STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs

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STUDIES OF MICROSTRUCTURE, MECHANICAL AND TRIBOLOGICAL PROPERTIES OF AL-2Cu-2.6Mg-7.8Zn MMCs Mohammed Talib Syed 1, N SAI Hemanth2, K S Prabhu3, Avinash L4 Shiv Pratap5 UG Student, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India 1, 2 Assistant Professor, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India 3, 4, 5 Bangalore, India

Abstract:

The aim is to study the mechanical, tribological property and wear behavior of Al7068 alloy/alumina composite with various weight fractions (3%, 5%, 7%) were prepared by stir casting method. In addition, Al7068 were cast for comparison purposes.

Microstructure, hardness and tensile properties of these composites were evaluated and compared with as-cast alloy and the composites. In addition, tribological properties of these composites were also evaluated. The wear and mechanical properties of composites improve with increasing the weight fraction of Alumina and then decreases gradually. This study provides an alternative way to enhance the tribological behavior of Al7068 alloy/Alumina composite. The study also highlights the different contribution of different input process parameters (like: composition of Al7068 alloy/Alumina and particle size of reinforcement material) on wear properties of Al7068 alloy/Alumina MMCs. Keywords: Al 7068 alloy, matrix, Alumina, Composite, tribological, wear

1. INTRODUCTION IDL - International Digital Library

Today in Modern day technology there is an ever increasing demand in materials which achieves good combination of strength, stiffness, toughness and density. But the conventional monolithic materials have limitations in achieving these combinations. To overcome these shortcomings and to meet the ever increasing demand of modern day technology, composites are most promising materials of recent interest. A broad definition for a composite is: a combination of two components separated by a distinct interface, thermodynamically irreversible, and has properties which can be „engineered‟ using composite principles.

Automotive, medical and sport equipment industries pushed advances in materials further to introduce new generation materials particularly having low density and very light weight with high strength, hardness and stiffness. Since 1960‟s there has been an everincreasing demand for newer, stronger, stiffer and yet lighter-weight materials in fields such as aerospace, transportation, automobile and construction sectors.

With the vast and rapid progress in science and technology, modern industry has introduced a new generation of composite materials having low density and very light weight with high strength, hardness and stiffness to meet the current needs of modern 1|P a g e

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International e-Journal For Technology And Research-2017 technology and the challenges against liberalization and global competitiveness in market. Particlereinforced aluminium alloys have the potential to be used in a wide range of such engineering applications due to their higher stiffness and strength when compared with conventional aluminium alloys.

In the present investigation Al 7068 alloy was chosen as matrix material because of its wider applications for markets like the aerospace and automotive industries (valve body and connecting rod applications), as well as recreational products (bicycles) .At present very limited information is available on the Alumina reinforced Al 7068 alloy composites. Therefore the present investigation makes an attempt to synthesize the Alumina reinforced Al 7068 alloy composites by stir casting method. Later these composites will characterized in terms of their Optical Microscope, SEM studies, hardness, mechanical and Tribological properties.

2. LITERATURE SURVEY There is abundant amount of literature available on Metal Matrix Composites pertaining to Al7068 with various reinforcements, Stir Casting and Hybrid composites. This chapter gives a brief narration of the significant research carried out on MMCs in the recent past, conclusions drawn from them and objectives of the present investigation.

Aluminium 7068 alloy is a heat treatable wrought alloy with good fatigue strength, good anodizing response, and high thermal conductivity. It was designed as a higher strength alternative to aluminium7075 for ordnance applications. It also provides the highest mechanical strength of all aluminium alloys.

2.1.Physical Properties The physical properties of aluminium 7068 alloy are outlined in the following table 1.

Properties Metric Imperial Density 2.85 mg/cm³ 0.103 lb/in³

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Melting Point

476-635 ºC

890-1175 ºF

2.2. Mechanical Properties The mechanical properties of aluminium 7068 alloy are outlined in the following table 2.

Properties Metric Imperial Tensile strength 641 MPa 93 ksi Yield strength 590 MPa 85.7 ksi Elongation 8% 8%

2.3.Thermal Properties The thermal properties of aluminium 7068 alloy are outlined in the following table 3.

