Effects of pressure on microstructure and mechanical properties of SiCp/2024 Al-based composites fabricated by powder thixoforming

SiCp/2024 composites were fabricated by powder thixoforming, and the effects of pressure on the microstructure and mechanical properties were studied. The results indicate that the pressure applied during thixoforming affected the secondary solidification behavior by altering the solidification rate, microstructure compactness, plastic deformation, loading capacity of SiCp, and thus the fracture regimes and the mechanical properties. The tensile strengths increased as the pressure increased from 128 to 224 MPa because of the improved compactness, enhanced work hardening and loading capacity of SiCp, and increased concentration of the θ-phase and then decreased owing to the serious stress concentration and θ-phase harmfulness. The composite thixoformed under 224 MPa exhibited the largest improvements, with an ultimate tensile strength of 388 MPa, a 0.2 % offset yield strength (YS) of 297 MPa, and an elongation of 3.8 %, which were increased by 29.3 and 35 % and decreased by 63.5 %, respectively, compared with those of the 2024 alloy. The increment in the tensile strength was due to the synergetic contributions resulting from the strengthening mechanisms of load transfer, thermal mismatch, geometrically necessary dislocations, and grain refinement.