Electron beam welding method for super-light high-modulus magnesium-lithium alloy large-size component

Abstract

This invention discloses an electron beam welding method for large-size ultralight, high-modulus magnesium-lithium alloy components, belonging to the field of magnesium-lithium alloy electron beam welding technology. This method employs subsurface focusing electron beam welding under vacuum conditions, controlling the focusing current, accelerating voltage, electron beam current, and welding speed, followed by solution-aging heat treatment after welding. By precisely matching heat input, welding speed, and focusing parameters, this invention effectively suppresses lithium element burn-off, grain coarsening, and localized hardening. The weld formation is excellent, free of defects such as porosity and cracks. The yield strength and tensile strength of the welded joint reach over 97% of the base material, and the elongation reaches over 66% of the base material. This method is suitable for high-precision, high-performance welding of magnesium-lithium alloy components with various lithium contents and structural forms.

Description

Technical Field

[0001] This invention relates to the field of electron beam welding technology for magnesium-lithium alloys, and specifically to an electron beam welding method for large-size ultralight, high-modulus magnesium-lithium alloy components. Background Technology

[0002] Magnesium-lithium alloys stand out due to their extremely low density, excellent specific strength, and specific stiffness, making them one of the lightest metallic structural materials currently available, with a density ranging from approximately 1.3 to 1.6 g / cm³. 3 Its strength and modulus are significantly lower than other types of aluminum and magnesium alloys. Besides its substantial weight advantage, this alloy also possesses good electrical and thermal conductivity, excellent damping properties, and efficient electromagnetic shielding. Through appropriate alloying treatments and advanced processing techniques such as rotary forging, its strength and modulus can be increased while maintaining its low density. Therefore, ultralight high-modulus magnesium-lithium alloys are widely used in aerospace, transportation, and electronics industries, such as satellite internal structures, automotive parts, and electronic device housings, reducing weight and improving efficiency. However, in these applications, especially when dealing with complex shapes or large components, highly reliable welding technology is crucial to ensuring the safe use of ultralight high-modulus magnesium-lithium alloy components.

[0003] Unlike traditional magnesium alloys, the welding process of ultralight, high-modulus magnesium-lithium alloys requires consideration not only of welding defects such as porosity and cracks caused by the wide recrystallization temperature range of the alloy, but also of inclusions such as oxides and embrittlement phases formed by reactive elements like magnesium and lithium under atmospheric conditions, as well as oxidation, evaporation, and burn-off. Currently, the more mature welding technologies for magnesium-lithium alloys mainly include traditional fusion welding techniques (such as tungsten inert gas welding and laser welding) and friction stir welding.

[0004] Traditional fusion welding techniques suffer from low thermal efficiency and energy density, slow welding speed, and wide energy distribution, resulting in excessively high energy input and widespread heat distribution during welding. These factors easily lead to defects such as shallow penetration, a large heat-affected zone, high residual stress, and porosity and cracks, resulting in poor weld quality and reduced joint performance. Literature review revealed that in tungsten inert gas (TIG) welding experiments on LAZ832-0.5Y alloy (Journal of Materials Research and Technology. 20 (2022) 4114-4129.), researchers observed a large heat-affected zone and long cracks. In laser welding experiments on LAZ1033 alloy (Journal of Manufacturing Processes. 57 (2020) 871-880.), researchers found numerous pores and cracks in the weld. Although friction stir welding can completely eliminate fusion welding defects, it causes significant damage to the workpiece surface and cannot be applied to the welding of precision and complex components. Furthermore, the complex tooling design and manufacturing significantly increase the cost of friction stir welding.

[0005] Electron beam welding is an advanced vacuum welding technology that uses a focused and accelerated high-energy electron beam generated in a vacuum to bombard a metal workpiece, converting the electron kinetic energy into heat energy to melt the metal and form a weld. Because it operates in a vacuum chamber, electron beam welding prevents electron scattering or energy loss caused by air molecule collisions, providing significantly higher thermal efficiency and energy density than traditional welding techniques. Simultaneously, the welding speed and post-weld cooling rate are extremely fast. These advantages allow for narrow and deep welds and extremely narrow heat-affected zones, greatly limiting the impact of heat input on component performance, better maintaining joint integrity, and enabling precise control of weld formation under appropriate parameters.

