Method for producing an aluminum-titanium-boron prealloy for use as a grain refiner

Abstract

The invention relates to a method for producing a grain refiner on the basis of an aluminum-titanium-boron prealloy. According to the inventive method, starting materials that contain Ti and B are introduced into an aluminum melt while TiB 2 particles are formed, and the prealloy melt produced is allowed to solidify. The prealloy is set in motion at a temperature between the liquidus temperature (T L Al3Ti ) of the Al 3 Ti phase and the solidus temperature (T S V ) of the prealloy for a period (Δt d ) sufficient to disperse the TiB 2 particles in the melt. The melt is simultaneously cooled off at a first rate of cooling (v 1 ) so that the TiB 2 particles function as the nuclei for the Al 3 Ti phase that is formed below the liquidus temperature (T L Al3Ti ) and the surface of the TiB 2 particles is at least partially covered by an Al 3 Ti coating. The prealloy is then cooled off to a temperature below the solidus temperature (T S V ) of the prealloy at a second rate of cooling (v 2 ) that is higher than the first rate of cooling (v 1 ). The inventive method is especially useful in the production of grain refiners for the grain refinement of aluminum and aluminum alloys.

1 . Process for the manufacture of a grain refinement medium on the basis of an aluminium-titanium-boron pre-alloy through the introduction of raw materials containing Ti and B into an aluminium melt under formation of TiB2 particles and a solidifying of this pre-alloy melt, characterised in that 
 the pre-alloy is set in motion between the liquidus temperature (T L   Al3Ti ) of the Al 3 Ti phase and the solidus temperature (T S   V ) of the pre-alloy for a sufficient time period (Δt d ) for the dispersal of TiB 2  particles in the melt, and at the same time the pre-alloy is cooled at a first cooling rate (v 1 ) so that the TiB 2  particles serve as nuclei for the Al 3 Ti phase occurring below the liquidus temperature (T L   Al3Ti ) and the surface of the TiB 2  particles are at least partly covered with a coating of Al 3 Ti, and in that the pre-alloy is then cooled below the solidus temperature (T S   V ) of the pre-alloy at a cooling rate (v 2 ) higher than the first cooling rate (v 1 ).    
     
     
         2 . Process according to  claim 1 , characterised in that the pre-alloy is set in motion before the temperature falls below the liquidus temperature (T L   Al3Ti ) of the Al 3 Ti phase.  
     
     
         3 . Process according to  claim 1  or  2 , characterised in that if the temperature prematurely falls below the liquidus temperature (T L   Al3Ti ) or in the event of pre-solidifying of the pre-alloy, already separated Al 3 Ti particles in the melt are heated to above the liquidus temperature (T L   Al3Ti ) until fully dissolved.  
     
     
         4 . Process according to one of  claims 1  to  3 , characterised in that the motion of the melt is achieved through stirring or vibration of the melt.  
     
     
         5 . Process according to one of  claim 1  to  4 , characterised in that the motion of the melt is achieved through cavitation.  
     
     
         6 . Process according to  claim 5 , characterised in that the motion of the melt is achieved by means of sound, especially by means of ultrasonic.  
     
     
         7 . Process according to  claim 6 , characterised in that the melt is exposed to sound at a frequency of 50 Hz to 50 kHz, preferably 10 to 30 kHz.  
     
     
         8 . Process according to  claim 5 , characterised in that the motion of the melt is achieved by means of a magneto-hydrodynamic resonator.  
     
     
         9 . Process according to one of  claims 1  to  8 , characterised in that the second cooling rate (v 2 ) is greater than 1° C./sec, preferably greater than 2° C./sec, in particular greater than 5° C./sec.  
     
     
         10 . Process according to one of  claims 1  to  9 , characterised in that the pre-alloy melt is cast into a strand.  
     
     
         11 . Process according to  claim 10 , characterised in that a continuous strand is manufactured, preferably through horizontal continuous casting.  
     
     
         12 . Process according to  claim 10  or  11 , characterised in that the strand is drawn further into grain refinement strands or wires.  
     
     
         13 . Process according to one of  claims 1  to  12 , characterised in that the pre-alloy has a composition, the total titanium content of which exceeds the stoichiometric ratio of TiB 2 .  
     
     
         14 . Process according to one of  claims 1  to  13 , characterised in that the pre-alloy contains Ti and B in a weight ratio of 5:2 to 10:1.  
     
     
         15 . Process according to one of  claims 1  to  14 , characterised in that the pre-alloy contains 0.05 to 20, preferably 0.1 to 5, in particular 0.5 to 2, w. % Ti and 0.01 to 4, preferably 0.02 to 1, especially 0.05 to 0.5, w. % B.  
     
     
         16 . Use of the process according to onr of  claims 1  to  15  for the manufacture of a grain refinement medium for the grain refinement of aluminium and aluminium alloys.