The Effect of Thermal-mechanical Treatment on Abnormal Grain Growth on Friction Stir Welded Al-Li 2195

Richard Wellnitz & Anthony D. Barajas

Dr Howard – project superviser

What is Abnormal Grain Growth?

SAMPLE H STD

Abnormal Grain Growth Normal Grain Growth

Massive Grains(.5-1 mm)

Small Rounded Grains (3-5 microns)

Objective To Find Out

Does Hot rolling have an affect on grain growth?Does cold rolling have an affect on grain growth?Does step heating have an affect on grain growth?

Possible Applications

Other possible applications

Other possible applications in pictures examples of cars trains planes etc.

Presentation Organization

Introduction TheoryMethods and EquipmentChartsDescription of ResultsSummary and Conclusions

Theory

Introducing a process of cold working or cold rolling may inhibit this formation of abnormal grain growth by breaking the structures along the slip plane.

Shifting along the Slip plane

Face Centered Cubic on 1 1 1 plane

The FSW equipment

FSW AT 200 RPM

4 IPM

TOOL ANGLE 3.5 DEG

POSITION CONTROL WITH 0.010 “HEEL PLUNGE

Plate and Oven Anneal Oven Temperatures

0

200

400

600

800

0 20 40 60 80 100

Time, min.

T, F

Plate

Oven

TinitTime to

reach 790

100 54 Toven=810 F200 51 tc=15 min.300 49400 45500 41600 35700 26790 0

ctte

fToTf

TT

Thermal Response of Hot Roll Furnace

t min

T F

0 7811 8386 873

11 88316 88221 90026 869

Grain Initiation Thermal History

750

800

850

900

950

0 10 20 30

time, min

T, F

Actual Thermal History of a Monitored Sample During Grain Initiation

Hot Roll Thermal Chart

750

800

850

900

950

0 5 10 15 20 25 30 35 40 45 50

Time,Minutes

T,F

OvenSample

5 880 81110 878 81115 829 79320 891 78625 932 78430 910 81335 867 81540 892 81945 851 82250 869 817

Sample layout

Cold Work Hot work Step Heating Samples

Bead on Plate down center of plate

Step Heating

Step heating-Initially brought up to 750 F And continually increased by 50 degrees each hour afterwards to 950 F

750 F

950 F

50 F

50 F

50 F

50 F 1 HOUR

1 HOUR

1 HOUR

1 HOUR

Time

Temp

Oven and samples heated to 750 degrees prior to step heating

Standard Samples

STD

H-Heated with hot roll samples

STD-FSW Only

ASAW – FSW and Solution Heat treatment

ASFSW- FSW Only

Rolling

Processing schedules

Hot work- 10%,20%,30%,40%Cold work- 5%,20%,25%,30%

T 1 T 2

% OF REDUCTION

THICKNESS OF SAMPLE

PolishingSamples surfaces were polished with silicon carbide

240 grit

400 grit

600 grit

800 grit

1200 grit

alumina suspension polish to .1 micron

Etching

Samples were etched with

10% Sodium Hydroxide solution – 60 seconds

Rinsed –distilled water

Washed in– 50% Nitric Acid Solution

Rinsed –distilled water

Etching- bringing out the grain

Results of Hot Roll

10%

20%

30%

40%

Reduction

.320

Original

Thickness

Results of Cold Roll

5%

20%

25%

30%

.320

Original

Thickness

Reduction

Conclusions

Substantial Grain growth occurs in Al-Li 2195Hot working doesn’t eliminate or reduce grain growthHot work might actually increase grain growthThere is substantial grain growth reduction above 20% cold rollingStep heating does not decrease grain growth

Suggested additional work

Image analysis for grain size (statistical)Additional cold work between 5% and 20%Further metallurgical testing for hardness toughnessTensile strength ductilityFatigue lifeMicroscopy

Acknowledgements

Bill Arbegast-AMPDr. Stone-METSantosh KoduriK.B. AnandSrikanth Labhala

Eric HendersonTyler EngstromColleen GustafsonCasey AllenBrian Tweedy

Discussion

Why is cold work effectiveAt what point is cold work effectiveDoes hot rolling increase the grain growth