Efficient Zr-containing grain refiner for magnesium alloy and application of efficient Zr-containing grain refiner

Abstract

The invention discloses an efficient Zr-containing grain refiner for magnesium alloy and application of the efficient Zr-containing grain refiner. In particular to a magnesium alloy efficient Zr-containing grain refiner, the Zr-containing grain refiner comprises Zr and other alloy elements, and the other alloy elements are selected from one or more of Zn and Ca. The invention further discloses application of the Zr-containing grain refiner in refining treatment of magnesium alloy. The low-melting-point binary or multi-element Zr-containing intermediate alloy grain refiner is prepared through the method, the magnesium alloy melt is refined, rapid dissolution and diffusion of Zr in the magnesium alloy melt can be achieved at the low Zr alloying temperature, the refining effect of Zr on magnesium alloy is greatly improved, the refining decline effect of Zr is improved, and the magnesium alloy refining effect is improved. And the technical scheme is simple, and is very suitable for industrial popularization and application.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy casting technology, and specifically to a magnesium alloy grain refiner, and more particularly, to a high-efficiency Zr-containing grain refiner for magnesium alloys and its application. Background Technology

[0002] Magnesium alloys possess characteristics such as low density, high specific strength and specific stiffness, and good damping and vibration reduction properties, making them promising candidates for lightweight equipment in the aerospace and transportation sectors. Grain refinement can simultaneously improve the strength and toughness of magnesium alloys, as well as their casting process performance, making it a crucial step in the magnesium alloy casting process. For magnesium alloys lacking elements such as Al, Mn, Si, and Fe, Zr is often used as a grain refiner. In practical applications, Mg-Zr master alloys are primarily used as Zr carriers for Zr addition refinement.

[0003] However, when using conventional Mg-Zr master alloys to refine magnesium alloy melts, problems such as unstable refining effects and low Zr yield arise. The main reason is that Zr has extremely low solubility in Mg (almost zero at room temperature). Zr in Mg-Zr master alloys mainly exists as undissolved pure Zr particles (melting point as high as 1855℃). These high-melting-point Zr particles dissolve slowly and settle quickly in molten magnesium, severely reducing the grain refining effect and Zr yield. Therefore, industrially, methods such as increasing the Zr addition temperature and applying mechanical stirring of the melt are often used to promote Zr dissolution. However, magnesium alloys are chemically very reactive, and these methods can cause oxidation and combustion of the melt. Therefore, there is an urgent need to develop new Zr refining processes to improve the grain refining effect of magnesium alloys.

[0004] Some researchers have used large plastic deformation methods to pre-crush Zr particles and agglomerates in Mg-Zr master alloys, thereby promoting the dispersion and dissolution of Zr in molten magnesium during the refinement process, with excellent results. Patent CN201810186568.5 discloses a pretreatment method for Mg-Zr master alloys based on friction stir processing, which effectively disperses Zr agglomerates in commercial Mg-30wt%Zr master alloys through friction stir processing. The literature Grain refinement of pure magnesium using rolled ZIRMAX (R) master alloy (Mg-33.3Zr) (Symposium on Magnesium Technology, 2003; pp215-220) describes a rolling pretreatment of Mg-30wt%Zr master alloys, in which Zr particles are crushed and refined after rolling, resulting in faster dissolution in molten magnesium and improved refinement effect. However, commercial Mg-Zr master alloys have a high Zr content and are brittle, making them prone to cracking during large plastic deformation processes, thus limiting their engineering applicability.

[0005] Unlike the aforementioned methods involving large plastic deformation, some researchers, employing metallurgical principles, have pre-emptively transformed particulate Zr into solute Zr in Mg-Zr alloys, thereby improving the Zr refinement effect on magnesium alloys. Patent ZL202010616056.5 discloses a pretreatment method involving multi-pass wire filling processing of Mg-Zr master alloy plates using high-frequency pulsed AC TIG welding, combined with rapid cooling after remelting. This method simultaneously disperses Zr agglomerates and transforms particulate Zr into solute Zr. Patent CN202111591163.8 discloses a method of heating and remelting Mg-Zr master alloys followed by heat treatment. This method increases the solute Zr content in the Mg-Zr master alloy and significantly refines the Zr particle size, improving its orientation within the Mg matrix. However, due to the extremely low maximum solid solubility of Zr in Mg, these methods still have certain limitations.

[0006] Some studies have employed other Zr-containing refining media to refine magnesium alloys. Patent CN202110413714.5 discloses a Zr-containing composite salt for refining magnesium alloy grains. Because the Zr-containing composite salt has a melting point of only 400-500℃, it melts rapidly upon addition to molten magnesium and reacts in situ with the magnesium to form fine Zr particles. The fine Zr particles formed by the reaction dissolve and diffuse quickly, resulting in a good refining effect. However, a small amount of molten salt and reaction byproducts remain in the molten magnesium, making them difficult to separate and severely reducing the purity of the melt.

[0007] In conclusion, it is very important to develop a novel and efficient Zr-containing grain refiner suitable for magnesium alloys. Summary of the Invention

[0008] To address the aforementioned shortcomings of existing technologies, the present invention aims to develop a novel Zr-containing grain refiner for magnesium alloys and its application. This Zr-containing grain refiner can very easily achieve rapid dissolution and diffusion of Zr in magnesium alloy melts, resulting in superior grain refinement. When using this refiner to refine magnesium alloy melts, it not only significantly improves the dissolution and diffusion rate of Zr in molten magnesium but also does not produce other side effects, effectively improving the grain refinement effect of magnesium alloys.

