Method for producing cured lightweight aluminum alloy or magnesium alloy

Abstract

Lightweight aluminum or magnesium alloys include aluminum or magnesium and one or more alloying elements, including dispersed (colloid) forming elements that increase the liquidus temperature of the alloy. The alloy is ejected from at least one nozzle (5) in a molten state and rapidly solidifies. The lightweight alloy is produced from at least one lightweight metal-based component (3) mainly comprising aluminum or magnesium. The component is heated in a first heating step to a first temperature lower than the liquidus temperature of the alloy in order to produce a melt (31) of said lightweight metal-based component, which melt is fed through a conduit (4) to a nozzle (5). In the conduit (4), the light alloy melt (30) is further heated to have a second temperature, which is preferably higher than the liquidus temperature of the alloy. The first temperature can be kept sufficiently low to reduce the tendency of magnesium oxidation even explosion and to avoid the problems of aluminum oxidation and hydrogen formation without the need to use a vacuum or inert or reducing atmosphere, while the second temperature can be higher to dissolve all alloying elements because no air or water vapor is present in the duct (4) leading to the nozzle (5).

Description

[0001] The present invention relates to a method for producing a solidified lightweight aluminum alloy or magnesium alloy having a liquidus temperature and a solidus temperature. The alloy comprises a lightweight metal (i.e., aluminum or magnesium) and one or more alloying elements. The lightweight alloy is produced from at least one starting component, the starting component comprising at least one lightweight metal based composition, the lightweight metal based composition mainly comprising a lightweight metal (i.e., aluminum or magnesium). The lightweight alloy is ejected from at least one nozzle in a molten state, and the molten lightweight alloy leaving the nozzle is rapidly solidified, thereby producing a solidified lightweight alloy.

[0002] The advantage of making the light alloy melt rapidly solidify is that the formation of coarse grain structure can be avoided during the solidification of the molten alloy. The solidified alloy can be produced in the form of strips or in the form of small particles by melt spinning, for example. Then, strips or particles can be consolidated to produce larger solidified light alloy parts by plastic consolidation process, for example, by extrusion process. Then, these larger pieces (pieces) experience further heat and / or cold forming process. The final alloy structure preferably has a fine grained alloy structure. It can be achieved that the grain size is less than several microns or even less than one micron, which improves the strength of the alloy by so-called grain boundary strengthening (grain boundary strengthening) or Hall-Petch strengthening (Hall-Petch strengthening). When using the alloying element forming precipitate or dispersed (colloid) body (dispersoid) in aluminum matrix or magnesium matrix, rapid solidification can avoid forming coarse primary intermetallic phase (coarse primary intermetallic phases). When such precipitates or dispersions are small, they can increase the strength of the alloy by so-called precipitation hardening, which is usually obtained by additional heat treatment. Alternatively or additionally, the dispersions can increase the thermal stability of the alloy to prevent coarsening of the grain structure, for example when the alloy is subjected to hot working such as hot forging.

[0003] The intermetallic phases / dispersions (colloids) produced by the alloying elements should have a small size to achieve these effects. The desired effects on the mechanical properties and / or thermal stability of the alloy can then be achieved with the aid of small amounts of alloying elements.

[0004] Frank Palm et al., Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010 The production of a rapidly solidified aluminum alloy comprising 3.6 wt.% Mg, 1.4 wt.% Sc, 0.2 wt.% Zr and 0.3 wt.% Mn is described in . In order to be able to dissolve the alloying elements, in particular scandium and zirconium, the alloy must be heated to a temperature of 900°C. The alloy is heated in an argon atmosphere to prevent oxidation of the aluminum and the formation of hydrogen. The molten alloy is rapidly solidified by melt spinning to avoid the formation of intermetallic phases, in particular Al2O3, during the rapid solidification. 3 (SC 1-x ; Zr x ) phase. The rapidly solidified alloy has a low hardness and, therefore, generates lower stress during the subsequent hot extrusion. 3 (SC 1-x ; Zr x ) precipitates, the strength of the alloy can be increased by precipitation hardening to a hardness of up to 240 HV. The disadvantage of this method is that it is not suitable for large-scale production, not only because scandium is an expensive element, but also because the rapid solidification process must be carried out in an inert argon atmosphere. Therefore, in practice, Only suitable for high-end applications, especially aerospace applications.

[0005] EP 1 111 079 discloses an aluminium alloy supersaturated with an alloying element. This alloy is not rapidly solidified but cast in the form of ingots. The aluminium alloy is produced starting from an aluminium alloy component which is already saturated or nearly saturated with the alloying element. In order to obtain the supersaturated alloy, a rapidly solidifying master alloy containing the alloying element in solid solution is produced and added to the molten aluminium alloy component before casting the alloy. The rapidly solidifying master alloy is produced in the form of a melt-spun ribbon using standard rapid solidification techniques. In this example, the composition of the melt-spun ribbon is Al-6 wt.% Zr and an amount is added to obtain an Al-0.21% wt.% Zr alloy. By adding the master alloy during the final solidification stage, the formation of coarsening intermetallics during the casting process can be avoided. Furthermore, when zirconium is used as an alloying element, the grain size of the as-cast ingot can be reduced by a factor of about 5 compared to the grain size of an aluminum alloy saturated with zirconium alone (i.e., containing 0.12 wt% zirconium). However, a disadvantage of this prior art method is that, due to the slow solidification process, the aluminum alloy in the ingot has a relatively large grain size, which provides no or almost no grain boundary strengthening effect. Therefore, the alloy is a standard alloy with only limited strength. Moreover, in this prior art method, only relatively small amounts of alloying elements can be added, so that only relatively small amounts of dispersions (colloids) can be formed in the final alloy. These dispersions (colloids) are only intended to increase the recrystallization temperature in order to inhibit grain growth during hot working. Another disadvantage of this prior art method is that it is very difficult and expensive to produce a rapidly solidified master alloy by standard rapid solidification techniques. In fact, much more alloying elements must be dissolved in the master alloy than in the final alloy, so that the master alloy components must be heated to very high temperatures to produce the melt required for the rapid solidification process. According to the Al-Zr phase diagram, for example, an alloying temperature of at least about 1100° C. is required to completely dissolve 6 wt. % Zr.

[0006] Heating aluminum alloys to elevated temperatures in order to dissolve large amounts of alloying elements does raise some important issues. Due to the relatively high vapor pressure of molten aluminum, the temperature of the aluminum alloy melt should be kept low enough to prevent evaporation of the molten aluminum. In addition, at higher temperatures, aluminum reacts easily with water (vapor) present in the atmosphere. The metallic aluminum is thus oxidized and hydrogen is produced. At higher temperatures, these reactions become more important. In addition, at higher temperatures, the solubility of hydrogen in aluminum is also quite high. For example, at 660°C, the solubility of hydrogen in molten aluminum is about 0.69 ml / 100 g (at 20°C and 1 bar), while at 850°C, the solubility of hydrogen in aluminum has increased to about 2.18 ml / 100 g. The actual liquid and solid solubility in pure aluminum is just above and below the solidus, 0.65 ml / 100 g and 0.034 ml / 100 g, respectively. Therefore, most of the hydrogen is released when the molten aluminum solidifies, which has a detrimental effect on the strength of the solidified aluminum or aluminum alloy. When producing rapidly solidifying aluminum alloys which require higher temperatures to dissolve one or more alloying elements, special precautions should be taken to avoid these deleterious effects.

[0007] US 4 743 317 discloses a method for rapidly solidifying an aluminum-transition metal alloy, in which the oxidation of the aluminum alloy is minimized and the generation of hydrogen is therefore minimized. The alloy components are applied in a crucible, which is heated by means of an induction heater. A vacuum or inert gas atmosphere (argon) is provided in the crucible to minimize undesirable oxidation. The molten aluminum alloy is applied to a rotatable chill roll, which rotates at a circumferential speed of 2000 m / min to 2750 m / min. A non-reactive gas atmosphere is provided to the quenching zone to minimize the oxidation of the aluminum alloy in the zone. The use of an inert or reducing gas or a vacuum to minimize the oxidation of the aluminum alloy during its rapid solidification is also disclosed in US 4 917 739 and US 4 726 843.

