Friction and Wear Behavior of Different Volume Fraction SiC_p/Al Composites by Stir Casting Combined with Friction Stir Processing

SiC_p/Al composites with SiC particle volume fractions of 20%, 25% and 30% were prepared by stir casting combined with friction stir processing. The microstructure and mechanical properties of the composites were studied. The friction and wear tests were designed based on the actual operating conditions of trains in the city (braking pressure of 0.57, 0.67, 0.72 MPa), and the friction and wear behavior of different composites was studied. The results show that SiC_p/Al composites with different SiC particle volume fractions had dense structure with no cracks and porosity defects, and SiC particles were uniformly distributed in the aluminum alloy matrix without agglomeration. The tensile strength, percentage elongation after fracture and hardness of the composites met the requirements of the brake disc industry standard. With the increase of SiC particle volume fraction, the tensile strength change range was small, the percentage elongation after fracture decreased and the hardness increased. The average friction coefficient of composites with 25% and 30% volume fraction of SiC particles remained stable in the range of 0.3–0.5, meeting the high-speed braking requirements of urban trains; no obvious grooves or delamination were found on the wear surface, and a complete friction film was formed on the surface. However, the brake disc pairing with composites with SiC particle volume fraction of 30% had high wear amount, and the friction stability coefficient was low at 0.57 MPa braking pressure, indicating poor matching of friction pair. The maximum average friction coefficient of composites with SiC particle volume fraction of 20% was greater than 0.55, and the wear surface showed obvious grooves and delamination with severe abrasive wear, and the maximum groove depth reached 45 μm; the composites could not meet the high-speed braking requirements of urban trains.