Friction stir spot welding of TiO2 nanoparticle-reinforced interstitial free steel

The purpose of the current study was to investigate the effect of different content of TiO2 nanoparticles and FSSW parameter such as tool rotational speed on microstructure and mechanical properties of IF steel FSSW joints. FSSW joints were realized by adding 0.45, 1.14, 2 wt% of TiO2nanoparticles to IF steel. Optical microscopy and scanning electron microscopy and energy dispersive spectroscopy studied along with the results of microhardness measurements and tensile shear analyses. The obtained results showed that the optimal welding conditions were a tool rotational speed of 1120 rpm and a dwell time of 9 s. Microstructural observations demonstrated a good dispersion of TiO2 reinforcements in the steel matrix. TiO2 nanoparticles addition led to a remarkable increase in the mechanical properties of the produced welds. This was attributed to the fine grain size obtained thanks to the ceramic particles addition. The hardness and ultimate load of joints produced by TiO2 amount of 1.14 wt% are optimum welding conditions for fabrication of the best quality of welds which have attributed to the uniform dispersion of TiO2 nanoparticles in the weld regions. For higher than 1.14 wt% content of TiO2, nanoparticles agglomeration occurred, this resulted in the decrease in strength and ductility.