Enhancing Wear Resistance of A356 Alloy by Adding CNFs Based on Ultrasonic Vibration Casting

A356-carbon nanofibers (CNFs) composites with different contents of CNFs were fabricated by ultrasonic vibration casting to investigate the effect of CNFs in the matrix on the mechanical properties and wear resistance. The worn surfaces were investigated using scanning electron microscopy (SEM). As the CNFs content was increased, strength, hardness and wear resistance were significantly enhanced and the coefficient of friction was extremely reduced. The nanocomposite containing 1.2 wt% of CNFs exhibited more than 109 HV in hardness and less than 0.35 in the coefficient of friction. Compared with the as-cast matrix, the wear rate of the optimal composite was less than one-third of the matrix sample and the microhardness exhibited about 47% enhancement of the matrix. Meanwhile, steadier and lower friction coefficient was also achieved by the composite. CNFs were observed to be either partially or fully crushed forming a carbon film that covered the surface and acted as a solid lubricant, enhancing the wear behavior significantly.