Ultrasonic Attenuation Evaluation for Friction Stir Processing Quality of Carbon-nanotubes Reinforced Aluminum Matrix Composites

For the main defect named carbon-nanotubes (CNTs) reunion of carbon-nanotubes reinforced aluminum matrix (CNTs/Al) composites which was processed by friction stir method, ultrasonic attenuation method is proposed for nondestructive evaluation. By changing the times of friction stir processing, the different CNTs/Al composites in which the severity of CNTs reunite is different could be obtained. And then the CNTs reunion defects could be evaluated by measuring attenuation coefficient of the different CNTs/Al composites from the macro perspective, and it has 50 times difference between maximum and minimum attenuation coefficients, and the results had been validated by ultrasonic feature scan imaging testing method. At the same time, the attenuation coefficient from pure aluminum specimens which were processed three times and six times respectively were measured as 0.032 dB/mm and 0.029 dB/mm, by which the influence from the changes of the pure aluminum grain can be excluded after friction stir processing on the result of experiment. Finally the CNTs reunion defects is evaluated from the micro perspective as well, and attenuation coefficient changes from 0.178 dB/mm to 0.025 dB/mm and is reduced about 1 times after each stirring with the increase of stirring times, and so the same result shows that the severity of CNTs reunion is aggravating, the attenuation coefficient increasing.