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A Comprehensive Study of Aluminum Based Metal Matrix Composites: Challenges and Opportunities
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 23937–23944
www.materialstoday.com/proceedings
IConAMMA_2017
A Comprehensive Study of Aluminum Based Metal Matrix Composites: Challenges and Opportunities P.B.Pawara, R.M.Wabalea, A.A.Utpatb a
b
Department of Mechanical Engg. SVPM’s ITE Malegaon (BK), MH,India,413115 Professor, Department of Mechanical Engg., SVERI’s COE Pandharpur, MH India
Abstract MMCs are prepared by dispersing a reinforcing material into a metal matrix. Composites are prepared by stir casting, powder metallurgy, squeeze casting, spray deposition etc. MMC offer improved mechanical and tribological properties over conventional metals and currently are considered as potential material for light weight application. Due to high strength to weight ratio, high tensile strength, toughness, high wear resistance, these materials are used in automobile, aerospace, sports, and many more fields. Irrespective of these advantages there are some technological barriers in development of composites. Some of them are obtaining uniform distribution of reinforcement among matrix, high processing cost with methods other than casting, availability of low cost reinforcement and machining of composites after preparation if required. Currently SiC, TiB2, Al2O3, B4C are used as reinforcement with Al alloys. Some research carried out on hybrid composite with fly ash, lignite ash, coconut husk has also given better results than single reinforcement. This paper reviews current development in Aluminum matrix composite preparation, processing methods, mechanical properties and some challenges in development of composites. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials and Manufacturing Applications [IConAMMA 2017]. Keywords: MMC’s; Aluminium Matrix Composites; Powder Metallurgy; Stir Casting
1. Introduction The use of composites began early in the twentieth century with a phenolic paper laminate used for electrical insulation. Composites differ from alloys, polymers, and ceramic compounds in that the matrix and reinforcement is separate from each other. Composite materials are having high potential for replacement of conventional materials in many applications like automobile, defense, aerospace, etc. 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials and Manufacturing Applications [IConAMMA 2017].Corresponding Author- +919960936910 [email protected]
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Nomenclature Yc Yf Ym Vf Vm
Young’s Modulus of Composite Young’s Modulus of Fibre Young’s Modulus of matrix Volume fraction of fibre Volume fraction of matrix
Al matrix elements reinforced with SiC, B4C, TiB2, B4C etc. offer many advantages like higher strength to weight ratio, higher tensile strength, hardness, improved toughness, stable thermal properties, higher wear and corrosion resistance. AMCs can be classified into four types depending on the type of reinforcement. Particle-reinforced AMCs (PAMCs) Whisker-or short fibre-reinforced AMCs (SFAMCs) Continuous fibre-reinforced AMCs (CFAMCs) Mono filament-reinforced AMCs (MFAMCs) An attempt has been made in this paper to take a review of Aluminum matrix composite preparation methods, reinforcements used, challenges and opportunities in further development of AMC’s. Al MMC’s have better mechanical and thermal properties compared to conventional metals with considerable low weight. Properties of composite depend upon volume fraction of reinforcement, processing method, distribution of reinforcement [1]. Study carried out for evaluating effect of reinforcement on hardness, impact strength and material toughness, has found almost 2.1 times increase in values of these properties over unreinforced material [2]. Al MMC have better mechanical properties than conventional metals and this has lead to increased use of these MMC’s in automobile and aerospace applications. Quality of composite i.e. properties depends upon processing parameter and choice of material. Use of hybrid reinforcement has lead to much better properties than that obtained with single reinforcement [3]. A considerable increase in wear resistance of Aluminium has been observed with addition of TiB2 as reinforcement [4]. Properties of Al SiC composite can be evaluated by preparing samples with varying percentage of SiC i.e. 5%, 10%, 15% etc. and conducting various tests. Based on experimental results it has been concluded that highest value of hardness, tensile strength and wear resistance have been found at 20% volume fraction of reinforcement but non homogeneous distribution also has been observed in microstructure [5]. Al MMCs prepared with SiC, Al2O3 and Graphene as reinforcement in different volume percentage by powder metallurgy has given best results at 10% volume fraction of reinforcement for SiC and Al2O3 [6]. Microstructure study of Al6082 alloy with Graphite particle as reinforcement has given uneven distribution of reinforcement in matrix and decrease in hardness with addition of Graphite. So it has been suggested that it is not beneficial to add Graphite particle in Al alloy [7]. It has been found that major concern with casting process is non homogeneous distribution of reinforcement and wettability of reinforcement particles. There is need of some simulation technique for casting process as many process parameters need to be controlled for obtaining better results [8]. A synthetic and agro waste derivative has also been used as reinforcement [9]. There is need to investigate more with agro waste derivatives as reinforcement in hybrid composites which have offered better properties over single reinforcement composite. There is no clear relation between volume fraction of reinforcement and composite properties as different researcher have obtained different results, but size of reinforcement particles definitely affect properties of composite and it has been advised to use reduced size particles in order to improve properties [10]. It has been found that fracture toughness and ductility decreases with increasing reinforcement volume fraction. AMC are going to be proved as a potential material in energy and fuel savings with least manufacturing cost. There is need of providing low cost reinforcement materials and processing facility of AMC’s should be made available in affordable cost. AMC processing methods include casting, powder metallurgy, spray deposition, Infiltration process etc [11].
