Austrian Foundry Research Institute

Leoben, Austria

Austrian Foundry Research Institute

Leoben, Austria
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Cziegler A.K.,University of Leoben | Schumacher P.,University of Leoben | Schumacher P.,Austrian Foundry Research Institute
International Journal of Cast Metals Research | Year: 2017

The growth restriction factor Q of the alloying elements of the Cu-system was determined using thermodynamic software tools to obtain accurate Q-values. A comprehensive list was given for a nominal solute content of 1 wt-%. Based on the calculations, melting experiments were carried out under defined casting conditions given by the TP-1 test to evaluate the correlation between Q and grain size in Cu alloys. © 2017 Informa UK Limited, trading as Taylor & Francis Group


Li J.H.,University of Leoben | Zarif M.Z.,University of Leoben | Albu M.,University of Graz | McKay B.J.,University of Leoben | And 3 more authors.
Acta Materialia | Year: 2014

A series of high-purity Al-5 wt.% Si alloys with trace additions of Sr, Fe and P were prepared by using arc-melting and subsequent melt-spinning. The nucleation phenomenon incorporating the free growth criterion of eutectic Si was investigated by using the entrained droplet technique, atomic resolution scanning transmission electron microscopy and differential scanning calorimetry. It was found that Sr addition exerts no positive effect on the nucleation process; instead, an increased undercooling was observed. A combined addition of Sr and Fe further increased the undercooling, as compared with the addition of Sr only. Only trace P addition has a profound effect on the nucleation of Si by a proposed formation of AlP patches on primary Al. The estimated AlP patch size was found to be sufficient for the free growth of Si to occur inside the eutectic droplet. Nucleation kinetics was discussed on the basis of classical nucleation theory and the free growth model. For the first time, realistic and physically meaningful nucleation site values were obtained. The interactions between Sr and P were also highlighted. This investigation demonstrates strong experimental supports for the free growth nucleation kinetics and the well-accepted impurity-induced twinning growth mechanism, as well as the poisoning of the twin plane re-entrant edge growth mechanism. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Li J.H.,University of Leoben | Albu M.,University of Graz | Hofer F.,University of Graz | Schumacher P.,University of Leoben | Schumacher P.,Austrian Foundry Research Institute
Acta Materialia | Year: 2015

The solute adsorption and/or segregation as well as the solute entrapment of Sr, Na and Yb atoms during eutectic Si growth in a series of high-purity Al-5 wt.% Si alloys was investigated by multi-scale microstructure characterization techniques, including high-resolution transmission electron microscopy and atomic-resolution scanning transmission electron microscopy. The adsorption of Sr atoms was directly observed along the 〈1 1 2〉Si growth direction of Si and/or at the intersection of multiple Si twins, which can be used to interpret the poisoning of the twin plane re-entrant edge and impurity induced twinning modification mechanisms, respectively. In contrast, Yb shows a different mechanism compared to the adsorption of Sr atoms. No significant Yb-rich cluster was observed at the intersection of Si twins. However, considerable Yb-rich segregation lines were observed along the 〈1 1 2〉Si direction, which can be attributed to the solute entrapment caused by a few Si twins through the natural twin plane re-entrant edge and growth mechanism. Active poisoning of the twin plane re-entrant edge and impurity induced twinning growth mechanisms cannot be observed due to the absence of Yb atoms within eutectic Si. Furthermore, the solute entrapment of modifying elements (X, Sr or Yb) together with Al and Si was proposed to interpret the formation of Al2Si2X phases or X-rich clusters within eutectic Si. Such types of Al2Si2X phases or X-rich clusters were further proposed to be an "artefact" caused by the solute entrapment during eutectic Si growth, rather than an active factor affecting the modification. The observed solute adsorption and entrapment can be used to interpret the different observations in the cases of different modifying elements, including impurity effects and so-called "quenching modification", thereby elucidating the modification of eutectic Si in Al-Si alloys. © 2014 Acta Materialia Inc.


Reglitz G.,University of Munster | Oberdorfer B.,University of Graz | Oberdorfer B.,Austrian Foundry Research Institute | Fleischmann N.,University of Graz | And 5 more authors.
Acta Materialia | Year: 2016

Difference dilatometry and differential scanning calorimetry (DSC) are used to investigate defect annealing in ultrafine grained nickel processed by equal channel angular pressing (ECAP) at various temperatures. Different defect types and processes such as vacancies, dislocations, grain boundaries and grain-boundary relaxation can be detected. They can be distinguished due to their distinct kinetics as revealed by the release of excess volume and excess heat during linear heating. The data are quantified in combination with a detailed characterization of the microstructure. Values for the absolute vacancy concentration, the dislocation density, the grain boundary expansion and the excess of grain boundary expansion in ECAP-processed nickel are derived. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Haberl K.,University of Leoben | Krajewski W.K.,AGH University of Science and Technology | Schumacher P.,University of Leoben | Schumacher P.,Austrian Foundry Research Institute
Archives of Metallurgy and Materials | Year: 2010

The influence of various titan-containing grain refiners on an AlZn20-alloy was examined using thermal analysis, light microscopy and scanning electron microscopy, and evaluation of grain size. The aim of this study was to determine microstructural features. The study showed that the magnitude of the melts undercooling, initial temperatures of primary nucleation and grain refinement are highly influenced by the grain refiner used.


