Porous granular refining agent for smelting high-purity magnesium alloy and preparation method

Abstract

The invention discloses a porous granular refining agent for high-purity magnesium alloy smelting and a preparation method, and belongs to the technical field of metal melt purification, the refining agent is composed of a basic covering component, an active purification component and a pore-forming hydrogen removal component, the basic covering component comprises MgCl2, SrCl2, KCl and BaCl2, the active purification component comprises CaF2, B2O3, MoO3 and MnCO3, and the pore-forming hydrogen removal component is Na2SiF6; according to the method, efficient synergy of a refining agent porous structure and a purification and hydrogen removal function and synergistic interaction of melt deep purification and solidification structure optimization are achieved, controllable construction of the porous structure is achieved, and finally comprehensive improvement of the quality of the high-purity magnesium alloy melt is achieved; according to the invention, an ideal porous structure, deep purification capability and stable hydrogen removal characteristic are integrated, an upgraded solution capable of replacing a traditional refining agent is provided, and the core problems of insufficient purification efficiency, single function, limited melt quality improvement and the like in the prior art are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of metal melt purification technology, and in particular to porous granular refining agents and their preparation methods for high-purity magnesium alloy smelting. Background Technology

[0002] Magnesium alloys, as the most lightweight metallic structural materials, have shown broad application prospects in aerospace, rail transportation, and 3C products. Especially in the field of precision manufacturing, where the purity of materials is extremely important, high-purity magnesium alloys are gradually becoming key basic materials due to their excellent corrosion resistance and mechanical stability.

[0003] The smelting quality of high-purity magnesium alloys directly affects their final properties. Due to the extremely high chemical reactivity of magnesium, it readily reacts with oxygen and water vapor during the smelting process to form oxide inclusions and absorb hydrogen. These melt defects severely restrict the mechanical properties and corrosion resistance of the material. Therefore, it is essential to effectively purify the melt using refining agents. However, traditional block or powdered refining agents generally have inherent defects such as limited effective area and short action time, making it difficult to meet the stringent requirements of high-purity magnesium alloys for melt quality.

[0004] In recent years, porous refining agents have attracted attention due to their large specific surface area, theoretically capable of significantly improving purification efficiency. However, in practical applications, these refining agents face the challenge of insufficient pore structure stability, making them susceptible to damage during storage and use due to moisture absorption or mechanical action. Meanwhile, existing preparation techniques often treat the pore-forming process separately from the purification function; for example, simply adding a foaming agent, while creating pores, may introduce new impurities or affect the chemical stability of the refining agent system. Furthermore, some processes capable of forming porous structures are either complex and costly, or struggle to guarantee the uniformity and connectivity of the pore structure, hindering their industrial application.

[0005] Therefore, although porous structures are considered an effective way to improve the performance of refining agents, current technologies have not yet provided a complete solution that can both construct stable porous structures and achieve efficient purification functions while ensuring the feasibility of the preparation process. This technological gap severely restricts the development of high-purity magnesium alloy preparation processes. Summary of the Invention

[0006] The purpose of this invention is to provide a porous granular refining agent and its preparation method for high-purity magnesium alloy smelting, so as to solve the technical problem that existing refining agents cannot simultaneously achieve stable porous structure construction, deep purification and efficient hydrogen removal, and break through the technical bottleneck of traditional refining agents in that there is a mutual constraint between physical morphology optimization and chemical purification function, as well as the difficulty in balancing purification efficiency and pore stability.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] The key feature of the porous granular refining agent used in the smelting of high-purity magnesium alloys is that the refining agent is composed of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component; the basic covering component includes MgCl2, SrCl2, KCl, and BaCl2; the active purification component includes CaF2, B2O3, MoO3, and MnCO3; and the pore-forming and hydrogen-removing component is Na2SiF6.

[0009] Specifically, the aforementioned basic covering components include 24 to 32 parts of MgCl2, 8 to 12 parts of SrCl2, 25 to 35 parts of KCl, and 8 to 12 parts of BaCl2; the aforementioned active purification components include 8 to 12 parts of CaF2, 3 to 5 parts of B2O3, 0.6 to 2 parts of MoO3, and 0.5 to 1.5 parts of MnCO3; the aforementioned pore-forming and hydrogen-removing component is 3 to 8 parts of Na2SiF6.

[0010] Preferably, the mass ratio of SrCl2 to MgCl2 is 1:(2-4).

[0011] Preferably, the mass ratio of MoO3 to B2O3 is 1:(2-5).

[0012] Preferably, the mass ratio of Na2SiF6 to MnCO3 is (4-6):1.