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In Aluminum matrix composites (AMCs), the ceramic reinforcements are generally oxides or carbides or borides such as Al2O3, TiB2, TiO2, SiC, TiC, B4C, etc. The study carried out to investigate effect of these reinforcements on properties of AMC has found that for obtaining improved properties of AMC’s process parameters needs to be controlled precisely. Stir casting is the most economical processing method and process parameter such as stirring speed, stirring time, pouring temperature play an important role in deciding properties of composite [12]. It has been found that there is almost 30% increase in hardness and tensile strength double that of base metal. Aluminium matrix reinforced with Al2O3 gives high strength to weight ratio, high tensile strength, high fracture toughness etc. If reinforcement with submicron or nano sized particles is used it provides better results and almost 92% increase in hardness , 57% increase in tensile strength has been observed compared to pure aluminium [13]. Investigation has been carried out to study effect of lignite fly ash as reinforcement on Aluminum MMC prepared by powder metallurgy. Different samples of composite with 5%, 10%, 15% fly ash has been prepared and these samples were then compacted and sintered at 600oC for two hours and six hours respectively. Various tests conducted on composite samples have given better properties at 15% fly ash content [14]. Hybrid composite formed with fly ash and SiC as reinforcement differs in every aspect from pure aluminium alloy. A significant increase in hardness and tensile strength has been observed with 10% fly ash and 10% SiC. Combination of Al-SiC-Fly ash gives better strength and density found to be decreased with increased reinforcement content. This composite proved to be the best alternative in applications where reduction in weight is desirable [15]. Along with tensile strength impact strength has been found increased but decrease in elongation in tension test indicates brittle nature of material [16]. In situ reaction process has also been used for production of composite by certain chemical reaction. In this process ceramic compound and Mg-Al alloy are place in crucible and allowed to heat for some period in nitrogen gas surrounding. There are some limitations of this method due to combination of metals and chemical reaction [17]. Use of graphite particles as a reinforcement instead of SiC gives better wear resistance and offer improved tribological properties. Hybrid composite developed with Al and 20%SiC and added graphite as solid lubricant has offered low coefficient of friction and show better wear resistance at increased load and speed [18]. Coconut husk is a fibrous material and obtained as a waste after coconut has been used. Is such waste is used as reinforcement it will certainly reduce production cost of composite. Also porosity level has been found increased which decreases density of material [19]. Al composites offer better corrosion resistance than pure Aluminum at room temperature. Corrosion resistance has been found to be increased linearly with increasing volume fraction of reinforcement and reinforcement particle size. But with increasing temperature corrosion rate also increases for Al composite [23]. Carbonized maize stalk waste has also been used as reinforcement in Al-Mg-Si alloy and has given improved properties than pure aluminium [24]. Al-TiC composite prepared by powder metallurgy technique has been proved useful for structural applications. Al composite with other ceramic reinforcements such as SiC, Al2O3, and TiB2 also has been studied by various researchers [27]. 2. Reinforcement materials The reinforcement used varies from short fibres, flakes, and particles to filament and wires to continuous woven fibres and honeycomb. The metal matrix composites use metal alloys for their matrices with reinforcement provided by particle or filament of high performance materials [20]. Examples of discontinuous materials are glass fibres, silicon carbide whiskers, and alumina particles or short polymer fibres; continuous fibres may be of carbon, boron, alumina, or silicon carbide. 3. Preparation of Aluminum Based Metal Matrix Composite Many composites require two processes before they are able to meet a material need, the first one to create the composite itself and the second to shape or fit the composite materials to final application. In other cases a composite may be prepared and shaped to meet final requirement on one step. 3.1 Liquid State Processing-The most straight forward of the MMC methods involves casting the molten metal around solid reinforcement, using either conventional casting techniques or a pressurized gas on the liquid matrix to
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force it into and around a preformed reinforcement which is often made of metal sheet or wire, or ceramic fibre. Figure 1 shows schematic set up used for preparing composite material by stir casting method. Though stir casting has proved most economical preparation method, and variety of shapes and sizes can be cast from this process but obtaining homogeneous reinforcement distribution is major limitation of this process. 3.2 Powder Metallurgy Technique- The reinforcement fibres, whiskers or particles are carefully mixed with the powdered metallic matrix so they are uniformly distributed in the mixture. The mixture of powdered metal and reinforcement is then compacted to form the desired part. An initial compacting may be done cold, followed by sintering or all the compacting may be done at the sintering temperature. The sintering fuses the various particles together into a shape and size that should be very close the desired dimensions.
