A method for refining the grain of magnesium-aluminum series alloys by carbonaceous inoculation

Abstract

The application discloses a method for refining magnesium-aluminum alloy crystal grains by carbon inoculation, and belongs to the technical field of magnesium alloy material processing. The method comprises the following steps: heating magnesium-aluminum alloy to 680-800 DEG C under a protective atmosphere, melting the magnesium-aluminum alloy, adding carbon inoculant hexachloroethane (C2Cl6), the adding amount being 0.1%-1.5% of the mass of the melt, adding by means of bell jar pressing, and keeping the temperature at 680-800 DEG C for 5-60 minutes, so that carbon and aluminum in the melt react in situ to generate high-density and dispersedly-distributed Al4C3 particles, which serve as effective heterogeneous nucleation cores of alpha-Mg, thereby significantly refining the crystal grains. The application is also provided with a tail gas treatment system for absorbing harmful gases such as Cl2. The method has the advantages of remarkable refining effect, strong anti-recession property, low cost, and suitability for magnesium-aluminum alloys with different aluminum contents, and solves the problems of instability, easy failure or environmental pollution in the prior art.

Description

Technical Field

[0001] This invention discloses a method for refining the grains of magnesium-aluminum alloys using carbon inoculation, belonging to the field of magnesium alloy material processing technology. Background Technology

[0002] Magnesium-aluminum alloys are currently the most widely used magnesium alloy series in industry, possessing advantages such as low density, high specific strength, and excellent casting properties. However, magnesium has a close-packed hexagonal crystal structure, which easily forms coarse dendrites during solidification, leading to a significant decrease in the alloy's mechanical properties, corrosion resistance, and processing formability. Grain refinement is an effective means to improve the overall properties of magnesium-aluminum alloys; therefore, developing efficient, stable, and low-cost grain refinement methods has always been a research hotspot in this field.

[0003] Currently, grain refinement methods for magnesium-aluminum alloys mainly include zirconium refinement, rare earth element refinement, boride alloy modification, and carbonaceous inoculation. However, all of these methods have significant limitations in practical applications. Zirconium is a recognized high-efficiency grain refiner for magnesium alloys, but it is only suitable for aluminum-free magnesium alloys (such as Mg-Zn and Mg-RE alloys). For magnesium-aluminum alloys, zirconium preferentially reacts with aluminum to form a high-melting-point Al3Zr phase. This phase cannot serve as an effective heterogeneous nucleation core for α-Mg, and instead consumes zirconium, resulting in complete failure of the grain refinement effect. Although rare earth element refinement can obtain a finer equiaxed grain structure and simultaneously purify the melt and improve oxidation resistance, rare earth resources are scarce and expensive, significantly increasing production costs and making it difficult to meet the economic requirements of large-scale industrial production. Boron-based alloy modification methods, such as Al-Ti-B master alloy (e.g., Al-5Ti-1B) grain refinement techniques, are widely used in aluminum alloy grain refinement. However, when directly applied to magnesium-aluminum alloys, the refinement effect is unstable. On the one hand, TiAl3 and TiB2 particles have a much weaker heterogeneous nucleation ability for α-Mg than for α-Al; on the other hand, in magnesium alloys with high aluminum content, grain refiner "poisoning" can easily occur, even inducing surface wrinkles in castings and affecting product quality.

[0004] The carbonaceous inoculation method utilizes the reaction of carbonaceous materials with aluminum in molten magnesium and aluminum to generate Al4C3 particles, which then serve as α-Mg heterogeneous nucleation sites to achieve grain refinement. Commonly used carbonaceous grain refiners include magnesium carbonate (MgCO3), hexachloroethane (C2Cl6), and graphite powder. However, when MgCO3 or graphite powder is used alone, the reaction kinetics between the carbon source and the melt are poor, resulting in insufficient and uneven Al4C3 formation and distribution. This leads to unstable grain refinement, often requiring larger amounts or longer holding times, increasing the difficulty of process control.

