A high rate solidification casting method for magnesium alloy investment precision casting

Abstract

This invention discloses a high-rate solidification casting method for precision investment casting of magnesium alloys, belonging to the field of non-ferrous metal casting technology. The method includes: manufacturing an investment casting mold assembly; preparing a surface slurry mainly composed of aluminum sol and zircon powder, a transition layer slurry mainly composed of silica sol and corundum powder, and a back coating mainly composed of silica sol and coal gangue powder; preparing a precast shell by layering and sprinkling sand on the mold assembly; firing the shell; preheating the shell to above 800°C; pouring the magnesium alloy; and rapidly cooling the shell after pouring using high-rate solidification equipment. This invention significantly improves the shell's resistance to high-temperature reactions from the magnesium alloy melt by developing a highly chemically inert surface material system, enabling high-temperature preheating of the shell and ensuring that the magnesium alloy melt remains in a pure liquid state during filling, resulting in excellent filling capacity. Simultaneously, combined with high-rate solidification equipment, it achieves controllable rapid solidification under large supercooling, refining grains, suppressing interfacial reactions, and eliminating shrinkage defects. This invention effectively solves the technical problems of severe interfacial reaction, low and uncontrollable solidification rate in magnesium alloy investment casting, significantly improves the metallurgical quality and mechanical properties of castings, and can be widely used in the manufacture of high-performance magnesium alloy precision castings in aerospace and other fields.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal casting technology, specifically relating to a high-speed solidification casting method for magnesium alloy investment casting precision casting. Background Technology

[0002] The demand for highly lightweight and high-precision forming in the field of next-generation aerospace equipment is becoming increasingly urgent. At the same time, the highly integrated component design significantly increases the difficulty of machining, thus highlighting the need for innovation in casting technology. Magnesium alloys, as lightweight structural materials with low density and high specific strength, can effectively achieve the strategic goal of highly lightweighting. However, under current casting processes, magnesium alloy castings suffer from serious deficiencies in manufacturing precision, appearance quality, internal quality, mechanical properties, and reliability, making it difficult to support the demands of the rapidly developing next-generation aerospace manufacturing technology.

[0003] Investment casting technology boasts advantages such as high-precision forming and excellent surface quality. Combining magnesium alloys with investment casting can leverage the strengths of both technologies. However, magnesium alloys have high chemical reactivity and will exhibit strong physicochemical reactions with existing ceramic mold materials. Furthermore, current investment casting technology cannot effectively control the melt filling and solidification processes macroscopically, thus limiting the improvement of the metallurgical quality and microstructure of the castings.

[0004] In the process of investment casting of magnesium alloys, due to the relatively active chemical properties of magnesium alloys, they will produce strong physicochemical reactions with the mold shell, especially under prolonged high-temperature contact. As a result, the mold shell cannot be heated to a high preheating temperature during the investment casting process. However, the low preheating temperature will cause the magnesium alloy melt to enter a pasty solidification state too early during the pouring and filling process, thus affecting the solidification and feeding effect of the entire casting and ultimately forming metallurgical defects such as porosity. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by proposing a high-rate solidification casting method for magnesium alloy investment casting. Through the preparation of high-performance ceramic molds and the development of high-rate solidification equipment, this invention solves the manufacturing drawbacks of interfacial reactions, slow molten cooling rates, and uncontrollable solidification processes in the precision casting of magnesium alloy investment casting. It achieves controllable and directional solidification of the magnesium alloy melt, enabling high-quality production of precision magnesium alloy investment casting parts.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A high-rate solidification casting method for precision investment casting of magnesium alloys includes the following steps: Step 1: Manufacture the investment casting module according to the structural characteristics of the casting; Step 2: Prepare the surface layer slurry, transition layer slurry, and back layer coating for the ceramic shell; Step 3: Apply the surface layer slurry, transition layer slurry, and back layer coating obtained in Step 2 to the casting mold obtained in Step 1, and then apply sand to obtain the precast shell. Step 4: Firing the precast shell to obtain the shell; the precast shell obtained in Step 3 is fired at high temperature to remove the modules and give the shell the final strength and air permeability.

[0007] Step 5: Preheat the shell obtained in Step 4 before casting; preheat the shell after baking in Step 4 before casting. Thanks to the high-temperature chemical inertness of the surface material system in Step 2, this method can raise the shell preheating temperature to over 800℃. At this high temperature, the magnesium alloy melt remains above the liquidus line during the filling process, rapidly filling the cavity in a pure liquid state. This fundamentally avoids the "premature solidification" phenomenon caused by low-temperature shells, greatly improving the melt's ability to fill complex thin-walled structures and reducing defects such as cold shuts and incomplete casting.

