Effects of rheocasting parameters on the microstructure of rheo-centrifuged cast Al-7.1Â wt%Si alloy

Increased interest in semisolid metal processing during the recent years has created the need for accurate evaluation of the effects of processing parameters on the microstructure of primary features formed in semisolid metal slurries. This paper reports the effects of initial solid fraction and stirring speed on the microstructure of a rheo-centrifuged cast Al-7.1 wt%Si alloy. Results showed that size of the primary features increased by increasing the solid fraction or decreasing the stirring speed. Moreover roundness of primary granules increased with increasing the solid fraction or stirring speed. However, roundness of primary granules groupings increased with decreasing the solid fraction or increasing the stirring speed. The results were discussed using two distinct mechanisms, namely fragmentation-agglomeration and nucleation and separation from the wall mechanisms, proposed for formation and evolution of semisolid microstructure. Both mechanisms were able to reasonably explain the experimental results.