effect of rock dust, cenosphere and e-waste glass addition...

Indian Journal of Engineering & Materials Sciences Vol. 24, August 2017, pp. 270-282

Effect of rock dust, cenosphere and E-waste glass addition on mechanical, wear and machinability behaviour of Al 6061 hybrid composites

K Soorya Prakash*, P M Gopal & V Kavimani Department of Mechanical Engineering, Anna University Regional Campus Coimbatore, Coimbatore 641 046, India

Received 29 January 2016; accepted 20 February 2017

This paper has a propensity to identify low cost and ordinarily available reinforcements besides comparatively reviewing fly ash, bagasse ash, rice husk ash reinforced aluminium composites. This has led to microstructure, mechanical and wear characteristic investigation of newer composite developed through stir casting with cenosphere, rock dust and e-waste cathode ray tube (CRT) panel glass powder. Comparison over experimental results with available reported data of said reinforcements clarifies that newer reinforcements have also yielded equivalent properties. Addition of these newer reinforcements up to 10% increases the tensile strength whereas maximum of 65.12% hardness raise is attained for cenosphere and 63.04% for CRT addition to that of Al 6061 T6. Tensile strength increases up to 9.84% for 15% cenosphere reinforcement, 9.02% for 10% CRT addition. Addition of cenosphere and rock dust up to 15% increases the wear resistance but in the case of CRT powder, wear resistance is high up to 10% and then decreases due to formation of glass globes for further CRT addition. In perspective of the research an admissible increment in wear resistance and machinability of the developed novel hybrid composites is evidenced through scanning electron microscope (SEM) micrographs besides indicating better surface finish while turning.

Keywords: Composite, Cenosphere, Rock dust, CRT, Wear, Machining Aluminium is the lightest material next to magnesium and hence widely used in many industrial applications. Aluminium compounds make up a full 8% of the Earth’s crust in variety of forms. The properties of aluminium include: low density and therefore low weight, high strength, greater malleability, uncomplicated machining, admirable corrosion resistance and fine thermal and electrical conductivity. One of the best known properties of aluminium besides being easily recyclable is that it is light, with a density of 2.7 kg/m3 which accounts only for one third as that of steel. These valuable points make aluminium as the second most metal used in the world next to iron. Conversely the foremost negative aspect of aluminium materials is its poor wear resistance when compared to steel and only for this said cause aluminium could not replace steel in most of their suitable applications.

Aluminium based metal matrix composites (MMC) are introduced to overcome these snags of base alloys in which the hard reinforcements are added to base metals. Mostly oxides, nitrides and carbides of aluminium, boron and silicon are used as the reinforcing material, i.e., in the form of Al2O3, BN, SiC, etc1,2. Even though the reinforced composites

possess well improved properties, their cost is the major point which drags back their successful commercialization. The major things that influence the material cost are reinforcements and composite production methods. In the recent past, newer techniques like stir casting3, powder metallurgy4, rheo casting5 and infiltration techniques6 were thoroughly instigated and are supposed to be the most commonly used methods in development of particulate reinforced composites. It is already proven that stir casting is the least expensive method for composite fabrication when compared to other processes7. Further the composites obtained through this method exhibit higher hardness and compressive strength compared to powder metallurgy processed components8. Therefore, it has become an alarming work of art and is also indispensable to discover suitable low cost reinforcements in order to reduce the cost of material. Again from the global scenario it is important to notify that the low cost reinforcements might be of naturally available or reuse of fallow/obsolete products or else should be a waste by-product.

As directed by these originations, many low cost reinforcements are attempted in the past and typically that are ashes of rice husk, bagasse, coal (fly ash) and lately fly ash cenosphere have found attention9-12. The

___________________ *Corresponding author (E-mail: [email protected])

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most common thing is that these reinforcements are silica rich. Since these reinforcements are acquired from the leftover materials, they are also inexpensive. Hardness of Al MMC increases while density decreases by fly ash addition when compared to the base alloy and also improvisation in mechanical properties were identified under compression13. Similarly hardness, tensile and compression strength of Al alloy has increased to a greater extent whereas ductility decreases with eventual increase in weight fraction of rice husk ash10. Likewise, number of researchers used these reinforcements and found considerable improvements in properties which may possibly be compared to composites reinforced with costlier reinforcements. For the aforementioned causes, the current work hails in to identify silica rich reinforcements that are abundantly available on earth without being given any considerations.

