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In this study, 6 mm thick AA6061-T6 plates were friction stir welded (FSWed) at different traveling speeds while Al 2 O 3 nano-particles were incorporated between adjoining plates. The solution heat treatment was applied on samples for one hour at 540 C and subsequently aged for 18 h at 180 C to investigate the effect of post-weld heat treatment on mechanical properties of specimens. All joints were investigated macro-and micro-structurally. The microstructural characterization of the FSWed samples was carried out using scanning electron microscopy (SEM) and light microscopy techniques. Distribution of Al 2 O 3 nano-particles in the stir zone was studied by SEM. The specimen FSWed at 40 mm/ min exhibited the most homogeneous particles distribution. Tensile properties including ultimate tensile strength, elongation, and fracture surfaces were studied. Microhardness of specimens was also investigated. Surprisingly, all specimens exhibited inferior hardness compared to the as-received AA6061-T6 alloy. This phenomenon was attributed to the dissolution of precipitates during FSW process.

In this study, 6 mm thick AA6061-T6 alloy was friction stir-welded at different traveling speeds while Al 2 O 3 nanoparticles were incorporated between adjoining plates. All joints were investigated macro-and micro-structurally. In addition, distribution pattern of Al 2 O 3 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 Al 2 O 3 nano-particles introduction, on the other hand, wear resistance improved tremendously.