Introduction to Aluminum Sheet The Aluminum Transportation Group Presenter
Debdutta Roy, Ph.D. Novelis Senior Scientist, R&D Automotive
2019 Aluminum Transportation Group Presenter
Russ Long Arconic Chief Engineer – Ground Transportation Products
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
2019 Aluminum Transportation Group Automotive Aluminum Sheet: Production Flow Path and General Metallurgy
The Aluminum Transportation Group Overview
• Application • Requirements guide ❑ Heat Treatable • Alloy selection
Inner Panels Inner (Precipitation Attachments Hardenable) 6xxx
❑ Non Heat
Treatable 5xxx
BodyStructure Body in White in Body
Typical Process Flow
Hot Rolling Cold Rolling Annealing 2019 Aluminum Transportation Group Cast House Process Flow (DC Casting)
Melting + skimming Furnace treatment In line treatment
Batch Degassing preparation
Melting furnace Casting furnace Ingots Casting
Grain refiner
Filtration
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)
TREATMENT GAS (Ar + Cl2) 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.
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)
• 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.
R. Nadella et al, Progress in Materials Science, 53 (3), 2008
2019 Aluminum Transportation Group As-Cast Microstructures
As Cast As Cast
Mg2Si Fe phases
2019 Aluminum Transportation Group -12- R&T Center Sierre / ©2015 Novelis Inc. Scalping of Ingots
True Edge
Edge scalper
2019 Aluminum Transportation Group Homogenization - Purpose
Breakdown Tandem Casting Homogenization Hot Rolling Cold Rolling CASH Forming 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) AA6xxx As-Cast Microstructure
2019 Aluminum Transportation Group Homogenization Practice: Temperature, Time
700 T [°C]
600
500 ℓ
400 Heat-up Phase Soak Cool to Hot- 300 Rolling T
Temperature(°C) α+ℓ 200
100 Standard Eutectic 0 0 5 10 15 20 25 30 35 40 α Time (hours)
solid state diffusion α+β
• 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 C [%] the eutectics • With increasing solute content (e.g., Mg), the allowable temperature decreases
2019 Aluminum Transportation Group Redistribution of Solute (6xxx) 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 Reduction of micro-segregation
2019 Aluminum Transportation Group Homogenization: Temperature Effect on Particle Structure
Breakdown Tandem Casting Homogenization Hot Rolling Cold Rolling CASH Forming AA6016
24 hr at 450°C 24 hr at 520°C 24 hr at 560°C 100µm
2019 Aluminum Transportation Group Hot Rolling Purpose
Breakdown Tandem Casting Homogenization Hot Rolling Cold Rolling CASH Forming
Purpose • Reduce the ingot thickness • Break up large second phase particles Fe phase • Recrystallize grains to produce a randomly oriented crystal structure
Exit Temperature = 358°C
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 Coiling temperature influences:
• 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 High FHRT Low FHRT
Mg2Si particles
2019 Aluminum Transportation Group Cold Rolling Purpose
Breakdown Tandem Casting Homogenization Hot Rolling Cold Rolling CASH Forming Cold Rolling defined as rolling below temperature for recrystallization (< 150°C). Purpose • Reduce down to final gauge • Give the final surface finish to the metal (surface texture)
Undeformed Grains Deformed Grains Most of heat of deformation contained within strip Mill Finish EDT (and hence coil)
2019 Aluminum Transportation Group Cold Rolling
Cold reduction of 80%
Elements of Metallurgy and Engineering Alloys F.C. Campbell, editor, p 487-508 DOI: 10.1361/emea2008p487
2019 Aluminum Transportation Group Cold Rolling - Effect of Cold Work on Recrystallization
The level of cold work affects the 25% Cold Work 50% Cold Work driving force for recrystallization, and the resultant final gauge grain size and aspect ratio.
75% Cold Work 80% Cold Work Increase of cold work → finer grain size after annealing
2019 Aluminum Transportation Group Annealing
Hot Rolling Cold Rolling Annealing
After cold rolling • High strength • Low ductility Annealing • Soluble phases are precipitated • Heavily deformed microstructure with high density of dislocations and vacancies -> Highly Unstable
2019 Aluminum Transportation Group Annealing
Hot Rolling Cold Rolling Annealing
Schematic Showing the Process of Recovery and Recrystallization
Deformed Microstructure Recovered Microstructure Partial Recrystallization Full Recrystallization
2019 Aluminum Transportation Group Annealing
Hot Rolling Cold Rolling Annealing Microstructural changes during heating after cold rolling
2019 Aluminum Transportation Group Annealing
Hot Rolling Cold Rolling Annealing
Type Description Carried out at intermediate stage of a fabricating process so that material may Interannealing be worked to a further degree.
Full annealing Annealing to give a fully recrystallized, soft material (O-temper).
Partial softening of a material which has been cold rolled to a temper harder Partial annealing than that required (some recrystallization may occur).
Recovery annealing Annealing carried out such that no recrystallization occurs.
