Magnesium alloy smelting and casting method and equipment

Abstract

The invention relates to a magnesium alloy smelting and casting method and equipment, and the method comprises the following steps: heating and melting raw materials required for preparing a magnesium alloy to obtain a melt; refining gas is introduced into the melt for refining, and waste residues are removed; standing and cooling the refined melt; casting the melt subjected to standing and cooling; wherein the heating and melting process, the refining process, the standing and cooling process and the casting process are carried out in a protective atmosphere; the protective atmosphere comprises sulfur hexafluoride and carbon dioxide, and the volume flow rate of the sulfur hexafluoride is 30 mL / min to 40 mL / min. According to the method, the quality of the magnesium alloy cast ingot is improved, and the prepared magnesium alloy is low in impurity content, few in defect and excellent in mechanical property.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to methods and equipment for smelting and casting magnesium alloys. Background Technology

[0002] Magnesium alloys play a vital role in the automotive, electronics, and medical fields due to their lightweight, shock absorption, and electromagnetic shielding properties. Because molten magnesium is easily combustible and oxidized, magnesium alloy smelting and casting typically employs a flux coating method. This method uses flux to isolate the molten magnesium from air, inhibiting combustion and oxidation. However, the flux coating method is prone to cracking or failure of the flux coating layer due to mechanical stirring or temperature fluctuations, thus reducing the quality of the magnesium alloy. Furthermore, maintaining a stable flux coating layer during continuous pouring is difficult. Therefore, when using the flux coating method for semi-continuous smelting and casting of magnesium alloys, severe oxidation of the melt results in magnesium alloy ingots with high impurity levels and a high defect rate. Summary of the Invention

[0003] Therefore, it is necessary to provide a magnesium alloy melting and casting method and equipment, which can improve the quality of magnesium alloy ingots.

[0004] One aspect of this application provides a method for melting and casting a magnesium alloy, comprising the following steps:

[0005] The raw materials required for preparing magnesium alloys are heated and melted to obtain a melt;

[0006] Refining gas is introduced into the melt for refining to remove waste residue;

[0007] The refined melt is allowed to cool statically.

[0008] The melt, after being allowed to stand and cool, is then cast.

[0009] The heating and melting, refining, static cooling and casting processes are all carried out in a protective atmosphere.

[0010] The protective atmosphere comprises sulfur hexafluoride and carbon dioxide, wherein the volumetric flow rate of sulfur hexafluoride is 30 mL / min to 40 mL / min.

[0011] The above method uses sulfur hexafluoride and carbon dioxide as protective gases to isolate the molten metal from air, and refines the melt using refining gases. The resulting magnesium alloy has low impurity content, few defects, and excellent mechanical properties. This method uses sulfur hexafluoride and carbon dioxide as protective gases throughout the smelting and casting process, and refines the melt using refining gases. The absence of mechanical stirring during refining reduces gas entrapment and further improves the quality of the magnesium alloy. The above method uses a mixture of sulfur hexafluoride and carbon dioxide as a protective gas. Sulfur hexafluoride reacts with the magnesium melt at high temperature, forming a dense protective film mainly composed of MgF2 crystals on the surface of the melt. This film effectively blocks oxygen and water vapor from contacting the magnesium, thus preventing its oxidation and combustion. Carbon dioxide also reacts with the magnesium to form a thin film of MgO. The MgO film becomes stable under the reinforcement of the dense protective film of MgF2, thus producing a synergistic protective effect. A small amount of sulfur hexafluoride can better isolate oxygen and water vapor. By controlling the volumetric flow rate of sulfur hexafluoride at 30 ml / min to 40 ml / min, the corrosion of equipment by sulfur hexafluoride is reduced while improving the quality of magnesium alloy.

[0012] The above method uses gas refining, which can be applied to the flux-free melting and casting of magnesium alloys in semi-continuous magnesium alloy melting and casting equipment. This improves production efficiency, reduces the molten salt inclusions and environmental pollution problems caused by traditional flux-covered refining processes, and lowers the risks to environmental pollution and worker health and safety.

