Tribological Properties of Aluminium 2024 Alloy Beryl Particulate MMC s

Transcription

1 Bonfring International Journal of Industrial Engineering and Management Science, Vol. 2, No. 4, December Tribological Properties of Aluminium 2024 Alloy Beryl Particulate MMC s H.B. Bhaskar and Abdul sharief Abstract--- Metal Matrix Composites (MMCs) are emerging as the most versatile materials for advanced structural, automotive, aviation, aerospace, marine, defense applications and other related sectors because of their excellent combination of properties. In the present investigation, Al2024-Beryl composites were fabricated by liquid metallurgy route by varying Weight Percentage (wt. %) of reinforcement from 0 wt. % to 10 wt. % in steps of 2 wt. %. The dry sliding wear tests were conducted to examine the wear behavior of the Al2024 alloy and its composites. The sliding wear tests were conducted for various loads, speeds and sliding distances. The result reveals that wear rates of the composite is lower than that of the matrix alloy and friction coefficient was minimum when compared to monolithic alloy. The incorporation of beryl particles as reinforcement material in Al2024 alloy improves the tribological characteristics. Keywords--- MMCs, Al2024, Wear Rate, Beryl, Pin-on- Disc, Coefficient of Friction A I. INTRODUCTION LUMINIUM Metal Matrix Composites (AMMCs) are the new candidate materials used in varieties of engineering applications. Aluminum and its alloys have been used as matrix material owing to its wide applications in industrial sector. To increase the mechanical and tribological properties, hard reinforcement phase such as particulate, fiber or whiskers are uniformly distributed. These materials have emerged as the important class of advanced materials giving engineers the opportunity to tailor the material properties according to their needs. Essentially these materials differ from the conventional engineering materials from the viewpoint of homogeneity.[1] AMMCs are a class of composite materials which are having desirable properties like low density, high specific stiffness, high specific strength, controlled co efficient of thermal expansion, increased fa 1 tigue resistance and superior dimensional stability at elevated temperatures etc. [2]. AMMCs have emerged as the advanced engineering materials giving engineers the opportunity to tailor the material properties according to their H.B. Bhaskar, Research Scholar, Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Maralur Post, Tumkur , Karnataka, India. bhaskarhbssit@gmail.com Abdul sharief, Professor and Head, Department of Mechanical Engineering, P.A. College of Engineering, Mangalore , Karnataka, India. abdulsharief2010@gmail.com DOI: /BIJIEMS.1845 needs. The mechanical and tribological properties of the matrix material was improved by reinforcing the various reinforcements ranging from very soft materials like Graphite, Talc etc., to high hardened ceramic particulates like SiCp, Al 2 O 3, etc., [3]. In recent years, particulate reinforced aluminum alloy composites fabricated have shown significant improvement in tribological properties, including sliding wear, abrasive wear, friction and seizure resistance [4]. An excellent review on the dry sliding wear of discontinuously reinforced aluminum composites by Sannino et al., [5] reported about the principal tribological parameters that control the friction and wear performance of discontinuously reinforced aluminum composites. The mechanical and physical factors have been identified as sliding velocity and normal load whereas the material factors are volume fraction, type of reinforcement and size of reinforcement. The volume fractions of reinforcement have the strongest effect on the wear resistance and have been studied [6-9]. Many researchers have carried out the work to increase the wear resistance of MMCs by different types of reinforcements. The main outcome of these is that the reinforcement improves the resistance to sliding wear [10-11]. However, the research works on the dry sliding wear of aluminium alloys containing beryl particles were limited. Therefore in the present investigation an attempt is made to study the sliding wear behavior of Al2024-Beryl particulate composites for different weight percentages of beryl particles. II. EXPERIMENTAL DETAILS 2.1 Material The matrix alloy selected for the development of composite material is Al-Cu-Mg alloy and designated by the aluminium association as Al2024-T6. The chemical composition of the matrix material is given in the Table 1. Beryl, which is naturally occurring and chemically having beryllium alumina silicate [Be 3 Al 2 (SiO 3 ) 6 ] was used as the reinforcement material. The chemical composition of beryl particles used for development of the composite are mentioned in the Table 2. Table 1: Chemical Composition of Al2024 Alloy (wt.%) Al Cu Fe Mg Mn Si Ti Ni Zn Cr Pb Sn Table 2: Composition of Reinforcement Material (wt.%)

