T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
951–960
MACHINING PARAMETERS INFLUENCING IN ELECTRO
CHEMICAL MACHINING ON AA6061 MMC
PARAMETRI STROJNE OBDELAVE, KI VPLIVAJO NA
ELEKTROKEMIJSKO STROJNO OBDELAVO AA6061 MMC
Chenthil Jegan Thankaraj Mariapushpam1, Durairaj Ravindran2, Manaharan Dev Anand3
1St. Xavier's Catholic College of Engineering, Department of Mechanical Engineering, Kanyakumari District, India
2National Engineering College, Department of Mechanical Engineering, K.R.Nagar, Kovilpatti, Thuthukoodi District, India
3Noorul Islam Centre for Higher Education, Department of Mechanical Engineering, Kumaracoil, Kanyakumari District, India
optrajegan@yahoo.co.in
Prejem rokopisa – received: 2015-08-18; sprejem za objavo – accepted for publication: 2015-11-05
doi:10.17222/mit.2015.260
In this study the mechanical and microstructural behaviours of AA6061 reinforced with silicon carbide (SiC) and AA6061
reinforced with boron carbide (B4C), obtained from the enhanced stir-casting process, were investigated using scanning electron
microscopy (SEM) and X-ray diffraction (XRD) with various weight percentages, i.e., 2.5 %, 5 % and 7.5 %. The testing shows
that the tensile and microhardness properties of the AA6061 were improved in both the reinforced aluminium-matrix
composites. The influence of the electrochemical machining process parameters like current, voltage, electrolyte concentration,
feed rate, gap and flow rate were considered as the input parameters. The output responses are the material removal rate (MRR),
the surface roughness (SR) and the radial overcut (ROC). The study shows that the dominant output parameter MRR was directly
proportional to the input parameters current, voltage and feed rate. The SR was significantly influenced by the input parameters
current, feed rate and gap. The ROC was considerably balanced by the input parameters current and feed rate.
Keywords: metal-matrix composites, material removal rate, electrochemical machining, surface roughness, radial overcut
V {tudiji so bile preiskovane mehanske lastnosti in mikrostruktura AA6061, izdelanega z naprednim postopkom ulivanja s
preme{avanjem in oja~anega z razli~nim masnim dele`em silicijevega karbida (SiC) ali borovega karbida (B4C) (2,5 %, 5 % in
7,5 %). Preiskave so bile izvedene s pomo~jo vrsti~nega elektronskega mikroskopa (SEM) in z rentgensko difrakcijo (XRD).
Preizku{anje ka`e, da sta natezna trdnost in mikrotrdota AA6061 narasli pri obeh vrstah kompozita na osnovi aluminija. Za
vpliv vhodnih procesnih parametrov pri elektrokemijski strojni obdelavi so bili upo{tevani: tok, napetost, koncentracija
elektrolita, hitrost podajanja, re`a in hitrost pretoka. Izhodni odgovori so bili: hitrost odstranjevanja materiala (MRR), hrapavost
povr{ine (SR) in pove~anje radiusa (ROC). [tudija ka`e, da je prevladujo~i izhodni parameter MRR neposredno proporcionalen
vhodnim parametrom; toku, napetosti in hitrosti podajanja. Na SR so mo~no vplivali vhodni parametri: tok, hitrost podajanja in
re`a. ROC je bil posebej uravnote`en z vhodnima parametroma, tokom in hitrostjo podajanja.
Klju~ne besede: kompoziti na kovinski osnovi, hitrost odstranjevanja materiala, elektrokemijska strojna obdelava, hrapavost
povr{ine, pove~anje radiusa
1 INTRODUCTION
Electrochemical machining (ECM) is a well-known
process used for the manufacture of various sophisticated
parts, such us turbine blades, rifle bores, hip-joint im-
plants, micro-components as well as many other applica-
tions. ECM provides an economical and effective
method for shaping high-strength, heat-resisting mate-
rials into complex shapes and producing high-quality
products from composites and other hard materials.1 In
ECM the machining is done at low voltage compared to
other processes with a high metal removal rate. It is suit-
able for mass production work and low labour require-
ments. ECM is one of the most widely used advanced
machining processes to make complicated shapes of
varying sizes with electrically conducting, but difficult to
machine, materials such as super alloys, Ti alloys, alloy
steel, tool steel, stainless steel, etc.2 These materials are
extensively used in aerospace, automobile, space, nuc-
lear, defence, cutting tools, dies and mould making
applications. The material used for ECM tools should be
electrically conductive and easily machinable to the
required geometry. The various materials used for this
purpose include copper, brass, stainless steel, titanium,
and copper-tungsten. Tool insulation controls the side
electrolyzing current and hence the amount of oversize.
