METHOD FOR PRODUCING A SOLIDIFIED LIGHTWEIGHT ALUMINIUM OR MAGNESIUM ALLOY

Abstract

A lightweight aluminium or magnesium alloy comprises aluminium or magnesium and one or more alloying elements, including dispersoid forming elements increasing the liquidus temperature of the alloy. The alloy is ejected in a molten state from at least one nozzle and is rapidly solidified. The lightweight alloy is produced from at least one lightweight metal based composition that comprises predominantly aluminium or magnesium. This composition is heated, in a first heating step, to a first temperature that is lower than the liquidus temperature of the alloy to produce a melt of the lightweight metal based composition that is supplied through a piping to the nozzle. In the piping, the lightweight alloy melt is heated to have a second temperature that is preferably higher than the liquidus temperature of the alloy. The first temperature reduces the tendency of magnesium to oxidize whilst the second temperature dissolves all of the alloying elements.

Claims

1. A method for producing a solidified lightweight alloy based on aluminium or magnesium as lightweight metal, wherein the lightweight alloy has a liquidus temperature and a solidus temperature, and a predetermined difference between the liquidus and the solidus temperature, and wherein the lightweight alloy comprises the lightweight metal and one or more alloying elements, the method comprises the steps of: providing at least one starting composition for producing the lightweight alloy, including at least one lightweight metal based composition which comprises predominantly the lightweight metal; producing the lightweight alloy in a form of a melt from the at least one starting composition; ejecting the lightweight alloy melt from at least one nozzle; and rapidly solidifying the lightweight alloy melt exiting the at least one nozzle thereby producing the solidified lightweight alloy, the lightweight alloy melt exiting the at least one nozzle having a predetermined temperature upon exiting the at least one nozzle and being cooled down within a predetermined period of time to the solidus temperature of the lightweight alloy at an average cooling rate which is determined as a ratio of the difference between the predetermined temperature and the solidus temperature over the predetermined period of time and which is in particular higher than 10,000 C./sec, wherein the lightweight metal based composition is heated, in a first heating step, to a first temperature which is lower than the liquidus temperature to produce a melt of the lightweight metal based composition having the first temperature, which lightweight metal based composition melt is supplied through a piping to the at least one nozzle; and the lightweight alloy melt, which comprises at least the lightweight metal based composition melt, is heated in the piping to have a second temperature before being ejected from the at least one nozzle, which second temperature is higher than the first temperature and is at least 75% of the liquidus/solidus temperature difference higher than the solidus temperature.

2. The method according to claim 1, wherein the second temperature is equal to or higher than the liquidus temperature, preferably at least 10 C. and more preferably at least 20 C. higher than the liquidus temperature.

3. The method according to claim 1, wherein the predetermined temperature is equal to or higher than the liquidus temperature, preferably at least 10 C. and more preferably at least 20 C. higher than the liquidus temperature.

4. The method according to claim 1, wherein the lightweight alloy melt has a residence time of at least 10 seconds, preferably at least 15 seconds and more preferably at least 20 seconds in the piping.

5. The method according to claim 1, wherein the lightweight alloy is an aluminium alloy and the one or more alloying elements comprise one or more elements forming dispersoids in the aluminium alloy, the elements being transition metals, in particular transition metals selected from the group consisting of manganese (Mn), chromium (Cr), vanadium (V), titanium (Ti), zirconium (Zr), molybdenum (Mo), cobalt (Co), niobium (Nb), scandium (Sc), hafnium (Hf), nickel (Ni), yttrium (Y) and iron (Fe).

6. The method according to claim 5, wherein the one or more alloying elements comprise chromium (Cr), vanadium (V), titanium (Ti), zirconium (Zr), molybdenum (Mo), cobalt (Co) and/or niobium (Nb), the total amount of Cr, V, Ti, Zr, Mo, Co and Nb being preferably at least equal to 0.50 wt. %, more preferably at least equal to 0.70 wt. % and most preferably at least equal to 1.00 wt. % of the aluminium alloy and the maximum amounts of these alloying elements being preferably 1.50 wt. % for Cr, 1.50 wt. % for V, 1.00 wt. % for Ti, 1.00 wt. % for Zr, 1.50 wt. % for Mo, 1.50 wt. % for Co and 1.00 wt. % for Nb.

7. The method according to claim 5, wherein the one or more alloying elements comprise one or more elements forming a solid solution in the aluminium alloy, which solid solution forming elements comprise copper, zinc, magnesium and/or manganese, the aluminium alloy preferably comprising between 3.00 and 10.00 wt. % of magnesium (Mg) and more than 1.00 but less than 6.00 wt. % of manganese.

