CN113278839B - Magnesium rare earth alloy melt purification and refinement composite treatment flux and application thereof - Google Patents
Magnesium rare earth alloy melt purification and refinement composite treatment flux and application thereof Download PDFInfo
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Abstract
The invention discloses a magnesium rare earth alloy melt purification and refinement composite treatment flux. The compositions in percentage by mass are 30-40% of magnesium chloride, 8-15% of potassium chloride, 8-15% of sodium chloride, 15-20% of barium chloride, 5-8% of barium sulfate, 10-15% of zirconium diboride and 10-15% of zirconium sulfate. Firstly, melting and mixing magnesium chloride, potassium chloride, sodium chloride, barium chloride and barium sulfate, cooling and solidifying to obtain a refining agent composite salt block, and then mixing and sieving the refining agent composite salt block, zirconium diboride and zirconium sulfate to prepare the purifying and refining composite treatment flux. The composite flux can improve the melt purification efficiency, prolong the Zr refining action time, realize the refining and purification treatment of the alloy melt by one step and greatly shorten the preparation process of the magnesium rare earth alloy melt.
Description
Technical Field
The invention belongs to the technical field of magnesium alloy, relates to a flux for magnesium alloy melt treatment, and particularly relates to a magnesium rare earth alloy purification and refinement composite treatment flux and application thereof.
Background
The magnesium rare earth alloy has the advantages of low density, high specific strength, good heat resistance and the like, so that the magnesium rare earth alloy is one of the priority development materials in the fields of aerospace, national defense and military industry and the like in all developed countries, and is applied to key parts such as carrier rocket cabin bodies, missile cabin bodies, aircraft engine casings and the like, thereby realizing great weight reduction and remarkable improvement of maneuvering performance of aircrafts. Therefore, the magnesium rare earth alloy has very wide market prospect. And the high-performance casting can be prepared only by the high-quality alloy melt. The melt treatment of the magnesium rare earth alloy mainly has two key contents, namely melt purification treatment; secondly, refining the melt. The purification treatment can remove the inclusions such as magnesium oxide, rare earth oxide and the like in the magnesium melt so as to improve the casting quality. The refining treatment can reduce the grain size of the alloy and improve the mechanical property of the casting.
The preparation of the high-quality magnesium rare earth alloy melt is very difficult. The magnesium rare earth alloy melt purification treatment mainly adopts a flux refining method, impurities are captured and wetted in the melt by virtue of a refining agent, and then the impurities wrapped by the density difference of the magnesium melt are settled to the bottom of a crucible in the standing process to achieve the melt purification effect. The refining temperature is 730-750 ℃, and the physicochemical properties of the refining agent, such as density, viscosity, surface tension and the like, can be influenced by overhigh or overlow temperature, so that the purification effect is reduced. However, the density of the rare earth element is higher, and the density of the magnesium rare earth alloy melt is higher than that of the traditional magnesium alloy melt. Therefore, when the traditional magnesium alloy refining agent is used for refining the magnesium rare earth alloy melt, the settling speed of the refining agent is reduced, so that the ideal purification effect can be achieved only by longer standing time after refining, and the purification efficiency is seriously reduced.
The refining treatment of the magnesium rare earth alloy melt mainly adopts a Zr refining method, Zr is introduced by adding Mg-Zr intermediate alloy into the melt, and grain refinement is realized by depending on heterogeneous nucleation of undissolved Zr particles and the component supercooling effect of dissolved Zr element. However, the density of the Zr particle is about 4 times that of the magnesium liquid, and the Zr particle can rapidly settle to the bottom of the crucible in the melt to lose the refining effect. The studies showed that the smaller the particle size of Zr particles, the slower the settling rate. Therefore, when adding Mg — Zr master alloy to magnesium melt, it is necessary to raise the temperature of the melt to 780-800 ℃ to promote sufficient dissolution of Zr particles at high temperature to avoid its precipitation. Therefore, the repeated heating and cooling of the melt not only reduces the production efficiency, but also reduces the yield of Zr and the alloy refining effect because Zr is easily oxidized to generate zirconium dioxide to be burnt at the high alloying temperature.