Spraying or dipping is generally the simplest method of
applying insulation. Teflon, urethane, phenol, epoxy, and
powder coatings are commonly used for tool insulation.3
The material removal rate of an aluminium work-
piece has been obtained by electrochemical machining
using a NaCl electrolyte at different current densities and
compared with the theoretical values.4 It has been
observed that the resistance of the electrolyte solution
decreases sharply with increasing current densities. The
increase in the peak current increases the MRR, TWR
and ROC significantly in a nonlinear fashion, MRR and
ROC increased with the increase in the pulse on time and
the gap voltage was found to have some effect on the
three responses.5,6 The influence of electrochemical pro-
cess parameters such as the applied voltage, electrolyte
Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960 951
UDK 621.7:67.017:661.665.1:661.665.3 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(6)951(2016)
concentration, electrolyte flow rate and tool feed rate on
the metal removal rate and surface roughness to fulfil the
effective utilization of electrochemical machining can be
used.7
For non-passivating electrode systems, the reduction
in electrolyte concentration and an increase in its tem-
perature improve the quality of surfaces.8 The use of a
gap voltage between 20 V and 25 V saves energy and
reduces the production cost.9 The machining current
increases linearly with the tool feed rate. Sparking
causes damage to both the tool and the workpiece due to
the critical feed rate, which is because of the rapid
moment of the tool towards the workpiece. The feed rate
was the main parameter affecting the material removal
rate.10 So it is better to maintain the feed rate according
to the anodic dissolution rate for proper machining.11
The electrolyte temperature, pressure variations in the
inter electrode gap and the choice of an optimum gap
voltage also avoid the occurrence of sparking and the
consequent loss of the tool and workpiece.12
A metal-matrix composite (MMC) contains matrix
materials where reinforcements can be made from poly-
mers, ceramics or metals. MMCs are divided into
composites reinforced by fibres (fibrous composites) and
composites filled with fine particles that are insoluble in
the base-metal-strengthened composites.13 Aluminium-
matrix composites consist of a uniform distribution of
strengthening ceramic particles embedded within an
aluminium matrix. Many researchers discovered alumi-
nium materials and found they exhibit higher strength
and stiffness, in addition to isotropic behaviour at a
lower density, when compared to the un-reinforced
aluminium matrix.14–16 The ceramic’s ability to withstand
high velocity impacts and the high toughness of the
metal matrix, which helps in preventing total shattering,
are one of the main reason for AMC strength. The com-
posites possess good mechanical properties at high
temperature and thus an AMC can be a favourite choice
for cost-effective alternatives and shows potential in
large-scale applications such as automotive, aerospace
and airframe applications. It is proved that among the
aluminium alloys, AA6061 was quite a popular choice as
a matrix material.17 In our previous work the ductile and
microhardness properties of silicon-carbide, boron-car-
bide-based AMCs were analysed and it was reported that
both AMCs are suitable for unconventional machining.18
The fabrication of a MMC with various ceramic particles
such as Si3N4, TiB2, B4C and machining the fabricated
MMC individually was analysed by many resear-
chers.19–21
Fabrication by the pressure-less infiltration process
under a nitrogen gas atmosphere and the grinding of the
aluminium-based MMC reinforced with SiC particles
show that the physical and chemical compatibility bet-
ween the SiC particles and the Al matrix is the main
concern in the preparation of SiC/Al composites.22 Due
to the low coefficients of thermal expansion for maxi-
mizing heat dissipation and minimizing thermal stress,
high-performance thermal management materials are
most commonly used in the packaging of micropro-
cessors, power semiconductors, high-power laser diodes,
light-emitting diodes and micro-electromechanical
systems.23,24
Limited research work has been reported on AMCs
reinforced with B4C due to higher raw-material costs and
poor wetting. Stir casting is accepted as a general com-
mercial technique for producing MMCs.25 Boron carbide
was an attractive reinforcement for aluminium and its
alloys, showing many of the mechanical and physical
properties required of an effective reinforcement, in
particular high stiffness and hardness. These factors
combined with a density less than that of solid alumi-
nium indicate that large specific property improvements
are possible.26 Boron-carbide-particulate-reinforced alu-
minium composites possessed a unique combination of
high specific strength, high elastic modulus, good wear
resistance and good thermal stability compared to the
corresponding non-reinforced matrix alloy system.27
This study covers the fabrication and machining of an
aluminium-based MMC reinforced with SiC particles.
The mechanical properties of the fabricated MMC and
the influence on the ECM machining process parameters
were analysed with experiments. The mechanical and
microstructural properties of AA6061 reinforced with
silicon carbide and AA6061 reinforced with boron
carbide attained from the enhanced stir casting method
were discussed. The influence of the ECM process para-
meters current, voltage, electrolyte concentration, feed
rate, gap and flow rate on the predominant output para-
meters material removal rate, surface roughness and
radial overcut were also analysed.
2 SPECIMEN PREPARATION USING AA6061
The matrix material for the study was AA6061. The
composite material consists of AA6061 alloy as a matrix
material reinforced with three different weight per-
centage of SiC and varying weight percentages of B4C
(2.5 %, 5 % and 7.5 %) prepared through the enhanced
stir-casting technique. The SiC has better mechanical
properties such as high hardness, low density and retains
its properties even at higher temperatures. The B4C is a
hard reinforcement particle that has neutron absorbing
characteristics in nature. The percentage of silicon
content in AA6061 is high compared to other aluminium
alloys and its melting point is low. The chemical com-
position of AA 6061 by weight percentage is Cu 0.1 %,
Mg 0.4 %, Si 10 %, Mn 0.3 %, Ni 0.1 %, Zn 0.1 %, Pb
0.05 % and Sn 0.2 %.The average particle size of the SiC
is 200 mesh, with a density of 3.2 g/cm–3 and a thermal
conductivity 3.2 W cm–1 K–1 and also an average particle
size of the B4C is 200 mesh.
