Hot chamber die casting of semisolids

Abstract

A hot chamber method of die casting material in a semisolid state. The semisolid material has a high viscosity, which can be controlled by controlling the fraction of solid phase and the morphology of the solid phase. By controlling the viscosity of the melt, turbulence and consequent gas entrapment can be minimized or eliminated. Further, shrinkage is substantially reduced, thereby reducing porosity and hot tearing to form stronger, more reliable castings.

What is claimed is:  
     
         1 . A method of die casting, comprising 
 holding a composition at a temperature between the liquidus temperature and the solidus temperature of the composition;    agitating the composition to form a slurry of primary solids comprising discrete solid particles in liquid while preventing the formation of interconnected solid dendritic networks;    pumping the composition into a die with a pump at least partially immersed in the composition; and    solidifying the material in the die.    
     
     
         2 . The method of    claim 1   , wherein agitating is accomplished by mechanical stirring.  
     
     
         3 . The method of    claim 1   , wherein agitating is accomplished by electromagnetic stirring.  
     
     
         4 . The method of    claim 1   , wherein the composition comprises a majority component of a metal selected from the group consisting of magnesium, zinc, and aluminum.  
     
     
         5 . The method of    claim 4   , wherein a surface of the pump in contact with the composition comprises a ferrous material.  
     
     
         6 . The method of    claim 1   , further comprising applying a pressure greater than atmospheric pressure to the slurry.  
     
     
         7 . A hot-chamber die caster, comprising: 
 a container for holding a semisolid composition between its liquidus and solidus temperatures;    means for agitating the semisolid composition to form a slurry of primary solids comprising discrete solid particles in liquid while preventing the formation of interconnected solid dendritic networks;    a die for casting the composition; and    a pump, at least partially immersed in the semisolid composition and arranged to pump the composition into the die.    
     
     
         8 . The hot-chamber die caster of    claim 7   , wherein the agitation means comprise a mechanical agitator.  
     
     
         9 . The hot-chamber die caster of    claim 7   , wherein the agitation means comprise an electromagnetic agitator.  
     
     
         10 . The hot-chamber die caster of    claim 7   , wherein the caster is adapted to cast an alloy comprising a metal selected from the group consisting of aluminum, magnesium, and zinc.  
     
     
         11 . The hot-chamber die caster of    claim 10   , wherein a surface of the pump in contact with the semisolid composition comprises a ferrous material.  
     
     
         12 . The hot-chamber die caster of    claim 7   , further comprising a pressure inlet for applying a pressure greater than atmospheric pressure to the semisolid composition.