Development of AA2024/TiB2 + Y2O3 Hybrid Composites with Improved Mechanical Properties Through Stir Rheocasting.

Semisolid cast AA2024 matrix composites reinforced with 2.0 wt% titanium boride (TiB2) and varying amounts of yttria (Y2O3) (0.5 wt%, 1.0 wt%, 1.5 wt%) were developed using stir rheocasting. The metallurgical characterisation was done by X-ray diffraction, optical microscopy, and scanning electron microscope, and mechanical characterisation by Vickers's hardness testing machine and universal testing machine. The microstructure evolution and mechanical properties such as hardness, tensile strength, and fracture toughness (KQ) of the developed composites were correlated. Pure AA2024 and AA2024 reinforced with TiB2 samples were also fabricated as a benchmark to compare the effect of yttria. The highest hardness, ultimate tensile strength, and yield strength achieved were 122 HV, 310 MPa, and 230 MPa, respectively, for the AA2024/2 wt% TiB2 + 1.5 wt% Y2O3 composite. They are 25%, 45%, and 57% higher compared to the unreinforced sample. The maximum conditional fracture toughness (KQ) achieved was 25.56 MPa m1/2 for the unreinforced specimen and 19.77 MPa m1/2 for AA2024/2 wt% TiB2 + 1.5 wt% Y2O3 composite. With the addition of Y2O3 particles in the matrix, the porosity in the samples increased, resulting in lower elongation. The processing route enhanced the mechanical properties of the composite in comparison with the liquid cast matrix due to a uniform distribution of particles and grain refinement. [ABSTRACT FROM AUTHOR]