International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 2- March 2016
“Investigations of heat treatment effect on dry
sliding wear behavior of as cast, grain refined
and modified gravity cast A356 by using
Taguchi’s method”
1
Ravindra Babu G, 2Dr Girish D P, 3Pavitra Ajagol
1
Assistant Professor-SG, Department of Mechanical Engineering, Sahyadri College of Engineering & Management,
Mangalore-575007, Karnataka, India1 Email:ravindra.mech@sahyadri.edu.in
2
Professor, Department of Mechanical Engineering, Government Engineering College, Ramanagar, Karnataka,
India2
3
Assistant Professor, Department of Mechanical Engineering, Sahyadri College of Engineering & Management,
Mangalore-575007, Karnataka, India3Email:pavitra.ajagol@gmail.com
Abstract
In the present study, Al-Si alloy A356 grain refined
and modified using Al-5Ti-1B and Al-10Sr
respectively was cast in pre-heated permanent mold
using liquid metallurgy route. They were further heat
treated (T6) by solutionising at 5400 C, quenched in
water at 700 C and aged for 5 hours at 180 0 C. They
were tested for hardness and wear resistance using
taguchi method. A quantum rise in wear resistance
was observed in Grain refined, Modified and heat
treated A356 compared to as cast A356, Grain
refined and modified A356. The improvement in
wear resistance may be attributed to the refined
microstructure, grain refinement and modification
and improved hardness due to heat treatment.
Keywords: Wear; Orthogonal Array, ANOVA,
Taguchi Method
I. Introduction:
In the last two decades, the development of
aluminum –silicon alloys has been one of the major
innovations in the materials. Their potential is based
on the combination of properties such as low density,
high stiffness and strength; good wear resistance,
corrosion resistance, thermal and electrical properties
as well as other properties. Aluminum-based
composite have evoked a keen interest in recent times
for potential applications in aerospace and
automotive industries, owing to their superior
strength-to-weight ratio and high temperature
strength [1]. Li et al. [2] compared microstructures of
ISSN: 2231-5381
aluminum A359 alloy with those of A359/SiC
composite. They found SiC particles crowded along
the eutectic phase of the matrix. Vickers micro
hardness measurements showed that the hardness of
the matrix material is very similar to the unreinforced
parent alloy. According to Kannan and Kishawy [3]
the micro hardness of aluminum metal matrix
composites varied inversely with the volume fraction
and fineness of the reinforced particles. This means
that for analytical modeling, rate-dependent
properties of the matrix can be considered same as
that of the unreinforced alloy. Francis Uchenna et al
[4] studied the effect of parameters on dry sliding
wear characteristics of Al-Si alloys. Micro structural
characterization was done using optical microscope
(OM) and scanning electron microscope (SEM).
Hardness and wear characteristics of different
samples have shown near uniform behaviour. From
this experimentation they found that the wear rate
decreased when the percentage of silicon increases
and wear was observed to increase at higher applied
load, higher sliding speed and higher sliding distance.
Also they observed that the wear characteristics of
Al-14%Si was superior to those of Al-7%Si and Al12%Si due to the degree of refinement of their
eutectic silicon.
Riyadh A et al [5] studied the effect of load and
speed on sliding friction coefficient using a pin-ondisc Tribometer with three different loads (10, 20,
and 30 N) at three speeds (200, 300, and 400 r/min)
and relative humidity of 70%. From the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 2- March 2016
experimentation they showed that the wear rate
increased with increasing load and decreased with
increasing sliding distance, whereas the friction
coefficient decreased with increasing sliding speed
before a stable state was reached. Also the friction
coefficient decreased with increasing load. They
suggested that after maintaining appropriate sliding
speed and normal load level combination, frictional
force and wear rate can be reduced which will
improve the mechanical processes.