Fig.1 Schematic set up for Stir casting [5]
3.3 Liquid Solid Processing- This is casting technology in which the reinforcement being added to the metallic matrix is in the mushy state that is partly frozen, partly liquid. 3.4 Spark Plasma Sintering- Composites can be sintered by spark plasma, created by pulsed direct current; it leads to increase in powder and mold temperature. The sintering process is carried out under high pulse direct current in vacuum. Uniaxial pressure of 10Mpa is applied and increased to 20 MPa. Once sufficient temperature is reached pressure is decreased to 10 MPa and maintained for cooling time [25]. Even Al composite can be produced by microwave heating saving energy and time [26]. Ultrasonic assisted squeeze casting process has shown better grain refinement compared with composite prepared by stir casting [28]. Table 1 Comparison of Composite Preparation Methods Process Stir Casting Parameter Reinforcement Inhomogeneous distribution Distribution Wettability Poor, Some reagent required Mechanical Good Properties Cost Most cost effective Volume Fraction Up to 20%, Range of shape Not limited by size and size
Powder Metallurgy Homogeneous distribution Better Best results obtained Expensive More than 30% possible Varity of shapes, size limited
4. Mechanical Properties 4.1 Tensile strength In composite materials an attempt is made to increase the stiffness without the disadvantage of brittleness. Ductile materials withstand accidental overloading without catastrophic failure and these materials are suitable for structural
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components. The density of composite being quite low, it can compete in terms of stiffness and strength for the same weight with some of the high strength steels. Improvement in tensile strength in composite has been shown in Fig.2 for fly ash and SiC. 4.1.1Young’s Modulus The stiffness of a material is its ability to resist elastic deformation on loading. The stiffness is dependent on the shape of the structural component. For identical shapes, it is proportional to elastic modulus. Therefore elastic modulus is an important material parameter in mechanical design. The young’s modulus Yc of a composite in a direction parallel to the fibers can be expressed as a linear function of the moduli of the fibre and the matrix, Yf and Ym[21]. Yc=VfYf+VmYm Where Vf and Vm are the volume fraction of the fibre and the matrix. Thus a 40 volume percent of boron in an aluminum matrix can raise the Young’s modulus from 71 GN/m2 for pure aluminum to 219 GN/m2 for composite. This composite would then be as stiff as steel but less than one third its density. The volume fraction of the fibre in a composite cannot be increased indefinitely as at some stage the problems of aligning the fibres and keeping them separated from one another becomes serious.
(a)
(b) Fig.2 Tensile Strength of composite for various (a) Wt % of Fly ash [22] (b) Wt % of SiC
4.2 Hardness The property of hardness is related to the elastic and plastic properties of metals. Hardness of composite material has been found to be increased with addition of reinforcement percentage. Figure 3 shows increase in hardness of composite with addition of reinforcement for SiC and Al2O3. More increased in hardness value leads to brittleness and such components are susceptible to catastrophic failure in variable and high loading.
(a)
(b) Fig.3 Hardness values for various weight (a) ) % of Al2O3 as reinforcement [22] (b) % of SiC
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4.3 Toughness Toughness is function of rate of loading, temperature and notch effect, and it has been observed that toughness goes on decreasing with increase in loading and temperature. The fracture resistance of a material in the presence of cracks or discontinuities is known as its fracture toughness. Increasing fracture toughness in composite materials is one of the challenges in front of researchers. 4.4 Microstructure Composite samples itched with dilute acid and having mirror finish are observed under metallurgical microscope at 500X, 3000X or even higher magnification in order to observe microstructure of material, it reveals distribution of reinforcement in matrix, if some defects present in cast component, in case of processing has been done by casting, such as blow holes, micro pores. 4.5 Wear resistance Wear resistance of composite is measured by pin on disc method. Wear rate per unit amount of reinforcement has been considered for defining load carrying capacity of composite by many researchers. Wear resistance is a function of volume fraction of reinforcement and it is not a function of hardness. 4.6 Corrosion resistance Initially Oxidation was the term used to describe chemical reaction occurring on metal surface with surrounding, now days it has been replaced by corrosion. Metals react with their service environment and leads to oxidation, so coatings are provided on conventional materials to prevent oxidation. Aluminum has its natural ability to prevent corrosion. 5. Process variables and their effects on properties Process variables need to be controlled while preparing composite for obtaining better results. Many researchers have investigated effect of process variables on composite properties, some of them have been described below. 5.1 Speed of rotation Rotational speed of stirrer is kept near about 10m/sec and in this case stirring time is also important. After initial stirring vortex is formed in metal and after reinforcement has been poured it is stirred for almost 10 minutes so that it get properly mixed with molten metal. 5.2 Pouring temperature Reinforcement particles are preheated and poured into molten metal. Pouring temperature should be sufficiently high so that strong bond should be formed between reinforcement and matrix. If pouring temperature is low molten metal will start solidifying and it leads to improper mixing of reinforcement. 5.3 Pouring speed Major problem associated with stir casting process is segregation of reinforcement particle on molten metal surface. Pouring speed is important factor to be controlled for proper mixing, so slow pouring speed is advisable while preparing composite. 6. Challenges and opportunities The composite material has been proved as a potential alternative for replacement of conventional materials, but still there are some barriers in development and research of these materials. i. Major concern in front of researchers is obtaining more better properties of composite, which depends up on processing method, composition and process parameters.. ii. Obtaining homogeneous distribution of reinforcement in matrix is major challenge with casting process, which has been proved as the most favorable processing route. iii. Composite development starts almost on 70’s, but still no standardization has been performed related to process parameter, composition, etc. Some standardization institutes should carry out work in controlled environment and some standardized norms should be formulated in connection with composite preparation.
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iv. v.
vi. vii.
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Some research should be carried out for using some low cost material such as agriculture waste as a reinforcement, which will help in reducing overall cost of composite. In India currently there are very few manufactures working with Aluminum sintered components, so only option taken by most is casting. There should be some policy from government side to promote development and use of light weight composites so that manufacturers get attracted towards these materials. If process parameters controlled properly composite material certainly replace conventional material in many fields, especially automobile and bring revolution in this field. It is light weight, high strength, having more wear and corrosion resistance, more toughness. Due to presence of hard reinforcement it is difficult to machine composite and good surface finish and integrity. Graphite reinforcement has better lubricating property and its presence in composite improves machinability [29].
