Younes Sina, High temperature deformation ,Creep, AZ91

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Younes Sina's presentation for Professor T.G.Nieh's class, High Temperature Deformation, Creep , AZ91 Alloy, Coble creep mechanism

Younes Sina's presentation for Professor T.G.Nieh's class, High Temperature Deformation, Creep , AZ91 Alloy, Coble creep mechanism

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  • 1. On Coble creep in Mg–9Al–1Zn alloy with ultrafine-grained microstructure
    W.J. Kim
    December 2007
    Professor T.G.Nieh
    The University of Tennessee, Knoxville
    Younes Sina
  • 2. Magnesium alloy designations
    AZ91C-T6
    2 digits
    Quantity of principal alloys
    9 = 9% Al
    1 = 1% Zn
    1 letter
    Distinguishing code
    C = Third alloy of this type
    2 letters
    Principal 2 alloy elements
    A = aluminum
    Z = zinc
    Temper designation
    -T6 = solution treated and artificially aged
    • A - Aluminum
    • 3. E - Rare earths
    • 4. H - Thorium
    • 5. K - Zirconium
    • 6. M - Manganese
    • 7. Q - Silver
    • 8. T - Tin
    • 9. Z - Zinc
    • 10. F - As fabricated
    • 11. O - Annealed
    • 12. H10 and H11 - slightly strain hard
    • 13. H23, H24, H26 - strain hardened and partially annealed
    • 14. T4 - artificially aged
    • 15. T6 - Solution treat, aged
    • 16. T8 - Solution treat, cold work, aged
  • Oil Pan housing
    Radiator support
    Key Lock housing
    Door- Lupo
    Oil Pan- Honda
    Magnesium alloys are the lightest metallic structural materials and are, hence, very attractive in applications such as automotive, railway and aerospace industries.
  • 17. Deformation mechanism of Mg, Cu, Mg alloys
    Nano grain= 1-100 nm
    Ultra fine=100-500 nm
  • 18. DMM for pure Mg
    Correct value
    D0=7.79*10-3 m2s-1
    D0=5*10-12 m2s-1
  • 19.
  • 20.
  • 21. process concept for forward extrusion of magnesium alloys, prior (left) and during (right).
  • 22. Twist hydro-extrusion
    ECAP : 2-turn square pass
    ECAP : 3-turn square pass
    ECAP : 3-turn round
    Hydro-Mechanical Extrusion
  • 23. Recovery, Rex. & Grain growth during rolling
    SPD
  • 24. SEM images on (a) the weakly deformed front part of the sample
    after four passes and (b) the severely strained internal part of the specimen after eight asses.
    TEM micrograph of the HRDSRed AZ91
    L=0.8 , d Ex=6.2 μ & d HRDSR=1.74μ
    High density dislocation
    L=3.6 for β-Mg17Al12
    Many precipitate (0.1-0.5 μ)
    d=1.4L
  • 25. Hot-extruded AZ91 alloy with an initial grain size of 1.7 m.
  • 26. α-Mg
    β-Mg17Al12
  • 27. Prestrain
    A true stress–true strain curve of the HRDSRed AZ91 from the SRC test at 553 K.
    |T=[(ln (έ2/έ1)] / [ln (σss2/σss1)]
    n=
  • 28. .
    ss= C n exp (- Q diffusion/ RT)
    Temperature dependence
    Stress dependence
    Constants
  • 29. T
    493
    553
    473
    553
    493
    523
    ?
    573
    The SRC results as double-log plots of strain rate vs. stress at different temperatures for the HRDSRed AZ91 and the EX AZ91
    n=d ln έ /d ln σ
  • 30. ? Grain growth @ 573, Large decrease in volume fraction of β-Mg17Al12
    .α 1/d2 and 3
  • 31. Grain coarsening
  • 32. σEX=σHRDSR
    σEX<σHRDSR
  • 33. 493
    523
    553
    493
    553
    573
    Strain rate compensated by Dgb vs. /E for the HRDSRed AZ91 and the EX AZ91.
    D0=7.79*10-3 m2s-1
    Qgb=92 kJmol-1
    Dgb=D pipe=D0 exp (-Qgb/k T)
  • 34.
  • 35. Dynamic recovery occurs during forming, and is followed by static recovery subsequent to forming
    b. The grains recrystallize after deformation
    c. Dynamic recrystallization (recrystallization during deformation) takes place and is followed by static recrystallization
  • 36. N=1
    N=7
    EX AZ91
    N=1
    HRDSR AZ91
    N=2
    N=2
    Deformation mechanism maps for Mg alloys at several temperatures in the range 300–573 K
  • 37.
  • 38. HRDSRed AZ91
    GBS
    Coble Creep
    Dislocation climb creep
    Comparison between the experimental data of the HRDSRed AZ91 and the values predicted by the three creep models at 553 K
  • 39. Coble
    GBS
    D p-slip creep(Dislocation Climb Creep)
    d=3.5μ
  • 40. έ=10-8 s-1
    έ=10-6 s-1
    έ=10-4 s-1
    έ=10-8 s-1
    Mg
    έ=10-6 s-1
    έ=10-4 s-1
    Cu
    Critical grain size for copper is significantly smaller
  • 41. Future works:
    Comparison with ECAP and other SPD methods
    (microstructure developed after SPD depends on #of passes)
    Evaluation of grain homogenousity
    (check if there is a significant growth during deformation)
    Measuring of dislocation density
    The same research for other Mg alloys
  • 42. Thank you
    Kurdistan, Iran