[0013] A method for preparing the above-mentioned refining agent, the key feature of which is that it includes the following steps:

[0014] S1. Raw material dehydration: The above MgCl2, SrCl2, KCl, and BaCl2 are dehydrated by heating at 200℃~300℃ for 2h~4h, and the above CaF2, B2O3, MoO3, MnCO3, and Na2SiF6 are dehydrated by heating at 150℃~250℃ for 1h~3h.

[0015] S2. Mixing: Mix all the dehydrated raw materials from step S1 under an inert gas protection to obtain a mixed powder;

[0016] S3. Melt foaming: The mixed powder obtained in step S2 is heated to a molten state at 620℃~680℃ under inert gas protection, and stirred for 10min~25min.

[0017] S4. Cooling, shaping and crushing: The molten material after foaming in step S3 is quickly poured into a cooling mold and cooled to room temperature. Then it is crushed and screened to obtain a porous granular refining agent product.

[0018] Furthermore, the rotation speed of the above-mentioned heat preservation and stirring is 180 r / min to 220 r / min.

[0019] Furthermore, the heating temperature mentioned above is 630℃~650℃.

[0020] Furthermore, the aforementioned cooling mold is a metal mold, and forced air cooling is used after casting.

[0021] Furthermore, the inert gas mentioned above is argon.

[0022] The present invention discloses the following technical effects:

[0023] The porous granular refining agent for high-purity magnesium alloy smelting provided by this invention, through its unique integrated design of basic component reconstruction and porous structure-purification function, successfully overcomes the technical bottleneck of traditional refining agents in the mutual constraints between physical morphology optimization and chemical purification function, as well as the difficulty in simultaneously achieving purification efficiency and structural stability. Specific technical effects include:

[0024] First, this invention achieves a highly efficient synergistic effect between the porous structure of the refining agent and its purification and hydrogen removal functions. Addressing the core issues of limited effective surface area and insufficient interaction with the melt in existing refining agents, this invention innovatively utilizes the dual functional characteristics of the pore-forming and hydrogen-removing components. Through a precisely controlled foaming process, a stable porous structure with high porosity, large specific surface area, and suitable pore size distribution is constructed. This unique structure not only significantly increases the reaction interface between the refining agent and the magnesium melt, making the purification reaction more rapid and thorough, but also achieves an intrinsic unity between the pore-forming process and the hydrogen removal function, fundamentally solving the problem of low efficiency in traditional dense refining agents.

[0025] Secondly, this invention achieves a synergistic effect of deep melt purification and solidification microstructure optimization. The porous structure constructed in this invention provides ample interfaces and channels for the adsorption and capture of inclusions, enabling efficient removal of oxide inclusions and defects such as hydrogen from the melt, significantly improving melt purity. Simultaneously, the clean melt environment creates favorable conditions for grain refinement during alloy solidification. This effect of indirectly optimizing the microstructure through deep purification solves the performance fluctuation problem of high-purity magnesium alloys caused by insufficient melt purity.

[0026] Third, this invention achieves controllable construction of porous structures through precise design of components and processes. Addressing the shortcomings of traditional porous material preparation processes, such as complexity and poor structural stability, this invention establishes a stable and reliable preparation method through optimization of basic components and precise matching of process parameters, ensuring batch-to-batch stability and reproducibility of the refining agent product performance.

[0027] Fourth, the synergistic effect of the components in this invention ultimately achieves a comprehensive improvement in the quality of high-purity magnesium alloy melt. The carefully designed base coating components form a stable platform with suitable physicochemical properties, which, in conjunction with the modules possessing active purification and pore-forming hydrogen removal functions, creates a synergistic effect. The resulting refining agent exhibits superior comprehensive performance during the smelting process. The high-purity magnesium alloy castings refined in this way show substantial improvements in melt purity, solidification structure, room temperature and high temperature mechanical properties, and corrosion resistance, meeting the stringent material quality requirements of the high-end equipment manufacturing field.

[0028] In summary, this invention integrates an ideal porous structure, deep purification capability, stable hydrogen removal characteristics, and excellent process performance, providing an upgraded solution that can replace traditional refining agents. It effectively solves the core problems in existing technologies, such as insufficient purification efficiency, single function, poor structural stability, and limited improvement in melt quality. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] In the embodiments and comparative examples of this invention, the purity of each component in the refining agent is 99.9% (by mass).

