1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
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MICROSTRUCTURAL AND MECHANICAL BEHAVIOUR OF ZINC-
ALUMINIUM CAST ALLOYS
L.Nirmala1
, C.Yuvaraj2
, K. Prahlada Rao3
, Seenappa4
1
Research Scholar, Department of Mechanical Engineering, JNTUCE, Anantapur,
Andhra Pradesh, India
2
Professor, Department of Mechanical Engineering, MITS, Madanapalle, Andhra Pradesh, India
3
Professor, Department of Mechanical Engineering, JNTUCE, Anantapur, Andhra Pradesh, India
4
Associate Professor, Department of Mechanical Engineering, GEC, Ramanagara, Karnataka, India
ABSTRACT
The objective of this paper is to study the micro structural and mechanical behaviour of ZA27
alloy containing nickel in the range from 1 to 3 wt. %. Elemental analysis was performed by means
of energy dispersive X-ray spectroscopy (EDS) analyzer and XRD technique was employed to
identify the phase formation of the alloy. The microstructure of the alloy was also examined by
SEM. The increase in tensile strength, yield strength and hardness has been discussed and it was
noticed that the tensile strength, yield strength and hardness of the alloys increases with increase in
nickel content. Metallographic studies showed that addition of nickel resulted in microstructural
modifications of the alloy involving the formation of complex intermetallic compounds.
Keywords: EDS, Microstructure, SEM, XRD, Zinc-Aluminum alloys
1. INTRODUCTION
The expeditious advancement in industrial activities, in the past decades, has resulted in the
need for new multifunctional materials that possess characteristics not obtainable from any
individual material. ZA alloys possess significantly higher strength and have been used increasingly
in recent years for industrial applications mainly because of their good mechanical properties,
excellent fluidity and castability [1]. These alloys have been used increasingly during the past few
years. In recent times, zinc-aluminium based alloys have found considerable industrial applications
mainly due to their good mechanical properties, excellent fluidity and castability and present
advantages in comparison with copper based and aluminium based alloys, especially high strength
with a low casting temperature [2,3]. Studies on ZA alloy with high aluminium percentage showed
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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that they exhibit good mechanical properties, excellent wear resistance, superior hardness and
modulus. Cu and Mg are added to the Zn-Al based alloys to improve the mechanical properties
[4,5,11].The Mg additions used in these alloys to increase the hardness, tensile strength and
intergranular corrosion resistance of these alloys. The nickel content used in these alloys increases
the hardness, tensile strength and creep resistance of these materials [1,10].More recently, some
investigators have determined the mechanical properties and microstructural features of standard ZA
alloys [3,9], but no previous work appears to have been reported on ZA27 alloy containing higher
percentage of nickel (1-3%). Therefore this study has been carried out to quantify the effect of nickel
content on mechanical properties and microstructure of the modified ZA27 alloy.
2. EXPERIMENTAL PROCEDURE
2.1. Materials and Moulds used
Zinc based alloys were prepared by liquid metallurgy route. The raw materials used to
prepare these alloys are 99.99 % Zinc and 99.99 % aluminium and are melted up to 6300
C, then
poured into a preheated die of cylindrical pattern of diameter 22 mm and 165 mm long.
2.2. Casting practice
The compositions were melted in an electrical resistance furnace, using graphite crucible and
poured into a permanent metal mould, which was preheated to 1000
C, the alloys were cast with a
1500
C melt superheat. The aluminium and nickel master alloy was stirred carefully into the molten
Zn-27% A1 alloys before casting.
2.3. Chemical composition analysis
The composition of the alloy was determined using wet chemical (atomic absorption)
spectroscopy and also chemistry of the same alloy was quantified by EDAX analysis as a double
check.
2.4. Measurement of tensile, impact and hardness properties
Tensile test was conducted as per ASTM A370 standards at ambient temperature with a strain
rate of 1.3x10-3
/s using universal testing machine. The impact test was performed in accordance with
ASTM E23 standards. Hardness of metallographically prepared samples was measured using a
Micro Vickers hardness tester as per ASTM E10 standards.
2.5. Microstructural studies
Microstructural studies of the alloys were carried out using Scanning electron microscope
(SEM) and Energy dispersive X-ray spectroscopic (EDXS) facility. The specimens were polished
according to standard metallographic practice and etched. The reagent for etching was a solution
containing 5 g CrO3, 0.5g Na2SO4 and 100 ml H2O and etched for 10-15 minutes.
3. CHEMICAL COMPOSITION
Elemental quantification was performed by atomic absorption spectroscopy. The following
table gives chemistry of different developed alloys.

