A low anisotropy magnesium alloy and a method for preparing large structural parts by a short process

Abstract

The application belongs to the technical field of magnesium alloy and provides a low anisotropy magnesium alloy, which comprises the following raw materials in percentage by mass: Gd 5.80-7.20 wt%, Y 0.02-2.00 wt%, Zr 0.30-0.60 wt%, Zn 0-0.60 wt%, Mn 0-0.10 wt%, Sb 0.02-0.3 wt%, Sr 0.02-0.05 wt%, Sn 0.04-0.1 wt%, and the balance being magnesium. The application also provides a method for preparing large structural parts in a short process. The application utilizes the atomic misplacement and the difference in elastic modulus between the matrix and the Gd and Y elements to improve the mechanical properties, thereby ensuring the basic performance indicators of the alloy system, and utilizes the combined action of rare earth elements and precise control of the forming process to realize the short process preparation of large structural parts.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy technology, and particularly relates to a low anisotropy magnesium alloy and a short-process method for manufacturing large structural components. Background Technology

[0002] Magnesium alloys are widely used as structural materials due to their low density and high specific strength. However, because magnesium alloys have a hexagonal close-packed (HCP) crystal structure, their plastic deformation capacity is poor, and the slip systems that can be activated are insufficient to coordinate deformation. This makes magnesium alloy ingots prone to cracking during rolling and forging. In addition, due to the low symmetry of HCP metals, the mechanical behavior of deformed magnesium alloys exhibits tensile-compressive asymmetry and anisotropy, with obvious loading path and orientation correlation. This results in severe anisotropy of mechanical properties in large magnesium alloy structural components produced by rolling and forging, making it difficult for the performance of the structural components in one direction to meet the application requirements. Therefore, large-size, complex, high-performance magnesium alloy structural components are mostly manufactured by casting. However, magnesium alloy structural components prepared by casting have defects such as porosity and inclusions, and the grains are coarse, making it difficult to obtain magnesium alloy structural components with high strength and high ductility.

[0003] Currently, to avoid defects in magnesium alloy castings and improve cracking and anisotropy issues in deformed magnesium alloy ingots, a processing method is gradually being adopted that involves pre-forging and pre-extruding magnesium alloy billets followed by secondary processing to prepare magnesium alloy structural parts. For example, Chinese patent application number 202011595112.8 discloses a forging method for large-diameter magnesium alloy ring forgings, wherein the embodiment uses: AZ80 ingot → XYZ three-dimensional upsetting and rounding (hot material reheated three times) → machining through holes to form a ring billet → ring billet heating and ring rolling → reheating and ring rolling into a structural part; Chinese patent application number 202111128440.1 discloses a manufacturing method for high-formability magnesium alloy forgings for aerospace applications, wherein the embodiment uses: rare earth magnesium alloy ingot → ingot preheating and radial forging → reheating and axial upsetting → repeating the "radial forging and axial upsetting" process 1-2 times. Due to limitations in ingot cracking and anisotropy, existing processes for manufacturing wrought magnesium alloy structural components involve numerous processing steps, making it difficult to achieve short-process fabrication. Furthermore, with increasing preheating cycles, the mechanical properties continuously decrease. Additionally, existing magnesium alloy processing equipment suffers from limitations in ingot dimensions due to the "pre-forging and pre-extrusion" processes. Therefore, it is urgent to develop a low-anisotropy magnesium alloy material for short-process fabrication of large, high-performance wrought magnesium alloy structural components. Summary of the Invention

[0004] The purpose of this invention is to provide a low anisotropy magnesium alloy, which aims to solve the problems mentioned in the background art.

[0005] The present invention is implemented as follows: a low anisotropic magnesium alloy comprises the following raw materials in the following mass percentages: Gd 5.80-7.20wt%, Y 0.02-2.00wt%, Zr 0.30-0.60wt%, Zn 0-0.60wt%, Mn 0-0.10wt%, Sb 0.02-0.3wt%, Sr 0.02-0.05wt%, Sn 0.04-0.1wt%, with the balance being magnesium.

