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“Grain Refinement of Al-Si Alloys by Nb-B Inoculation.Part 1: Concept Development and Effect on Binary Alloys.Part 2: Application to Commercial Alloys”
1
Grain refinement of Al-Si alloys by Nb-B inoculation
M. NowakL. Bolzoni
N. Hari Babu
Brunel Centre for Advanced Solidification Technology
Brunel University London, UK
The Charles Hatchett Award 2016 Lecture
Outline
• Grain refinement in Al alloys with Al-5Ti-B
• Concept development
• Application to Al-Si cast alloys
• Al-Nb-B master alloy
• Comparative study between Al-Nb-B and Al-5Ti-B master alloys
The Charles Hatchett Award 2016 Lecture
ALUMINIUM ALLOYSINTRODUCTION
PROPERTIES• LOW DENSITY, 2.7 g/cc
• GOOD MECHANICAL PROPERTIES
• HIGH CORROSION RESISTANCE
• HIGH THERMAL CONDUCTIVITY
• LOW ELECTRICAL RESISTIVITY
WROUGHTALLOYS
GRAIN REFINEMENT
IMPROVEMENT
FLUIDITY/CASTABILITY MECHANICAL PROPERTIES
MACHINABILITY SURFACE QUALITY
CHEMICAL HOMOGENEITY REDUCED SHRINKAGE POROSITY
CAST (Al-Si)
The Charles Hatchett Award 2016 Lecture
Factors determining grain size in as cast microstructure
Nucleation & Growth
Heterogeneous nucleation Homogeneous nucleation Growth Kinetics
• Temperature• Atmosphere/Pressure• Growth restriction • Fragmentation• Cooling rate
Under cooling (DT)
Nucle
ation / g
row
th r
ate
DT = TL-TgTL
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EFFICIENT HETEROGENEOUS
NUCLEATION SITES
1. High melting Temp
2. Low lattice mismatch
(atom position matching)
3. Chemical stability
(should not react with alloying
elements)
A
B
A
BASE MATERIAL
N. Hari Babu et al., Nature Materials 2005;4:476
The Charles Hatchett Award 2016 Lecture
GRAIN REFINEMENT: Al-Ti-B
Al-Ti-C
MODIFICATION: Sr modification of the Si morphology
P to nucleate the primary Si particles
GRAIN REFINERS IN ALUMINIUM INDUSTRY
TiB2 Particle
Al3Ti Layer
Al Nuclei
HREM image of Al/Al3Ti/TiB2 interface
• Orientation Relationships
{111}Al//{112}Al3Ti//{001}TiB2
<110>Al//<201>Al3Ti
<110>Al3Ti//<110>TiB2
Source: B. J McKay
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TiB2 & Al3Ti
Mats JohnssonPatent, 2000
Casting alloysWrought alloys
Influence of Al-Ti-B grain refiner for Al-Si alloys
Ti-Si phase formation
Not effective
M. Johnsson, Influence of Si And Fe on the Grain-Refinement of
Aluminum, Zeitschrift für Metallkunde, 85 (1994), 781-785
Ti reaction with Si in Al-Si alloys
Ti is consumed by the formation of TiSi2 and TiSi
T. E. Quested et al, Mater. Sci.
Technol. 22, 1126 (2006)
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Analogy between Al-Ti & Al-Nb phase diagrams
Al3TiAl3Nb
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LATTICE MISMATCH
0.384 nm
Al
Al (face centred cubic)
Al3Nb
Lattice mismatch ~0.9%
Low Lattice Mismatch – Coherent Interface
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Nb–Ti–Si ternary system
Nb silicides form at higher temperature
than Ti silicides thus preventing poisoning
Nb–Si binary phase diagram
J.L. Muray and A. J. Alister, Bulletin
of Alloy Phase Diagrams 1984;5:74
Nb chemical stability with Si
J.C. Zhao et al., Materials
Science and Engineering
A 2004;372:21
Al 660 °C Al 680 °C Al 700 °C Al 720 °C
Al-Nb 660 °C Al-Nb 680 °C Al-Nb 700 °C Al-Nb 720 °C
20 mm 20 mm 20 mm 20 mm
20 mm 20 mm 20 mm 20 mm200 μm
Al matrix
Nb
particles
Addition of Nb metal powder to liquid Al
Unreacted Nb metallic particulates
The Charles Hatchett Award 2016 Lecture
750 - 800 C
Nb
2Al
Nb
3Al
NbNbAl3
Nb3Al
Nb2Al
20 μm
Requires high temperature for larger Nb particles and high concentrations
Poor dissolution of Nb in liquid Al
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Addition of Nb fine metal powder to liquid Al
