RU2103404C1 - Method of preparing magnesium alloy - Google Patents

Abstract

FIELD: nonferrous metallurgy. SUBSTANCE: invention relates to preparing high-purity magnesium alloy in which alloy-forming components are added to molten magnesium in molten state. Predetermined quantity of primary magnesium is heated and melted in bowl. In the second one, predetermined quantities of alloying metals are heated to their melting temperatures. Molten alloying metals are added to molten magnesium to immediately form alloy as a result of exothermic reaction. Elementary manganese, when preliminarily added to alloy with other alloying elements, proved to reliably reduce iron impurity content to the level less than 50 ppm. Addition of molten manganese alloy with one or several rare-earth metals to magnesium alloy prevents rare-earth metals from precipitation out of melt and raises assimilation degree of rare-earth metal to the level exceeding 80%. EFFECT: enhanced efficiency of process, reduced power consumption, and excluded formation of sodium chloride slag and gaseous hydrogen chloride.

Description

 The invention is directed to a method for producing high-purity magnesium alloys with a low iron content.

 A more specific aspect of the invention lies in a method for increasing the efficiency of alloy formation in the manufacture of high-purity magnesium alloys by adding alloy-forming components in the molten state to the molten magnesium bath.

 Another aspect of the invention relates to a method of forming an alloy in which elemental manganese or a mixture of elemental manganese and aluminum is dissolved in a bath of molten alloy forming metals before adding molten alloy forming components with molten magnesium. Alloy-forming components can be added to molten magnesium before or after the addition of other alloy-forming components. The addition of manganese to the molten magnesium in the form of a solution noticeably reduces the content of iron impurities in the melt.

 Another objective of the invention is to increase the efficiency of alloy formation for rare earth (RE) metal or a mixture of rare earth metals in magnesium alloys.

 Another objective of the invention is to increase the alloying efficiency of rare-earth metals, for example, misch metal, to more than 80%, usually more than 90% and usually more than 95% when added to molten Mg-Mn-Al alloys.

 And another objective of the invention is to avoid the formation of magnesium chloride and chlorine gas, which are usually formed when manganese chloride is added to the melt.

 The term “alloy component” or “alloy forming component” as used herein includes any metals added to the primary metal, that is, magnesium to form an Mg alloy with any desired properties. Primary alloying components include, for example, Al, Zn, Mn and RE metal or a mixture of RE metals. Other metals, including alloy properties, are included in the term "alloy component".

 Prototype methods for producing magnesium (Mg) alloys include adding solid alloy-forming components (e.g. aluminum, zinc, manganese, etc.) to a bath with molten Mg, heating and mixing the molten metal in the bath until all solid alloy-forming components are melted and mixed in a bath with molten Mg.

 The quality of Mg alloy depends on its purity. Some applications of Mg alloy are more sensitive to impurities (such as oxides and flux inclusions) than others. However, from such applications that are extremely sensitive to the presence of impurities, it refers to the Mg alloy used for extrusion. The fact is that when extruding an alloy preform with a high gear ratio into a smaller form, the preform is exposed to a large surface area, Impurities on or near the surface of the extrudable product create defects on its surface. If such defects are associated with flux, i.e. any salt phase used to protect the metal from the influence of the atmosphere and to prevent the oxidation of Mg during casting operations in the molten state, they can also cause acceleration of corrosion on the surface of the extrudable product. Products, such as parts of the casting matrix, are usually characterized by a high surface area to mass ratio, and, as in the case of extrudable products, there is a high probability that impurities will be exposed on the surface of the parts of the casting matrix, and as a result there is a possibility of an increase in the corrosion rate .

 In the usual mixing of molten Mg alloys, these difficulties are summarized due to shear phenomena inherent in conventional mixing systems. Impeller mixers and centrifugal pumps mix the metal due to its shear by rotating blades, which can cause significant grinding of any insoluble particles in the melt, for example: metal oxides and chlorides. Thus, relatively large oxide particles, possibly present in the Mg melt, will turn into particles of ever smaller size (as a rule, the greater the shear force, the smaller the insoluble particles). After the formation of the alloy from the molten metal, the melt is usually left to settle for a predetermined period of time to allow suspended impurities to settle on the bottom of the crucible in the form of slurry or slag. The purified alloy can then be decanted from the crucible and separated from the slag. Since the particle size of impurities decreases with a high shear, the time required for the deposition of impurities increases accordingly. Moreover, all this adversely affects the efficiency and productivity of the process with a corresponding increase in the cost of production. In fact, the shear effect on the molten metal can be high enough to finally emulsify impurities in the metal, which for all practical purposes makes it impossible to precipitate these impurities. In such circumstances, the presence of emulsified insoluble oxides, metal chlorides and other impurities in the final product reduces the corrosion resistance of the alloy or otherwise degrades the physical properties of the alloy to such an extent that the alloy no longer meets the required performance characteristics.

