In-situ formation of Al2O3 nanoparticles during friction stir processing of AlSiO2 composite

Abstract Aluminum matrix composites reinforced with nanometer-sized Al 2 O 3 particles were produced from Al SiO 2 powder mixture by using friction stir processing (FSP). In the composites, Al 2 O 3 particles were produced in situ by oxide-aluminum displacement reactions. This approach combined the hot working nature of FSP and an exothermic reaction between Al and SiO 2 . The Al 2 O 3 particles were formed at the Al/SiO 2 interface, and dispersed in the aluminum matrix by the stirring action of the rotating tool during FSP. Microstructural examinations revealed the Al 2 O 3 particles present mainly in the form of clusters of nano-sized (approximately 20 nm) particles, which were identified as α-Al 2 O 3 . Because of the fine dispersion of nano-sized particles in an ultrafine-grained aluminum matrix, the composites exhibit superior tensile strength and ductility. Quantitative phase analysis indicated that the extent of the Al SiO 2 reaction increased in conjunction with an increasing tool rotation rate and a decreasing tool traverse speed in FSP.