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Heat Treatment of AM60B

VIEWS: 7 PAGES: 27

									Development of Fluidized Bed
 Heat Treatment for AM60B
          Advisor: Dr. Mark Plichta
  Project Team:
  Allen Hunter
  Josh Bero
  John Pomeroy
  Jarrod Cunnings


  Dave Hunt
  Leanne Sedar
 Industry Support
Bruce Cox, DaimlerChrysler
Eric McCarty, DaimlerChrysler
Rich Jacques, SPX Contech
        Outline
   Project Focus
   Objectives
   Background
   Experimental Procedure
   Results
   Conclusions
            Problem Statement
   Develop a fluidized bed heat treatment process
    for squeeze cast AM60B magnesium automotive
    components which improves mechanical
    properties to meet safety critical standards
                      Objectives

Use a fluidized bed heat treatment process to:
     Increase mechanical properties
        Tensile strength
        Ductility

        Hardness

     Decrease heat treatment times compared to
      conventional forced air furnaces
        Magnesium vs. Aluminum
                                 Disadvantages of Mg
                                   Inferior mechanical
                                    properties
                                   Greater material cost
   Advantages of Mg               Low operating
     Lighter material              temperature (<190°C)
     Better damping

     Lower melting point

     Allows for longer die
      life
    High Integrity Magnesium
Automotive Components (HIMAC)
   Improve fuel economy through weight
    reduction of parts
   Use of magnesium instead of aluminum
   Improve mechanical properties of magnesium
     Call for minimum 7% elongation for safety critical
      parts
     Most as-cast magnesium alloys don’t meet this
      requirement
                    Casting Mg
   Die Casting
     Majority of automotive magnesium castings
     Unable to be heat treated due to blistering


   Squeeze Casting
     Slower solidification
     Lower turbulence
     Minimizes porosity
     Able to be heat treated
                        Squeeze Casting
                                                  Metal fills
                               Metal ‘Squeezed’   mold over
              Top Die
 Bottom Die                    into mold cavity   2-3
                                                  seconds
                                                  and
                                                  solidifies
                                                  from the
                                                  top down

 Molten
Magnesium
        What comprises precipitation
         hardening heat treatment?
   Solution treatment
     As-cast structures contain multiple phases that are
      detrimental to mechanical properties
     Solution treatment creates a single phase solid
      solution
   Age Hardening
     Causes fine uniformly-dispersed second phase to
      precipitate
     This results in increased mechanical properties
AM60B Alloy
     ASTM B94-94

Component       Wt. %
   Mg            Bal
    Al         5.5 - 6.5
   Mn         0.24 - 0.6
    Zn        0.22 Max
    Si         0.1 Max
    Cu        0.01 Max
    Ni        0.002 Max
    Fe        0.005 Max
Other, each   0.02 Max
Al – Mg Phase Diagram




                        S




                A
     Fluidized Bed Heat Treatment
    What is it?
       Heated air forced through granular media
       Media is fluidized by the air

       Samples are immersed inside bed
                                            Air Line

    Samples in
    wire basket
    placed in bed                           Carbon Dioxide
                                            Line
Fluidized Bed
                  Fluidized Bed
   Why use it?
     Significant reduction of time with Al alloys
     Similar results anticipated for Mg alloys



   Used for Solutionizing and Aging
     Solution treated samples at temperatures below
      eutectic temperature of 437°C
     Age samples at 177°C
                 Fluidized Bed
   More uniform and faster heating than
    conventional convection furnace
     Sand has a higher density
     Heat capacity of sand is much higher than air or gas
         Experimental Procedure
   Identify Solution Treatment Parameters with ingot
    samples
   Ingot cubes were solution treated at temperatures
    ranging from 415°C to 440°C
   Volume fractions of Mg17Al12 remaining eutectic
    measured using point counting method
   Samples examined for incipient melting
           Heat Treatment Results
   Ingot samples tested at temps of 415°C, 420°C, 430°C
    and 440°C at times of 2, 4, 6, and 8 hours
   Results revealed amount of Mg17Al12 remaining
       Volume fraction Mg17Al12 decreases with time and
        temperature
         Solutionizing and Aging
   Temp of 435°C was chosen for solutionizing
     Below the eutectic melting temp of 437°C
     Above the solutionizing temp of 430°C which had
      good results of reducing the percentage of Mg 17Al12


   Identify Aging Parameters
     Pre-arranged temp of 177°C
     Optimize strength and elongation
                  Project Delays
   Squeeze cast tensile bars were intended for
    project
     Squeeze cast cell was not operational due to local fire
      codes
     Variance was obtained but not enough time
      remained to produce quality magnesium squeeze cast
      parts
   Low pressure permanent mold (LPPM) tensile
    bars were used instead
        Experimental Procedures
   LPPM tensile bars solution treated at 435°C for
    various times
   Aged at 177°C for various times
   Mechanical properties were measured
     Tensile
     Hardness
          Solution/Age Results
Hardness data follows normal age hardening trend
     6 Hour Solution Treatment
Best elongation – 6.5% at 0 and 1 hour of aging
     8 Hour Solution Treatment
Best elongation – 7.5% reached at 1 hour of aging
                       Metallography



As-cast eutectic structure (20 μm SB)         8 hour solution treated (100 μm SB)




                    8 hour solution treated 36 hour over-aged (20 μm SB)
                   Conclusions
   Prefer to have more samples/data
     Most bars contained oxides
     Tensile bars failed prematurely at oxide areas

   Best Heat Treatment for AM60B
     Solution heat treatment of 8 hours
     Aging of 1 hour

     Both hardness and elongation peaked out at this
      combination
Questions?

								
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