Mechanical Behaviour of Al7075-[B4C/TiC] Hybrid Metal Matrix Composite using Stir Casting Process

Mechanical Behaviour of Al7075-[B4C/TiC] Hybrid Metal Matrix Composite using Stir Casting Process

Boopathiraam C, Sambathkumar M Department of Mechanical Engineering, Kongu Engineering College,

Erode-638060.

Abstract:- Aluminium have excellent castability properties and widely used for various mechanical application but has some limitation of pure aluminium alloys due to lower strength, stiffness and wear resistance. This limitation can be improved by producing hybrid metal matrix aluminium composites with addition of reinforcement particle. This paper deals with an attempt to study the mechanical behaviour of aluminium hybrid metal matrix composite. The Aluminium 7075 Metal Matrix Composite (MMC) is reinforced (5, 10, 15 Vol. %) with equal amount of Boron Carbide (B4C) and Titanium Carbide (TiC), fabricated by using stir casting method. The specimens will be prepared for testing process, to examine the density, porosity, microstructure, micro hardness and tensile strength for the developed Al 7075 hybrid metal matrix composite.

Keywords- Aluminium7075, hybrid metal matrix composite, Stir casting, microstructure

1. INTRODUCTION

   Aluminium Metal Matrix Composite (AMMC) are mostly used in automobile and aerospace industries for light weight applications due to its mechanical properties like higher strength to low weight ratio, controlled co-efficient of thermal expansion, wear resistance and higher stiffness[1, 2]. The stir casting technique are mostly used in the fabrication of metal matrix composite due its uniform distribution of reinforcement particle with the base materials[3, 4] The aluminium metal matrix composite has the superior properties of the tensile properties like elastics modulus, yield and ultimate strength. By addition of reinforcement with aluminium increases the composite hardness [5, 6]. Aluminium metal matrix composite wide application in daily life and now it is used in thermal management areas, industrial products, aerospace and automotive application such as brake disc, engine piston etc [7, 8]. Hybrid Metal Matrix Composites are engineering materials reinforced by a mixture of two or more different type of material in order to accomplish the combined benefits of both of them [9]. In recent years hybrid metal matrix composites (HMMCs) are plays a vital role especially in material science in the field of aerospace, marine, transportation, military and structural applications[10].

   Baradeswaran, A. and A. E. Perumal [11] have investigate the study on the mechanical properties of Al7075/Al2O/graphite hybrid metal matrix composite and found the hardness, compression strength and flexural strength by increasing the weight percentage in ceramic phase. Mohanavel, V., et al. [12] have present the study on the microstructure and the mechanical behaviour of the parent alloy and the produced composites were studied. The reinforcing effect of Al2O3/Gr combined with the parent alloy is studied wherein the investigation went into the intensity of microhardness, microhardness, tensile strength and flexural strength. Sharma, M. T. S. V., et al. [13] presents a review on the effects of Al2O3, B4C, Gr, Y2O3 and SIC reinforcements on the tribological and mechanical behaviour of a AMMCs fabricated by various methods such as powder metallurgy, stir casting etc. Pandey, U., et al.[14] have investigated study on Fabrication, Testing and Characterization of Al/TiC Metal Matrix Composites through different Processing Techniques. Ye, T., et al.[15] have presented study on Mechanical property and microstructure evolution of aged 6063 aluminium alloy under high strain rate deformation. Prasad, T., et al. [16] have investigate study on aluminium 6061 and rise husk ash. Less percentage of fly ash given strength and machinability to the matrix were analysed. Owoeye, S. S., et al. [17] Mechanical characteristics in terms of tensile strength, hardness, wear resistance, and elastic modulus were reported to improve significantly with increase in reinforcement content by hybrid MMC.

2. MATERIALS USED

   The Aluminium 7075 (Perfect metal works, Bangalore) is used as the matrix material for the experimental studies and its chemical composition (in Vol. %) of AL7075 is tabulated in Table 1. TiC and B4C (Metal mart, Coimbatore) are used as reinforcement particles. TiC have good mechanical properties and corrosion resistance property, so it is chosen for reinforcement particle. B4C have good chemical resistance property, thermal stability and high melting point.

   Table 1. Chemical composition of matrix material AL7075

   Element	Al	Cr	Cu	Mg	Mn	Zn	Si	Ti
   (Wt%)	87-91.4%	0.18- 0.28%	12-2%	2.1-2.9%	0.3%	5.1- 6.1%	0.4%	0.2%

3. FABRICATION OF HYBRID METAL MATRIX COMPOSITE

   The stir casting process is used for fabricating the metal matrix composite due to its cost effectiveness, simplicity, applicability to mass production, uniform distribution of composite materials, easier control of composite structure and almost net shaping. In this type of a casting process in which mechanical stirrer is introduced to form vortex to mix reinforcement in the matrix material[1, 18]. The hybrid composites were prepared by stir casting process with varying the volume percentage of reinforcing particles are tabulated in Table 2.

   Table 2. Volume percentage of reinforcement

   Composition (ABT-Al7075+B4C+TiC)	AL7075 (Vol. %)	B4C (Vol. %)	TiC (Vol. %)
   ABT0	100	–	–
   ABT5	95	2.5	2.5
   ABT10	90	5	5
   ABT15	85	7.5	7.5

   The stir casting setup is shown in the Figure 1, consist of electrical furnace and mechanical stirrer. The electric furnace is used for heating and melting of raw materials. The mechanical stirrer is used to mixing the reinforcement materials which are introduced in the melt. Stirrer consist of the stirring rod and the impeller blade. This stirrer is connected to the variable speed motors, the regulator attached with the motor to control the rotation speed of the stirrer. The die is the special tool that is used to fabricate the specimen for the required shape and size. The die and specimen are shown in Figure 2.