Therefore, the preparation of the high-quality magnesium rare earth alloy melt has three unsolved bottleneck problems: first, there is a contradiction between the purification and refining of the alloy melt. The reason is that: after the magnesium rare earth alloy melt is refined, the magnesium rare earth alloy melt must be kept stand for a long time to enable inclusions to be settled to the bottom of the crucible to achieve an ideal purification effect, and meanwhile, high-density Zr particles can be quickly settled to cause the reduction of the refining effect, so that the contradiction relationship between purification and refining treatment is caused. Secondly, the difference between the process temperature required by melt purification and refining is too large, and the temperature of the magnesium rare earth alloy melt must be repeatedly increased and decreased in the preparation process of the magnesium rare earth alloy melt, so that the preparation efficiency of the melt is seriously reduced. Thirdly, the higher Zr alloying temperature leads Zr mass points to be easy to be oxidized to generate zirconium dioxide to be burnt and damaged, and the grain refining effect is reduced. Aiming at the problems existing in the purification and refining treatment processes of the magnesium rare earth alloy melt, a great deal of research is carried out in academia and industry.
The method of inhibiting Zr particle sedimentation by applying ultrasonic waves to a magnesium melt is described in the literature Effect of ultrasonic wave treatment on the alloying and grain refining efficiency of Mg-Zr master alloy in magnesium alloy with added pressure/peritectic components (Journal of Crystal Growth 2019; 512: pp 20-32), but the convection of melt caused by ultrasonic waves also causes inclusions already sedimented to be rewound into the melt to affect the purification Effect, so the engineering applicability of this method is not strong.
Patent CN108359822B discloses a method for pretreating Mg-Zr intermediate alloy by friction stir processing, which can crush and refine large-particle Zr particles in Mg-Zr intermediate alloy to reduce the sinking speed of Zr particles in the melt. However, the technology does not consider the problem of long standing time when the conventional refining agent is used for purifying the magnesium rare earth alloy melt, and Zr particles with small particle size also sink in the long-time refining standing process.
Patent CN1151294C discloses a magnesium alloy desilicication flux and a production method thereof, the components of the flux by mass percent are: 15-30% of magnesium chloride, 15-30% of potassium chloride, 10-20% of calcium fluoride, 8-12% of barium chloride, 10-25% of magnesium fluoride, 2-5% of potassium zirconium fluoride, 10-20% of titanium compound and 1-10% of carbonate, and the patent has good effect on reducing the content of harmful element silicon in magnesium melt. Although 2-5% of potassium fluorozirconate is added into the magnesium alloy refining agent in the patent, the purpose of adding a small amount of potassium fluorozirconate is mainly to improve the effect of the refining agent on removing silicon elements, and the comprehensive consideration of the refining problem of the magnesium rare earth alloy is not involved or not carried out.
Patent CN1277940C discloses a magnesium rare earth alloy refining flux and a production method thereof, the components of the flux by mass percent are: 20-40% of calcium chloride, 10-25% of potassium chloride, 10-20% of sodium chloride, 15-25% of barium chloride, 2-5% of calcium fluoride, 3-10% of cryolite and 3-10% of active rare earth compound. The patent is a special flux developed for purifying magnesium rare earth alloy melt, and the proportion of chloride salt and fluoride salt in the flux is greatly adjusted, particularly the content of barium chloride as a weighting agent in a refining agent is adjusted to 15-25%, so that the sedimentation of the refining agent in the magnesium melt can be effectively accelerated. However, the patent does not comprehensively consider the refining problem of the magnesium rare earth alloy. The patent CN100529129C develops a refining flux and a production method thereof specifically aiming at Mg-Gd-Y-Zr series magnesium rare earth alloy, and the mass percentages of the components are as follows: 30-50% of potassium chloride, 5-20% of barium chloride, 2-10% of sodium chloride, 10-20% of calcium chloride, 2-8% of calcium fluoride, 1-5% of cryolite, 3-8% of gadolinium compound, 3-8% of yttrium compound and 2-8% of zirconium compound, and the flux can remarkably reduce the loss of gadolinium, yttrium and zirconium elements in the magnesium rare earth alloy melt. In other words, the patent adds 2-8% of zirconium compound on the basis of magnesium alloy purifying flux to reduce the loss of Zr element in the alloy, thereby achieving the purpose of improving the working performance of the refining agent. Therefore, the two patents are developed aiming at the refining agent for purifying the magnesium rare earth alloy melt, the refining effect is not comprehensively considered in the same melt system, and the bottleneck problem that the purifying effect and the refining effect are mutually restricted cannot be solved. Therefore, in order to comprehensively consider the purification and refinement treatment effects of the magnesium rare earth alloy melt, it is necessary to select the Zr salt with strong grain refinement capability, and properly increase the Zr salt content in the magnesium alloy melt to improve the grain refinement effect of the alloy. However, more Zr salt added into the flux is bound to generate an interactive reaction with the existing components in the flux, and influences the original physical and chemical properties and working performance of the flux, such as melting point, viscosity, surface tension, spreadability and the like. Therefore, the development of the composite flux with ideal refining effect on the magnesium rare earth alloy melt is very important while the physicochemical parameters required by flux purification are met.
