İkiz merdane döküm tekniği ile üretilmiş 1050 alüminyum alaşımının mikroyapı ve mekanik özelliklerine tane incelticinin etkisi
Effect of grain refiner on the microstructure and mechanical properties of 1050 aluminum alloy produced by twin roller casting technique
Yazar: TUĞÇE YUNAK
Danışman: DOÇ. DR. SERDAR ASLAN
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Metalurji Mühendisliği = Metallurgical Engineering ; Mühendislik Bilimleri = Engineering Sciences

Özet:
Alüminyum alaşımları; özellikle hafiflik, işlenebilirlik, ısı-elektrik iletkenliği ve korozyona karşı dirençli olması gibi üstün özellikleri nedeniyle geniş bir kullanım yelpazesine sahiptir. Alüminyum alaşımlarında malzemenin mikroyapısı kontrol edilerek, üstün mekanik özellikler ve yüzey kalitelerisine ulaşabilmek için tane incelticiler kullanılmaktadır. Katılaşma işlemi sırasında kullanılan tane incelticiler ince ve eş eksenli tanelerin oluşumunu sağlayarak, malzemelerin mekanik özelliklerinin iyileşmesine yardımcı olmaktadır. Ayrıca, tane inceltici kullanılmış alüminyum malzemelerde beslenme kabiliyetlerinin yüksek olması porozitesiz ve homojen bir yapının oluşmasında alüminyum malzemelere avantaj sağlamaktadır. Alüminyum alaşımlarında yüzey dayanıklılığını artırmak için anodik oksidasyon (eloksallanma) işlemi yapılmaktadır. Fakat ikiz merdane döküm yöntemi ile üretilen malzemelerin yüzey kalitesi bu işlem için uygun olmamaktadır. 
Bu çalışma, tane incelticilerin alüminyum alaşımlarının  üzerindeki etkisini araştırmakta ve çeşitli endüstriyel uygulamalar için önemli çıkarımlar ortaya koymaktadır. Araştırmada, alüminyum levhalar üretmede hassasiyeti ve verimliliği ile tanınan ikiz merdaneli döküm metodundan yararlanılmıştır. Bu metot ile üretilen AA1050 alüminyum alaşımı üzerinde Al-5Ti-0,2B ve Al-5Ti-1B olan iki farklı tane incelticinin malzemedeki mikroyapısal, mekanik ve yüzey kaliteleri üzerindeki incelemeleri gerçekleştirilmiştir. Malzemelerin mikroyapısal, mekanik ve yüzey özelliklerini karşılaştırmak amacıyla spektrometre, optik mikroskop, SEM (Taramalı Elektron Mikroskobu), pürüzlülük cihazı, çekme ve sertlik cihazları kullanılmıştır. Ayrıca eloksal kaplamadan sonraki nihai ürünün yüzey kalitesini incelemek için gözle kontrol gerçekleştirilmiştir.
Sonuçlar, Al-5Ti-1B tane incelticisi kullanılan AA1050 alüminyum alaşımında daha fazla bulunan borun belirgin etkisi ortaya çıkarılmıştır. Bu alaşımı SEM analizinde incelediğimizde intermetalik yapıların azaldığını ve daha homojen bir yapının ortaya çıktığı net bir şekilde görülmüştür. Bunun ile birlikte optik mikroskop görüntülerinde tane boyutlarının küçüldüğü ve daha tanecikli bir yapı oluşmasına sebebiyet vermesinin yanında  akma , çekme ve makro-mikro sertlik değerleri sırasıyla ortalama 75MPa, 97MPa, 27HB ve 32,9 HV 'den 84MPa, 102MPa, 30HB ve 38,2HV 'ye yükselmesi Al-5Ti-1B alaşımının mikroyapı ve mekanik özelliklerindeki iyileşmelerin net bir göstergesi haline gelmiştir. Mikroyapıda elde edilen bu gelişmeler ile özellikle ikiz merdane döküm tekniği ile üretilen malzemelerde anodik oksidasyon(eloksallanma) işleminin de uygulanabilirliğini ortaya koymuştur.

Abstract:
Aluminum is a widely used metal globally, finding extensive applications across various industries. It is recognized for its lightweight nature, high strength-to-weight ratio, excellent formability, and corrosion resistance. These attributes make it a preferred choice, notably in industries such as aerospace, automotive, construction, food packaging, and the electrical sector. Additionally, aluminum is a recyclable material, which holds significant importance in terms of sustainability. Often utilized in alloy form, its properties can be enhanced by combining it with different elements. With its durability, lightweight structure, and ease of processing, aluminum enjoys broad applications within the industry.
Grain refiners are used in aluminum alloys to achieve superior mechanical properties and surface quality by controlling the microstructure of the material. Grain refiners used during the solidification process help improve mechanical properties by ensuring the formation of fine and equiaxed grains. In addition, the high nutritional capabilities of aluminum materials in which grain refiners have been used and the formation of a porosity-free and homogeneous structure provide an advantage for aluminum materials.