[0006] Another objective of this invention is to provide a method for short-process fabrication of large forged ring structures, comprising the following steps:

[0007] (1) The above-mentioned low anisotropic magnesium alloy was prepared into an ingot by semi-continuous casting;

[0008] (2) Homogenize the ingot at a temperature of 460-480℃ for 20-26 hours.

[0009] (3) Machining a through hole with a diameter of 150-250mm into the homogenized magnesium alloy ingot and rounding the inner and outer edges to obtain the billet;

[0010] (4) The billet is preheated at a temperature of 440-480℃ for 3-5 hours. The rolling mill rolls, rollers, clamping rolls and upper and lower cone rolls are preheated to 200-300℃ and kept at that temperature for 0.5 hours.

[0011] (5) The billet is subjected to ring rolling. The rolling speed of the rolling roller is 15-50 r / min and the linear feed speed of the mandrel is 1-3 mm / s. Large magnesium alloy forged ring structural parts are prepared by one ring rolling.

[0012] Preferably, in step (1), the ingot is a round ingot with a diameter of 650-750 mm.

[0013] Another objective of this invention is to provide a method for short-process fabrication of complex cross-section structural components, comprising the following steps:

[0014] (1) The above-mentioned low anisotropic magnesium alloy was prepared into an ingot by semi-continuous casting;

[0015] (2) Homogenize the ingot to obtain billet. The homogenization temperature is 440-460℃ and the time is 18-24h.

[0016] (3) The prepared billet is preheated at a temperature of 440-460℃ for 3-5 hours. The billet is then extruded by the movement of the upper and lower dies to fill the entire die cavity. The temperature of the upper and lower dies is 490-510℃, the final forging temperature of the forging is 350-400℃, and the deformation speed is 5-20mm / s. A large structural part with a complex cross section is forged in one hot forging.

[0017] Preferably, in step (1), the ingot is a round ingot with a diameter of 400-650mm.

[0018] Another objective of this invention is to provide a method for short-process fabrication of wide-width sheet metal structural components, comprising the following steps:

[0019] (1) The above-mentioned low anisotropic magnesium alloy was prepared into an ingot by semi-continuous casting;

[0020] (2) Homogenize the ingot to obtain billet. The homogenization temperature is 460-480℃ and the time is 24-30h.

[0021] (3) The billet is preheated at a temperature of 460-480℃ for 5-8 hours, and the upper and lower rolls of the rolling mill are preheated to 440-480℃ and kept at that temperature for 1 hour.

[0022] (4) The rolling mill rolls the billet in one pass with a reduction of 5-20mm per pass and a processing rate of 2-20% per pass. The final rolling temperature is 420-460℃. Wide plate structural parts are produced by rolling in one pass.

[0023] Preferably, in step (1), the ingot is a flat ingot with an ingot size of 450×900×5000mm.

[0024] This invention provides a low-anisotropy magnesium alloy that improves mechanical properties by utilizing interatomic misalignment and the difference in elastic modulus between the matrix and Gd and Y elements, thereby ensuring the basic performance indicators of the alloy system of this invention. This magnesium alloy belongs to a heat-treatable strengthening system. Through a subsequent reasonable aging heat treatment process, it utilizes the fine Mg5Gd and Mg atoms formed by Gd and Y elements. 24 Y5, Mg 24 (Gd, Y)5, as a precipitation strengthening phase, hinders the movement of dislocations and slip systems when resisting external deformation in structural components made from this alloy, thereby improving the overall tensile strength of the structural components.

[0025] This magnesium alloy exhibits low anisotropy, a key characteristic that distinguishes it from other magnesium alloys. Magnesium alloys typically exhibit significant anisotropy, which is extremely disadvantageous for manufacturing large structural components, sometimes even causing the mechanical properties in a particular direction to fail to meet the requirements of the structure. Existing technologies generally employ multi-directional repeated forging and extrusion to address the anisotropy problem of magnesium alloys, which complicates the manufacturing process and makes short-process machining difficult. This invention addresses this issue by adding no more than 2.00 wt% Y element. The addition of Y element allows the submicron-sized second phase Mg particles to agglomerate at the grain boundaries. 24 Y5, Mg 24 (Gd, Y)5, thereby suppressing the rotation of compression twins and tensile twins formed during plastic processing, causing the grain rotation orientation to tend to be irregular, greatly weakening the plate texture strength formed during forging and rolling. In addition, the Y element increases the stacking fault energy of the slip system, ultimately changing the axial ratio c / a of the alloy lattice and reducing the basal texture strength of the alloy. Compared with other alloys, the embodiments of the present invention achieve the design and preparation of low anisotropic magnesium alloy materials by adding the Y element without increasing the difficulty of plastic processing.