8. The method according to claim 1, wherein the lightweight alloy is a magnesium alloy and the one or more alloying elements comprise silicon (Si), germanium (Ge), zirconium (Zr) and/or cobalt (Co).

9. The method according to claim 1, wherein at least one of the alloying elements is present in the lightweight alloy in an amount higher than a solubility of the element at the solidus temperature in the lightweight alloy.

10. The method according to claim 1, wherein the liquidus temperature is at least 25 C., in particular at least 50 C. and more particularly at least 75 C. or at least 100 C. higher than the solidus temperature.

11. The method according to claim 1, wherein the first temperature is lower than 750 C., preferably lower than 725 C. and more preferably lower than 700 C.

12. The method according to claim 1, wherein the first temperature is at least 10 C., in particular at least 20 C. and more particularly at least 30 C. lower than the liquidus temperature.

13. The method according to claim 1, wherein the lightweight metal based composition melt is urged, by pipe flow, through the piping to the at least one nozzle.

14. The method according to claim 1, wherein the lightweight metal based composition melt is degassed before being supplied through the piping to the at least one nozzle.

15. The method according to claim 1, wherein the piping comprises at least one heating chamber for further heating the lightweight alloy melt.

16. The method according to claim 1, wherein the lightweight metal based composition is only partially molten to produce the lightweight metal based composition melt by heating it to the first temperature and is further molten by heating it to the higher temperature in the piping.

17. The method according to claim 16, characterised in wherein the lightweight alloy is produced from one starting composition, which starting composition is only partially molten by heating it to the first temperature to produce the lightweight metal based composition melt forming the lightweight alloy melt, which lightweight alloy melt is further molten in the piping by heating it to the second temperature in the piping.

18. The method according to claim 1, wherein the lightweight alloy is produced from at least two starting compositions including the at least one lightweight metal based composition and at least one further composition, which further composition is added in the piping to the lightweight metal based composition melt to produce the lightweight alloy melt.

19. The method according to claim 18, characterised in wherein the further composition is added to the lightweight metal based composition melt in a solid form.

20. The method according to claim 18, characterised in wherein the further composition is added to the lightweight metal based composition melt in a liquid form.

21. The method according to claim 1, wherein the piping comprises a mixing device for mixing the lightweight alloy melt.

22. The method according to claim 1, wherein the first heating step is carried out in a furnace which is in liquid connection via the piping to the at least one nozzle, the lightweight metal based composition melt being fed at the first temperature from the furnace to the piping.

23. The method according to claim 1, wherein the solidified lightweight alloy is plastically consolidated by plastic deformation under pressure, in particular by being extruded with a cross section reduction of at least 3, preferably of at least 6, more preferably of at least 8 and most preferably of at least 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Other particularities and advantages of the method according to the present disclosure will become apparent from the following description of some embodiments thereof. The reference numerals used in this description refer to the drawings wherein:

[0079] FIG. 1 shows schematically a first embodiment of an installation for producing the lightweight alloy melt and for rapidly solidifying the molten alloy by a melt spinning device;

[0080] FIG. 2 shows schematically a second embodiment of an installation for producing the lightweight alloy melt and for rapidly solidifying this melt, which installation has a heating chamber in the piping between the melting furnace and the melt spinning device;

[0081] FIG. 3 shows schematically a third embodiment of an installation for producing the lightweight alloy melt and for rapidly solidifying this melt, which installation has an additional melting furnace for melting a further starting composition that is fed in a liquid state into the heating chamber;

[0082] FIG. 4 shows schematically a fourth embodiment of an installation for producing the lightweight alloy melt and for rapidly solidifying this melt, which installation has a feeding device for feeding the further starting composition in a solid state into the heating chamber;

[0083] FIG. 5 is an SEM image showing the microstructure of the Al-7Mg-1V alloy with coarse primary Al.sub.3V intermetallic phases produced in the RS example wherein the alloy composition was rapidly solidified at a temperature of 650 C.; and

[0084] FIGS. 6 and 7 are similar to FIG. 5 but show the microstructure of the Al-7Mg-1V alloy rapidly solidified at a temperature of 750 C. and 850 C. and showing less or no coarse primary Al.sub.3V intermetallic phases.

DETAILED DESCRIPTION

[0085] The present disclosure generally relates to a method for producing a solidified lightweight alloy that is either an aluminium alloy or a magnesium alloy. The lightweight alloy has a liquidus and a solidus temperature. The liquidus temperature is the lowest temperature at which the alloy, in an equilibrium state, is completely liquid while the solidus temperature is the highest temperature at which the alloy, in an equilibrium state, is completely solid. Both temperatures can be seen on the equilibrium phase diagram of the alloy.

