Engineering, 2010, 2, 172-178
doi:10.4236/eng.2010.23024 lished Online March 2010 (http://www.SciRP.org/journal/eng/) Pub
Structure and Properties of Sn-9Zn Lead-Free Solder
Alloy with Heat Treatment
Mahmoud Hammam1, Fardos Saad Allah2, El Said Gouda2, 3, Yaser El Gendy1, Heba Abdel Aziz1
1Physics Department, Helwan University, Helwan, Egypt
2Metal Physics Lab., Department of Solid State Physics, National Research Center, Dokki, Egypt
3Physics department, Jazan University, Jazan, KSA
Received November 20, 2009; revised December 17, 2009; accepted December 22, 2009
Abstract
The Sn-9Zn lead-free solder alloy was prepared by conventional casting technique then cold-rolled into long
sheets of 1 mm thickness and 3 mm width. It was annealed at 80, 120 and 160°C for 60 min to investigate
the effect of isochronal heat treatment on structure and mechanical properties of the cold rolled Sn-9Zn alloy.
The results showed that, the crystallite size and lattice strain have opposite behavior with increasing anneal-
ing temperature due to recovery and recrystalization processes associated with the heat treatment process.
Vickers micro-hardness number increases continuously from 155 to 180 MPa with increasing annealing
temperature. Ultimate tensile strength (UTS) was also calculated. It was found that, it is equal to 61.4 MPa for
the non annealed sample and slightly decreases to 60.5 and 58.2 MPa for samples annealed at 80 and 120°C,
respectively. While, increases to 65.4 MPa for the sample annealed at 160°C. Also, ductility increases with
increasing annealing temperature in opposite manor with the UTS. The new method for Micro-creep behav-
ior as well as the creep rate calculated by this method has been characterized at room temperature.
Keywords: Cold Rolling, Annealing, Lead-Free Solder Alloy, Micro-Creep, Micro-Hardness
1. Introduction
There are some characteristics which play a major role in
the consideration of substitutes for tin-lead solders in
electronic soldering, such as a lower melting temperature
of solder, adequate strength, the environmental issues
related to the toxicity, good electrical/thermal conduc-
tivity, low cost, good wetting properties, and availability
in sufficient quantities as concerns the base metal. These
properties are mostly affected by the methods of prepara-
tion of the alloys such as rapid solidification, conven-
tional casting or unidirectional solidification. Further-
more, the working process of the alloys, isochronal, iso-
thermal heat treatments and aging time all of these pa-
rameters are mostly affect on the properties of these al-
loys [1-3]. The present paper concerns with the effect of
isochronal heat treatment on structure and properties of
Sn-9Zn cold rolling alloy. This alloy is one of the most
alloys recommended being alternative to Pb-Sn alloy
[4-7]. This recommendation is due to its lower melting
point close to that of Sn-Pb (183°C) eutectic alloy and its
mechanical properties, e.g. tensile strength is better than
that of the Sn-Pb alloy [8]. Moreover, Sn-Zn alloy is
advantageous from the economic point of view because
Zn is a low cost metal.
2. Experimental
The materials in the alloy of composition Sn-9Zn of pu-
rities of 99.98% were weighted out and melted in a por-
celain crucible using an electrical furnace with calevony
as a fluxing agent. The casting was done in a graphite
mold at a temperature of 500°C and thermally agitated to
perform the homogenization. The resulting alloy was cold
rolling into long sheets of about 3 mm in width and 1 mm
in thickness. The alloy samples as illustrated in Table 1
were isochronal heat treated at 80, 120 and 160°C for 60
min to perform the effect of heating temperature on
structure and properties of these samples. X-ray diffrac-
tion analysis was performed using a 1390 Philips Dif-
fractometer with Cu-K radiation (λ = 1.54056 A) to de-
termine the phases present. Differential thermal analysis
test (DTA) during heating with heating rate of 10°C/min
was used to identify the melting reaction of these sam-
ples. The polished samples were tested in a Vickers mi-
crohardness tester, where a diamond pyramid indenter