7. Conclusion From the review carried out above following conclusions have been drawn, i. The major advantage of composite material is high strength and low weight. When composite material is 40 percent aluminium and 60 percent alumina the resulting tensile strength and modulus of elasticity are about three and half times that of heat treated aluminium. ii. Composite material has properties that are higher than those of steel but at 45 percent the weight. iii. Large components can more easily be made from composite materials than from metals. iv. Further research can be carried out on heat treatment methods for composite, which will help in obtaining more improved properties. v. There should be some initiative from standardization authorities and government in developing standardized norms for composite processing and promoting their use in many engineering field areas. Acknowledgement Author acknowledges support from faculties of SVPM Institute of Technology and Engineering Malegaon (BK) for their support. References [1] Amitesh, V.C.Kale, Aluminium Based Metal Matrix Composites for Aerospace Application: A Literature Review, IOSR Journal of Mechanical and Civil Engineering, Volume 12, Issue 6 Ver. V (Nov. - Dec. 2015), PP 31-36. [2] Ali Hubi Haleem, Newal Muhammad Dawood, Silicon Carbide Particle Reinforced Aluminum Matrix Composite Prepared by Stir-Casting Babylon University –Materials Engineering Collage. [3] J.Jenix Rino, D.Chandramohan, K.S.Sucitharan,An Overview on Development of Aluminium Metal Matrix Composites with Hybrid Reinforcement, International Journal of Science and Research (IJSR), India Online ISSN: 2319‐7064, Volume 1 Issue 3, December 2012, pp196203 [4] S Suresh, N, Shenbaga Vinayaga Moorthy, Aluminum Titanium Diboride MMC: Challenges and Opportunities, Procedia Engineering 38, 2012, pp 89-97. [5] Md. Habibur Rahmana, H. M. Mamun Al Rashed, Characterization of silicon carbide reinforced aluminum matrix composites, Procedia Engineering 90 (2014), pp 103 – 109 [6] P. Ashwatha, M. Anthony Xavior, The Effect of Ball Milling & Reinforcement Percentage on Sintered Samples of Aluminium Alloy Metal Matrix Composites, Procedia Engineering 97 (2014), pp 1027 – 1032. [7] Pardeep Sharma, Satpal Sharma, Dinesh Khanduja A study on microstructure of aluminium matrix composites, Journal of Asian Ceramic Societies 3 (2015) 240–244. [8] Sijo M T, K R Jayadevan, Analysis of stir cast aluminium silicon carbide metal matrix composite: A comprehensive review, Procedia Technology 24 (2016), pp- 379 – 385. [9] Michael Oluwatosin Bodunrin, Kenneth Kanayo Alaneme, Lesley Heath Chown, Aluminium matrix hybrid composites: a review of reinforcement philosophies; mechanical, corrosion and tribological characteristics, Journal of Material Technology, 2015; 4(4), pp 434–445. [10] R. S. Rana. Rajesh Purohit,S.Das, Review of recent Studies in Al matrix composites, International Journal of Scientific & Engineering Research Volume 3, Issue 6, June-2012. [11] M K Surappa, Aluminium matrix composites: Challenges and opportunities, Sadhana Vol. 28, Parts 1 & 2, February/April 2003, pp. 319– 334. [12] C. Saravanan, K. Subramanian, V. Ananda Krishnan, R. Sankara Narayanan, Effect of Particulate Reinforced Aluminium Metal Matrix Composite –A Review, Mechanics and Mechanical Engineering, Vol. 19, No. 1 (2015) 23–30.
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[13] Dinesh Kumar Koli, Geeta Agnihotri, Rajesh Purohit, Properties and Characterization of Al-Al2O3 Composites Processed by Casting and Powder Metallurgy Routes (Review), International Journal of Latest Trends in Engineering and Technology (IJLTET), Vol. 2 Issue 4 July 2013, pp 486-496. [14] Angeliki Moutsatsou, Grigorios Itskos, Nikolaos Koukouzas, Panagiotis Vounatsos, Synthesis of Aluminum Based Metal Matrix Composite with Lignite Fly Ash as Reinforcement Material, 2009 World of Coal Ash Ceonference, 4-7 May 2009. [15] Mahendra Boopathi, M., K.P. Arulshri, N. Iyandurai, Evaluation Of Mechanical Properties Of Aluminium Alloy 2024 Reinforced With Silicon Carbide And Fly Ash Hybrid Metal Matrix Composites, American Journal of Applied Sciences, 10 (3): 219-229, 2013. [16] Sandeep Kumar Ravesh , T. K. Garg, Prepration & Analysis For Some Mechanical Property Of Aluminium Based Metal Matrix Composite Reinforced With Sic & Fly Ash, International Journal of Engineering Research and Applications (IJERA), Vol. 2, Issue 6, November- December 2012, pp.727-731. [17] Kashish Goyal and Karthikeyan Marwaha, Processing and Properties of Aluminium Matrix Composites: A Short Review, European Journal of Advances in Engineering and Technology, 2016, 3(8): 54-59. [18] M. Asif, K. Chandra, P.S. Misra, Development of Aluminium Based Hybrid Metal Matrix Composites for Heavy Duty Applications, Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.14, pp.1337-1344, 2011. [19] Siddharth Jain, Vidit Aggarwal, Mohit Tyagi, R.S. Walia, Ramakant Rana, “Development Of Aluminium Matrix Composite Using Coconut Husk Ash Reinforcement”, International Conference on Latest Developments in Materials, Manufacturing and Quality Control (MMQC-2016), pp 352-359. [20]R. Gregg Bruce, William Dalton, John Neely, Richard Kibbe, Modern Materials and Manufacturing Processes, Third Edition, Pearson, 2007, pp 327-340. [21] V Raghavan, Material Science and Engineering, fifth edition, PHI learning India, 2013, pp243-250. [22] P. Shanmughasundaram,Some Studies on Aluminium – Fly Ash Composites Fabricated by Two Step Stir Casting Method, European Journal of Scientific Research Vol.63 No.2 (2011), pp.204-218. [23] H.M. Zakaria, Microstructural and corrosion behavior of Al/SiC metal matrix composites, Ain Shams Engineering Journal (2014) 5, 831838. [24] J.E. Oghenevweta , V.S. Aigbodion b, G.B. Nyior , F. Asuke, Mechanical properties and microstructural analysis of Al–Si Mg/carbonized maize stalk waste particulate composites, Journal of King Saud University – Engineering Sciences (2016) 28, 222–229. [25] Mansour Razavi, Ali Reza Farajipour, Mohammad Zakeri,Mohammad Reza Rahimipour, Ali Reza Firouzbakht, Production of Al2O3–SiC nano-composites by sparkplasma Sintering, b o l e t í n d e l a s o c i e d a d e s p a ñ o l a d e c e r á m i c a y v i d r i o. [26] M. Penchal Reddy, F. Ubaid , R.A. Shakoor, A.M.A. Mohamed, W. Madhuri, Structural and mechanical properties of microwave sintered AlNi50Ti50 composites, Journal of Science: Advanced Materials and Devices 1 (2016) 362e366. [27] Sangita Mohapatraa, Anil K. Chaubeya, Dilip K. Mishrab,c, Saroj K. Singh, Fabrication of Al–TiC composites by hot consolidation technique: its microstructure and mechanical properties, journal of Material Tech., 2016; 5(2):117–122. [28] Mayuresh singh, R.S. Rana, Rajesh Purohit, krishnkant sahu, Development and Analysis of Al-Matrix Nano Composites fabricated by ultrasonic assisted Squeeze casting process, Materials Today: Proceedings 2 (2015) 3697 – 3703. [29] Anthony Xavior M, Ajith Kumar J P, Machinability of Hybrid Metal Matrix Composite - A Review, Procedia Engineering 174 (2017) 1110 – 1118. [30]Mohankumar K C, Rajshekhar H., Ghanraj S.,Ajitprasad S.L., Development and Mechanical Properties of SiC Reinforced Cast and Extruded Al Based Metal Matrix Composite, Procedia Materials Science 5 ( 2014 ) 934 – 943.