[0086] The alloy is preferably a wrought alloy, i.e., an alloy that is suited for being forged. The alloy may be a wrought aluminium alloy or a wrought magnesium alloy. In practice, there exists already a lot of wrought aluminium alloys. In accordance with the International Alloy Designation System these alloys are classified in eight different series. The 1000 series are essentially pure aluminium, the 2000 series are alloyed with copper, the 3000 series are alloyed with manganese, the 4000 series are alloyed with silicon, the 5000 series are alloyed with magnesium, the 6000 series are alloyed with magnesium and silicon, the 7000 series are alloyed with zinc and the 8000 series are alloyed with other elements. A list of the different wrought alloy numbers and their chemical compositions can be found in the publication International Alloy Designations and Chemical Composition Limits for Wrought Aluminium and Wrought Aluminium Alloys of The Aluminium Association as revised on January 2015. Both the present and the inactive alloys are disclosed in this publication.

[0087] Most of the industrial alloys comprise the alloying elements in such amounts that they can be dissolved completely at a relatively low temperature, in particular at a temperature at which the aluminium metal does not have to be shielded from the atmosphere to avoid excessive oxidation and formation of hydrogen. These traditional alloys can thus be produced and solidified on a large scale in standard installations, at relatively low costs. Some aluminium alloys and also magnesium contain however higher amounts of alloying elements that require higher melting temperatures.

[0088] To achieve higher strengths and higher thermal stabilities, alloying elements forming precipitates or dispersoids may indeed, for example, be added for certain applications. These precipitates are usually intended to achieve precipitation hardening of the alloy. Aerospace aluminium alloys may comprise for example scandium, which is an expensive element. Usually it is included in the alloy in an amount of between 0.1 and 0.5 wt. %, that is less than the solubility of scandium at the solidus temperature of the alloy. Heating the alloy to high temperatures is thus not required to dissolve such amounts of scandium in the aluminium alloy. The supersaturated alloy needs subsequently to be heat treated to achieve the required precipitation hardening. An advantage of the nanoscale precipitates such as Al.sub.3Sc, which give the alloy its strength, is that they are quite coarsening resistant at relatively high temperatures, i.e. at temperatures up to about 350 C. whilst typical commercial 2xxx and 6xxx alloys quickly lose their strength at temperatures above 250 C. due to rapid coarsening of their strengthening precipitates.

[0089] The method of the present disclosure enables to use alloying elements in amounts higher than their solubility at the solidus temperature of the alloy. Alloying elements that have a lower solubility at the solidus temperature in the alloy can thus be used or larger amounts of alloying elements, in particular amounts larger than the solubility of the element at the solidus temperature of the alloy, without having to shield the molten alloy from the atmosphere for an aluminium alloy or without increasing the oxidation of the alloy for a magnesium alloy.

[0090] The solidified lightweight alloy produced by the method according to the disclosure comprises the lightweight metal, i.e. aluminium or magnesium, and one or more alloying elements. In a first step, at least one starting composition for producing the lightweight alloy is provided. This starting composition includes at least one lightweight metal based composition which comprises predominantly the lightweight metal, i.e. the aluminium for an aluminium alloy or the magnesium for a magnesium alloy. By the expression which comprises predominantly the lightweight metal is meant that the lightweight metal based composition comprises at least 50 wt. % of the lightweight metal element. The lightweight metal based composition comprises in particular at least 65 wt. % of the lightweight metal or more in particular at least 80 wt. % of the lightweight metal. Due to the high aluminium content, the aluminium based composition is subject to oxidation when it comes in contact at a higher temperature, in particular at a temperature of 800 C., with air that contains water vapour. A magnesium based composition is even more prone to oxidation, and oxidizes very quickly when the magnesium is in a molten state, i.e. when it is at a temperature higher than the solidus temperature of the magnesium alloy.

[0091] The lightweight alloy can be produced from one such lightweight metal based composition or from two or more of such lightweight metal based compositions. The lightweight metal based composition(s) can be used in combination with other starting compositions, i.e. with starting compositions that contain no or less than 50 wt. % of the lightweight metal. These other starting compositions thus contain one or more of the alloying elements.

[0092] The lightweight alloy is produced in the form of a melt from these starting composition or compositions. This melt is heated to a temperature to a temperature that is at least 75% of the difference between the solidus and the liquidus temperature of the alloy higher than the solidus temperature thereof. Preferably, it is heated to a temperature higher than the liquidus temperature of the alloy to enable to dissolve all of the alloying elements. The lightweight alloy melt is then ejected in a molten state from at least one nozzle. The lightweight alloy melt that exits the nozzle or nozzles is rapidly solidified to produce the solidified lightweight alloy.