[0008] US 4 540 546 discloses an alternative process capable of producing the alloy at a lower temperature. During the rapid solidification process, the alloy is avoided from being heated to a temperature higher than its liquidus temperature by using a melt mixing reaction technique. The process starts with two starting alloys, the liquidus temperatures of which are lower than those of the final alloy, so they can be completely melted at a lower temperature. Once the two starting alloys are mixed, they react with each other to produce a reaction product in the form of submicron particles in the aluminum alloy. Due to the presence of the reaction product, the final alloy has a higher liquidus temperature than the two starting alloys. The rapidly solidified alloy component has a temperature as close to its solidus temperature as possible, and is preferably equal to the liquidus temperature of the highest molten starting alloy. In this way, compared with the case of starting to cool at a higher liquidus temperature of the final alloy, particle formation can be limited to occur in a smaller temperature interval and a shorter cooling time. The shorter cooling time is not only because the temperature interval between the mixture temperature and the alloy solidus temperature is smaller, but also because a more effective cooling rate can be achieved in a shorter solidification temperature range. By a shorter cooling time, the formation of large precipitate particles can be prevented. The melt may cool slightly before leaving the nozzle. However, US 4 540 546 also discloses the possibility of keeping the melt temperature constant in the mixing zone and in the nozzle by arranging induction heating coils around the mixing zone and the nozzle. An essential feature of the method disclosed in US 4 540 546 is that the alloy melt prepared by the method disclosed in US 4 540 546 is prepared at a lower temperature (i.e. at a temperature as close as possible to the solidus temperature of the alloy) compared to the prior art methods, in which the final alloy is premixed and melted at the liquidus temperature and subsequently ejected from the nozzle without further heating.

[0009] However, the shortcoming of the method disclosed in US 4 540 546 is that it can only be applied to a specific alloy component that must contain at least two alloying elements, which must also react with each other. In addition, in order to make the required reaction between the two alloying elements, they should be mixed and kept in a liquid state for a sufficiently long time. Therefore, the mixing zone should be large enough, but not too large at the same time. In the mixing zone, the molten alloy component is in fact at a temperature lower than the liquidus temperature of the alloy, so crystals can be formed, and if they are left in the liquid alloy, the crystals may grow into coarsened particles. Shorter mixing times can be used, but then heat treatment or annealing is required to produce reaction products in a solvent matrix. This heat treatment or annealing process must be carefully designed according to the alloying elements and their amounts, and must be accurately carried out to achieve the required strengthening effect. All of these require additional development time and processing and installation costs. Even if it is thermally stabilized by alloying elements, heat treatment also has a negative impact on the grain structure.

[0010] EP 0 166 917 discloses a high-strength, rapidly solidified magnesium-based metal alloy. The alloy contains intermetallic phases (such as Mg 2 Si、Mg 2 Ge、Mg 2 Sb 3 and MgCo 2 ) alloying elements. These finely dispersed intermetallic phases increase the strength of the alloy and help maintain a fine grain size by pinning grain boundaries during consolidation of rapidly solidifying powders at elevated temperatures. The addition of alloying elements aluminum and zinc strengthens the matrix through solid solution strengthening and the formation of certain age hardening precipitates (such as Mg 17 Al 12 and MgZn) to improve strength. In the example, Mg 86 Al 10 Si 4 (containing 84.5wt% Mg, 10.9wt% Al and 4.5wt% Si) and Mg 89 Al 8 Si 3 (containing 87.8 wt% Mg, 8.8 wt% Al and 3.4 wt% Si) the highest yield strength was obtained. From the binary Mg-Si phase diagram, it can be observed that such a high Si content increases the liquidus temperature of the alloy. Other alloying elements described in EP 0166 917 form intermetallic phases and increase the liquidus temperature of the alloy, and these other alloying elements include germanium, zirconium and cobalt.

[0011] The disadvantage of using alloying elements such as Si, Ge, Zr and Co is that they increase the liquidus temperature of the alloy, and therefore, a higher temperature is required to produce the melt required for the rapid solidification alloy. It is known that magnesium alloys are susceptible to oxidation and even burn when heated above the ignition temperature. Therefore, the molten magnesium must be isolated from the atmosphere by using a shielding gas. As disclosed in EP 0 166 917, this shielding gas can be a mixture of helium, nitrogen, argon, carbon monoxide, and carbon dioxide with sulfur hexafluoride, etc. Not only must a shielding gas be provided on the top of the melt in the furnace for melting the magnesium alloy component, but also a shielding gas must be applied around the nozzle outlet during the rapid solidification of the melt to replace the ambient atmosphere near the nozzle. In this way, oxidation of the melt pool should be minimized. In the example disclosed in EP 0 166917, an overpressure of argon or helium is applied above the molten magnesium alloy to force the melt to enter a water-cooled copper alloy wheel through the nozzle. On this wheel, the solidifying alloy is further isolated from the atmosphere by blowing an inert gas over the melt applied to the wheel. Obviously, the higher the temperature of the magnesium alloy melt, the more the magnesium alloy tends to oxidize and even burn.

[0012] The object of the present invention is to provide a novel method for producing rapidly solidified light alloys, which enables the light metal alloy melt to be heated to a higher temperature during the production of the light alloy to dissolve more dispersed (colloidal) alloying elements without providing a vacuum or an inert atmosphere or a reducing atmosphere above the molten alloy, thereby avoiding the problems of aluminum oxidation and hydrogen formation in the case of light aluminum alloys, or increasing the risk of oxidation or combustion of the magnesium alloy in the case of light magnesium alloys. Thus, the method of the present invention enables the industrial production of solidified light alloys on a larger scale without the need for expensive equipment and high processing costs.

[0013] Therefore, the present invention relates to a method for producing a solidified light alloy based on aluminum or magnesium as light metal, the light alloy having a liquidus temperature and a solidus temperature, and a predetermined difference between the liquidus temperature and the solidus temperature, and the light alloy comprising the light metal and one or more alloying elements, the method comprising the following steps:

[0014] - providing at least one starting component for producing the light alloy, the starting component comprising at least one light metal-based component, the light metal-based component mainly comprising a light metal;

[0015] - producing said light alloy in the form of a melt from at least one starting component;

[0016] - ejecting the light alloy melt from at least one nozzle; and

[0017] - Rapidly solidifying the light alloy melt exiting from the at least one nozzle, thereby producing a solidified light alloy.

[0018] By rapidly solidifying the light alloy melt leaving at least one nozzle is meant that when the light alloy melt leaving the nozzle has a predetermined temperature, the light alloy melt is cooled to the solidus temperature of the light alloy within a predetermined period of time, the average cooling rate being in particular higher than 10000°C / sec (10 4 ℃ / sec) and preferably even higher than 100 000 ℃ / sec (10 5 ℃ / second), the average cooling rate is determined as the ratio of the difference between the predetermined temperature of the light alloy melt when leaving the nozzle and the solidus temperature of the light alloy to the predetermined time period. In practice, the average cooling rate will be less than 10 10 °C / sec.

[0019] In order to achieve the purpose of the present invention, the method according to the present invention is characterized in that:

[0020] - the light metal-based component is heated to a first temperature below the liquidus temperature in a first heating step to produce a melt of the light metal-based component having the first temperature, the light metal-based component melt being supplied to at least one nozzle through a pipe; and

[0021] The light alloy melt (30) including at least the light metal-based component melt (31) is heated in the pipe (4, 4A) before being ejected from the at least one nozzle to have a second temperature, which is higher than the first temperature and is higher than the solidus temperature by at least 75% of the difference between the liquidus / solidus temperatures.

[0022] The light alloy melt may be heated by heating the light alloy melt itself, or may be heated by heating one or more of the starting components when the light alloy melt is produced from two or more starting components.

[0023] The temperature of a light alloy or a light alloy melt refers to the average temperature of the light alloy or the light alloy melt. Therefore, the predetermined temperature is the average temperature of the light alloy when it leaves the nozzle. However, since the temperature of the melt is roughly uniform at the position of the outlet of the nozzle, the average temperature of the melt leaving the nozzle is roughly equal to its actual temperature. However, the actual temperature of the melt is not uniform at the position where the average temperature of the melt becomes equal to the solidus temperature. For example, in a melt spinning process, the temperature of the alloy in the area in contact with the cooling surface will be lower than the temperature in the area far from the cooling surface. Then, the temperature of the alloy at this position is the volume weighted average temperature of the alloy.

[0024] In the method of the present invention, a light alloy is produced by initially heating a light metal-based component to a relatively low temperature (i.e., to the first temperature), which is the temperature of the light metal-based component melt when it reaches the pipe leading to one or more nozzles. Only when the light metal-based component melt is already in the pipe leading to one or more nozzles, the light metal-based component melt is heated to a higher temperature so that the light alloy melt has a second temperature, which is higher than the solidus temperature of the alloy by at least 75% of the difference between the liquidus / solidus temperature. When the second temperature is below the liquidus temperature of the alloy, a small portion of one or more alloying elements will not dissolve in the light alloy melt, and will therefore appear in the final alloy in the form of a small amount of coarse particles. In order to avoid the presence of such coarse particles, the second temperature is preferably equal to or higher than the liquidus temperature of the alloy, or even at least 10°C higher than the liquidus alloy and more preferably at least 20°C higher than the liquidus alloy. Higher temperatures will be able to reduce the residence time required for alloying elements to dissolve in the pipe, especially when these alloying elements produce larger intermetallic phases. The residence time of the light alloy melt (i.e., the melt including all alloying elements) in the conduit leading to the nozzle is preferably at least 10 seconds, more preferably at least 15 seconds and most preferably at least 20 seconds. In addition, when leaving one or more nozzles, the temperature of the light alloy melt is preferably equal to or higher than the liquidus temperature, preferably at least 10°C higher than the liquidus temperature and more preferably at least 20°C higher than the liquidus temperature. In this way, the light alloy melt will solidify rapidly at least in the interval from its liquidus temperature to the solidus temperature so as to avoid the formation of a coarse primary metal phase. Preferably, the second temperature and the temperature of the melt leaving the nozzle are less than 100°C higher than the liquidus temperature of the light alloy.

