Preparation method of high-impact-toughness deformed pure magnesium and product

Abstract

The invention relates to the field of light-weight metal materials, in particular to a preparation method and product of high-impact-toughness deformed pure magnesium, and the method comprises the following steps: step 1, using common commercial pure magnesium as a raw material to carry out vacuum clean and dense cast ingot smelting to obtain a pure magnesium clean and dense cast ingot; and 2, the pure and dense pure magnesium cast ingot is subjected to low-temperature extrusion after being scalped, and the high-impact-toughness deformed pure magnesium is obtained. The preparation and deformation scheme of vacuum clean and dense ingot casting and low-temperature extrusion is adopted, pure deformed pure magnesium which is free of obvious basal texture and uniform and refined in crystal grain is obtained through the process of high-purity raw material-pure smelting clean and dense ingot casting-low-temperature extrusion, and the impact toughness of the pure magnesium is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of lightweight metallic materials, specifically to a method and product for preparing high-impact toughness deformed pure magnesium. Background Technology

[0002] Magnesium is one of the lowest density metals among engineering materials (approximately 1.74 g / cm³), possessing extremely high specific strength and specific stiffness, good thermal and electrical conductivity, excellent damping and vibration reduction properties, and good biocompatibility and recyclability. These characteristics make it a promising candidate for applications in aerospace, automotive, 3C products, and biomedical fields. However, magnesium has a hexagonal close-packed (HCP) crystal structure, and its plastic deformation capacity at room temperature mainly depends on basal plane slip. Due to the limited number of active slip systems and the coarse grains in the cast state, pure magnesium exhibits significant deficiencies in plasticity and fracture toughness at room temperature, with particularly low impact toughness. This severely limits the application of pure magnesium in situations requiring the bearing of impact loads and complex stress states.

[0003] Currently, the purity of commercially available pure magnesium is mainly 99.9% (wt.%), and most of it is in the as-cast state. It is primarily used as a raw material in magnesium alloy smelting, and rarely is it directly used to process parts for application. The main reason is that the properties of as-cast pure magnesium are difficult to meet practical application requirements. Therefore, by remelting to remove metallurgical defects and impurities from as-cast pure magnesium and by plastic deformation processing to achieve homogenization of the microstructure and improve mechanical properties, the application range of pure magnesium can be expanded. The impact performance (Charpy V-notch, 55*10*10mm standard sample) of ordinary commercially available deformed pure magnesium is 2-3 J / cm². 2 The range, compared to the impact properties of deformed pure aluminum (Charpy V-notch, 55*10*10mm standard sample, 10-20 J / cm²). 2 There is still a certain gap. Therefore, whether it is to improve the impact toughness of deformed pure magnesium itself, expand its commercial application range, or provide a new approach for the design of high impact toughness magnesium alloys, it is necessary to further improve the impact toughness of pure magnesium.

[0004] Numerous factors influence the impact toughness of deformed pure magnesium, which can be broadly categorized into external and internal factors. External factors mainly include temperature, deformation process, and heat treatment conditions, while internal factors mainly include grain size, trace alloying elements, and trace second phases.

[0005] In response to these influencing factors, existing technologies for improving the impact toughness of pure magnesium mainly include reducing metallurgical defects, alloying, and various plastic deformation methods.

[0006] Traditionally, pure magnesium is obtained through smelting and casting or simple extrusion / rolling. Pure magnesium prepared by these methods often has coarse grains and a strong basal texture, resulting in a room-temperature impact toughness typically below 5 J / cm², or even lower. While adding rare earth elements (such as Y, Gd, Nd, Zn, and Ca) can effectively improve the toughness of magnesium alloys, these methods alter the material's "purity," and the introduction of alloying elements may also lead to increased costs, changes in corrosion resistance, or biocompatibility issues, making them unsuitable for applications requiring the properties of pure magnesium. Although conventional extrusion or rolling can refine the grains and introduce some texture, the plastic deformation capacity of pure magnesium is limited, making it difficult to achieve significant grain refinement and effective weakening or alteration of texture, thus limiting its effect on improving impact toughness.

