An ultra-plastic high-thermal-conductivity magnesium alloy suitable for forging forming and a preparation method thereof

Abstract

The application discloses a superplastic high-thermal-conductivity magnesium alloy suitable for forging forming and a preparation method thereof, and belongs to the technical field of magnesium alloy preparation.The superplastic high-thermal-conductivity magnesium alloy suitable for forging forming comprises the following steps: a micro-alloyed preform with atomic percentage of Mg-1Ca-1Mn-1La is prepared; zinc, magnesium and the micro-alloyed preform are mixed uniformly in a protective atmosphere according to a set amount, so that the Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La magnesium alloy with atomic percentage of micro-alloyed elements Mn, Ca and La is obtained; and plastic forming is carried out on the Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La magnesium alloy.The micro-alloyed preform is prepared preferentially through deconstruction design of the target alloy system, and the final precise alloying preparation is achieved through modularization of the micro-alloyed preform and main element metals.The multiple liquid flow mixing technology is adopted in the application, the main element pure metals and the micro-alloyed preform are liquid-state mixed after physical removal of oxidation inclusions, and the precise alloying preparation with no (little) burning loss is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium alloy preparation, and in particular relates to a superplastic high thermal conductivity magnesium alloy suitable for forging and a preparation method thereof. Background Art

[0002] With the vigorous development of 5G communications in recent years, there has been a clear trend towards high-energy and dense equipment upgrades. Distributed 5G base stations are constantly developing towards multi-frequency integration, and the power thermal density of base stations continues to increase. Local high heat flux density areas have become heat dissipation bottlenecks, posing a huge challenge to base station thermal management. However, traditional heat dissipation solutions such as expanding the heat dissipation area and introducing basic two-phase components (heat pipes / VC / PCI) are no longer able to meet the needs of "high power, full bandwidth, and lightweight." For the upgrade of the next generation of communication equipment, products need to continuously iterate "lightweight, high thermal conductivity" heat dissipation technology solutions to enhance product competitiveness and meet market demand.

[0003] Magnesium alloy is the lightest metal structural material (ρ=1.8g / cm 3 ), which is comparable to the density of commonly used engineering plastics, and is 1 / 3 and 3 / 4 lower than the density of aluminum alloys and steel, respectively, which is very suitable for the lightweight development of the new generation of communication equipment. Unfortunately, there is a large gap between the thermal conductivity (λ=50-100W / (m·K)) of ordinary commercial magnesium alloys (such as Mg-Al magnesium alloys) and mainstream aluminum alloy materials (such as 6082, 7075, λ=130-160W / (m·K), and the latter has excellent forming properties and higher mechanical properties than ordinary commercial magnesium alloys. In summary, the lower thermal conductivity, limited forming properties and mechanical properties hinder the release of the lightweight advantages of magnesium alloys in the field of communication equipment.

[0004] Existing design methods for magnesium alloys include:

[0005] 1. High thermal conductivity particle composite reinforcement design

[0006] High thermal conductivity magnesium alloys are produced by using a composite particle reinforcement design with a thermal conductivity close to or higher than that of pure magnesium. For example, by adding appropriate amounts of high thermal conductivity non-metallic Si (λ ~ 150 W / (m·K)) or metallic copper (λ ~ 400 W / (m·K)), or metallic silver (λ ~ 430 W / (m·K)), a high thermal conductivity magnesium alloy with a thermal conductivity of 120-140 W / (m·K) can be achieved. For example, [CN200710121458.2] discloses a method of alloying Mg-Zn-Cu-Mn-Ag alloys by adding 0.1-2.5 wt.% Ag to Ag or Mg-Ag master alloys. This can increase the thermal conductivity of the Mg-Zn-Cu-Mn-Ag alloy to 120 W / (m·K). At the same time, when combined with appropriate plastic forming processes (extrusion, drawing, etc.), it can also possess high comprehensive mechanical strength. [CN201710350352.3] also uses Ag or Mg-Ag intermediate alloy to achieve 0.1-2.5wt.% Ag content alloying addition, which can increase the thermal conductivity of Mg-Zn-Cu-Ag alloy to 140W / (m·K) and the yield strength to nearly 300MPa. [CN202110201544.4] also uses the addition of Cu to obtain a 200MPa yield strength magnesium alloy at the level of 130W / (m·K), and the elongation of the die-cast alloy can reach 10%. The addition of the above-mentioned high thermal conductivity elements or particles, on the one hand, achieves high thermal conductivity of the magnesium alloy, and also plays a role in composite strengthening and toughening, thereby improving the mechanical properties of the material.