[0025] For aluminum alloys, when heating the aluminum-based component (lightweight metal-based component), due to the initial heating of the aluminum-based component to a lower temperature (i.e., due to the lower first temperature), the oxidation of aluminum, the generation of hydrogen, and the evaporation of aluminum are no longer a problem. In addition, the solubility of hydrogen in the aluminum-based component is relatively low, so that less hydrogen can be dissolved in the aluminum-based component melt, and any excess hydrogen can be easily removed from the aluminum-based component melt if necessary. Therefore, the aluminum-based component can be melted on a larger scale in a conventional furnace. If there is any oxidation and hydrogen formation in the pipeline leading to one or more nozzles at higher temperatures, such oxidation / hydrogen formation is not a problem due to the limited residence time in the pipeline. In addition, the pipeline is usually free of air, or only includes a small amount of air, so that there is no water vapor in the pipeline that can be used to react with aluminum. Therefore, for example, when it is necessary to completely dissolve and / or homogenize the final alloy component, the residence time in the pipeline can be increased.

[0026] For magnesium alloys, the first temperature (i.e., the temperature in the furnace used to produce the melt) for the same liquidus temperature of the alloy can also be lower, so that the magnesium-based melt has a lower oxidation tendency. The method according to the invention also enables the use of a larger amount of alloying elements to increase the liquidus temperature of the magnesium alloy, because the temperature in the furnace can be kept below the liquidus temperature of the alloy. At the outlet of the nozzle, the magnesium alloy solidifies and cools rapidly, so that oxidation of the alloy at the outlet of the nozzle can be avoided with a minimum amount of protective gas.

[0027] In an embodiment of the method according to the present invention, the light alloy is an aluminum alloy, and the one or more alloying elements include one or more elements that form a dispersion (colloid) in the aluminum alloy. These elements are 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). Preferably, the one or more alloying elements include 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 is preferably at least equal to 0.50wt.% of the aluminum alloy, more preferably at least equal to 0.70wt.% of the aluminum alloy and most preferably at least equal to 1.00wt.% of the aluminum alloy. The maximum amounts of these alloying elements are preferably: 1.50 wt.% Cr, 1.50 wt.% V, 1.00 wt.% Ti, 1.00 wt.% Zr, 1.50 wt.% Mo, 1.50 wt.% Co and 1.00 wt.% Nb. Such transition elements have relatively low diffusion coefficients, so that the dispersion (colloid) formed by these elements can contribute to the thermal stability of the alloy. In addition, a considerable strengthening effect can be achieved with relatively small amounts of the above transition elements. These transition elements are particularly capable of achieving a very fine grain structure, thereby providing a very high Hall-Petch strengthening effect.

[0028] The problem with alloying elements that form a dispersion (colloid) in an alloy is that once the alloy components solidify, the alloying elements can form a coarse primary phase in the temperature interval between the liquidus temperature and the solidus temperature of the alloy. Typically, this primary phase includes intermetallic Al 3 M phase, wherein M is a transition metal or a mixture of transition metals.

[0029] By means of a rapid solidification process, the formation of such primary intermetallic phases can be avoided or limited. Preferably, the liquid alloy is thus cooled at a rate at least equal to the critical cooling rate of the alloy (ie, to avoid equilibrium Al 3M phase nucleation cooling rate) solidification. At room temperature, a supersaturated solid solution will be obtained. In particular, when the alloy is reheated, especially for rapid solidification, plastic consolidation will begin to form secondary intermetallic phases from the supersaturated solid solution. These secondary intermetallic phases will precipitate in the form of very small particles, so that the alloy is significantly strengthened. The advantage of this secondary intermetallic phase is that at higher temperatures (for example, at 400°C), the diffusion coefficients of the various transition metals in aluminum are much smaller than those of copper or magnesium and silicon in aluminum. Therefore, compared to materials such as θ'-Al 2 Cu and β'-Mg 2 Traditional precipitation hardening phases such as Si, dispersed (colloidal) formed by preferred alloying elements have higher thermal stability. However, the problem with these preferred alloying elements is that they increase the liquidus temperature of the alloy, while Cu, Mg and Si additions even reduce the liquidus temperature to the eutectic point.

[0030] Preferably, in addition to the dispersion (colloid) forming elements, the one or more alloying elements include one or more elements that form a solid solution in the aluminum alloy, the solid solution forming elements include copper, zinc, magnesium and / or manganese, and the aluminum alloy preferably includes: between 3.00wt.% and 10.00wt.%, in particular between 4.00wt.% and 10.00wt.% magnesium (Mg); and, greater than 1.00wt.% but less than 6.00wt.% manganese.

[0031] It has been found that combining dispersion (colloidal) forming elements with solid solution forming elements, in particular magnesium and manganese, can result in rapidly solidifying and plastically consolidated aluminum alloys having high strength during hot forming and high thermal stability combined with relatively low flow stresses.

[0032] In an embodiment of the method according to the invention, the light alloy is a magnesium alloy and the one or more alloying elements comprise silicon (Si), germanium (Ge), zirconium (Zr) and / or cobalt (Co).

[0033] These elements have relatively low diffusion coefficients, so that the dispersion (colloid) formed by these elements can contribute to the thermal stability of the alloy. In addition, a considerable strengthening effect can be achieved with relatively small amounts of the above transition elements. These transition elements are particularly capable of achieving a very fine grain structure, thereby providing a very high Hall-Petch strengthening effect.

[0034] The problem with alloying elements that form a dispersion (colloid) in an alloy is that once the alloy components solidify, the alloying elements can form a coarser primary phase in the temperature range between the liquidus temperature and the solidus temperature of the alloy, especially Mg. 2 Si,Mg 2Ge and MgCo 2 The formation of this primary intermetallic phase can be avoided or limited by a rapid solidification process.

[0035] In an embodiment according to the method of the invention or according to any of the preceding embodiments, at least one of the alloying elements is present in the light alloy in an amount higher than the solubility of the element in the light alloy at the solidus temperature.

[0036] This high concentration of one or more alloying elements allows the desired amount of dispersion (colloid) to be easily formed in the alloy structure.

[0037] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the liquidus temperature is at least 25° C., in particular at least 50° C. and especially at least 75° C. or at least 100° C. higher than the solidus temperature. Preferably, the liquidus temperature is less than 400° C., more preferably less than 300° C. higher than the solidus temperature.

[0038] Typically, lightweight alloys therefore include relatively high amounts of one or more alloying elements. Also, by means of a rapid solidification process, the formation of primary intermetallic phases can be avoided or limited, which are undesirable due to precipitation in the form of coarser particles, despite the relatively large temperature interval between the liquidus temperature and the solidus temperature.

[0039] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the rapidly solidifying molten light alloy component, in particular the molten aluminum alloy component, has a liquidus temperature below 950° C., preferably below 900° C., more preferably below 850° C. and most preferably below 800° C. Preferably, the liquidus temperature is above 600° C.

[0040] Therefore, aluminum alloys can be melted at relatively low temperatures, especially at temperatures where oxidation of aluminum and the formation of hydrogen can be more easily avoided or reduced without the use of vacuum or inert gas. In other words, due to the low liquidus temperature of such alloys, they can be more easily produced industrially.

[0041] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the first temperature is below 750°C, preferably below 725°C and more preferably below 700°C.

[0042] At such low temperatures, in the case of aluminum alloys, when water vapor is present, the oxidation of aluminum in the aluminum-based component melt and the formation of hydrogen are quite limited. In addition, at such low temperatures, the vapor pressure of aluminum is also quite low.

[0043] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the first temperature is at least 10°C, in particular at least 20°C and especially at least 30°C below the liquidus temperature.

[0044] In this embodiment, the oxidation of aluminum and the formation of hydrogen are much less than in an aluminum alloy that is completely melted at a temperature above the liquidus temperature of the alloy. For magnesium alloys, the oxidation tendency at the first temperature is also much less than the oxidation tendency at the higher liquidus temperature of the alloy.

[0045] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the lightweight alloy is a magnesium alloy and the first temperature is at most 30°C higher, preferably at most 20°C higher and more preferably at most 10°C higher than the solidus temperature.