[0093] By the expression rapidly solidified is meant that when being solidified the lightweight alloy melt is cooled down at an average cooling rate that is higher than 10 000 C./sec (10.sup.4 C./sec) and preferably higher than 100 000 C./sec (10.sup.5 C./sec). The average cooling rate is, in particular, calculated over a time interval starting from the moment the accelerated extraction of heat from the lightweight alloy melt has started until the average temperature of the lightweight alloy has dropped to its solidus temperature. The accelerated extraction of heat is preferably started as from an average temperature of the lightweight alloy melt that is equal to or higher than the liquidus temperature of the lightweight alloy. The average cooling rate is preferably higher than 10 000 C./sec (10.sup.4 C./sec) and more preferably higher than 100 000 C./sec (10.sup.5 C./sec) over the time interval between the moment in time when the alloy is at its liquidus temperature and the moment in time when the temperature of the alloy has dropped to its solidus temperature.

[0094] Rapid solidification starts when the lightweight alloy melt exits the nozzle or nozzles. At the outlet of the nozzle, the lightweight alloy melt has a predetermined temperature that is substantially uniform. If not uniform, this predetermined temperature is the volume weighted average temperature of the lightweight alloy upon exiting the nozzle. The average cooling rate has to be calculated over the interval wherein the volume-weighted average temperature of the lightweight alloy melt drops from the predetermined temperature at the outlet of the nozzle to the solidus temperature of the lightweight alloy. The difference between these two temperatures divided by the time it takes to cool the lightweight alloy melt down from the predetermined temperature to the solidus temperature is the average cooling rate that has to be higher than 10 000 C./sec (10.sup.4 C. per second) to have a rapid solidification process.

[0095] When appropriate measurement devices are available, this average cooling rate can be measured but it can also be calculated based on different parameters. The required cooling rate can also be determined experimentally by testing incrementally increasing cooling rates starting from a cooling rate at which primary intermetallic phases are formed until a cooling rate is reached at which primary intermetallic phases are no longer formed during the rapid solidification step.

[0096] For a rapid solidification process by melt spinning the average cooling rate can be calculated based on calculations as disclosed in the article Analyses of the melt cooling rate in the melt-spinning process of B. Karpe et al. in Journal of Achievements in Materials and Manufacturing Engineering, Vol. 51, Issue 2, April 2012. The content of this article is incorporated herein by way of reference. In a number of the figures of this articles, the initial quick drop of the temperature from about 700 C. to 660 C., i.e. to the solidus temperature of pure aluminium, can be seen and this for different ribbon thicknesses and different distances from the surface of the chill wheel. When dividing this temperature drop by the solidification time, and averaging these values for the different distances from the surface of the chill wheel, the average cooling rate can be calculated.

[0097] For a rapid solidification process by gas (or liquid) atomisation the average cooling rate can be calculated based on calculations as disclosed in the article Rapidly Solidified Gas-Atomized Aluminium Alloys Compared with Conventionally Cast Counterparts: Implications for Cold Spray Materials Consolidation by Bryer C. Sousa et al., Coatings 2020, 10, 1035. The content of this article is incorporated herein by way of reference. The formula enabling to calculate the cooling rate is given in this article. In FIG. 3 of this article it can be seen that the cooling rate is in particular dependent from the particle size of the atomised droplets. Other parameters are the specific heat of the metal droplet and the thermal conductivity of the gaseous species utilized during gas atomisation.

[0098] During the rapid solidification the solidified lightweight alloy is either produced in the form of small particles, for example by atomizing the molten lightweight alloy, or in the form of larger pieces that could be cut or ground into smaller particles. The particles may be spherical or elongated or may even have the shape of fibres. These particles can then be plastically consolidated by plastic deformation under pressure, for example by extruding them. When consolidating the particles they are preferably heated, in particular to a temperature higher than 350 C., and preferably to a temperature higher than 400 C. The lightweight alloy is preferably consolidated at a temperature lower than 550 C., preferably lower than 525 C. The lightweight alloy is preferably plastically consolidated by extrusion, in particular by means of an extrusion press.

[0099] In the method of the present disclosure, at least the lightweight metal based composition or at least one of the lightweight metal based compositions is first heated to a first temperature that is lower than the liquidus temperature of the alloy to produce a melt. The lightweight metal based composition is either completely molten at this first temperature or is only partially molten at this first temperature so that the lightweight metal based composition melt may still contain some solid particles that are usually formed by intermetallic phases. The lightweight metal based composition melt is then supplied through a piping to the nozzle(s). Before arriving at the nozzle(s) it is brought in the piping leading to the nozzle(s) to a second, higher temperature.