[0009] This invention proposes a novel Zr-containing grain refiner for magnesium alloys, which is completely different from existing Mg-Zr master alloy grain refiners in both chemical composition and practical application. Specifically, this invention is achieved through the following technical solution: In a first aspect, the present invention provides a high-efficiency Zr-containing grain refiner for magnesium alloys, wherein the Zr-containing grain refiner includes Zr and other alloying elements selected from at least one of Zn and Ca.

[0010] Preferably, the Zr-containing grain refiner includes Zr and Zn.

[0011] In some specific embodiments of the present invention, the Zr-containing grain refiner contains Zr at a mass percentage of 1%~19% or 58%~79%, with the balance being Zn. When the Zr content in the prepared Zr-Zn master alloy is in the range of 1%~19% or 58%~79%, the melting point of the formed master alloy can be controlled at 1020℃ or below, which is beneficial to the subsequent dissolution and diffusion of Zr in the magnesium melt.

[0012] As some specific embodiments of the present invention, when preparing Zr-containing grain refiners, one or more other alloying elements (Zn, Ca, etc.) need to be added to Zr first to prepare low-melting-point binary or multi-element Zr-containing grain refiners. After adding one or more other alloying elements to Zr, these added alloying elements can significantly reduce the melting point of Zr by forming low-melting-point intermetallic compounds with Zr or by acting as solute elements in Zr solid solutions, thus promoting its rapid dissolution and diffusion in magnesium melts. Zn and other alloying elements are several common alloying elements in magnesium alloys. The introduction of these elements will not affect the quality of magnesium melts; more importantly, compared with other common alloying elements, the addition of an equal mass of Zn is more significant in reducing the melting point of Zr solid solutions.

[0013] As some specific embodiments of the present invention, the preparation method of the Zr-containing grain refiner is selected from at least one of the following: thermal reduction method, molten salt electrolysis method, powder metallurgy method, and co-doping method. Using the thermal reduction method, molten salt electrolysis method, powder metallurgy method, or co-doping method to prepare the Zr-containing grain refiner can yield a more homogeneous Zr-containing grain refiner, which is beneficial for achieving sufficient dissolution and diffusion of the Zr-containing grain refiner in the magnesium alloy melt.

[0014] As some specific embodiments of the present invention, the high-efficiency Zr-containing grain refiner is prepared by molten salt electrolysis, specifically including the following steps: using a molten salt mixture formed by a mixture of Zr and other alloying elements as an electrolysis system, using a mixture of Zr and other alloying elements as raw materials, electrolysis is performed to obtain an intermediate alloy containing Zr and other alloying elements; the intermediate alloy is subjected to homogenization heat treatment to obtain the final product.

[0015] As some specific embodiments of the present invention, at least one of the following technical features is included: A1. The electrolytic cell used for electrolysis is a graphite electrolytic cell. The cathode of the graphite electrolytic cell is tungsten, the anode is graphite, and a molybdenum crucible is set below the tungsten cathode. Zr ions and other alloy ions (such as Zn ions) are reduced, co-deposited and alloyed on the tungsten cathode, and flow into the molybdenum crucible at the bottom along the tungsten cathode rod. A2. The other alloying elements include Zn, and the mixed fluoride includes ZnF2 and K2ZrF6; or, the mixed chloride includes ZnCl2 and ZrCl4; the mixed oxide includes ZnO and ZrO2; A3. The other alloying elements include Ca, the mixed chlorides include CaCl2 and ZrCl4; the mixed oxides include CaO and ZrO2; A4. The electrolysis temperature is 700~1000℃, and the DC voltage is 10~20V; A5. The homogenization heat treatment is performed at a temperature of 300~700℃ for a time of 1~30h.

[0016] When Zn is the other alloying element, the co-deposition efficiency of Zn and Zr is highest under the above process. Simultaneously, the entire electrolysis process is carried out within a molten salt solution, effectively isolating air and resulting in a Zr-Zn master alloy with uniform composition and low slag content. Finally, the Zr-Zn master alloy undergoes homogenization treatment to ensure sufficient diffusion of Zn within Zr, minimizing the melting point of the Zr solid solution, and eliminating Zn-Zr compounds formed during casting due to insufficient cooling rate and component segregation.

[0017] As some specific embodiments of the present invention, the preparation of the high-efficiency Zr-containing grain refiner by powder metallurgy includes the following steps: ball milling and mixing pure Zr powder with other alloying element metal powders, followed by multi-stage hot pressing and sintering to obtain a Zr-containing master alloy; extruding and deforming the Zr-containing master alloy to obtain the Zr-containing grain refiner.

[0018] As some specific embodiments of the present invention, at least one of the following technical features is included: B1. The particle size of the pure Zr powder and other alloying element metal powders is 100~200 mesh, and an inert gas is introduced for protection during ball milling and mixing. B2, the multi-stage hot pressing sintering includes: The first stage of hot pressing sintering involves a heating temperature of 800~1010℃, a heating time of 60~120min, and an axial pressure of 10~50MPa. The second stage of hot pressing sintering involves a heating temperature of 1015~1020℃, a heating time of 10~30min, and an axial pressure of 5~20MPa. B3. The extrusion temperature for the extrusion deformation is 800~1010℃.

