Inductive Reheating of Steel Billets into the Semi-Solid State Based on Pyrometer Measurements

2006 ◽  
Vol 116-117 ◽  
pp. 734-737 ◽  
Author(s):  
Alexander Schönbohm ◽  
Rainer Gasper ◽  
Dirk Abel
Keyword(s):  
Solid State ◽  
Measurement Errors ◽  
Liquid Fraction ◽  
Solidus Temperature ◽  
Measurement Data ◽  
Heating Process ◽  
Production Environment ◽  
Loop Control ◽  
Control Scheme ◽  
Semi Solid

The aim of the paper is to demonstrate a control scheme by which it is possible to reproducibly reheat steel billets into the semi-solid state. Usually a heating program is used to reheat the billet into the semi-solid state. Our experiments showed that this control scheme leads to varying semi-solid fractions from one experiment to the next. To gain information about the billet’s state its temperature is often used since there is a known relationship between the temperature and the liquid fraction. Direct measurement of the temperature via thermocouples is not feasible in a production environment, therefore a radiation pyrometer has been used as a contact-less measurement device. The accuracy of the pyrometer depends heavily on the exact knowledge of the radiation coefficient, which can vary from billet to billet due to different surface properties and which is subject to change during the heating process. These uncertainties prohibit the implementation of a closed-loop control scheme since the exact temperature cannot be measured with the required accuracy. In order to be independent of the measurement errors the proposed control scheme only relies on the slope of the temperature. By detecting the distinct change of slope which occurs when the solidus temperature is crossed, the beginning of the melting process can be determined. The energy fed to the billet from this point onward determines the resulting liquid fraction. By detecting the entry into the solidusliquidus interval and then feeding the same amount of energy to each billet, it is guaranteed that the billet reaches the desired liquid fraction even by uncertain absolute value of the temperature and by small variations of the alloy composition. For the experiments the steel alloy X210 has been used and measurement data demonstrate the feasibility of the proposed control scheme.

Flatness Based Inductive Reheating of A356 Billets into the Semi-Solid State

2006 ◽  
Vol 116-117 ◽  
pp. 766-770 ◽  
Author(s):  
Alexander Schönbohm ◽  
Rainer Gasper ◽  
Dirk Abel
Keyword(s):  
Solidus Temperature ◽  
Open Loop ◽  
Heating Process ◽  
Billet Temperature ◽  
Loop Control ◽  
Control Scheme ◽  
A356 Aluminum ◽  
Semi Solid ◽  
The Given ◽  
Feedstock Material

An important step in the processing of semi-solid metals is the inductive re-heating of the feedstock material. The heating should lead to an uniform billet temperature in order to obtain good forming results. The billet is supposed to be heated to the target temperature as fast as possible and at the same time it must be guaranteed, that the outer area of the billet does not melt prematurely. Conventionally the open-loop trajectories consist of simple power over time diagrams and are generated by extensive experiments. By using an open-loop control scheme it is possible to chose a desired trajectory for the middle axis temperature of the billet which respects the given constraint on the heating process. By taking advantage of the flatness property of the system, an open loop trajectory for the coil current can be calculated which ensures the desired behavior of the axis temperature. The shape of the trajectory is determined by the shape of the desired trajectory and the temperature dependent material properties, which have to be known with the needed accuracy. The losses of the converter and induction coil are estimated online so that the induced power is known. The trajectory ensures that the billet is heated to a temperature just below the solidus temperature without overheating of the billet’s surface and with a very homogeneous temperature distribution. The Experiments have been conducted using A356 aluminum alloy.