Rock dust (RD) is a naturally available abundant material with higher silica content. Additionally, it was observed that elements existing in rock dust are virtually a replica of elemental contents of fly ash, i.e., most of the elements in both rock dust and fly ash are similar with a negligible deviation in available percentage. Rock dust can be collected from stone crushing/processing plants or quarries with ease, however the major bottleneck is that its chemical composition varies with locality since it is a natural element acquired from earth’s crust.

Globally 50 million ton of E-waste is produced annually and major share of the E-waste is hold by televisions (TV) and monitors. CRT is accounted as 55% of the entire weight of a TV and 32% of the computer monitor and CRT contains 85% glass14. CRT glass identifies major attention here in electronic waste recycling for the reason of discomfort it upholds due to their large volume, recycling cost and toxicity15. A thorough insight over the available literatures and further study on manufacturer’s catalogue details that there is no significant difference in composition of CRT glasses produced by diverse manufactures. But it is reported that there could be significant difference in composition of colour CRTs and aged black and white CRTs16. So, it is clear that mix and match of either black and white (B/W) or colour CRT glasses of different manufactures is

possible but anyhow B/W and colour CRT cannot be crushed together for analysis. As it is difficult to dump or store because of large volume accumulations, these CRT glasses have to be reused in any other different way to avoid landfills. Amongst the four main components of CRTs namely glass panel, shadow mask, glass funnel and electron gun, the panel glass weighs two third of total CRT and has rich silica content. CRTs have more silica ( 60%) content which makes a strong and attentive point that why it cannot be reused as reinforcement in MMCs. At this juncture and based on the above said artefacts, the current study emphasis on usage of rock dust and CRT panel glass powder obtained by crushing outdated colour CRT monitors.

All the vital properties were investigated for the newly developed composites. Further the obtained results were compared with the properties of existing composites reinforced with rice husk ash, bagasse ash and fly ash supposed to be fabricated through the same method (stir casting). There are many composites reported in the literatures with rice husk ash, bagasse ash and fly ash reinforced aluminium composites their base metal grade differs, i.e., Al 6061, Al7%Si, etc which possess different properties in nature. With these consequences, this study put in efforts to consider the percentage effect of reinforcement on the base metal instead of simply comparing the property values of developed composites. It is inevitable to demonstrate the functionality characteristics and machining paradigms of the newly developed composite so as to make it a candidate material for commercial applications. Therefore, after the comparative study, wear and machinability behaviour of the composite with newer reinforcements were studied and tested in detail for the composite specimens fabricated with and without graphite addition

Experimental Procedure

Materials Aluminium 6061 T6 alloy was chosen as the base

metal as it highly motivates for its inherent properties besides promoting relatively good strength, workability nature and wide availability and most importantly lower in cost. Chemical composition of the base metal utilized for this novel research is shown in Table 1.

Table 1 Chemical composition of Al6061

Element Mg Si Fe Cu Ti Cr Zn Mn Al wt% 0.88 0.65 0.24 0.23 0.1 0.14 0.08 0.03 97.65

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As of the reinforcements are concerned cenosphere is purchased as such from the market. Rock dust is collected from the nearby quarries and CRT glass powder is prepared through crushing the colour CRT panel glass by manual hammering. Irrespective of the type of reinforcement, ball milling method was used for size reduction and thereby uniform particle size in an acceptable range was succeeded. Ball milling was performed in a stainless steel (SS) vessel setup whereas the SS ball to powder ratio is maintained as 5:1. Ball milled particles were characterized through SEM and EDS (energy-dispersive X-ray spectroscopy) analysis in ZEISS (SIGMA HV – Carl Zeiss with Bruker Quantax 200 – Z10 EDS Detector) setup and the results are shown as Figs 1 and 2, respectively. From the SEM micrographs it can be noted that the particles are coarse. It is a known fact that coarse particles do not agglomerate as of finer particles and

hence the coarse particles were preferred as such for composite preparation through stir casting route. Further analysis over the SEM results reveal that the size of the obtained cenosphere, rock dust and CRT particles were found approximating in the range of 40 µm.

