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, alpha-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 alpha-Al and exist good lattice matching coherence in (01-1-1)(TiB2p)//(200)(alpha-)(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. (C) 2021 The Author(s). Published by Elsevier B.V.