Steel Grades Adapted to the Thixoforging Process: Metallurgical Structures and Mechanical Properties

2006 ◽  
Vol 116-117 ◽  
pp. 712-716 ◽  
Author(s):  
Marc Robelet ◽  
Ahmed Rassili ◽  
Dirk Fischer
Keyword(s):  
Mechanical Properties ◽  
Liquid Fraction ◽  
Solidus Temperature ◽  
Process Temperature ◽  
Heating Process ◽  
Work Piece ◽  
Inductive Heating ◽  
Steel Grades ◽  
Automotive Part ◽  
Semi Solid

Thixoforming of steel offers the advantages of casting technology in combination with high mechanical strength that can only be achieved by forging. The progress in establishing this technology in industry depends on the success in the development of suitable steel grades. Recent investigations dealt with the development of steel grades that are especially adapted to the thixoforming process. For this, alloys were developed with a lower solidus temperature and a wider process temperature range compared to classic forging steels. In consequence, the inductive heating process is more tolerant to inaccuracies and for a given liquid fraction the process temperature window is easier to handle. It is desired to obtain great degrees of deformation at rather low forming forces as these parameters determine the size of the needed presses. This behaviour is affected by the present liquid fraction in the slug and the heat transfer between work piece and die. It was detected that variations of the forming force have a direct influence on the quality of the thixoformed parts. In order to make the thixoforming technology of steels competitive versus other forming technologies, the parts must show a favourable microstructure and thus, good in-use properties. In this paper various solutions are compared. The main results obtained in the optimization research, namely, the steel grades adapted to semi-solid forming, the resulting process parameters and the mechanical properties of thixoforming parts will be presented for two exemplary steel grades. By producing a real automotive part, thixoforging of steels with regard to the adapted materials and to the ongoing industrial implementation of this process is proved.

Microstructure Evolution and Coarsening Mechanism of 7075 Semi-Solid Aluminum Alloy Pre-Deformed by ECAP Method

2016 ◽  
Vol 256 ◽  
pp. 294-300 ◽  
Author(s):  
Jin Long Fu ◽  
Yu Wei Wang ◽  
Kai Kun Wang ◽  
Xiao Wei Li
Keyword(s):  
Aluminum Alloy ◽  
Solid State ◽  
Ostwald Ripening ◽  
Liquid Fraction ◽  
Isothermal Holding ◽  
Angular Pressing ◽  
Average Grain Size ◽  
Semi Solid ◽  
Equiaxed Grains ◽  
Kinetics Of

To investigate the influence of refined grains on the microstructure of 7075 aluminum alloy in semi-solid state, a new strain induced melting activation (SIMA) method was put forward containing two main stages: pre-deformation with equal channel angular pressing (ECAP) method and isothermally holding in the semi-solid temperature range. The breaking up and growth mechanisms of the grains and kinetics of equiaxed grains coarsening during the semi-solid holding were investigated. The results showed that the average grain size after ECAP extrusion decreased significantly, e.g., microstructure with average globular diameter less than 5μm was achieved after four-pass ECAP extrusion. Obvious grain coarsening had been found during isothermal holding in the semi-solid state and the roundness of the grains increased with the increasing holding time. The proper microstructure of 66.8μm in diameter and 1.22 in shape factor was obtained under proper soaking condition (at 590°C for 15 min). Two coarsening mechanisms, namely, coalescence in lower liquid fraction and Ostwald ripening in higher liquid fraction contributed to the grain growth process.

scholarly journals Effect of Experimental Conditions on 7075 Aluminium Response during Thixoextrusion

2012 ◽  
Vol 504-506 ◽  
pp. 345-350 ◽  
Author(s):  
Adriana Neag ◽  
Véronique Favier ◽  
Mariana Pop ◽  
Eric Becker ◽  
Régis Bigot
Keyword(s):  
Aluminum Alloy ◽  
Microstructure Evolution ◽  
Deformation Behavior ◽  
Liquid Fraction ◽  
Heat Losses ◽  
Heating Process ◽  
Semisolid State ◽  
Experimental Conditions ◽  
Solid Aluminum ◽  
Semi Solid

