EP0633948B1

EP0633948B1 - Alloying additive

Info

Publication number: EP0633948B1
Application number: EP94904291A
Authority: EP
Inventors: Richard Charles Cameron Nixon; Stuart Ross Thistlethwaite; John Warren Wright
Original assignee: London and Scandinavian Metallurgical Co Ltd
Current assignee: London and Scandinavian Metallurgical Co Ltd
Priority date: 1993-01-29
Filing date: 1994-01-20
Publication date: 1999-06-09
Anticipated expiration: 2014-01-20
Also published as: ZA94278B; AU674392B2; GB9301825D0; DE69418938D1; ES2132375T3; AU5841494A; NO305662B1; NO943538D0; DE69418938T2; EP0633948A1; CA2130819A1; GB2274656B; GB2274656A; NO943538L; WO1994017217A1

Abstract

An alloying additive of fine metallurgical structure is made by providing a melt of a suitable alloying material, for example an aluminium-based melt containing one or more alloying components for treating an aluminium-based melt for grain refinement, modification, conductivity reduction and/or addition of alloying metal, and applying one or more substantially unatomised streams of the melt to a cooling surface, e.g. the cylindrical exterior surface of a water-cooled rotating metal drum, to produce a splat product, which is then arranged into a dosage form suitable for making measured alloying additions, preferably having first been granulated.