[0008] Step 6: Cast the magnesium alloy using a preheated mold shell; Step 7: After pouring, rapidly cool the shell.

[0009] In one possible embodiment, in step 1, the investment molding module is manufactured using 3D printing. This can significantly improve the module's precision, shorten the manufacturing cycle, and lay the foundation for subsequent high-precision shell preparation.

[0010] In one possible embodiment, in step 2, the surface slurry includes aluminum sol colloid, zircon powder, wetting agent and defoamer, wherein the weight of zircon powder is 2.6-2.8 times the weight of aluminum sol colloid, and the weight of wetting agent and defoamer is 0.2% to 0.3% of the weight of aluminum sol colloid.

[0011] Formulation and Mechanism of the Surface Layer Slurry: The surface layer slurry uses alumina sol as a binder, zircon powder as the refractory powder, and adds wetting agents and defoamers. The weight of the zircon powder is 2.6-2.8 times that of the alumina sol, and the weights of the wetting agent and defoamer are 0.2%-0.3% of the weight of the alumina sol, respectively. This invention constructs a highly inert surface layer system by using zircon powder with extremely high chemical stability and combining it with alumina sol that can form a dense alumina layer at high temperatures. This surface layer can effectively prevent direct contact between the molten magnesium alloy and the active components in the mold shell at high temperatures, thus inhibiting violent interfacial chemical reactions at the source. This is a prerequisite for subsequent high-temperature preheating and high-rate filling.

[0012] In one possible embodiment, in step 2, the transition layer slurry includes silica sol colloid and corundum powder, wherein the amount of corundum powder added is 2.2 to 2.4 times the weight of the alumina sol colloid. Transition layer slurry formulation and mechanism: The transition layer slurry uses silica sol as a binder and corundum powder as a refractory powder, with the amount of corundum powder added being 2.2 to 2.4 times the weight of the silica sol. Corundum powder has the characteristics of low thermal expansion coefficient and good high-temperature volume stability. As a transition layer, it can effectively alleviate the thermal stress caused by the difference in thermal properties between the surface layer (zircon powder) and the back layer (coal gangue), preventing the shell from cracking during high-temperature firing and casting, and ensuring the overall structural integrity of the shell.

[0013] In one possible embodiment, the backing coating comprises silica sol and coal gangue powder, with the amount of coal gangue powder added being 2.0 to 2.2 times the weight of the colloid. The backing coating formulation and mechanism: The backing coating uses silica sol as a binder and coal gangue powder as the refractory powder, with the amount of coal gangue powder added being 2.0 to 2.2 times the weight of the silica sol. Coal gangue powder is inexpensive and has certain thermal insulation properties; as a backing material, it can ensure shell strength while also being economical.

[0014] In one possible embodiment, the preparation method of the surface slurry includes the following steps: first, pour the aluminum sol colloid into a stainless steel bucket, start the mixer and stir rapidly for 30 minutes, then slowly add zircon powder while stirring continuously, the amount added being 2.6-2.8 times the weight of the aluminum sol colloid; after stirring rapidly for about 3 hours, add the wetting agent and defoamer respectively, then reduce the stirring speed to half of the original speed and continue stirring for 12 hours.

[0015] In one possible embodiment, the preparation method of the transition layer slurry includes the following steps: first, pour the silica sol colloid into a stainless steel bucket, start the mixer and stir rapidly for 30 minutes, then slowly add corundum powder while continuously stirring, the amount added being 2.2 to 2.4 times the weight of the alumina sol colloid. After stirring rapidly for about 3 hours, reduce the stirring speed to half of the original speed and continue stirring for 12 hours.

[0016] In one possible embodiment, the preparation method of the back coating includes the following steps: adding coal gangue powder to a continuously stirred silica sol, the amount added being 2.0 to 2.2 times the weight of the sol, and then continuing to stir for 24 hours.

[0017] In one possible embodiment, in step 3, after the casting mold assembly is sequentially coated and sanded layer by layer in the surface layer slurry, transition layer slurry, and back layer coating, it is then coated and sanded at least three times in the back layer coating to obtain the precast shell. This ensures that the shell has sufficient thickness and strength.

[0018] In one possible embodiment, in step 6, the alloy is filled using an insulated ladle under the protection of a mixed gas. This ensures the purity and temperature stability of the alloy melt during the casting process.