[0100] When the lightweight metal based composition contains all the elements of the lightweight alloy, i.e. when the lightweight alloy is produced from this lightweight metal based composition as only starting composition, the lightweight metal based composition is only partially molten at the first temperature so that the lightweight metal based composition melt contains solid phases of the alloying element(s), in particular intermetallic phases produced by this alloying element(s). These solid phases are further dissolved when the lightweight alloy melt formed by the lightweight metal based composition melt is heated in the piping leading to the nozzle(s) to the second temperature which is at least 75% of the difference between the solidus and the liquidus temperature of the alloy higher than the solidus temperature thereof. To enable to dissolve all of the solid phases in the aluminium alloy melt, the second temperature is temperature is equal to or higher than the liquidus temperature of the alloy, and preferably at least 10 C. and more preferably at least 20 C. higher than this liquidus temperature. The higher the second temperature, the less time it takes for the solid phases to dissolve in the aluminium alloy melt.

[0101] The first temperature is lower than the liquidus temperature of the alloy in order to make the melt less prone to oxidation. Preferably, the first temperature is at least 10 C., in particular at least 20 C. and more particularly at least 30 C. lower than the liquidus temperature of the lightweight alloy. For a magnesium alloy, the first temperature should preferably be kept as low as possible. The first temperature is more particularly preferably at most 30 C. higher, more preferably at most 20 C. higher and most preferably at most 10 C. higher than the solidus temperature of the magnesium alloy.

[0102] When the lightweight metal based composition does not contain all the elements of the lightweight alloy, i.e. when the lightweight alloy is produced from this lightweight metal based composition and from at least one further starting composition (which may also be a lightweight metal based composition containing more than 50 wt. % of the lightweight metal), the lightweight metal based composition may either be only partially molten, as described hereabove, or it may be completely molten at the first temperature so that the lightweight metal based composition melt no longer contains solid phases. The further starting composition is then added in the piping leading to the nozzle(s) to the lightweight metal based composition melt so that the lightweight alloy melt is produced from the lightweight metal based composition and from this further starting composition. Also in this embodiment, the lightweight alloy melt formed by the lightweight metal based composition melt and by the further starting composition or compositions is heated in the piping leading to the nozzle(s) to the second temperature that is at least 75% of the difference between the solidus and the liquidus temperature of the alloy higher than the solidus temperature thereof. The second temperature is again preferably equal to or higher than the liquidus temperature of the alloy, and more preferably at least 10 C. and most preferably at least 20 C. higher than this liquidus temperature. The lightweight alloy melt may be heated itself to the second temperature in the piping leading to the nozzle and/or one or more of the starting compositions may be heated before being mixed with the other starting composition or compositions to produce the lightweight alloy melt in the piping.

[0103] The further starting composition may be a so-called master alloy containing the alloying element or elements in a matrix of the lightweight metal. The master alloy may contain more than 50 wt. % of the lightweight metal so that it is also a lightweight metal based composition. It is, however, used in a smaller amount than the main lightweight metal based composition. It can be added for example in a solid form to the lightweight based composition melt so that it doesn't have to be heated to a higher temperature. It can however also be molten to produce a melt. Preferably, it is also heated, in the same way as the main lightweight metal based composition, to a first temperature that is lower than the liquidus temperature of the alloy. At such a temperature, the melt produced from the master alloy will still contain solid phases, in particular intermetallic phases. Instead of being composed by a master alloy, one or more of the further starting compositions may also consist of one or more of the alloying elements as such.

[0104] FIG. 1 shows schematically an installation that can be used to produce the solidified lightweight alloy when it is produced from one single starting composition 3, more particularly from one single lightweight metal based composition that has the same composition as the lightweight alloy that is to be produced. This installation comprises a furnace 1, which is provided with a heater 2. As illustrated in FIG. 1 this heater 2 may be an induction heater 2. Other heaters are however also possible, for example an electric resistance heater or a gas heater. The different elements of the lightweight alloy, including the lightweight metal, are introduced in this furnace, either as pure elements or as mixtures to produce the starting composition 3 in the furnace 1. The lightweight metal may be added as substantially pure lightweight metal whilst the other element or elements are preferably added in the form of a master alloy (which also contains a portion of the lightweight metal). When the lightweight alloy that is to be produced comprises a lightweight metal matrix formed by a solid solution, this solid solution is preferably already made in the furnace 3. This can be done by feeding the lightweight metal and the metal dissolved therein separately into the furnace or by feeding a starting alloy consisting of the solid solution into the furnace 3. This latter embodiment is preferred since the solid solution often has a lower liquidus temperature so that this solid solution can be dissolved at a lower temperature in the furnace 3.

