Fabrication and Study of the Mechanical Properties of AA2024 Alloy Reinforced with B4C Nano-particles using Ultrasonic cavitation method

IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)
e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 7, Issue 4 (Jul. - Aug. 2013), PP 01-07
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Fabrication and Study of the Mechanical Properties of AA2024
Alloy Reinforced with B4C Nano-particles using Ultrasonic
cavitation method
Dr.Govind Nandipati 1
, Dr.Ravindra kommineni2
, Dr.Nageswara Rao Damera3
,
Dr.Ramanaiah Nallu4
.
1
Associate.Professor, Department of Mechanical Engineering , R.V.R&J.C college of Engineering ,Guntur,
2
Professor & Head of the Department of Mechanical Engineering, R.V.R&J.C college of Engineering ,Guntur,
3
Vice chancellor Centurion University of Technology and Management, Parlakhemundi, Odisha,
4
Associate Professor, Department of Mechanical Engineering, Andhra university college of Engineering
Visakhapatnam.
Abstract: Metal matrix nanocomposites (MMNCs) with the addition of nano-sized ceramic particles can be of
significance for automobile, aerospace and numerous other applications. The physical and mechanical
characteristics of the light refractory carbides such as SiC, TiC and B4C make them suitable for being used as
reinforcement in aluminium base metal matrix composites This paper presents a technique for an inexpensive
fabrication of bulk lightweight MMNCs with reproducible microstructures and superior properties by use of
ultrasonic nonlinear effects, namely transient cavitation and acoustic streaming; to achieve uniform dispersion
of nano-sized B4C particles in molten aluminum alloy. Nano-sized B4Cp enhanced properties of aluminium
matrix composites, with 1.5%wt of B4C. As compared to the base metal alloy, the mechanical properties
including tensile strength and yield strength of the nanocomposites were improved significantly, while the
ductility of base metal alloy matrix castings was retained. Micro structural study was carried out with an
optical microscope and SEM which validates a good dispersion of nano-sized B4Cp in metal matrix. Mechanical
properties of the as-cast MMNCs have been improved significantly even with a low weight fraction of nano-
sized B4C.
Key Words: Metal matrix nano composites, Ultrasonic cavitaion, Boron carbide nanoparticles.
I. Introduction
Aluminium alloy 2024-T3 is an alloy, with copper as the primary alloying element. It is used in
applications requiring high strength to weight ratio, as well as good fatigue resistance. It is weldable only
through friction welding and has average machinability. Due to poor corrosion resistance, it is often clad
with aluminium or Al-1Zn for protection.
Metal matrix composites (MMCs) are very interesting in various applications due to their improved
properties. Efforts have been made to develop aluminium metal matrix nano composites in recent years due to
their low density, high strength, superior creep resistance, high damping capacity and good dimensional
stability. Magnesium matrix composites are excellent candidates as structural materials and have great potential
in automotive and aerospace applications. Discontinuous micro-scale reinforcements such as short fibers,
particles or whiskers, have been used to produce magnesium MMCs. Nano-sized SiC enhanced magnesium
matrix nanocomposites Mg-2Al-1SiC with 2% SiC and Mg-4Al-1Si with 2% SiC, were successfully fabricated
by ultrasonic cavitation based dispersion of SiC nanoparticles in Mg-(2,4)Al-1Si magnesium alloy melts. As
compared to the magnesium alloy matrices, the mechanical properties including tensile strength and yield
strength of the Mg-2Al-1Si/2% SiC and Mg-4Al-1Si/2% SiC nanocomposites were improved significantly,
while the ductility of magnesium alloy matrix castings was retained [1]. The ultrasonic non-linear effects are
used to disperse nano-sized SiC ceramic particles in AZ91D magnesium molten metal. The dispersion of nano-
sized ceramic particles uniformly in molten metal is done by ultrasonic nonlinear effects, namely transient
cavitation and acoustic streaming, into molten aluminum alloy A356. High-resolution scanning electron
microscopy (SEM), X-ray photo spectroscopy (XPS), and high-resolution X-ray diffractometer (XRD)
techniques show a nearly uniform distribution and good dispersion of the SiC nanoparticles within the nano-
composites (MMNCs) can be of significance for automobile, aerospace and numerous other light weight
applications. It also indicates that partial oxidation of SiC nanopartilces results in the formation of SiO2 in the
matrix. Mechanical properties of the as-cast MMNCs have been improved significantly even with a low weight
fraction of nano-sized SiC [2,3].