<45 mmNb- Superconductivity – 9KTo verify the Nb dissolution, magnetic moment vs temperature measured
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700ºC
CP-Aluminium
Al with Nb-B
EFFECT OF Nb on CP Al
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COMPARISON OF Al-Ti-B AND Nb-B ON CP Al
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Al-1Si
Reference
Al-2Si Al-10SiAl-8SiAl-6SiAl-5SiAl-4Si
0.1wt.% Al-5Ti-1B
0.1wt.% Nb & B (powders)
COMPARISON OF Al-Ti-B AND Nb-B TO HYPOEUTECTIC BINARY Al-Si Alloys
The Charles Hatchett Award 2016 Lecture
COMPARISON OF Al-Ti-B AND Nb-B TO HYPOEUTECTIC BINARY Al-Si Alloys
Practical alloyscomposition
700ºC
The Charles Hatchett Award 2016 Lecture
Al-Si alloys for automotive applications
Engine & transmission Components
Crankcases
Cylinder heads
Intake manifolds
Housings manual/automatic transmissions
Housings power transfer units
Chassis Components
Subframes Knuckles
Steering housings
Structural Components
Body structures
Instrument panels
Door frames
Wheels
VW
Source: VW
VW
HL
VW
ΔTRef = 2.1ºC
Undercooling for Al-10Si alloy
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0.3 oC/s
Grain size up to 1 cmReference
ΔTRef = 2.1ºC
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ΔTNb-B = 1.3ºC
Undercooling in the presence of NbB2/Al3Nb
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0.3 oC/s
Grain size up to 1 cmReference Nb-B Grain size: 2-3 mm
ΔTNb-B = 1.3ºCΔTRef = 2.1ºC
GRAIN STRUCTURE
380 400 420 440 460 480 500 520 540
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
LM6
dT/dt
Time [ s ]
Te
me
ratu
re [
oC
]
-3
-2
-1
0
1
dT
/dt
Trec
T nucl =588 0 C
T min =584.5 0 C
T g =5870 C
ΔT=2.5°C
400 420 440 460 480 500
585
586
587
588
589
590
591
592
593
594
595
LM6+NGR
dT/dt
Time [ s ]
Te
me
pra
ture
[ o
C ]
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2d
T/d
t
T nucl =588.8 0 C
T min =586.8 0 C
T g =587.5 0 C
ΔT=0.7°C
a) b)Cooling curves for Al-11Si (LM6) alloy
LM6
20 mm
LM6 with Grain refiner addition
Nb-B
200 μm
α-Al
dendrite
200 μm
α-Al
dendrite
HYPEREUTECTIC BINARY Al-Si ALLOYS
Al-14Si700ºC
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HYPEREUTECTIC BINARY Al-Si ALLOYS - EUTECTIC
20 μm 20 μm
20 μm 20 μm
20 μm 20 μm
Al-16Si
Al-18Si
Al-27Si
700ºC
The Charles Hatchett Award 2016 Lecture
200 μm
200 μm200 μm
200 μm
200 μm200 μm
HYPEREUTECTIC BINARY Al-Si ALLOYS – PRIMARY SI
Al-16Si
Al-18Si
Al-27Si
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Application of Nb-B grain refiner to Al-Si commercial alloys
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Commercial alloys tested with Nb-B
GB USA Si Mg Mn Cu Ni Zn Fe
LM6 A413 10.0-13.0 0.1max 0.5max 0.1max 0.1max 0.1max 0.6max
LM13 336 10.0-13.0 0.2-0.4 0.5max 0.7-1.5 1.5max 0.1max 1max
LM24 A380 7.5-9.5 3 max 0.5max 3.0-4.0 0.5 3 1.3max
LM25 A356 6.5-7.5 0.2-0.6 0.3 0.2 0.1 0.1 0.5
9.99 0.005 0.005 0.0017 0.0044 0.005 0.09
10.98 0.268 0.21 2.134 0.068 0.778 0.83
6.06 0.275 0.265 2.725 0.0257 0.305 0.356
11.9 0.8 0.005 3.7 2 0.003 0.12
The Charles Hatchett Award 2016 Lecture
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
The Charles Hatchett Award 2016 Lecture
500 μm 500 μm 500 μm
500 μm 500 μm 500 μm
500 μm 500 μm 500 μm
LM25
LM6
LM24
Reference Nb-BAl-5Ti-1B
COMMERCIAL HYPOEUTECTIC Al-Si ALLOYS
650ºC
0
100
200
300
400
500
600
700
800
900
600 610 620 630 640 650 660 670 680 690
α-A
l gra
in s
ize
[µ
m]
Pouring temperature [°C]
REFERENCE Nb-B Al-5Ti-1B
LM25
LM24
LM6
The Charles Hatchett Award 2016 Lecture
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloys
Fine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
The Charles Hatchett Award 2016 Lecture
PorosityAl-11Si (LM6)no addition
Al-11Si (LM6) with Nb-B
