Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.13, pp.1243-1254, 2011 Printed in the USA. All rights reserved
Machinability Study of Al-5Cu-TiB2 In-situ Met al Matrix C omposites
Fabricated by Flux-assisted Synthesis
A. Mahamani
Department of Mechanical Engineering, Swetha Institute of Technology and S cience for
Women ,
Tirupati-517561, India
Corresponding author:
In-situ composites are multiphase materials where the reinforcing phase is synthesized by a
chemical reaction. The reinforcement generated by this route is very small in size and
homogeneously distributed in the matrix. Adoption of the engineering application of this
material requires a systematic study of machinability characteristics. This work is an attempt to
understand the machinability behavior of the Al-5Cu-TiB2 in-situ metal matrix composites
fabricated by Flux-assisted Synthesis. The focus of this study is to investigate the effect of the
cutting speed and feed rate on flank wear, cutting force, and surface roughness. The contribution
of this paper is to study the influence of in-situ-formed TiB 2 reinfor cement on the machinability
of Al-5Cu alloy. It was found that the increase in cutting speed increased the flank wear, reduced
the cutting force, and minimized the surface roughness. Increase in the feed rate increased the
flank wear, cutting force, and surface roughness. A higher reinforcement ratio increased the t ool
wear, reduced the cutting force, and increased the surface roughness. These findings can provide
suitable machining parameters in turning of Al-5Cu-TiB2 in-situ metal matrix composites.
Keywor d s: In-situ composite, Flank wear, cutting force, surface roughness
Composite materials produced by the in-situ route are an innovation of th e light weight material
system. Flux-assisted synthesis is a more popular method to produce in-situ composites with
TiB2 and ZrB2 reinforcements. In-situ composites offer better mechanical properties when
compared to the composites produced b y the conv entional method [1]. Greater bonding strength
and good thermodynamic stability of these composites makes them suitable for various
engineering applications [2]. Pure, small, and fine reinforcement particl es are generated b y high
temperature exothermic reactions, while in-situ synthesis [3]. In-situ chemical reaction boils the
molten composite. Therefore, the reinforcement particles are distributed throughout the mold.
1244 A. Mahamani Vol.10, No.13
This action facilitates the homogeneous distribution of reinforcements [4]. Typical application of
in-situ composites includes the wear parts of pumps, valves, and chute liners [5]. The Al-TiB2
composite has better high temperature properties than conventional composites [6]. Synthesis,
charact erizati o n , and mechanical properties of in-situ Al-TiB2 composites are widel y reported in
literatures [7-9]. Fan, T et al., [10] s tudied the eff ect of adding alloying elements in the Al-TiB2
in-situ composites fabricated by flex-assisted synthesis. They concluded that the addition of the
copper elements promotes the reinforcement precipitation. Lu, L et al., [11] synthesized Al-4Cu-
TiB2 in-situ metal matrix composite. The characterization of this composite indicates that the
size of the TiB2 particles is 0.5µm to 1 µm size. Lia ng Y et al., [12] conducted a thermod ynamic
analysis of formation of in-situ TiB 2 formation as cast Al-4.5Cu alloy in flux-assisted synthesis
process. Herbert, M.A. et al., [13] carried out a microstructure study of Al-4Cu alloy and Al-
4Cu-TiB2 in-situ composite. The analysis of the result indicates that the formation of coarse
dendrite structures in Al-4Cu alloy whereas in the composite there are irregular rosette-shaped
grains with TiB2 particles at the boundaries of the grains. Kumar, S. et al., [14] studied the
influence of in-situ-formed TiB2 particles on the abrasive wear behavior of Al-4Cu alloy.
Abrasive wear resistance of the Al-4Cu alloy improved with the addition of TiB2 particles. The
hardness of the composite increased wh en the TiB2 content was rai sed . The component produced
by composite materials requires a machining process to achieve the required dimensions.
Therefore, industrial application of these composites will be impossible without addressing the
machinability issues. Surface finish, tool wear, and cutting force are the important indices
assessing machinability behavior. Surface integrity of the machined-component determines the
ability of materials to withstand severe conditions of stress, temperature, and corrosion [15].