   	(a)
   	(b)
   Figure 1. Schematic of Stir casting setup	Figure 2. (a) Die (b) Specimen

4. MICROSTRUCTURE CHARACTERIZATION AND MECHANICAL TESTING

   1. Microstructure

      The samples are polished using a normal metallographic procedure and sample specimen is shown in figure 3. The microstructure of the specimen was observed by optical microscope.

      Figure 3. Samples of specimen

   2. Microhardness

      Microhardness Testing is a method of determining a materials hardness or resistance to penetration when test samples are very small or thin, or when small regions in a composite sample or plating are to be measured.

   3. Density Porosity

      Dnsity and porosity measurements were carried out on the base metal and reinforced samples using the Archimedes principle. This method of density and porosity measurement simply involves weighing the sample in air and in another fluid of known density[19].

   4. Tensile test

   The tensile specimens were prepared as per the ASTM E8M -13a sub size as shown Figure 4. The test was carried out with samples in the Universal tensile testing machine (Instron) with a strain rate of 1 mm/min.

   (a)	(b)

   Figure 4. Tensile Specimen (a) Preparation of sample (b) Specimen

5. RESULT AND DISCUSSION

   1. Microstructure

      The optical microscope is used to analysis the microstructure and interface characteristics between matrix and reinforcement. The Figure 5 represent the optical microstructure of the composite materials. From the optical photomicrographs, it can be seen that reinforcements were uniformly distributed in the matrix material and also clearly show the increased reinforcement content in the composite.

      (a)	(b)
      (c)	(d)

      Figure 5. Microstructure of the composite materials (a) ABT0

      (b) ABT5 (c) ABT10 (d) ABT15

   2. Microhardness

      The resistance of materials against surface indentation is termed as hardness. The micro hardness of composites evaluates the interface bonding strength between reinforcing particles and matrix[20].

      Table 2. Vickers hardness of B4C and TiC reinforced with Al7075

      Materials	Vickers Hardness
      ABT0	24.50
      ABT5	39.32
      ABT10	43.92
      ABT15	46.10

      The Vickers hardness value of AMC shows in Table 2. The shows that addition of (TiC + B4C) reinforcement particles in Al matrix composite enhances the hardness of AMC when compared with unreinforced Al. When pure Al has Vickers hardness value of (24.50), hardness value increases with increasing (TiC + B4C) content and maximum obtained hardness value is 46.10 for 15 wt. % (TiC + B4C) reinforced AMC. The presence of harder and well bonded (TiC + B4C) particles in Al matrix that impede the movement of dislocations increases the hardness of AMCs.

   3. Density Porosity

      The Theoretical density, Actual density and Porosity variation of base metal and the hybrid composites is shown in Table 3. Based on the measured and theoretical densities the porosity of aluminium alloy and the hybrid composites was measured and found to increase with the increase in reinforcement. The variation difference to founded on theoretical and actual density.

      Table 3. Theoretical density, Actual density and Porosity

      Composition	Theoretical Density (g cm-3)	Actual Density (g cm-3)	Porosity (%)
      ABT0	2.81	2.78	1.067
      ABT5	2.85	2.80	2.361
      ABT10	2.90	2.84	2.764
      ABT15	2.94	2.88	3.072

   4. Tensile test

      The composite has superior tensile strength than Al 7075 alloy with lower ductility. The increase in tensile strength of fabrication composite contrat with alloy, Al 7075 is due to the consistent distribution of the reinforcement phase B4C and TiC in the matrix form. The Figure 6. shows the tested sample of the specimen. The Figure 7. shows the tensile strengsth value of the Al7075 hybrid composite reinforced with B4C and TiC. Al7075 hybrid composite show improved tensile strength as compared to base alloy. The relationship between stress and strain for an Al7075 hybrid metal matrix composites is shown in the Figure 8. The increase in the volume fraction of reinforcement from 5% to 10% increased the tensile strength and yield strength respectively.

      Figure 6. Tensile samples

      Figure 7. Ultimate tensile Strength	Figure 8. Stress-Strain curve for B4C and TiC reinforced aluminium 7075 composites

6. CONCLUSION

In this experimental study, Aluminium metal matrix composite is reinforced with (5, 10, 15 Vol%) equal amount of B4C and TiC were fabricated by using stir casting process. Microstructural aspects, hardness, density porosity and tensile strength for the prepared composite were studied. Testing results have provided the following conclusions. The optical microscope reveals homogeneous distribution of reinforcement particle in the matrix material.

• Addition of B4C and TiC in Al matrix increased Vickers hardness when compared with unreinforced Al. The maximum hardness obtained by 15 Vol.% of B4C and TiC.

• By Archimedes principle, the reinforced composite material has higher density that unreinforced matrix material.

• Ultimate tensile strength increases with the increase in B4C and TiC content. The strength improvement of hybrid composites can be attributed to the increase in the dislocation density.

• In 15% Vol. of reinforcement have found high ultimate tensile strength of 220.607 N/mm2.

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