[0013] The above methods can be applied to semi-automatic production lines for magnesium alloy ingots and rods with a capacity of ton or more, providing a foundation for large-scale automated production lines for fluxless smelting of magnesium alloys.

[0014] In some embodiments, the volume ratio of sulfur hexafluoride to carbon dioxide is 1:(500~1000); and / or,

[0015] The carbon dioxide gas pressure is 0.2 MPa to 0.4 MPa; and / or,

[0016] The volumetric flow rate of the carbon dioxide is 20 L / min to 30 L / min; and / or,

[0017] The sulfur hexafluoride is at a pressure of 0.25 MPa to 0.5 MPa.

[0018] In some embodiments, the pressure of the sulfur hexafluoride is greater than the pressure of the carbon dioxide, and the pressure difference between the sulfur hexafluoride and the carbon dioxide is 0.05 MPa to 0.3 MPa.

[0019] In some embodiments, the introduction of refined gas includes the following steps:

[0020] Multiple evenly distributed ventilation points are selected inside the melt, and the ventilation points are located at 1 / 2 to 3 / 4 of the depth of the melt;

[0021] The refined gas is introduced into each ventilation point for refining.

[0022] In some embodiments, the refining gas is argon;

[0023] Optionally, the volumetric flow rate of the argon gas is 5 L / min to 15 L / min.

[0024] In some embodiments, the refining temperature is 720°C to 740°C; and / or,

[0025] The refining time is 15 min to 25 min; and / or,

[0026] The raw materials include magnesium ingots, aluminum ingots, zinc ingots, and aluminum-manganese master alloy.

[0027] In some embodiments, after the removal of waste residue and before the refining melt is allowed to stand for cooling, the refining melt is allowed to stand for 10 to 20 minutes.

[0028] In some embodiments, the static cooling includes cooling the refined melt to a temperature of 705 °C to 715 °C.

[0029] In some embodiments, the magnesium alloy comprises, by mass percentage, 7.5% to 9.0% Al, 0.2% to 0.8% Zn, 0.15% to 0.5% Mn, with the balance being Mg and unavoidable impurities.

[0030] A second aspect of this application provides a magnesium alloy melting and casting equipment, including a melting device, a settling device, a casting device, a protective gas supply device, and a refining gas supply device.

[0031] The protective gas supply device is used to provide protective gas, which includes sulfur hexafluoride and carbon dioxide. The outlet of the protective gas supply device is connected to the smelting device, the settling device and the casting device respectively.

[0032] The refining gas supply device is used to provide refining gas, and the outlet of the refining gas supply device is connected to the smelting device. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a magnesium alloy semi-continuous melting and casting system according to one embodiment.

[0034] Figure 2This is a top surface morphology diagram of the ingot prepared in Example 1.

[0035] Figure 3 This is a bottom surface morphology diagram of the ingot prepared in Example 1.

[0036] Figure 4 This is a side view of the ingot prepared in Example 1.

[0037] Figure 5 The image shows the fracture morphology of the ingot prepared in Example 1.

[0038] Figure 6 This is a morphology diagram of the cast rod obtained in Example 2.

[0039] Figure 7 This is a topographic image of the cast rod obtained in Example 2 after it has been rolled into a sheet.

[0040] Explanation of reference numerals in the attached figures:

[0041] 101. First smelting furnace; 102. First settling furnace; 103. Ingot casting machine; 104. Protective gas supply device; 201. Second smelting furnace; 202. Second settling furnace; 203. Front liquid tank; 204. Crystallizer. Detailed Implementation

[0042] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown herein. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] In the process of magnesium alloy smelting, in order to isolate oxygen and inhibit the combustion and oxidation of magnesium liquid, flux is usually covered on the surface of the melt. The flux needs to be within a specific temperature range to form an effective covering layer. Temperature fluctuations can easily lead to the failure of protection, and vigorous stirring or long-term smelting may cause the flux layer to crack, requiring replenishment. Frequent replenishment of flux can easily introduce impurities and increase the complexity of operation.