The Taguchi technique is a powerful design of
experiment tool for acquiring the data in a controlled
way and to analyze the influence of process variable
over some specific variable which is unknown
function of these process variables and for the design
of high quality systems [6, 7]. Taguchi creates a
standard orthogonal array to accommodate the effect
of several factors on the target value and defines the
plan of experiment [8, 9]. The experimental results
are analyzed using analysis of means and variance to
study the influence of parameters.
II. MATERIALS
Table 1: Chemical Composition of A356
Element
Weight %
7.25
0.45
0.086
0.010
0.018
0.025
0.005
0.028
Balance
III. METHODOLOGY
a.
Microstructure:
The
specimens
for
microstructure were prepared as per standard
metallurgical procedures, etched in etchant prepared
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b. Hardness test: The hardness tests were conducted
as per ASTM E10 norms using Rockwell Hardness
Tester, where the tests were performed at randomly
selected points on the polished surface of samples by
providing sufficient space between indentations and
distance from the edge of specimen.
c. Wear test: Dry sliding Wear tests were carried out
at room temperature using Pin-on-Disc apparatus for
various sliding distances. The experiments were
conducted as per the standard L9 orthogonal array for
various factors and levels given in table 2. The wear
parameters selected for the experiment are abrading
distance in m, and type of material. The response
studied was wear in terms of grams with the objective
of “smaller is the better” type of quality
characteristic. The loss of weight was measured using
an electronic balance to the accuracy of 0.0001gm.
The disc was thoroughly cleaned using acetone after
every test.
Table 2: Testing Parameters and their Values
Grain refined and modified A356 were cast in preheated permanent mold in the form of cylindrical
rods of diameter 25 mm and length 250 mm and heat
treated
(T6).Test
specimens
required
for
Microstructure, hardness and wear were obtained by
machining the rods and tested as per ASTM
standards.
Si
Mg
Fe
Cu
Mn
Ni
Zinc
Others
Al
using 90 ml water, 4 ml HF, 4 ml H2S04 and 2g Cr03
and photographed using Optical Microscope.
Factors
Level 1
Level 2
Type of material
A356
AGRM
Sliding Distance (m)
300
600
Level 3
AGRMH
900
4. Result and Discussions
4.1 Hardness
The hardness values of as-cast A356, Grain refined
and Modified A356 and Grain refined and Modified
and heat treated A356 are shown in Table 2. It is
clear from the Fig.1 that AGRM has higher hardness as
compared to A356 with hardness 60. A further
increase in hardness is obtained in AGRM after heat
treatment. After heat treatment, 8.33% increase in
hardness of AGRM was observed.
Table 2: Hardness values of as-cast and Heat
Treated A356, Grain refined and Modified A356
Sl.
Designati
Hardness
Alloy
no
on
(RB)
1
A356
A356
60
A356 with Grain
2
refinement and
AGRM
65
modification
Heat treated A356
with Grain
3
AGRM-H
91
refinement and
modification
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 2- March 2016
100
80
60
40
20
0
Series1
Plate.3: Microstructure of AGRM-H
Type of Material
Fig 1: Hardness values of As-cast, Grain Refined
Modified and Heat Treated A356
4.2 Microstructure (200x)
Plate.1 shows the distribution of the primary dendrite
alpha phase (aluminum rich phase) in as-cast alloy
which is predominant in the matrix. Grey coloured
needle shaped silicon particles seen in and around the
inter dendrite regions resulted in increased aspect
ratio.
Plate.1: Microstructure of As-cast A356
Plate.2 shows the Microstructure of combined Grain
refined and modified alloy. Grain refinement resulted
in fine grain structure and reduction in size of
primary aluminum grains. Grain modification
produced fibrous and finely dispersed Si and
promoted the formation of finer particles of Iron-rich
inter-metallic compounds which are hard compared
with as-cast material. Further, it led to refined
porosity dispersion leading to increased hardness and
wear resistance.
Plate.3 shows the microstructure of AGRM-H in which
complete spherodisation of Silicon particles with
aspect ratio nearing 1 and uniform distribution of Si
in the matrix.