[0007] 2. Heavy rare earth alloying design

[0008] The addition of rare earth alloying elements, such as Gd, Y, Nd, Ce, and La, to magnesium alloys not only achieves higher thermal conductivity, but also forms intermetallic compounds that strengthen the second phase, improving the mechanical properties of the die-cast and extruded alloys. For example, [CN201210168014.5] discloses an extruded Mg-Zn-Ca-La-Ce high thermal conductivity alloy prepared by adding Ce and La mixed rare earths. The alloy has a thermal conductivity of 120-130 W / (m·K) and high mechanical properties. [CN201911215432.3] discloses an Mg-Zn-Gd-Er-Zr alloy containing up to 10 wt.% of rare earth elements, including Gd, Er, and Zr. The alloy has a room temperature thermal conductivity of 137 W / (m·K) and an elongation of 24%. [CN202210028442.1] discloses a method of regulating the solid solution content of high-solubility and high-content rare earth alloy elements Gd, Sm, and Y in the matrix by adding Al alloy elements to the Al-RE rare earth phase of the profile, thereby increasing the thermal conductivity of the alloy to greater than 100 W / (m·K).

[0009] 3. Low-cost (micro) rare earth-free design

[0010] This type of alloy utilizes Zn and Mn, two alloying elements that have minimal impact on the thermal conductivity of the magnesium matrix, as primary elements. Mg-Zn-based alloys such as Mg-Zn-Mn [CN201410564789.3], Mg-Zn-Ca [CN202110790189.9], and Mg-Zn-Sn [CN201610533132.X] are designed. The mechanical properties of these alloys are further enhanced by the addition of microalloying elements such as Ca, Mn, Sn, La, Zr, and Ce. Other Mg-Mn-based alloys include Mg-Mn-Ca( / La / Al) (CN201410299662.3, CN202010108724.3, and CN201410298397.7). These alloys all achieve a combination of high thermal conductivity and mechanical properties.

[0011] Although the above technical solutions can achieve good performance in some aspects, the technical requirements for thermal management components of communication equipment still have low thermal conductivity, limited formability and low mechanical properties, which hinder the release of the lightweight advantages of magnesium alloys in the field of communication equipment. The details are as follows:

[0012] 1. The corrosion resistance of the high thermal conductivity particle composite reinforcement design is poor, and the cost of using rare and precious metals is high.

[0013] 2. The design cost of heavy rare earth alloying is relatively high and is not suitable for promotion in the civilian field.

[0014] 3. No rare earth or less rare earth and precious metals are used, which has better economic applicability. However, the forging performance of this type of alloy is currently unknown, and its high Zn content generally leads to poor corrosion resistance.

[0015] 4. The thermal stability of the tissue is poor, and it is impossible to balance the relationship between high temperature formability and tissue stability. Summary of the Invention

[0016] The object of the present invention is to provide a superplastic high thermal conductivity magnesium alloy suitable for forging and a preparation method to solve the above problems.

[0017] To achieve the above object, the present invention adopts the following technical solutions:

[0018] A method for preparing a superplastic high thermal conductivity magnesium alloy suitable for forging, comprising:

[0019] preparing a microalloyed preform having an atomic percentage content of Mg-1Ca-1 Mn-1 La;

[0020] The zinc, magnesium and microalloyed preform are reacted and mixed uniformly in a protective atmosphere according to a set amount to obtain a magnesium alloy having a microalloying element content of Mn, Ca, La and the like in atomic percentages;

[0021] Plastic forming of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La magnesium alloy was performed.