3. International Journal of Mechanical Engineering and Technology
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July
Table 1. Chemical composition of the
Nickel
content
Al Ni
0 24.71 0.001
1 24.53 1.09
2 23.98 1.95
3 24.10 3.10
Table 2. Mechanical properties
Nickel
content
UTS
(MPa)
Yield Strength
(MPa)
0 236.00 203.00
1 288.65 224.57
2 295.18 238.3
3 328.84 248.95
Fig. 1 Typical EDXS of ZA27 with
Fig. 3 UTS & Yield strength Vs Wt% Ni
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
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hemical composition of the experimental ZA27 alloy (wt %)
Cu Mg Fe Ti Pb Mn
0.03 0.105 0.09 0.00069 0.0031 0.007
0.03 0.102 0.09 0.0007 0.003 0.007
0.034 0.108 0.09 0.0007 0.003 0.007
0.035 0.120 0.092 0.0007 0.003 0.007
Mechanical properties of ZA27 obtained from the experiments
Yield Strength
(MPa)
Ductility
(%)
Hardness
(MVHN)
203.00 10.80 115
224.57 8.77 121
238.30 6.03 127
248.95 3.65 135
of ZA27 with 3% Ni Fig. 2 Typical XRD of ZA27 with 3% Ni
UTS & Yield strength Vs Wt% Ni Fig. 4 Ductility Vs Wt% Ni
(IJMET), ISSN 0976 –
August (2013) © IAEME
ZA27 alloy (wt %)
Mn Zn
0.007 Rem
0.007 Rem
0.007 Rem
0.007 Rem
obtained from the experiments
Impact
Energy(J)
4
6
7
8
27 with 3% Ni
Ductility Vs Wt% Ni

4. International Journal of Mechanical Engineering and Technology
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July
Fig. 5 MVHN Vs Wt % Ni
a
c
Fig. 7 SEM microstructures of as cast ZA27 alloy containing: (a) 1% Ni, (b) 2% Ni,
% Ni (5KX), Single arrow: η Zinc rich phase, Double arrow:
primary α
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME
246
MVHN Vs Wt % Ni Fig. 6 Impact energy Vs Wt % Ni
b
d
SEM microstructures of as cast ZA27 alloy containing: (a) 1% Ni, (b) 2% Ni,
Zinc rich phase, Double arrow: α+ η eutectoid phase, Triple arrow:
primary α phase , ε- Meta stable phase α+ η
εεεε
(IJMET), ISSN 0976 –
August (2013) © IAEME
Impact energy Vs Wt % Ni
SEM microstructures of as cast ZA27 alloy containing: (a) 1% Ni, (b) 2% Ni, (c) 3% Ni (d)3
eutectoid phase, Triple arrow:

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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4. RESULTS AND DISCUSSION
The results obtained from the tests, clearly reveal that the addition of nickel to the developed
alloy has a significant effect on mechanical properties.
EDXS analysis and XRD was carried out on the developed alloys in order to know the exact
composition as shown Fig.1 and Fig.2. Fig.3 shows that ultimate tensile strength, yield strength
increases as nickel content increases. The increase in ultimate tensile strength, yield strength and
hardness is due to solid strengthening effect and also due to formation of intermetallic phases
observed along the grain boundaries. Fig.4 shows that ductility decreases continuously with increase
in nickel percentage. This is because the intermetallics acts as barriers for the elongation [9]. Fig.5
shows that hardness increases as nickel content increased. The impact energy increases marginally
with nickel content as shown in Fig. 6.
Microstructural examination of the alloys was conventionally carried out using Scanning
electron microscope. The etching agent used was CrO3 and Na2SO4. As the nickel content increases,
the microstructure seems to get refined appreciably as seen in Fig 7. XRD analysis was carried out to
identify the phases present in the alloys. The various intermetallic compounds noticed are AlNi3, Zn,
AlNi3 and Al0.403 Zn0.597 as shown in Fig.2. The diffraction diagram shows peaks corresponding to
those of the Zn-rich and Al-rich phases of the binary Zn–Al system and the presence of Zn, AlNi3,
AlNi3, and Al0.403 Zn0.597 were seen from the XRD pattern (Fig.2). Zn, AlNi3 and AlNi3 peaks are
observed at 2θ =36.45, 43.42 and 22.92 degrees, where as Al0.403 Zn0.597 observed at 38.94 and 45
degrees.
4.1. Effect of Nickel content on microstructure
From the experimental results it is found that the tensile strength, yield strength and hardness
of the alloys increased as wt% nickel increases. It is observed from the microstructure that the
addition of nickel led to the formation of ε phase in the interdendritic regions of the zinc–aluminum–
nickel alloys which is shown in Fig. 7(a-d). Basically the intermetallic phases are very hard and
brittle which results in increase in the strength and hardness at the cost of ductility. In addition, the
nickel- rich particles may also acts as barriers for the elongation because they are harder and more
brittle. These are the reasons why the yield strength and tensile strength of the alloys increase with
increase in nickel content [9-10]. The histogram Fig.5 shows that hardness of the alloys increases as
the nickel content increased. The increase in this property may be related to the solid solution
hardening and formation of hard and brittle nickel-rich intermetallic phases along the grain
boundaries. Similar explanations have been offered in the literature [1, 4]. The microstructure of the
alloy shown in Fig.7 consists of aluminum-rich (α) phase and zinc-rich (η) phase, while the grey
structure surrounding is a mixture of zinc-rich and aluminum rich phases (α+η). The dark regions
are the zinc-rich (η) phase.
5. CONCLUSIONS
The results of current study indicate that with the addition of nickel in the range of 1–3 wt.%,
increases the tensile strength, yield strength and hardness of the developed alloys. The addition of
nickel in Zn–Al alloys reported the formation of AlNi3, Zn, AlNi3 and Al0.403 Zn0.597 intermetallics.
Which increases hardness of alloy. The decrease in ductility was due to formation of hard and brittle
intermetallics. Impact energy absorbed will increase slightly with increase in nickel content.
Microstructural analysis revealed the alloy comprised primary α dendrites surrounded by the
eutectoid α+ η and metastable phase ε.

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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