[0045] Traditional flux-coated semi-continuous melting and casting methods for magnesium alloys suffer from the inability to maintain a stable coating during continuous pouring. This leads to severe oxidation of the melt, resulting in an oxide scale thickness typically exceeding 50 μm and a defect rate of over 15% for cold shuts or shrinkage cavities, resulting in low-quality magnesium alloys. While some researchers have attempted to introduce flame-retardant sulfur hexafluoride (SF6) as a protective gas, this method proves ineffective at low concentrations, while excessive amounts can corrode steel equipment. Furthermore, it is difficult to operate, control, and is costly.

[0046] Based on this, one aspect of this application provides a magnesium alloy melting and casting method, comprising the following steps:

[0047] The raw materials required for preparing magnesium alloys are heated and melted to obtain a melt;

[0048] Refining gas is introduced into the melt for refining to remove waste residue;

[0049] The refined melt is allowed to cool statically.

[0050] The melt, after being allowed to stand and cool, is then cast.

[0051] The heating and melting, refining, static cooling and casting processes are all carried out in a protective atmosphere;

[0052] The protective atmosphere consists of sulfur hexafluoride and carbon dioxide, with a sulfur hexafluoride volumetric flow rate of 30 mL / min to 40 mL / min.

[0053] The above method uses sulfur hexafluoride and carbon dioxide as protective gases to isolate the molten metal from air, and refines the melt using refining gases. The resulting magnesium alloy has low impurity content, few defects, and excellent mechanical properties. This method uses sulfur hexafluoride and carbon dioxide as protective gases throughout the smelting and casting process, and refines the melt using refining gases. The absence of mechanical stirring during refining reduces gas entrapment and further improves the quality of the magnesium alloy. The above method uses a mixture of sulfur hexafluoride and carbon dioxide as a protective gas. Sulfur hexafluoride reacts with the magnesium melt at high temperature, forming a dense protective film mainly composed of MgF2 crystals on the surface of the melt. This film effectively blocks oxygen and water vapor from contacting the magnesium, thus preventing its oxidation and combustion. Carbon dioxide also reacts with magnesium to form a thin film of MgO. The MgO film becomes stable under the reinforcement of the dense MgF2 protective film, thus producing a synergistic protective effect. A small amount of sulfur hexafluoride can better isolate oxygen and water vapor. By controlling the volumetric flow rate of sulfur hexafluoride at 30 ml / min ~ 40 ml / min, the corrosion of equipment by sulfur hexafluoride is reduced while improving the quality of magnesium alloy.

[0054] The above method uses gas refining, which can be applied to the flux-free melting and casting of magnesium alloys in semi-continuous magnesium alloy melting and casting equipment. This improves production efficiency, reduces the molten salt inclusions and environmental pollution problems caused by traditional flux-covered refining processes, and lowers the risks to environmental pollution and worker health and safety.

[0055] The above methods can be applied to semi-automatic production lines for magnesium alloy ingots and rods with a capacity of ton or more, providing a foundation for large-scale automated production lines for fluxless smelting of magnesium alloys.

[0056] Understandably, sulfur hexafluoride and carbon dioxide are introduced above the melt as a protective atmosphere; refining gas is introduced into the melt.

[0057] As an example, the volumetric flow rate of sulfur hexafluoride can be 30 ml / min, 31 ml / min, 32 ml / min, 33 ml / min, 34 ml / min, 35 ml / min, 36 ml / min, 37 ml / min, 38 ml / min, 39 ml / min or 40 ml / min, or it can be within the range formed by any two of the above point values ​​as endpoints.

[0058] Furthermore, the volumetric flow rate of sulfur hexafluoride is 30 ml / min to 35 ml / min. Within this range, not only can the risk of melt combustion and equipment corrosion be reduced, but the amount of potential non-metallic inclusions introduced by the protective gas itself is also reduced, thereby improving the purity of magnesium alloy ingots.

[0059] In some embodiments, the volume ratio of sulfur hexafluoride to carbon dioxide is 1:(500~1000).

[0060] In some embodiments, the carbon dioxide pressure is 0.2 MPa to 0.4 MPa.

