Grain Refinement of Aluminum Alloys

Presented By

SUBRATA SAHA

Whats and Whys?

�Grain Refinement is a process used for grain boundarystrengthening of casting material.

� Aluminum alloys with ultra fine grain structure has received

Objectives

� Aluminum alloys with ultra fine grain structure has received

tremendous increase in research interest in various disciplines

specially in automotive and aerospace industries for properties

like low density and good castability.

�Grain refinement of Al and its alloys improve the mechanical

properties of casting along with surface finish, soundness etc.

Grain Refining Effect

a. Grain refiner added: fine, equiaxed structure; b. no grain refiner: coarse, columnar

structure; c. no grain refiner: predominantly twinned columnar grains (feather grains)Source: Quested, 2004

Methods of grain refinements used in castingprocess are mainly classified into following threegroups

Thermal method i.e. Cooling rate control

Methods of Grain Refinement

Thermal method i.e. Cooling rate control

Chemical method i.e. Grain size refiners addition

Mechanical method i.e. agitation of melt during solidification

Grain Refinement Technology

TiAl3 nucleates aluminum grain Source: Backerud, 1983

Cooling Curve

Cooling curve during solidification

Source: Sigworth and Kuhn, 2008

Comparison of Effect of Grain Refinement

Grain refining of A356 alloy by three master alloys

Source: Lu, Wang and Kung, 1981

What’s the Figure Says?

� TiAl3 crystals are poor nuclei.

� TiB2 particles are excellent nuclei.

Mostly usedMostly used

� AlB2 is the best nucleus.

Not Suitable for

Industry.

� Al-Si Alloys : like A356 and A357 best result by adding

10-20 ppm of boron in the form of Al-5Ti-1B or Al-3Ti-1B

rod.

�Al-Cu Alloys: for Al-4.5%Cu-0.5%Mn alloys best result

Best Grain Refinement Practices

�Al-Cu Alloys: for Al-4.5%Cu-0.5%Mn alloys best result

by titanium less than 0.05% and adding 10-20 ppm of boron

as Al-5Ti-1B or Al-3Ti-B rod.

� Al-Si-Cu Alloys : like A319 alloys (Al-3%Cu-5.5%Si)

best 10-20 ppm of boron in the form of Al-5Ti-1B or Al-3Ti-

1B rod.

� Al-Zn-Mg Alloy: For these alloys best result found with 0.02 to

0.05% of titanium and addition of 10-20 ppm of boron as Al-5Ti-

1B or Al-3Ti-1B rod.

�Al-Mg Alloys: like 535 alloys (Al-7%Mg) best result found

with addition of 30 ppm B in the form of Al-3%Ti-1%B master

Best Grain Refinement Practices (Continued)

with addition of 30 ppm B in the form of Al-3%Ti-1%B master

alloy.

Major benefits:

� better distribution of Porosity.

Benefit of Grain Refinement Process

� improved Feeding.

� improved Fluidity.

� improved Surface finish & Machinability.

�better mechanical properties

� Development of a model to predict grain size

in the presence of significant thermal gradient.

� Development of an economical viable

method allowing tight control of the size

Future Work

distribution of inoculants particles present in

the melt. This might be achievable via filtering

of the molten maser alloys or by direct

inoculation of ceramic

�Application of grain refinement theories to

non-aluminum based system

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