EFFECTS OF RAPID SOLIDIFICATION ON MICROSTRUCTURE

Department of Mechanical and Industrial Engineering

ME 8109

Casting and Solidification of Materials

AND PROPERTIES OF AL, MG & TI ALLOYS

Presented by

Mohammad Anwar Karim

Id : 500458773

Winter 2012

ORGANIZATION OF PRESENTATION

� Introduction

� Objectives and Methodology

� Overview of Rapid solidification

TechnologyTechnology

� Rapid solidification effects on Al alloys

� Rapid solidification effects on Mg alloys

� Rapid solidification effects on Ti alloys

� Summary and Conclusion

INTRODUCTION

� Rapid solidification process is a technique-

� To solidify the melt of the material

� To employ the high cooling rate in excess of 1000 -10000 k/s during solidification

� To develop microstructure, mechanical and physical� To develop microstructure, mechanical and physicalproperties of the structure materials.

� It is important for the automotive, aerospace andplastic industries.

� As a low-density materials, lightweight metals likealuminum, magnesium, and titanium as primecandidates for structural applications.

OBJECTIVES AND METHODOLOGY

Objectives� To explore the basic concept of

solidification behavior and rapidsolidification (RS) process

� To recognize contemporary

Methodology

� Review from the books

� Review from the Journals

Internet Browsing� To recognize contemporary

fields of application of rapidsolidification technology

� To summarize the effects of RSon microstructure & mechanicalproperties development of Al,Mg and Ti alloys

� Internet Browsing

BENEFITS OF RAPID SOLIDIFICATION TECHNOLOGY

Rapid solidification technology (RST) has been used

� To achieve unique microstructure

� To improve mechanical and physical properties

� To increase the range and quantity of alloying elements elements

� To refine grain size

� To enhance solid solubility

� To refine the segregation pattern

� To develop metastable phases

� To reduce dendrite arm spacing

EUTECTIC PHASE DIAGRAM

EUTECTIC PHASE DIAGRAM

� The minimum affects of nucleation behavior occur atlower cooling rate range 100-1000 K/s.

� At higher cooling rates, local equilibrium cannot becontinued at the solid-liquid interface.

� Below the solidus line (below point 1), the melt willtransform enormously to the α-phase of the samecomposition.

� Microstructural reformations in an alloy occur whencontent of the solute is higher than the maximum solidsolubility Cmax.

EUTECTIC PHASE DIAGRAM

� From the equilibrium phase diagram, alloycomposition C2 must contain a mixture of α and βphases

� At composition C3 ,there is an opportunity for theformation of metastable phases applying theundercooling produced by rapid solidification.

� Grain sizes of rapidly solidified materials are 0.1-10µm.

DENDRITE ARM SPACING VS COOLING RATE

(DURING RAPID SOLIDIFICATION)

�As the cooling rate is increased from 0.01 to

1000000 K/s, the dendrite arm spacing in

different alloys is reduced from 100 µm to 1

µm .

CHARACTERISTICS OF ALUMINUM, MAGNESIUM AND

TITANIUM

Property units Mg Al Ti

Atomic number 12 13 22

Atomic weight g/mole 24.31 26.98 47.90

Metallic valance 2 3 4

Electronegativity 1.2 1.5 1.6Electronegativity 1.2 1.5 1.6

Crystal structure h.c.p. f.c.c. h.c.p./ b.c.c.