[0026] Zr acts as a nucleation point during the solidification process of ingots, refines grains, and reduces the tendency of ingots to crack hot. In this embodiment of the invention, the amount of Zr added is 0.30 to 0.60 wt%, within which a combination of strength and plasticity can be achieved.

[0027] LPSO phase (Mg) is widely present in Mg-Gd-Y-Zn alloys. 12 The structure of Mg-Gd-Y-Zn alloy is a long-range ordered structure. The LPSO phase can greatly improve the strength and plasticity of the alloy. The volume fraction of LPSO phase in the Mg-Gd-Y-Zn alloy increases with the increase of Zn content. However, since the Y content is strictly limited in this alloy, when the Zn content is too high (more than 0.6wt%), that is, the Y / Zn ratio decreases, not only is the added Y element consumed too much, but coarse W phase (Mg3Zn3Y2) appears at the grain boundary, and the beneficial LPSO phase is not formed.

[0028] In this embodiment of the invention, Mn is used at 0 to 0.10 wt%. The purpose of adding a small amount of Mn is mainly to control the Fe content by forming the Mn-Fe phase during the alloy smelting process, thereby improving the corrosion resistance of the magnesium alloy. However, in Mg-Re magnesium alloys with relatively small total alloying, when Mn > 0.10 wt%, it will have the opposite effect on corrosion resistance.

[0029] Due to the significant difference in atomic radii between Mg and Sb, and the extremely low solubility of Sb in Mg, Sb is unlikely to form a solid solution in Mg. During solidification, the high-temperature stable phase of Mg3Sb will preferentially precipitate. Simultaneously, Sb readily aggregates with Gd and Y elements, which will induce the aging precipitation of Gd and Y elements during subsequent aging processes, accelerating the precipitation of Mg5Gd and Mg3Sb. 24 Y5, Mg 24 The precipitation of a series of nanoscale second-phase particles with age-enhancing effects (Gd, Y)5 is due to the auxiliary induction effect of Sb, which maximizes the precipitation enhancement effect of Gd and Y elements.

[0030] In this embodiment of the invention, Sn and Sr elements are added together. Preferably, Sn:Sr≈2:1. Large structural components prepared using the magnesium alloy of this embodiment can be applied to high-temperature conditions in the aerospace field. The addition of trace amounts of Sn and Sr elements is mainly used to form the MgSnSr phase. In addition to the strong grain refinement effect, the submicron-sized MgSnSr phase effectively inhibits the propagation of microcracks, thereby improving the high-temperature yield strength and high-temperature fatigue performance. The preferred Sn:Sr≈2:1 ratio is to ensure the formation of a certain amount of MgSnSr phase. The remaining Sn elements will participate in the formation of the Mg2Sn phase. Mg2Sn can reduce the critical shear stress, activate the conical slip system to coordinate the deformation between adjacent grains of rare earth magnesium alloy, improve plastic processing capability, and ensure the short-process preparation of large structural components. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0033] Example 1

[0034] A Φ1.9m forged ring is prepared by direct ring rolling of Mg-6.00Gd-1.5Y-0.3Zr-0.2Zn-0Mn-0.3Sb-0.08Sn-0.04Sr alloy ingots in a single-fire casting process. The preparation method includes the following steps:

[0035] (1) The ingot was prepared by semi-continuous casting; the ingot was a round ingot with a diameter of Ф700mm;

[0036] (2) Homogenize the ingots at a temperature of 470℃ for 24 hours.

[0037] (3) Machining a Ф200mm through hole into the homogenized magnesium alloy ingot and rounding the inner and outer edges;

[0038] (4) The machined billet is preheated at 460℃ for 3.5h, and the rolling mill rollers, rolling wheels, clamping rollers and upper and lower tapered rollers are preheated to 200℃ and kept at that temperature for 0.5h.