[0019] In one possible embodiment, in step 7, a wind-cooling solidification device is used, in which a high-speed airflow under high pressure flows from the bottom of the shell to the top of the shell for rapid cooling.

[0020] This step is one of the core components of this invention. Its working mechanism is as follows: by forced convection heat transfer, a huge degree of supercooling (i.e., large supercooling) is created around the mold shell, providing a very strong driving force for the solidification of the melt. The beneficial effects of this high-rate solidification are multiple: First, it refines the grains. The extreme supercooling causes a sharp increase in the nucleation rate, thereby obtaining a fine equiaxed grain structure and significantly improving the mechanical properties (strength and plasticity) of the casting. Second, it shortens the interfacial reaction time. Rapid solidification compresses the high-temperature contact time between the magnesium alloy melt and the mold shell to an extremely short time, further inhibiting the interfacial chemical reaction. Third, it improves feeding. High-rate solidification helps to achieve "simultaneous solidification" or quasi-"layer-by-layer solidification," effectively dispersing and suppressing micro-shrinkage porosity and improving the density of the casting. Furthermore, by designing the air ducts and vents of the air-cooling device, it is possible to achieve targeted and selective cooling, focusing on the thick and hot parts of the casting to promote the quasi-layer solidification of the magnesium alloy melt in the designed direction, thereby obtaining high-quality castings with no macroscopic shrinkage cavities and uniform structure.

[0021] The beneficial effects of this invention include: (1) By combining the development of a new high-resistance ceramic shell material system and the preparation of the shell, and the development and application of a high-speed solidification device, the alloy melt can achieve high-speed controllable solidification under high subcooling, thereby suppressing interfacial chemical reactions and improving the metallurgical quality of the casting.

[0022] (2) The shell surface material system uses aluminum sol colloid, zircon powder and zircon sand as the main components, which effectively improves the high temperature resistance of the shell and inhibits the chemical reaction between the shell and the magnesium alloy melt.

[0023] (3) Design and manufacture high-speed solidification equipment to enable the alloy melt to achieve high-speed controllable solidification under large subcooling, thereby suppressing interfacial chemical reactions and improving the metallurgical quality of castings.

[0024] (4) The high-temperature inert shell surface layer and the solidification rate with large supercooling allow the shell to be preheated at a temperature above 800℃. The temperature of the magnesium alloy melt is above the liquidus line at the beginning of the entire filling process, and it can maintain a pure liquid melt state throughout the filling process, resulting in better filling effect.

[0025] (5) The high-speed solidification equipment uses high-pressure compressed air generated by a high-pressure centrifugal fan as a cooling source, resulting in a greater cooling rate and faster solidification speed.

[0026] (6) High-speed solidification equipment can realize the solidification process control of positioning and selective cooling, enhance the cooling effect of thick parts of the casting structure, promote the quasi-layer solidification of magnesium alloy melt, and improve metallurgical quality.

[0027] (7) Add corresponding ventilation ducts at the air inlet and outlet of the high-speed solidification equipment to unify the air volume at each location and ensure consistent cooling efficiency of the castings.

[0028] (8) By adding an air storage box to the high-speed solidification equipment, the air volume is increased, the cooling rate is further improved, and the cooling air path is increased.

[0029] This invention improves the resistance of the inner surface of the ceramic mold shell to high-temperature reactions of the magnesium alloy melt by developing a novel shell material system. This allows the magnesium alloy melt to complete high-rate filling at a higher shell preheating temperature. At this time, the temperature of the magnesium alloy melt is always above the liquidus temperature, maintaining relatively good liquid fluidity. Subsequently, through the development and application of high-performance, high-rate solidification equipment, the alloy melt can achieve high-rate, controllable solidification under large subcooling, suppressing interfacial chemical reactions while improving the metallurgical quality of the casting.

[0030] The method of this invention can significantly improve the manufacturing technology of magnesium alloy castings, deepen the application of magnesium alloy lightweight structural materials in the aerospace field, and promote my country's strategic goal of lightweight aerospace. On the other hand, it can be extended to the fields of investment casting of titanium alloys, aluminum alloys and high-temperature alloys, significantly improving my country's aerospace manufacturing technology level and helping to achieve the national strategic goal of becoming an aviation power. At the same time, this method can be used for both military and civilian purposes, with broad market prospects and significant economic and social benefits. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0032] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setup and method set forth below, but covers any improvements, substitutions, and modifications to the structures, methods, and devices without departing from the spirit of the invention. In the following description, well-known structures and techniques are not shown to avoid unnecessarily obscuring the invention.

