VINAYAK KUMAR - 212314011

SANJAY SINGH - 212314013

Discovered at MIT in 1970

During research on hot tears

Molded by Lead-Tin alloys in the annular space created by two concentric cylinder.

Outer cylinder was rotated & discovered that the when the outer cylinder was continuously rotated the semisolid alloy exhibits low shear strenght even at high fraction of solidified.

So a novel nondendritic (spheroidal) microstructure .

Semisolid alloys displayed viscosity that depends on shear rate and that risers hundred to thousand of poise when at rest and yet increase to less than 5 to 50 poise upon vigorous agitation.

So we can control the viscosity of alloy metal.

Under forced convection Fragmentation of primary dendrites by

Root melting of secondary dendritic arms

Bending and shearing of secondary dendritic arms

Bending and root melting of secondary arms

Fragments of primary dendrites grow into globular grains under forced convection

Thixo is a general term used to describe the near-net shape forming process from a partially melted nondendritic alloy slug within a metal die.

“Thixotropy”- viscosity decreases with time due to constant agitation or strain.

If the component shaping is performed in a closed die it is called Thixocasting.

If the component shaping is performed in an open die it is called ThixoForming.

Bar could be cast from semi-solid that possesses non dendritic microstructure.

These bar then represent a raw material that could be heated.

Process is conducted using a cold chamber high pressure die casting.

Medium frequency induction heater is used.

Specimen are formed 50% liquid fraction and different injection speed

Temperature of the die is maintained at 150˚C

Semi-solid metal working offers lower operating temperature and reused metal heat content.

Viscous flow behavior could provide laminar casting fill which reduce gas entrapment.

solidification shrinkage would be reduced in direct proportion to fractional solidification within the semi-solid metalworking alloy, which should reduce both shrinkage porosity and tendency towards hot tears.

Viscous nature of SSA provides environment for metal-matrix composites.

Blister – (occasionally ) on the surface of Al at 540˚c.

Cold shut, fold and laps- (infrequent) Where two metal meet but fusion is incomplete.

Non fill- (infrequent) Due to premature freezing, low pressure or metal velocity or entrapped mold atmospheric air prevent the complete filling of die cavity.

Remedy- increase the liquid fraction in slug, raising die temperature, increase venting & higher pressure and high velocity.

Surface blow- (occasionally) When lubricant and hydraulic fluid trapped on the die surface.

Remedy- Ensuring that all the die surface are clean and dry.

Hot tears (infrequent)

Shrinkage porosity

Remedy- by adjusting of die temperature and feeding section and by high temperature and pressure during dwell time.

Gas porosity- (very infrequent)can be due to high gate velocity resulting excessive turbulence and atmospheric gas entrapped.

Remedy- Decrease the velocity.

Flow lines(occasionally)

Manufacturing with complex shape thin wall etc.

Good mechanical properties.

High dimensional tolerance and accuracy.

Globuletic micro structure.

Near net shaped product.

Lower forming temperature.

longer die life.

Need for special feed stock with near net spheroid primary crystal.

Expensive.

Automotive wheel, motor brake cylinder, antilock brake valve, disk brake caliper, engine piston

Thank you