[0006] Applying electron beam welding technology to the welding of large-sized ultralight, high-modulus magnesium-lithium alloy components results in welds with extremely fine microstructures and very narrow heat-affected zones, significantly reducing the impact of residual stress and heat input on the joint. Simultaneously, welding under vacuum conditions avoids oxidation and burn-off of magnesium and lithium, and the faster welding speed suppresses the evaporation of reactive elements such as magnesium and lithium, greatly reducing welding defects. Furthermore, through automation technology, computer-programmed welding paths can achieve precise welding of structurally complex workpieces, particularly in applications such as high-precision medical devices, aerospace equipment, and electronic components. Based on these advantages, electron beam welding technology is expected to become a research hotspot in the welding of ultralight, high-modulus magnesium-lithium alloys, playing a crucial role in promoting the research and application of lightweight structural materials.

[0007] However, existing electron beam welding technology cannot be directly reused: ordinary magnesium alloys do not contain lithium, so there is no need to consider the evaporation of lithium. Their heat input per unit length is generally designed to be high to achieve deep weld penetration, and this parameter is far beyond the tolerance range of magnesium-lithium alloys. In the field of light alloys, in order to suppress lithium evaporation, relevant literature (Fusion-diffusion electronbeam welding of aluminum-lithium alloy with Cu nano-coating. Materials and Design, 2020, 188:108439) proposed a fusion-diffusion electron beam welding method. This method uses a defocused electron beam and docking pressure to reduce the temperature of the molten pool, and combines it with a Cu nano-coating to promote atomic diffusion in the unmelted area. However, this process is designed for aluminum-lithium alloys, is complex, and depends on the nano-coating. The introduction of the nano-coating will change the matrix composition of the magnesium-lithium alloy and affect the overall performance of the joint, so it is also difficult to reuse directly.

[0008] In summary, considering the material properties of magnesium-lithium alloys, breaking through the inherent thinking of existing light alloy unit length heat input design, and achieving defect-free forming of magnesium-lithium alloy welded joints with high efficiency and strong plasticity, has become an urgent need to promote the engineering application of magnesium-lithium alloys, and is also the core of this invention. Summary of the Invention

[0009] Therefore, the purpose of this invention is to provide an electron beam welding method for large-size ultralight high-modulus magnesium-lithium alloy components.

[0010] The objective of this invention is achieved through the following technical solution: <First Aspect> An electron beam welding method for magnesium-lithium alloy components includes the following steps: Under vacuum, the electron beam is controlled to be subsurface focused, with a focusing current of 1050~1300 mA, an accelerating voltage of 60~120 kV, an electron beam current of 4~8 mA, a welding speed of 400~800 mm / min, and single-sided welding. After welding, the workpiece is heat-treated.

[0011] As one implementation scheme, the heat input E per unit length is taken as 0.5~0.975, where E U is the electron beam accelerating voltage, I is the electron beam current, v is the welding speed, and η is the welding energy utilization efficiency.

[0012] As one implementation scheme, when the Li content in the magnesium-lithium alloy does not exceed 8 wt.%, the ratio of E to the Li content ( (Not less than 0.100)

[0013] As one implementation scheme, when the Li content in the magnesium-lithium alloy is greater than 8 wt.% and less than 14 wt.%, the ratio of E to Li content is between 0.036 and 0.100.

[0014] As one implementation scheme, when the Li content in the magnesium-lithium alloy is not less than 14 wt.%, the ratio of the value of E to the Li content is not higher than 0.036.

[0015] As one implementation, the subsurface focusing is such that the focal distance from the upper surface of the workpiece is 0.5~2 mm.

[0016] In some embodiments, the subsurface focusing is defined as a focal distance of 0.5 to 1.9 mm from the upper surface of the workpiece.

[0017] As one implementation, the focusing current is 1050~1300 mA.

[0018] In some embodiments, the focusing current is 1080~1300 mA.

[0019] As one implementation, the heat treatment involves solution treatment followed by aging treatment.

[0020] As one implementation, the solution treatment is performed by holding at 300~400 ℃ for 2~24 h.

[0021] In some embodiments, the heat treatment time is 3.5 to 5 hours.

[0022] In some embodiments, the solution treatment temperature is 300~350 °C.

[0023] As one implementation scheme, the aging treatment is to keep warm at 100~175 ℃ for 10~60 min.

[0024] In some embodiments, the heat preservation time for the aging treatment is 10-15 minutes.

[0025] In some embodiments, the aging treatment temperature is 100~150 ℃.

[0026] In some embodiments, the aging treatment is to keep warm at 100°C for 10-15 minutes.

[0027] In some embodiments, the aging treatment is to keep warm at 150°C for 10 min.

[0028] As one implementation scheme, the vacuum level is ≤5×10 -2 Pa.

