Thixoforming : Semi-solid Metal Processing

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Figure 9.44 Microstructure of Zr/Sc-microalloyed AA1420: homogeneity (top) and phase detection (bottom): as-cast (left) and heat treated (right); sampling position of the flat bar tension specimen. 9.4 Rheoroutej359 (calculated by ThermoCalc) in the HPDC machine. Manufactured tie rods were analysed microscopically, and heat treated and tensile tested. During HPDC processing, rapid solidification of the remaining melt took place in non-equilibrium by the formation of an unexpected eutectic, including the phases Al2LiMg, Al12Mg17 and Al8Mg5 [51] (Figure 9.44). During heat treatment for 24 h at 460 C (the solidus
360j 9 Rheocasting of Aluminium Alloys and Thixocasting of Steels temperature was determined by differential thermal analysis and found to be 480 C), these phases (Al2LiMg, Al8Mg5, Al12Mg17) were to a large extent dissolved in the alpha solid solution, leading to a more or less single-phase structure (Figure 9.44). The added elements Sc and Zr formed Al3(ScxZr1 x) dispersoids, which inhibited undesired grain growth during the solution treatment [52, 54]. After water quenching from the solution temperature, the components were aged for 17 h at 160 C under an argon atmosphere. According to the literature, the primary strengthening phase Al3Li was formed [52]. From the cast tie rods, flat bar tension specimens were sectioned and tested. Figure 9.44 shows the sampling locations and the good homogeneity of the microstructure over the total length of the component. Via heat treatment, the mechanical properties of A1420 (AlLi2.1Mg5.5 þ Sc and Zr) were improved significantly. In this way, the tensile strength was increased to over 400 MPa, the yield strength up to 250 MPa and the elongation to fracture to an average of 6.4%, almost three times higher than in the thixocast condition [53]. Chemical analyses showed that the tie rods were manufactured homogeneously [53]. To investigate the improvement potential of the heat treatment, sectioned samples of the connecting rod were solution annealed (24 h at 460 C), quenched in water and subsequently aged for various times in an oil bath at different temperatures (140, 160, 180 C) at the Swiss Federal Institute of Technology (ETH) Z€urich. The pyramid diamond hardness [Vickers hardness (HV)] (HV5) was measured and plotted against ageing time. The hardness before heat treatment was 84 HV and after solution annealing 94 HV. On increasing the ageing temperature, the maximum hardness (130 HV in each experiment) requires a shorter ageing time. In order to achieve maximum hardness, the following annealing parameters are advisable: 180 C/10 h, 160 C/25 h or 140 C/>35 h [53]. This revised heat treatment was tested during thixocasting experiments with the modified AA1420 (see the next section). Despite casting in the semi-solid state, hot cracks appear at the bearing points. To solve this problem, simulations regarding the hotspots at the bearings were carried out using MAGMAsoft and verified during thixocasting of modified AA1420. 9.4.3.4 Thixocasting of Tailored AlLi2.1Mg5.5 The as-cast feedstock billets (Sc- and Zr-modified AA12; see Chapter 2) were produced to a diameter of 78 mm and a length of 160 mm for the thixoforming process. By means of MAGMAsoft simulations, the hot-tear problem was solved. Because of the absence of thermomechanical data for AlLi2.1Mg5.5, A356 was used as a cast alloy for the simulations. A removable steel core was used for building up the large bearing. If the steel core was hot, a hotspot directly behind the core was the result. Otherwise, with a cold steel core the hotspot is displaced into the over flow. The simulation results using a 60 C cold steel core compared with a 300 C hot steel core show this effect (Figure 9.45). Regarding this, the steel core was cooled before each shot, and the effect of this is visualized in Figure 9.46. On decreasing the core temperature, the hot tearing tendency also decreases. Using a cold core that was inserted only directly before forming, no further hot tear appears.
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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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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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Page 331 and 332: 308j 8 Tool Technologies for Formin
Page 334 and 335: 9 Rheocasting of Aluminium Alloys a
Page 336 and 337: Figure 9.2 Processes for the semi-s
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Page 340 and 341: 9.2 SSM Casting Processesj317 For t
Page 342 and 343: Figure 9.7 Oil pump cover for Honda
Page 344 and 345: Figure 9.9 Middle temperature cours
Page 346 and 347: Figure 9.12 Components of cartridge
Page 348 and 349: Figure 9.15 Process adapted multipa
Page 350 and 351: step-shot experiments. It is also s
Page 352 and 353: Figure 9.18 (a) Meander tool for fl
Page 354 and 355: Figure 9.19 (a, b) Wear appears in
Page 356 and 357: Table 9.2 Temperature determination
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Page 360 and 361: Figure 9.27 Development of the micr
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Page 364 and 365: Figure 9.31 Simulation of the metal
Page 366 and 367: Figure 9.33 So-called Constant Temp
Page 368 and 369: Figure 9.35 Comparison of the micro
Page 370 and 371: 9.4 Rheoroutej347 If rounding of th
Page 372 and 373: 9.4.1.2 Parameters: Cooling to the
Page 374 and 375: Figure 9.36 Results of the 2D-MICRE
Page 376 and 377: homogeneous microstructure and no d
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Page 384 and 385: Figure 9.45 MAGMAsoft simulation: c
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Page 388 and 389: D grain diameter of a circle DGM De
Page 390 and 391: 27 Doppelbauer, M. (2003) Wirtschaf
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Page 394 and 395: 1970s [7]. Also, the quality of the
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Page 408 and 409: Figure 10.12 Segregation in compone
Page 410 and 411: 10.3.4 Thixoforging of Steel In thi
Page 412 and 413: 10.3.5 Thixojoining of Steel In the
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Page 426 and 427: Table 10.2 Definition of boundary c
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Page 430 and 431: 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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