“Grain Refinement of Al-Si Alloys by Nb-B …...Grain refinement of Al-Si alloys by Nb-B...

“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


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)


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


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


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


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)


Analogy between Al-Ti & Al-Nb phase diagrams

Al3TiAl3Nb


LATTICE MISMATCH

0.384 nm

Al

Al (face centred cubic)

Al3Nb

Lattice mismatch ~0.9%

Low Lattice Mismatch – Coherent Interface


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


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


Addition of Nb fine metal powder to liquid Al

<45 mmNb- Superconductivity – 9KTo verify the Nb dissolution, magnetic moment vs temperature measured


700ºC

CP-Aluminium

Al with Nb-B

EFFECT OF Nb on CP Al


COMPARISON OF Al-Ti-B AND Nb-B ON CP Al


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


COMPARISON OF Al-Ti-B AND Nb-B TO HYPOEUTECTIC BINARY Al-Si Alloys

Practical alloyscomposition

700ºC


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


0.3 oC/s

Grain size up to 1 cmReference

ΔTRef = 2.1ºC


ΔTNb-B = 1.3ºC

Undercooling in the presence of NbB2/Al3Nb


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


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


200 μm

200 μm200 μm

200 μm

200 μm200 μm

HYPEREUTECTIC BINARY Al-Si ALLOYS – PRIMARY SI

Al-16Si

Al-18Si

Al-27Si


Application of Nb-B grain refiner to Al-Si commercial alloys


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


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


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



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


PorosityAl-11Si (LM6)no addition

Al-11Si (LM6) with Nb-B

10 mm

~200mm

~1200mm

~160mm

~200mm


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


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]





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 [%

]


Nv(ref)

Nv(Nb-B inoculation)

ΔNv

ΔNv / Nv(ref)



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


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


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


Reduced Macro-porosity with Nb-B

Al-11Si (LM6)

with Al-5Ti-B

with Nb-B

1 mm

1000µm

1000µm

1 mm

1 mm


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


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


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


Reference (Al-13Si) with Nb-B


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


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


Al-13Si piston alloy


Al-Nb-B


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


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


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


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


MASTER ALLOYDEVELOPMENT

Al-Nb-B Master Alloy


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.%


Al-2Nb-2B (METHOD 2)

AlB2-12

NbB2

Al3Nb


Al-4Nb-1B ON LM25

Reference

Nb-B (M.A.) Al-Nb-B (powders)

680ºC

Al-4Nb-1B ON LM6

680ºC


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


RESULTS

PISTON ALLOY (HYPER-EUTECTIC: 13 Wt.% Si) 740°C



The Charles Hatchett Award 2016 Lecture740 oC


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)


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


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


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


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


“Grain Refinement of Al-Si Alloys by Nb-B …...Grain refinement of Al-Si alloys by Nb-B...

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