[0005] Therefore, how to provide a grain refinement method that has good refining effect, controllable cost and is applicable to magnesium-aluminum alloys is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention aims to overcome the problems of unstable grain refinement effect, poor resistance to fading, unsuitability for high aluminum content alloys, and environmental pollution in existing magnesium-aluminum alloy grain refinement technologies. It provides a method for refining magnesium-aluminum alloy grains using carbon inoculation. This method uses hexachloroethane (C2Cl6) as a carbon inoculator, and achieves efficient, stable, and repeatable grain refinement under optimized temperature and time windows. It also achieves green production through supporting environmental protection measures.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for refining the grains of magnesium-aluminum alloys using a carbonaceous inoculation method, characterized in that a magnesium-aluminum alloy is selected, wherein the mass percentage of aluminum in the magnesium-aluminum alloy is 2% to 12%, more preferably 6% to 10%; the alloy is selected from one or more of AZ31, AZ61, AZ91D, AM50, and AM60; the alloy form can be ingots, chips, or granules, specifically including the following steps: Step 1: Raw material pretreatment.

[0008] Remove the oxide scale and oil stains from the surface of the alloy raw material with sandpaper or wire brush, then ultrasonically clean it in acetone and anhydrous ethanol for 10-15 minutes in sequence, and dry it in an oven at 150°C for more than 2 hours.

[0009] Step 2: Preparation of smelting equipment and protective atmosphere.

[0010] (1) Smelting furnace: The resistance heating crucible furnace is adopted. The crucible material is low carbon steel or graphite clay crucible. Before use, the crucible is preheated to dark red (about 600°C). The inner wall is evenly coated with ZnO-water glass coating and dried to prevent iron contamination.

[0011] (2) Protective atmosphere system: A protective atmosphere is introduced throughout the smelting process. The atmosphere composition is 0.2% to 2% SF6 + the balance is high-purity Ar or CO2, and the total gas flow rate is 1 to 3 L / min. Alternatively, a covering agent can be sprinkled on the surface of the melt as an auxiliary protection.

[0012] (3) Tail gas treatment system: Since C2Cl6 is used, its decomposition will produce acidic gases such as Cl2 and HCl. Therefore, a sealed gas collection hood is set above the furnace body and connected to a two-stage alkaline spray tower and an activated carbon adsorption device. The absorbent in the alkaline spray tower is a 10% NaOH solution.

[0013] Step 3: Alloy smelting.

[0014] The pretreated magnesium-aluminum alloy raw material is added to a crucible and heated to 680–800°C. After the alloy is completely melted, the melt is gently stirred with a stirring spoon to ensure uniform composition. A protective atmosphere is continuously introduced during the melting process, and the melt temperature is checked every 15 minutes, with a temperature control accuracy of ±5°C.

[0015] Step 4: Add carbonaceous inoculant.

[0016] (1) Preparation of inoculant: Use hexachloroethane (C2Cl6) powder with a purity of ≥99.5% or press it into cylindrical blocks. Before use, dry it in a vacuum drying oven at 50°C for 4 hours to remove adsorbed moisture.

[0017] (2) Amount of C2Cl6 added: The amount of C2Cl6 added is 0.1% to 1.5% of the mass of the alloy melt, preferably 0.3% to 0.8%, and most preferably 0.5%.

[0018] (3) Addition method: The bell jar pressing method is used. The weighed C2Cl6 is wrapped in aluminum foil and fixed to the bottom of the bell jar. The bell jar is preheated to 200-300℃, and then slowly immersed into the center of the melt to a depth of about 1 / 2 to 2 / 3. The bell jar is rotated and moved up and down to completely release C2Cl6 within 30-60 seconds.

[0019] Step 5: Nurturing and keeping warm.

[0020] After the C2Cl6 is added, continue to maintain the temperature within the range of 680–800℃ for 5–60 minutes to ensure the reaction proceeds fully, allowing Al4C3 particles to be generated in situ and dispersed. During the holding period, gently stir the melt with a graphite rod every 10 minutes to promote uniform suspension of Al4C3 and prevent agglomeration and sedimentation.

[0021] Step Six: Refining and Resting.

[0022] (1) Refining: After the inoculation and heat preservation are completed, the melt temperature is reduced to 720-740℃, and 0.2%-0.5% of sodium-free refining agent is added. Stir with a stirring spoon at a speed of 100-150 rpm for 3-5 minutes to further remove impurities and gases.

[0023] (2) Let stand: Stop stirring, raise the temperature to 750-760℃, let stand for 10-15 minutes to allow the impurities to float or sink, and then skim off the surface scum.

