87

________________

Corresponding author: R. Keshavamurthy

E-mail address: keshavamurthy.r@gmail.com

Doi: http://dx.doi.org/10.11127/ijammc.2014.08.02

Copyright@GRIET Publications. All rights reserved.

Advanced Materials Manufacturing & Characterization Vol4 Issue 2 (2014)

Advanced Materials Manufacturing & Characterization

journal home page: www.ijammc-griet.com

Tribological properties of Hot forged Al2024-TiB2 in-situ composite R. Keshavamurthya, S.Suhael Ahmedb, A.Mudashi Laxmanb, N.H.Anil Kumarb, M.N.Shashidharab, Y.Vimarshan Reddyb aDepartment of Mechanical Engineering, Dayananda Sagar College of Engineering, Bangalore, Karnataka, India. bDepartment of Mechanical Engineering, Government Engineering College, Ramanagaram, Karnataka, India

A R T I C L E I N F O Article history: Received: 10-04-2014 Accepted: 26-05-2014 Keywords: Aluminum alloy, In-situ composite, forging, Coefficient of friction, Wear.

A B S T R A C T

Al2024-TiB2 in-situ composite was fabricated by liquid metallurgy route using Al-Titanium and Al-Boron master alloys. The developed composites were subjected to hot forging at a temperature of 500oC using a 200T hydraulic hammer. Microstructure studies, X-ray diffraction studies(XRD), grain size analysis, microhardness and dry friction and wear tests were carried out on as cast and hot forged matrix alloy and its composites. Pin on disc type machine was employed to perform friction and wear tests over a load range of 20-100N and sliding velocities of 0.314-1.57m/s. Microstructure and XRD studies reveal presence of fine TiB2 particles in both as cast and hot forged condition. It is observed that, both as cast and hot forged composites do exhibit significant grain refinement. When compared with as cast matrix alloy and its composite, hot forged alloy and its composite exhibits higher extent of grain refinement. Both as cast and hot forged composites exhibit improved microhardness, wear resistance and lower coefficient of friction when compared with the unreinforced alloy under identical test conditions.

1. Introduction

Aluminum based metal matrix composites have been emerged as an important class of materials for structural, wear, thermal, transportation and electrical applications, primarily as a result of their ability to exhibit superior strength to weight and strength to cost ratios when compared to equivalent monolithic commercial alloys. Aluminum matrix filled with particles, fibers or whiskers may exhibit superior mechanical and tribological properties as reported by many researchers [1-5].

However, there exist problem in producing high quality metal matrix composites. Non-uniform distribution of reinforcing particles, poor interfacial bond between matrix and reinforcement, poor wettabilty of reinforcing particles, formation

inherent casting defects due to incomplete adhesion of reinforced particles in the matrix, are the common problems associated with the composites fabricated by convention techniques [6-10]. Fabrication of aluminum composites which involves synthesis of reinforcing particles within the matrix (In-situ technique) offers solution to above mentioned problems. In-situ methods of fabricating metal matrix composites posses several advantages over ex-situ techniques [11-14].

Some of the advantages of the composites prepared by in-situ technique are,

1. Reduced size and uniform distribution of reinforced particles.

2. Good interfacial bond between matrix and reinforcement

3. Economy in processing.

On the other hand, it is reported that secondary processing of aluminum composites by extrusion, rolling and forging helps in further improving bond between matrix and reinforcement, reduction or elimination of porosity along with homogeneous distribution of reinforcement leading to improvement in the