M. Hammam ET AL. 173
with square base is used and the Vickers hardness num-
ber is given by HV = 0.185 F/d2, where F is the applied
load in N and d, is the average diagonal length in mm.
Each reading was an average of at least ten separate
measurements taken at random places on the surface of
the specimens. All of the indentations were at least 0.5
mm away from the edges and from other indentations.
Micro-creep measurements [2,9] were carried out on all
samples using a fixed load 0.49 N for dwell time up to
300 s. Tensile properties were determined using a con-
ventional testing machine with fixed cross head speed at
10 mm/min.
3. Results and Discussion
3.1. Structure of Sn-Zn Alloy Samples
Figure 1 shows the profiles of XRD patterns of the Sn-
9Zn cold rolled alloy samples before and after isochronal
Table 1. Chemical analysis of the Sn-9Zn alloy before and after annealing.
Sample Chemical formula Zn Pb Sn Annealing temperature °C
Sample 1 Sn-9Zn 9.02 0.04 Bal. Pre-annealed
Sample 2 Sn-9Zn 9.02 0.04 Bal. 80
Sample 3 Sn-9Zn 9.02 0.04 Bal. 120
Sample 4 Sn-9Zn 9.02 0.04 Bal. 160
20 30 4050 60 7080 90
Intensity (arb.unit)
Pre annealed
2 θ (degree)
♦
♦ ♦♦♦
♦♦
♦ Zn
 - Sn
♦
20 30 40 50 6070 80 90
2 θ (degree)
Intensity (arb.unit)
annealed at 80 °C
♦
♦
♦
♦♦
♦♦♦

M. Hammam ET AL. 174
20 30 40 50 60 70 80 90
annealed at 120 °C
2 θ (degree)
Intensity (arb.unit)
♦
♦♦
♦♦
♦♦
20 30 40 506070 80 90
annealed at 160 °C
Intensity (arb.unit)
2 θ (degree)
♦
♦
♦
♦
♦♦
♦
♦
♦
Figure 1. XRD patterns of Sn-9Zn alloy samples before and after annealing.
heat treatment at 80, 120, and 160°C for 60 min. Each of
the alloy samples exhibit the X-ray diffraction peaks due
to β-Sn matrix phase with some precipitations of Zn as a
secondary phase. The effect of the isochronal heat treat-
ment is restricted only on the lattice strain and crystallite
size [10] of the Sn-matrix phase as illustrated in Figure 2.
The crystallite size of Sn-matrix is continuously increase-
ed, while the lattice strain has an opposite behavior with
increasing the annealing temperature as shown in Figure
2. Actually, cold rolling process may cause an increase in
dislocation density then caused the lattice to be strained.
Such an array of dislocations gives rise to a substantial
strain energy stored in the lattice, so it becomes unstable
thermodynamically relative to the undeformed one.
Consequently, the deformed alloy will try to return to a
state of lower free energy, i.e. a more perfect state through
the continuous heat treatment process where thermally
activated processes such as diffusion, cross slip and
climb take place.
0
20
40
60
80
100
120
Sample 1Sample 2Sample 3Sample 4
Crystallite size nm
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Lattice strain %
Crystallite size nm
Lattice strain
Figure 2. Crystallite size and lattice strain of Sn-9Zn sam-
ples before and after annealing.

M. Hammam ET AL. 175
3.2. Thermal Properties of Sn-Zn Alloy Samples
Figure 3 shows the typical DTA profiles of Sn-9Zn alloy
samples before and after annealing at 80, 120 and 160ºC
for 60 min during heating with heating rate 10°C/min. A
large endothermic peak corresponding to the melting
reaction was observed for each sample and seems to have
the same physical origin. There is no any phase transition
occur other than the melting. The melting point of each
sample was determined as illustrated in Table 2. It
shows a slight decrease of the melting point in a narrow
range of temperatures (199.9 to 198.7°C). Also, the heat
of fusion, ΔH, can be determined by H =KA/m, [11]
where K, is a constant which is defined as a calibration
coefficient that depends on the crucible shape and re-
gards as a constant in the DTA system, m is the mass of
the sample, and A is the area under the endothermic peak.
A slight change of heat of fusion in the range of 82.9 to
87 was observed as illustrated in Table 2, which are
lower values compared with that of Pb-Sn (104.2) [12].
This means, the Sn-Zn alloy is considered as the most
beneficial material for saving energy.
3.3. Tensile Measurements
Figure 4 shows the stress-strain curve of Sn-9Zn alloy
samples before and after heat treatment. It shows an in-
crease in the strain as the stress is increased by different
amounts. The stress-strain curves can be divided into two
regions; the first region which is a linear relation be-
tween stress and strain ends at the strain ratio ~ 0.1 of the
second region. The second region is slightly curved due
to the yielding. Also, it is noticed that the annealed sam-
ples have higher values than that of the non-annealed
sample. It is also seen from Figure 4 that, after the peak
tensile stresses at 0.1 strains, the alloy samples have a
050100 150 200250 300
Sample 1
Sample 2
Sample 3
Sample 4
ΔT (arb.unit)
Tem
p
erature ºC
200.6
199.4
199.7
199.8
Figure 3. DTA endothermic peak of Sn-9Zn alloy samples.
Table 2. Melting properties of Sn-9Zn samples before and after annealing.
Sample Melting point ˚C Onset ˚C Offset ˚C ΔH ( J/g)
Sample 1 199.9 193.8 212.7 82.9
Sample 2 198.7 187.5 211 84.2
Sample 3 198.9 188.9 211.2 87
Sample 4 199.1 190.1 211.8 86.6
0
10
20
30
40
50
60
70
80
0 0.1 0.20.3 0.4 0.5 0.6
Pre-annealed Sample
annealed at 120 ℃
annealed at 160 ℃
Str ain
Stress Mpa
Figure 4. Stress-strain curve of the Sn-9Zn alloy samples.

