Characterization of AlN Inclusion Particles Formed in Commercial Purity Aluminum

Abstract

The detailed characterization of nitride inclusion particles formed in the commercial purity Al melt has been carried out using advanced analytical electron microscopy assisted with pressure melt filtration and focused ion beam sample preparation techniques. It is found that the nitride inclusion particles have short rod-like morphology with an average length of 375 nm and an average width of 104 nm. Moreover, these nitride particles are identified to be hexagonal wurtzite AlN particles with the most close-packed plane, {0001}, as the exposed broad plane. Based on the crystallographic information, the potency of AlN as nucleation substrate for α-Al grain has been theoretically estimated from the lattice matching point of view. It is revealed that the interatomic spacing misfit along the close-packed directions on the close-packed planes between AlN and Al is 6.66 pct, indicating relatively strong potency of AlN as nucleation substrate for α-Al. However, it is suggested that AlN particles would rarely be involved in the nucleation and initiation of α-Al grains when competing with other oxide and boride inclusion particles normally present in the Al melt because AlN particles have larger misfit with Al, comparable or even smaller size, and lower number density than oxides and borides.