Effects of small additions of Ag, Al, and Ga on the structure and properties of the Sn–9Zn eutectic alloy
Introduction
The Sn–Zn eutectic alloy has recently been considered as one of the lead-free solder materials that can replace the Sn–37Pb solder without increasing soldering temperature. Sn–Zn alloy has greater mechanical properties than the conventional Sn–Pb solders [1], [2], [3], [4] and a lower cost than other lead-free solders [2], [5]. However, the tendency of oxidation, and poor wetting ability of this alloy system confine its application [5], [6]. In recent years, to overcome the shortfall of Sn–9Zn, some authors have tried to add a third element, such as In [7], Bi [8], [9], [10], Al [11], [12], [13], [14], [15], Ag [16], [17], [18], and Ce/La [19], [20], [21] to the Sn–Zn binary system to improve the melting temperature, wettability, oxidation resistance, corrosion, and mechanical properties of the alloy.
McCormack and Jin [7] found that In added to the Sn–Zn binary system can improve the wetting characteristics of the alloy and lowers the melting temperature. Kim et al. [8] reported that with the increase of additional Bi content, the melting point decreases from 198.4 to 186.1 °C. It has been found that the Sn–Zn–Ag [16] solders have good wettability on Cu substrate. Lin et al. [13], [14] added the Al element into the Sn–Zn alloy, and showed that Al can improve the wetting properties and oxidation resistance. Wu et al. [19], [20], [21] found that added Ce/La into the Sn–Zn system could improve wettability, creep strength, and tensile strength.
The objective of this study is aimed at investigating the effects of the addition of small amounts of Ag, Al, and Ga on melting temperature, microstructure, and mechanical properties of Sn–9Zn alloys.
Section snippets
Experimental procedures
The Sn–9Zn, Sn–9Zn–0.5Ag, Sn–9Zn–0.45Al, Sn–9Zn–0.5Ga (wt%) lead-free solders and the Sn–37Pb (wt%) solder were made with pure tin, zinc, silver, aluminum, gallium, and lead (purity of 99.99%). The constituent elements were melted in a quartz tube with an inside diameter of 8 mm under an argon atmosphere. The molten alloys (in quartz tube) were homogenized at 800 °C for 3 h and furnace cooled to 250 °C, and then quenched with water (25 °C) with the quartz tube jacket on. The solder rods were then
Melting temperature
Table 1 shows the melting temperatures of the investigated Sn–9Zn, Sn–9Zn–0.5Ag, Sn–9Zn–0.45Al, and Sn–9Zn–0.5Ga alloys. With the addition of Ag, Al elements, the melting temperatures changed only slightly. The melting temperatures were 199.2 and 198.3 °C for the Sn–9Zn–0.5Ag and Sn–9Zn–0.45Al, respectively, as compared with 198.3 °C for Sn–9Zn eutectic alloy. It was also shown in [22] that the addition of 0.5 wt% of Ag did not significantly affect the melting point of the Sn–8.55Zn–0.45Al alloy.
Summary
The melting temperature, microstructures and mechanical properties of the Sn–9Zn–0.5Ag, Sn–9Zn–0.45Al, and Sn–9Zn–0.5Ga alloys have been investigated. The effects of small additions of Ag, Al, and Ga on the structure and properties of the Sn–9Zn eutectic alloy are summarized in Table 2. It is found that Ga is uniformly distributed in the Sn-matrix, Al is detected in the grain boundaries and Zn-rich phases and Ag combines with Zn form an Ag–Zn compound. The 0.5 wt% Ag addition to the Sn–9Zn alloy
Acknowledgement
Financial support of this work is from National Science Council of the Republic of China under NSC 92-2216-E-272-002 and is gratefully acknowledged.
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