[0046] At such a temperature, a melt can be produced. In particular for magnesium alloys, since magnesium alloys are very susceptible to oxidation, it is important to keep the first temperature as low as possible.

[0047] In an embodiment according to the method of the invention or according to any one of the preceding embodiments, the light metal-based component melt is pushed to the at least one nozzle through a pipe flow. In the case of using two or more starting components, the light metal-based component reaches the nozzle as a mixture with one or more other starting components. The light metal-based component melt can be supplied to the nozzle under pressure or gravity.

[0048] In the pipe flow, the liquid has no free surface, so that the molten light metal-based component has no surface in contact with the gas. In this embodiment, contact with oxygen and water vapor is thus avoided in the pipeline.

[0049] In an embodiment of the method according to the invention, the light metal-based component melt is degassed before being supplied via the conduit to the at least one nozzle, ie before being heated to the second temperature.

[0050] Therefore, when degassing is performed, the molten light metal-based component is still at a lower temperature, so that more hydrogen that may have been generated therein can be removed from the molten light metal-based component. However, due to the lower first temperature, degassing of the molten light metal-based component is generally not required.

[0051] In an embodiment according to the method of the invention or according to any one of the preceding embodiments, the pipeline comprises at least one heating chamber for further heating the light alloy melt. As described herein above, the light alloy melt can be heated by heating the light alloy melt itself in the at least one heating chamber, or by heating one or more of the starting components, in particular the light metal-based component when the light alloy melt is produced from more than two starting components.

[0052] The existence of the heating chamber increases the residence time in the pipeline, so that the light alloy melt can be heated to the second temperature more accurately. In addition, the increased residence time makes all elements in the light alloy more easily dissolved in the light alloy melt.

[0053] In an embodiment of the method according to the invention, the light metal-based component is only partially melted by heating the light metal-based component to a first temperature to produce a light metal-based component melt, and the light metal-based component is further melted by heating the light metal-based component to a higher temperature in a pipeline.

[0054] Therefore, the light metal-based component melt includes a certain amount of at least one alloy element, which cannot be completely dissolved in the light metal-based component melt at the first temperature, but can be further dissolved, preferably completely dissolved in the light metal-based component melt at the higher second temperature.

[0055] The light alloy may be produced from a starting component, the light metal-based component melt forming a light alloy melt being produced by heating the starting component to the first temperature so that the starting component is only partially melted, and the light alloy melt is further melted in the pipe by heating to the second temperature in the pipe.

[0056] In this embodiment, all alloy components can be composed first. All alloy components are only partially melted by heating all alloy components to the first temperature (lower temperature), and all alloy components are further melted by heating all alloy components to the second temperature (higher temperature) in the pipeline. In the case where one of the alloying element or multiple alloying elements forms an intermetallic phase with the light metal, the intermetallic phase will be formed at the first temperature. Coarsened intermetallic particles may be produced, but this is not a problem. When the light alloy melt is further heated to the second temperature in the pipeline, the intermetallic particles will indeed dissolve again in the light alloy melt. The advantage of this embodiment is that only one furnace is needed to prepare and partially melt the light alloy components.

[0057] In an alternative embodiment of the method according to the invention, the light alloy is produced from at least two starting components, comprising at least one light metal-based component and at least one other component, which is added to the light metal-based component melt in the pipeline to produce the light alloy melt.

[0058] In this embodiment, the light metal-based component can be completely melted at the first temperature. The other components can be added to the light metal-based component melt in solid form or liquid form. More than one other component can also be added to the light metal-based component in the pipeline. These other components can each be added in solid form or liquid form.

[0059] When other components are added in solid form, the other components must be dissolved in the light metal-based component in the pipe. Other components can also be melted first. This can be done at a temperature higher than the first temperature or even higher than the liquidus temperature of the final alloy. Other components are preferably substantially non-oxidized when they are in contact with air at a higher temperature, or other components are melted under vacuum or inert gas or reducing gas to prevent oxidation of other components. However, in a preferred embodiment, the other components are a main alloy including one or more alloying elements in a light metal matrix, particularly a main alloy in the form of an intermetallic phase. The main alloy is only partially melted before being added to the light metal-based component melt, so that the intermetallic phase contained in the main alloy reaches the light metal-based component melt, and the intermetallic phase is dissolved in the light metal-based component melt by additionally heating the light alloy component thus obtained to a higher second temperature.

[0060] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the conduit comprises mixing means for mixing the light alloy melt.

[0061] The mixing device enables a more homogeneous mixture to be obtained in the pipeline, in particular when the light alloy is produced from more than two starting components or when the light metal-based component comprises particles that still have to be dissolved in the pipeline, such as intermetallic phases.

[0062] In an embodiment according to the method according to the invention or according to any one of the preceding embodiments, the first heating step is carried out in a furnace which is liquid-connected to the at least one nozzle via the conduit, the light metal-based component melt being fed from the furnace into the conduit at the first temperature.

[0063] Due to the viscous nature of light metal-based components in the furnace, the temperature of such light metal-based components in the furnace may not be uniform. Therefore, the first temperature is defined as the temperature of the light metal-based components when they arrive in the pipe connecting the furnace to the one or more nozzles.

[0064] In the method according to the invention, the light alloy melt leaving the at least one nozzle is rapidly solidified to produce a solidified light alloy. The light alloy melt is rapidly solidified in the form of rapidly solidified material pieces. These rapidly solidified material pieces are then plastically consolidated to produce a plastically consolidated light alloy.

[0065] By rapidly solidifying the molten alloy components, the formation of primary phases, which are usually brittle phases, is avoided. In addition, the formation of dendrites is also avoided. All of these phases / structures have a negative impact on the strength and / or thermal stability of the alloy and the forces required during the hot forging of the alloy. The rapid solidification of the alloy produces more uniform phases and structures, which have high internal energy. During the subsequent plastic consolidation step, the rapidly solidified alloy part not only consolidates, but also produces a fine-grained alloy structure and forms a dispersion (colloid) to stabilize the fine-grained alloy structure, particularly at an energy level lower than the initial energy level of the rapidly solidified material.

[0066] After plastic consolidation, the dispersion (colloid) formed by the alloying elements still stabilizes the alloy at a relatively high energy level. As a result, the alloy has increased strength. In addition, due to the fine grain structure of the alloy, the grain boundary sliding process is more easily and more significantly activated, thus reducing the hot forming forces.

[0067] In an embodiment according to the method according to the invention or according to any of the preceding embodiments, the solidifying lightweight alloy is plastically consolidated by plastic deformation under pressure, which is carried out by extrusion with a cross section reduction λ of at least 3, preferably at least 6, more preferably at least 8 and most preferably at least 10.

[0068] For the consolidation process, not only compressive stresses but also shear stresses are applied to the rapidly solidifying material. The greater the cross-sectional reduction, the better the consolidation of the material. For lower cross-sectional reductions, good consolidation may require one or more additional plastic working steps.

[0069] In an embodiment of the method according to the invention or according to the preceding embodiment, the rapidly solidifying material piece is plastically consolidated by plastic deformation under pressure at a temperature of at least 300°C.

[0070] During the plastic consolidation step, the rapidly solidified material pieces are subjected to both compressive stresses and shear stresses. The individual rapidly solidified pieces are in very close contact, thereby forming new interatomic bonds. Plastic deformation is required to produce new surfaces without oxides, so that they can bond to each other. Due to the shear stress generated by plastic deformation, the surface area to volume ratio of the particles increases, thereby exposing new surfaces without oxides. At the same time, smaller grains are produced. During plastic consolidation, the rapidly solidified material preferably has a temperature above 300°C. In this way, less force needs to be applied to the material. In addition, since the alloy undergoes dynamic recrystallization due to such a higher temperature during plastic consolidation, the formation of dislocations is avoided or at least greatly reduced, and the thermal stability of the alloy is improved.

[0071] In an embodiment according to the method according to the invention or according to any of the preceding embodiments, the temperature at which the rapidly solidifying material piece is consolidated is below the solidus temperature of the alloy, preferably at least 10°C below the solidus temperature but above 350°C, preferably above 375°C and more preferably above 400°C, the temperature being most preferably comprised between 400°C and 550°C.

[0072] Such high plastic consolidation temperatures promote consolidation. The flow stress of the alloy is lower at higher temperatures, which facilitates the deformation of the rapidly solidifying material piece, which is necessary to achieve intimate contact. In addition, higher temperatures increase local diffusion processes, improving the effectiveness of interparticle bonding.

[0073] In an embodiment of the method according to the present invention or according to the aforementioned embodiment, the rapidly solidified material piece is consolidated by plastic deformation to reduce the average grain size of the consolidated light alloy measured according to standard ASTM E2627-13 (2019) to a value of less than 2000nm, preferably less than 1000nm, more preferably less than 800nm ​​and most preferably less than 600nm.

