Thermal-stability high-elasticity-modulus magnesium-lithium alloy and precision casting forming method for complex components of magnesium-lithium alloy

Abstract

The invention discloses a thermal-stability high-elasticity-modulus magnesium-lithium alloy and a precision casting forming method of a complex component thereof, and relates to the technical field of materials, through alloy component design and treatment process innovation, a solid solution strengthening and precipitation strengthening synergistic mechanism is constructed, the flow characteristic and solidification behavior of an alloy melt are regulated and controlled, and the high-elasticity-modulus magnesium-lithium alloy is obtained. And by means of feeding design, temperature control and the like, comprehensive improvement of the alloy performance is achieved. The prepared magnesium-lithium alloy has excellent thermal stability and high elastic modulus and can meet the application index requirements that the tensile strength is 300 MPa or above, the elastic modulus is 60 GPa or above and the plasticity is larger than 5%, and the strength attenuation is smaller than 8% after one year of natural aging at the room temperature.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a thermally stable high elastic modulus magnesium-lithium alloy and a precision casting method for complex components thereof. Background Art

[0002] Complex structural components with thin walls, multiple cavities, and reinforced ribs are widely used in fields such as aerospace and weaponry. These components place stringent demands on weight control, rigidity maintenance, and service stability. Magnesium-lithium alloys, with their low density, high specific strength, and excellent processability, are a preferred material for lightweight design.

[0003] However, for magnesium-lithium alloys, when the Li content is higher than 10.3wt.%, the matrix phase is a β-Li solid solution, the matrix has strong plasticity and low density, and is one of the lightest metal structural materials currently used in industrial applications. However, the inherent defects of the β-phase solid solution are also very significant. Its atomic arrangement is loose and the bonding force between atoms is weak, resulting in room temperature tensile strength generally lower than 200MPa, yield strength mostly below 150MPa, low elastic modulus (40-45GPa), easy aging softening and other problems, making it difficult to meet the requirements of stiffness and service stability of complex components under high vibration or long-life service conditions. At present, some technologies have attempted to improve the mechanical properties and casting characteristics of the alloy. For example, the Chinese invention patent with announcement number CN 108179336B discloses an ultra-light magnesium-lithium alloy and its heat treatment method. By introducing Zn and Gd to form a quasi-crystalline phase, the strength of the magnesium-lithium alloy can be increased to about 200MPa. The Chinese invention patent application with publication number CN107893180A discloses a single-phase β-magnesium-lithium alloy with excellent casting and heat transfer properties. Some properties are synergistically improved by elements such as Cu-Bi, but the tensile strength is only 140-160 MPa. In the existing alloying methods, in the preparation process of complex components (such as thin-walled, multi-cavity structures), the difficulty of filling the mold needs to be considered. When adding elements to pursue strength, such as introducing elements such as Al and Zn to achieve solid solution strengthening, adding elements such as Si, Y, and Gd to form a thermally stable high modulus phase, an attempt is made to synergistically improve the elastic modulus and resistance to aging softening of the magnesium-lithium alloy. However, the generation of a large amount of solute elements and high modulus phases will cause the viscosity of the magnesium-lithium alloy melt to increase, the fluidity to decrease, and aggravate the difficulty of filling the mold. Especially when manufacturing complex components such as cabins or frames, it is easy to cause casting defects such as insufficient filling, shrinkage cavities, shrinkage, and hot cracking. It can be seen from this that simply optimizing the alloy design is far from enough. It is also necessary to simultaneously improve the molding process and adjust the flow characteristics and solidification behavior of the alloy melt in order to promote the practical application of magnesium-lithium alloys in the precision casting of complex components.

