Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems

The processing window is important for the semisolid processability of alloys. Applications of semi-solid metal (SSM) processing, especially aluminium alloys have been expanding for their excellent mechanical properties. However, the alloys well suited and commercially used for SSM processing today...

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Main Author: Zhang, Duyao
Other Authors: Atkinson, Helen; Dong, Hongbiao
Published: University of Leicester 2015
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620
Online Access:http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657590
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spelling ndltd-bl.uk-oai-ethos.bl.uk-6575902016-08-04T04:00:38ZThermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systemsZhang, DuyaoAtkinson, Helen; Dong, Hongbiao2015The processing window is important for the semisolid processability of alloys. Applications of semi-solid metal (SSM) processing, especially aluminium alloys have been expanding for their excellent mechanical properties. However, the alloys well suited and commercially used for SSM processing today are limited in types. The main purpose of this Ph.D. project is to understand what makes an alloy suitable for SSM processing on both aspects of thermodynamics and kinetics. This research started with a fundamental study of binary alloys based on Al-Si, Al-Cu and Al-Mg systems (wt%): Al-1Si, Al-5Si, Al-12Si and Al-17Si; Al-1Cu, Al-2Cu and Al-5Cu; Al-0.5Mg, Al-3Mg and Al-5.5Mg. These are representative of Si, Cu and Mg contents in commercial alloys used for SSM processing. The Single-Pan Scanning Calorimeter (SPSC) and Differential Scanning Calorimeter (DSC) were used to investigate the liquid fraction changes during heating and cooling of these binary alloys. Thermo-Calc and DICTRA (DIffusion-Controlled TRAnsformations) software have been used to predict the fraction liquid versus temperature taking into account both thermodynamics and kinetics. Comparison of the predictions with experimental data revealed that the simulation results show the same pattern with experimental results in the fraction liquid-temperature relationship. However, the SPSC results are closer to the prediction than DSC curves are, even with the relatively large sample size associated with SPSC. This is potentially a significant result as predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing remains one of the challenges. The results also suggest that the fraction liquid sensitivity to time should be identified as a critical parameter of the process window for semi-solid processing in addition to the fraction liquid sensitivity to temperature. For microstructure investigation, microanalysis techniques, including Scanning Electron Microscopy (SEM) and micro-indentation testing, have been used on polished sections, and compared to theoretical predictions. In addition, some parts of this project are in cooperation with General Research Institute for Nonferrous Metals (GRINM), which aims to design and develop high performance semi-solid alloys. Thermodynamic analysis (both predictions and experiments) were carried out on thixoformed 319s (2.95Cu, 6.10Si, 0.37Mg, wt%) and 201 (4.80Cu, 0.7Ag, wt%) aluminium alloys. SEM techniques and Transmission Electron Microscopy (TEM) were used for the microstructural characterisation. The results showed that the DSC curves were sensitive to microsegregation in SSM alloys and resulted in a lower liquid fraction than the cast alloys calculated through the integration method from the DSC results. Al2Cu phase in SSM alloys 319s and 201 can be dissolved into matrix up to 0.4 % before melting temperature under 3K/min heating rate when compared with 10K/min heating rate. The DSC scan rate should be carefully selected as higher heating rate can inhibit dissolution of the intermetallic phases during heating leading to less accurate liquid fractions predictions.620University of Leicesterhttp://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657590http://hdl.handle.net/2381/32538Electronic Thesis or Dissertation
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sources NDLTD
topic 620
spellingShingle 620
Zhang, Duyao
Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems
description The processing window is important for the semisolid processability of alloys. Applications of semi-solid metal (SSM) processing, especially aluminium alloys have been expanding for their excellent mechanical properties. However, the alloys well suited and commercially used for SSM processing today are limited in types. The main purpose of this Ph.D. project is to understand what makes an alloy suitable for SSM processing on both aspects of thermodynamics and kinetics. This research started with a fundamental study of binary alloys based on Al-Si, Al-Cu and Al-Mg systems (wt%): Al-1Si, Al-5Si, Al-12Si and Al-17Si; Al-1Cu, Al-2Cu and Al-5Cu; Al-0.5Mg, Al-3Mg and Al-5.5Mg. These are representative of Si, Cu and Mg contents in commercial alloys used for SSM processing. The Single-Pan Scanning Calorimeter (SPSC) and Differential Scanning Calorimeter (DSC) were used to investigate the liquid fraction changes during heating and cooling of these binary alloys. Thermo-Calc and DICTRA (DIffusion-Controlled TRAnsformations) software have been used to predict the fraction liquid versus temperature taking into account both thermodynamics and kinetics. Comparison of the predictions with experimental data revealed that the simulation results show the same pattern with experimental results in the fraction liquid-temperature relationship. However, the SPSC results are closer to the prediction than DSC curves are, even with the relatively large sample size associated with SPSC. This is potentially a significant result as predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing remains one of the challenges. The results also suggest that the fraction liquid sensitivity to time should be identified as a critical parameter of the process window for semi-solid processing in addition to the fraction liquid sensitivity to temperature. For microstructure investigation, microanalysis techniques, including Scanning Electron Microscopy (SEM) and micro-indentation testing, have been used on polished sections, and compared to theoretical predictions. In addition, some parts of this project are in cooperation with General Research Institute for Nonferrous Metals (GRINM), which aims to design and develop high performance semi-solid alloys. Thermodynamic analysis (both predictions and experiments) were carried out on thixoformed 319s (2.95Cu, 6.10Si, 0.37Mg, wt%) and 201 (4.80Cu, 0.7Ag, wt%) aluminium alloys. SEM techniques and Transmission Electron Microscopy (TEM) were used for the microstructural characterisation. The results showed that the DSC curves were sensitive to microsegregation in SSM alloys and resulted in a lower liquid fraction than the cast alloys calculated through the integration method from the DSC results. Al2Cu phase in SSM alloys 319s and 201 can be dissolved into matrix up to 0.4 % before melting temperature under 3K/min heating rate when compared with 10K/min heating rate. The DSC scan rate should be carefully selected as higher heating rate can inhibit dissolution of the intermetallic phases during heating leading to less accurate liquid fractions predictions.
author2 Atkinson, Helen; Dong, Hongbiao
author_facet Atkinson, Helen; Dong, Hongbiao
Zhang, Duyao
author Zhang, Duyao
author_sort Zhang, Duyao
title Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems
title_short Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems
title_full Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems
title_fullStr Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems
title_full_unstemmed Thermodynamic characterisation of semi-solid processability in alloys based on Al-Si, Al-Cu and Al-Mg binary systems
title_sort thermodynamic characterisation of semi-solid processability in alloys based on al-si, al-cu and al-mg binary systems
publisher University of Leicester
publishDate 2015
url http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657590
work_keys_str_mv AT zhangduyao thermodynamiccharacterisationofsemisolidprocessabilityinalloysbasedonalsialcuandalmgbinarysystems
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