Effect of Bi on the microstructure and mechanical properties of Sn-Zn alloys processed by rolling

Sn-Zn based alloys including Sn-3Zn, Sn-3Zn-1Bi, and Sn-3Zn-5Bi were prepared by casting and rolling, in efforts to assess their feasibility for the application as cladding materials in detonating and explosive cords. It was found that Bi significantly refined the solidification microstructure, changing the configuration of Sn-Zn eutectic from well-aligned Zn-rich precipitates/needles to misaligned Zn-rich flakes. During deformation, second phases like Zn-rich precipitates and Bi particles, and Bi solutes were effective in grain refinement since second phase particles provided more sites for nucleation and more obstacles to growth of new recrystallized grains. Tensile results revealed that Bi addition enhanced both strength and ductility of the rolled Sn-Zn-Bi alloys. The Sn-3Zn-5Bi alloy possessed superior strength and ductility (UTS: 84.4 MPa; Yield strength: 68.3 MPa; Elongation: 75.2%) due to its finest and most homogeneous equiaxed grains. Based on decent mechanical properties, the Sn-Zn-Bi alloys could be well qualified for the application as cladding materials.