[0105] The solid solution may be a solution of elements such as copper, zinc, magnesium and manganese in aluminium. The aluminium alloy that is produced preferably comprises magnesium and manganese. These elements provide for a solid solution hardening effect to strengthen the alloy whilst the other alloying elements assist in obtaining a fine grained structure and a higher thermal stability of the rapidly solidified and plastically consolidated alloy. By combining the solid solution strengthening effect with the grain boundary strengthening effect (Hall-Petch effect) a high strength aluminium alloy can be achieved that still has a low flow stress during the subsequent hot forming operations due to the fine grained structure of the alloy.

[0106] The solid solution may also be a solution of elements such as aluminium and zinc in magnesium. These elements provide for a solid solution hardening effect to strengthen the alloy whilst other alloying elements, in particular silicon, germanium, zirconium and cobalt may assist in obtaining a fine grained structure and a higher thermal stability of the rapidly solidified and plastically consolidated alloy. By combining the solid solution strengthening effect with the grain boundary strengthening effect (Hall-Petch effect) a high strength magnesium alloy can be achieved. Reference can be made to the magnesium alloy compositions and the rapidly solidified and plastically consolidated magnesium alloys disclosed in EP 0166917.

[0107] In the embodiment illustrated in FIG. 1 there is only one starting composition. The furnace 1 which contains this starting composition is connected via a piping 4 to a nozzle 5. The piping 4 comprises only one pipe 6. This pipe 6 is provided with a further heater 7, which is again an induction heater 7 provided around the pipe 6. The starting composition or lightweight metal based composition 3 is heated to the first temperature in the furnace 1 and the thus obtained lightweight metal based composition melt 31 is fed at this temperature to the inlet of the piping 4. The furnace 1 and the piping 4 are arranged one above the other so that the lightweight metal based composition melt 31 can flow by gravity from the furnace 1 to the nozzle 5. An extra pressure can be applied onto the lightweight metal based composition melt 31 by closing the furnace 1 by means of a lid 8 and by introducing gas under pressure into the furnace 1. In case of a magnesium based composition melt, this gas is preferably a protective gas such as a mixture of air or CO.sub.2 and SF.sub.6, a reducing gas such as CO or an inert gas such as argon, nitrogen or helium. The piping 4 is preferably completely filled with the lightweight metal based composition melt 31, which forms the lightweight alloy melt 30 since there is only one starting composition 3, so that the lightweight alloy melt 30 flows by pipe-flow through the piping 4. In the piping 4, the lightweight alloy melt 30 is further heated to the second temperature that is preferably higher than the liquidus temperature of the lightweight alloy 10. The piping 4 comprises a widened area that forms a heating chamber 13 increasing the residence time of the lightweight alloy melt 30 in the piping 4 and thus the time available to reach the second temperature. The second temperature is the highest temperature that is reached by the lightweight alloy melt in the piping 4. This highest temperature may be reached at the nozzle 5 or at a distance before the nozzle 5. In this latter case, the lightweight alloy melt 30 may cool down somewhat before reaching the nozzle 5. Especially for a magnesium alloy this may be advantageous since the magnesium alloy melt ejected from the nozzle 5 will then have a somewhat lower temperature. When reaching the nozzle 5, it preferably still has a temperature that is at least 75% of the difference between the solidus and the liquidus temperature of the alloy higher than the solidus temperature thereof.

[0108] The lightweight alloy melt 30, which is ejected from the nozzle 5, arrives on a rotatable chill roll 9 that may be made for example of copper, copper-beryllium or stainless steel. The roll 9 is cooled internally, for example by means of water, and is rapidly rotated to achieve the above-described cooling rates. The liquid lightweight alloy 10 is solidified in the form of a ribbon, or in the form of several ribbons in case more nozzles 5 are provided at the end of the piping 4. The ribbon thickness can be controlled by the rotational speed of the chill roll 9, the ejection pressure, the nozzle slot size and the gap between the nozzle 5 and the roll 9. When reducing the ribbon thickness, a higher cooling rate will be achieved. The nozzle 5 preferably makes an oscillating movement along the chill roll 5 so that the heat can be more effectively extracted from the roll 9. By the oscillating movement of the nozzle 5, or of the roll 9, a larger surface of the roll 9 can be used to extract the heat from the lightweight alloy melt 30 and the temperature of the surface of the roll 9 can thus be kept lower.

[0109] Instead of using a chill roll 9 for rapidly solidifying the molten alloy, it can also be solidified rapidly by other existing methods, in particular by a spray forming process wherein the molten alloy is sprayed in the form of droplets out of the nozzle. The nozzle may also eject the molten alloy in water, in particular in accordance with the known in-rotating water quenching technique.