Ultrasonic cavitation is a best way to disperse SiC nanopowders in magnesium melt and for
manufacturing of Mg/SiC nanocomposites. SiC nanoparticles inside the matrix were mostly separated by

Fabrication and Study of the Mechanical Properties of AA2024 Alloy Reinforced with NanoB4Cp
magnesium. Due to the addition of nano SiCp, the grain size of magnesium was refined. SiC nanoparticles
bonded well with Mg matrix without forming an intermediate phase. The mechanical properties of the Mg/SiC
nanocomposites, the yield and tensile strengths, were improved significantly, while the ductility of pure
magnesium was retained [4]. The yield strength and ultimate tensile strength of Mg/ 2%SiC, Mg-4Zn/1.5%SiC
and Mg-(2, 4)Al-1Si/2%SiC nanocomposites were improved significantly as compared to those of unreinforced
pure magnesium, Mg-4Zn and Mg- (2, 4)Al-1Si matrices. The good ductility of the matrices was twice that of
pure Mg-4Zn [5]. Yong Yang, Xiaochun Li[6] have fabricated Bulk Al-based nanocomposites that enhanced the
mechanical properties with nanosized SiCp by an ultrasonic based nanomanufacturing process. The
microstructural study reveals that high-power ultrasonic cavitation is an effective method to disperse nano SiCp
particles in aluminum A356 alloy which enhances the wettability between the particles and Al matrix..
Magnesium alloys--one third lighter than an equal volume of aluminum alloys--are one of the lightest
metallic structural materials and are very attractive for applications in automotive and aerospace systems. The
need for complex structural components of high performance magnesium materials is expected to continuously
increase as automotive and aerospace industries are forced to improve the energy efficiency of their products.
Nanoparticle reinforcements can increase the matrix mechanical strength by more effectively promoting particle
hardening mechanisms than micron size particles. A fine and uniform dispersion of nanoparticles provides a
good balance between the strengthener (non deforming particles) and inter-particle spacing effects to maximize
the yield strength and creep resistance (by mechanisms such as dislocation bowing around the particles and
pinning down dislocations at the particles by rapid diffusional stress relaxation at elevated temperatures) while
retaining the good matrix ductility [7].
S. M.Zebarjad et al.[8] concentrated their study on the role of particle size of silicon carbide (SiC) on
dimensional stability of aluminium. Al/SiC composites were reinforced with different sizes of SiC particles
(25μm, 50μm, and 70 nm).The results showed that for all materials, there was an increase in length as
temperature increased and the temperature sensitivity of aluminum decreased in the presence of both micro- and
nanosized silicon carbide and dimensional stability of Al/SiC nanocomposite was better than the conventional
Al/SiC composites.
Different volume fractions of nano-alumina(Al2O3)particles were dispersed into the A356 aluminum
alloy by a mechanical stirrer to avoid agglomeration and for segregation of particles. The microstructural
characterization of the composite samples showed uniform distribution of reinforcement, grain refinement of
aluminium matrix and presence of the minimal porosity. Due to the presence of nano-Al2O3, significant
improvement in hardness, 0.2% yield strength, UTS and ductility were observed [9].Due to the unique
tailorability, aluminium composite materials have wide applications in aerospace and automotive industries.
Earlier, fine particles of SiCp are to be reinforced in aluminium 6061 alloy which improve mechanical
properties slightly. Due to the presence of cavities and agglomerates there is less significant improvement in the
properties [10].
In recent years, Lan et al. and Yang and Li [11,12] developed a new nanomanufacturing method that
combines solidification processes with ultrasonic cavitation based dispersion of nanoparticles in metal melts.
Ultrasonic waves can produce transient cavitations of the order of nanoseconds, “micro-hot-spots” that can have
temperatures of about 5000°C, pressures above 1000 atm. that distribute and disperse nano particles uniformly.
