Microstructural evolutions and enhanced mechanical performance of novel Al-Zn die-casting alloys processed by squeezing and hot extrusion

Abstract

The present investigation demonstrated the manufacturing of Al – x wt.% Zn (x = 0, 10, 20, & 30) die-casting alloys through liquid metallurgy route followed by squeezing and hot-extrusion processes. The phase analyses and microstructural evolutions were investigated by x-ray diffractometer and electron microscopes (FESEM with EDAX, EBSD, and HRTEM) respectively. The mechanical behaviour was examined by the Vickers micro-hardness and tensile tests. The results revealed that the solid solution formation of the Al-Zn phase (α+η) along with an individual α-Al phase was obtained. The distribution of (α+η) nanocrystallites nucleates in the α-Al and (α+η) major phases was observed with the formation of spider-leg like dislocations due to thermal misfit. Hot-extruded alloys exhibited different structural changes, namely, grains flow pattern, cracking/fragmentation, redistribution, shrinkages, porosities, and micron-sized voids. Al-20Zn alloy exhibited improved microstructural observation whereas Al-30Zn alloy displayed more shrinkages and porosities. The EBSD analyses illustrated the variation in grain flow patterns (coloured maps) and deformation mean uniform density (pole figures) values with the solid solution of Zn addition. The Al – 20Zn alloy exhibited improved mechanical properties (strength and ductility) owing to the effective solid solution of α-Al with the precipitated coherent α+η phases in addition to the absence of defects which can be recommended for die-casting products.