The document discusses the discovery of semisolid metal processing at MIT in 1970 during research on hot tears in lead-tin alloys molded in an annular space between two concentric cylinders. When the outer cylinder was rotated, the semisolid alloy exhibited low shear strength even at high fractions of solidification, resulting in a novel nondendritic microstructure. Semisolid alloys were found to display thixotropic properties, with viscosity dependent on shear rate ranging from hundreds to thousands of poise at rest to less than 50 poise during agitation, allowing control of alloy viscosity.

1. VINAYAK KUMAR - 212314011
SANJAY SINGH - 212314013

2.  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.

4.  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

6.  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 Thixo
casting.
 If the component shaping is performed in an open die it is called Thixo
Forming.

7.  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

9.  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.

10.  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.

11.  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.

12.  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)

13.  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.

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

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

16. Thank you