UCTEA Chamber of Metallurgical & Materials Engineers’s Training Center Proceedings Book

1198 IMMC 2018 | 19th International Metallurgy & Materials Congress

Aluminum Matrixed Graphen Reinforced Composite Materials

Okan Aydın, Aziz Kocaveli, Özen Gürsoy, Eray Erzi, Derya Dışpınar

Istanbul University, Faculty of Engineering, Metallurgical and Materials Engineering Department, 34320, Avcılar, Istanbul, TURKEY

SUMMARY

In this study, due to the high strength property of the graphene, it is aimed to make metal matrix composite by placing the matrix in aluminum. During metal matrix composite casting, graphene reinforced aluminum matrix composite castings were investigated by using lost foam cast process, squeeze casting method, sand mold casting, gravity die casting methods. In these studies, the post-production mechanical test results of graphene powders placed in matrix aluminum were evaluated on a wide scale and the increase in strength values was observed.

1. Introduction

The composite term is broadly defined as "Composite Material" where materials in the same or different groups of two or more materials are assembled at the macro level to combine the best features together or to create a new feature. In other words, to obtain superior qualities by correcting the weakness of each other, it can be called as material consisting of different kinds of materials combined with the aim[1].

Aluminum is an element in the group IIIA of the Periodic Table with an atomic number of 13,+3 valence with an atomic weight of 26.89, a density of 2,7 gr/cm3 at 20°C, a melting point of 659.8°C and a boiling point of 2450°C[2].

Aluminum alloys are copper, zinc, silicon, magnesium, manganese, iron, nickel, titanium and like elements. Features; they must be lightweight, heat and electrical conductivity, suitable for heat treatments, and resistant to certain chemical effects. Aluminum alloys are suitable for casting. At the same time, aluminum alloys which are formed by forging, drawing and rolling are also prepared. They are resistant to corrosion and are used as preservatives in drug and vegetable gardens because they do not create a toxic hazard[3].

Graphene is the name given to a single layer of graphite, an allotropy of carbon element capable of hybridizing sp, sp2, and sp3. It was first introduced in 1994 by Boehm, Setton and Stumpp[4].

Table 1. General Properties of Single Layer Grafen[4] Properties Value

Hybrid Shape sp2

Number of Layers Monolayer Crystal Structure Hexagonal

Dimension Two Degree of Purity (%) 99 Mass (Bulk) Density

(g/cm3) ~0.3 True Density (g/cm3) 2.25

Thickness (nm) ~1-2 Surface Area (m2/g) 2600 High Temperature

Resistance -75 +200 0C there features do

not change between. Thermal Conductivity

(WK-1/m) 4840-5300 Electro Mobility

[cm2/(V.s)] ~2.5x105 Elastic Modulus (Tpa) ~1

2. Experimental

The castings were begun by lost foam cast process. In the first casting, graphene was put between 3 same foam plates with dimensions of 10x10x30. The aluminum melted in the resistance furnace at 750 °C for 2 hours was cast into the sand. EDS analyzes were performed in scanning electron microscopy (SEM) after metallography and ultrasonic cleaning. After graphene powder was placed between the foam layers, the cube foam was carved inside the dimensions of 20x20x20. The cavity was filled with powder graphene, and the foam was buried in the sand. In the resistance furnace, aluminum was melted at 750°C for 2 hours and then cast into cubic foam in the sand. SEM analysis was performed after waiting 10 minutes for the cold.

TMMOB Metalurj i ve Malzeme Mühendisleri Odas ı Eğ i t im MerkeziBildir i ler Kitab ı

119919. Uluslararas ı Metalurj i ve Malzeme Kongresi | IMMC 2018

After the lost foam cast process was tried, 5 mm 3 roll plates were cut from previously cast 15 mm diameter tension chord with a length of 150 mm. By adding a powder graphene between the plates, it is aimed to wrap the liquid aluminum over the powder graphene by melting.

In this method, graphene powder was added between the interrupted 3 cylinder plates. The samples placed in the resistance furnace waited for 1, 2 and 3 hours at 700 °C. The samples taken from the resistance furnace were cooled in air. After the samples were cooled, they were cut from the center and SEM studies were performed after the metallography and ultrasonic cleaning.

In the squeeze casting method, a pre-cast A356 tensile sample was cut into 3 cylindrical plates with a length of 5 mm and 10 mm. Graphene powder was added between the plates and was waited in the resistance furnace at 700°C for 2 hours. The samples taken from the furnace were pressed under a pressure of 150 bar.After pressing, samples were cut and metallography, ultrasonic cleaning and SEM studies were performed.

Then sand mold casting method was used. The samples obtained as result of the casting were brought to a semi-solid phase at 630°C in the resistance furnace.