The inventor thinks that: on one hand, except for adding a high-density refining component into the existing refining agent to accelerate the sinking speed of inclusions wrapped by the refining agent, a component capable of being quickly wetted with the inclusions is selected and added to accelerate the capturing speed of the refining agent on the inclusions, so that the standing time required by refining the magnesium rare earth alloy melt can be reduced to the maximum extent; on the other hand, the Zr salt with high content, high density and low melting point is adopted to replace the traditional Mg-Zr intermediate alloy as a novel refiner, the dissolved atomic Zr is generated through in-situ reaction instead of large undissolved Zr particles in the intermediate alloy, the sedimentation speed of the Zr is greatly reduced, and the melting point, the viscosity, the surface tension and other physical and chemical properties of the novel flux are comprehensively considered, so that the contradiction problems of purification and refinement are expected to be solved. Finally, the novel refining agent and the refiner are organically combined to prepare the composite flux integrating purification and refining effects, so that the purification and refining effects can be realized in one step, and the problem of low preparation efficiency of the magnesium rare earth alloy melt is expected to be solved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to solve the three bottleneck problems that the purification and refining treatment effects of the melt are mutually restricted, the temperature needs to be repeatedly increased and decreased, and severe oxidation burning loss exists in Zr when the magnesium rare earth alloy melt is treated by adopting a conventional purification and refining step-by-step treatment method, and provides the magnesium rare earth alloy melt purification and refining composite treatment flux and the application thereof. When the composite flux prepared by the invention is used for carrying out melt treatment on the magnesium rare earth alloy, the purification and refinement treatment of the magnesium rare earth alloy melt can be realized in one step in one process link, the purification and refinement treatment effects can be considered, and the preparation quality of the magnesium rare earth alloy melt is greatly improved.
In order to realize the technical effects, the invention provides a brand-new magnesium rare earth alloy melt purification and refinement composite flux which is obviously different from the existing magnesium rare earth alloy refining agent.
The invention provides a magnesium rare earth alloy melt purification and refinement composite treatment flux which comprises the following components in percentage by mass: 30-40% of magnesium chloride, 8-15% of potassium chloride, 8-15% of sodium chloride, 15-20% of barium chloride, 5-8% of barium sulfate, 10-15% of zirconium diboride and 10-15% of zirconium sulfate. Namely, firstly, a zirconium sulfate component is introduced into the flux on the premise of not greatly changing the content of magnesium chloride (the magnesium chloride is the most main component for removing oxide inclusions). Zirconium sulfate is a Zr-containing catalyst that accelerates the rate of reaction of the refining agent with inclusions while releasing large amounts of atomic Zr in solution into the melt to refine the grains. Thus, the speed of the refining agent for wetting the inclusions is remarkably accelerated; and meanwhile, barium sulfate which is a weighting agent and has higher density than barium chloride is introduced into the flux, the barium sulfate is greatly different from other weighting agents, the barium sulfate is more stable and has higher melting point, and the addition of the barium sulfate not only can improve the density of the flux, but also can obviously improve the viscosity and the spreading property of the flux at high temperature. And the content of high-density barium chloride in the flux is properly improved, the content of low-density molten salt components such as sodium chloride, potassium chloride and the like is reduced, and the density of the refining agent is promoted to be improved, so that the speed of the refining agent to wrap and mix the impurities and sink to the bottom of the crucible is accelerated. After the refining agent is wetted and the speed of wrapping the inclusions is increased, the standing time required by refining is naturally and greatly reduced.
