Machinability of AA7075-T6/carbon nanotube surface composite fabricated by friction stir processing

Chip adhesion on rake face of cutting tool and subsequent formation of built-up-edge are critical problems in machining of aluminum alloys. In the current work, carbon nanotube as a solid lubricant has been integrated with aluminum 7075-T6 alloy through friction stir processing and the machinability of fabricated surface composite has been evaluated. Here, firstly, a series of friction stir processing experiment has been carried out to find optimum pass number regarding uniform dispersion of carbon nanotube in aluminum matrix. Then, a total number of 27 drilling experiments under different values of spindle speed and travel speed have been carried out on raw material, friction stir processed material without addition of carbon nanotube, and friction stir processed with addition of carbon nanotube. The obtained results showed that addition of carbon nanotube as reinforcement causes reduction of machining thrust force and surface roughness due to excellent lubrication property. Tribological observations through scanning electron microscopy and wear test revealed that the main mechanism for enhancing the machinability is reduction of friction coefficient as a result of carbon nanotube addition.