[0007] Currently, there is a lack of effective technical solutions that can significantly improve the room temperature impact toughness of pure magnesium without significantly altering its chemical composition, in order to meet the growing demand for comprehensive material performance in high-end applications. Summary of the Invention

[0008] To address the problem that pure magnesium exhibits relatively weak room-temperature impact toughness without altering its chemical composition in existing technologies, this invention provides a method and product for preparing high-impact toughness deformed pure magnesium.

[0009] This invention is achieved through the following technical solution: A method for preparing high-impact toughness deformed pure magnesium includes the following steps: Step 1: Vacuum-sealed ingot smelting is carried out using ordinary commercial pure magnesium as raw material to obtain pure magnesium ingots. Step 2: After peeling, the pure magnesium ingot is subjected to low-temperature extrusion to obtain high-impact toughness deformed pure magnesium.

[0010] Preferably, in step 1, the vacuum clean casting ingot melting is carried out under argon protection.

[0011] Preferably, in step 1, during vacuum-sealed ingot melting, the vacuum level is below 7 Pa, and the cooling rate is controlled by temperature regulation to achieve layer-by-layer solidification, thereby obtaining a pure magnesium ingot.

[0012] Preferably, during vacuum ingot casting, the furnace body is divided into a raw material placement zone and an ingot forming zone according to different temperatures. The temperature of the raw material placement zone is 900℃, the temperature of the ingot forming zone is 820℃, and the holding time is 200min.

[0013] Preferably, the raw material placement area adopts a two-stage heating method during the heating process, referred to as the first heating and the second heating. During the first heating process, the temperature was raised from 0 to 600℃ and held for 30 minutes. During the second heating, the temperature was increased from 600℃ to 900℃ and held for 200 minutes; The heating rate of the raw material storage area is 10℃ / min.

[0014] Preferably, the raw material placement area is cooled at a cooling rate of 5°C / min.

[0015] Preferably, the ingot forming zone adopts a two-stage heating method during the heating process, referred to as the first heating and the second heating. In one heating cycle, the temperature rises from 0 to 600℃ and is held for 30 minutes. During the second heating, the temperature was raised from 600℃ to 820℃ and held for 208 minutes; The heating rate of the ingot formation zone is 10℃ / min.

[0016] Preferably, the ingot forming zone is cooled in two stages to achieve solidification layer by layer, referred to as the first cooling and the second cooling. During the first cooling process, the temperature was reduced from 820℃ to 660℃ and held for 10 minutes, with a cooling rate of 5℃ / min. During the second cooling, the temperature dropped from 660℃ to 500℃ at a rate of 5℃ / min.

[0017] Preferably, in step 2, during low-temperature extrusion, the preheating temperature of the peeled pure magnesium ingot is 230℃±20℃, the extrusion die temperature is 230℃±20℃, the holding time is 4.5-6h, the extrusion cylinder temperature is set to 220℃±20℃, the extrusion speed is 0.2~0.5mm / s, the extrusion ratio is 16, and the traction force of the material straightening traction system is 15kg.

[0018] A product obtained according to the method for preparing high impact toughness deformed pure magnesium.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing high-impact toughness deformed pure magnesium using a "vacuum-sealed ingot casting + low-temperature extrusion" preparation and deformation scheme. Through a process of high-purity raw materials, purification melting, seam-sealed ingot casting, and low-temperature extrusion, pure deformed pure magnesium with no obvious basal texture and uniformly refined grains is obtained, resulting in significantly improved impact toughness. Furthermore, the "vacuum-sealed ingot casting" method reduces the inclusion content in the pure magnesium, which helps prevent fracture during impact from occurring at brittle inclusion sites. The aforementioned uniform grain refinement and low-density inclusion distribution enable the preparation of high-quality deformed pure magnesium with high impact toughness, providing a certain approach and method for preparing magnesium alloys with higher impact toughness.

[0020] Furthermore, pure magnesium has a melting point of around 650℃. Generally, the temperature of the graphite parts in the furnace will be lower than the set temperature. The raw material placement area is set to 900℃ and held for a certain period of time to allow the pure magnesium raw material to fully melt. During the melting process, the molten magnesium metal droplets will drip through the graphite perforated plate. The temperature of the ingot forming area is set to 820℃ to create a temperature difference between the raw material placement area and the ingot forming area, so that the ingot will solidify layer by layer from bottom to top to obtain a vacuum-sealed ingot.

