A low-alloyed non-rare earth type high-strength magnesium alloy and a preparation method thereof

Abstract

The application discloses a low-alloyed non-rare earth type high-strength magnesium alloy and a preparation method thereof, and the chemical component mass percentage of the magnesium alloy is as follows: Cu 0.3-1.5 wt%, Al 0.7-2.0 wt%, Ca 0.1-0.7 wt%, Mn 0.2-0.8 wt%, and the rest is Mg and inevitable impurities. Alloying elements are introduced into the magnesium by preparing materials, smelting and pouring, and then the magnesium alloy is further subjected to heat treatment, cutting and deformation processing, so that a large number of nanoscale Mg2Cu, MgAlCu phase, Mg2Ca phase, Al-Mn phase and Mn particles are generated in the magnesium alloy in situ, a large number of ultra-fine grain structures are regulated, and a large number of solute segregation structures are constructed at the grain boundaries and subgrain boundaries. The total content of alloying elements is not more than 5 wt%, the yield strength of the magnesium alloy can reach 518 MPa at the highest, the magnesium alloy has good plasticity, and a non-rare earth type high-strength magnesium alloy with excellent mechanical properties is obtained.

Description

Technical Field

[0001] This invention relates to the field of metallic materials and metallic material processing, and particularly to the preparation technology of low-alloyed non-rare earth high-strength magnesium alloys. Background Technology

[0002] Magnesium has a density of approximately 1.74 g / cm³. 3 It is 2 / 3 the weight of aluminum alloy and 1 / 4 the weight of steel. As the lightest metal structural material currently available, it has advantages such as being lightweight, abundant in resources, and environmentally friendly. It also has advantages such as high specific strength and specific stiffness, strong shock absorption, electromagnetic shielding and radiation resistance, and easy machining. It has broad application prospects in transportation, aerospace, electronics, electrical appliances, oil and gas development, and weaponry. It also has the potential to be developed into biomedical materials, battery functional materials and solid hydrogen storage materials. It is hailed as the green engineering material of the 21st century.

[0003] However, compared to aluminum alloys and steel, the vast majority of magnesium alloys currently have relatively low absolute strength and poor plastic forming ability, which greatly limits their application as new green materials. The strength of commercially available high-strength AZ-series and ZK-series magnesium alloys after deformation is generally still below 350 MPa, which is insufficient to meet the requirements of high-performance structural materials. Therefore, developing high-strength magnesium alloys is of great significance for expanding the application fields of magnesium alloys.

[0004] In recent years, a large number of research efforts have been conducted to prepare high-strength magnesium alloys using various methods, including adding large amounts of rare earth elements and employing special processing methods such as powder metallurgy or large plastic deformation. Gradually, some high-strength magnesium alloys have been developed. For example, Chinese patent CN103290292A discloses a high-strength magnesium alloy with a yield strength of 350-380 MPa, a tensile strength of 410-450 MPa, and an elongation of over 6%. The composition by weight percentage is: Cd 1.0-15 wt%, Bi 2.0-10.0 wt%, Zn 5.0-13 wt%, Y 7.0-15.0 wt%, Zr 0.4-1.0 wt%, Nb 0.1-5.0 wt%, and the total amount of impurity elements Si, Fe, Cu, and Ni is less than 0.02 wt%. Due to the large number of alloying elements and high rare earth content, the cost of the alloy material and preparation inevitably increases. Furthermore, to ensure uniform mixing, an electromagnetic stirring continuous casting method is required to prepare the alloy ingot. The prolonged heat treatment after deformation further increases the alloy preparation cost. Chinese patent CN1924054A discloses a novel high-strength magnesium alloy, which uses W with a weight percentage of 3-20%. 14 Al 86High-strength magnesium alloys can be prepared by combining 80-97% Mg powder with semi-solid rheological forging technology. The tensile strength ranges from 305 to 492 MPa, but the process is complex and the strength is insufficient. Chinese patent CN201010219696.9 discloses an ultra-high-strength magnesium alloy bar prepared by high-force deformation. Its alloy composition is 6-13 wt% Gd, 2-6 wt% Y, and 0.3-0.8 wt% Zr. Its tensile strength is greater than 600 MPa, and its yield strength is greater than 540 MPa. Although the material has high strength, its elongation is very low, only about 1%, and its plasticity is extremely poor, making it difficult to apply in engineering. Furthermore, it requires unconventional large plastic deformation methods and isothermal aging treatment for 20-100 hours, placing high demands on production conditions. In addition, the alloy contains a large amount of rare earth elements, significantly increasing the alloy cost. Chinese patent CN201510675191.6 discloses a low-cost, non-rare earth, high-strength Mg-Bi-Ca-Mn magnesium alloy with the following chemical composition by mass percentage: Bi 2~10.0wt%, Ca 0.1~1.5wt%, Mn 0.1~1.0wt%, and the remainder being magnesium. Its tensile strength is 395.1-412.4 MPa, yield strength is 383.7-402.8 MPa, and elongation is 5.01-6.78%. Although it exhibits high yield strength, its alloy element content is high, and the alloy's plasticity is relatively low. Chinese patent CN201410029415.1 discloses a method for preparing Mg-Zn-Al-Cu ultra-high strength magnesium alloy plates. The alloy composition is Al 3-5wt%, Zn 1-2wt%, Cu 2.0-5.0wt%, RE 0.35-0.8wt%, Ti 1.2-1.8wt%, and the total amount of impurity elements Si, Fe, Cu, and Ni is less than 0.02wt%, with the balance being Mg. Its tensile strength is ~455.3MPa, yield strength ~349.4MPa, and elongation ~6.3%. Overall, the yield strength and elongation of the alloy are still relatively low. Furthermore, additional aging treatment is required after deformation during the preparation process, which increases costs and can easily damage the alloy surface. The presence of 0.35-0.8wt% RE and 1.2-1.8wt% Ti in the alloy further increases the raw material cost and preparation difficulty. Furthermore, it should be noted that the relevant documents of this invention require the Cu element content in the alloy to be 2.0-5.0 wt%, while emphasizing that "the total amount of impurity elements: Si, Fe, Cu and Ni is less than 0.02 wt%" appears repeatedly, and the description of Cu element is obviously self-contradictory.

