Grain refining agent for cast aluminum or magnesium products

Abstract

The invention relates to a grain refining agent for cast aluminum or magnesium products, comprising particles having an average particle size of 0.1 to 30 μm and each formed of an agglomerate of grains with each grain comprising a nanocrystal of a transition metal boride or carbide of the formula: Me a X b (I) wherein Me is a transition metal, X is boron or carbon, a ranges from 1 to 10 and b ranges from 1 to 20. The grain refining agent according to the invention does not require to be formed into a master alloy prior to being added to the molten aluminum or magnesium to be cast.

1 . A grain refining agent for cast aluminum or magnesium products, comprising particles having an average particle size of 0.1 to 30 μm and each formed of an agglomerate of grains with each grain comprising a nanocrystal of a transition metal boride or carbide of the formula:  
       Me a X b   (i)  
       wherein me is a transition metal, x is boron or carbon, a ranges from 1 to 10 and b ranges from 1 to 20:  
     
     
         2 . A grain refining agent according to  claim 1 , wherein Me is a transition metal selected from the group consisting of titanium and vanadium.  
     
     
         3 . A grain refining agent according to  claim 2 , wherein Me is titanium.  
     
     
         4 . A grain refining agent according to  claim 3 , wherein X is boron.  
     
     
         5 . A grain refining agent according to  claim 4 , wherein a is 1 and b is 2.  
     
     
         6 . A grain refining agent according to  claim 4 , wherein a is 3 and b is 1.  
     
     
         7 . A grain refining agent according to  claim 4 , wherein a is 5 and b is 1.  
     
     
         8 . A grain refining agent according to  claim 3 , wherein X is carbon.  
     
     
         9 . A grain refining agent according to  claim 8 , wherein a is 1 and b is 1.  
     
     
         10 . A grain refining agent according to  claim 1 , wherein said average particle size ranges from 1 to 5 μm.  
     
     
         11 . A method of preparing a grain refining agent as defined in  claim 1 , comprising the steps of: 
 a) providing a first reagent selected from the group consisting of transition metals and transition metal-containing compounds;    b) providing a second reagent selected from the group consisting of boron, boron-containing compounds, carbon and carbon-containing compounds; and    c) subjecting said first and second reagents to high-energy ball milling to cause solid state reaction therebetween and formation of particles having an average particle size of 0.1 to 30 μm, each particle being formed of an agglomerate of grains with each grain comprising a nanocrystal of a transition metal boride or carbide of the formula (I) as defined in  claim 1 .    
     
     
         12 . A method according to  claim 11 , wherein said first reagent comprises a transition metal selected from the group consisting of titanium and vanadium.  
     
     
         13 . A method according to  claim 12 , wherein said transition metal is titanium.  
     
     
         14 . A method according to  claim 11 , wherein said first reagent comprises a titanium-containing compound selected from the group TiH 2 , TiAl 3  and TiB.  
     
     
         15 . A method according to  claim 11 , wherein said second reagent comprises boron.  
     
     
         16 . A method according to  claim 11 , wherein said second reagent comprises a boron-containing compound selected from the group consisting of AlB 2  and AlB 12 .  
     
     
         17 . A method according to  claim 11 , wherein said second reagent comprises carbon.  
     
     
         18 . A method according to  claim 11 , wherein said second reagent comprises tetraboron carbide.  
     
     
         19 . A method according to  claim 11 , wherein step (c) is carried out in a vibratory ball mill operated at a frequency of 8 to 25 Hz.  
     
     
         20 . A method according to  claim 19 , wherein said vibratory ball mill is operated at a frequency of about 17 Hz.  
     
     
         21 . A method according to  claim 11 , wherein step (c) is carried out in a rotary ball mill operated at a speed of 150 to 1500 r.p.m.  
     
     
         22 . A method according to  claim 21 , wherein said rotary ball mill is operated at a speed of about 1000 r.p.m.  
     
     
         23 . A method according to  claim 11 , wherein step (c) is carried out under an inert gas atmosphere.  
     
     
         24 . A grain refining agent according to  claim 23 , wherein said inert gas atmosphere comprises argon or nitrogen.  
     
     
         25 . A grain refining agent according to  claim 11 , wherein step (c) is carried out under a reactive gas atmosphere.  
     
     
         26 . A grain refining agent according to  claim 25 , wherein said reactive gas atmosphere comprises hydrogen, ammonia or a hydrocarbon.  
     
     
         27 . A method according to  claim 11 , wherein step (c) is carried out for a period of time of about 5 hours.  
     
     
         28 . A method of preparing a grain refining agent as defined in  claim 5  or  9 , comprising subjecting TiB 2  or TiC to high-energy ball milling to cause formation of particles having an average particle size of 0.1 to 30 μm, each particle being formed of an agglomerate of grains with each grain comprising a nanocrystal of TiB 2  or TiC.  
     
     
         29 . A method according to  claim 28 , wherein said high-energy ball milling is carried out in a vibratory ball mill operated at a frequency of 8 to 25 Hz.  
     
     
         30 . A method according to  claim 27 , wherein said vibratory ball mill is operated at a frequency of about 17 Hz.  
     
     
         31 . A method according to  claim 28 , wherein said high-energy ball milling is carried out in a rotary ball mill operated at a speed of 150 to 1500 r.p.m.  
     
     
         32 . A method according to  claim 31 , wherein said rotary ball mill is operated at a speed of about 1000 r.p.m.  
     
     
         33 . A method according to claim  0 . 28 , wherein said high-energy ball milling is carried out under an inert gas atmosphere.  
     
     
         34 . A method according to  claim 33 , wherein said inert gas atmosphere comprises argon or nitrogen.  
     
     
         35 . A method according to  claim 28 , wherein said high-energy ball milling is carried out under a reactive gas atmosphere.  
     
     
         36 . A method according to  claim 35 , wherein said reactive gas atmosphere comprises hydrogen, ammonia or a hydrocarbon.  
     
     
         37 . A method according to  claim 28 , wherein said high-energy ball milling is carried out for a period of time of about 20 hours.