Aluminum Extrusion Quality for Anodizing Characteristic · 6xxx – Al + Magnesium + Silicon (Soft)...

IHAA 17th Technical Symposium

Aluminum Extrusion Quality for Anodizing Characteristic

Jerome Fourmann – September 19-21, 2018 – Seattle, WA

17th Technical Symposium – 19-21 September, 2018 – Seattle, WA© Rio Tinto 2018

Proprietary Statement

The following information is the property of Alcan Primary Products Company LLC, a member of the Rio Tintocompanies (collectively "Rio Tinto"). This information is being provided to the attendees of the 17th TechnicalSymposium by IHAA under a limited right and license to use said information in furtherance of a businessrelationship with Rio Tinto.

Rio Tinto makes no representations or warranties to the attendees of the 17th Technical Symposium in relation tothe information contained herein and shall have no liability for 1) any actions taken by reliance on suchinformation; or 2) any actions taken by any individuals or entities who attendees of the 17th TechnicalSymposium chooses to share said information with.

2018 Rio Tinto – September 2018

© Rio Tinto 20173

“As pioneers in mining and metals, we produce materials essential to human progress.”

Commercial


Rio Tinto - An integrated aluminium supplier

4

Bauxite mines05 Alumina refineries04 Power stations08 Aluminium casthouses19 Customers550

8 Mt Secured power

3.6 Mt44 Mt In 60 countries


Outline

5

1. Aluminum alloys 2.Alloys selection

3.Extrusion process 4. Defects


Designation System For Wrought Alloys

6

• *1000 series: Al – dilute alloys Al > 99%

• *2000 series: Al + Cu

• *3000 series: Al + Mn

• *4000 series: Al + Si

• 5000 series: Al + Mg

• *6000 series: Al + Mg + Si

• *7000 series: Al + Zn + Mg/Cu

• *8000 series: Al + Other elements

* Most extrusions are made from these alloy series

Heat treatable alloys, other are non-heat treatable


2xxx – Al + Copper

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• Where strength is a primary consideration with good fracture toughness

Applications

Structural members aerospace & military (2014 / 2024)

Machining stock (2011)

DisadvantagesLow extrudability

High demands on cooling speed

Bad corrosion properties


4xxx – Al + Silicon

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Not widely used in extruded form, except:

• 4032

Forging stock for pistons where wear resistance

and thermal stability are required

• 4021

ABS brake components, machineable, strength

close to AA6061 / AA6082

http://www.alibaba.com/product-gs/312886722/Hydraulic_Manifolds_block.html


5xxx – Al + Magnesium

• Where good corrosion resistance is needed

• Where good weldability and good post-welded strength are required

• Alloys with useful strength (~5% Mg) are difficult to extrude

Applications

Ship superstructures

Cryogenic applications

Offshore construction

Automotive

9


6xxx – Al + Magnesium + Silicon (Soft)

• 6060 / 6063 / 6360 / 6560− Most popular extrusion alloys− Fast extruding, lower strength, anodize well− General applications i.e. door and window,

heat sinks, architectural, transportation

• 6463 / 6463A− Specialized “6063” type to give bright finish after

chemical brightening.i.e. tub and shower, picture frame

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6xxx – Al + Magnesium + Silicon (Medium Strength)

• 6061 / 6082 / 6005 / 6005A− Medium strength, transportation, ladders, scaffolding, general engineering, gas

cylinders, forging stock, welded construction…

11


7xxx – Al + Zinc-Magnesium

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• Where strength >6xxx is required, along with extrudability, ease of

quenching and weldability. Stress corrosion has to be managed

• Can be processed on standard presses

Applications

Bumpers systems

Automotive

Transportation

Military bridging

http://upload.wikimedia.org/wikipedia/commons/2/23/TGV-Duplex_Paris.jpg


7xxx – Al + Zinc-Magnesium-Copper

13

• Where high strength and toughness are required

• Available Complex process route, low extrudability - not compatible

with standard extrusion operations

Applications

Major structural members - Aerospace

Military application

Medical cylinders


8xxx – Other aluminum alloys

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• Other alloying elements: Li, Fe, Zr…

Applications

Al-Li: high stiffness, low density Aerospace structural components


Outline

15




Alloy Selection – extrudability

16

Extrudability falls with increasing flow stress

and lower melting point


Alloy Selection – Mechanical Properties


Alloy Selection – Heat treatment process

1xxx3xxx5xxx

Formal SHT*

2xxx7xxx

(Al-Zn-Mg-Cu)