[0005] Therefore, in order to better meet the requirements of transportation, aerospace, electronics, electrical appliances, oil and gas development, weaponry and equipment and other fields for low cost, easy processing and high performance of high-strength magnesium alloys, it is urgent to develop low cost high strength magnesium alloy materials that can be prepared by simple and continuous production and processing processes. This will greatly expand the further application of magnesium alloys in the future, and has important strategic significance in the fields of national defense and aerospace, as well as significant economic and social significance. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems that the strength of existing high-strength magnesium alloys is still relatively low compared to high-strength aluminum alloys, that a few high-strength magnesium alloys contain a lot of rare earth elements or high-priced alloying elements, resulting in excessively high material costs and complex processing technology, making it difficult to achieve large-scale commercial production, and that most high-strength magnesium alloys generally have low plasticity.

[0007] This invention relates to a low-alloyed non-rare earth high-strength magnesium alloy and its preparation method. The low-alloyed non-rare earth high-strength magnesium alloy is a Mg-Cu-Al-Ca-Mn magnesium alloy, and its chemical composition by mass percentage is: Cu 0.3~1.5wt%, Al 0.7~2.0wt%, Ca 0.1~0.7wt%, Mn 0.2~0.8wt%, with the remainder being magnesium and unavoidable impurities.

[0008] The method for preparing low-alloyed non-rare earth high-strength magnesium alloy of the present invention includes the following steps:

[0009] Step (1) Raw material preparation: Select commercial pure Mg ingots, Mg-Cu master alloy, commercial pure Al ingots, pure Ca or Mg-Ca master alloy and Mg-Mn master alloy as raw materials, and prepare the materials according to the mass percentage of the magnesium alloy composition after surface cleaning.

[0010] Step (2) Alloy smelting: Place pure Mg ingots into the crucible of the smelting furnace, set the furnace temperature to 680~760℃ and maintain it, and melt it under the protection of a protective solvent or protective atmosphere. Then add pure Al blocks, pure Ca or Mg-Ca master alloy, Mg-Cu master alloy and Mg-Mn master alloy preheated to 50~250℃ into the magnesium melt; keep it at the temperature for 5~60 minutes, then stir for 1~10 minutes, remove the slag, and keep it at the temperature for another 5~60 minutes in preparation for casting.

[0011] Step (3) Casting: The uniformly smelted magnesium alloy melt is cast using sand casting, metal mold casting or semi-continuous casting under a protective atmosphere to obtain a cast billet;

[0012] Step (4) Heat treatment: The alloy ingot obtained in step (3) is heat treated in a heat treatment furnace at a temperature of 390~530℃ for 2~48 hours, and then cooled to room temperature by air cooling or water cooling.

[0013] Step (5) Machining: Cut the heat-treated billet into the corresponding specifications and remove the surface oxide scale;

[0014] Step (6) Deformation processing: The de-oxidized blank obtained in step (5) is heated to 200~400 ℃, and then placed in a deformation mold for hot deformation processing with a deformation strain rate of 0.01s. -1 -5s -1 Between these conditions, the cumulative deformation is 0.8 or more. The hot-deformed billet is directly cooled to room temperature or annealed first and then cooled to room temperature to obtain the low-alloyed non-rare earth high-strength magnesium alloy material.

[0015] Compared with the prior art, the significant advancements and advantages of the present invention are as follows:

[0016] 1) The novel Mg-Cu-Al-Ca-Mn magnesium alloy of this invention is a completely new high-strength magnesium alloy system. Through simple alloying methods, a large number of different types of in-situ endogenous nanoparticle reinforcing phases are successfully introduced into the magnesium alloy and dispersed in the matrix. This overcomes the limitation that the size of precipitated reinforcing phases in magnesium alloys is generally large (above 100 nm), and the phases are generated in situ with good interfacial bonding. The large number of nano-reinforcing phases can effectively pin grain boundaries and dislocation movement, thus playing a strengthening role. On the other hand, they can control the deformation and recrystallization process of the matrix, thereby controlling a large number of ultrafine grain structures in the matrix.

