Abstract
<title>Abstract</title> <p>The effect of cerium (Ce) microalloying on the microstructural evolution, thermal behavior, and mechanical properties of SAC305 lead-free solder was investigated to establish quantitative correlations between microstructure and mechanical performance. SAC305 alloys containing 0.2, 0.3, and 0.5 wt.% Ce were systematically investigated. The addition of 0.2 wt.% Ce produced the greatest microstructural refinement, reducing the β-Sn volume fraction from 35 ± 3% to 26 ± 2% and the average β-Sn grain size from 20 ± 2 µm to 10 ± 2 µm. This refinement resulted in the highest tensile strength (51.5 MPa), toughness (12.9 MJ m⁻³), and hardness (18.5 HV), corresponding to improvements of 22.6%, 30.3%, and 34%, respectively, compared with the base SAC305 alloy. Higher Ce additions diminished the refinement effect, leading to coarser β-Sn regions and reduced mechanical performance. DSC analysis revealed negligible changes in melting behavior, with peak melting temperatures remaining between 222.07 and 223.40°C, indicating compatibility with conventional reflow soldering. Overall, 0.2 wt.% Ce provides the optimum balance of microstructural refinement, mechanical strengthening, and thermal stability in SAC305 solder.</p>