[0029] As one implementation, in the welding method, the workpiece does not need to be preheated before welding.

[0030] As one implementation, the welding method is applicable to welding magnesium-lithium alloys from Mg-6Li to Mg-14Li systems.

[0031] In some embodiments, the welding method is applicable to welding Mg-8Li to Mg-14Li magnesium-lithium alloys.

[0032] As one implementation, the welding method is applicable to welding between magnesium-lithium alloy forged workpieces, between rotary forged workpieces, and between forged and rotary forged workpieces.

[0033] As one implementation, the welding method can achieve welding of one or more weld types, including straight welds, arc welds, curved line welds, circumferential circumferential welds, and closed circumferential welds.

[0034] As one implementation, the welding method is applicable to welding one or more components among sample-grade arc-shaped plates, product-grade lugs, product-grade hollow cylindrical cabins, and product-grade hollow cylindrical cabins with lug grooves.

[0035] <Second aspect> A magnesium-lithium alloy electron beam welding component, by mass fraction, comprises Li 6~14wt.%, Al 1~5wt.%, Zn 1~5wt.%, RE 0.2~3wt.%, with the balance being Mg and unavoidable impurities.

[0036] The yield strength and tensile strength of the welded joint reach more than 97% of the base material, and the elongation reaches more than 66% of the base material.

[0037] As one implementation, the RE element includes one or more of Yb, Gd, Dy, Er, Tb, Ho, and Y.

[0038] As one implementation, the elongation of the welded joint is not less than 77% of the base material.

[0039] As one implementation, the elongation of the welded joint is not less than 80% of the base material.

[0040] As one implementation, the elongation of the welded joint is not less than 93% of the base material.

[0041] Compared with the prior art, the present invention has the following beneficial effects: This invention employs vacuum electron beam welding, which boasts high energy density and rapid cooling. The weld and heat-affected zone exhibit significant fine-grain strengthening and precipitation strengthening effects, effectively maintaining the yield strength and tensile strength of the welded joint, even approaching or exceeding the levels of the base material, with minimal strength loss. However, due to the rapid solidification of the weld, its intrinsic plasticity is lower than that of the deformed base material. Furthermore, the presence of lithium makes the alloy more sensitive to welding heat input, easily leading to localized hardening. Consequently, the joint elongation is relatively lower than that of the base material. This invention effectively suppresses lithium burn-off, grain coarsening, and localized hardening effects by precisely controlling the heat input per unit length, welding speed, focusing current, and post-weld heat treatment, significantly reducing plasticity loss. This allows the welded joint to maintain high strength while retaining good plasticity and forming stability, achieving a highly efficient balance between strength and plasticity.

[0042] The electron beam welding process employed in this invention offers significant advantages. Its thermal efficiency and energy density are far superior to traditional fusion welding. The welding process can be precisely controlled through computer and automation technology, enabling high-precision welding and excellent weld formation for complex components or paths. Joints obtained using this welding process exhibit excellent mechanical properties, particularly high weld strength. The welds produced by this process also demonstrate good formability, a neat appearance, and no deformation. Furthermore, this welding process offers high controllability, strong design flexibility, high welding precision, simplicity, ease of operation, extremely high efficiency, and low cost, enabling high-precision, high-quality connections of complex ultra-lightweight, high-modulus magnesium-lithium alloy structural components.

[0043] This invention performs solution heat treatment on the welded components, thereby achieving overall solution strengthening of the components. This avoids aging softening caused during the welding process and reduces welding thermal stress, which helps to improve the overall uniformity of the welded components and further improves their mechanical properties.

[0044] This invention effectively solves the problems of welding cracks, porosity, depressions, incomplete penetration, oxidation, and burn-off that frequently occur in the welding process of ultralight high-modulus magnesium-lithium alloy workpieces by studying the relationship between welding parameters such as accelerating voltage, electron beam current, and welding speed and the performance of welded joints. It obtains welds with excellent shape and extremely small range, realizes high-precision welding of ultralight high-modulus magnesium-lithium alloy components, and establishes an electron beam welding process for ultralight high-modulus magnesium-lithium alloy workpieces from sample level to product level. Attached Figure Description

[0045] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A schematic diagram of the electron beam welding process after the butt joint of curved plate components; Figure 2A schematic diagram of the electron beam welding process after the cylindrical components are joined together. Figure 3 This is a schematic diagram of the electron beam welding process after the lugs are fitted into the hull holes. Detailed Implementation

[0046] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0047] To facilitate understanding, the abbreviations or nouns mentioned below will be explained first: Heat input per unit length E Where: U is the electron beam accelerating voltage, I is the electron beam current, v is the welding speed, η is the welding energy utilization efficiency, and E represents the heat input per unit length of weld during the welding process.

