Influence of Titanium Oxide on Structure, Corrosion and Soldering Properties of Sn 82 Bi 15 Zn 3 Alloy

Our work study the effect of titanium oxide on structure, soldering properties such as melting temperature, wetting process and corrosion behavior of Sn 82 Bi 15 Zn 3 alloy. Microstructure of Sn 82 Bi 15 Zn 3 alloy changed after adding different ratio from titanium oxide. Lattice microstrain of Sn 82 Bi 15 Zn 3 alloy varied (increased) after adding titanium oxide. Melting temperature of Sn 82 Bi 15 Zn 3 alloy varied after adding Ti2O. Sn 81.4 Bi 15 Zn 3 (Ti 2 O) 0.6 alloy has low melting temperature. The contact angle Sn 82 Bi 15 Zn 3 alloy decreased after adding different ratio from titanium oxide. Corrosion resistance of Sn 82 Bi 15 Zn 3 alloy varied (increased) after adding Ti 2 O. From our results, soldering properties (melting temperature and contact angle) and corrosion resistance of Sn 82 Bi 15 Zn 3 alloy improved after adding Ti 2 O.


Introduction
Soldering is a low temperature metallurgical joining process. In electronics applications low temperature and reversibility are especially important because of the materials involved and the necessity for reworking and making engineering changes. Solder joining is a wetting process followed by a chemical reaction. Wettability is a function of the materials to be joined, with Cu, Ni, Au, and Pd, as well as alloys rich in one or more of these metals, being particularly amenable to soldering. The chemical reaction following wetting is between the molten solder and the joining metallurgy to form an intermetallic phase region at the interface. Microstructure, wettability and physical properties of Sn 96x Zn 4 Bi x alloys are reported by El-Bediwi et al. [1]. The melting temperature of Sn 96 Zn 4 alloy decreased after adding bismuth. But contact angle of Sn 96 Zn 4 alloy varied after adding bismuth. Adding silver caused a significant increase in bismuth-tin-zinc alloy strengthens with a little decreased in melting temperature [2]. El-Bediwi et al. [2] reported that, there is a significant decrease in melting temperature of bismuth-tin-zinc alloy with a very little increase in strengthens after adding indium. Microstructure, thermal parameters, wettability and electrochemical corrosion process of Bi 30 Sn 50 Sb 10 A l5 Zn 3 Cu 2 , Bi 25 Sn 61 Sb 5 Zn 4 Al 3 Ag 2 , and Bi 20 Sn 60 Sb 7 A l5 Zn 3 Cd 3 Cu 2 , alloys have been studied [3]. Microstructure, wettability behavior, corrosion parameters, thermal properties of quaternary bismuth-tin based alloy have been investigated using different experimental techniques and the results show that, some properties of Bi 60 Sn 40 alloy improved after adding Sb-Zn or Sb-Ag elements [4]. Tin-zinc eutectic alloy has been considered as a candidate for lead free solder materials because of its low melting point, excellent mechanical properties and low cost [5][6][7]. Mostly solders are based on Sn-containing binary and ternary alloys. Several elements have been selected as alloying elements such as Zn, Bi, Cu, Ag, Sb and so on [8][9][10]. Specific researchers [11][12][13][14][15] reported that, tin-zinc eutectic solder alloy is poor wettability, reliability, strength, easy oxidation and microvoid formation. To avoid these disadvantages or improve the properties of it, they added minor amount of Bi, Cu, In, Ag, Al, Ga, Sb, Cr, Ni, Ge elements to develop ternary and even quaternary Pb free alloys. The aim of our work was to study the effect of titanium dioxide on microstructure, soldering properties and corrosion of tin bismuthzinc alloy.