[0035] Example 1

[0036] This embodiment provides a porous granular refining agent for high-purity magnesium alloy smelting. The refining agent consists of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component, specifically comprising, by mass parts:

[0037] Basic covering components: 28 parts MgCl2, 10 parts SrCl2, 30 parts KCl, 10 parts BaCl2;

[0038] Active purification components: 10 parts CaF2, 4 parts B2O3, 1 part MoO3 and 1 part MnCO3;

[0039] Pore-forming and hydrogen-removing component: 5 parts Na2SiF6;

[0040] In this embodiment, the mass ratio of SrCl2 to MgCl2 is 1:2.8; the mass ratio of MoO3 to B2O3 is 1:4; and the mass ratio of Na2SiF6 to MnCO3 is 5:1.

[0041] The preparation process of this refining agent specifically includes the following steps:

[0042] S1. Raw material dehydration:

[0043] The weighed MgCl2, SrCl2, KCl, and BaCl2 were heated at 250℃ for 3 hours to remove water, and the weighed CaF2, B2O3, MoO3, MnCO3, and Na2SiF6 were heated at 200℃ for 2 hours to remove water.

[0044] S2, Mixing:

[0045] All the dehydrated raw materials from step S1 were mixed at a speed of 200 r / min for 30 min under argon protection to ensure uniform mixing and obtain a mixed powder.

[0046] S3, Melt foaming:

[0047] The mixed powder obtained in step S2 is placed in a graphite crucible and heated to a molten state at 640°C under argon gas protection. It is then kept at this temperature and stirred for 15 minutes at a speed of 200 r / min. During this process, Na2SiF6 and MnCO3 decompose upon heating to generate gas, forming a uniformly distributed microbubble system in the melt.

[0048] S4. Cooling and Crushing:

[0049] The foamed molten material is quickly poured into a preheated metal mold and rapidly cooled using a forced air cooling system. After the material has completely cooled to room temperature, it is coarsely crushed using a jaw crusher and then screened by a vibrating screen to obtain 0.5mm to 5mm granular products, which are recorded as sample 1.

[0050] Example 2

[0051] This embodiment provides a porous granular refining agent for high-purity magnesium alloy smelting. The refining agent consists of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component, specifically comprising, by mass parts:

[0052] Basic covering components: 24 parts MgCl2, 12 parts SrCl2, 25 parts KCl, 8 parts BaCl2;

[0053] Active purification components: 8 parts CaF2, 5 parts B2O3, 1 part MoO3 and 1.5 parts MnCO3;

[0054] Pore-forming and hydrogen-removing component: 6 parts Na2SiF6;

[0055] In this embodiment, the mass ratio of SrCl2 to MgCl2 is 1:2; the mass ratio of MoO3 to B2O3 is 1:5; and the mass ratio of Na2SiF6 to MnCO3 is 4:1.

[0056] The preparation process of this refining agent specifically includes the following steps:

[0057] S1. Raw material dehydration:

[0058] The weighed MgCl2, SrCl2, KCl, and BaCl2 were heated at 200℃ for 4 hours to remove water, and the weighed CaF2, B2O3, MoO3, MnCO3, and Na2SiF6 were heated at 150℃ for 3 hours to remove water.

[0059] S2, Mixing:

[0060] All the dehydrated raw materials from step S1 were mixed at a speed of 180 r / min for 25 min under argon protection to ensure uniform mixing and obtain a mixed powder.

[0061] S3, Melt foaming:

[0062] The mixed powder obtained in step S2 was placed in a graphite crucible and heated to a molten state at 630°C under argon gas protection. The mixture was then stirred at 180 r / min for 25 min. During this process, Na2SiF6 and MnCO3 decomposed upon heating to generate gas, forming a uniformly distributed microbubble system in the melt.

[0063] S4. Cooling and Crushing:

[0064] The foamed molten material is quickly poured into a preheated metal mold and rapidly cooled using a forced air cooling system. After the material has completely cooled to room temperature, it is coarsely crushed using a jaw crusher and then screened by a vibrating screen to obtain 0.5mm to 5mm granular products, which are recorded as sample 2.

[0065] Example 3

[0066] This embodiment provides a porous granular refining agent for high-purity magnesium alloy smelting. The refining agent consists of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component, specifically comprising, by mass parts:

[0067] Basic covering components: 32 parts MgCl2, 8 parts SrCl2, 35 parts KCl, 12 parts BaCl2;

[0068] Active purification components: 12 parts CaF2, 4 parts B2O3, 0.8 parts MoO3 and 0.5 parts MnCO3;

[0069] Pore-forming and hydrogen-removing component: 3 parts Na2SiF6;

[0070] In this embodiment, the mass ratio of SrCl2 to MgCl2 is 1:4; the mass ratio of MoO3 to B2O3 is 1:5; and the mass ratio of Na2SiF6 to MnCO3 is 6:1.

