Innovative approach to structure control in light alloys

Dmitry Eskin, Hari-Babu NadendlaBrunel Centre for Advanced

Solidification Technology

BCAST: Vision• BCAST is an international leader in liquid metal engineering with focus on

solidification research, strategic technology developments and user-led industrial applications. We conduct fundamental research to generate world-class knowledge in solidification science. We develop and exploit innovative and sustainable technologies and enable the metal casting industry and its customers to improve their competitiveness in global markets.

Brunel University8 constituent academic schools10 research institutes15,200 full-time students 2,500 staff

BCAST3 Professors5 Lecturers11 Research Fellows8 PhD students5 Support staff

Research• Fundamental research: Nucleation–based solidification research

including the structure of liquid metal, mechanisms of heterogeneous nucleation and the generic approach for enhancing and controlling nucleation through both physical and chemical methods.

• Technology development: Innovative generic technologies for liquid metal treatment and applications of developed to the existing shape casting and continuous casting processes.

• Industrial applications: Proprietary applied research with individual industrial partners to exploit fundamental research and generic technological development to support the metal casting industry in implementing innovative processing technologies and new products.

Outline

• Why we think that metals are underestimated in European programmes

• Scandium – ultimate addition to Al alloys• Grain refinement using designed master alloys• Ultrasonic cavitation processing – universal

technology• Conclusions

What is the age we are living now in?

Stone age

2.5 mln BC-2000 BC

Bronze age

3300 BC-600 BC1300 BC-300 BC

Iron age

Middle age

Renaissance

Industrial age

Electronic a

ge

Nano- age?

What are the important materials?Metal Annual production, mln t Annual production, mln m3

Iron and steel 1921 243

Plastic* 245 190

Aluminium 33.9 12.5

Copper 15.23 1.7

Zinc 10.76 1.5

Magnesium 0.429 0.24

Zirconium 0.9 0.138

Titanium 0.09 0.02

Niobium 0.081 9.45 x 10-3

Scandium 10 x 10-9 (2 x 10-6, oxide)

3.39 x 10-11 m3

What can be called extreme processing conditions?

Temperature: 700-800 °C for Al melting and castingSpeed: cm/sPressure: 1 atmTime-scale: minutes to hoursLength-scale: cm to meters

What can be called extreme processing conditions?

Temperature: more than 5000 KSpeed: faster than 1500 m/sPressure: up to 10000 atmTime-scale: less than 100 µsecLength-scale: 5 to 500 µm

“The conditions inside the collapsing bubbles are theoretically extreme enough to allow nuclear

fusion to take place.” Nature 440, p.132 (9 March 2006)

Potential of Scandium

Al-Sc master alloy

Al alloy billet

Effects of ScandiumSc is prone to supersaturation in (Al)

Al3Sc is the only one phase in Al-based systems:•Equilibrium L12 phase•Lattice parameters perfectlymatching Al – can be coherent•Precipitates at 200-300 °C

Primary: perfect grain refinerSecondary: powerful, coherent,

equilibrium hardenerSecondary: powerful, equilibrium,

stable grain blocker

L. Toropova et al.

How to realize the potential of scandium in aluminium alloys

•Scandium is expensive soa much cheaper master alloy produced directly from oxidesis an alternative

•Scandium can be added in combination with other elements, e.g. Zr, with resulting 2-3 times lower addition level

•Scandium is not a rare metal, it is scattered. Increased bulk demand would result in lower costs and price

Designed grain refiners based on less-common transition elements

0.384 nm0.384 nm

0.405 nm 0.405 nm

Al

Al (face centred cubic)New grain refiner has• Higher melting temperature than Al• Good lattice matching (with Al and Al-Si matrix crystals)• Chemical stability with Al and other commonly used alloying elements• No compounds with alloying elements (no poisoning)

Al-Si alloys are the base for most castings used in cars, aircrafts, pumps, engines etc

Al-Si binary alloys

Tp1 test700 OC

Practical alloyscomposition

-1 0 1 2 3 4 5 6 7 8 9 10

500

1000

1500

2000

2500

Gra

in s

ize [ m

m ]

Si [ wt.% ]

Al-Si alloy Al-Ti-B novel grain refiner

M. Nowak & N. Hari Babu

Patentapplication

LM6

20 mm

LM6 with Grain refiner addition

Slow cooling rate0.07 K/s

With NGR additionWithout addition

M. Nowak & N. Hari Babu

Cavitation

Cavitation zone

Acoustic streaming

Non affected area

(D. Eskin et al., 2010)

(N. Alba-Baena et al., 2011)

(Garcia-Rodriguez et al , 2011)

Cavitation

Structure refinement in light alloysIn the liquid state: activation

of nonmetallic inclusions

In the liquid state: dispersion and refinement of nucleating substrates, e.g. intermetallics

In the solidification range: fragmentation of dendrites and dispersion of fragments

Primary intermetallics: fragmentation, nucleation

Al2O3 wetting

Al3(Zr, Ti)

D. Eskin et al.

Degassing in Al (GA 286344)

N. Alba Baena & D. Eskin, 2012

Nanocomposite materials

Nanocomposite materials

Conclusions

• The potential of advanced “conventional” metal is great and is related to less-common and scattered metals and to extreme processing.

• Advances bring about economical, technical, societal and environmental impact.

• There is large potential for fundamental scientific advances for support of advanced metallic materials.