[0061] Understandably, the gas pressure refers to the inlet pressure. Since the flow rates of carbon dioxide and sulfur hexafluoride differ significantly, their partial pressures also differ significantly. The inlet pressure of the two gases can be controlled by installing a pressure reducing valve on the protective gas supply device, and the flow rates can be controlled to ensure that carbon dioxide and sulfur hexafluoride can be mixed in equal proportions in the pipeline.

[0062] In some embodiments, the volumetric flow rate of carbon dioxide is 20 L / min to 30 L / min.

[0063] As an example, the volumetric flow rate of carbon dioxide can be 20 L / min, 21 L / min, 22 L / min, 23 L / min, 24 L / min, 25 L / min, 26 L / min, 27 L / min, 28 L / min, 29 L / min or 30 L / min, or it can be within the range formed by any two of the above point values ​​as endpoints.

[0064] Furthermore, the volumetric flow rate of carbon dioxide is 25 L / min to 30 L / min. Within this range, it is beneficial to form a more stable MgO / MgF2 composite protective layer on the melt surface, thereby further reducing the impurity content of magnesium alloy ingots and improving the mechanical properties of magnesium alloy ingots.

[0065] In some embodiments, the sulfur hexafluoride is at a pressure of 0.25 MPa to 0.5 MPa.

[0066] As an example, the pressure of sulfur hexafluoride is 0.25 MPa, 0.3 MPa, 0.4 MPa or 0.5 MPa, or any two of the above point values ​​can be used as the end values.

[0067] Furthermore, the pressure of sulfur hexafluoride is 0.3 MPa to 0.5 MPa.

[0068] In some embodiments, the pressure of sulfur hexafluoride is greater than the pressure of carbon dioxide, and the pressure difference between sulfur hexafluoride and carbon dioxide is 0.05 MPa to 0.3 MPa.

[0069] Furthermore, the pressure difference between sulfur hexafluoride and carbon dioxide is 0.05 MPa to 0.1 MPa. Within this pressure difference range, trace amounts of sulfur hexafluoride can be actively and smoothly integrated into the mainstream of carbon dioxide, preventing backflow or retention of sulfur hexafluoride, thereby achieving a highly uniform mixing of the two gases and improving the uniformity of the surface microstructure of the magnesium alloy ingot.

[0070] In some embodiments, introducing refined gas includes the following steps:

[0071] Multiple evenly distributed ventilation points are selected inside the melt, with the ventilation points located at 1 / 2 to 3 / 4 of the melt depth;

[0072] Refined gas is introduced into each ventilation point for refining.

[0073] In some of these embodiments, the refining gas is argon;

[0074] Optionally, the volumetric flow rate of argon is 5 L / min to 15 L / min.

[0075] In one embodiment, the volumetric flow rate of argon gas is 5 L / min to 15 L / min.

[0076] As an example, the volumetric flow rate of argon gas is 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min or 15 L / min, or any two of the above values ​​can be used as endpoints within the range.

[0077] Furthermore, the volumetric flow rate of argon gas is 5 L / min to 10 L / min. Within this range, gas entrapment can be further reduced, thus decreasing inclusions in magnesium alloy ingots.

[0078] In some of these embodiments, the refining temperature is 720°C to 740°C.

[0079] As an example, the refining temperature can be 720 ℃, 721 ℃, 722 ℃, 723 ℃, 724 ℃, 725 ℃, 726 ℃, 727 ℃, 728 ℃, 729 ℃, 730 ℃, 731 ℃, 732 ℃, 733 ℃, 734 ℃, 735 ℃, 736 ℃, 737 ℃, 738 ℃, 739 ℃, or 740 ℃, or it can be within the range formed by any two of the above point values ​​as endpoints.

[0080] Furthermore, the refining temperature is 730 ℃~740 ℃.

[0081] In some implementations, the refining time is 15 min to 25 min.

[0082] In some embodiments, the raw materials include magnesium ingots, aluminum ingots, zinc ingots, and aluminum-manganese master alloys.

[0083] In some embodiments, after removing the waste residue, the refined melt is allowed to stand for 10 to 20 minutes before being allowed to cool.