[0019] Zr is chemically reactive. Ball milling Zr powder with Zn powder or other elemental metal powders under an inert gas atmosphere can inhibit oxidation of the alloy powder. Smaller alloy powder particle size facilitates uniform mixing of the two powders, resulting in a more homogeneous Zr-containing grain refiner. In the multi-stage hot-pressing sintering process, the first stage has a lower temperature and higher axial pressure, which promotes the closure of pores in the Zn and Zr powders while preventing severe oxidation at high temperatures. The second stage hot-pressing process has a temperature higher than the eutectic temperature of the Zr-Zn binary alloy. Under short-time, low-pressure holding conditions, the partially formed eutectic liquid phase in the alloy can fill the unclosed pores. This multi-stage hot-pressing sintering is beneficial for metallurgical bonding between Zr and Zn powders and for preparing a homogeneous Zr-Zn intermediate alloy grain refiner. Zr-Zn master alloys exhibit high thermoplasticity within the temperature range of 800–1010 °C, and no eutectic liquid phase is formed in the alloy. Hot extrusion of the hot-pressed Zr-Zn master alloy within this temperature range can effectively promote the closure of pores and defects in the alloy, while also breaking down and dissolving coarse second phases, which is beneficial for further improving the homogenization degree of the Zr-Zr master alloy grain refiner. Zr solid solutions in Zr-Zr master alloys with a higher degree of homogenization will have lower melting points because Zn mainly exists in the form of solid-solution atoms in the Zr matrix.

[0020] In a second aspect, the present invention provides the application of the Zr-containing grain refiner as described in any of the above claims in the refining treatment of magnesium alloys.

[0021] As some specific embodiments of the present invention, the magnesium alloy includes at least one of Mg-Zn, Mg-Gd, Mg-Y, Mg-Nd, Mg-La, and Mg-Ce alloys.

[0022] As some specific embodiments of the present invention, when refining magnesium alloys using the Zr-containing grain refiner, the process includes first adding the Zr-containing grain refiner to the magnesium alloy melt, and then adding a Mg-Zr master alloy to the magnesium alloy melt.

[0023] As some specific embodiments of the present invention, the mass of the Zr grain refiner is 70% to 90% of the Mg-Zr master alloy.

[0024] When using the Zr-containing grain refiner prepared according to this invention to refine the grains of magnesium alloys, Zr can fully dissolve and diffuse due to the low melting point of the Zr solid solution. Therefore, first using the Zr-containing grain refiner prepared according to this invention to refine the grains of magnesium alloys can significantly increase the Zr content in the magnesium alloy melt at a lower alloying temperature. Since Zr in commercial Mg-Zr master alloys mainly exists in the form of undissolved Zr particles, a small amount of commercial Mg-Zr master alloy is subsequently added to introduce more Zr heterogeneous nucleation particles into the melt. In this way, the growth-limiting effect of dissolved Zr solute atoms and the heterogeneous nucleation effect of undissolved Zr particles work together to achieve a better grain refinement effect. The Zr-containing grain refiner added is 70% to 90% of the mass of the commercial Mg-Zr master alloy, which can effectively ensure the ratio of solute Zr to particulate Zr in the magnesium alloy melt, which is conducive to achieving a better grain refinement effect.

[0025] As some specific embodiments of the present invention, the temperature at which the Zr grain refiner and Mn-Zr master alloy are added to the magnesium alloy melt is 700~800°C. The addition temperature of the Zr grain refiner is 30~50°C higher than that of the Mg-Zr master alloy. This is because the melting point of the Zr solid solution in the Zr grain refiner is low, and the higher alloying temperature allows for sufficient dissolution and diffusion of Zr. Commercial Mg-Zr master alloys contain a large number of undissolved Zr particles. At a lower addition temperature, these Zr particles are prevented from oxidizing, thus achieving a better heterogeneous nucleation effect.

[0026] As some specific embodiments of the present invention, the addition of the Zr grain refiner and the Mg-Zr master alloy results in a Zr mass percentage of 0.5% to 1% in the final magnesium alloy, wherein the mass percentage of solute Zr is ≥0.45%. Under such conditions of total Zr content and solute Zr content, the refining effect is optimal.

[0027] This invention optimizes both the chemical composition and application of the Zr grain refiner. Currently, the Zr in Mg-Zr master alloys mainly consists of pure Zr particles with a melting point as high as 1855℃. These particles are difficult to fully dissolve and diffuse at the conventional melting temperature of magnesium alloys (700~800℃), resulting in poor grain refinement. This invention, however, prepares a Zr-Zn master alloy by adding one or more alloying elements, such as Zn, to Zr. The addition of Zn lowers the melting point of the Zr matrix (e.g., when the Zn content is approximately 21 wt.%, the melting point of the Zr matrix decreases from 1855℃ to 1015℃), thereby reducing the temperature difference between the conventional melting temperature of magnesium alloys and the Zr solid solution, promoting rapid dissolution and diffusion of Zr in molten magnesium. It is worth noting that elements such as Zn have high solid solubility in Zr; the greater the amount of Zn added, the lower the melting point of the resulting Zr-containing solid solution. In this way, the high-melting-point, difficult-to-dissolve pure Zr particles in the original Mg-Zr master alloy are transformed into a low-melting-point, easily soluble Zr solid solution containing Zn. At the same time, the introduced Zn and other elements are commonly used alloying elements in magnesium alloys, and the added content is low, so it will not have a negative impact on the quality of the magnesium melt.

