Microstructural study of Zn-11% Al and Zn-27% Al alloys

Zinc-aluminium alloys with small amounts of copper and magneisum (ZA alloys) are used in a number of casting processes. They offer the foundry industry a family of zinc alloys with a wide range of mechanical properties able to meet a large spectrum of performance criteria. However promising the characteristics of these alloys, microstructural studies of them are incomplete. It has been shown that copper additions to ZA alloys modify the number of the phase existing in the binary zinc-aluminium system as well as their transformation kinetics. Microstructural studies have shown not only the heterogeneity of the microstructure but also the presence of a zinc-rich metastable phase and the evolution of the composition of the ternary phase Zn-Al-Cu (T) during ageing. This situation is not surprising as several studies have shown the existence of metastable phases in the binary system Al-Zn with high aluminium content. the complexity of the microstructure leads us to search further for a better understanding of the binary Zn-Al alloys, with Al contents corresponding to ZA 12 and ZA 27 wihout any Cu and Mg, in order to precise about the complex evolution to stable phases observed in these alloys.