Thermal Properties and Phase Formation in Zn-Modified Pb–Sn Alloys

This study investigates the influence of a 2% zinc (Zn) addition on the thermal properties and crystallization kinetics of a Pb-5Sn solder alloy to understand its impact on processing characteristics. Non-isothermal differential scanning calorimetry (DSC) was employed to analyze the melting and crystallization behavior of both the base Pb-5Sn and the modified Pb-5Sn-2Zn alloys at heating and cooling rates of 5, 10, 15, and 25 °C·min?¹. The Kissinger method was applied to the crystallization peak data to determine the activation energy (E?) for the process. The results revealed a significant decrease in the activation energy for crystallization upon the addition of zinc, from 103.54 kJ/mol for the base Pb-5Sn alloy to 57.93 kJ/mol for the Pb-5Sn-2Zn alloy. Furthermore, the crystallization peak temperatures for the Zn-modified alloy were consistently lower across all cooling rates, indicating an increased propensity for crystallization. This substantial reduction in the energy barrier suggests that zinc atoms act as effective heterogeneous nucleation sites, thereby facilitating the transition from the liquid to the solid phase. These findings demonstrate that minor Zn alloying can significantly alter the phase transformation kinetics, providing a practical route for tailoring the solidification behavior and optimizing the thermal processing for Pb-Sn alloys.

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