Annealing which occurs after hot rolling (re-roll gauge) without the application of Self annealing a separate heat treatment.
2019 Aluminum Transportation Group Annealing
Hot Rolling Cold Rolling 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
2019 Aluminum Transportation Group 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 S Recrystallize SHT H Solutionize T
T4 material • Soft • Formable • Hardening potential
2019 Aluminum Transportation Group Solution Heat Treatment Schematic figure of solution heat treatment
heating up soaking cooling
• 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
2019 Aluminum Transportation Group Microstructures of AA 6xxx Alloys
As cast As rolled final gauge As solutionised
(c) (a) (b)
Coarse primary particles High density of intermetallic Most of the Mg2Si particles are (Mg2Si, -Al5FeSi, particles: dissolved AlCuSi in Cu containing alloys) Mg2Si and AlFeSi phases at the as cast cell boundaries
2019 Aluminum Transportation Group Precipitation Hardening
100 • Precipitation hardening is the primary strengthening 80 mechanism for heat treatable alloys 60 • Natural aging/T4 temper — spontaneous aging of W 40
temper alloy at room temperature 20 Rp0.2 Rp0.2 [MPa] • T6 Temper — Artificially aged and contains a uniform 0 dispersion of fine precipitates 0 20 40 60 Time after SHT [h] Strongest increase of strength during the first hours after SHT
2019 Aluminum Transportation Group Precipitation Mechanism
Mg Si ’’ (needles) Mg5Si6 2
’
Temperature ’’ incoherent Maximum Strength Contribution
GP semi- zones coherent
Mg2Si clusters coherent ssss
Precipitates form by nucleation and growth from supersaturated solid solution 2019 Aluminum Transportation Group Sequence Artificial Aging
Peak age
Rp0.2 ’’
Overaged ’
Underaged
T4 (ssss)
Time in temperature (log)
2019 Aluminum Transportation Group Paint Drying at Customer Provides Bake Hardening
Typical cycles: • 185°C – 20 min • 170°C – 20 min
2019 Aluminum Transportation Group 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 - Roping Cause of roping: spatial alignment of grains of similar orientation along RD (“grain colonies“)
Intensive roping Limited roping texture in an intensively roping texture in a roping-free sheet sheet Any processing that shortens the texture alignment, for example, inter annealing, reduces the tendency to roping
2019 Aluminum Transportation Group Roping – Texture Evolution During Processing No Inter annealing – Roping Intensive Presence of Inter annealing – Roping Free
2019 Aluminum Transportation Group Typical Mechanical Properties – Exterior with Flat Hemming
As received After paint bake1 Comments Grade Typical Typical Typical Minimum Minimum Typical Typical Typical Typical Alloy
Yield Ultimate T. Elong U. Elong rave r45 Yield Ultimate T. Elong (MPa) (MPa) (%) (%) (MPa) (MPa) (%)
6EH 95-135 195-260 27 19 0.50 0.30 220 280 23 6022, 6016
12%PS + 20 minutes at 185°C
2019 Aluminum Transportation Group Typical Mechanical Properties – Exterior Without Flat Hemming As received After paint bake1 Comments Grade Typical Typical Typical Minimum Minimum Typical Typical Typical Typical Alloy
Yield Ultimate T. Elong U. Elong rave r45 Yield Ultimate T. Elong (MPa) (MPa) (%) (%) (MPa) (MPa) (%)
6DR1 105-145 200-270 27 19 0.50 0.30 230 300 22 6022, 6016
12%PS + 20 minutes at 185°C
2019 Aluminum Transportation Group Typical Mechanical Properties – Interior Reinforcements
As received After paint bake Comments Grade Typical Typical Minimum Typical Minimum Typical Minimum Typical Typical Alloy
Yield Ultimate T. Elong U. Elong rave r45 Yield Ultimate T. Elong (MPa) (MPa) (%) (%) (MPa) (MPa) (%)
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
2019 Aluminum Transportation Group Flat Hem Testing
2019 Aluminum Transportation Group 5xxx Automotive Sheet
AA 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 Typical Minimum Minimum Minimum Alloy Yield Ultimate T. Elong U. Elong (MPa) (MPa) (%) (%) rave
5HF 105-155 250-300 27 20 0.60 5182-O
5ST 100-140 215-270 25 18 0.60 5754-O
2019 Aluminum Transportation Group 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 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 2019 Aluminum Transportation Group 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
2019 Aluminum Transportation Group Hood Example
Ref. A2MAC1
2019 Aluminum Transportation Group Hood Example – Cadillac ATS
Part Material Gauge Weight (kg) (mm) 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
2019 Aluminum Transportation Group Typical Hood Gauges
2019 Aluminum Transportation Group Affordable Aluminum Door Concept
2019 Aluminum Transportation Group 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 Tell Us How We Did!
1. Open a browser on your laptop, tablet or mobile device
2. Visit: pollev.com/aassociation001
3. Give us feedback!
2019 Aluminum Transportation Group