Porous metallic product and method for making same

Abstract

This invention pertains to a product and a method for making the product. The product is a lightweight solid porous metallic product containing small solid spheres having a coating of a primary alpha phase thereon disposed in a solid metal alloy eutectic matrix. The method includes the steps of mixing the hollow rigid spheres and a metal alloy, which metal alloy can be preheated to render it molten, in order to form a dispersion of the spheres distributed in the molten alloy; initially cooling the dispersion to render it semi-solid whereby the spheres are coated by a solid and the coated spheres are disposed in the semi-solid mixture of the solid and liquid; and finally cooling the sphere-containing semi-solid mixture to a temperature at which the sphere-containing semi-solid mixture becomes solid and the product is formed.

1 . A method for preparing a lightweight porous metallic product comprising the steps of 
 (a) mixing rigid, hollow and solid spheres with a metal alloy in order to obtain a dispersion of the spheres in a semi-solid alloy; and    (b) cooling the semi-solid alloy containing some liquid and the solid coated spheres to a solid.    
   
   
       2 . The method of  claim 1  which includes the step of heating the metal alloy to a temperature at which it is in a liquid state and the spheres remain solid, rigid and hollow.  
   
   
       3 . The method of  claim 2  wherein the alloy is composed of at least one metal and at least one alloying component and the spheres are selected from the group consisting of metallic and ceramic spheres.  
   
   
       4 . The method of  claim 3  wherein size of the spheres is in the range of 10-100,000 nm in diameter; the sphere coating thickness is in the range of 1-100% of sphere radius; and volume fraction of the spheres relative to the alloy is 10-90%.  
   
   
       5 . The method of  claim 3  wherein size of the spheres is in the range of 100-10,000 nm in diameter; the sphere coating thickness is in the range of 10-50% of average sphere radius; and volume fraction of the spheres relative to said alloy is 30-70%.  
   
   
       6 . The method of  claim 5  wherein said spheres are inert to said molten alloy.  
   
   
       7 . The method of  claim 6  wherein said alloy is an alloy of a metal “A” and an alloying component “B” having a phase diagram characterized by a liquid region at upper extremity thereof, a primary a phase at the left thereof where composition of “A” is in the majority, a semi-solid region below the liquid region above eutectic temperature and defined by liquidus and solidus lines, and a solid eutectic region below the eutectic temperature.  
   
   
       8 . The method of  claim 7  wherein the primary a phase at the left side of the phase diagram is defined by solidus line at the upper extremity and a solvus line at the right side thereof; and the solid eutectic region is defined at its left side by the solvus line, by another solvus line at its right side, and by the eutectic temperature at its upper extremity; said initial and final cooling steps are conducted along a vertical line passing through the semi-solid region.  
   
   
       9 . The method of  claim 8  wherein the vertical line crosses over less than one-half of the horizontal central extent in the semi-solid region.  
   
   
       10 . The method of  claim 8  wherein the vertical line crosses over less than one-third of the horizontal central extent in the semi-solid region.  
   
   
       11 . A method for preparing a lightweight, porous and net-shape metallic product comprising the steps of 
 (a) mixing rigid and hollow spheres with a metal alloy in order to obtain a dispersion of the spheres in the molten alloy;    (b) initially cooling the dispersion to render it semi-solid whereby the spheres are coated with a solid phase and the coated spheres are dispersed in the liquid metallic material;    (c) filling a mold cavity with the solid phase coated spheres dispersed in a molten metallic material; and    (d) finally cooling the solid phase coated spheres dispersed in the molten material to a solid state in the mold vavity.    
   
   
       12 . The method of  claim 11  which includes the step of heating the metal alloy to a temperature at which it is in a liquid state and the spheres remain rigid, hollow and solid.  
   
   
       13 . The method of  claim 12  wherein the alloy is selected from the group consisting of magnesium alloys, aluminum alloys, zinc alloys and other lightweight alloys; and the spheres are selected from the group consisting of metallic, ceramic and coated composite spheres.  
   
   
       14 . The method of  claim 13  wherein size of the spheres is in the range of 10-100,000 nm in diameter; the sphere coating thickness is in the range of 1-100% of average sphere radius; and volume fraction of the spheres relative to the alloy is 10-90%.  
   
   
       15 . The method of  claim 13  wherein size of the spheres is in the range of 100-10,000 nm in diameter; and the sphere coating thickness is in the range of 10-50% of average sphere radius.  
   
   
       16 . The method of  claim 15  wherein the spheres are inert to the molten alloy.  
   
   
       17 . The method of  claim 16  wherein the alloy is an alloy of a metal “A” and an alloying component “B” having a phase diagram characterized by a liquid region at upper extremity thereof, a primary a phase at the left thereof where composition of “A” is in the majority, a semi-solid region below the liquid region above eutectic temperature and defined by liquidus and solidus lines, and a solid eutectic region below the eutectic temperature.  
   
   
       18 . The method of  claim 17  wherein the primary a phase at the left side of the phase diagram is defined by solidus line at the upper extremity and a solvus line at the right side thereof; and the solid eutectic region is defined at its left side by the solvus line, by another solvus line at its right side, and by the eutectic temperature at its upper extremity; said initial and final cooling steps are conducted along a vertical line passing through the semi-solid region  
   
   
       19 . The method of  claim 18  wherein the vertical line crosses over less than one-half of the horizontal central extent in the semi-solid region.  
   
   
       20 . The method of  claim 18  wherein the vertical line crosses over less than one-third of the horizontal central extent in the semi-solid region.  
   
   
       21 . A product comprising hollow rigid spheres having a solid coating thereon disposed in a solid metal alloy eutectic.  
   
   
       22 . The product of  claim 21  wherein said solid coating on said spheres is primary proeutectic alpha phase and volume fraction of said spheres relative to said alloy is 10-90%.  
   
   
       23 . The product of  claim 22  wherein said alloy is composed of at least one metal component and at least one alloying component.  
   
   
       24 . The product of  claim 23  wherein said metal alloy eutectic is α and β phases.  
   
   
       25 . The product of  claim 24  wherein said primary alpha phase coating is featureless in the microscope and is of different microstructure than is the α+β eutectic mixture.  
   
   
       26 . Lightweight porous net-shape product having physical properties that are better than that of bulk product physical properties comprising ceramic hollow spheres having a solid coating thereon disposed in a solid metal alloy eutectic.  
   
   
       27 . The product of  claim 26  wherein said solid coating on said spheres is primary proeutectic alpha metal alloy phase and volume fraction of said spheres relative to said alloy is 30-70%.  
   
   
       28 . The product of  claim 27  wherein said alloy is selected from the group consisting of magnesium alloys, aluminum alloys and zinc alloys.  
   
   
       29 . The product of  claim 28  wherein size of said spheres is 100-10,000 nm; said sphere coating thickness is 10-50% of average sphere radius; and volume fraction of said spheres relative to said alloy is 30-70%.  
   
   
       30 . The product of  claim 29  wherein said alloy eutectic is α and β phases and wherein said primary alpha phase is of a different microstructure than said eutectic mixture.