88

quality of composites [15-16]. Zhao etal [17] have carried out extrusion studies on SnO2-coated Al18B4O33 whisker reinforced aluminum matrix composites fabricated by squeeze casting technique. They have found that yield strength of the composites is improved after extrusion and their elongation is increased by 300%. Zhangwei wang etal [18] have studied the combined effects of extrusion and reinforcement volume fraction on the SiC particles reinforced aluminum alloy composites and have reported that, extrusion can improve the distributed homogeneity of SiC particles in the matrix and enhance the interfacial bonding strength of the composites. Khalifa et al. [19] have studied the tensile properties of as cast and extruded Al6063-10wt%SiC composites. They have observed that increased content of SiC particles increases the strength in both as cast and extruded conditions. The strength of extruded composites is higher than that of cast composites. Raja et al. [20] have carried out studies on cast and forged Al6082/SiCp composites. They have reported that, tensile strength of forged composites is higher when compared with cast ones. Among all the secondary processing routes available, forging is emerged as an important route owing to its ability to produce high strength components within a short duration. Meager information is available as regards the tribological properties of in-situ composites processed by liquid metallurgy route. In the light of the above, the present investigation deals with tribological characterization of as cast and hot forged Al2024-TiB2 composites processed by in-situ technique.

2.0 Experimental Details: 2.1 Material Selection: Al2024 alloy is chosen as matrix material owing to its wide application in many engineering sectors including automotive and aerospace sectors. Further, this alloy exhibits good strength and formability. Table -1 show the chemical composition of Al2024 alloy used in this study.

Table: 1 Chemical composition of Al2024 alloy

Element Percentage

Cu 3.9

Cr 0.1

Mn 0.5

Mg 1.5

Si 0.5

Ti 0.15

Zn 0.25

Fe 0.5

Al Balance

Commercially available Al-10%Ti and Al-3%Br master alloys were used along with Al2024 matrix material to synthesis TiB2

particles. The chemical composition of master alloys used in the present study is reported in the Table:2. Both matrix material and master alloys were procured from M/s Fen fee Metallurgicals, Bangalore, India.

Table: 2 Chemical composition of master alloys

Al–10%Ti master alloy Al–3%B master alloy

Element Percentage Element Percentage

Ti 10.27 B 2.94

Fe 0.37 Fe 0.32

Others 0.11 Others 0.10

Al Balance Al Balance

2.2 Composite preparation and Hot Forging: In-situ Al2024-TiB2 composite was fabricated by stir casting technique owing to its simplicity and low cost [21]. A mixture of 3kgs of Al 2024 alloy with 5wt% of Al-Ti alloy and 10wt% of Al-3%Br master alloys were melted in the furnace to a temperature of 800 oC. Details of in-situ reaction and TiB2 formation are discussed elsewhere [22]. The molten alloy was mixed by use of mechanical stirrer rotating at a speed of 200 rpm for duration of 15 minutes. The composites melt maintained at a temperature of 800oC was then poured in to metallic moulds. The percentage of TiB2 formation in the composite was estimated by dissolving known quantity of sample in hydrochloric acid [22]. The matrix was dissolved in the acid and leaving TiB2 / Al3Ti particles. The extracted particles were cleaned, dried and weighed. The difference in the weight of the composite and extracted particles was considered for estimating percentage of TiB2 and Al3Ti particles. The percentage of TiB2 in the extracted particles was measured by comparing the ratios of peak intensities of TiB2 and Al3Ti obtained from XRD studies. The cast Al2024 alloy and developed composites were subjected to open die hot forging (Flattening) at a temperature of 5000C using 200T hydraulic hammer at M/s Forging and allied products private Limited, Bangalore, India. The cast alloy and composites were machined to the size of 20mm diameter and 50mm height. A constant strain rate of 0.012mm/sec and deformation ratio of 1:2.5 was adopted for both matrix alloy and composite.

2.3 XRD, microstructure, Grain size and microhardness: Both as cast and hot forged alloy and its composites were subjected to optical microstructure studies. Standard metallographic procedure was adopted to polish the samples. Polished surfaces were etched with kellers’ reagent (5ml HNO3, 3ml HCl, 2ml HF and 190ml H2O). Microphotographs were captured using NIKON metallurgical microscope (Model: ECLSE LV 150). Grain size analyses were carried out as per ASTM E112 standard test method at Advanced Metallurgical Laboratory, Peenya, Bangalore, India, using Clemex Image analyzer software. Microhardness tests were carried out on polished samples of both as cast and hot forged alloy and its composites, by applying 100 grams of load for a period of 10 seconds using Vickers micro hardness tester. X-ray diffraction patterns were recorded using Philips X-ray diffractometer.