SHT* in Press

6xxx7xxx

(Al-Zn-Mg)

Specialized ProcessDifficult to cast

Possible on most commercial presses

Some extruders specialize in these products

* SHT: Solution heat treatment

Natural ageing: ambient temperature slow hardness increase over timeArtificial ageing: heat treat. forming precipitates enhancing the properties


Outline

19



Photo courtesy of FEM, Schwäbisch Gmünd, Germany

© Rio Tinto 201817th Technical Symposium – 19-21 September, 2018 – Seattle, WA

Thermal profile of the extrusion process

20

Tem

pera

ture

ºC / ˚F

Billet supplier Dependent Extruder Dependent

PreheatingHomogenisationCasting Extrusion Cooling Ageing

6501200

500932

450842

185365

TimeDC casting mold


Temperature through the extrusion process

21

Extr

usio

n

0 5 10 15 20 25 30

Time (mins)

Tem

pera

ture

(oF)

100

200

300

400

500

600

700

800

900

1000

1100

1200

Criticalpreheatrange

Criticalquenchrange

Inductionfurnace

900oF/min250oC/min

Mg and Si in solution (solvus)

Melting starts (solidus)

Preheat

Quench 600

500

400

300

200

100

650

550

450

350

250

150

50

Tem

pera

ture

(oC

)

Process has to put Mg and Si in the correct form for ageing

Nano-sized MgSi precipitates


How is this metallurgical process monitored?

22

Billet temperatureExtrusion temperatureQuench rateAgeing temperature

= Thermal Profile of the Extrusion Process

http://propertybum.com/wp-content/uploads/2013/04/location-location-location-229730.jpg


Outline

23




Defects framework – the alloy influence

24

Common Extrusion Alloys

6360 “high performance”

6063 “general purpose”

6063 “high strength” -T54, -T65

6005A

6061 / 6351

6082

Soft Alloys

Medium Strength Alloys

Propertiesincrease

Extrudabilitydecrease


Defects framework – the extrusion process influence

25

EXTRUSION SPEED

POORSURFACEFINISH

SOFT ALLOY

COMPLEX SHAPE

INSUFFICIENT PRESSURE

SOFT ALLOY

MORE AVAILABLEPRESSURE

HIGH EXTRUSION RATIO

COMPLEX SHAPE

BILLET TEMPERATURE

LOW MECHANICAL PROPERTIES

TEARINGPICK-UPSURFACE MELTING

COARSE Mg Si2THICKSECTIONS

MAX PROPERTIES

NON-CRITICALPROPERTIES

OPERATING WINDOW


26

During Extrusion / Mill Finish

Pick-up

Speed Cracking

Die line

Front-end TW

Die streak

Longit. weld

Blister

Tearing

Micro die line

Back-end Coring

Snap mark

Hot spots

After Extrusion - Metallurgical

Coarse MgSi

Coarse grain

banding

Corrosion pitting

Spacer marking

Corrosion fretting

Inclusion cast-in

MgSi at grain

boundary

Orange peel

Corrosion fingerprint

Excess lubricant

Water stain

Inclusion extrusion process

After Anodization

Atmos. corrosion

Alkali corrosion

Spacer marking

White etch bloom

Dull finish

Inadequate rinse

Acid corrosion

Rinse water corrosion

Chloride contami.

Spangle

Coloring due to MgSi

Castle and moat


Welds

27


Pick-up

Speed Cracking

Die line

Front-end TW

Die streak

Longit. weld

Blister

Tearing

Micro die line

Back-end Coring

Snap mark

Hot spots


28

Transverse Weld Longitudinal Weld

ID OD

Back-end condition / Coring

Transverse weld (non-balance port)

Coring

Longitudinal welds

Welds definition


1- Longitudinal weld

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1- Longitudinal weld

30

Bad

Good


1- Longitudinal welds - can be unsatisfactory for several reasons

31


2- Metal flow in direct extrusion

32

Extrusion

Container

Die

Extrusion

Container

Die

Billet Surface ‘Drag’

Coring

Stem


2- Front-end flow: Transverse Weld

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Old billet

Transverse weld

Die stop mark

Continuous extrusion means “joints” billet to die pocket billet to billet

Mechanisms


3- Back-end flow: Coring

34


Streaks

35


Pick-up

Speed Cracking

Die line

Front-end TW

Die streak

Longit. weld

Blister

Tearing

Micro die line

Back-end Coring

Snap mark

Hot spots


Streaks – Industry context

36

Common problem for extruders

Difficult to identify the root cause: – Billet – Extrusion process– Finishing process

