Method of producing ingot with variable composition using planar solidification

Abstract

Molten metal of a first composition is fed into a mold cavity, via a first control apparatus, wherein the control apparatus is open, wherein the feeding comprises flowing out of a first feed chamber. The first control apparatus is closed. A second control apparatus is opened. Molten metal of a second composition is fed into the mold cavity, via the second control apparatus, wherein at least a portion of the metal of the first composition in the mold cavity is sufficiently molten so that an initial feed of molten metal of the second composition mixes with the molten metal of the first composition in the mold cavity, wherein the feeding comprises flowing out of a second feed chamber, wherein the second composition is different from the first composition. An ingot is removed from the mold cavity, wherein the ingot has a top section, a middle section, and a bottom section, wherein the bottom section is composed of metal of the first composition, wherein the top section is composed of metal of the second composition, wherein the middle section is composed of a mixture of metal of the first composition and the second composition.

What is claimed is: 
     
         1 . A method of casting metal, comprising the following steps:
 feeding molten metal of a first composition into a mixing apparatus, via a first control apparatus at an initial rate that decreases to 0 lbs/minute,
 wherein the molten metal of the first composition is an aluminum alloy, wherein the control apparatus is open, wherein the feeding comprises flowing out of a first feed chamber; 
   feeding molten metal of a second composition into the mixing apparatus, via a second control apparatus at a rate of 0 lbs/minute increasing to the initial rate of the first control apparatus,
 wherein the molten metal of the second composition is an aluminum alloy, 
 wherein the feeding comprises flowing out of a second feed chamber, wherein the 
 second composition is different from the first composition; 
   feeding molten metal from the mixing apparatus into a mold cavity, wherein feeding occurs horizontally with molten metal entering the mold cavity below a surface of molten metal already in the mold cavity;   removing an ingot from the mold cavity after the molten metal solidifies
 wherein the solidification front remained substantially planar, 
 wherein the ingot has a thickness, a top portion, a bottom portion, and a middle portion between the top and bottom portions, wherein the bottom portion is composed of metal of the first composition, wherein the top portion is composed of metal of the second composition, wherein the middle portion of the ingot includes a continuous gradient, wherein the continuous gradient is a gradient of metals of the first and second compositions, wherein an amount of metal of the first composition decreases gradually from the bottom portion of the ingot through the thickness to the top portion of the ingot, wherein an amount of metal of the second composition increases gradually from the bottom portion of the ingot through the thickness to the top portion of the ingot, and 
 wherein no oxide inclusions exist between portions of the ingot.