2 Bonfring International Journal of Industrial Engineering and Management Science, Vol. 2, No. 4, December SiO 2 Al 2 O 3 BeO Fe 2 O 3 CaO MgO Preparation of the Composite The Al2024 alloy and Al2024-Beryl reinforced composites were fabricated by liquid metallurgy method. This method is the most economical to fabricate composites materials. The matrix material was first superheated to above its melting temperature by using 5 KW electrical resistance furnace and preheated beryl particulates were added into molten metal. The molten metal was stirred for duration of 8 min using a mechanical stirrer and speed of the stirrer was maintained at 350 rpm. The mixed molten metal at 710 C was poured into the pre-heated cast iron molds. Al2024-Beryl composites were casted by adding proportionate of weight percentage of reinforcement from 0 wt.% to 10 wt.% in steps of 2 wt.%. This liquid metallurgy method has been used for developing the MMCs by many researchers. [10-16]. The castings were tested to know the common casting defects using ultrasonic flaw detector. 2.3 Testing of Composites The metallographic and hardness tests were carried out on Al2024 alloy and Al2024 / Beryl reinforced composites as per ASTM standards. A pin-on-disc apparatus was used to investigate the dry sliding wear characteristics of the composite. The wear specimens were machined to the pin size of diameter 8 mm and height 30 mm and then polished metallographically as per American Society for Testing and Materials (ASTM) G99-95 standards. During the test, the pin was pressed against the rotating counterpart carbon case hardening steel disc with hardness 60 Rockwell C Hardness by applying the load and speed. After running through a fixed sliding distance, the wear and frictional force are tabulated. The specimen is cleaned with acetone and dried. The each experiment was repeated thrice and means response values were considered. Also the wear of the Al2024 alloy and its composites can be determined by measuring the weight loss in specimens before and after the test for different load and speed. The specimens were tested as per the procedure reported in papers Uyyuru et al., [19] and C.S.Ramesh et al., [20]. III. RESULTS AND DISCUSSION 3.1 Microstructure Analysis The samples for the microscopic examination were prepared by standard metallographic procedures etched with killer s agent and examined under optical microscope. Figure 1 (a & b) shows the optical micrograph of as-cast Al2024 alloy and Al2024/4wt.% of beryl particulate composite respectively. Micrograph indicates the nearly uniform distribution of the reinforcement particles in the composite. Figure 1a: Micrograph of as-cast Al2024 alloy Figure 1b: Micrograph of as-cast Al2024/4 wt.% of beryl Composites 3.2 Hardness The variation of hardness of Al2024 alloy and its composite materials are shown in the figure 2. This graph explains the effect of particulate reinforcement on the micro hardness. The hardness of the Al2024/10wt.% of beryl composite increased by around 26% as compared to Al2024 matrix alloy. It is observed that with increased content of beryl in the matrix alloy, there was a significant improvement in the hardness of the composites. This trend is similar to the result of other researchers [21-25].

3 Bonfring International Journal of Industrial Engineering and Management Science, Vol. 2, No. 4, December Figure 2: Effect of Reinforcement Content on the Microhardness of Al2024 Alloy and its Composites 3.33 Wear Characteristics The figure 3 shows the variation of wear rate for different wt.% of reinforcement at constant load of 40N and speed of 400rpm for unreinforced alloy and its composites. It illustrates the influence of wt.