On the other hand, the Zr-containing molten salt components of zirconium diboride and zirconium sulfate are introduced on the basis, the densities of the two Zr-containing molten salts are both high, and the overall density of the composite flux is not influenced after the Zr-containing molten salts are introduced. The melting points of the two Zr salts are far lower than the conventional refining temperature of the magnesium rare earth alloy, the two Zr salts can generate atom Zr in a dissolved state through in-situ reaction in a melt, and the in-situ reaction can be synchronously carried out with the impurity removal reaction of a refining agent. That is, the flux of the invention can realize the effects of purification and refinement in one step in the same process link, thereby avoiding the fussy repeated temperature rise and fall of the melt. Zirconium sulfate, in addition to acting as a catalyst for the purification process, is capable of forming zirconium dioxide by decomposition reactions at elevated temperatures, resulting in small amounts of zirconium dioxide in the melt. Thus, the activity of zirconium dioxide which is a product of a chemical equation of the Zr oxidation reaction is improved, the oxidation tendency of Zr in a melt is reduced, and the oxidation burning loss of Zr is inhibited. The zirconium diboride containing the boron element can be precipitated by reacting with the impurity element iron element in the magnesium melt to generate solid iron boride, so that the impurity iron content in the magnesium rare earth alloy melt is effectively reduced, and the mechanical property and the corrosion resistance of the magnesium rare earth alloy casting are obviously improved.
Therefore, the invention can solve the bottleneck problems that the purification and refining treatment effects are mutually restricted, the melt needs to be repeatedly heated and cooled during purification and refining treatment, the Zr is oxidized and burned at high temperature and the like in the traditional magnesium rare earth alloy melt treatment process, and provides a new preparation idea of the magnesium rare earth alloy melt purification and refining composite treatment flux.
As an embodiment of the invention, firstly, magnesium chloride, potassium chloride, sodium chloride, barium chloride and barium sulfate are melted, mixed, cooled and solidified to obtain a refining agent composite salt block, then the prepared refining agent composite salt block, zirconium diboride and zirconium sulfate are mixed and added into a ball mill for full mixing, and the purification and refinement composite treatment flux is prepared after sieving. Thus, the prepared composite flux has the purification effect of the refining agent and the refining effect of the refiner.
As an embodiment of the invention, magnesium chloride is firstly added (into a crucible) and heated to 720-750 ℃ to be in a molten state, then potassium chloride, sodium chloride, barium chloride and barium sulfate are added in batches in sequence, and after all salts are completely molten, the mixture is fully stirred and cast to obtain the refining agent composite salt block. Firstly, the magnesium chloride with the lowest melting point is melted into a liquid state at a lower temperature, and the molten salt components with higher and higher melting points are gradually added, so that the reaction contact area among the molten salts is favorably increased, and eutectic reaction is generated among the molten salt components to form the eutectic molten salt with the low melting point.
As an embodiment of the invention, firstly, the refining agent composite salt block is smashed and sieved by a 50-200-mesh sieve, then the sieved refining agent composite salt powder, zirconium diboride and zirconium sulfate are put into a ball mill, and are taken out after ball milling for 5-10 h, and the mixture is sieved by the 50-200-mesh sieve again to obtain the purification and refinement composite treatment flux. Thus, the refining agent composite salt and the Zr composite salt used for refining can be uniformly mixed, and the purification and refining effects of the composite flux can be simultaneously exerted. Meanwhile, the 200-mesh sieve is beneficial to reducing the granularity of the composite fusing agent and increasing the reaction contact area and the reaction rate of the composite fusing agent in the melt treatment process.
The invention also relates to the application of the flux for purifying and refining the magnesium rare earth alloy melt in the preparation of the magnesium rare earth alloy; the composite treatment flux realizes the purification and refining treatment of the magnesium rare earth alloy melt in one step.
As an embodiment of the invention, the purifying and refining composite treatment flux is uniformly scattered on the surface of the magnesium melt, stirred up and down for 5-10 min after the magnesium melt is melted (by using a stirring spoon), and then directly cast after standing for 5-10 min after refining is completed. Therefore, on one hand, the refining agent can be fully contacted and reacted with the inclusions in the melt, and the Zr salt can be promoted to rapidly react to generate fine and dispersed Zr particles. Because the density of the composite flux is high, the speed of the entrained and mixed matter together settling is high, and the required standing time is only 5-10 min. The purification and refinement treatment of the melt can be simultaneously completed by the one-step process, and then the melt is directly cast, so that the problems that the conventional magnesium rare earth alloy melt treatment needs repeated temperature rise and fall and is implemented step by step are solved.
According to one embodiment of the invention, the temperature of the magnesium alloy melt is 730-750 ℃. The addition amount of the purifying and refining composite treatment flux is 2-6% of the mass of the magnesium alloy melt. Therefore, the reaction of the composite flux can be promoted to the maximum extent, and the magnesium rare earth alloy melt is prevented from being seriously oxidized at high temperature. Meanwhile, the addition amount of the composite treatment flux of 2-6% can ensure that the purifying and refining effects are optimal, and simultaneously, the phenomenon that new flux impurities are formed in the melt due to the excessively high addition amount of the flux is avoided.
