INVESTIGATION OF HEAT TREATMENT ON THE PROPERTIES OF FRICTION STIR WELDSfsrl.byu.edu/presentations/Investigation.pdf · · 2005-06-24INVESTIGATION OF HEAT TREATMENT ON THE PROPERTIES

AEROMAT 2001PAGE: 1 T.W. Nelson

(801)-378-6233E-Mail: [email protected]

INVESTIGATION OF HEAT TREATMENT ON THE PROPERTIES OF FRICTION STIR WELDS

T. W. Nelson*, R. J. Steel* and W. J. Arbegast***Brigham Young University

Provo, UT**Lockheed Martin Manned Space Systems

New Orleans, LA

*This Research is sponsored by Lockheed Martin under IRAD M-40D.



Outline

• BackgroundQuench sensitivity of age hardenable aluminum alloysLast years results

• Objectives• Quench Sensitivity of alloys 2024 and 2219

ProcedureResults

• Effects of Pre- and Post-Weld Temper on 2219, 7075, and 2195

ProcedureResults

• Summary



Background• Many age hardenable aluminum alloys are “quench

sensitive”The rate of cooling from elevated temperatures can enhance the aging response



Background • Means of actively (weld side) cooling and heating the welds

Active cooling - spray mist (80 psi, 45°F) immediately behind toolActive heating – hot air (600°F) immediately behind tool



Background• Mechanical property response of A/P cooled and heated

FSW in 7075-T7351

0

10

20

30

40

50

60

70

1 10 100 1000Time (hours)

Stre

ngth

(Ksi)

&E

long

atio

n (%

)

7 0 7 5S A70 7 5A C70 7 5A H70 7 5P C70 7 5P H



Background• Correlation of NA and tensile failures

80

90

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170

180

0 0.5 1 1.5 2 2.5 3

Distance (in)

Har

dnes

s (H

v 10

0g)

7075SAAC-0hrs

7075SAAC-96hrs

7075SAAC-1000Hrs



Background• Fracture morphologies at 0, 96 and 1000 hours PWNA

all tensile specimens in 7075 failed in the HAZfailure location moved outward with increasing PWNA time

7.0X

0 hrs PWNA 1000 hrs PWNA96 hrs PWNA



Summary of previous results

• Alloy 2195-T8 exhibits relatively low quench-sensitivity Ultimate tensile and yield strengths were affected <3% (falls within standard deviation)

• Alloy 7075-T7351 exhibits good quench-sensitivity Tensile and Yield strengths improved by more than 8% in passively cooled, and 10% in actively cooled AFSW.



Objectives

• Evaluate the effects of active cooling/heating conditions on FSW in 2024-T3 and 2219-T87

• Investigate effects of various pre- and post-weld temper conditions on mechanical properties and corrosion for 2219, 2195 and 7075

Effect of active cooling/heating conditions on the same



Procedures for Active Cooling and Heating

• Active heating and cooling of 2024-T3 and 2219-T87 Test panels 6mm X 20 cm x 60 cm (0.25” x 8” x 24”) were produced using near optimized parameters using tools provided by LockheedMartinEstablish baseline FSW mechanical properties (no active/passive conditions)Produce FSW under various A/P cooling and heating conditions

Actively cooled (AC)-chilled water 7°C (45°F) spray mist immediately behind tool on surface of weldActively heated (AH)-hot air 317°C (600°F) immediately behind tool on surface of weld

Thermocouples were imbedded at the centerline of each weld



Procedures• Microhardness and tensile test coupons for each A/P

condition were removed from two AFSW panels



Procedures

• Microhardness and tensile samples were removed from all welds

Tensile tests were performed in accordance with ASTM E8PWNA tests were performed at intervals of <5, 24, 48, 72, 96 and 1000 hours

Microhardness traverses were made along centerline of transverseFSW samples (non-mounted samples)

Tests were performed at time intervals of <5, 48, 96 and 1000 hours after welding



Procedures• Base material properties

1018

Elong.(%)

5750

Yield Strength

(Ksi)

69T87221970T32024

UTS (Ksi)

TemperAlloy



PWNA Response in 2219-T87 and 2024-T3

• Mechanical property response to the active heating and cooling conditions

2024-T3 exhibits little or no changes in NA response due to active heating or cooling2219-T87 exhibits little or no natural aging after FSW

0

10

20

30

40

50

60

1 10 100 1000

Time (hours)

Stre

ngth

(Ksi)

&E

long

atio

n (%

)

BaselineActively heatedActively Cooled

0

10

20

30

40

50

60

70

1 10 100 1000Time (hours)

Stre

ngth

(Ksi)

&E

long

atio

n (%

)

Baseline

Actively Heated

Actively Cooled

Alloy 2024-T3 Alloy 2219-T87



PWNA Response in 2219-T87

• Natural aging response across weldsLittle or no NA response in 1000 hrs

Some NA response at 1500+ hours

Active heating minimized NA Failures consistently in DXZ

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0 10 20 30 40 50 60 70Distance (mm)