[0021] The impact toughness of the product obtained by the preparation method of high impact toughness deformed pure magnesium according to the present invention can be improved by 70%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the arrangement of graphite components during the baking process of a tubular heating furnace.

[0023] Figure 2 This is a schematic diagram of the arrangement of graphite parts during the vacuum-sealed melting of pure magnesium ingots.

[0024] Figure 3 Heating curves for different temperature zones of the tubular furnace: (a) during furnace baking; (b) during vacuum ingot casting and melting.

[0025] Figure 4 The image shows the XRD pattern of the residue on the orifice plate after vacuum-sealed ingot melting. Orifice plate 1 and orifice plate 2 correspond to... Figure 2 The filter plate 1 and filter plate 2 are shown in the figure.

[0026] Figure 5 Metallographic photographs of high impact toughness deformed pure magnesium in Case 1: (a) and (b) are ordinary commercial 3N deformed pure magnesium; (c) and (d) are 3N deformed pure magnesium after vacuum net-density casting and melting.

[0027] Figure 6 The impact toughness of high impact toughness deformed pure magnesium is shown in Case 1, which describes the impact toughness of ordinary commercial (black) and vacuum-sealed ingots melted at typical temperatures.

[0028] Figure 7 Macroscopic and microscopic impact fracture surfaces of ordinary commercial deformed pure magnesium at typical temperatures in Case 1 for high impact toughness deformed pure magnesium: (a) 25℃, (b) 200℃, (c) 220℃, (d) 300℃; (e), (f), (g), and (h) are the 500x magnified fracture surfaces corresponding to (a), (b), (c), and (d), respectively; (i), (j), (k), and (l) are the 1000x magnified fracture surfaces corresponding to (a), (b), (c), and (d), respectively.

[0029] Figure 8Macroscopic and microscopic impact fracture surfaces of high impact toughness deformed pure magnesium after vacuum net-tight casting and melting at typical temperatures in Case 1: (a) 25℃, (b) 200℃, (c) 220℃, (d) 300℃; (e), (f), (g), (h), (i), (j), (k), (l) are the 1000x magnified fracture surfaces corresponding to (a), (b), (c), and (d), respectively.

[0030] Figure 9 Metallographic photographs of high impact toughness deformed pure magnesium in Case 2: (a) and (b) are ordinary commercial (low purity) 3N deformed pure magnesium; (c) and (d) are 4N deformed pure magnesium after vacuum-sealed ingot melting (high purity).

[0031] Figure 10 Grain orientation diagrams and pole figures for high-impact toughness deformed pure magnesium in Case Study 2: (a) Grain orientation diagram of low-purity deformed pure magnesium; (b) Pole figure of low-purity deformed pure magnesium; (c) Grain orientation diagram of high-purity deformed pure magnesium; (d) Pole figure of high-purity deformed pure magnesium.

[0032] Figure 11 (a) Load-displacement curves and (b) Impact toughness comparison diagrams of high impact toughness deformed pure magnesium in Case Study 2, showing deformed pure magnesium of different purities.

[0033] Figure 12 The macroscopic and microscopic impact fracture surfaces of high-impact toughness deformed pure magnesium at room temperature in Case 2 are as follows: (a) macroscopic impact fracture surface of low-purity deformed pure magnesium, (b) 500x microscopic fracture surface, (c) 1000x microscopic fracture surface, (d) 1500x microscopic fracture surface; (e) macroscopic impact fracture surface of high-purity deformed pure magnesium, (f) 500x microscopic fracture surface, (g) 1000x microscopic fracture surface, (h) 400x microscopic fracture surface. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0035] This invention discloses a method for preparing high-impact toughness deformed pure magnesium, referring to... Figure 1 This includes the following steps: Step 1: Using ordinary commercial pure magnesium as raw material and graphite as oxide, vacuum clean casting ingot smelting is carried out to obtain pure magnesium clean casting ingot.

[0036] The specific process of vacuum-sealed ingot casting and smelting is as follows: (a) Clean the graphite parts, and then put the cleaned and dried graphite parts into an oven at 200°C for 2 hours until dry.

