Title of Invention	"A PROCESS FOR PERPARATION OF MASTER ALLOY FOR GRAIN REFINEMENT OF ALUMINIUM AND ITS ALLOYS"
Abstract	preparation of mater alloy for grain refinement of aluminium and its alloys its alloy. The process comprises in miltion commrcial purity aluminium in a resistance furnace at a temperarute between 750-900 degree celsius and maintained. Chluride salt flux on top of the melt to minimise oxidation and dayassing of the melt. The dress is removed and a mixture of fluor ide salt is added to the melt to obtain master allyoy cantaining ranging from 1 to 10%, Boron ranging from 0.3 ti 3% . The melt is stirred inermittently to facilitate reaction between the salt and melt. The slag is removed, after allowing a reaction time of about 1/2 to 3 hours, and subjecting the melt to a step of moulding.

Title of Invention

"A PROCESS FOR PERPARATION OF MASTER ALLOY FOR GRAIN REFINEMENT OF ALUMINIUM AND ITS ALLOYS"

Abstract

preparation of mater alloy for grain refinement of aluminium and its alloys its alloy. The process comprises in miltion commrcial purity aluminium in a resistance furnace at a temperarute between 750-900 degree celsius and maintained. Chluride salt flux on top of the melt to minimise oxidation and dayassing of the melt. The dress is removed and a mixture of fluor ide salt is added to the melt to obtain master allyoy cantaining ranging from 1 to 10%, Boron ranging from 0.3 ti 3% . The melt is stirred inermittently to facilitate reaction between the salt and melt. The slag is removed, after allowing a reaction time of about 1/2 to 3 hours, and subjecting the melt to a step of moulding.