[0048] Welding energy utilization efficiency η: Since the electron beam is transmitted in a vacuum environment, there are no losses such as arc radiation and airflow convection. Therefore, the total power output by the electron gun is approximately considered to be transferred to the workpiece, and the energy utilization efficiency η is taken as 1.

[0049] This invention provides an electron beam welding method for ultralight, high-modulus magnesium-lithium alloy components. It is applicable to welding various structural forms such as bent plate components, cylindrical components, and cabins with lugs, and can cover magnesium-lithium alloys with different lithium contents from Mg-6Li to Mg-14Li series. Three welding scenarios can be achieved: butt welding between forged alloy components, butt welding between rotary forged alloy components, and butt welding between forged and rotary forged alloy components.

[0050] As an example, in some embodiments, the bent plate components are fabricated using wire electrical discharge machining (EDM) to obtain two corresponding bent plate components with a radius of curvature of 362mm and a thickness of 4mm from a rotary-forged ultralight high-modulus magnesium-lithium alloy hollow cylinder with a wall thickness of 4mm. The two bent plate components are then joined together and subjected to electron beam welding. Figure 1 As shown, the weld is a continuous polygonal weld formed by a curved surface.

[0051] As an example, in some embodiments, the cylindrical components are cut using electrical discharge machining (EDM) from a 362mm radius, 4mm wall thickness, ultra-lightweight, high-modulus magnesium-lithium alloy hollow cylinder. A pair of cylindrical components, each 300mm high, are then cut from the cylinder. The two cylindrical components are then joined together and electron beam welded. Figure 2 As shown, the weld is a circumferential annular weld.

[0052] As an example, in some embodiments, the cabin with lugs is composed of forged ultralight high-modulus magnesium-lithium alloy lugs with a bottom curved plate radius of 362mm and a thickness of 4mm, and a rotary-forged ultralight high-modulus magnesium-lithium alloy hollow cylindrical cabin with an inner diameter of 362mm and a thickness of 4mm. Holes are opened in the cabin wall to allow the lugs to fit perfectly into the openings in the cabin. After the lugs are aligned with the openings in the cabin, electron beam welding is performed. Figure 3 As shown, the weld is a closed circumferential weld formed by a curved surface.

[0053] This invention uses vacuum electron beam welding as its core, combined with post-weld solution treatment. Aging heat treatment, with full control of electron beam parameters, vacuum degree and heat input, suppresses defects such as welding oxidation, element burn-off, porosity and cracks, and significantly improves the strength, plasticity and structural stability of welded joints.

[0054] A series of preparatory work needs to be carried out before the actual welding to ensure the smooth progress of the welding process and the quality of the weld joint. These preparatory work includes the pretreatment of the surfaces to be welded, the assembly requirements of the components, and the control of the welding environment.

[0055] Pre-treatment of the surfaces to be welded includes mechanical grinding and degreasing. By processing and grinding the surfaces to be welded, the surfaces to be welded can be put together, so that there are no gaps between the two surfaces to be welded.

[0056] As an example, the specific method of mechanical cleaning is as follows: use a grinding wheel to grind the surface of the workpiece to be welded, and after mechanical cleaning, use anhydrous ethanol to remove the oil stains.

[0057] The components are assembled and positioned to ensure that the surfaces to be welded are clean, fit tightly, and have no obvious gaps or misalignments. The assembled components are then fixed in a special fixture inside the vacuum chamber of the electron beam welding machine, ready to enter the welding process.

[0058] As an example, after pretreatment, the workpieces to be welded are fixed on a fixture in the vacuum chamber of the electron beam welding machine. When welding components, there is no gap between the surfaces to be welded, and the step difference is less than 0.5 mm.

[0059] Electron beam welding of magnesium-lithium alloy components is performed in a vacuum environment. After the component is properly installed inside the electron beam welding machine chamber and the chamber door is closed, the chamber is evacuated until the vacuum level inside the chamber is ≤5×10⁻⁶. -2In a vacuum environment, the absence of air or other gas molecules to scatter or absorb electrons helps maintain the high energy density and linearity of the electron beam, making the welding process more precise and controllable. It also prevents air molecules from reacting with the molten pool, thus avoiding oxidation and burn-off of elements such as Mg and Li, which would reduce weld quality. While elements with high vapor pressures like Mg and Li are easily vaporized when heated at higher vacuum levels, the evaporation of Mg and Li can be minimized by adjusting parameters such as electron beam current and welding speed to keep the heat input within a reasonable range, due to the extremely small area affected by the electron beam.