[0033] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the stated directions or positional relationships and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0035] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in turn. The present invention will now be described in detail with reference to the embodiments.

[0036] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to several embodiments and comparative examples. It should be noted that the following embodiments and comparative examples are only for explaining the invention and are not intended to limit the invention. Unless otherwise specified, all raw materials used are commercially available products conventional in the art.

[0038] Example 1 This embodiment provides a complete high-rate solidification casting method for magnesium alloy investment casting precision casting, and the specific steps are as follows: (1) Investment casting module manufacturing Based on the three-dimensional model of a certain complex thin-walled magnesium alloy structural part, the gating system is designed to form a casting process plan. Using a stereolithography 3D printer and photosensitive resin material, an integrated investment casting module including the casting cavity, runner, and riser is directly printed. After printing, it is cleaned and cured by ultraviolet light to obtain a high-precision investment casting module.

[0039] (2) Preparation of ceramic shell slurry 1) Preparation of surface layer slurry: Pour 10 kg of aluminosilicate binder into a stainless steel bucket, start the mixer and quickly stir at a speed of about 300 r / min for 30 minutes. Subsequently, while continuously stirring, slowly add 26 kg of zircon powder with a mesh size of 325 (2.6 times the weight of the aluminosilicate). After adding the materials, maintain high-speed stirring for 3 hours. Then, add 25 g of wetting agent (JFC) and defoaming agent (n-octanol) respectively (both are 0.25% of the weight of the aluminosilicate). Subsequently, reduce the stirring speed to about 150 r / min and continue stirring for more than 12 hours. Use a Chinese standard flow cup (capacity 100 mL, outflow aperture Φ6 mm) to measure the viscosity of the slurry. When the flow rate stabilizes at 24 seconds, it is judged as qualified, and the surface layer slurry is obtained.

[0040] 2) Preparation of transition layer slurry: Pour 10 kg of silica sol binder into a stainless steel bucket, start the mixer and quickly stir for 30 minutes. While continuously stirring, slowly add 23 kg of corundum powder with a mesh size of 325 (2.3 times the weight of the silica sol). After high-speed stirring for 3 hours, reduce the stirring speed to half of the original speed and continue stirring for more than 12 hours. Use a standard flow cup to measure. When the flow rate reaches 19 seconds, it is judged as qualified, and the transition layer slurry is obtained.

[0041] 3) Preparation of back layer coating: Slowly add 21 kg of coal gangue powder with a mesh size of 320 (2.1 times the weight of the silica sol) to 10 kg of continuously stirred silica sol. After adding the materials, continue stirring for more than 24 hours. Use a standard flow cup to measure. When the flow rate reaches 12 seconds, it is judged as qualified, and the back layer coating is obtained.

[0042] (3) Coating and sanding of the investment casting module to make the shell 1) Surface layer: Immerse the investment casting module in the surface layer slurry, uniformly coat it and then lift it out. When the dripping stops and there is no excess slurry flowing down, uniformly sprinkle 80-mesh zircon sand. Subsequently, place it in an environment with a temperature of 23±2°C, a humidity of 55±10%, and no forced-flowing wind, and air dry it for more than 12 hours to form the surface layer shell.

[0043] 2) Transition layer: Immerse the surface layer shell in the transition layer slurry for coating, and uniformly sprinkle 60-mesh corundum sand. Subsequently, in an environment with a temperature of 23±2°C, a humidity of 55±10%, and a gentle breeze, air dry it for more than 12 hours to form the transition layer shell.

[0044] 3) Backing layer: Immerse the transition layer shell in the backing layer coating and coat it with it, then evenly spread 46-mesh coal gangue sand. Air dry for more than 6 hours in an environment with a temperature of 24±3℃, humidity of 40±15% and strong airflow to form the third layer shell.

[0045] 4) Reinforcing layer: Repeat step 3 three times, each time sprinkling coal gangue sand with particle sizes of 30 mesh, 46 mesh and 60 mesh respectively, and air-drying for more than 6 hours each time, to form the fourth to sixth shell layers in sequence.

[0046] 5) Sealing layer: Immerse the sixth shell layer in the back coating and coat it (without sprinkling sand). Air dry for more than 24 hours in a strong airflow environment to finally form a precast shell with a total of seven layers (including 1 surface layer, 1 transition layer, 4 back layers, and 1 sealing layer).

