Equal Channel Angular Pressing of High Purity Aluminum

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Equal Channel Angular Pressing of High Purity
Aluminum

• Julio A. Nunez
• Chris Hovanec
• Dr. Surya R. Kalidindi
• Dr. Roger D. Doherty
• Mechanics of Microstructures Group

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Equal Channel Angular Pressing(ECAP)

• Deformation process that imposes high strains
  with the benefit of retaining the cross-sectional
  area of the work piece.

Shear Plane
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Motivation

• The likelihood that ultra fine grain aluminum and
  its alloys can be produced by ECAP processing
  with both increased strength and fracture
  toughness.
• To achieve a more in-depth understanding of the
  physical mechanisms behind the evolution of grain
  size and shape during severe plastic deformation.

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Social/Economical
F-22
Space Shuttle
10 Reduction/6 efficiency
Thrust
High
Higher Acceleration
Weight
Dodge Viper
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Microstructure Performance
Performance
Processing
Microstructure
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Two Ways to Strengthen Metals

• Precipitation Hardening
• Strain Hardening

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Precipitation Hardening

• Precipitation Hardening is a thermodynamic
  reaction that involves creation of a new phase
  change
• Precipitation Heat Treatment
• precipitates form on grain boundaries
• lower fracture toughness compared to strain
  hardening

Grain Boundaries
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Strain Hardening

• Strain Hardening occurs when a ductile metal
  becomes harder and stronger as it is plastically
  deformed
• rolling, compression, and ECAP

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Rolling

• Widely used for strain hardening
• Pass a piece of metal between two rolls
• Although imposes strain on the metal, it reduces
  thickness
• Sample thickness limits amount of strain induced

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Aluminum

• Generally precipitation heat treated because of
  inherent properties
• Lowers fracture toughness
• Dr. Doherty and colleagues discovered high solute
  alloys increase fracture toughness when strained

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ECAP

• Same strength as precipitation hardening but
  higher fracture toughness
• Rolling e 2.3 VS. ECAP e 10

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Objectives

• Successfully process high purity Al by ECAP to
  high strains
• Extract mechanical properties as a function of
  imposed strain
• Extract mechanical properties as a function of
  microstructure
• Validate the MMG ECAP process through comparisons
  of experimental data published data

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Procedure

• Run each sample twice and heat treat at 450C for
  1hr
• Run ten samples to different strains through
  route A
• Cut samples
• Run compression test
• Perform metallography to measure grain size and
  analyze texture

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Microstructure

• Metallography is the process of preparing samples
  such that any deform or unrepresented surface is
  removed so the specimen is ready for analysis.
• Grain Size
• Texture OIM (measure of crystal orientations).

SEM
OIM
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Grinding wheel
Grinding/Polishing

• Grinding is done on a spinning wheel with water
  running on the surface.
• Round SiC grinding paper are used to scratch the
  surface with all the lines going in one
  direction.
• Polishing creates a smooth, mirror-like finish.
• Non-abrasive cloth is used and lubricant is added
  and a diamond suspension which acts as grit.

Different grit papers
Cloth, lubricant, and diamond suspension
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Mechanical Properties

• Theoretically we expect the envelope expand to
  the right

Fracture Toughness
KIC
Yield Strength
sy
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Mechanical Properties

• Theoretically we expect the envelope expand to
  the right

Fracture Toughness
KIC
Yield Strength
sy
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Results

• Results from testing will be used to compare
  data from previous published findings.
• If the data correlates, this will validate proper
  technique and give us a base line for our overall
  project.

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Thank You
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Dislocations
Linear or one dimensional defects where some of
the atoms are misaligned.