Description

This invention relates to an alloying additive. More particulary it relates to a method of making an alloying additive of fine metallurgical structure.
It has for many years been appreciated that it can be advantageous for an alloying additive to have such a structure, and that such a structure can be achieved by casting a melt of the alloy in such a way that the cooling to which the alloy is subjected when passing from the molten to solid states is relatively rapid.
For example, our French Patent Specification No. 2133439 relates to aluminum-based alloying additives comprising a transition metal, normally titanium, and boron. Such alloying additives are added to aluminium-based melts to provide grain refinement. The main active component of the alloying additive is boride particles, normally titanium diboride, TiB₂. In order to maximise the effectiveness of those particles, the specification teaches subjecting the melt of the alloying material, as soon as possible after formation of the TiB₂ particles, to rapid cooling to form the solid alloy, thereby minimising the extent to which the TiB₂ particles can grow in size. The preferred method of rapid cooling taught in FR 2133439 is casting into a mould of thermally conducting material such as copper, which is preferably water cooled. A less preferred alternative suggested is a splat quenching process comprising atomising the melt to form droplets and projecting the molten droplets by means of a current of inert gas against a cooled smooth surface, so that the molten droplets are rapidly solidified by impact against the smooth surface without adhering to it. The former method entails the danger that the rate of cooling will be insufficient, and also the moulded product will not be of suitable form for many applications. The latter method is expensive to operate.
European Patent Specifications Nos. 0398449 A1 and 0421549 A1 disclose methods of producing strontium-aluminium alloying additives to be used as modifiers for aluminium-silicon alloys. They both make use of the knowledge that solidification of the melt at a relatively high rate of cooling will result in a fine metallurgical structure in the solidified alloying additive. In both cases the process for achieving the required rate of cooling involves atomisation of the melt. In EP 0398449 Al, the atomised droplets are quick-cooled to obtain solid particles which are subsequently processed to consolidate them. In EP 0421549 A1 the atomised particles are collected as solid material on a collecting surface. The atomisation process is expensive to operate, and in many cases requires steps, such as the provision of a special atmosphere, to guard against air contamination of the alloying material.
US Patent Specification No 4259270 describes an apparatus for treating alloys to give them a very fine structure to provide optimum properties in the treated alloy, such treatment requiring a very high solidification rate, for example one which is more than 10⁵ °C per second. That specification mentions earlier attempts involving atomisation, either using a rotating perforated syphon or disintegrating the melt with a pressurised gas, and explains that the earlier proposals have produced unsatisfactory results, in particular because too many of the particles are insufficiently small to allow solidification to occur rapidly enough, and also because the melts tend to react adversely with the materials into which they come into contact. In the process of US 4259270, the alloy is treated in an enclosed apparatus in which the alloy forms a self-consuming electrode, which melts and drops melt droplets onto a rotating counter electrode, where they are flung onto an internally cooled rotating conical plate, at which they are then rapidly cooled to form thin foils. The process is normally carried out in an inert atmosphere and/or under reduced pressure.
According to the present invention there is provided a method of making an alloying additive of fine metallurgical structure, comprising providing a melt of alloying material, providing cooling means comprising a cooling surface, applying one or more unatomised streams of the melt to the cooling surface to produce a splat product, and arranging the splat product into a dosage form suitable for making measured alloying additions.
Thus, it will be appreciated that the process of the invention provides a relatively inexpensive to operate process which is capable of reliably producing an alloying additive of fine metallurgical structure. We have discovered that with many alloying materials which are such that when subjected to atomisation they need a special atmosphere to prevent unacceptable contamination of the melt, the process of the present invention can be practised in an ambient atmosphere. However, in certain cases it may nevertheless be desirable to provide a suitable protective atmosphere for the melt of alloying material as the unatomised melt is applied to the cooling surface.
We have found that employing the method of the invention it is possible to produce alloying additives in which the alloying component content is higher than can be achieved using more conventional casting techniques. Also, because of the relatively high cooling rates involved, where a melt of alloying material would undergo unacceptable segregation if conventionally cast, as would be the case with a 20 weight % strontium-aluminium alloy or a 20 weight % titanium-aluminium alloy, for example, it is often possible to make an alloying additive of the same composition by the method of the invention, by arranging that the unatomised stream or streams applied to the cooling surface are above the liquidus of the melt.
Conveniently, the splat product is comminuted, for example by granulation, as described later, before it is arranged into the dosage form suitable for making alloying additions.
In order to achieve a desirable fineness in the metallurgical structure of the splat product, the rate of cooling of the unatomised stream or streams by the cooling means is preferably from 20 to 1000 °C per second, most preferably from 50 to 500 °C per second. In order to maintain a rate of cooling within those ranges it is generally necessary to apply a flow of cooling fluid, such as air or water for example, in thermal communication with the alloying material applied to the cooling surface. Preferably the cooling means comprises thermally conductive material so as to facilitate the removal of heat from the alloying material on the cooling surface, and it desirably should also be such as readily to permit the release of the splat product from that surface; suitable materials are steel and copper, for example.
