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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.

The objective of the present study is to investigate the effect of Al 2 O 3 nanoparticles volume percentage on tribological, mechanical and microstructural characteristics of 6061-T6 aluminum alloy based particulate-nanocomposite (P-NCs) fabricated using friction stir welding (FSW) process. Optical microscopy (OM) and scanning electron microscopy (SEM) was employed to evaluate the (a) microstructures of the produced nanocomposites to ascertain the distribution of Al 2 O 3 nanoparticles in the nugget zone; (b) nanocomposite depth formed on Al-alloy matrix, and (c) fractured and wear characteristics. Results reveal that the produced P-NCs had a depth of 3286 mm across the perpendicular x-section of the weld nugget zone of P-NCs. With the increase in a volume percentage of Al 2 O 3 nanoparticles there was a tremendous increment in the microhardness up to 125 HV which is higher than as-received AA6061-T6. It was also noticed that the tensile strength and the wear resistance of produced P-NCs were significantly increased at 0.3 vol% of Al 2 O 3 nanoparticles as compared to 0.2 and 0.4 vol%. The corresponding mechanical and wear properties results were correlated to microstructure and fractography results.

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Heat-treatable AA6061-T6 weldability leads to a decline in the physio-mechanical and tribological properties due to strengthening precipitates dissolution in the nugget zone of FS-welded joints. Improvement in these properties is governed by reinforcement particles addition in the weld joint line for non-heat treatable Al-alloys. Although, its application to AA6061-T6 is scant. In the present work, FS-welded joints were produced by reinforcing Al 2 O 3 nanoparticles into the faying surface of the base matrix. The purpose of Al 2 O 3 nanoparticles addition is to refine the microstructure of the nugget zone and to obstruct the granular growing in the heat-affected zone. FSW was conducted at constant rotating 2000 rpm, transverse 70 mm min −1 speed to illustrate the influence of Al 2 O 3 addition on mechanical, microstructure, micro-hardness, and wear properties of welds compared to parent alloy and unreinforced joints. Findings revealed that Al 2 O 3 nanoparticles addition along the joint line leads to noteworthy grains refinement structure of weld zone (6μm) compared with the base material (38μm) and unreinforced nugget (18μm) joints. In addition, reinforced FS-W nugget zone have banded structure of alternate regions namely, nanoparticles-rich and free those have a difference in grain size, such that, the nanoparticle-rich region has fine grain size (6μm) than nano particle-free (14μm) region. Due to Zener-influence occurred via Al 2 O 3 nanoparticles helps to avoid the grain growth accompanied by dynamic recrystallization throughout FSW process which results in granular size reduction. Tensile strength (246 MPa/73%), microhardness (88HV/52%), and wear properties was notably increased for reinforced FSW joint compared to unreinforced joint (tensile strength (180MPa), micro-hardness (46 HV), and lower wear resistance, under similar parameters which attribute to nanoparticles presence in processed area. Moreover, single FSW pass leads to nonuniform distribution of Al 2 O 3 nanoparticles and nucleation of voids at Al/Al 2 O 3 boundary in the heat-affected zone which leads to early fracture of welded joint during tensile loading.