Abstract:
In the present study 3.0 weight percent Bi is added in the Sn-9Zn eutectic
solder alloy to investigate the effect of Bi on the microstructure, mechanical and
thermal properties of Sn-9Zn alloys. Effect of micron size Ni powder addition on the
microstructure, mechanical and thermal properties of both the Sn-9Zn and Sn-8Zn-
3Bi alloy systems are investigated. Nickel is added in three different weight
percentages of 0.25, 0.5 and 1.
The melting temperature and solidification range of the solder alloys are
determined by Differential thermal Analysis (DTA). Microstructure of all the alloys
are investigated with an optical microscope and a scanning electron microscope.
Energy dispersive X-ray (EDX) analysis is used to analyze the phases present in the
structure. X-ray Diffraction (XRD) is performed to determine the compounds present
in the solder alloys. To determine the mechanical properties at first Brinell Hardness
test is carried out. Then tensile tests are carried out on an Instron testing machine
(Instron 3369 Universal Testing Machine) at a rate of 3.00 mm.min-1 at 298K. Shear
strength of soldered joint is measured using an Instron testing machine (Instron 3369
Universal Testing Machine) at a rate of 5.00 mm.min-1 at 298K.
It is found that melting temperature of Sn-9Zn solder alloy decrease with the
addition of 3% Bi. Melting temperature is increased with the addition of Ni in both
the Sn-9Zn and Sn-8Zn-3Bi alloy. Solidification range of the alloys is increased with
the addition of both the Bi and Ni. The structure of newly developed solder alloys are
fine needle-like α-Zn phase with some Zn spheroids distributed in the β-Sn matrix. Bi
rich particle are observed in Bi containing alloys. The size of the Zn needle are found
to increase with the addition of Bi in Sn-9Zn alloy. It is also found that addition of
small amount of Ni (0.25%) refines the Zn needles of both the Sn-9Zn and Sn-8Zn-3Bi
alloys. However, coarsening of Zn needles occurs with increasing Ni content in both
the alloys. From XRD analysis it is found that all the alloys consist of only two phases
i.e. a body centered tetragonal β-Sn matrix phase and a secondary phase of
hexagonal Zn. But both the Bi and Ni addition causes the Zn precipitation in the β-Sn
ix
matrix. Additon of Bi in Sn-9Zn alloy increases the hardness and ultimate tensile
strength. Ni addition in both the Sn-9Zn and Sn-8Zn-3Bi alloys also increases the
hardness and ultimate tensile strength. However, for higher than 0.5% Ni addition,
hardness is slightly decreased for both the Sn-9Zn and Sn-8Zn-3Bi alloys. It is also
found that the tensile strength decreases for higher Ni addition. The maximum
ultimate tensile strength is observed for 0.25% Ni addition in Sn-9Zn alloy and 0.5%
Ni addition in Sn-8Zn-3Bi alloy. The improvement in tensile strength is achieved with
the sacrifice in elongation. Shear strength of soldered joint is found maximum for 0.5
wt.% Ni addition in both the Sn-9Zn and Sn-8Zn-3Bi alloys.
The results indicate that the addition of Bi improves the mechanical
properties and lowers the melting point of Sn-9Zn alloy. The addition of Ni in both
the Sn-9Zn and Sn-8Zn-3Bi alloy systems initially refines the Zn needles and improves
mechanical properties. From the present study it can be suggested that a better
combination of thermal and mechanical properties may be achieved by the addition
of 0.25% Ni in Sn-8Zn and 0.5% Ni in Sn-8Zn-3Bi alloy.