ScienceDirect Materials Today: Proceedings 5 (2018) 23937–23944
www.materialstoday.com/proceedings
IConAMMA_2017
A Comprehensive Study of Aluminum Based Metal Matrix Composites: Challenges and Opportunities P.B.Pawara, R.M.Wabalea, A.A.Utpatb a
b
Department of Mechanical Engg. SVPM’s ITE Malegaon (BK), MH,India,413115 Professor, Department of Mechanical Engg., SVERI’s COE Pandharpur, MH India
Abstract MMCs are prepared by dispersing a reinforcing material into a metal matrix. Composites are prepared by stir casting, powder metallurgy, squeeze casting, spray deposition etc. MMC offer improved mechanical and tribological properties over conventional metals and currently are considered as potential material for light weight application. Due to high strength to weight ratio, high tensile strength, toughness, high wear resistance, these materials are used in automobile, aerospace, sports, and many more fields. Irrespective of these advantages there are some technological barriers in development of composites. Some of them are obtaining uniform distribution of reinforcement among matrix, high processing cost with methods other than casting, availability of low cost reinforcement and machining of composites after preparation if required. Currently SiC, TiB2, Al2O3, B4C are used as reinforcement with Al alloys. Some research carried out on hybrid composite with fly ash, lignite ash, coconut husk has also given better results than single reinforcement. This paper reviews current development in Aluminum matrix composite preparation, processing methods, mechanical properties and some challenges in development of composites. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials and Manufacturing Applications [IConAMMA 2017]. Keywords: MMC’s; Aluminium Matrix Composites; Powder Metallurgy; Stir Casting
1. Introduction The use of composites began early in the twentieth century with a phenolic paper laminate used for electrical insulation. Composites differ from alloys, polymers, and ceramic compounds in that the matrix and reinforcement is separate from each other. Composite materials are having high potential for replacement of conventional materials in many applications like automobile, defense, aerospace, etc. 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advances in Materials and Manufacturing Applications [IConAMMA 2017].Corresponding Author- +919960936910 [email protected]
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Nomenclature Yc Yf Ym Vf Vm
Young’s Modulus of Composite Young’s Modulus of Fibre Young’s Modulus of matrix Volume fraction of fibre Volume fraction of matrix
Al matrix elements reinforced with SiC, B4C, TiB2, B4C etc. offer many advantages like higher strength to weight ratio, higher tensile strength, hardness, improved toughness, stable thermal properties, higher wear and corrosion resistance. AMCs can be classified into four types depending on the type of reinforcement. Particle-reinforced AMCs (PAMCs) Whisker-or short fibre-reinforced AMCs (SFAMCs) Continuous fibre-reinforced AMCs (CFAMCs) Mono filament-reinforced AMCs (MFAMCs) An attempt has been made in this paper to take a review of Aluminum matrix composite preparation methods, reinforcements used, challenges and opportunities in further development of AMC’s. Al MMC’s have better mechanical and thermal properties compared to conventional metals with considerable low weight. Properties of composite depend upon volume fraction of reinforcement, processing method, distribution of reinforcement [1]. Study carried out for evaluating effect of reinforcement on hardness, impact strength and material toughness, has found almost 2.1 times increase in values of these properties over unreinforced material [2]. Al MMC have better mechanical properties than conventional metals and this has lead to increased use of these MMC’s in automobile and aerospace applications. Quality of composite i.e. properties depends upon processing parameter and choice of material. Use of hybrid reinforcement has lead to much better properties than that obtained with single reinforcement [3]. A considerable increase in wear resistance of Aluminium has been observed with addition of TiB2 as reinforcement [4]. Properties of Al SiC composite can be evaluated by preparing samples with varying percentage of SiC i.e. 5%, 10%, 15% etc. and conducting various tests. Based on experimental results it has been concluded that highest value of hardness, tensile strength and wear resistance have been found at 20% volume fraction of reinforcement but non homogeneous distribution also has been observed in microstructure [5]. Al MMCs prepared with SiC, Al2O3 and Graphene as reinforcement in different volume percentage by powder metallurgy has given best results at 10% volume fraction of reinforcement for SiC and Al2O3 [6]. Microstructure study of Al6082 alloy with Graphite particle as reinforcement has given uneven distribution of reinforcement in matrix and decrease in hardness with addition of Graphite. So it has been suggested that it is not beneficial to add Graphite particle in Al alloy [7]. It has been found that major concern with casting process is non homogeneous distribution of reinforcement and wettability of reinforcement particles. There is need of some simulation technique for casting process as many process parameters need to be controlled for obtaining better results [8]. A synthetic and agro waste derivative has also been used as reinforcement [9]. There is need to investigate more with agro waste derivatives as reinforcement in hybrid composites which have offered better properties over single reinforcement composite. There is no clear relation between volume fraction of reinforcement and composite properties as different researcher have obtained different results, but size of reinforcement particles definitely affect properties of composite and it has been advised to use reduced size particles in order to improve properties [10]. It has been found that fracture toughness and ductility decreases with increasing reinforcement volume fraction. AMC are going to be proved as a potential material in energy and fuel savings with least manufacturing cost. There is need of providing low cost reinforcement materials and processing facility of AMC’s should be made available in affordable cost. AMC processing methods include casting, powder metallurgy, spray deposition, Infiltration process etc [11].
