FSW .pdf

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FILE: MET 492-082 Week 6 Rev New

REVISION DATE: 01 October 2003PAGE: 1

W. J. Arbegast

(605)-394-6924E-Mail: [email protected]

South Dakota School o f Mines and Technology

AMPSDSM&T

Advanced Mater ials Processing Center Advanced Mater ials Processing Center

Week 6

Friction Stir Joining:

Characteristic Defects

William J. Arbegast

Director, Advanced Materials Processing Center

South Dakota School of Mines and Technology

Rapid City, South Dakota

MET 492-Special Topics

Friction Stir Processing

October 8, 2003

7/16/2019 FSW .pdf




W. J. Arbegast



AMPSDSM&T


Outline

Questions from previous week

Review of Quiz #3

Definition of a Defect

Source of Defects

Defect Types

Effect of Defects on Lap Joint Properties

Short Quiz #4

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W. J. Arbegast



AMPSDSM&T


What Is a Characteristic Defect in a Friction Stir Weld?

• A “ Characteristic Defect” is defined as a Microstructural or

Geometric Anomaly peculiar to a FSW that adversely affects

Form, Fit or Function.

• An “ Indication” is defined as a Microstructural or Geometric

Anomaly that DOES NOT adversely affects Form, Fit or Function

of a friction stir weld- BUT MAY NOT BE DESIRABLE

• A “ Defect” may adversely affect any or all of the following

properties

• Mechanical Properties (Ultimate, Yield, Elongation)

• Dynamic Properties (Fracture and Fatigue)

• Corrosion Resistance• Formabili ty and Ducti lity

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W. J. Arbegast



AMPSDSM&T


What Is a the Source of Defects in a FSW?

• Defects in Friction Stir

Welds are related to

Processing Temperatures,Metal Flow Patterns, and

Joint Geometry

• Both Processing

Temperatures and MetalFlow Patterns are a

Function of Processing

Parameters and Pin Tool

Design

• Joint Geometry is a

function of Fit-up and

Alignment

Begin Tip

Radius

Bottom Of

Tool

DISPLACED DOWN

AND BEHIND

PULLED INTO

FLOW ARM

THREADS ALTERNATELY FILL FROMLEADING THEN FLOW ARM MATERIAL IN

INITIAL INTERLEAVING ZONE

LAMINAR

INTERLEAVING

VORTEX SWIIRL

ZONE

FLOW ARM MATERIAL

PRIMARILY FROM

RETREATING SIDE

ADVANCING SIDE MATERIAL

INTERLEAVES WITH LEADING

SIDE MATERIAL

INITIAL FILL ZONE

VORTEX SWIRL ZONE AROUND PIN RADIUS

SHOWS VERY LITTLE VERTICAL FLOW MOTION

Based on Metallographic analysis of David Braun, LMMSS

Longitudinal View

Upper Material Feeds

Shoulder Zone

Initial Deformation

Zone

Extrusion

Zone

Vortex Swirl

Zone

Pmax

Vf

Shoulder

Zone

Pre- Heat

Zone

Forging

Zone

Initial Deformation

Zone

Extrusion

Zone

Vortex Swirl

Zone

Pmax

Vf Vf

Shoulder

Zone

Pre- Heat

Zone

Forging

Zone

FRONTREAR

t

ht

he

hs

Vf

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W. J. Arbegast



AMPSDSM&T


* Defects in BLUE are easily controlled by RPM and IPM parameters.** Defects in RED are related to penetration (LOP) and seam tracking (LOF).

FSW Processing Maps Can Be Used to

Determine Points of Optimum Metal Flow and

Points of Defect Formation

I P M

RPM

Faying Surface*

Scalloping*

Collapsed Nugget*

Wormhole*

Chip LOF*

Root Flow*

Surface Galling*

Surface LOF*

Ribbon Flash*

COLD

HOT

Lack of Penetration (LOP) **

Lack of Fusion (LOF) **

P r o c e s s

E n v e l o p eOperatingWindow

NominalSchedule

Excessive Indentation**

What are the Types of Defects in a FSW?

• Cold Processing Defects• Wormhole

• “ Chip” Lack of Fill

• Scalloping• Cold Lap (lap joints)

• Hot Processing Defects• Ribbon Flash

• Surface LOF

• Nugget Collapse• Surface Galling

• Faying Surface

• Root Flow Defect

• Sheet Thinning (lap joint)

• Geometry Related Defects• Lack of Penetration (LOP)

• Lack of Fusion (LOF)

• Excessive Indentation

7/16/2019 FSW .pdf




W. J. Arbegast



AMPSDSM&T


What Is a “ Wormhole” Defect in a FSW?

Description

An advancing side tunnel of inadequately consolidated and

forged material running in thelongitudinal direction.

Cause

Insufficient metal flow into theZone I interleaving area on theadvancing side above the swir lZone IV.