The state of affairs being very new for the identified materials, with the help of EDS analysis chemical composition of cenosphere, rock dust and CRT powder were found and the same is given in Fig. 2. As demanded, the composition of rival low cost reinforcements already castoff were obtained from literatures and given in Table 2 so as to understand the precedence of the utilized reinforcements nature. Also, the presence of higher range of silicon and oxides in reinforcements can easily be confirmed by examining the EDS patterns. An eye over the EDS results reveals that composition of CRT powder

Fig. 1 SEM micrographs of reinforcements

Fig. 2 EDS spectrum of reinforcements


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differs from other reinforcements due to the presence of BaO, SrO and ZrO2. Yet again an in-depth exploration of the literatures discloses that addition of these different elements into the matrix will definitely enhance the vital properties like hardness and tensile strength17,18. Hence overseen by these interpretations it is hardly believed that presence of these elements in CRT powder will act as a beneficiary and improve the properties of the composite developed. The term “others” denoted in Table 2 represents for balance of compositional elements that includes negligible amount of Li2O, CeO2, As2O3 etc. Method

Stir casting method was chosen to fabricate the novel composite wherein the reinforcement is added with molten metal and mechanically stirred to get the uniform distribution of reinforcements. The setup utilized for composite fabrication is shown in Fig. 3. Initially to understand the addition behaviour, on trial and error basis reinforcements were added up to 25% but could not yield better results, as a consequence it was then started to gradually reduce the mixing proportions. Further it was confirmed that increase in reinforcement from 10% to 20% reduces the mechanical properties of the material4 and so in this study maximum of 15% reinforcements were added. The reinforcement percentage was varied at 5, 10 and 15 wt% for cenosphere, rock dust and CRT powder. Kok19 stated that the optimum conditions for the composite production in stir casting process be as pouring temperature was 700oC, preheated temperature of the mold was 550oC, the speed of stirring was 900 rpm and after completion of particle feeding the stirring time should be 5 min. The same parameter range was fixed for the current study also.

Initially the reinforcements were weighed and preheated in muffle furnace at 350oC. Base metal is

melted in the graphite crucible by using induction furnace maintained at 700oC and then preheated reinforcements were added. In addition to this, as a standard procedure 1.5% of magnesium is added to increase the wettability of developed MMC. In order to get uniform distribution of the reinforcement particles, the mixture is continuously stirred for 5 min using mechanical stirrer holding a rotational speed of 900 rpm. Then the mixture is poured into preheated die to acquire desired shape of the component. A base metal sample was also fabricated for comparison and nine samples of specified composition as shown in Fig. 4 were fabricated. There are no blow holes and even any other surface defects could not be detected in a naked eye view. This possibly may be due to the adoption of optimum casting conditions. Testing of MMC

SEM analysis is a widely utilized method for analyzing microstructure of the materials. In this context, the developed cenosphere, rock dust and CRT reinforced composites are analyzed through SEM in

Table 2 Chemical composition of reinforcements

Some common elements in selected reinforcements (in wt%) Constituent SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O TiO2 SO3 LOI Rice husk ash9 97.09 1.13 0.31 0.07 0.82 0.09 0.18 - 0.14 0.96 Bagasse ash9 77.28 10.95 3.66 2.08 1.48 0.38 3.15 - 0.48 3.27 Fly ash11 59.96 28.44 8.85 - - - - 2.75 - 1.43 Cenosphere 59.4 28.7 6.3 2.3 0.6 0.5 1.4 0.8 - - Rock dust 51 18.4 9.29 10.2 5 2.1 0.59 0.78 - - CRT 61.00 3.50 0.12 2.00 1.00 6.00 4.50 0.6 - -

Other Elements in CRT (in wt%)

