Microstructural evolution during partial remelting of in situ Si_p/ZA27 composite with developed dendrites

Abstract

Microstructural evolution during partial remelting of in situ Si_p/ZA27 composite with developed dendrites has been investigated. Simultaneously, the phase transformations occurring during this process have also been discussed. Results indicate that the microstructural evolution can be divided into three stages: coarsening of primary dendrites, structural separation and spheroidisation. The coarsening is attributed to the reaction of α+η+ϵ→β. The structural separation results from β+η+ϵ+Si→L, β→α′+L and α′+Si→L, and the spheroidisation is ascribed to the two reverse reactions of α′+Si→L and L→α′+Si. The Si particles have no effect on the general microstructural evolution steps of the ZA27 matrix, but they can slow the evolution progress. The Si particle size first decreases due to partial melting and then increases due to Ostwald ripening. Correspondingly, their morphologies first become more and more blunt and then become into large and spheroidal particles.

Keywords:

• Si_p/ZA27 composite
• Thixoforming
• Partial remelting
• Microstructural evolution
• Phase transformation

This work was supported by the Development Program for Outstanding Young Teachers and the Doctor Foundation of Lanzhou University of Technology.