[0004] Therefore, it is necessary to control the precision casting of complex magnesium-lithium alloy components while meeting the requirements of high modulus and thermal stability, and to build a comprehensive manufacturing system that matches material properties with structural forming. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a thermally stable, high elastic modulus magnesium-lithium alloy and a precision casting method for complex components thereof. By optimizing the combination of alloying elements, a variety of high modulus strengthening phases are formed in the Mg-Li matrix, and the strengthening phases are stabilized by combining the heat treatment control process, significantly improving the alloy strength and elastic modulus and inhibiting aging softening. Based on the above alloy, a precision casting method is adopted, combined with the integrated design of 3D printed sand cores, risers and metal molds, and vacuum low-temperature melting and casting, to achieve one-time molding of complex structural parts such as cabins or frames.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] <First Aspect>

[0008] The present invention provides a thermally stable magnesium-lithium alloy with a high elastic modulus. The alloy comprises, by mass percentage, 11-16% Li, 3-9% Al, 1-6% Zn, 1-3% Mn, 0.5-2% Si, 0.5-6% Sn, 0.5-3% Ca, 1-5% RE1, 1-5% RE2, and the remainder being Mg and unavoidable impurities, wherein RE1 and RE2 are two different rare earth elements.

[0009] As an embodiment, RE1 and RE2 are respectively one of Y, Gd, Er, and Yb.

[0010] As an embodiment, in the thermally stable high elastic modulus magnesium-lithium alloy, the content of Zn in the composition is 5 to 6% by mass.

[0011] In some embodiments, the composition includes 5% Zn by mass.

[0012] In some embodiments, the magnesium-lithium alloy comprises, by mass percentage, 12-15% Li, 4-8% Al, 2-5% Zn, 1-3% Mn, 1-1.5% Si, 1-6% Sn, 1-3% Ca, 2-5% Y, and 1-5% Gd, with the remainder being Mg and unavoidable impurities.

[0013] As an embodiment, the thickness of the magnesium-lithium alloy is 1.5 to 10 mm.

[0014] In some embodiments, the thickness of the magnesium-lithium alloy is 3 mm.

[0015] As an embodiment, the magnesium-lithium alloy has a tensile strength of 310 to 340 MPa, an elastic modulus of 60 to 65 GPa, and an elongation of 6 to 15%.

[0016] As an embodiment, the magnesium-lithium alloy has a tensile strength retention rate of 92% to 97% after one year of natural aging.

[0017] <Second Aspect>

[0018] The present invention provides a precision casting method for the above-mentioned heat-stable high elastic modulus magnesium-lithium alloy, in particular a precision casting method for complex components of the heat-stable high elastic modulus magnesium-lithium alloy, comprising the following steps:

[0019] S1. Raw material preparation and pretreatment, as well as casting mold preheating treatment;

[0020] S2, magnesium-lithium alloy melting and casting;

[0021] S3. Perform double-stage solid solution and aging treatment.

[0022] As an embodiment, the raw materials are pure Mg, pure Li, pure Al, pure Zn, pure Si, pure Sn, and Mg-Ca, Mg-Mn and Mg-RE master alloys.

[0023] In some embodiments, the Mg-RE master alloy in the raw materials is Mg-Y and Mg-Gd master alloy.

[0024] As an embodiment, the raw materials except Li are subjected to a heating treatment at 150-200° C. for 1-2 hours.

[0025] As an embodiment, the casting mold preheating temperature is 150-200° C., and the preheating time is 1-2 hours.

[0026] As an implementation scheme, the raw materials except Li are first smelted under a protective atmosphere, Li is added when the temperature reaches 650-670°C, stirring is started when the temperature reaches 690-700°C, the stirring rate is 200-400 r / min, the stirring time is 10-15 minutes, the temperature is controlled not to exceed 720°C, after stirring, it is allowed to stand for 5-10 minutes, and finally the temperature is controlled at 700-720°C for casting, and naturally cooled to obtain a casting.

[0027] As an embodiment, the protective atmosphere is argon, which is first evacuated to below 1 Pa and then filled with 5 to 8 × 10 4 Pa of protective gas.

[0028] As an embodiment, the casting is heat treated under a protective atmosphere, first solution-treated at 300-330°C for 2-4 hours, then heated to 380-400°C for solution-treated for 30-60 minutes and then water-quenched, then aged at 50-150°C for 0.5-24 hours, air-cooled to room temperature, and finally the magnesium-lithium alloy is obtained.

