Ultrasonic enhancement of direct chill cast materials

Abstract

A method and apparatus for direct chill casting of metals and metal alloys which includes application of vibrational energy to the molten material in an open-ended mold and at the outlet of the mold are provided. In an aspect, the method is directed to the production of cast aluminum alloys.

1 . A method for direct chill casting of a metal or metal alloy, comprising:
 supplying a fluid melt comprising a molten metal or molten metal alloy to a direct chill mold having an inlet and an outlet;   cooling the fluid melt in the mold to obtain a billet having a molten core forming an inwardly tapering sump and a solid outer shell that thickens at increasing distance from the mold outlet;   applying vibrational energy to the fluid melt in the molten core sump of a billet exiting the mold with a device positioned within the mold;   optionally, injecting a flow of a purge gas into the fluid melt in the molten core sump of the billet;   applying vibrational energy to the solid outer shell of the billet beyond the outlet of the mold in a region of the tapering sump;   removing the billet from the mold outlet;   further cooling the billet beyond the mold outlet to obtain a solid billet.   
     
     
         2 . The method of  claim 1 , wherein the vibrational energy applied to the fluid melt in the molten core sump of a billet exiting the mold and the vibrational energy applied to the solid outer shell of the billet beneath the outlet of the mold in a region of the tapering sump is provided by at least one ultrasonic transducer, at least one mechanically-driven vibrator, or a combination thereof. 
     
     
         3 . The method of  claim 1 , wherein applying ultrasound vibrational energy to the solid outer shell of the billet in the region of the tapering sump includes applying the vibrational energy from a plurality of vibrational energy sources located in a plurality of positions around the circumference of the billet. 
     
     
         4 . The method of  claim 1 , wherein applying ultrasound vibrational energy to the solid outer shell of the billet in the region of the tapering sump includes applying the vibrational energy through a layer of coolant sprayed on the outer surface of the billet at the outlet of the mold. 
     
     
         5 . The method of  claim 1  wherein a purge gas is employed and the applying of ultrasound vibrational energy to the fluid melt in the molten core sump of a billet exiting the mold with an ultrasound device positioned in the mold and the injecting a flow of a purge gas into the fluid melt in the molten core sump of the billet is conducted with one device. 
     
     
         6 . The method of  claim 1  wherein a purge gas is employed and the purge gas comprises nitrogen or argon. 
     
     
         7 . The method of  claim 1  wherein a frequency of the vibrational energy applied to the fluid melt in the core sump of the billet is from 5 to 400 kHz. 
     
     
         8 . The method of  claim 1  wherein a frequency of the vibrational energy applied to the solid outer shell of the billet is from 5 to 400 kHz. 
     
     
         9 . The method of  claim 3  wherein a frequency of the vibrational energy applied to the layer of coolant on the solid outer shell of the billet is from 5 to 400 kHz. 
     
     
         10 . The method of  claim 1  wherein a metal alloy is DC cast and the metal alloy is an aluminum alloy. 
     
     
         11 . A direct chill (DC) casting mold, comprising:
 a vertically oriented open-ended mold having an upper positioned inlet and lower positioned outlet;   a feed trough for supply of a fluid melt to the upper inlet of the mold;   a liquid cooling system providing a fluid cooling jacket at the outlet of the mold;   a vibrational energy source positioned vertically above the mold inlet and extending into the mold;   optionally, a purge gas feed unit positioned vertically above the mold inlet and extending into the mold and beyond the mold outlet; and   a plurality of vibrational energy sources circumferentially arranged beneath the outlet of the mold;   wherein the vertical position of the circumferentially arranged plurality of vibrational energy sources is located in close proximity of the mold outlet such that the vibrational energy is applied to a billet exiting the mold in a region of an inwardly tapering melt sump within the billet.   
     
     
         12 . The direct chill casting mold of  claim 11 , wherein the vertically positioned vibrational energy source comprises at least one ultrasonic transducer, at least one mechanically-driven vibrator, or a combination thereof. 
     
