This paper attempts to investigate the influence of the microstructure and mechanical property changes on Al-Si 18% alloy by combined action of both (Al-TiB2+ Na2SiF6) grain refinement and modification and without grain refinement and modification effect by cooling under three different conditions very fast cooling, moderate cooling and slow cooling.. The microstructures of the castings are studied by optical microscopes. The microstructure and mechanical properties (tensile strength, hardness and wear) was tested of as cast, treated (grain refined and modified) samples. The result demonstrated that significant refinement of α Al was due to the addition of refiner. Similarly addition was responsible for the modification of Si particles. These refinement and modification in microstructure resulted in improvement of hardness value, tensile strength and resistance for wear.

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Influence Of Combined Grain Refinement And
Modification On Microstructure And
Mechanical Properties Of Al-Si18% Alloy.
Ashish Dahala
, Debesh karkia
, Nischal P. Rajbhandaria,
,Kotgi Kotreshb
a
Department of Mechanical Engineering, NitteMeenakshi Institute of Technology, Bangalore, 560064,India
b
Asst.Proffesor ,Department of Mechanical Engineering, NitteMeenakshi Institute of Technology, Bangalore, 560064,India
Abstract
This paper attempts to investigate the influence of the microstructure and mechanical property changes on Al-Si
18% alloy by combined action of both (Al-TiB2+ Na2SiF6) grain refinement and modification and without grain
refinement and modification effect by cooling under three different conditions very fast cooling, moderate cooling
and slow cooling.. The microstructures of the castings are studied by optical microscopes. The microstructure and
mechanical properties (tensile strength, hardness and wear) was tested of as cast, treated (grain refined and
modified) samples. The result demonstrated that significant refinement of α Al was due to the addition of refiner.
Similarly addition was responsible for the modification of Si particles. These refinement and modification in
microstructure resulted in improvement of hardness value, tensile strength and resistance for wear.
Introduction
Al-Si eutectic alloy are the mostly used alloys for
industrial applications due to their unique mechanical
properties such as high strength to weight ratio and
corrosion resistance. In addition, the low coefficient
of thermal expansion and good wear resistance make
these alloys suitable for manufacture of components
such as cylinder blocks and piston [1].Grain
refinement is considered to be one of the most
important and popular melt treatment processes for
aluminum–silicon alloys castings. The use of grain-
refiners to improve castings mechanical properties is
widespread in aluminium industry, and its associated
benefits on final products are well documented
[2].The advantages of grain refinement of aluminum
alloys are both technical and economic, which
include reduced ingot cracking, better ingot
homogeneity [3], being less susceptible to hot
cracking [4] and mechanical properties are improved
significantly. Grain refinement improves the quality
of castings by reducing the size of primary α-Al
grains nucleated in the as-cast product, which
otherwise will solidify naturally with coarse co-
laminar grain structure in the absence of grain refiner.
Fine equiaxed grain structure is desired because it
comes along with several benefits such as uniform
distribution of second phases and microporosity to
improve homo-geneity, improved feeding ability to
avoid incomplete filling of mold [5], reduced
porosity and the elimination of hot tearing, high yield
strength, high toughness, im-proved machinability
and excellent deep drawability of the products [6].
The present investigation is an attempt to improve the
mechanical properties of Al-Si 18% by cooling under
different conditions with and without grain refiner
and modifier Al-TiB2& Na2SiF6.The microstructure,
tensile strength, wear hardness was studied with and
without using grain refiner and modifier.
Fig1. Stir casting setup

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II. EXPERIMENTAL PROCEDURE:
The Al-Si alloy was melted in graphite crucible in
induction melting furnace and the melt was held at
850°C. Titanium-diboride powder, sodium silico
flouride, 2% of the total volume, duly packed in
aluminum foil were added to the melt for grain
refinement and modification. The melt was stirred for
2 minutes after the addition of grain refiner and/or
modifier. And the molten metal was cooled under
different conditions. The melt with the grain and
refiner were prepared under three different cooling
conditions. One of it was poured into a rectangular
cast iron mould for fast cooling and another one was
left in mold itself for very slow cooling until it gets
the room temperature and to achieve moderate
cooling the graphite crucible was taken out of the
furnace and buried under sand until it gets solidified.
After solidification the casting was taken out from
the mould and are cut to required shape and sizes for
microstructure, wear testing, hardness testing and
tensile strength testing. And the same process was
repeated without using grain refiner and modifier.
Casting Specimen
Very fast
cooling
Without grain
refinement and
modifier
With grain
refinement
and modifier
Moderate
cooling
Without grain
refinement and
modifier
With grain
refinement
and modifier
Very slow
cooling
Without grain
refinement and
modifier
With grain
refinement
and modifier
Table 1. Specimen condition
III. RESULTS & DISCUSSION
1. Microstructure
Fig. (2-7) show photomicrographs of Al-Si 18%
alloy. It is observed that the addition of 2% of total
volume of Al-TiB2& Na2SiF6 grain refiner and
modifier to Al-Si 18% alloy significantly refine
coarse αaluminum dendrites to fine equiaxed α-
aluminum dendrites. Modification refines the primary
and eutectic silicon crystals and changes the
morphology of these crystals. The change in
microstructure from coarse columnar grain structure
to fine equiaxed grain structure and coarse dendritic
structure to fine dendritic structure.
Under fast cooling the cast material, after addition of
Al-TiB2& Na2SiF6 the primary silicon is refined and
large eutectic are visible.
Under moderate cooling the cast material has large
silicon structure before addition of Al-TiB2&
Na2SiF6 .after the addition the significantly refine
coarse primary aluminum and primary silicon to fine
grain size.
Under slow cooling the cast material has large
eutectic crystals and primary silicon is large. After
the addition of Al-TiB2& Na2SiF6, the Modification
refines the primary and eutectic silicon crystals and
changes the morphology of these crystals
Fig: 2 as cast (fast cooling)
Fig: 3 using grain refiner& modifier
(Fast cooling)