[0029] In some embodiments, the casting is heat treated under a protective atmosphere, first solution-treated at 300°C for 3-4 hours, then heated to 400°C for solution-treated for 30-60 minutes, then aged at 50-100°C for 24 hours, air-cooled to room temperature, and finally the magnesium-lithium alloy is obtained.

[0030] <Third Aspect>

[0031] The present invention provides a casting mold for precision casting of magnesium-lithium alloy complex components, comprising an outer mold, a sand core and a riser, wherein:

[0032] The outer mold is provided with a hollow mold cavity with an upper opening, the bottom surface of the mold cavity is provided with a conical bottom cavity with a larger upper portion and a smaller lower portion, and the top of the mold cavity is a top cavity for embedding and supporting the riser;

[0033] The bottom of the sand core is a conical structure that matches the bottom cavity of the mold cavity, and is used to slide into the mold cavity in a self-guided manner during assembly, and a casting space is formed between the outer wall of the sand core and the mold cavity wall;

[0034] The riser is annular, with an outer wall having a shape matching the top cavity of the mold cavity, and an inner wall having a tapered structure with a larger top and a smaller bottom;

[0035] The riser is fitted in the top cavity with the smaller inner wall end facing the inside of the mold cavity and is covered on the upper part of the sand core. A main runner with a larger upper part and a smaller lower part is formed between the inner wall of the riser and the outer wall of the sand core.

[0036] As an embodiment, the outer mold is split.

[0037] As an embodiment, the bottom surface of the main runner coincides with the top surface of the casting space.

[0038] As an embodiment, the sand core located at the riser position is a conical structure that is smaller at the top and larger at the bottom.

[0039] As an embodiment, the thickness of the casting space is 1.5 to 10 mm.

[0040] In some embodiments, the casting space is annular.

[0041] As an embodiment, the outer mold is made of metal.

[0042] As an embodiment, the outer mold is made of gray cast iron, ductile iron or hot working die steel.

[0043] As an embodiment, the sand core material is quartz sand, zircon sand or ceramic sand.

[0044] As an embodiment, the riser material is quartz sand, zircon sand or ceramic sand.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. This invention achieves comprehensive improvements in alloy performance through innovative alloy composition design and processing technology, establishing a synergistic mechanism of solid solution strengthening and precipitation strengthening. On the one hand, the strengthening ability of the β-Li solid solution is enhanced by adding elements such as Al and Zn, while the introduction of Si, Mn, and rare earth elements promotes the formation of high-modulus phases such as Mg2Si, Al2RE, and Al8Mn5. On the other hand, a two-stage solid solution + aging treatment is combined to promote the precipitation of nano-scale dispersion-strengthening phases such as Mg2Sn, Mg2Ca, and Al2RE, effectively inhibiting the coarsening and growth of the Mg3(Al,Zn) phase, thereby significantly improving the alloy's strength, elastic modulus, and aging stability.

[0047] 2. The magnesium-lithium alloy prepared by the present invention has excellent thermal stability and high elastic modulus, which can meet the application index requirements of tensile strength above 300 MPa, elastic modulus above 60 GPa, and plasticity greater than 5%. The strength attenuation after natural aging at room temperature for one year is less than 8%.

[0048] 3. In terms of molding technology, the present invention proposes a magnesium-lithium alloy precision casting molding method suitable for large-scale complex components. It optimizes the material matching of the outer mold, sand core and riser of the casting mold, adopts a mold design method that combines 3D printed sand cores with metal molds, and combines customized 3D printed risers for directional shrinkage feeding, which effectively improves the filling capacity and shrinkage feeding efficiency of the thermally stable and high elastic modulus magnesium-lithium alloy in the casting process of complex structural parts.

[0049] 4. This invention significantly improves the mold filling and hot cracking resistance of a thermally stable, high-elastic modulus magnesium-lithium alloy through alloy composition design and controlled casting process parameters. Within the optimal casting temperature range of 700-720°C, the alloy achieved full mold filling of 1550 mm in a single-spiral specimen, while exhibiting no cracks within a hot crack ring width range of 5-40 mm.