[0074] The advantage of such fine-grained alloys is that they have increased strength due to the small grain size (ie, Hall-Page effect). In addition, smaller grain size has been found to reduce flow stresses during hot forming of the alloy by better activating the grain boundary sliding process.

[0075] In an embodiment of the method according to the invention or according to any of the preceding embodiments, the consolidated light alloy is hot-forged, in particular die-forged. Alternatively, the shaped product can already be obtained directly by a plastic consolidation process, in particular by an extrusion process.

[0076] By extrusion or hot forging of the alloy, the shape of the part to be produced can be obtained or at least approximated, so that no or less machining is required to obtain the final shape. The production process of the part therefore requires less material, consumes less time and energy, and generates less material in the form of scrap that needs to be recycled, especially considering the fine grain structure that allows low-energy hot forming processing.

[0077] Other characteristics and advantages of the method according to the invention will become apparent from the following description of some embodiments of the invention. The reference numerals used in this specification refer to the accompanying drawings, in which:

[0078] Figure 1 A schematic diagram showing a first embodiment of an apparatus for producing a light alloy melt and for rapidly solidifying the melt by a melt spinning device;

[0079] Figure 2 A schematic diagram of a second embodiment of an apparatus for producing a light alloy melt and for rapidly solidifying the melt is shown, the apparatus having a heating chamber in a conduit between a melting furnace and a melt spinning device;

[0080] Figure 3 A schematic diagram of a third embodiment of a device for producing a light alloy melt and for rapidly solidifying the melt is shown, the device having an additional melting furnace for melting other starting components fed to the chamber in the liquid state;

[0081] Figure 4 A schematic diagram of a fourth embodiment of a device for producing a light alloy melt and for rapidly solidifying the melt is shown, the device having a feed device for feeding further starting components in the solid state into a heating chamber;

[0082] Figure 5 The RS example in which the alloy components are rapidly solidified at a temperature of 650°C has a coarse primary Al 3 SEM images of the microstructure of the Al-7Mg-1V alloy with V intermetallic phase; and

[0083] Figure 6 and Figure 7 and Figure 5 Similar but showing the microstructure of Al-7Mg-1V alloys rapidly solidified at 750°C and 850°C and showing no or little coarse primary Al 3 V intermetallic phase.

[0084] The present invention generally relates to a method for producing a solidified light alloy, which is an aluminum alloy or a magnesium alloy. Such a light alloy has a liquidus and a solidus temperature. The liquidus temperature is the lowest temperature at which the alloy is in equilibrium and completely liquid, while the solidus temperature is the highest temperature at which the alloy is in equilibrium and completely solid. Both temperatures can be seen on the equilibrium phase diagram of the alloy.

[0085] The alloy is preferably a wrought alloy (i.e., an alloy suitable for wrought). The alloy may be a wrought aluminum alloy or a wrought magnesium alloy. In practice, there are already a large number of wrought aluminum alloys. According to the international alloy naming system, these alloys are divided into eight different series. The 1000 series is essentially pure aluminum, the 2000 series is a copper alloy, the 3000 series is a manganese alloy, the 4000 series is a silicon alloy, the 5000 series is a magnesium alloy, the 6000 series is a magnesium and silicon alloy, the 7000 series is a zinc alloy, and the 8000 series is an alloy of other elements. A list of 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 revised in January 2015 by the Aluminum Association. This alloy and inactive alloys are both disclosed in this publication.

[0086] Most industrial alloys contain alloying elements in amounts sufficient to allow them to dissolve completely at relatively low temperatures, especially at temperatures where the aluminum metal does not have to be isolated from the atmosphere to avoid excessive oxidation and the formation of hydrogen. Therefore, these conventional alloys can be produced and solidified on a large scale in standard equipment at relatively low cost. However, some aluminum alloys and magnesium alloys contain higher amounts of alloying elements, which require higher melting temperatures.

[0087] In order to achieve higher strength and higher thermal stability, for example, alloying elements that form precipitates or dispersions (colloids) can indeed be added in some applications. These precipitates are generally used to achieve precipitation hardening of the alloy. Aerospace aluminum alloys may include, for example, scandium, which is an expensive element. Typically, it is contained in the alloy in an amount between 0.1wt.% and 0.5wt.%, which is lower than the solubility of scandium at the solidus temperature of the alloy. Therefore, it is not necessary to heat the alloy to a high temperature in order to dissolve such an amount of scandium in the aluminum alloy. The supersaturated alloy needs to be subsequently heat treated to achieve the desired precipitation hardening. Nanoscale precipitates (such as Al2O3) that impart strength to the alloy are 3An advantage of Sc) is that they are very resistant to coarsening at relatively high temperatures (i.e., up to about 350°C), whereas typical commercial 2xxx and 6xxx alloys quickly lose strength at temperatures above 250°C due to rapid coarsening of strengthening precipitates.

[0088] The method of the present invention enables the use of alloying elements in amounts above their solubility at the solidus temperature of the alloy. Thus, alloying elements with lower solubility at the solidus temperature of the alloy or greater amounts of alloying elements, particularly amounts greater than the solubility of the element at the solidus temperature of the alloy, can be used without having to isolate the molten alloy from the atmosphere for aluminum alloys or without increasing oxidation of the alloy for magnesium alloys.

[0089] The solidified light alloy produced by the method according to the present invention comprises a light metal (i.e., aluminum or magnesium) and one or more alloying elements. In the first step, at least one starting component for producing a light alloy is provided. The starting component comprises at least one light metal-based component, which mainly comprises a light metal (i.e., aluminum for aluminum alloys or magnesium for magnesium alloys). The expression "mainly comprising light metals" means that the light metal-based component comprises at least 50wt.% of light metal elements. In particular, the light metal-based component comprises at least 65wt.% of light metals, or more particularly comprises at least 80wt.% of light metals. Due to the high aluminum content, the aluminum-based component oxidizes when it is in contact with air containing water vapor at a relatively high temperature, in particular at a temperature of 800°C. The magnesium-based component is even more susceptible to oxidation, and the oxidation rate is very fast when magnesium is in a molten state (i.e., when its temperature is higher than the solidus temperature of the magnesium alloy).

[0090] Light alloys can be produced from one such light metal-based component or from two or more such light metal-based components. Light metal-based components can be used in combination with other starting components (i.e., with starting components that do not contain or contain less than 50 wt.% of light metal). Therefore, these other starting components include one or more alloying elements.

[0091] The light alloy is produced from one or more of these starting components in the form of a melt. The melt is heated to a temperature that is higher than the solidus temperature of the alloy by at least 75% of the difference between the solidus temperature and the liquidus temperature of the alloy. Preferably, it is heated to a temperature higher than the liquidus temperature of the alloy so that all alloying elements can be dissolved. The light alloy melt is then ejected from at least one nozzle in a molten state. The light alloy melt flowing from one or more nozzles is rapidly solidified to produce a solidified light alloy.

[0092] The expression "rapid solidification" means that during solidification, the light alloy melt is heated at a speed of more than 10 000°C / s (10 4℃ / sec), preferably higher than 100 000 ℃ / sec (10 5 The average cooling rate is preferably higher than 10 000°C / second (10 000°C / second) during the time interval between the moment when the alloy is at its liquidus temperature and the moment when the temperature of the alloy drops to its solidus temperature. 4 ℃ / sec) and more preferably higher than 100000℃ / sec (10 5 °C / sec).

[0093] When the light alloy melt leaves one or more nozzles, rapid solidification begins. At the outlet of the nozzle, the light alloy melt has a substantially uniform predetermined temperature. If not uniform, the predetermined temperature is the volume-weighted average temperature of the light alloy when it leaves the nozzle. The average cooling rate must be calculated over the interval in which the volume-weighted average temperature of the liquid weight alloy melt drops from the predetermined temperature at the nozzle outlet to the solidus temperature of the light alloy. The difference between these two temperatures divided by the time required to cool the light alloy melt from the predetermined temperature to the solidus temperature is the average cooling rate, which must be higher than 10,000°C / second (10 4 ℃ / second) to achieve rapid solidification process.

[0094] The average cooling rate can be measured when suitable measuring equipment is available, but it can also be calculated from different parameters. The required cooling rate can also be determined experimentally by starting with a cooling rate at which primary intermetallic phases are formed and gradually increasing the cooling rate until a cooling rate is reached at which no primary intermetallic phases are formed during the rapid solidification step.

[0095] For the melt spinning rapid solidification process, the average cooling rate can be calculated according to the calculation method disclosed in B. Karpe et al. in Journal of Achievements in Materials and Manufacturing Engineering, Vol. 51, No. 2, April 2012. The content of this article is incorporated herein by reference. In many figures of this article, it can be seen that the starting temperature drops rapidly from about 700°C to 660°C (i.e., the solidus temperature of pure aluminum), which is used for different strip thicknesses and different distances from the cooling wheel surface. When this drop in temperature is divided by the solidification time and these values ​​are averaged to different distances from the cooling wheel surface, the average cooling rate can be calculated.

