Metallic Foam

Metallic Foams

• Metallic foam can be defined as a metallic

material with a cellular structure.

• Metal foams have plenty of pores inside

and their density is much lower than the

solid one.

• Cellular materials are multifunctional

materials with porous structure.

Sandwich Composites- An Overview 2

Preparation of Metal Foam

• Liquid Metallurgy Route Aluminium is melt in stir casting furnace The foaming agent is added to Aluminium melt Aluminium and foaming agent decompose and release the gases When trapped gases in the solidifying metal convert it into a closed-

cell foam

• Foaming Agent

– Titanium hydride - Effective Foaming Agent

– Zirconium hydride - High Cost

– Calcium carbonate - Low Cost ,Easily Available

– Sodium Carbonate - Low Cost , Easily available

Preparation of Metal Foam

• First stage

• 1.1 kg of Aluminium alloy is melt in stir casting furnace

• The melt reaches 650 ºc, the furnace is turned off

• Start the stirrer until the temperature reaches 635 ºC

• Add the 3.3 wt % of foaming agent to the molten metal

• Continue stirring up to 60sec

• When the temperature reaches 580ºC,the rotating stirrer is stopped

• After that crucible with foam can be taken out from the furnace

• The metallic Foam is cooled by air

• Second Stage

• Insert the precursor into sintering furnace

• Bake the precursor for 15min at 650ºc

• Precursor (Foam) can be left cool in air 4

Experimental Results

Sample Material

&foaming

agent

Proportion Density of

Foam

Relative

density

%

Porosity

1. LM6 with

Na2

Co3

1.1kg

3.3wt%

0.96g/cm30.36 63

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Macrostructure Image Results

Macro structure

image

Materials Pore size Micro Vickers

hardness

Value(load

0.3kg)

LM6 with Na2

CO3

Minimum pore

size 2mm

Maximum

poresize

8mm

67

6

The micro-structural analysis of the Al-33wt % of Na2

CO3

is carried out. The

microstructure is shown in Figure

The areal porosity was found to be 63%.

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S.No: Material Specification

Face Aluminium 6061

(same material for both

side)

Density 2.71g/cm3

Foam (Core) LM6 added with Na2

Co3

Density 0.96/cm3

Adhesive Epoxy / Hardener

Redux 322

The resin and

hardener mixing

ratio 10 : 1 Curing

time is 7-10hrs.

Summary of case study1 The density of the Al alloy+CaCo3 and Al alloy+Na2Co3

was found to be 1.65g/cc and 0.96g/cc respectively.

2. The porosity of the Al alloy+CaCo3 and Al alloy+ Na2Co3 was found to be 36 % and 63% respectively.

3. A sandwich panel is developed with dimensions of ASTM standards to conduct three point loading test. The maximum deflection for al alloy+ Na2co3 foam at a load of 2300N is found to be 1.61mm. The values obtained were compared with theoretical formula at load of 2300N is found to be 2.22mm.

Comparison of Foam core

• PVC (closed cell)

- ‘linear’ – High ductility, low properties

- ‘cross-linked’ – High strength and stiffness but brittle

- ~ 50% Reduction of properties at 40-60oC

- chemical breakdown (HCl vapour) at 200oC

• PU

- inferior to PVC at ambient temperatures

- better property retention (max. 100oC)

• Phenolic

- Poor mechanical properties

- Good fire resistance

- Strength retention to 150oC

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Polyurethane Foam

Comparison of Foam Core

• Syntactic Foam

- Glass or polymer microspheres

- Used as sandwich core or buoyant filler

- High compressive strength

• Balsa

- Efficient and low cost

- Absorbs water (swelling and rot)

- Not advisable for primary hull and deck structures

- OK for internal bulkheads

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Mechanical Thermal Protection System(for Skin)

(For a hypersonic aircraft - 5 Mach Number)

Requirement : To withstand surface temperature of 1100oC

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Ceramic wool of thickness 40mm

Facing sheet – Ni alloy of 0.08 - .1mm

Core - Ni alloy of 4mm cell size honeycomb structure

Core - Ti alloy of 4mm cell size honeycomb structure

Facing sheet – Ti alloy of 0.3 - .4mm

Sandwich Panel with Thermal Barrier Coating

• Exposed surface temperature found under such conditions was 5240C

• Temperature of the air outside the colder (inner) surface of the

sandwich panel was sustained at 210C (room temperature)

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High Strength Applications

• Diamond orientation 304 stainless steel textile sandwich panel with

relative core density (12.6%).

• Tetrahedral structures are stacked node to node with an interleaved

planar hexagonal perforated layer

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SMA Composite