Recent Research Progress in
Grain Refinement of Cast Metals
Mingxing Zhang
School of Mechanical and Mining Engineering, University ofQueensland, St Lucia, QLD, Australia
ARC Centre of Excellence for Design in Light Metals, Australia

Grain Refinement

1• Australian Research Council (ARC) Centre of Excellence for
Design in Light Metals, established in 2005. $3.0 million fr.om
ARC each year
• 6 participation institutions, Headquarter is based at Monash
University.
• 17 CIs, 9 PIs, over 60 full-time researchers, over 100
postgraduates• Research activities include:•••••

Alloy design
Process designHybrid materials
Surface engineering
Mg, Al and Ti alloys, including light metal based BMG andcomposite

Outline• The best grain refiners for light alloys andthe established theories of grain refinement.
• The edge-to-edge matching crystallographic
model and its applications to grainrefinement.
• The roles of peritectic reaction and growth
restrict factor in grain refinement.
• What is beyond us in understanding themechanisms of grain refinement?
Grain Refinement

3Established Work

Grain Refinement

4

The most effective grain refiners• Al3Ti/TiB2/TiC for Al alloys– Al3Ti is the most effective one– Peritectic reaction– Large growth restrict factor – Q value• Zr for Al/Mn/Si-free Mg alloys– Peritectic reaction– Large growth restrict factor – Q value

Grain Refinement

5Major accepted theories/model• Peritectic reaction

Addition of boron has little effect on the Al-Ti phase diagram
Grain Refinement

Actual grain
refinement
start at
0.05wt%Ti
addition, which
is far below themaximum solid
solubility, Thus,
it is considered
there is noperitectic
reaction andthis hypothesis
is discarded6

Major accepted theories/model• Duplex nucleation theory– Formation of Al3Ti shell on TiB2 (Vader et al andBäckerud et al)– Ti segregates to TiB2 (Mohanty et al, Schumacherand Greer)• Solute theory – growth restrict factor– Johnsson, and then StJohn and Easton– ࡽ ൌ ࢓ࢉ૙ (k-1) (c0: concentration; m: gradientof the liquidus; and k = cs/cl)– The higher the Q value, the smaller grains
Grain Refinement

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Major accepted theories/model• Classic heterogeneous nucleation– Development of more effective grain refiners
and the associated master alloys• The edge-to-edge matching model– To minimize the interfacial energy between
the nucleants (the heterogeneous nucleationsites) and the solidified primary solids.

Grain Refinement

8New grain refiners for cast Mg alloys• The carbon group – Al4C3 or Al2CO– Kurfamn, Yano et al, Tamura et al, Lim’s team, X Liu
and J DuG Ma et al: J. Alloys Compd. 491 (2010) 165

J Du et al: J. Alloys Compd. 470 (2009) 134

Grain Refinement

9New grain refiners for cast Mg alloys• Others – AlN, TiB2, SiC, ZnO, Al2Gd and RE

H Fu et al: J. Alloys Compd. 478 (2009) 809

Y Wang et al: Scripta Mater. 54 (2006) 269

Grain Refinement

10New grain refiners for cast Ti alloys
• TiB

• Si

M Bermingham et al: Scripta Mater. 59 (2008) 538

M Bermingham et al: Scripta Mater. 58 (2008) 1050

Grain Refinement11Efficiency• None of them is as efficient and good as
Al3Ti and TiB2 in Al alloys and as Zr in Mg
alloys.
• Why?

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12

The Edge-to-edge
Matching (E2EM) Modeland Its Applications

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The most successful caseIn the past years, the most successful grain refiner isthe Al2Y in Mg alloys developed by the E2EM model.

Without addition

With addition
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Edge-to-edge matching model
Plane-on-plane matching[110]CC

1[11]B[111]BCC(110)BCC(111)FCC
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Edge-to-edge matching model[110]CC1[11(111)FCC]B(110)BCC
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Edge-to-edge matching modelInteratomic spacing misfit =fi =S f − Sb
SfSfSb× 100% < 10%Interplanar (d-value)mismatch =fd =d f − dbdf× 100% < 10%df

Grain Refinementdb17

Application of the E2EM to grain refinement

E2E

Examineexistinggrain
refiners

Grain Refinement

NOSTOP18

Application of the E2EM to grain refinement• M-X. Zhang, P. M. Kelly, M. A. Easton and J. A.
Taylor, Acta Mater. 2005, 53, 1427.

• M-X. Zhang, P. M. Kelly, M. Qian and J. A. Taylor,Acta Mater., 2005, 53, 3261.