2.4 Friction and wear: Friction and wear studies were carried out at room temperature using pin-on-disc wear test machine as per ASTM G99 standard

89

test method. (Model: TR20, Make: Ducom, India). Cylindrical specimen of 8mm diameter and 20 mm length were used as test pins against a hardened (58-60HRc) steel disc. The test surfaces were polished metalographically. Studies were carried out under varying load (20-100N in steps of 20N) and sliding velocity (0.314 – 1.57 m/sec). Frictional force was measured using load cell of accuracy 0.1N while the wear loss was measured in terms of weight loss. Test duration of 30 minutes was adopted for all the tests.

3.0 Results and Discussions: 3.1 XRD of Al2024-TiB2 composite. Fig.1 shows the XRD pattern of extracted powder consisting of TiB2 and Al3Ti particles. The estimated percentage of TiB2 particles from the ratio of peak intensity in XRD pattern is found to be 4.9% approximately.

Fig.1 XRD pattern of TiB2 : Al3Ti

3.2 Microstructure:

(a) Cast Al2024 alloy (b) Cast Al2024 –TiB2

composite

(c) Forged Al2024 alloy (d) Forged Al2024 –TiB2

composite Fig.2 Optical micrographs of as cast and forged Al2024 alloy and Al2024-TiB2 composites

Fig.2 shows the optical microphotographs of both as cast and hot forged Al2024 alloy and Al2024-TiB2 composites. The microstructure clearly shows fairly uniform distribution of TiB2 particles in the matrix material. The TiB2 particles in the forged composites are in general smaller than those in corresponding as cast composites. A refined grain structure is observed in hot forged alloy and composite. Both as cast and hot forged composites are free from casting defects. Further, there exist good bond between the matrix and the particle reinforcement even after forging.

3.3 Grain Size analysis: Fig.3 shows the results of grain size analysis carried out on as cast and hot forged alloy and its composites. It is observed that, there is a reduction in the grain size of the composite in both as cast and hot forged conditions. This may be attributed to presence of TiB2 particles which acts as nucleating sites during solidification and refined the grain size extensively. However, when compared with as cast composite, hot forged composite shows larger extent of grain refinement. The improved grain refinement on forging of alloy and all the composites can be mainly attributed to the dynamic recrystallisation during forging [23-24].

151311975310

ASTME112-96

0

40

80

120

160

200

Coun

t

0

20

40

60

80

100

Cum

ula

tive (

%)

Rating 6.64

(a) Cast Al2024 alloy

151311975310

ASTME112-96

0

50

100

150

200

250

Coun

t

0

20

40

60

80

100

Cum

ula

tive

(%

)

Rating 6.69

(b) Cast Al2024 –TiB2 composite

151311975310

ASTME112-96

0

40

80

120

160

200

Coun

t

0

20

40

60

80

100

Cum

ula

tive (

%)

Rating 6.72

(c)Forged Al2024 alloy

151311975310

ASTME112-96

0

80

160

240

320

400

Coun

t

0

20

40

60

80

100

Cum

ula

tive

(%

)

Rating 7.17

(d) Forged Al2024 –TiB2 composite Fig.3 (a-d) Grain size analysis of as cast and hot forged Al2024 alloy and it’s composite

90

3.4 Microhardness: Fig.4. shows the variation of microhardness of Al2024 alloy and Al2024-TiB2 composites in as cast and hot forged conditions. From the graph, it is observed that there is a significant improvement in microhardness of composites.