10 mm
~200mm
~1200mm
~160mm
~200mm
The Charles Hatchett Award 2016 Lecture
Al-Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structure
Grain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
The Charles Hatchett Award 2016 Lecture
EFFECT OF COOLING RATE
20 mm 20 mm
700ºC
d = 2072 (dT/dt)-0.34
d = 514 (dT/dt)-0.14
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 20 40 60 80 100
α-A
l gra
in s
ize
, d[µ
m]
Cooling rate, dT/dt [°C/s]
Reference Nb-B inoculation
100
1000
10000
0.1101000
α-A
l gra
in s
ize
, d[µ
m]
Cooling rate, dT/dt [°C/s]
EFFECT OF COOLING RATE
The Charles Hatchett Award 2016 Lecture
EFFECT OF COOLING RATE
0.00E+00
5.00E+09
1.00E+10
1.50E+10
2.00E+10
2.50E+10
3.00E+10
3.50E+10
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100
Nu
mb
er
of g
rain
s, Nv
[m-3
]
ΔN
v /
Nv r
ef [%
]
Cooling rate, dT/dt [°C/s]
Nv(ref)
Nv(Nb-B inoculation)
ΔNv
ΔNv / Nv(ref)
The Charles Hatchett Award 2016 Lecture
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rate
Highly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
The Charles Hatchett Award 2016 Lecture
REFERENCE
Al-Nb-B ADDITION
Al-9Si-2Cu-0.7Mg-0.15Fe
Al-9Si-2Cu
Alloy Condn. %Cu %Mg %Si %Fe %Mn %Ni %Zn %Pb %Sn %Ti %Sr
A354 CAST 1.60-2.0
0.50-
0.60 8.6-9.44 0.154
0.05-
0.10 0.054 0.10 0.014 0.054
0.10-
0.154
0.02-
0.030
The Charles Hatchett Award 2016 Lecture
A354
Al-Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditions
Reduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
The Charles Hatchett Award 2016 Lecture
Reduced Macro-porosity with Nb-B
Al-11Si (LM6)
with Al-5Ti-B
with Nb-B
1 mm
1000µm
1000µm
1 mm
1 mm
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Aluminium Al-Ti-B Novel grain refiner
0
50000
100000
150000
200000
Porosity
Poro
sity [ m
m2 ]
Reduced porosity in Nb-B grain refiner added castings
Porosity
Tp1 test700 OC
Al-7Si alloy
Al-7Si+Al-5Ti-B
Al-7Si + Nb-B
~ /cm2
WithoutWith Nb-B addition
Fine grain structureReduced porosity
Al-7Si alloy
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defects
Fine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
The Charles Hatchett Award 2016 Lecture
Fine eutectic structure
Al-11Si (LM6) with Nb-B
Cooling rate [ C/s]
Eu
tec
tic
Si [µ
m]
LM6 (Reference)
LM6 + Nb-B
HPDC
Finer Eutectic Si - wider range of cooling rates
20 μm
20 μm
Al-10Si With Nb-B
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Reference (Al-13Si) with Nb-B
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallics
Improved ductility & strengthTolerant to Fe contaminationRecycling of Al-Si scrap
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2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0
170
180
190
200
210
220
230
240
LM6
LM6+Nb-B
UT
S [ M
Pa ]
Elongation [ % ]
Gravity mould
Melting temp: 800oC
Casting temp: 800oC
Improved strength & ductility
Machined from cast bars
Improved•Crash performance•Fatigue performance
yield82.4 Mpa 102 Mpa
Al-11Si alloy
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Al-13Si piston alloy
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Al-Nb-B
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strength
Tolerant to Fe contaminationRecycling of Al-Si scrap
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Control of Fe-intermetallics in Al scrap
1% Fe
Grain refiner to control Al-Fe-Si intermetallics
Al5FeSi
Al-Fe-Si large needle structuredetrimental to mechanical properties
A354 A354 + 1%Fe + 0.1%Nb-B
140
150
160
170
180
190
200
0 0.5 1 1.5 2
Elongation, 4D (%)
Virgin alloy with1 wt% Fe impurity
Reduced properties due to larger, needle
structured intermetallics
UTS
(M
Pa)
Properties recovery through refinement of
intermetallics
Virgin alloy