Tool wear plays an important role in forming the machined surface, controlling cutting, reducing
the tool cost, and the machining time [16]. Cutting force carries the information about frictional
characteristics in the machining interface. Machinability of the ex-situ composites are widely
reported in literature. The studies on machinability behavior of in-situ composites are very
limited. Ozcatalbas Y., [17] carried out an experimental investigation on machinability behavior
of Al-Al4C3 in-situ composites. The micro-crack propagation at the particle-matrix interface
facilitates the fracturing through the chip cross-section whose effects reduce the cutting force.
The homogeneous microstructure and high hardness of the composite reduce the build-up edge
formation that improves the surface roughness. Ozcatalbas Y., [18] investigated the chip and
build-up edge formation in machining of the in-situ Al-Al4C3 composites. The morphologies of
chip routes were determined by using the quick stop device. It was observed that the small size
of the particle and high hardness of the composite caused discontinuous chip formation and
increased the chip cutting ratio. Rai R.N., et al., [19] conducted the experiments on the
machining of Al-TiC in-situ composite. They reported the chip formation and cutting force
measurements during the shaping operation. High volume fraction of the TiC particles caused
discontinuous and favorable chip formation without any build-up edge formation. The cutting
force was minimized due to the propa gation of micro cracks at the particle-matrix i nterface. S iz e
and morphology of the TiC particles present in the composite were found to have influenced
surface roughness. Anandakrishnan V., Mahamani A., [20] investigated machinability of the in-
situ Al6061-TiB2 composi tes. The y reported th e e ffects of speed , feed , and depth of cut on flank
wear, cutting force, and surface roughness. It was observed that the presence of small and fine
TiB2 particles exercised significant influence on machinability. The literature survey indicates
that the machinability study of Al-4Cu-TiB2 has not been addressed. In this direction, an attempt
has been made to study the effects of cutting speed and feed rate on flank wear, cutting force,
Vol.10, No.13 Machinability Stud y of Al-5Cu-TiB2 1245
and surface roughness in turning these composites with the different reinforcement ratio. The
contribution of this paper is to study the influence of in-situ formed TiB2 reinforcement on the
machinability of Al-5Cu alloy.
Al-4.5Cu/TiB2 in-situ composites are produced from K2TiF6, KBF4, Cu-Al salt system by
mixed salt reaction. Measured quantities of these preheated halides salts added in the aluminum
melt at 850º C. These halide salts induce an exothermic chemical reaction and increase the
temperature of the melt up to 1300ºC. There is a two-stage chemical reaction that occurs at this
temperature. In the first stage, Al3Ti and AlB2 phases are formed, then, these phases are
decomposed as TiB2 and Cryolite slag. The equation for the reaction is shown below. Cryolite
slag (KAlF4and K3AlF6 phases) floating on the molten melt is removed. Now the molten melt
contains Al-Cu-Ti-B- system. The molten melt is poured in to the 55Ø X 350 mm cast iron mold.
Composites are fabricated with the reinforcement ratio of 0%, 3%, and 6% TiB 2 particles in the
Al-5Cu alloy.
