Abstract
Aluminum alloys would have much wider usage in bearing applications if their wear-resistance could be significantly improved. This investigation developed a solid-state surface engineering process to form an aluminum-alumina composite surface by friction stirring ceramic particles into an aluminum surface to improve the surface hardness and wear-resistance without sacrificing the bulk ductility and conductivity. Composite layers have been successfully processed on pure aluminum (Al 1100) surfaces with a relatively uniform particle distribution with a concentration up to 25 vol%. Microscopic examination showed that particles were severely fractured during friction stir processing and, accordingly, the particle size decreased from the original 10-50 �m to 1-5 �m in the friction stir processed composite layer. The microindentation hardness of the aluminum surface was increased from 0.33 to 0.70 GPa (HV) after processing. It has been demonstrated that powder placement methods and process parameters can be tailored to improve particle dispersion and surface hardness. Unlike most other surface engineering techniques, this process can form very thick layers, up to centimeters in thickness, avoiding delamination because of the inherent material continuity.