Constituent BaO PbO SrO Sb2O3 ZnO ZrO2 Others 7.00 1.10 8.12 0.50 0.4 1.8 2.36

Fig. 3 Stir casting setup used for composite fabrication


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view of confirming the presence of reinforcement particles. Hardness of the developed composites is identified through Brinell hardness tester at an applied load of 500 kg retained for a period of 15 s in accordance with ASTM E10 (American Society for Testing and Materials) standards. Mostly hardness value was measured at five different locations over the surface of sample composite specimen and then the average of these values was calculated for establishing the hardness. The tensile tests were conducted according to ASTM E08 standards using a system integrated Universal Testing Machine (UTM) maintained at room temperature. The test specimens used were machined from the as cast composites with holding diameter of 12 mm and gauge length of 40 mm such that gauge length of the specimen is parallel to the longitudinal axis of the casting specimen. Pin on disc test method shown in Fig. 5 was used to analyze the wear behaviour of the developed composites under dry

conditions. As a procedure, the pin made of developed composite slides against harder surface (EN 32 steel with a hardness of 65 HRC (Rockwell Hardness C scale)). ASTM G99 standard was followed for conducting wear analysis and therefore the composite samples are prepared for 30 mm length and 10 mm diameter. During dry sliding wear examination, the testing parameters were kept constant as follows: applied load 30 N, velocity 4 m/s and sliding distance 1000 m.

Results and Discussion

Microstructure

From the SEM micrographs represented as Fig. 6, it is evident that the reinforcements are distributed evenly and perhaps a homogeneous mixture of the matrix material can be notified. Again it is observed clearly from SEM micrographs that the distributions of cenosphere and rock dust particles are more uniform than the dispersal of CRT powder. This may be due to the amorphous nature of the CRT glass which agglomerates on heating and in turn forms glass globe20.

As of the examinations over the SEM micrographs it was experiential to say that the porosity level has well decreased for composites when compared to base metal. These identities make evident that the micro sized particles have got infused well in to the matrix which in turn results in less porosity. All over the composite specimen there was no substantiation of voids and discontinuities. The EDS analysis is also performed for newly developed composites for confirming the presence of reinforcements and the same is presented as Fig. 7. The peak indicating

Fig. 4 As cast specimens

Fig. 5 Pin on disc wear test setup


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silicon and other oxide presence varies for each composite due to the specific nature of reinforcement added.

Observance over the SEM and EDS results feasibly generate a confirmation study in close adherence to the specific aim of this work, i.e., all the newer

Fig. 6 SEM micrographs of developed composites

Fig. 7 EDS pattern of the composite samples


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reinforcements could possibly act as a promising reinforcement material and can further subjective for generic property evaluation. This proclamation upon newly introduced reinforcements is because microstructural analysis of the material plays important role in characterizing the materials performance besides helping in functional property considerate. Hardness

Hardness of the developed composites increases with increase in reinforcement level and has fine conformity with all other rival low cost composites performance. This property increase is due to the presence of reinforcement particles which increases the surface area of the matrix. Existence of these harder surface areas provides more resistance to plastic deformation which results in increased hardness10.

Hardness of the composite increases with increase in reinforcement for all the reinforcements considered except for CRT panel glass powder as shown in Table 3. Addition of CRT powder more than 10% (i.e. 15%) decreases the hardness of composite up to 72 BHN (Brinell Hardness Number) which is around 76 BHN for the composite reinforced with 10% CRT powder. Further it was observed that there is drastic difference in hardness at different places of 15% CRT powder

reinforced composite and might be due to the uneven distribution of reinforcements. Consequently higher hardness could be discovered at the areas where reinforcement presence was tangible and lower hardness was observed at the areas where negligible amount of reinforcement is present. From Table 3 it is apparent that when compared to the base metal, an increment of 65.22% hardness was attained for addition of 15% cenosphere and around 63.04% increase for 10% CRT panel glass powder addition. This property increase is very high when compared to rice husk and bagasse ash addition. Even though it is somewhat similar to those of composite with fly ash addition, the newly developed composites are slightly harder than fly ash composites.

