چكيده به لاتين
The aim of this study is to improve weld characteristics employing a new proposed method in adding SiC reinforcement nanoparticles to friction stir spot welds (FSSW). 6061-T6 aluminum alloy plates 3 mm in thickness and SiC reinforcement nanoparticles 45 to 65 nm in diameter were used in FSSW. Design of experiments, S/N ratio analysis and optimization of joint ultimate strength were conducted using Taguchi method. In this way, the amount of nanopowder, tool rotational speed and dwell time were considered as input parameters and joint ultimate strength as the output parameter. Then Taguchi suggested optimum specimen was fabricated and tensile tested and results confirmed optimal measure predicted by Taguchi. Four specimens from experiments table were examined next and the effect of incorporating reinforcement nanoparticles on ultimate strength, microhardness and grain size of the welds were evaluated. The examined specimens included: the best and the worst specimens in experiments table in terms of strength, Taguchi suggested optimum specimen and its powder-free equivalent. The fracture mode of each examined specimen was specified by an investigation of the behavior of all specimens during tensile test. Moreover, shape of their force-displacement graphs and failed nugget surfaces were also discussed. The microstructure of weld cross-section was observed by optical microscopy (OM) and field emission scanning electron microscopy (FESEM). Grain size, wideness of nanocomposite area and reinforcement nanoparticles distribution in different specimens were studied and achieved results justified joint mechanical properties. Energy dispersive spectroscopy (EDS) indicated that nanoparticles assembled in grain boundaries during dynamic recrystallization and prevented the growth of grain size. Incorporation of SiC nanoparticles in FSSW increased joint ultimate strength and average hardness in stir zone (SZ) up to 25% and 24%, respectively.
