Surface modification of aluminum alloys to create in situ surface composites by design

Engineered aluminum surface metal matrix composites were created by incorporating ceramic particles like WC, SiC, Al₂O₃, WC + SiC, and a mixture of hard particle with solid lubricant, SiC + MoS₂, using friction stir processing. Processing parameters were studied and optimized to produce uniform distribution of these particles in the near surface region. Optical and scanning electron microscopy showed that the stirred region developed as deep as the pin probe. Proper tooling enables the thickness of the surface composite to be controlled from thin (2 mm) to orders of magnitude thicker (10 mm) than conventional coatings. The composite is defect free and forms a graded metallurgical bond with the underlying surface. No interface is developed between the composite zone and the base material. Study of properties such as hardness of the discontinuously reinforced surface composite, microstructural stability, wetting, stiffness and other mechanical properties showed commendable increase. Volume fraction, particle size and properties, and process parameters were observed to have a major effect on the resulting material properties. Control over the aforementioned variables was achieved leading to creation of surface metal matrix composites by design --Abstract, page iii