Abstract
This study presents a solid state surface engineering process to form a nanocomposite layer on aluminum surface. Friction stir processing (FSP) was used to stir and mix nano-sized Al2O3 particles into a commercially pure aluminum surface to form an Al-Al2O3 nanocomposite layer of up to several millimeters thick. Compared with a non-processed aluminum surface, a nanocomposite surface with 15 vol% nano-particles has demonstrated increased hardness (by 3X) and yield strength (by 10X), and reduced friction coefficient (by 55%) and wear rate (by 100X). Transmission electron microscopy (TEM) has revealed high matrix dislocation density in the nanocomposite surface that is believed to be largely responsible to such significant property improvements. Neutron diffraction measurements suggested tensile residual stress in the aluminum matrix. The stress was mainly induced by thermal-expansion-mismatch between aluminum and alumina.