[0022] Further, preparation of microalloyed preform:

[0023] A vacuum protective atmosphere melting furnace with a tilting pouring machine is used. Magnesium, Mg-30La, Mg-20Ca, and Mg-5Mn are mixed in a graphite crucible in a composition ratio of Mg-1Ca-1 Mn-1 La by atomic percentage and heated. After all the materials are melted, the graphite crucible is tilted to pour the melt into a rod-shaped graphite mold with a feeding riser. The mold is naturally cooled to obtain a micro-alloyed preform rod-shaped ingot with an atomic percentage of Mg-1Ca-1Mn-1 La. The ingot is taken out and crushed into 1-2 cm blocks for standby use.

[0024] Furthermore, the protective atmosphere is a mixed protective atmosphere of argon + carbon dioxide + sulfur hexafluoride, wherein the flow ratio of carbon dioxide to sulfur hexafluoride is 100:1, and the purity of argon is 99.999%.

[0025] Further, the graphite crucible heating process:

[0026] Heat the graphite crucible containing the material to 300℃ and keep it warm for 1-2 hours, then continue to heat it to 650-700℃ and keep it warm for 1 hour, then observe the melting situation through the observation window and heat it to 750-800℃ and keep it warm for 1-2 hours.

[0027] Furthermore, a magnesium alloy having the atomic percentage of microalloying elements Mn, Ca, and La as Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La is prepared:

[0028] A vertical vacuum protective atmosphere furnace is used, and the melting slag chamber of the protective atmosphere furnace is divided into a main element chamber and a micro element chamber. Metal magnesium and zinc are added to the main element chamber according to set content, and a blocky microalloyed preform is added to the micro element chamber according to set content, and heated. The pure melts of the two are evenly mixed in an ingot graphite crucible. After cooling, a net dense ingot is formed to obtain an Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La alloy with equal atomic percentage content.

[0029] Furthermore, the protective atmosphere during the entire process is argon gas, and the purity of the argon gas is 99.999%; the furnace body cooling rate is 10-50°C / min.

[0030] Furthermore, the heating process is as follows: the furnace temperature is raised to 300°C and kept warm for 1-2 hours for preheating, and then the temperature is raised to 750-800°C and kept warm for 1-2 hours to ensure that the material in the chamber is melted and flows into the net dense ingot area under the action of gravity. A porous slag plate is placed under the above two chambers, and the metallic magnesium, zinc and microalloyed preform are melted in different melting chambers respectively, and the oxide inclusions are removed by passing through the slag plate.

[0031] Furthermore, the magnesium alloy is plastically formed:

[0032] A dense ingot of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La alloy containing microalloying elements such as Mn, Ca and La in atomic percentage is homogenized under a protective atmosphere, and then the alloy is thermomechanically treated by extrusion, forging and rolling plastic forming methods.

[0033] Furthermore, the homogenization temperature is 400-450°C, the homogenization time is 20-56h, and the cooling method is water quenching;

[0034] For extrusion forming, the billet preheating temperature is 300-350℃, the extrusion die temperature is 350-400℃, the extrusion feed speed is 0.3-1mm / s, the extrusion barrel temperature is set at 300-350℃, the extrusion ratio is set at 10-30, and the extruded material is pulled by a traction machine with a traction force of about 100-500N;

[0035] For forging, the billet preheating temperature is 280-320℃, the forging die temperature is 300-400℃, and the forging speed is 1.5-5mm / min.

[0036] A superplastic high thermal conductivity magnesium alloy suitable for forging is prepared by adopting a preparation method of a superplastic high thermal conductivity magnesium alloy suitable for forging.

[0037] Compared with the prior art, the present invention has the following technical effects:

[0038] The present invention preferentially prepares a micro-alloyed preform by deconstructing and designing the target alloy system, and achieves the final precise alloying preparation through the modular mixed metallurgical combination of the micro-alloyed preform and the main element metal.

[0039] The design of the present invention adopts a multi-liquid flow blending technology, which blends the main element pure metal and the micro-alloyed preform in liquid form after physical removal of oxidation inclusions, thereby achieving precise alloying preparation with no (little) burning loss.