Har

dnes

s (H

v 10

0g)

48 Hours

96 Hours

1000 Hours

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80

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120

140

160

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0 10 20 30 40 50 60 70Distance (mm)

Har

dnes

s (H

V 10

0g)

0 Hours48 Hours

96 Hours1000 Hours

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120

140

160

180

0 10 20 30 40 50 60 70

Distance (mm)

Har

dnes

s (H

V 10

0g)

0 Hours48 Hours

96 Hours1000 Hours2219-T87 Actively Heated

2219-T87 Baseline Condition

2219-T87 Actively Cooled



PWNA Response in 2024-T3• Natural aging response across welds

Actively cooling only slightly enhances NA of HAZMore severe quenching may improveFailures consistently in HAZ

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0 10 20 30 40 50 60 70

Distance (mm)

Har

dnes

s (H

v 10

0g)

0 Hours48 Hours96 Hours1000 Hours2024-T3 Baseline Condition

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0 10 20 30 40 50 60 70Distance (mm)

Har

dnes

s (H

v 10

0g)

0 Hours48 Hours

96 Hours1000 Hours

2024-T3 Actively Heated60

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100

120

140

160

180

0 10 20 30 40 50 60 70Distance (mm)

Har

dnes

s (H

v 10

0g)

0 Hours48 Hours96 Hours1000 Hours

2024-T3 Actively Cooled



Summary of Active Heating and Cooling• 2219-T87

Generally, active heating or cooling had little or no effect on the PWNA response

However, may need more time to assess

Active heating produced consistent failures in the DXZ

• 2024-T3 exhibited moderate natural aging post FSWActive cooling exhibited slight improvement on the PWNA response



Procedures-Evaluation of Pre and Post Weld Temper Conditions

• Pre and Post weld temper conditions in alloys 2219, 2195 and 7075

n/ayesyesyes

n/an/an/a

n/ayesyesyes

Active heat/cool

nononono

nonono

nononono

Active heat/cool

Anneal, FSW, SHT, no Stretch, AgeSHT, FSW, no Stretch, Age

SHT, no Stretch, FSW and AgeSHT, no Stretch, Age, FSW, Overage

-T8-T8-T8-T7

OT4T37T87

2195

Anneal, FSW, SHT and AgeSHT, FSW and Age

SHT, Age, FSW, Overage

-T6-T6-T7

T0T4T7

2219

Anneal, FSW, SHT and AgeSHT, FSW and AgeSHT, Age, and FSW

SHT, Age, FSW, Overage

-T6-T6-T6-T7

OT4T6T6

7075

Sequence of EventsFinal Temper

Weld Temper

Alloy



Procedures-Evaluation of Pre and Post Weld Temper Conditions

• Out of 24” weld panels:One half was tested in as-welded condition, and One half was post weld heat treated then testedWelds were PWNA for no less than 5 days prior to heat-treatment and testing

• Microhardness and tensile tests were removed from both halves of each panel to characterize both the as-welded and PWAA responses

Tensile tests were performed in accordance with ASTM E8Microhardness traverses were made along centerline of transverse FSW samples (non-mounted samples)



Procedures• Base material properties

126372T7???T4

111710102018

Elong.(%)

731457422711

Yield Strength

(Ksi)

83T632O707569T8760T6252T425O2219

UTS (Ksi)

TemperAlloy



Procedure

• Weld and heat treatment schedule for the various alloys

Alloy Temper Weld date HT date Heat Treatment7075 T4-T6 29-Jan-01 5-Feb-01 24 hrs @ 250 F7075 T6-T7 29-Jan-01 5-Feb-01 13 hrs @ 250 F7075 T0-T6 3-Feb-01 8-Feb-01 1hr @ 900 F, 24 hr @ 250 F7075 T6-T7 29-Jan-01 4-May-01 13 hrs @ 250 F 2195 T0-T8 21-Dec-01 4-Apr-01 36 hrs @290F, 40 deg./hr increase from RT2195 T8-T7 28-Mar-01 4-Apr-01 15 hrs @250 F2219 T0-T6 20-Dec-00 5-Jan-01 1hr @ 995 F, 36 hrs @ 375 F2219 T4-T6 14-Feb-01 4-Jun-01 36 hrs @ 375 F2219 T6-T7 12-Feb-01 4-Jun-01 15 hrs @ 350 F



Results of Pre and Post FSW Temper Conditions in Alloy 2219

05

101520253035404550

Ult. Bas

eYiel

d Bas

e% Elong. B

ase

Ult. AH

Yield A

H% Elong. A

H

Ult. AC

Yield A

C% Elongati

on AC

Stre

ss (K

si),

Elon

gatio

n (%

) T4-T4T4-T6T6-T6T6-T7




• Artificial aging resultsO-T6 produce highest tensile and yield, but poor ductility

difficult to perform on large structures

Combination of T4 and T4-T6 could be functional but difficult

0

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20000

30000

40000

50000

60000

70000

80000

90000

T4-T4 T6-T6 T4-T6 T6-T7 T0-T6 T0-T0Heat Treatment

Tens

ile S

treng

th (p

si)

