Geometry Tool Influence on the Microstructure of MMC Al-SiC Friction Stir Welds

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Welding as a manufacturing process on aeronautical industry is necessary for component integration. In the aircraft manufacturing, the use of aluminum alloys is widely extended. However, in these alloys if fusion welding is applied, some microstructural alterations, deleterious phases, and distortion are presented and decrease the mechanical properties of the joint. The aluminum matrix composites (AMCs) present many advantages of traditional aluminum alloys; superior properties are achieved when ceramic particles are added making them suitable for aeronautic industry. The disadvantages for AMCs with fusion welding processes are: agglomeration of the particles, lack of fusion, porosity, and many other welding defects. Recently, the solid-state welding processes are gaining acceptance due to high-quality joints, defect-free, and environmental cleaner processes, mainly the friction stir welding (FSW). Hence, FSW is commonly employed for joining these materials, and many studies have been published where the tool is the principal subject; they are mainly focused in tool wear rather than geometry influence on microstructure. Therefore, this investigation was performed in order to observe the effects of geometry differences; the aim was to examine the microstructural evolution of the welded joints. Optical and scanning microscopes (OM and SEM) were employed for the evaluation, resulting in a partial grain refinement in the thermomechanical affected zone, for the aluminum matrix and eutectic silicon, and for the fracture of the silicon carbides. In addition, orientation imaging microscopy (OIM) using electron backscatter diffraction (EBSD) technique was employed to analyze the dynamic recrystallization. Some welding defects were presented along the joint for one tool. Finally, hardness Vickers evaluation on the joints was completed resulting in differences between the two employed tools.