Mechanical and corrosion characteristics of 6061–T6 aluminum alloy samples reinforced with alumina micro and nanoparticles fabricated by friction stir processing

Abstract

The present study investigates the mechanical and corrosion properties of reinforced 6061 $-$ T6 aluminum samples after friction stir processing. Three different composites are fabricated: one without any powder and the others with micrometer and nanometer alumina powder (Al₂O₃) as reinforcing particles. The hardness, tensile, and potentiodynamic polarization tests are performed to compare the new samples with the base metal. The results show that friction stir processing has increased the tensile and ultimate strength of the composites by an average of 181% compared to the base metal which is due to the microstructure changes including grain distribution refinement and the elimination of defects and micro-voids through localized plastic deformation. The strength of the composites with additives is significantly affected by the size of the particles. The hardness of the processed samples has also increased compared to the base metal by 200%. Despite these enhancements, the corrosion resistance of new samples has decreased by 70%, which can be due to the numerous dislocations in the stress-induced stir zone, creating lattice deformations and causing the breakdown of the passive protective layer. The analysis of fracture surface topography through a Fractography method revealed a specific anaglyph consisting of dimples of various shapes, sizes, and dispersion and further confirmed the tensile test results.