When Mg is in a molten state, there is a possibility of its ignition in air. To reduce the tendency to ignite, a flux is placed on the surface of the melt. The flux melts under the action of the temperature of molten Mg and forms a protective film on the surface of the molten Mg. Such a film protects the molten Mg from contact with air and thereby prevents the oxidation and ignition of Mg. Another effective way to reduce the tendency of molten Mg to ignite, well known to those skilled in the art, is to use a protective gaseous atmosphere of a mixture of sulfur hexafluoride (SFG), carbon dioxide (CO ₂ ) and air, which forms a stable oxide film on the surface of the Mg melt.

In prototype methods, it is common practice to add manganese chloride (MnCl ₂ ) to the melt. The reaction of MnCl ₂ with molten Mg leads to the formation of insoluble magnesium chloride (MgCl ₂ ), which is deposited on the bottom of the melting crucible in the form of sludge or slag. Such slag should be separated from the pure alloy and discarded. Liquidation or processing of slag is inefficient and expensive. In addition, the use of MnCl ₂ leads to loss of metallic Mg due to the formation of MgCl ₂ and as a result further reduces the efficiency of the process and increases the cost of manufacturing the alloy. The cost of MnCl ₂ itself is higher than the cost of elemental Mn, which also prevents the use of MnCl ₂ .

In the reaction between MnCl ₂ and Mg due to the hydrolysis of any halide with atmospheric moisture (H ₂ O), gaseous hydrochloric acid (HCl) is formed, which creates another problem, since the release of HCl into the atmosphere leads to environmental pollution and does not have an acceptable solution. Accordingly, the isolation and safe disposal of HCl further increases the cost of production and as a result reduces the efficiency of the alloy formation process.

In methods for producing Mg alloys, it is well known practice to add Mn to the melt in order to reduce the Fe content. Mn can be added as elemental Mn or as an industrial metal mixture in the form of particles or powder, usually in the form of a briquette containing about 75% Mn and about 25% Al. At present, elemental Mn is added to molten Mg in the solid state. Due to the lack of interaction of MnCl ₂ with Mg with the formation of an undesirable MgCl ₂ slag, melt losses in the form of MgCl ₂ slag do not occur. However, the addition of elemental Mn in solid form has a negligible effect on the decrease in the Fe content in the melt.

In conventional methods for producing an Mg alloy using MnCl ₂ as a Fe reducing agent, the total time required for the precipitation of chlorides and other impurities in the form of sludge, for example, to the bottom of the crucible, takes a significant gap, depending on the size of the charge converted to the alloy. For example, the preparation of an extrusion type Mg alloy of AZ 318 may require additional purification, such as (but not limited to) flux purification with additional time. The production of extruded type AZ 318 alloy typically involves the following steps.

1. The melting of Mg in a crucible, as a rule, at 660-750 ^o C.

2. Weighing alloy-forming components, for example aluminum (Al) and zinc (Zn), and their preliminary heating to 100 ^o C with the removal of any moisture present in the metals. The preheated metals in solid form are then placed in a basket or perforated container mounted in such a way that is partially located below the surface of the molten Mg in the crucible. A mixing device is included, for example, an impeller mixer, mixing molten Mg in such a way that the melt flows through the basket with washing the solid alloy-forming components until their melting points are reached or until their components dissolve and form an alloy with Mg. During this period, a drop in temperature occurs, since the added solid metals have a lower temperature than that of molten Mg.

3. After thoroughly mixing the molten Al and Zn with the molten Mg and raising the temperature of the melt, preferably to about 720 ^° C., an anhydrous MnCl ₂ is added to the melt as a bead. As in the previous step, the melt is mixed with an impeller mixer to guarantee the required alloy formation.

4. Subsequent cooling of the molten alloy to a temperature of about 640 ^° C., which is nevertheless high enough to guarantee the precipitation of metal chlorides and other impurities, in particular iron (Fe), forming binary or ternary compounds with the participation of Mg, Al or Mn , MgCl ₂ formed when MnCl _{2 is} added to the melt is also left to settle to the bottom of the crucible in the form of a slurry.

 5. Decanting the molten alloy and spilling into molds.

 6. Subsequent removal of sludge deposited to the bottom of the crucible. Because the sludge still contains valuable Mg residues, it is usually recycled.

 Alloy formation techniques are described in the publication Magnesium and Magnesium Compounds, a review of materials by H.B. Comstok, US Department of the Interior, Mining Division, 1963, in particular, in the chapter entitled "Melting and Alloying", pp. 54-59.

 US Pat. No. 4,891,065, issued January 2, 1990, discloses a method for producing magnesium by contacting a melt with a mixture of elemental zirconium (Zr) and elemental silicon (Si) in order to reduce iron contamination without introducing undesirable amounts of regulatory elements into the resulting Mg.

 US Pat. No. 4,961,783, issued October 9, 1990, discloses a method for removing iron impurities from molten magnesium by adding a mixture of a boron-containing compound and flux to the melt.

