pow - artificial ageing 10 14 2016 print - …ˆ’form al-fe-mn-si intermetallics ( phase &...
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10/31/2016
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ArtificialAging
JeromeFourmann–RioTinto Aluminium
Chicago, Illinois
October 25‐26, 2016
© 2016 Rio Tinto. All rights reserved.
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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.
© 2016 Rio Tinto. All rights reserved.
10/31/2016
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© 2016 Rio Tinto. All rights reserved.
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…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?
© 2016 Rio Tinto. All rights reserved.
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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
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© 2016 Rio Tinto. All rights reserved.
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Basic Slip Systems in FCC Metals (Aluminum)
Al is a face-centered cubic metal. This gives it multiple 111 plane slip systems.
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Basic Slip Systems in FCC Metals (Aluminum)
Metals deform through the motion of layers of atoms, usually along the planes where they are most closely packed together.
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Basic Slip Systems in FCC Metals (Aluminum)
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?
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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
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Why does aging increase strength?
A dislocation
All “plastic” deformation of metals requires dislocation motion
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Deformation Mechanism for Metals
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Deformation Mechanism for Metals
We strengthen metals by blocking dislocation motion
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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
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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
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MgSi Precipitates in AA6061
100 nm 1 nmAA6061
TEM and Atom-probe techniqueMg:Si ratio in precipitates close to 1:1
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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…).
© 2016 Rio Tinto. All rights reserved.
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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.
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
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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
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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
© 2016 Rio Tinto. All rights reserved.
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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
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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
© 2016 Rio Tinto. All rights reserved.
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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
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© 2016 Rio Tinto. All rights reserved.
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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
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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
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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
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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.
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
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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
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
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
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
41
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
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© 2016 Rio Tinto. All rights reserved.
42
Fracture – Ductility Effect
When % Elongation is exceeded on bend O.D., fracture will occur
Ductility can be increased by low temperature aging
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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
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© 2016 Rio Tinto. All rights reserved.
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What is Springback?
3
Springback = elastic recovery when load is removed
Springback increases with yield strength
1
2
1
2
3
stre
ss
strain
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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
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
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
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
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.
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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.
© 2016 Rio Tinto. All rights reserved.
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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
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© 2016 Rio Tinto. All rights reserved.
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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
© 2016 Rio Tinto. All rights reserved.
ThankYou
Jerome Fourmann - Rio Tinto Aluminium
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