[0024] Step 7: Post-processing.

[0025] (1) Adjust the temperature of the refined and settled melt to 680-720℃ and then pour it.

[0026] (2) Cleaning: Remove the casting, cut off the gating and riser, and remove the surface oxide scale by sandblasting or pickling.

[0027] (3) Grain size detection: Metallographic samples are cut from the same part of the casting, and after grinding, polishing and etching, the grain morphology is observed under an optical microscope or scanning electron microscope. The average grain size is calculated by using the cut-off method or image analysis software.

[0028] Furthermore, the heat preservation temperature mentioned in step five is preferably 780℃.

[0029] Furthermore, the optimal incubation and heat preservation time is 5 minutes. Furthermore, ultrasonic treatment is applied during the incubation and heat preservation stage to break up Al4C3 aggregates using the ultrasonic cavitation effect, thereby further refining the particles and promoting uniform distribution.

[0030] Furthermore, for magnesium alloys with an aluminum content higher than 9 wt.% (such as AZ91D), the amount of C2Cl6 added can be increased to 0.8%–1.0%, and the holding time can be extended to 15–20 minutes to compensate for the competitive consumption of aluminum in the Al4C3 formation reaction.

[0031] Furthermore, to reduce the generation of Cl2 gas, magnesium carbonate (MgCO3) powder, accounting for 10% to 30% of its mass, can be added to C2Cl6, and the two can be mixed and pressed into blocks for use.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) The average grain size of the magnesium-aluminum alloy prepared by the present invention is higher than that of the unrefined average grain size, and the refining effect is significantly improved.

[0033] (2) C2Cl6 is a bulk chemical raw material in industry. It is inexpensive and only requires 0.3% to 0.8% of the amount added. Compared with other methods, the overall cost is low.

[0034] (3) This invention is not only applicable to conventional AZ series magnesium-aluminum alloys (Al 2%~10%), but also to alloys with high aluminum content (10%~12%), such as AZ111, AE44, etc., overcoming the problem of "poisoning" failure of Al-Ti-B refining method under high aluminum content.

[0035] (4) Because the C2Cl6 decomposition reaction is thorough and rapid, and the generated Al4C3 particles have high thermal stability, the refining effect between different furnaces fluctuates little, which facilitates quality control and standardized production. Attached Figure Description

[0036] Figure 1 This is a flowchart of the present invention; Figure 2 Comparison chart of the effects of refining agents. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Please refer to the figure. This invention aims to overcome the problems of unstable grain refinement effect, poor resistance to fading, unsuitability for high aluminum content alloys, and environmental pollution in existing magnesium-aluminum alloy grain refinement technologies. It provides a method for refining magnesium-aluminum alloy grains using carbon inoculation. This method uses hexachloroethane (C2Cl6) as a carbon inoculator, achieving efficient, stable, and repeatable grain refinement under optimized temperature and time windows, and realizing green production through supporting environmental protection measures.

[0039] To achieve the above objectives, the present invention provides the following technical solution: a method for refining the grains of magnesium-aluminum alloys using a carbonaceous inoculation method, characterized in that a magnesium-aluminum alloy is selected, wherein the mass percentage of aluminum in the magnesium-aluminum alloy is 2% to 12%, more preferably 6% to 10%; the alloy is selected from one or more of AZ31, AZ61, AZ91, AM50, and AM60; the alloy form can be ingots, chips, or granules, specifically including the following steps: Step 1: Raw material pretreatment. Remove the surface oxide scale and oil stains from the alloy raw material with sandpaper or wire brush, then ultrasonically clean it in acetone and anhydrous ethanol for 10-15 minutes in sequence, and dry it in an oven at 150°C for more than 2 hours.

[0040] Step 2: Melting equipment and preparation.

[0041] (1) Smelting furnace: The resistance heating crucible furnace is adopted. The crucible material is low carbon steel or graphite clay crucible. Before use, the crucible is preheated to dark red (about 600°C). The inner wall is uniformly coated with ZnO-water glass coating under protective atmosphere and dried to prevent iron contamination.