The Foundations of Magnesium Technology, EF Emley, 1st Edition, 1966, Pergamon Press, states that Mn is usually added to molten Mg in the form of MnCl ₂ powder, which when shaken gives the reaction on the metal surface: MnCl ₂ + Mg = MgCl ₂ + Mn. With melt mixing, a certain amount of free Mn dissolves in Mg. Alternatively, electrolytic Mn can be directly added to the molten Mg. Emley EF reports that the efficiency of Mn in alloy formation typically reaches 50-80%.

 In a series of technical documents SAE (International Congress and Exhibition of February 24-28, 1992), W.E. Mercer et al. Cited a report entitled “Critical Limits of Pollution and Salt Water Corrosion Indices of Magnesium AE 42 Alloy”.

 US Pat. No. 4,668,170, issued Jan. 13, 1987, discloses an electromagnetic pump for circulating and stirring in a molten metal vessel. The pump is located in a chamber resistant to the action of liquid metal, through which the pump channel passes.

 The purpose of the invention is to provide a method for producing an Mg alloy, characterized by a relatively high degree of purity and low content of iron impurities.

Another objective of the invention is to improve the efficiency of alloy formation, increase productivity, reduce production costs and eliminate the release of gaseous HCl and the formation of MgCl ₂ as undesirable by-products in the method of producing high-purity Mg alloys.

 Another objective of the invention is to provide a method for producing a high-purity Mg alloy, especially alloys containing 89% or more Mg, in which the admixture of iron in the alloy is reduced to less than 50 ppm (ppm), preferably less than 20 ppm. ppm, more preferably less than 10 ppm. An impurity Fe content of less than 10 ppm is particularly desirable for extrudable products.

 A particular object of the invention is to increase the alloying efficiency of the method of the invention by melting alloy forming components before adding molten alloy forming components to molten Mg.

And another objective of the invention is to add elemental Mn as such or in the form of a powder mixture of metals containing elemental Mn and Al to molten Mg, in combination with other alloy-forming components in the molten state, resulting in a reduction in Fe impurity in the alloy. The formation of MgCl ₂ sludge in the melt, as well as the evolution of gaseous HCl, which are characteristic of the existing methods for introducing MnO ₂ into molten Mg, in this case, can be avoided
Another objective of the invention is to obtain Mg alloys with rare-earth (RE) metals by introducing RE metals in the molten state into molten Mg with substantially improved alloy formation efficiency. RE metal (s) are recommended to be driven into molten Mg in a mixture with other molten metals forming the alloy. When using the methodology of the invention, the efficiency of alloy formation for rare-earth metals exceeds 80%, usually above 90% and more often exceeds 95% if the components forming the alloy are added to the molten Mg in the molten state.

 And another objective of the invention is to prevent the emulsification of impurities, such as oxides and chlorides, in the melt using an electromagnetic (EM) pump as a mixing device, and not a pumping device.

 Other objectives and advantages of the invention will become apparent to the reader from the following recommended embodiments of the invention.

 Typical Mg alloy production techniques employ equipment including a melting crucible or retort capable of holding the required amount of molten Mg, heating devices, such as a gas furnace or electric coil, to heat the crucible to a temperature at which Mg and other alloy forming components melt, and mixing devices, for example a mechanical mixer, an air-driven pump, an electric pump, etc. for mixing alloy-forming components with molten Mg.

The formation of Mg alloys is usually carried out at 660-750 ^o C, preferably 690-730 ^o C. To obtain the Mg alloys of the invention, a temperature of about 720 ^o C is most preferred. Although the formation of the alloy according to the invention can be carried out outside the specified range, the temperature is still lower 660 ^o C does not lead to a good alloy-forming efficiency with respect to part of the alloy-forming components, actually miscible with Mg. A temperature above 750 ^o C is not required to achieve good alloy forming efficiency, and its use leads to excessive energy consumption for heating the crucible and alloy.

 Mg alloys obtained by the methods of the present invention can contain a wide variety of metals, generally referred to herein as alloying components, alloying components or alloying ingredients. Such metals include (but are not limited to only the most commonly used metals), for example Al, Zn, Mn, Si, Zr, Ti, Be, Cu, Li, Y, Ag, Th, one or more rare earth metals of the lanthanide group metals or mixtures thereof. To improve the properties and / or purity of a particular final alloy, other metals not specifically mentioned above may be added to the primary Mg melt.

 It is also common practice to add alloy forming components to a bath of molten Mg, in which Mg has already formed an alloy with the required amount of another alloy forming component or components. Accordingly, a simple technique for producing an AE42 alloy, for example, is to first melt the required amount of primary Mg and then produce an Mg alloy with a rare-earth metal by adding the target amount of a solid rare-earth metal or a mixture of rare-earth metals to the melt. After that, the alloy formation is completed by adding other alloy-forming components, for example, Al-Mn in the solid state, to the molten alloy Mg-RE.

