POW - Artificial Ageing 10 14 2016 PRINT - …ˆ’Form Al-Fe-Mn-Si intermetallics ( phase & phase)...

10/31/2016

1

ArtificialAging

JeromeFourmann–RioTinto Aluminium

Chicago, Illinois

October 25‐26, 2016

© 2016 Rio Tinto. All rights reserved.

2

Disclaimer

The following information is the property of Alcan Primary Products Company LLC, a member of the Rio Tinto Aluminiumproduct group and its affiliates (collectively "Rio Tinto").

The presentation is provided to the Attendees of the AEC Process Optimization Workshop 2016 (“POW’16”).

This presentation is provided for informational purposes only. Rio Tinto Inc. makes no representations or warranties in relation to its contents.


10/31/2016

2


3

…The extrusion is now ready for heat treat…

Casting Homogenization

Ext

rusi

on Aging

Temperature

Pre

heat

ing

Coo

ling

Time

Liquid

Solid,Mg & Sidissolved

Deformationtemperature

How muchMg & Siavailable ?

Cooling quickenough to preventcoarsening of MgSi?

Cooling quick enough to prevent coarsening of MgSi?

Natural aginglong enough?

Exit temperaturehigh enough to dissolve MgSi?

Artificial agingoptimised?

Preheatingfast enoughto prevent coarseningof MgSi?


5

Outline

• What is Aging?

• Tempers designation

• Natural Aging

• Artificial Aging and Aging Curves

• Floor Aging/ Heat Up Effects

• Bending properties related to aging

• Loading pattern

• Aging Calibration and Maintenance

10/31/2016

3


6

Basic Slip Systems in FCC Metals (Aluminum)

Al is a face-centered cubic metal. This gives it multiple 111 plane slip systems.


7


Metals deform through the motion of layers of atoms, usually along the planes where they are most closely packed together.

10/31/2016

4


8


To perform the operation shown above on a perfect crystal would require enormous

Force as every bond would have to be broken and reformed (1/2 million lbf/in2).

Metals are not observed to be that strong. Why?


9

Dislocation Mechanism for Metal Deformation

…Flaws exist in the crystal structure…

Dislocations Provide a Mechanism that makes metals soft and ductile (most times, too soft)

• Obstacles to dislocations in order to strengthen the metal

• May include particles, solute atoms, grain boundaries, other dislocations

• One of the strongest obstacles: thermally precipitated phases

10/31/2016

5


10

Why does aging increase strength?

A dislocation

All “plastic” deformation of metals requires dislocation motion


13

Deformation Mechanism for Metals

10/31/2016

6


14

Deformation Mechanism for Metals

We strengthen metals by blocking dislocation motion


15

Dislocation Mechanism for Metal Deformation

Si

Mg

Mg atom 13% bigger than AlSi atom 17% smaller than Al

Substitutional atom

Mg and Si atoms can go “in solution” and occupy Al atom sites

10/31/2016

7


16

Mechanism of Age Hardening

Solvus Temperature

Time

Tem

per

atu

re (

°F)

As-worked

Solutionize

Quenching

Aging

0.20.000008in

Mg2Si

CuAl2

Precipitate,i.e.

Aging produces fine “MgSi” particles


17

MgSi Precipitates in AA6061

100 nm 1 nmAA6061

TEM and Atom-probe techniqueMg:Si ratio in precipitates close to 1:1

10/31/2016

8


18

Main Alloying Elements effect on aging

Dominant elements: Mg and Si

− Form Mg-Si precipitates which determine alloys strength

− Have significant impact on extrudability (especially Mg)

Important element: Fe

− Form Al-Fe-Mn-Si intermetallics ( phase & phase)

− Have significant impact on surface finish & extrudability

Other elements: Mn, Cr and Cu

− Form dispersoids affecting Mg-Si precipitation and thus quench

sensitivity;

− Affect the features of intermetallics, thus extrudability;

− Other effects (toughness, grain size, corrosion resistance, etc…).


19

What is Aging? - definitions

A heat treatment process to obtain the required mechanical

& physical properties (i.e. T4, T5 & T6);

Natural aging

– Leaving extrusions at room temperature for more than 12 hours;

Artificial aging

– “Cooking” extrusions at elevated temperatures (330 - 410°F) for a

number of hours (1 - 12 hours);

Mg and Si precipitate out of solid solution to form fine Mg-

Si precipitates of various sizes (”, ’ and );

No change in Fe-containing intermetallics.