Streaking is revealed at last step of the process

Many contributing factors from previous steps Evidence removed after anodizing

Need to understand why before we can know how


Die lines / Micro die lines / Streaks

37

Aluminum

Mounting media

Die line: deep grove

Aluminum

Mounting media

Micro die line: fine lines Streaks: bands of dark or light colors

A

B

A

B


Textural streaks

38

TYPE ICaused by

contaminants

TYPE IICaused by die or profile design

TYPE IIICaused by

extrusion process


Textural streaks

39

Textural streak anodizedSurface topography 0.2µmVariable grain size and attack


Streaks - Dead metal zone

40

Contaminants that build up in dead metal zone

Dead Zone

Billet #

60

59

58

57

Die Face

Feeder Wall

Feeder

Die

Old metal

New metal

Core / mandrel

Rim of body


Pick-up

41


Pick-up

Speed Cracking

Die line

Front-end TW

Die streak

Longit. weld

Blister

Tearing

Micro die line

Back-end Coring

Snap mark

Hot spots


Pick-up

42

Coating of aluminum oxide on the die bearing exit


Not always pick-up

43

CrCrSi FeMgC FeFeO

Al

0 1 2 3 4 5 6 7 8 Pleine échelle 768 cps Curseur : 10.094 (0 cps )

Cl KNa KMg

O Cl

C

Al

0 1 2 3 4 Pleine échelle 731 cps Curseur : 10.094 (0 cps )

Example of carbon base lubricant


Grain size

44

After Extrusion - Metallurgical

Coarse MgSi

Coarse grain

banding

Corrosion pitting

Spacer marking

Corrosion fretting

Inclusion cast-in

MgSi at grain

boundary

Orange peel

Corrosion fingerprint

Excess lubricant

Water stain

Inclusion extrusion process


Orange peel

45

Bad partAppearance of the PCG area

Good partuniform grain


Coarse grain banding

46

Machining Grade AA6061

Standard AA6061


Coarse grain banding – Causes and prevention measures

47

• Objective: Produce a fully Rx structure or a completely un-Rx structure

• Die conditions– Bearing length and choke angle influence the PCG thickness in quenched profiles– Extrusion speeds with acceptable PCG thickness can be several times higher with

long choked bearings and in addition the onset of speed cracking can be delayed.


Corrosion

48

After Anodization

Atmos. corrosion

Alkali corrosion

Spacer marking

White etch bloom

Dull finish

Inadequate rinse

Acid corrosion

Rinse water corrosion

Chloride contami.

Spangle

Coloring due to MgSi

Castle and moat

• AA6063 non-protected cladding on RTA research center installed in 1949

• 65 years exposure in industrial environment

• Only ~ 400 microns of localized pitting corrosion


Atmospheric pitting corrosion

49

Rate of pitting slows down with time due to passivation by build up of corrosion productSolution – make metal thick enough or protect!

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12

Pit D

epth

mils

Time (years)

AA6061 T6Seawater Exposure

Brixham UK

depth = 28.4(time)0.34

depth = kt1/3

Corrosion product build up leading to passivation


Acid / Alkali pitting

50

Typical form of pitting where the etching has removed evidence

Alkali pitting – general attack

typical source alkali contamination, i.e. cement dust

Acid pitting – intergranulartypical source acid fume from

chemical processes


Alkali pitting prior to anodization

51

The small round pits are covered with a continuous anodic layer 8-10µm. The defect was formed prior to anodizing process.

The corrosion pits are shallow and rounded with a smooth surface, no sign of inter-granular attack (alkali corrosion vs. acidic corrosion)

Longitudinal section as polishedMacrographic surface appearance

6th Australasian Aluminium Extrusion Conference – 10-12 September, 2018 - Melbourne

Thank you for your attention Al

Contact information

Jerome Fourmann, Eng., M.Sc.

Technical Director, Global Customer Support and Product Development –Commercial, Primary Metal

Aluminium

Rio Tinto

200 E Randolph St., Suite 7100 - Chicago, IL 60601-7329, USA

M: + 1 440 520 4975

[email protected] http://www.riotinto.com/aluminium

mailto:[email protected]

http://www.riotinto.com/aluminium

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