Compared with the prior art, the invention has the following beneficial effects:
1. on the basis of ensuring the content of magnesium chloride required by removing oxide inclusions, zirconium sulfate is introduced as a catalyst for impurity removal reaction of a refining agent, so that the speed of wetting and capturing inclusions by the refining agent is increased; meanwhile, barium sulfate which has higher density and can adjust the spreading performance of the fusing agent is introduced into the fusing agent, so that the density of the fusing agent is increased, and the wetting and capturing speed and the sinking speed of the occluded foreign substances are improved; this reduces the required standing time after melt refining in a combined manner in two ways.
2. On the basis of the components of the designed novel refining agent, low-melting-point and high-density Zr salt components such as zirconium diboride and zirconium sulfate with low melting points are added, so that the flux can play a good composite effect of refining treatment at the same time of refining; thus, through the use of the purifying and refining composite treatment flux, the purifying and refining treatment of the magnesium rare earth alloy melt can be realized under the condition of no need of repeatedly heating and cooling the melt in the same process link.
3. The zirconium sulfate introduced into the flux of the present invention will slowly decompose into a small amount of zirconium dioxide at the high temperature of the melt. Thus, the zirconium dioxide in the melt can reduce the activity of the zirconium dioxide in the oxidation reaction equation of Zr, thereby reducing the oxidation tendency of Zr in the magnesium melt and improving the yield of Zr when Zr salt is refined.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a metallographic microstructure of Mg-8Gd-3Y-0.5Zr magnesium rare earth alloy treated by the composite flux in the invention (standing time 10 min);
FIG. 2 is a metallographic microstructure of Mg-8Gd-3Y-0.5Zr magnesium rare earth alloy prepared by a conventional magnesium rare earth alloy melt step-by-step treatment process (standing time 10 min).
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
The composite flux is adopted to carry out melt processing by taking Mg-8Gd-3Y-0.5Zr (wt%) magnesium rare earth alloy as an example.
The purifying and refining composite treatment flux comprises the following components in percentage by mass: 30% magnesium chloride, 8% potassium chloride, 8% sodium chloride, 16% barium chloride, 8% barium sulfate, 15% zirconium diboride, 15% zirconium sulfate.
Adding magnesium chloride into a crucible, heating to 720 ℃ to enable the magnesium chloride to reach a molten state, then adding potassium chloride, sodium chloride, barium chloride and barium sulfate in batches in sequence, fully stirring and casting after all salts are completely molten to obtain a refining agent composite salt block, then mashing the refining agent composite salt block and sieving by a 200-mesh sieve, then putting the sieved refining agent composite salt powder, zirconium diboride and zirconium sulfate into a ball mill, taking out after ball milling for 5 hours, and sieving by a 50-mesh sieve again to obtain the purification and refinement composite treatment flux.
When the temperature of the magnesium alloy melt is 730 ℃, the purifying and refining composite treatment flux is uniformly scattered on the surface of the magnesium melt, after the magnesium alloy melt is melted, a stirring spoon is used for stirring up and down for 5min, and after the refining is finished, the magnesium alloy melt is directly cast after standing for 5 min. The addition amount of the flux for the purification and refinement composite treatment is 2 percent of the mass of the magnesium alloy melt.
And after all the processes are finished, sampling and observing the casting. As shown in FIG. 1, the inclusion content in the metallographic structure was 0.1%, which was 500% lower than that before the treatment. The as-cast alloy grain size was about 50 μm, which was 300% lower than the grain size before the treatment. The purifying and refining effects of the composite flux are good, and the service requirements are met.
Example 2
The composite flux is adopted to carry out melt processing by taking Mg-8Gd-3Y-0.5Zr (wt%) magnesium rare earth alloy as an example.
The purifying and refining composite treatment flux comprises the following components in percentage by mass: 40% magnesium chloride, 10% potassium chloride, 10% sodium chloride, 15% barium chloride, 5% barium sulfate, 10% zirconium diboride, 10% zirconium sulfate.
Adding magnesium chloride into a crucible, heating to 730 ℃ to enable the magnesium chloride to reach a molten state, then adding potassium chloride, sodium chloride, barium chloride and barium sulfate in batches in sequence, fully stirring and casting after all salts are completely molten to obtain a refining agent composite salt block, then mashing the refining agent composite salt block and sieving by a 200-mesh sieve, then putting the sieved refining agent composite salt powder, zirconium diboride and zirconium sulfate into a ball mill, taking out after ball milling for 6 hours, and sieving by a 100-mesh sieve again to obtain the purification and refinement composite treatment flux.
