A high-strength and tough rare earth magnesium alloy wire for additive manufacturing and its preparation method

Abstract

A high-strength and tough rare earth magnesium alloy wire for additive manufacturing and a preparation method thereof, comprising the following components by weight: Gd 4.0-9.5%, Y 2.0-4.0%, Ca 1.0-2.5%, Al 0.5-1.2%, with the sum of other impurities ≤0.3%, and the balance comprising Mg; wherein the ratio of the Ca content to the Gd content is ≥0.25, and the ratio of the Ca content to the Al content is ≥1.2. This invention overcomes the shortcomings of existing magnesium alloy products manufactured using fused filament additive manufacturing, such as coarse grains and low mechanical properties, and achieves enhanced toughness in additively manufactured magnesium alloys. Furthermore, the rare earth magnesium alloy wire is not prone to breakage, ensuring smooth wire feeding during 3D printing. Formed parts manufactured using the high-strength and tough rare earth magnesium alloy using fused filament additive manufacturing have a yield strength ≥200 MPa, a tensile strength ≥300 MPa, and an elongation ≥10%.

Description

Technical Field

[0001] The present invention relates to magnesium alloy technology, and in particular to a high-strength and toughness rare earth magnesium alloy wire for additive manufacturing and a preparation method thereof. Background Art

[0002] Lightweighting is a key trend in the development of materials for aerospace and defense industries. On the one hand, the weight of aerospace vehicles determines the requirements for launch and delivery vehicles, as well as transportation costs. On the other hand, the weight of modern weaponry directly impacts its maneuverability and endurance. Lightweighting enables armed forces to respond quickly, facilitate deployment, and increase strike range. As the lightest metal structural material, magnesium alloys offer advantages such as high specific strength, excellent damping and shock absorption, and strong electromagnetic shielding capabilities. They are ideal for meeting lightweighting requirements and are playing an increasingly important role in aerospace and defense industries.

[0003] Additive manufacturing (commonly known as 3D printing) is an emerging technology based on the discrete-deposition principle, using metal powder or wire as raw materials to melt and deposit layer by layer according to three-dimensional model data to create complex parts. This technology offers advantages such as mold-free near-net-shape formation, high material utilization, and significantly shortened manufacturing cycles. It is particularly suitable for the rapid prototyping of difficult-to-form materials such as magnesium alloys. Due to the active chemical properties of magnesium powder and its flammability and explosion risks, large-scale application of magnesium powder-based 3D printing technology has been difficult. In contrast, fused filament 3D printing technology based on magnesium wire offers advantages such as safety, low cost, and high efficiency, making it more feasible for practical engineering applications. Furthermore, this technology, essentially a micro-casting free deposition process, allows point-by-point control of the solidified melt pool composition, effectively reducing or avoiding common casting defects in magnesium alloys such as compositional segregation, oxide inclusions, and porosity cracks. Therefore, fused filament 3D printing of magnesium alloys offers unique advantages and broad application prospects as aerospace, military, and defense industries develop increasingly large-scale, integrated, and highly reliable components.

[0004] However, the current magnesium alloy grades are all developed based on traditional casting and deformation processing, and there is a lack of redesign and development of magnesium alloy compositions based on the process characteristics of fused wire additive manufacturing. The mismatch between the alloy and the process has an adverse effect on the mechanical properties and microstructure of the formed components. The heat input in the fused wire additive manufacturing process is large and the thermal cycle process is complex, resulting in problems such as coarse grain size and low mechanical properties in magnesium alloy products. The yield strength of the existing fused wire additively manufactured magnesium alloys is usually less than 200MPa, and the tensile strength is less than 300MPa, which is difficult to meet the application requirements of magnesium alloys in the aerospace and military defense fields. Therefore, the development of a high-strength and toughness magnesium alloy specifically for fused wire additive manufacturing and the study of its wire preparation process are of great significance to the lightweight development of aerospace and military equipment.