[0028] Secondly, regarding the application method and mechanism of action, existing Zr refining methods involve adding a Mg-Zr master alloy to the magnesium melt at a relatively high temperature (780~800℃) in a single step. This method primarily utilizes the high temperature of the melt to promote the dissolution of Zr particles in the Mg-Zr master alloy, thus achieving refining. In contrast, this invention first adds a novel Zn-Zr master alloy grain refiner to the magnesium alloy melt at a higher temperature, causing the low-melting-point Zr solid solution to dissolve rapidly and release Zr solute atoms. Then, a Mg-Zr master alloy is added at a lower temperature to replenish the Zr particles in the magnesium melt. As a result, the Zr solute atoms obtained from the dissolution of the Zn-Zr refiner exert a growth-limiting effect on Mg dendrites, while the Zr particles introduced by the Mg-Zr refiner provide sufficient heterogeneous nucleation sites for Mg dendrites. With the growth-limiting effect of solute Zr and the heterogeneous nucleation effect of particulate Zr working together, the potential for Zr to refine the grains of magnesium alloys is effectively realized.

[0029] It is evident that this invention can solve the bottleneck problem of poor grain refinement effect and significant fading effect caused by the difficulty in dissolving and diffusing high-melting-point pure Zr particles in Mg-Zr master alloys when using Mg-Zr master alloys for grain refinement treatment of magnesium alloys. Furthermore, it proposes a new approach to a highly efficient Zr-containing grain refiner for magnesium alloys and its application method.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1) The addition of alloying elements such as Zn to Zr in this invention significantly reduces the melting point of the Zr solid solution in the grain refiner. Therefore, when this grain refiner is used to refine magnesium alloy melt, the dissolution and diffusion of Zr in the grain refiner is accelerated, effectively improving the grain refinement effect of magnesium alloy.

[0031] 2) In the process of refining magnesium alloy melt, by adding Zr-containing grain refiner and commercial Mg-Zr master alloy sequentially and controlling the corresponding addition temperature, the relative content of solute Zr and particle Zr in magnesium alloy melt can be controlled, which is conducive to further improving the grain refinement effect.

[0032] 3) This invention does not require high-temperature stirring of the magnesium melt during the refining process, nor does it require complex plastic deformation or other pretreatment of the Mg-Zr master alloy. By preparing novel Zr-containing grain refiners such as Zr-Zn, the Zr refining effect of magnesium alloys is improved, which is very suitable for industrial promotion and application. Attached Figure Description

[0033] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The image shows the metallographic microstructure of the Mg-9Gd-3Y-0.5Zr-0.2Zn alloy prepared using a commercial Mg-Zr grain refiner in Example 1. Figure 2 The image shows the metallographic microstructure of the Mg-9Gd-3Y-0.5Zr-0.2Zn alloy prepared using the Zr-Zn grain refiner of the present invention in Example 1. Figure 3 The binary equilibrium phase diagram for Zn-Zr grain refiners. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0035] Example 1 Taking the smelting of a magnesium alloy of Mg-10wt%Gd-3wt%Y-1wt%Zn-0.5wt%Zr as an example, experiments were conducted in two groups.

[0036] I. Preparation of Zr-containing grain refiners The raw material calculation was based on a Zn-Zr master alloy containing 1% Zr. Electrolysis was performed in a graphite electrolytic cell using a molten salt mixture (ZnF2 and K2ZrF6 in a 2:1 mass ratio) to form an electrolytic system. The raw material consisted of oxides such as ZnO and ZrO2 (ZnO and ZrO2 in a 12:1 mass ratio). The electrolysis temperature was 700℃ and the DC voltage was 10V. Zn and Zr ions were reduced, co-deposited, and alloyed at the tungsten cathode, flowing down the tungsten cathode rod into a molybdenum crucible at the bottom. The collected Zr-containing grain refiner was subjected to a homogenization heat treatment at 300℃ for 30 hours.

[0037] II. Melting and casting Mg-10wt%Gd-3wt%Y-1wt%Zn-0.5wt%Zr magnesium alloy Group 1: The first group of smelting experiments pre-prepared pure Mg, pure Zn, Mg-25wt%Y, Mg-25wt%Gd, and Mg-30wt%Zr master alloys according to the target composition and proportions, along with the Zr-containing grain refiner prepared in the aforementioned steps. First, the Zr-containing grain refiner prepared in the first step was added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The mass of the Zr-containing grain refiner added was 70% of that of the commercial Mg-30wt%Zr master alloy. The addition temperature of the Zr-containing grain refiner was 800℃, and the addition temperature of the commercial Mg-30wt%Zr master alloy was 770℃. Metallographic grain size statistical analysis showed that the average grain size of the alloy prepared using the Zr-containing grain refiner of this invention was 39μm. Compositional testing results indicated that the Zr content of the solute in the first alloy was 90% of the total Zr content.

[0038] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the metallographic grain size statistical analysis, the average grain size of the alloy prepared in the second melting experiment was 87μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 30% of the total Zr content.

[0039] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, and significantly increase the Zr content of the solute in the alloy and the grain refinement effect.

[0040] like Figure 1 The image shown is a metallographic microstructure of the alloy prepared using a commercially available Mg-Zr grain refiner in Group 2; as shown... Figure 2 The image shows the metallographic microstructure of the alloy prepared using the Zr-Zn grain refiner in Group 1. It is clearly visible that the alloy prepared using the Zr-Zn grain refiner in Group 1 has significantly finer grains, indicating a better grain refinement effect.

[0041] Example 2 Taking the smelting of a magnesium alloy of Mg-4wt%Y-2wt%Nd-1wt%Gd-1wt%Zn-0.5wt%Zr as an example, experiments were conducted in two groups.