Recovery of properties in Fe-rich aluminium scrap
Nb-B Grain Refiner for Al-Si cast alloys
Highly effective for Al-Si alloys & Mg alloysFine & uniform grain structureGrain size is less sensitive to cooling rateHighly effective in sand casting cooling conditionsReduced porosity & macro defectsFine eutectic structure & intermetallicsImproved ductility & strengthTolerant to Fe contamination
Re-melting & Fading study
FADING STUDY
680ºC
d = 1.12 (t) + 340R² = 0.95
0
200
400
600
800
1000
1200
0 30 60 90 120 150 180 210 240 270
Gra
in s
ize,
d[µ
m]
Contact time, t [min]
LM6The Charles Hatchett Award 2016 Lecture
REQUIRED TIME TO SEDIMENT/FADE
0
2
4
6
8
10
12
14
16
18
20
0 10 20 30 40 50
Sed
ime
nta
tio
n h
eig
ht,
h[c
m]
Contact time, t [h]
NbB2 Al3Nb AlB2
20 µm 15 µm 10 µm
Φ or ρ
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No addition Al-Nb-B Addition
~ 3-4 mm
Remelting
Al-9Si-1.5Cu-0.6Mg-0.15Fe / RE-MELT1st Re-Melt
2nd Re-Melt 3rd Re-Melt 4th Re-Melt
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MASTER ALLOYDEVELOPMENT
Al-Nb-B Master Alloy
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1. Nb metallic powder+ KBF4
2. Addition of Nb metallic powder to diluted Al-B master alloy
MASTER ALLOY (METHOD 1)
Al
B
Nb
Al
B
Nb
Al
AlNb
Nb
B
B
Al3Nb
NbB2
Al = 68.17 at.%Nb = 26.43 at.% O = 5.40 at.%
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Al-2Nb-2B (METHOD 2)
AlB2-12
NbB2
Al3Nb
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Al-4Nb-1B ON LM25
Reference
Nb-B (M.A.) Al-Nb-B (powders)
680ºC
Al-4Nb-1B ON LM6
680ºC
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Al-2Nb-1B ON Al-10Si
EFFECT OF Al-2Nb-2B ON UNDERCOOING FOR COMMERCIAL Al-Si ALLOYS
EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS
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RESULTS
PISTON ALLOY (HYPER-EUTECTIC: 13 Wt.% Si) 740°C
EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS
EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS
The Charles Hatchett Award 2016 Lecture740 oC
EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS
0
200
400
600
800
1000
1200
1400
1600
0 20 40 60 80 100
α-A
l g
rain
siz
e [
µm
]
Cooling rate, dT/dt [ C/s]
Al-7Si (Ref) Al-7Si (Al-2Nb-2B)
Al-8.5Si (Ref) Al-8.5Si (Al-2Nb-2B)
Al-10.5Si (Ref) Al-10.5Si (Al-2Nb-2B)
The Charles Hatchett Award 2016 Lecture
Co
lum
nar
gra
in s
tru
ctu
re
Chill zone
Fin
e (<
0.5
mm
) eq
uia
xed
grai
ns
Al-10 Si alloy - Direct Chill Cast Billets
colu
mn
ar
Equ
iaxe
d
Referencewith
Al-Nb-B
Zone 4:
equiaxed crystals
Zone 3: long
columnar crystals
Zone 2:
columnar crystals
Zone 1:
chilled zone
Zone 1:
chilled zone
Zone 2: very fine
equiaxed crystals
Zone 3: fine
equiaxed crystals
Reference
Inoculated
Nb-based compounds as heterogeneous nuclei
Al-10Si DC billets
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DC-SIMULATOR
Comparative study between Al-Nb-B and Al-5Ti-B master alloys
Al-2Nb-B master alloy addition
~ 300 µm
Al-10Si
~ 4-5 mm
Al-5Ti-B master alloy addition
0.1%Ti0.1% Nb
Comparison between Ti-B and Nb-B
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GRAIN REFINEMENT EFFICIENCY COMPARISON
WHEEL ALLOYS (HYPO-EUTECTIC: 7 Wt.% Si)
REFERENCE 0.1% Nb (AL-2Nb-2B)
0.1% Ti (Al-5Ti-1B)0.2% MA (Al-5Ti-1B)
740°C
The Charles Hatchett Award 2016 Lecture
Summary
•Nb-B addition to Al-Si melt refines the grain structure of casting
• End-user benefits:• Improved strength & ductility Lighter/thinner structures
•Homogeneous properties (thick & thin sections) Complex structures
•Tolerant to Fe contamination Closed loop recycling of scrap containing higher Fe
• Reduced shrinkage porosity - Improved soundness Component rejection ratio can be minimised
The Charles Hatchett Award 2016 Lecture