Fig.4 Variation of microhardness of Al2024 alloy and its composites

An improvement of 18% and 31 % increase is noticed in as cast and hot forged composites respectively. This drastic improvement in the hardness value of matrix alloy may be attributed to facts that, TiB2 being hard reinforcement do exhibit greater resistance to indentation of hardness tester, by rendering its inherent property of hardness to matrix alloy [25].

3.5 Coefficient of friction: 3.5.1 Effect of Reinforcement: Fig. 5 shows the variation of coefficient of friction of as cast and hot forged composites. It is observed that coefficient of friction of composites reduces in both as cast and hot forged conditions. This reduction in co-efficient of friction of Al2024-TiB2 composites can be attributed to improvement in anti frictional behavior of reinforced particles which acts as load bearing elements. Smaller reinforcement size and clean interface between matrix and reinforcement reduces of coefficient of friction as reported by many researchers [25-26].

Hot forged Al2024-TiB2 composite exhibited least coefficient of friction when compared with as cast and hot forged matrix alloy and as cast Al2024-TiB2 composite which may be attributed to fine and uniform distribution of TiB2 particles after forging.

Fig.5 Variation of COF of Al2024 alloy and Al2024-TiB2 composites

3.5.2 Effect of Load: Fig. 6 shows the variation of coefficient of friction of as cast and hot forged alloy and its composites with respect to load. It is observed that for both matrix alloy and its composites, a reduction in coefficient of friction is observed with increase in load in both as cast and hot forged conditions.

Fig.6 Variation of COF of Al2024 alloy and Al2024-TiB2 composite

However, at all the loads studied, Al2024-TiB2 composites exhibited reduced coefficient of friction when compared with matrix alloy. Increase in the normal load leads to increased transfer of TiB2 particles onto the interface between pin and disc which will increases the lubrication at the sliding interfaces. Further, the improved load bearing capacity of the in situ composites is responsible for its anti frictional behavior at higher loads [27]. Further, when compared with cast matrix alloy and its composites, hot forged alloy and its composites exhibited lower coefficient of friction under all the load conditions studied.

3.5.3 Effect of Sliding Velocity:

Fig.7 Variation of COF of Al2024 alloy and Al2024-TiB2 composite

Fig. 7 shows the variation of coefficient of friction of as cast and hot forged alloy and its composites with respect to sliding velocity. It is observed that coefficient of friction increases with increase in sliding velocity for both matrix alloy and its composites. When compared with cast matrix alloy and its composites, hot forged alloy and its composites exhibited lower coefficient of friction at all the sliding velocities studied. Increased coefficient of friction may be attributed to increased

91

frictional force at higher sliding velocities. However, composites poses lower coefficient of friction due to fact that at higher velocities hard TiB2 particles in the composites get cracked and form a thin adherent lubricating film and oxide layer (aluminum oxide) owing to higher temperature at higher speed at the interface. Further, under all the sliding velocities studied, hot forged alloy and composite exhibited lower coefficient of friction, when compared with as cast matrix alloy and composite.

3.6 Wear: 3.6.1 Effect of Reinforcement: Fig.8 shows the variation of weight loss of Al2024 alloy and Al2024-TiB2 composite in as cast and hot forged conditions. It is observed that the composite exhibited lower weight loss in both as cast and hot forged conditions when compared with matrix alloy. The reduced weight loss of the composites may be attributed to presence of hard TiB2 particles. Improvement in the hardness and lower grain size of the composites are the other reasons for reduced weight loss. It is also observed that forged alloy and forged composite exhibited superior wear resistance when compared with the as cast ones. Excellent interfacial bond between matrix and reinforcement played a significant role in reducing wear loss of the composite. Presence of good interfacial bond reduces the possibility of pull out of TiB2 particles from the matrix alloy there by eliminating the chances of three body wear.