[0060] Regarding the weld joint type, all components in this invention use butt joints with no bevel, and the welding process does not require filler wire. The welding method is single-sided welding.

[0061] Regarding the welding environment temperature, the electron beam welding method of the present invention maintains an ambient temperature of 25°C, and the workpiece does not require preheating before welding.

[0062] During electron beam welding, after the electron gun is turned on, the electron beam current reaches a stable state after a period of preheating. Similarly, after welding is completed, it takes a period of time to return to its initial state. Both transition times are relatively short; in this invention, the time required for the electron beam current to reach a stable state or return to its initial state is approximately 0.5 seconds. The stable state of the electron beam current in this invention refers to the fact that during the formation of a single weld point, the key parameters of the electron beam current (focusing current, accelerating voltage, and electron beam current, etc.) maintain minimal fluctuations within the welding area, ensuring stable energy input and thus obtaining a uniform weld. The effect of this design is that changes in the electron beam current do not substantially affect the welding performance before the weld point appears.

[0063] Furthermore, during electron beam welding, the focusing current is controlled at 1050~1300 mA to ensure that the electron beam current remains in a subsurface focused state. Subsurface focusing refers to a focusing control method in electron beam welding where the focal point of the electron beam, after being focused by an electromagnetic lens, is located at a certain depth below the workpiece surface (for thinner workpieces, the focal point is typically 0.5~2 mm from the workpiece surface). This process allows the electron beam energy to be coupled more effectively into the workpiece interior, forming a high-energy-density region below the surface, thereby increasing the penetration depth, optimizing the weld depth-to-width ratio, and obtaining a nearly parallel weld cross-sectional shape. Simultaneously, subsurface focusing reduces overheating and evaporation of metal on the workpiece surface, reduces the metal vapor back-plating effect, effectively suppresses defects such as weld black edges and porosity, and reduces molten pool spatter, improving the weld surface formation quality. In addition, this focusing method has a certain tolerance for micro-geometric deviations on the workpiece surface, reducing the impact of surface condition fluctuations on welding heat input, ensuring that the electron beam energy acts stably on the fusion zone, thereby improving the consistency and repeatability of welding quality.

[0064] It should be noted that there is no unified standard for the relationship between focusing current and focal depth for electron beam welding machines from different manufacturers, models, and under different accelerating voltage conditions. This relationship is independently calibrated by the equipment manufacturers based on their own equipment structure at the time of shipment. This invention, by controlling the focusing current within the range of 1050~1300 mA, can stably ensure that the electron beam focus falls on the subsurface region 0.5~2 mm below the upper surface of the workpiece. The focal depth can be precisely set and controlled based on the equipment's own calibration parameters, as shown in Table 1.

[0065] Table 1

[0066] In some embodiments of the present invention, during electron beam welding, the accelerating voltage is 60~120kV, the electron beam current is 4.0~8.0mA, and the welding speed is 400~800mm / min.

[0067] This invention solves the problem of energy input and distribution imbalance in magnesium-lithium alloy electron beam welding by accelerating the regulation of voltage, electron beam current and welding speed. Furthermore, it was found that controlling the three parameters within a reasonable range does not necessarily achieve high-quality welding, and defects may still occur due to improper energy matching.

[0068] In some preferred embodiments of the present invention, the thermal input E per unit length is 0.5 to 0.975.

[0069] This invention discovers that when the E value is synergistically controlled, the electron beam welding process exhibits significant advantages, achieving stability and repeatability in the electron beam welding process of magnesium-lithium alloys.

[0070] In some more preferred embodiments of the present invention, when the Li content in the magnesium-lithium alloy does not exceed 8 wt.%, the ratio of the value of E to the Li content ( Not less than 0.100; When the Li content in the magnesium-lithium alloy is greater than 8 wt.% and less than 14 wt.%, the ratio of E to Li content is between 0.036 and 0.100. When the Li content in the magnesium-lithium alloy is not less than 14 wt.%, the ratio of E to Li content is not higher than 0.036.

[0071] Under the control of the above welding parameters and focusing method, the electron beam welding method is used to perform single-sided welding of the component to be welded along the programmed welding path. After welding, the weld surface is cleaned by grinding with a stainless steel wire brush.

[0072] After electron beam welding is completed, the welded workpiece (including the weld seam and the base material) is subjected to heat treatment, including solution treatment and aging treatment.

