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In this study, 6 mm thick AA6061-T6 alloy was friction stir-welded at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. All joints were investigated macro- and micro-structurally. In addition, distribution pattern of Al2O3 nano-particles in the stir zone was observed via scanning electron microscopes. Although the specimen friction stir-welded at 40 mm/min exhibited the most homogeneous particles distribution, friction stir welding at 1600 rpm and 45 mm/min yielded highest tensile strength. Fractographs achieved from tensile test specimens were in close agreement with corresponding percent elongations. Surprisingly, the foregoing specimen exhibited inferior hardness to the as-received AA6061-T6 alloy. Accordingly, it was concluded that dissolution of strengthening precipitates dominated the effect of hard reinforcement particles on enhancement of hardness value. As a result of Al2O3 nano-particles introduction, on the other hand, wear resistance improved tremendously. [ABSTRACT FROM AUTHOR]

In this paper, a threaded tapered pin tool was employed to fabricate a 2-pass friction stir welded (FSWed) joint. To investigate the benefits of nano-sized SiC particles on microstructural and mechanical properties of the joint, the experiment was repeated while SiC particles had been inserted along the joint line. In another joint, a square pin tool was applied in the second pass to evaluate the effectiveness of switching pin geometry between passes on the aforementioned properties. Microstructural features including grain size, second phase particles and reinforcement distribution were examined via optical and scanning electron microscopy (SEM) techniques. In addition to satisfactory connections between SiC particles and the matrix, the most homogenous particles distribution was observed in the specimen FSWed with both pin tools. This observation was further supported by atomic force microscopy (AFM) examination. Additionally, the foregoing joint demonstrated the maximum tensile strength which was synonymous with its smallest grain size. During tensile testing, SiC-free joint and SiC-reinforced ones fractured from stir zone (SZ) and base metal, respectively. Moreover, SiC-free joint showed necking phenomenon. SEM results showed that the SiC-reinforced specimens possessed ductile fracture morphologies. On the other hand, SiC-free specimen showed a quasi-cleavage fracture mode confirming its moderate percent elongation. In the meantime, SiC-reinforced specimens exhibited superior hardness level to SiC-free specimen. [ABSTRACT FROM AUTHOR]

Highlights: [•] AA7075/SiC nano-composite was fabricated in stir zone via FSW. [•] Using triangular pin tool resulted in the highest tensile strength. [•] In exception of four-flute cylindrical specimens, all specimens fractured from base metal. [•] Threaded tapered specimen showed the most uniform distribution of SiC particles. [ABSTRACT FROM AUTHOR]

Highlights: [•] AA7075/SiC nano-composite developed employing friction stir welding technique. [•] 1250rpm and 40mm/min were the optimum welding speeds. [•] Increasing rotational speed resulted in improved powders dispersion. [•] An excellent bonding between reinforcement and the matrix was observed. [•] UTS and ductility improved by up to 31% and 76.1% due to grain size refinement associated with SiC nano-particles. [ABSTRACT FROM AUTHOR]