Mechanical Properties of (Ce plus Yb) Modified in situ TiB2/Al-Si Matrix Composites Enhanced via Thermal Deformation Combined with Heat Treatment

In the current work, the microstructure evolution and mechanical properties of (Ce + Yb) modified in situ TiB2/Al-Si matrix composite were systematically investigated by thermal deformation at strain rates of 0.0005-0.0125 s(- 1) and temperatures of 250-450 degrees C. The enhanced strength and plasticity of the composite have a good correlation with the microstructure evolution under different thermal deformation parameters. The obtained results indicated that under the hot deformation parameters of strain rate of 0.0025 s(- 1) and deformation temperature of 250 degrees C, the defects of micropores can be reduced or even eliminated and improved the density of the composite. The coarse a-Al grains, eutectic Si and Fe-rich phases and undissolved primary (Ce + Yb)-containing intermetallics were significantly refined under high shear stress. At the same time, the distribution of in-situ synthesized submicron TiB2 particles in the Al matrix tends to be more uniform. The substructures such as high density dislocations and low angle grain boundaries were introduced under the thermal deformation of 250 degrees C/0.0025 s(- 1), which provided the necessary conditions for the formation of recrystallized grains that are less likely to overgrow and further promoted the aging precipitation of nano-strengthening precipitates. Finally, the UTS, YS and elongation of the composite reached the maximum values of 385 MPa, 316 MPa and 9.6% respectively, which were 60.4%, 85.9% and 45.5% higher than the as-cast and undeformed composite.