[0071] The preparation process of this refining agent specifically includes the following steps:

[0072] S1. Raw material dehydration:

[0073] The weighed MgCl2, SrCl2, KCl, and BaCl2 were heated at 300℃ for 2 hours to remove water, and the weighed CaF2, B2O3, MoO3, MnCO3, and Na2SiF6 were heated at 250℃ for 1 hour to remove water.

[0074] S2, Mixing:

[0075] All the dehydrated raw materials from step S1 were mixed at a speed of 220 r / min for 25 min under argon protection to ensure uniform mixing and obtain a mixed powder.

[0076] S3, Melt foaming:

[0077] The mixed powder obtained in step S2 is placed in a graphite crucible and heated to a molten state at 650°C under argon gas protection. It is then kept at this temperature and stirred for 10 minutes at a speed of 220 r / min. During this process, Na2SiF6 and MnCO3 decompose upon heating to generate gas, forming a uniformly distributed microbubble system in the melt.

[0078] S4. Cooling and Crushing:

[0079] The foamed molten material is quickly poured into a preheated metal mold and rapidly cooled using a forced air cooling system. After the material has completely cooled to room temperature, it is coarsely crushed using a jaw crusher and then screened by a vibrating screen to obtain 0.5mm to 5mm granular products, which are recorded as sample 3.

[0080] Example 4

[0081] This embodiment provides a porous granular refining agent for high-purity magnesium alloy smelting. The refining agent consists of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component, specifically comprising, by mass parts:

[0082] Basic covering components: 24 parts MgCl2, 8 parts SrCl2, 25 parts KCl, 8 parts BaCl2;

[0083] Active purification components: 8 parts CaF2, 3 parts B2O3, 0.6 parts MoO3 and 0.5 parts MnCO3;

[0084] Pore-forming and hydrogen-removing component: 3 parts Na2SiF6;

[0085] In this embodiment, the mass ratio of SrCl2 to MgCl2 is 1:3; the mass ratio of MoO3 to B2O3 is 1:5; and the mass ratio of Na2SiF6 to MnCO3 is 6:1.

[0086] The preparation process of this refining agent specifically includes the following steps:

[0087] S1. Raw material dehydration: Same as step S1 in the embodiment.

[0088] S2, Mixing: Same as step S2 in the embodiment.

[0089] S3, Melt foaming:

[0090] The mixed powder obtained in step S2 was placed in a graphite crucible and heated to a molten state at 620°C under argon gas protection. The mixture was then stirred at 200 r / min for 15 min. During this process, Na2SiF6 and MnCO3 decomposed upon heating to generate gas, forming a uniformly distributed microbubble system in the melt.

[0091] S4. Cooling and Crushing:

[0092] The foamed molten material is quickly poured into a preheated metal mold and rapidly cooled using a forced air cooling system. After the material has completely cooled to room temperature, it is coarsely crushed using a jaw crusher and then screened by a vibrating screen to obtain 0.5mm to 5mm particles, which are recorded as sample 4.

[0093] Example 5

[0094] This embodiment provides a porous granular refining agent for high-purity magnesium alloy smelting. The refining agent consists of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component, specifically comprising, by mass parts:

[0095] Basic covering components: 32 parts MgCl2, 12 parts SrCl2, 35 parts KCl, 12 parts BaCl2;

[0096] Active purification components: 12 parts CaF2, 5 parts B2O3, 2 parts MoO3 and 1.5 parts MnCO3;

[0097] Pore-forming and hydrogen-removing component: 8 parts of Na2SiF6;

[0098] In this embodiment, the mass ratio of SrCl2 to MgCl2 is 1:2.67; the mass ratio of MoO3 to B2O3 is 1:2.5; and the mass ratio of Na2SiF6 to MnCO3 is 5.33:1.

[0099] The preparation process of this refining agent specifically includes the following steps:

[0100] S1. Raw material dehydration: Same as step S1 in the embodiment.

[0101] S2, Mixing: Same as step S2 in the embodiment.

[0102] S3, Melt foaming:

[0103] The mixed powder obtained in step S2 is placed in a graphite crucible and heated to a molten state at 680°C under argon gas protection. It is then kept at this temperature and stirred for 15 minutes at a speed of 200 r / min. During this process, Na2SiF6 and MnCO3 decompose upon heating to generate gas, forming a uniformly distributed microbubble system in the melt.