[0073] In some embodiments of the present invention, the solution treatment temperature is 300~400 ℃ and the holding time is 2~24 h. It should be noted that the disadvantages of excessively high solution temperature are: (1) under excessively high temperature and long holding time, the grains at the weld will grow, weakening the grain refinement effect and deteriorating the weld performance; (2) although excessively high temperature also has a solution strengthening effect, studies have found that the solution strengthening effect is better at 300~400 ℃, and the solution strengthening effect weakens as the temperature increases.

[0074] In some embodiments of the present invention, the solution treatment is followed by water quenching, and then aging treatment is performed.

[0075] In some embodiments of the present invention, the aging treatment temperature is 100~175 ℃ and the holding time is 10~60 min. It should be noted that the disadvantages of excessively long aging time are: (1) if the holding time is too long, a large number of strengthening precipitates in the alloy will be transformed into softening phases, the joint will be severely softened, and the overall strength will be greatly reduced; (2) although extending the aging time can effectively improve the plasticity of the alloy, studies have found that the alloy has the best comprehensive mechanical properties under aging treatment at a temperature of 100~175 ℃ and a time of 10~60 min.

[0076] In some embodiments of the present invention, the composition of the magnesium-lithium alloy workpiece, by mass fraction, is: Li 6~14 wt.%, Al 1~5 wt.%, Zn 1~5 wt.%, RE 0.2~3 wt.%, with the balance being Mg and unavoidable impurities. Rare earth elements (RE) include one or more of Yb, Gd, Dy, Er, Tb, Ho, and Y; Impurities include one or more of Fe, Si, Cu, and Ni, with a total impurity content of less than 0.02 wt%.

[0077] In some embodiments of the present invention, the total mass fraction of Zn and Al is greater than or equal to 1 wt.% and less than or equal to 6 wt.%. When the amount of Al and Zn added is small, there are fewer precipitated phases (such as Mg3(Al,Zn)), resulting in lower alloy strength and modulus; however, a larger amount of Al and Zn added will lead to an increase in density.

[0078] The raw materials include pure Mg, pure Li, pure Al, pure Zn, and Mg-RE master alloy.

[0079] It should be noted that the raw materials are first weighed according to the component ratio and melted in a vacuum melting furnace under argon protection. The melt is then heated to 670°C and stirred at 300 rpm for 8 minutes. After stirring, the melt is allowed to stand for 7 minutes. Finally, the melt temperature is raised to 730°C and then poured into a plate mold to obtain an alloy ingot.

[0080] The prepared alloy ingot was preheated at 300°C for 5-7 hours before formal forging, while the anvil of the forging machine was also maintained at 300°C. After preheating, the cast alloy was placed on the anvil and subjected to triaxial free forging to obtain the forged plate. Three passes were made in each of the x, y, and z directions, with a reduction of 30% per pass. After each forging, the sample was tilted at a 90° angle. After forging, it was air-cooled. The forged workpiece was then obtained after wire cutting.

[0081] The prepared alloy ingot is preheated at 300°C for 5-7 hours before formal forging, while the mold is also maintained at 300°C. The preheated mold is clamped onto the hydraulic press, ensuring alignment of the upper and lower molds. The ingot is then placed inside the mold, maintaining alignment with the molds, and the hydraulic press is controlled to press down on the mold at a speed of 8-12 mm / s. After the mold is fully closed, the hydraulic press continues to run to hold the pressure for 20-30 seconds. After holding the pressure, the mold is opened, and the ejector rod is used to remove the workpiece. After air cooling, the forged workpiece is removed.

[0082] Example 1 In this embodiment, a bent plate component with an alloy composition of Mg-8Li-3Al-2Zn-0.5Y was subjected to electron beam welding at a vacuum degree of 2×10⁻⁶. -2 Pa, with the focusing current set to 1300 mA, the electron beam current is kept in a subsurface focusing state. Electron beam welding is performed under the process conditions of 120 kV acceleration voltage, 5.0 mA electron beam current, and 750 mm / min welding speed. After welding, the welded workpiece is kept at 300 ℃ for 4 h for solution treatment, then quenched in water and kept at 100 ℃ for 10 min for aging.

[0083] In this embodiment, E=0.8.

[0084] In this embodiment, the value of E is the ratio of the Li content. M 合金 For the quality of magnesium-lithium alloy, M Li This represents the mass of Li in the alloy.