In the aluminum industry, grain refiners such as Al-Ti, Al-B, and Al-Ti-B are widely employed. Titanium particles create new nucleation sites, whereas boron supports the formation of fine and equiaxed grains. Due to boron's grain refining effect on aluminum material, the Al-Ti-B combination has become the most preferred grain refiner in use today.
Al-Ti-B grain refiners are a type of grain control agent commonly used in aluminum alloys, comprising a mixture of titanium and boron elements added to these alloys. This combination typically enhances the durability, strength, and workability of alloys, enabling the production of higher-performance materials. It contributes to the improvement of structural and mechanical properties of aluminum alloys, facilitating the customization of materials according to desired specifications.
The major advantage of Al-Ti-B grain refiner lies in preventing the dissolution of TiAl3 in the liquid aluminum system and minimizing the tendency of TiB2 particles to agglomerate. TiAl3 particles are typically found to be around 30-40 µm in aluminum, while TiB2 particles range from 1-2 µm in size. The distinct behavior and sizes of these particles in liquid aluminum have led several researchers to propose various nucleation theories.
This study investigates the effect of grain refiners on aluminum alloys and reveals important implications for various industrial applications. In the research, the twin-roll casting method, known for its precision and efficiency in producing aluminum sheets, was used. The twin-roll casting method presents several advantages when applied to materials. This process facilitates the production of metal sheets or strips with enhanced properties, including improved surface quality and uniformity. One significant advantage lies in its ability to create materials with fine microstructures and reduced porosity, leading to enhanced mechanical properties such as increased strength and durability. Moreover, the twin-roll casting technique allows for precise control over the final product's thickness, enabling the production of thinner materials without compromising their integrity or structural integrity.
Various coating processes are preferred to increase surface durability in aluminum alloys. These methods encompass applications such as anodizing, chromium and nickel plating, plasma spraying, cathodic electrophoretic coating, and electrostatic painting. The anodizing method involves creating an Al2O3 layer on the surface, leveraging the oxidizing property of aluminum alloys. Through this technique, desired corrosion resistance can be achieved on the aluminum alloy surface, enhancing surface hardness for improved wear resistance, and achieving a more aesthetically pleasing appearance. However, the surface quality of materials produced by the twin-roll casting method is not suitable for this process.
In this study, AA1050 alloy produced by twin roll casting method was used. At the same time, two different grain refiners were used in the study: Al-5Ti-0.2B and Al-5Ti-1B. The study started by preparing the alloy consisting of 99.5% aluminum, which was subjected to a controlled melting process in a furnace operating at temperatures between 700-750 °C. The molten aluminum was then transferred to the holding furnaces without interruption. From these designated holding furnaces, the liquefied aluminum is directed towards the runners leading to the rolls at a precisely determined angle. The liquid, which passed through the addition of grain refiner (Al-5Ti-0,2 / Al-5Ti 1B), hydrogen removal and mechanical filtering, was transferred to the tundish system through aluminum runners and fed to the rollers through the type. As soon as the liquid aluminum transferred between the rollers came into contact with the water-cooled roller surfaces moving in opposition to each other, solidification occurred and plate production took place.
Elemental analysis was performed to determine the chemical composition of the produced sheets. Scanning electron microscope (SEM) was used to examine the surface topography of the samples taken from the plate. An optical microscope was used to examine the microstructure images of samples selected from the plate. In order to obtain a better appearance in terms of morphology, the samples were removed from cold bakelite and left to dry for 24 hours before polishing and polishing. After the bakelite samples were frozen, they were sanded. 500, 1200 and 2400 SiC drilling operations were performed on the sanding device, respectively. Application of silica, lubricant and diamond resolution method for polishing process. Etching was carried out with an electrolytic etching device using tetraflora boric acid. Macro-hardness properties are checked with a steel ball of 2.5 mm in diameter by applying a force of 62.5 kgf. A load of 50 gf was applied to the cross-sectional samples taken for microhardness measurements for 10 seconds, and this load was applied to the sample in 5 different ways for more accurate measurements, and the average cross-section value was determined as the data value. A device with a capacity of 50 kN was used for the tensile test. The test speed for the samples was determined as 10 mm/min and the measurement length was set as 50 mm. All sample measurements were carried out on a total of four samples, two for each diluent, in the 0° and 90° directions, in accordance with the DIN EN ISO 6892-1 test capacity.
The results showed that in the spectral analysis, the amount of boron in the AA1050 aluminum alloy plate using Al-5Ti-1B grain refiner was 5 times higher than Al-5Ti-0.2B. When we examined this alloy in SEM analysis, it was clearly seen that the intermetallic structures decreased and a more homogeneous structure emerged. In addition to this reduction in grain sizes determined via optical microscope. This reduction in grain size result in increase in mechanical properties namely yield strength increased from 75MPa to 84 MPa, tensile Strength increased from 97 MPa to 102 MPa, hardness in brinell increased from 27 HB to 30 HB and brinell in Vickers increased from 32,9 HV to 38,2 HV. These developments in microstructure have demonstrated the applicability of the anodic oxidation (anodizing) process, especially in materials produced by the twin roll casting technique.