[0096] For rapid solidification processes by gas (or liquid) atomization, the average cooling rate can be calculated according to the calculations disclosed in "Rapidly Solidified Gas-Atomized Aluminum Alloys Compared with Conventionally Cast Counterparts: Implications for Cold Spray Materials Consolidation" by Bryer C. Sousa et al., Coatings 2020, 10, 1035. The contents of this article are incorporated herein by reference. The article gives a formula that can calculate the cooling rate. In the article Figure 3 As can be seen in , the cooling rate is particularly dependent on the particle size of the atomized droplets. Other parameters include the specific heat of the metal droplets and the thermal conductivity of the gas used during gas atomization.

[0097] During rapid solidification, the solidified light alloy is either produced in the form of small particles (e.g., by atomizing a molten light alloy) or in the form of large pieces that can be cut or ground into smaller particles. The particles can be spherical or elongated, and can even have a fibrous shape. These particles can then be plastically consolidated by plastic deformation under pressure, for example, by extruding them. When solidifying the particles, they are preferably heated, in particular heated to a temperature above 350° C. and preferably heated to a temperature above 400° C. The light alloy is preferably solidified at a temperature below 550° C., preferably below 525° C. The light alloy is preferably plastically consolidated by extrusion, in particular by an extruder.

[0098] In the method of the present invention, at least the light metal-based component or at least one of the light metal-based components is first heated to a first temperature below the liquidus temperature of the alloy to produce a melt. The light metal-based component is completely melted at the first temperature, or only partially melted at the first temperature, so that the light metal-based component melt may still include some solid particles generally formed by intermetallic phases. The light metal-based component melt is then supplied to the nozzle through a pipe. Before reaching the nozzle, it is introduced into a pipe leading to the nozzle to reach a higher second temperature.

[0099] When the light metal-based component includes all elements of the light alloy, that is, when the light alloy is produced with only this light metal-based component as the starting component, the light metal-based component is only partially melted at the first temperature, so that the light metal-based component melt includes a solid phase of the alloy element, in particular an intermetallic phase produced by the alloy element. When the light alloy melt formed by the light metal-based component melt is heated to a second temperature in a pipe leading to the nozzle, these solid phases are further dissolved, and the second temperature is at least a temperature higher than the solidus temperature of the alloy by 75% of the difference between the solidus temperature and the liquidus temperature of the alloy. In order to be able to dissolve all solid phases in the aluminum alloy melt, the second temperature is a temperature equal to or higher than the liquidus temperature of the alloy, and is preferably at least 10°C higher than the liquidus temperature and more preferably at least 20°C higher than the liquidus temperature. The higher the second temperature, the shorter the time for the solid phase to dissolve in the aluminum alloy melt.

[0100] The first temperature is below the liquidus temperature of the alloy so that the melt is not easily oxidized. Preferably, the first temperature is at least 10°C lower, particularly at least 20°C lower and more particularly at least 30°C lower than the liquidus temperature of the light alloy. For magnesium alloys, the first temperature is preferably 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.

[0101] When the light metal-based component does not contain all the elements of the light alloy, that is, when the light alloy is produced by the light metal-based component and at least one other starting component (which can also be a light metal-based component containing more than 50wt.%), the light metal-based component can be only partially melted as described above, or can be completely melted at a first temperature so that the light metal-based component melt no longer contains a solid phase. Then, the other starting components are added to the light metal-based component melt in the pipeline leading to the nozzle, so that a light alloy melt is produced by the light metal-based component and the other starting components. Similarly, in this embodiment, the light metal-based component melt and the light alloy melt formed by one or more other starting components are heated to a second temperature in the pipeline leading to the nozzle, and the second temperature is a temperature that is higher than the solidus temperature of the alloy by at least 75% of the difference between the solidus temperature and the liquidus temperature of the alloy. 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 the liquidus temperature. The light alloy melt itself may be heated to the second temperature in the conduit leading to the nozzle, and / or one or more starting components may be heated before mixing with one or more other starting components to produce the light alloy melt in the conduit.

[0102] The other starting components can be a so-called main alloy, which contains one or more alloying elements in a light metal matrix. The main alloy can contain more than 50wt.% of light metal, so that it is also a light metal-based component. However, its usage is less than the main light metal-based compound. For example, it can be added to the light-based component melt in solid form, so that it does not have to be heated to a higher temperature. However, it can also be melted to produce a melt. Preferably, it is also heated to a first temperature below the liquidus temperature of the alloy in the same way as the main light metal-based component. At this temperature, the melt produced by the main alloy still contains a solid phase, in particular an intermetallic phase. Instead of being composed of the main alloy, one or more of the other starting components can also be composed of one or more alloying elements.

[0103] Figure 1 A schematic diagram of an apparatus for producing a solidified light alloy when produced from a single starting component 3, more specifically from a single light metal-based component having the same composition as the light alloy to be produced, is shown. The apparatus comprises a furnace 1 provided with a heater 2. Figure 1As shown, the heater 2 can be an induction heater 2. However, other heaters are also possible, such as resistance heaters or gas heaters. The different elements of the light alloy (including light metals) are introduced into the furnace as pure elements or mixtures to produce the starting component 3 in the furnace 1. The light metal can be added as a substantially pure light metal, and the other one or more elements are preferably added in the form of a main alloy (which also contains part of the light metal). When the light alloy to be produced includes a light metal matrix formed by a solid solution, the solid solution is preferably already made in the furnace 3. This can be achieved by feeding the light metal and the metal dissolved therein into the furnace separately or by feeding the starting alloy composed of the solid solution into the furnace 3. The latter embodiment is preferred because the solid solution generally has a lower liquidus temperature, so that the solid solution can be dissolved at a lower temperature in the furnace 3.

[0104] The solid solution may be a solution of elements such as copper, zinc, magnesium and manganese in aluminum. The aluminum alloy produced preferably contains magnesium and manganese. These elements provide a solid solution strengthening effect to strengthen the alloy, while other alloying elements contribute to a fine grain structure and higher thermal stability of the alloy for rapid solidification and plastic consolidation. By combining the solid solution strengthening effect with the grain boundary strengthening effect (Hall-Page effect), a high-strength aluminum alloy can be obtained that, due to its fine grain structure, still has lower flow stresses during subsequent hot forming operations.

[0105] The solid solution may also be a solution of elements such as aluminum and zinc in magnesium. These elements provide a solid solution strengthening effect to strengthen the alloy, while other alloying elements (particularly silicon, germanium, zirconium and cobalt) may contribute to a fine grain structure and higher thermal stability of the alloy for rapid solidification and plastic consolidation. By combining the solid solution strengthening effect with the grain boundary strengthening effect (Hall-Petch effect), a high-strength magnesium alloy may be obtained. Reference may be made to the magnesium alloy compositions and the magnesium alloys for rapid solidification and plastic consolidation disclosed in EP 0 166 917.

[0106] exist Figure 1In the embodiment shown, there is only one starting component. The furnace 1 containing the starting component is connected to the nozzle 5 via a pipe 4. The pipe 4 comprises only one pipe 6. The pipe 6 is provided with a further heater 7, which is also an induction heater 7 arranged around the pipe 6. The starting component or light metal-based component 3 is heated to a first temperature in the furnace 1, and the light metal-based component melt 31 thus obtained is fed to the inlet of the pipe 4 at this temperature. The furnace 1 and the pipe 4 are arranged one above the other so that the light metal-based component melt 31 can flow from the furnace 1 to the nozzle 5 by gravity. Additional pressure can be applied to the light metal-based component melt 31 by closing the furnace 1 with a cover 8 and introducing a pressurized gas into the furnace 1. In the case of a magnesium-based component melt, the gas is preferably a protective gas (such as air or CO 2 and SF 6 , mixture), reducing gas (such as, CO) or inert gas such as argon, nitrogen and helium. The pipe 4 is preferably completely filled with the light metal-based component melt 31, and since there is only one starting component 3, a light alloy melt 30 is formed, so that the light alloy melt 30 passes through the pipe 4 in a pipe flow. In the pipe 4, the light alloy melt 30 is further heated to a second temperature, which is preferably higher than the liquidus temperature of the light alloy 10. The pipe 4 includes a widened area forming a heating chamber 13, which increases the residence time of the light alloy melt 30 in the pipe 4, thereby increasing the time to reach the second temperature. The second temperature is the maximum temperature reached by the light alloy melt in the pipe 4. The maximum temperature can be reached at the nozzle 5 or at a certain distance before the nozzle 5. In the latter case, the light alloy melt 30 can be slightly cooled before reaching the nozzle 5. This may be advantageous in particular for magnesium alloys, because the magnesium alloy melt ejected from the nozzle 5 will then have a slightly lower temperature. When reaching the nozzle 5, its temperature is preferably still higher than the solidus temperature of the alloy by at least 75% of the difference between the solidus temperature and the liquidus temperature.