3K2TiF6 +13Al
3TiAl3 + 3KAlF4 + K3AlF6
2KBF4 + 3Al
AlB2 + 2KAlF4
The fabricated composites are characterized by EDAX, SEM, and micro-hardness analysis. The
EDAX pattern for the Al -4Cu- 6% TiB2 in-situ compos ite was r ecorded (H itach i S-300H model)
and displayed in Figure 1. Lithium drift silicon detector analyzer with the operating voltage of
20KV and 500x magnification was used to record the spectrum. Figure 1 confirms the presence
of Cu and TiB2 reinforcements. Presence of potassium and fluoride elements due to the slag
entrapments in the aluminum matrix are not detected in th e spect ru m, whi ch rev eals th e chem ic al
stability of the composite. The micro-structure an alyses of t he compos ite sam ples are car ried out
by using scanning electron microscopy (JEOL 6360 LV model). Figure 2 shows the
micrographic view of Al-4Cu alloy. The CuAl 2 f ormation is found in the grain boundaries of the
matrix. Al2Cu is uniformly distributed in the matrix. Boiling the molten composite at high
temperat u res will distribute the reinforcement particles and Al2Cu uniformly. This action will
minimize the heterogeneity in microstructure of the composite. There are very fine Al2Cu phase
precipitated from the matrix. Al 2Cu and Al bond well. So the precipitation of Al2Cu strengthens
Al-4.5Cu matrix. Figure 3 shows the scanning electron microscopy of Al-4Cu- 6% TiB 2 in-situ
metal matrix composite. The micron-size TiB2 particle along with Al2Cu is trapped in to the
grain boundaries of the aluminum matrix. Figure 4 shows a typical microscopic view focused on
the Al2Cu phase. The TiB2 particles are surrounded by the Al2Cu phase. Table 1 shows the
micro-hardness of the composites is evaluated by using the Vickers’s micro-hardness tester
(MH06 model) at a load of 25 grams with 3 seconds dwell time. Hardness values are measured in
three different places in the composite and the average value is reported in Table 1. Table 1
shows that there is an 8% increase in hardness observed when adding 3% TiB2 in the Al-4Cu
alloy. It is also seen from Table 1 that a significant improvement in the hardness of Al-4Cu-6 %
TiB2 in-situ composite was observed when compared to the Al-4Cu alloy. Therefore, the
increase in hardness of the composite confirms the presence of reinforcement. It is also noted
that the hardness of these in-situ composites increases when increasing the reinforcement ratio.
1246 A. Mahamani Vol.10, No.13
Table 1 Micro hardness analysis of the composites
Micro hardness (H
Al-4Cu alloy
Al-4Cu -3 %
Al-4Cu -6 %
Figure 1 EDAX spectrum of Al –Cu-6 % TiB2
Vol.10, No.13 Machinability Stud y of Al-5Cu-TiB2 1247
Figure 2 Microstructure of Al –Cu alloy
Figure 3 Microstructure of Al –Cu-3% TiB2 in-situ metal matrix composite
Figure 4 Microstructure of Al –Cu-6 % TiB2 in-situ metal matrix composite
A machinability study was carried out on T urn m aster-35 lathe supplied b y Kirloskar, India. The
experimental setup for machining test is shown in Figure-5. Uncoated tungsten carbide insert
with the specification of SNMG120408 MTTT5100 was clamped in a rigid tool holder. The
insert has clearance angle 7o, cutting edge angle75 o, and nose radius 0.8 mm. Specification of
1248 A. Mahamani Vol.10, No.13
the tool holder was PSBNR-2525M12. The length of turning is 110mm. No chip breaker was
used in the experiment. The average flank wear was measured using Mitutoya microscope with
30× magnification. SJ210 stylus type roughness tester (Mitutoya make, 0.001 µm) was used for
measuring surface roughness. The cut of length of roughness measurement was 25mm. The
cutting force was measured using a Kistler Dynamometer (model 9257B). Data acquisition was
carried out by appropriate software Dynaware Kistler. Machining test was conducted in dry
cutting condition. During experiments, only one parameter was varied while others were held
constant to observe the effects of variation of an individual input parameter on the output
parameter. The selected machining parameters and their ranges are given in Table-2.
Table 2 Experimental conditions
Paramet ers Uni ts Ranges
Cutting speed m/min 50,75,100,125 and 150
Feed rate mm/rev 0.1,0.15, 0.2 , 0.25and 0.3
Cutting depth mm 0.5,0.75,1,1.25 and 1.5
Figure 5 photographic view of experimental set up with kistler dynamometer
4.1 Mechanism of In-Situ Formation
Al-5Cu-TiB2 in-situ composite was successfully produced by flux-assisted synthesis. The
material characterization confirmed the presence of ZrB2 indicating the purity of materials.
