viiiThe material was rolled up to e =3, 817 (total true strain) from the initial thickness of 10mm to the final thickness of 0,22mm. Specimens taken from the different stages of the production process, were taken for heat treatments, mechanical tests such as hardness, tensile and Erlchsen, and metallografic examinations. The recrystallization heat treatments were carried out at some temperatures for 3 hours to determine the recrystallization temperatures and mechanical properties depending on the composition. Grain structures and intermetallic phases were examined on the metallografic samples using optical and scanning electron microscopy. These experiments were done on the specimens containing different amounts of Si and Fe which are in the range of nominal composition of 8011 Al alloy. Recrystallization temperatures were detected by annealing in the thickness of 0,5 mm 8011 Aluminum alloy materials which have two different compositions under the constant annealing time. Mechanical properties such as yield an tensile strengths, % strain were studied depending on the temperature on the same materials. Mean strain hardening exponent ( n ), mean normal anisotropy coefficient (r) and Erichsen depth values were investigated depending on the annealing temperature and composition of 8011 Aluminum alloy material which has a thickness of 0,5 mm. Erichsen depth values were also investigated in two different compositions of at the thickness of 0,22 mm 8011 Aluminum materials which are ready for the lid production. Metal lographic examinations were carried out by optical and SEM in each step of the production process while of 8011 Aluminum alloy. It was found from this work that the composition of 8011 Aluminum alloy in the continuous strip casting can not be controlled sensitively. For this reason, when a deviation is observed from the desired composition (alloying elements of 0,60 % silicon and 0,70 % iron) process parameters in the production period, especially annealing step should be recontrolled carefully. ixIncreasing silicon amount at a level of approximately 0,27 % decreases the recrystallization temperature of the material from 300°C to 250°C in 8011 Aluminum alloys. In the constant annealing time condition, with the increasing annealing temperature yield and tensile strengths decreased and ductility increased up to 300°C which is approximately recyrstallization temperature of the material depending on the rolling directions which are 0°, 45° and 90°. Ani sot ropy has been a problem when the temperature was higher than 300°C. The best formability was obtained at the heat treatment performed at 350°C for 3 hours and the least earing was obtained at 300°C for 3 hours in the tested 8011 Aluminum alloys. The increase of the silicon content in this alloy from 0,60 % to 0,96 %, increased the deformation hardening exponent to 0,205 t 0,001 value and planar anisotropy coefficient to -0,70 t 0,34 value. This increase of the silicon content decreased the formability index (r) of the material ( r=l, 26*0,09 ). The formability of material also decreased with increasing amount of silicon content when the materials were annealed at 450°C for 3 hours. The increase of the silicon content from 0,60% to 0,82% and iron content from 0,74% to 0,79% in this alloy also decreased the Erichsen depth values from 5,5 * 0,37 mm to 4,3 * 0,08 mm. It should be taken into consideration that cracks occurring during deep drawing process of the 8011 pilfer proof alloy does not only result from material defects but also result from the bottle lid production press parameters such as die design, blankholder pressure, etc.
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