The effect of temperature variation on Aluminum Matrix Composite (AMC) Sintering with CNT

Material selection is a very important part of the design due to the variety of functions and extreme applications. There is always a need for materials that are light, strong, hard, with good thermal conductivity. Aluminum matrix composites (AMC) are potential candidates for applications that require proper material selection. The most popular AMC processing technique is the powder metallurgy/PM method to produce products with precise dimensions. Powder metallurgy for the mass production of components is the most promising and versatile method. carbon Nanotube (CNT) particle reinforced AMC fabrication is an advanced material for the automobile, aircraft, aerospace, defense, petroleum, chemical industries at a relatively low price with high performance. Al powder 4.98 gr, CNT 0.02 gr with a mixing time of 8 hours at 650 rpm. The specimens were made using a cold uniaxial pressing process at room temperature 27°C. Aluminium – CNT powder is compacted in a rigid molding with a compaction pressure of 160 MPa. Variation of sintering 100°C, 200°C, 300°C, 400°C, 500°C with a time of 60 minutes. The PM method proves that the mechanical properties and physical properties of the material are improved. Material shrinkage after sintering is large by forming shrinkage. Hardness test results with Rockwell, 26.5HR, 27.9HR, 28.8HR 29.9HR, 32.5HR. Wear rate 0.196 mm3/m, 0.078mm3/m, 0.054mm3/m, 0.052mm3/m 0.049mm3/m. Porosity values are 6.30%, 6.28%, 5.98%, 4.51%, 4.58%. The higher the sintering tem-perature, the higher the hardness value, the lower the porosity and wear.


Introduction
The high demands for lightweight materials, high specific strength, high temperature performance, excellent corrosion resistance, high wear resistance [2].The growing activity encourages the development of specific composites, namely aluminum matrix composites (AMC) [3].AMC is a lightweight material resulting from a microscopic combination of two or more different materials, having an interface that aims to find better physical and mechanical properties than the previous material properties.[4].Aluminum matrix composite (AMC) with powder metallurgy method is a very popular method and is of interest to various automotive industries because of its mass production applications with high dimensions [3,5].In (AMC) the matrix is alloy and the reinforced material is embedded in a metal matrix [6].The reinforcing materials are generally non-metallic materials such as AlO, SiC, carbon nanotube (CNT) ceramics, etc.The type of reinforcing material and its volume fraction in the matrix will change the properties of the aluminum matrix composite [7].Where AMC has several advantages of higher strength, controlled coefficient of thermal expansion, resistance to high temperatures, reduced density, high abrasion and wear resistance, increased electrical conductivity and damping ability [8].
Powder metallurgy/PM is one of the alternative methods that has advantages in manufacturing and economics in component manufacturing, more efficient use of powders and high production capacity [9].Powder metallurgy/PM is a powder forming operation which is combined into the desired shape by applying pressure.The powder is compacted uniaxially and then a compacted green body is formed [10].In the compaction process (compaction) there is a bonding of the powder surface which causes adhesion and cohesion forces.Sintering is an advanced stage after compaction, sintering occurs at temperatures ranging from 70% -90% of the melting temperature [11].The increase in sintering variation gives the effect that the hardness value will increase, the wear rate and porosity will decrease [12].Aluminum is one of the important materials used in various fields, but the specific strength of aluminum is of high value when combined with other materials [13,14].Research has shown that the inclusion of CNTs in aluminum matrix composites (AMC) can improve the mechanical and physical properties [15].Even though CNT shows good mechanical and physical properties.CNTs have the main disadvantage that AL/CNT composites are difficult to spread the reinforcement throughout the matrix.The carbon nanotube-reinforced aluminum matrix showed properties that were influenced by the stability of the chemical properties, distribution and interfacial bonds between the matrix and the CNT reinforcement [16,17].In order to produce uniform CNT dispersion in aluminum matrix composites, methods of ball milling, magnetic stirring and wet shake mixing have been carried out [17].Wet shake mixing was carried out resulting in poor Al-CNT, high AL viscosity and strong CNT agglomeration [18].The present approach is to disperse CNTs in an aluminum matrix which is informed by conventional mechanical mixing technique, ball milling is the most commonly used technique [19].Carbon nanotubes are nanomaterials that are widely used as reinforcing materials in matrices because of their high strength and stiffness.Carbon nanotubes (CNTs) are reported to have a good elastic modulus (about 1 TPa) and a tensile strength of about (10 -100 times that of steel).Carbon nanotubes (CNTs) are considered to be able to strengthen metals, because CNTs can survive 20% -30% before deformation failure [20].Consolidation of CNTs with an aluminum metal matrix will produce composites with improved properties.CNT-reinforced aluminum matrix composite (AMC) has the potential to revolutionize the aerospace, sports, automotive, aircraft industries.Al/CNT results in light weight combined with the desired high rigidity and strength, where the lightweight material saves fuel.The main obstacle in using advanced aluminum is low wear resistance by adding CNT to the aluminum matrix will change the wear resistance, hardness, strength, corrosion resistance [3,5,6].Mixing (mixing) aluminum -CNT for 8 hours with a rotation of 600 rpm, compaction pressure (compaction) 160 MPa, with variations in sintering temperature.Hardness values using Rockwell at temperatures of 100OC 26.5HR, 200 O C 27.9HR, 300 O C 28.8HR, 400 O C 29.9HR, 500 O C 32.5HR.This shows that the temperature affects the hardness where the higher the sintering temperature the higher the hardness of the material.Mixing (mixing) aluminum -CNT for 8 hours with a rotation of 600 rpm, compaction pressure (compaction) 160 MPa, with variations in sintering temperature.Hardness values using Rockwell at temperatures of 100 O C 26.5HR, 200 O C 27.9HR, 300 O C 28.8HR, 400 O C 29.9HR, 500 O C 32.5HR.This shows that the temperature affects the hardness where the higher the sintering temperature the higher the hardness of the material.Mixing (mixing) aluminum -CNT for 8 hours with a rotation of 600 rpm, compaction pressure (compaction) 160 MPa, with variations in sintering temperature.Hardness values using Rockwell at temperatures of 100 O C 26.5HR, 200 O C 27.9HR, 300 O C 28.8HR, 400 O C 29.9HR, 500 O C 32.5HR.This shows that the temperature affects the hardness where the higher the sintering temperature the higher the hardness of the material.