[0005] Chinese Patent Publication No. CN110195179A discloses a "Rare Earth Magnesium Alloy for Wire 3D Printing." This alloy is a composite Mg-9Al-2Zn alloy with rare earth elements such as Pr, Sc, Y, and Ce. The grain size of annealed 3D-printed parts is twice that of conventional Mg-9Al-2Zn alloy. However, the alloy's maximum tensile strength is only 273 MPa, and the yield strength is not specified, failing to meet the performance requirements of magnesium alloys for aerospace applications.

[0006] Chinese Patent Publication No. CN112207480A discloses "An Ultrafine Corrosion-Resistant Magnesium Alloy Welding Wire for 3D Printing and Its Processing Technology." This invention is a magnesium alloy containing Zn, Ca, Cu, Mn, and Si, and is produced using a cold drawing process to produce ultrafine magnesium alloy wire with a diameter of 0.3 to 0.9 mm. However, since the patent does not mention the mechanical properties of the alloy in the 3D printed state, the strength and plasticity of the invented alloy are unknown. Furthermore, magnesium alloys are hexagonal metals (HCPs) with poor room temperature plastic forming capabilities, making the cold drawing process difficult to use for forming the wire of the high-strength magnesium alloy invented in this patent.

[0007] Chinese Patent Publication No. CN109576544A discloses "A Rare Earth Magnesium Alloy Fusion Welding Wire, Its Manufacturing Method, and Use." This alloy is a magnesium alloy rich in rare earth elements such as Gd, Y, Nd, Zr, and Ce, formed by hot extrusion into a wire with a diameter of 1 to 6 mm. However, this alloy was developed as a welding wire material for fusion welding and defect repair of high-rare earth magnesium alloys. Unlike the starting point of this patent, the alloy was not developed based on the characteristics of the fused wire additive manufacturing process.

[0008] Chinese patent publication number CN113732442A discloses a "method for arc-fuse additive forming of fully equiaxed fine-grained magnesium alloy components." This is a method for preparing a fused additive magnesium alloy that can achieve fully equiaxed fine grains. The average grain size of the AZ31 magnesium alloy prepared by this method is 24.7μm, but the yield strength is only 109.1MPa, which is significantly lower than the strength of forgings of the same grade (GB / T 26637-2011). Therefore, there is still a gap from actual structural application.

[0009] In summary, the material strength of existing fused filament additively manufactured magnesium alloy components cannot meet the application requirements of magnesium alloy parts in the aerospace and military defense fields. There is no description or report of high-strength and tough fused filament additively manufactured magnesium alloys with a yield strength higher than 200 MPa, a tensile strength higher than 300 MPa and good plasticity. Summary of the Invention

[0010] The purpose of the present invention is to provide a high-strength and toughness rare earth magnesium alloy wire for additive manufacturing and a preparation method thereof, so as to overcome the shortcomings of existing fused filament additively manufactured magnesium alloy products such as coarse grains and low mechanical properties, and realize the strengthening and toughening of additively manufactured magnesium alloys; moreover, the rare earth magnesium alloy wire is not easy to break, ensuring smooth wire feeding during the 3D printing process; the yield strength of the formed parts prepared by fused filament additive manufacturing using the high-strength and toughness rare earth magnesium alloy wire is ≥200MPa, the tensile strength is ≥300MPa, and the elongation is ≥10%.

[0011] To achieve the above object, the technical solution of the present invention is:

[0012] A high-strength and tough rare earth magnesium alloy wire for additive manufacturing, comprising the following components by weight: Gd 4.0-9.5%, Y 2.0-4.0%, Ca 1.0-2.5%, Al 0.5-1.2%, the sum of other impurities being ≤0.3%, and the balance comprising Mg; wherein the ratio of the Ca content to the Gd content is ≥0.25, and the ratio of the Ca content to the Al content is ≥1.2.

[0013] The yield strength of the formed part prepared by the fused additive manufacturing method using high-strength and tough rare earth magnesium alloy wire in the present invention is ≥200MPa, further 210-270MPa, the tensile strength is ≥300MPa, further 340-390MPa, and the elongation is ≥10%.