Created by excessive travelspeed (ipm) for givenrotational speed (rpm)

Cold weld

Too low weld pitch

Effect on mechanical properties

Severe wormhole creates areduction in mechanicalproperties

Inadequate fill of Advancing

Side above Swirl Zone

Advancing Side

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W. J. Arbegast



AMPSDSM&T


What Is a “ Chip Lack of Fill” Defect in a FSW?

Description

Similar to wormhole defect.

The void contains small

shards of metal that weresheared off the parent material(chips)

Cause

Insufficient heating results in

shearing and cutting of theparent metal leaving smallshards of metal wi thin thetunnel (wormhole).

Excessively cold weld

Too low weld pitch

Effect on mechanical properties Severe chip LOF creates a

reduction in mechanicalproperties

Advancing Side

Chip or

Shards of

Metal inVoid

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W. J. Arbegast



AMPSDSM&T


What Is a “ Scalloping” Defect in a FSW?

Description

A series of small voids locatedin the advancing side

interleaving Zone I along thelength of the weld.

Cause

Insuffic ient flow and metalforging in the forging zone.

Lower limiting case of thewormhole defect

Moderately cold weld

Insufficient forge pressure

Too low weld pitch


Severe scalloping will show areduction in mechanicalproperties

Moderate scalloping may notshow effect on properties

Fracture Surface of Tensile Specimen

Longitudinal View

Welding Direction

Interlayer

Voids

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W. J. Arbegast



AMPSDSM&T


What Is a “ Ribbon Flash” Defect in a FSW?

Description

Excessive expulsion of material on the top surface

leaving a corrugated or ribbon-like effect along the retreatingside

Cause

Excessive forge load or plungedepth

Thickness mismatch betweenadvancing side and retreatingside

Excessively hot weld

Too high weld pitch

Effect on mechanical properties Excessive heating may result

in reduction in properties

Excessive flash may reducefatigue life

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W. J. Arbegast



AMPSDSM&T


What Is a “ Surface Lack of Fill” Defect in a FSW?

Description

A continuous or intermittenttop surface void on the

advancing side

Cause

Insufficient flow arm formationacross top surface

Insufficient forge pressure Improper backside support

Insufficient plunge depth.

Separation of the plates

Effect on mechanical properties Excessive surface lack of fi ll

may result in reduction inproperties

Advancing Side Advancing Side Advancing Side

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W. J. Arbegast



AMPSDSM&T


How Does Pressure Distribution Affect Surface Fill?

Anvil

Pin Diameter Lead Trail

1Anvil

Pin Diameter Lead Trail

2

Pin Diameter

Anvil

Lead Trail

3Anvil

Lead TrailPin Diameter

4

Shoulder Zone/

Flow Arm

Shoulder Zone/

Flow Arm

Retreating SideExtrusion Zone

Advancing SideExtrusion Zone

Swirl / Vortex

Zone

Advancing Retreating Advancing Retreating

Advancing Retreating Advancing Retreating

7/16/2019 FSW .pdf




W. J. Arbegast

(605)-394-6924E-Mail: [email protected] Dakota School o f Mines and Technology

AMPSDSM&T



BP BP

NBP NBP

NBP BP

BP NBP

1 2

3 4 NBP = No Back Pressure BP = Back Pressure

Retreating Side

Flow Arm

shoulder affected

zone

Retreating Side

Flow Arm

Shoulder affected

zone

Retreating Side

Extrusion Zone

Material

Retreating Side

Extrusion Zone

Material

Retreating Side

Flow Arm

shoulder affected

zone

Retreating SideExtrusion Zone

Material

Advancing Retreating

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W. J. Arbegast


AMPSDSM&T



Retreating

Side Extrusion

Zone Material

Flow Arm

Shoulder

Affected Zone

Swirl orVortex Zone

Beneath Pin

Tip

Cavity on Advancing side to be

filled with shoulder zone and

Advancing Side material

Ripple pitch same as weld

pitch- ie, rpm/ipm

Sample prepared with no

backside pressure on

retreating side

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W. J. Arbegast


AMPSDSM&T


What Is a “ Nugget Collapse” Defect in a FSW?

Description

Improper formation of DXZnugget shape

Cause

Excessive flow arm formation

Excessive material flow intoZone I advancing side


Too high weld pitch


Excessive heating may resultin reduction in properties

Excessive nugget collapsemay reduce properties

Excessive Flow Arm Formation

and injection of material into

Advancing Side (Zone I)

Collapse of DXZ Nugget

Advancing Side

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W. J. Arbegast


AMPSDSM&T


What Is a “ Surface Galling” Defect in a FSW?

