Microstructural evolution and mechanical properties of friction stir processed ZrB2/6061Al nanocomposites

In the present work, homogeneously dispersed ZrB2 nanoparticles and fine-grained structures were successfully achieved by friction stir processing (FSP) of in situ 0-2 vol% ZrB2/6061Al nanocomposites. The effects of ZrB2 additions on the microstructures and tensile properties were investigated. A combination of EBSD and TEM analyses revealed that ZrB2 nanoparticles strongly suppressed (sub)grain boundary migration and/or orientation, and thus led to a continuous decrease in grain size, HAGBs fraction as well as B/B¯ shear texture intensity at higher ZrB2 content. Moreover, compared with the processed 6061Al alloy, microhardness, strengths and elongation of the FSPed composites were significantly improved mainly due to the refined grains and ZrB2 nanodispersoids. Quantitative calculation indicated that as ZrB2 content increased, Orowan strengthening instead of grain refinement strengthening contributed the most to the yield strength.