Critical Evaluation and Thermodynamic Optimization of the Al-P and Fe-Al-P Systems
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Critical Evaluation and Thermodynamic Optimization of the Al-P and Fe-Al-P Systems Zhimin You1 • In-Ho Jung2
Submitted: 20 May 2020 ASM International 2020
Abstract The Al-P system and Fe-Al-P system have been thermodynamically optimized using the CALculation of PHAse Diagrams (CALPHAD) method based on critical evaluation of all available experimental data. The liquid phases and solid solutions were modeled using the Modified Quasichemical Model and Compound Energy Formalism, respectively. The Gibbs energies of stoichiometric AlP compound and liquid Al-P solution were critically optimized to reproduce the melting point of AlP and the liquidus of Al-P system on the Al-rich corner. In the ternary Fe-Al-P system, the behavior of P in the liquid was also well optimized with introduction of Toop interpolation technique (Al as an asymmetric component). In addition, various phase equilibria of Fe-Al-P alloys containing up to 30 wt.%Al and 15 wt.%P, isothermal sections at 450, 650 and 800 C, and the solubility of P in BCC_A2 Fe-Al alloys were excellently described, compared to experimental data. According to the present optimization, an accurate and consistent thermodynamic database of the FeAl-P system has been developed. Keywords AlP Al-P system CALPHAD Fe-Al-P system thermodynamic database & Zhimin You [email protected] In-Ho Jung [email protected] 1
Department of Mining and Materials Engineering, McGill University, 3610 University Street, Montreal, QC H3A 0C5, Canada
2
Department of Materials Science and Engineering, and Research Institute of Advanced Materials (RIAM), Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, South Korea
1 Introduction With increasingly high demand for the safety and energyefficiency of automotive, light alloy such as Al is often added into the new generation automotive steels for reducing the weight and improving the mechanical properties simultaneously. To further enhance the corrosion resistance, paintability and also the weldability of steels, the galvannealing coatings were always applied on the steel plate surface.[1] In high Al steels, phosphorus on one hand plays a positive role in solid solution strengthening and corrosion resistance of the steels, but on the other hand, enrichment of P in the grain boundary inhibits formation of coating layers.[2] Besides, the galvannealing coating layer pulverization and flaking off the substrate are very challenging difficulties during the stamping process, which largely increase the defective and repairing rate. Moreover, P, as the typical metalloid impurity of steels, can also cause unexpected steel defects like brittleness and inner cracks. Therefore, it is very necessary to tightly control the P impurity of the steels below the allowed level. In the Fe-Al alloys containing high concentration of P, formation of aluminum phosphide (AlP) and various iron phosphides depends on the temperature and composition. As is well known, AlP is highly toxic compound widely used as rodenticide, insecticide, fumigant.[3]
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