[0017] 2) The novel Mg-Cu-Al-Ca-Mn magnesium alloy of the present invention has a large number of solute segregation structures at the grain boundaries of recrystallized grains and at the subgrain boundaries of deformed grains. These structures work synergistically with the above-mentioned nanoprecipitates to significantly refine the grains and greatly improve the mechanical properties of the alloy.

[0018] 3) The alloy system of this invention has a low content of elements, with the maximum content of each alloying element not exceeding 2wt% and the total content of all alloying elements not exceeding 5wt%. Combined with the control of processing and preparation technology, the size of the micron-sized second phase in the alloy is also relatively small, reaching about 2 microns. While optimizing the alloy structure and improving the mechanical properties of the alloy, it will not cause obvious cutting effect on the matrix.

[0019] 4) Through the synergistic regulation of alloy composition and processing technology, a large number of ultrafine grain structures with a size of less than 500 nm were successfully constructed in the alloy of the present invention. At the same time, a small number of strongly textured deformed grains also exist in the alloy. This synergistic effect of multi-scale microstructure significantly improves the strength and toughness of the alloy.

[0020] 5) The alloy of this invention has excellent mechanical properties. Currently, the yield strength of commercial high-strength magnesium alloy AZ80 under the same extrusion conditions is only about 272 MPa, while the alloy of this invention has excellent strength-plasticity matching. Its yield strength can reach up to 518 MPa, and its elongation can reach up to 14.7%. It has excellent strength and plasticity matching, and achieves a level of toughness matching that is comparable to ultra-high strength aluminum alloys. It is expected to become a new low-cost non-rare earth ultra-high strength magnesium alloy system.

[0021] 6) The total content of alloying elements in the alloy of the present invention does not exceed 5 wt%, and the second phase in the alloy has high thermal stability, which makes the alloy have excellent plastic processing performance. It can be hot-processed and deformed in a wide temperature range, thereby reducing the resistance to hot deformation and improving processing or production efficiency.

[0022] 7) The novel high-strength magnesium alloy of this invention does not contain any rare earth elements or high-valence alloying elements. The corresponding element resources are abundant and the raw materials are widely available. The prices of metallic Mg, Al, Mg-Cu master alloys, pure Ca, Mg-Ca master alloys and Mg-Mn master alloys are low, which can reduce the production cost of the alloy.

[0023] 8) The magnesium alloy composition design of this invention adopts the principle of multi-element trace alloying, giving full play to the role of each element. At the same time, there is no mutual reduction effect between them, but rather a mutual promotion effect. The total amount of alloying elements is low, especially the content of Al element is low. The solidus temperature of the alloy is higher. The higher alloying magnesium alloy will be closer to the melting point of pure magnesium. At the same time, the solute segregation structure at the grain boundary will further improve the strength of the grain boundary. It is expected to be a material for high-strength heat-resistant magnesium alloy parts.

[0024] 9) The Cu element in the magnesium alloy of the present invention also has a bactericidal effect and can be used as a potential material for biomedical devices.

[0025] 10) The alloy of this invention exhibits relatively uniform and stable melting. Due to the good flame-retardant properties of Ca in magnesium alloys, the melt is also relatively stable. Simultaneously, since the melting point of Al, one of the main alloying elements, is similar to that of Mg, and the melting point of the Mg-Cu master alloy is low, it is easy to achieve uniform alloy melt. Furthermore, some Ca and Mn elements can reduce the adverse effects of impurities on the alloy's microstructure and properties by forming Ca- or Mn-containing compounds with impurities in the melt, thereby weakening the harmful effects of impurities.

[0026] 11) The magnesium alloy preparation process of this invention is simple and breaks through the limitations of special processing methods such as large plastic deformation required by most high-strength magnesium alloys. At the same time, it can achieve ultra-high strength and good plasticity without special heat treatment after deformation processing. Existing magnesium alloy extrusion equipment, rolling equipment and forging equipment can all continuously process and produce it without additional modifications, and the requirements for production equipment are low. Attached Figure Description

[0027] Figure 1 This is a typical tensile stress-strain curve for the magnesium alloy in Example 1. Figure 2 The OM microstructure parallel to the extrusion direction is shown in Example 1. Figure 3 This is a typical tensile stress-strain curve of the magnesium alloy in Example 2. Figure 4 This is the OM microstructure parallel to the extrusion direction in Example 2. Figure 5 This is a typical tensile stress-strain curve for the magnesium alloy in Example 3. Figure 6 The OM microstructure parallel to the extrusion direction is shown in Example 3. Figure 7 This is a low-magnification SEM microstructure of Example 3, parallel to the extrusion direction. Figure 8 This is a high-magnification SEM microstructure of Example 3, parallel to the extrusion direction. Figure 9 This is a bright-field TEM image of alloy Example 3. Figure 10 This is a high-angle annular dark-field image of alloy in Example 3. Implementation

[0028] This invention relates to a low-alloyed non-rare earth high-strength magnesium alloy and its preparation method. The low-alloyed non-rare earth high-strength magnesium alloy is a Mg-Cu-Al-Ca-Mn magnesium alloy, and its chemical composition by mass percentage is: Cu 0.3~1.5wt%, Al 0.7~2.0wt%, Ca 0.1~0.7wt%, Mn 0.2~0.8wt%, with the remainder being magnesium and unavoidable impurities.