[0040] The present invention removes oxides by physical methods, thereby preventing: a) residual chloride ions (Cl-) in the flux from affecting subsequent corrosion resistance; and b) sodium ions (Na+) in the flux from being easily reduced by calcium (Ca), a more active metal in the alloy, to introduce low-melting-point impurities such as Na, which increases the alloy's tendency to hot brittleness and deteriorates subsequent isothermal forging performance.

[0041] While ensuring room-temperature thermal conductivity exceeding 130 W / (m·K) in both the as-cast and transformed forms, this alloy can achieve a uniform uniaxial forging volume exceeding 80% (30 mm → 5 mm) at 300°C. The transformed alloy exhibits a tensile strength exceeding 240 MPa and a total elongation at break exceeding 45%. It also exhibits excellent thermal conductivity over a wide temperature range (25-200°C), formability, and superior mechanical properties, making it suitable for the manufacture of high-performance, lightweight heat dissipation components. The alloy's high microstructure thermal stability makes it suitable for high-temperature superplastic forming, reducing forming stress and improving forming efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The microstructure of the as-cast Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy, where (a) is the optical microstructure and (b) is the secondary electron microstructure obtained by scanning electron microscopy.

[0043] Figure 2 The optical microstructure, secondary electron scanning (SEM) image and corresponding energy dispersive X-ray spectroscopy (EDS) composition distribution map of Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy after homogenization treatment at 450℃ / 53h are shown.

[0044] Figure 3 Secondary electron scanning image of extruded Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy;

[0045] Figure 4 The room temperature thermal conductivity of the extruded Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy is significantly higher than that of the general commercial magnesium alloys AZ31 B and AZ80A.

[0046] Figure 5 Optical microstructure of Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy homogenized at 350℃ / 6h;

[0047] Figure 6 Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy ingot (Φ20×30 mm) homogenized at 350℃ / 6h to achieve 83% single-pass forging (flattened from 30 mm to 5 mm in height) at 300℃, where (a) is the side view and (b) is the top view.

[0048] Figure 7 AZ31 B alloy ingot (Φ20×30 mm) homogenized at 350℃ / 6h to achieve 83% single-pass forging (flattened from 30 mm to 5 mm in height) at 300℃, where (a) is the top view and (b) is the oblique view.

[0049] Figure 8 (a) is the room temperature engineering stress-strain curve of the alloy extruded plate, (b) is the curve of the tangent modulus of the extruded plate of the patented alloy and the AZ31 B plate as a function of tensile stress at room temperature;

[0050] Figure 9 .Differential thermal analysis curve of Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) cast alloy at room temperature-480℃. DETAILED DESCRIPTION

[0051] The present invention will be further described below with reference to the accompanying drawings:

[0052] See also Figure 1 The present invention provides a superplastic, high-thermal-conductivity magnesium alloy suitable for forging and a preparation method. First, by optimizing the microalloying element combination and adopting an equiatomic ratio (0.1 at.% to 0.2 at.%), a design composition of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La (at.%) is formed. Second, the alloy is prepared by dense casting. Finally, forging tests confirm that the alloy exhibits excellent forging properties, while the extruded sheet exhibits good mechanical properties.

[0053] The specific plan is as follows:

[0054] (1) Preparation of Mg-1Ca-1Mn-1La (at.%) microalloyed preforms: A vacuum protective atmosphere melting furnace with a tilting pouring mechanism was used. The protective atmosphere was a mixed protective atmosphere of high-purity argon (99.999%), high-purity carbon dioxide, and sulfur hexafluoride, wherein the flow ratio of carbon dioxide to sulfur hexafluoride was 100:1. High-purity magnesium (99.98%), Mg-30La, Mg-20Ca, and Mg-5Mn were added to a high-purity, high-density graphite crucible in the proportion of Mg-1Ca-1Mn-1La (at.%). The graphite crucible containing the materials was heated to 300°C and held for 1-2 hours, then further heated to 650-700°C and held for 1 hour. Then, the melting condition was observed through an observation window, and the temperature was raised to 750-800°C and held for 1-2 hours. After all the materials are melted, the graphite crucible is tilted to pour the melt into a rod-shaped graphite mold with a feeding riser. The mold is cooled naturally to obtain a rod-shaped ingot of a microalloyed preform with a composition of Mg-1Ca-1Mn-1La (at.%). The ingot is taken out and broken into 1-2 cm blocks for later use.