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In Aluminum matrix composites (AMCs), the ceramic reinforcements are generally oxides or carbides or borides such as Al2O3, TiB2, TiO2, SiC, TiC, B4C, etc. The study carried out to investigate effect of these reinforcements on properties of AMC has found that for obtaining improved properties of AMC’s process parameters needs to be controlled precisely. Stir casting is the most economical processing method and process parameter such as stirring speed, stirring time, pouring temperature play an important role in deciding properties of composite [12]. It has been found that there is almost 30% increase in hardness and tensile strength double that of base metal. Aluminium matrix reinforced with Al2O3 gives high strength to weight ratio, high tensile strength, high fracture toughness etc. If reinforcement with submicron or nano sized particles is used it provides better results and almost 92% increase in hardness , 57% increase in tensile strength has been observed compared to pure aluminium [13]. Investigation has been carried out to study effect of lignite fly ash as reinforcement on Aluminum MMC prepared by powder metallurgy. Different samples of composite with 5%, 10%, 15% fly ash has been prepared and these samples were then compacted and sintered at 600oC for two hours and six hours respectively. Various tests conducted on composite samples have given better properties at 15% fly ash content [14]. Hybrid composite formed with fly ash and SiC as reinforcement differs in every aspect from pure aluminium alloy. A significant increase in hardness and tensile strength has been observed with 10% fly ash and 10% SiC. Combination of Al-SiC-Fly ash gives better strength and density found to be decreased with increased reinforcement content. This composite proved to be the best alternative in applications where reduction in weight is desirable [15]. Along with tensile strength impact strength has been found increased but decrease in elongation in tension test indicates brittle nature of material [16]. In situ reaction process has also been used for production of composite by certain chemical reaction. In this process ceramic compound and Mg-Al alloy are place in crucible and allowed to heat for some period in nitrogen gas surrounding. There are some limitations of this method due to combination of metals and chemical reaction [17]. Use of graphite particles as a reinforcement instead of SiC gives better wear resistance and offer improved tribological properties. Hybrid composite developed with Al and 20%SiC and added graphite as solid lubricant has offered low coefficient of friction and show better wear resistance at increased load and speed [18]. Coconut husk is a fibrous material and obtained as a waste after coconut has been used. Is such waste is used as reinforcement it will certainly reduce production cost of composite. Also porosity level has been found increased which decreases density of material [19]. Al composites offer better corrosion resistance than pure Aluminum at room temperature. Corrosion resistance has been found to be increased linearly with increasing volume fraction of reinforcement and reinforcement particle size. But with increasing temperature corrosion rate also increases for Al composite [23]. Carbonized maize stalk waste has also been used as reinforcement in Al-Mg-Si alloy and has given improved properties than pure aluminium [24]. Al-TiC composite prepared by powder metallurgy technique has been proved useful for structural applications. Al composite with other ceramic reinforcements such as SiC, Al2O3, and TiB2 also has been studied by various researchers [27]. 2. Reinforcement materials The reinforcement used varies from short fibres, flakes, and particles to filament and wires to continuous woven fibres and honeycomb. The metal matrix composites use metal alloys for their matrices with reinforcement provided by particle or filament of high performance materials [20]. Examples of discontinuous materials are glass fibres, silicon carbide whiskers, and alumina particles or short polymer fibres; continuous fibres may be of carbon, boron, alumina, or silicon carbide. 3. Preparation of Aluminum Based Metal Matrix Composite Many composites require two processes before they are able to meet a material need, the first one to create the composite itself and the second to shape or fit the composite materials to final application. In other cases a composite may be prepared and shaped to meet final requirement on one step. 3.1 Liquid State Processing-The most straight forward of the MMC methods involves casting the molten metal around solid reinforcement, using either conventional casting techniques or a pressurized gas on the liquid matrix to
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force it into and around a preformed reinforcement which is often made of metal sheet or wire, or ceramic fibre. Figure 1 shows schematic set up used for preparing composite material by stir casting method. Though stir casting has proved most economical preparation method, and variety of shapes and sizes can be cast from this process but obtaining homogeneous reinforcement distribution is major limitation of this process. 3.2 Powder Metallurgy Technique- The reinforcement fibres, whiskers or particles are carefully mixed with the powdered metallic matrix so they are uniformly distributed in the mixture. The mixture of powdered metal and reinforcement is then compacted to form the desired part. An initial compacting may be done cold, followed by sintering or all the compacting may be done at the sintering temperature. The sintering fuses the various particles together into a shape and size that should be very close the desired dimensions.