Full Text	A PROCESS FOR PREPARATION OF MASTER ALLOY FOR GRAIN REFINEMENT OF ALUMINIUM AND ITS ALLOYS This invention relates to a process for preparation of master alloy for grain refinement of aluminium and its alloys. The grain refinement of aluminium and its alloys by the addition of small amount of certain master alloys to the melt before casting, results in the complete conversion of otherwise coarse columnar grains of the castings to very fine equiaxed grain structure. These fine equiaxed grains can improve to a large extent, the strength, toughness, surface finish and other properties of the aluminium alloy castings. The conventional process of grain refinement of aluminium and its alloys involved addition of salts containing Ti and B. The disadvantage of this process is that the process doed not allow precise control over Ti and B additions. Further disadvantage of the process is that the addition of such salts results in release of undesirable fumes. Some other processes known in the art for grain refinement of aluminium and its alloys, use commercially available master alloys like 5/1 TiBAl, 3/1 TiBAl as grain refiners. These master alloys are prepared by the reaction of molten aluminium with complex halide salts of Ti and B. The disadvantage of these processes is that these processes require use of high purity aluminium. Another disadvantage of these processes is that while presence of Boron leads to long lasting refinement of grains in the alloy, it suffers from the drawback that the master alloy is slow acting . The processes are also known in the art where Boron in the available master alloy has been replaced by other elements or boron has been diluted by addition of an element that could make the master alloy faster acting. In one of such processes, boron is replaced by carbon and/or nitrogen for specific applications. These additions are done in the elemental form or in the form of dissociable carbon and/or nitrogen containing components in amounts lower than 0.2% . The disadvantage of this process is that the grain size achieved by this process is of the order of 280 µm at a Ti addition level of 0,01% with retained amounts of carbon as 0.19% and Nitrogen as 0,11%. This grain size is higher than the acceptable level of grain size which is 220 µm. Another disadvantage of the above processes is that while presence of carbon or sulphur results in faster acting grain refiner, but these refiners are not long lasting and fade quickly. There is therefore a need for a master alloy which leads to grain size below the acceptable level and which is both faster acting as well as longer lasting. The primary object of the present invention is to propose a process for the preparation of master alloy, for grain refinement of aluminium and its alloys. Another object of the present invention is to propose a process for the preparation of master alloy using commercial purity aluminium. Further object of the present invention is to propose a process for the preparation of master alloy which incorporates, besides Boron, 0.025% Calcium in lieu of Carbon or Sulphur or Nitrogen or Phosphorus as used in existing processes. Still further object of the present invention is to propose a process which provides master alloy wherein the calcium incorporated in the alloy counteracts the deleterious effect of silicon which is invariably present in the commercial purity aluminium which is used in the preparation of master alloy by this process. Still further object of the present invention is to propose a process for preparation of grain refiner master alloy which yields grain size below the acceptable level of 220 mm Another object of the present invention is to provide a process which provides master alloy which is both faster acting as well longer lasting. Yet further object of the present invention is to provide a process for preparation of master alloy which optimises the effect of various parameters like superheating, reaction time, effect of stirring, stirring tool and crucible used which affect the grain refining ability of the master alloy, by the right combination of these variables. According to the present invention, there is provided a process for preparation of master alloy for grain refinement of aluminium and its alloy, comprising steps of (a) melting commercial purity aluminium in a resistance ftirnace at a temperature of 750 to 900°C, maintaining conventional chloride salt flux on the top of the meh to minimise oxidation; (b) degassing by adding solid hexachloroethane taken in quantity 1,0 to 1.1% by weight of commercial purity aluminium and removing the dross thus obtained, (c) adding K2 Ti F6 and KB F4 with intermittant stirring where K2 Ti F6 is taken in quantity 22 to 25% by weight of commercial purity aluminium and where KBF4 is taken in quantity 15 to 20% by weight of comjnercial purity aluminium; (d) removing the slag after allowing reaction