in-situ fabrication of functionally graded al/mg 2 si by electromagnetic separation li jianguo...
TRANSCRIPT
In-situ fabrication of functionally graded
Al/Mg2Si by electromagnetic separation
School of Materials Science and Engineering,
Shanghai Jiaotong University, Shanghai 200030, China
2nd Sino-Germany Workshop on Electromagnetic Processing of Materials
Outline:
1. Motivation
2. Principle of the process
3. Experiments and results
4. Summary
Motivation
The in-situ Al-Mg2Si composites have great potential applications in the automotive and aerospace industries due to their excellent properties.
1.Problems:Hard and fragile primary phases (eg. Mg2Si in Al-Mg-Si) may harmful to mechanical properties
2.Solution:Gradient distributed from the surface to the center—Functionally graded materials(FGMs).
The process of FGMs by EMS
The process of in-situ FGMs by electromagnetic separation (EMS) method is recently proposed by our laboratory. It produces the in-situ FGMs using usual casting under electromagnetic field by one-step. So it lower the production cost. And it can produce the thermodynamically stable systems by in-situ nucleation and growth of the reinforcing particles from the parent melt.
Principle of the process
I
Electromagnetic forcesElectromagnetic Archimedes forces
B
Particle
Melt
Principle of the process of in-situ FGMs by Electromagnetic Separation method
Movement direction
B
I
Primary particles
Melt
Casting mould
Movement analysis of particle
• Electromagnetic Archimedes force acting on a spherical primary particle can be written:
BJd
FE
622
3 3
21
21
• The buoyant force due to gravity imposed on the primary particle is stated as:
gdFG 21
3
6
(1)
(2)
• The terminal migration velocity of primary particle as:
• The motion drag force of the primary particles in the molten metal is expressed as:
2
1
2
24
vdCF DR (3)
)(22
3
3
421
21
21
1
2
gBJ
C
dv
Dt
(4)
• When these forces are in the balance:
0 GER FFF
(5)
where v is the velocity of the primary particle and the viscosity of the melt.
)1( eRAnd when the mode of the movement is transition flow ,
gBJd
vt 1221
212
22
3
18
( 6 )
CD is the drag coefficient, which is related to the Reynolds number
. with laminar flow,
( 7 )
Re
10DC
3
2
1221
21
3
1
115
2
25
1
gBJd
vt
)1( eR Re
24DC
vd 1Re
Experiments and results
• Equipments of experiment
• Effects of Element Ti
• Effects of process parameters
Equipment
Electromagnet
Molten metal
Casting mould
DC Power
N
S
CathodeAnode
Upper mould
Lower mould
Casting gate
(a) (b)
Schematic of equipments used in the process of FGMs by EMS method: ( a ) Top view of the equipments, ( b ) Front view of the equipments.
Effects of element Ti on Microstructures of particle packed region
(b)
0.5mm
0.5mm
(c)
0.5mm
(c)
Process parameters:Pouring temperature: 850oC
Mould temperature: 400oC
Electromagnetic force: 5×104 N/m3
Composition:
Al-15Mg2Si –5Si
Composition:
Al-15Mg2Si –5Si-4Ti
α
β δ
50μm
(a)
50μm
(b) β
• β is Al3Ti• δ is a kind of Al-Si-Ti ternary intermetallic compounds, an
d composition is 65.12at.%Al-13.47at.%Si-21.41at.%Ti
Microstructures at higher magnification of Al-15Mg2Si –5Si-4Ti samples
Process parameters:Pouring temperature: 850oCMould temperature of : 400oCElectromagnetic force: 5×104 N/m3
Composition: Al-15Mg2Si –5Si-4Ti
0.5mm
(a)
(b)
0.5mm
0.5mm
(c)
30mm
20mm
A
D
B
C
E
0.2mm
(d)
0.2mm
(e)
Microstructures of in-situ Al/MgSi FGMs by EMS Method
B
I
0.5mm
(b)
0 5 10 15 20 25 30
0
3
6
9
12
15
18
Lower sideUpper side
Vo
lum
e fr
acti
on
, V
ol%
Distance, mm
5× 104 N m／ 3
3× 104 N m／ 3
1× 104 N m／ 3
Microstructures of upper side in the samples
0.5mm
(a)
0.5mm
(c)
5×104 N/m3
3×104 N/m3
1×104 N/m3
Effects of the electromagnetic force on particle distributions
1 2 3 4 5 6 7 8 90.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3.0
1mm
/vt ,
Sec
Electromagnetic force, 104 N/m3
20 um 50 um 80 um 110 um 140 um
Movement time of particles for unit distance (1m
m) vs the electromagnetic force
0.5mm
(a)
0.5mm
(b)
0.5mm
(c)
0 5 10 15 20 25 30
0
4
8
12
16
20
24
Lower sideUpper side
Vo
lum
e fr
acti
on
,V
ol%
Distance, mm
600oC
400oC
200oC
Microstructures of upper side in the samples
600oC
400oC
200oC
Effects of mould temperature on particle distribution
0.5mm
(b)
0.5mm
(c)
0.5mm
(a)
Microstructures of upper side in the samples
0 5 10 15 20 25 30
0
4
8
12
16
20
Lower sideUpper side
Vo
lum
e fr
acti
on
, V
ol%
Distance, mm
850oC
800oC
750oC
850oC
800oC
750oC
Effects of pouring temperature on the particle distributions
0 3 6 9 12 15 18 21 24550
600
650
700
750
800
850
Liquidustemperature
Eutectic reactiontemperature
Tem
per
atu
re,
oC
Solidification time, Min
200 oC
400 oC
600 oC
Cooling curves of melt
0 3 6 9 12 15 18 21550
600
650
700
750
800
850
900
Eutectic reaction temperature
Liquidus temperature
Solidification time, Min T
emp
erat
ure
,oC
900 oC
850 oC
Effects of mould temperature
Effects of Pouring temperature
Al-15Mg2Si-5Si-4Ti
0.5mm
(b)
0.5mm
(c)
0.5mm
(a)
0 5 10 15 20 25 30
0
4
8
12
16
20
24
28
Lower side
15wt.% 20wt.% 25wt.%
Upper side
Vo
lum
e fr
acti
on
, V
ol%
Distance, mm
Microstructures of upper side in the samples
Al-20Mg2Si-5Si-3.75Ti
Effects of the composition on particle distributions
Al-25Mg2Si-5Si-3.5Ti
Summary
1. In-situ Al/Mg2Si FGMs was successfully prepared by EMS method.
2. Additional element Ti can prevent primary Mg2Si particles from forming the particle clusters.
3. There exists a critical value of electromagnetic force, and the In-situ Al/Mg2Si FGMs can be prepared by EMS method only when the electromagnetic force is beyond it.
4. Increasing of the electromagnetic force and the content of Mg2Si and decreasing of the solidification rate can make the particle volume fraction of the particle packed region and the gradient of particle distributions increase.
Acknowledgements:
The work is supported by the National Natural Science Foundation of China.
We express our sincere thanks for their financial support.
The end
Thank you!