[0055] (2) Preparation of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La (at.%) magnesium alloy: A vertical vacuum protective atmosphere furnace was used, and the protective atmosphere throughout the process was high-purity argon (99.999%). The protective atmosphere furnace consisted of three parts: a melting slag chamber, a slag baffle, and a net dense ingot casting area. The melting slag chamber was divided into a main element chamber and a microelement chamber. The main alloy element was made of pure metal high-purity magnesium (99.98%) and high-purity zinc (99.99%), which were added to the main element chamber at a set content. The micro elements of Mn, Ca, and La alloys were made of blocky Mg-1Ca-1 Mn-1 La (at.%) microalloyed preforms, which were added to the microelement chamber at a set content. The furnace temperature is raised to 300°C and maintained for 1-2 hours for preheating, then raised to 750-800°C and maintained for 1-2 hours to ensure that the materials in the chamber are melted and flow into the net dense ingot area under the action of gravity. A porous slag plate is placed under the above two chambers. The main alloy element and the micro-alloyed preform are melted in different melting chambers respectively. After the slag plate removes oxide inclusions, the pure melts of the two are evenly mixed in the ingot casting graphite crucible. Finally, the furnace cooling rate is set to 10-50°C / min to achieve the formation of the net dense ingot of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La (at.%) alloy.

[0056] (3) Plastic forming: First, homogenization treatment is required: the Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La (at.%) alloy net dense ingot is homogenized under a protective atmosphere (such as high-purity argon, etc.), the homogenization temperature is 400-450℃, the homogenization time is 20-56h, and the cooling method is water quenching. Then, the above alloy is thermomechanically treated by plastic forming methods such as extrusion, forging, and rolling. For extrusion forming, the billet preheating temperature is 300-350℃, the extrusion die temperature is 350-400℃, the extrusion feed speed is 0.3-1mm / s, the extrusion barrel temperature is set to 300-350℃, the extrusion ratio is set to 10-30, and the extruded material is pulled by a traction machine with a traction force of about 100-500N. For forging, the preheating temperature of the billet is 280-320°C, the forging die temperature is 300-400°C, and the forging speed is 1.5-5 mm / min. The patented alloy of the present invention can achieve a single forging strain of 80% at 280-320°C.

[0057] Explanation of terms

[0058] 1. Thermal conductivity:

[0059] Thermal conductivity, also known as the coefficient of heat transfer, reflects a material's ability to conduct heat. According to Fourier's law, it is defined as the amount of heat transferred per unit time through a unit heat-conducting surface for a unit temperature gradient (a temperature drop of 1K over a length of 1m). Inside an object, two parallel planes, each measuring 1m in area and 1m apart, perpendicular to the direction of heat conduction, are taken. If the temperature difference between the two planes is 1K, the amount of heat transferred from one plane to the other in 1 second is defined as the thermal conductivity of the material. Its units are Watt·meter-1·Kelvin-1 (W·m-1·K-1).

[0060] 2. High thermal conductivity magnesium alloy:

[0061] Under the same test conditions, magnesium alloys with higher thermal conductivity are called high thermal conductivity magnesium alloys. Generally, the room temperature thermal conductivity exceeds 100W·m-1·K-1.

[0062] 3. Divorced eutectic:

[0063] In alloys with eutectic reactions, if the components are far apart from the eutectic point, due to the large number of primary crystals and the small number of eutectics, the phase in the eutectic structure that is the same as the primary crystal phase grows dependent on the primary crystals, and the other phase in the eutectic structure is distributed separately, causing the eutectic structure to lose its unique organizational characteristics.

[0064] 4.Tensile strength:

[0065] The maximum load-bearing capacity of a metal under static tension. Tensile strength characterizes a material's resistance to maximum uniform plastic deformation. Measured in MPa.