[0085] Under these welding conditions, mechanical property tests were conducted on the heat-treated base material and the welded joint. The results showed that the yield strength, tensile strength, and elongation of the heat-treated base material were 223.3 MPa, 257 MPa, and 9.8%, respectively, while the yield strength, tensile strength, and elongation of the joint were 219.6 MPa, 254.8 MPa, and 7.6%, respectively. The yield strength, tensile strength, and elongation of the joint reached 98.3%, 99.1%, and 77.6% of those of the base material, respectively.

[0086] Example 2 In this embodiment, a bent plate component with an alloy composition of Mg-9Li-3Al-3Zn-0.5Y was subjected to electron beam welding at a vacuum degree of 2×10⁻⁶. -2 Pa, with the focusing current set to 1300 mA, the electron beam current is kept in a subsurface focusing state. Electron beam welding is performed under the process conditions of accelerating voltage of 60 kV, electron beam current of 5.5 mA, and welding speed of 500 mm / min. After welding, the welded workpiece is kept at 300 ℃ for 4 h for solution treatment, then quenched in water and kept at 100 ℃ for 15 min for aging.

[0087] In this embodiment, E=0.66.

[0088] In this embodiment, the value of E is the ratio of the Li content. .

[0089] Under these welding conditions, mechanical property tests were conducted on the heat-treated base material and the welded joint. The results showed that the yield strength, tensile strength, and elongation of the heat-treated base material were 211.3 MPa, 245.2 MPa, and 15.2%, respectively, while the yield strength, tensile strength, and elongation of the joint were 213.9 MPa, 242.8 MPa, and 12.3%, respectively. The yield strength, tensile strength, and elongation of the joint reached 101.2%, 99%, and 80.9% of those of the base material, respectively.

[0090] Example 3 In this embodiment, a bent plate component with an alloy composition of Mg-10Li-3Al-2Zn-1Y was subjected to electron beam welding at a vacuum degree of 3×10⁻⁶. -2 Pa, the focusing current is set to 1150 mA to keep the electron beam current in a subsurface focusing state, and electron beam welding is performed under the process conditions of 60 kV acceleration voltage, 7.5 mA electron beam current and 500 mm / min welding speed; After welding, the welded workpiece is kept at 350 ℃ for 3.5 h for solution treatment, then water quenched and kept at 150 ℃ for 10 min for aging.

[0091] In this embodiment, E=0.9.

[0092] In this embodiment, the value of E is the ratio of the Li content. .

[0093] Under these welding conditions, mechanical property tests were conducted on the heat-treated base material and the welded joint. The results showed that the yield strength, tensile strength, and elongation of the heat-treated base material were 219.2 MPa, 250.7 MPa, and 9.7%, respectively, while the yield strength, tensile strength, and elongation of the joint were 214.4 MPa, 248.7 MPa, and 8.1%, respectively. The yield strength, tensile strength, and elongation of the joint reached 97.8%, 99.2%, and 83.5% of those of the base material, respectively.

[0094] Example 4 In this embodiment, a cylindrical component with an alloy composition of Mg-12Li-3Al-2Zn-1Y was subjected to electron beam welding at a vacuum degree of 3×10⁻⁶. -2 Pa, the focusing current is set to 1150 mA to keep the electron beam current in a subsurface focusing state, and electron beam welding is performed under the process conditions of accelerating voltage of 60 kV, electron beam current of 6.5 mA, and welding speed of 400 mm / min; After welding, the welded workpiece is kept at 350 ℃ for 5 h for solution treatment, then water quenched and kept at 150 ℃ for 10 min for aging.

[0095] In this embodiment, E=0.975.

[0096] In this embodiment, the value of E is the ratio of the Li content. .

[0097] Under these welding conditions, mechanical property tests were conducted on the heat-treated base material and the welded joint. The results showed that the yield strength, tensile strength, and elongation of the heat-treated base material were 224.2 MPa, 253.7 MPa, and 18.8%, respectively, while the yield strength, tensile strength, and elongation of the joint were 221.9 MPa, 248.7 MPa, and 15.4%, respectively. The yield strength, tensile strength, and elongation of the joint reached 99%, 98%, and 81.9% of those of the base material, respectively.

[0098] Example 5 In this embodiment, an electron beam weld was performed on a chamber with lugs, with an alloy composition of Mg-14Li-1Al-1Zn-0.5Y, and a vacuum degree of 5×10⁻⁶. -2 Pa, with the focusing current set to 1080 mA, the electron beam current is kept in a subsurface focusing state. Electron beam welding is performed under the process conditions of accelerating voltage of 60 kV, electron beam current of 5.0 mA, and welding speed of 600 mm / min. In this embodiment, E=0.5.