[0014] In the composition design of the high-strength and toughness rare earth magnesium alloy wire for additive manufacturing according to the present invention:

[0015] Gd and Y are key alloying elements with high solubility in the magnesium matrix. This provides excellent solid solution strengthening. Furthermore, under the inherent thermal cycling of additive manufacturing, uniform, fine MgxGd and MgxY precipitates dynamically form within the magnesium matrix, providing excellent precipitation strengthening to enhance the strength of the magnesium alloy. The Gd and Y contents of the present invention are designed to be 4.0-9.5% and 2.0-4.0%, respectively, to ensure sufficient solid solution and precipitation strengthening.

[0016] Al, adding 0.5-1.2% Al, during the solidification process of the alloy of the present invention, Al preferentially reacts with Gd and Y to produce Al2Gd and Al2Y particles. Both have extremely low mismatch with the magnesium matrix and can act as effective heterogeneous nucleation particles to promote grain refinement of magnesium alloys. Existing high rare earth magnesium alloys containing Gd and Y usually add Zr elements to achieve good grain refinement effects. However, the inventors found in their research that Zr cannot maintain the stability of the grain size, and the subsequent heat input during the filament additive process will cause the grains to coarsen and grow. Al2Gd and Al2Y particles not only have a grain refinement effect equivalent to that of Zr elements, but the Al2Gd and Al2Y phases distributed at the intersection of grain boundaries can play a role in pinning the grain boundaries, thereby effectively preventing the grains from growing further under heat. Therefore, a fully equiaxed fine-grained microstructure can be obtained, while improving the strength and plasticity of the alloy.

[0017] Ca. The composite addition of Ca element will, on the one hand, precipitate a new type of Mg-Gd-Ca ternary precipitate phase under the action of thermal cycling in the additive manufacturing process. This phase is perpendicular to the growth direction of the above-mentioned MgxGd and MgxY precipitate phases, which can more effectively hinder dislocation slip, thereby significantly improving the precipitation strengthening effect of the alloy and thus improving the strength of the magnesium alloy; on the other hand, Mg2Ca strengthening phase is generated and dispersed at the grain boundaries; since Ca has a low solubility in the magnesium matrix and is a low solid-solution element, even under high heat input in the fused filament additive process, the Mg2Ca grain boundary strengthening phase can remain stable and will not be decomposed by thermal solid solution.

[0018] The Ca content is also related to Gd and Al. The inventors have found in long-term research that the Ca / Gd content ratio needs to be ≥0.25 to ensure that the new Mg-Gd-Ca ternary precipitate phase can be dynamically precipitated during the additive manufacturing process. In addition, if the Ca / Al content ratio is less than 1.2, Ca will preferentially form the Al2Ca phase, and the number of Al2Gd and Al2Y particles generated will decrease, which will adversely affect the equiaxed fine-grained structure of the present invention. Therefore, the Ca / Al content ratio needs to be ≥1.2 to ensure that the Mg2Ca phase required by the present invention is preferentially formed and avoid negative impact on the grain refinement effect.

[0019] The method for manufacturing a high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to the present invention comprises the following steps:

[0020] 1) Preparing materials using pure Mg, pure Al, Mg-Gd master alloy, Mg-Y master alloy, and Mg-Ca master alloy as raw materials;

[0021] 2) mixing and smelting the raw materials obtained in step 1) according to the above composition under a protective atmosphere at a smelting temperature of 740-760° C., and after the raw materials are completely melted, standing for 10-30 minutes before casting to obtain a magnesium alloy ingot at a casting temperature of 710-730° C., with a magnesium alloy ingot diameter of ≥100 mm;

[0022] 3) performing homogenization annealing treatment on the magnesium alloy ingot and water cooling; then extruding the magnesium alloy ingot into a wire billet with a diameter of 8.0 to 10.0 mm;

[0023] 4) performing solution treatment on the wire blank and water cooling; then polishing the surface of the wire blank;

[0024] 5) The wire blank is subjected to a continuous multiple-pass hot drawing process, the wire and the die are lubricated with a lubricant before each drawing process, the area reduction rate of each process is 20-25%, and an intermediate annealing process is performed at 300-400° C. for 3-6 minutes after every 3-6 hot drawing processes, until a wire with a diameter of 1.2-6.0 mm is obtained.