[0042] (2) Protective atmosphere system: A protective atmosphere is introduced throughout the smelting process. The atmosphere composition is 0.2% to 2% SF6 + the balance is high-purity Ar or CO2, and the total gas flow rate is 1 to 3 L / min. Alternatively, a covering agent can be sprinkled on the surface of the melt as an auxiliary protection.

[0043] (3) Tail gas treatment system: Since C2Cl6 is used, its decomposition will produce acidic gases such as Cl2 and HCl. Therefore, a sealed gas collection hood is set above the furnace body and connected to a two-stage alkaline spray tower and an activated carbon adsorption device. The absorbent in the alkaline spray tower is a 10% NaOH solution.

[0044] Step 3: Alloy Melting. Add the pretreated magnesium-aluminum alloy raw material to a crucible and heat to 680–800°C. After the alloy has completely melted, gently stir the melt with a stirring spoon to ensure uniform composition. During melting, continuously purge with a protective atmosphere and check the melt temperature every 15 minutes, maintaining a temperature control accuracy of ±5°C.

[0045] Step 4: Add carbonaceous inoculant.

[0046] (1) Preparation of inoculant: Use hexachloroethane (C2Cl6) powder with a purity of ≥99.5% or press it into cylindrical blocks. Before use, dry it in a vacuum drying oven at 50°C for 4 hours to remove adsorbed moisture.

[0047] (2) Amount of C2Cl6 added: The amount of C2Cl6 added is 0.1% to 1.5% of the mass of the alloy melt, preferably 0.3% to 0.8%, and most preferably 0.5%.

[0048] (3) Addition method: The bell jar pressing method is used. The weighed C2Cl6 is wrapped in aluminum foil and fixed to the bottom of the bell jar. The bell jar is preheated to 200-300℃, and then slowly immersed into the center of the melt to a depth of about 1 / 2 to 2 / 3. The bell jar is rotated and moved up and down to completely release C2Cl6 within 30-60 seconds.

[0049] Step 5: Incubation and Temperature Holding. After the C2Cl6 is added, continue to hold the temperature at 680–800℃ for 5–60 minutes to ensure the reaction proceeds fully, allowing Al4C3 particles to form in situ and disperse. During the holding period, gently stir the melt with a graphite rod every 10 minutes to promote uniform suspension of Al4C3 and prevent agglomeration and sedimentation. Ultrasonic treatment is also used during the incubation and temperature holding stage to utilize the ultrasonic cavitation effect to break up Al4C3 agglomerates, further refining the particles and promoting uniform distribution.

[0050] Step Six: Refining and Resting.

[0051] (1) Refining: After the inoculation and heat preservation are completed, the melt temperature is reduced to 620-640℃, and 0.2%-0.5% of sodium-free refining agent is added. Stir with a stirring spoon at a speed of 100-150 rpm for 3-5 minutes to further remove impurities and gases.

[0052] (2) Let stand: Stop stirring, raise the temperature to 750-760℃, let stand for 10-15 minutes to allow the impurities to float or sink, and then skim off the surface scum.

[0053] Step 7: Post-processing.

[0054] (1) Adjust the temperature of the refined and settled melt to 680-720℃ and then pour it.

[0055] (2) Cleaning: Remove the casting, cut off the gating and riser, and remove the surface oxide scale by sandblasting or pickling.

[0056] (3) Grain size detection: Metallographic samples are cut from the same part of the casting, and after grinding, polishing and etching, the grain morphology is observed under an optical microscope or scanning electron microscope. The average grain size is calculated by using the cut-off method or image analysis software.

[0057] Furthermore, for magnesium alloys with an aluminum content higher than 9 wt.% (such as AZ91D), the amount of C2Cl6 added can be increased to 0.8%–1.0%, and the holding time can be extended to 15–20 minutes to compensate for the competitive consumption of aluminum in the Al4C3 formation reaction.

