Thixoforming : Semi-solid Metal Processing

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For A356, there is a temperature shift of 7.5 C, and for AZ91 the shift is 12 C. For the alloy AlSi7Mg, it must also be noted that a 50% solid fraction at the upper compositional limit cannot be reached without any eutectic solidification in the slug. If eutectic is present during the holding period of the slug, a very coarse eutectic phase will be formed. This reduces the mechanical properties, especially elongation values. However, in general, it can be stated that both alloys are well suited for semisolids. Let us assume that SSM forming takes place at 570 C, aiming for a 50% solid fraction in the alloy AZ91. If the alloy is at the upper limit of the tolerance field, the actual solid fraction would only be around 44%, whereas if the alloy is at the lower limit fS would be about 55%, and only a little influence on product quality can be assumed. For the steel X210CrW12, fluctuations of 2.0–2.3% C, 11–13% Cr and 0.6–0.8% W are tolerated, resulting in a temperature shift of about 35 C. This corresponds to a solid fraction variation from about 42% to 57%, which is also considered to be not very harmful. The situation is more complicated for the Al wrought alloy AA6082, with tolerated fluctuations of 0.7–1.3% Si, 0.6–1.2% Mg and 0.1–0.45% Mn. Here the temperature shift is approximately 11 C, but with the high S value of 0.027 K 1 this corresponds to an intolerable solid fraction variation of about 30%. Similar problems are expected for the steel grade 100Cr6. The accepted chemical variations are 0.97–1.1% C, 1.3–1.6% Cr, 0.15–0.3% Si and 0.25–0.45% Mn. This implies a possible temperature shift of about 18 C or a variation in solid fraction of almost 20%. 2.6 Conclusion 2.6 Conclusionj41 The impressive bundle of advantages mentioned in the Introduction has been the driving force for continued SSM research worldwide. In contrast to what was expected several years ago, the acceptance of SSM technology in industry is still at a relatively low level. The essential demand is to produce components at a constant high-quality level. From a metallurgical point of view, only a few alloy systems fulfil the requirements for high-quality SSM production. However, also in case of optimal alloy selection, unintentional fluctuations in solid fraction due to fluctuations in alloy composition may cause quality problems. For a given set of formingparameters,analloywithacompositionatthelowerorupperendofits standard may generate severe defects such as macro-segregation. This does not mean that SSM processing at high or low solid fractions is generally bad, or that it cannot yield high-quality components. If variations in solid fraction occur, the forming parameters have to be adjusted properly. On the other hand, if the process parameters are kept constant, only a limitation in compositional fluctuation can help to reduce scrap production. In order to stabilize the SSM process, the use of temperature control in combination with chemical monitoring is highly recommended.
42j 2 Metallurgical Aspects of SSM Processing List of Abbreviations and Symbols SoD slurry-on-demand SSM semi-solid metal TFR terminal freezing range f S initial solid fraction fL liquid fraction fS solid fraction k element content in solid phase/element content on liquid phase ml slope of the liquidus line S temperature sensitivity T50 temperature at which there is 50% liquid DTC constitutional undercooling References 1 Fan, Z. (2002) International Materials Reviews, 47 (2), 49–84. 2 Liu, D., Atkinson, H.V. and Jones, H. (2005) Acta Materialia, 53, 3807–3819. 3 P€uttgen, W. and Bleck, W. (2004) Steel Research International, 75, 531–536. 4 Easton, M.A. and StJohn, D.H. (2001) Acta Materialia, 49, 1867–1878. 5 Kleiner, S., Beffort, O. and Uggowitzer, P.J. (2004) Scripta Materialia, 51, 405–410. 6 Kaufmann, H. and Uggowitzer, P.J. (2007) Metallurgy and Processing of High-integrity Light Metal Pressure Castings, Schiele & Sch€on, Berlin. 7 Hallstedt, B. and Schneider, J.M. (2009) In Thixoforming – Semi-solid Materials Processing (ed. G. Hirt), Wiley-VCH Verlag GmbH, Weinheim, Chapter 4. 8 P€uttgen, W., Hallstedt, B., Bleck, W., L€offler, J.F. and Uggowitzer, P.J. (2007) Acta Materialia, 55, 6553–6560. 9 P€uttgen, W., Hallstedt, B., Bleck, W. and Uggowitzer, P.J. (2007) Acta Materialia, 55, 1033–1042. 10 Hale, G.E. and Nutting, J. (1984) International Materials Reviews, 29, 273–298. 11 Djurdjevic, M.B. and Schmid-Fetzer, R. (2006) Materials Science and Engineering A, 41, 24–33. 12 Uhlenhaut,D.I.,Kradolfer,J.,P€uttgen, W., L€offler,J.F.andUggowitzer,P.J. (2006) Acta Materialia, 54, 2727– 2734. 13 Kaufmann, H., Fragner, W. and Uggowitzer, P.J. (2005) International Journal of Cast Metals Research, 18 (5), 279–285.
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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
Page 13 and 14: X Contents 7.4.2 Isothermal Non-ste
Page 15 and 16: XII Contents 9.4.1.3 Simulation Res
Page 18: Preface Semi-solid forming of metal
Page 21 and 22: XVIII List of Contributors Andreas
Page 23 and 24: XX List of Contributors Alexander S
Page 25 and 26: 2j 1 Semi-solid Forming of Aluminiu
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Page 45 and 46: Table 1.1 Overview of semi-solid pr
Page 52: Part One Material Fundamentals of M
Page 55 and 56: 32j 2 Metallurgical Aspects of SSM
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Page 67 and 68: 44j 3 Material Aspects of Steel Thi
Page 113 and 114: Temperature (ºC) 1550 1500 1450 14
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92j 3 Material Aspects of Steel Thi
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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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5 Thermochemical Simulation of Phas
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here it can be assumed that the dat
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Figure 5.2 Calculated temperature v
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Figure 5.4 Composition profiles of
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It is clear that C has by far the s
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Figure 5.7 The density of X210CrW12
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5.3 Calculations for the Bearing St
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Figure 5.11 Composition profiles of
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Figure 5.14 The density of 100Cr6.
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area which is available for heat tr
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Part Two Modelling the Flow Behavio
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170j 6 Modelling the Flow Behaviour
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7 A Physical and Micromechanical Mo
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3. Macroscopic averages or homogeni
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displacement boundary conditions or
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and liquid are both assumed to be i
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are the strain rate concentration t
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Semi-solid viscosity (Pa s) into cl
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Load (kN) strain to rupture, leadin
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Load (kN) 7 6 5 4 3 2 1 0 0 7.5 Con
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adius R radius of the spherical inc
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Part Three Tool Technologies for Fo
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242j 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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