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TRANSCRIPT
Introduction to Aluminum Sheet
The Aluminum Transportation Group
2019 Aluminum Transportation Group
Debdutta Roy, Ph.D.
Novelis
Senior Scientist, R&D Automotive
Presenter
2019 Aluminum Transportation Group
Russ Long
Arconic
Chief Engineer – Ground Transportation Products
Presenter
2019 Aluminum Transportation Group
Day 1 Agenda• Sheet production – flowpath
• Aluminum alloys commonly used for BIW and closures
• Sheet properties
• Yield, ultimate and elongations as received
• Properties after paint bake
• Natural aging
• Formability measures
• Joining – spot welding, SPR, adhesives, flow drill screws, etc.
• Design example – aluminum hood, aluminum door
Automotive Aluminum Sheet: Production
Flow Path and General Metallurgy
The Aluminum Transportation Group
2019 Aluminum Transportation Group
OverviewB
od
y St
ruct
ure
Inn
er
Pan
els
Att
ach
me
nts
Bo
dy
in W
hit
e
• Application• Requirements
guide• Alloy selection
❑ Heat Treatable (Precipitation Hardenable) 6xxx
❑ Non Heat Treatable 5xxx
AnnealingCold RollingHot Rolling
Typical Process Flow
2019 Aluminum Transportation Group
Cast House Process Flow (DC Casting)
Batch
preparation
Melting furnace
Melting + skimming
Casting furnace
Furnace treatment In line treatment
Degassing
Grain refiner
Filtration
CastingIngots
2019 Aluminum Transportation Group
Cast House Process Flow (DC Casting)
• Heavy gauge scrap + major alloying additions to reach target
compositions is loaded into large melting furnaces.
• If necessary, final alloying additions are made in the holder. This is the
last chance to control chemical composition.
2019 Aluminum Transportation Group
Cast House Process Flow (DC Casting)
Degassing: removal of hydrogen from molten metal by
bubbling a mixture of gases through the melt.
Fluxing: causes impurities, such as alkaline, sodium, and
lithium to rise to the surface of the bath. Skimming is done
to remove the dross from the surface of the molten metal.
TREATMENT GAS (Ar + Cl2)
2019 Aluminum Transportation Group
Cast House Process Flow (DC Casting)
Filtration: removal of inclusions from molten metal
by passing through a filter media, typically
different types of ceramic filters. Inclusions are
retained at the surface of the filter media.
Ingot Casting in the Aluminum Industry, Treatise on Materials Science &
Technology, Volume 31, 1989, D.A. GRANGER
2019 Aluminum Transportation Group
Cast House Process Flow (DC Casting)
R. Nadella et al, Progress in Materials Science, 53 (3), 2008
• Direct chill (DC) casting developed in 1930s –
made possible higher quality, larger ingots,
more alloys.
• As the metal fills the mold and begins to solidify,
the bottom block is lowered at a controlled rate.
Water directly chills the solid Al shell.
• 4 to 6 ingots can be cast at a time and can
weigh 10-15 tons each.