[0110] FIG. 2 shows an installation that additionally comprises a pump 11, a flow control valve 12, a heating chamber 13 and a mixing device 14 in the piping 4 connecting the furnace 1 to the nozzle 5. The heating chamber 13 is provided with a heater 15, in particular with an induction heater. Upstream the heating chamber 13 a heating section 16 is provided in the piping 4, which comprises a heater 17, preferably an induction heater. Also downstream the heating chamber 13 a further (induction) heater 18 is provided, in particular around the mixing device 14. The different heaters 15, 17, 18 may provide a higher heating capacity and a more accurate control of the temperature of the aluminium alloy melt 30. The pump 11 and the valve 12 enable a better control of the flow rate of aluminium alloy melt 30 through the nozzle 5 and thus of the thickness of the ribbons made of the solidified aluminium alloy 10.

[0111] FIG. 3 shows a same installation as illustrated in FIG. 2 but which comprises additional components that enable to produce the lightweight alloy starting from two starting compositions 3A, 3B. The starting compositions 3A, 3B are each molten in a separate furnace 1A and 1B. Both furnaces 1A and 1B are provided with a heater 2A, 2B, more particularly with an induction heater. The installation comprises a common nozzle 5, or common nozzles, and a common rotatable chill roll 9 for rapidly solidifying the lightweight alloy melt 30, which is produced by mixing the starting composition melts 31A and 31B.

[0112] The first furnace 1A is arranged to melt the first starting composition 3A, which is a lightweight metal based composition, or the main lightweight metal based composition, containing more than 50 wt. % of the lightweight metal. This lightweight metal based composition 3A is heated to the first temperature and is preferably completely molten in the first furnace 1A to produce the first lightweight metal based composition melt 31A. The main lightweight metal based composition 3A comprises less alloying elements than the final lightweight alloy 10, in particular less alloying element that form dispersoids in the final alloy, so that it has a lower liquidus temperature than the final alloy. Although the first temperature is lower than the liquidus temperature of the final alloy 10, it may be equal to or higher than the liquidus temperature of the main lightweight metal based composition 3A so that this composition may be completely molten in the furnace 1A.

[0113] The first furnace 1A is connected by a piping 4A to the nozzle 5. The piping 4A comprises a pump 11A, a control valve 12A and a heating section 16A provided with a heater 17A and ending in the heating chamber 13.

[0114] The second furnace 1B is arranged to melt the second starting composition 3B which is for example a master alloy. The second furnace 1B is also connected by a piping 4B to the nozzle 5. The piping 4B also comprises a pump 11B, a control valve 12B and a heating section 16B provided with a heater 17B and ending in the heating chamber 13.

[0115] Both pipings 4A and 4B comprise the common heating chamber 13, which is provided with the heater 15, in particular an induction heater. Both starting compositions 3A, 3B arrive in this heating chamber 13 and can be further heated therein. The heating chamber 13 is connected by means of a tube 19 to the nozzle 5. This tube 19 comprises static mixing elements 20 so that the tube 19 forms the mixing device 14. The tube 19 is moreover provided with the heater 18, in particular an induction heater.

[0116] The second starting composition 3B may contain a master alloy containing the lightweight metal with a higher concentration of the alloying element or elements. This master alloy is normally used in a smaller amount than the first starting composition 3A, which is the main lightweight metal based composition. It may be heated to a higher temperature in the second furnace 1B, in which case the master alloy is preferably shielded from the atmosphere by means of an inert or a reducing gas or in which case a vacuum can be provided above the master alloy. Preferably, it is however also heated to a temperature that is lower than the liquidus temperature of the lightweight alloy 10. When the second starting composition comprises a larger amount of the dispersoid forming alloying element or elements, it normally has a liquidus temperature that is even higher than the liquidus temperature of the final alloy 10 so that it is only partially molten in the second furnace 1B. Once the second starting composition melt 31B flows through the piping 4B, it can further be heated by the heaters 17B, 15 and 18 so that, at the end, the mixture of first and second starting compositions, i.e. the final lightweight alloy melt 30, may be completely molten.

[0117] The second starting composition 3B may also contain the alloying element or elements not alloyed with the lightweight metal, or only with a small amount of the lightweight metal so that the lightweight metal will not be oxidised. In that case, the second starting composition 3B may be molten completely in the second furnace 1B by heating it to a sufficiently high temperature, which may even be higher than the temperature of the alloy when being ejected from the nozzle 5. When mixed with the first starting composition melt 31A, the second starting composition melt 31B will indeed be cooled down and aluminium alloy melt 30 will already have a somewhat increased temperature so that less further heating is required to reach the second temperature. For a magnesium alloy containing aluminium and silicon, the second starting composition 3B may for example consist of an aluminium-silicon master alloy, which is less prone to oxidation than for example a magnesium master alloy containing aluminium and silicon.

