The types and distribution characterization of Al-Mn phases in the AZ61 magnesium alloy

The types and distribution of Al-Mn phases in semi-continuous casting AZ61 magnesium alloy has been investigated in detail by microstructure observation, component analysis, and thermodynamic calculation. The results showed that there were two types of compounds in the AZ61 alloy, Al8Mn5 and Al11Mn4. The former existed as particles, and the latter was formed as needle, angular particle and flower. The Al-Mn phase distributed mainly in the interdendritic boundaries and few Al-Mn phases appeared in the alpha-Mg matrix. There were also a number of Al-Mn phases in the Mg17Al12 phase, which had been proved as Al8Mn5. In addition, based on the calculation of Planar lattice disregistry, the mismatch of interface between Mg17Al12 (111) and Al8Mn5 (111) was found to be only 1.21%, which suggested that the Al8Mn5 is highly effective as a nucleation site for Mg17Al12. However, the corresponding mismatch between close packed planes between Al8Mn5 and alpha-Mg matrix was found to be greater than 22.07%, indicating a poor crystallographic matching between the two crystalline phases. (C) 2011 Published by Elsevier Ltd.