[0025] Preferably, step 1) further comprises preheating the prepared raw materials to 180-240° C., and performing preheating and drying treatments.

[0026] Preferably, in step 2), the protective atmosphere is SF6+N2 or SF6+CO2 or pure SF6 gas.

[0027] Preferably, in step 2), an automated semi-continuous casting process is used to produce the ingot, and the ingot diameter is 150 to 400 mm.

[0028] Preferably, in step 3), the homogenization annealing temperature is 490-520° C., and the homogenization annealing time is 4-16 hours.

[0029] Preferably, in step 3), a reverse extrusion process is used to prepare the wire blank, the extrusion temperature is 400-450° C., and the extrusion speed is 0.5-1.5 m / min.

[0030] Preferably, in step 4), the solution treatment is carried out in an Ar atmosphere with a purity of ≥98%, the solution temperature is 490-520° C., and the solution time is 2-4 h.

[0031] Preferably, in step 5), the hot drawing temperature is 350-400° C., and the drawing speed is 1.0-2.0 m / min.

[0032] Preferably, in step 5), after every 4 to 5 passes of hot drawing, an intermediate annealing treatment at 350 to 400° C. for 4 to 5 minutes is performed.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) In the rare earth magnesium alloy composition of the present invention, a certain amount of Al element is introduced to generate Al2Gd and Al2Y second phases, which can not only replace the commonly used Zr element to achieve a good grain refinement effect, but also play a role in pinning grain boundaries, further curbing the subsequent grain coarsening during the additive manufacturing process, thereby achieving a fully equiaxed uniform fine-grained microstructure and improving the strength and plasticity of the additive magnesium alloy; the composite introduction of a certain amount of Ca element, on the one hand, under the inherent thermal cycle of additive manufacturing, will dynamically precipitate a new type of Mg-Gd-Ca ternary precipitation phase in the magnesium matrix, which can significantly enhance the precipitation strengthening effect and further improve the strength of the magnesium alloy; on the other hand, the Mg2Ca thermally stable strengthening phase generated along the grain boundaries can avoid solid solution decomposition under large heat input conditions, ensuring the stability of the mechanical properties of the magnesium alloy printed products. Therefore, compared with the existing WE brand (Mg-Y-RE-Zr) and VW brand (Mg-Gd-Y-Zr) high rare earth magnesium alloys, the alloy of the present invention is more suitable for the process characteristics of fused filament additive manufacturing.

[0035] (2) The difficulty of plastic processing of high rare earth magnesium alloys has been overcome, making it possible to successfully produce millimeter-scale rare earth magnesium alloy wires. By preparing 8.0-10.0 mm wire billets by extruding ingots with a diameter of ≥100 mm in one step, a fine and uniform equiaxed crystal structure can be obtained, and casting porosity defects can be eliminated, ensuring that the subsequent drawing process is easier to plastically deform and improving the pass rate; and using an intermediate annealing treatment at 350-400°C in every 3-6 drawing passes can effectively improve the deformation texture, so that the obtained wire has both good strength and plasticity, which can ensure smooth and stable wire feeding during 3D printing and not easy to break.

[0036] (3) The formed parts prepared by the magnesium alloy wire of the present invention based on the fused filament additive manufacturing method have an average grain size of ≤20μm, a yield strength of ≥200MPa, a tensile strength of ≥300MPa, and an elongation of ≥10%. They have excellent strength and plasticity (strengthening and toughening), and good printing formability, which can meet the high performance requirements of magnesium alloys for lightweighting in fields such as aerospace, military industry and national defense.

[0037] (4) The present invention adopts an automated semi-continuous casting and reverse extrusion process, which has high production efficiency and low energy consumption and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a TEM image of the microstructure of the 3D printed sample of Example 1 of the present invention;

[0039] Figure 2 This is the EDX analysis result of the Mg-Gd-Ca precipitate phase in the microstructure of the 3D printed sample of Example 1 of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further illustrated below by examples and drawings. The examples of the present invention are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific operating procedures are given. However, the scope of protection of the present invention is not limited to the following examples.