[0050] 5. The present invention promotes the practical application of thermally stable and high elastic modulus magnesium-lithium alloys in the precision casting of complex components by regulating the flow characteristics and solidification behavior of the alloy melt, and supplemented by shrinkage design and temperature control. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0052] Figure 1 Schematic diagram of the structure of the casting mold provided in Example 1 of the present invention, wherein the left figure is a schematic diagram of the structure of the hidden right mold, and the right figure is a schematic cross-sectional diagram along the interface between the left mold and the right mold;

[0053] In the figure, 1. Riser; 2. Sand core; 3. Outer mold. DETAILED DESCRIPTION

[0054] The present invention will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that those skilled in the art may make several adjustments and improvements without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0055] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the structure referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0056] Example 1

[0057] This embodiment provides a casting mold for preparing magnesium-lithium alloy, which is particularly suitable for precision casting of complex components, including an outer mold 3, a sand core 2 and a riser 1.

[0058] The outer mold 3 forms a mold cavity by closing the left and right molds. Figure 1 The left picture shows only the left mold of the outer mold 3.

[0059] The mold cavity is divided into three parts: top cavity, sidewall cavity and bottom cavity.

[0060] The bottom surface of the top cavity extends downwardly to form a side wall cavity, and the bottom surface of the side wall cavity extends downwardly to form a bottom cavity. When viewed from above, the three cavities are in a concave stepped shape.

[0061] The bottom cavity is a conical cavity that is larger at the top and smaller at the bottom.

[0062] The sand core 2 is an integrated structure, which is divided into three parts: an upper sand core located in the top cavity section, a middle sand core located in the side wall cavity section, and a lower sand core located in the bottom cavity section.

[0063] The lower sand core has a conical structure that matches the bottom cavity. It has a self-guiding function during installation and can slide naturally into the conical cavity of the mold cavity to prevent the position of the sand core 2 from shifting, while facilitating smooth disassembly after cooling.

[0064] The middle sand core is located in the side wall cavity, and the diameter of the side wall cavity is larger than the outer diameter of the middle sand core, so that a cavity is formed as a casting space.

[0065] The upper sand core section is conical in shape, smaller at the top and larger at the bottom.

[0066] The riser 1 is in the shape of a circular ring, the outer surface of which is adapted to the shape of the top cavity, and the inner surface of which is in the shape of a cavity with a larger top and a smaller bottom. It is sleeved on the outside of the upper sand core, and a cavity is formed between it and the upper sand core as the main runner, that is, the main runner is a conical ring structure with a larger top and a smaller bottom.

[0067] The bottom surface of the main runner coincides with the top surface of the casting space.

[0068] Figure 1 A thin-walled cylindrical structure with two open ends is shown. Figure 1 The cross-sections of the mold cavity and the sand core 2 shown in the figure are both circular, and the side wall cavity and the middle sand core are both cylindrical, that is, the casting space is a thin-walled cylindrical structure. Figure 1 The casting mold shown can be used to prepare thin-walled parts with a thickness of 1.5 to 10 mm.

[0069] During actual implementation, the structure of the casting space can be adjusted according to the shape of the actual complex component.

[0070] In this embodiment, the left mold and the right mold are symmetrically arranged, and the left and right molds are combined to form a complete mold cavity.

[0071] The outer mold 3 is made of metal, such as gray cast iron, ductile iron, hot working die steel, etc. (ductile iron in this embodiment), and is used to form the outer contour of the casting, and has good thermal conductivity and reusability.

[0072] The sand core 2 is prepared by 3D printing to achieve high-dimensional precision shape forming, and the material is quartz sand, zircon sand, ceramic sand, etc. (quartz sand in this embodiment).

[0073] The riser 1 is made of sand material, such as quartz sand, zircon sand, ceramic sand, etc. (quartz sand in this embodiment). Based on thermal node analysis and solidification path simulation, the feeding riser 1 is prepared by 3D printing to achieve feeding of key parts.

[0074] In this embodiment, the riser 1 is located at the top of the casting space and is completely fitted with the metal outer mold 3. The main runner space with a larger top and a smaller bottom is used, which helps to adjust the local cooling rate and control the solidification sequence, making it the last solidification area, thereby effectively achieving shrinkage compensation and avoiding shrinkage defects inside the casting.