[0029] The preparation method of the low-alloyed non-rare earth high-strength magnesium alloy of the present invention includes the following steps:

[0030] Step (1) Raw material preparation: Select commercial pure Mg ingots, Mg-Cu master alloy, commercial pure Al ingots, pure Ca or Mg-Ca master alloy and Mg-Mn master alloy as raw materials, and prepare the materials according to the mass percentage of the magnesium alloy composition after surface cleaning.

[0031] Step (2) Alloy smelting: Place pure Mg ingots into the crucible of the smelting furnace, set the furnace temperature to 680~760℃ and maintain it, and melt it under the protection of a protective solvent or protective atmosphere. Then add pure Al blocks, pure Ca or Mg-Ca master alloy, Mg-Cu master alloy and Mg-Mn master alloy preheated to 50~250℃ into the magnesium melt; keep it at the temperature for 5~60 minutes, then stir for 1~10 minutes, remove the slag, and keep it at the temperature for another 5~60 minutes in preparation for casting.

[0032] Step (3) Casting: The uniformly smelted magnesium alloy melt is cast using sand casting, metal mold casting or semi-continuous casting under a protective atmosphere to obtain a cast billet;

[0033] Step (4) Heat treatment: The alloy ingot obtained in step (3) is heat treated in a heat treatment furnace at a temperature of 390~530℃ for 2~48 hours, and then cooled to room temperature by air cooling or water cooling.

[0034] Step (5) Machining: Cut the heat-treated billet into the corresponding specifications and remove the surface oxide scale;

[0035] Step (6) Deformation processing: The de-oxidized blank obtained in step (5) is heated to 200~400 ℃, and then placed in a deformation mold for hot deformation processing with a deformation strain rate of 0.01s. -1 -5s -1 Between these conditions, the cumulative deformation is 0.8 or more. The hot-deformed billet is directly cooled to room temperature or annealed first and then cooled to room temperature to obtain the low-alloyed non-rare earth high-strength magnesium alloy material.

[0036] The preparation methods described above include the Mg-Ca master alloy Mg-20Ca master alloy, Mg-Mn master alloy Mg-5Mn master alloy, and Mg-Cu master alloy Mg-30Cu mentioned in step (1).

[0037] In the preparation method described above, the stirring in step (2) is mechanical stirring, argon blowing stirring, electromagnetic stirring, or a combination thereof.

[0038] In the preparation method described above, the protective solvent in step (2) is preferably RJ-5.

[0039] In the preparation method described above, the protective atmosphere in step (2) is preferably a mixed gas with a volume ratio of CO2:SF6 = 50~100:1.

[0040] In the preparation method described above, the protective atmosphere in step (3) is preferably a mixed gas with a volume ratio of CO2:SF6 = 50~100:1.

[0041] The preparation method described above, the heat treatment in step (4) is a single-stage heat treatment or a double-stage heat treatment. The single-stage heat treatment is to hold at a constant temperature between 410 and 500°C for 2 to 48 hours and then cool. The double-stage heat treatment is to first heat treat at a constant temperature between 390 and 450°C for 2 to 24 hours and then heat to a temperature between 460 and 530°C for 1 to 24 hours.

[0042] The preparation method described above, the annealing process in step (6) is to keep the temperature at 100-225℃ for 1-45 minutes and then air cool to room temperature.

[0043] The preparation method described above, the mold in step (6) is a mold used to form plates, rods, pipes, wires, profiles, or cylindrical parts.

[0044] The essential features of this invention are as follows: obtaining a large proportion of ultrafine grain structure, a variety of dispersed nano-precipitates, and corresponding solute agglomerates are important measures to endow the alloy with excellent strength, but it is generally difficult to construct such microstructures in magnesium alloys. The Mg-Cu-Al-Ca-Mn magnesium alloy of this invention, through comprehensive control of alloy composition and processing technology, enables Al and Cu elements in the alloy to form 5-100 nm nano-sized Mg2Cu and MgAlCu nano-precipitates in situ with Mg; Mn elements in the alloy can form nano-sized spherical Mn particles and Al-Mn phases with a width of approximately 20-50 nm; in addition, during deformation processing, Ca, Al, Cu, and other elements in the matrix can agglomerate around the recrystallized grains, forming stable solute agglomerates. The nano-precipitates and solute agglomerates in the alloy can, on the one hand, play a strengthening role, and on the other hand, control the deformation and recrystallization process of the matrix, simultaneously obtaining a large amount of ultrafine grain structure and some non-recrystallized deformed structure containing residual dislocations in the alloy. Furthermore, the fine micron-sized second phase that was not dissolved into the matrix during heat treatment is further broken down and refined during deformation, then dispersed on the matrix. This second phase works synergistically with the dynamically precipitated nanoparticles and grain boundary segregating elements during hot deformation, effectively promoting recrystallization nucleation and inhibiting recrystallized grain growth, which is also beneficial for the formation of ultrafine grains. Simultaneously, these fine second phases can pin dislocations in the grain boundaries and matrix when the alloy is deformed by external forces, improving the overall mechanical properties of the alloy. Through the synergistic control of alloy composition and processing technology, a large number of ultrafine grains with sizes below 500 nm were successfully constructed in the alloy of this invention. At the same time, a small amount of strongly textured deformed grains also exist in the alloy. This synergistic effect of multi-scale microstructures significantly improves the strength and toughness of the alloy. Finally, a small amount of Cu, Al, Ca, and Mn elements dissolved in the matrix can also play a certain role in solid solution strengthening. Considering all these factors, the prepared Mg-Cu-Al-Ca-Mn alloy exhibits excellent strengthening and toughening effects.

