Calculation of phase diagrams for the metastable Al-Fe phases forming in direct-chill (DC)-cast aluminum alloy ingots |
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| Affiliation: | 1. State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai, 200240, China;2. Innovation Academy for Microsatellites of Chinese Academy of Sciences, Shanghai, 201203, China;3. Shanghai Institute of Satellite Engineering, No. 3666 Yuanjiang Road, Shanghai, 201109, China;4. School of Physics and Electronic Information College, Huaibei Normal University, Huaibei, 235000, China;5. Anhui Aluminium Matrix Composites Engineering Research Centre, Huaibei, 235000, China;1. Department of Production Engineering, Faculty of Engineering, King Mongkut''s University of Technology Thonburi, Bangkok 10140, Thailand;2. National Metal and Material Technology Center, National Sciences and Technology Development Agency, 114 Thailand Science Park, Klong Luang, Pathumthani 12120, Thailand;1. International Joint Laboratory for Light Alloys (Ministry of Education), College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, China;2. Electron Microscopy Center of Chongqing University, Chongqing, 400044, China;3. Zhengzhou Research Institute of CHALCO, Zhengzhou, Henan, 450041, China;4. School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, China;5. Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491, Trondheim, Norway;6. Key Laboratory for Light-weight Materials, Nanjing Tech University, Nanjing, 210009, China;1. TU Bergakademie Freiberg, Institute of Materials Science, Gustav-Zeuner-Str. 5, 09599 Freiberg, Germany;2. TU Bergakademie Freiberg, Institute of Ceramic, Glass and Construction Materials, Agricolastr. 17, 09599 Freiberg, Germany;1. Department of Materials Engineering, Indian Institute of Science, Bangalore, 560012, Karnataka, India;2. Max-Planck-Institut für Eisenforschung GmbH, 40237, Düsseldorf, Germany |
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| Abstract: | In direct-chill (DC)-cast 1xxx-and 5xxx-series Al sheet-ingots, the presence of mainly Fe and some Si, and cooling rates increasing from ≤1 °C/s in the ingot center to ~20 °C/s near the surface cause the formation of metastable intermetallic Al6Fe and AlmFe compounds in addition to the stable Al3Fe, and hence the fir-tree defect. Since the Al-Fe and Al-Fe-Si phase diagrams are not useful in predicting the metastable phase formation, a binary phase diagram study was conducted to calculate the Al-Al6Fe and Al-AlmFe metastable phase equilibria using a thermodynamic software and an Al-alloy database. The Al-Al3Fe phase diagram was calculated using the existing Gibbs energy data which gives the eutectic point at 1.85wt% Fe and the eutectic temperature as 654 °C. The missing Gibbs energy data for the metastable phases were estimated using substitutional and graphical methods and the phase diagrams were calculated. In the Al-Al6Fe phase diagram, the eutectic temperature is depressed from 654 °C (equilibrium) to 648 °C and the eutectic point is shifted from 1.85wt% Fe to 3.4wt% Fe. In the Al-AlmFe phase diagram, the eutectic temperature is 643 °C and the eutectic point is at 4.6wt% Fe. The verification of the calculated eutectic temperatures was carried out by DSC measurements which were conducted on samples removed from Al-Fe alloy rods directionally grown in a Bridgman-type solidification furnace. A good agreement is observed between the calculated and measured values. |
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