Quantifying microstructural features and finding structure-property linkages in aging process of Al6061

Ali Khosravani

ME8883 Materials Informatics

Introduction

Alloys in this group have high strength-to-weight ratio Good weldability good formability good corrosion resistance

Solid Solutio

n

Coherent Precipitates

(β”)

Partially Coherent(β

’)

Incoherent Precipitates(

β)

Soft

Strength increase Peak Strength Overaged

Application Aircraft fittings

camera lens mounts

electrical fittings and connectors

brake pistons, hydraulic pistons

valves and valve parts

bike frames.

Strengthen by Precipitation of Mg2Si, higher levels of Mg2Si leeds to higher strength

MicrostructureMicrostructural features of

impact exist at different length scales

• Coherent GP zones and semi-coherent precipitate particles (TEM or SEM)

Volume fraction

Size (nm)

Aspect ratio

Spacing (nm)

• Al-Fe-Si-type constituent particles (OM) Volume fraction

Size (microns)

Aspect ratio

Spacing (microns)

• Grain structure, including degree of recrystallization and texture (EBSD)

Size (microns)

Aspect ratio

Texture

Mechanical Properties and microstructure

Mechanical Properties is a result of :

Precipitate hardening strengthen material

Precipitate Volume fraction Precipitate Size (nm) Precipitate Aspect ratio Precipitate Spacing (nm) Particle Volume fraction Particle Size (microns) Particle Aspect ratio Particle Spacing (microns) Grain structure Grain Size Grain Aspect ratio Texture Grain Boundary

Experiments

Mechanical testing Uniaxial Tensile Test

Five tests were run for each condition.

ASTM E8-13a (Round specimens with a diameter and gage length of 0.25” of 1” respectively.

The machine was run at a constant cross head speed to achieve a strain rate of 0.005 in/in /s

Al 6061 Specimen Type

Average Yield

Strength (ksi)

Average Ultimate Tensile Strength

(ksi)400F HT 43.136 46.400525F HT 26.022 33.188650F HT 13.493 24.439775F HT 8.633 20.321AR RD 44.114 47.660

Microstructural Datasets

EBSD 75 scans and combined

into scan size of7x7 mm2

4 µm resolution

SEM 10 BSE images at random

regions

View field: 100x100 µm2

Optical Microscope (OM) 10 images at random

regions

View field: 800x600 µm2

EBSD dataset

Grain aspect ratio =

• Grain size distribution Grain size distribution is

calculated based on number of pixels in each grain.

• Grain aspect ratio distribution The aspect ratio is defined

as the length of the minor axis divided by the length of the major axis and thus ranges from 0 to 1

Original Image Corrected Image Segmented Image

400F

775F

OM dataset Images were corrected and segmented Volume fraction, Size, Aspect ratio, and Spacing of

particle were measured

Chord Length

0 50 100 150 200 250 300 350 400 450 5000

1

2

3

x 10-4

Number of Pixels

Freq

uenc

y

AR

400 F

525 F

650 F

775 F

Calculating chord lengths row by row on x direction and column by column in y directions on binary images

Performing this operation over 10 images

TEM images required to provide information about precipitate in higher resolution and information about precipitate/matrix interface

SEM dataset

Images were segmented Volume fraction, Size, and Spacing of particle were

measured

2-Point Statistics vs Measures Values

2-point statistics contains all information about particle size, aspect ratio, volume fraction and their spacing.

PCA can be performed on 2-point statistic instead of the calculated parameters (Size, spacing, aspect ratio)

PCA on 2-Point Statistics

-40 -20 0 20 40 60-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

PC 1

PC

2

AR400 F525 F650 F775 F

-40 -20 0 20 40 60-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

PC 1

PC

3

-0.3 -0.2 -0.1 0 0.1 0.2-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

PC 1

PC

2

AR400 F525 F650 F775 F

-0.3 -0.2 -0.1 0 0.1 0.2-0.03

-0.02

-0.01

0

0.01

0.02

0.03

PC 1

PC

3

PCA on Chord length(Particle Spacing),

Size, Aspect Ratio

-30 -20 -10 0 10 20 30 40 50-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

PC 1

PC

2

AR400 F525 F650 F775 F

-30 -20 -10 0 10 20 30 40 50-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

PC 1

PC

3

PCA on 2-Point Statistics

Averaging on Measured Values Image dimensions from each OM,

EBSD, and SEM datasets are

different.

The images were taken at random

regions on sample EBSD

OMSEM

To combine all Data together, OM and SEM datasets need to be averaged out

fr00

150 200 250

150

200

250

0.01

0.02

0.03

0.04

fr11

150 200 250

150

200

2500.92

0.93

0.94

0.95

-50 0 50

50

-50

0

0

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50

0

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50

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0

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50

150 200 250

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0.04

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0.04

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0.02

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0.03

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0.01

0.02

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0.04

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0.01

0.02

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0.04

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0.02

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0.04

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0.01

0.02

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0.01

0.02

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0.04

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0.01

0.02

0.03

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0.01

0.02

0.03

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0.01

0.02

0.03

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0.01

0.02

0.03

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0.04

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0.02

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0.04

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0.02

0.03

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0.01

0.02

0.03

0.04

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0.02

0.03

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250

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0.02

0.03

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0.02

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0.01

0.02

0.03

050

-50050

-50050

-50

050-500

50

-50

050

-50050

-50050

-50

050

-50

2-point Statistics in quantifying each microstructural features

2-point statistics contains all information about particle size, aspect ratio, volume fraction and their spacing.

PCA can be performed on 2-point statistic instead of the calculated parameters (Size, spacing, aspect ratio)

PCA on Average values from optical images (2-Point Statistics) and EBSD values (Grain size, Grain

aspect ratio)

-20 -10 0 10 20 30 40-0.15

-0.1

-0.05

0

0.05

0.1

PC 1

PC

2

AR

400 F

525 F650 F

775 F

-20 -10 0 10 20 30 40-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

PC

3

PC 1

Principal Component Analysis

Structure-property (Yield Strength) linkages

-20 0 20 405

10

15

20

25

30

35

40

45

Yie

ld S

tre

ng

th (

ksi)

PC 1

AR400 F525 F650 F775 F

-0.2 -0.1 0 0.1 0.25

10

15

20

25

30

35

40

45

Yie

ld S

tre

ng

th (

ksi)

PC 2

-0.1 -0.05 0 0.05 0.15

10

15

20

25

30

35

40

45

Yie

ld S

tre

ng

th (

ksi)

PC 3

Structure- property (Ultimate Tensile Strength) linkages

-20 0 20 4020

25

30

35

40

45

50

Ulti

ma

te T

en

sile

Str

en

gth

(ksi

)

PC 1

AR400 F525 F650 F775 F

-0.2 -0.1 0 0.1 0.220

25

30

35

40

45

50

Ulti

ma

te T

en

sile

Str

en

gth

(ksi

)

PC 2

-0.1 -0.05 0 0.05 0.120

25

30

35

40

45

50

Ulti

ma

te T

en

sile

Str

en

gth

(ksi

)

PC 3

Future work

High Throughput Experiments

EBSD

OMSEM

Local propertiesMeasuring local properties through nano- and miro-indentation

Local microstructureCollecting EBSD and OM images at the same area, and SEM images at the known locations within marks

Acknowledgments

Dr. Surya Kalidindi Dr. Tony Fast

Jordan Weaver Jon Yabansu Ahmet Cecen Andrew Castillo