[0104] S4. Cooling and Crushing:

[0105] The foamed molten material is quickly poured into a preheated metal mold and rapidly cooled using a forced air cooling system. After the material has completely cooled to room temperature, it is coarsely crushed using a jaw crusher and then screened by a vibrating screen to obtain 0.5mm to 5mm granular products, which are recorded as sample 5.

[0106] Comparative Example 1

[0107] This comparative example provides a refining agent for magnesium alloy smelting. The specific implementation method is the same as in Example 1, except that the pore-forming and hydrogen-removing components are omitted, specifically including:

[0108] Basic covering components: 28 parts MgCl2, 10 parts SrCl2, 30 parts KCl, 10 parts BaCl2;

[0109] Active purification components: 10 parts CaF2, 4 parts B2O3, 1 part MoO3 and 1 part MnCO3;

[0110] In this comparative example, the mass ratio of SrCl2 to MgCl2 is 1:2.8; the mass ratio of MoO3 to B2O3 is 1:4.

[0111] The preparation process of this refining agent specifically includes the following steps:

[0112] S1. Raw material dehydration:

[0113] The weighed MgCl2, SrCl2, KCl, and BaCl2 were heated at 250℃ for 3 hours to remove water, and the weighed CaF2, B2O3, MoO3, and MnCO3 were heated at 200℃ for 2 hours to remove water.

[0114] S2, Mixing: Same as step S2 in Example 1.

[0115] S3, Melt foaming: Same as step S3 in Example 1, but in this process only MnCO3 is heated and decomposed to produce a small amount of CO2 gas. The gas source is insufficient and singular, and only a small number of sparse and discontinuous large bubbles are formed in the melt, which cannot form a uniform and delicate microbubble system.

[0116] S4. Cooling and crushing: Same as step S4 in Example 1, the obtained particulate product is designated as control product 1.

[0117] Comparative Example 2

[0118] This comparative example provides a refining agent for magnesium alloy smelting. The specific implementation method is the same as in Example 1, except that the auxiliary pore-forming agent MnCO3 is omitted. Specifically, it includes:

[0119] Basic covering components: 28 parts MgCl2, 10 parts SrCl2, 30 parts KCl, 10 parts BaCl2;

[0120] Active purification components: 10 parts CaF2, 4 parts B2O3 and 1 part MoO3;

[0121] Pore-forming and hydrogen-removing component: 5 parts Na2SiF6;

[0122] In this comparative example, the mass ratio of SrCl2 to MgCl2 is 1:2.8; the mass ratio of MoO3 to B2O3 is 1:4.

[0123] The preparation process of this refining agent specifically includes the following steps:

[0124] S1. Raw material dehydration:

[0125] The weighed MgCl2, SrCl2, KCl, and BaCl2 were heated at 250℃ for 3 hours to remove water, and the weighed CaF2, B2O3, MoO3, and Na2SiF6 were heated at 200℃ for 2 hours to remove water.

[0126] S2, Mixing: Same as step S2 in Example 1.

[0127] S3, Melt foaming: Same as step S3 in Example 1, but in this process only Na2SiF6 is heated and decomposed to produce gas. Due to the lack of synergistic nucleation effect of MnCO3 decomposition, the generated bubbles are uneven in size and concentrated in distribution, making it difficult to form the uniform and interconnected multi-level porous structure achieved by this invention.

[0128] S4. Cooling and crushing: Same as step S4 in Example 1, the obtained particulate product is designated as control product 2.

[0129] Comparative Example 3

[0130] This comparative example provides a refining agent for magnesium alloy smelting. The specific implementation method is the same as in Example 1, except that MoO3 is replaced with an equal mass of SiO2, specifically including:

[0131] Basic covering components: 28 parts MgCl2, 10 parts SrCl2, 30 parts KCl, 10 parts BaCl2;

[0132] Active purification components: 10 parts CaF2, 4 parts B2O3, 1 part SiO2 and 1 part MnCO3;

[0133] Pore-forming and hydrogen-removing component: 5 parts Na2SiF6;

[0134] In this comparative example, the mass ratio of SrCl2 to MgCl2 is 1:2.8; the mass ratio of SiO2 to B2O3 is 1:4; and the mass ratio of Na2SiF6 to MnCO3 is 5:1.

[0135] The preparation process of this refining agent specifically includes the following steps:

[0136] S1. Raw material dehydration:

[0137] The weighed MgCl2, SrCl2, KCl, and BaCl2 were heated at 250℃ for 3 hours to remove water, and the weighed CaF2, B2O3, SiO2, MnCO3, and Na2SiF6 were heated at 200℃ for 2 hours to remove water.