[0041] The chemical compositions of the magnesium alloy wires of the embodiments of the present invention and the comparative examples are shown in Table 1;

[0042] The preparation of magnesium alloy wire in the embodiment of the present invention and the comparative example includes the following steps:

[0043] (1) Preparing materials using pure Mg, pure Al, Mg-30Gd master alloy, Mg-25Y master alloy, Mg-20Ca master alloy, and Mg-25Zr master alloy as raw materials;

[0044] (2) The raw materials obtained in step (1) were mixed and smelted according to the above composition in a 2% SF6 + CO2 protective atmosphere at a smelting temperature of 750°C; after they were completely melted, the temperature was lowered to 720°C, followed by standing for 20 minutes, and an automated semi-continuous casting method was used to produce a magnesium alloy round ingot with a diameter of 200 mm;

[0045] (3) homogenizing annealing treatment of the magnesium alloy ingot and water cooling; then reverse extruding the ingot into a wire billet with a diameter of 9.0 mm; then solution treating the wire billet in an argon atmosphere, water cooling, and grinding and peeling the surface of the wire billet;

[0046] (4) The polished wire blank is continuously subjected to a multi-pass drawing process. The wire and the drawing die are lubricated with a lubricant before each drawing pass. The single-pass reduction rate is controlled at 20-25%. After every four hot drawing passes, an intermediate annealing process is performed. After peeling, a magnesium alloy wire with a diameter of 1.2 mm is obtained.

[0047] The key process parameters of the magnesium alloy wires of the embodiments of the present invention and the comparative examples are shown in Table 2.

[0048] The resulting magnesium alloy wire product was printed using an arc-fuse 3D printer. Samples cut from these samples were analyzed using electron backscatter diffraction (EBSD) to determine average grain size. Mechanical properties were then tested according to GB / T 228.1-2010. Table 3 compares the grain size and mechanical properties of the samples printed in Examples 1-12 and Comparative Example 1.

[0049] Figure 1This is a TEM image of the microstructure of the 3D printed sample obtained in Example 1. It can be seen that Mg5Gd, Mg5Y and a new precipitate phase are dynamically precipitated in the magnesium matrix, and the new precipitate phase is distributed perpendicular to the Mg5Gd and Mg5Y precipitates.

[0050] from Figure 2 It can be seen that the novel precipitate phase is rich in Gd and Ca elements and is a ternary precipitate phase of Mg-Gd-Ca.

[0051] The above examples and comparative examples show that alloying elements such as Gd, Y, Al, and Ca have a significant impact on the grain size and mechanical properties of 3D-printed magnesium alloy specimens (see Table 3). Gd and Y, as primary strengthening elements, significantly increase strength with increased content. The addition of Al and Ca further improves the yield strength, tensile strength, and elongation of the 3D-printed specimens, with the yield strength of the examples exceeding 200 MPa. Specifically, increasing the Al content improves grain refinement, thereby improving the elongation (plasticity) of the alloy. However, adding 2.5% Ca significantly increases the yield strength of the alloy, but adversely affects the plasticity to some extent.

[0052] In general, the mechanical properties of Examples 1-12 of the present invention are better than those of the comparative examples. The results show the effectiveness of the technology of the present invention, and the performance will be further improved by optimizing the subsequent heat treatment process.

[0053] Table 1 Unit: Weight percentage

[0054] Gd Y Ca Al Zr Mg Example 1 4.0 2.0 1.0 0.5 - margin Example 2 9.5 4.0 2.5 1.2 - margin Example 3 8.0 3.0 2.2 1.0 - margin Example 4 8.5 3.5 2.5 0.5 - margin Example 5 7.5 2.5 2.0 1.2 - margin Example 6 6.0 3.5 1.6 0.8 - margin Example 7 7.0 3.2 1.8 1.1 - margin Example 8 6.5 2.8 1.7 1.2 - margin Example 9 5.5 3.8 1.5 0.7 - margin Example 10 5.0 2.2 1.3 0.6 - margin Example 11 4.5 2.6 1.2 0.5 - margin Example 12 9.0 3.3 2.4 1.0 - margin Comparative Example 8.0 3.0 - - 0.6 margin

[0055] Table 2

[0056]

[0057]

[0058] Table 3

[0059]

Claims

1. A high-strength and tough rare earth magnesium alloy wire for additive manufacturing, comprising the following components by weight: Gd 4.0-9.5%; Y 2.0-4.0%; Ca 1.0-2.5%; Al 0.5-1.2%; the sum of other impurities ≤ 0.3%; the balance being Mg; wherein: The ratio of the Ca content to the Gd content is ≥0.25, and the ratio of the Ca content to the Al content is ≥1.