[0084] Understandably, the melt is allowed to stand in the smelting apparatus for 10 to 20 minutes before being transferred to the settling apparatus for cooling.

[0085] In some embodiments, static cooling includes cooling the refined melt to a temperature of 705°C to 715°C.

[0086] In some embodiments, the casting frequency is 30 Hz to 45 Hz.

[0087] In some embodiments, the casting interval is 10 s to 12 s.

[0088] In some embodiments, the magnesium alloy comprises, by mass percentage, 7.5% to 9.0% Al, 0.2% to 0.8% Zn, 0.15% to 0.5% Mn, with the balance being Mg and unavoidable impurities.

[0089] Furthermore, magnesium alloys include, but are not limited to, ZM5 magnesium alloys.

[0090] A second aspect of this application provides a magnesium alloy melting and casting equipment, including a melting device, a settling device, a casting device, a protective gas supply device, and a refining gas supply device.

[0091] The protective gas supply device is used to provide protective gas, which includes sulfur hexafluoride and carbon dioxide. The outlet of the protective gas supply device is connected to the smelting device, the settling device and the casting device respectively.

[0092] The refining gas supply device is used to supply refining gas, and the outlet of the refining gas supply device is connected to the smelting device.

[0093] In one embodiment, the smelting apparatus employs a smelting furnace.

[0094] In one embodiment, the settling device is a settling furnace.

[0095] In one embodiment, the casting apparatus employs an ingot casting machine or a crystallizer.

[0096] Understandably, continuous casting involves casting the molten material into a block-shaped ingot using a metering casting tube to deliver the molten material into the mold cavity of each ingot casting machine; continuous casting involves solidifying the molten material into an ingot using a crystallizer and continuously casting it into a rod using a casting system.

[0097] To make the objectives, technical solutions, and advantages of this application clearer and more concise, the following specific embodiments are used for illustration, but this application is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of this application and can be used to describe this application, but should not be construed as limiting the scope of this application. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

[0098] To better illustrate this application, the following description, in conjunction with specific embodiments, further explains its content. The following are specific embodiments.

[0099] Please refer to the casting equipment used in the following embodiments. Figure 1It includes a first smelting furnace 101, a first settling furnace 102, an ingot casting machine 103, a protective gas supply device 104, and a refining gas supply device; the protective gas supply device 104 is used to provide protective gas, which includes sulfur hexafluoride and carbon dioxide, and the outlet of the protective gas supply device 104 is connected to the first smelting furnace 101, the first settling furnace 102, and the ingot casting machine 103 through a quantitative casting pipe; the refining gas supply device is used to provide refining gas, and the outlet of the refining gas supply device is connected to the first smelting furnace 101;

[0100] It also includes a second smelting furnace 201, a second settling furnace 202, a front liquid tank 203, a crystallizer 204, a protective gas supply device 104, and a refining gas supply device; the protective gas supply device 104 is used to provide protective gas, which includes sulfur hexafluoride and carbon dioxide, and the outlet of the protective gas supply device 104 is connected to the second smelting furnace 201, the second settling furnace 202, and the crystallizer 204 respectively; the refining gas supply device is used to provide refining gas, and the outlet of the refining gas supply device is connected to the second smelting furnace 201.

[0101] Example 1

[0102] A semi-continuous melting and casting method for ZM5 magnesium alloy includes the following steps:

[0103] (1) Material preparation: Weigh and proportion the magnesium ingots, aluminum ingots, zinc ingots, and aluminum-manganese master alloy required for production, and crush them to a suitable size for easy feeding. The purity of magnesium ingots should be ≥99.95%, aluminum ingots ≥99.85%, zinc ingots ≥99.99%, and the manganese content in the aluminum-manganese master alloy should be 10%. The feeding port size is 160mm*250mm. The width of a standard 25 kg / bar aluminum ingot is 180 mm and the thickness is 120 mm, which can be directly fed in. Some small pieces of aluminum ingot need to be prepared for weighing. Zinc ingots need to be crushed to a size of 2kg~3kg to prevent them from sinking rapidly to the bottom of the smelting furnace during the feeding process, which would cause alloy composition segregation.