The deformation behavior of semi-solid aluminum alloy is strongly dependent on the microstructure. This paper illustrates several experimental research works concerning thixoextrusion of 7075 aluminum alloy which was carried out at “Arts et Métiers ParisTech” of Metz. Inductive re-heating of the aluminum billet is the method used in order to obtain the target liquid fraction for thixoextrusion. To minimize the heat losses, a sample obtained from a direct extruded bar is inserted in a die for reheating in semisolid state and thixoextrusion. During the experimental re-heating process, the temperature was directly controlled by using thermocouples for temperature measurements in the sample and also in the die. The influence of different working ram speeds and reheating temperature on the microstructure evolution was studied by optical microscopy. The experimental results on extrusion load and microstructure evolution of the component are reported.

scholarly journals Application of X-Ray Microtomography to Quantify the Liquid Fraction of M2 Steel for Semi-Solid Forming Process

2013 ◽  
Vol 554-557 ◽  
pp. 547-552 ◽  
Author(s):  
Guo Chao Gu ◽  
Raphaël Pesci ◽  
Eric Becker ◽  
Laurent Langlois ◽  
Régis Bigot
Keyword(s):  
Mechanical Properties ◽  
Solid State ◽  
Liquid Fraction ◽  
High Energy ◽  
Material Behavior ◽  
Model Alloy ◽  
Processing Temperature ◽  
Volume Percentage ◽  
X Ray ◽  
Semi Solid

Thixoforging, one variant of semi-solid metal processing in which the metallic alloys are processed at low liquid fraction (0.1< Fl < 0.3), is used to produce complex parts with high mechanical properties. Steel thixoforging faces more challenges as compared to that of low melting point materials due to high processing temperature and lack of understanding of the thermomechanical behavior of materials in the given conditions. It is crucial to study the microstructure at the semi-solid state to improve the understanding of the thixoforging process since the material behavior strongly depends on main parameters: the liquid fraction, its distribution as well as the coherence of the solid skeleton. The microstructure has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Here, the characterization of the volume percentage and distribution of liquid fraction at the semi-solid state with high energy 3D X-ray microtomography was investigated on M2 steel grade as a ‘model’ alloy. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state.

Werkstückerwärmung für das Thixoforming*/Heating workpieces for Thixoforming - Using inductor as sensor for monitoring the heating process of semi-solid material

2017 ◽  
Vol 107 (05) ◽  
pp. 340-345
Author(s):  
J. Uphoff ◽  
A. Lechler ◽  
A. Prof. Verl
Keyword(s):  
Solid State ◽  
Solid Fraction ◽  
Material Properties ◽  
Solid Material ◽  
Heating Process ◽  
Inductive Heating ◽  
Inductor Coil ◽  
Specific Material ◽  
Semi Solid

Das Thixoforming nutzt bei der Formgebung besondere Materialeigenschaften zur Herstellung metallischer Bauteile. Die verwendeten Legierungen müssen dazu in den sogenannten teilflüssigen Bereich erwärmt werden. Das Einstellen des geforderten Fest-Flüssig-Verhältnisses stellt besondere Anforderungen an die Erwärmung. Betrachtet werden verschiedene Messverfahren, welche die Induktorspule bei der induktiven Erwärmung als Sensor nutzen. &nbsp; Thixoforming uses specific material properties for shaping metal workpieces. For this purpose, the alloys need to be heated to the so-called semi-solid state. The adjustment of the desired semi-solid fraction imposes high requirements on the heating process. Various measurement principles, which use the inductor-coil as a sensor in inductive heating processes, are presented.

scholarly journals A New Approach to Determine Tensile Stress-Strain Evolution in Semi-Solid State at Near-Solidus Temperature of Aluminum Alloys

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 396
Author(s):  
Jovid Rakhmonov ◽  
Mohamed Qassem ◽  
Daniel Larouche ◽  
Kun Liu ◽  
Mousa Javidani ◽  
...  
Keyword(s):  
Solid State ◽  
Aluminum Alloys ◽  
Accurate Determination ◽  
Solidus Temperature ◽  
Hot Tearing ◽  
Image Correlation ◽  
Correlation Technique ◽  
Stress Strain ◽  
Strain Evolution ◽  
Semi Solid