The test specimens were prepared using the simplest
and most commercially used technique known as
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
952 Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960
enhanced stir-casting technique. In the stir-casting
process the pre-heated ceramic particles were mixed with
a vortex of molten alloy created by the rotating impeller.
As a result of the interaction between the suspended
ceramic particles and the moving solid-liquid interface
during solidification, there was a possibility of inhomo-
geneity in the reinforcement distribution. Generally, it is
possible to incorporate up to 30 % of ceramic particles in
the size range 5 μm to 100 μm in a variety of molten
aluminium alloys. AA6061 was placed inside the cru-
cible and the temperature was set 1000 °C. Some 1 % of
the degasser Hexa Chloro Ethane was added to the
melted AA6061. The molten metal was stirred and the
crucible was held with forks to eliminate the gases. The
same process was repeated for various weight percen-
tages of SiC-reinforced AMC and B4C-reinforced AMC.
3 ELECTROCHEMICAL MACHINING
For this experiment the whole work was carried out
with an ECM set up having a power supply of 415 V,
3-phase AC, 50 Hz and it consists of three major sub
systems: the machining cell, the control panel and the
electrolyte circulation tank. The parameter that is able to
change the output parameters by increasing and decreas-
ing the level is known as the controlling parameters or
the input parameters. In this paper the considered input
parameters are the current, voltage, electrolyte concen-
tration, feed rate, gap and flow rate. The output para-
meters considered are the MRR, SR and ROC. The
various levels of input parameters selected for the
machining are listed in Table 1.
Table 1: Input parameters and levels
Tabela 1: Vhodni parametri in njihovi nivoji
Variables
Values of different levels
1 2 3 4 5
Current (A) 90 120 150 180 210
Voltage (V) 8 10 12 14 16
Electrolyte
concentration (g/L) 3.34 6.67 10 13.34 16.67
Feed rate (mm/min) 0.1 0.2 0.3 0.4 0.5
Gap (mm) 0.1 0.2 0.3 0.4 0.5
3.1 Machining process
The machine cell has a tool area of 300 mm2, a
cross-head stroke 150 mm, a job holder 100 mm open-
ing, 50 mm depth and 100 mm width. A DC servo-type
tool feed motor was used for the tool movement. The
control panel consists of an electrical output rating
ranging from 0 A to 300 A DC for any voltage from
0 μm to 20 V, tool feed of 0.2 to 2 mm/min, while the
supply given to the machining was 3-phase AC with
50 Hz. The specimen to be machined was fixed in the
machine vice. The tool was brought near the job with the
help of press buttons provided on the control panel and a
table-lifting arrangement, maintaining a particular gap.
The tool progress was maneuverered vertically by the
servomotor and is governed by a microcontroller-based
programmable drive. The c cathode tool is made of
non-reacting copper material. The process parameters
like current, voltage, electrolyte concentration, feed rate,
gap and flow rate were set. The process was started in
the presence of an electrolyte flow. This electrolyte flow
was adjusted using a flow-control valve. After the
desired time interval, a hooter gives an indication of the
completion of the time and the process. The specimen
prepared was a cylindrical blank of 16 mm in diameter
and 32 mm in height. The electrolyte composition used
was NaCl solution.
4 RESULTS AND DISCUSSION
The hardness of the specimens was measured by a
Rockwell hardness and a tensile test. The Rockwell
hardness number measures the overall response of the
material and it is relatively insensitive to localized
effects. The Rockwell scale is a hardness scale based on
the indentation hardness of a material. The Rockwell test
determines the hardness by measuring the depth of the
penetration of an indenter under a large load compared to
the penetration made by a preload. The chief advantage
of Rockwell hardness is its ability to display hardness
values directly, thus obviating tedious calculations
involved in other hardness-measurement techniques. The
Rockwell Hardness number for AA 6061 and the other
experimental MMC are shown in Figure 1. It is clear
that the hardnesses of the MMCs are closer to one
another, but the values are high compared with AA 6061.
For microstructure analysis the machined samples
were polished using silicon carbide paper (60, 80, 120,
220 and 400) grit and finally using a soft cloth with fine
alumina powder as a slurry. Kerosene was used for
cleaning and polishing to prevent the embedding of
foreign particles in the sample. The samples were then
etched using the modified diamond paste for 140 s. The
long etching time was due to the large oxide content of
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960 953
Figure 1: Rockwell hardness number for experimental samples
Slika 1: Rockwell trdota preizkusnih vzorcev
the aluminium powder. The light microscope photo-
graphs of the seven combinations of composite samples
using an optical microscope of 20× lens are shown in
Figure 2. Figure 2a shows various elements present in
AA6061. Figures 2b to 2d represents AA6061+ rein-
forced silicon carbide particles. AA6061+ reinforced
boron carbide particles are shown in Figures 2d to 2f. It
can be shown that the silicon carbide particles and boron
carbides are homogenously distributed in the aluminium
matrix.