[0066] 5.Total elongation at break:

[0067] When a material is subjected to external force and is pulled apart, the ratio of the elongation after stretching to the length before stretching is called the total elongation at break, expressed as a percentage.

[0068] 6. Formability:

[0069] This patent specifically refers to the process in which a material is formed through plastic deformation processing. If a large amount of plastic deformation is achieved without damage (or minimal damage), it is considered to have good forming performance.

[0070] Example 1:

[0071] Preparation and verification of high thermal conductivity Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%).

[0072] A vacuum protective atmosphere melting furnace with a tilting pouring mechanism is used. The protective atmosphere is a mixed protective atmosphere of high-purity argon (99.999%), high-purity carbon dioxide, and sulfur hexafluoride, with the flow ratio of carbon dioxide to sulfur hexafluoride being 100:1. High-purity magnesium (99.98%), Mg-30La, Mg-20Ca, and Mg-5Mn in a composition ratio of Mg-1Ca-1Mn-1La (at.%) are added to a high-purity, high-density graphite crucible. The crucible is heated to 300°C and held for 1-2 hours. The temperature is then raised to 650-700°C and held for 1 hour. The melting condition is then observed through an observation window, and the temperature is raised to 750-800°C and held for 1-2 hours. After all the materials are melted, the graphite crucible is tilted to pour the melt into a rod-shaped graphite mold with a feeding riser. The mold is cooled naturally to obtain a rod-shaped ingot of a microalloyed preform with a composition of Mg-1Ca-1Mn-1La (at.%). The ingot is taken out and broken into 1-2 cm blocks for later use.

[0073] A vertical vacuum protective atmosphere furnace is used, with a protective atmosphere of high-purity argon (99.999%) throughout the entire process. The protective atmosphere furnace consists of three parts: a melting slag chamber, a slag baffle, and a dense ingot casting area. The melting slag chamber is divided into a main element chamber and a microelement chamber. The main alloy element is pure metal high-purity magnesium (99.98%) and high-purity zinc (99.99%), added to the main element chamber at a set content of Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%). The microelement of Mn, Ca, and La is a blocky Mg-1Ca-1Mn-1La (at.%) microalloy preform, added to the microelement chamber at set content. The furnace temperature is raised to 300°C and held for 1-2 hours to preheat, then raised to 750-800°C and held for 1-2 hours to ensure that the material in the chamber melts and flows into the dense ingot casting area under the action of gravity. A porous slag plate is placed under the two chambers. The main alloy element and the microalloyed preform are melted in different melting chambers respectively. After the oxide inclusions are removed by the slag plate, the pure melts of the two are mixed evenly in the ingot casting graphite crucible. Finally, the furnace cooling rate is set at 10-50℃ / min to achieve the formation of Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy net dense ingot ( Figure 1 ).

[0074] The above Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy ingot was homogenized under a protective atmosphere (such as high-purity argon). The homogenization temperature was 450°C, the homogenization time was 53h, and the cooling method was water quenching. The microstructure was as follows: Figure 2 .

[0075] The homogenized alloy was then extruded. The ingot size before extrusion was Φ65×150mm, the extrusion die was a 55×3.5mm plate, the ingot preheat temperature was 350°C, the extrusion die temperature was 400°C, the extrusion feed speed was 0.3mm / s, the extrusion barrel temperature was set at 350°C, and the extruded material was pulled by a traction machine with a pulling force of about 100N. The final Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) extruded plate was obtained, and its microstructure is shown in the following figure: Figure 3 The room temperature thermal conductivity of the extruded magnesium alloy sheet and the commercially available AZ31 B and AZ80A magnesium alloy sheets was measured. The results are shown in Figure 1. The room temperature thermal conductivity of three randomly selected samples of the patented alloy was 148.785 W / (m·K), 139.314 W / (m·K), and 148.888 W / (m·K), respectively. The average value exceeded that of the commercially available AZ31 B magnesium alloy extruded sheet by 63% and that of the commercially available AZ80A magnesium alloy extruded sheet by 245%.

[0076] Table 1. Test results of three random samples of room temperature thermal conductivity of this patented alloy

[0077]

[0078] Example 2:

[0079] Preparation and verification of easily forgeable Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%).