[0104] (2) Drying: Dry the weighed raw materials: magnesium ingots, aluminum ingots, zinc ingots, and aluminum-manganese master alloy at 200 ℃~300 ℃ for 2 hours;

[0105] (3) Before starting the furnace, check whether the equipment is in normal condition and whether the raw materials meet the production requirements; the protective gas supply device 104 is controlled by the valve on the protective gas supply device 104 to supply protective gas to the first smelting furnace 101, the first settling furnace 102 and the ingot casting machine 103.

[0106] (4) Feeding and heating: Add magnesium ingots, start heating, and fix the heating power at 110kw. Set the melting temperature to 730 ℃. When the melting furnace reaches 350 ℃, introduce protective gas through the protective gas supply device. The protective gas is a mixture of carbon dioxide and sulfur hexafluoride. The pressure of carbon dioxide is 0.3 MPa and the volumetric flow rate of carbon dioxide is 25 L / min. The pressure of sulfur hexafluoride is 0.35 MPa and the volumetric flow rate of sulfur hexafluoride is 35 ml / min.

[0107] (5) When the temperature of magnesium liquid rises to 730 ℃, add aluminum ingots and aluminum-manganese intermediate alloy. After dissolving, add zinc ingots. When adding zinc, use a slag scoop to hold the zinc about 5 cm above the liquid surface. After it melts, immediately stir mechanically to prevent it from sinking. The stirring frequency is 35 kw ~ 40 kw and the stirring time is 10 min.

[0108] (6) High-purity argon gas is introduced through the refining gas supply device and refined twice, each time for 10 minutes. The volume flow rate of argon gas is controlled at 10 L / min so that the melt rolls but does not splash. Among them, the refining adopts the five-point ventilation method. The gas supply pipe of the refining gas supply device is inserted into the melt depth at 3 / 4 position (that is, the ventilation point is located at 3 / 4 position of the melt depth, and the distance from the ventilation point to the bottom of the melting furnace is 1 / 4 of the melt depth). Gas is vented one by one at the five positions of the melting furnace (top, bottom, left, right and center) for 2 minutes.

[0109] (7) After refining, remove the scum and bottom scum, and let it stand for 10 min to 20 min;

[0110] (8) After standing, take a sample to test the composition. If the test result is not qualified, add appropriate amounts of magnesium ingots, aluminum ingots, metallic zinc or magnesium-manganese intermediate alloy, refine with argon for 10 minutes, and then retest the composition. If the composition is still not qualified, continue to repeat the current step until the composition is qualified, that is, the composition meets the following: Al mass percentage is 7.5%~9.0%, Zn mass percentage is 0.2%~0.8%, Mn mass percentage is 0.15%~0.5%, and the balance is Mg and unavoidable impurities.

[0111] (9) Transfer the liquid to stand, turn on the liquid transfer pump, transfer the melt that has passed the composition test to the standing furnace, and when the melt temperature cools down to 705 ℃~715 ℃, cast ZM5 ingots through the ingot casting machine. The cooling time is the standing time.

[0112] (10) Turn on the casting pump, the casting frequency is 30 HZ~45 HZ, the ingot interval is 10 s~12 s, and the protective gas valve will open automatically during the casting process.

[0113] Example 2

[0114] Example 2 is basically the same as Example 1, except that in step (3), the protective gas supply device 104 is controlled by the valve on the protective gas supply device 104 to supply protective gas to the second smelting furnace 201, the second settling furnace 202 and the crystallizer 204.

[0115] In step (10), the production of the casting rod involves transferring the melt to the front liquid tank 203 through a metering pump and metering tube. The metering pump operates at a frequency of 40 Hz. The cooling water pump is turned on, and the casting can begin after the water flow in the crystallizer is uniform, thus producing the casting rod.

[0116] Example 3

[0117] Example 3 is basically the same as Example 1, except that in step (4), the volumetric flow rate of sulfur hexafluoride is 40 ml / min.

[0118] Example 4

[0119] Example 4 is basically the same as Example 1, except that in step (4), the volumetric flow rate of carbon dioxide is 20 L / min.

