Studying microstructure and mechanical properties of SiC-incorporated AZ31 joints fabricated through FSW: the effects of rotational and traveling speeds

In this study, friction stir welding (FSW) technique was employed for joining AZ31 magnesium plates. Since SiC particles had been injected along the joint line, AZ31/SiC nano-composite was developed in the stir zone (SZ). To find the optimum condition, FSW was conducted under the combination of three rotational and two traveling speeds. Microstructural investigations were carried out through optical and scanning electron microscopes. Onion ring structure consisting SiC-rich and SiC-free regions was observed in SZ. In addition, reasonable particle dispersion happened in the specimen friction stir welded (FSWed) at 800 rpm and 75 mm/min. Thanks to the SiC reinforcements, grain size reduced from 44 mu m in base metal to 5 mu m in the SZ. Compared to previous researches, microstructural evolution associated with reinforcement particles exerted positive effects on the mechanical properties of the joint. Meanwhile, fracture surfaces of tensile specimens were closely examined and an extreme correlation with ductility results was observed. As expected, on the other hand, composite joints exhibited superior hardnesses to the base metal. Despite indiscernible difference, the foregoing specimen showed the highest hardness.