Nearest interatomic

distance

A˚ 3.20 2.85 2.93

Density g/cm³ 1.74 2.70 4.51

Melting point ˚C 650 660 1668

Normal electrode Normal electrode Normal electrode Normal electrode

potentialpotentialpotentialpotential

V -2.375 -1.706 -1.63

RANGES OF THE MAXIMUM EQUILIBRIUM SOLID SOLUBILITY’S OF

X IN AI-X, MG-X AND TI-X BINARIES

System Type Solubility Range (at.%)

<0.1 0.1-1 1-5 5-25 >25

AL-X E Be,Y,B,Re

Acti, VIIIa, Ca

Vb,VIb,Sr, Ba,Sn

Be,Sc, Mn

Si, Cu, Ge Ga, Li, Mg,

Ag

Zn (66.4)

P Mo,Nb,Ta,W,Zr Cr,Hf,V,Ti

M Bi,In,K,Na,Pb

Tl,Cs

Mg-X E As,Ba,Ce,Co

Cu,Eu,Fe,Ge

La,Na,Ni,Pd

Pr,Sb,Si,Sr

Au,Ca,Ir,Nd,

Th

Ag,Bi,Dy,Ga

Gd,Hg,Pu,Sn

Y,Yb,Zn,Zr

AL,Er,Ho,Li

Lu,Pb,TI.Tm

P Mn,Ti Zr In,Sc

I Cd(100)

Ti-X BI V,Nb,Ta,Mo

Eid Fe,Co,Ni,Cu

Si,B

Cr

PidPidPidPid BBBB CCCC Ge,Sn,O,HGe,Sn,O,HGe,Sn,O,HGe,Sn,O,H Al,AgAl,AgAl,AgAl,Ag

MMMM----PPPP Y,La,Ce,NdY,La,Ce,NdY,La,Ce,NdY,La,Ce,Nd

Er,GdEr,GdEr,GdEr,Gd

MAXIMUM EQUILIBRIUM SOLID SOLUBILITY

OF ALUMINUM BINARY SYSTEMS

� Maximum elements form eutectic-type systems and

have a maximum TSS which is greater than 1 %.

� Seven elements (beryllium, silicon, zinc, gallium,

germanium, tin, and magnesium) form simple

eutectic systems with aluminum.eutectic systems with aluminum.

� Outer transition metals belong to high melting points

form peritectic type systems with Al with TSSs

lower than 0.6 %.

� Other elements are partially miscible with Al and

solidify monotectically with TSSs lower than .02 %.

MAXIMUM EQUILIBRIUM SOLID SOLUBILITY

OF MAGNESIUM BINARY SYSTEMS

� Maximum elements form eutectic-type systems

with Mg and have a maximum TSS which is

greater than 1 %. for 20 elements.

� Only Five elements (indium, manganese,

scandium, titanium, and zirconium) arescandium, titanium, and zirconium) are

recognized to form peritectic type systems with

magnesium.

� Cadmium is only single isomorphous element

which displays 100% TSS in magnesium.

MAXIMUM EQUILIBRIUM SOLID SOLUBILITY

OF TITANIUM BINARY SYSTEMS

Beta Stabilizers-

� Four elements form Beta Isomorphous systems with

Titanium which has maximum TSS lower than 25%

� Six elements form Beta Eutectoid type systems with

Titanium having maximum TSS 5 – 25 %Titanium having maximum TSS 5 – 25 %

Alpha Stabilizers

� Eight elements form Peritectoid type systems most

of which have maximum TSS higher than 5 %

� Six elements form Peritectic type systems which

have maximum TSS lower than 1%

EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE

OF AL-6MN-3MG ALLOY

SEM IMAGE: Structure of as-extruded Al-6Mn-3Mg alloy:

a) IM material; b) RS material

� Relatively coarse particles observed in IM microstructure

� The size of particles in IM material is varied within 10-100 µ m. Large

particles were fractured during the hot extrusion that resulted in the

increase of the material porosity.� Rapid solidification results in efficient refining of the particles, which are

50-600 nm in size

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF AL-6MN-3MG ALLOY

� A preliminary microstructure of as-extruded RS

material and the microstructure of the sample

annealed at 500ºC / 7 day.

�Particles coarsening are attained by long-term

annealing of RS material at 500ºC and then particles

size reached 1-3 µm after annealing at 500ºC / 7 days.

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF MG-AL ALLOYS

� Optical micrographs of as-cast-

a) Mg-5Al alloy b) Mg-15Al alloy

c) Mg-30Al alloy ingots.

