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Djurdjevic M.B.,Nemak Linz GmbH | Sokolowski J.H.,University of Windsor | Odanovic Z.,IMS Institute
Journal of Thermal Analysis and Calorimetry | Year: 2012

The dendrite coherency point (DCP) temperature refers to the state of a solidifying alloy at which a coherent dendrite network is established during the formation of grains. Several relatively complex methods for detection of the DCP temperature have been developed. There are four main DCP temperature testing approaches: (i) the rheological technique, (ii) thermal analysis of the minimum temperature difference between two cooling curves, (iii) thermal analysis of the second derivative of one cooling curve, and (iv) the thermal diffusivity measurement technique. This paper follows up the proposed thermal analysis of one center cooling curve for the determination of the DCP characteristics such as: temperature, time, instantaneous solidification rate, and fraction solid. The first derivative of the cooling curve is plotted versus the temperature and time and the thermal characteristics of all metallurgical reactions, including the DCP are determined with the same accuracy achieved using the two thermocouple technique developed by Bäckerud et al. [4, 5]. Statistical analysis of the DCP temperature using the one versus two thermocouple techniques shows R2 equal to 0.99. This research revealed that utilization of dT/dt versus the temperature curve methodology also allows for analysis of the a-Al dendrite nucleation and growth characteristics and consequent determination of the grain size. On-going work on this new methodology for characterization of other solidification events will be presented in subsequent papers. © Akadémiai Kiadó, Budapest, Hungary 2011.

Kopun R.,AVL Advance Simulation Technology D.o.o. | Skerget L.,University of Maribor | Hribersek M.,University of Maribor | Zhang D.,AVL List GmbH | And 2 more authors.
Applied Thermal Engineering | Year: 2014

The present paper outlines the recently improved Computational Fluid Dynamics (CFD) model to simulate the immersion quench cooling process. The main application area of the presented method is heat treatment of cast aluminium parts, mostly cylinder heads in automotive internal combustion engines, where an accurate heat treatment prediction plays an important role in conceptual and thermal analysis. In order to achieve low residual stress levels resulting from even temperature distribution during the cooling process, and thereby to prevent component failure during operation, the numerical model of the quenching process, as developed within the commercial CFD code AVL FIRE®, was improved by allowing for variable Leidenfrost temperature. Preliminary results of variable Leidenfrost temperature model together with the implementation of additional interfacial forces, such as lift and wall lubrication forces are presented. Only the enthalpy equation is solved in the solid domain to predict the thermal field, whereas the Euler-Eulerian multi-fluid modelling approach is used to handle the boiling two-phase flow and the heat transfer between the heated structure and the sub-cooled liquid. The results of the improved quenching model are compared with available measurement data for various water temperatures ranging from 303 K to 353 K. Using the step plate with variable thickness sections along its height as the model test case, different solid part orientations were investigated and obtained temperature profiles were analysed. The temperature histories predicted by the presented model correlate very well with the provided measurement data at different monitoring positions. The temperature distribution within the solid part, obtained from the CFD simulation, can therefore serve as a realistic input for subsequent Finite Element Analysis (FEA) of thermal stresses within the quenched solid part. © 2014 Elsevier B.V. All rights reserved.

Djurdjevic M.B.,Nemak Europe | Huber G.,Nemak Linz GmbH | Odanovic Z.,Serbian Institute for Testing of Materials IMS
Journal of Thermal Analysis and Calorimetry | Year: 2013

Available databases presently used by commercial simulation software packages for the aluminum casting industry are usually armed with material properties for only a few selected standard alloys. In the case of other alloys with different chemical compositions and refinement or modification treatment, thermal analysis could be an invaluable tool to gain necessary properties. The aim of this article is to demonstrate the potential application of the cooling curve analysis in the existing simulation software by improving its accuracy. © 2012 Akadémiai Kiadó, Budapest, Hungary.

Edelbauer W.,AVL List GmbH | Zhang D.,AVL List GmbH | Kopun R.,AVL AST D.o.o. | Stauder B.,Nemak Linz GmbH
Applied Thermal Engineering | Year: 2016

An Eulerian spray model for simulations of spray quenching and cooling in water mist chambers has been developed. Spray quenching allows targeted cooling of heated mechanical components to obtain increased material strength properties by modifying the micro-structure evolution. For the numerical multi-domain simulation it was necessary to implement a heat transfer model for the fluid-solid interface taking into account the increased heat transfer due to phase change of impinging droplets. The droplet size distribution of the spray is represented by discrete size classes for which separate transport equations are solved. The main challenge of the simulation was the long process time of several minutes. To reduce simulation time, a new time step sub-cycling method for the evaporation model and a method for periodically frozen fluid flow have been developed. The aim of this paper is to present an enhanced Euler-Eulerian spray model capable for the simulation of the spray quenching process. For model validation, measurements of the temperature history at certain locations within a quenched test geometry have been performed and compared with the numerically predicted results from the CFD simulations. The paper discusses the numerical method, the experimental set-up, and demonstrates the feasibility of the workflow for industrial applications. © 2016 Elsevier Ltd. All rights reserved.