Scanning electron microscopy (SEM) was used to
reveal the morphological features in the machined sam-
ples. For the study of their microstructure the specimen
preparation or polishing is important. The procedure for
preparing the specimen involved the selection of the
specimen and the mounting of the specimen in the
machine, obtaining a flat specimen surface, intermediate
and fine grinding, rough polishing using diamond pow-
der with an oil-soluble paste, fine polishing with alumina
powder along with distilled water and etching using
dilute hydrofluoric acid. The morphological structure of
the AMC was obtained using a ZEISS (NIIST) SEM at
an accelerating voltage of 20 kV. The AA6061 speci-
mens were mounted with conductive adhesives and
coated with gold powder. Then, the SEM images were
taken at the centre of the machined surface of the sample
specimen.
From the above examination both MMCs exhibited
similar microstructural features in terms of homogeneous
particle distributions associated with similar carbide
particle sizes. The SEM analysis of the B4C-reinforced
composites and SiC-reinforced composites exhibited
very similar microstructures. However, it was possible to
observe some large size pores that were not in the
B4C-reinforced composites. The distribution of the
particles was also altered by the growth of the grains. In
the B4C-reinforced MMC microstructure both coarser
grains and finer grains were identified, but the grain size
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
954 Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960
Figure 2: Light microscope (20×) images of seven samples showing the distribution of the reinforcement in the matrix: a) AA6061, b) AA6061 +
2.5 % SiC, c) AA6061 + 5 % SiC, d) AA6061 + 7.5 % SiC, e) AA6061 + 2.5 % B4C, f) AA6061 + 5 % B4C, g) AA6061 + 7.5 % B4C
Slika 2: Svetlobna mikroskopija (20×) sedmih vzorcev, ki ka`e razporeditev delcev za utrditev v osnovi: a) AA6061, b) AA6061 + 2,5 % SiC,
c) AA6061 + 5 % SiC, d) AA6061 + 7,5 % SiC, e) AA6061 + 2,5 % B4C, f) AA6061 + 5 % B4C, g) AA6061 + 7,5 % B4C
Figure 3: SEM microstructure of: a) SiC-reinforced AA6061 and
b) B4C-reinforced AA6061
Slika 3: SEM-posnetek mikrostrukture: a) AA6061, oja~an s SiC in
b) AA6061, oja~an z B4C
was less compared to that of SiC. Similarly, the pore size
was also less for the B4C-reinforced MMC.
The SEM microstructure of the AMCs is shown in
Figure 3. From the Figures 3a and 3b it is evident that
the distributions of the SiC and B4C particles were
homogeneous in the AA6061. Most of the ceramic
particles were found within the grain boundaries. The
distribution of the particles becomes intra granular. The
basic atomic structure of AA6061 is body-centred cubic,
so that the B4C particles were bonded together in rein-
forcement. Good wettability was also seen in both
MMCs, but it was especially high in the B4C.
To determine the rate of penetration of each alumi-
nium alloy, a series of partial infiltrations were per-
formed in order to study the growth rate at short times
(less than 2 h). XRD micro-diffraction of the SiC-rein-
forced AMC and the B4C-reinforced AMC was shown in
Figure 4.
The XRD peak list of the SiC-reinforced AA6061
and B4C-reinforced AA6061 are listed in Tables 2 and 3,
respectively.
Table 2: Peak list for SiC reinforced AA6061
Tabela 2: Seznam vrhov pri AA6061, oja~anem s SiC
Pos.
2 (°)
Height
(cm)
FWHM
2 (°)
d-spacing
(nm)
Rel. Int.
(%)
28.4044 59.37 0.0816 0.313967 8.57
38.4426 692.59 0.1632 0.233979 100.00
44.6516 307.84 0.1632 0.202778 44.45
47.2508 38.12 0.1224 0.192212 5.50
49.0100 4.93 0.0816 0.185716 0.71
56.0546 19.32 0.2856 0.163931 2.79
57.6437 0.75 0.2448 0.159784 0.11
65.0870 156.16 0.1224 0.143194 22.55
78.1848 161.46 0.2448 0.122159 23.31
82.3912 47.66 0.2040 0.169540 6.88
87.9251 6.83 0.4896 0.110964 0.99
Table 3: Peak List for B4C reinforced AA6061
Tabela 3: Seznam vrhov pri AA6061, oja~anem z B4C
Pos.
2 (°)
Height
(cm)
FWHM
2 (°)
d-spacing
(nm)
Rel. Int.
(%)
28.5168 55.08 0.1632 0.312755 5.71
36.5506 6.86 0.1224 0.245644 0.71
38.5654 963.85 0.1632 0.233262 100.00
44.8543 372.10 0.1836 0.201909 38.61
47.3974 42.42 0.1632 0.191651 4.40
56.2284 12.82 0.3264 0.163466 1.33
65.2212 206.18 0.0816 0.142932 21.39
76.4518 7.85 0.3264 0.124490 0.81
78.3073 240.23 0.1632 0.121998 24.92
82.5530 64.93 0.2448 0.116766 6.74
83.4711 3.89 0.4080 0.115714 0.40
88.0604 10.43 0.3264 0.110828 1.08
From Figure 4 it was observed that the waves were
almost the same and symmetrical. The ambiguous struc-
ture was available in both AMCs. As compared to the
SiC-reinforced particle, the other one possessed good
hardness and an even distribution of particles. The start-
ing angle was also high for the B4C-reinforced AA6061.
