Heating Rate Effect on Superplastic Behaviors
of an As-cold-rolled 5083 Al-Mg-Mn Alloy
J.Y. Uan
Department of Materials Science and Engineering
National Chung Hsing University,No. 145, Xing Da Rd., Taichung city, Taiwan
Email: jyuan@dragon.nchu.edu.tw
G.S. Daehn, M.J. Mills
Department of Materials Science and Engineering
The Ohio State University, Columbus, Ohio, USA
Department of Materials Scienceand EngineeringOutline• Superplasticity• Superplastic forming: advantages and limitations• Possible solutions proposed• Effect of Heating Rate (before Loading)• Superplastic forming in Taiwan (e.g., High-pricedbicycle frame)• SummaryDepartment of Materials Scienceand Engineering

Microstructure Requirements for superplasticity:
fine grain size

high angle boundary
Frequency

Relative Frequency (% )520 m432100

1121314151
M isorientation A ngle (degree)

Misorientation angle

Exhibit superplasticity over a limited strain rate
at high temperature
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61

Deformation mechanism: grain boundary sliding

100 mmResults of this study
Department of Materials Scienceand EngineeringSome materials which shows “superplasticity” are:Department of Materials Scienceand EngineeringAdvantages and Limitations
Advantages

Department of Materials Scienceand Engineering

Examples:Joints

Airplane Engine Bay Panel (D. Stephen (1987))

Cooperative research program with industry in NCHU, Taiwan
Department of Materials Scienceand EngineeringLimitations
Long Cycle Time

Targetdomain510

SPF time (minutes)
A.J. Barnes, Superform, USA(MRS proceedings, 1999)
Department of Materials Scienceand Engineering

20Current
domainPossible solution

Elongation

Optimum condition

Off optimum(higher strain rate)- Strain Rate +As-cold-rolled 5083 Al-Mg-Mn Alloy
Department of Materials Scienceand EngineeringLimitations

Cavity VolumeCavitation during superplastic deformation

Superplastic Strain
Important research topic:
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100 mhow to decrease cavitation

Pre-existing Cavity??
• Large amount of hot and cold rolling,
decohesion between particle/matrix• Al6(Mn,Fe) or Al(Mn,Fe)Si particle breaking

50 m
the present study
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Possible solution
Heating Rate vs. Densification during Sintering( Researches from D.L. Johnson and V.A. Ivensen)
T oC

Ni Powder Compact(a)IIIIII(b)V.A. Ivensen, J. Sci. Sinter. (1978)

Department of Materials Scienceand EngineeringMaterialMg Mn Fe Cr
Si Zn Zr Al
4.34 0.76 0.20 0.09 0.08 0.03 0.01 bal.

(in wt.%)Al6(Mn,Fe);
Al(Mn, Fe)Si

As-cold-rolled 5083 Al-Mg-Mn Alloy
Department of Materials Scienceand EngineeringEffect of Heating Rate (before Loading)Tensile Temperature

500oTemperature ( C)

600

400300low heating rate
high heating rate

200100051015Time (min)infrared heating element
Department of Materials Scienceand Engineering2025

Microstructure difference prior to deformation??
High heating rate

Low heating rate
Grain size

10.0 m

3 d L  d ST  d LTm
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11.1 mRelative
RelativeFrequency
Frequency (% )(%)

High-angle grain boundary
54
32100

1121
31
41
51
61
M isorientation A ngle (degree) o

Misorientation angle ( )Department of Materials Scienceand Engineering

450

Elongation (% )400high heating rate
low heating rate

350
300
250
200

Off optimum(higher strain rate)

150100
10-410-310-210-1-1

Initial Strain Rrate (s )Specimen gauge length (L0) = 25.4 mm
Department of Materials Scienceand EngineeringVolume Fraction of Cavity (% )10-13E-3 s high heating rate
-183E-3 s low heating rate

642000.2

0.4

0.6 0.8

11.2 1.4

1.6

Strain100%

200% 300% 400%

Elongation

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200 mM. Matsuo (1994)
5083 at 500oC

present study,
0.2% Fe and 0.083% Si

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Mismatch of thermal expansion coefficient ??
Thermal expansion Coefficient:
Al6Mn : 14  10-6 K-1
Al6(Mn,Fe) : 14.5  10-6 K-1
Al - 5% Mg alloy : 22.8  10-6 K-1
Tensile force at matrix/particle interface

Department of Materials Scienceand Engineeringcavity Volume

Due to pre-existingcavity

Superplastic Strain

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Previous efforts to reduce pre-existing cavities:• High temperature exposure
Chandra and Chen(1999)

Material: 5083
Treatment: 550 oC, 40 min
Results: reduce the number and size of pre-existing cavities
Iwasaki et al. (1995)

Material: 5083
Treatment: 510 oC 1 hr, then post-annealing at 510 oC, 4 hror 560 oC, 1 hr
Result: cavity volume fraction 0.43% for 200% elongation
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Possible solution
Heating Rate vs. Densification during Sintering( Researches from D.L. Johnson and V.A. Ivensen)
T oC

Ni Powder Compact(a)
IIIIII(b)

V.A. Ivensen, J. Sci. Sinter. (1978)

Department of Materials Scienceand EngineeringSummaryHigh heating rate before loading• effect of pre-existing cavity on cavitation• cavitation• cavitation at higher strain rate deformation• holding at high temp. (>10 min) help to reduce
cavitation, especially heated at higher heating rate

Department of Materials Scienceand Engineering