Accurate determination of the materials’ strength and ductility in the semi-solid state at near-solidus temperatures is essential, but it remains a challenging task. This study aimed to develop a new method to determine the stress-strain evolution in the semi-solid state of aluminum alloys within the Gleeble 3800 unit. Stress evolution was determined by the newly developed “L-gauge” method, which converted the displacement of the “restrained” jaw, measured using an L-gauge, into the force. This method gives the possibility to determine the flow stress more accurately, especially for the very low stress rang (1–10 MPa) in the semi-solid state at near-solidus temperatures. The digital image correlation technique implemented in the Gleeble unit allowed effective measurement of the heterogeneous strain fields evolving within the specimen under tensile loading. Therefore, the stress-strain curves measured in the semi-solid state help to better understand the alloy’s susceptibility to hot tearing. The results of an AA6111 alloy under different liquid fractions (2.8% at 535 °C and 5.8% at 571 °C) were demonstrated. The reliable stress-strain data and heterogenous strain distribution are beneficial to develop the thermomechanical models and hot-tearing criteria.

Microstructure Evolution of Deformed Magnesium Alloy in Semi-Solid State

2005 ◽  
Vol 488-489 ◽  
pp. 313-316
Author(s):  
Sen Yuan ◽  
Wu Xiao Wang ◽  
Bai Ling Jiang
Keyword(s):  
Solid State ◽  
Magnesium Alloy ◽  
Microstructure Evolution ◽  
High Energy ◽  
Mg Alloy ◽  
Continuous Heating ◽  
Heating Process ◽  
Semisolid State ◽  
Semi Solid ◽  
Temperature Time

Magnesium alloy slurry was prepared using Strain-Induced Melt Activation(SIMA) technique. The samples were quenched into water so as to fix the high temperature instantaneous microstructures. The microstructure evolution of compressed deformation Mg alloy is studied in the process of continuous heating and iso-temperature of semi-solid state. The results indicate that deformed Mg alloy (AZ91) has first occurred to have the conversion of dendrite crystal-oriented isometric crystals in the continuous heating process. When the temperature rises to the range of semisolid state, the region with high energy at the pressed stripes begins to melt, showing that the cellular structures emerge in the crystal boundary and melting micro-pool phenomena appear within the crystals. With the iso-temperature time in semisolid state prolongs, the isometric crystals can be gradually converted into spherical crystal grains.

Structural Evolution and Deformation Behavior of Extruded AZ91 with Ca Addition in the Semi-Solid State

2006 ◽  
Vol 116-117 ◽  
pp. 775-778
Author(s):  
S.M. Liang ◽  
Rong Shi Chen ◽  
Jean Jacques Blandin ◽  
Michel Suéry ◽  
En Hou Han
Keyword(s):  
Solid State ◽  
Microstructural Evolution ◽  
Mechanical Response ◽  
Liquid Fraction ◽  
Structural Evolution ◽  
Solid Particles ◽  
Az91 Alloy ◽  
Compression Behavior ◽  
Ca Addition ◽  
Semi Solid

The microstructural evolution and mechanical response in compression in the semi-solid state of previously extruded AZ91 alloys containing two levels of Ca additions (1mass%Ca (AZC911) and 2mass%Ca (AZC912)) have been studied. Ca additions have a significant effect on microstructural evolution and compression behavior of the AZ91 alloy. At 515°C, the liquid fraction in AZC911 is larger than that in AZC912, so that the compression stress of the AZC912 alloy was found to be much larger than that of the AZC911 alloy. This behavior is explained through DSC analysis which suggests that some solid Al2Ca phase remains in AZC912 alloy at this temperature. Increasing the remelting temperature for this alloy leads to more liquid and coarsening of the solid particles occurs with increasing holding time.

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