[0045] The technical solution of the present invention will be described in detail below through specific embodiments. The following embodiments are all implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. Example

[0046] The mass percentages of the alloy components are: 0.4wt% Cu, 0.8wt% Al, 0.2wt% Ca, 0.25wt% Mn, with the balance being unavoidable impurities and magnesium.

[0047] (1) Ingredients: Pure Mg (99.95wt%) ingots, pure Al (99.95wt%) blocks, pure Ca (99.95wt%) granules, Mg-20Cu master alloy (actual Cu content is 20.12wt%) and Mg-10Mn master alloy (actual Mn content is 10.1wt%) are used as raw materials. After surface pretreatment (such as removing dirt, oxide scale, etc., the same in the following examples), the ingredients are prepared according to the above weight percentage of magnesium alloys.

[0048] (2) Alloy smelting: Clean and preheat the crucible. Place the magnesium ingot, preheated to 150°C, into the crucible of the smelting furnace. Set the furnace temperature to 720°C and heat the magnesium ingot. When the temperature reaches 500°C, start introducing a mixed gas of Ar:SF6 = 100:1 (volume flow ratio) to protect against combustion. After the magnesium is completely melted, add pure Ca, preheated to 60°C, to the melt. After melting, add pure Al blocks, then add Mg-20Cu master alloy, and finally add Mg-10Mn master alloy. After melting, mechanically stir for 2 minutes, remove the surface slag, and let stand at the temperature for 15 minutes to ensure that all alloying elements are evenly distributed in the magnesium alloy melt.

[0049] (3) Casting: Skim off the slag on the surface of the melt, and then cast it into a cylindrical mold with a diameter of 37 mm under the protection of a mixed gas of CO2:SF6 = 90:1 (volume flow ratio) to obtain the cast billet;

[0050] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 400°C in the furnace and held at this temperature for 24 hours for homogenization treatment. Then it is quenched in warm water and cooled to room temperature. The heating time is 60 minutes. This heat treatment process does not require gas protection.

[0051] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and it is machined into a cylindrical bar with a diameter of 36 mm.

[0052] (6) Plastic processing: The billet is heated for 30 minutes to reach the required extrusion temperature, and then placed into the extrusion cylinder of the extruder for extrusion processing to obtain a bar with a diameter of 6mm. The main process parameters during extrusion are: billet temperature 280℃, extrusion cylinder temperature 280℃, die temperature 280℃, extrusion speed 2m / min, extrusion ratio 36, and the extruded material is cooled by air cooling to obtain a low-cost non-rare earth high-strength magnesium alloy.

[0053] Alloy performance testing and microstructure analysis: A 50 mm long sample was cut from the extruded magnesium alloy bar and processed into a cylindrical tensile specimen with a gauge length of 20 mm and a gauge diameter of 4 mm. The axial direction of the cylindrical specimen was aligned with the extrusion flow lines of the material. The tensile strength of the magnesium alloy described in this invention was measured to be 525.9 ± 4 MPa, the yield strength to be 515.2 ± 3 MPa, and the elongation to be 11.8 ± 1%. The typical tensile curve of the magnesium alloy obtained in this example is shown below. Figure 1 As shown, the magnesium alloy obtained in this embodiment has both ultra-high strength and good elongation. Figure 2 The image shows the microstructure of the magnesium alloy prepared in this embodiment, parallel to the extrusion direction. It can also be seen from the metallographic image that dynamic recrystallization occurred in most areas of the alloy during the extrusion process, with a recrystallization fraction of about 65%, and the grain size in the recrystallized area was extremely small. Example

[0054] The mass percentages of the alloy components are: 1 wt% Cu, 1.5 wt% Al, 0.35 wt% Ca, 0.45 wt% Mn, with the balance being unavoidable impurities and magnesium.

[0055] (1) Batching: Pure Mg (99.95 wt%) ingots, pure Al (99.95 wt%) blocks, Mg-20Ca master alloy (actual Ca content is 19.91 wt%), Mg-30Cu master alloy (actual Cu content is 30.12 wt%) and Mg-5Mn master alloy (actual Mn content is 5.1 wt%) are used as raw materials. After surface pretreatment, the raw materials are batched according to the above-mentioned magnesium alloy weight percentages.

[0056] (2) Alloy smelting: Clean and preheat the crucible, place the magnesium ingot preheated to 150°C into the crucible of the smelting furnace, set the furnace temperature to 740°C to heat the magnesium ingot, and cover the surface of the magnesium alloy with RJ-5 solvent. After the magnesium is completely melted, add the pure Al block preheated to 150°C and the Mg-20Ca master alloy to the melt in sequence. After melting, add the Mg-30Cu master alloy, and after melting, add the Mg-5Mn master alloy. After melting, mechanically stir for 2 minutes, let stand for 5 minutes, then introduce argon gas to the bottom of the melt and treat for 2 minutes. Then remove the surface slag, and introduce a CO2:SF6 = 99:1 (flow ratio) mixed gas above the surface of the melt for protection. Keep it at the temperature and let it stand for 15 minutes to make all alloying elements evenly distributed in the magnesium alloy melt.