[0058] Furthermore, to reduce the generation of Cl2 gas, magnesium carbonate (MgCO3) powder, accounting for 10% to 30% of its mass, can be added to C2Cl6, and the two can be mixed and pressed into blocks for use. Example

[0059] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, and dried in an oven at 150°C for more than 2 hours. Before use, the crucible was preheated to a dark red color, and the inner wall was uniformly coated with ZnO-water glass coating and dried. A protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min. The pretreated magnesium-aluminum alloy raw material was added to the crucible, heated to 780°C, C2Cl6 was added, and the temperature was maintained at 780°C for 5 minutes. The melt temperature was reduced to 640°C, and 0.4% sodium-free refining agent by mass of the melt was added. The temperature was raised to 750°C, and the mixture was allowed to stand for 15 minutes. Then, the surface slag was skimmed off, and the final treatment was completed. Example

[0060] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, placed in an oven and dried at 150°C for more than 2 hours, the crucible was preheated to dark red before use, the inner wall was uniformly coated with ZnO-water glass coating and dried, a protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min, the pretreated magnesium-aluminum alloy raw material was added to the crucible, the temperature was raised to 780°C, Al4C3 was added, and the temperature was held at 780°C for 5 minutes. The melt temperature was lowered to 640°C, 0.4% sodium-free refining agent of melt mass was added, the temperature was raised to 750°C, and it was allowed to stand for 15 minutes. Then the surface slag was skimmed off and the final treatment was completed. Example

[0061] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, placed in an oven and dried at 150°C for more than 2 hours, the crucible was preheated to dark red before use, the inner wall was uniformly coated with ZnO-water glass coating and dried, a protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min, the pretreated magnesium-aluminum alloy raw material was added to the crucible, the temperature was raised to 780°C, SiC was added, and the temperature was held at 780°C for 5 minutes. The melt temperature was lowered to 640°C, 0.4% sodium-free refining agent by mass of melt was added, the temperature was raised to 750°C, and it was allowed to stand for 15 minutes. Then the surface slag was skimmed off and the final treatment was completed. Example

[0062] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, and dried in an oven at 150°C for more than 2 hours. Before use, the crucible was preheated to a dark red color, and the inner wall was uniformly coated with ZnO-water glass and dried. A protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min. The pretreated magnesium-aluminum alloy raw material was added to the crucible, heated to 740°C, C2Cl6 was added, and the temperature was maintained at 780°C for 5 minutes. The melt temperature was reduced to 640°C, and 0.4% sodium-free refining agent by mass of the melt was added. The temperature was raised to 750°C, and the mixture was allowed to stand for 15 minutes. Then, the surface slag was skimmed off, and the final treatment was completed. Example

[0063] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, placed in an oven and dried at 150°C for more than 2 hours, the crucible was preheated to dark red before use, the inner wall was uniformly coated with ZnO-water glass coating and dried, a protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min, the pretreated magnesium-aluminum alloy raw material was added to the crucible, the temperature was raised to 700°C, C2Cl6 was added, and the temperature was held at 780°C for 5 minutes. The melt temperature was lowered to 640°C, 0.4% sodium-free refining agent of melt mass was added, the temperature was raised to 750°C, and it was allowed to stand for 15 minutes. Then the surface slag was skimmed off and the final treatment was completed. Example

[0064] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, placed in an oven and dried at 150°C for more than 2 hours, the crucible was preheated to dark red before use, the inner wall was uniformly coated with ZnO-water glass coating and dried, a protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min, the pretreated magnesium-aluminum alloy raw material was added to the crucible, the temperature was raised to 780°C, C2Cl6 was added, and the temperature was held at 780°C for 30 minutes. The melt temperature was lowered to 640°C, 0.4% sodium-free refining agent of melt mass was added, the temperature was raised to 750°C, and it was allowed to stand for 15 minutes. Then the surface slag was skimmed off and the final treatment was completed. Example

[0065] According to the preparation method described in the invention, the grain refinement of magnesium-aluminum alloy was carried out. The specific parameters and steps are as follows: AZ91 material was selected, ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes, and dried in an oven at 150°C for more than 2 hours. Before use, the crucible was preheated to a dark red color, and the inner wall was uniformly coated with ZnO-water glass and dried. A protective atmosphere was introduced throughout the process with a gas flow rate of 2L / min. The pretreated magnesium-aluminum alloy raw material was added to the crucible, heated to 780°C, C2Cl6 was added, and the temperature was maintained at 780°C for 30 minutes. The melt temperature was reduced to 640°C, and 0.4% sodium-free refining agent by mass of the melt was added. The temperature was raised to 750°C, and the mixture was allowed to stand for 60 minutes. Then, the surface slag was skimmed off, and the final treatment was completed.