The techniques employed in the manufacture of amorphous metals can produce cooling rates of the order to 10⁶ °C per second, but such techniques are relatively expensive to operate, and, if applied to a melt of alloying material, generally would not produce a worthwhile improvement in the fineness of the metallurgical structure of the alloying material, as compared with that achievable by the splat cooling used in the present invention.
The temperature of the alloying material when applied to the cooling surface will, of course, be above its solidus. It should preferably not be more than 200 °C above the liquidus.
Preferably, the cooling means comprises a cooling surface which moves in an endless path. Such a cooling means may comprise, for example, a rotating cylinder or recirculating belt having an external cooling surface. Where the cooling surface is one which moves in an endless path, we have found that it is beneficial to cool it by applying a flow of cooling fluid, for example a water spray, to an internal surface of the cooling means, the internal surface being in thermal communication with the cooling surface. The required thermal communication can be achieved by arranging that the cooling means comprises a suitable thermally conductive material such as steel or copper, for example. This arrangement can provide efficient, even removal of heat from the alloying material impinging on the cooling surface.
According to a preferred embodiment of the invention, impurities in the melt are concentrated at an upper zone in the melt, and the unatomised stream or streams are fed to the cooling surface from below the said upper zone. That has the advantage that impurities in that zone are not included in the melt applied to the cooling surface. The unatomised stream or streams can be fed from below the upper zone by underpouring from below it. In a preferred arrangement, the melt is held in a metallurgical vessel and is released through one or more apertures in the vessel below the upper zone. We have found that it is advantageous to oscillate the melt so as to urge impurities in it to rise towards the upper zone. The oscillation is preferably in a generally vertical plane.
In certain cases, where the alloying material is a high melting one and impurities in the melt are not concentrated at an upper zone in the melt, it may be of benefit to feed the unatomised stream or streams to the cooling surface by pouring the melt from its surface, such as by lip pouring, for example. In such cases, where more than one stream is required, this can be achieved by lip pouring from a vessel having castellations formed along the width of a surface over which the melt is to be poured. With such an arrangement, one can avoid the problems of hole blockages which can arise when a high melting alloying material is fed by the arrangement described in the previous paragraph, and one can also achieve a higher rate of feeding.
As a result of tests, we have found that in order to obtain splat product having a reasonably fine metallurgical structure which is also sufficiently thin as to be easily granulated, while at the same time not excessively restricting the rate of production, the thickness of the splat product desirably should be from 0.1 to 5 mm, preferably less than 3 mm. The width of the splat product is of less importance, and can conveniently be from 2 to 200 mm, for example. Its length can be unlimited, but generally will also be from 2 to 200 mm.
There are several ways in which the splat product produced in the method of the invention can be arranged into a dosage form suitable for making measured alloying additions, for example:
1. Packaging into unit quantities.Splat material in loose form is packaged into unit quantities. Where the unit quantities are relatively small, for example, 250 g, 500 g or 1 kg, the alloying addition can be made by adding the required number of packaged unit quantities directly to the melt. In such cases the unit quantities of splat material are conveniently packed into suitable packages that can release the splat material, for example by being melted or burnt away when the package is added to the melt to which the alloying addition is to be made. Where the package is to be added to the melt in this way, care should be taken to select it such that it will not give rise to products which will be deleterious from the health and safety point of view or from the point of view of the chemical analysis of the alloyed material. As regards health and safety, it will be appreciated that if the packaging is of combustible material, suitable precautions will have to be provided to prevent operators being exposed to excessive amounts of combustion products, whatever the nature of the combustible material. Bearing that in mind, suitable combustible packaging materials are plastics such as a chlorine-free, low melt, low density polyethylene. An alternative approach in cases where packaged unit quantities are to be added directly to the melt to be alloyed is to package the splat material in material which can add a useful component to the melt which is being alloyed; aluminium foil is an example of such a packaging material which would be appropriate in many instances. The packaged unit quantities may be substantially larger than as described above, e.g. 10 kg or more. In such cases it may be convenient to add the splat material to the melt which is to be alloyed by means of suitable dosing apparatus such as injection apparatus.
2. Compressing into unit quantities.Splat material in loose form is compressed into unit quantities. There are several possibilities for this:
(i) Briquetting. The splat material in loose form is formed into suitable self-supporting unit bodies by means of any of the various kinds of briquetting apparatus known in the art. If desired, any suitable binders or other desired additives may be added to the splat material before briquetting. The briquetted product may be of any suitable form, for example cylinders, pucks, pillows, lumps or cubes. We prefer cylinders between 50 and 200 mm in diameter and between 5 and 200 mm in height. Suitable unit weights of the briquetted products are 100 g, 250 g, 500 g or 1 kg, for example.
(ii) Compressing to a metallurgical bulk shape. This may be achieved by techniques similar to the briquetting techniques described above. However, the shapes produced are somewhat larger, e.g. 5 kg, 10 kg or 25 kg. The bulk shapes may be waffle plates or ingots, for example. They may be added directly to the melt which is to be alloyed. Alternatively, they may be extruded to an elongated form, such as rod or wire, for example, which is suitable for continuous feeding to the melt which is to be alloyed. A rod of about 9 mm diameter is a preferred form.
(iii) Cold extruding to an elongated form. Splat material in loose form is cold extruded through a die to an elongated form, rod or wire for example, suitable for continuous feeding to a melt. Again rod of about 9 mm diameter is preferred. A suitable cold extrusion process is known as the Conform process; see the paper by J. A. Padre "The continuous extrusion of wire and sections from non-ferrous metal powders by the CONFORM process", presented at the International Powder Metallurgy Conference, Washington, U.S.A., on 24th June 1980.
