Method for producing foamed aluminum products by use of selected carbonate decomposition products

Abstract

A method for producing an aluminum foam product wherein reactive gas producing particles are introduced into an aluminum alloy melt under controlled conditions and subjected to agitation to induce the production of foam-stabilizing by-products, and, under certain conditions, the production of gases used to produce the molten metal foam itself. Foam products produced through this method have intrinsically formed metal oxides and other solid particles dispersed therein and are devoid of the large extrinsically added stabilizing ceramic additions traditionally used in the production of aluminum foams. The invention claims a rapid, single step method for producing an inoculated, foamable melt using low cost precursor materials.

1 . A method of making foamed aluminum comprising: 
 providing reactive gas producing particles having a decomposition temperature at atmospheric pressure from about 350° C. to about 850° C.;    combining the reactive gas producing particles with molten metal alloy comprising aluminum;    agitating the molten metal alloy containing the reactive gas producing particles to decompose at least a portion of the reactive gas producing particles into reactive gas, wherein the reactive gas vigorously combines with the molten metal alloy to produce a foamable suspension of metallic oxide phases and gas bubbles;    dispersing chemical foaming agents into the foamable suspension to produce an inoculated foamable suspension;    foaming the inoculated foamable suspension to produce a liquid metal foam; and    solidifying the liquid metal foam to create a foamed aluminum product.    
   
   
       2 . The method of  claim 1 , wherein the reactive gas producing particles comprise magnesium carbonate, calcium carbonate, dolomite or mixtures thereof.  
   
   
       3 . The method of  claim 2 , wherein the reactive gas producing particles are calcium carbonate.  
   
   
       4 . The method of  claim 1 , wherein the chemical foaming agents comprise magnesium carbonate, calcium carbonate, dolomite, titanium hydride, zirconium hydride or mixtures thereof.  
   
   
       5 . The method of  claim 4 , wherein the chemical foaming agents are calcium carbonate.  
   
   
       6 . The method of  claim 1 , wherein the molten metal alloy comprises commercial grade purity aluminum, scrap aluminum, aluminum containing silicon and magnesium, or mixtures thereof.  
   
   
       7 . The method of  claim 3 , wherein the calcium carbonate has an average diameter of less than 40 microns.  
   
   
       8 . The method of  claim 3 , wherein the calcium carbonate comprises between 0.5 wt. % and 4 wt. % of the molten metal alloy.  
   
   
       9 . The method of  claim 5 , wherein the calcium carbonate constitutes between 0.5 wt. % and 4 wt. % of the molten metal alloy.  
   
   
       10 . The method of  claim 1 , wherein the molten metal alloy comprises between 0.5% and 8% magnesium by weight percent.  
   
   
       11 . The method of  claim 1 , wherein the inoculated foamable suspension is solidified and remelted prior to the foaming of the inoculated foamable suspension to produce the liquid metal foam.  
   
   
       12 . The method of  claim 1  wherein the step of foaming the inoculated foamable suspension further comprises heating the foamable inoculated suspension to increase the chemical foaming agents rate of decomposition.  
   
   
       13 . The method of  claim 12  comprising heating the foamable inoculated suspension to a temperature ranging from about 670° C. to about 740° C.  
   
   
       14 . A method of making foamed aluminum comprising: 
 providing reactive gas producing particles having a decomposition temperature at atmospheric pressure from about 350° C. to about 850° C.;    combining the reactive gas producing particles with molten metal alloy comprising aluminum;    agitating the molten metal alloy containing the reactive gas producing particles to decompose a first portion of the reactive gas producing particles into a reactive gas and retain a second portion of the reactive gas producing particles in an unreacted state, wherein the reactive gas vigorously combines with the molten metal alloy to produce metallic oxide phases and gas bubbles and the second portion of the reactive gas producing particles in the unreacted state are chemical foaming agents in an inoculated foamable suspension;    foaming the inoculated foamable suspension to produce a liquid metal foam; and    solidifying the liquid metal foam to create a foamed aluminum product.    
   
