Structure and chemical composition of nanophase particles in Mg-based alloys
Conventional and high resolution transmission electron microscopy, as well as microchemical analyses, are playing an important role in identifying precipitates in Mg based alloys for aerospace applications, especially for nanometer sizes. During aging of Mg-Al-Nd-Zn based alloys, Al-Nd-Zn based particles precipitate which affect the mechanical properties. These alloys, which serve as the metal matrix for MMC materials containing SiC particulates as reinforcement, are processed by rapid solidification/powder metallurgy techniques, and they are designed for relatively high temperature (250-300° C) applications.Figure 1 shows the typical structure of second-phase particles in the Mg-based matrix. The spread in the particle size range is quite large, e.g., roughly between 70 and 100 nm. Close examination of these particles shows (Fig. 2) that there is no coherency with the Mg-based matrix, and no specific crystallographic relationship has been established. In some cases the growing direction of large particles was found to be within 5° of the C-axis of the Mg matrix.