Grain Refinement and Hardness Improvement of Sn-Zn Solders with Nickel-Coated Precipitate Calcium Carbonate

Abstract

In this study, the effects of 0.5 wt.% of micro-sized and nano-sized nickel-coated precipitated calcium carbonate (PCC) on the structural, microstructural, and mechanical properties of tin-zinc (Sn-Zn) solder alloys were examined. X-ray diffraction analysis revealed the formation of a monoclinic Ni₃Sn₄ phase, indicating significant structural transformation due to Ni-coating. Microstructural investigation showed refined Zn-rich grains in the composite solder alloys with micro-sized Ni-coated PCC, attributed to grain boundary strengthening. Elemental study confirmed a reduced Zn content of around 3.69 at.%, suggesting diffusion-induced redistribution during phase formation. Vickers microhardness testing using diamond indentation revealed that Sn-Zn solder with micro-sized Ni-coated PCC exhibited the highest hardness at 16.98 ± 5 HV, which is 12% higher than pure Sn-Zn solder. The results demonstrate the combined influence of phase reinforcement and microstructural evolution in enhancing the mechanical performance.