Transcript 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)
Deformation process
that imposes high
strains with the
benefit of retaining
the cross-sectional
area of the work
piece.
Shear Plane
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
F-22
Dodge Viper
10%
Reduction/
6%
efficiency
Space Shuttle
Thrust
High
Weight
=Higher Acceleration
Microstructure = Performance
Properties
Performance
Processing
Microstructure
Two Ways to Strengthen
Metals
Precipitation Hardening
Strain 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 occurs when a ductile
metal becomes harder and stronger as it is
plastically deformed
– rolling, compression, and ECAP
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
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
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
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
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
Theoretically we
expect the
envelope expand
to the right
Fracture
Toughness
KIC
Yield Strength
σy
Mechanical Properties
Theoretically we
expect the
envelope expand
to the right
Fracture
Toughness
KIC
Yield Strength
σy
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.
Thank You
Dislocations
Linear or one dimensional defects where some of
the atoms are misaligned.