[0037] (b) Assemble the graphite parts using a threaded connection, place the assembled graphite parts into a vertical, controllable three-zone tubular furnace, and seal using a flange; Figure 1 As shown, the graphite parts are arranged in the order a1-a10, where a1 is a graphite part with a length of 25mm, a2-a7 are graphite parts with a length of 50mm, and a8-a10 are graphite parts with a length of 100mm.

[0038] A single-hole graphite plate b1 is placed between a1 and a2, a six-hole graphite plate b2 is placed between a7 and a8, a graphite blind plate b3 is placed between a8 and a9, and a multi-hole graphite plate b4 is placed between a9 and a10.

[0039] (c) Close the gas inlet and outlet of the tubular furnace, turn on the vacuum pump switch, evacuate the vacuum level in the tubular furnace to below 10 Pa, set the temperature control program, and perform high-temperature vacuum furnace baking.

[0040] (d) After the furnace is dried, wait for the tubular furnace to cool naturally to about room temperature, close the vacuum valve and vacuum pump, open the gas outlet valve of the tubular furnace to restore the internal pressure of the tubular furnace to normal pressure, open the flange and remove the dried graphite parts.

[0041] (e) The raw pure magnesium is processed to a suitable size using methods such as wire cutting, acid washing, and sanding (polishing machine). The raw material size must be smaller than the inner diameter of the graphite part and larger than the aperture of the perforated plate. It is then placed in the raw material placement area of ​​the graphite part and assembled. For example... Figure 2 As shown, the graphite parts are arranged in the order of a1-a10, where a1 is a graphite part with a length of 25mm, a2-a7 are graphite parts with a length of 50mm, and a8-a10 are graphite parts with a length of 100mm. A single-hole graphite plate b1 is placed between a1 and a2, a six-hole graphite plate b2 is placed between a6 and a7, a multi-hole graphite plate b3 is placed between a7 and a8, and a graphite blind plate b4 is placed between a8 and a9. The graphite parts a4-a6 are the raw material placement area, where low-purity pure magnesium is placed. The six-hole graphite plate of b2 and the porous graphite plate of b3 separate the raw material placement area from the ingot forming area. The graphite part of a8 is the ingot forming area, and b4 is a graphite blind plate.

[0042] (f) Place the assembled graphite parts into the tubular furnace, seal it with a flange, check the sealing of the tubular furnace and each gas circuit switch to ensure that the tubular furnace is in a good sealing condition, turn on the vacuum pump switch, evacuate the vacuum until the vacuum level is lower than 7 Pa, and then close the vacuum valve.

[0043] (g) Open the argon gas inlet valve and the argon cylinder switch, turn the gas flow meter on the gas line to the maximum, observe the change in the pressure gauge reading at the flange of the tubular heater, and close the argon gas inlet valve of the tubular heater after the gas is filled to a level slightly lower than the positive pressure value.

[0044] (h) Repeat steps (f) and (g) three times. On the third time, after evacuating the vacuum, fill the furnace with argon gas to a slightly positive pressure value and reduce the gas flow rate so that the gas inlet and outlet in the tubular furnace are in a balanced state.

[0045] (i) Turn on the temperature controller of the tubular furnace and set the temperature control program. Set the temperature of the upper temperature zone (raw material placement zone) to 900℃ and the temperature of the lower temperature zone (ingot forming zone) to 820℃. The specific control method is as follows: During vacuum ingot casting, the furnace body is divided into a raw material placement zone and an ingot formation zone according to different temperatures. The temperature of the raw material placement zone is 900℃ and the temperature of the ingot formation zone is 820℃. The holding time is 200min.

[0046] The raw material storage area adopts a two-stage heating method during the heating process, which is referred to as the first heating and the second heating. During the first heating process, the temperature was raised from 0 to 600℃ and held for 30 minutes. During the second heating, the temperature increased from 600℃ to 900℃; The heating rate of the raw material storage area is 10℃ / min.

[0047] The raw material storage area is cooled at a rate of 5°C / min.

[0048] The ingot formation zone is heated in two stages, referred to as primary heating and secondary heating. In one heating cycle, the temperature rises from 0 to 600℃ and is held for 30 minutes. During the second heating, the temperature was raised from 600℃ to 820℃ and held for 208 minutes; The heating rate of the ingot formation zone is 10℃ / min.