The formation of alloys with one or more rare-earth (RE) metals of a number of lanthanides (e.g. cerium, lanthanum, praseodymium, neodymium, etc.) is a well-studied technology. However, in the prototype methods, only about 60% of the total amount of RE metals added to the melt is capable of forming an alloy with molten Mg. This is due to the fact that RE metals predominantly reduce MgCl ₂ and other commonly encountered chlorides that accompany melting of Mg and the formation of its alloys, including MnCl ₂ with the formation of RE metal chlorides. In the present invention, the efficiency of alloy formation in the case of rare-earth metals is significantly improved. Thus, usually achieved efficiency exceeds 80%, as a rule, exceeds 90% and even 95%.

 The alloy formation method of the present invention can be used for any of a number of known Mg alloys with standard characteristics given, for example, in the 1988 ASTM Yearbook of Standards under the designations B93, B94 and B275.

 Mixing the molten metal with an impeller pump has an undesirable effect on the shear properties of any insoluble impurities suspended in the melt, such as oxides or chlorides. Intensive shear action on the melt can lead to emulsification of insoluble impurities, as a result of which they remain in suspension for a longer time or, in the most extreme case, do not precipitate at all and remain in suspension. The present invention uses an electromagnetic (EM) pump as a more efficient mixing device that does not shear the molten metal, since the pump does not have moving parts. Due to the fact that the molten alloy is not subjected to shear, any insoluble impurities remain in the form of large particles, which are more easily deposited on the bottom of the crucible, and can be separated from the melt by decantation, resulting in an alloy of higher purity.

 An EM pump is recommended to be mounted on the crucible casing, while the pump is at least partially, preferably completely, immersed in the melt. By using an EM pump in the method of the present invention, intensive mixing is avoided, in which the surface part of the melt can be destroyed. If the surface of the molten metal is damaged, the metal is exposed to the atmosphere to form unwanted metal oxides as a result. Accordingly, using an EM pump, cleaner alloys are obtained. Other advantages of an EM pump are its reversibility and reduced noise level compared to commonly used mechanical mixing devices.

 In the method of the invention, one or more alloy-forming components are placed in the solid state in the first crucible and brought to the melting points of these metals. After converting the alloy-forming components to the molten state, the temperature is equalized with the temperature of the molten Mg and then introduced into the bath with molten Mg. It was found that if this technique is applied, when molten Al is added to the molten Mg, a reaction occurs in which the temperature of the melt rises by several degrees. A favorable temperature increase contributes to the formation of the alloy without the need for additional external heat to be supplied to the molten alloy in the crucible. The formation of alloys quickly occurs from metals, and the metals are mixed to achieve homogeneity. This technique leads to a high efficiency of formation of an alloy with Al, reaching at least 95%, more often at least 98%.

To obtain an Mg alloy of high purity and low Fe content, agents are traditionally used for purification of Fe and its deposition, for example: Mn, Cr, Mg, Si and compounds of these elements. An acceptable method of forming an alloy of Mn with Mg consists, for example, in adding anhydrous MnCl _2, as opposed to simply dissolving elemental Mn in a Mg melt, which is typical for essentially all other alloying elements. The reason for adding MnCl ₂ instead of adding elemental Mn both in pure form or in the form of a mixture is that this significantly increases the deposition efficiency of Fe, as well as increases the efficiency of the formation of an alloy with Mn. Repeated observations showed that the content of Mn in primary Mg can be increased to a significantly higher level by the addition of MnCl ₂ compared with the level achieved by adding elemental Mn, for example, in the form of electrolytic flakes.

The explanation of this difference between the two Mn sources may be that elemental Mn is formed in situ upon the addition of MnCl ₂ , i.e. by the equation:
MnCl ₂ + Mg (metal) _ → Mn (Mg pp) + MgCl ₂
should be in phase or compound, significantly different from those that are formed upon dissolution of elemental Mn both in the form of pure electrolytic flakes and in the form of a mixture of 75% Al - 25% Mn.

The fact that the preliminary formation of an elemental Mn alloy or a mixture of Mn - Al with Al before adding them to the Mg melt leads to an Fe content similar to that obtained by adding an equivalent amount of MnCl ₂ , which implies the formation of the same active phase. Bearing in mind the existence of the transition state of the phase — the compound involved in this process, we come to the conclusion that hydride is involved in it, although nothing is generally known about the formation of such Mn compounds. The reason for this is the fact that hydrogen is difficult to determine in solid metal samples. Al has a much lower ability to dissolve hydrogen than Mg and, as is known, Al forms stable intermetallic compounds with Mn and Fe. The phase deposited from Al-containing Mg alloys has been identified as a triple intermetallic phase comprising variable amounts of three elements: Al, Mn and Fe (Hillis et al., SAE Technical Paper Series - 1985, part 7). Other researchers have allegedly identified the phase as Al ₆ Mn or Al ₄ Mn (Lunder, Aune, IMA, 1990), but an X-ray diffraction analysis identified a sample of a triple precipitate of the formula Al ₅ Mn ₂ in which the Mn atom is randomly replaced by varying amounts of Fe (iron forms an isomorphic compound with aluminum (Al ₅ Fe ₂ )).