For the sand mold casting method, firstly a square prismatic mold of 20x20x120 dimensions was prepared. Aluminum charged in the furnace for casting was heated for 2 hours at 750°C. Firstly, Aluminum was poured without grafhene reinforcement. In other castings, a powder grafhene was added into the liquid aluminum. After half of the sand mold was filled with liquid aluminum, a powder graphene was added and the remaining space was filled with aluminum again. After cooling at air, the aluminum semi-solid phase was heated for 20 minutes at 630°C in an resistance furnace. Pressing was carried out to samples under pressure of 220 bar. The three-point bending test was performed on the samples subjected to the pressing process.

After this method, grafhene was added to the aluminum foil and the casting process was continued. Liquid aluminum heated at the same temperature and time, half of the sand mold was filled and then the aluminum foil was deposited on the liquid aluminum surface. Theremaining space was filled with aluminum again. After cooling the sample at air, the aluminum semi-solid phase was kept in the furnace until 630°C. The samples removed from the furnace were pressed under a pressure of 220 bar. Squeezed samples were sent to three point bending devices.

This method was tried by placing it in 3 different ways. In the first casting, the liquid was poured by placing foil in the middle of the aluminum.The second casting was made by placing foil at the bottom the mold.In the third casting was made by placing the foil perpendicularly in the middle of the mold.

3. Discussion and Conclusion

As a result of the lost foam cast process, it was observed that the casting surface was heterogeneously gathered due to the density difference of the powder graphene (density value in the literature is between 0.8-1.6 g/cm3) with aluminum (2.7 g/cm3) and the graphene nonwetting properties. As a result of the SEM examinations, it was observed that heterogeneously wet a very small amount of graphene deposited in a region with aluminum.

After casting with cube foam content, SEM examinations showed the same results as the first tests.

Figure 1: SEM Images of lost foam cast process

After the lost foam cast process, aluminum melting and graphene powder coating method and squeeze casting methods were tried.

The graphene powder added between the tension sample in the method was left in the resistance furnace for 1, 2 and 3 hours, after which the samples were allowed to cool down at air. At the end of the 1 hour, it was observed that the layers of aluminum could not cover the graphene surface. At the end of 2 hours, the aluminum covered the surface of the graphene, but during the metallography process the layers of the samples disappeared. After 3 hours, it was seen that aluminum covered the graphene surface. In the SEM examinations performed after the metelography, the carbon peaks were found locally between the layers.

UCTEA Chamber of Metallurgical & Materials Engineers’s Training Center Proceedings Book

1200 IMMC 2018 | 19th International Metallurgy & Materials Congress

Subsequently, the samples made by the same method were pressed without being left to cool. It was observed that the SEM results were the same as the first results.

(1)

(3)Figure 2. SEM Images of Squeeze Casting result

At the end of these methods, it was observed that the graphene was collected only locally because of its low density and wetting properties with aluminum.

Then tested sand mold casting method similar tissue made with graphene wetting property and due to the low density aluminum surface was observed to be fluid. After these observations, three-point bending tests of castings made by placing base, middle and vertical shape in aluminum foil were carried out.

Three point bending tests were performed with a mesh clearance of 8 cm and a bending speed of 1 mm per minute. Test results;

Figure 3. Graphene Powder added Medium of A356 alloy - A356 Aluminum Alloy Three-Point Bending Test

Results

In Figure 3, the tensile strength of the A356 aluminum alloy without graphene was found to be up to 20 MPa.It was observed that the tensile strength of the samples added with graphene were 25-30 MPa.

Figure 4. Graphene Powder in Aluminum Foil – Aluminum alloy without graphene Three Point Bending

Test Results

In Figure 4, the tensile strength of the A356 aluminum alloy without graphene is up to 20 MPa, while the tensile strength of graphene added samples into aluminum foil ranges between 20-25 MPa.

TMMOB Metalurj i ve Malzeme Mühendisleri Odas ı Eğ i t im MerkeziBildir i ler Kitab ı

120119. Uluslararas ı Metalurj i ve Malzeme Kongresi | IMMC 2018

Figure 5. Strain values according to three-point bending test results

Figure 6. Extension Values According to Three Point Bending Test Results

In the sand mold casting method, the results obtained by adding graphene to the middle of liquid aluminum were found to be based on higher stresses than the casting method by adding graphene into the aluminum foil.

4. Conclusion

The results of the tests show that it is observed that the aluminum tension value without graphene is 20 MPa while the graphene is added into the liquid aluminum and the tensile values reached 25-30 MPa. As a result of this study, it was observed that the tensile values of aluminum matrix reinforced composites increased from 25% to 50% compared to non-graphane aluminum.

References[1]<https://www.polerfiber.com/images/kataloglar/3eb2331a-4.pdf> Dated: 13.11.2017. [2] TMMOB Metalurji Mühendisleri Odası, Alüminyum Raporu, Eri im 14.11.2017 [3] <https://malzemebilimi.net/ aluminyum-alasimlari.html> Dated: 14.05.2018 [4]Mahmut Can enel, Mevlüt Gürbüz, Erdem Koç,Grafen Takviyeli Alüminyum Matrisli Yeni Nesil Kompozitler, Dated: 14.11.2017