Microstructural Analysis of Cast and Heat-Treated Mg–3.2Ce–2Mn Alloy

Abstract—A distingtive eutectic structure with Mn particles observed in as-cast Mg–3.2Ce–2Mn (wt %) alloy was investigated in detail in the present study. Three phases (α-Mg + Mn + Mg₁₂Ce) in the eutectic region were identified by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The intermetallic compound Mg₁₂Ce-type composition was determined to be Mg_11.4Ce with a solubility of 0.7 at % Mn by electron probe microanalysis (EPMA). The enthalpy of formation ΔH of Mg–Ce, Mg–Mn, and Mn–Ce was also calculated with the Miedema model and applied to explain the formation mechanism of the Mg₁₂Ce-type intermetallic compound in the alloy. While, after heating at 350°C for 72 hours, thin rod-like linear and intersecting Mn precipitates were observed. Since they were originated from the matrix; their linear structure could be attributed to the coherent interface between the matrix and precipitation. In addition, Mn particles associated with the Mg₁₂Ce-type intermetallic compound also appeared due to the atomic radius mismatch and enthalpy of formation.