Effects of processing parameters on microstructure of thixoformed ZA27 alloy

In this paper, the effects of processing parameters on microstructures of thixoformed ZA27 alloy cylindrical rods were investigated. The results indicated that the microstructure of the formed rod was basically uniform except that of the section near the inner gate. But the detailed microstructure observation or quantitative examination showed that the primary particle fraction slightly decreased along the axial direction but it relatively more obviously decreased along the radial direction. The primary particle size increased and the primary particle fraction decreased with the increase of reheating duration. Both the size and fraction of primary particles decreased with elevating the reheating temperature and increased with increasing the die temperature. The secondary solidification began with the direct growth of the secondary primary phase on the surface of the primary α′ particles and completed by forming lamellar eutectics. The secondarily solidified structure was significantly affected by die temperature while the other two parameters, reheating temperature and reheating time had no obvious effect.