[0039] (5) The rolling mill speed is 30r / min and the mandrel linear feed speed is 2mm / s. A magnesium alloy forging ring with an outer diameter of Ф1901mm, a wall thickness of 40.4mm and a height of 310mm is produced by one ring rolling.

[0040] Example 2

[0041] A Φ1.2m forged ring is prepared by direct ring rolling of an alloy ingot made from Mg-5.8Gd-0.02Y-0.45Zr-0.1Zn-0.05Mn-0.02Sb-0.06Sn-0.03Sr in a single-fire casting process. The preparation method includes the following steps:

[0042] (1) The ingot was prepared by semi-continuous casting; the ingot was a round ingot with a diameter of Ф700mm;

[0043] (2) Homogenize the ingots at a temperature of 470℃ for 24 hours.

[0044] (3) Machining a Ф200mm through hole into the homogenized magnesium alloy ingot and rounding the inner and outer edges;

[0045] (4) The machined billet is preheated at 460℃ for 4 hours, and the rolling mill rollers, rolling wheels, clamping rollers and upper and lower tapered rollers are preheated to 250℃ and kept at that temperature for 0.5 hours.

[0046] (5) The rolling mill speed is 30r / min and the mandrel linear feed speed is 2mm / s. A magnesium alloy forging ring with an outer diameter of Ф1550mm, a wall thickness of 65mm and a height of 500mm is produced by one ring rolling.

[0047] Example 3

[0048] A complex cross-section structural component with a diameter of Φ1m was prepared using a Mg-7.20Gd-2.00Y-0.60Zr-0Zn-0.1Mn-0.3Sb-0.1Sn-0.05Sr alloy through a one-fire ingot direct forging process. The preparation method includes the following steps:

[0049] (1) The ingot was prepared by semi-continuous casting; the ingot was a round ingot with a diameter of Ф500mm;

[0050] (2) Homogenize the ingots at a temperature of 440℃ for 24 hours.

[0051] (3) The prepared billet is preheated at 440℃ for 5 hours. The magnesium alloy billet is squeezed by the movement of the upper and lower dies to fill the entire die cavity and forge the final shape of the large structural part with complex cross section. The temperature of the upper and lower dies is 490℃, the final forging temperature of the forging is 350℃, and the deformation speed is 10mm / s.

[0052] Example 4

[0053] A 1.2m wide plate was prepared from a Mg-6.0Gd-1.0Y-0.45Zr-0.1Zn-0.05Mn-0.02Sb-0.04Sn-0.02Sr alloy using a one-pass direct rolling process. The preparation method includes the following steps:

[0054] (1) The ingot was prepared by semi-continuous casting; the ingot was a flat ingot with a size of 450×900×5000mm.

[0055] (2) Homogenize the ingots at a temperature of 480℃ for 30 hours.

[0056] (3) Preheat the machined billet to 480℃×6h, and preheat the upper and lower rolls of the rolling mill to 440℃ and keep them at that temperature for 1h.

[0057] (4) The hot rolling process adopts a single-pass rolling process with a pass reduction of 5-18mm, a pass processing rate of 2-15%, a final plate thickness of 20mm, and a final rolling temperature of 433℃.

[0058] In the above embodiments, the step of preparing the ingot using semi-continuous casting specifically includes the following steps:

[0059] (1) Batching: Calculate the amount of materials according to the chemical composition requirements of magnesium alloy, use magnesium ingots with a purity of 99.95% or higher for remelting, and add alloying elements Gd, Y and Zr in the form of Mg-40Gd, Mg-30Y and Mg 30Zr master alloys;

[0060] (2) Smelting: Put the raw materials into the smelting furnace, control the smelting temperature at 835-855℃, use an electromagnetic stirrer to stir the melt, and after the furnace charge is completely melted, remove the oxide slag on the surface and take samples for pre-furnace analysis and adjust the chemical composition until the composition requirements are met.

