The formation mechanism and interface structure characterization of in situ AlN/Al composites

Abstract

The fabrication of AlN/Al composites through nitrogen-bearing gas (NH3) bubbling method into Al melts or Al–Mg melts was once experimentally and analytically studied. The experimental results show that Mg addition greatly enhanced the nitridation rate and volume fraction of AlN. However, a detailed characterization of these changes is still incomplete. This paper presents results of an extensive experimental study and theoretical analysis carried out to investigate the profound effect of the formation of AlN with Mg addition. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy were used to characterize the microstructure. The edge-to-edge matching crystallographic model which applied to the three common crystal structures (body-centered cubic, face-centered cubic, and hexagonal close packed) was used to analyze and investigate this notable phenomenon. The calculation and analysis of theoretical model manifested that AlN is formed by the direct interfacing of pure Al or Al–Mg and NH3 with active nitrogen, instead of forming into the precursor Mg3N2 first and then the precursor transformed to AlN.