10/31/2016

9


23

Outline

• What is Aging?


• Natural Aging




• Loading pattern



24

Temper Designations

24

e.g. T6510

M/F as manufactured/fabricated

O fully annealed

H strain hardened (e.g. 3003 H112)

W solution treated

T heat treated

Basic Temper

Subdivision of

basic temper

e.g. T1 - T10

Further variations

10/31/2016

10


25

Heat Treated - “T” Tempers

Furnace Solution Treated*T4 naturally aged

T3 cold worked + naturally aged (i.e. 2024-T3)

T6 artificially aged

T7 overaged/stabilized (i.e. 7075-T73)

T8 cold worked and artificially aged(i.e. 6063 T832)

Press quenched:T1 naturally aged

T5 artificially aged

*for 6XXX, can be applied after hot working process


26

Outline

• What is Aging?


• Natural Aging




• Loading pattern


10/31/2016

11


27

Natural Aging – Room Temperature

0

2

4

6

8

10

12

14

16

1 10 100 1000 10000

Time Hours

Web

ster

Har

dn

ess

1 year

60616082

6063 GP

6063 – Bending

6XXX alloys naturally age at room temperature after extrusion

Hardness proportional to log time


28

Outline

• What is Aging?


• Natural Aging




• Loading pattern


10/31/2016

12


29

Artificial Aging

Increase strength and hardness

1. Used to control precipitation of fine Mg-Si

2. Requires exposure to elevated temperature

3. Can control mechanical and physical

properties of extruded product


30

Aging Curves

MgSi particles grow and coarsen with time, changing strength

Peak aged

Overaged

Underaged

Str

eng

th

Time

solute clusterswith fine ” Mg-Si

dense ” Mg-Si

& ’ Mg-Si

100 nm

10/31/2016

13


32

Tensile Test Definitions

0

5

10

15

20

25

30

35

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Eng Strain

En

g.

Str

es

s (

ks

i)

Yield or proof stressTensile strength

Elongation

Elastic Portion

stress/strain = const E

=10,000 ksiLoad

cross section

area

extension

original length


33

AA6063 – Aging Curve Tensile Strength

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18 20 22 24

Soak Time (hrs)

Ten

sile

Str

eng

th (

ksi)

340 oF (170°C)

420 oF (215°C)

390 oF (200°C)

365 oF (185°C)

6063 GP

Peak strength drops with higher temp.

Peak moves to shorter times at higher temp.

10/31/2016

14


34

AA6061 – Aging Curve Tensile Strength

36

38

40

42

44

46

48

0 5 10 15 20 25

Soak Time (hrs)

UT

S (

ksi)

6061 GP

320 oF (160°C)

390 oF (200°C)

365 oF (185°C)

350 oF (175°C)

Same basic shape as AA6063, over-aging faster with AA6061


35

AA6061 Aging Curve - Ductility

0

5

10

15

20

25

0 5 10 15 20 25

Soak Time (hrs)

% E

lon

gat

ion

(2”

)

390 oF (200°C) 365 oF (185°C)

6061 GP

Lower temp. can improve %El for same strength

Underage gives better %El than overage

Same UTS

10/31/2016

15


36

Outline

• What is Aging?


• Natural Aging




• Loading pattern



37

Floor Aging Good or Bad?

6082

0.1 1 10 100 1000

17

18

16

15

14

13

12

11

10

9

8

Floor Age hrs

Har

dn

ess

-W

ebst

er

60636060

10% UTS6061

Aged 5 hrs/365°F

6005A

6061/6005A/6082 - short floor age beneficial

6060 longer - floor age beneficial

6360

10/31/2016

16


38

Heating Rate – Fast or Slow

Slower heating increases the strength of most alloys

20

22

24

26

28

30

32

34

0 1 2 3 4 5 6 7 8 9

Soak Time (hours)

Ten

sile

Str

eng

th k

si

AA60632hr Floor AgeAged at 365°F


41

Outline

• What is Aging?


