Development of Fluidized Bed Heat Treatment for AM60B

1
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
2
Industry Support

• Bruce Cox, DaimlerChrysler
• Eric McCarty, DaimlerChrysler
• Rich Jacques, SPX Contech

3
Outline

• Project Focus
• Objectives
• Background
• Experimental Procedure
• Results
• Conclusions

4
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

5
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

6
Magnesium vs. Aluminum

• Disadvantages of Mg
• Inferior mechanical properties
• Greater material cost
• Low operating temperature (lt190C)

• Advantages of Mg
• Lighter material
• Better damping
• Lower melting point
• Allows for longer die life

7
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 dont meet this
  requirement

8
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

9
Squeeze Casting
Metal fills mold over 2-3 seconds and solidifies
from the top down
Metal Squeezed into mold cavity
Top Die
Bottom Die
Molten Magnesium
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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

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AM60B AlloyASTM B94-94
12
Al Mg Phase Diagram
S
A
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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
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Fluidized Bed
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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 437C
• Age samples at 177C

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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

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Experimental Procedure

• Identify Solution Treatment Parameters with ingot
  samples
• Ingot cubes were solution treated at temperatures
  ranging from 415C to 440C
• Volume fractions of Mg17Al12 remaining eutectic
  measured using point counting method
• Samples examined for incipient melting

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Heat Treatment Results

• Ingot samples tested at temps of 415C, 420C,
  430C and 440C at times of 2, 4, 6, and 8 hours
• Results revealed amount of Mg17Al12 remaining
• Volume fraction Mg17Al12 decreases with time and
  temperature

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Solutionizing and Aging

• Temp of 435C was chosen for solutionizing
• Below the eutectic melting temp of 437C
• Above the solutionizing temp of 430C which had
  good results of reducing the percentage of
  Mg17Al12
• Identify Aging Parameters
• Pre-arranged temp of 177C
• Optimize strength and elongation

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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

21
Experimental Procedures

• LPPM tensile bars solution treated at 435C for
  various times
• Aged at 177C for various times
• Mechanical properties were measured
• Tensile
• Hardness

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Solution/Age Results

• Hardness data follows normal age hardening trend

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6 Hour Solution Treatment

• Best elongation 6.5 at 0 and 1 hour of aging

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8 Hour Solution Treatment

• Best elongation 7.5 reached at 1 hour of aging

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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)
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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

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• Questions?