4.3 S/N Ratios Analysis
The standard L9 orthogonal array consists of nine
tests as shown in the Table 3. The first column is
assigned by type of material second column was
assigned by sliding distance. The response studied
was wear in terms of grams with the objective of
“smaller is the better” type of quality characteristic.
Table 3: Orthogonal Array (L9) of Taguchi for
Wear Test
Material
Plate.2: Microstructure of Grain refined and Modified A356
(AGRM)
A356
A356
A356
AGRM
AGRM
AGRM
AGRM-H
AGRM-H
AGRM-H
Sliding
Distance
(m)
300
600
900
600
900
300
900
300
600
wear
rate
gm/m
e-5
0.53
1.05
1.12
0.92
1.03
0.44
1.00
0.40
0.89
SNRA1
MEAN1
RESI1
5.51448
-0.42379
-0.98436
0.72424
-0.25674
7.13095
0.00000
7.95880
1.01220
0.53
1.05
1.12
0.92
1.03
0.44
1.00
0.40
0.89
-0.0066667
0.0166667
-0.0100000
-0.0100000
0.0033333
0.0066667
0.0066667
-0.0000000
-0.0066667
The influence of control parameters such as sliding
distance, types of material on wear has been
evaluated using S/N ratio response analysis. The
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 2- March 2016
sliding wear quality characteristic selected was
smaller is the better type and same type of response
was used for signal to noise ratio which is given
below.
Table.4 Response Table for Signal to Noise Ratios
Smaller is better
Level MATERIAL Distance
1
1.3688 6.8681
2
2.5328 0.4376
3
2.9903 -0.4137
Delta 1.6216 7.2818
Rank
2
1
From the above table it is clear that sliding distance
plays major role in wear as compared to different
type of aluminum material in this study. Fig 2 and 3
show the main effects plots of S/N ratios and main
effect plot for means.
4.4 ANOVA Analysis
The analysis of variance (ANOVA) was used to
analyze the influence of wear parameters like type of
materials and sliding distance. The ANOVA
establishes the relative significances of factors in
terms of their percentage contribution to the
response. We can observe from the ANOVA analysis
(Table 5) that the type of materials and sliding
distance have the influence on wear of aluminium
material. The last column of the Table 5 indicate the
percentage contribution of each factor on the total
variation indicating their degree of influence on the
result. One can observe from the ANOVA Table 5
that the sliding distance (95.12%) have great
influence on the wear of the aluminium material, type
of materials (4.76%) have less influence on the wear
of the A356 alloy.
Table.5 Analysis of Variance for wear rate gm/m
e-5, using Adjusted SS for Tests
Source
DF Seq SS Adj SS Adj MS P
Material
2 0.03047 0.03047 0.01523 4.76
Sliding Distance 2 0.60807 0.60807 0.30403 95.12
Error
4 0.00067 0.00067 0.00017
Total
8 0.63920
S = 0.0129099 R-Sq = 99.90% R-Sq(adj) = 99.79%
Fig.2 Main effects plot for SN ratios
Fig.3 Main effects plot for means
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Conclusions:
The following conclusions, from the experiential
investigation can be made,
1. The DOE technique is successfully used to dry
sliding wear behaviour of as cast, grain refined and
modified gravity cast A356
2. The ANOVA analysis shows that the sliding
distance (95.12 %) have significant influence on wear
of aluminium in dry condition as compared to type of
material (4.76%)
3. Grain refinement resulted in fine grain structure
and reduction in size of primary aluminium grains.
Grain modification produced fibrous and finely
dispersed Si and promoted the formation of finer
particles of Iron rich inter-metallic compounds which
are hard compared with as-cast material.
4. Heat treatment resulted in Spherodisation of needle
shaped Silicon particles leading to reduced aspect
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 2- March 2016
ratio improved Hardness and wear resistance was
achieved in AGRM-H as compared to As-Cast A356 and
Grain refined, modified A356.
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