Effect of multi-pass friction stir processing on textural evolution and grain boundary structure of Al–Fe3O4 system

Abstract

A mixture of pre-milled Fe3O4 and Al powder was added to the surface of an aluminum alloy 1050 substrate to obtain hybrid surface nanocomposites using friction stir processing. In situ nano-sized products were formed by the exothermic reaction of Al and Fe3O4. The reaction is triggered by hot working characteristics of the process. The microstructure and crystallographic microtexture transition and grain boundaries evolution of the fabricated nanocomposite were investigated using optical microscopy, X-ray diffraction, field emission scanning electron microscopy, and electron backscattered diffraction analyses. It is illustrated that matrix means grain size decreased in the specimens, which is processed without and with the introduction of the powder mixture to ∼8 and 2 μm, respectively. In addition, high angle grain boundaries showed marked increasing that demonstrates the happening of dynamic restoration phenomenon in the aluminum matrix. Moreover, the fraction of low ΣCSL boundaries showed increasing (remarkably in the presence of hard particles); these boundaries play the main role in dynamic recrystallization. The incorporation of nano-sized products such as Al13Fe4 and Al2O3 in the dynamically recrystallized aluminum matrix produced a pre-dominantly CubeTwin texture component induced by the stirring function of the rotating tool. As a result, the effect of nano-sized products is constrained. Keywords: Friction stir processing, Grain refinement, Microtexture, Grain boundary, Nanocomposites, Aluminum matrix composite