Liquidus and solidus temperatures of Mg-rich Mg–Al–Mn–Zn alloys

The phase equilibria and solidification process for Mg-rich Mg–Al–Mn–Zn alloys are analyzed based on a combination of computational thermochemistry and differential thermal analysis and differential scanning calorimetry measurements. Our main concern is the proper interpretation of the experimental results of thermal analysis. For a wide range of Mg-rich alloys it is demonstrated that: (i) the high-temperature signal does not represent the actual liquidus temperature and this signal is related to the phase boundary, L + Al8Mn5/L + Al8Mn5 + (Mg); and (ii) the low-temperature signal in thermal analysis is associated not with the end of the solidification process but with the precipitation of γ-Mg17Al12 phase under the Scheil condition. In addition, we demonstrate that the actual solidification temperature, either at a slow cooling rate (1 K/min) or in casting, is virtually identical to the incipient melting temperature of as-cast alloys during subsequent heating.