Methodology
The materials used in this research are pure aluminum powder with a powder size of 325 mesh and carbon nanotubes (CNT).The mass weight of the powder in aluminum is 4.98 gr, CNT is 0.02 gr.The next process is mixing aluminum powder and CNT.The compaction pressure is 160 MPa.Mixing time   positive impact and the increase in sintering temperature.The role of the reinforcing particle properties also affects the wear resistance significantly.Composites containing CNTs offer advantages in terms of hardness and strength [22].Porosity is a measure of the free space between materials, which is the fraction of the volume of free space to the total volume.Porosity has become the identity of powder metallurgy products.Pores in the material trigger cracks which can reduce quality, but on the other hand the presence of controlled porosity can function as a lubricant storage which increases wear resistance.So that the level of porosity as an important physical property of the material is identified.The results of the porosity test show the effect of temperature variations on the level of porosity.The lowest temperature is 100 O C, the porosity value is 6.3% and the highest porosity is 4.45% at a temperature of 500oC.The formation of pores is based on the ability of the particles to be arranged during compaction as pores.Particle size and the influence of temperature can form the distance between the particles closer to support the formation of low porosity.This phenomenon is evidenced by the increase in temperature showing the lowest porosity value.The mechanical properties of the material are also influenced by the level of porosity content [23].

Conclusion
The results obtained on the material Al 4.98gr and CNT 0.02gr from testing the mechanical properties and physical properties by varying the sintering temperature, obtained the maximum hardness at a temperature of 500 O C 32.5HR.In testing the physical properties where the wear rate and porosity are obtained, the higher the sintering temperature the lower the wear rate at a temperature of 500 O C 0.049mm2/m, the value of porosity is 4.45% at a temperature of 500 O C.

Figure 7 .
Figure 7. Wear Rate VS Sintering Temperature Variation