Microstructural refinement in a high elastic modulus Al-18Si-8Ni casting alloy

Abstract

A new Al-Si-based casting alloy with high elastic modulus in the range of 90‐100 GPa and low density, less than 3 g/cm3, was developed by alloy design and microstructural refinement approaches. The addition of 8 wt.% Ni to a hypereutectic Al-18Si alloy introduces large volume fractions (∼40 vol.%) of hard primary Si and primary Al3Ni phases. Coarse primary Si and primary Al3Ni formed in the early stage of solidification, however, can interfere with the melt flow, reducing the castability, and also were deleterious to elongation. By the assessments of the crystallographic misfit between a nucleant substrate and a nucleated solid, we discovered key inoculants, AlP and TiB2, which can successfully refine such coarse and brittle primary phases, Si and Al3Ni, respectively. More importantly, along with the improved elastic modulus, the combined addition of AlP and TiB2 results in a significant increase in the elongation up to 1% with an advantageous yield strength of over 230 MPa. The important role of an inoculant, particularly TiB2 in nucleating the Al3Ni phase is also discussed based on the theoretical lattice misfit calculations and experimental characterization, further confirming their orientation relationship between the Al3Ni and the TiB2 as (110)[11¯0]Al∥ (0001)[12¯10]TiB.