� Microstructure consists of twoconstituents (i) α-Mg solid and (ii)Eutectic.Eutectic.

� The eutectic structure existing alongthe grain boundaries increases inamount with increasing Al content.

� The microstructure in the Mg-30Alalloy is almost entirely made up of

the eutectic constituent.

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF MG-AL ALLOYS

Optical micrographs of RSP flakes

(a)–(c) transverse and

(d)–(f) longitudinal sections.

(a) and (d) Mg-5Al,

(b) and (e) Mg-15Al,

(c) and (f) Mg-30Al alloys.(c) and (f) Mg-30Al alloys.

� Well-developed dendriticstructures are observed in thetransverse direction

� Dendrite arm spacing is verygood which is about 2 µm in theRSP Mg-15Al flakes whichoccurred during RSP.

EFFECT OF RAPID SOLIDIFICATION ON MECHANICAL

PROPERTIES OF MG-AL ALLOYS

� As Al content increases, the

hardness of the alloys also

increased.

� It increased from about 50 VHN

for the Mg-5Al ingot to about 185

VHN for the Mg-30Al ingot.VHN for the Mg-30Al ingot.

� Flake material has a higher

hardness than as-cast ingot

material due to the fine

microstructure.

� The hardness of the flakes also

increased from about 60 VHN for

Mg-5Al to about 210 VHN for

Mg-30Al.

EFFECT OF RAPID SOLIDIFICATION ON MECHANICAL

PROPERTIES OF MG-AL ALLOYS

� The tensile strength

increases with

increasing Al content.increasing Al content.

� As a Al content

increases, the

elongation decreases.

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY

SEM image (backscattered) shows

� Needle-shaped boride phase (black),

� Cuboidal yttria particles (white) and

� Martensitic titanium matrix (grey)

in Ti-6A1-4V-1B-0.5Y ingot solidified in a

water-cooled copper hearth.

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY

SEM image shows the cross-section of a multi-layer melt-

spun fibre.

� For a single layer, there are two microstructural zones:

A. the equiaxed dendrite zone at free side (F) and

B. the columnar grain zone at wheel side (W).

�The coarse yttria particles (white) can also be seen in

this micrograph.

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY

�SEM image (secondary) of the consolidated

Ti-6A1-4V-1B-0.5 Y rapidly solidified alloy

shows the uniform distribution of fine boride

and yttria particles in the titanium matrix.

EFFECT OF RAPID SOLIDIFICATION ON

MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY

�Bright-field TEM image of the consolidated

RS Ti-6A1-V-1B-0.5Y alloy shows-

� the detailed morphology of boride and yttria

particles in the titanium matrix.

EFFECTS OF COOLING RATE ON TENSILE PROPERTIES

OF A TI-MO-AI ALLOY

Production method UTS

(MPa)

RA(%)

Casting 895 12

Cast + Hot worked 1070 22

1000/10000 cooling + Hot isostatic pressing 1070 22

Flake 1000000/10000000 cooling +Hot isostatic pressing 1035 30

During rapid solidification of as-cast Ti-Mo-Al

alloy, both strength and ductility increase with

cooling rate.

CONCLUSIONS

� New production techniques and use of new materials are very important considerations

in the high technology industries.

RS has several barriers-

� need for optimization of processing routes

� needs heavy capital investment and competitive new technologies

� present high cost of RS materials

Elevated temperature aluminum alloys have more potential than high-strength aluminum � Elevated temperature aluminum alloys have more potential than high-strength aluminum

alloy.

� Intermetallic compounds based on aluminum are the major potential area for high-

temperature applications.

� Low density magnesium systems based on magnesium are the major potential area for

requiring optimization.

� The hardness and tensile strength of the RSP alloys is higher than in the IM alloys due to

the fine size of the α-Mg and β-Mg-Al phases.

� Refined and more desirable microstructures can be attained by rapid solidification of

titanium from conventional alloys .

THANK YOUTHANK YOU