[0042] I. Preparation of Zr-containing grain refiners The raw material calculation was based on a Zn-Zr master alloy with a Zr content of 19%. A molten salt mixture consisting of a mixed fluoride (ZnF2 and K2ZrF6, mass ratio of ZnF2 to K2ZrF6) was used as the electrolysis system in a graphite electrolytic cell. Electrolysis was performed using oxides including ZnO and ZrO2 (ZnO to ZrO2, mass ratio of ZnO to ZrO2, 5:1) as raw materials at a temperature of 800℃ and a DC voltage of 15V. Zn and Zr ions were reduced, co-deposited, and alloyed at the tungsten cathode, flowing down the tungsten cathode rod into a molybdenum crucible at the bottom. The collected Zr-containing grain refiner was subjected to a homogenization heat treatment at 500℃ for 15 hours.

[0043] II. Melting and casting Mg-4wt%Y-2wt%Nd-1wt%Gd-1wt%Zn-0.5wt%Zr magnesium alloy Group 1: The first group of smelting experiments pre-prepared pure Mg, pure Zn, Mg-25wt%Y, Mg-25wt%Gd, Mg-25wt%Nd, and Mg-30wt%Zr master alloys according to the target composition and proportions, as well as the Zr-containing grain refiner prepared in the aforementioned steps. First, the Zr-containing grain refiner was added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The mass of the Zr-containing grain refiner added was 80% of that of the commercial Mg-30wt%Zr master alloy. The addition temperature of the Zr-containing grain refiner was 770℃, and the addition temperature of the commercial Mg-30wt%Zr master alloy was 730℃. Metallographic grain size statistical analysis showed that the average grain size of the alloy prepared using the Zr-containing grain refiner of this invention was 51μm. Compositional testing results indicated that the Zr content of the solute in the first alloy was 91% of the total Zr content.

[0044] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the metallographic grain size statistical analysis, the average grain size of the alloy prepared in the second melting experiment was 102μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 35% of the total Zr content.

[0045] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, significantly increasing the Zr content of the solute in the alloy and the grain refinement effect. Figure 3 As shown, when the Zr content in the Zn-Zr master alloy is 19%, the melting point of the Zn-Zr master alloy is less than 1100℃, which is much lower than the melting point of pure Zr particles in the Mg-Zr master alloy (1855℃). This can help Zr to dissolve and diffuse rapidly in the magnesium liquid, and help improve the grain refinement effect of Zr on magnesium alloy.

[0046] Example 3 Taking the smelting of Mg-6wt%Zn-0.5wt%Zr magnesium alloy as an example, experiments were conducted in two groups.

[0047] I. Preparation of Zr-containing grain refiners The raw material calculation was based on a Zn-Zr master alloy with a Zr content of 58%. A molten salt mixture consisting of a mixed chloride of ZnCl2 and ZrCl4 (ZnCl2 to ZrCl4 mass ratio of 2:1) was used as the electrolysis system in a graphite electrolytic cell. Electrolysis was performed using oxides including ZnO and ZrO2 (ZnO to ZrO2 mass ratio of 1:1) at a temperature of 1000℃ and a DC voltage of 20V. Zn and Zr ions were reduced, co-deposited, and alloyed at the tungsten cathode, flowing down the tungsten cathode rod into a molybdenum crucible at the bottom. The collected Zr-containing grain refiner was subjected to a homogenization heat treatment at 700℃ for 1 hour.

[0048] II. Melting and casting Mg-6wt%Zn-0.5wt%Zr magnesium alloy Group 1: The first group of smelting experiments pre-prepared pure Mg, pure Zn, a Mg-30wt%Zr master alloy, and the Zr-containing grain refiner prepared in the aforementioned steps according to the target composition and proportions. First, the Zr-containing grain refiner was added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The mass of the Zr-containing grain refiner added was 90% of that of the commercial Mg-30wt%Zr master alloy. The addition temperature of the Zr-containing grain refiner was 730℃, and the addition temperature of the commercial Mg-30wt%Zr master alloy was 700℃. Metallographic grain size statistical analysis showed that the average grain size of the alloy prepared using the Zr-containing grain refiner of this invention was 78μm. Compositional testing results indicated that the Zr content of the solute in the first alloy was 91% of the total Zr content.

[0049] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the metallographic grain size statistical analysis, the average grain size of the alloy prepared in the second melting experiment was 113μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 23% of the total Zr content.

[0050] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, and significantly increase the Zr content of the solute in the alloy and the grain refinement effect.

[0051] Example 4 Taking the smelting of a Mg-2wt%La-2wt%Ce-1wt%Ca-0.5wt%Zr magnesium alloy as an example, experiments were conducted in two groups.

[0052] I. Preparation of Zr-containing grain refiners The raw material calculation was based on a Zr-Ca master alloy with a Ca content of 20%. A molten salt mixture consisting of a mixed chloride of CaCl2 and ZrCl4 (mass ratio of CaCl2 to ZrCl4 1:1) was used as the electrolysis system in a graphite electrolytic cell. Electrolysis was performed using oxides including CaO and ZrO2 (mass ratio of CaO to ZrO2 1:4) at a temperature of 1000℃ and a DC voltage of 20V. Ca and Zr ions were reduced, co-deposited, and alloyed at the tungsten cathode, flowing down the tungsten cathode rod into a molybdenum crucible at the bottom. The collected Zr-containing grain refiner was subjected to a homogenization heat treatment at 700℃ for 1 hour.