• Natural Aging




• Loading pattern


10/31/2016

17


42

Fracture – Ductility Effect

When % Elongation is exceeded on bend O.D., fracture will occur

Ductility can be increased by low temperature aging


43

AA6061 Aging Curve - Ductility

0

5

10

15

20

25

0 5 10 15 20 25

Soak Time (hrs)

% E

lon

gat

ion

(2”

)

390 oF (200°C) 365 oF (185°C)

6061 GP

Lower temp. can improve %El for same strength

Underage gives better %El than overage

Same UTS

10/31/2016

18


44

What is Springback?

3

Springback = elastic recovery when load is removed

Springback increases with yield strength

1

2

1

2

3

stre

ss

strain


47

Effect of Quench Rate – AA6061

Air quenching produce grain boundary Mg2Si - makes boundaries brittle

0.5°F/sec 2°F/sec 5°F/sec

11°F/sec 14°F/sec WQ

10/31/2016

19


48

Outline

• What is Aging?


• Natural Aging




• Loading pattern



49

Load pattern in aging oven

Load

Air stream

• Ensuring adequate air passages, with minimum obstruction to each face of the extrusion in the load;

• Filling the cross-section of the oven with no wide gaps to eliminate “short circuit” of air flow;

• Loading solid profiles near the hot end and hollow profiles near the cold end.

Air always follows the path of least resistance

10/31/2016

20


50

Aging oven type

Single End Flow Age Oven:Simple, low-maintenance design delivers uniform temperatures

Reversing End Flow Oven:Fast heat-up, excellent temperature uniformity

Double End Flow Age Oven:Faster heat-up with higher temperature uniformity

Side Flow Age Oven:Cross-flow circulation for highest thermal uniformity

Continuous Aging Oven:Continuous production flow for highest throughput

Courtesy from Frontier Aluminum


51

Aging oven conditions – key rules

• Fan & motor: Fan speed & motor power affect the velocity of air flow;

• Baffles: Broken or missing baffles affect uniformity of air flow;

• Door: Leak around the oven door affects recovery time;

• Thermocouples: Calibration & maintenance affect temperature control.

10/31/2016

21


52

ASTM B221 requirements

B221 states that “Aging processes and equipment shall meet thepractice and requirements of B918 Standard for Heat Treatment”.Therefore, to meet B221 extruders need to perform aging ovensurveys.

• Uniformity within the age oven should be better than +/- 10ºF.• All ovens need to be calibrated and surveyed.• Weekly checks are required to show the temp. measuring system

and control thermocouples agree within +/- 2ºF.• Surveys need to be carried out using 40 thermocouples (one at

each corner and one in center a must). Once equilibrium has beenreached, temperatures should be measured at 5 minute intervals for30 minutes to demonstrate uniformity of +/- 10ºF.

• Surveys have to be done monthly for 6 months followed by every 6month intervals.

• Contact pyrometers shall be calibrated once per Quarter.• Non contact sensors (infrared) shall be verified with contact

pyrometers on weekly intervals.


53

Aging oven survey

Aging oven survey should be conducted at least once a year to ensure proper operation of the aging oven

Crates in Crates out

T/C. 2 (on top crate)T/C. 4 (on top crate)T/C. 3 (on lowest crate) T/C. 1 (on lowest crate)

20

40

60

80

100

120

140

160

180

200

220

0 50 100 150 200 250 300 350

Time (min)

Tem

p (

C)

Pos.3

Pos.4

Pos.1 (manual)

Pos.2 manual)

Start soak (67.5min)

FURNACE 4C - T6 cycle

20min to end cycle

10/31/2016

22


54

Take Home

Objective: Increase strength and hardness

• Extrusion conditions set up the baseline

• Aging is controlled by time and temperature

• Aging curves are the map for the process

• All 6XXX alloys naturally age after extrusion

• Floor age and heating rate modify the curves

• Ductility can be optimized with quench and aging

• Uniform temperature in oven to minimising variation


ThankYou

Jerome Fourmann - Rio Tinto Aluminium

POW - Artificial Ageing 10 14 2016 PRINT - …ˆ’Form Al-Fe-Mn-Si intermetallics ( phase & phase)...

Documents

Transcript of POW - Artificial Ageing 10 14 2016 PRINT - …ˆ’Form Al-Fe-Mn-Si intermetallics ( phase & phase)...