冷却速度对无铅焊料Sn-3.5Ag合金微观组织和显微硬度的影响

Influence of Cooling Rates on the Microstructure and Microhardness of Lead-free Sn-3.5Ag Solders

在～10^2K／s、～10^3K／s和～10^4K／s的冷速条件下研究了凝固速度对无铅焊料Sn-3．SAg合金微观组织和显微硬度的影响。结果表明：由于非平衡凝固条件下动力学过冷的影响，导致了该共晶合金实际凝固过程开始于平衡共晶凝固点以下，合金凝固组织中包含初生β-Sn枝晶，且该初生β-Sn枝晶组织随合金凝固速度的提高而发生细化。另外，维氏硬度测试结果表明，无铅焊料Sn-3．5ag合金在不同冷速条件下的凝固组织与显微硬度的关系符合经典Hall-Petch关系式，即初生β-Sn枝晶细化能显著提高焊料合金的显微硬度。

The microstructure and microhardness of Sn-3. SAg solders are explored at the cooling rates of 102 K/s, 10a K/s and 104 K/s. In non-equilibrium solidification condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium euteetie point and results the formation of primary β-Sn crystal dendritic structure. The higher the applied cooling rate is, the finer the primary β-Sn crystal forms. Additionally, the Vicker＇s hardness test result of the obtained lead-free solders fits well with the prediction of Hall-Peteh relationship that the refinement of primary β-Sn crystal grains can obviously himprove the mierohard- ness of Sn-3.5Ag solder.