Fabrication of in situ carbon fiber/aluminum composites via friction stir processing: Evaluation of microstructural, mechanical and tribological behaviors

Carbon fiber reinforced AA5052 bulk composites were successfully fabricated by multi-pass friction stir processing (FSP), aiming to improve the wear-resistance of AA5052. The microstructural, mechanical and tribological performances of the composites were documented and investigated. Microstructure observations indicated that, in the composites, carbon fibers were homogeneously dispersed in large volume, where no obvious Al4C3 layer was detected between the matrix and the carbon fibers. The orientation of carbon fibers in the composites were random owing to the severe plastic deformation brought on by FSP. Further mechanical tests showed that the hardness of the composites increased by 46.8% comparing to the base metal, and that the composite fabricated at 1000 rpm and 75 mm/min showed 18.6% higher UTS and 13.0% higher elongation in comparison with the base metal. The wear tests illustrated that wear process of the composites was more stable and the wear volume loss was reduced by more than 70%. The strengthening of mechanical properties was attributed to formation of GNDs, crack deflection and load transfer of carbon fibers. The further analysis on the worn surfaces revealed that abrasive wear occurred in the composites, while adhesive wear occurred in both the based metal and FSPed matrix. The addition of carbon fibers segments in the aluminum could suppress the nucleation and propagation of micro-cracks, which effectively prevented the material peeling during the wear process and thus improved the tribological properties. In addition, the formation of mechanical mixing layer would be another contributing factor to the improvement of wear resistance.