   
       15 . The method of  claim 14 , wherein the reactive gas producing particles comprise magnesium carbonate, calcium carbonate, dolomite or mixtures thereof.  
   
   
       16 . The method of  claim 15 , wherein the reactive gas producing particles are calcium carbonate.  
   
   
       17 . The method of  claim 14 , wherein the molten metal alloy comprises commercial grade purity aluminum, scrap aluminum, aluminum containing silicon and magnesium, or mixtures thereof.  
   
   
       18 . The method of  claim 16 , wherein the calcium carbonate has an average diameter of less than 40 microns.  
   
   
       19 . The method of  claim 15 , wherein the calcium carbonate comprises between 2% and 16% of the molten metal alloy by weight percent.  
   
   
       20 . The method of  claim 17 , wherein the molten metal alloy comprises between 0.5% and 8% magnesium by weight percent.  
   
   
       21 . The method of  claim 14 , wherein the inoculated foamable suspension is solidified and remelted prior to the foaming of the inoculated foamable suspension to provide the liquid metal foam.  
   
   
       22 . A method of making a foamable liquid+gas+solid suspension in molten aluminum comprising: 
 providing reactive gas producing particles having a decomposition temperature at atmospheric pressure from about 350° C. to about 850° C.;    combining the reactive gas producing particles with molten metal alloy comprising aluminum;    agitating the molten metal alloy containing the reactive gas producing particles to decompose at least a portion of the reactive gas producing particles into reactive gas, wherein the reactive gas vigorously combines with the molten metal alloy to produce a foamable suspension of gas bubbles and metallic oxide phases within the molten metal alloy.    
   
   
       23 . The method of  claim 22  further comprising a volumetric expansion of the foamable suspension ranging from about 5% to about 50% following the step of agitating the molten metal alloy containing the reactive gas producing particles.  
   
   
       24 . The method of  claim 22  wherein the molten metal alloy comprises from 0.5 wt % Mg to 8.0 wt % Mg.  
   
   
       25 . An apparatus for the making a foamable suspension comprising: 
 a feeding system for providing reactive gas producing particles and molten metal alloy, wherein the molten metal alloy is provided at a pre-selected flow rate;    a reactor unit in communication with the feeding system comprising:    a mixing unit for combining the reactive gas producing particles and the molten metal alloy into an inoculated foamable suspension, the mixing unit having a stirrer contained therein and having a volume configured to provide a transit time through the mixing unit for decomposing at least a portion of the reactive gas producing particles within the mixing unit at the pre-selected flow rate, at least one vent in the reactor unit to release gaseous byproducts, and a furnace housing the reactor unit; and    a tip in communication with the reactor unit.    
   
   
       26 . The apparatus of  claim 25  wherein the tip comprises a mold having a geometry for an aluminum foam product.  
   
   
       27 . The apparatus of  claim 25  comprising a transport system to transfer the inoculated foamable suspension from the reactor unit to the tip.  
   
   
       28 . The apparatus of  claim 25 , further comprising a positive displacement pump for transferring the inoculated foamable suspension from the reactor unit to the tip.  
   
   
       29 . The apparatus of  claim 26 , wherein said positive displacement pump is a rotary gear pump or a rotary lobe pump.  
   
   
       30 . The apparatus of  claim 25 , wherein the tip is electrically heated or gass fired heated.  
   