Materials and Methods
High purity (tin, bismuth and zinc) metal and titanium dioxide (white color) are used to prepare Sn 82 Bi 15 Zn 3 (Ti 2 O) x (x=0,0.3,0.6,0.9 and 1.2) alloys. These alloys (mixed metals and Ti 2 O by weight percentage) are melted then normal casted on substrate in air. The samples from alloys are prepared in convenient shape for all tests such as microstructure, thermal parameters, wettability and corrosion behavior. Microstructure of used alloys was performed using Shimadzu X-ray Diffractometer, (Dx-30, Japan) Cu-Ka radiation with l=1.54056 Å at 45kV and 35mA and Ni-filter, in the angular range 2q ranging from 0 to 100° in continuous mode with a scan speed 5deg/min and scanning electron microscope (JEOL JSM-6510LV, Japan). The polarization studies were performed using Gamry Potentiostat/Galvanostat with a Gamry framework system based on ESA 300. Gamry applications include software DC105 for corrosion measurements and Echem Analyst version 5.5 software packages for data fitting. The differential scanning calorimetry (DSC) thermographs were obtained by Universal V4. 5A TA instrument with heating rate 10k/min in the temperature range 0-400 C.    X-ray diffraction patterns, Figure 1, of Sn 82 Bi 15 Zn 3 (Ti 2 O) x (x=0.3,0.6,0.9 and 1.2) alloys have lines corresponding to tetragonal β-Sn phase, hexagonal Bi phase, Zn phase with undetected Ti 2 O or intermetallic compounds and solid solution from dissolved atoms changed its matrix structure. The details of x-ray analysis such as the peak intensity (crystallinity), peak broadness (crystal size) and peak position (orientation) of Sn 82 Bi 15 Zn 3 alloy changed after adding different ratio of titanium dioxide as listed in Table 1 determined from the relation between full width half maximum, FWHM, and 4tan using Williamson and Hall equation [15] is presented in Figure 2. Lattice microstrain of Sn 82 Bi 15 Zn 3 alloy varied (increased) after adding titanium dioxide as listed in Table 2.    Figure 3a-3e. SEM of Sn 82 Bi 15 Zn 3 alloy has lamellar structure (tin phase is a gray color, bismuth phase is a black color) contained white color (which is zinc or bismuth-tin or cluster from dissolved atoms) with different shape and size. Sn 81.7 Bi 15 Zn 3 (Ti 2 O) 0.3 alloy has homogenous structure from tin phase (gray color), slabs and spherical shape from bismuth phase (black color) and little spherical grain or around slab from undetected phases (white\or gray) such as zinc or Ti 2 O or intermetallic phases. Sn 81.4 Bi 15 Zn 3 (Ti 2 O) 0.6 alloy has heterogeneous structure formed from tin phase as a gray color contained bismuth phase as black color and little spherical with slab at grain boundary of undetected phases (zinc or Ti 2 O or intermetallic phases) as gray/ or white color. Sn 81.1 Bi 15 Zn 3 (Ti 2 O) 0.9 alloy has heterogeneous matrix structure (slabs and spherical with different size\ orientation) as gray color contained lamellar structure bismuth phase as black

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Volume 6 -Issue -1 color and undetected phases (spherical/ around grains) as gray or white color. Sn 80.8 Bi 15 Zn 3 (Ti 2 O) 1.2 alloy has heterogeneous matrix structure of tin phase (gray color) contained spherical bismuth phase (black color) surround by white\or gray color as zinc or Ti 2 O or intermetallic phases. From SEMA, adding Ti 2 O to Sn 82 Bi 15 Zn 3 alloy caused a change in its matrix microstructure (quantity, size and orientation of formed phases).         The contact angle Sn 82 Bi 15 Zn 3 alloy decreased after adding different ratio from titanium dioxide as presented in Table 4. That is meant, the spreading of molten Sn 82 Bi 15 Zn 3 alloy increased in copper surface substrate.   15 Zn 3 alloy caused a change in its matrix microstructure (crystallinity, size and orientation of formed phases in matrix).

4.
The contact angle Sn 82 Bi 15 Zn 3 alloy decreased after adding different ratio from titanium dioxide.

6.
Soldering properties such as melting temperature and spreading (contact angle) of Sn 82 Bi 15 Zn 3 alloy improved and very closed to lead-tin commercial solder alloy (M.P=183 C and contact angle  19) after adding Ti 2 O.

7.
Corrosion resistance of Sn 82 Bi 15 Zn 3 alloy also is improved by adding T i2 O.