[0053] II. Melting and casting Mg-2wt%La-2wt%Ce-1wt%Ca-0.5wt%Zr magnesium alloy Group 1: The first group of smelting experiments followed a pre-prepared composition of pure Mg, Mg-25wt%La, Mg-25wt%Ce, Mg-30wt%Zr, Mg-10wt%Ca master alloys, and the Zr-containing grain refiner prepared in the aforementioned steps. First, the Zr-containing grain refiner was added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The Zr-containing grain refiner was added at 90% of the mass of the commercial Mg-30wt%Zr master alloy. The addition temperature of the Zr-containing grain refiner was 730℃, and the addition temperature of the commercial Mg-30wt%Zr master alloy was 700℃. Metallographic grain size statistical analysis showed that the alloy prepared using the Zr-containing grain refiner of this invention had an average grain size of 77μm. Compositional testing results indicated that the Zr content in the first alloy composition was 92% of the total Zr content.

[0054] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the metallographic grain size statistical analysis, the average grain size of the alloy prepared in the second melting experiment was 122μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 21% of the total Zr content.

[0055] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, and significantly increase the Zr content of the solute in the alloy and the grain refinement effect.

[0056] Example 5 Taking the smelting of a magnesium alloy of Mg-10wt%Gd-3wt%Y-1wt%Zn-0.5wt%Zr as an example, experiments were conducted in two groups.

[0057] I. Preparation of Zr-containing grain refiners Pure Zr powder and pure Zn powder were ball-milled and mixed. The Zr powder content was 1% by mass, and the particle size of the alloy powder was 100 mesh. An inert gas was introduced for protection during the ball milling process. The mixed alloy powder was then subjected to multi-stage hot pressing sintering. The first stage heating temperature was 800℃, the heating time was 60 min, and the axial pressure was 10 MPa. The second stage heating temperature was 1015℃, the heating time was 10 min, and the axial pressure was 5 MPa. The resulting Zr-containing master alloy was extruded and deformed at 800℃ to obtain a Zr-containing grain refiner.

[0058] II. Melting and casting Mg-10wt%Gd-3wt%Y-1wt%Zn-0.5wt%Zr magnesium alloy Group 1: The first group of smelting experiments pre-prepared pure Mg, pure Zn, Mg-25wt%Y, Mg-25wt%Gd, and Mg-30wt%Zr master alloys according to the target composition and proportions, along with the Zr-containing grain refiner prepared in the aforementioned steps. First, the Zr-containing grain refiner was added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The Zr-containing grain refiner was added at 70% of the mass of the commercial Mg-30wt%Zr master alloy. The addition temperature of the Zr-containing grain refiner was 800℃, and the addition temperature of the commercial Mg-30wt%Zr master alloy was 770℃. Metallographic grain size statistical analysis showed that the average grain size of the alloy prepared using the Zr-containing grain refiner of this invention was 42μm. Compositional testing results indicated that the Zr content of the solute in the first alloy was 87% of the total Zr content.

[0059] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the statistical analysis of the metallographic grain size, the average grain size of the alloy prepared in the second melting experiment was 79μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 25% of the total Zr content.

[0060] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, and significantly increase the Zr content of the solute in the alloy and the grain refinement effect.

[0061] Example 6 Taking the smelting of a magnesium alloy of Mg-4wt%Y-2wt%Nd-1wt%Gd-1wt%Zn-0.5wt%Zr as an example, experiments were conducted in two groups.

[0062] I. Preparation of Zr-containing grain refiners Pure Zr powder and pure Zn powder were ball-milled and mixed. The Zr powder content was 19% by mass, and the particle size of the alloy powder was 150 mesh. Inert gas was introduced for protection during ball milling. The mixed alloy powder was then subjected to multi-stage hot pressing sintering. The first stage heating temperature was 900℃, the heating time was 90 min, and the axial pressure was 30 MPa. The second stage heating temperature was 1017℃, the heating time was 20 min, and the axial pressure was 10 MPa. The resulting Zr-containing master alloy was extruded and deformed at a temperature of 900℃ to obtain a Zr-containing grain refiner.

[0063] II. Melting and casting Mg-4wt%Y-2wt%Nd-1wt%Gd-1wt%Zn-0.5wt%Zr magnesium alloy The first set of smelting experiments pre-configured pure Mg, pure Zn, Mg-25wt%Y, Mg-25wt%Gd, Mg-25wt%Nd, and Mg-30wt%Zr master alloys according to the target composition and proportions, along with the Zr-containing grain refiner prepared in the aforementioned steps. The Zr-containing grain refiner was first added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The Zr-containing grain refiner was added at 770℃, and the commercially available Mg-30wt%Zr master alloy was added at 730℃. Metallographic grain size statistical analysis showed that the alloy prepared using the Zr-containing grain refiner of this invention had an average grain size of 48 μm. Compositional testing results indicated that the Zr content in the first alloy composition was 82% of the total Zr content.

[0064] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the statistical analysis of the metallographic grain size, the average grain size of the alloy prepared in the second melting experiment was 98μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 29% of the total Zr content.

[0065] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, and significantly increase the Zr content of the solute in the alloy and the grain refinement effect.

[0066] Example 7 Taking the smelting of Mg-6wt%Zn-0.5wt%Zr magnesium alloy as an example, experiments were conducted in two groups.

