Magnezyum levha alaşımlarının üretimi ve geliştirilmesi

Özet

Türkiye'nin ilk magnezyum alaşımı levhası, ikiz merdaneli sürekli döküm tekniği ile üretilmiştir. Magnezyum AZ31, AZ61, AZ91, AM50 ve AM60 alaşımı levhalar 4-8 mm kalınlığında, 1500 mm eninde başarılı bir şekilde elde edilmiştir. Levhalar daha sonra homojenleştirme ısıl işlemlerine maruz bırakılmıştır. Levhaların mikroyapıları yüzey, en ve boy yönlerinde optik mikroskop ve Taramalı Elektron Mikroskobu (SEM) ile incelenmiştir. Daha detaylı mikroyapı incelemeleri Geçirim-li Elektron Mikroskobu (TEM) ile yapılmıştır. Yarı nicel ve nicel elementel analizler SEM-EDS (Enerji Dağılım Spektrometresi), TEM-EDS ve EPMA (Elektron Prob Mikro Analiz Cihazı)-WDS (Dalgaboyu Dağılım Spektrometresi) sistemleri ile yapılmıştır. X-ışınlart difraksiyonu (XRD) teknikleri karakterizasyon ve yönlenme incelemeleri amaçlı olarak kullanılmıştır. Malzemelerin mekanik özellikleri çekme deneyi ve sertlik deneyleri ile ölçülmüştür. Çekme deneyleri hadde yönü, hadde yönüne 45 derece açı ve 90 derece açı olmak üzere üç farklı yönde ekstensometre yardımı ile yapılmıştır. Ayrıca numune yüzeylerinde ve farklı kesitlerde mikro Vickers ve Brinell Sertlik taramaları yapılmıştır. Elde edilen levhalar üzerinde soğuk hadde, sıcak hadde ve ısıl işlem gibi termomekanik işlemler denemeleri de gerçekleştirilmiştir. Levhalar öncelikle laboratuar ölçeğinde sıcak hadde ile inceltilmişlerdir. Daha sonra elde edilen bilgiler ışığında magnezyum AZ31 alaşımı levhalar ısıtıldıktan sonra endüstriyel ölçekli hadde sistemi ile 1 mm kalınlığa kadar inceltilmiştir. Elde edilen sonuçlar ışığında otomotiv, savunma ve elektronik endüstrileri için uygun magnezyum levha alaşımlarının üretimi olası gözükmektedir.

Abstract

Magnesium alloy sheet has been produced by twin roll strip casting first time in Turkey. Magnesium AZ31, AZ61, AZ91, AM50 and AM60 alloy sheets of 4-8 mm thick, 1500 mm wide were successfully achieved. Afterwards, homogenization heat treatments were applied on the sheets. Microstructures of the sheets have been analysed by optical microscope and scanning electron microscope, SEM by plan, longitudinal and transverse views. More detailed microstructure investigation was analysed by transmission electron microscope, TEM. Semiquantitative and quantitative elemental analyses has been performed by SEM-EDS (Energy Dispersive Spectrometer), TEM-EDS and EPMA (Electron Probe Micro Analyser)-WDS (Wavelength Dispersive Spectrometer) systems. XRD (X-ray Diffraction) techniques are used for both characterization and also texture purposes. Mechanical properties have been investigated by tensile tests and also hardness measurements. Tensile tests have been performed at. three different directions: rolling direction, 45 degrees to rolling direction and transverse direction by using an extensometer. Micro Vickers and Brinell Hardness test measurements were done on plan view and different cross-section directions. In addition, produced sheets were investigated by cold rolling, hot rolling and annealing tests. From the results of this study production of wrought magnesium alloys suitable for automotive, military and electronics industries seems possible.Magnesium is the lightest of all structural metals with a density of 1.74 g/cm3. Aluminum is 1.5 times, titanium is 3 times xtnd iron is 4 times of magnesium in density. Magnesium alloys have high specific strength, high specific stiffness, good castability and machinability, low heat content per unit of volume, high damping capacity, and good electro-magnetic (EMI) shielding. Magnesium is dimensionally stable, it welds easily, and it has impact and dent resistant. It is the sixth most abundant metal and eighth element on the earth's surface. Furthermore, magnesium is readily recyclable. Magnesium alloys also have effective heat dissipation. Due to these properties, there is increasing interest in using magnesium alloys especially in electronics and transportation industries. Almost 30% of the applications are structural applications (portable electronic equipment, such as laptop computers, cellular phones and video cameras; military equipment; aircraft parts; sporting goods and hand tools.Recently, using magnesium alloys that are lighter than aluminum alloys are being investigated for the automotive industry. Magnesium alloys are already used within the automotive interior as instrumental panel substrate, seat frame, seat riser, seat pan, console bracket, steering wheel, steering column parts; in the power train as valve cover, transmission cases; in the body as door and roof frames, sunroof panel, mirror bracket, tailgate; in the chassis as wheel, brake pedal brackets.High flexural/buckling stiffness and bending strength are needed for automotive body components such as doors, boot, and bonnet. VW 3L Lupo bonnet is a good prototype example for future application of magnesium sheets. Other possible wrought alloy automotive applications are extruded profiles such as window frames, seat and supporting structures. Magnesium components are usually produced by the die casting process. In spite of cost effective, the die casting process is not suitable for manufacturing large flat parts, such as hood, door, and lift-gate substrates. Also, mechanical properties of the cast parts, particularly fatigue resistance, can be substandard. Parts requiring good mechanical properties and fatigue endurance strength are best produced from wrought alloys. Replacement of conventional sheet metals with magnesium can reduce the vehicle mass, thus promote energy efficient transportation. By using wrought magnesium alloys, a decrease in vehicle weight up to 100 kg and a reduction of5% fuel consumption can be realized.Application of wrought magnesium alloys especially in the form of sheet is limited due to the price of conventional rolling product. However, the demand for decreasing the magnesium sheet prices is high and can be met through twin-roll casting.