Properties Metric Imperial Thermal 190 W/mK 1317 BTU conductivity in/hr.ft².°F Table 4: Chemical composition of Al7068 alloy (weight percentage).

3. OBJECTIVES Our study can lead one to investigate the possibility of identifying the use of these composites for commercial applications in the in aerospace and automotive industries (valve body and connecting rod applications), as well as recreational products (bicycles).Therefore the work taken up had the following objectives:   

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Fabrication of Al7068/ Alumina composites by Stir Casting Method.

Microstructure characterization of the composites using optical microscopes and SEM Evaluation of mechanical properties of the composites.

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Evaluation of Tribological properties of the composites.

Comparing the results of mechanical and Tribological properties of as-cast alloy with composites.

Drawing Conclusion based on the obtained result.

4. METHODOLOGY

Aluminium 7068 alloy is chiefly used in the following areas:  Aerospace and automotive industries  Auto-sport gearbox actuators and wheel components  Prosthetic limbs  Load cells  Hydraulic valve components  High pressure solenoids  Flexible shaft coupling  Snowmobile engine shafts  Automobile shock absorbers  Fuel pumps for racing engines  Motorcycle gears  Recreational products such as tents, ski and backpack rods, bicycles and mountain climbing equipment  Automotive valve body and connecting rod

6. OUTCOMES 

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We can expect uniform distribution of reinforcement(Alumina) withm atrix material (Al7068) by Stir Casting Method Uniform distribution may lead to good Microstructure of As-cast as well as composites Further there will be a good improvement in mechanical and tribological properties of Composites

Optical Microscopic Studies

Figure1: Flow Chart of Experimental Work Fig 2(a): As-cast 7068

Fig 2(b) As-cast 7068 +3% Alumina

5. IMPLEMENTATION

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Fig 2(c) As-cast 7068 +5% Alumina

Fig 2(d) As-cast 7068 +7% Alumina

Figure 2: Optical Micrographs of A357 alloy Figure 2(a), 2(b), 2(c), 2(d) shows the micro photographs of both the matrix alloy Al7068 and its composites system. The microstructure clearly indicates fairly uniform distribution of reinforcement with minimal porosity in the matrix alloy in all the cast composite systems studied. Microstructure consists of fine precipitates in a matrix of dendritic Aluminium solid solution. Segregation or porosity is not seen in the section. The majority of the Alumina particles are located inside the matrix itself which indicates that it has been wetted better due to the addition of Mg as a wetting agent.

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From Figure 5 it is found that hardness increase with increasing Alumina content in the material. As compared to as-cast (A7068 alloy), 3% Alumina addition shows an increase of 7.2 BHN (10.52%). In contrast 5% and 7% Alumina addition shows an increase of 15.9 BHN (23.24%) and 21.7 BHN (31.72%) respectively. The improvement in hardness in casted composites may be attributed to uniform distribution of reinforcement (Alumina) in the matrix material.

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Tensile Test Result:

Table 6: Tensile strength of A7068 alloy and its Composites

Hardness Test Result:

Table 5: Hardness of A7068 alloy and its Composites

Fig 6: Tensile strength of A7068 alloy and its Composites Fig 5: Hardness of A7068 alloy and its Composites

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International e-Journal For Technology And Research-2017 Fig 7: Tensile strength of A7068 alloy and its Composites

From Figure 7 it is found that compression strength increase with increasing Alumina content in the material. As compared to as-cast (A7068 alloy), 3% Alumina addition shows an increase of 16.05 UCS (12.87%). In contrast 5% and 7% Alumina addition shows an increase of 22.86 UCS (18.33%) and 30.18 UCS (24.20%) respectively. The improvement in UCS in casted composites may be attributed to uniform distribution of reinforcement (Alumina) in the matrix material.