[0138] S2, Mixing: Same as step S2 in Example 1.

[0139] S3, Melt foaming: Same as step S3 in Example 1.

[0140] S4. Cooling and crushing: Same as step S4 in Example 1, the obtained particulate product is designated as control product 3.

[0141] Comparative Example 4

[0142] This comparative example provides a refining agent for magnesium alloy smelting. The specific implementation method is the same as in Example 1, except that SrCl2 is omitted and its proportion is added back to MgCl2. Specifically, it includes:

[0143] Basic covering components: 38 parts MgCl2, 30 parts KCl, and 10 parts BaCl2;

[0144] Active purification components: 10 parts CaF2, 4 parts B2O3, 1 part MoO3 and 1 part MnCO3;

[0145] Pore-forming and hydrogen-removing component: 5 parts Na2SiF6;

[0146] In this comparative example, the mass ratio of MoO3 to B2O3 is 1:4; the mass ratio of Na2SiF6 to MnCO3 is 5:1.

[0147] The preparation process of this refining agent specifically includes the following steps:

[0148] S1. Raw material dehydration:

[0149] The weighed MgCl2, KCl, and BaCl2 were heated at 250℃ for 3 hours to remove water, and the weighed CaF2, B2O3, MoO3, MnCO3, and Na2SiF6 were heated at 200℃ for 2 hours to remove water.

[0150] S2, Mixing: Same as step S2 in Example 1.

[0151] S3, Melt foaming: Same as step S3 in Example 1.

[0152] S4. Cooling and crushing: Same as step S4 in Example 1, the obtained particulate product is designated as control product 4.

[0153] Comparative Example 5

[0154] This comparative example provides a refining agent for magnesium alloy smelting, and its formula is exactly the same as that of Example 1; the only difference is that in preparation step S3, the melting foaming temperature is changed to 600℃, and the other steps and parameters are the same as those in Example 1. The resulting product is referred to as control product 5.

[0155] Comparative Example 6

[0156] This comparative example provides a refining agent for magnesium alloy smelting, and its formula is exactly the same as that of Example 1; the only difference is that in preparation step S3, the melting foaming temperature is changed to 700℃, and the other steps and parameters are the same as those in Example 1. The resulting product is referred to as control product 6.

[0157] Analysis and Testing

[0158] Samples 1-5 prepared in Examples 1-6 and control samples 1-6 prepared in Comparative Examples 1-6 were applied to the smelting and casting process of the same batch of high-purity magnesium alloy (wherein the purity of Mg is 99.96% by mass).

[0159] All smelting experiments were conducted at 720℃±5℃ under the protection of an SF6+CO2 mixed gas atmosphere. The amount of refining agent added was 1.5% of the total mass of the furnace charge. After refining, the furnace charge was allowed to stand for 25 minutes before casting. The standard test bars used for testing were all taken from the same part of the ingot.

[0160] It should be noted that this invention is primarily applied to the preparation of high-quality magnesium alloys using high-purity primary magnesium ingots as raw materials. In such applications, the main threats to melt purity come from the products of secondary oxidation during the smelting process (i.e., oxide inclusions) and hydrogen absorbed from the environment, while the content of specific impurity elements such as alkali metals is not a major concern due to the extremely low background values ​​of the raw materials. Therefore, this invention selects the alloy hydrogen content, the percentage of inclusion area, and the iron impurity content as core indicators for evaluating the purification effect, which can most directly and effectively characterize the performance of the refining agent of this invention in practical application scenarios.

[0161] Of course, those skilled in the art will understand that the refining agent described in this invention, with its huge specific surface area and active components, also has good removal potential for a variety of molten impurities, including alkali metal impurities.

[0162] I. Melt purification and hydrogen removal effect test

[0163] The hydrogen content of the alloy was determined using a hydrogen analyzer; the content of key impurity elements in the ingot was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES); and the percentage of inclusion area was calculated by statistically analyzing 30 fields of view of the ingot cross-section using metallographic image analysis software. The test results are shown in Table 1.

[0164] Table 1: Test Results of Purification Effect of High-Purity Magnesium Alloy Melt

[0165]

[0166] As can be seen from the results in Table 1, the refining agent samples 1 to 5 of the present invention all exhibited excellent comprehensive purification and hydrogen removal performance in the smelting of high-purity magnesium alloys, with hydrogen content all below 17 ppm and inclusion rate below 0.05%.