[0075] During assembly, the left mold and the right mold are aligned and combined into the outer mold 3, which is fixed by bolts or snaps to form a complete mold cavity; then the lower sand core end of the sand core 2 is embedded in the bottom cavity; then the riser 1 (the end with the smaller inner diameter facing downward) is sleeved on the outside of the upper sand core, and the outer wall is fitted with the top cavity of the mold cavity, and supported on the step surface formed between the top cavity and the side wall cavity of the outer mold 3.

[0076] This specific embodiment also provides a method for precision casting a complex component of a thermally stable and high elastic modulus magnesium-lithium alloy using the mold provided in the above embodiment 1, the steps being:

[0077] S1, ingredient preparation and pretreatment, as well as mold preheating;

[0078] S2, magnesium-lithium alloy melting and casting;

[0079] S3. Perform double-stage solid solution and aging treatment.

[0080] The above method is introduced below through several embodiments and comparative examples.

[0081] Example 2

[0082] This embodiment provides a precision casting method for a complex magnesium-lithium alloy component. The component is a thin-walled tube with an outer dimension of Φ350×800mm and a wall thickness of 3mm.

[0083] The components of the magnesium-lithium alloy are, by mass percentage, Li 14%, Al 8%, Zn 5%, Mn 2%, Si 1.5%, Sn 1%, Ca 2%, Y 4%, Gd 3%, and the balance is Mg and unavoidable impurities.

[0084] Ingredient preparation and pretreatment, specifically:

[0085] Prepare pure Mg, pure Li, pure Al, pure Zn, pure Si, pure Sn, and intermediate alloys Mg-Ca, Mg-Mn, Mg-Y, and Mg-Gd according to the composition of the magnesium-lithium alloy. It should be noted that the raw materials must first be descaled using sandpaper and an angle grinder, then rinsed with alcohol and dried for later use.

[0086] All raw materials except Li were baked in an oven at 180°C for 1.5 hours. It should be noted that a skimmer was used to clean the melt residue inside the crucible, and tools and equipment such as the mold, vacuum furnace seal, and furnace cover were wiped to ensure there was no dust contamination.

[0087] Preheat treatment of casting mold, specifically:

[0088] The outer mold 3, sand core 2 and riser 1 are preheated at 200°C for 1.5 hours, assembled, and placed in the designated position of the vacuum furnace.

[0089] Magnesium-lithium alloy melting and casting, specifically:

[0090] First, put the raw materials except Li into the crucible in the order of "pure Mg (half of Mg) - the rest of the alloy - pure Mg (the balance Mg)". Wrap Li with aluminum foil and place it at the feed port.

[0091] The vacuum furnace was evacuated to below 0.8 Pa and a 6×10 4 Pa of protective gas, and then turn on induction heating to melt the raw materials;

[0092] When the temperature reaches 660°C, Li is added, and the temperature is maintained at 690°C, and mechanical stirring is started. The stirring time is 12 minutes, and the stirring rate is 250 r / min. After stirring, it is allowed to stand for 8 minutes. Finally, the temperature is controlled at 700°C and cast into a preheated casting mold, and cooled naturally.

[0093] Heat treatment, specifically:

[0094] The naturally cooled castings were placed in an argon-protected heat treatment furnace, solutionized at 300°C for 3 hours, then heated to 400°C for solutionized for 40 minutes and water quenched. The solutionized ingots and components were aged at 50°C for 24 hours and then air-cooled to room temperature.

[0095] The prepared magnesium-lithium alloy was tested by ICP, and the actual alloy composition, calculated by mass fraction, was: Li 13.7%, Al 8.1%, Zn 4.8%, Mn 2.2%, Si 1.4%, Sn 0.8%, Ca 2.1%, Y 3.7%, Gd 2.8%, and the balance was Mg.

[0096] Example 3

[0097] This embodiment provides a precision casting method for a complex magnesium-lithium alloy component. The component is a thin-walled tube with an outer dimension of Φ350×800mm and a wall thickness of 3mm.

[0098] The components of the magnesium-lithium alloy are, by mass percentage, Li 12%, Al 4%, Zn 2%, Mn 1%, Si 1.5%, Sn 6%, Ca 3%, Y 2%, Gd 5%, and the balance is Mg and unavoidable impurities.

