Grain refinement of primary Cu6Sn5 in the Sn-3wt%Ag-5wt%Cu alloy by Ge

Abstract

Fine grain structure is generally favoured in the alloy system. Here, we demonstrate that the fine intermetallic compounds (IMCs) in Sn-3wt%Ag-5wt%Cu (SAC35) alloy by coupling with different amount of Ge (0–0.15wt%). The effect of Ge addition on the microstructure, elemental distribution, thermal properties, solidification, and corresponding grain refinement mechanisms were studied. The results showed that Cu6Sn5 was explicitly refined in Ge added SAC35 alloys, with a maximum 59% reduction in the size of Cu6Sn5 found in the as-cast bulk SAC35-0.1wt%Ge alloy. Also, the presence of Ge reduced the thickness and grain size at the interfacial IMC layer by 21% and 22%, respectively. Synchrotron micro-XRF results revealed that the Ge preferentially exist in matrix phase. The cooling curve analyses revealed that the solidification time of Ge-coupled is shorter than that of the SAC35 alloy. The undercooling values was found to have decreased with increased Ge addition. The growth restriction factor, Q, was calculated with the aid of Thermo-Calc software, and it was found to have increased in tandem with increasing Ge amounts. The findings suggest the suitability of Ge as a grain refiner for SAC35.

Keywords

• Lead-free solder
• Grain refinement
• Growth restriction factor
• Solidification