[0120] Example 5

[0121] Example 6 is basically the same as Example 1, except that in step (4), the pressure of sulfur hexafluoride is 0.5 MPa.

[0122] Comparative Example 1

[0123] Comparative Example 1 uses the traditional flux covering method to prepare ZM5 magnesium alloy ingots, including the following steps:

[0124] (1) Preparation stage: preheat to dark red (400 ℃~500 ℃), evenly sprinkle RJ-2 covering agent on the bottom of the inner wall, dry the weighed raw materials: magnesium ingot, aluminum ingot, zinc ingot, aluminum manganese master alloy at 200 ℃~300 ℃ for 2 hours, and dry the covering agent and refining agent (such as RJ series) at 160 ℃ for 30 min to remove crystal water;

[0125] (2) During the smelting stage, first add magnesium ingots and aluminum ingots, and sprinkle RJ-2 covering agent on the surface to prevent oxidation during melting. Raise the temperature to 650℃~700℃ and the furnace charge will gradually melt. If the liquid surface is exposed and sparks are emitted, immediately add more covering agent. When the temperature reaches 700℃~730℃, add preheated Al-Mn master alloy. After it melts, add pure zinc to ensure uniform composition.

[0126] (3) Refining and removing impurities: After the furnace charge is fully melted, mechanically stir for 5 min to 8 min to ensure uniform composition. Take a sample for pre-furnace composition analysis. If the test results are not qualified, add magnesium ingots / aluminum ingots / zinc / magnesium-manganese master alloy as appropriate. Heat to 720 ℃ to 740 ℃. Use a bell jar to press the refining agent into the melt in batches to 2 / 3 depth. Slowly move and stir for 5 min to 8 min until the liquid surface is a bright mirror surface.

[0127] (4) After refining, cool down to 700 ℃~720 ℃ and let stand for 15 min~30 min to allow the flux inclusions to settle to the bottom of the crucible. Use a coated slag skimmer to skim off the surface slag and settled slag to avoid stirring the bottom flux. After skimming, sprinkle a small amount of RJ-2 covering agent to prevent secondary oxidation.

[0128] (5) Casting: Adjust the temperature to 680 ℃~720 ℃ and start casting.

[0129] Comparative Example 2

[0130] Comparative Example 2 is basically the same as Example 1, except that in step (4), argon gas with the same volume flow rate is used instead of carbon dioxide in the protective gas.

[0131] Comparative Example 3

[0132] Comparative Example 3 is basically the same as Example 1, except that in step (4), the flow rate of sulfur hexafluoride is 20 mL / min.

[0133] Comparative Example 4

[0134] Comparative Example 4 is basically the same as Example 1, except that in step (4), the flow rate of sulfur hexafluoride is 50 mL / min.

[0135] The magnesium alloy ingots or rods prepared in each embodiment and comparative example were subjected to compositional analysis and performance testing. The compositional analysis results are shown in Table 1, and the performance test results are shown in Table 2.

[0136] The testing standards for each performance test item are as follows:

[0137] Magnesium alloy composition testing: GB / T 1177-2018.

[0138] Mechanical property testing of magnesium alloys: GB / T 228.1-2021.

[0139] Table 1

[0140]

[0141] Table 2

[0142]

[0143] As shown in Tables 1 and 2 above, Examples 1-5 used sulfur hexafluoride and carbon dioxide as protective gases to isolate the air, and used inert gases to refine the melt. This method of preparing magnesium alloys without flux coverage was applied to a semi-continuous casting apparatus, resulting in magnesium alloys with low impurity content, few defects, and excellent mechanical properties. Figures 2-5 It can be seen that the magnesium alloy ingot prepared in Example 1 has a bright silvery-white surface, a fine and smooth microstructure, and no obvious surface defects such as cold shuts or flow marks. Furthermore, the cross-sectional microstructure is uniform, without obvious central shrinkage porosity, shrinkage cavities, or cracks. Figure 6 and Figure 7 It can be seen that the casting rod is straight, and the surface of the car body has a uniform metallic luster.