[0047] (4) Demolding and firing of the shell The completely dried precast shell is placed in a high-temperature gas furnace for demolding and firing. The temperature is increased to 300°C at a rate of 2°C / min and held for 1 hour to completely remove the mold. Then, the temperature is increased to 1220°C and held for 2.2 hours for sintering. After sintering, the shell is cooled to below 200°C in the furnace and removed from the furnace. The inner cavity of the shell is cleaned with compressed air to obtain a high-strength, clean inner cavity ceramic shell ready for casting.

[0048] (5) Preheating treatment of the shell The shell to be poured is placed in another gas furnace for preheating at a temperature of 810℃ for 50 minutes, so that the shell reaches a uniform preheating temperature before pouring.

[0049] (6) Magnesium alloy casting Use a forklift to quickly transfer the preheated mold shell to the platform of the air-cooling and solidification device. Immediately introduce protective gas (composition: 1.5% SF6 + 98.5% CO2) into the mold shell riser for 55 seconds to displace the air in the cavity. Then, using a preheated ladle to 600°C, pour the molten AZ91D magnesium alloy (pouring temperature 720°C) steadily and continuously into the pouring cup of the mold shell until it is full.

[0050] (7) Forced rapid cooling After casting, the air-cooling and solidification device is immediately activated. According to the cooling program set in the casting process plan, the device automatically controls various valves and opens multiple high-pressure air nozzles located at the bottom of the mold shell. A high-speed airflow at a pressure of 0.7 MPa washes over the outer surface of the mold shell from bottom to top, rapidly carrying away heat from the mold shell and the casting through strong convection. This cooling process continues until infrared thermography confirms that the core temperature of the casting has dropped below 200°C (approximately 18 minutes), at which point the air cooling is shut off.

[0051] (8) Post-processing After the casting has completely cooled, the shell is removed by mechanical vibration and high-pressure water jet to obtain the magnesium alloy casting blank.

[0052] Example 2 The main difference between this embodiment and Embodiment 1 lies in the control of the forced cooling parameters, which aims to achieve a higher cooling rate.

[0053] Step (7) Adjustment: During the forced rapid cooling stage, the airflow pressure of the air-cooling device is increased to 0.9MPa, the cooling airflow speed is faster, and the cooling intensity is greater.

[0054] Results: This adjustment further improved the solidification and cooling rate of the casting. Testing showed that the average grain size of the resulting casting was approximately 15% finer than that of Example 1, achieving a superior grain refinement effect, especially suitable for applications with more stringent grain size requirements.

[0055] Example 3 The main difference between this embodiment and Embodiment 1 lies in the back layer structure, which aims to balance shell strength and cost.

[0056] Step (3) Adjustment: Reduce the total number of coatings for the back layer (including the reinforcing layer) to 3, and the final shell has a total of five layers (top layer 1, transition layer 1, back layer 2, sealing layer 1).

[0057] Step (7) Adjustment: In order to ensure the safety of the shell under rapid cooling, the air pressure of forced air cooling is appropriately reduced to 0.5MPa.

[0058] Results: This method shortens the shell-making cycle and reduces material costs while ensuring basic cooling effect and casting quality. The performance of the resulting castings is still significantly better than that of traditional natural cooling processes, making it suitable for castings that are more cost-sensitive and have slightly lower performance requirements but still need improvement.

[0059] Comparative Example 1 (Traditional Natural Cooling) This comparative example aims to compare the effectiveness of traditional investment casting cooling methods.

[0060] Process differences: Steps (1) to (6) of Example 1 are used in their entirety, but the forced rapid cooling in step (7) is omitted. After casting is completed, the shell and casting are placed in the workshop environment to allow them to cool naturally to room temperature.

[0061] Results: The casting cooled slowly, with a total cooling time exceeding 2 hours. Dissection analysis revealed coarse grains, with an average grain size approximately 2.8 times that of Example 1. Mechanical property tests showed that its tensile strength and elongation were approximately 28% and 35% lower than those of the casting in Example 1, respectively, and it exhibited a more pronounced tendency for micro-shrinkage.

[0062] Comparative Example 2 (Mismatched shell and intense cooling) This comparative example aims to illustrate the problems that arise when the shell preparation process and the forced cooling process are mismatched.

[0063] Process differences: The shell preparation is simplified, with only a top layer and a transition layer applied, and no reinforcing back layer, for a total of three layers. After casting, it is cooled using the same strong air cooling (0.7MPa) as in Example 1.

