Thixoforming : Semi-solid Metal Processing

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about the mechanisms involved in the interactive effect between grain refinement and modifying agents. Within the framework of melt testing, using the modelsupported testing plan, various chemical compositions were produced and then evaluated in respect of the effect variables important for thixoforming. Particular attention was devoted to the grain size in the primary phase, modification of the eutectic phase, the melt range and the rheological characteristics. For these parameters, a mathematically linear approach was chosen for determination of the efficiency. For the parameters titanium concentration and reheating time, the focus is on the question of how the parameters can be set in order to achieve optimum results for the effect variables. The standard grain refiner AlTi5B1 was used for chemical grain refinement. Lead was selected to test its possible positive effect on grain refinement. In minimal concentrations Pb already reduces the surface tension of aluminium and should therefore have a positive effect on grain refinement and/or modification. For strontium and sodium, 200 ppm was defined as the upper step value, in order to ensure its efficiency but at the same time to avoid over-modification. For the reheating time, periods between 5 and 15 min are technically relevant. Particularly long holding times may be unavoidable, however, in the event of process malfunctions during reheating, so the suitability of the raw material was also tested in this respect. The titanium content and the reheating time can be identified as significant influences on the grain size. As the titanium content increases, the grain size can be expected to decrease in the a-aluminium phase. With longer reheating time, as a result of maturing processes, grain growth can be expected to occur. In addition, a significant interaction between titanium and strontium can be identified, although the effect of strontium alone is only minimal and can be identified as being statistically insignificant. The grain refining effect of titanium is evidently weakened by the addition of strontium. To indicate the affectability of the grain size, in the following detailed evaluations the titanium and strontium contents and the reheating time were considered in particular (Figure 4.3). By the addition of 0.4% titanium (in the form of AlTi5B1), the grain size can be decreased from about 85 to 65 mm. As the reheating time is extended. grain growth can be expected to occur; however, this is inhibited by the addition of titanium. This effect of the grain refiner is also dependent on the strontium content. A systematic positive effect of manganese and lead addition cannot be ruled out. The change in the grain size as a result of grain refining treatment, and also the effect of the duration of the reheating time with simultaneous modification using strontium, are illustrated in Figure 4.3a. 4.2.3 Influence on the Form Factor of the Primary Phase 4.2 Chemical Grain Refinement of Commercial Thixoalloysj111 A further criterion for evaluation in the assessment of thixoforming materials is the form factor. The rounder the grain or the greater the form factor is, the more pronounced the thixotropic material characteristic in a forming operation will become. The duration of reheating is recognized as an essential parameter affecting
112j 4 Design of Al and Al–Li Alloys for <strong>Thixoforming</strong> Figure 4.3 Grain size ¼ f(titanium content, reheating time), (a) without Sr and (b) with Sr. (b) Modification of the eutectic grain structure depending on the content of Sr (ppm) and Ti. the form factor. The effect of alloying elements on forming is, however, largely unexplained. For the material A356 (EN AC-AlSi7Mg0.3), the main parameter affecting the form factor of the primary phase (a-aluminium) surprisingly appears to be the addition of strontium, which seems to have an even greater effect in comparison with the reheating time. The other elements, on the other hand, cannot be identified as significant parameters. The dependence of the form factor on the titanium added and on the reheating time with manganese added and also modification using strontium is shown in Figure 4.4. Figure 4.4 Dependence of form factor on reheating time and titanium content (0.3% Mn, 200 ppm Sr, 0 ppm Na, 0% Pb).
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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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Page 170 and 171: 5 Thermochemical Simulation of Phas
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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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