     
         13 . The direct chill casting mold of  claim 11 , wherein a purge gas feed is present and the vertically positioned vibrational energy source and the purge gas feed unit are combined as an ultrasonic degasser unit wherein the ultrasonic degasser comprises: an elongated probe comprising a first end and a second end, the first end attached to a ultrasonic transducer and the second end comprising a tip located at the outlet of the mold, and a purging gas delivery comprising a purging gas inlet and a purging gas outlet, the purging gas outlet disposed at the tip of the elongated probe for introducing a purging gas into the region at the outlet of the mold. 
     
     
         14 . The direct chill casting mold of  claim 11 , wherein each of the plurality of vibrational energy sources circumferentially arranged beneath the outlet of the mold comprise at least one ultrasonic transducer, at least one mechanically-driven vibrator, or a combination thereof. 
     
     
         15 . The direct chill casting mold of  claim 11 , wherein each of the plurality of vibrational energy sources circumferentially arranged beneath the outlet of the mold are positioned to directly contact a solid surface of a billet exiting the mold. 
     
     
         16 . The direct chill casting mold of  claim 11 , wherein each of the plurality of vibrational energy sources circumferentially arranged beneath the outlet of the mold are positioned to contact a cooling fluid jacket on a solid surface of a billet exiting the mold. 
     
     
         17 . A direct chill (DC) casting mold, comprising:
 a horizontally oriented open-ended mold having an inlet and outlet;   a feed trough for supply of a fluid melt to the inlet of the mold;   a liquid cooling system providing a fluid cooling jacket at the outlet of the mold;   a vibrational energy source positioned in the mold;   optionally, a purge gas feed unit extending into the mold; and   a plurality of vibrational energy sources circumferentially arranged beyond the outlet of the mold;   wherein the position of the circumferentially arranged plurality of vibrational energy sources is located in close proximity of the mold outlet such that the vibrational energy is applied to a billet exiting the mold in a region of an inwardly tapering melt sump within the billet.   
     
     
         18 . The direct chill casting mold of  claim 17 , wherein the vibrational energy source positioned in the mold comprises at least one ultrasonic transducer, at least one mechanically-driven vibrator, or a combination thereof. 
     
     
         19 . The direct chill casting mold of  claim 17 , wherein a purge gas feed is present and the vibrational energy source positioned in the mold and the purge gas feed unit are combined as an ultrasonic degasser unit wherein the ultrasonic degasser comprises: an elongated probe comprising a first end and a second end, the first end attached to a ultrasonic transducer and the second end comprising a tip located at the outlet of the mold, and a purging gas delivery comprising a purging gas inlet and a purging gas outlet, the purging gas outlet disposed at the tip of the elongated probe for introducing a purging gas into the region at the outlet of the mold. 
     
     
         20 . The direct chill casting mold of  claim 17 , wherein each of the plurality of vibrational energy sources circumferentially arranged beyond the outlet of the mold comprise at least one ultrasonic transducer, at least one mechanically-driven vibrator, or a combination thereof. 
     
     
         21 . The direct chill casting mold of  claim 17 , wherein each of the plurality of vibrational energy sources circumferentially arranged beyond the outlet of the mold are positioned to directly contact a solid surface of a billet exiting the mold. 
     
     
         22 . The direct chill casting mold of  claim 17 , wherein each of the plurality of vibrational energy sources circumferentially arranged beyond the outlet of the mold are positioned to contact a cooling fluid jacket on a solid surface of a billet exiting the mold. 
     
     
         23 . A metal or metal alloy billet obtained by the method of  claim 1 , wherein the billet does not comprise a grain refining chemical and the billet has not been subjected to a thermal homogenation treatment. 
     
     
         24 . The metal or metal alloy billet of  claim 23 , wherein the billet is an aluminum or aluminum alloy billet.