When the temperature of the magnesium alloy melt is 735 ℃, the purifying and refining composite treatment flux is uniformly scattered on the surface of the magnesium melt, after the magnesium alloy melt is melted, a stirring spoon is used for stirring up and down for 6min, and after the refining is finished, the magnesium alloy melt is directly cast after standing for 6 min. The addition amount of the flux for the purification and refinement composite treatment is 3 percent of the mass of the magnesium alloy melt.
And after all the processes are finished, sampling and observing the casting. The inclusion content in the metallographic structure is 0.15 percent, and is reduced by 400 percent compared with the inclusion content before the treatment. The as-cast alloy grain size was about 60 μm, which was 270% lower than the grain size before the treatment. The purifying and refining effects of the composite flux are good, and the service requirements are met.
Example 3
The composite flux is adopted to carry out melt processing by taking Mg-8Gd-3Y-0.5Zr (wt%) magnesium rare earth alloy as an example.
The purifying and refining composite treatment flux comprises the following components in percentage by mass: 34% magnesium chloride, 10% potassium chloride, 10% sodium chloride, 16% barium chloride, 6% barium sulfate, 12% zirconium diboride, 12% zirconium sulfate.
Adding magnesium chloride into a crucible, heating to 740 ℃ to enable the magnesium chloride to reach a molten state, then adding potassium chloride, sodium chloride, barium chloride and barium sulfate in batches in sequence, fully stirring and casting after all salts are completely molten to obtain a refining agent composite salt block, then mashing the refining agent composite salt block and sieving by a 200-mesh sieve, then putting the sieved refining agent composite salt powder, zirconium diboride and zirconium sulfate into a ball mill, taking out after ball milling for 8h, and sieving by a 150-mesh sieve again to obtain the purification and refinement composite treatment flux.
When the temperature of the magnesium alloy melt is 740 ℃, the purifying and refining composite treatment flux is uniformly scattered on the surface of the magnesium melt, after the magnesium alloy melt is melted, a stirring spoon is used for stirring up and down for 7min, and after the refining is finished, the magnesium alloy melt is directly cast after standing for 7 min. The addition amount of the flux for the purification and refinement composite treatment is 4 percent of the mass of the magnesium alloy melt.
And after all the processes are finished, sampling and observing the casting. The inclusion content in the metallographic structure is 0.11 percent, and is reduced by 360 percent compared with the inclusion content before the treatment. The as-cast alloy grain size was about 55 μm, which was 280% lower than the grain size before the treatment. The purifying and refining effects of the composite flux are good, and the service requirements are met.
Example 4
The composite flux is adopted to carry out melt processing by taking Mg-4Y-2Nd-1Gd-0.5Zr (wt%) magnesium rare earth alloy as an example.
The purifying and refining composite treatment flux comprises the following components in percentage by mass: 32% magnesium chloride, 12% potassium chloride, 12% sodium chloride, 16% barium chloride, 6% barium sulfate, 11% zirconium diboride, 11% zirconium sulfate.
Adding magnesium chloride into a crucible, heating to 750 ℃ to enable the magnesium chloride to reach a molten state, then adding potassium chloride, sodium chloride, barium chloride and barium sulfate in batches in sequence, fully stirring and casting after all salts are completely molten to obtain a refining agent composite salt block, then mashing the refining agent composite salt block and sieving by a 200-mesh sieve, then putting the sieved refining agent composite salt powder, zirconium diboride and zirconium sulfate into a ball mill, taking out after ball milling for 10 hours, and sieving by the 200-mesh sieve again to obtain the purification and refinement composite treatment flux.
When the temperature of the magnesium alloy melt is 750 ℃, the purifying and refining composite treatment flux is uniformly scattered on the surface of the magnesium alloy melt, after the magnesium alloy melt is melted, a stirring spoon is used for stirring up and down for 10min, and after the refining is finished, the magnesium alloy melt is directly cast after standing for 10 min. The addition amount of the flux for the purification and refinement composite treatment is 6 percent of the mass of the magnesium alloy melt.
And after all the processes are finished, sampling and observing the casting. The inclusion content in the metallographic structure is 0.11 percent, and is reduced by 360 percent compared with the inclusion content before the treatment. The as-cast alloy grain size was about 55 μm, which was 280% lower than the grain size before the treatment. The purifying and refining effects of the composite flux are good, and the service requirements are met.
