Reassessment of the Al–Mn system and a thermodynamic description of the Al–Mg–Mn system

• Published in: International journal of materials research Vol. 98; no. 9; pp. 855 - 871
• Main Authors: Du, Yong, Wang, Jiong, Zhao, Jingrui, Schuster, Julius Clemens, Weitzer, Franz, Schmid-Fetzer, Rainer, Ohno, Munekazu, Xu, Honghui, Liu, Zi-kui, Shang, Shunli, Zhang, Wenqing
• Format: Journal Article
• Language: English
• Published: Munich De Gruyter 01.09.2007; Hanser
• Subjects: Applied sciences; Differential thermal analysis; Exact sciences and technology; Metals. Metallurgy; Phase diagram Al – Mg – Mn; Thermodynamic calculations; X-ray diffraction; Thermodynamics; Aluminium base alloys; Phase diagram; Magnesium alloy; X-ray diffraction; Calculation; Differential thermal analysis; Phase diagram Al-Mg-Mn; X ray diffraction; Thermodynamic calculations
• ISSN: 1862-5282; 2195-8556
• DOI: 10.3139/146.101547

A thermodynamic optimization for the Al – Mn system is performed by considering reliable literature data and newly measured phase equilibria on the Al-rich side. Using X-ray diffraction, differential thermal analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy methods, the melting behavior of λ-Al Mn was correctly elucidated, and two invariant reactions associated with λ-Al Mn (L + μ-Al Mn λ-Al Mn at 721 ± 2 °C and L + λ-Al Mn Al Mn at 704 ± 2 °C) are observed. The model Al Mn (Al, Mn) previously used for Al Mn was modified to be Al Mn (Al, Mn) based on crystal structure data. In addition, the high-temperature form of Al Mn is included in the assessment. Employing fewer adjustable parameters than previous assessments, the present description of the Al – Mn system yields a better overall agreement with the experimental phase diagram and thermodynamic data. The obtained thermodynamic description for the Al – Mn system is then combined with those in the Al – Mg and Mg – Mn systems to form a basis for a ternary assessment. The thermodynamic parameters for ternary liquid and ternary compound Mn Mg Al (τ) are evaluated on the basis of critically assessed experimental data. The enthalpy of formation for τ resulting from CALPHAD (CALculation of PHAse Diagrams) approach agrees reasonably with that via first-principles methodology. Comparisons between the calculated and measured phase equilibria in the Al – Mg – Mn system show that the accurate experimental information is satisfactorily accounted for by the present description. A reaction scheme for the whole ternary system is presented for practical applications.