Microstructural Characterization of Zinc Alloy ZA27 with Modification and Heat Treatments

Abstract

The influence of Ti and Zr incorporated modification and heat treatments on microstructure of ZA27 zinc alloy were investigated in this work. The results of XRD and optical microscopy analyses showed that modification with the addition of 0.03 wt.% Ti and 0.05 wt.% Zr changed the morphology of primary α-Al dendrite in ZA27 alloy from large branch-shape to small flower-shape without variation of phase constitution. It has been proposed that the segregation of Ti and Zr elements in the front of solidification interface influenced solute distributions and constitutional supercooling, and resulted in the change in growth pattern of block α-Al dendrite and in the formation of secondary dendrite. It was found that modification improved the distribution of η-Zn phase in α-Al matrix after solution heat treatment at 370℃ for 10h, and obviously restrained the coarsening of eutectics during anneal heat treatments at 320℃ for 3h and 18h, respectively.