time of 1/2 to 3 hours and then subjecting the meh to the step of moulding to obtain the desired master alloy. The master alloy obtained by this process results in fine equiaxed grains of aluminium within 2 minutes of holding. The grain size obtained is of the order 103 mm which is much below the acceptance level of 220 mm specified for grain refiners The grain size of the aluminium castings remains essentially the same even upto 120 min of holding and no fading is observed with master alloy obtained by this process. The macrostnictures of the Aluminium, castings at different holding times are shown in fig 1. The 0 min sample clearly shows columnar grain structure. Within 2 min of holding the master alloy in the Aluminium melt, there was a complete conversion of the columnar structure into fine equiaxed grain structure as shown in this fig 1. The macrostructure remained fine equiaxed on further holding even upto 120 min. The grain size of Aluminium casting within 2 min holding is 103mm which is much below the acceptance level of 220 mm specified for grain refiners. The grain size of the Aluminium castings essentially remains the same even upto 120 min of holding and no fading is observed with the alloy prepared by this process, thereby establishing that the master alloy prepared by this process is not only fast acting but also long lasting. Fig 2(a) and (b) shows typical SEM photomicrographs of the master alloy at different magnifications showing the range of the particle sizes of TiAl3. The master alloy which exhibited the ability to give a very fine grain size at short times, contained varying amounts of aluminium particles. EDX SPECTRUM (Fig. 2(c) ) taken from one of these particles identifies them as Ti aluminides. Transmission Electron Microscopic (TEM) studies (Fig 3(a) ) carried out on the master alloy to identify TiB2 particles, revealed the presence of the latter which are more or less equiaxed with average particles size of 0.2 µm. the selected area diffraction pattern (Fig 3(b) ) conforms to the (0001) zone axis of hexagonal TiB2. Some of he particles are faceted. The facets of the particle which have favourable orientation relation with Aluminium act as nucleating sites during solidification So the presence of faceted particles aids in grain refinement. The invention is now illustrated but not limited by the following example;- EXAMPLE-1 467g of commercial purity aluminium was melted at 800 degree C. Aluminium was degassed with about 5 g of solid hexachloroethane and the dross was removed. Sufficient chloride salt flux was maintained on top of the melt to prevent oxidation of Aluminium, The temperature of molten aluminium was maintained at 800 degree celsius A mixture of 130g to K2TiF6 and 87g of KBF4 was fed into the melt and allowed to react During this period, the melt was stirred at regular intervals of 10 minutes The molten bath was held for 60 minutes in the resistance flirnance. Then the slag was removed and the master alloy was poured into a water cooled mould. About 0.5 kg of master alloy was obtained. The chemical composition of the alloy was A1-5 3, Ti - 1,3 B with traces of carbon. EXAMPLE-2 478 g of commercial aluminium was melted in a resistsnce furnace at 800 degree C. After degassing the molten aluminium vith abcut 5g of solid hexachloroethane, the dross was removed. To minimise oxidation of Aluminium/ sufficient quality of chloride salt flux was maintained ever the surface of the molten aluminium. The temperature of molten aluminium was maintained at 800 degree C. A mixture of 110g of K TiF6 and 70g of KBF4 salts was added with constant stirring* The aluminium bath was later stirred intermittently. After a reaction time of 60 minutes, the slag was removed. The resutant master alloy was then poured into a water cooled copper mould. About 0.5 kg of master alloy having composition of Al-2.7 Ti-0.9B with traces of carbon was obtained. CLAIM 1. A process for preparation of master alloy for grain refinement of aluminium and its alloy, comprising steps of :- (a) melting commercial purity aluminium in a resistance furnace at a temperature of 750 to 900°C, maintaining conventional chloride salt flux on the top of the melt to minimise oxidation; (b) degassing by adding solid hexachloroethane taken in quantity 1.0 to 1.1% by weight of commercial purity aluminium and removing the dross thus obtained; (c) adding K2 Ti F6 and KB F4 with intermittant stirring where K2 Ti Fe is taken in quantity 22 to 25% by weight of commercial purity aluminium and where KBF4 is taken in quantity 15 to 20% by weight of commercial purity aluminium; (d) removing the slag after allowing reaction time of 1/2 to 3 hours and then subjecting the melt to the step of moulding to obtain the desired master alloy. 2, A process for preparation of master alloy for grain refinement of aluminium and its alloys as herein substantially described and illustrated.