[0099] Ingredient preparation and pretreatment, specifically:

[0100] Prepare pure Mg, pure Li, pure Al, pure Zn, pure Si, pure Sn, and intermediate alloys Mg-Ca, Mg-Mn, Mg-Y, and Mg-Gd according to the composition of the magnesium-lithium alloy. It should be noted that the raw materials must first be descaled using sandpaper and an angle grinder, then rinsed with alcohol and dried for later use.

[0101] All raw materials except Li were placed in an oven at 150°C for 2 h. It should be noted that a skimmer was used to clean the melt residue inside the crucible, and tools and equipment such as the mold, vacuum furnace seal, and furnace cover were wiped to ensure there was no dust contamination.

[0102] Preheat treatment of casting mold, specifically:

[0103] The outer mold 3, sand core 2 and riser 1 are preheated at 180°C for 2 hours, then assembled and placed in the designated position of the vacuum furnace.

[0104] Magnesium-lithium alloy melting and casting, specifically:

[0105] First, put the raw materials except Li into the crucible in the order of "pure Mg (2 / 3 of Mg) - the rest of the alloy - pure Mg (balance Mg)", and wrap Li with aluminum foil and place it at the feed port;

[0106] The vacuum furnace was evacuated to below 0.5Pa, and 8×10 4 Pa of protective gas, and then turn on induction heating to melt the raw materials;

[0107] When the temperature reaches 670°C, Li is added, and the temperature is maintained at 700°C and mechanical stirring is started. The stirring time is 15 minutes and the stirring rate is 200 r / min. After stirring, it is allowed to stand for 10 minutes. Finally, the temperature is controlled at 710°C and cast into a preheated casting mold and cooled naturally.

[0108] Heat treatment, specifically:

[0109] The naturally cooled castings were placed in an argon-protected heat treatment furnace, solutionized at 300°C for 4 hours, then heated to 400°C for solutionized for 30 minutes and water quenched. The solutionized ingots and components were aged at 100°C for 24 hours and then air-cooled to room temperature.

[0110] Example 4

[0111] This embodiment provides a precision casting method for a complex magnesium-lithium alloy component. The component is a thin-walled tube with an outer dimension of Φ350×800mm and a wall thickness of 3mm.

[0112] The components of the magnesium-lithium alloy are, by mass percentage, 15% Li, 6% Al, 3% Zn, 3% Mn, 1% Si, 3% Sn, 1% Ca, 5% Y, 1% Gd, and the balance is Mg and unavoidable impurities.

[0113] Ingredient preparation and pretreatment, specifically:

[0114] Prepare pure Mg, pure Li, pure Al, pure Zn, pure Si, pure Sn, and intermediate alloys Mg-Ca, Mg-Mn, Mg-Y, and Mg-Gd according to the composition of the magnesium-lithium alloy. It should be noted that the raw materials must first be descaled using sandpaper and an angle grinder, then rinsed with alcohol and dried for later use.

[0115] All raw materials except Li were baked in an oven at 200°C for 1 hour. It should be noted that a skimmer was used to clean the melt residue inside the crucible, and tools and equipment such as the mold, vacuum furnace seal, and furnace cover were wiped to ensure there was no dust contamination.

[0116] Preheat treatment of casting mold, specifically:

[0117] The outer mold 3, sand core 2 and riser 1 are preheated at 200°C for 1 hour, then assembled and placed in the designated position of the vacuum furnace.

[0118] Magnesium-lithium alloy melting and casting, specifically:

[0119] First, put the raw materials except Li into the crucible in the order of "pure Mg (1 / 2 Mg) - the rest of the alloy - pure Mg (balance Mg)". Wrap Li with aluminum foil and place it at the feed port.

[0120] The vacuum furnace was evacuated to below 1Pa, and 5×10 4 Pa of protective gas, and then turn on induction heating to melt the raw materials;

[0121] When the temperature reaches 650°C, Li is added, and the temperature is maintained at 690°C and mechanical stirring is started. The stirring time is 10 minutes, and the stirring rate is 300 r / min. After stirring, it is allowed to stand for 5 minutes. Finally, the temperature is controlled at 720°C and cast into a preheated casting mold, and cooled naturally.

