Particles' distribution enhancing in aluminum-based composites produced by upward friction stir processing

A new variant of friction stir processing named upward friction stir processing (UFSP) is a promising approach to control particles' distribution and promote a more uniform distribution over a larger processed area. This variant involves using two sheets with functional particles between them to produce metallic composites. A spacer is used to ensure the desired quantity and uniform distribution of the particles and prevent sputtering. This technique promotes an upward flow to introduce more particles with a uniform distribution in the processed volume, avoiding discrete holes or grooves. This study involved enhancing the particles' distribution by varying process parameters. The resulting trial with the best particles' distribution was characterized by means of light microscopy, eddy current testing, microhardness mapping, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The study revealed that UFSP can improve the particles' distribution in the stir zone of metallic composites, especially when multi-passes are performed towards the retreating side of the plates. The process parameters that produced an improvement in particles' distribution were six passes with an offset of 1 mm towards the retreating side, the tool rotation and processing speed of 900 rev/min, and 180 mm/min, respectively, and a spacer's thickness of 0.5 mm. The resulting hardness and electrical conductivity profiles show that the UFSP technique can significantly affect material's properties, including mechanical strength, particularly when processing with tool offset towards the retreating side. Furthermore, the hardness increased by about 22% in composites produced with the addition of reinforcement particles. However, for some aluminum alloys, the properties decreased under such conditions. These findings highlight the potential of UFSP for producing functionalized materials with tailored properties, while also underscoring the importance of careful parameters selection to optimize the material ' s performance.