 It is believed that the elemental Mn added is inactive due to the formation of a hydride phase / compound upon prolonged exposure / storage in the presence of atmospheric moisture. If such a "hydride phase" preliminarily forms an alloy with an Al melt, the hydride is destroyed as a result of the combined influence of factors such as the low solubility of hydrogen in Al and the formation of a relatively stable Al phase. It is this Al phase that then combines with soluble Fe contained in the Mg melt to form the less soluble ternary phase Fe-Mn-Al.

 Accordingly, the addition of elemental Mn in the solid state to the Mg melt leads to inefficient formation of an alloy with Mn and to poor regulation of the Fe content, if at all amenable to adjustment. We found that elemental Mn in combination with Al as an alloying element in the molten state when Mg is added to the melt effectively reduces the Fe content in Mg alloys to below 40 ppm, which meets the requirements for high frequency alloys.

Instead of the traditional addition of MnCl ₂ salt to Mg melt, which effectively precipitates Fe, but at the same time causes MgCl ₂ to form in gaseous HCl, in the present invention, elemental Mn or a mixture of elemental Mn and Al is added to the molten Mg melt. MgCl ₂ formed in this case upon addition of MnCl ₂ binds to the salt and as a result is not present in the alloy in the form of Mg.

The formation of the alloy is recommended in a flux-free system (without salt), in which unwanted metal chlorides are not formed. In a flux-free system, the melt is protected by an atmosphere of gas, which is a mixture of less than 1% SF ₆ in approximately equal volumes of dry air and CO ₂ .

MgCl ₂ reacts with RE to form RE chlorides according to the equation
2P3 (metal) + 3MgCl ₂ _ → 2 (P3) Cl ₃ + 3Mg (metal).
However, when adding a metal rare earth or a mixture of metal rare earths, such as, for example, a misch metal containing 50% Ce, 25% La, 18% Nd and 75% Pr, in a flux-free process simultaneously with the addition of elemental Mn in the molten state or mixtures of elemental Mn and Al, the efficiency of alloy formation with RE metal or metals is significantly improved and amounts to more than 80%, more often than 90% and usually more than 95%. This is a significant advantage both in the production of fresh alloy and in recycling scrap of rare-earth alloy. Accordingly, by direct addition of elemental Mn in liquid state to the liquid Mg as an alloying component in the alloying method of the invention, a rare-earth alloy is obtained with a significantly higher alloy formation efficiency with rare-earth metals, a low level of Fe impurity and the absence of MgCl ₂ in the melt
Once based on the foregoing, the features, advantages and objectives of the invention and the like have become clear, the following examples are provided to illustrate the recommended embodiments of the invention. These examples are not intended to limit the scope of the invention, since the invention may be embodied as other equally effective equivalent embodiments.

 All percentages are given as a percentage by weight.

Example 1 (Non-Example)
A291D type magnesium alloy is obtained from a charge of 203 pounds (94.4 kg) of primary magnesium of 99.9% pure. An admixture of iron in primary Mg is at least 350 parts per million (ppm). Primary magnesium is melted in a crucible at 728 ^° C. under a protective atmosphere of a gas consisting of less than about 1% SF ₆ in a mixture with equal amounts of CO ₂ and air. The following solid alloy-forming components are successively added to the Mg melt: 20.8 pounds (9.44 kg) of Al at a Mg melt temperature of 728 ^° C, then 1.7 pounds (0.77 kg) at a Mg melt temperature of 717 ^° C and 2, 9 lbs (1.32 kg) of the anhydrous king of MnCl ₂ at a melt temperature of Mg 715 ^° C. The melt temperature of Mg drops after each solid alloy forming component is added to the melt. During the addition of solid alloy-forming components to accelerate their melting and to obtain a homogeneous alloy, the melt is mixed. Then the alloy is cooled to 643 ^o C with a gradual precipitation of the metal impurities from the melt to the bottom of the crucible. Analysis of the alloy showed the following metal content,%
Al - 8.6
Zn - 0.63
Mn - 0.22
Fe - 1 ppm

This example shows that the addition of MnCl ₂ effectively reduces the level of impurity Fe in the melt. The presence of Al in the melt is also effective in reducing the solubility of Fe, i.e. the higher the Al content, the lower the solubility of Fe, which leads to precipitation of Fe in the form of Fe compounds. However, MnCl ₂ reacts with Mg to form MgCl ₂ , which precipitates to the bottom of the crucible and is removed as sludge. The addition of MnCl ₂ leads to an undesirable evolution of gaseous HCl from the melt.

 The efficiency of the melting process is undesirably affected by energy losses associated with the addition of solid alloy-forming components to the melt having a temperature significantly lower than the Mo melt.

A cost analysis using MnCl ₂ showed that only about 0.35% of Mn is consumed in the melt, since for every pound (0.454 kg) of added MnCl _2, about 0.12 pounds (54 g) of Mg is lost as MgCl ₂ sludge.