Fig.8 Variation of weight loss of Al2024 alloy and Al2024-TiB2 composite

3.6.2 Effect of Load: Fig.9 shows the variation of weight loss of Al2024 alloy and Al2024-TiB2 composite with increase in load in as cast and hot forged conditions. It is observed that weight loss increases with increase in load for all the materials studied. Increased weight loss with increase in load can be attributed to the fact that at higher loads, there is a tendency for large plastic deformation which promotes the extent of wear debris formation leading to higher weight loss. However, under all the loads studied composites exhibited lower weight loss when compared with the matrix alloy. Further, when compared with as cast alloy and composite, hot forged alloy and composite exhibited superior wear resistance.

Fig.9 Variation of weight loss of Al2024 alloy and Al2024-TiB2 composite

3.6.3 Effect of Sliding Velocity: Fig.10 shows the variation of weight loss of Al2024 alloy and Al2024-TiB2 composite with increase in speed in as cast and hot forged conditions. With an increase in speed there is an increase in weight loss for both matrix alloy and it’s composite in both as cast and hot forged conditions. However, at all the sliding velocities studied, the weight loss of the composites was much lower when compared with the matrix alloy. This can be attributed to enhancement in hardness of the composites as discussed earlier. Increase in hardness results in improvement of wear and seizure resistance of materials. Further, increased sliding velocity increases the temperature at the contact surface due to which the surface of the material get softened and tends to get in to plastic state. Greater extent of plastic deformation leads to larger material removal.

Fig.10 Variation of wear rate of Al2024 alloy and Al2024-TiB2 composite

Conclusion Al2024-TiB2 composite is prepared from stir casting technique using Al-10%Ti and Al-3%Br master alloys. The developed composite was hot forged successfully at a temperature of 500oC. Microstructure reveals fairly uniform distribution of TiB2 particles. Al2024-TiB2 composite exhibited higher hardness, lower coefficient of friction and lower wear loss when compared with matrix alloy in both as cast and hot forged conditions. Further, forged composite exhibited lower coefficient of friction

92

and superior wear resistance when compared with cast alloy and composites under all the load and sliding velocities studied.

References

1. Bhargavi Rebba, N.Ramanaiah, Studies on Mechanical Properties of 2024 Al –B4c Composites, Advanced Materials Manufacturing & Characterization Vol 4 Issue 1 (2014), pp.42-46.

2. Umit Cocen, Kazim Onel, Ductility and strength extruded aluminum alloy composites, composites Science and Technology, vol.62, (2002), pp. 275-282.

3. H.Chen,A.T.Alpas,Wearof aluminum matrix composites reinforced with nickel-coated carbon fibers Wear, vol.192, 1–2 (1996) ,pp.186-198.

4. W.D. Fei, Z.J. Li, Y.B. Li, Effects of T4 treatment on hot rolling behavior and tensile strength of aluminum matrix composite reinforced by aluminum borate whisker with NiO coating, Materials Chemistry and Physics, vol.97, 2–3, (2006), pp.402-409.

5. M. Kok Production and mechanical properties of Al2O3 particle-reinforced 2024 aluminum alloy composites, Journal of Materials Processing Technology, vol.161( 3), (2005) ,pp.381-387.

6. Leon CA, Drew RAL. Preparation of nickel-coated powders as precursors to reinforce metal matrix composites. Journal of Material Science, vol.35 (2000), pp.4763–8.

7. Foo KS, Drew RAL. Interface characterization of an SiC particulate/6061 aluminum alloy composite. Composites , vol.25 (1994), pp.677–83.

8. Ren S, He X, Qu X, Li Y. Effect of controlled interfacial reaction on the microstructure and properties of the SiCp/Al composites prepared by pressureless infiltration. Journal of Alloys and Compound, vol.455 (2008), pp.424–31.

9. Asthana AJ. Reinforced cast metals, part II evolution of the interface. Journal of Material Science, vol.35 (1998), pp.1959–80.