Comparative example 1
The melting process and alloy composition of this comparative example are substantially the same as example 1, except that: the purifying and refining composite treatment flux is not used, and the existing JDMJ flux is refined and then refined by using Mg-Zr intermediate alloy. The method employed is essentially identical to the procedure in current industrial practice, namely: mg-30Zr (30 means mass percent) master alloy is added to the magnesium alloy melt at 790 ℃ and stirred well. After the refining treatment is finished, after the temperature of the magnesium alloy melt is reduced to 740 ℃, the JDMJ flux is uniformly scattered on the surface of the magnesium melt, after the magnesium alloy melt is melted, the magnesium alloy melt is stirred up and down for 10min by a stirring spoon, and after the refining is finished, the magnesium alloy melt is directly cast after standing for a period of time.
The timing sampling shows that the inclusion content of the magnesium melt can be reduced to below 0.2 percent only by standing for more than 30 min. However, the refining effect of Zr begins to obviously decline from 10min, and when the casting is left standing for 10min as shown in FIG. 2, although the good refining effect can be ensured, a large amount of inclusions exist in the casting. The purification and refinement in the magnesium rare earth alloy melt treatment process are carried out step by step, so that the melt treatment efficiency is low, and the purification and refinement treatment effects are not ideal.
Comparative example 2
The melting process and alloy composition of this comparative example are substantially the same as example 2, except that: no barium sulfate is added, and the mass of other components is kept unchanged.
And after all the processes are finished, sampling and observing the casting. The as-cast alloy grain size is about 60 μm. The refining effect is good, but a small amount of impurities exist in the metallographic structure, and the purifying effect is not good. The main reason is that the density of the refining agent is reduced when no barium sulfate is added, so that the sinking speed of the refining agent is reduced, and the refining effect is greatly reduced under the same standing time.
Comparative example 3
The melting process and alloy composition of this comparative example are substantially the same as example 2, except that: the barium sulfate is replaced by the same amount of barium chloride, and the mass of other components is kept unchanged.
And after all the processes are finished, sampling and observing the casting. The as-cast alloy grain size was about 65 μm. The refining effect is good, but a small amount of impurities exist in the metallographic structure, and the purifying effect is not good. The main reason is that the addition of barium sulfate not only can increase the density of the flux, but also can adjust the viscosity and the spreading performance of the flux at high temperature. The refining agent lacking barium sulfate has overlarge viscosity on the surface of the high-temperature melt, is not easy to capture impurities, and greatly weakens the refining effect under the same standing time.
Comparative example 4
The melting process and alloy composition of this comparative example are substantially the same as example 3, except that: in the flux of the comparative example, zirconium diboride and zirconium sulfate were not added, the proportions of the other components were unchanged, and a Mg-Zr master alloy was used in place of the Zr salt.
After all the processes are finished, the grain size of the cast structure is about 150 μm under the premise of standing for the same time. The refining effect is poor, and the main reason is that when the conventional Mg-Zr intermediate alloy is adopted to refine the melt, Zr cores with large grain size and large density can rapidly settle in the refining and standing process to cause the decline of the refining effect.
Comparative example 5
The melting process and alloy composition of this comparative example are substantially the same as example 4, except that: zirconium chloride was used instead of zirconium sulfate.
And after all the processes are finished, sampling and testing the casting. More inclusions are found in the metallographic structure. The main reason is that the zirconium sulfate can not only introduce Zr element into the melt to realize refining, but also can be used as a catalyst of a purification reaction, and the zirconium sulfate can accelerate the wetting and capturing speed of the flux to the inclusion. After zirconium chloride is used for replacing zirconium sulfate, the speed of wetting and capturing the inclusions by the flux is reduced, and the refining effect is greatly weakened under the same standing time.
Comparative example 6
The melting process and alloy composition of this comparative example are substantially the same as example 4, except that: the zirconium sulfate was replaced with potassium fluorozirconate.
And after all the processes are finished, sampling and testing the casting. More inclusions are found in the metallographic structure. The main reason is that the zirconium sulfate can not only introduce Zr element into the melt to realize refining, but also can be used as a catalyst of a purification reaction, and the zirconium sulfate can accelerate the wetting and capturing speed of the flux to the inclusion. After the zirconium sulfate is replaced by the potassium fluozirconate, the speed of wetting and capturing the inclusion by the flux is reduced, and the refining effect is greatly weakened under the same standing time.