[0061] (3) Heat preservation refining: The magnesium alloy melt contains a lot of gas, especially hydrogen, which makes the ingots prone to serious porosity. In addition, the melt is easy to oxidize and burn, which will produce a lot of oxide inclusions and non-metallic inclusions. Therefore, heat preservation refining is very necessary in magnesium alloy casting. RJ-6 flux and magnesium fluoride are selected as refining agents. The refining temperature is 775-785℃ and the refining time is 20-30min. The melt is analyzed again before the furnace and the composition is finely adjusted. The temperature is raised to 800℃ and held for 5min. Finally, the temperature is lowered to 760℃ for casting.

[0062] (4) Casting: The casting method adopts a semi-continuous casting process of low-pressure transfer of metal by compressed gas.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0064] Performance testing:

[0065] The mechanical properties of the components prepared in Examples 1-4 were tested in both the longitudinal and transverse directions, and the results are shown in Table 1.

[0066] Table 1

[0067]

[0068] The differences between Examples 1-4 are due to the different preparation methods, which result in different degrees of deformation. The low anisotropy is manifested in different directions within the same example.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low anisotropy magnesium alloy characterized by, The raw material comprises the following mass percentages: Gd 5.80-7.20wt%, Y 0.02-2.00wt%, Zr 0.30-0.60wt%, Zn 0-0.60wt%, Mn 0-0.10wt%, Sb 0.02-0.3wt%, Sr 0.02-0.05wt%, Sn 0.04-0.1wt%, and the balance being magnesium.

2. A method of short-cycle production of large forged ring structural components, characterized by, The method comprises the following steps: (1) preparing the low anisotropy magnesium alloy as claimed in claim 1 into an ingot by semi-continuous casting; (2) homogenizing the ingot, the homogenizing temperature being 460-480℃ and the time being 20-26h; (3) machining the magnesium alloy ingot after homogenizing into a through hole with a diameter of 150-250mm, and rounding the inner and outer edges to obtain a blank; (4) preheating the blank at a temperature of 440-480℃ for 3-5h, preheating the rolling mill rolling roller, rolling wheel, holding roller and upper and lower taper rollers to 200-300℃ and keeping for 0.5h; (5) ring rolling the blank, the rolling roller rotating at 15-50r / min, the core shaft linear feeding speed being 1-3mm / s, and preparing a large magnesium alloy forging ring structure by one heating ring rolling.

3. A method of short flow production of large forged ring structural components according to claim 2, characterized in that, In step (1), the ingot is a round ingot, and the ingot diameter is 650-750mm.

4. A method of short-cycle production of a complex cross-section structural member, characterized by, The method comprises the following steps: (1) preparing the low anisotropy magnesium alloy as claimed in claim 1 into an ingot by semi-continuous casting; (2) homogenizing the ingot to obtain a blank, the homogenizing temperature being 440-460℃ and the time being 18-24h; (3) preheating the blank after processing at a temperature of 440-460℃ for 3-5h, and extruding the blank by the movement of the upper and lower dies to fill the entire die cavity by die forging, the upper and lower die temperature being 490-510℃, the forging final forging temperature being 350-400℃, and the deformation speed being 5-20mm / s, and forging a large structure with complex cross section by one heating.

5. The method of short flow production of complex cross-section structural members according to claim 4, characterized in that, In step (1), the ingot is a round ingot, and the ingot diameter is 400-650mm.

6. A method of short flow production of a wide-flange plate structural member, characterized by, The method comprises the following steps: (1) preparing the low anisotropy magnesium alloy as claimed in claim 1 into an ingot by semi-continuous casting; (2) homogenizing the ingot to obtain a blank, the homogenizing temperature being 460-480℃ and the time being 24-30h; (3) preheating the blank at a temperature of 460-480℃ for 5-8h, and preheating the upper and lower rollers of the rolling mill to 440-480℃ and keeping for 1h; (4) rolling the blank by one heating and multiple passes, the pass reduction being 5-20mm, the pass processing rate being 2-20%, and the final rolling temperature being 420-460℃, and rolling a wide plate structure by one heating.

7. The method of short-run production of wide-flange structural members of claim 6, wherein, In step (1), the ingot is a flat ingot, and the ingot size is 450×900×5000mm.

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