Effect of inter-cavity spacing in friction stir processed Al 5083 composites containing carbon nanotubes and boron carbide particles

Carbon nanotubes and boron carbide particles were added in aluminum alloy 5083 by friction stir processing to obtain hybrid surface composites. Single pass approach was adopted to investigate the effect of metal loss in cavities produced to incorporate reinforcements at the inter-cavity spacing of 8 mm and 10 mm. Optical and scanning electron microscopy were used for microstructural investigation and presence of any defects. Mechanical characterization showed up to 38% and 18% improved performance of 10 mm inter-cavity spacing composites containing boron carbide particles in tensile strength and hardness, respectively. Cold formability of friction stir processed composites was evaluated by U-bend ductility test. The composites containing carbon nanotubes with 8 mm inter-cavity spacing failed due to severe cracking caused by clustering and lower compensation to accommodate the material loss, which played a vital role in final mechanical properties. The sinking of reinforcement in the matrix was found to be essential to compensate the material loss. In case material loss in the form of cavity for reinforcements remains uncompensated, higher empty volume results in the deterioration of mechanical properties. 10 mm inter-cavity spacing allowed maximum sinking of reinforcements and minimum clustering with carbon nanotubes in single pass friction stir processing.