[0167] Reference standard 1 completely omits the pore-forming and hydrogen-removing components, relying solely on the limited gas generated by the decomposition of MnCO3 to form only a small number of sparse and discontinuous large bubbles in the melt, failing to form a uniform and delicate microbubble system, resulting in a significant reduction in purification efficiency and the highest hydrogen content and slag inclusion rate.

[0168] Reference product 2 omits the auxiliary pore-forming agent MnCO3. Due to the lack of synergistic nucleation effect from MnCO3 decomposition, the pore-forming mechanism is singular, and the generated bubbles are uneven in size and concentrated in distribution. It is difficult to form the uniform and interconnected multi-level pore structure achieved by this invention, thus limiting the purification effect.

[0169] Reference standard 3, which replaced MoO3 with SiO2, formed a porous structure, but its pore stability was poor. This is because MoO3, as an acidic oxide, can form a glass network with B2O3 and other materials, regulating the viscosity and surface tension of the melt at the foaming temperature, which is crucial for bubble stability and pore wall strength. SiO2, on the other hand, has a too high melting point and is difficult to dissolve effectively in this system to achieve the same regulating effect, leading to bubble coalescence and structural collapse.

[0170] Reference standard 4 omits SrCl2. Due to the excessively high proportion of MgCl2 in the basic components and the lack of stabilizing effect of SrCl2, the thermal stability and viscosity of the refining agent system are altered, affecting the initial formation and final shaping of bubbles. This leads to a decrease in the thermal stability and covering performance of the basic components, thus affecting the overall performance of the refining agent.

[0171] The melt foaming temperatures of reference standards 5 and 6 deviated from the optimal range. When the temperature was too low, the mixture failed to melt sufficiently, resulting in excessively high system viscosity, which severely hindered the foaming reaction, making it difficult for gas to form and remain effectively. When the temperature was too high, the decomposition reaction of the pore-forming components was too vigorous, causing a large amount of gas to escape rapidly and merge, resulting in large, uneven bubbles, and some pore structures collapsing before cooling. Both situations severely affected the quality of the porous structure, demonstrating that temperature directly affects melt viscosity and the rate of gas decomposition and escape, thus jointly determining the final porosity, pore size, and distribution.

[0172] II. Solidification Structure and Mechanical Property Testing

[0173] The average grain size was measured on polished metallographic specimens etched with picric acid using the truncated section method. Room temperature tensile strength, yield strength, and elongation were tested on a universal testing machine according to ASTM E8 / E8M standards. The test results are shown in Table 2.

[0174] Table 2: Solidification microstructure and mechanical properties of high-purity magnesium alloys

[0175]

[0176] As shown in Table 2, the magnesium alloy samples using the refining agent of this invention exhibited significantly refined grains and overall improved mechanical properties. This is closely related to the excellent purification effect of the samples from this invention; the clean melt provides the foundation for uniform grain refinement, and the refined grains directly lead to a significant improvement in mechanical properties.

[0177] Reference 1, due to its poorest purification effect, contains a large number of heterogeneous nuclei in its melt, resulting in abnormally large grains and the lowest mechanical properties.

[0178] The purification effects of reference standards 2, 3, and 4 were better than those of reference standard 1 but inferior to those of the present invention. Their grain size and mechanical properties also showed corresponding intermediate levels, proving that there is a clear positive correlation between the degree of purification and the solidification structure and mechanical properties.

[0179] Reference samples 5 and 6 suffered from incomplete purification due to improper processing, resulting in the failure of their porous structure and a corresponding deterioration in their grain size and mechanical properties.

[0180] III. High-Temperature Mechanical Property Testing and Corrosion Resistance Testing

[0181] High-temperature tensile tests were conducted at 300°C using a universal testing machine equipped with a high-temperature furnace. Corrosion resistance was evaluated by measuring the corrosion current density (expressed as I_corr) in a 3.5% NaCl solution using an electrochemical workstation and the potentiodynamic polarization method. The results are shown in Table 3.

[0182] Table 3: Test Results of High-Temperature Mechanical Properties of High-Purity Magnesium Alloys

[0183]

[0184] As shown in Table 3, the high-temperature performance of the alloy is directly related to its grain size and purity. Samples 1-5 exhibit excellent performance at high temperatures due to their fine grains and clean melt. All comparative samples showed a significant decrease in high-temperature performance, either due to coarse grains or impure melt.

[0185] Corrosion resistance primarily depends on the uniformity of material composition and the number of defects. The sample of this invention, benefiting from extremely low inclusion rates and hydrogen content, exhibits the lowest corrosion current density. All comparative examples, due to varying degrees of inclusions, porosity, and other defects, provided pathways for corrosion, resulting in significantly poorer corrosion resistance.