In the SiC-reinforced AA6061, the SiC particle peaks
were identified at angles of 28.4044, 44.6516, 49.0100,
57.6437, 65.0870 and 87.9251. The remaining peak
values in Table 3 and 4 were related to the AA6061
alloy. Similarly, in the B4C-reinforced AA6061, the B4C
particle peaks were obtained at angles of 28.5168,
36.5506, 44.8543, 56.2284, 65.2212, 76.4518 and
88.0604.
The ductility of the MMC was improved by the
addition of ceramic particles with AA6061. The stress
vs. elongation analyses of the AA6061 samples were
compared with the AA6061 + SiC MMC, and it was
shown in Figure 5. From Figure 5a it was noted that the
strength of the specimen increases with an increase in
the addition of silicon carbide particles. The maximum
strength was obtained for sample 3, with aluminium and
SiC, in a ratio of 100:7.5. Similarly, for the AA6061 +
B4C MMC samples the results were shown in Figure 5b.
In AA6061 + B4C MMC also better tensile strength was
obtained with high percentage of B4C reinforcement.
From the analysis it was concluded that the ductile
nature of AA6061 increased with the addition of SiC and
B4C particles.
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960 955
Figure 4: XRD patterns of: a) SiC-reinforced AA6061 and b)
B4C-reinforced AA6061
Slika 4: Rentgenograma: a) AA6061, oja~anega z SiC in b) AA6061,
oja~anega z B4C
The tensile strength vs. strain analysis of the samples
is shown in Figure 6 from which it is noted that the
ultimate strength, plasticity and elasticity increased with
the percentage of added ceramics. The ultimate point and
yield point of the B4C + AA6061 MMC were high
compared to those of the SiC + AA6061 MMC. The
ductility of both MMCs were high and it can be treated
using unconventional machining process as well as
conventional machining, and also the workability of the
material was very good. Thus SiC-reinforced AA6061
and B4C-reinforced AA6061 MMC were suited for
metal-forming processes such as hot and cold forging,
rolling, drawing and spinning.
4.1 Factors affecting ECM process parameters
4.1.1 Factors influencing the material removal rate
In ECM the current is the major influencing
parameter on the MRR of aluminium-based alloys. The
values of the MRR obtained in experimentation with
different levels of current for the selected samples were
shown in Figure 7a. From Figure 7a it was observed
that when the current was less the MRR was also less.
The AA6061 + 7.5 % B4C gave a lower MRR compared
to AA6061 + 7.5 % SiC. When the current was low the
material removal rate was low and it gradually increased
with increases in the current. A high current will lead to
more material removal and optimum material removal
appeared at a current value of 150 A. For better ECM
indices, higher accuracy, and a better surface finish, it is
essential to choose the proper current density. Low
values of current efficiency may indicate a failure to
choose the optimum machining conditions that lead to
high removal rates and surface roughness.
The influence of voltage over MRR for different
samples is shown in Figure 7b. From the graph it was
clear that the material removal rate was proportional to
rate of change of voltage. When the maximum voltage
was applied in between the workpiece and the tool, the
maximum material can be removed from the workpiece.
If the potential differences in between the copper elec-
trode and aluminium alloys were very low, minimum
material removal occurred from the workpiece.
The influence of electrolyte concentration over MRR
is shown in Figure 7c. For the consideration of electro-
lyte concentration, best material removal occurred at a
10 g/L concentration. A very low electrolyte concen-
tration produced minimum material removal due to the
lack of ionic particles present in the electrolyte. At high
range values the ionic concentration was high and the
reaction phase at this stage was lagging. Hence, a lower
rate of material removal was caused at a high concen-
tration of electrolyte than with the medium electrolyte
concentration of 10 g/L.
The influence of feed rate on MRR is shown in
Figure 7d. The directly proportional effect was shown in
discussion of the feed rate of the tool on the aluminium
alloys. When the feed rate was 0.1 mm/min, then mate-
rial removal was minimum. This process gradually
increased with increases in the feed rate. It was a maxi-
mum at the maximum feed rate of 0.5 mm/min.
The influence of the gap on MRR is shown in Figure
7e. The gap plays a vital role in electrochemical ma-
chining. In electrochemical machining there is no direct
physical contact in between the copper electrode and the
aluminium workpiece. The reaction was carried out in
the presence of an electrolyte that was circulated in bet-
ween the tool and the workpiece. Therefore, to set the
correct gap is an important factor to produce high mate-
rial removal from the workpiece. In our experiment the
maximum material removal could be obtained from the
gap with an optimal value at 0.3 mm. Only a minimum
amount of material was removed from the workpiece at a
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
956 Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960
Figure 6: Stress strain diagram of MMC samples
Slika 6: Diagram odvisnosti napetost-raztezek MMC vzorcev
Figure 5: Stress vs. elongation of: a) SiC-reinforced AA6061 and b)
B4C-reinforced AA6061
Slika 5: Napetost v odvisnosti od raztezka: a) AA6061, oja~an z SiC
in b) AA6061 oja~an z B4C
gap of 0.5 mm. If the gap is a maximum then a lack of
reaction will be carried out in between the tool and the
minimum MRR will be obtained in the workpiece.