[0080] The ingot preparation method is the same as that in Example 1.

[0081] The above Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy ingot was homogenized under a protective atmosphere (such as high-purity argon). The homogenization temperature was 350°C, the homogenization time was 6 hours, and the cooling method was water quenching. The microstructure was as follows: Figure 5 .

[0082] The ingot after the homogenization treatment is forged and cut into Φ20×30mm billets. The preheating temperature is 300℃, the forging die temperature is 300℃, and the forging speed is 1.5 / min. The patented alloy of the present invention achieves 83% single-pass forging volume (flattening from 30mm to 5mm in height) at 300℃. The actual forging process is shown in the figure below. Figure 6 As shown in the figure, the forged samples are uniform, with no cracks or microcracks on the edges, which is significantly better than pure magnesium and AZ31 B alloy (with edge cracks, such as Figure 7 Table 2 compares the forging results of the two alloys mentioned above.

[0083] Table 2. Comparison of forming effects between this patented alloy and AZ31 B ingot under the same forging conditions

[0084] alloy Homogenization Forging temperature Forging rate Deformation result This patented alloy 350℃ / 6h 300℃ 1.5mm / s 83％ Well formed, no cracks AZ31B 350℃ / 6h 300℃ 1.5mm / s 83％ Poor forming, edge cracking

[0085] Example 3:

[0086] Preparation and verification of ultra-high plasticity extruded Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%).

[0087] The method for preparing the extruded alloy is the same as that in Example 1.

[0088] The room temperature mechanical properties test of the extruded alloy was carried out. The test results are as follows: Figure 8 As shown. The yield strength of this patented alloy exceeds 140MPa and the total elongation at break is 49%. While the elongation at break of general AZ31 B extruded sheet is less than 25%, this patented alloy achieves a nearly 200% increase in total elongation at break. Figure 8As shown in Figure (b), the tangent modulus of the extruded alloy of the patented material remains high (>42 GPa) up to a tensile stress of approximately 120 MPa, while the tangent modulus of conventional AZ31 B extruded sheet decreases to below 40 GPa and continues to decrease at tensile stresses below 80 MPa. This indicates that the patented alloy exhibits better stiffness retention under higher tensile stresses than the extruded AZ31 B magnesium alloy.

[0089] Example 4:

[0090] Preparation and verification of high thermal stability Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%).

[0091] The ingot preparation method is the same as that in Example 1.

[0092] The differential thermal analysis results of the above Mg-1Zn-0.1Mn-0.1Ca-0.1La (at.%) alloy net dense ingot ( Figure 9 ) demonstrates that the patented alloy exhibits no endothermic or exothermic peaks below 480°C, indicating at least the absence of a second phase melting characteristic. Corresponding test results also indicate that high-temperature treatment at 350-400°C for 6-53 hours does not reveal the formation of a localized low-melting-point second phase, consistent with the differential thermal analysis results.

[0093] The comparative results of differential thermal analysis between the patented alloy and conventional Mg-Zn magnesium alloy (ZK60) (Table 3) show that the patented alloy has higher structural stability during the forming process and supports hot forming at higher temperatures to achieve reduced forming stress.

[0094] Table 3. Comparison of differential thermal analysis results of this patented alloy and high Zn content ingot ZK60 ingot

[0095]