2019 Aluminum Transportation Group-12- R&T Center Sierre / ©2015 Novelis Inc.
Fe phasesMg2Si
As CastAs Cast
As-Cast Microstructures
2019 Aluminum Transportation Group
Scalping of Ingots
True Edge
Edge scalper
2019 Aluminum Transportation Group
Homogenization - Purpose
Purpose
• Improve workability
• Eliminate coring – i.e. segregation of alloying elements
• Dissolve Mg2Si particles
• Modify Fe phases
• Form dispersoid particles
• But cannot alter inclusions and inverse segregation (which must be removed by scalping)
Casting HomogenizationBreakdown Tandem
Hot Rolling Cold Rolling CASH Forming
AA6xxx As-Cast Microstructure
2019 Aluminum Transportation Group
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30 35 40
Time (hours)
Te
mp
era
ture
(°C
)
Heat-up
Phase Soak Cool to Hot-
Rolling T
Standard
Homogenization Practice: Temperature, TimeT [°C]
α+ℓ
α
C [%]
ℓ
α+β
Eutectic
• As diffusion is strongly T dependent, shorter homo. times can be achieved at higher T
• T must be kept below the solidus (don’t melt!) and watch the eutectics
• With increasing solute content (e.g., Mg), the allowable temperature decreases
solid state diffusion
2019 Aluminum Transportation Group
As cast After homogenization 550°C 10h
• In the “as cast’’ state, a lot of cast precipitates/particles are present in the microstructure, especially at grain boundaries
• Homogenization can dissolve soluble phases
• Homogenization produces a more uniform solute distribution
Redistribution of Solute (6xxx)
Reduction of micro-segregation
2019 Aluminum Transportation Group
24 hr at 560°C
Homogenization: Temperature Effect on Particle Structure
Casting HomogenizationBreakdown Tandem
Hot Rolling Cold Rolling CASH Forming
100µm24 hr at 450°C 24 hr at 520°C
AA6016
2019 Aluminum Transportation Group
Hot Rolling Purpose
Exit Temperature = 358°C
Casting HomogenizationBreakdown Tandem
Hot Rolling Cold Rolling CASH Forming
Purpose
• Reduce the ingot thickness
• Break up large second phase particles
• Recrystallize grains to produce a randomly oriented crystal structure
Fe phase
2019 Aluminum Transportation Group
Hot Rolling – Parameters To Control Microstructure
Preheat Roughing mill Finishing Mill Coiling
• Temperature – controlled via input temperature, roll speed and reduction schedule
• Strain – controlled via reduction schedule
• Strain rate – controlled via roll speed
• Interpass times – controlled via roll speed; in reversing mill also by reduction schedule (slab length), can affect temperature
Temperature almost always wins!
2019 Aluminum Transportation Group
Hot Rolling – Parameters To Control Microstructure
• Precipitation of particles: Mg2Si, Si, Q-phase (for Cu containing alloys)
→ strength, formability, bendability at final gauge
• Grain structure and size, isotropy of grain
→ texture→ essential for bendability at final gauge, formability
→ roping tendency at final gauge
Coiling temperature influences:
Mg2Siparticles
High FHRT Low FHRT
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Cold Rolling Purpose
Purpose • Reduce down to final gauge
• Give the final surface finish to the metal (surface texture)
Mill Finish EDT
Casting HomogenizationBreakdown Tandem
Hot Rolling Cold Rolling CASH Forming
Deformed GrainsUndeformed Grains
Cold Rolling defined as rolling below temperature for recrystallization (< 150°C).
Most of heat of deformation contained within strip (and hence coil)
2019 Aluminum Transportation Group
Cold Rolling
Elements of Metallurgy and Engineering Alloys
F.C. Campbell, editor, p 487-508
DOI: 10.1361/emea2008p487
Cold reduction of 80%
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Cold Rolling - Effect of Cold Work on
Recrystallization
The level of cold work affects the
driving force for recrystallization,
and the resultant final gauge grain
size and aspect ratio.
25% Cold Work 50% Cold Work
75% Cold Work
Increase of cold work → finer grain size after annealing
80% Cold Work
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Annealing
AnnealingCold RollingHot Rolling
After cold rolling• High strength
• Low ductility
• Soluble phases are precipitated
• Heavily deformed
microstructure with high
density of dislocations and
vacancies
-> Highly Unstable
Annealing
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Annealing
AnnealingCold RollingHot Rolling
Schematic Showing the Process of Recovery and Recrystallization
Deformed Microstructure Recovered Microstructure Partial Recrystallization Full Recrystallization
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Annealing
AnnealingCold RollingHot Rolling
Microstructural changes during heating after cold rolling
2019 Aluminum Transportation Group
Annealing
AnnealingCold RollingHot Rolling
Type Description
InterannealingCarried out at intermediate stage of a fabricating process so that material may
be worked to a further degree.
Full annealing Annealing to give a fully recrystallized, soft material (O-temper).
Partial annealingPartial softening of a material which has been cold rolled to a temper harder
than that required (some recrystallization may occur).
Recovery annealing Annealing carried out such that no recrystallization occurs.
Self annealingAnnealing which occurs after hot rolling (re-roll gauge) without the application of
a separate heat treatment.
