Assessment of Sb Content on Solidification Behavior, Microstructure, and Hardness of Zn‐Sb Alloys

Zn‐Sb systems show promise for soldering applications, yet detailed studies on their solidification remain scarce. Sb was chosen for its properties, availability, and cost, though its effect on solidification and eutectic morphology is still unclear. The present work investigates the effect of antimony (Sb) on the macrostructural and microstructural evolution, thermal parameters (cooling rate—Ṫ, growth rate for liquidus isotherm— V _L and eutectic front— V _E ), macrosegregation, and hardness in directionally solidified binary Zn‐1.0 wt.%Sb, Zn‐2.0 wt.%Sb, and Zn‐4.0 wt.%Sb alloys under nonequilibrium conditions. The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X‐ray fluorescence (XRF), and X‐ray diffraction (XRD), and Vickers hardness (HV) tests. Thermodynamic calculations were performed by the CALPHAD method using Thermo‐Calc software to obtain information such as transformation temperatures, solidification paths, predicted phases, and their fractions. Increasing the Sb content to 4.0 wt.% suppressed the columnar growth observed at lower Sb levels (1–2 wt.%), as the higher solute concentration enhanced constitutional supercooling ahead of the solid–liquid interface, thereby promoting the nucleation of equiaxed grains and leading to a fully equiaxed macrostructure. The Zn‐1.0 wt.%Sb and Zn‐2.0 wt.%Sb alloys showed Zn‐rich dendrites surrounded by a Zn + Zn ₄ Sb ₃ eutectic with a fibrous morphology. Zn ₄ Sb ₃ plates appeared at cooling rates below 2.80°C/s and 2.2°C/s, respectively. The Zn‐4.0 wt.%Sb alloy displayed a Zn + Zn ₄ Sb ₃ eutectic with fibrous intermetallics and plate formation at Ṫ < 2.90°C/s, together with primary idiomorphic Zn ₄ Sb ₃ particles, indicating a hypereutectic composition. In general, for all three alloys, cooling rates below 2.2°C/s favored the formation of Zn ₄ Sb ₃ plates. It is noted that the Zn‐4.0 wt.%Sb alloy has a quasieutectic composition, diverging from previous observations in the literature. The increase from 1%Sb to 2%Sb did not promote changes in the scale of the dendritic arrangement, but with the 4%Sb content, a refinement of the fibrous eutectic spacing was observed compared to the other two compositions, in addition to a decrease in the liquidus and solidus temperatures. The increase in Sb content caused an increase in HV, due to the microstructural refinement (refined eutectic arrangement) and the higher fraction of the Zn ₄ Sb ₃ hardening phase.