Addition of 10% CRT powder yields better results when compared to that of composite with 15% fly ash and cenosphere additions. Upon experimentation the major problem encountered is the agglomeration of CRT powder when added at higher level and this characteristic nature was supposed to further supplement for performance shrunk of the composite. So it is believed that once agglomeration of CRT is avoided by the way of doping or stabilizing with other elements or by any other means, definitely a considerable increase in the amount of reinforcement

Table 3 Hardness of the MMCs

Base Metal Reinforcement Reinforcement Percentage Hardness UNIT % Increase Reference

Al -7%Si Rice husk ash

0 70

HV

-

9 5 79 12.86 10 89 27.14 15 96 37.14

Al -7%Si Bagasse ash

0 70 -

9 5 73 4.29 10 78 11.43 15 83 18.47

Al 6061 Fly ash

0 48

BHN

-

11 10 62 29.16 15 68 41.67 20 78 62.5

Al 6061 Cenosphere

0 46 -

Experimental values

5 61 32.61 10 66 43.48 15 76 65.22

Al 6061

Rock dust

0 46 -

5 48 4.35

10 57 23.91

15 74 60.87

Al 6061 CRT

0 46 - 5 62 34.78 10 75 63.04 15 72 56.52

HV-Vickers Pyramid Number, BHN - Brinell Hardness Number


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may be possible and so property enhancement could be irresistible. On the other hand, this problem can also be eliminated by employing solid state processing methods for composite fabrication through which higher level of uniform distribution of reinforcements can be obtained. Tensile strength

From Table 4 it is perceptible that tensile strength increases with increase in reinforcement level up to 10%. As far as the reinforcement are well below 10%, only a fewer amount of reinforcing particles are made available and hence more of ductile matrix could only be experienced. This compositional tendency certainly will separate the reinforcing particulates from each other and thereby sustains or improves the ductility of composites. By isolating the reinforcing particulates, adhesive force between the matrix and the reinforcement increases in the case of smaller amount of reinforcement in the matrix which leads to increase in tensile strength21. It can be noted that, on loading reinforcement particles in the matrix definitely obstructs the dislocations and in consequence leads to improved strength.

Further it can be observed that increase in reinforcement level over 10% (i.e. 15%) decreases the tensile strength for all type of reinforcements and is

given in Table 4. This effect could happen because higher reinforcement will be an add-on supplementary for crack initiation causing reduction on the load bearing capacity and subsequently the tensile strength. Comparing the effects of reinforcements on matrix metal it is for sure that tensile strength of the developed composites ensues well within the satisfactory limits and also express consistency with other rival materials considered from referenced literatures. Tensile strength increases up to 9.84% for 10% cenosphere reinforcement, 9.02% for 10% CRT addition which is almost equal to that of rice husk ash (9.70%) reinforcement. Hence these outcomes prove to be a manifestation for admittance of these newer reinforcements introduced through this study and possess improved tensile properties than that of similar other rival materials in existence. Wear

Wear rate is examined for the different composite specimens at specified regular testing conditions were as illustrated in Fig. 8, which aid in to demonstrate that wear rate of the material has reduced greatly due to identical presence of harder reinforcements. Correspondingly its known through trialling that increase in reinforcement level have significantly decreased the material loss in case of cenosphere and

Table 4 Tensile strength of the MMCs

Base Metal Reinforcement Reinforcement Percentage Tensile strength (MPa) % Increase Reference

Al -7%Si Rice husk ash

0 165 -

9 5 175 6.06

10 181 9.70 15 169 2.42

Al -7%Si Bagasse ash

0 165 -

9 5 173 4.85

10 177 7.27 15 150 -9.09

Al 6061 Fly ash

0 124 -

11 10 128 3.23 15 130 4.84 20 129 4.00

Al 6061 Cenosphere

0 122 -

Experimental values

5 126 3.28 10 134 9.84 15 128 4.91

Al 6061

Rock dust

0 122 -

5 124 1.64

10 131 7.38

15 128 4.91

Al 6061 CRT

0 122 - 5 127 4.10

10 133 9.02 15 129 5.74


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rock dust; rather for CRT powder the wear rate decreases gradually up to 10% and further addition of CRT powder increased the degree of wear.

Presence of silicon and aluminium like elements in the form of oxides prominently helps these newer reinforcements to provide better wear properties. Introduction of these low cost, easily available reinforcements increases the wear resistance of the stir cast composite materials to a better extent but the difference being made through reinforcement level. Among the considered and experimented reinforcements, cenosphere and CRT powder additions offers better wear resistance than rock dust. In case of cenosphere and CRT powder, it was observed that the later provides better wear resistance than former. But the addition of CRT powder over 10% reduces the resistance to wear due to non uniform distribution in the matrix.

