Effect of soft Bi particles on grain refinement during severe plastic deformation

Two aluminum alloys, Al-8Zn and Al-6Bi-8Zn were subjected to equal channel angular pressing (ECAP) up to 5 passes at room temperature. The microstructural evolution and the grain refinement behavior of these alloys were systematically studied by electron backscatter diffraction (EBSD). After 5 passes of ECAP, ultrafine grained microstructures formed in both alloys. However, the grain structure in the Al-6Bi-8Zn alloy is much finer than that of Al-8Zn alloy, showing that the soft Bi particles have a strong influence on enhancing the grain refinement during ECAP. The strengths of the ECAP-processed materials were measured by hardness test and it showed that after 5 passes of ECAP, the hardness of the Al-6Bi-8Zn alloy was higher than that of the Al-8Zn alloy. The effects of soft Bi particles on the deformation behavior during ECAP and the final strength of the Al-6Bi-8Zn alloy were discussed.