M. Hammam ET AL. 176
neck. Also, it indicates the deformation up to failure is
distributed much more uniformly throughout the alloy
volume. The ultimate tensile strength, UTS, which is the
maximum engineering stress that a material can with-
stand in tension, was calculated as illustrated in Figure 5.
It is equal to 61.4 MPa for sample 1, which slightly de-
creases to 60.5 and 58.2 MPa for samples 2 and 3, re-
spectively. While, the value increases to its maximum
value 65.4 MPa for sample 4.
3.4. Micro Hardness Measurement
Micro-hardness measurement is a very sensitive to detect
the structural changes of different soft solders. Usually, it
is a non-destructive testing and can be the easiest way to
determine the mechanical properties of the different
phases of the structure. Figure 6 shows the variation of
Vickers hardness number of Sn-9Zn alloy samples before
and after heat treatment using loads of 0.098, 0.245 and
52
54
56
58
60
62
64
66
68
sample1sample 2sample 3sample 4
Ultimate tensile strength MPa
0
0.1
0.2
0.3
0.4
0.5
0.6
True strain
UTS MPa
True strain
Figure 5. UTS and true strain of Sn-9Zn samples before and after annealing.
140
150
160
170
180
190
200
210
sample 1sample 2sample 3sample 4
Hardness MPa
0.098 N
0.245 N
0.49 N
Figure 6. Hardness values of Sn-9Zn samples before and after annealing.

M. Hammam ET AL. 177
0.49 N for fixed dwell time of 10 s. The hardness in-
creases continuously as the annealing temperature is in-
creased for the three load systems by the same manor.
This increase can be attributed to the effect of heat
treatment that decreases the lattice strain induced through
the cold rolling process. The hardening in metals and
alloys induced by forming structure in which dislocation
mobility is reduced due to the interaction of dislocations
with impurity atoms and the formation of second phase
particles. Also, reduction of the lattice strain leads to
increase the hardness. Another point is noticed from this
figure that the values of HV in all samples are decreased
with increasing applied load, which well known as in-
dentation size effect and agree with the results observed
elsewhere [13,14].
3.5. Micro-Creep Behavior
Figure 7 shows the variation of local strain with indenta-
tion time through the interval 0 to 300 s. All of the alloy
samples have two stages namely as primary and secon-
dary creep. The first stage starts from the beginning to
120 s, followed by the second stage up to 300 s. This
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
050100 150 200250 300 350
sample 1
sample 2
sample 3
sam
p
le 4
25
º
C
Time sec
True strain
Figure 7. Micro-creep curve of Sn-9Zn samples before and after annealing.
0
0.1
0.2
0.3
0.4
sample 1sample 2sample 3 sample 4
Creep rate % s
-1
Figure 8. Creep rate of Sn-9Zn alloy samples.

M. Hammam ET AL. 178
stage called the steady state region in which the strain
increases linearly with indentation time. The third stage
of creep is not noticed here since it is impossible because
this method is a compressed method. From the steady
state region, the creep rate of the alloy samples can be
calculated and the results are illustrated in Figure 8. It
shows a continues decrease of creep rate with increasing
annealing temperature which indicates that, the annealed
samples have higher creep resistance due to the decrease
of the lattice strain as illustrated from the X-ray diffrac-
tion analysis.
4. Conclusions
The present paper aimed to study the effect of annealing
temperature i.e. 80, 120 and 160°C for 60 min on struc-
ture and mechanical properties of Sn-9Zn alloy prepared
by conventional casting technique then subjected to
cold-rolling process. The results showed that:
1) The crystallite size of Sn-matrix phase was incre-
ased continuously with increasing annealing temperature,
while the lattice strain induced through the cold rolling
process was decreased.
2) Vickers hardness number of this alloy increased
continuously with increasing annealing temperature.
Also, the hardness values were decreased with increasing
applied load, which agree with other previous works.
3) The micro-creep behavior of this alloy was also de-
scribed, which differ than that obtained by tensile meth-
ods by the third stage of creep. So, the micro-creep
method is not destructive method and useful for small
samples of alloys.
4) The creep rate calculated by this method was decre-
ased continuously with increasing annealing temperature.
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