[0118] The installation illustrated in FIG. 4 comprises the same elements as the installation illustrated in FIG. 3 for melting and feeding the first starting composition melt 31A, which is the main lightweight metal based composition melt, to the nozzle 5. The second starting composition 3B is however not molten before being added to the first starting composition melt 31A. The installation comprises an extruding device 21 by means of which the solid second starting composition 3B can be fed into the piping 4A, more particularly in the heating chamber 13 thereof. The extruding device 21 comprises a die 22 that is arranged to receive a billet 23 made of the second starting composition 3B. By means of a ram 24 the second starting composition can be forced/injected into the heating chamber 13. Preferably, the extruding device 21 is heated so that a smaller pressure is required to extrude the second starting composition 3B into the heating chamber 13. In the heating chamber 13, the second starting composition 3B is molten and is mixed with the first starting composition melt 31A to produce the aluminium alloy melt 30. A more homogeneous melt 30 can be achieved in the mixing device 14 before the aluminium alloy melt 30 is ejected from the nozzle 5.

[0119] The second starting composition 3B may also be a granular material, for example a master alloy that is in the form of particles. This granular material can be fed for example with a screw feeder instead of with the extruding device 21 into the heating chamber 13.

[0120] When more than two starting compositions are used, more than two furnaces can be provided in the installation, or a combination of one or more furnaces with one or more extruding devices. It is thus for example possible to arrange the extruding device 21 of FIG. 4 above the heating chamber 13 of the installation illustrated in FIG. 3 so that a first starting composition 3A, which is a lightweight metal based composition, is supplied in the form of a liquid/melt via furnace 1A into the heating chamber 13, a second starting composition 3B is supplied also in the form of a liquid/melt via furnace 1B into the heating chamber 13 and a third starting composition is supplied in the form of a solid material that is extruded via the extruding device 21 in the heating chamber 13. The third starting composition may also be a granular material that is fed for example with a screw feeder into the heating chamber 13.

[0121] A unit for degassing the molten starting composition(s) may also be arranged in between the furnace 1 and the piping 4. Such a degassing unit or fluxing unit is for example disclosed in EP 1111079.

Example

[0122] A ternary alloy composition was made consisting of aluminium, 7 wt. % of magnesium and 1 wt. % of vanadium. The alloy composition was made and rapidly solidified in an installation as shown schematically in FIG. 1.

[0123] Based on the binary Al-V phase diagram the alloy would have, in the absence of magnesium, a liquidus temperature of about 820 C. The aluminium, magnesium and the vanadium were applied in the furnace 1 and were heated therein to a temperature of 650 C. This temperature is lower than the solidus temperature of pure aluminium (660 C.) but the solidus temperature of the aluminium/magnesium solid solution is considerably lower (only about 550 C.). The alloy composition was only partially molten in the furnace 1 so that the aluminium based composition melt 31 entering the piping 4 contained, based on the phase diagram, an amount of undissolved Al.sub.3V intermetallic phases.

[0124] The aluminium alloy melt 30 composed of the aluminium based composition melt 31 was further heated in the heating chamber 13 by means of the further heater 7 and was then rapidly solidified by melt spinning onto the water cooled copper chill roll 9. The water used to cool this chill roll had a temperature of between 10 to 20 C. The temperature of the surface of the chill roll was kept above the dew point of the atmosphere surrounding the chill roll in order to avoid condensation of water onto the surface of the chill roll. The produced ribbons 10 had a thickness of about 50 m and a width of about 3 mm. The residence time of the alloy in the chamber was equal to about 30 s.

[0125] FIG. 5 shows the microstructure of the rapidly solidified aluminium alloy melt that has not been extra heated by means of the heater 7. A high number of primary Al.sub.3V intermetallic phases with a maximum diameter not higher than 20 m can be seen.

[0126] FIGS. 6 and 7 show the microstructures of the rapidly solidified alloy melts that have been extra heated by means of the heater 7 to a temperature of 750 C. and 850 C. respectively. In the structure of FIG. 6 there are a lot less (only one) particles formed by Al.sub.3V intermetallic phases whilst in FIG. 7 there are no longer intermetallic particles larger than 1 m. As a matter of fact, the alloy was heated to a temperature higher than its liquidus temperature so that the aluminium alloy melt 30 did not contain any primary intermetallic phases. The alloy was moreover rapidly solidified so that no primary intermetallic phases could be formed during the crystallization phase, i.e. when cooling down from its liquidus temperature to its solidus temperature.

[0127] In this last experiment, the distance between the location where the liquid alloy composition was applied onto the roll 9 and the solidification front was determined with a camera. It took about 0.00025 s for the alloy to reach the solidification front. The temperature of the alloy composition dropped in this period of time on the roll 9 from about 850 C. to about 550 C., thus at an average cooling rate that could be estimated at about 106 C./s.