[0122] Heat treatment, specifically:

[0123] The naturally cooled castings were placed in an argon-protected heat treatment furnace, solutionized at 300°C for 4 hours, then heated to 400°C for solutionized for 1 hour and water quenched. The solutionized ingots and components were aged at 50°C for 24 hours and then air-cooled to room temperature.

[0124] Comparative Example 1

[0125] This comparative example provides a method for precision casting a complex component of a magnesium-lithium alloy. The composition of the raw materials is different from that of Example 2 (does not contain Si, Sn, and Ca). Specifically, the composition of the magnesium-lithium alloy is, by mass percentage, Li 14%, Al 8%, Zn 5%, Mn 2%, Y 4%, Gd 3%, and the balance is Mg and unavoidable impurities.

[0126] The preparation method is consistent with that of Example 2.

[0127] Comparative Example 2

[0128] This comparative example provides a method for precision casting a complex component of a magnesium-lithium alloy. The composition of the raw materials is different from that of Example 2 (excluding Mn, Y, and Gd). Specifically, the composition of the magnesium-lithium alloy is, by mass percentage, 14% Li, 8% Al, 5% Zn, and the remainder is Mg and unavoidable impurities.

[0129] The preparation method is consistent with that of Example 2.

[0130] Comparative Example 3

[0131] This comparative example provides a method for precision casting a complex magnesium-lithium alloy component, and the raw materials are the same as those in Example 2.

[0132] The preparation method is basically the same as that of Example 2, except that:

[0133] A metal mold is used, and the remaining steps are the same as those in Example 2.

[0134] The metal mold has the same structure as the casting mold of Example 1, but the outer mold 3, the sand core 2 and the riser 1 are all made of ductile iron.

[0135] Comparative Example 4

[0136] This comparative example provides a method for precision casting a complex magnesium-lithium alloy component, and the raw materials are the same as those in Example 2.

[0137] The preparation method is basically the same as that of Example 2, except that:

[0138] In the magnesium-lithium alloy smelting and casting steps, the casting temperature is 750° C., and the remaining steps are consistent with those of Example 2.

[0139] Comparative Example 5

[0140] This comparative example provides a method for precision casting a complex magnesium-lithium alloy component, and the raw materials are the same as those in Example 2.

[0141] The preparation method is basically the same as that of Example 2, except that:

[0142] In the magnesium-lithium alloy smelting and casting steps, the casting temperature is 680° C., and the remaining steps are consistent with those of Example 2.

[0143] Performance testing:

[0144] In order to systematically evaluate the comprehensive properties of the prepared magnesium-lithium alloys, the alloy samples prepared in each embodiment and comparative example were tested from two dimensions: mechanical properties and process performance. The test results are shown in Tables 1 to 8.

[0145] In terms of mechanical properties testing, a universal material testing machine is used to test the tensile strength and elongation of standard tensile specimens in accordance with GB / T 228.1-2021 "Tensile Tests on Metallic Materials Part 1: Room Temperature Test Methods". The tensile strength limit and elongation at break of the alloy are accurately obtained through the stress-strain curve; the elastic modulus is determined using a dynamic elastic modulus damping internal friction analyzer.

[0146] It should be noted that the mechanical properties test consists of two parts, one is the room temperature mechanical properties of the newly prepared magnesium-lithium alloy, and the other is the room temperature mechanical properties of the magnesium-lithium alloy after one year of natural aging.

[0147] In terms of process performance testing, the main tests are designed for fluidity and thermal cracking tendency, specifically:

[0148] Fluidity test: The melts from Examples 2 to Comparative Example 5 were cast into a single-helix alloy fluidity tester preheated to 200°C. The melts were allowed to flow under gravity and capillary action and eventually solidified. The longer the filling length, the better the alloy fluidity.