Since the CRT is a glass of amorphous nature it obviously tends in for agglomeration of particles on heating and further tries to form glass globe at ease. The same is a notified case in this study for higher addition of CRT powder and also further endorses for nonuniform distribution of particles. The same problem was faced by Hoseini and Meratian20 while fabricating aluminium-alumina composite by using glass powder. Further they suggest that formation of this glass globe (clustering of glass particles) can be eliminated by introducing copper oxide or similar other particles into the matrix which again suits well for strategic enhancement of the current study. This may possibly be achieved by the way of evolving a hybrid composite through addition of ball milled graphite for being proven that it reduces the materials affinity towards agglomeration22. Hybrid composite

Graphite is the most widely used solid lubricant and gives better results for Al MMCs reinforced with

SiC, Al2O3 and B4C. Addition of graphite into the aluminium matrix in lower level (3%) also decreases the mechanical properties23. But, Suresh et al. 24 found that addition of 2% graphite with Al6061 composite increases the mechanical properties. So the novel hybrid composite was fabricated with 2% addition of graphite to the same aforesaid proportions; this is for the reason that these material mixtures satisfy the basic requirements for further study. Developed hybrid composite is tested for hardness, strength, wear as well as for their machining characteristics. In this paper, it is illustrious to say that accumulation of lower percentage of graphite to the existing material mixture did not yield ample significant changes in hardness and tensile strength. It is also important to state that as perceived, the addition of graphite did not furnish better improvements in avoiding the property of agglomeration. Consequently, the effect of graphite particles performing as a lubricant in the material mixture may tend to decrease the coefficient of friction between the MMC and counterpart in contact. Wear performance

Wear test is performed under the same testing conditions as reported earlier in this paper. The attained result confirms that even a minor inclusion of graphite particles affects the materials tendency to resist wear. This possibly could be for the reason that graphite act as a lubricating layer between the sliding surfaces and hence the inference of less friction and heat generation25. The comparison of wear loss data for with and without graphite particles clarifies that significant reductions on wear could be witnessed and are shown in Fig. 9. From the time graph represented as Fig. 10 it can be observed that the wear rate of the composite increases with simultaneous increase in time. This is due to the fact that the heat generated during sliding increases with time and in turn results in softening the material. As a supportive fiction for the said artefacts, through Fig. 11 representations of the worn out surface micrographs of the composite samples that fashioned superior (Al+10% CRT) and comparatively inferior (Al+5% Rock dust) wear performances are given.

Figure 11a shows the presence of rock dust particles in the worn out surface and the grooves developed due to loss of material during sliding against a disc made of harder material. Additionally, a close magnification on the obtained micrographs notifies that the grooves are wide enough in its direction and so perceive as an indication for a state

Fig. 8 Wear rate of the developed composites


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of higher wear loss. Analyzing the micrographs shown in Fig. 11b, it is seen that the surface is smooth due to the presence of soft lubricant layer and also the grooves have become shallower when compared to the worn surface of composite without graphite. These phenomenal existences in conjunction to the

literatures prove that the addition of graphite have improved wear resistance.

In the case of 10% CRT reinforced composites, the worn out surface did not exhibit any noteworthy grooves as of rock dust composite which again confirms for improvised wear resistance. Fine scratches are observed over the surface and fine cracks could also be detected as distinguished in Fig. 11c. On the other hand while graphite was added cracks does not appear, but presence of micro voids could easily be observed as showcased in Fig. 11d. A possible cause for this could be the removal of soft graphite from the matrix that tends to reform as a lubricant layer during sliding. The existence of this lubricant layer restricts the further loss of material26.

Fig. 9 Effect of reinforcement and graphite on wear loss

Fig. 10 Wear rate of 10% CRT composite with respect to time

Fig. 11 SEM micrograph of samples after wear test


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Machining

Every material should undergo at least minor machining to get finished and certainly surface roughness of the material plays an important role in characterizing their performance. So, machinability of the developed composites has to be checked for eventual appreciations. The developed composites with and without addition of graphite is turned using CNC (Computer Numerical Control) turning centre at no lubricant condition using a carbide tool. Turning parameters namely speed: 1273 rpm, feed: 0.1 mm/rev and depth of cut: 0.2 mm were kept constant. As resembled in Fig. 12, each specimen was machined for the specified constants at least for three distinctions. Obviously such type of machining attributes will help in to attain better results while subjected for surface testing. Surface roughness of the machined areas was measured at various locations using MITUTOYO SJ-201 surface roughness tester and the average of the test results were calculated and given in Table 5.