2019 Aluminum Transportation Group
Annealing
Batch annealing:
• Processing of whole coils or blanks
• Relatively slow heating and long thermal exposure at PMT
• Also used for inter annealing
Continuous annealing:
• Solution heat treat or anneal
• Coil pre-treatment
• CASH line:
• Annealing of AA5xxx and AA6xxx
• SHT of AA6xxx
AnnealingCold RollingHot Rolling
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Solution Heat Treatment (SHT)Solution heat treatment consists of heating the strip up to ~ 500°C to 570°C followed by rapid
cooling to room temperature – used in precipitation hardenable alloys.
After rolling
• High strength
• Low ductility
• Soluble phases are precipitated
RecrystallizeSolutionize
SHT
T4 material
• Soft
• Formable
• Hardening potential
SHT
2019 Aluminum Transportation Group
• Solutionising involves heating an alloy into the single phase (-Al) region of the phase diagram above its solvus temperature
• Fast cooling to retain solute in solid solution
heating up soaking cooling
Schematic figure of solution heat treatment
Solution Heat Treatment
2019 Aluminum Transportation Group
As cast
(a)
(c)
As solutionisedAs rolled final gauge
(b)
High density of intermetallic particles:Mg2Si and AlFeSi phases
Most of the Mg2Si particles aredissolved
Coarse primary particles(Mg2Si, -Al5FeSi, AlCuSi in Cu containing alloys)at the as cast cell boundaries
Microstructures of AA 6xxx Alloys
2019 Aluminum Transportation Group
Precipitation Hardening
• Precipitation hardening is the primary strengthening mechanism for heat treatable alloys
• Natural aging/T4 temper — spontaneous aging of W
temper alloy at room temperature
• T6 Temper — Artificially aged and contains a uniform
dispersion of fine precipitates
0
20
40
60
80
100
0 20 40 60
Rp
0.2
[M
Pa]
Time after SHT [h]Strongest increase of strength during the firsthours after SHT
2019 Aluminum Transportation Group
GP zones
’’
’
clusters coherent
semi-coherent
Tem
pe
ratu
re
ssss
Precipitation Mechanism
Sequence
Mg2Si
Mg2Si’’ (needles) Mg5Si6
incoherent
Precipitates form by nucleation and growth from supersaturated solid solution
Maximum Strength Contribution
2019 Aluminum Transportation Group
Artificial Aging
T4 (ssss)
Rp
0.2
Time in temperature (log)
’’
Peak age
Underaged
’
Overaged
2019 Aluminum Transportation Group
Paint Drying at Customer Provides Bake Hardening
Typical cycles:
• 185°C – 20 min
• 170°C – 20 min
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Impact of Paint Bake Cycles
2019 Aluminum Transportation Group
Effects of Texture - Roping
Roping:
surface
roughening that
occurs when sheet
is deformed
Formed panel: example of bad roping performance
2019 Aluminum Transportation Group
Effects of Texture - RopingCause of roping: spatial alignment of grains of similar orientation along RD
(“grain colonies“)
texture in an intensively roping sheet
Any processing that shortens the texture
alignment, for example, inter annealing, reduces
the tendency to roping
texture in a roping-free sheet
Intensive roping Limited roping
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Roping – Texture Evolution During Processing
No Inter annealing – Roping Intensive Presence of Inter annealing – Roping Free
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Typical Mechanical Properties – Exterior with Flat Hemming
As received After paint bake1 Comments
Grade Typical
Yield
(MPa)
Typical
Ultimate
(MPa)
Typical
T. Elong
(%)
Minimum
U. Elong
(%)
Minimum
rave
Typical
r45
Typical
Yield
(MPa)
Typical
Ultimate
(MPa)
Typical
T. Elong
(%)
Alloy
6EH 95-135 195-260 27 19 0.50 0.30 220 280 23 6022, 6016
12%PS + 20 minutes at 185°C
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Typical Mechanical Properties – Exterior Without Flat Hemming
As received After paint bake1 Comments
Grade Typical
Yield
(MPa)
Typical
Ultimate
(MPa)
Typical
T. Elong
(%)
Minimum
U. Elong
(%)
Minimum
rave
Typical
r45
Typical
Yield
(MPa)
Typical
Ultimate
(MPa)
Typical
T. Elong
(%)
Alloy
6DR1 105-145 200-270 27 19 0.50 0.30 230 300 22 6022, 6016
12%PS + 20 minutes at 185°C
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Typical Mechanical Properties – Interior Reinforcements
As received After paint bake Comments
Grade Typical
Yield
(MPa)
Typical
Ultimate
(MPa)
Minimum
T. Elong
(%)
Typical
U. Elong
(%)
Minimum
rave
Typical
r45
Minimum
Yield
(MPa)
Typical
Ultimate
(MPa)
Typical
T. Elong
(%)
Alloy
6HS2 125-185 220-300 22 19 0.50 0.30 2351 302 22 6111
6HS2 125-185 220-300 22 19 0.50 0.30 2602 320 13 6111
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Flat Hem Testing
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5xxx Automotive SheetAA Chemical Composition Limits
Alloy Si Fe Cu Mn Mg Cr
5754 0.40 0.40 0.10 0.50 2.6-3.6 0.30
5182 0.20 0.35 0.15 0.20-0.50 4.0-5.0 0.10
5052 0.25 0.40 0.10 0.10 2.2-2.8 0.15-0.35
• The main alloys used for automotive body sheet are 5754 and 5182. Some 5052 also used in Europe.