2.

2. The high-strength and toughness rare earth magnesium alloy wire for additive manufacturing according to claim 1, characterized in that: The yield strength of the formed parts prepared by fused wire additive manufacturing using high-strength and toughness rare earth magnesium alloy wire is ≥200MPa, the tensile strength is ≥300MPa, and the elongation is ≥10%.

3. The high-strength and toughness rare earth magnesium alloy wire for additive manufacturing according to claim 1, characterized in that: The yield strength of the formed parts prepared by fused additive manufacturing using high-strength and toughness rare earth magnesium alloy wire is 210-270 MPa, the tensile strength is 340-390 MPa, and the elongation is ≥10%.

4. The method for preparing a high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to claim 1, 2 or 3, wherein: The steps include: 1) Preparing materials using pure Mg, pure Al, Mg-Gd master alloy, Mg-Y master alloy, and Mg-Ca master alloy as raw materials; 2) Mixing and smelting the raw materials prepared in step 1) according to the composition of claim 1 under a protective atmosphere at a melting temperature of 740-760° C. After the raw materials are completely melted, the mixture is allowed to stand for 10-30 minutes before casting to obtain a magnesium alloy ingot at a casting temperature of 710-730° C. The diameter of the magnesium alloy ingot is ≥100 mm; 3) performing homogenization annealing treatment on the magnesium alloy ingot and water cooling; then extruding the magnesium alloy ingot into a wire billet with a diameter of 8.0 to 10.0 mm; 4) performing solution treatment on the wire blank and water cooling; then polishing the surface of the wire blank; 5) The wire blank is subjected to a continuous multiple-pass hot drawing process, lubricating the wire and the die with a lubricant before each drawing process, with an area reduction rate of 20-25% per drawing process, and performing an intermediate annealing process at 300-400° C. for 3-6 minutes after every 3-6 hot drawing processes; until a wire with a diameter of 1.2-6.0 mm is obtained.

5. The method for preparing high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to claim 4, wherein: Step 1) also includes preheating the prepared raw materials to 180-240° C., and performing preheating and drying treatments.

6. The method for preparing a high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to claim 4, wherein: In step 2), the protective atmosphere is SF6+N2 or SF6+CO2 or pure SF6 gas.

7. The method for preparing a high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to claim 4 or 6, characterized in that: In step 2), an automated semi-continuous casting process is used to produce magnesium alloy ingots, wherein the diameter of the magnesium alloy ingots is 150 to 400 mm.

8. The method for preparing a high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to claim 4, wherein: In step 3), the homogenization annealing temperature is 490-520° C., and the homogenization annealing time is 4-16 hours.

9. The method for preparing a high-strength and tough rare earth magnesium alloy wire for additive manufacturing according to claim 4 or 8, wherein: In step 3), a reverse extrusion process is used to prepare the wire blank, the extrusion temperature is 400-450° C., and the extrusion speed is 0.5-1.5 m / min.

10. The method for preparing high-strength and toughness rare earth magnesium alloy wire for additive manufacturing according to claim 4, wherein: In step 4), the solution treatment is carried out in an Ar atmosphere with a purity of ≥98%, the solution temperature is 490-520° C., and the solution time is 2-4 hours.

11. The method for preparing high-strength and toughness rare earth magnesium alloy wire for additive manufacturing according to claim 4, wherein: In step 5), the hot drawing temperature is 350-400° C., and the drawing speed is 1.0-2.0 m / min.

12. The method for preparing high-strength and toughness rare earth magnesium alloy wire for additive manufacturing according to claim 4, wherein: In step 5), an intermediate annealing treatment at 350-400° C. for 4-5 minutes is performed after every 4-5 passes of hot drawing.

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