C.F.Deng et. al [13], reinforced Carbon nano tubes(CNT) in the aluminum alloy matrix with iso-static
pressing followed by hot extrusion techniques. The mechanical properties are affected by carbon nano tubes
content. At 1.0%wt of CNTs the mechanical properties increased and decrease at higher %weight. The more
percentage of Si constrains the reaction between the SiC and Al in the matrix. It is observed that viscosity of the
molten metal increased due to the addition of the nano SiC particles [14].
In this paper, B4C/AA2024 composites are fabricated by casting using high-intensity ultrasonic wave
technique. The microstructure and microhardness of these composites are investigated.
II. Experimental Procedure
The base material used in this study is AA2024alumunium alloy has the following chemical
composition.
Table.1 Chemical composition of AA2024
Alloy
element
Al Cu Si Fe Mg Mn Cr Ti Zn
% by
weight
90.7 4.9 0.5 0.5 1.8 0.9 0.1 0.15 0.25
B4C nano particulate of size 50 nm are used in the study. B4C is selected as its density is close to the
Al, and thus there will not be any agglomeration of the particulate during the process. The experimental setup

consists of an electrical resistance heating unit for melting the AA2024 aluminum alloy in a EN-8 steel crucible
at 6380
C. The Ultrasonic transducer probe of the sonicator is dipped into the melt for sonication process. Boron
carbide (B4C) particles are added at various weight percentages [0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 1.5% and
2%] to the melt during the cavitation process.
Fig.1. Schematic of experiment setup
The molten metal is protected from atmospheric air by Argon gas during melting. The metal is poured
into a die of size 200x130x9mm3
and plates are cast. The as cast plates are heat treated, (solutionised at 5600
c
for1hr) and ageing is done at 1600
C for12hrs. Tensile specimens are prepared as per the ASTM-E8 standards
from these plates. The heat treated plates are processed through rolling to remove the casting defects and for
grain elongations. The enhanced mechanical properties of the cast plates as well as rolled sheets are observed.
For Microstructural analysis MMNC cast plates are cut to size of 10x10x5mm3
, ground and polished to mirror
finishing. The samples are etched with Keller’s reagent (composed of 2ml HF, 3ml HCl, 5ml HNO3 and 190ml
water). Optical images and SEM images are taken to study the grain refinement and grain structures and
elongations.
III. Results And Discuscussion
The mechanical properties and microstructures of the parent metal, the fabricated composites and
rolled sheets are studied and the results are presented.
3.1. Hardness Tests
The nano B4C particles are added to the molten metal. While adding, the particulate tend to float on the
surface of the melt. The B4C particles have a slightly lesser specific density than that of the molten aluminium
alloy. As the surface tension of the melt is high, there is poor wetting between B4C particulate and the melt. By
applying the high intensity ultrasonic waves, the acoustic streaming traps the nano particles into the melt
effectively.
The Hardness of the MMNCs is measured at different locations on the samples. The hardness increased
nearly linear with various weight percentages of the nanoB4C particulate. The hardness of the aluminum
AA2024 alloy is found to be Hv-137. The hardness values of the as cast MMNCs, heat treated and after rolling
are presented in the table below. The decrease of value at 2wt% is due to the formation of voids and
agglomerates
Table.2.Table showing the hardness values of MMNCs and after rolling
%wt of B4C 0.1 0.2 0.3 0.4 0.5 1.0 1.5 2.0
Hv-of
MMNCs
140 143 148 151 154 157 160 155
Hv-after
rolling
142 145 149 153 156 158 162 157
3.2. TENSILE TESTS:
The tensile specimens are prepared with gauge length 28mm and cross sectional area as 5x6mm2
.The
tests are conducted on 2Ton extensometer. The ultimate tensile strength and yield strength of the base metal

AA2024 are found to be 420MPa and 276MPa respectively. Also the tensile tests are conducted on metal matrix
nano composites and after rolling and the results presented in tables below. With only 1.5% by weight of nano
B4C particles the ultimate tensile strength has been increased by 6% and reads 442MPa.The higher dislocation
density in the MMNC is responsible for strengthening mechanism. This dislocation phenomenon is due to the
difference in thermal expansion coefficients between matrix and uniformly dispersed nano B4C particulate,
which act as barriers for dislocation movements. The coefficient of thermal expansion mismatch the strain
between the aluminum alloy metal matrix and the reinforcing nano B4C particulate. The plastic deformation of
the ductile aluminum alloy metal matrix in the presence of discontinuous B4C reinforcements, is non uniform.