[0057] (3) Casting: Skim off the slag on the surface of the melt, and then cast it in a metal mold under the protection of a mixed gas of CO2:SF6 = 99:1 (volume flow ratio). Then, a non-rare earth magnesium alloy ingot with a diameter of 60 mm is prepared by metal mold casting.

[0058] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 460℃ in the furnace and held for 36 hours, and then quenched in warm water.

[0059] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a size suitable for extrusion processing;

[0060] (6) Plastic processing: Heat the billet for 30 minutes to reach the required extrusion temperature, put it into the extrusion cylinder of the extruder for extrusion processing, and obtain a bar with a diameter of 10 mm. The main process parameters during extrusion are: billet temperature 300℃, extrusion cylinder temperature 300℃, die temperature 300℃, extrusion speed 1m / min, extrusion ratio 36, and the extruded material is cooled by air cooling, thus obtaining a low-cost non-rare earth type high-strength magnesium alloy.

[0061] Alloy performance testing and microstructure analysis: A 50mm long sample was cut from the extruded magnesium alloy rod and processed into a cylindrical tensile specimen with a gauge length of 20mm and a gauge diameter of 4mm. The axial direction of the cylindrical specimen was aligned with the extrusion flow lines of the material. The tensile strength of the magnesium alloy described in this invention was measured to be 529.7±5MPa, the yield strength to be 518.1±3MPa, and the elongation to be 12.1±0.5%. The typical tensile curve of the magnesium alloy obtained in this example is shown below. Figure 3 As shown, the magnesium alloy obtained in this embodiment has both ultra-high strength and good elongation. Figure 4 The image shows the microstructure of the magnesium alloy prepared in this embodiment, parallel to the extrusion direction. It can also be seen from the metallographic image that dynamic recrystallization occurred in most areas of the alloy during the extrusion process, with a recrystallization fraction of about 80%, and the grain size in the recrystallized area was extremely small. Example

[0062] The mass percentages of the alloy components are: 1.4wt% Cu, 1.8wt% Al, 0.61wt% Ca, 0.75wt% Mn, with the balance being unavoidable impurities and magnesium.

[0063] (1) Batching: Pure Mg (99.95 wt%) ingots, pure Al (99.95 wt%) blocks, Mg-20Ca master alloy (actual Ca content is 19.91 wt%), Mg-30Cu master alloy (actual Cu content is 30.12 wt%) and Mg-5Mn master alloy (actual Mn content is 5.1 wt%) are used as raw materials. After surface pretreatment, the raw materials are batched according to the above-mentioned magnesium alloy weight percentages.

[0064] (2) Alloy smelting: Clean and preheat the crucible. Place the magnesium ingot, preheated to 150°C, into the crucible of the smelting furnace. Set the furnace temperature to 720°C and heat the magnesium ingot. When the temperature reaches 500°C, start introducing a CO2:SF6 = 100:1 (flow ratio) mixed gas to protect against combustion. After all the magnesium has melted, add the Mg-20Ca master alloy, preheated to 150°C, to the melt. After melting, add pure Al blocks, then add the Mg-30Cu master alloy, and finally the Mg-5Mn master alloy. After melting, mechanically stir for 2 minutes, remove the surface slag, and keep it at the temperature for 15 minutes to ensure that all alloying elements are evenly distributed in the magnesium alloy melt.

[0065] (3) Casting: Skim off the slag on the surface of the melt, and then cast it into a cylindrical mold with a diameter of 60 mm under the protection of a mixed gas of CO2:SF6 = 100:1 (flow ratio) to prepare a non-rare earth magnesium alloy ingot.

[0066] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 410°C in the furnace and held at this temperature for 12 hours. Then, the temperature is increased to 450°C in 10 minutes and held for 24 hours. Then, it is quenched in warm water and cooled to room temperature.

[0067] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a size suitable for extrusion processing;

[0068] (6) Plastic processing: The billet is heated for 30 minutes to reach the required extrusion temperature, and then placed into the extrusion cylinder of the extruder for extrusion processing to obtain a bar with a diameter of 12 mm. The main process parameters during extrusion are: billet temperature 330℃, extrusion cylinder temperature 330℃, die temperature 330℃, extrusion speed 3m / min, extrusion ratio 25, and the extruded material is cooled by air cooling to obtain a low-cost non-rare earth high-strength magnesium alloy.

