Partition coeff. at constant temp. and press. if ml < 0 k < 1. İf ml > 0 k >1

Transcription

1 Microsegregation

2 Partition coeff. k=cs/cl at constant temp. and press. if ml < 0 k < 1 İf ml > 0 k >1

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9 Models for Microsegregation 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

10 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

11 (6 Model). Eq solidification (Level Rule)

12 p=1-k

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17 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

18 1 model

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26 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

27 2 model

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30 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

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33 CL=Co(1-fs)^(k-1) CL=Cofl^(k-1) Cs=kCofl^(k-1) fs+fl=1 k=cs/cl

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40 Co= Gulliver-Scheil Eq. Cs k=0.1 k=0.2 k=0.4 k=0.6 k=0.8 k= fs

41 50 40 Gulliver-Scheil Eq. Co=4.5Cu CL k=0.1 k=0.2 k=0.4 k=0.6 k=0.8 k= fs

42 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

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45 Cs=kCo(1-(1-k*beta)*fs)^((k-1)/(1-k*beta))

46 Beta=2*alpha/(1+2*alpha) Ohnaka Beta=2*alpha/(1+2*alpha+1/2k)

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51 CL Beta=0 beta=0.01 beta=0.1 beta=0.4 beta=0.8 beta=1 Ohnaka Eq. Co=4.5Cu k=

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53 T Ohnaka Eq. Co=4.5Cu k=0.166 beta=0 beta=0.01 beta=0.1 beta=0.4 beta=0.8 beta= fs

54 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid

55 Beta=2*alpha/(1+2*alpha) Ohnaka

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63 Solidification in Ternary System

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65 Solidification in Al-Cu-Mg Alloys

66 7050 Plate Focus on one alloy (7050) and product (thick hot rolled plate) Components machined from 7050 alloy thick plate are widely used in load bearing applications e.g. wing spars 7050 composition specification

67 Processing Sequence Plate Cast Direct chill Age Homogenize ~475 o C, 24h Solution treat 475 o C, 1h spray quenched Hot roll ~ o C 20+ passes reduction~70%

68 Temperature Microstructural Changes Time RD 50nm Cast Homogenized Rolled Solutionized Aged

69 -AlMg -AlMg Temperature (C) Temperature (C) Temperature (C) Simple Phase Diagrams Even for simple 2xxx alloy (Al-Cu-Mg), need data for 3 binaries and information about ternary phases Al Al-Cu System (Al-Rich) Liquid + -Al Liquid -Al + -Al 2 Cu Liquid + -Al 2 Cu -Al 2 Cu wt.% Cu Al Al-Mg System (Al-Rich) Liquid + -Al -Al + -AlMg Liquid wt.% Mg -AlMg Cu + Laves - C15 L + -Cu Liquid + Laves - C15 Laves - C15 Ternary Phases S - Al 2 CuMg, T - Mg 32 (Al,Cu) 49, V - Al 5 Cu 6 Mg 2, Q - Al 7 Cu 3 Mg 6 Cu-Mg System CuMg2 L + CuMg wt.% Mg Liquid CuMg2 + Mg Liquid + Mg MTDATA predicted phase diagrams Real, commercial Al-alloys may contain > 10 alloying elements! Success of thermodynamic models relies on availability of sufficient, high quality, thermodynamic data

70 Mass Phase Fraction Predictions for Binary Al-Cu Alloy Al 2 Cu Eutectic Reaction Freezing Range fcc -Al Liquid Temperature (C) - Al 2 Cu eutectic fcc -Al eutectic fcc -Al dendrites

71 Predictions for Ternary Al-Cu- Mass Phase Fraction 1.0 Mg alloy Predictions for 2xxx (Al-4.5Cu-1.5wt%) Mg alloy T S fcc -Al Liquid 0.2 S - Al 2 CuMg Al 2 Cu Temperature (C) Ternary Eutectic Predicted at ~ 500ºC DT T L

72 Prediction of Freezing Range To reduce tendency for solidification cracking, need to minimize absolute freezing range Use thermodynamic model to predict freezing range for different alloy compositions DT (Freezing Range of Eutectic) Optimum composition range Effect of Mg content on freezing range of eutectic in Al-4.5Cu-x Mg alloy Binary Eutectic [ + ] Ternary Eutectic [ + S] Saddle Point [ + S] wt.% Mg

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74 Fe-C-Mn Aloys

75 Fe-C-Mn Phase Diagram

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77 Color Etching

78 Color Etching

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