The influence of flow rate on MRR is shown in
Figure 7f. The electrolyte flow rate across the tool and
the workpiece stamped the noted impressions. During
machining the chips were formed on the surface of the
workpiece. Electrolyte flow plays the major role in the
material removal process with the removal of contami-
nated chip particles presented on the surface of the
machining area. If the flow rate of the electrolyte is too
low to splash out the removed chips material on the ma-
chined surface, then the minimum amount of material
will be removed from the workpiece. From Figure 7f it
is clear that the material removal rate was increased by
increasing the flow of electrolyte. The maximum flow
rate can be obtained from 8 L/min. Beyond this level it
was slightly reduced due to the high flow of electrolyte,
which will cause a lean electrolyte concentration.
4.1.2 Factors influencing surface roughness
Generally the ECM process is used for the machining
of hard materials with good surface finish. But material
removal rate and surface roughness are inversely propor-
tional to each other. Therefore, if the material removal
rate is high, a poor surface finish will be obtained in the
machining process.
The influence of current on the SR for the selected
samples is shown in Figure 8a. It was found that there
was an inverse effect between the surface roughness and
the current. At low current conditions a good surface
finish was obtained and it was gradually decreased with
an increase in the current. At high current conditions the
least surface roughness was obtained. The best value of
surface roughness was achieved at minimum material
removal and with respect to the hardness of material.
The influence of voltage on the SR for AMCs is
shown in Figure 8b. If the potential difference in bet-
ween the electrode and the workpiece is very high, then a
poor surface roughness can be achieved from the alumi-
mium workpiece. At low voltage the surface finish was
high, and it was slightly increased at 10 V. Then it was
smoothly reduced with an increase in the voltage and
finally poor surface roughness occurred due to the
maximum voltage level.
The SR obtained at the different levels of electrolyte
concentration for selected samples is shown in Figure
8c. In the figure the surface roughness and electrolyte
concenration were directly proportional to each other. If
the electrolyte concentration was less, a poor surface
finish obtained. It is increased with increasing the con-
centration of electrolyte. A high range of surface rough-
ness can be achieved at a high electrolyte concentration.
It was mainly due to the lubrication and good reaction
between the electrode and the workpiece.
The influence of feed rate on SR is shown in Figure
8d. For considering the surface roughness feed rate and
inter electrode gap plays the same role. A good surface
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960 957
Figure 7: Influencing parameters with MRR: a) current, b) voltage, c) electrolyte concentrations, d) feed rate, e) gap, f) flow rate
Slika 7: Parametri, ki vplivajo na MRR: a) tok, b) napetost, c) koncentracija elektrolita, d) hitrost podajanja, e) re`a, f) hitrost pretoka
finish was obtained with a proper gap and a minimum
feed rate. The feed rate was increased when the surface
roughness of the workpiece was reduced.
The value of SR for different levels of gap is plotted
and shown in Figure 8e. The optimal value of the inter
electrode gap was maintained for a better surface rough-
ness. The minimium electrode gap produced the mini-
mum material removal rate and hence provided a good
surface finish. A high surface roughness was obtained
for a 0.2 mm gap and the surface finish was reduced with
increases in the gap between the tool and the workpiece.
The electrolyte flow rate governs the surface finish in
the right way. The influence of flow rate on SR was
shown in Figure 8f. A very low flow rate creates a poor
surface finish due to the non-flushing of the chip mate-
rials on the surface of the workpiece. A good surface
roughness was obtained at a 6 L/min flow of electrolyte.
The flushing pressure was high for very high electrolyte
flow condtions like 10 L/min. A very high flushing
pressure tends to produce a vertex on the machining
zone, and it will produce abrasive action on the surface
of the machined zone. Hence, under high flow rate con-
ditions, the surface roughness was compatively low.
4.1.3 Factors influencing radial overcut
The ROC values obtained at different levels of
current for the selected samples are shown in Figure 9a.
The ROC was increased with an increase in the current.
If the current was low then the minimum material was
removed from the surface of the machined zone. Hence,
the ROC was low. When the current was increased gra-
dually, then the ROC was increased. When a high current
was applied in between the tool and the workpiece, then
the maximum amount of material was removed from the
workpiece and a high ROC was produced.
The influence of the applied voltage on the ROC is
shown in Figure 9b. When the applied voltage between
the electrodes was high, a high ROC was obtained. The
optimal value of the ROC was achieved at a 12 V poten-
tial difference. At very low and very high voltages the
flow of electrons through the electrodes is improper and
hence it will tend to produce a variable machining rate.
So the extreme levels of voltages were produced maxi-
mum ROC and minimum ROC was happened at mid-
range values.
The effects of the electrolyte concentration on radial
overcut for different AMCs are shown in Figure 9c.
When the electrolyte concentration was high, the ROC
was low. High lubrication was provided in a high con-
centration of electrolyte solutions and hence a better
surface finish was obtained. The concentrated electrolyte
solution has a good number of ions that will act as the
catalyst to improve the reaction between the electrode
and the workpiece. In the above condition an enormous
amount of hydrogen was generated and an unwanted
reaction in the machining zone was avoided. So, the
minimum ROC was obtained with high electrolyte con-
centrations.