Continuous chips were produced during machining of composite without graphite addition. However, a small discontinuous chip was the outcome while machining graphite supplemented hybrid composites27. This shows that the machinability nature of newly developed low cost material reinforced composite increases with graphite addition and this can be further confirmed from the data given in Table 5 which shows that surface roughness of the hybrid composite is less than that of the composite without graphite.

Table 5 explicit a spontaneous comparison and denotes that aluminium reinforced with 5% CRT provides better surface finish and that with 15% cenosphere addition gives poor surface finish. Surface roughness of the material is hardness dependent and yet again resembled in this study, i.e., composite with 15% cenosphere gives better hardness which in turn offers poor surface roughness for the reason that hard reinforcement offers higher roughness values27. For the reason that harder material provides higher resistance to deformation while machining and it results in higher friction and exploits tool work interface temperature. Higher interface temperature softens the tool which in turn reduces the performance. Addition of 2% graphite lowers the surface roughness value by acting as a lubricant between the tool and work samples which effects in to have lower friction and thereby attain good surface finish.

Since rough turning is performed under no lubricant conditions, the obtained surface is coarser and is apparent when looked through SEM micrographs of the machined surface shown as Fig. 13. Smooth surface was obtained for the composites with graphite when compared to composite samples without graphite inclusions. In Figs 13a and 13c larger grooves are visible over the machined surface which could presumed to be the indication of tool travel path over the samples without graphite. This could possibly be for the reasons that increase in tool work interface temperature soften the tool tip. In the case of graphite added composites micrographed in Figs 13b and 13d the grooves become shallow and demonstrates better surface finish than former. Presence of graphite layer curbs the heat generation which determines for better tool life and performance. Harder materials always give poor surface finish, because harder materials require higher force to deform plastically and hence from the comparatives,

Fig. 12 Composite samples after machining

Table 5 Surface roughness of machined surface

Sl.No Material Surface Roughness (µm)

Without Graphite

With Graphite

1. Al 6061 0.98 0.86 2. Al 6061 + 5% Cenosphere 1.28 1.14 3. Al 6061 + 10% Cenosphere 1.38 1.23 4. Al 6061 + 15% Cenosphere 1.46 1.32 5. Al 6061 + 5% Rock dust 1.26 1.14 6. Al 6061 + 10% Rock dust 1.32 1.15 7. Al 6061 + 15% Rock dust 1.41 1.27 8. Al 6061 + 5% CRT 1.24 1.12 9. Al 6061 + 10% CRT 1.4 1.29 10. Al 6061 + 15% CRT 1.29 1.15


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the harder material (Al/15% cenosphere) offers poor surface finish than soft material (Al/ 5% CRT) instigated for same operating conditions.

Conclusions Economical hybrid composites were fabricated

through inexpensive stir casting route by reinforcing with ordinarily available cenosphere, rock dust and the E-waste (CRT panel glass powder). Hardness and tensile strength of the composites were evaluated and a comparative study is done with other rival composites developed with similar other low cost reinforcements. Wear and machinability behaviour of the composite were also investigated and satisfactory results were obtained. The hybrid composite with graphite addition was also produced through stir casting route and their properties were evaluated. The following conclusion can be drawn from this study:

(i) Cenosphere, rock dust and CRT panel glass powder reinforced composites gives better performance as of fly ash composites.

(ii) Maximum of 65.12% hardness raise is attained for cenosphere addition and 63.04% for CRT addition. Tensile strength increases up to 9.84% for 15% cenosphere reinforcement, 9.02% for 10% CRT addition.

(iii) Addition of E-waste over 10% results in agglomeration that again results in uneven

distribution of reinforcements on heating due to the amorphous nature of glass.

(iv) Better wear resistance was attained for the novel low cost composites. Addition of graphite in the matrix promotes increased wear resistance and also enhances machining behaviour.

(v) The machinability nature was appreciable for lower percentage of graphite inclusions and was identifiable by examining the micrographs.

(vi) The reuse of E-waste may help to reduce the environmental problems.

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