[0049] The ingot formation zone is cooled in two stages to achieve layer-by-layer solidification, referred to as the first cooling and the second cooling. During the first cooling process, the temperature was reduced from 820℃ to 660℃ and held for 10 minutes, with a cooling rate of 5℃ / min. During the second cooling, the temperature dropped from 660℃ to 500℃ at a rate of 5℃ / min.

[0050] (j) After the heat preservation is completed, wait for the tubular heating furnace to cool to about room temperature, close the argon gas inlet valve, open the flange, take out the graphite parts, and obtain a high-purity pure magnesium ingot.

[0051] Step 2: After peeling, the pure magnesium ingot is subjected to low-temperature extrusion (extrusion processing parameters are shown in Table 1) to obtain high-impact toughness deformed pure magnesium. The preheating temperature of the peeled pure magnesium ingot is 230℃±20℃, the extrusion die temperature is 230℃±20℃, the holding time is 4.5-6h, the extrusion cylinder temperature is set at 220℃±20℃, the extrusion speed is 0.2~0.5mm / s, the extrusion ratio is 16, and the traction force of the material straightening traction system is 15kg.

[0052] Table 1 Extrusion Processing Parameters

[0053] This invention discloses a method for preparing high-impact toughness deformed pure magnesium. Ordinary commercial pure magnesium raw material is placed in a graphite material placement area equipped with a perforated plate, and vacuum-sealed ingot melting is performed under argon protection. Vacuum melting of the graphite ingot ensures melt purity, and the cooling rate during the melting process is controlled by adjusting the temperature to achieve layer-by-layer solidification, resulting in a fine and uniform as-cast microstructure. The addition of a porous graphite plate effectively removes some oxide inclusions, reducing the influence of oxides. The high-purity pure magnesium ingot obtained from the vacuum-sealed ingot melting is then subjected to low-temperature extrusion. By optimizing the single-stage plastic deformation process, the temperature is set at 200℃ and the extrusion speed at 0.5 mm / s to obtain fine and uniform grains. The resulting high-purity deformed pure magnesium exhibits a 70% increase in impact toughness, successfully improving the impact resistance of deformed pure magnesium.

[0054] The present invention also discloses a product obtained by the preparation method of high impact toughness deformed pure magnesium.

[0055] Example 1 The raw material used in this example is pure magnesium cast rod produced by Henan Mingmei Magnesium Industry Technology Co., Ltd., whose specific composition is shown in Table 2. It contains a lot of oxide inclusions inside and on the surface. The specific preparation steps are as follows: Table 2 Chemical composition of 3N grade commercial pure magnesium ingots

[0056] (1) Clean the graphite parts and dry them at 200℃ for 2 hours; according to Figure 1 Assemble the graphite parts (place the 25mm / 50mm / 100mm long graphite parts and graphite perforated plates in the order shown in the diagram), and connect the graphite parts in sequence using threads; place the assembled graphite parts into a tubular heating furnace and seal it with a flange; evacuate to negative pressure and bake at high temperature, with the temperature control settings as follows. Figure 3 (a) Remove after cooling; (2) The total mass of the raw material pure magnesium casting rod was found to be 820g. According to Figure 2 Reassemble the graphite parts and place the raw materials inside the graphite parts in sections a5 to a7; place the assembled graphite parts inside the tubular furnace and seal them with flanges; (3) Turn on the vacuum pump to evacuate the furnace. When the vacuum level inside the furnace is lower than 7 Pa, turn off the vacuum pump, open the argon cylinder switch and the argon inlet valve. When the gas pressure inside the furnace is slightly lower than the positive pressure, close the argon inlet valve. Repeat the above operation three times. On the third time, fill the furnace with argon to a slightly positive pressure value and reduce the gas flow rate to make the gas inlet and outlet in the tubular heating furnace balanced. Figure 3 (b) Set the temperature control program, setting the temperature of the raw material placement area to 900℃ and the temperature of the ingot forming area to 820℃; (4) After cooling, the high-purity pure magnesium ingot is obtained; the ingot is peeled off and checked to find that there are no obvious shrinkage cavities and porosity; it is then machined into a Φ60 mm×150 mm bar for extrusion. (5) Preheat the high-purity pure magnesium ingot and extrusion die in a muffle furnace. Set the temperature to 230℃, the holding time to 4.5h, the extrusion cylinder temperature to 220℃, the extrusion speed to 0.5mm / s, and the extrusion ratio to 16. Place the preheated extrusion die and the high-purity pure magnesium ingot into a horizontal extruder for extrusion. Use a material correction traction system with a traction force of 15kg to remove the 15cm long material head and tail to obtain high-purity deformed pure magnesium rod. (6) Set up a control group experiment. Take the same batch of raw pure magnesium casting rods and extrude them directly according to the same extrusion parameters as in step (5) above. Remove the 15cm long material head and tail to obtain low purity deformed pure magnesium rods.