The influence of feed rate on the ROC is shown in
Figure 9d. The material removal rate and the ROC were
directly proportional to each other. The higher feed rate
of the tools produced a poor surface roughness and a
high material removal rate. The higher rate of material
removal from the workpiece increased the ROC. The
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
958 Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960
Figure 8: Influencing parameters with SR: a) current, b) voltage, c) electrolyte concentrations, d) feed rate, e) gap, f) flow rate
Slika 8: Parametri, ki vplivajo na SR: a) tok, b) napetost, c) koncentracija elektrolita, d) hitrost podajanja, e) re`a, f) hitrost pretoka
ROC was high at a very high range of the tool feed on
the workpiece. The ROC values obtained in the different
gaps for the selected samples were plotted in Figure 9e.
The inter electrode gap was maintained with an optimal
range of values. If the gap between the tool and the
workpiece was too low, then the contact took place and
the very minimum material was removed from the work-
piece. Hence, the ROC in the low gap was a minimum.
The spark in between the tool and the workpiece material
might be produced because of an improper gap and
irregular machining on the workpiece. Due to the
irregular machining the ROC was very high.
The influence of flow rate on ROC is shown in
Figure 9f. When the flow of the electrolyte was very low
then the sludge was stagnated at the machining zone.
Further machining was on the chip with a new machin-
ing surface and a poor surface finish leads to high ROC.
Similarly, the high velocity of the stream of electrolyte
created the flow of the abrasive action with sludge chips
and hence the ROC was increased. The optimal flow of
electrolyte was needed for the proper removal of sludge
formation and good machining accuracy.
5 CONCLUSION
In this paper the microstructure and mechanical pro-
perties of AA6061 reinforced with silicon carbide and
AA6061 reinforced with boron carbide obtained from an
enhanced stir-casting method was investigated. Three
different weight percentages, i.e., 2.5 %, 5 % and 7.5 %,
of silicon carbide and boron carbide were used for the
reinforcement. The presence of silicon- and boron-based
particles employs a key role in the microstructure deve-
lopment of the composites. The ductility of the AA6061
was increased in both the reinforced AMCs with signi-
ficantly good tensile properties. The microhardness was
markedly influenced by both the alloying elements.
From the study it was observed that the selected AMCs
were suitable for unconventional machining process like
electrochemical machining. In ECM the input parame-
ters influence the output variables Material Removal
Rate (MRR), Surface Roughness (SR) and Radial Over-
cut (ROC). The higher input parameters increased the
Material Removal Rate. The higher value of Material
Removal Rate during the machining produced poor-sur-
face-quality materials. The RO was also in close agree-
ment with the SR.
Acknowledgement
The author gratefully acknowledges the contributions
of National Institute for Interdisciplinary Science and
Technology Trivandrum, National Institute of Techno-
logy Trichy and Annamalai University Chithambaram.
6 REFERENCES
1 K. P. Rajurkar Sekar. T. Marappan, R. Experimental investigations
into the influencing parameters of electrochemical machining of
AISI 202, Journal of Advanced Manufacturing Systems, 7 (2008) 2,
337–43, doi:10.1142/S0219686708001486
2 A. DeBarr, D. A. Eand Oliver, Electro-chemical Machining, Mac-
donald & Co. Ltd, 1968
3 Metals Handbook, Vol. 16, Machining, ASM International, Materials
Park, OH 1989
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960 959
Figure 9: Influencing parameters with ROC: a) current, b) voltage, c) electrolyte concentrations, d) feed rate, e) gap, f) flow rate
Slika 9: Parametri, ki vplivajo na ROC: a) tok, b) napetost, c) koncentracija elektrolita, d) hitrost podajanja, e) re`a, f) hitrost pretoka
4 S. K. Mukherjee, S. Kumar, P. Shrivastava, A. Kumar, Effect of
valency on material removal rate in electrochemical machining of
aluminium, Journal of Materials Processing Technology, 202 (2008),
398–401, doi:10.1016/j.jmatprotec.2007.09.065
5 J. A. Westley, J. Atkinson, A. Duffield, Generic aspects of tool de-
sign for electrochemical machining, Journal of Materials Processing
Technology, 149 (2004), 384–392, doi:10.1016/j.jmatprotec.2004.
02.046
6 S. Dhar, R. Purohit, N. Saini, A. Sharma, G. H. Kumar, Ma-
thematical modelling of electric discharge machining of cast
Al-4Cu-6Si alloy-10 wt.% SiCp composites, Journal of Materials
Processing Technology, 194 (2007), 24-29, doi:10.1016/j.jmatprotec.