For all of the above ways of arranging the splat product produced in the method of the invention into a dosage form, we very much prefer that the splat material in loose form which is employed has been produced by a process comprising comminuting the splat product. Preferably the comminuted splat product has a mean maximum dimension of from 0.5 to 10 mm, more preferably from 1 to 5 mm. The required comminution of the splat product can be achieved by means of a metallurgical granulation machine, which has rotating blades which can reduce the size of the splat product pieces to the required degree.
The alloying material used to produce the alloying additive in accordance with the method of the invention may be of any suitable kind. Preferably it is an aluminium based material, where the alloying additive is to be used to make alloying additions to an aluminium-based melt. Examples of aluminium-based alloying materials are:
1. A modifier comprising strontium.Such alloying materials are suitable for making alloying additions to hypoeutectic and eutectic aluminium-silicon alloy melts for the purpose of improving the crystal structure of the aluminium-silicon eutectic crystals when the alloy solidifies. The preferred such alloy is a strontium-aluminium alloy containing strontium in the range from 3 to 30 weight %, preferably from 8 to 20 weight %, more preferably about 10 weight %. Because of the fine metallurgical structure of strontium-aluminium alloying additives produced by the method of the invention, it is possible to produce the alloying additions in rod form, even at higher strontium levels than can be formed to rod from strontium-aluminium alloys produced by more conventional methods. The strontium-aluminium modifier may additionally comprise titanium, and boron; such an alloying addition can be added to hypoeutectic aluminium-silicon melts to produce grain refinement of the aluminium component as well as modification of the aluminium-silicon component of the solidified aluminium-silicon alloy. Such an alloying addition may comprise, in weight %: 5% to 25% strontium, 0.5% to 12% titanium, 0.1% to 2% boron. Three preferred compositions comprise in weight %: (a) about 10% strontium, about 1 % titanium and about 0.2% boron; (b) about 10% strontium, about 5 % titanium and about 1% boron; and (c) about 5% strontium, about 10% titanium and about 1% boron.
2. A grain refiner.Grain refiners for adding to aluminium-based melts may comprise titanium; they usually comprise boron as well as titanium. When produced by the method of the invention their activity can be enhanced as a result of the improvement in the fineness of the metallurgical structure. The rate of dissolution may also be enhanced. With those comprising boron as well as titanium, this is especially the case when the melt of the alloying material is applied to the cooling surface within a short time of the beginning of the co-existence of the boron and the titanium in the melt. FR 2133439 describes techniques which can readily be adapted to the method of the present invention whereby it will be possible to minimise the length of that time period. Examples of suitable compositions of aluminium-based grain refiners which can be produced by the method of the invention are those comprising, in addition to the aluminium, in weight %:
(a) 5% to 25% titanium, preferably about 10% titanium;
(b) about 3% titanium, plus boron; e.g.
(i) about 3% titanium and about 1% boron;
(ii) about 3% titanium and about 0.1% boron;
(iii) about 3% titanium and about 0.2% boron, and
(iv) about 3% titanium and about 0.5% boron.
(c) about 5% titanium, plus boron; e.g.
(i) about 5% titanium and about 1% boron;
(ii) about 5% titanium and about 0.1% boron;
(iii) about 5% titanium and about 0.2% boron; and
(iv) about 5% titanium and about 0.6% boron.
3. A conductivity-enhancing additive.Such additives generally comprise aluminium and boron, and are added to aluminium melts to precipitate out conductivity-impairing impurities such as vanadium. When produced by the method of the invention, they can have an improved rate of dissolution and rate of precipitating out of the conductivity-impairing impurities. The preferred such alloy is a boron-aluminium alloy comprising boron in the range from 3 to 10 weight %, preferably about 4 weight %.
4. An alloying additive for adding an alloying metal.Such alloying additives can be employed to add an alloying metal such as zirconium, manganese, copper, vanadium, iron or chromium, for example, to an aluminium-based melt. When produced by the method of the invention their rate of dissolution may be enhanced. Preferred compositions for such alloying additives are:
(a) zirconium-aluminium, comprising zirconium in the range from 5 to 30 weight %, preferably about 15 weight %;
(b) manganese-aluminium, comprising manganese in the range from 5 to 40 weight %, preferably about 20 weight % ;
(c) copper-aluminium, comprising copper in the range from 20 to 60 weight %, preferably about 50 weight % ;
(d) vanadium-aluminium, comprising vanadium in the range from 5 to 30 weight %, preferably about 10 weight %;
(e) iron-aluminium, comprising iron in the range from 5 to 40 weight %, preferably about 20 weight % ; and
(f) chromium-aluminium, comprising chromium in the range from 5 to 40 weight %, preferably about 20 weight %.
Where it is desired to make an alloying additive by the method of the invention such that the additive contains more than one alloying component, one can arrange that the original melt of alloying material contains all of the required alloying components, as illustrated in the following Example 3. However, we have found that in many circumstances the same object can be achieved with greater convenience by arranging that a splat product having a first composition is mixed with at least one additional splat product having a different composition to provide a mixed splat product for arranging into a dosage form in accordance with the invention. This is illustrated in the following Example 4. The first and additional splat products are preferably comminuted as described above, either before or after they are mixed together.
The present invention also comprehends a method of making an alloying addition to an aluminium melt, comprising adding to the melt a dosage form which has been produced by a method in accordance with the invention.
In order that the invention may be more fully understood, some embodiments in accordance therewith will now be described with reference to the accompanying drawings. Figures 1(a) and 1(b) are photographs at the same size as the original. The rest of the Figures are all photomicrographs at a magnification of 500. In the drawings:

Fig. 1(a): shows the structure of untreated aluminium metal as used in Example 1.
Fig. 1(b): shows the structure of aluminium metal after being grain refined with the grain refiner alloying briquettes produced in accordance with Example 1.
Fig. 2(a): shows the structure of untreated LM24 alloy as used in Examples 2 to 4.
Fig. 2(b): shows the structure of LM24 alloy after being modified with modifier alloying briquettes produced in accordance with Example 2.
Fig. 3: shows the structure of LM24 alloy after being modified and grain refined with modifier and grain refiner alloying briquettes produced in accordance with Example 3.
Fig.4: shows the structure of LM24 alloy after being modified and grain refined with modifier and grain refiner alloying briquettes produced in accordance with Example 4.

Example 1

A 300 kg melt of alloying material comprising 5 weight % titanium, 1 weight % boron balance aluminium of 99.7 weight % purity (5/1 TiBAl) was prepared by reacting potassium fluotitanate, K₂TiF₆, and potassium borofluoride, KBF₄, with molten aluminium in an induction furnace.
The alloying material was then converted to a splat product in an apparatus comprising a tundish which was mounted vertically above cooling means comprising a water-cooled, standard cylindrical metallurgical packaging drum of 1 mm thick mild steel having a length of 880 mm and a diameter of 660 mm. It was mounted for rotation about its cylindrical axis, with the axis disposed horizontally, and was connected to a motor arranged to drive it at a rate of 30 r.p.m. The drum was openended, and was cooled by means of a spray bar which projected from the open end within the drum's interior so as to direct a spray of water to the interior of the drum, centred at approximately the 1 o'clock position.
The tundish having a capacity of 10 kg of alloying material was arranged about 400 mm above the 12 o'clock position. It comprised a steel body of substantially V-section and extending over almost the whole of the axial length of the drum, and was lined internally with suitable refractory material. The base of the "V" of the tundish included a horizontal internal floor section 50 mm wide which was provided with a line of 8 evenly spaced 6 mm diameter circular apertures to enable the contents of the tundish to exit in a line of streams which could be directed to the drum along its axial length at the 12 o'clock position.
The tundish was mounted so that it could be oscillated vertically, perpendicular to the axis of the drum, and was connected to an oscillator arranged to move it in that direction over a distance of 20 mm, at a rate of 100 oscillations per minute.
The splat producing apparatus had been prepared to receive the molten alloying material, by activating the drum drive motor and the oscillator, and supplying cooling water at a temperature of 15 °C at a rate of 100 kg per minute. Molten alloying material at 850 °C was supplied to the tundish from the induction furnace continuously at a rate such as to keep it approximately three quarters full. The melt exited the holes in the base of the tundish, thus being underpoured. It then fell in a series of semi-continuous streams onto the surface of the drum at the 12 o'clock position, that surface acting as a cooling surface causing the melt to solidify at an estimated rate of about 400 °C per second, to form splat pieces of mean dimensions approximately 50 mm wide x 100 mm long x 1 mm thick. The solidified splat pieces fell away from the drum at approximately the 3 o'clock position, and were continuously removed for processing in a granulator. Approximately 300 kg of splat product were produced, over a period of 40 minutes. The final 3 kg to exit the tundish were discarded, as they would have contained a large part of the impurities which had been accumulating at the surface of the melt of alloying material.
The granulator used was a Blackfriars granulator, and comprised rotating blades for comminuting the splat product. It had been manufactured by Blackfriars Rotary Cutters Ltd., of Redhill, Surrey, England, and was designated as their 18 inch ASHD Rotary Cutter. The comminuted splat product exiting the granulator had a mean maximum dimension of 3 mm.
It was then fed to a metallurgical briquetting apparatus comprising a hydraulic press for formation into dosage units. The press cold compacted the comminuted splat product into the dosage units, each of which comprised a tablet in the form of a cylinder 90 mm in diameter and 25 mm long. Each tablet weighed 300 g. The tablets were used as a grain refiner alloying additive. They were added to molten aluminium of 99.7 weight % purity at an addition rate of 2 kg per tonne. A sample of the treated melt was then solidified in accordance with a comparative test based on the AA TPl grain refiner test; the structure of the solidified sample is shown in Fig. 1(b); Fig. 1(a) shows the structure of an untreated sample of the aluminium.