Fig 6: Tensile strength of A7068 alloy and its Composites

From Figure 6 it is found that Tensile strength increase with increasing Alumina content in the material. As compared to as-cast (A7068 alloy), 3% Alumina addition shows an increase of 30.5 UTS (17.77%). In contrast 5% and 7% Alumina addition shows an increase of 53.1 UTS (30.94%) and 61.7 UTS (35.95%) respectively. The improvement in UCS in casted composites may be attributed to uniform distribution of reinforcement (Alumina) in the matrix material. The superior tensile properties of the composite over the alloy should be attributed to the existence of the Alumina reinforcing particles to strengthen the α‑ Al phase.

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Tribological Studies

Dry sliding wear tests were conducted as per ASTMG99 norms. The wear rate was based on the average value of 3 tests. Two loads of 10N and 30N at a sliding velocity of 3.5m/sec and sliding distance of 2100m. During the test the following specifications were used:

Compression Test Result :

Table 8: Specifications used in wear studies Calculations: Table 7: Tensile strength of A7068 alloy and its Composites

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As-Cast 7068 Alloy

As-Cast 7068 Alloy +3% Alumina

Table 9: Wear behaviour of A7068 alloy and Composites

As-Cast 7068 Alloy +3% Alumina

As-Cast 7068 Alloy +3% Alumina

Fig 10: Wear Surface Morphology of A7068 alloy and its Alumina reinforced composites at a Sliding velocity of 2.5m/sec and Sliding distance of 1500meters.

Fig 9: Effect of load on wear (Âľm) of the A7068 alloy and its Alumina composites (Sliding Velocity: 3.5m/s, Sliding distance: 2100m, load: 10 and 30N)

From the fig 9 it can be see that as the load increases the wear rate increases. Maximum wear rate can be observed in A7068 alloy and least wear rate is observed in As-cast alloy with 7% alumina. The decrease in wear rate may be attributed to the alumina particles which act as load bearing in the A7068 matrix and resist wear. Due to the absence of ceramic particle as reinforcement in as-cast alloy it has a maximum wear rate.

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The worn-out surface of some selected /typical specimens after the wear test are observed under optical microscope Figs. 13 , (a-d) shows the surface morphology of A7068 alloy reinforced alumina composite, tested under two different load and speed conditions .it appears that cavities are formed in the composite matrix and have aligned parallel to the direction of sliding. Some particles also have chopped off during sliding. The amount of cavitations is less than that of the previous case. In some regions, the substructures are aligned parallel to the sliding direction. In some area smaller particulate have come out from the composite matrix.

Wear Surface Morphology

7. CONCLUSION The following conclusions were drawn from the present study: From the tests conducted in order to determine the mechanical and Tribological properties of Alumina

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International e-Journal For Technology And Research-2017 reinforced Al7068 composites of different weight fractions of the reinforcement, it was found that:  Microstructure indicates uniform distribution of ceramics in the matrix resulting in good bonding of the particulates and showed primary dendrite

 -Dendrite phase rich in aluminium.

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The composite with 7% Alumina has highest hardness, UTS and wear resistance. The Alumina particles help in matrix strengthening acting as barriers to the dislocations moments when load is applied.  The wear rate is maximum for A7068 alloy and least for A7068 with 7% Alumina.  The temperature due to friction at the interface increased with sliding velocity and increased load.

The increase in sliding velocity resulted in increased strain rate leading to increased hardness which in turn leads to reduced area of contact resulting in reduced wear rate.

8. FUTURE SCOPE In the present study, the analysis of as-cast and composite (A7068/Al2O3) were made to determine the mechanical properties and tribological behaviour.

Research can be further extended to study the following: 

The study of the mechanical properties, tribological behaviour with different heat treatment tempers such as T4, T5 can be made and compared with alloys and its composite.