[0107] The light alloy melt 30 ejected from the nozzle 5 arrives on the rotatable cooling roller 9, which can be made of copper, copper beryllium or stainless steel, for example. The roller 9 is cooled internally (for example by water) and is rotated rapidly to achieve the above-mentioned cooling rate. The liquid light alloy 10 solidifies in the form of a strip, or in the form of multiple strips when more nozzles 5 are arranged at the end of the pipeline 4. The thickness of the strip can be controlled by the rotation speed of the cooling roller 9, the ejection pressure, the nozzle slot size and the gap between the nozzle 5 and the roller 9. When the thickness of the strip is reduced, a higher cooling rate will be obtained. The nozzle 5 preferably performs an oscillating motion along the cooling roller 5 so that heat can be extracted from the roller 9 more effectively. Through the oscillating motion of the nozzle 5 or the roller 9, the larger surface of the roller 9 can be used to extract heat from the light alloy melt 30, so that the surface temperature of the roller 9 can be kept low.

[0108] Instead of using cooling rollers 9 to rapidly solidify the molten alloy, it can also be rapidly solidified by other existing methods, in particular by an injection molding process in which the molten alloy is ejected from a nozzle in the form of droplets. The nozzle can also eject the molten alloy in water, in particular according to the known in-rotating waterquenching technique.

[0109] Figure 2 An arrangement is shown which additionally comprises a pump 11, a flow control valve 12, a heating chamber 13 and a mixing device 14 in the pipe 4 connecting the furnace 1 to the nozzle 5. The heating chamber 13 is provided with a heater 15, in particular an induction heater. Upstream of the heating chamber 13, a heating section 16 is provided in the pipe 4, which comprises a heater 17, preferably an induction heater. Furthermore, a further (induction) heater 18 is provided downstream of the heating chamber 13, in particular around the mixing device 14. The different heaters 15, 17, 18 can provide a higher heating capacity and a more accurate control of the temperature of the aluminum alloy melt 30. The pump 11 and the valve 12 enable a better control of the flow rate of the aluminum alloy melt 30 through the nozzle 5, thereby enabling a better control of the thickness of the strip made of the solidified aluminum alloy 10.

[0110] Figure 3 Shown with Figure 2 The same device as shown in FIG. 1 , but the device includes an additional component capable of producing a light alloy from two starting components 3A, 3B. The starting components 3A, 3B are each melted in a separate furnace 1A and 1B. Both furnaces 1A and 1B are provided with heaters 2A, 2B, more specifically, induction heaters. The device includes one or more common nozzles 5 and a common rotatable cooling roller 9 for rapidly solidifying a light alloy melt 30 produced by mixing the starting component melts 31A and 31B.

[0111] The first melting furnace 1A is arranged to melt a first starting component 3A, which is a light metal-based component or a main light metal-based component containing more than 50 wt.% of light metal. The light metal-based component 3A is heated to a first temperature and preferably completely melted in the first melting furnace 1A to produce a first light metal-based component melt 31A. The main light metal-based component 3A contains less alloying elements than the final light alloy 10, in particular less alloying elements that form a dispersion (colloid) 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 can also be equal to or higher than the liquidus temperature of the main light metal-based component 3A, so that the component can be completely melted in the melting furnace 1A.

[0112] The first melting furnace 1A is connected to the nozzle 5 through a pipe 4A. The pipe 4A includes a pump 11A, a control valve 12A, and a heating section 16A provided with a heater 17A and ending in a heating chamber 13.

[0113] The second melting furnace 1B is arranged to melt the second starting component 3B, which is for example the main alloy. The second melting furnace 1B is also connected to the nozzle 5 via a pipe 4B. The pipe 4B also comprises a pump 11B, a control valve 12B and a heating section 16B provided with a heater 17B and ending in a heating chamber 13.

[0114] Both pipes 4A and 4B comprise a common heating chamber 13, which is provided with a heater 15, in particular an induction heater. Both starting components 3A, 3B reach this heating chamber 13 and can be further heated therein. The heating chamber 13 is connected to the nozzle 5 via a pipe 19. This pipe 19 comprises a static mixing element 20, so that the pipe 19 forms a mixing device 14. In addition, the pipe 19 is also provided with a heater 18, in particular an induction heater.

[0115] The second starting component 3B may include a main alloy containing a light metal with a higher concentration of one or more alloying elements. The amount of this main alloy is usually less than the amount of the first starting component 3A as the main light metal-based component. It can be heated to a higher temperature in the second melting furnace 1B, in which case the main alloy is preferably isolated from the atmosphere by an inert gas or a reducing gas, or in this case, a vacuum can be provided above the main alloy. However, it is preferably also heated to a temperature below the liquidus temperature of the light alloy 10. When the second starting component contains a large amount of one or more dispersed (colloid) body-forming alloying elements, it usually has a liquidus temperature even higher than the liquidus temperature of the final alloy 10, so that it is only partially melted in the second melting furnace 1B. Once the second starting component melt 31B flows through the pipeline 4B, it can be further heated by the heater 17B, the heater 15 and the heater 18, so that the mixture of the first starting component and the second starting component (that is, the final light alloy melt 30) can be completely melted at the end.

[0116] The second starting component 3B can also comprise one or more alloying elements that are not alloyed with light metal, or only contain a small amount of light metal alloy, so that light metal can not be oxidized. In this case, the second starting component 3B can be completely melted in the second melting furnace 1B by being heated to a sufficiently high temperature, and this temperature can even be higher than the temperature of the alloy when ejected from the nozzle 5. When mixing with the first starting component melt 31A, the second starting component melt 31B is actually cooled, and the aluminum alloy melt 30 will have a slightly rising temperature, so that the heating that needs to reach the second temperature is less. For the magnesium alloy comprising aluminum and silicon, the second starting component 3B can for example be composed of an aluminum-silicon main alloy that is more difficult to oxidize than the magnesium main alloy that for example comprises aluminum and silicon.

[0117] Figure 4 The device shown includes Figure 3The same elements of the apparatus shown are used to melt the first starting component melt 31A as the main light metal-based component melt and feed it to the nozzle 5. However, the second starting component 3B is not melted before being added to the first starting component melt 31A. The apparatus includes an extrusion device 21, by which the solid second starting component 3B can be fed into the pipe 4A, more specifically, into the heating chamber 13 of the pipe 4A. The extrusion device 21 includes a die 22, which is arranged to receive a billet 23 made of the second starting component 3B. The second starting component can be pushed / injected into the heating chamber 13 by a plunger 24. Preferably, the extrusion device 21 is heated so that the pressure required to extrude the second starting component 3B into the heating chamber 13 is small. In the heating chamber 13, the second starting component 3B is melted and mixed with the first starting component melt 31A to produce the aluminum alloy melt 30. Before the aluminum alloy melt 30 is ejected from the nozzle 5, a more uniform melt 30 can be achieved in the mixing device 14.

[0118] The second starting component 3B may also be a granular material, for example, the second starting component may be the main alloy in granular form. The granular material may be fed into the heating chamber 13, for example, using a screw feeder instead of an extrusion device 21.

[0119] When more than two starting components are used, more than two furnaces, or a combination of one or more furnaces and one or more extrusion devices, may be provided in the apparatus. Thus, for example, Figure 4 The extrusion device 21 is arranged at Figure 3 The heating chamber 13 of the device shown is provided so that the first starting component 3A as a light metal-based component is supplied to the heating chamber 13 via the furnace 1A in the form of liquid / melt, the second starting component 3B is also supplied to the heating chamber 13 via the furnace 1B in the form of liquid / melt, and the third starting component is supplied in the form of a solid material, which is extruded by the extrusion device 21 in the heating chamber 13. The third starting component can also be a granular material, which is fed into the heating chamber 13, for example, by a screw feeder.

[0120] A unit for degassing the molten starting components may also be provided between the furnace 1 and the line 4. Such a degassing unit or fluxing unit is disclosed in EP 1 111 079, for example. Example

[0121] The ternary alloy composition is composed of aluminum, 7 wt.% magnesium and 1 wt.% vanadium. The alloy components are as follows Figure 1 The device shown in the schematic diagram is made and quickly solidified.

[0122] According to the binary Al-V phase diagram, the liquidus temperature of the alloy in the absence of magnesium is about 820°C. Aluminum, magnesium and vanadium are applied to the furnace 1 and heated to 650°C in the furnace. This temperature is lower than the solidus temperature of pure aluminum (660°C), but the solidus temperature of the aluminum / magnesium solid solution is much lower (only about 550°C). The alloy components are only partially melted in the furnace 1, so according to the phase diagram, the aluminum-based component melt 31 entering the pipe 4 contains a certain amount of undissolved Al 3 V intermetallic phase.