Description

Galling and tearing of themetal on the top surface of theweld beneath the pin tool

Cause

Sticking of metal to pin tool


Too high weld pitch


Severe surface gall ing mayreduce mechanical properties

7/16/2019 FSW .pdf




W. J. Arbegast


AMPSDSM&T


What Is a “ Faying Surface” Defect in a FSW?

Description

Discontinuous / continuousline of second phase particles

@ the location remnant of theoriginal faying surface

Cause

Original joint faying surfacenot broken up during FSW


Too high weld pitch

Contamination of fayingsurface.

Improper seam tracking (toofar offset to advancing side)

Effect on mechanical properties Excessive faying surface

defect may result in reductionin properties1000X

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W. J. Arbegast


AMPSDSM&T


What Is the Point of Divergence?

Faying Surface is Contained

Within Thread Extrusion Zone

And is Consumed

Vf

w CL

ADVANCING

RETREATINGExtrusion Zone

Initial DeformationZone

Xdc2 r s

Vf

w CL

ADVANCING

RETREATINGExtrusion Zone

Initial DeformationZone

Xdc2 r s

Faying Surface is at Periphery

of Thread Extrusion Zone and is

Partially Broken Up

POD POD

The Point of Divergence (POD) is that point within the Initial Deformation

Zone ahead of the pin tool where the original Faying Surface begins to

transition around the pin tool

Too Hot

A Point of Divergence (POD) too far ahead of the pin tool results in the

faying surface defect

7/16/2019 FSW .pdf



REVISION DATE: 01 October 2003

PAGE: 18

W. J. Arbegast

(605)-394-6924

E-Mail: [email protected]


AMPSDSM&T


What Is a “ Root Flow” Defect in a FSW?

Description

Chevron shaped f low patternsvisible on backside (root)

surface Cause

Excessive metal flow withinswir l zone beneath pin tip(Zone IV) and “ breakout” of flow patterns to back surface

Excessive pin length

Improper pin tip radius


Too high weld pitch


Excessive Root Flow Defectmay result in reduction inproperties

320 Demo Panel4.5X

Advancing Side Standard 320 Tool

0.320” 2195 (Root Flow)

Advancing Side

MP-1-M24.5X0.250” 2195 (Root Flow)

Flat Nosed Tool

Bottom

View of

Weld

Good

Root

Structure

Root

FlowDefect

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


What Is a “ Lack of Penetration” Defect in a FSW?

Description

Remnant of or iginal fayingsurface on root side of weld

beneath DXZ Cause

Inadequate recrystallization of Swirl Zone IV on back surface

Insuffic ient metal flow in SwirlZone (IV)

Inadequate pin length

Improper pin tip radius

Cold weld

Too low weld pitch


Excessive Lack of PenetrationDefect may result in reductionin properties

LOP

Faying

SurfaceRemnant

DXZ

Insuff icient Nugget Penetration

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


LOF

What Is a “ Lack of Fusion” Defect in a FSW?

Description

Remnant of or iginal fayingsurface on root side of weld

beneath DXZ

Cause

Improper seam tracking

Weld seam is missed and

consequently one portion of aweld joint is not fused to anadjacent portion of a weld joint


Excessive Lack of Fusion

Defect may result in reductionin properties

Faying

Surface

Remnant

DXZ

Sufficient Nugget Penetration but

Joint is Missed

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


What are the Defects in a FSW Lap Joint?

Lap welds have two additional defect types in addition to thoseobserved in butt joints

SHEET THINNING DEFECT

COLD LAP DEFECT

Cold Lap Defect

Effective Shear Area

Retreating

Sheet Thinning Defect

Advancing

50x or iginal

Cold Lap Defect

Advancing

Effective

Shear Area


Retreating

Faying

Surface

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


200X

TMZ DXZ

Sheet

Thinning

Defect

200X

TMZ DXZ

Sheet

Thinning

Defect

What is a Lap Joint Sheet Thinning (ST) Defect?

Description

Up-turning (or down-turning)of original joint line faying

surface resulting in reduct ionof sheet thickness in a lapweld

Cause

Hot processing parameterssetting up excessive vertical

flow patterns Faying surface is “ pulled” up

or down in the TMZ as a resultof these flow patterns


Increasing the Sheet Thinning(ST) defect may decreases thelap shear strength

Increasing the ST defectreduces fatigue life

Advancing Side

Joint Line/

Faying

Surface

Top Sheet

Bottom Sheet

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


What is a Lap Joint Cold Lap Defect (CLD)?

