Abstract

1. 20μm 20μm [5] [5] Figure 2. Variation of eutectic spacings with growth rate and comparison of the experimental values with the values obtained by J-H eutectic theory in the Zn-Al eutectic alloy. (a) (b) (a) • Figure 3. (a) Variation of microhardness as a function of growth rate, (b) Variation of microhardness as a function of eutectic spacings. (b) • Abstract • In this study, Zn-5wt.%Al eutectic alloy was directionally solidified upwards with different growth rate (5.32 mm/s to 250.0 mm/s) at constant temperature gradient (8.50 K/mm) using a Bridgman–type growth apparatus. The dependence of eutectic spacing on the growth rate (V) and undercoolings (DT) was determined. The results have been compared with the eutectic theory and the similar experimental results. Microhardness (HV) of the samples was also measured anddependency of the HV on V was investigated. Afterwards, variations of electrical resistivity (r) of casting alloy with the temperature (T) in the range of 300630 K were measured. The enthalpy of fusion (DH) and specific heat (Cp) for the Zn-Al eutectic alloy was measured by means of differential scanning calorimeter (DSC) from heating trace during the transformation from solid toliquid. Directionally Solidification and Measurements of the Physical Properties of the Zinc-Aluminum Eutectic AlloyH.Kayaa, S. Enginb, U. Böyüka, N. Maraşlıc, aDepartment of Science Education, Education Faculty, Erciyes University, Kayseri, TurkeybDepartment of Physics, Institute of Science and Technology, Erciyes University, Kayseri, Turkey cDepartment of Physics, Faculty Arts & Sciences, Erciyes University, Kayseri, Turkey 3. Conclusions It was found that the values of HV increase with increasing values of V and G, whereas values of HV decrease with increasing values of . The electrical resistivity of Zn-Al eutectic alloy increases with increasing temperature. The line of electrical resistivity versus temperature for Zn-Al eutectic alloy is higher than the lines of resistivity versus temperature for pure Ag and Zn elements but fairly close to the line of resistivity versus temperature for pure Sn. The enthalpy of fusion and specific heat for Zn-Al eutectic alloy were also determined from the trace of heat flow versus temperature.. References 1-D.A. Porter, K. E. Easterling, Phase transformations in metals and alloys, Second Edition, CRC Press (1992), 185. 2-C.M.L. Wu, D.Q. Yu, C.M.T. Law, L. Wang, Mater. Sci. Eng. R, 44 (2004) 1–44. 3-S. Knott, H. Flandorfer, A. Mikula, Z. Metallkd., 96 (2005) 38–44. 4-F. M. Smiths, The Bell Sys. Tech. J., 37 (1958) 711. 5-Resistivities of metallic elements http://www.kayelaby.npl.co.uk/general_physics/ 2.2. The measurement of electrical and thermal properties The temperature dependence of electrical resistivity for Zn-Al alloywas measured by the fourpoint probe method [4]. Measurements were made in the temperature range of 300630 K. Enthalpy of fusion (DH) and specific heat (Cp) of the eutectic alloy were measured becausetheyare veryimportant parameters for industrialapplications. A DSC thermal analysis was performed in the ttemperature range of 300670 K with a heatingrate of 10 K/min and under a constant stream ofnitrogen at atmosphericpressure. Theenthalpy of fusion (DH) and specific heat(Cp) werecalculated by numerical integration as theareaunder the peak. 1.Introduction Zinc-aluminum alloys constitute an important class of wrought alloys are widely used as anti-corrosion coatings of steel sheets [1]. To address the increasing demand for high performance high quality die castings, a class of zinc based engineering cast alloys have been developed, in particular for applications in the automotive industry. The Zn-Al alloys usually deliver high strength and superior hardness when compared to the most widely used non-ferrous alloys, combined with a good corrosion resistance [2]. Owing to its good anti-corrosive and forming properties as well as good technical performances, the coating attracts wide interest and has been put into industrial production rapidly [1]. 2. Experimental Procedure 2.1 Solidification and measurement of microhardness Zn-5wt.%Al eutectic alloy was directionally solidified upwards with different growth rate (5.32 mm/s to 250.0 mm/s) at constant temperature gradient (8.50 K/mm) using a Bridgman–type growth apparatus. The quenched samples were removed from the graphite crucible and the metallographic process, the microstructures of the samples were revealed (Fig. 1). Figure 4. Variation of electrical resistivity as a function temperature and comparison of temperature dependence of the electrical resistivities of pure Zn, pure Al, and Zn-Al eutectic alloy. Figure 5. Heat flow curve versus the temperature for Zn-Al eutectic alloy at heating rate of 10 K/min. (a) Figure 1. Micrographs of the directional solidified Zn-5wt.%Al eutectic alloy showing the eutectic microstructure and microindentation traces (a) V=5.32 µm/s and G =8.50 K/mm, (b) V=250 µm/s and G =8.50 K/mm,