Example 2

A 300kg melt comprising 10 weight % strontium, balance aluminium of 99.7 weight % purity (10SrAl) was prepared by alloying 30 kg of strontium metal into a melt of 270 kg of molten aluminium in an induction furnace.
The alloying material was then converted to a splat product in the apparatus described in Example 1, under substantially the same conditions, with the exception that the temperature of the strontium-aluminium melt supplied to the splat casting apparatus was 870 °C.
The resulting splat product was then granulated and briquetted, as in Example 1, the comminuted splat product exiting the granulator having a mean maximum dimension of 3 mm, and the cylindrical briquetted tablets each being 90 mm in diameter x 25 mm in length, and weighing 300 g.
A trial was conducted in which the briquetted tablets were used as an alloying additive to modify a melt of LM24, being added at the rate of 3 kg/tonne. LM24 is a hypoeutectic aluminium-silicon alloy containing copper, and conforms to the specification, in weight %: 3.0 to 4.0 copper, 7.5 to 9.5 silicon, maximum 1.3 iron, maximum 3.0 zinc and maximum 0.5 manganese. Although this alloy is generally used in the un-modified state, it is an alloy which can be used to show modification particularly well.
The structure of the modified alloy on solidification is shown in Fig. 2(b); Fig. 2(a) shows the structure of an untreated sample of the alloy.

Example 3

A 300 kg melt of an alloying material comprising 10 weight % strontium, 1 weight % titanium, 0.2 weight % boron, balance aluminium of 99.7 weight % purity (10/1/0.2 SrTiBAl) was prepared by reacting the appropriate amounts of K₂TiF₆ and KBF₄ with molten aluminium as in Example 1 and alloying 30 kg of strontium metal as in Example 2.
The alloying material was then converted to a splat product in the apparatus described in Example 1, under substantially the same conditions, with the exception that the temperature of the strontium-aluminium melt supplied to the splat casting apparatus was 870 °C.
The resulting splat product was then granulated and briquetted, as in Example 1, the comminuted splat product exiting the granulator having a mean maximum dimension of 3 mm, and the cylindrical briquetted tablets each being 90 mm in diameter x 25 mm in length, and weighing 300 g.
A trial was conducted in which the briquetted tablets were used as an alloying additive to modify and grain refine a melt of LM24, being added at the rate of 3 kg/tonne.
The structure of the modified and grain refined alloy on solidification is shown in Fig. 3.

