Understanding the influencing mechanism of sub-micron sized TiB2p on the microstructures and properties of rheological squeeze casting hypereutectic Al–Si alloys

This present work aims to understand the strengthening mechanism of TiB2p reinforced rheological forming of Al matrix composites. The mechanism of in-situ TiB2p on microstructure evolution and mechanical properties strengthening of semi-solid Al–20Si (wt%) alloy was studied. The experiments show that the primary Si phase, α-Al phase, and eutectic Si are refined by in-situ TiB2p combined semi-solid forming. The primary Si phase is distributed uniformly in the matrix and the morphology of eutectic Si phase changed from needle-like to short rod-like. In addition, the Si/TiB2p interface is clear and well-bonded but no orientation relationship existed. On the contrary, the TiB2 are tightly bound to the α-Al and exist good lattice matching coherence in (01-1-1)TiB2p//(200)α-Al. The tensile strength and elongation are an increase from 110 MPa to 2.3% to 215.7 MPa and 4.2% with the content of in-situ TiB2p from 0 to 6%, respectively, own to dislocation strengthening, fine grain strengthening, and second phase grain strengthening induced by TiB2p. The fracture form from cleavage fracture to cleavage-ductile mixed-mode fracture due to the incorporation of TiB2p inhibits the crack propagation.