• Used in the fully recrystallized condition – for maximum formability
• O-temper – no OEM requirements for surface quality after forming. Used in totally hidden locations, such as
unexposed door inners
• RSS-temper (reduced stretchers strain) – has OEM requirements for surface quality after forming. Used for
exposed or partially exposed applications, such as some door, hood, deck lid inner applications, etc.
• Mg contents greater than 3.5 are not recommended for extended elevated temperature exposure > 150̊ F to
avoid developing sensitivity to stress corrosion cracking
2019 Aluminum Transportation Group
Typical Mechanical Properties – 5754-O and 5182-O
As received Comments
Grade Typical
Yield
(MPa)
Typical
Ultimate
(MPa)
Minimum
T. Elong
(%)
Minimum
U. Elong
(%)
Minimum
rave
Alloy
5HF 105-155 250-300 27 20 0.60 5182-O
5ST 100-140 215-270 25 18 0.60 5754-O
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5182-O Stress Strain Curve
• In 5xxx alloys, Mg
atoms interact very
strongly with
dislocations as they try
to move through the
aluminum crystal
lattice
• Two types of surface
features can be
created in 5xxx (and
some other Mg
containing alloys)
Because of these features, 5xxx is not used for outer panels (Use 6xxx for outer panels)
2019 Aluminum Transportation Group
Work Hardening and Bake Softening of 5xxx
Alloys
2019 Aluminum Transportation Group
Conclusions• Automotive aluminum alloys can be broadly classified into 2 major groups:
• Heat treatable (or precipitation hardenable) 6xxx series
• Processing of alloys can be modified to optimize strength, formability and
crash properties depending on final application
• Aging behavior of these alloys provide strengthening during paint bake cycles
at customer
• Non heat treatable 5xxx series
• Strengthening component - mainly through solid solution strengthening
caused by Mg atoms
• Interaction of Mg atoms with dislocations -> dynamic strain ageing -> stretcher
strain marks or Ludering -> not suitable for exterior applications
2019 Aluminum Transportation Group
Questions?
2019 Aluminum Transportation Group
2019 Aluminum Transportation Group
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2019 Aluminum Transportation Group
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2019 Aluminum Transportation Group
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Arc Length Calculation
K factor for calculating arc
length during bending
Steel K = normally 0.38
Aluminum K = normally
0.43
For bend radius of T to
bend radius of 3T
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Hood Example
Ref. A2MAC1
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Hood Example – Cadillac ATS
Part Material Gauge
(mm)
Weight (kg)
Hood outer 6000-IH-90 0.9 2.06
Hood inner 6000-IBR-100 0.8 1.3
Palm reinforcement 6000-IBR-100 1.25 0.2
Hinge reinforcement Al-S-6000-R-110-U 1.65 0.12 x 2 = 0.24
Latch reinforcement Al-S-6000-R-110-U 1.25 0.18
Latch ring assembly steel 0.05
Totals 3.8
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Typical Hood Gauges
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Affordable Aluminum Door Concept
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Affordable Aluminum Door Concept
2019 Aluminum Transportation Group
Affordable Aluminum Door Concept
2019 Aluminum Transportation Group
Affordable Aluminum Door Concept
2019 Aluminum Transportation Group
Questions?
2019 Aluminum Transportation Group
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