Fig.1 Schematic set up for Stir casting [5]
3.3 Liquid Solid Processing- This is casting technology in which the reinforcement being added to the metallic matrix is in the mushy state that is partly frozen, partly liquid. 3.4 Spark Plasma Sintering- Composites can be sintered by spark plasma, created by pulsed direct current; it leads to increase in powder and mold temperature. The sintering process is carried out under high pulse direct current in vacuum. Uniaxial pressure of 10Mpa is applied and increased to 20 MPa. Once sufficient temperature is reached pressure is decreased to 10 MPa and maintained for cooling time [25]. Even Al composite can be produced by microwave heating saving energy and time [26]. Ultrasonic assisted squeeze casting process has shown better grain refinement compared with composite prepared by stir casting [28]. Table 1 Comparison of Composite Preparation Methods Process Stir Casting Parameter Reinforcement Inhomogeneous distribution Distribution Wettability Poor, Some reagent required Mechanical Good Properties Cost Most cost effective Volume Fraction Up to 20%, Range of shape Not limited by size and size
Powder Metallurgy Homogeneous distribution Better Best results obtained Expensive More than 30% possible Varity of shapes, size limited
4. Mechanical Properties 4.1 Tensile strength In composite materials an attempt is made to increase the stiffness without the disadvantage of brittleness. Ductile materials withstand accidental overloading without catastrophic failure and these materials are suitable for structural
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components. The density of composite being quite low, it can compete in terms of stiffness and strength for the same weight with some of the high strength steels. Improvement in tensile strength in composite has been shown in Fig.2 for fly ash and SiC. 4.1.1Young’s Modulus The stiffness of a material is its ability to resist elastic deformation on loading. The stiffness is dependent on the shape of the structural component. For identical shapes, it is proportional to elastic modulus. Therefore elastic modulus is an important material parameter in mechanical design. The young’s modulus Yc of a composite in a direction parallel to the fibers can be expressed as a linear function of the moduli of the fibre and the matrix, Yf and Ym[21]. Yc=VfYf+VmYm Where Vf and Vm are the volume fraction of the fibre and the matrix. Thus a 40 volume percent of boron in an aluminum matrix can raise the Young’s modulus from 71 GN/m2 for pure aluminum to 219 GN/m2 for composite. This composite would then be as stiff as steel but less than one third its density. The volume fraction of the fibre in a composite cannot be increased indefinitely as at some stage the problems of aligning the fibres and keeping them separated from one another becomes serious.
(a)
(b) Fig.2 Tensile Strength of composite for various (a) Wt % of Fly ash [22] (b) Wt % of SiC
4.2 Hardness The property of hardness is related to the elastic and plastic properties of metals. Hardness of composite material has been found to be increased with addition of reinforcement percentage. Figure 3 shows increase in hardness of composite with addition of reinforcement for SiC and Al2O3. More increased in hardness value leads to brittleness and such components are susceptible to catastrophic failure in variable and high loading.
(a)
(b) Fig.3 Hardness values for various weight (a) ) % of Al2O3 as reinforcement [22] (b) % of SiC
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4.3 Toughness Toughness is function of rate of loading, temperature and notch effect, and it has been observed that toughness goes on decreasing with increase in loading and temperature. The fracture resistance of a material in the presence of cracks or discontinuities is known as its fracture toughness. Increasing fracture toughness in composite materials is one of the challenges in front of researchers. 4.4 Microstructure Composite samples itched with dilute acid and having mirror finish are observed under metallurgical microscope at 500X, 3000X or even higher magnification in order to observe microstructure of material, it reveals distribution of reinforcement in matrix, if some defects present in cast component, in case of processing has been done by casting, such as blow holes, micro pores. 4.5 Wear resistance Wear resistance of composite is measured by pin on disc method. Wear rate per unit amount of reinforcement has been considered for defining load carrying capacity of composite by many researchers. Wear resistance is a function of volume fraction of reinforcement and it is not a function of hardness. 4.6 Corrosion resistance Initially Oxidation was the term used to describe chemical reaction occurring on metal surface with surrounding, now days it has been replaced by corrosion. Metals react with their service environment and leads to oxidation, so coatings are provided on conventional materials to prevent oxidation. Aluminum has its natural ability to prevent corrosion. 5. Process variables and their effects on properties Process variables need to be controlled while preparing composite for obtaining better results. Many researchers have investigated effect of process variables on composite properties, some of them have been described below. 5.1 Speed of rotation Rotational speed of stirrer is kept near about 10m/sec and in this case stirring time is also important. After initial stirring vortex is formed in metal and after reinforcement has been poured it is stirred for almost 10 minutes so that it get properly mixed with molten metal. 5.2 Pouring temperature Reinforcement particles are preheated and poured into molten metal. Pouring temperature should be sufficiently high so that strong bond should be formed between reinforcement and matrix. If pouring temperature is low molten metal will start solidifying and it leads to improper mixing of reinforcement. 5.3 Pouring speed Major problem associated with stir casting process is segregation of reinforcement particle on molten metal surface. Pouring speed is important factor to be controlled for proper mixing, so slow pouring speed is advisable while preparing composite. 6. Challenges and opportunities The composite material has been proved as a potential alternative for replacement of conventional materials, but still there are some barriers in development and research of these materials. i. Major concern in front of researchers is obtaining more better properties of composite, which depends up on processing method, composition and process parameters.. ii. Obtaining homogeneous distribution of reinforcement in matrix is major challenge with casting process, which has been proved as the most favorable processing route. iii. Composite development starts almost on 70’s, but still no standardization has been performed related to process parameter, composition, etc. Some standardization institutes should carry out work in controlled environment and some standardized norms should be formulated in connection with composite preparation.