2007.03.121
7 C. Senthilkumar, G. Ganesan, R. Karthikeyan, Study of electroche-
mical machining characteristics of Al/SiCp composites, Journal of
Materials Processing Technology, 43 (2009), 256–263, doi:10.1007/
s00170-008-1704-1
8 T. Masuzawa, H. K. Tonshof, Three Dimensional Micro Machining
by Machine Tools, Annals of CIRP, 42 (1997) 2, 621–628,
doi:10.1016/S0007-8506(07)60882-8
9 A. F. Rashed, H. Youssef, H. El-Hofy, Effect of Some Process Para-
meters on the Side Machining During Electrolytic Sinking,
PEDAC-3 Conf., Alexandria, 1986, 733–746
10 J. C. da Silva Neto, E. M. da Silva, M. B. da Silva, Interventing
variables in electrochemical machining, Journal of Materials Pro-
cessing Technology, 179 (2006) 1–3, 92–96, doi:10.1016/
j.jmatprotec.2006.03.105
11 H. Youssef, H. El-Hofy, Y. El-Mehdawy, Sparking Phenomena and
Hole Oversize by ECM, Effect of Some Process Parameters,
Alexandria Engineering Journal, 28 (1989) 4, 247–259
12 M. Datta, R. V. Shenoy, L. T. Romatkiw, Recent Advances in the
Study of Electrochemical Micromachining, Journal of Engineering
for Industry, 118 (1996), 29–36, doi:10.1115/1.2803644
13 T. W. Clyne, P. J. Withers, An introduction to metal matrix compo-
sites, Cambridge University Press, 1993
14 K. K. Chawla, Composite materials-science and engineering, Sprin-
ger-Verlag, New York (1998) 2, 165–211, doi:10.1007/978-0-387-
74365-3_1
15 D. L. McDanels, Analysis of stress–strain, fracture, and ductility
behavior of aluminium matrix composites containing discontinuous
silicon carbide reinforcement, Metall Trans A, 16 (1985), 1105–15,
doi:10.1007/BF02811679
16 F. Toptan, A. Kilicarslan, M. Cigdem, I. Kertil, Processing and micro
structural characterization of AA 1070 and AA 6063 matrix B4C
reinforced composites, Advanced Component Manufacture from
Light Materials International Conference on Materials for Advanced
Technologies, 31 (2010) 1, 87–91, doi:10.1016/j.matdes.2009.11.064
17 C. San Marchia, M. Kouzelia, R. Raoc, J. A. Lewisc, D. C. Dunanda,
Alumina-Aluminum Interpenetrating Phase Composites With Three
Dimensional Periodic Architecture, Journal of Scripta Materialia, 49
(2003) 9, 861–866, doi:10.1016/S1359-6462(03)00441-X
18 T. M. Chenthil Jegan, D. Ravindran, M. Dev Anand, Material Cha-
racterization Study on Aluminium Metal Matrix Composites by
Enhanced Stir Casting Method, Advanced Materials Research,
984–985 (2014), 326–330, doi:10.4028/www.scientific.net/AMR.
984-985.326
19 K. M. Shorowordi, T. Laoui, A. S. M. A. Haseeb, J. P. Celis, L.
Froyen, Microstructure and interface characteristics of B4C, SiC,
Al2O3 reinforced Al matrix composites: a comparative study, J.
Mater. Process. Technol., 142 (2003), 738–743, doi:10.1016/S0924-
0136(03)00815-X
20 L. E. G. Cambronero, E. Sanchez, J. M. Ruiz-Roman, J. M. Ruiz-
Prieto, Mechanical characterization of AA7015 aluminum alloy rein-
forced with ceramics, Proceedings of the International Conference on
the Advanced Materials Processing Technology, 143–144 (2003),
378–383, doi:10.1016/S0924-0136(03)00424-2
21 E. Mart, A. Forn, R. Nogue, Strain hardening behaviour and tem-
perature effect on Al-2124/SiCp, Proceedings of the International
Conference on the Advanced Materials Processing Technology,
143–144 (2003), 1–4, doi:10.1016/S0924-0136(03)00292-9
22 J. S. Kwak, Y. S. Kim, Mechanical properties and grinding perfor-
mance on aluminum-based metalmatrix composites, Journal of Mate-
rials Processing Technology, 201 (2008) 1–3, 596–600, doi:10.1016/
j.jmatprotec.2007.11.139
23 M. Tan, Q. Xin, L. Zhenghua, B. Y. Zong, Influence of SiC and
Al2O3 particulate reinforcements and heat treatments on mechanical
properties and damage evolution of Al-2618 metal matrix compo-
sites, Journal of Materials Science, 36 (2001), 2045–2053,
doi:10.1023/A:1017591117670
24 D. T. Chung, Development of new actuators for flapping wing flight,
Materials Science Forum, 543 (2007), 36–41, doi:10.4028/
www.scientific.net/MSF.539-543.36
25 P. T. B. Shaffer, Engineered Materials Handbook, 4, 1991, 804-810
26 I. Kerti, F. Toptan, Microstructural variations in cast B4C-reinforced
aluminium matrix composites (AMCs), Journal of Materials Letters,
62 (2008) 8–9, 1215–1218, doi:10.1016/j.matlet.2007.08.015
27 J. Hashim, L. Looney, M. S. J. Hashmi, Metal matrix composites:
production by the stir casting method, Journal of Materials Process-
ing Technology, 92–93 (1999), 1–7, doi:10.1016/S0924-0136(99)
00118-1
T. M. CHENTHIL JEGAN et al.: MACHINING PARAMETERS INFLUENCING IN ELECTRO CHEMICAL MACHINING ...
960 Materiali in tehnologije / Materials and technology 50 (2016) 6, 951–960