[0069] Alloy performance testing and microstructure analysis: A 50mm long sample was cut from the extruded magnesium alloy bar and processed into a round bar tensile specimen with a gauge length of 20mm and a gauge diameter of 4mm. The axial direction of the round bar specimen was aligned with the extrusion flow lines of the material. The tensile strength of the magnesium alloy described in this invention was measured to be 511.1±4MPa, the yield strength to be 498.2±2MPa, and the elongation to be 14.7±1%. The typical tensile curve of the magnesium alloy obtained in this example is shown below. Figure 5 As shown, the magnesium alloy obtained in this embodiment has both ultra-high strength and good elongation. Figure 6The image shows the microstructure of the magnesium alloy obtained in this embodiment, parallel to the extrusion direction. The metallographic image also reveals that dynamic recrystallization occurred in most areas of the alloy during extrusion, with a recrystallization fraction reaching approximately 90%. The grain size in the recrystallized region is extremely fine. Compared to the alloys obtained in Examples 1 and 2, the recrystallized grain size in the resulting alloy is similar, but the proportion of recrystallized structure is significantly increased. Simultaneously, the strength of the alloy is slightly lower than that in Examples 1 and 2, but the elongation is somewhat improved. Considering that the alloying element content in this embodiment is higher than in Examples 1 and 2, while the alloy plasticity is improved, it is speculated that the increased number of micron-sized second phases in the alloy can promote the increase in the proportion of dynamic recrystallization. The resulting recrystallized structure generally has a weaker texture strength than the non-recrystallized deformed structure, which is beneficial to the improvement of alloy plasticity. To obtain more refined microstructure characteristics of the present invention and the alloy, SEM and TEM analyses were further performed on Example 3. Figure 7 and Figure 8 The images show the low-magnification and high-magnification SEM microstructures of Example 3, parallel to the extrusion direction. It can be seen that the size of the recrystallized grains is less than 1 micrometer, and the matrix is ​​dispersed with fine micron-sized second phase particles and a large number of fine nano-precipitates. Among them, the micron-sized second phase is MgAlCu, and its size is less than 2 micrometers. Figure 9 The TEM bright-field image of the alloy in Example 3 further revealed the presence of a large number of nano-precipitates in the alloy, with a size of about 10 nm. These precipitates are Mg2Cu nano-precipitates, MgAlCu nano-precipitates, Mg2Ca nano-precipitates, and spherical Mn nano-precipitates. Figure 10 The high-angle annular dark-field image of the alloy in Example 3 reveals significant solute segregation at the fine recrystallization grain boundaries, primarily formed by the segregation of Ca, Al, Cu, and Mn elements. This demonstrates that the microstructure of the alloy of this invention can be specifically controlled through alloy composition and processing techniques to obtain recrystallized structures with varying proportions, constructing microstructures containing micron-sized particles, multiple nano-precipitates, and solute segregation structures, thereby obtaining alloy billets with controllable strength and plasticity. Example

[0070] The mass percentages of the alloy components are: 1 wt% Cu, 1.5 wt% Al, 0.35 wt% Ca, 0.45 wt% Mn, with the balance being unavoidable impurities and magnesium.

[0071] (1) Batching: Pure Mg (99.95 wt%) ingots, pure Al (99.95 wt%) blocks, Mg-20Ca master alloy (actual Ca content is 19.91 wt%), Mg-30Cu master alloy (actual Cu content is 30.12 wt%) and Mg-5Mn master alloy (actual Mn content is 5.1 wt%) are used as raw materials. After surface pretreatment, the raw materials are batched according to the above-mentioned magnesium alloy weight percentages.

[0072] (2) Alloy smelting: Clean and preheat the crucible. Place the magnesium ingot, preheated to 150°C, into the crucible of the smelting furnace. Set the furnace temperature to 720°C and heat the magnesium ingot. When the temperature reaches 500°C, start introducing a CO2:SF6 = 100:1 (flow ratio) mixed gas to protect against combustion. After all the magnesium has melted, add the Mg-20Ca master alloy, preheated to 150°C, to the melt. After melting, add pure Al blocks, then add the Mg-30Cu master alloy, and finally the Mg-5Mn master alloy. After melting, mechanically stir for 2 minutes, remove the surface slag, and keep it at the temperature for 15 minutes to ensure that all alloying elements are evenly distributed in the magnesium alloy melt.

[0073] (3) Casting: Skim off the slag on the surface of the melt, and then use semi-continuous casting under the protection of CO2:SF6 =100:1 (flow ratio) mixed gas to prepare a cylindrical semi-continuous casting alloy ingot with a diameter of 70 mm through a crystallizer.

[0074] (4) Heat treatment: After removing the riser, the alloy ingot prepared in step (3) is heated to 460℃ in the furnace and held for 36 hours, and then quenched in warm water.

[0075] (5) Machining: Turning is used to remove the oxide layer on the surface of the alloy ingot after heat treatment in step (4) and to process it into a size suitable for extrusion processing;

[0076] (6) Plastic processing: The cylindrical blank with a height of 110 mm and a diameter of 65 mm obtained after machining is placed into a mold for forging deformation processing. The blank temperature is 350℃, the forging mold temperature is 350℃, and the forging is carried out with a pressing head speed of 10 mm / s. After forging, a disc-shaped sample with a height of 20 mm is obtained. Then, it is kept at 120℃ for 10 minutes and then air-cooled to room temperature to obtain a low-cost non-rare earth high-strength magnesium alloy.

[0077] Alloy performance testing and microstructure analysis: A 50mm long sample was cut from the forged magnesium alloy billet and machined into a cylindrical tensile specimen with a gauge length of 20mm and a gauge diameter of 4mm. Tensile tests were then conducted. The tensile strength of the magnesium alloy described in this invention was measured to be 454.3±4MPa, the yield strength to be 432.5±3MPa, and the elongation to be 9.3±0.5%. Although the mechanical properties of the forged alloy are lower than those of the extruded alloy specimen with the same composition, it still retains a yield strength of over 430MPa and an elongation of over 8%, exhibiting ultra-high strength and toughness.