This is due to the hard, brittle and refractory particles resisting the plastic flow of the soft, ductile and
plastically deforming aluminium alloy metal matrix. The Ultimate tensile strength and Yield strength of the
MMNC is increased for various wt% of nano particlesupto1.5wt% and decreased at 2wt%.This decrease is due
to the formation of agglomerates and voids in the matrix.
Table.3. Mechanical properties of MMNCs
%wt of B4C 0.1 0.2 0.3 0.4 0.5 1.0 1.5 2.0
Yield
strength of
MMNCs-
Mpa
282 283 285 290 295 301 310 306
Ultimate
strength of
MMNCs-
Mpa
422 425 428 431 435 440 445 442
Table.4. Mechanical properties of MMNCs after rolling
%wt of B4C 0.1 0.2 0.3 0.4 0.5 1.0 1.5 2.0
Yield
strength of
MMNCs-
Mpa
283 285 287 293 296 303 312 305
Ultimate
strength of
MMNCs-
Mpa
424 427 430 434 439 444 449 401
Fig-2 Stress Vs Strain relationship for MMNCs
The Fig-2 shows the stress-strain relationship for various percentages of nano B4C particles. The plastic
deformation, induced dislocations, or slip dislocations become dominant when the plastic strain exceeds the
thermal mismatch strain and the two effects eventually act in combination. The increased yield strength of the
MMNCs is due to dislocation generation and accumulation and assuming the dislocations to be uniformly
dispersed in the metal matrix. The residual dislocations are likely to be trapped at the reinforcing B4Cp. This
results in local regions of high dislocation density; i.e. the density is highest near the reinforcing B4Cp or at the
reinforcement matrix interfaces.Fig-3 shows the relation between %wt of nano particles and strength of the
MMNCs. The strength of the MMNCs reduced at 2% of the nano particulate due the formation of agglomerates
in the matrix, failure occurred at the interfaces of the matrix and particulate.
0
50
100
150
200
250
300
350
400
450
500
0 0.02 0.04
StressinMpa
Strain
Strain Vs Stress 0.2
0.3
0.4
0.5
1
1.5
2

Fig-3 Strength of MMNCs
Fig-4 Strength of MMNCs after rolling
3.2.1. DAMAGE DURING TENSILE DEFORMATION: With the influence of tensile load fine microscopic
voids appear to grow confirming a possible contribution from particle constraint induced triaxiality on failure of
composite matrix. Failure of MMNCs is governed by combined effect of local plastic constraints, particle size
and agglomeration. The fracture is highly localized at the discontinuous B4Cp reinforcement with the formation
of voids. Fracture occurred in the regions of particle clustering due to the enhanced localised stresses resulting
from restriction of plastic deformation. The stress immediately adjacent to a reinforcing nano B4C particle is a
combination of stress components imposed by the macroscopic applied stress and the stress component that
developed on a microscopic scale. The microscopic scale components arise as a result of conjoint influence of
strain incompatibility between the reinforcing particle and deforming matrix, individual stresses arising from
thermal expansion mismatch between the second phase inclusion and the matrix and load sharing by the
reinforcing particulates. A combination of thermally induced stress, local stress concentration and macroscopic
applied stress and intrinsic brittle nature of reinforcing particle is responsible for cracking. Furthermore,
assuming that the aluminium alloy metal matrix-B4C particle interfaces are strong, the triaxial stresses generated
during far field tensile loading favors limited growth of microscopic voids in the matrix of the composite. The
limited growth of voids during far field tensile loading coupled with lack of their coalescence and thus inhibiting
the dominant fracture mode to be ductile failure.
IV. Microstructures
The enhanced properties of the metal matrix nano composites depend on distribution of the reinforcing
particles and interface bonding between metal matrix and the dispersed particles. The optical micrograph and
200
225
250
275
300
325
350
375
400
425
450
475
0 0.5 1 1.5 2 2.5
StrengthinMpa
% by weight of NanoB4C
StrengthVs %nanoparticles
ultimatetensile
strength
yield strength
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3
strengthinMpa
%wt of nano particles
Strength for MMNCs after rolling
yield strength
ultimatetensile
strength

SEM images of MMNCs reinforced with 1.5wt% of nano B4Cp are presented in figures below. The optical
images of the base metal and MMNCs are shown in Fig-5(a),(b) where the grain boundaries are clearly
observed. With the optical microscopy no pores are observed. The grains in Fig 5(a) are larger in size and that of
MMNC’s are smaller as seen in Fig-5(b).
