Effects of solidification time on mechanical properties

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 02 | Feb-2014, Available @ http://www.ijret.org 71
EFFECTS OF SOLIDIFICATION TIME ON MECHANICAL PROPERTIES
AND WEAR BEHAVIOUR OF SAND CAST ALUMINIUM ALLOY
S. Ilangovan
Assistant Professor (SG), Department of Mechanical Engineering, Amrita School of Engineering, Amrita Vishwa
Vidyapeetham, Ettimadai Post, Coimbatore – 641105, Tamil Nadu, India.
Abstract
An investigation was carried out to understand the effects of solidification time of the cylindrical specimen on hardness, wear rate and
the coefficient of friction of Aluminium alloy (LM4). The commercially available LM4 Aluminium alloy was melted in a crucible
furnace under argon atmosphere. The molten metal was poured into sand moulds having dissimilar size holes. The cast rods were
tested for Vickers micro-hardness, wear rate and the coefficient of friction. The solidification time increases from 0.22 to 0.61 seconds
when the diameter varied from 20 to 35mm. It was found that the hardness of the alloy vary with the diameter of the rod. Wear rate is
inversely proportional to the hardness of the alloy. It was observed that the yield strength and tensile strength are increases with
hardness, whereas the % elongation decreases. Further, the coefficient of friction is independent of hardness and not affected by the
sliding time. Wear rate decreases linearly with hardness.
Keywords: LM4- alloy, coefficient of friction, wear rate, solidification time, sand cast.
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1. INTRODUCTION
The surface-to-volume ratio is an significant quantity in
thermal physics. It governs the behaviour of heating/cooling of
physical substance as a function of size. The solidification
time is a function of the volume of a casting and its surface
area [1]. Chvorinov's Rule is a mathematical relationship first
expressed by Nicolas Chvorinov in 1940, that relates the
solidification time for a simple casting to the volume and
surface area of the casting. In simple terms the rule establishes
that under otherwise identical conditions, the casting with
large surface area and small volume will cool more rapidly
than a casting with small surface area and a large volume [2].
Cooling rate can be an indication of material quality. Areas of
the casting that cool rapidly generally have a more favorable
grain structure and therefore tend to have better mechanical
properties. The areas of the casting that cool more slowly
generally tend to have poorer material properties [3, 4].
Therefore, it is responsible of the foundry engineer to control
the solidification time to the best of skill so that the
microstructure of the final product can be controlled to
optimize the properties desired.
In this work, the mechanical properties and the wear
behaviour of the Aluminium alloy was studied by varying the
solidification time using dissimilar component diameters in
sand casting process.
2. EXPERIMENTAL PROCEDURE
2.1 Material Preparation
The Aluminium alloy (LM4) castings were produced from
commercially available LM4 Aluminium billets as shown in
Figure1. The billets were melted in a graphite crucible using
an electric furnace. Inert gas such as argon is used to prevent
oxidation of the molten metal. The molten metal is poured at a
temperature of 720ºC into the sand moulds at room
temperature to make rods of Ø20, Ø25, Ø30 and Ø35
diameters and length of 150 mm.The photographic image of
the cast rods is shown in Figure 2. The chemical composition
of the cast alloy was tested using spectrometer and the results
are reported in Table 1.
Fig-1: LM4 Aluminium billet