[0067] I. Preparation of Zr-containing grain refiners Pure Zr powder and pure Zn powder were ball-milled and mixed, with the Zr powder comprising 79% by mass and the alloy powder having a particle size of 200 mesh. An inert gas was introduced for protection during the ball milling process. The mixed alloy powder was then subjected to multi-stage hot pressing sintering. The first stage heating temperature was 1010℃, the heating time was 120 min, and the axial pressure was 50 MPa; the second stage heating temperature was 1020℃, the heating time was 30 min, and the axial pressure was 20 MPa. The resulting Zr-containing master alloy was extruded and deformed at 1010℃ to obtain a Zr-containing grain refiner.

[0068] II. Melting and casting Mg-6wt%Zn-0.5wt%Zr magnesium alloy The first set of smelting experiments pre-configured pure Mg, pure Zn, a Mg-30wt%Zr master alloy, and the Zr-containing grain refiner prepared in the aforementioned steps, according to the target composition and proportions. The Zr-containing grain refiner was first added to the magnesium alloy melt, followed by the addition of a commercially available Mg-30wt%Zr master alloy. The Zr-containing grain refiner was added at 90% of the mass of the commercial Mg-30wt%Zr master alloy. The addition temperature of the Zr-containing grain refiner was 730℃, and the addition temperature of the commercial Mg-30wt%Zr master alloy was 700℃. Metallographic grain size statistical analysis showed that the alloy prepared using the Zr-containing grain refiner of this invention had an average grain size of 71 μm. Compositional testing results indicated that the Zr content of the solute in the first alloy composition was 92% of the total Zr content.

[0069] Group 2: The melting and casting conditions of the second melting experiment were the same as those of the first experiment. The only difference was that the Zr grain refiner used in the first experiment was replaced with a commercially available Mg-30wt%Zr master alloy. According to the metallographic grain size statistical analysis, the average grain size of the alloy prepared in the second melting experiment was 104μm. The composition test results showed that the Zr content of the solute in the alloy in the second group was 33% of the total Zr content.

[0070] The comparison of the above two sets of experimental results shows that when the magnesium alloy Zr-containing grain refiner of the present invention is used to refine the magnesium alloy melt, it can achieve rapid dissolution and diffusion of Zr in the magnesium alloy melt, and significantly increase the Zr content of the solute in the alloy and the grain refinement effect.

[0071] Comparative Example 1 The preparation method of this comparative example is basically the same as that of the Zr grain refiner in Example 1, and the same method is used in the process of melting and refining to prepare the alloy.

[0072] The only difference is that the mass percentage of Zn added is 35% when preparing the Zr-containing grain refiner. The target alloy was prepared using the prepared Zr-containing grain refiner, referring further to the method in Group 1 of Example 1.

[0073] Metallographic grain size statistical analysis revealed that the average grain size of the prepared alloy was 56 μm. Compositional analysis showed that the Zr content in the alloy was 77% of the total Zr content. This is because the added Zn exceeded the eutectic point of the Zr-Zn alloy, which affected the melting point of the Zr solid solution and thus the dissolution and diffusion rate of Zr in the magnesium alloy melt.

[0074] Comparative Example 2 The comparative example is basically the same as the method for preparing the Zr-containing grain refiner in Example 1, and the same method is used in the process of smelting and refining to prepare the alloy.

[0075] The only difference is that, in preparing the Zr-containing grain refiner, the Zr-containing grain refiner was not subjected to a homogenization heat treatment. Further referring to the method in Group 1 of Example 1, the target alloy was prepared using the Zr-containing grain refiner prepared in the above steps.

[0076] Metallographic grain size statistical analysis revealed that the average grain size of the alloy was 61 μm. Compositional analysis showed that the Zr content in the alloy was 67% of the total Zr content. This was because the lack of homogenization heat treatment resulted in Zn in the Zr grain refiner not existing entirely as solid solution atoms in the Zr matrix, but rather forming a partial Zn-Zr second phase. Consequently, the melting point of the Zr solid solution did not decrease significantly, thus affecting the dissolution and diffusion rate of Zr in the magnesium alloy melt.

[0077] Comparative Example 3 The preparation method of this comparative example is basically the same as that of the Zr grain refiner in Example 4, and the same method is used in the process of melting and refining to prepare the alloy.

[0078] The only difference is that, during the hot pressing sintering of the alloy powder, a multi-stage hot pressing sintering method was not used; the alloy powder was only heated at 800°C for 70 minutes to obtain a Zr-containing grain refiner. The target alloy was then prepared using the method described in Group 1 of Example 4.

[0079] Metallographic grain size statistical analysis revealed that the average grain size of the prepared alloy was 58 μm, and compositional analysis showed that the Zr content in the alloy was 71% of the total Zr content. This was because sintering was not performed above the eutectic temperature, resulting in not all Zn in the Zr grain refiner existing as solid solution atoms in the Zr matrix. Consequently, the melting point of the Zr solid solution did not decrease significantly, thus affecting the dissolution and diffusion rate of Zr in the magnesium alloy melt.

[0080] Comparative Example 4 The preparation method of this comparative example is basically the same as that of the Zr grain refiner in Example 4, and the same method is used in the process of melting and refining to prepare the alloy.

[0081] The only difference is that, when hot pressing and sintering the alloy powder, a multi-stage hot pressing and sintering method was not used; the alloy powder was only heated at 1015℃ for 70 minutes.

[0082] Because the heating time above the eutectic temperature was too long, a large amount of eutectic liquid phase was generated and escaped from the gap between the molds, resulting in the failure of the preparation of Zr grain refiner.

[0083] Comparative Example 5 The comparative example is prepared using the same method as the Zr grain refiner in Example 1, and the methods used in the melting and refining process for preparing the alloy are basically the same.

