Thixoforming : Semi-solid Metal Processing

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6.1 Empirical Analysis of the Flow Behaviourj193 Ostwald ripening can be neglected in capillary experiments, because the experimental time is orders of magnitude shorter that the time necessary for particle growth. Wall slip causes the core flow to slip along the wall on a thin pure liquid layer and falsify the measured relation of rotation speed and turning moment and the flow rate and pressure drop considering rotational and capillary rheometers. Conventional evaluation yields an apparent shear stress gradient which is less steep than it would be in the case of true wall adhesion. In order to reduce or even avoid wall slip, the walls of the rheometer can be grooved evenly (as mentioned in Section 6.1.4). Thereby microeddies and thus near-wall mixing are induced and the slip layer is destroyed. However, it is important to note that by that at least near the wall viscosimetric flow can no longer be assumed, which also may influence the measurement results for small capillary heights. It has been observed that wall adhesion increases with an applied treatment to the capillary surface. Roughening of the surface can be achieved either by a mechanical treatment such as grinding or milling of defined structures or by coating the surface. However, the surface treatments reduce but do not completely destroy the liquid layer. Second, wall slip can also be accounted for by subsequent correction of smooth wall measurement results. Beforehand, a correlation of shear stress and slip velocity has to be determined. applying well-established methods. These are based on comparing measurement results from different geometric setups for both capillary and rotational rheometers [23]. However, this procedure is applicable only to steady-state measurements and not to transient measurements. 6.1.6.3 Compression Tests The material is first pressed via a conventional experimental technique with a standard cylinder specimen starting with hot forming temperatures up to temperatures above the solidus. As shown in Figure 6.31, the flow stresses of the compressed samples decrease drastically when the solidus is passed. Beginning with expected flow behaviour, the material shows less formability when the solidus (Ts 1220 C) is passed. Metallography confirms this behaviour with the resulting microstructure. Below the solidus, the microstructure shows an austenitic matrix with small areas of dropped out chromium carbides. Depending on the position, a forming structure appears. Above the solidus, eutectics occur at the grain boundaries, which grow with increasing temperature and cause debilitation of the microstructure against tensile stresses. The test specimen disintegrates in this condition, even when only slightly loaded mechanically, so that a precise flow curve cannot be calculated because of the missing cross-sectional area. To avoid the disintegration of the test specimen, it is covered with a thin layer of a higher melting material. This method to determine flow curves of such materials is the so-called coat test [29]. The early development of cracks is inhibited by the hydrostatic pressure caused by the shell. During evaluation of flow curves, the effect of the shell on the measured force is determined by calculation (inverse modelling). The prerequisite for this is the knowledge of the flow curve of the shell material. Figure 6.32 shows the samples and the shell in its initial geometry and after forming. Even a compression with a high deformation can be carried out without disintegration of the material.
194j 6 Modelling the Flow Behaviour of Semi-solid Metal Alloys Figure 6.31 Results of the compression test for steel grade X210CrW12 around the solidus temperature: shape of the compressed specimens with their microstructures and the resulting load curves [28]. Figure 6.32 Specimen and coat for avoiding disintegration, compressed sample and cross-section of a compressed sample (X210CrW12/S235JR).
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Thixoforming Semi-solid Metal Proce
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Further Reading Herlach, D. M. (ed.
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The Editors Prof. Dr. G. Hirt Insti
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VI Contents 1.3.5.2 Other Aluminium
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VIII Contents 4.6.1 Thixocasting 13
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X Contents 7.4.2 Isothermal Non-ste
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XII Contents 9.4.1.3 Simulation Res
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Preface Semi-solid forming of metal
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XVIII List of Contributors Andreas
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XX List of Contributors Alexander S
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2j 1 Semi-solid Forming of Aluminiu
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10j 1 Semi-solid Forming of Alumini
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Table 1.1 Overview of semi-solid pr
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Part One Material Fundamentals of M
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32j 2 Metallurgical Aspects of SSM
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44j 3 Material Aspects of Steel Thi
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Temperature (ºC) 1550 1500 1450 14
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100j 3 Material Aspects of Steel Th
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106j 4 Design of Al and Al-Li Alloy
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Page 170 and 171: 5 Thermochemical Simulation of Phas
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Page 174 and 175: Figure 5.2 Calculated temperature v
Page 176 and 177: Figure 5.4 Composition profiles of
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Page 180 and 181: Figure 5.7 The density of X210CrW12
Page 182 and 183: 5.3 Calculations for the Bearing St
Page 184 and 185: Figure 5.11 Composition profiles of
Page 186 and 187: Figure 5.14 The density of 100Cr6.
