A novel approach for development of surface nanocomposite by friction stir processing

▶ Surface metal–matrix nanocomposite fabricated by a new approach utilizing atmosphere plasma spray and friction stir processing. ▶ The Al 2O 3 nanoparticles were almost homogenously distributed in nanocomposite surface layer without any evidence of structural defects. The average thickness of the surface nanocomposite layer formed by this method was 600 μm. ▶ The average hardness of the resulting surface nanocomposite increased to about 230 Hv which is much higher than that of unreinforced material at same condition. ▶ Addition of Al 2O 3 nanoparticles to the Al2024 matrix changed the wear mechanism; the wear of surface nanocomposite layer involves delamination and removal of layers from the surface, creating debris of soft metallic flakes. ▶ The wear properties of the Al2024 alloy were considerably improved by the addition of Al 2O 3 nanoparticles, and the wear resistance of material was much higher than that of the unreinforced Al2024 alloy. A new approach was used to produce Al–10%Al 2O 3 surface nanocomposite on Al2024 substrate. This novel approach involved air plasma spraying of Al–10%Al 2O 3 powder to produce Al–10%Al 2O 3 coating on substrate. The coated material was then subjected to friction stir processing (FSP) to distribute Al 2O 3 particles into the substrate. Microstructure and mechanical properties of samples were investigated by optical microscopy (OM), scanning electron microscopy (SEM), micro-hardness and wear measurements. As a result, it was found that the Al 2O 3 particles were distributed uniformly inside the substrate with an average penetration depth of about 600 μm. The surface nanocomposites produced in this way had excellent bonding with the substrate. The micro-hardness of the surface nanocomposite was ∼230 Hv, much higher than ∼90 Hv for Al2024 substrate. The surface nanocomposites also exhibited lower friction coefficient and wear rate. It was found that the addition of Al 2O 3 nanoparticles to the Al2024 matrix alloy affect the mechanism of wear.