[0084] The only difference is that, when refining the alloy, the commercial Mg-30wt%Zr master alloy was not used, but the Zr-containing grain refiner prepared in this invention was used entirely.

[0085] Metallographic grain size statistical analysis revealed that the average grain size of the prepared alloy was 61 μm, and compositional analysis showed that the Zr content in the alloy was 89% of the total Zr content. This is because the number of Zr heterogeneous nucleation sites in the alloy melt was relatively small, resulting in a reduced grain refinement effect.

[0086] Comparative Example 6 The comparative example is prepared using the same method as the Zr grain refiner in Example 1, and the methods used in the melting and refining process for preparing the alloy are basically the same.

[0087] The only difference is that when refining the alloy, the addition temperature of both the Zr grain refiner and the commercial Mg-30wt%Zr master alloy is 800℃.

[0088] Metallographic grain size statistical analysis revealed that the average grain size of the prepared alloy was 58 μm. Compositional analysis showed that the Zr content in the alloy was 92% of the total Zr content. This is because the addition temperature of both the Zr grain refiner and the commercial Mg-30wt%Zr master alloy was relatively high, resulting in a large amount of Zr being oxidized and burned off, leading to a smaller number of Zr heterogeneous nucleation sites in the alloy melt and a reduced grain refinement effect.

[0089] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A highly efficient Zr-containing grain refiner for magnesium alloys, characterized in that, The Zr-containing grain refiner includes Zr and other alloying elements, wherein the other alloying elements are selected from at least one of Zn and Ca.

2. The Zr-containing grain refiner according to claim 1, characterized in that, The Zr-containing grain refiner includes Zr and Zn; In the Zr-containing grain refiner, the mass percentage of Zr is 1%~19% or 58%~79%, and the balance is Zn.

3. The Zr-containing grain refiner according to claim 1, characterized in that, The preparation method of the Zr-containing grain refiner is selected from at least one of the following: thermal reduction method, molten salt electrolysis method, powder metallurgy method, and doping method.

4. The Zr-containing grain refiner according to claim 3, characterized in that, The high-efficiency Zr-containing grain refiner is prepared by molten salt electrolysis, specifically including the following steps: using a molten salt mixture formed by a mixture of Zr and other alloying elements as an electrolysis system, and using a mixture of Zr and other alloying elements as raw materials to perform electrolysis to obtain an intermediate alloy containing Zr and other alloying elements; and subjecting the intermediate alloy to homogenization heat treatment to obtain the final product.

5. The Zr-containing grain refiner according to claim 4, characterized in that, Includes at least one of the following technical features: A1. The electrolytic cell used for electrolysis is a graphite electrolytic cell, with tungsten as the cathode and graphite as the anode. A2. The other alloying elements include Zn, and the mixed fluoride includes ZnF2 and K2ZrF6; or, the mixed chloride includes ZnCl2 and ZrCl4; the oxide includes ZnO and ZrO2; A3. The other alloying elements include Ca, the mixed chlorides include CaCl2 and ZrCl4; the mixed oxides include CaO and ZrO2; A4. The electrolysis temperature is 700~1000℃, and the DC voltage is 10~20V; A5. The homogenization heat treatment is performed at a temperature of 300~700℃ for a time of 1~30h.

6. The Zr-containing grain refiner according to claim 3, characterized in that, The preparation of the high-efficiency Zr-containing grain refiner by powder metallurgy includes the following steps: pure Zr powder and other elemental metal powders of alloying elements are ball-milled and mixed, and then subjected to multi-stage hot pressing sintering to obtain a Zr-containing master alloy; the Zr-containing master alloy is extruded and deformed to obtain the Zr-containing grain refiner.

7. The Zr-containing grain refiner according to claim 6, characterized in that, Includes at least one of the following technical features: B1. The particle size of the pure Zr powder and other alloying element metal powders is 100~200 mesh, and an inert gas is introduced for protection during ball milling and mixing. B2, the multi-stage hot pressing sintering includes: The first stage of hot pressing sintering involves a heating temperature of 800~1010℃, a heating time of 60~120min, and an axial pressure of 10~50MPa. The second stage of hot pressing sintering involves a heating temperature of 1015~1020℃, a heating time of 10~30min, and an axial pressure of 5~20MPa. B3. The extrusion temperature for the extrusion deformation is 800~1010℃.

8. The application of a Zr-containing grain refiner as described in any one of claims 1-7 in refining magnesium alloys; wherein the magnesium alloy comprises at least one of Mg-Zn, Mg-Gd, Mg-Y, Mg-Nd, Mg-La, and Mg-Ce alloys.

9. The application according to claim 8, characterized in that, When refining magnesium alloys using the Zr-containing grain refiner, the process includes first adding the Zr-containing grain refiner to the magnesium alloy melt, and then adding a Mg-Zr master alloy to the magnesium alloy melt.

10. The application according to claim 9, characterized in that, The mass of the Zr grain refiner is 70% to 90% of that of the Mg-Zr master alloy; And / or, the temperature at which Zr grain refiner and Mn-Zr master alloy are added to magnesium alloy melt is 700~800℃, and the addition temperature of Zr grain refiner is 30~50℃ higher than the addition temperature of Mg-Zr master alloy. And / or, the addition of the Zr grain refiner and Mg-Zr master alloy results in a Zr mass percentage of 0.5% to 1% in the final magnesium alloy, wherein the mass percentage of solute Zr is ≥0.45%.

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