10. Ray S. Review: synthesis of cast metal matrix particulate composites. J Mater Sci, vol.28 (1993), pp.5397–413.

11. S. Kumar, M. Chakraborty, V. Subramanya Sarma, B.S. Murty, Tensile and wear behaviour of in situ Al–7Si/TiB2 particulate composites, Wear vol.265 (2008) pp.134–142.

12. Min. Zhao, Gaohui. Wu, Longtao. Jiang, Zuoyong. Dou, Friction and wear properties of TiB2P /Al composite Composite Part A: Applied Science and Manufacturing vol.37 (2006), pp.1916–1921.

13. K.L. Tee, L. Lu, M.O. Lai, Application of thermodynamic calculation in the in-situ process of Al/TiB2, Composite Structure, vol.47 (1999), pp.589–593.

14. Hirose Akio, Hasegawa Mitsuo, Kobayashi Kojiro F. Microstructures and mechanical properties of TiB2 particle reinforced TiAl composites by plasma arc melting process. Material Science and Engineering A, 239(240), (1997), pp. 46–54.

15. Durrant, G., Scott, V.D., 1993. The effect of forging on properties and microstructure saffil fibre reinforced aluminum. Composite Science and Technology vol.49, pp.153–164.

16. Ozdemir, I., Cocen, U., Onel, K., 2000. The effect of forging on the properties of particulate reinforced aluminium alloy composites. Composite Science and Technology, vol.60, pp.411–419.

17. P T Zhao, L D Wang, Z M Du, S C Xu, P P Jain. Low temperature extrusion of aluminum matrix composites reinforced with SnO2-Coated Al18B4O33 whiskers Composite Part A : Applied Science and Manufacturing, vol.43 (2012), pp.183-188.

18. Zhangwei Wang, Min song, Chao Sun, Daihong Xiao, Effect of extrusion and particle volume fraction on the mechanical properties of SiC reinforced Al-Cu alloy composite, Material Science and Engineering A, vol.527, 24(25), (2010),pp.6537-6542.

19. Tarek, A.Khalifa and Tamer S. Mahmoud, Elevated Temperature Mechanical Properties of Al Alloy AA6063/SiCp MMCs, Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K. 978-988.

20. Raja Thimmarayan, G Thanigayarasu, Effect of particle size, forging and ageing on the mechanical fatigue characteristics of Al6082/SiCp metal matrix composites, The International Journal of Advanced Manufacturing Technology, 48 5(8), (2010),pp. 625-632.

21. Arvin Mewar, K.K.S. Mer, Dry Sand Abrasion Wear of Aluminium-Graphite Composite Synthesized in Open Hearth Furnace with Manually Controlled Stirring Method, Advanced Materials Manufacturing & Characterization, Vol3, Issue 1(2013), pp.223-226.

22. C.S. Ramesh, S. Pramod, R. Keshavamurthy A study on microstructure and mechanical properties of Al 6061–TiB2 in-situ composites Materials Science and Engineering: A, vol.528, 12 (2011), pp.4125-4132.

23. B.Inem, Dynamic recrystallisation in a thermo mechanical processed metal matrix composite. Material Science & Engineering A1 vol.97 (1995), pp. 91–94.

24. F.J.Humpherys, Nucleation of Recrystallisation at Second Phase Particles in Deformed Aluminum. Acta Metallurgica vol.25 (1977),pp. 1323.

25. U.Yang Jingy and D.D.L. Chung Wear of bauxite-particle-reinforced aluminum alloys, Wear vol.135(1), (1989), pp.53-65.

26. F.E.Kennedy, A.C.Balahadur and D.S.Lashmore, The friction and wear of Cu based Silicon carbide particulate metal matrix composites for brake application. Wear vol.203 (1997), pp.715.

27. C.S. Ramesh, Abrar Ahamed, Friction and wear behavior of cast Al 6063 based in situ metal matrix Composites, Wear vol.271 (2011) ,pp.1928–1939.