Example 2 (Not an example of the invention)
Following the same general procedure of Example 1, the A291D alloy was prepared without the addition of MnCl ₂ . A batch of 150 pounds (63.1 kg) of primary magnesium is melted at 720 ^° C. After two minutes, a preheated batch of 15.2 pounds (6.9 kg) is added in the form of solid metals to molten Mg at 720 ^° C. Al and a charge of 1.4 lbs) 0.64 kg) Zn. After another eleven minutes at 732 ^° C., a charge of 1.7 pounds (0.77 kg) of solid Mn - Al curing agent was added to the melt. After 10 minutes, the temperature of the melt decreases to 724 ^° C. Then, the temperature of the melt is allowed to gradually decrease to 650 ^° C. During the temperature reduction period, the mechanical impurities present in the melt precipitate from the melt and concentrate on the bottom of the crucible. A sample was taken from the melt and analyzed. The analysis showed that the alloy contains the following elements,%:
Al - 10%
Zn - 0.87%
Mn - 0.29%
Fe - 81 ppm

 This example illustrates that the addition of a solid Mn - Al curing agent is not effective for the deposition of impurity iron to an acceptable level of a maximum of 40 ppm, as recommended by the 1988 ASTM Book of Standards. Al loading of 9% alone can reduce Fe impurity content to the level achieved in this example.

Example 3 (Example of the invention)
According to the general procedure of Example 1, a 185.3 lb (83.9 kg) primary Mg charge is placed in a 300 lb (135.9 kg) stainless steel crucible and heated to 721 ^° C., at which Mg goes into a molten state. A charge of 18.7 pounds (8.47 kg) of molten Al at 721 ^° C. was poured into molten Mg. To mix Mg with Al and obtain a homogeneous alloy, an impeller mixing device is used. After 20 seconds, when the temperature rises to 725 ^° C., an alloy sample is taken and then samples are taken for 9 minutes with an interval of 1 minute (see table 1).

 The results obtained show that the rapid and complete formation of the alloy already occurs even before the first sample is taken, 20 s after the addition of the Al charge.

After adding molten Al to the crucible, no external heat is supplied to the crucible. The melt temperature, determined with an interval of one minute, was as follows:
The data presented in Table 2 show that the temperature of the melt rises at the time of adding molten Al to the molten Mg, i.e. without supplying external heat to the melt. This phenomenon was unexpected and at present cannot be explained, although it is assumed that the temperature increase is associated with an exothermic reaction or a dissolution reaction between Mg and Al. An increase in temperature is noted essentially immediately after the addition of molten Al to molten Mg. The temperature reaches a maximum within 1 min after addition and then gradually decreases. According to earlier observations, temperature does not increase when solid Al (with a much lower temperature) is added to the melt. Accordingly, the addition of molten Al to the Mg melt gives undeniable advantages, since an unexpected increase in temperature leads to a more efficient alloy formation process that does not require additional time or energy required to maintain the melt at the alloy formation temperature or to bring the melt back to the target temperature.

Example 4 (Example of the invention)
In this method of the invention, the general procedure of Example 3 is used as follows.

A 180 lb (81.7 kg) primary magnesium charge is placed in the first crucible and heated to a melting point of 721 ^° C. A second batch of aluminum is charged at 18.2 pounds (8.31 kg) and heated to a melting point of 711 ^o C. To the molten aluminum is added 1.4 pounds (0.64 kg) of dehydrated solid Zn preheated to 300 ^o C. After 10 minutes, the molten Al - Zn alloy is manually stirred with a ceramic rod at 700 ^o C and then further heated to 721 ^o C. The melted mixture was Al - Zn (at 721 ^o C) was poured into the crucible with molten Mg and smesh Bani molten metals include impeller stirrer. After 3 minutes, determine the temperature of the alloy. The temperature rises to 730 ^o C.

 This Example again illustrates the fact that when a molten mixture of Al and Zn is added to the molten Mg, the temperature rises without adding additional heat to the melt. Thus, the temperature increase is not associated with the addition of Al alone, but also occurs when a mixture of alloy-forming components in the molten state is added to the primary Mg melt.

Example 5 (Example of the invention)
By the general procedure of Example 1, the A291D alloy is obtained without the use of MnCl ₂ . A batch of 150 pounds (68.1 kg) of primary Mg is melted at 720 ^° C. Therefore, a batch of metal is obtained from a batch of 15.2 pounds (6.9 kg) of Al, 1.4 pounds (0.64 kg) of Zn and 1 , 7 lbs (0.77 kg) of elemental Mn and melted in a separate crucible at 710 ^° C. The molten alloy forming components Al - Zn - Mn are then added to the molten Mg. After lowering the melt temperature to 650 ^° C., a sample is taken from the melt to precipitate metallic impurities from the melt. The analysis showed the content of the following elements in the alloy,%:
Al - 8.5,
Zn - 0.97,
Mn - 0.26,
Fe - 0.0006 (6 ppm).

