Effect of nano-sized particles on grain structure and mechanical behavior of friction stir welded Al-nanocomposites

Abstract

Weldability of heat-treatable 6061-T6 aluminum alloy results in deterioration of mechanical properties due to dissolution of strengthening precipitates in the nugget zone of friction stir welded joints. These properties were improved by addition of reinforcement particles in the weld joint line. In the present work, attempts were made to produce 6061-T6 Al-based nanocomposites using the friction stir welding process by incorporating titanium oxide nanoparticles into the aluminum matrix for microstructure refining of the nugget zone and prevent the grain growth in the heat-affected zone. The effect of addition of nanoparticles on the evolution of grains structure and mechanical behavior of friction stir welded samples based on different combinations of rotational and travel speed was studied and discussed. Results revealed that the unreinforced samples were successfully welded at both low and high heat inputs, whereas the reinforced samples are not feasible at tool rotational speed (ω) < 2000 r/min and transverse speed (v) > 70 mm/min, respectively. The significant refining of grains in the nugget zone is possible with addition of nanoparticles via the Zener-pinning effect. A more pronounced increment in tensile strength, microhardness, and wear properties was observed compared to sample without nanoparticles under the same processing parameters due to embedment of nano-sized particles in the weld nugget zone.