[0078] Comparative Example

[0079] The comparative example is a currently commercially available high-strength magnesium alloy: Mg-7.4Al-0.45-Zn-0.3Mn (wt%, AZ80) magnesium alloy. Pure Mg (99.95 wt%) ingots, pure Al (99.95 wt%) blocks, pure Zn (99.95 wt%) blocks, and Mg-5Mn master alloy (actual Mn content measured to be 5.1 wt%) were used as raw materials. After surface pretreatment, the alloys were prepared according to the weight percentages of the comparative example magnesium alloy. The remaining processing and preparation steps were the same as in Example 1. The resulting AZ80 alloy had a tensile strength of 360.2 ± 3 MPa, a yield strength of 272.7 ± 2 MPa, and an elongation of 8.21 ± 1%. As can be seen from the comparison, the novel low-alloyed non-rare earth magnesium alloy of the present invention has significantly higher strength and plasticity than conventional commercial AZ80 magnesium alloy, achieving mechanical properties similar to ultra-high strength wrought aluminum alloy. It is a new type of low-cost low-alloyed non-rare earth high-strength magnesium alloy with a very competitive market.

[0080] The raw materials and equipment used in the above embodiments are all obtained through known means, and the operating processes used are mastered by those skilled in the art.

Claims

1. A method for preparing a low-alloyed, non-rare earth type high-strength magnesium alloy, the chemical composition of the magnesium alloy being, in mass percent: Cu 0.4-1.5 wt%, Al 0.7-2.0 wt%, Ca 0.2-0.7 wt%, Mn 0.2-0.8 wt%, the remainder being magnesium and unavoidable impurities, characterized in that, The steps include: Step (1) batching: using commercial pure Mg ingot, Mg-Cu intermediate alloy, commercial pure Al ingot, pure Ca or Mg-Ca intermediate alloy and Mg-Mn intermediate alloy as raw materials, after surface cleaning, preparing the materials according to the mass percentage of the magnesium alloy composition; Step (2) alloy smelting: placing the pure Mg ingot into the crucible of a smelting furnace, setting the furnace temperature to 680-760 ℃ and keeping, melting under the protection of a protective solvent or a protective atmosphere, then adding the preheated pure Al block, pure Ca or Mg-Ca intermediate alloy, Mg-Cu intermediate alloy and Mg-Mn intermediate alloy to the magnesium melt; keeping for 5-60 minutes, then stirring for 1-10 minutes, after slagging, keeping for another 5-60 minutes for pouring; Step (3) pouring: pouring the uniformly smelted magnesium alloy melt under the protection of a protective atmosphere by sand casting, metal mold casting or semi-continuous casting to obtain a cast blank; Step (4) heat treatment: heat treating the alloy ingot prepared in step (3) in a heat treatment furnace, the heat treatment temperature is 390-530 ℃, the time is 24-48 hours, then cooling to room temperature in air or water; Step (5) machining: cutting the heat treated blank into corresponding specifications and removing the surface oxide skin; Step (6) deformation processing: the oxide scale removed billet obtained in step (5) is heated to 200-400℃, and then put into a deformation die to perform hot deformation processing, the deformation strain rate is 0.01s -1 -5s -1 above, the hot deformed billet is directly cooled to room temperature or first annealed and then cooled to room temperature, to obtain the low-alloyed non-rare earth type high-strength magnesium alloy material.

2. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The Mg-Ca intermediate alloy Mg-20Ca intermediate alloy, the Mg-Mn intermediate alloy Mg-5Mn intermediate alloy and the Mg-Cu intermediate alloy Mg-30Cu in step (1).

3. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The stirring in step (2) is mechanical stirring or argon blowing stirring or electromagnetic stirring or a combination thereof.

4. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The protective solvent in step (2) is preferably RJ-5.

5. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The protective atmosphere in step (2) is preferably a mixed gas with a volume ratio of CO2:SF6=50-100:

1.

6. The method for preparing low-alloyed non-rare earth high-strength magnesium alloy according to claim 1, characterized in that: The protective atmosphere in step (3) is preferably a mixed gas with a volume ratio of CO2:SF6=50-100:

1.

7. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The heat treatment in step (4) is single-stage heat treatment or double-stage heat treatment, wherein the single-stage heat treatment is keeping at a certain constant temperature between 410-500 ℃ for 24-48 hours, then cooling, and the double-stage heat treatment is first keeping at a certain constant temperature between 390-450 ℃ for 12-24 hours, then heating to a certain temperature between 460-530 ℃ for 12-24 hours of high-temperature heat treatment.

8. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The annealing process in step (6) is keeping at 100-225 ℃ for 1-45 minutes, then air cooling to room temperature.

9. The method of claim 1, wherein the low-alloyed, non-rare earth, high-strength magnesium alloy is characterized by: The mold in step (6) is a mold for forming a plate, or a rod, or a pipe, or a wire, or a profile, or a cylindrical part.

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