Method of forming a part with a globular microstructure

Abstract

A method forms a die-cast metal part having a globular microstructure. The method includes the steps of introducing a metal charge into a chamber in a molten state above the liquidus temperature, and holding the metal charge in the chamber without stirring or agitation until it attains a solid fraction state with a non-homogenous, substantially dendritic microstructure. The metal charge is forced from the chamber through an orifice such that passage through the orifice imparts sheer that breaks the substantially dendritic microstructure to a substantially globular non-dendritic microstructure. The metal charge with the substantially globular non-dendritic microstructure is forced into a cavity having the shape of the die-cast part.

1 . A method of forming a die-cast metal part having a globular microstructure, comprising: 
 introducing a metal charge into a chamber in a molten state above the liquidus temperature;    holding the metal charge in the chamber without stirring or agitation until the metal charge attains a solid fraction state with a non-homogenous, substantially dendritic microstructure;    forcing the metal charge having the solid fraction state with the non-homogenous, substantially dendritic microstructure from the chamber through an orifice such that passage of the metal charge through the orifice imparts shear that breaks the substantially dendritic microstructure to a substantially globular non-dendritic microstructure; and    forcing the metal charge with the substantially globular non-dendritic microstructure into a cavity having the shape of the die-cast part.    
   
   
       2 . A method as defined in  claim 1  wherein the metal is aluminum.