Peritectic Reaction And Microstructures Evolution During High Pressure Solidification Of Zn-Cu Alloys

Peritectic solidification had been attracted widespread concerns as it was extensivelyexisted in structural materials and functional materials. Peritectic solidification phasetransition had been played an important role in the process of solidification and abundantmicrostructures were observed during peritectic solidification. In this study, Zn-Cuperitectic alloy with four different compositions as Zn-2.0wt.%Cu, Zn-2.7wt.%Cu,Zn-3.0wt.%Cu and Zn-4.3wt.%Cu were solidified under different pressures. Meanwhile,the Zn-Mg hypoperitectic alloy exhibiting faceted growth interface were selected as acomparison. Evolution of solidification microstructure, transition rules of microstructuresand phases, heterogeneity of a larger sample and its relevant causes were analyzed basedon the experimental results came from peritectic alloy under high pressures. Themicrostructures and phase compositions solidified under different pressures wereinvestigated by metallographic, X-ray diffraction and scanning electron microscopy.The results showed that the phase composition of Zn-Cu peritectic alloy which are ηand ε phase did not change after high pressure. But the phase morphology, distribution andvolume fraction of each phase had undergone great changes. The primary phase after highpressure of hypoperitectic alloy with a composition of Zn-2.0wt.%Cu was very little, so itsmicrostructure and morphology were not observed. With the increase of pressure, theprimary phase of peritectic alloy with a composition of Zn-2.8wt.%Cu and Zn-4.3wt.%Cuwas gradually increased. It can be concluded that the copper content in the primary phasegradually reduced with the increase of pressure by the method of element content analysisof each phase. But peritectic alloys with a composition of Zn-3.0wt.%Cu andZn-4.3wt.%Cu under a pressure of3GPa showed a reverse situation, its copper content inthe primary phase was even more than it was under normal pressure. A column-shapedcrystal growth of η cellular which forming a layer structure was found the first time in thehigh-pressure solidification microstructure of peritectic alloys with a composition ofZn-2.0wt.%Cu. The influence of high pressure solidification temperature field on themicrostructure of entire sample was analyzed.With the studies of faceted growth interface of peritectic alloy with a composition of Zn-5.0wt.%Mg found that, the peritectic solidification layer was disappeared and themorphology of each phase was changed.