• D. Qiu, J.A. Taylor, M.-X. Zhang and P.M. Kelly, ActaMater., 2007, 55, 1447.

• D. Qiu, M.-X. Zhang, J.A. Taylor, H.-M. Fu and P.M.
Kelly, Acta Mater., 2007, 55, 1863.

• D. Qiu, M.-X. Zhang, H.-M. Fu , J.A. Taylor and P.M.
Kelly, Phil. Mag. Letters, 2007, 87, 505.
Grain Refinement

19Application of the E2EM to grain refinement

E2E

Examineexisting
grain
refiners

NO

STOP

YES
Computer
Program

E2E DB
About 10 possible grain
refiners for Mg alloys wereidentified

Grain Refinement20Application of the E2EM to grain refinement• Reduce the number to 4.
 ZnO (new), AlN, Al2Y (new) andAl2Ca (new)• All have good edge-to-edge
matching

Grain Refinement21

Effect of ZnO

For pure Mg
H Fu et al: J Alloys Compd. 456 (2008) 390

Grain Refinement

22Effect of AlN
Mg-3Al alloy

Mg-3Al alloy

H Fu et al: J Alloys Compd. 478 (2009) 809

Grain Refinement

23Effect of Al2CaAZ31 – twin rolled casting

B Jiang et al: Mater Chem. Phys. 133 (2012) 611
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The most successful case – Al2Y

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The most successful case – Al2Y
• D. Qiu, M-X. Zhang, Metall Mater Trans A. 2012,accepted.

• D. Qiu, M-X. Zhang, Metall Mater Trans A., 2010, 41A,3412.

• D. Qiu, M-X. Zhang, J Alloy Compd., 2009, 488, 260.
• D. Qiu, M.-X. Zhang, Scripta Mater., 2009, 61, 312.
• D. Qiu, M.-X. Zhang, Acta Mater., 2009, 57, 3052.

Grain Refinement26

Application of the E2EM to grain refinement• ZnO, AlN and Al2Ca are not as good as
Al2Y.
• All have good matching• Only difference is that Al2Y involves
peritectic reaction:
Al2Y + L → α-Mg

• Peritectic may play a role
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The roles of peritectic
reaction and growth restrict
factor in grain refinement

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The role of peritectic reaction in grain
refinement in cast Al
Group 1(approx. Q=12 k)

Group 2(approx. Q=5 k)Group 3(approx. Q=2 k)Group 4(approx. Q=1 k)

SoluteNominalAddition
Level

GrowthRestriction
FactorNominalAddition
Level

GrowthRestriction
FactorNominalAddition
Level

GrowthRestriction
FactorNominalAddition
Level

GrowthRestriction
Factor

Ti

0.05

11.2

0.02

4.5

0.01

2.3

0.005

1.1

0.15

4.5

0.40

5.1
0.07

2.1

0.04

1.0

0.60

5.11.00

5.1
0.12

0.8

0.20

1.0

0.50

1.0

0.10

0.7

0.20

0.7

0.30

0.7

0.50

0.7

VNb

Zr

--

--

--

--------

--

--

--

--

--

----

Cu

4.50

12.7

1.60

4.5

--

--

0.40

1.1

Mg

4.00

12.2

1.50

4.6

--

--

0.35

1.1

Si

--

--

0.80

4.7

0.35

2.1

0.20

1.2

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The role of peritectic reaction in grain
refinement in cast Al

Pure Al

Addition of
0.35wt%Mg

Addition of
1.5wt%Mg

Addition of
4.0wt%Mg

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The role of peritectic reaction in grainrefinement in cast Al

Pure Al

Addition of0.1wt%Zr

Addition of
0.2wt%Zr

Addition of
0.3wt%Zr

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The role of peritectic reaction in grain
refinement in cast Al

Pure Al

Addition of
0.12wt%Nb

Addition of
0.2wt%Nb

Addition of
0.5wt%Nb

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The role of peritectic reaction in grain
refinement in cast Al

Addition of eutectic-forming
alloying elements

Grain Refinement

Addition of peritectic-forming
alloying elements

33

What are the key factorsthat govern the grain
refinement in cast metals?

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Possible answers• Peritectic reaction• Growth restrict factor• Heterogeneous nucleation• All of them
• What else?

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Acknowledgement• Dr Dong Qiu – UQ
• A/Prof John Taylor – UQ
• Dr Mark Easton – Monash• Mr Feng Wang – UQ
• Mr Zhilin Liu – UQ
• Dr Chun Li – UQ

• Australian Research Council (ARC)
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