Solidification microstructure of aggregate molded shaped castings

Abstract

A shaped metal casting made in an aggregate mold comprises fine solidification microstructure that is finer than the solidification microstructure of an analogous metal casting made from conventional molding processes. The solidification microstructure may be up to five times finer than the solidification microstructure of a conventionally prepared casting. In preferred embodiments, as a result of directional solidification, the fine solidification microstructure is substantially continuous from a distal end of the casting to a proximal end of the casting, and exhibits greatly enhanced soundness. Because of the control of the uniformity of freezing of the casting, its properties are substantially uniform.

1 . A shaped metal casting formed in a mold comprising an aggregate by an ablation casting process, the casting comprising a fine solidification microstructure that is finer than the microstructure of a casting having a similar metal of a similar weight or section thickness that is produced by a conventional aggregate molded casting process, wherein the fine microstructure comprises one or more of grains, dendrites, eutectic phases or combinations thereof, wherein the fine solidification microstructure is about five times finer than the microstructure of a casting of a similar metal that is produced by a conventional aggregate casting process. 
     
     
         2 . The shaped metal casting according to  claim 1 , wherein the casting is substantially free of porosity. 
     
     
         3 . The shaped metal casting according to  claim 1 , further comprising a dual solidification microstructure region comprising (i) a coarse solidification microstructure portion, and (ii) a fine solidification microstructure portion interspersed within the coarse solidification microstructure portion. 
     
     
         4 . The shaped metal casting according to  claim 3 , wherein the dual solidification microstructure region is substantially continuous from a distal end of the casting to a proximal end thereof. 
     
     
         5 . A metal casting formed in a mold comprising an aggregate via a rapid cooling process and exhibiting a cast microstructure, the microstructure comprising: a first region located adjacent a surface of the metal casting, the first region comprising a coarse solidification microstructure; and a second region located internal to the first region, the second region comprising a fine solidification microstructure, wherein the second region comprises dendrites having a dendrite arm spacing of about 5 to about 15 micrometers, wherein the first region comprises dendrites having a dendrite arm spacing of about 50 to about 200 micrometers. 
     
     
         6 . The metal casting according to  claim 5 , wherein the fine solidification microstructure of the second region is finer than a fine solidification microstructure of a casting of a similar metal having a similar weight or section thickness that is formed by a conventional aggregate casting process. 
     
     
         7 . The metal casting of  claim 5 , wherein the casting is substantially free of at least one of (i) shrinkage porosity, and (ii) damaging iron-rich platelets. 
     
     
         8 . The metal casting of  claim 5 , wherein the first region comprises approximately 100% course solidification microstructure, and the second region comprises approximately 100% fine solidification microstructure. 
     
     
         9 . The metal casting of  claim 8  further comprising a third region located between the first and second regions, wherein the third region comprises a dual solidification microstructure comprising (i) one or more coarse solidification microstructure portions, and (ii) one or more fine solidification microstructure portions. 
     
     
         10 . The metal casting of  claim 9 , wherein the one or more coarse solidification microstructure portions of the dual solidification microstructure region comprises dendrites having a dendrite arm spacing of about 50 to about 200 micrometers and the one or more fine solidification microstructure portions of the dual solidification microstructure region comprises dendrites having a dendrite arm spacing of about 15 micrometers or less. 
     
     
         11 . A metal casting formed in a mold comprising an aggregate via a rapid cooling process and exhibiting a cast microstructure, the microstructure comprising:
 a first region located adjacent a surface of the metal casting, the first region comprising a coarse solidification microstructure having dendrites with a dendrite arm spacing of 50 to 200 micrometers; and a second region located internal to the first region, the second region comprising a fine solidification microstructure having dendrites with an arm spacing of 30 micrometers or less.   
     
     
         12 . The metal casting of  claim 11 , wherein the second region comprises dendrites having a dendrite arm spacing of 20 micrometers or less. 
     
     
         13 . The metal casting of  claim 12 , wherein the second region comprises dendrites having a dendrite arm spacing of 5 to 15 micrometers. 
     
     
         14 . The metal casting of  claim 11 , wherein the casting is free of at least one of (i) shrinkage porosity, and (ii) damaging iron-rich platelets. 
     
     
         15 . The metal casting of  claim 11 , wherein the first region comprises 100% coarse solidification microstructure, and the second region comprises 100% fine solidification microstructure.