Evaluation of the Cryogenic Effect on Friction Stir Processed AA7075/Si Matrix Nanocomposites

Friction-stir processing is a green manufacturing process for surface composite fabrication and surface modification. To achieve this critical goal, the type of cooling and lubrication are of great importance. Therefore, in this paper, the cryogenic effects were investigated on friction-stir processing (FSP) tool wear and surface quality of an aluminum matrix nanocomposite. Silicon carbide (SiC) nanopowder was used as the reinforcing phase. The effects of cooling strategy and tool rotation speed on the tool wear, microhardness, surface roughness, and energy dispersive spectroscopy (EDS) analysis were studied. The cooling procedure was conducted under dry and cryogenic conditions. Additionally, the rotation speed was set at three levels, while other parameters were kept constant. The FSP tools were examined under a scanning electron microscope, and the wear mechanisms were investigated under different conditions. The results showed that tool wear, surface roughness, and microhardness were improved under cryogenic conditions compared to air conditions. Furthermore, in the presence of liquid nitrogen, the metal matrix composite did not exhibit any microstructural defects, such as micro-cracks. Energy dispersive spectroscopy analysis also demonstrated that SiC had better penetration into the base material under cryogenic conditions compared to dry conditions.