MC-TRCMelt conditioned twin roll casting

MC-TRCMelt conditioned twin roll casting

Z BCAST (Brunel Centre for Advanced Solidification Technology)

Brunel University

UK

Introduction

Key challenges in the development of twin roll casting (TRC) include elimination of central line segregation, increasing cast speed, increasing the range of twin roll castable alloys.

MC-TRC=TRC+MCAST

Melt conditioned alloy melt contains well dispersed oxide particles which enhances heterogeneous nucleation

Enhanced nucleation allows fully equiaxed solidification

Fine and equiaxed grains reduces/eliminates central line segregation

All these will increase casting speed and enlarge the ranges of twin roll castable alloys.

MC-TRC ProcessMC-TRC Process

Melt Conditioned Twin Roll Casting Process

Microstructure of TRC Al-alloy strip

Microstructure of TRC Al-alloy strip

TL

TRC

5754 (0.4%Fe)

MicrostructureMicrostructure

TL

MC-TRC + GR

5754 (0.4%Fe)

MicrostructureMicrostructure

MC-TRC

AZ31 strip, 4mm thickness, as-cast

TRC

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

500

600

700 TRCMC-TRC

Gra

in s

ize

(mic

ron

)

Normalised thickness

AZ91D

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

500

600

700 TRCMC-TRC

Gra

in s

ize

(mic

ron

)

Normalised thickness

AZ91D

Microstructural variationMicrostructural variation

4mm AZ91D strip

Elemental distributionElemental distribution

 

              

 

             

 

0.0 0.2 0.4 0.6 0.8 1.05

10152025

01234

78849096

Normalized thickness

Al

Zn

Mg,

Al a

nd Z

n co

nten

t (w

t. %

) Mg

0.0 0.2 0.4 0.6 0.8 1.05

10152025

01234

78849096

Nomorlized thickness

Al

Zn

Mg,

Al a

nd Z

n co

nten

t (w

t. %

) Mg

TRC

4mm AZ91D strip

MC-TRC

Microstructural evolutionMicrostructural evolution

AZ31 stop sample

TRC

TRC

MC-TRC

Solidification mechanismsSolidification mechanisms

Tip Roll

L L+S S Nip

L

L+S

S

L

L+S

S

L

L+S

S

L

L+S

S

MC-TRCTRC

Mechanical propertiesMechanical properties

AZ91

(As-cast)

YS.

(MPa)

UTS

(MPa)

Elongation

(%)

TRC, tested at 3500C 11.0 47.0 43.4

MC-TRC, tested at 3500C 8.5 38.5 118.1

Mechanical propertiesMechanical properties

AZ31

(Rolled)

YS.

(MPa)

UTS

(MPa)

Elongation

(%)

TRC, Rolled at 4000C 181.6±4.3 243.1±6.1 9.6±1.6

MC-TRC, Rolled at 4000C 177.7±8.0 251.1±5.2 27.7±5.2

Advantages of MC-TRC over TRC

Increased melt fluidity, reduced sensitivity to processing conditions

Fine and uniform microstructure through the strip thickness

Eliminated/reduced central line segregation

Increased casting speed

Increased tolerance to impurity elements and inclusions

Enlarged twin roll castable alloy range

Increased deformability

Enhanced mechanical properties

Applicable to both Al-alloys and Mg-alloys