[0057] The high-purity magnesium ingots obtained after vacuum-sealed ingot melting and the residue from the perforated filter plate were weighed, and the results are shown in Table 3. The perforated filter plate can effectively block some of the molten magnesium. XRD analysis was performed on the residue from the perforated filter plate, and the results are as follows. Figure 4 As shown, the main component is pure magnesium and some magnesium oxide. The filter plate can also effectively remove some magnesium oxide. Samples were taken from the same location (50 cm from the tip) of both low-purity and high-purity deformed pure magnesium rods. Metallographic characterization was performed on the samples without using metallographic etching solution to obtain the original internal morphology of the samples, as shown. Figure 5 As shown, where Figure 5(a) and (b) are ordinary commercial 3N deformed pure magnesium, and (c) and (d) are 3N deformed pure magnesium after vacuum-sealed ingot melting. It can be observed that the number of black spots inside the deformed pure magnesium is significantly reduced after vacuum-sealed ingot melting. Characterization of these black spots reveals that they are mainly composed of magnesium oxide, iron oxide, and carbides. This indicates that vacuum-sealed ingot melting can effectively remove some oxide inclusions, achieving the effect of purifying pure magnesium.

[0058] Table 3. Mass of each part after vacuum-sealed ingot melting

[0059] The Charpy pendulum impact test method was used to test the impact properties of deformed pure magnesium rods with different purities. Four typical test temperatures were used: 25℃, 200℃, 220℃, and 300℃. Standard Charpy V-notch specimens (55×10×10mm) were used, and the strain rate was 655 / s. Triple measurements were performed for each temperature. The test results are as follows: Figure 6 As shown, the samples after vacuum-refined casting and melting exhibit higher impact toughness and better stability at room temperature and in the medium and low temperature ranges. The impact toughness of the purified samples at the medium and high temperature range is increased by almost 200%, and the purified samples have great application potential at medium and high temperatures.

[0060] Reference Figure 7 At room temperature, small grains deform and undergo intergranular fracture, exhibiting some tear ridges and pores. At 200℃ and 220℃, small grain deformation increases, and a distinct shear lip appears. Simultaneously, the initiation and propagation of secondary cracks hinder the propagation of the main crack, and the impact absorption energy increases slowly, but there are no obvious ductile-brittle transition characteristics at this point. At 300℃, the microscopic fracture surface is entirely composed of dimples, indicating that the ductile-brittle transition has occurred, and it exhibits good toughness.

[0061] Reference Figure 8 At 5℃ and 200℃, grain fracture is mainly intergranular and transgranular. As the temperature increases, the proportion of transgranular fracture decreases significantly and gradually becomes intergranular fracture. At 220℃, obvious tensile dimples appear, and the ductile-brittle transition begins. At 300℃, all grains exhibit tensile dimples.

[0062] The above experimental results demonstrate that the vacuum-sealed ingot melting method can effectively remove oxides from pure magnesium and obtain pure and dense pure magnesium through layer-by-layer solidification. Low-temperature extrusion can effectively refine the grain size of cast pure magnesium, obtaining uniform and fine equiaxed crystals without plastic damage, thus obtaining deformed pure magnesium with significantly improved impact toughness.