[0144] The magnesium alloy ingots prepared in Comparative Examples 1-3 had high contents of impurity elements Be, O and C, with C content reaching as high as 0.0095%; in Comparative Example 4, due to the excessive flow rate of added sulfur hexafluoride, there was equipment corrosion problem.

[0145] Moreover, when the volumetric flow rate of sulfur hexafluoride in the protective gas is 30 ml / min ~ 35 ml / min, the pressure difference between sulfur hexafluoride and carbon dioxide is 0.05 MPa ~ 0.1 MPa, the volumetric flow rate of carbon dioxide is 25 L / min ~ 30 L / min, or the volumetric flow rate of argon is 5 L / min ~ 10 L / min, the magnesium alloy ingot has less impurity content and higher quality.

[0146] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0147] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for melting and casting magnesium alloys, characterized in that, Includes the following steps: The raw materials required for preparing magnesium alloys are heated and melted to obtain a melt; Refining gas is introduced into the melt for refining to remove waste residue; The refined melt is allowed to cool statically. The melt, after being allowed to stand and cool, is then cast. The heating and melting, refining, static cooling and casting processes are all carried out in a protective atmosphere. The protective atmosphere comprises sulfur hexafluoride and carbon dioxide, wherein the volumetric flow rate of sulfur hexafluoride is 30 mL / min to 40 mL / min.

2. The magnesium alloy smelting and casting method according to claim 1, characterized in that, The volume ratio of sulfur hexafluoride to carbon dioxide is 1:(500~1000); and / or, The carbon dioxide gas pressure is 0.2 MPa to 0.4 MPa; and / or, The volumetric flow rate of the carbon dioxide is 20 L / min to 30 L / min; and / or, The sulfur hexafluoride is at a pressure of 0.25 MPa to 0.5 MPa.

3. The magnesium alloy smelting and casting method according to claim 1, characterized in that, The pressure of the sulfur hexafluoride is greater than the pressure of the carbon dioxide, and the pressure difference between the sulfur hexafluoride and the carbon dioxide is 0.05 MPa to 0.3 MPa.

4. The magnesium alloy smelting and casting method according to any one of claims 1 to 3, characterized in that, The process of introducing refined gas includes the following steps: Multiple evenly distributed ventilation points are selected inside the melt, and the ventilation points are located at 1 / 2 to 3 / 4 of the depth of the melt; The refined gas is introduced into each ventilation point for refining.

5. The magnesium alloy smelting and casting method according to any one of claims 1 to 3, characterized in that, The refining gas is argon; Optionally, the volumetric flow rate of the argon gas is 5 L / min to 15 L / min.

6. The magnesium alloy smelting and casting method according to any one of claims 1 to 3, characterized in that, The refining temperature is 720 ℃~740 ℃; and / or, The refining time is 15 min to 25 min; and / or, The raw materials include magnesium ingots, aluminum ingots, zinc ingots, and aluminum-manganese master alloy.

7. The magnesium alloy smelting and casting method according to any one of claims 1 to 3, characterized in that, After the removal of waste residue and before the refining melt is allowed to stand and cool, the refining melt is allowed to stand for 10 min to 20 min.

8. The magnesium alloy smelting and casting method according to any one of claims 1 to 3, characterized in that, The static cooling process includes cooling the refined melt to a temperature of 705 ℃~715 ℃.

9. The magnesium alloy smelting and casting method according to any one of claims 1 to 3, characterized in that, The magnesium alloy comprises, by mass percentage, 7.5% to 9.0% Al, 0.2% to 0.8% Zn, 0.15% to 0.5% Mn, with the balance being Mg and unavoidable impurities.

10. A magnesium alloy smelting and casting equipment, characterized in that, This includes smelting equipment, settling equipment, casting equipment, protective gas supply equipment, and refining gas supply equipment; The protective gas supply device is used to provide protective gas, which includes sulfur hexafluoride and carbon dioxide. The outlet of the protective gas supply device is connected to the smelting device, the settling device and the casting device respectively. The refining gas supply device is used to provide refining gas, and the outlet of the refining gas supply device is connected to the smelting device.

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