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2 2017

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Combined thermal, microstructural and microchemical analysis of solidification of Al25Si3Cu alloy

Guba P., Gesing A., Sokolowski J., Conle A., Sobiesiak A., Kasprzak M.

Archives of Materials Science and Engineering

2017

Vol. 85, nr 2

49--79

Purpose: This paper present thermal and microstructural and microchemical analyses were conducted on the unmodified experimental alloy Al20Si3Cu (B390.1) solidified in the High Temperature Universal Metallurgical Simulator and Analyser (HT UMSA) under atmospheric pressure (0.1 MPa) and a relatively low solidification rate (-1.2 K/s just after end of solidification), for identification of the thermal events during solidification and the phases in the as-cast structure. Design/methodology/approach: The HT UMSA platform, using a low thermal mass stainless steel cup, enabled the acquisition of high resolution thermal analysis data. Design/methodology/approach: A new approach for de-convolution of the first derivative thermal curves allowed detailed thermal and microstructural phase histories to be documented for solidification of Al-Si alloys. Recently developed SEM/EDS methodology allowed to determine composition and distribution of individual phases that are smaller than the X–ray volume. Findings: Simultaneous consideration of thermal microstructural and microchemical information allowed detailed understanding of the series of events that take place during solidification of Al casting alloy with complex chemistry. In our hypereutectic alloy we document growth of Al(1) dendrites and formation of secondary Si(2) and Al(2) phases all at temperatures higher than the binary equilibrium Al-Si eutectic temperature of 850 K. Practical implications: Even at this slow solidification rate detailed understanding of the solidification microstructure requires consideration of non-equilibrium processes during solidification. Originality/value: We propose an original set of hypotheses that consistently explain the observed non-equilibrium solidification behaviour. Proof of these hypotheses is beyond the scope of this work.

ThermoCalc Application for the Assessment of Binary Alloys Non-Equilibrium Solidification

Zyska A., Konopka Z., Łągiewka M., Kordas P.

Archives of Foundry Engineering

2017

Vol. 17, iss. 1

163--168

The paper presents the possibility of application of the developed computer script which allows the assessment of non-equilibrium solidification of binary alloys in the ThermoCalc program. The script makes use of databases and calculation procedures of the POLY-3 module. A solidification model including diffusion in the solid state, developed by Wołczyński, is used to describe the non-equilibrium solidification. The model takes into account the influence of the degree of solute segregation on the solidification process by applying the so-called back-diffusion parameter. The core of the script is the iteration procedure with implemented model equation. The possibility of application of the presented calculation method is illustrated on the example of the Cr-30% Ni alloy. Computer simulations carried out with use of the developed script allow to determine the influence of the back-diffusion parameter on the course of solidification curves, solidus temperature, phase composition of the alloy and the fraction of each phase after the solidification completion, the profile of solute concentration in liquid during solidification process, the average solute concentration in solid phase at the eutectic temperature and many other quantities which are usually calculated in the ThermoCalc program.