[0123] The aluminum alloy melt 30 composed of the aluminum-based component melt 31 is further heated in the heating chamber 13 by an additional heater 7 and then rapidly solidified by melt spinning on a water-cooled copper cooling roller 9. The temperature of the water used to cool the cooling roller is between 10° C. and 20° C. The temperature of the surface of the cooling roller is maintained above the dew point of the atmosphere surrounding the cooling roller to avoid condensation of water onto the surface of the cooling roller. The produced strip 10 has a thickness of about 50 μm and a width of about 3 mm. The residence time of the alloy in the chamber is equal to about 30 s.

[0124] Figure 5 The microstructure of the rapidly solidified aluminum alloy melt without additional heating by the heater 7 is shown. A large amount of primary Al 3 V intermetallic phase, the maximum diameter of which does not exceed 20μm.

[0125] Figure 6 and Figure 7 The microstructures of the rapidly solidified alloy melts additionally heated to 750°C and 850°C by heater 7 are shown. Figure 6 In the structure of Al 3 The V intermetallic phase forms far fewer particles (only one), while Figure 7 In the embodiment of the present invention, there are no more intermetallic particles larger than 1 μm. In fact, the alloy is heated to a temperature above its liquidus temperature, so that the aluminum alloy melt 30 does not contain any primary intermetallic phase. In addition, the alloy solidifies rapidly, so that no primary intermetallic phase is formed during the crystallization stage (i.e., when cooling from its liquidus temperature to its solidus temperature).

[0126] In this final experiment, the distance between the point where the liquid alloy component was applied to roller 9 and the solidification front was determined by a camera. It took about 0.00025 seconds for the alloy to reach the solidification front. During this time, the temperature of the alloy component on roller 9 dropped from about 850°C to about 550°C, so the average cooling rate was estimated to be about 10 6 ℃ / s.

Claims

1. A method for producing a solidified light alloy (10) based on aluminum or magnesium as a light metal, the light alloy having a liquidus temperature and a solidus temperature, and a predetermined difference between the liquidus temperature and the solidus temperature, and comprising the light metal and one or more alloying elements, the method comprising the following steps: - providing at least one starting component (3, 3A, 3B) for producing the light alloy (10), the starting component (3, 3A, 3B) comprising at least one light metal-based component (3, 3A), the at least one light metal-based component mainly comprising the light metal; - producing said light alloy (10) in the form of a melt (30) from said at least one starting component (3, 3A, 3B); - ejecting a light alloy melt (30) from at least one nozzle (5); as well as - rapidly solidifying the light alloy melt (30) leaving the at least one nozzle (5) to produce the solidified light alloy (10), the light alloy melt (30) leaving the at least one nozzle (5) having a predetermined temperature when leaving the at least one nozzle (5) and being cooled to the solidus temperature of the light alloy (10) at an average cooling rate within a predetermined time period, the average cooling rate being determined as the ratio of the difference between the predetermined temperature and the solidus temperature to the predetermined time period, and in particular, the average cooling rate being higher than 10 000° C. / second, It is characterized in that - the light metal-based component (3, 3A) is heated to a first temperature below the liquidus temperature in a first heating step to produce a light metal-based component melt (31, 31A) having the first temperature, the light metal-based component melt (31, 31A) being supplied to the at least one nozzle (5) through a pipe (4, 4A); and - the light alloy melt (30) comprising at least the light metal-based component melt (31, 31A) is heated in the pipe (4, 4A) to have a second temperature before being ejected from the at least one nozzle (5), the second temperature being higher than the first temperature and the second temperature being higher than the solidus temperature by at least 75% of the liquidus / solidus temperature difference.

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

3. The method according to claim 1 or 2, characterized in that: The predetermined temperature is equal to or higher than the liquidus temperature, preferably at least 10°C higher than the liquidus temperature, and more preferably at least 20°C higher than the liquidus temperature.

4. The method according to any one of claims 1 to 3, characterized in that The residence time of the light alloy melt (30) in the pipe (4, 4A) is at least 10 seconds, preferably at least 15 seconds and more preferably at least 20 seconds.

5. The method according to any one of claims 1 to 4, characterized in that The lightweight alloy is an aluminum alloy, and the one or more alloying elements include one or more elements that form a dispersion (colloid) in the aluminum alloy, and the elements are transition metals, especially 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, characterized in that The one or more alloying elements include chromium (Cr), vanadium (V), titanium (Ti), zirconium (Zr), molybdenum (Mo), cobalt (Co) and / or niobium (Nb), and the total amount of Cr, V, Ti, Zr, Mo, Co and Nb is preferably at least equal to 0.50wt.% of the aluminum alloy, more preferably at least equal to 0.70wt.% of the aluminum alloy and most preferably at least equal to 1.00wt.% of the aluminum alloy, and the maximum amount of these alloying elements is preferably: 1.50wt.% Cr, 1.50wt.% V, 1.00wt.% Ti, 1.00wt.% Zr, 1.50wt.% Mo, 1.50wt.% Co and 1.00wt.% Nb.

7. The method according to claim 5 or 6, characterized in that: The one or more alloying elements include one or more elements that form a solid solution in the aluminum alloy, the solid solution forming elements include copper, zinc, magnesium and / or manganese, and the aluminum alloy preferably includes between 3.00wt.% and 10.00wt.% magnesium (Mg), and greater than 1.00wt.% but less than 6.00wt.% manganese.

8. The method according to any one of claims 1 to 4, characterized in that The lightweight alloy is a magnesium alloy, and the one or more alloying elements include silicon (Si), germanium (Ge), zirconium (Zr) and / or cobalt (Co).

9. The method according to any one of claims 1 to 8, characterized in that At least one of the alloying elements is present in the lightweight alloy in an amount that is higher than the solubility of the element in the lightweight alloy (10) at the solidus temperature.

10. The method according to any one of claims 1 to 9, characterized in that The liquidus temperature is at least 25°C higher than the solidus temperature, in particular at least 50°C higher than the solidus temperature and especially at least 75°C or at least 100°C higher than the solidus temperature.

11. The method according to any one of claims 1 to 10, characterized in that The first temperature is below 750°C, preferably below 725°C and more preferably below 700°C.

12. The method according to any one of claims 1 to 11, characterized in that The first temperature is at least 10°C lower, in particular at least 20°C lower and especially at least 30°C lower than the liquidus temperature.

13. The method according to any one of claims 1 to 12, characterized in that The light metal-based component melt (31, 31A) is pushed by pipe flow through the pipe (4, 4A) to the at least one nozzle (5).

14. The method according to any one of claims 1 to 13, characterized in that The light metal-based component melt (31, 31A) is degassed before being supplied to the at least one nozzle (5) through the conduit (4, 4A).

15. The method according to any one of claims 1 to 14, characterized in that The pipeline (4, 4A) comprises at least one heating chamber (13) for further heating the light alloy melt (30).

16. The method according to any one of claims 1 to 15, characterized in that The light metal based component (3, 3A) is only partially melted by heating the light metal based component to the first temperature to produce the light metal based component melt (31, 31A), and the light metal based component (3, 3A) is further melted by heating the light metal based component to the higher temperature in the pipe (4, 4A).

17. The method according to claim 16, characterized in that The light alloy (10) is produced from a starting component (3) which is only partially melted by heating the starting component to the first temperature to produce the light metal-based component melt (31) forming the light alloy melt (30), which is further melted in the pipe (4) by heating the light alloy melt to the second temperature in the pipe (4).

18. The method according to any one of claims 1 to 16, characterized in that The light alloy (10) is produced from at least two starting components (3A, 3B), the at least two starting components (3A, 3B) including the at least one light metal-based component (3A) and at least one other component (3B), the other component (3B) being added to the light metal-based component melt (31A) in the pipe (4A) to produce the light alloy melt (30).

19. The method according to claim 18, characterized in that The other components (3B) are added in solid form to the light metal-based component melt (31A).

20. The method according to claim 18, characterized in that The other components (3B) are added in liquid form to the light metal-based component melt (31A).

21. The method according to any one of claims 1 to 20, characterized in that The pipeline (4, 4A) comprises a mixing device (14) for mixing the light alloy melt (30).

22. The method according to any one of claims 1 to 21, characterized in that The first heating step is performed in a furnace (1, 1A) which is liquid-connected to the at least one nozzle (5) via the conduit (4, 4A), and the light metal-based component melt (31, 31A) is fed from the furnace (1, 1A) to the conduit (4, 4A) at the first temperature.

23. The method according to any one of claims 1 to 22, characterized in that The solidified light alloy (10) is plastically consolidated by plastic deformation under pressure, in particular by extrusion with a cross-sectional reduction λ of at least 3, preferably at least 6, more preferably at least 8 and most preferably at least 10.

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