[0064] Results: During forced air cooling, the shell, due to insufficient strength and poor permeability, could not withstand the severe thermal shock and internal pressure changes, resulting in cracking, leakage of molten metal, and scrapping of the casting. This result demonstrates the necessity of the specific multi-layer shell structure (especially the reinforced back layer) in this invention for withstanding subsequent forced rapid cooling.

[0065] Comparative Example 3 (Water Quenching Cooling) This comparative example is intended to contrast another common rapid cooling method.

[0066] Process differences: The same shell and casting process as in Example 1 is used. After casting is completed and the outer metal of the shell has solidified (after waiting for about 90 seconds), the entire red-hot shell is quickly immersed in a room temperature water bath for water quenching.

[0067] Results: The mold shells generally cracked upon immersion in water due to severe thermal shock. The castings suffered severe deformation and cracking due to uneven cooling and excessive stress, resulting in an extremely low yield. Even the few castings with intact appearances contained numerous micro-cracks internally, failing to meet performance requirements. This result highlights the significant advantages of the "directional controllable airflow cooling" method of this invention compared to "violent water quenching" in ensuring casting integrity and quality stability.

[0068] Performance Testing and Comparative Analysis The qualified castings (from the same furnace, AZ91D alloy) obtained in the above embodiments and Comparative Example 1 were sampled and subjected to mechanical property and metallographic testing. The results are shown in the table below:

[0069] Conclusion: A comparison of Examples 1-3 and Comparative Examples 1-3 clearly demonstrates that the combination of the specific shell preparation process (optimized multilayer structure and materials) and the directional forced air cooling process provided by this invention is key to achieving high-quality, high-rate solidification of magnesium alloy investment castings. This combination ensures that while obtaining significantly refined grain structure (42 μm in Example 1 vs. 118 μm in Comparative Example 1) and excellent mechanical properties, it maintains extremely high process stability and casting integrity (compared to the failure cases in Comparative Examples 2 and 3). Examples 2 and 3 show that adjusting the cooling intensity or shell structure within the scope of the claims can achieve stability superior to traditional processes, proving the robustness and wide applicability of the technical solution of this invention.

[0070] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A high-speed solidification casting method for magnesium alloy investment casting, characterized in that, Includes the following steps: S1. Prepare the investment casting module; S2. Preparation of surface layer slurry, transition layer slurry and back layer coating for ceramic shells; S3. On the casting mold assembly, the surface layer slurry, the transition layer slurry and the back layer coating are applied sequentially, and sand is sprinkled after each layer is applied and then dried to form a prefabricated shell. S4. The pre-made shell is fired to obtain the shell; S5. Preheat the baked shell; S6. Pour the molten magnesium alloy into the preheated mold shell; S7. After pouring, the mold containing the casting is subjected to forced rapid cooling.

2. The method according to claim 1, characterized in that, In step S1, the investment molding module is manufactured using 3D printing technology.

3. The method according to claim 1, characterized in that, In step S2, the surface slurry comprises the following components by weight: 100 parts aluminum sol binder, 260-280 parts zircon powder, 0.2-0.3 parts wetting agent, and 0.2-0.3 parts defoamer.

4. The method according to claim 1, characterized in that, In step S2, the transition layer slurry comprises the following components by weight: 100 parts of silica sol binder and 220-240 parts of corundum powder.

5. The method according to claim 1, characterized in that, In step S2, the back coating comprises the following components by weight: 100 parts of silica sol binder and 200-220 parts of coal gangue powder.

6. The method according to claim 3, characterized in that, The preparation method of the surface slurry is as follows: first stir the aluminum sol binder, then add zircon powder while stirring, stir at high speed for 3-4 hours, then add wetting agent and defoamer, and then switch to low speed stirring for 12-24 hours.

7. The method according to claim 4, characterized in that, The preparation method of the transition layer slurry is as follows: first stir the silica sol binder, then add corundum powder while stirring, stir at high speed for 3-4 hours, and then switch to low speed stirring for 12-24 hours.

8. The method according to claim 5, characterized in that, The preparation method of the back coating is as follows: coal gangue powder is added to the stirred silica sol binder and stirred continuously for 24-36 hours.

9. The method according to claim 1, characterized in that, In step S3, after the initial application and sanding of the back coating is completed, the application and sanding of the back coating is repeated at least three times.

10. The method according to claim 1, characterized in that, In step S7, the forced rapid cooling is performed using a wind-cooling solidification device, specifically by placing the mold shell containing the casting in the device, so that a high-pressure, high-speed airflow flows directionally from the bottom to the top of the mold shell at high speed.

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