Description

A “ Dragging” of the original joint line into the DXZ on the

retreating side without mixingor consolidation

Cause

Cold processing parametersresulting in inadequate verticalmixing within DXZ

Faying surface is “ pulled”around pin and into the DXZ asa result of these flow patterns


Increasing the Cold Lap Defect

(CLD) may reduces the lapshear strength

Retreating Side

Joint Line/

Faying

Surface

Top Sheet

Bottom Sheet

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PAGE: 24

W. J. Arbegast

(605)-394-6924



AMPSDSM&T


What is a the Effective Shear Area (ESA)? Description

The effective Shear Area is that area where the faying surface in a lap joint isCONSUMED AND CONSOLIDATED to produce a SOUND JOINT

It is the remaining area within the DXZ when the Cold Lap Defect (CLD) is

subtracted from the width of the DXZ along the original joint line


The Effective Shear Area (ESA) is that area that carries the load dur ing a lapshear test of a lap joint

Increasing the ESA increases the lap shear strength of a joint

50x or iginal

Cold Lap Defect

Advancing

Effective

Shear Area


Retreating

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


How Do Processing Parameters Affect ST and CLD? The Sheet Thinning and Cold Lap Defect are “ Competing” defects

HOT welds INCREASE Sheet Thinning and DECREASE Cold LapDefect

COLD welds DECREASE Sheet Thinning and INCREASE Cold LapDefect

50 x

EffectiveShear Area

Sheet

Thinning

Cold Lap DefectLeading

5.0 x

Leading

FSW Direction

0.080”Sheet

50 x

EffectiveShear Area

Sheet

Thinning


5.0 x

Leading

FSW DirectionFSW Direction

0.080”Sheet

Advancing

50 x

EffectiveShear Area

Sheet

Thinning


5.0 x

Leading

FSW Direction

0.080”Sheet

50 x

EffectiveShear Area

Sheet

Thinning


5.0 x

Leading

FSW DirectionFSW Direction

0.080”Sheet

Advancing

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


How Do ST and CLD Affect Joint Strength? By controlling the direction of welding, the ST Defect can be

“ included” (Type I Joint) or “ excluded” (Type II Joint) from the loadpath in a lap shear test.

Type I

Sheet Thinning in Load PathCold Lap Defect

Effective Shear AreaFSW Direction

Pin Tool Rotation

Free Edge on Trailing Side+ST: reduce str ength

-ST: no effect on strength

Sheet Thinning in Load PathCold Lap Defect

Effective Shear AreaFSW DirectionFSW Direction

Pin Tool Rotation

Free Edge on Trailing Side+ST: reduce str ength

-ST: no effect on strength

Type II

Free Edge on Leading Side

+ST: no effect on strength

-ST: reduce strength

Cold Lap Defect in Load Path

Type II

Free Edge on Leading Side

+ST: no effect on strength

-ST: reduce strength

Cold Lap Defect in Load Path

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


How Do ST and CLD Affect Joint Strength? Lap Shear Strengths is generally higher for Type II Joints

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0.050 / 0.050 0.050 / 0.063 0.063 / 0.063 0.050 / 0.080 0.063 / 0.080 0.080 / 0.080

Welded Thickness (top / bottom sheet - in ches)

Load

(lbs)

Type II

Type I

CCW Pin Tool Rotation

Type II - Free Edge on Leading Side

Type I - Free Edge on Trailin g Side

Lap Shear Strength (pounds per inch of weld) for varioussheet thickness combinations- 2024 aluminum

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


How Do ST and CLD Affect Fatigue Life? Placing the Sheet Thinning Defect in the Load Path can reduce fatigue

life for lap joint tests and “ peel” tests

y =5089x-0.179

R2

=0.997

y =5389.9x-0.1793

R2

=0.9999

0

200

400

600

800

1000

1200

1400

1600

1000 10000 100000 1000000

Cycles

L o a d ( l b s )

Type II

Type I

CCW Pin Tool Rotation

Type II - Free Edge on Leading Side

Type I - Free Edge on Trailing Side

y =528.71x-0.1944

R2

=0.9988

y =737.12x-0.2699

R2

=0.9515

0

50

100

150

200

250

100 1000 10000 100000 1000000

Number of Cycles to Failure

L o a d ( l b s )

Type IV

Type III

Type IV

FSW Direction

Type III

Fatigue Propert ies for 0.080” /0.080” 2024 aluminum

Friction Stir Lap Welds

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PAGE: 29

W. J. Arbegast

(605)-394-6924



AMPSDSM&T


Summary

Defects in Frict ion Stir Welds are primarily related to Metal

Flow Patterns

Pin Tool Design and Joint Geometry can also induce

defects

Cold Welds can show defects unique to cold processing

parameters

Hot Welds have defect unique to hot processingparameters

Lap Joints have two additional defects over those seen in

butt joints (ST and CLD defects)

A defect is NOT A DEFECT UNLESS it adversely affectsFORM, FIT, or FUNCTION

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W. J. Arbegast

(605)-394-6924



AMPSDSM&T


References

W.J. Arbegast, E.R. Coletta and Z. Li, "Characterization of

Friction Stir Weld Defect Types" , presented at the TMS 2001

Annual Spring Meeting, New Orleans, LA, February 11-15,

2001

FSW .pdf

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