[0063] Example 2 The raw material used in this example is 4N grade pure magnesium ingot produced by Shaanxi Guoke Magnesium Industry Technology Co., Ltd. The specific preparation steps according to the specific implementation method are as follows: (1) Clean the graphite parts and dry them at 200℃ for 2 hours; according to Figure 1 Assemble the graphite parts (place the 25mm / 50mm / 100mm long graphite parts and graphite perforated plates in the order shown in the diagram), and connect the graphite parts in sequence using threads; place the assembled graphite parts into a tubular heating furnace and seal it with a flange; evacuate to negative pressure and bake at high temperature, with the temperature control settings as follows. Figure 3 (a) Remove after cooling; (2) According to Figure 2 Reassemble the graphite parts and place the raw materials inside the graphite parts in sections a5 to a7; place the assembled graphite parts inside the tubular furnace and seal them with flanges; (3) Turn on the vacuum pump to evacuate the furnace. When the vacuum level inside the furnace is lower than 7 Pa, turn off the vacuum pump, open the argon cylinder switch and the argon inlet valve. When the gas pressure inside the furnace is slightly lower than the positive pressure, close the argon inlet valve. Repeat the above operation three times. On the third time, fill the furnace with argon to a slightly positive pressure value and reduce the gas flow rate to make the gas inlet and outlet in the tubular heating furnace balanced. Figure 3 (b) Set the temperature control program, setting the temperature of the raw material placement area to 900℃ and the temperature of the ingot forming area to 820℃; (4) After cooling, the high-purity pure magnesium ingot is obtained; the ingot is peeled off and checked to find that there are no obvious shrinkage cavities and porosity; it is then machined into a Φ60 mm×130 mm bar for extrusion. (5) Preheat the high-purity pure magnesium ingot and extrusion die in a muffle furnace. Set the temperature to 230℃, the holding time to 4.5h, the extrusion cylinder temperature to 220℃, the extrusion speed to 0.5mm / s, and the extrusion ratio to 16. Place the preheated extrusion die and the high-purity pure magnesium ingot into a horizontal extruder for extrusion. Use a material correction traction system with a traction force of 15kg to remove the 15cm long material head and tail to obtain high-purity deformed pure magnesium rod. (6) Set up a control group experiment. Take ordinary commercial 3N grade pure magnesium casting rods and extrude them directly according to the same extrusion parameters as in step (5) above. Remove the 15cm long material head and tail to obtain low purity deformed pure magnesium rods.

[0064] Samples were taken from the same location (50 cm from the tip) of both low-purity and high-purity deformed pure magnesium rods. Metallographic characterization was performed on the samples without using metallographic etching solution to obtain the original internal morphology of the samples. Figure 9 As shown. Among them. Figure 9(a) and (b) are ordinary commercial 3N deformed pure magnesium, while (c) and (d) are 4N deformed pure magnesium after vacuum-sealed ingot melting. The number of black spots inside the deformed pure magnesium decreased after vacuum-sealed ingot melting. Characterization of these black spots revealed that they were mainly composed of magnesium oxide, iron oxide, and carbides. This indicates that vacuum-sealed ingot melting can effectively remove some oxide inclusions, achieving the effect of purifying pure magnesium. To eliminate the influence of grain size on the impact toughness of deformed pure magnesium, deformed pure magnesium with similar grain sizes and different purities was prepared by adjusting the extrusion temperature. Figure 10 As shown, the grain size of magnesium of different purity levels is almost the same, and as can be seen from the pole figure, there is no obvious texture. The only variable is purity.

[0065] The impact performance of deformed pure magnesium rods with different purities was tested using the Charpy pendulum impact test method. The test temperature was room temperature (25℃), the test specimen size was a standard Charpy V-notch specimen (55×10×10mm), the strain rate was 655 / s, and three parallel tests were performed. The test results are as follows: Figure 11 As shown, after purification, the peak load of deformed pure magnesium did not increase significantly, but the position of the peak load shifted to the right, resulting in a significant increase in the area enclosed by the load-displacement curve and the horizontal axis. This means that purification allows deformed pure magnesium to absorb more energy during plastic deformation under impact, thereby improving its plastic deformation capacity. Simultaneously, the load-displacement curve of the purified sample exhibited a larger displacement, indicating that more energy was absorbed during crack propagation, which beneficially improves its resistance to fracture. Purification can improve the impact toughness of deformed pure magnesium from the perspective of crack initiation and propagation. Figure 11 (b) is a comparison of the impact toughness of magnesium in different purity forms. It can be seen that the impact toughness is significantly improved after purification.