Fernandez Gutierrez R.,Vienna University of Technology | Requena G.,Vienna University of Technology | Stauder B.,Nemak Linz GmbH
Praktische Metallographie/Practical Metallography | Year: 2014

The three dimensional microstructural evolution of cast B206 (AlCu5Mg0.3Mn0.3) and AlCu7 (AlCu7Mn0.4) alloys is studied as a function of solution treatment time by synchrotron tomography. Both alloys are formed by an a-Al matrix, Al2Cu and Al7Cu2(FeMn). 3D microstructural parameters of the aluminides such as volume fraction and interconnectivity are presented for the alloys in as-cast condition and after 4 h, 8 h and 16 h of solution treatment at 530 °C. Morphological evolution is obtained from the mean and Gauss curvature distribution. Finally, target metallography is combined with energy dispersive x-ray analysis to identify the phases remaining after 16 h of solution treatment. © Carl Hanser Verlag GmbH & Co. KG.

The present invention relates to an aluminium casting alloy having (in % by weight) Cu: 6.0-8.0%, Mn: 0.3-0.055%, Zr: 0.18-0.25%, Si: 3.0-7.0%, Ti: 0.05-0.2%. Sr: up to 0.03%, V: up to 0.04%, Fe: up to 0.25%, remainder aluminium and unavoidable impurities, and a casting for a combustion engine. The aluminium casting alloy according to the invention has high mechanical properties after a longer operating duration at high temperatures and at the same time can be cast without any problems. Furthermore, the casting according to the invention has optimised mechanical properties during operation at high temperatures and at the same time can be produced in an operationally reliable manner in terms of casting technology.

Nemak Linz GmbH | Date: 2012-09-17

A method for controlling a casting plant has at least one mould for receiving a fluid material, the fluid material solidifying in the mould during a solidifying time, at least one process parameter being detected during the production process and the solidifying time being determined in accordance with the process parameter detected.

Nemak Linz Gmbh | Date: 2014-12-02

A casting mould is pivoted about a horizontal pivot axis for casting cast parts in a casting machine. The casting mould has a lid and a reference side wall. A main plane is placed into the reference side wall. A tundish is coupled to the casting mould and the casting mould is then pivoted into a pouring-in position. The tundish filled with a molten metal portion is pivoted with the casting mould about the pivot axis, so that the molten metal flows into the casting mould. An angle 1 enclosed between the main plane of the reference side wall and a bath level of the molten metal portion in the tundish is constantly <180 until the melt hits the bottom of the casting mould.

Huter P.,University of Leoben | Oberfrank S.,University of Leoben | Grun F.,University of Leoben | Stauder B.,Nemak Linz GmbH
International Journal of Fatigue | Year: 2016

In this paper, different hypo-eutectic Al-Si cast alloys with varying silicon, copper and iron contents were tested under thermo-mechanical fatigue (TMF) conditions to achieve a unified approach to damaging and fatigue endurance behaviour. The cylinder heads from which the specimens were taken were serially produced with T79 heat treatment. This includes homogenisation, quenching and ageing. The alloy used by these investigations are commonly used for automotive cylinder heads. Under operational conditions, a complex interaction of mechanical and thermal cyclic loadings is inherent. Hence, the main purpose here is to distinguish between the influences of the alloying elements of hypo-eutectic Al-Si cast alloys and propose its effects to mechanical and environmental damages. The results underlined the important role of hard phases for crack nucleation especially in high copper alloys. The hard phases, like eutectic silicon or primary AlCu, AlFeSi phases in general got ruptured, independent of the applied mechanical loading. In contrast, damages in low copper alloys were caused by high plastic matrix deformations and the loss of adhesion of eutectic silicon particles. For both types of alloys, the crack propagation was mostly constrained on the eutectic itself. An improved TMF endurance was achieved by AlSi9Cu1(Sr) and primary AlSi8Cu3. Here, probably the increased matrix strength by precipitation hardening and the manifold crack deflections on the eutectic silicon reduced intrinsically the microstructural damage. Further, in TMF regimes it is recommended to use Al-Si cast alloys with low iron contents because present ternary α-Al15(Fe,Mn)3Si2 and quaternary β-Al5FeSi2 supported crack nucleation and lowered the fatigue endurance. Additionally, an over-aged AlSi7MgCu alloy in T74 condition significantly lacks in fatigue endurance because of a minor fatigue strength by incoherent θ-precipitations. However, the results presented here identify the major damages of hypo-eutectic Al-Si cast alloys and the influences of the alloying elements on TMF endurance. This enables further unified fatigue modelling by the automotive designer and additional optimizations of the metallurgical systems by the foundry which underlines the demand of improved knowledge of the cylinder head under real-life operational conditions. © 2016 Elsevier Ltd. All rights reserved.

Djurdjevic M.B.,Nemak Linz GmbH | Huber G.,Nemak Linz GmbH
Journal of Alloys and Compounds | Year: 2014

The aim of this paper is to introduce a new method for determining Rigidity temperature applying cooling curve analysis. The determined values of Rigidity temperatures for three AlSi8Cu3 alloys with different contents of Strontium using thermal analysis technique have been compared with Rigidity temperatures obtained using mechanical technique (viscosity measurement). It was established that there is good correlation between measured values of Rigidity temperatures determined using both above mentioned techniques. Characteristic solidification temperatures such as liquidus, dendrite coherency point, Rigidity and solidus temperature have been recognized as important parameters of solidify aluminum alloys because they mark transitions between several types of feeding mechanisms. So far the Rigidity temperature can be only determined using mechanical technique. Potential application of Rigidity temperature as an input parameter for simulation software has been also discussed. © 2013 Elsevier B.V. All rights reserved.

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