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a superplastic high thermal conductivity magnesium alloy suitable for forging, characterized in that: include: preparing a microalloyed preform having an atomic percentage content of Mg-1Ca-1Mn-1La; The zinc, magnesium and microalloyed preform are reacted and mixed uniformly in a protective atmosphere according to a set amount to obtain a magnesium alloy having a microalloying element content of Mn, Ca, La and the like in atomic percentages; Plastic forming of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La magnesium alloy containing microalloying elements such as Mn, Ca and La in atomic percentage was performed; Preparation of microalloyed preforms: A vacuum protective atmosphere melting furnace with a tilting pouring machine is used to mix magnesium, Mg-30La, Mg-20Ca, and Mg-5Mn in a ratio of Mg-1Ca-1Mn-1La by atomic percentage, add them to a graphite crucible, and heat them. After the materials are completely melted, the graphite crucible is tilted to pour the melt into a rod-shaped graphite mold with a feeding riser. The mold is naturally cooled to obtain a microalloyed preform rod-shaped ingot with an atomic percentage of Mg-1Ca-1Mn-1La. The ingot is then taken out and crushed into 1-2 cm blocks for later use. Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La magnesium alloy with microalloying elements Mn, Ca, La and other atomic percentages was prepared by multi-liquid flow blending method: A vertical vacuum protective atmosphere furnace is used, and the melting slag chamber of the protective atmosphere furnace is divided into a main element chamber and a micro element chamber. Metal magnesium and zinc are added to the main element chamber according to set content, and a blocky microalloyed preform is added to the micro element chamber according to set content, and heated. The pure melts of the two are evenly mixed in an ingot graphite crucible. After cooling, a net dense ingot-shaped microalloying element Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La alloy with atomic percentages of Mn, Ca, La, etc. is obtained.

2. The method for preparing a superplastic and highly thermally conductive magnesium alloy suitable for forging according to claim 1, wherein: The protective atmosphere of the vacuum protective atmosphere melting furnace is a mixed protective atmosphere of argon + carbon dioxide + sulfur hexafluoride, wherein the flow ratio of carbon dioxide to sulfur hexafluoride is 100:1, and the purity of argon is 99.999%.

3. The method for preparing a superplastic and highly thermally conductive magnesium alloy suitable for forging according to claim 1, wherein: Graphite crucible heating process: Heat the graphite crucible containing the material to 300℃ and keep it warm for 1-2 hours, then continue to heat it to 650-700℃ and keep it warm for 1 hour, then increase the temperature to 750-800℃ and keep it warm for 1-2 hours while observing the melting situation through the observation window.

4. The method for preparing a superplastic and highly thermally conductive magnesium alloy suitable for forging according to claim 1, wherein: A vertical vacuum protective atmosphere furnace is used. The protective atmosphere throughout the process is argon gas with a purity of 99.999%. The furnace cooling rate is 10-50 ℃ / min.

5. The method for preparing a superplastic and highly thermally conductive magnesium alloy suitable for forging according to claim 1, wherein: The heating process is as follows: the furnace temperature is raised to 300°C and kept warm for 1-2 hours for preheating, and then the temperature is raised to 750-800°C and kept warm for 1-2 hours to ensure that the material in the chamber is melted and flows into the net dense ingot area under the action of gravity. A porous slag plate is placed under the above two chambers. Metal magnesium, zinc and micro-alloyed preforms are melted in different melting chambers respectively, and oxide inclusions are removed by passing through the slag plate.

6. The method for preparing a superplastic and highly thermally conductive magnesium alloy suitable for forging according to claim 1, wherein: Plastic forming of magnesium alloys: A dense ingot of an alloy containing microalloying elements such as Mn, Ca, and La in an atomic percentage of Mg-(1-1.2)Zn-(0.1-0.2)Mn-(0.1-0.2)Ca-(0.1-0.2)La is homogenized under a protective atmosphere, and then the alloy is thermomechanically treated by extrusion, forging, or rolling plastic forming.

7. The method for preparing a superplastic and highly thermally conductive magnesium alloy suitable for forging according to claim 6, wherein: The homogenization temperature is 400-450℃, the homogenization time is 20-56 hours, and the cooling method is water quenching; For extrusion forming, the billet preheating temperature is 300-350℃, the extrusion die temperature is 350-400℃, the extrusion feed speed is 0.3-1 mm / s, the extrusion barrel temperature is set at 300-350℃, the extrusion ratio is set at 10-30, and the extruded material is pulled by a traction machine with a traction force of 100-500N; For forging, the billet preheating temperature is 280-320℃, the forging die temperature is 300-400℃, and the forging speed is 1.5-5 mm / min.

8. A superplastic high thermal conductivity magnesium alloy suitable for forging, characterized in that: The superplastic and high thermal conductivity magnesium alloy suitable for forging is prepared by the preparation method of any one of claims 1 to 7.

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