[0066] In the comparison of the above embodiments, the optimal solution is to use C2Cl6 as the refining agent and maintain the temperature at 780℃ for 5 minutes. Under these parameters, the product performance is the best.

[0067] The present invention has been described in detail with reference to the foregoing embodiments. Those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for refining the grain size of magnesium-aluminum alloys using carbonaceous inoculation, characterized in that: A magnesium-aluminum alloy is selected, wherein the mass percentage of aluminum in the magnesium-aluminum alloy is 2% to 12%; the alloy is selected from one or more of AZ31, AZ61, AZ91D, AM50, and AM60; the alloy form can be ingot, chips, or granules, and the specific steps include: Step 1: Raw material pretreatment: Remove the oxide scale and oil stains from the surface of the alloy raw material with sandpaper or wire brush, then ultrasonically clean it in acetone and anhydrous ethanol for 10-15 minutes in sequence, and dry it in an oven at 150°C for more than 2 hours. Step 2: Preparation of smelting equipment and protective atmosphere: (1) Preheat the crucible to 600°C, coat the inner wall with ZnO-water glass coating evenly and dry it; (2) A protective atmosphere is introduced throughout the smelting process. The atmosphere consists of 0.2% to 2% SF6 + the balance being high-purity Ar or CO2, and the total gas flow rate is 1 to 3 L / min. (3) A sealed gas collection hood is installed above the furnace body and connected to a two-stage alkaline spray tower and an activated carbon adsorption device. The absorbent in the alkaline spray tower is a 10% NaOH solution. Step 3: Alloy Melting Add the pretreated magnesium-aluminum alloy raw material into the crucible and heat it to 680-800℃. After the alloy is completely melted, gently stir the melt with a stirring spoon to make the composition uniform. During the melting process, a protective atmosphere is continuously introduced and the melt temperature is checked every 15 minutes with a temperature control accuracy of ±5℃. Step 4: Add carbonaceous inoculant: The bell jar pressing method is used to add 0.1% to 1.5% of the mass of the alloy melt, of hexachloroethane (C2Cl6) powder with a purity ≥99.5%, or to press it into a cylindrical block. Step 5: Nurturing and Warming: After C2Cl6 is added, continue to keep the temperature in the range of 680 to 800°C for 5 to 60 minutes, and gently stir the melt with a graphite rod every 10 minutes during the holding period; Step Six: Refining and Settling: (1) After the incubation and heat preservation are completed, the melt temperature is reduced to 720-740℃, and 0.2%-0.5% of sodium-free refining agent by mass of melt is added and stirred for 3-5 minutes; (2) After stopping stirring, raise the temperature to 750-760℃, let it stand for 10-15 minutes, and skim off the surface scum; Step 7, Post-processing: (1) Adjust the temperature of the refined and settled melt to 680-720℃ and then pour it; (2) Remove the casting, cut off the gating and riser, and remove the surface oxide scale by sandblasting or pickling; (3) Take metallographic samples from the same part of the casting, grind, polish and etch them, observe the grain morphology under an optical microscope or scanning electron microscope, and use the cut-off method or image analysis software to count the average grain size.

2. The method for refining the grain size of magnesium-aluminum alloys using carbonaceous inoculation according to claim 1, characterized in that: The heat preservation temperature mentioned in step five is preferably 780℃.

3. A method for refining the grain size of magnesium-aluminum alloys using carbonaceous inoculation as described in claim 1 or 2, characterized in that: The optimal incubation and heat preservation time is 5 minutes.

4. The method for refining the grain size of magnesium-aluminum alloys using carbonaceous inoculation according to claim 1, characterized in that: Ultrasonic treatment is used during the incubation and warming stage.

5. A method for refining the grain size of magnesium-aluminum alloys using carbonaceous inoculation as described in claim 1, characterized in that: For magnesium alloys with an aluminum content higher than 9 wt.%, the amount of C2Cl6 added should be increased to 0.8%–1.0%, and the holding time should be extended to 15–20 minutes.

6. A method for refining the grain size of magnesium-aluminum alloys using carbonaceous inoculation as described in claim 1, characterized in that: To reduce the generation of Cl2 gas, magnesium carbonate (MgCO3) powder, accounting for 10% to 30% of its mass, is added to C2Cl6, and the two are mixed and pressed into blocks for use.

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