Fig 5(a) Fig-5(b)
Fig-6(a) Fig-6(b)
Fig-7 Fig-8
The SEM images of MMNCs reveal that, there is uniform distribution of the nano B4C particles in the
matrix (Fig-6) and small agglomerates of the powders and voids also be seen at higher magnification Fig-7. The
overall microscopic analysis shows that there is good bonding between the matrix and the refractory particulate
interface, indicating uniform distribution of particles due to ultrasonic cavitation and grain boundaries are seen
distinctly in Fig-8.
V. Conclusions
The metal matrix nano composites are fabricated using mechanical stirring and ultrasonic cavitation
methods. The effects of nano B4Cp dispersion on microstructure and mechanical properties are investigated.
a) The metal matrix nano composites have fine and more homogeneous microstructure with the increase of % wt
of nano B4Cp content.
b) The hardness of the aluminum MMNCs improved significantly by the addition of B4Cp particles into it.
c) The ultimate tensile strength, yield strength are increased with the increase of B4Cp content. The hardness,
UTS, Y.S increased by 14%, 6%, 11% respectively.
d) Ultrasonic nonlinear affects efficiently disperse nano particles into molten alloy by enhancing their
wettability.

References
[1]. G. Cao, H. Konishi, X. Li, “Mechanical properties and microstructure of SiC-reinforced Mg-(2,4)Al-1Si nanocomposites fabricated
by ultrasonic cavitation based solidification processing”. Materials Science and Engineering A 486 (2008) 357–362.
[2]. Jie Lan, Yong Yang, Xiaochun Li “Microstructure and microhardness of SiC nanoparticles reinforced magnesium composites
fabricated by ultrasonic method” Materials Science and Engineering A 386 (2004) 284–290.
[3]. Yong Yang, Jie Lan, Xiaochun Li “Study on bulk aluminum matrix nano-composite fabricated by ultrasonic dispersion of nano-
sized SiC particles in molten aluminum alloy” Materials Science and Engineering A 380 (2004) 378–383.
[4]. Guoping Cao, Hiromi Konishi, Xiaochun Li “Mechanical Properties and Microstructure of Mg/SiC Nanocomposites Fabricated by
Ultrasonic Cavitation Based Nanomanufacturing” Journal of Manufacturing Science and Engineering JUNE 2008, Vol. 130.
[5]. G. Cao, H. Konishi and X. Li “Recent Developments on Ultrasonic Cavitation Based Solidification Processing of Bulk Magnesium
Nanocomposites” International Journal of Metal casting/Winter 08, 57-68.
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[7]. Xiaochun Li et al. “Fundamental Study of Bulk Magnesium Alloy Matrix Nanocomposites Fabricated by Ultrasonic Cavitation
Based Solidification Processing” NSF Nanoscale Science and Engineering Grantees Conference, Dec 4-6, 2006.
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[10]. Vikram Singh and R.C. Prasad “Tensile and fracture behaviour of 6061 Al-SiCp metal matrix composites”, International symposium
of research students on materials science and engineering, December 20-22, 2004, Chennai, India.
[11]. Lan, J., Yang, Y., and Li, X., 2004, “Microstructure and Microhardness of SiC Nanoparticles Reinforced Composite Fabricated by
Ultrasonic Method,” Mater. Sci. Eng., A, 386, 1–2, pp. 284–290.
[12]. Yang, Y., and Li, X., 2007, “Ultrasonic Cavitation Based Nanomanufacturing of Bulk Aluminum Matrix Nanocomposites,” ASME
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[14]. Y.Yang et.al, 2004, “Study on bulk aluminium matrix nano composite fabricated by ultrasonic dispersion of nano sized SiC
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Fabrication and Study of the Mechanical Properties of AA2024 Alloy Reinforced with B4C Nano-particles using Ultrasonic cavitation method

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Fabrication and Study of the Mechanical Properties of AA2024 Alloy Reinforced with B4C Nano-particles using Ultrasonic cavitation method