Optimizing and investigating influence of manufacturing techniques on the microstructure and mechanical properties of AZ80-0.5Ca-1.5Al2O3 nanocomposite

In the present study, it has been attempted to evaluate the effect of stir and rheo-casting techniques on microstructure and mechanical properties of AZ80-0.5wt%Ca/1.5 vol%Al2O3 nanocomposite. In the first step, preference selection index (PSI) criterion was successfully utilized to achieve the best stirring conditions in both casting processes. Then, the nanocomposite samples were fabricated by two different routes of stir and rheo-casting processes. Microstructural studies of the samples indicated that type and amount of the eutectic phase and particles distribution were influenced remarkably by casting techniques. The rheo-cast nanocomposite with fully divorced eutectic phase provided higher strength, better reinforcement distribution and less porosity in comparison with the stir-cast one. Then nanocomposites were subjected to extrusion at 450 °C with an extrusion ratio of 12:1. Hot-extrusion of the nanocomposites induced dynamic recrystallization by two different mechanisms, consisting of rotational dynamic recrystallization (RDR) and particle stimulation nucleation (PSN), which caused refining grain size. Tensile properties of the extruded rheo-cast nanocomposite were higher than values of the extruded stir-cast nanocomposite, which was mainly attributed to more uniform distribution of Al2O3 nanoparticles.