The current research focuses on the mechanical properties and the microstructural behavior of friction stir spot-welded 6061-T6 aluminum alloy reinforced with SiC nanoparticles. Weld samples are produced with and without the addition of SiC nanoparticles to the joint. The microhardness and lap shear strength of the joints are investigated. The cross section of welds and the fracture surfaces are studied by a stereo zoom microscope. Microstructure and distribution of reinforced particles in the stir zone are examined through optical and scanning electron microscopies. It is observed that the reinforcement of SiC nanoparticles significantly influences the grain size and hence the weld properties. The highest hardness of 93 HV and the maximum shear load of 2650.5 N are observed at the stir zone of the sample with 29% SiC. All the weld samples exhibit the similar “W” shape hardness profile. From the observed results, the selected set of process parameters is found adequate in order to fabricate sound Al/SiC composite joints.

6061-T6 aluminium alloy is a tempered grade aluminium material that is extensively used, particularly in space and automotive applications. The conventional and swept friction stir spot welding (FSSW) joints are prepared by varying tool rotational speed at four different levels. The mechanical properties, microstructure and mode of failure in both types of FSSW are evaluated and reported. The high plastic deformation and fine grains influenced the increase in hardness of the weld joints based on the Hall-Petch equation. The highest lap shear strength of 5.31 kN is observed in swept FSSW sample prepared at 1400 rpm. Interestingly, 1600 rpm decreased the lap shear strength due to insufficient friction between base metal and tool in the higher tool rotational speed. The minimum microhardness is noticed in heat-affected zone (HAZ) of both cases. Conventional FSSW samples showed shear fracture, nugget pullout fracture and circumferential fracture under lap shear loading, whereas swept FSSW showed only the circumferential fracture.

Ceramic reinforced friction stir spot-welding (FSSW) is one of the unique welding techniques used to fabricate spot joints. This study is intended to investigate the effect of reinforcement additive particle size in achieving higher weld strengths. AA5083-H116 aluminum alloy plates were welded with nano- and micro-sized silicon carbide (SiC) particles. Investigations of the weld joints prepared using a tool rotational speed of 1300 rpm, tool plunge rate of 25 mm/min, and dwell time of 10 s revealed that the lap shear tensile strength and hardness of the nano-SiC particles added to aluminum joints were higher than those of the micro-SiC particles added to joints. In particular, the nano-SiC particles provided 29.6% higher strength and 23.3% higher hardness than the unfilled FSSW. The uniformly dispersed fine SiC particles in the processed zone provided more nucleation sites for the re-precipitation of new grains and the precipitates in the aluminum matrix. The X-ray diffraction results confirmed that there was no evidence of a new phase (intermetallic compounds). Reinforcement of SiC particles significantly enhanced the wear characteristics, as well (26.3%). Field emission scanning electron microscopy (FESEM) evidenced the uniform distribution of SiC particles in the weld nugget zone. In addition, the fractography of the samples is presented and discussed.