Comparative example 7
The melting process and alloy composition of this comparative example are substantially the same as example 4, except that: the zirconium diboride is replaced with a low density zirconium chloride.
And after all the processes are finished, sampling and testing the casting. More inclusions are found in the metallographic structure, more iron elements appear in ICP detection, the iron removal effect is poor, and the corrosion performance of the alloy is poor. The main reasons are that the lower density zirconium chloride can reduce the density of the refining agent, the capturing and settling capacity of the composite flux to the impurities in the melt is reduced, meanwhile, the refining agent is poor in iron removal effect due to the fact that the refining agent is lack of boron, and the refining effect is greatly reduced under the same standing time.
Comparative example 8
The melting process and alloy composition of this comparative example are substantially the same as example 4, except that: zirconium diboride was replaced with potassium tetraborate.
After all the processes are finished, the grain size of the cast structure is about 170 μm under the premise of standing for the same time. The refining effect is poor, and the main reason is that after zirconium diboride containing Zr is replaced by potassium tetraborate containing no Zr, although boron element can be introduced into the melt, the total Zr content of the composite flux is reduced, so that the refining effect of the alloy is poor.
Comparative example 9
The melting process and the alloy components in the comparative example are basically the same as those in the example 4, except that the components (mass percentage) of the purifying and refining composite treatment flux are adjusted as follows: 40% magnesium chloride, 13% potassium chloride, 10% sodium chloride, 15% barium chloride, 4% barium sulfate, 9% zirconium diboride, 9% zirconium sulfate.
After all the processes are finished, the grain size of the cast structure is about 180 mu m under the premise of standing for the same time. The refining effect is poor, and the inclusion content in the alloy is as high as 0.5 percent, mainly because the unreasonable mass ratio of the components reduces the working performance of the composite flux, so that the refining and purifying effects are weakened.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (9)
1. The magnesium rare earth alloy melt purification and refinement composite treatment flux is characterized by comprising the following components in percentage by mass: 30-40% of magnesium chloride, 8-15% of potassium chloride, 8-15% of sodium chloride, 15-20% of barium chloride, 5-8% of barium sulfate, 10-15% of zirconium diboride and 10-15% of zirconium sulfate.
2. The magnesium rare earth alloy melt purification and refinement composite treatment flux according to claim 1, wherein the magnesium chloride, potassium chloride, sodium chloride, barium chloride and barium sulfate are melted, mixed, cooled and solidified to obtain a refining agent composite salt block, and then the prepared refining agent composite salt block, zirconium diboride and zirconium sulfate are mixed in a ball mill to be fully mixed, and the purification and refinement composite treatment flux is prepared after sieving.
3. The magnesium rare earth alloy melt purification and refinement composite treatment flux according to claim 2, wherein the melt mixing comprises: adding magnesium chloride, heating to 720-750 ℃ to enable the magnesium chloride to reach a molten state, then adding potassium chloride, sodium chloride, barium chloride and barium sulfate in batches in sequence, fully stirring after all salts are completely molten, and casting to obtain the refining agent composite salt block.
4. The magnesium rare earth alloy melt purification and refinement composite treatment flux according to claim 2, wherein the mixing performed in the ball mill comprises: firstly, crushing and sieving the refining agent composite salt block, then putting the sieved refining agent composite salt powder, zirconium diboride and zirconium sulfate into a ball mill, carrying out ball milling for 5-10 h, taking out, and sieving again to obtain the purification and refinement composite treatment flux.
5. The magnesium rare earth alloy melt purification and refinement composite treatment flux according to claim 4, wherein the sieving is performed by a 50-200 mesh sieve.
6. The application of the magnesium rare earth alloy melt purification and refinement composite treatment flux as defined in claim 1 in the preparation of magnesium rare earth alloy melt; the composite treatment flux realizes the purification and refining treatment of the magnesium rare earth alloy melt in one step.
7. The application of the magnesium melt refining flux as claimed in claim 6, wherein the purifying and refining composite treatment flux is uniformly scattered on the surface of the magnesium melt, stirred up and down for 5-10 min after the magnesium melt is melted, and directly cast after standing for 5-10 min after refining is completed.
8. The use according to claim 6, wherein the magnesium alloy melt temperature is 730 to 750 ℃.
9. The application of claim 6, wherein the addition amount of the flux for the purification and refinement composite treatment is 2-6% of the mass of the magnesium alloy melt.
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