[0066] Observe the macroscopic and microscopic fracture surfaces of magnesium impact specimens with different purities and deformed forms at room temperature, such as... Figure 12 As shown, the fracture surfaces of low-purity samples are mainly transgranular and intergranular fractures, accompanied by some tearing ridges. The fracture surfaces of high-purity samples are also mainly transgranular fractures, but contain some micropores and small cracks. The similar but slightly different fracture modes result in a 70% improvement in the impact toughness of the high-purity samples.

[0067] The above experimental results demonstrate that the vacuum-sealed ingot melting method can effectively remove oxides from pure magnesium and obtain pure and dense pure magnesium through layer-by-layer solidification. Low-temperature extrusion can effectively refine the grain size of cast pure magnesium, obtaining uniform and fine equiaxed crystals without plastic damage, thus obtaining deformed pure magnesium with significantly improved impact toughness.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A method for producing a high impact toughness wrought phase pure magnesium, characterized by, Includes the following steps: Step 1: Vacuum-sealed ingot smelting is carried out using ordinary commercial pure magnesium as raw material to obtain pure magnesium ingots. Step 2: After peeling, the pure magnesium ingot is subjected to low-temperature extrusion to obtain high-impact toughness deformed pure magnesium.

2. The method for preparing high impact toughness deformed pure magnesium according to claim 1, characterized in that, In step 1, the vacuum-sealed ingot melting is carried out under argon protection.

3. The method for preparing high impact toughness deformed pure magnesium according to claim 1, characterized in that, In step 1, during the vacuum-sealed ingot melting process, the vacuum level is below 7 Pa, and the cooling rate is controlled by temperature regulation to achieve layer-by-layer solidification, thereby obtaining a pure magnesium ingot.

4. The method for preparing high impact toughness deformed pure magnesium according to claim 3, characterized in that, During vacuum ingot casting, the furnace body is divided into a raw material placement zone and an ingot formation zone according to different temperatures. The temperature of the raw material placement zone is 900℃ and the temperature of the ingot formation zone is 820℃.

5. The method for preparing high impact toughness deformed pure magnesium according to claim 4, characterized in that, The raw material storage area adopts a two-stage heating method during the heating process, which is referred to as the first heating and the second heating. During the first heating process, the temperature was raised from 0 to 600℃ and held for 30 minutes. During the second heating, the temperature was increased from 600℃ to 900℃ and held for 200 minutes; The heating rate of the raw material storage area is 10℃ / min.

6. The method for preparing high impact toughness deformed pure magnesium according to claim 4, characterized in that, The raw material storage area is cooled at a rate of 5°C / min.

7. The method for preparing high impact toughness deformed pure magnesium according to claim 4, characterized in that, The ingot formation zone adopts a two-stage heating method during the heating process, which is referred to as the first heating and the second temperature rise. In one heating cycle, the temperature rises from 0 to 600℃ and is held for 30 minutes. During the second heating, the temperature was raised from 600℃ to 820℃ and held for 208 minutes; The heating rate of the ingot formation zone is 10℃ / min.

8. The method for preparing high impact toughness deformed pure magnesium according to claim 4, characterized in that, The ingot formation zone is cooled in two stages to achieve layer-by-layer solidification, referred to as the first cooling and the second cooling. During the first cooling process, the temperature was reduced from 820℃ to 660℃ and held for 10 minutes, with a cooling rate of 5℃ / min. During the second cooling, the temperature dropped from 660℃ to 500℃ at a rate of 5℃ / min.

9. The method for preparing high impact toughness deformed pure magnesium according to claim 1, characterized in that, In step 2, during low-temperature extrusion, the preheating temperature of the peeled pure magnesium ingot is 230℃±20℃, the extrusion die temperature is 230℃±20℃, the holding time is 4.5-6h, the extrusion cylinder temperature is set at 220℃±20℃, the extrusion speed is 0.2~0.5mm / s, the extrusion ratio is 16, and the traction force of the material straightening traction system is 15kg.

10. A product obtained by the method for preparing high impact toughness deformed pure magnesium according to any one of claims 1 to 9.

Images