Formation of ZrB 2 occurred at 950oC, in the melt during the exothermic reaction. Therefore, no
oxide layer formation occurred on the surfaces of TiB2. The pure and active reinforcement
Vol.10, No.13 Machinability Stud y of Al-5Cu-TiB2 1249
promoted the thermodynamic stability of the composite. Fine size reinforcements of ZrB2
formed in the Al matrix due to phase nucleation, which facilitated the wetting and bonding of the
interface between the reinforcements and the matrix. The melt boiling at the high temperature
distributed the particles throughout the mold and ensured homogeneous distribution.
4.2 Flank Wear
Abrasion is the main wear mechanism in fl ank wear during machining. Flank wear i s one of the
major factors contributing to the geometric error and thermal damage in a machined work piece
[21]. The presence of fine TiB2 particles in the composites causes less damage when engaging
the cutting tool with the reinforcements. The Al 2C u formation surrounded b y the reinforcements
reduces the abrasive action at the flank face of the tool. Figure 6 shows the effects of cutting
speed on flank wear when machining the composites at 0.2 mm/rev feed rate and 1 mm depth of
cut. Figure 6 reveals that the increase in cutting speed, increases the flank wear under the same
machining conditions. At higher cutting speeds, the material passes away within a short interval
of time, which facilitates the machining interface to become the adiabatic system. Increase in
temperature softens the cutting tool and causes more tool wear. The effect of feed rate on flank
wear was recorded by keeping the cutting speed as 125 m/min and depth of cut as 1mm. Figure 7
shows that hi gher feed rate increases the flank wear. A rise in the federate increases the friction
between work p iece and hikes up heat generation which causes greater flank wear. It is observed
from Figure 7 that the flank wear increases through an increase in the reinforcement ratio. The
presence of small and fine reinforcement particles reduces the tool wear because of the absence
of coarseness. Al 2Cu phase surrounded by the TiB 2 particles acts as a lubricant and reduces the
effect of reinforcements.
Ef fect of c u tting speed on flank wear (0. 2mm/rev & 1 mm DOC)
5075100 125 150
Cutting speed (m/min)
Flank wear (mm)
0% TiB2
3% TiB2
6% TiB2
Figure 6 Effect of cutting speed on flank wear
4.3 Cutting Force
Cutting force signals are highly sensitive carriers of information about the status of the
machining process. The influence of cutting speed on cutting force is shown in Figure 8. This
shows that an increase in cutting speed decreases the cutting force. An inc rease in cuttin g speed
increases the temperature of the work piece, which reduces the hardness of the work piece.
Therefore, the cutting force is reduced when this softened work piece is machined. The effect of
1250 A. Mahamani Vol.10, No.13
the feed rate on the cutting force was measured by keeping the cutting speed constant at 125
m/min and the cut at 1 mm depth. As seen from Figure 9, an increase in feed rate increases the
cutting force. Generally, the cutting force along the horizontal axis increases when the feed rate
is in creased . An incr ease in fe ed rate i ncreas es t he max im um chi p thi cknes s, whi ch inc reas es th e
cutti ng for ce. A s s een from Figu res 8 and 9, as t he rei nfo r cemen t r at i o i ncre as es t he cu tt ing forc e
is reduced due to a reduction in strain.
