Time (s)

Max

imum

equivalen

tstres

s(M

Pa)

0.025 0.05 0.075 0.10

5

10

15

20

25

30

35

40

451% Cu3% Cu5% Cu7% Cu9% Cu

Time (s)

Gap

size

(m)

0.025 0.05 0.075 0.10

2E-06

4E-06

6E-06

8E-06

1E-05

1.2E-05

1.4E-05

1.6E-05 1% Cu3% Cu5% Cu7% Cu9% Cu

•Combined thermal, solutal

and momentum transport.• Assume a rigid mold.• Imperfect contact and air gap

formation at metal/mold interface

Design of mold surface topography during early stage solidification of

Al alloysPI: Prof. Nicholas Zabaras Participating students: Deep Samanta, Lijian Tan

Material Process Design and Control Laboratory

D. Samanta and N. Zabaras, “A coupled thermomechanical, thermal transport and segregation analysis of the solidification of Aluminum alloys on molds of uneven topographies ”, Materials Science and Engineering: A, in press.

Lijian Tan, Nicholas Zabaras, “A thermomechanical study of the effects of mold topography on the solidification of Aluminum alloys", Materials Science and Engineering: A, Vol. 404, 197-207, 2005.

D. Samanta and N. Zabaras, “Numerical study of macrosegregation in Aluminum alloys solidifying on uneven surfaces”, International Journal of Heat and Mass Transfer, Vol. 48, 4541-4556, 2005.

L. Tan, D. Samanta and N. Zabaras, “A coupled thermomechanical, thermal transport and segregation analysis of the solidification of aluminum alloys on molds of uneven surface topographies”, Proceedings of the 3rd M.I.T. Conference on Computational Fluid and Solid Mechanics, Massachusetts Institute of Technology, Cambridge, MA, June, 2005 .

Selected publications

Parametric analysis for the following parameters:

1) Wavelength(λ) 2) Concentration (CCu) 3) Superheat (ΔTmelt)

Time (s)

Airgap

size

(m)

0.025 0.05 0.075 0.10

2E-06

4E-06

6E-06

8E-06

1E-05

1.2E-05

superheat = 0 oCsuperheat = 30 oCsuperheat = 45 oC

Time (s)

Max

imum

equivalen

tstres

s(M

Pa)

0.025 0.05 0.075 0.1

10

15

20

25

30

35

40 superheat = 0 oCsuperheat = 30 oCsuperheat = 45 oC

Time (s)

Max

imum

equivalen

tstres

s(M

Pa)

0.025 0.05 0.075 0.15

10

15

20

25

30

35

40

45 = 3 mm= 5 mm= 7 mm= 9 mm

Time (s)

Airgap

size

(m)

0.025 0.05 0.075 0.1

2E-06

4E-06

6E-06

8E-06

1E-05

1.2E-05

1.4E-05

1.6E-05= 3 mm= 5 mm= 7 mm= 9 mm

low solid fraction high solid fractionLow solid fractions usually accompanied by melt feeding.

With increase in solid fraction, there is an increase in strength and bonding ability of dendrites.

13 T sh sw T I

qe

Left: Evolution of pressure at trough with time at selected wavelengths.Right: Mean shell thickness at gap nucleation time.

Cornell UniversityCollege of Engineering

Sibley school of Mechanical and Aerospace Engineering

Surface defects in casting

Sub-surface liquation Crack formation Ripple formation

Uneven mold surface topography effects

Undesirable growth using plain mold

Desirable growth using uneven mold

Modeling effects of uneven mold surface on solidification

Fluid flow

Heat transfer

Casting domain

Heat transfer

Mold

Contact pressure/ air gap criterion

Solute transport

Inelastic deformation

Phase changeand mushy zone

evolution

Deformable or non-deformable mold

• Heat transfer in the mold, solid shell and melt.• Heat transfer causes deformation (thermal stress).• Gaps or contact pressure affect heat transfer.• Solidification after air-gap nucleation not modeled.

Gap nucleation time (comparison with analytical study)

Maximum equivalent stress (MPa)

Frontu

nev

ennes

s(m

)

16 20 24 28 320

0.0004

0.0008

0.0012

0.0016

With inverse segregationWithout inverse segregation

= 1 mm

= 9 mm= 7 mm

= 3 mm= 5 mm

Copper concentration (wt %)

Equivalen

tstres

sat

den

drite

roots

(MPa)

0 2 4 6 8 100

2

4

6

8

10

12

14

16

18

Al-Cu alloy with 1.8% Cu is most susceptible to hot tearing

Wavelength less than 5mm

corresponds to an optimum

3 2

45 , 1 , 0.5 ,

, ( 93 10 / )

oV wall liquid

Platform liquid liquid

height mm

J m

Surface tension effects

Initial contact between mold and liquid

The size of micro-gap

Heat flux at early stages of solidification

Surface quality of aluminum casting

Mold topography Surface energy Gravity

A change of surface tension drastically changes the solidification speed at very early stages of solidification.

4

10 ,

2 10 ,

0.6wall liquid

height m

P Pa

Micro-scale effects

Macro-scale effects

4

10

10

height m

P Pa

4

10

2 10

height m

P Pa

10

25o

height m

27.124.421.719.016.313.610.98.15.42.7

891.1878.7866.2853.8841.3828.9816.4804.0791.5

901.5886.9872.3857.7843.1828.5813.9799.3784.7770.1

18.316.114.412.610.89.07.25.43.61.8

Equivalent stress (t = 0.1 s) Isotherms (t = 0.1s)

λ = 3 mm

λ = 5 mm