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Fig: 4 as cast (moderate cooling)
Fig: 5 using grain refiner& modifier
(Moderate cooling)
Fig: 6 as cast (slow cooling)
Fig: 7 using grain refiner& modifier (Slow
cooling)
2. Mechanical properties
a) Hardness properties
Following graph shows the hardness value of the Al-
Si18% in different conditions with addition of grain
refiner & grain modifier and without using of it.
I) as cast
Materials
Al-Si 18%
Diameter
under
indentation
(mm)
Brinell
hardness
number
N/mm2
Fast
cooling
3.5 246.568
Moderate
cooling
3.6 232.79
Slow
cooling
3.7 219.94
Table2. Hardness value of as cast
b) Using grain refiner and modifier

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Materials
Al-Si 18%
Diameter
under
indentation
(mm)
Brinell
hardness
number
(BHN) N/mm2
Fast
cooling
3.42 258.92
Moderate
cooling
3.56 238.316
Slow
cooling
3.62 232.86
Table3. Hardness value after grain refinement
and modification.
Fig 8. Hardness vs. Casting Condition
From the table and the graph, the specimen obtained
from very fast cooling has more hardness in
comparison to moderate and slow cooling. Addition
of grain refiner and modifier increases the hardness
value.
b) Wear properties
Graph below shows the comparison of wear
properties of Al-Si18% alloy in different conditions
with and without addition of grain refiner and
modifier.
Fig 9. Wear vs. Casting Condition
c) Tensile properties:
Graph below shows the tensile value of the Al-Si18%
in different conditions with and without addition of
grain refiner & grain modifier.
Fig 10. Engg. UTS vs. Casting Condition
0
10
20
30
40
50
60
70
80
fast coolingmoderate coolingslow cooling
wear comparision
Column2 Column1

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Fig11. Breaking load vs. Casting Condition
Case1: As cast:
In case of fast cooling we obtain value hardness
246.568BHN, Engg. Ultimate tensile strength 93.6
(N/mm2), breaking load 1235.7 N and wear 53 µm.
In case of moderate cooling we obtain value hardness
232.719 BHN, Engg. Ultimate tensile strength 79.6
(N/mm2), breaking load 705.6 N and wear 68 µm. In
case of slow cooling we obtain value hardness 219.94
BHN, Engg. Ultimate tensile strength 63.2 (N/mm2),
breaking load 504 N and wear 61 µm.
Case 2: Al-Si alloy (with grain refinement and
modification)
In case of fast cooling Increase hardness is 246.568to
258.92 BHN, Engg. Ultimate tensile strength 93.6 to
108.4 (N/mm2) and breaking load 1235.7 to 1368.2
N and wear 53 to 51 µm. In case of moderate cooling
Al-Si alloy (with grain refinement and modification).
Increase hardness is 232.719 to 238.316 BHN, Engg.
Ultimate tensile strength 79.6 to 62(N/mm2),
breaking load 705.6 to 774.8 N and wear 68 to 52
µm. In case of slow cooling Al-Si alloy (with grain
refinement and modification) Increase hardness is
219.94 to 232.86 BHN, Engg. Ultimate tensile
strength 63.2 to 67.9 (N/mm2), breaking load 504 to
537 N and wear 61 µm as compare to case 1. Here
increase in mechanical properties, due to addition of
grain refinement and modification occurred.
IV. CONCLUSION
From the tests conducted to determine the mechanical
properties, wear behavior, microstructure, by addition
of grain refiner and without addition of grain refiner
and modifier it can be concluded that:
 The specimen obtained from very fast cooling
has more hardness, less wear, more tensile
strength, more breaking load in comparison to
other cooling conditions.
 Addition of grain refiner and modifier increases
the hardness, tensile strength, breaking load and
decreases the wear rate.
 In addition of grain refinement, modification
combined action of both (Al-TiB2+ Na2SiF6) to
Al-Si18% alloy significantly refines coarse of
primary aluminum and primary silicon to fine
grain size and are properly refined.
References
[1] Shiva Prasad C.G Vijay Desai., Effect of
combined grain refinement and modification
on the microstructure and mechanical
properties of Al-12Si, Al-12Si-4.5Cu alloys.
Procedis material science, 2014, 5, pp.
1368-1375
[2] V.P.Patel, H.R PRAJAPATI.,
Microstructural and mechanical properties
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and modified using gravity-die and sand
casting. Vol. 2, Issue 3, May-Jun 2012,
pp.147-150
[3] Lim Ying Pio, Wang Chan Chin.,
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[4] D. Apelian, G. K. Sigworth and K. R.
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0
500
1000
1500
fast cooling moderate
cooling
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cooling
Breaking load
as cast using grain refiner & modifier

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[5] D. G. McCartney, “Grain Refining of
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