Effect of feed rate on flank wear (125 m/min & 1 mm DOC)
0.05 0.1 0.15 0.2 0.25
Feed rate ( mm/rev)
Flank wear (mm)
0% TiB2
3% TiB2
6% TiB2
Figure 7 Effect of feed rate on flank wear
Ef f ect of cutt ing speed o n cutt ing f or ce ( 0.2m m/r ev & 1 mm DOC)
5075100 125 150
Cutting speed (m/min)
Cutting force ( N)
0% TiB2
3% TiB2
6% TiB2
Figure 8 Effect of cutting speed on cutting force
Vol.10, No.13 Machinability Stud y of Al-5Cu-TiB2 1251
Effec t o f feed rate on cutting fo rce (1 25 m/min & 1 mm DOC)
0.05 0.1 0.150.2 0.25
Feed rate ( mm/rev)
Cutting force ( N)
0% TiB2
3% TiB2
6% TiB2
Figure 9 Effect of feed rate on cutting force
4.4 Surface Roughness
The machined surface qualit y of the composite is one of the most im portant facto rs aff ecting th e
actual application. Figure 8 shows the influence of cutting speed on surface roughness. The
surface roughness was evaluated under different cutting speeds, at a constant feed rate of (0.2
mm/rev) and a depth of cut (1 mm). As seen from Figure 8, an inc rease i n cutti ng speed reduces
the surface roughness. Higher cutting speeds are associated with an increase in the cutting
temperature which leads to the formation of suited-up edge formations and minimizing the
deposition of build-up edge formation. A higher cutt ing speed can howeve r, improve the surface
finish. As the cutting speed increases, the strain rate will also increase. This action facilitates
particle fracture and crack-minimizes particle pulling. Therefore, the amount of pin formation is
reduced and good surface finish can be achieved. The effect of feed rate on the surface roughness
exami ned by keepin g the cut ting speed at 125 mm/m and depth of cut as 1 mm is observed from
Figure 9. An increase in feed rate increases the surface roughness. An increase in feed rate
increases the pit and crack formation, and causes lar ger tool feed mark s. At higher f eed rates, the
tool has more vibration when shifting the cutting from Particle to matrix. This could be the
reason for larger feed marks at higher feed rates. The increase in feed rate increases the
temperat ure, which en ables particle pulling, and pits and crack form ation. These eff ects incre ase
the surface roughness at higher feed rates. These small sized TiB2 particles and improved
wettability minimize the possibility of particle pulling, de-bonding of the matrix reinforcement.
The uniform distribution of the particles undergoes uniform plastic deformation which reduces
subsurface damage. These effects minimize surface roughness in machining the composites.
Figures 8 and 9 show that the surface roughness has been increased by increasing the volume
fraction of the composite.
1252 A. Mahamani Vol.10, No.13
Ef fect of c u tting speed on surfa ce roughness (0.2mm/rev & 1 mm DOC)
5075100 125 150
Cutting speed (m/min)
Surface roughness
0% TiB2
3% TiB2
6% TiB2
Figure 10 Effect of cutting speed on surface roughness
Effe ct of fe ed rate on surfa ce roughne ss (125 m/m i n & 1 mm DOC)
0.05 0.1 0.150.2 0.25
Feed r at e (mm/r ev)
Surface roughness (µm)
0% TiB2
3% TiB2
6% TiB2
Figure 11 Effect of feed rate on surface roughness
The flank wear, cutting force, and surface roughness of the experimental study of machining the
Al-5Cu-TiB2 in-situ metal matrix composites indicated the following conclusions:
Al-5Cu-TiB2 in-situ metal matrix composite has been synthesized successfully with different
reinforcement ratio using flux -assisted synthesis.
The presence of TiB2 and ZrB2 phases in the Al-5Cu alloy is confirmed by EDAX analysis.
A significant improvement in the hardness was observed by adding reinforcements in t he A l-5Cu
The incre ase in cut ting sp eed increas ed the flank wear, reduced the cutting force, and minimized
the surface roughness.
An increase in feed rate increased the flank wear, cutting force, and surface roughness.
Vol.10, No.13 Machinability Stud y of Al-5Cu-TiB2 1253
An increase in reinforcement ratio increased the tool wear, reduced the cutting force, and
increased the surface roughness.
The machinability behavior of Al-5Cu-TiB2 is entirely different from the conventional
composites because of the presence of Al2Cu phase, TiB2, and ZrB2 p ar t icles .
This detailed of study of machining characteristics would be helpful for the economic and
efficient machining of this material.
The Author acknowledges the encouragement and support provided by the management of
Swetha Institute of Technology and Science for Women, Tirupati. Author also grateful to the
AICTE, India for the provision of grant (8024/RID/BOR/MOD/831/9/10) to carry out this
experimental work.
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