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iv. v.
vi. vii.
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Some research should be carried out for using some low cost material such as agriculture waste as a reinforcement, which will help in reducing overall cost of composite. In India currently there are very few manufactures working with Aluminum sintered components, so only option taken by most is casting. There should be some policy from government side to promote development and use of light weight composites so that manufacturers get attracted towards these materials. If process parameters controlled properly composite material certainly replace conventional material in many fields, especially automobile and bring revolution in this field. It is light weight, high strength, having more wear and corrosion resistance, more toughness. Due to presence of hard reinforcement it is difficult to machine composite and good surface finish and integrity. Graphite reinforcement has better lubricating property and its presence in composite improves machinability [29].
7. Conclusion From the review carried out above following conclusions have been drawn, i. The major advantage of composite material is high strength and low weight. When composite material is 40 percent aluminium and 60 percent alumina the resulting tensile strength and modulus of elasticity are about three and half times that of heat treated aluminium. ii. Composite material has properties that are higher than those of steel but at 45 percent the weight. iii. Large components can more easily be made from composite materials than from metals. iv. Further research can be carried out on heat treatment methods for composite, which will help in obtaining more improved properties. v. There should be some initiative from standardization authorities and government in developing standardized norms for composite processing and promoting their use in many engineering field areas. Acknowledgement Author acknowledges support from faculties of SVPM Institute of Technology and Engineering Malegaon (BK) for their support. References [1] Amitesh, V.C.Kale, Aluminium Based Metal Matrix Composites for Aerospace Application: A Literature Review, IOSR Journal of Mechanical and Civil Engineering, Volume 12, Issue 6 Ver. V (Nov. - Dec. 2015), PP 31-36. [2] Ali Hubi Haleem, Newal Muhammad Dawood, Silicon Carbide Particle Reinforced Aluminum Matrix Composite Prepared by Stir-Casting Babylon University –Materials Engineering Collage. [3] J.Jenix Rino, D.Chandramohan, K.S.Sucitharan,An Overview on Development of Aluminium Metal Matrix Composites with Hybrid Reinforcement, International Journal of Science and Research (IJSR), India Online ISSN: 2319‐7064, Volume 1 Issue 3, December 2012, pp196203 [4] S Suresh, N, Shenbaga Vinayaga Moorthy, Aluminum Titanium Diboride MMC: Challenges and Opportunities, Procedia Engineering 38, 2012, pp 89-97. [5] Md. Habibur Rahmana, H. M. Mamun Al Rashed, Characterization of silicon carbide reinforced aluminum matrix composites, Procedia Engineering 90 (2014), pp 103 – 109 [6] P. Ashwatha, M. Anthony Xavior, The Effect of Ball Milling & Reinforcement Percentage on Sintered Samples of Aluminium Alloy Metal Matrix Composites, Procedia Engineering 97 (2014), pp 1027 – 1032. [7] Pardeep Sharma, Satpal Sharma, Dinesh Khanduja A study on microstructure of aluminium matrix composites, Journal of Asian Ceramic Societies 3 (2015) 240–244. [8] Sijo M T, K R Jayadevan, Analysis of stir cast aluminium silicon carbide metal matrix composite: A comprehensive review, Procedia Technology 24 (2016), pp- 379 – 385. [9] Michael Oluwatosin Bodunrin, Kenneth Kanayo Alaneme, Lesley Heath Chown, Aluminium matrix hybrid composites: a review of reinforcement philosophies; mechanical, corrosion and tribological characteristics, Journal of Material Technology, 2015; 4(4), pp 434–445. [10] R. S. Rana. Rajesh Purohit,S.Das, Review of recent Studies in Al matrix composites, International Journal of Scientific & Engineering Research Volume 3, Issue 6, June-2012. [11] M K Surappa, Aluminium matrix composites: Challenges and opportunities, Sadhana Vol. 28, Parts 1 & 2, February/April 2003, pp. 319– 334. [12] C. Saravanan, K. Subramanian, V. Ananda Krishnan, R. Sankara Narayanan, Effect of Particulate Reinforced Aluminium Metal Matrix Composite –A Review, Mechanics and Mechanical Engineering, Vol. 19, No. 1 (2015) 23–30.
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