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Sliding wear tests may be conducted for the alloys and composites with further variation of parameters such as sliding distance, load.

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A study on heat treatment by varying different Solutioning and ageing temperature may be carried out and tested for strength and wear resistance.

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[2] Arun Kumar .M.B. And R.P. Swamy, „Evaluation of Mechanical Properties of Al7068, Fly Ash and EGlass Fiber Reinforced Hybrid Metal Matrix Composites‟, ARPN journal of engineering and applied science vol. 6 No.5 2011.

[3] R.D.Rawlings and F.L.Mathews, “Composite material: Engineering and science”, Text Book, London, 1994.

[4] M.Sreenivasa Reddy, Soma V. Chetty, Sudheer Premkumar, (2012)“Effect of reinforcements and heat treatment on tensile strength of Al-Si-Mg based hybrid composite” ARPN journal of engineering and applied science vol. 6 No.5 [5] T. Sasimurugan, K. Palanikumar, (2011) “Analysis of the Machining Characteristics on Surface Roughness of a Hybrid Aluminium Metal Matrix Composite (Al7068-SiC-Al2O3)”, IJIRSET Vol.3 N0.5 [6] R. Karthigeyan, G. Ranganath and S. Sankaranarayanan, (2012) “Mechanical properties and microstructure studies of Aluminium (7075) alloy matrix composite reinforced with short Basalt Fibre”, European Journal of Scientific Research, Vol. 68. No. 4, pp. 606-615, [7] Deepak Singla and S.R. Mediratta, (2013)“Effect of load and speed on wear properties of Al7075-Fly Ash composite material”, International Journal of Innovative Research in Science, Engineering and Technology, Vol. 2, Issue. 5, pp. 1-9.

[8] EzhilVannan and S. Paul Vizhian, (2014) “Microstructure and mechanical properties of as case aluminium alloy 7075/Basalt dispersed Metal Matrix Composites”, Journal of Minerals and Materials Characterization and Engineering No. 2, pp. 182-193.

[9] L Avinash, T RamPrabhu, Adithya Parthasarathy, KN Varun Kumar, Basavaraj Sajjan, (2016)“Wear and

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International e-Journal For Technology And Research-2017 mechanical behaviour of Hypo-eutectic Al-7%Si0.5%Mg alloy (A357) reinforced with Al 2O3 particles”, Applied Mechanics and Materials, Trans Tech Publications,829 pp 66-72 [10] C. Garcia-Cordovilla, J. Narciso, E. Louis,(1996) “Abrasive wear resistance of aluminium alloy /ceramic particulate Composites”, Wear 192 pp170-177 [11] Mohan Vanarotti, SA Kori, B.R. Sridhar, B.Shrishail Padasalgi,(2012)” Synthesis and Characterization of Aluminium Alloy A356 and Silicon Carbide Metal Matrix Composite”, International Conference on Industrial Technology and Management , 49 pp.11-15 [12] Rajeshkumar Gangaram Bhandare, Parshuram M. Sonawane, (2013) “Preparation of Aluminium Matrix Composite by Using Stir Casting Method”, International Journal of Engineering and Advanced Technology (IJEAT), Pune University.

[13] Jasim Hahim, PhD thesis, (2000) “The Production of MMC using the Stir Casting Technique”, Dublin City University.

[14] Aleksandar Vencl, A.Rac, (2004) “Tribological Behaviour of Al-Based MMCs and .their Application in Automotive Industries”, University of Belgrade.

[15] Devaraju A, Kumar A, Kotiveerachari B. (2013) “Influence of addition of Grp/Al2O3p with SiCp on wear properties of aluminum alloy 6061-T6 hybrid composites via friction stir processing.Trans Nonferrous Met Soc China; 23(5):1275–80.

[16] Devaraju A, Kumar A, Kotiveerachari B.(2013) “Influence of rotational speed and reinforcements on wear and mechanical properties of aluminum hybrid composites via friction stir processing”. Mater Des, 45:576–85.

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