Effects of Solute Segregation on Precipitation Phenomena and Age Hardening Response of High-Purity and Commercial AZ91 Magnesium Alloys

抄録

In the present study, the continuous and discontinuous precipitation behavior of the commercial AZ91 alloy containing manganese and the AZ91 alloy produced from high-purity elemental components with no manganese addition has been investigated. It was found that for the commercial alloy, the solute manganese segregated within the primary α-Mg dendrites during solidification and played a major role in the initiation of non-uniform distribution of β-precipitates within the matrix grains. In addition, the solute manganese significantly suppressed the growth of discontinuous (lamellar) precipitates. The high-purity alloy also exhibited non-uniform precipitation. However, the precipitation patterns differed from those observed in the commercial alloy due to the inhomogeneous distribution of aluminum, the origin of which was rooted in the solute segregation within the interdendritic regions of the solidification structure. These differences in the precipitation mode caused by the presence or absence of manganese influenced the age hardening of the alloys. The high-purity specimens aged at lower temperatures attained higher peak-hardness owing to greater area fractions of discontinuous precipitation cells.