% of reinforcement on wear rates of Al2024-Beryl MMCs against a steel counterface. It is observed that, the wear rate of the composites decreases with increased contents of the reinforcement in the matrix alloy. It is obvious that the reinforcements effectively reduces the wear and the reinforcements acts as load carrying elements at the beginning of rubbing and also acts as inhibitors against plastic deformation. However, for a given reinforcement content, the composites possess lower wear rates than the matrix alloy. The incorporation of beryl particles into the Al2024 matrix material improves the sliding wear resistancee as compared to the unreinforced matrix material. Figure 4: Variation of wear rate at different loads at constant speed 400 rpm The Figure 4 shows the variation of wear rate on the applied load for a constant sliding speed of 400rpm. Wear rate was small for a minimum applied load, but as the load was further increased up to 60 N, the wear rate of the unreinforced alloy and composite increases. The percentage of wear rate also decreases with increse in the reinforcement content. The wear resistance of the Al2024 alloy increaese by reinforcing with beryl particles and applied load increase wear resistance decreases. The figure 5 shows the variation of wear rate for different sliding distances at constant load of 40N and speed 400 rpm for matrix material and its composites. It can be seen that as the sliding distance increases, the wear rate of both the composites as well as the unreinforced material increases. The wear rate of the unreinforced material is more than that of the composites for all sliding distances. Further, as the percentage of reinforcement increases, the wear rate of the composite decreases. Figure 3: Wear Rate for Different wt. % of Reinforcements at Constant Load of 40N and Speed 400 rpm Figure 5: Variation of Wear Rate with Sliding Distance at Constant Load of 40N and Speed 400 rpm ISSN Bonfring

4 Bonfring International Journal of Industrial Engineering and Management Science, Vol. 2, No. 4, December Figure 7: Variation of Coefficient of Friction with Sliding Speed at Constant Load of 40N Figure 6: Variation of Wear Rate at Different Sliding Speed at Constant Load of 40N The Figure 6 shows the variation of wear rate for different sliding speeds at constant load of 40N for the unreinforced alloy and its composites. The wear rate of both unreinforced alloy and the composites decreases as sliding speed increases from m/s to m/s for a load of 40N and further, the wear rate of the composite decreases as the amount of reinforcement content increases. The noise and vibration were observed during the process and transfer of the pin material to the disc was also observed. The figure 7 shows the variation of coefficient of friction with sliding speed at constant load. The coefficient of friction of both unreinforced alloy and the composites decreases as sliding speed increases from m/s to m/s for a load of 40N. From the figure 8 it is observed that the coefficient of friction of the unreinforced material is more than that of the composites for all different loads and coefficient of friction increases as the load increase for matrix alloy and its composites. Further, as the percentage of reinforcement increases, the coefficient of friction of the composite decreases. [17] Figure 8: Variation of Coefficient of Friction at Different Load at Constant Speed 400rpm Figure 9: SEM of Worn Surface of as-cast Al2024 Alloy Figure 10: SEM of Worn Surface of as-cast Al wt.% Beryl Composite Figure 9 and 10 shows the Scanning Electron Micrograph (SEM) of worn surfaces of as-cast Al2024 alloy and Al wt.% Beryl composite respectively. The mechanism of material removal during wear process of the Al2024 alloy was by plastic deformation and gouging. The wear resistance of the composite material is improved due to the presence of hard

5 Bonfring International Journal of Industrial Engineering and Management Science, Vol. 2, No. 4, December reinforcement particles in the matrix material. The wear process in the composite material is by plastic deformation, gouging and reinforcement particles will crush to very minute particles and form a very thin sub surface layer designated as Mechanically Mixed Layer (MML) which provides protection to the matrix material. The MML forms a layer between the work hardened pin and the counter face which withstands high stresses and is very effective in reducing the sliding wear. It is evident that the influence of beryl particles will reduce the cutting and ploughing in the composite material. There are some slight traces of ploughing to be seen in the matrix area and the hardness of the particles was the reasons for wear resistance [18]. It is evident that the composite material indicates superior wear resistance than that of Al2024 alloy. This is because of improved hardness and strength of composites results in excellent wear resistance of the composite material. IV. CONCLUSION The Al2024-Beryl particulate reinforced composites were successfully developed using liquid metallurgy method. The Microstructural study clearly reveals nearly uniform distribution of beryl particulates in the Al2024 matrix alloy. The micro hardness of composites increases as reinforcement content increases in the matrix alloy. The incorporation of beryl particles into the matrix alloy