   
       31 . An apparatus for the making foamed aluminum comprising: 
 a feeding system for providing reactive gas producing particles and molten metal alloy, wherein the molten metal alloy is provided at a pre-selected flow rate;    a reactor unit in communication with the feeding system comprising:    a mixing unit for combining the reactive gas producing particles and the molten metal alloy into a foamable suspension, the mixing unit having a stirrer contained therein and having a volume configured to provide a transit time through the mixing unit suitable for decomposing at least a portion of the reactive gas producing particles within the mixing unit at the pre-selected flow rate, at least one vent in the reactor unit to release gaseous byproducts, and a furnace housing the reactor unit;    a dispersion unit in communication with the reactor unit comprising:    a foaming agent mixing chamber for receiving the foamable suspension;    a feeding system positioned to provide chemical foaming agent into the foamable suspension within the foaming agent mixing chamber;    a stirrer positioned in the foaming agent mixing chamber to disperse the chemical foaming agent to produce an inoculated foamable suspension; and    a transport system to transfer the inoculated foamable suspension from the dispersion unit to a tip.    
   
   
       32 . The apparatus of  claim 31 , wherein the pre-selected flow rate of the molten metal or the volume of the mixing unit is configured to fully decompose the reactive gas producing particles in producing the foamable suspension.  
   
   
       33 . The apparatus of  claim 31 , wherein the transport system is a positive displacement pump.  
   
   
       34 . The apparatus of  claim 33 , wherein the positive displacement pump is a rotary gear pump or a rotary lobe pump.  
   
   
       35 . The apparatus of  claim 31 , wherein the tip is electrically heated or gass fired heated.  
   
   
       36 . The apparatus of  claim 31  wherein the tip comprises a mold having a geometry for an aluminum foam product.  
   
   
       37 . An aluminum foam material comprising: 
 an aluminum alloy matrix comprising magnesium in a percentage ranging from about 0.5% to 8% by weight percent and a distribution of fine metallic oxides in a percentage ranging from 0.5% to about 16% by weight percent; wherein the average size of the fine metal oxides is less than 1.0 micron; and    a distribution of pores within said aluminum alloy matrix comprising a majority of closed pores with an average diameter ranging from about 200 microns to about 1500 microns; wherein said distribution of pores within said aluminum alloy matrix provides a product density between 0.30 g/cm 3  and 0.70 g/cm 3 .    
   
   
       38 . The aluminum foam material of  claim 37  wherein the metallic oxides are comprised of aluminum oxide, magnesium oxide, calcium oxide or combinations thereof.  
   
   
       39 . An aluminum foam material comprising: 
 an aluminum alloy matrix comprising an effective amount of magnesium;    a distribution of fine metallic carbonates;    a distribution of pores within the aluminum alloy matrix;    and substantially free of stable ceramic particles greater than 5 microns in diameter.    
   
   
       40 . The aluminum foam material of  claim 39  wherein the effective amount of magnesium is between 0.5 wt. % and 8 wt. %.  
   
   
       41 . The aluminum foam material of  claim 39  wherein the fine metallic carbonates comprise calcium carbonate, magnesium carbonate or combinations thereof.  
   
   
       42 . The aluminum foam material of  claim 39  wherein the distribution of pores comprise pores having an average diameter ranging from about 200 microns to about 1500 microns.  
   
   
       43 . The aluminum foam material of  claim 39  wherein the distribution of pores comprise between 70% and 90% of the volume of the aluminum foam material foam.  
   
   
       44 . The aluminum foam material of  claim 39  wherein the metallic carbonates are in a percentage ranging from 0.5% to about 16% by weight percent.  
   
   
       45 . The material of  claim 39  wherein the distribution of fine metallic carbonates comprise carbonates having an average size of less than 100 microns.  
   
   
       46 . A structural material for construction, automotive, or aerospace applications comprising the aluminum foam material of  claim 39 .  
   
   
       47 . The structural material of  claim 44  wherein said structural material is a flat panel.  
   
   
       48 . An aluminum foam material comprising: 
 an aluminum alloy matrix having a mean wall thickness ranging from about 5 microns to about 100 microns; and    a distribution of pores within the aluminum alloy matrix having an average pore diameter ranging from about 200 microns to about 1500 microns and constituting between 70% and 90% of the aluminum foam material by volume.    
   
   
       49 . The material of  claim 48  wherein the average pore diameter is less than 1000 microns.