Full Text

A PROCESS FOR PREPARATION OF MASTER ALLOY FOR GRAIN REFINEMENT OF ALUMINIUM AND ITS ALLOYS
This invention relates to a process for preparation of master alloy for grain refinement of aluminium and its alloys.
The grain refinement of aluminium and its alloys by the addition of small amount of certain master alloys to the melt before casting, results in the complete conversion of otherwise coarse columnar grains of the castings to very fine equiaxed grain structure. These fine equiaxed grains can improve to a large extent, the strength, toughness, surface finish and other properties of the aluminium alloy castings.
The conventional process of grain refinement of aluminium and its alloys involved addition of salts containing Ti and B. The disadvantage of this process is that the process doed not allow precise control over Ti and B additions. Further disadvantage of the process is that the addition of such salts results in release of undesirable fumes.
Some other processes known in the art for grain refinement of aluminium and its alloys, use commercially available master alloys like 5/1 TiBAl, 3/1 TiBAl as grain refiners. These master alloys are prepared by the reaction of molten aluminium with complex halide salts of Ti and B. The disadvantage of these processes is that these processes require use of high purity aluminium.
Another disadvantage of these processes is that while presence of Boron leads to long lasting refinement of grains in the alloy, it suffers from the drawback that the master alloy is slow acting .
The processes are also known in the art where Boron in the available master alloy has been replaced by other elements or boron has been diluted by addition of an element that could make the master alloy faster acting. In one of such processes, boron is replaced by carbon and/or nitrogen for specific applications. These additions are done in the elemental form or in the form of dissociable carbon and/or nitrogen containing components in amounts lower than 0.2% . The disadvantage of this process is that the grain size achieved by this process is of the order of 280 µm at a Ti addition level of 0,01% with retained amounts of carbon as 0.19% and Nitrogen as 0,11%. This grain size is higher than the acceptable level of grain size which is 220 µm.
Another disadvantage of the above processes is that while presence of carbon or sulphur results in faster acting grain refiner, but these refiners are not long lasting and fade quickly. There is therefore a need for a master alloy which leads to grain size below the acceptable level and which is both faster acting as well as longer lasting.
The primary object of the present invention is to propose a process for the preparation of master alloy, for grain refinement of aluminium and its alloys.
Another object of the present invention is to propose a process for the preparation of master alloy using commercial purity aluminium.
Further object of the present invention is to propose a process for the preparation of master alloy which incorporates, besides Boron, 0.025% Calcium in lieu of Carbon or Sulphur or Nitrogen or Phosphorus as used in existing processes.
Still further object of the present invention is to
propose a process which provides master alloy wherein the calcium incorporated in the alloy counteracts the deleterious effect of silicon which is invariably present in the commercial purity aluminium which is used in the preparation of master alloy by this process.
Still further object of the present invention is to propose a process for preparation of grain refiner master alloy which yields grain size below the acceptable level of 220 mm
Another object of the present invention is to provide a process which provides master alloy which is both faster acting as well longer lasting.
Yet further object of the present invention is to provide a process for preparation of master alloy which optimises the effect of various parameters like superheating, reaction time, effect of stirring, stirring tool and crucible used which affect the grain refining ability of the master alloy, by the right combination of these variables.
According to the present invention, there is provided a process for preparation of master alloy for grain refinement of aluminium and its alloy, comprising steps of (a) melting commercial purity aluminium in a resistance ftirnace at a temperature of 750 to 900°C, maintaining conventional chloride salt flux on the top of the meh to minimise oxidation; (b) degassing by adding solid hexachloroethane taken in quantity 1,0 to 1.1% by weight of commercial purity aluminium and removing the dross thus obtained, (c) adding K2 Ti F6 and KB F4 with intermittant stirring where K2 Ti F6 is taken in quantity 22 to 25% by weight of commercial purity aluminium and where KBF4 is taken in quantity 15 to 20% by weight of comjnercial purity aluminium; (d) removing the slag after allowing reaction time of 1/2 to 3 hours and then subjecting the meh to the step of moulding to obtain the desired master alloy.
The master alloy obtained by this process results in fine equiaxed grains of aluminium within 2 minutes of holding. The grain size obtained is of the order 103 mm which is much below the acceptance level of 220 mm specified for grain refiners The grain size of the aluminium castings remains essentially the same even upto 120 min of holding and no fading is observed with master alloy obtained by this process.
The macrostnictures of the Aluminium, castings at different holding times are shown in fig 1. The 0 min sample clearly shows columnar grain structure. Within 2 min of holding the master alloy in the Aluminium melt, there was a complete conversion of the columnar structure into fine equiaxed grain structure as shown in this fig 1. The macrostructure remained fine equiaxed on further holding even upto 120 min. The grain size of Aluminium casting within 2 min holding is 103mm which is much below the acceptance level of 220 mm specified for grain refiners. The grain size of the Aluminium castings essentially remains the same even upto 120 min of holding and no fading is observed with the alloy prepared by this process, thereby establishing that the master alloy prepared by this process is not only fast acting but also long lasting.
Fig 2(a) and (b) shows typical SEM photomicrographs of the master alloy at
different magnifications showing the range of the particle sizes of TiAl3. The master
alloy which exhibited the ability to give a very fine grain size at short times, contained
varying amounts of aluminium particles. EDX
SPECTRUM (Fig. 2(c) ) taken from one of these particles identifies them as Ti aluminides. Transmission Electron Microscopic (TEM) studies (Fig 3(a) ) carried out on the master alloy to identify TiB2 particles, revealed the presence of the latter which are more or less equiaxed with average particles size of 0.2 µm. the selected area diffraction pattern (Fig 3(b) ) conforms to the (0001) zone axis of hexagonal TiB2. Some of he particles are faceted. The facets of the particle which have favourable orientation relation with Aluminium act as nucleating sites during solidification So the presence of faceted particles aids in grain refinement.
The invention is now illustrated but not limited by the following example;-
EXAMPLE-1
467g of commercial purity aluminium was melted at 800 degree C. Aluminium was degassed with about 5 g of solid hexachloroethane and the dross was removed. Sufficient chloride salt flux was maintained on top of the melt to prevent oxidation of Aluminium, The temperature of molten aluminium was maintained at 800 degree celsius A mixture of 130g to K2TiF6 and 87g of KBF4 was fed into the melt and allowed to react During this period, the melt was stirred at regular intervals of 10 minutes The molten bath was held for 60 minutes in the resistance flirnance. Then the slag was removed and the master alloy was poured into a water cooled mould. About 0.5 kg of master alloy was obtained. The chemical composition of the alloy was A1-5 3, Ti - 1,3 B with traces of carbon.