improves the sliding wear resistance of the composites as compared to the unreinforced matrix alloy. The wear rate and coefficient of friction of the composites as well as the unreinforced material increases as the sliding distance and applied load increases. Further, as the percentage of reinforcement increases, the wear rate and coefficient of friction of the composite decreases. The wear rate and coefficient of friction of both unreinforced alloy and the composites decreases as the sliding speed increases up to 3 m/s for a load of 40N, after that wear rate and coefficient of friction slightly increases as the sliding speed increases. REFERENCES [1]. K.K. Chawla, Composite Materials Science and Engineering, Second edition. Springer- Verlag, New York, Pp.102, [2]. I. Sinclair, P.J. Gregson, Structural Performance of Discontinuous Metal Matrix Composites, Material Science and Technology, Vol. 3, Pp , [3]. Hsiao Yeh Chu, Jen Fin Lin. Experimental Analysis of the Tribological Behavior of Electroless Nickel-Coated Graphite Particles in Aluminum Matrix Composites under Reciprocating Motion, Wear Vol. 239, Pp , [4]. C.S. Lee, Y.H. Kim, K.S. Han, I. Lim, Wear behavior of aluminum matrix composites materials, Journal of material Science, Vol. 27, Pp , [5]. A.P. Sannino and H.J. Rack, Dry Sliding Wear of Discontinuously Reinforced Aluminium Composites: Review and Discussion, Wear, Vol.189, Pp.1-19, [6]. M.K. Surappa, S.V. Prasad and P.K. Rohatgi. Wear and Abrasion of Cast Al-alumina Particle Composites, Wear, Vol.77, Pp , [7]. A. Wang and H.J. Rack. Dry Sliding Wear in 2124 Al-SiCw/17-4 PH Stainless Steel Systems, Wear, Vol. 147, Pp , [8]. J.P. Tu and Y.Z. Yang. Tribological Behaviour of Al- Si-Mg-Matrix Composites under Dry Sliding Conditions, Compos. Sci. Technol., Vol 60, Pp , [9]. P.N. Bindhumadhan, H.K. Wah and O. Prabhakar. Dual Particle Size (DPS) Composites: Effect on Wear and Mechanical Properties of Particulate Matrix Composites. Wear, Vol. 248, Pp , [10]. B.P Krishnan, Performance of an Al-Si-Graphite particle composite Piston in a Diesel engine Wear, Vol. 60, Pp , [11]. M.K. Surappa and P.K. Rohatgi, Preparation and properties of cast aluminium-ceramic particle composites, Journal of Materials Science, Vol.16, No. 4, Pp , [12]. S. Basavarajappa and Chandramohan, Dry sliding Wear Behaviour of Hybrid Metal Matrix Composites, Material Science, Vol.11, No. 3. pp , [13]. R. Shivanath, P.K. Senguptha and T.S. Eyre, Wear of aluminum silicon alloys, The British Foundryman, Vol. 70, Pp , [14]. A.G. Wang and I.M. Hutchings Wear of alumina-fibre aluminum composites by two-body abrasion, Material science and Technology, Vol.5, Pp.71-76, [15]. XUY and D.D.L. Chung, Low volume fraction particulate performs for making metal matrix composites by liquid metal infiltration, Journal of Material Science, Vol. 33, Pp , [16]. S. Skolianos and T.Z. Kattamis Tribological properties of SiCpreinforced Al4.5%Cu- 1.5% Mg alloy composites, Material Science Engineering A, Vol.163, Pp , [17]. P.K. Rohatgi, R.Q. Guo, P. Huang and S. Ray. Friction and Abrasion Resistance of Cast Aluminium Alloy-Flyash Composites. Metal. Mater. Trans., A, Vol. 28A, Pp. 245, [18]. S.C. Tjong, S.Q. Wu and H. Liao. Wear Behaviour of an Al-12% Si Alloy Reinforced with a Low Volume Fraction of SiC Particles. Journal of Composite Science and Technology, Vol.57, No. 12, Pp. 1551, [19]. R.K. Uyyuru, M.K. Surappa and S. Brusethang, Effect of reinforcement volume fraction and size distribution on the tribological behavior of Al Composite, Wear, Vol.206, Pp , [20]. C.S. Ramesh, S.K. Sheshadri and K.J.L. Iyer, A survey of aspects of wear of metals, Indian Journal of Technology, Vol.29, Pp , [21]. S.C. Sharma, M. Krishna, P.S. Vizhian and A. Shashishankar, Thermal effects on mild wear transition in dry sliding of aluminium 7075-short glass fibre composites, IMECHE, J. Auto Eng. Part D: Vol.216, No. 12, Pp , [22]. N.R. Prabhu Swamy, C.S. Ramesh and T. Chandrashekar, Effect of heat treatment on strength and abrasive wear behaviour of Al6061 SiCp composites, Bull. Mater. Sci., Vol. 33, No.1, Pp , [23]. S.C. Sharma, B.M. Girish, R. Kamath and B.M. Satish, Aging characteristics of short glass fibre reinforced ZA 27 alloy composite materials, Journal of Materials Engineering and Performance, Vol.7, No. 6, Pp , [24]. C.S. Ramesh, A.R. Anwar Khan, N. Ravikumar, P. Savanprabhu, Prediction of wear coefficient of Al6061 TiO2 composites, Wear, Vol. 259, Pp , [25]. Szu Ying Yu, Hitoshi Ishii, Keiichiro Tohgo, Young Tae Cho, Dongfeng Diao, Temperature dependence of sliding wear behavior in SiC whisker or SiC particulate reinforced 6061 aluminum alloy composite, Wear, Vol. 213, Pp , 1997.