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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. Equal Channel Angular Pressing (ECAP).

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Equal channel angular pressing of high purity aluminum

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


Equal channel angular pressing ecap
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


Motivation
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.


Social economical
Social/Economical

F-22

Space Shuttle

10% Reduction/6% efficiency

Thrust

High

=Higher Acceleration

Weight

Dodge Viper


Microstructure performance
Microstructure = Performance

Performance

Processing

Microstructure


Two ways to strengthen metals
Two Ways to Strengthen Metals

  • Precipitation Hardening

  • Strain Hardening


Precipitation hardening
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


Strain hardening
Strain Hardening

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

    • rolling, compression, and ECAP


Rolling
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


Aluminum
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


ECAP

  • Same strength as precipitation hardening but higher fracture toughness

  • Rolling ε =2.3 VS. ECAP ε =10


Objectives
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


Procedure
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


Microstructure
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


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


Mechanical properties
Mechanical Properties

  • Theoretically we expect the envelope expand to the right

Fracture Toughness

KIC

Yield Strength

σy


Mechanical properties1
Mechanical Properties

  • Theoretically we expect the envelope expand to the right

Fracture Toughness

KIC

Yield Strength

σy


Results
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.



Dislocations
Dislocations

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


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