Effect of solidification parameters on the microstructure of directionally solidified Sn-Bi-Zn lead-free solder

Sn-Bi-Zn lead free solder alloy was directionally solidified upward at a constant temperature gradient (G=3.99 K/mm) with a wide range of growth rates (8.3-478.6 mu m/s) and at a constant growth rate (V=8.3 mu m/s) with a wide range of temperature gradients (1.78-3.99 K/mm) using a Bridgman type directional solidification furnace. Wavelength-Dispersive X-ray Fluorescence spectrometry and X-ray diffraction were used to identify the compositions and phases in the microstructure. Dependence of eutectic spacings (lambda) on the growth rate (V), temperature gradient (G) and cooling rate (a(1a)) were determined using linear regression analysis. From the experimental results, it can be concluded that the values of lambda decrease with the increasing the values of V, G and a(1a). The value of lambda V-2 was determined using the measured values of lambda and V. The results obtained in the present work have been compared with previous results obtained for binary or ternary alloys.