Baseline

Actively Heated

Actively Cooled

0

2

4

6

8

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T4-T4 T6-T6 T4-T6 T6-T7 T0-T6 T0-T0Heat Treatment

Elon

gatio

n (%

)

Baseline

Actively Heated

Actively Cooled

0

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20000

30000

40000

50000

60000

T4-T4 T6-T6 T4-T6 T6-T7 T0-T6 T0-T0

Heat Treatment

Yiel

d St

reng

th (p

si)

Baseline

Acttively Heated

Actively Cooled

c




• Artificial aging response across welds

O-T6 homogenized hardnessT4-T6 and T6-T7 overages hardness troughsT4-T4 left long enough, quassihomogenizes weld and HAZ

405060708090

100110120130140150160

0 10 20 30 40 50 60 70 80Distance (mm)

Har

dnes

s (H

V 10

0g)

T0T0-T6T4-T4T4-T6T6-T6T6-T7

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0 20 40 60 80Distance (mm)

Har

dnes

s (H

V 10

0g)

T4-T4T4-T6T6-T6T6-T7

60708090

100110120130140150160

0 10 20 30 40 50 60 70 80Distance (mm)

Har

dnes

s (H

V 10

0g)

T4-T4T4-T6T6-T6T6-T7

7075 Baseline Condition

7075 Actively Cooled 7075 Actively Heated




• Artificial aging resultsLittle effect from PWAA

Likely due to NO “stretch”

0

10000

20000

30000

40000

50000

60000

70000

T0 T0-T8 T3 T4 T8 T3-T8 T4-T8 T8-T7Heat treatment

Tens

ile S

tress

(psi

) SA

HA

WC

0

2

4

6

8

10

12

14


Elon

gatio

n (%

)

SA

HA

WC

05000

1000015000200002500030000350004000045000


Yiel

d St

ress

(psi

)

SA

HA

WC




• Artificial aging response across welds

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0 20 40 60 80

Distance (mm)

Har

dnes

s (H

V 10

0g)

T0T3-T8T4-T4T4-T8T8-T8T8-T7

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Distance (mm)

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T3-T8T4-T4T4-T8T8-T8T8-T7

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Distance (mm)

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T3-T8T4-T4T4-T8T8-T8T8-T7

2195 Baseline Condition

2195 Actively Cooled 2195 Actively Heated



Microstructure of SHT and Aged Welds• Photomacrographs illustrating differences in weld microstructure

after SHT and PWAA

•2219-0 - T8•Lazy “S” interface

•2195-0 - T8•Grain Growth thought entire weld nugget

•7075-0 - T6•Grain Growth along top surface of weld



Microstructure of SHT and Aged FSW 7075

• Grain growth along top surface of FSW during solution heat treatment of 7075-0

Abnormal Grain Growth



SUMMARY OF A/P COOLING STUDIES• Alloy 2219-T87 exhibits little or no natural aging post FSW

Active cooling does not improve the NA response Active heating results in DXZ failures

• Alloy 2024-T3 exhibits moderate NA post FSWActive heating and cooling seem to have little effect on NA response

Could possibly be effective with high quench rate

• Alloy 2195-T8 exhibits relatively low quench-sensitivity Ultimate tensile and yield strengths were effected <3% (falls within standard deviation)Natural aging of FSW in T8 conditions stabilizes after ~5 days

• Alloy 7075-T7351 exhibits good quench-sensitivity Tensile and Yield strengths improved by more than 8% in passively cooled, and 10% in actively cooled AFSW.As-welded NA response “never” stabilizes



Summary of Pre- and Post-Weld Tempers• Pre and post weld tempers in alloy 7075 exhibited the most dramatic

effect on propertiesO to T6 – produced highest tensile and yield strengths

Ductility was very poorImpractical for large structures

T6 to T7 produce additional over aging in HAZ as anticipatedT4 to T4 and T4 to T6 conditions poses some interesting results

Second only to O-T6 in TensileShould be able to improve yield with proper PWHT

• Pre and post weld tempers in alloy 2195 had little effect on propertiesMost likely due to no “stretch” prior to PWHT

Higher GB area resulted in higher number of course GB precipitatesT3 and T4 to T8 condition exhibit the highest tensile and yield, but still not as high as the as-welded T87 PWAA may be more effective with a PW “stretch”

Hard to introduce?Grain growth in weld nugget after SHT is major problem



Recommendations for Future Work• Improve effectiveness of active cooling or combination of

active/passive cooling in alloy 7075.

• Investigate the effects other PW treatments on the mechanical properties in A/P cooled AFSW.

• Detailed microstructural characterization.

Documents

INVESTIGATION OF HEAT TREATMENT ON THE PROPERTIES OF FRICTION STIR WELDSfsrl.byu.edu/presentations/Investigation.pdf · · 2005-06-24INVESTIGATION OF HEAT TREATMENT ON THE PROPERTIES