[0149] Thermal cracking tendency test: The melts after smelting in Examples 2 to Comparative Examples 5 were cast into a cross-shaped thermal cracking test device. After the melt was poured in, tensile stress was generated on the central node during solidification and contraction of the cross arms. The central part was the last to solidify and had a large temperature gradient, making it prone to thermal cracking. The thermal cracking tendency was determined by observing the cracks in the central node and arms.

[0150] Flaw detection: Use non-destructive testing technology to detect and evaluate whether there are shrinkage defects such as porosity and shrinkage holes inside the alloy.

[0151] Table 1

[0152]

[0153] Table 2

[0154]

[0155] Table 3

[0156]

[0157] Table 4

[0158]

[0159] Table 5

[0160]

[0161]

[0162] Table 6

[0163]

[0164] Table 7

[0165]

[0166] Table 8

[0167]

[0168] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A thermally stable high elastic modulus magnesium-lithium alloy, characterized in that: Calculated by mass percentage, the components are: Li: 11-16%, Al: 3-9%, Zn: 1-6%, Mn: 1-3%, Si: 0.5-2%, Sn: 0.5-6%, Ca: 0.5-3%, RE1: 1-5%, RE2: 1-5%, and the balance is Mg and unavoidable impurities, wherein RE1 and RE2 are two different rare earth elements.

2. The alloy according to claim 1, characterized in that The RE1 and RE2 are respectively one of Y, Gd, Er, and Yb.

3. The alloy according to claim 1, characterized in that The thickness of the magnesium-lithium alloy is 1.5 to 10 mm.

4. A precision casting method for a thermally stable high elastic modulus magnesium-lithium alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Raw material preparation and pretreatment, as well as casting mold preheating treatment; S2. Smelting and casting of magnesium-lithium alloy, specifically: first, smelting the raw materials except Li under a protective atmosphere, adding Li when the temperature reaches 650-670°C, starting stirring when the temperature reaches 690-700°C, stirring at a rate of 200-400 r / min, stirring for 10-15 minutes, controlling the temperature not to exceed 720°C, standing for 5-10 minutes after stirring, and finally controlling the temperature to 700-720°C for casting, and naturally cooling to obtain a casting; S3. Perform a two-stage solution and aging treatment, specifically: heat treat the casting under a protective atmosphere, first solutionize at 300-330° C. for 2-4 hours, then heat to 380-400° C. for solution for 30-60 minutes, and then water quench, then age at 50-150° C. for 0.5-24 hours, air cool to room temperature, and finally obtain the thermally stable high elastic modulus magnesium-lithium alloy.

5. The method according to claim 4, characterized in that The raw materials are pure Mg, pure Li, pure Al, pure Zn, pure Si, pure Sn, and Mg-Ca, Mg-Mn and Mg-RE master alloys.

6. The method according to claim 4, characterized in that Also includes at least one of the following technical features: A1. Except for Li, the raw materials are preheated at 150-200°C for 1-2 hours; B1. The casting mold is preheated to a temperature of 150-200°C for 1-2 hours.

7. The method according to claim 4, characterized in that The casting mold described in step S1 includes an outer mold, a sand core and a riser. The outer mold is provided with a hollow mold cavity with an upper opening, and the bottom surface of the mold cavity is provided with a conical bottom cavity with a larger upper part and a smaller lower part. The top of the mold cavity is a top cavity for embedding the riser and supporting the riser. The bottom of the sand core is a conical structure that matches the bottom cavity of the mold cavity, which is used to slide into the mold cavity in a self-guided manner during assembly. A casting space is formed between the outer wall of the sand core and the mold cavity wall. The riser is annular, and the outer wall is a shape that matches the top cavity of the mold cavity, and the inner wall is a conical structure with a larger upper part and a smaller lower part. The riser is fitted in the top cavity with the smaller inner wall end facing the interior of the mold cavity, and is covered on the upper part of the sand core. A main runner with a larger upper part and a smaller lower part is formed between the inner wall of the riser and the outer wall of the sand core.

8. The method according to claim 7, characterized in that The sand core located at the riser position is a conical structure that is small at the top and large at the bottom.

9. The method according to claim 7, characterized in that The thickness of the casting space is 1.5 to 10 mm.

10. The method according to claim 7, characterized in that The outer mold is split.

Images