Method for casting composite ingot

Abstract

A method and apparatus for the casting of a composite metal ingot comprising at least two separately formed layers of one or more alloys. An open ended annular mould has a feed end and an exit end and divider wall for dividing the feed end into at least two separate feed chambers, where each feed chamber is adjacent at least one other feed chamber. For each pair of adjacent feed chambers a first alloy stream is fed through one of the pair of feed chambers into the mould and a second alloy stream is fed through another of the feed chambers. A self-supporting surface is generated on the surface of the first alloy stream and the second alloy stream is contacted with the first stream such that the upper surface of the second alloy stream is maintained at a position such that it first contacts the self-supporting surface where the self-supporting surface temperature is between the liquidus and solidus temperatures of the first alloy or it first contacts the self-supporting surface where the self-supporting surface temperature is below the solidus temperatures of the first alloy but the interface between the two alloys is then reheated to between the liquidus and solidus temperatures, whereby the two alloy streams are joined as two layers. The joined alloy layers are then cooled to form a composite ingot. This composite ingot has a substantially continuous metallurgical bond between alloy layers with dispersed particles of one or more intermetallic compositions of the first alloy in a region of the second alloy adjacent the interface. The combination of an alloy of high strength bonded to a surface layer of higher ductility gives a sheet of improved bendability compared to the high strength alloy used alone.

1 . A method for the casting of a composite metal ingot comprising at least two layers formed of one or more alloys compositions, which comprises providing an open ended annular mould having a feed end and an exit end wherein molten metal is added at the feed end and a solidified ingot is extracted from the exit end, and divider walls for dividing the feed end into at least two separate feed chambers, the divider walls terminating at bottom ends thereof positioned above the exit end of said mould, with each feed chamber adjacent at least one other feed chamber, wherein for each pair of the adjacent feed chambers a first stream of a first alloy is fed to one of the pair of feed chambers to form a pool of metal in the first chamber and a second stream of a second alloy is fed through the second of the pair of feed chambers to form a pool of metal in the second chamber, the pools of metal each having an upper surface, contacting the first alloy pool with the divider wall between the pair of chambers to thereby cool the first alloy pool to form a self-supporting surface adjacent to the divider wall, and allowing the second alloy pool to contact the first alloy pool such that the upper surface of the second alloy pool contacts the divider wall at a position no more than 3 mm above the bottom end of the divider wall or contacts the self-supporting surface of the first alloy pool at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first alloy, whereby the two alloy pools are joined as two layers, and cooling the joined alloy layers to form a composite ingot.  
     
     
         2 . A method according to  claim 1  wherein the first alloy and second alloys have different compositions.  
     
     
         3 . A method according to  claim 1 , wherein the second alloy, when solidified, is more ductile than the first alloy.  
     
     
         4 . A method according to  claim 3 , wherein said second alloy is selected from 3000 series alloys and 1000 series alloys, and wherein the first alloy is selected from 6000 series alloys and 5000 series alloys.  
     
     
         5 . A method according to  claim 3 , wherein the layer formed from the second alloy is thinner than the alloy formed from the first alloy.  
     
     
         6 . A method according to  claim 5 , wherein the layer formed from the second alloy is less than about 25% of the thickness of the layer formed from the first alloy.  
     
     
         7 . A method according to  claim 1  wherein the mould has a rectangular cross-section and comprises two feed chambers of differing sizes oriented parallel to the long face of the rectangular mould so as to form a rectangular ingot with cladding on one face.  
     
     
         8 . A method according to  claim 7  wherein the second alloy is less ductile, when solidified, than the first alloy.  
     
     
         9 . A method according to  claim 1  wherein the mould has a rectangular cross-section and comprises three feed chambers oriented parallel to the long face of the rectangular mould, wherein the central chamber is larger than either of the two side chambers so as to form a rectangle ingot with cladding on two faces.  
     
     
         10 . A method according to  claim 9  wherein the first alloy is fed to the central chamber.  
     
     
         11 . A method according to  claim 10 , wherein the first alloy is less ductile, when solidified, than the second alloy.  
     
     
         12 . A composite metal ingot, comprising at least two layers of differing alloy composition, wherein pairs of adjacent layers consisting of a first alloy and second alloy are formed by applying the second alloy in a molten state to the surface of the first alloy while the surface of the first alloy is at a temperature of between the solidus and liquidus temperature of the first alloy.  
     
     
         13 . A composite metal ingot according to  claim 12  wherein the cross section of the ingot is rectangular and consists of a core layer of the first alloy and at least one surface layer of the second alloy on the long side of the rectangular.  
     
     
         14 . A composite metal ingot according to  claim 12  wherein the first alloy is an aluminum-manganese alloy and the second alloy is an aluminum-silicon alloy.  
     
     
         15 . A composite metal ingot according to  claim 12  wherein the first alloy is less ductile than the second alloy.  
     
     
         16 . A composite metal ingot according to  claim 15  wherein the layer of the first alloy is thicker than the layer of the second alloy.  
     
     
         17 . A composite metal ingot according to  claim 16  wherein the thickness of the second layer is less than about 25% of the thickness of the first layer.  
     
     
         18 . A composite metal ingot according to  claim 13  wherein said second alloy is selected from 3000 series alloys and 1000 series alloys, and wherein the first alloy is selected from 6000 series alloys and 5000 series alloys.