 This example shows that the addition of Mn in the molten state is effective to reduce the content of impurity Fe to a level much lower than that provided by ASTM standard for alloy A291D (40 ppm).

Example 6 (Example of the invention)
The previously described procedure of Example 4 is reproduced, but with an additional step of adding a mixture of elemental Mn and Al to the molten Al - Zn mixture before adding the entire molten Al - Zn - Mn mixture (alloy forming component) to the molten Mg. The Mn used was a commercial powder blend of 75% Mn and 25% Al. The alloy forming load consisted of 5.3 lb (2.41 kg) Al, 1.8 lb (0.82 kg) Zn, and 2.6 lb (1.18 kg) of the Mn-Al powder mixture. The alloy forming component is heated in a separate crucible until melted.

 Adding a mixture of elemental Al and Mn to an Al - Zn mixture makes it possible to obtain the alloy AZ 318 having the composition indicated in the ASTM Yearbook of Standards for 1988, under the designation B275, Table X4.1, according to which the maximum permissible level of impurity Fe is limited to 0.005 % (50 ppm).

The molten Al — Zn — Mn alloy is then added to the molten primary magnesium containing a minimum of 350 ppm Fe. The melt is mixed until the alloy forming component forms an alloy with molten Mg. The melt is allowed to cool to 650 ^° C. in order to precipitate metallic impurities from the melt. A sample was taken for analysis. The alloy has the following composition,%:
Mg - 96.5,
Al - 2.4,
Zn - 0.68,
Mn - 0.41,
Cu - 0.0006 (6 ppm),
Ni - 0.0004 (4 ppm),
Fe - 0.0002 (2 ppm).

 This example shows that the addition of a molten alloy forming component, i.e., an Al - Zn - Mn mixture to molten Mg, leads to a significant decrease in the level of Fe impurity. The level of Cu, Ni, and Fe impurities fully corresponds to the limits recommended by ASTM standards for melt AZ 318. Si analysis was not performed, since Si is not critical for alloy operation, and at the same time it is within the limits prescribed by ASTM standard. With careful mixing, the molten alloy-forming composition very quickly forms an alloy with molten Mg. Mn combines with Fe and precipitates from the melt in the form of an insoluble metal compound, which leads to a noticeable decrease in the level of impurity Fe.

The practice of introducing molten Mn (in the form of a mixture of Al - elemental Mn) does not lead to harmful release of HCl. Operational problems associated with HCl-induced corrosion of equipment and its components do not arise. The method of the invention brings savings because the cost of Mn in a mixture of elemental Mn - Al is less than the cost of metallic Mn in MnCl ₂ .

Example 7 (Not an example of the invention)
In accordance with the general methodology described in Example 1, castings of AE42X1 alloy with a total weight of 25,520 pounds (11586 kg) were manufactured at a foundry in Freeport, Texas. During the manufacturing process, molten Mg is protected from the atmosphere by M-130 flux, the salt composition of which is well known to those skilled in the art. Loads of Al, Al - Be hardener and PZ metal are added to the molten Mg in the form of solid ingots. MnCl _{2 was} added to the melt.

The crucible used has a capacity of 5,000 pounds (2,270 kg). The total amount of alloy forming components used was as follows, pounds:
Al - 1344 (610 kg),
PZ (mish metal) - 1250 (567.5 kg),
MnCl ₂ - 424 (215.2 kg),
Al - Be - 20.9 (9.5 kg).

The average analysis of 22 samples (≈ 4 samples per batch of metal) obtained the following results,%:
Al - 3.95,
Be - 2.62,
Mn - 0.297,
Fe - 0.001 (10 ppm),
Be - 0.00062 (6.2 ppm).

Based on an average analysis, the following efficiencies were obtained for each metal component,%:
Al - 86,
RE - 61,
Be - 17,
Mn - 42.

 In this process, an undesirable amount of gaseous HCl is formed. In addition, the alloying efficiency for Al, RE of the target metal and Mn is significantly lower than the alloying efficiency achieved in the method of the invention.

Example 8 (Not an example of the invention)
A 81 pound (36.8 kg) primary Mg charge is melted in a crucible with a capacity of 90 pounds (40.86 kg) under an oxidizing protective atmosphere of SF ₆ , CO ₂ and air.

For subsequent addition to the molten Mg, the following alloy-forming components were prepared, g:
Al - 362.2
Hardener Al - Be - 14.5 (Al 95% - Be 5%),
Mn - 154,
Nd (95% purity) - 377.7.

Before adding in solid form, all alloy-forming components are preheated to a minimum temperature of 100 ^o C. To achieve homogeneity of metals in the alloy, the molten metal is mixed during the addition of alloy-forming components using a marine type impeller. Initially, the primary Mg is heated to 760 ^° C. Elemental Mn is added over 35 minutes. The metal temperature is then lowered to 755 ^° C. and Al-Be hardener and Al charge are added. Two minutes later, Nd was added to the melt, and alloyed with molten Mg for 15 minutes. The temperature was lowered to 700 ^° C. to precipitate metal impurities from the melt, and samples were taken from the melt.