Li J.H.,University of Leoben | Wang X.D.,Zhejiang University | Ludwig T.H.,Hydro Aluminium | Tsunekawa Y.,Toyota Technological Institute | And 4 more authors.
Acta Materialia | Year: 2014

Al-5 wt.% Si-based alloys with 0.05 wt.% Eu addition were produced by controlled sand-casting and melt-spinning, respectively. The modification of eutectic Si caused by 0.05 wt.% Eu addition was investigated by thermal analysis, differential scanning calorimetry and multi-scale microstructure characterization techniques. In the case of controlled sand-casting, 0.05 wt.% Eu addition was found to modify the eutectic Si into a fibrous morphology. Multiply twinned Si particles were observed within eutectic Si. Furthermore, the Al2Si2Eu phase was also observed both in the vicinity of eutectic Si and within eutectic Si, which was believed to hinder Si growth. In the case of melt-spun samples, nanometer-sized Al2Si2Eu phases were observed. However, after controlled cooling in a differential scanning calorimeter, multiply twinned Si particles were observed. The formation of multiply twinned Si particles was attributed to the adsorption of Eu atoms along the 〈1 1 2〉Si growth direction of Si and at the intersection of two {1 1 1}Si facets. Twinning was observed in both fundamentally different casting processes: controlled sand-casting and melt-spinning. This is fully consistent with the well-known poisoning of the twin plane re-entrant edge and the impurity-induced twinning modification mechanisms. © 2014 Acta Materialia Inc.


Li J.H.,University of Leoben | Zarif M.Z.,University of Leoben | Dehm G.,University of Leoben | Dehm G.,Austrian Academy of Sciences | And 2 more authors.
Philosophical Magazine | Year: 2012

The nucleation and growth of Si has been investigated by TEM in a series of high purity melt spun Al-5Si (wt%)-based alloys with a trace addition of Fe and Sr. In the as-melt-spun condition, some twinned Si particles were found to form directly from the liquid along the grain boundary. The addition of Sr into Al-5Si-based alloys promotes the twinning of Si particles on the grain boundary and the formation of Si precipitates in the α-Al matrix. The majority of plate-shaped and truncated pyramid-shaped Si precipitates were also found to nucleate and grow along {111}-Al planes from supersaturated solid solution in the α-Al matrix. In contrast, controlled slow cooling decreased the amount of Si precipitates, while the size of the Si precipitates increased. The orientation relationship between these Si precipitates and the α-Al matrix still remained cube to cube. The β-Al5 FeSi intermetallic was also observed, depending on subsequent controlled cooling. © 2012 Copyright Taylor and Francis Group, LLC.


Li J.H.,University of Leoben | Schumacher P.,University of Leoben | Schumacher P.,Austrian Foundry Research Institute
International Journal of Cast Metals Research | Year: 2012

A series of Al-5 wt-%Si alloys with or without 200 ppm Y addition have been produced using conventional casting and melt spinning respectively. The effects of Y addition and cooling rates on the refinement of eutectic Si have been investigated using thermal analysis, differential scanning calorimetry and multiscale microstructure characterisation techniques. In the case of conventional casting, the addition of up to 200 ppm Y was found to cause no modification effect. The eutectic Si presented a plate-like structure rather than a fibrous morphology. No significant Si twinning was observed. In the case of melt spinning, a higher cooling rate caused a much finer eutectic Si and Si twinning. The addition of 200 ppm Y promoted heavier multiply Si twinning. After a continuous cooling from 873 to 673 K, an Al2SiY phase was observed beside or within the Si particle. The refinement mechanism was also discussed. © 2012 W. S. Maney & Son Ltd.


Li J.H.,University of Leoben | Schumacher P.,University of Leoben | Schumacher P.,Austrian Foundry Research Institute
IOP Conference Series: Materials Science and Engineering | Year: 2011

The solidification and age hardening behaviour of an Mg-6Zn-2Gd (wt. %) alloy has been investigated. It was found that the microstructure of the as-cast samples was composed of equiaxed α-Mg grains surrounded by some eutectic compound both at triple points and along grain boundary. The eutectic compound was composed of MgZn 2, Mg 5Gd phases and α-Mg matrix. After a solution treatment at 500°C for 18 h, the eutectic compound almost dissolved, but some discontinuous second phase particles still survived at grain boundaries. The Mg 3Gd 2Zn 3 phase also formed during subsequent ageing. The addition of Gd not only improved the thermal stability of the second phase formed during solidification, but also postponed the overaging during ageing at 200°C up to 100 h. The precipitates with three different morphologies: [0001] α rods/lath, (0001) α plates and blocky particles, were observed in the α-Mg matrix. The solute elements of Zn and Gd were found to significantly partition into the precipitates, especially for blocky particles. This significant partition can be correlated directly to improved mechanical properties at elevated temperature.


Li J.H.,University of Leoben | Schumacher P.,Austrian Foundry Research Institute
TMS Light Metals | Year: 2016

The addition of CrB2 and Sr into Al-10Si-0.3Mg (wt.%) based alloys not only modify the eutectic Si, but also refine the eutectic grains. CrB2 particles were found to nucleate the eutectic grains, despite the A1P particles being partly removed or depleted by the interaction between Sr and A1P. Furthermore, P level was found to be one of the dominant factors that affect the nucleation of eutectic grains. CrB2 addition with a low P level results in a refined eutectic grain size, despite less A1P particles being present to nucleate the eutectic grains. Porosity was found to be mainly located at the boundaries of eutectic grains, highlighting the importance of the refinement of eutectic grains to reduce the size and optimize the distribution of porosity. This investigation demonstrates a novel approach to refine eutectic grains and modify eutectic Si simultaneously into Al-10Si-0.3Mg (wt.%) based alloys, and thereby suggests possible industrial applications.

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