Friction stir welding of polypropylene based graphene nanocomposites fabricated with 3-D printing: An investigation on the microstructure and mechanical properties

Polymer nanocomposites find diverse applications in the aerospace, automobile and electronic industries due to good corrosion resistance, high specific strength and excellent processing ability. However, the production of complex and larger parts typically requires welding technology. In this research, fused filament fabrication technique was used to prepare polypropylene nanocomposite reinforced with graphene nanoplates. The polypropylene/graphene nanocomposites were then joined using the friction stir welding. Afterward, different analyses such as thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, tensile testing and hardness testing were applied to examine the effects of the process parameters on the microstructure and mechanical properties of the nanocomposite. The results of thermal analysis indicated that the addition of graphene nanoplates improved the melting point and crystallinity percentage of the polypropylene nanocomposite. Mechanical characterization of the welded samples indicated that the increase of rotational speed from 500 to 750 rpm enhanced the tensile strength of weld joint, while it reduced the hardness. Moreover, an increase in the welding speed from 10 to 30 mm/min resulted in a reduction in the tensile strength and an improvement in the hardness. The highest tensile strength of the weld was obtained by addition of 1 wt% graphene to polypropylene, whereas the hardness of the weld was maximized by addition of 2 wt% graphene. Nevertheless, the desirable combination of the process parameters for simultaneous enhancement of tensile strength and hardness was achieved by rotational speed of 667 rpm, welding speed of 16 mm/min and graphene content of 1.5 wt%.