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Fig-2: LM4 Aluminium cast rods
Table-1: Alloy composition
Al Si Cu
Other
Elements
91.41 5.11 2.57 Balance
2.2 Hardness Testing
To assess the effect of diameter, the hardness of the entire
specimens were measured using a micro-hardness tester
(Figure 3). A number of readings were taken at different
location for each specimen and an average value was
calculated. The specimens were prepared and tested as per
ASTM- E384 standard. The parameters used in this test were:
50 gm-f applied load and 20 s duration. The hardness values
varied in each sample was within ±5 HV.
Fig-3: Micro-hardness tester
2.3 Tensile Testing
The tensile test was conducted to predict the yield strength
(YS), tensile strength (TS) of the material as well as to find the
ductility in terms of % elongation of the alloy. The test
specimens were prepared according to ASTM - E4 standard.
Figure 4 and 5 shows the drawing and the photographic image
of the specimen.
The specimens were tested using computerized universal
testing machine (Make: Tinius Olsen; Model: H25KT). The
experimental setup is as shown in the Figure 6.
Fig-4: Drawing of the tensile test specimen
Fig-5: Photograph image of the tensile test specimen
Fig-6: Universal Tensile Testing Machine
2.4 Friction and Wear Testing
The friction and wear tests were performed on specimen of all
diameters. Pin-on-Disc wear tester was used. It is equipped
with LVDT sensors attendant with data acquisition software
(Make: Ducom; Model: TR-20LE). The experiment was
conducted in dry sliding condition in normal atmosphere. The
test specimens in the form of pin of 5 mm diameter and 40
mm length were prepared by machining the cast rods. The
counter face disc material was hardened steel (EN31). The
data acquisition system provides three kinds of plots: (a)
Height loss versus time (b) Coefficient of friction versus time
and (c) Frictional force versus time. ASTM G99 standard test
method was used to conduct the test. The experimental setup
is shown in the Figure 7. The wear rate was measured from the
volume loss per unit sliding distance. It is expressed in
mm3/m. Volume loss was calculated using the plot, height

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loss versus time. The test parameters used for the friction and
wear test are shown in Table 2.
Fig-7: Friction and wear testing setup
Table-2: Friction and wear testing parameters
Test parameters Unit Test values
Speed rpm 239
Velocity m/s 1
Track radius mm 40
Time s 600
Load applied N 15
3. RESULTS AND DISCUSSION
3.1 Solidification Time
The solidification time for each specimen is estimated by
using Chvorinov's Rule, which states that the solidification of
a casting is directly proportional to the square of the volume-
to-surface area of the casting (t = B (V/A) n) and the values
are reported in Table 3. The mould constant B, is assumed as
0.1 s/mm2. It is noted from the table that the solidification
time of the casting increases with increase in diameter of the
casting.
Table- 3: Shows the solidification time for various diameters
of the specimen
Dia.
(mm)
Vol. (V)
(mm3)
Area
(SA)
(mm2)
(V/SA)2
(mm2)
Time,
B(V/SA)2
in Sec.
20 47,143 10,057 22.09 0.22
25 73,661 12,768 33.64 0.34
30 1,06,071 15,557 46.24 0.46
35 1,44,375 18,425 60.84 0.61
3.2 Hardness
The influence of diameter on hardness of the cast rod is shown
in Figure 8. The hardness of the specimen decreases from 94
to 87 HV when the diameter of the specimen increases from
20 to 35 mm. The decrease in the hardness is owing to
difference in solidification time (0.61- 0.22 = 0.39s).
Fig-8: Hardness versus diameter
Figure 9 shows the variation of YS and TS of the alloy with
hardness measured at various diameters. Both YS and TS are
increasing with hardness of the alloy. Similarly the variation
of the % elongation of the alloy with hardness is shown in the
figure. It is noted from the figure that % elongation decreases
with hardness of the alloy. Hence, it may be concluded that the
YS and TS and % elongation are the functions of hardness of
the alloy. The behaviour observed in this study is consistent
with that of Schwartz and Plews [5].
Fig-9: YS, TS, and %elongation versus hardness