Example 4

A melt of 5/1 TiBAl alloying material was prepared and converted to a splat product and then granulated, as described in Example 1, and a melt of 10SrAl was prepared and converted to a splat product and then granulated as described in Example 2. Portions of the 5/1 TiBAl and 10SrAl splat products after comminution in the granulator were mixed in a weight ratio of 80 to 20, so that the resulting mixture was, in weight %: 4% titanium, 0.8% boron, 2% strontium, balance aluminium. The resulting mixture was briquetted as described in Example 1 to produce cylindrical briquetted tablets, each being 90 mm in diameter x 25 mm in length, and weighing 300 g.
A trial was conducted in which the briquetted tablets were used as an alloying additive to modify and grain refine a melt of LM24, being added at the rate of 5 kg/tonne.
The structure of the modified and grain refined alloy on solidification is shown in Fig. 4.

Claims

A method of making an alloying additive of fine metallurgical structure, comprising providing a melt of alloying material, providing cooling means comprising a cooling surface, applying one or more unatomised streams of the melt to the cooling surface to produce a splat product, and arranging the splat product into a dosage form suitable for making measured alloying additions.
A method according to claim 1, wherein the cooling of the melt on the cooling surface is at a rate of 20 to 1000 °C per second, preferably 50 to 500 °C per second.
A method according to claim 1 or claim 2, wherein the cooling means comprises a cooling surface which moves in an endless path, and preferably comprises a rotating cylinder having an external cooling surface or a recirculating belt having an external cooling surface.
A method according to claims 3, wherein the cooling surface is cooled by applying a flow of fluid to an internal surface of the cooling means, the internal surface being in thermal communication with the cooling surface.
A method according to any one of claims 1 to 4, wherein impurities in the melt are concentrated at an upper zone in the melt, and the unatomised stream or streams are fed from below the said upper zone and are preferably applied to the cooling surface by underpouring from below the said upper zone.
A method according to claim 5, wherein the melt is held in a metallurgical vessel, and the unatomised stream or streams are created by releasing the melt through one or more apertures in the vessel below the said upper zone.
A method according to claim 5 or claim 6, wherein the melt is oscillated so as to urge impurities in it to rise into the said upper zone.
A method according to any one of claims 1 to 7, wherein the thickness of the splat product is from 0.1 to 5 mm, and preferably less than 3 mm, and the width of the splat product is from 2 to 200 mm.
A method according to any one of claims 1 to 8, wherein arranging the splat product into a dosage form comprises packaging splat material in loose form into unit quantities.
A method according to any one of claims I to 8, wherein arranging the splat product into a dosage form comprises compressing splat material in loose form into unit quantities.
A method according to claim 10, wherein the splat material is briquetted.
A method according to claim 10, wherein the splat material is compressed to a metallurgical bulk shape.
A method according to claim 12, wherein the bulk shape is extruded to an elongated form suitable for continuous feeding to a melt.
A method according to any one of claims 1 to 8, wherein arranging the splat product into a dosage form comprises cold extruding splat material in loose form through a die to an elongated form suitable for continuous feeding to a melt.
A method according to any one of claims 9 to 14, wherein the said splat material in loose form has been produced by a process comprising comminuting the splat product, the comminution preferably comprising granulation.
A method according to claim 15, wherein the comminuted splat product has a mean maximum dimension of from 0.5. to 10 mm, preferably from 1 to 5 mm.
A method according to any one of claims 1 to 16, wherein the alloying material is an aluminium-based material.
A method according to any one of claims 1 to 17, wherein the alloying material is a modifier comprising strontium.
A method according to claim 18, wherein the modifier additionally comprises a grain refiner.
A method according to any one of claims 1 to 17, wherein the alloying material is a grain refiner.
A method according to claim 20, wherein the grain refiner comprises titanium, and preferably comprises titanium and boron.
A method according to any one of claims 1 to 17, wherein the alloying material is a conductivity-enhancing additive comprising boron.
A method according to any one of claims 1 to 17, wherein the alloying material comprises an alloying metal, for example chromium, zirconium, manganese, copper, vanadium or iron.
A method according to any one of claims 1 to 23, wherein a splat product having a first composition is mixed with at least one additional splat product having a different composition to provide a mixed splat product, and the mixed splat product is arranged into a dosage form suitable for making measured alloying additions.