Page 188 and 189: area which is available for heat tr
Page 190: Part Two Modelling the Flow Behavio
Page 193 and 194: 170j 6 Modelling the Flow Behaviour
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Page 244 and 245: 7 A Physical and Micromechanical Mo
Page 246 and 247: 3. Macroscopic averages or homogeni
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Page 250 and 251: and liquid are both assumed to be i
Page 252 and 253: are the strain rate concentration t
Page 254 and 255: Semi-solid viscosity (Pa s) into cl
Page 256 and 257: Load (kN) strain to rupture, leadin
Page 258 and 259: Load (kN) 7 6 5 4 3 2 1 0 0 7.5 Con
Page 260 and 261: adius R radius of the spherical inc
Page 262: Part Three Tool Technologies for Fo
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244j 8 Tool Technologies for Formin
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9 Rheocasting of Aluminium Alloys a
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Figure 9.2 Processes for the semi-s
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Two Italian companies gained the fi
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9.2 SSM Casting Processesj317 For t
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Figure 9.7 Oil pump cover for Honda
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Figure 9.9 Middle temperature cours
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Figure 9.12 Components of cartridge
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Figure 9.15 Process adapted multipa
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step-shot experiments. It is also s
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Figure 9.18 (a) Meander tool for fl
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Figure 9.19 (a, b) Wear appears in
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Table 9.2 Temperature determination
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and are plausible on the left. Furt
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Figure 9.27 Development of the micr
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some places can be observed as smal
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Figure 9.31 Simulation of the metal
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Figure 9.33 So-called Constant Temp
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Figure 9.35 Comparison of the micro
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9.4 Rheoroutej347 If rounding of th
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9.4.1.2 Parameters: Cooling to the
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Figure 9.36 Results of the 2D-MICRE
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homogeneous microstructure and no d
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grain fragment density [mm -1 ] 200
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can be considered for rheocasting o
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Figure 9.44 Microstructure of Zr/Sc
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Figure 9.45 MAGMAsoft simulation: c
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The cooling to the process temperat
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D grain diameter of a circle DGM De
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27 Doppelbauer, M. (2003) Wirtschaf
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10 Thixoforging and Rheoforging of
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1970s [7]. Also, the quality of the
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10.3 Heating and Forming Operations
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With the solution of the Equations
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10.3.1.2 Modelling of Inductive Hea
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material properties have to be cons
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10.3 Heating and Forming Operations
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Figure 10.9 Experimental results, d
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Figure 10.12 Segregation in compone
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10.3.4 Thixoforging of Steel In thi
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10.3.5 Thixojoining of Steel In the
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einforcing element. The possibiliti
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Figure 10.20 The robot controller a
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Figure 10.21 Experimental results w
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Figure 10.24 Design and working pri
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The investigations show that the rh
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Figure 10.31 Scheme of the heat tra
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Table 10.2 Definition of boundary c
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Figure 10.35 Experimental and simul
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References 1 Koesling, D., Tinius,
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steel billets into the semi-solid s
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412j 11 Thixoextrusion The followin
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414j 11 Thixoextrusion channel with
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416j 11 Thixoextrusion parameter co
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418j 11 Thixoextrusion Both concept
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420j 11 Thixoextrusion should be ju
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422j 11 Thixoextrusion Figure 11.8
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424j 11 Thixoextrusion Table 11.4 C
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426j 11 Thixoextrusion Temperature
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428j 11 Thixoextrusion impacts. Ext
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432j 11 Thixoextrusion shell format
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436j 11 Thixoextrusion Table 11.6 P
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440j 11 Thixoextrusion solidificati
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442j 11 Thixoextrusion GPa pressure
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444j Index arbitrary volume element
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446j Index equilibrium tests 141 eq
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448j Index - importance 273 ion flu
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450j Index oxygen-sensitive element
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452j Index - thixoforming 241 semi-
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454j Index - high pressure 131 - sc
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Thixoforming : Semi-solid Metal Processing

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