EXAMPLE-2
478 g of commercial aluminium was melted in a resistsnce furnace at 800 degree C. After degassing the molten aluminium vith abcut 5g of solid hexachloroethane, the dross was removed. To minimise oxidation of Aluminium/ sufficient quality of chloride salt flux was maintained ever the surface of the molten aluminium. The temperature of molten aluminium was maintained at 800 degree C. A mixture of 110g of K TiF6 and 70g of KBF4 salts was added with constant stirring* The aluminium bath was later stirred intermittently. After a reaction time of 60 minutes, the slag was removed. The resutant master alloy was then poured into a water cooled copper mould. About 0.5 kg of master alloy having composition of Al-2.7 Ti-0.9B with traces of carbon was obtained.

CLAIM
1. A process for preparation of master alloy for grain refinement of
aluminium and its alloy, comprising steps of :-
(a) melting commercial purity aluminium in a resistance furnace at a temperature of 750 to 900°C, maintaining conventional chloride salt flux on the top of the melt to minimise oxidation;
(b) degassing by adding solid hexachloroethane taken in quantity 1.0 to 1.1% by weight of commercial purity aluminium and removing the dross thus obtained;
(c) adding K2 Ti F6 and KB F4 with intermittant stirring where K2 Ti Fe is taken in quantity 22 to 25% by weight of commercial purity aluminium and where KBF4 is taken in quantity 15 to 20% by weight of commercial purity aluminium;
(d) removing the slag after allowing reaction time of 1/2 to 3 hours and then subjecting the melt to the step of moulding to obtain the desired master alloy.
2, A process for preparation of master alloy for grain refinement of
aluminium and its alloys as herein substantially described and
illustrated.

Documents:

29-del-1996-abstract.pdf

29-del-1996-claims.pdf

29-del-1996-correspondence-others.pdf

29-del-1996-correspondence-po.pdf

29-del-1996-description (complete).pdf

29-del-1996-drawings.pdf

29-del-1996-form-1.pdf

29-del-1996-form-2.pdf

29-del-1996-form-4.pdf

29-del-1996-gpa.pdf

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Patent Number

193566

Indian Patent Application Number

29/DEL/1996

PG Journal Number

30/2004

Publication Date

24-Jul-2004

Grant Date

30-Jan-2006

Date of Filing

05-Jan-1996

Name of Patentee

THE CHIEF CONTROLLER RESEARCH & DEVELOPMENT, MINISTRY OF DEFENCE GOVERNMENT OF INDIA

Applicant Address

TECHNICAL COORDINATION DTE., DEFENCE RESEARCH & DEV. ORGN, B-341, SENA BHAWAN, DHQ, P.O.,

Inventors:

#	Inventor's Name	Inventor's Address
1	ATMUDI ARJUNA RAO	THE DEFENCE METULLURGICAL RESEARCH LABORATORY, HYDERABAD
2	KADABA VENKATACHAR SREENIVASA PRASAD	THE DEFENCE METULLURGICAL RESEARCH LABORATORY, HYDERABAD
3	RAJGOPAL RAGHAVENDRA BAHT	THE DEFENCE METULLURGICAL RESEARCH LABORATORY, HYDERABAD
4	PANCHANAL PRAMANIK	THE DEFENCE METULLURGICAL RESEARCH LABORATORY, HYDERABAD
5	MADHUSUDAN CHAKRABORTY	THE DEFENCE METULLURGICAL RESEARCH LABORATORY, HYDERABAD
6	BUDARAJU SRINIVASA MURTY	THE DEFENCE METULLURGICAL RESEARCH LABORATORY, HYDERABAD

PCT International Classification Number

C22C 21/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA