Transcript Slide 1

Center for
Advanced
M aterials and
M anufacturing of
Automotive
Components
Mg AZ31B Sheet Formability: Experiment and Simulation
K. Piao and R. H. Wagoner
Department of Materials Science and Engineering, The Ohio State University
Sheet Tension / Compression Test
Room Temperature
RT
Mg AZ31B-O, RD
Thickness = 2.0 mm,  = 0.19
50 C
Absolute True Stress (MPa)
o
100 C
o
125 C
200
o
150 C
o
175 C
100
o
75 C
300
o
300
o
100 C
o
125 C
200
o
150 C
o
175 C
100
o
200 C
200 C
o
o
225 C
225 C
L>3mm
W=15.2mm
Tension
Compression
Compression
o
Tension
250 C
0
0.05
0.1
0.15
Accumulated Absolute True Strain
0.2
Tension
Compression
o
250 C
0
0
0
0.25
0.05
0.1
0.15
0.2
0.25
0.3
Accumulated Absoluted True Strain
Mg AZ31B, O-temper, 3.2mm
Critical temperature is between 130oC to 140oC
Measurement:
160
608 second
o
Target Temperature = 250 C
U = 105V, I = 1.85A
4) Simulate thermo-assistant deep drawing of Mg AZ31B, enhancing
formability using non-isothermal heating strategies
150
Simulation:
Surface Heat Flux
=0.048W/m
300 second
200 second
100
100 second
140
100
130
0
120
110
0
-100
-50
0
50
100
X (mm)
Boger et al., Int. J. Plast., 2005
True Stress
-100
Laser extensometer
Lou et al., Int. J. Plast., 2007
Temperature
400 second
2
200
True Stress (MPa)
Temperature(C)
200
Mg AZ31B T-C cyclic test, 2mm
500 second
Temperature (degree C)
(0.1/s-10-4/s,
Constitutive Equations, 150oC-300oC:
Mg AZ31B 1mm sheet
o
RT
Thickness = 2.0 mm,  = 0.19
o
75 C
300
1
Mg AZ31B-O, RD
o
50 C
Absolute True Stress (MPa)
G=36.8mm
400
400
2) Measure T / C plastic hardening curves for Mg AZ31B sheet
3) Develop constitutive laws for Mg AZ31B sheet alloys
150oC-300oC)
Sheet Tension / Compression Test
Elevated Temperature
B=50.8mm
Mg AZ31B sheet alloy has advantages of low density, relatively high
strength and high stiffness. However, it has limited formability at room
temperature, and unknown behavior at complex forming conditions,
especially in the thermo-assistant forming process.
The objective of this research is:
1) Design and optimize test devices for elevated-temperature tension /
compression (T / C) of sheet metal alloys
Sheet Tension / Compression Test
Elevated Temperature
Side Force
Background
100
0
3
2
200
400
600
800
1000
-200
1200
4
Time (sec)
Thermo-assistant Deep Drawing
Thermo-assistant Deep Drawing
Conclusions
• Develop high-temperature T/C device
Punch:
t = 1.0 mm
R = 60 mm
25 mm
300
300
M1 <7MPa>:
o
200 C, Posco Mg AZ31B, <std dev>,%
M1 vs. M2 : FEA vs. Experiments
o
150 C, Posco Mg AZ31B, <std dev>, %
M1 vs. M2 : FEA vs. Experiments
250
opt
250
opt
  f ( ) g ( )h(T )
M1 <22MPa>, 12%
Eng Stress (MPa)
Eng Stress (MPa)
200
200
-1
10 /s
M2 <6MPa>, 3%
M1 <9MPa>, 6%
150
-2.5
10
/s
M2 <3MPa>, 2%
10 /s
M2
M1 <16MPa>, 11%
M2 <4MPa>, 3%
M1 <13MPa>, 12%
-2.5
10
M2
-4
M1 <19MPa>, 26%
M2 <1MPa>, 2%
10 /s
0.4
Eng Strain
0.6
0
0.8
300
0.2
h 2 (T)  1  0.5629 
0.4
Eng Strain
0.6
Heating time = 10 minutes for 250oC
g  (0.0001)0.0916
<2MPa>, 2%
0
0
0.8
R = 5 mm
• High Temperature T/C testing of Mg AZ31B sheet:
T  273
T  273 2
 1.3863  (
)
273
273
50 mm
14 mm
Die
Inflected flow (twinning) disappears between 130oC - 140oC
Necking
• Constitutive equations for Mg AZ31B sheet:
300
o
M2opt <4MPa>:
o
250 C, Posco Mg AZ31B, <std dev>,%
M1 vs. M2 : FEA vs. Experiments
250
300 C, Posco Mg AZ31B, <std dev>,%
M1 vs. M2 : FEA vs. Experiments
250
opt
200
150
-1
10 /s
M1 <10MPa>,9%
100
-2.5
10
M2 <5MPa>,5%
M1 <12MPa>,17%
/s
M2 <2MPa>,3%
M1 <23MPa>,50%
50
-4
10 /s
M2
M1 <15MPa>,19%
-1
10 /s
100
M2
<2MPa>,3%
M1
0.2
0.4
Eng Strain
-2.5
10
<3MPa>,10%
0.6
0.8
1mm/s
0.1mm/s
150oC
1.9 (38mm)
1.9 (37mm)
1.9 (37mm)
200oC
1.9 (38mm)
1.9 (37mm)
1.9 (37mm)
250oC
1.9 (38mm)
1.9 (37mm)
1.8 (36mm)
300oC
1.9 (38mm)
1.9 (37mm)
1.8 (35mm)
• Finer Mesh in the corner of punch and die
150oC-200oC
2.3 (58mm)
2.2 (49mm)
2.2 (49mm)
• Velocity of punch = 10, 1, and 0.1 mm/s
150oC-250oC
2.4 (63mm)
2.6 (72mm)
2.6 (73mm)
150oC-300oC
3.2 (121mm)
3.2 (123mm)
3.3 (125mm)
150oC-300oC:
• Axisymmetric
K2  36.5  exp(859.3 / T)  16.7  log( )  80.6
• Material Model: M2opt
M2 <5MPa>,10%
/s
0
0.2
0.4
Eng Strain
<3.7MPa>
B  0.0014 T  0.0632 log( )  1.0313
<0.03>
C  0.0377  T  0.1227
<0.49>
<13MPa>,25%
0
0
10mm/s

  K 2 (1  B  exp( C  ))  (
)m
0.0001
150
50
0
LDR = Di/Df (Depth)
opt
200
Eng Stress (MPa)
Eng Stress (MPa)
/s
<8MPa>, 7%
50
0.2
DT (Gage Length) < 8oC
150oC
f V ()  420* (1  0.4302 exp(6.7328 ))
150
50
0
Blank holder
Temperature range: RT - 450oC
-1
M1 <12MPa>, 10%
-4
Uniform Temperature:
150oC-300oC
10 /s
100
100
R=60mm, Punch speed = 1mm/s
Failure criteria: thickness strain = -0.2
0.6
0.8
m  0.0152log( )  0.0323
<0.98>
5
• Friction coeffcient = 0.08
• Fix the positions of blank holder and die
hto air = 20 W/m2K
300oC
150oC
ht_s = 3000 W/m2K
6
*Diameter of finished cup: Df = 55.2mm
Experiments, numerical fitting and FEA verification
150oC - 300oC, 0.1-10-4/s, standard deviation = 4MPa
• Thermo-assistant deep drawing:
Non-isothermal heating improve the LDR from 1.9 to 3.3
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