[0186] IV. Characterization of the porous structure and adsorption kinetics of refining agents

[0187] To directly verify the porous structure characteristics of the refining agent and its impact on purification efficiency, the refining agent was physically characterized and its dynamic adsorption performance was tested.

[0188] The porosity and average pore size of the refining agent were measured using mercury intrusion porosimetry; its specific surface area was measured using the BET method; and the same mass of refining agent particles were added to a simulated slag suspension with a constant flow rate, and the adsorption and removal rate of suspended particles was measured within 3 minutes to evaluate its dynamic adsorption rate. The test results are shown in Table 4.

[0189] Table 4: Test Results of Porous Structure Characteristics and Dynamic Adsorption Performance of Refining Agent

[0190]

[0191] As can be seen from the results in Table 4, the refining agent samples 1-5 of the present invention have high porosity, large specific surface area and suitable average pore size, which provides a huge reaction interface and channel for rapid adsorption of inclusions during the smelting process; the high dynamic adsorption removal rate also proves the high efficiency of its porous structure in the purification process.

[0192] Reference 1 had the lowest porosity and the worst adsorption performance; however, its average pore size was unavailable because its structure was too dense, with almost no interconnected channels for mercury intrusion porosimetry measurement. References 2, 3, and 4, due to missing or substituted components, had inferior pore structure parameters compared to the sample of this invention, resulting in moderate adsorption efficiencies. References 5 and 6, due to improper processing, exhibited low porosity in the former and excessively large pore size in the latter, both severely impacting their effective specific surface area and adsorption capacity. This further demonstrates the necessity of precisely controlling the pore-forming process from a physical performance perspective.

[0193] In summary, this invention, through unique component design and process control, successfully prepared a refining agent with an ideal porous structure. Its high porosity, large specific surface area, and rapid adsorption kinetics characteristics together constitute the fundamental reason for achieving deep purification of high-purity magnesium alloys.

[0194] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A porous granular refining agent for smelting high-purity magnesium alloys, characterized in that, The refining agent consists of a basic covering component, an active purification component, and a pore-forming and hydrogen-removing component. The basic covering components include MgCl2, SrCl2, KCl, and BaCl2; the active purification components include CaF2, B2O3, MoO3, and MnCO3; and the pore-forming hydrogen removal component is Na2SiF6.

2. The refining agent according to claim 1, characterized in that, The basic covering component includes 24 to 32 parts of MgCl2, 8 to 12 parts of SrCl2, 25 to 35 parts of KCl, and 8 to 12 parts of BaCl2; the active purification component includes 8 to 12 parts of CaF2, 3 to 5 parts of B2O3, 0.6 to 2 parts of MoO3, and 0.5 to 1.5 parts of MnCO3; the pore-forming and hydrogen-removing component is 3 to 8 parts of Na2SiF6.

3. The refining agent according to claim 2, characterized in that, The mass ratio of SrCl2 to MgCl2 is 1:(2-4).

4. The refining agent according to claim 2, characterized in that, The mass ratio of MoO3 to B2O3 is 1:(2-5).

5. The refining agent according to claim 2, characterized in that, The mass ratio of Na2SiF6 to MnCO3 is (4-6):

1.

6. A method for preparing the refining agent as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Raw material dehydration: The MgCl2, SrCl2, KCl, and BaCl2 are dehydrated by heating at 200℃~300℃ for 2h~4h, and the CaF2, B2O3, MoO3, MnCO3, and Na2SiF6 are dehydrated by heating at 150℃~250℃ for 1h~3h. S2. Mixing: Mix all the dehydrated raw materials from step S1 under an inert gas protection to obtain a mixed powder; S3. Melt foaming: The mixed powder obtained in step S2 is heated to a molten state at 620℃~680℃ under inert gas protection, and stirred for 10min~25min. S4. Cooling, shaping and crushing: The molten material after foaming in step S3 is quickly poured into a cooling mold and cooled to room temperature. Then it is crushed and screened to obtain a porous granular refining agent product.

7. The preparation method according to claim 6, characterized in that, The stirring speed for heat preservation is 180 r / min to 220 r / min.

8. The preparation method according to claim 6, characterized in that, The heating temperature is 630℃~650℃.

9. The preparation method according to claim 6, characterized in that, The cooling mold is a metal mold, and forced air cooling is used after casting.

10. The preparation method according to claim 6, characterized in that, The inert gas mentioned is argon.

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