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3.3 Wear Behavior
A typical height loss versus sliding time plot for velocity 1m/s
at constant load of 15N is shown in the Figure 10. It can be
seen that the height loss increases linearly with the sliding
time. This behavior is in agreement with that of Singh et al.
[6].
Fig-10: Wear versus time
Figure 11 shows the relationship between wear rate and the
hardness of the alloy. The wear rate decreases as the hardness
of the alloy increases. It is in agreement with that of Archard’s
adhesion theory of wear as given in equation 1 [7].
WR=k×W/H---------------- (1)
Where, WR=wear rate in mm3/m; k=wear coefficient; W=
applied load in N; H=hardness in N/mm2.
Fig-11: Wear rate versus hardness
A typical plot of coefficient of friction of the alloy as a
function of sliding time is shown in the Figure 12. It can be
seen from the plot that the coefficient of friction of the alloy
reaches a steady state after showing a sharp increase during
the initial sliding period. The sharp increase is due to uneven
contact between specimen pin and the counterpart disc. Once
an ideal contact is achieved, then the result shows the steady
state value. The values of coefficient of friction obtained in the
steady state regime remains nearly constant (~0.4) for sliding
time. Hence, we may conclude that the coefficient of friction
of the alloy is not affected by the sliding time of the alloy.
Fig-12: Coefficient of friction versus sliding time
Figure 13 shows the variation of COF with hardness of the
alloy. The value of COF is found to be around 0.4 with
marginal variation. Hardness of the alloy does not affect the
COF value. Hence, we may conclude from the results that
COF value is not affected by the hardness of the alloy. An
observation of this study is in agreement with that of Zhang et
al. [8, 9] and Singh et al. [6].
Fig-13: COF versus hardness
CONCLUSIONS
The significant findings of the present study can be
summarized as follows.
• Solidification time increases as the diameter of the
specimen increases keeping other parametres constant.
• Hardness of the alloy decreases with an increase in the
diameter which is due to increased solidification time.
• Yield strength and tensile strength are increases with
hardness.
• % elongation decreases with an increase in hardness,
YS and TS of the alloy.

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• Wear rate is inversely proportional to the hardness of
the alloy as per Archard’s adhesion theory of wear.
• The coefficient of friction is found to be a constant and
is not a function of hardness.
REFERENCES
[1]. Gorazd Planinsic and Michael Vollmer (2008), “The
surface to-volume ratio in thermal physics”, European Journal
of Physics, Vol 29, No 2, pp 369-384
[2]. Eman J. Abed (2011), “The influence of different casting
method on solidification time and mechanical properties of
AL- Sn castings”, International Journal of Engineering &
Technology, Vol 11, No 6, pp 34-44.
[3]. Hurst S (1996), “Metal Casting”, Intermediate
Technology Publications.
[4]. Askeland R, “The Science and Engineering of Materials”,
4th Edition.
[5]. Schwartz LH and Plewes JT (1974), “Spinodal
Decomposition in a Cu-9 wt% Ni-6 wt% Sn-II, A Critical
Examination of Mechanical Strength of Spinodal Alloys”,
Acta Metallurgica, Vol 22, No 7, pp 911-921.
[6]. Singh JB, Cai W and Bellon P (2007), “Dry sliding of
Cu-15 wt%Ni-8 wt%Sn bronze: Wear behaviour and
microstructures”, Wear, Vol 263, No(1-6), pp 830-841.
[7]. Archard JF (1953), “Contact and rubbing of flat
surfaces”, Journal of Applied Physics, Vol 24, No 8, pp 981-
988.
[8]. Zhang SZ, Jiang BH and Ding WJ (2008), “Wear of Cu-
15Ni-8Sn spinodal alloy”, Wear, Vol 264, No (3-4), pp199-
203.
[9]. Zhang S, Jiang B and Ding W (2010), “Dry sliding wear
of Cu-15Ni-8Sn alloy”, Tribology International, Vol 43, No
(1-2), pp 64-68
BIOGRAPHIE:
The author has completed his Bachelor’s
Degree in Mechanical Engineering and
Master’s Degree in Production Engineering.
Also he has fourteen years of industrial
experience and sixteen years in teaching.
Further he has completed Ph.D. in Materials Engineering.

Effects of solidification time on mechanical properties

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