 Taking as 100% the theoretical efficiency of alloy formation, the theoretical analysis of the obtained alloy is compared with a practical analysis.

 The data given in table 3 show, in practice, the efficiency of alloy formation exceeds 100% theoretical efficiency. This is probably the result of oxidation of a certain amount of the initial charge of primary Mg, resulting in a decrease in the amount of primary Mg available for alloy formation, or the result of an acceptable analysis error.

Example 9 (Example of the invention)
In a first crucible with a capacity of 325 pounds (147.6 kg), a charge of 279.8 pounds (127 kg) of primary Mg was placed and kept under the protection of an atmospheric mixture of SF ₆ and equal parts of CO ₂ and air. In a second crucible with a capacity of 25 pounds (11.35 kg), an Al charge of 13.3 pounds (6.04 kg) was placed. Both crucibles are heated to 720 ^° C. The temperature of the molten Mg is increased to 752 ^° C., after which an impeller stirrer is switched on to guarantee the homogeneity of the melt. Two minutes later, at 765 ^° C., a charge of 8.3 pounds (3.77 kg) of a solid metal rare-earth metal mixture containing 53% cerium, 23% lanthanum, 18% neodymium, 5% praseodymium, and 1% other components was added to the molten Mg. . Fifteen minutes later, a load of 0.591 kg of a mixture of elemental Mn - Al (75% Mn, 25% Al) and a load of 30 g of Al - Be hardener were added to the Al melt and mixed with a ceramic rod. Al melt having a temperature of 725 ^o C. Thirteen minutes later, to the alloy Mg - rare-earth metals at 720 ^o C was added heated to 710 ^o C alloy Al - Mn - Be. 1.31 pounds (0.6 kg) of Al - Mn - Be alloy remains in the crucible. After 1.5 minutes, the melt temperature rises to 727 ^o C, after which the alloy is allowed to gradually cool to 680 ^o C with the deposition of metal impurities from the melt. The resulting melt is decanted and poured into molds. Samples taken from some ingots obtained by casting give the following analysis results (in parentheses the efficiency of alloy formation),%:
Al - 3.8 (92%),
RE - 2.72 (98.9),
Mn - 0.17 (58.6%),
Cu - 0.0022 -22 ppm,
Ni - 0.0002 - 2 ppm,
Fe - 0.0018 - 18 ppm,
Be - 0.0005 (55.6%)
The above data show that the efficiency of alloy formation for rare-earth metals is significantly higher compared to the indicators achieved in currently practiced alloy formation technologies (see Example 7). RE metals do not fall out of the melt with Mn with a decrease in the efficiency of alloy formation to a value in the range of 50 - 80%, which are characteristic of current technologies in which Mn is added to the melt in solid form or in the form of MnCl ₂ . The level of Fe impurity is quite consistent with the range acceptable for high purity alloys.

 The alloy formation technique may be modified without departing from the spirit and scope of the present invention.

Claims (5)

1. A method of producing a magnesium alloy, comprising introducing magnesium into the first crucible, heating it above 660 ^{° C.} until molten, mixing the magnesium melt to a homogeneous state, introducing an alloying component containing aluminum and manganese into the second crucible, melting it, introducing a molten alloying component, and mixing molten magnesium and molten alloy-forming component with rapid formation of the alloy, characterized in that when mixing the magnesium melt to a homogeneous state oyaniya above the melt surface creates oxidizing protective gas layer.  2. The method according to p. 1, characterized in that the alloy forming component is selected from the group: aluminum, zinc, manganese, silicon, zirconium, calcium, beryllium, yttrium, silver, at least one rare earth metal (REM) of a number of lanthanides or a mixture thereof .  3. The method according to p. 2, characterized in that as REM use a misch metal containing, by weight. Cerium 53
Lanthanum 23
Neodymium 18
Praseodymium 5
Other metals 1
4. The method according to p. 1, characterized in that at least one of the rare-earth metals of a number of lanthanides in the solid state is introduced into the magnesium melt before the alloy-forming component is introduced into the magnesium melt, it is melted in the magnesium melt and the alloy-forming component in the molten state is added to the molten Mg-REM mixture. with the achievement of the degree of assimilation of rare-earth metals by alloy more than 80%
5. The method according to p. 1, characterized in that after mixing the magnesium melt and the alloy-forming component, the melt is cooled for a time sufficient to precipitate insoluble impurities on the crucible bottom, the alloy is cast into a mold or injection mold, and the molded or cast alloy is cooled to form a product containing an admixture of iron of less than 50 hours per 1 million hours  6. The method according to p. 1, characterized in that they use molten magnesium free of magnesium chloride.  7. The method according to p. 1, characterized in that the process is conducted with the formation of an alloy containing impurities of iron in an amount of less than 20 hours per 1 million

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