[0099] In this embodiment, the value of E is the ratio of the Li content. .

[0100] After welding, the welded workpiece is kept at 350 ℃ for 5 h for solution treatment, then water quenched and kept at 150 ℃ for 10 min for aging.

[0101] Under these welding conditions, mechanical property tests were conducted on the heat-treated base material and the welded joint. The results showed that the yield strength, tensile strength, and elongation of the heat-treated base material were 227.8 MPa, 256.2 MPa, and 17.9%, respectively, while the yield strength, tensile strength, and elongation of the joint were 229.3 MPa, 253.1 MPa, and 16.7%, respectively. The yield strength, tensile strength, and elongation of the joint reached 100.7%, 98.8%, and 93.3% of those of the base material, respectively.

[0102] Example 6 In this embodiment, an electron beam weld was performed on a chamber with lugs, with an alloy composition of Mg-14Li-1Al-1Zn-0.5Y, and a vacuum degree of 5×10⁻⁶. -2 Pa, with the focusing current set to 1080 mA, the electron beam current is kept in a subsurface focusing state. Electron beam welding is performed under the process conditions of accelerating voltage of 60 kV, electron beam current of 5.0 mA, and welding speed of 600 mm / min. After welding, the welded workpiece is kept at 400 ℃ for 5 h for solution treatment, then quenched in water and kept at 175 ℃ for 10 min for aging.

[0103] In this embodiment, E=0.5.

[0104] In this embodiment, the value of E is the ratio of the Li content. .

[0105] Under these welding conditions, mechanical property tests were conducted on the heat-treated base material and the welded joint. The results showed that the yield strength, tensile strength, and elongation of the heat-treated base material were 244.1 MPa, 273.8 MPa, and 7.8%, respectively, while the yield strength, tensile strength, and elongation of the joint were 239.7 MPa, 263.9 MPa, and 5.2%, respectively. The yield strength, tensile strength, and elongation of the joint reached 98.2%, 96.4%, and 66.7% of those of the base material, respectively.

[0106] Comparative Example 1 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 1, except that: No aging treatment is performed after electron beam welding is completed.

[0107] After all processes were completed, mechanical property tests were conducted on the joint, and it was found that the yield strength, tensile strength and plasticity of the joint were 121%, 124.5% and 53.1% of those of the welded joint after heat treatment, respectively.

[0108] Comparative Example 2 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 3, except that: The electron beam current for welding the workpiece is 12.0 mA.

[0109] In this embodiment, E=1.44.

[0110] After all the processes were completed, it was found that the weld formation quality was poor, there was spatter on the weld surface, and there was obvious excess height at the bottom.

[0111] The main reason for these defects is that when the accelerating voltage is 60kV, the electron beam current is 12.0mA, and the welding speed is 500mm / min, the welding process parameters result in an excessively high heat input per unit length, which is not conducive to the formation of high-quality electron beam welded joints of Mg-10Li-3Al-2Zn-1Y magnesium-lithium alloy.

[0112] Comparative Example 3 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 3, except that: The electron beam current for welding the workpiece is 3 mA.

[0113] In this embodiment, E=0.36.

[0114] After all the processes were completed, it was found that there was an obvious lack of fusion at the bottom of the weld, the workpiece was not fully penetrated, and the weld depth-to-width ratio was small, resulting in undercut defects.

[0115] The electron beam degenerates into a "conductive welding mode" similar to a regular electric arc, and the weld morphology changes from a deep and straight "nail shape" to a shallow and wide "bowl shape," making it impossible to penetrate the workpiece of the expected thickness, resulting in a precipitous drop in the joint's load-bearing capacity.

[0116] Comparative Example 4 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 3, except that: The electron beam current for welding the workpiece is 9 mA.

[0117] In this embodiment, E=1.08.

[0118] After all processes were completed, undercut defects were found in the weld, and the grains in the heat-affected zone were coarsened.

[0119] Excessive beam current causes violent vaporization of the metal inside the molten pool, generating high back pressure that forcibly pushes a large amount of liquid metal to the rear and sides of the molten pool. In addition, the high beam current prolongs the high-temperature residence time in the overall heat-affected zone of the workpiece, leading to grain coarsening in the heat-affected zone.

[0120] Comparative Example 5 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 4, except that: The aging treatment process for welded workpieces is as follows: heat treatment at 150 ℃ for 20 min.

[0121] After all processes were completed, the joint was subjected to mechanical property tests. It was found that the yield strength, tensile strength and plasticity of the joint were 79.8%, 87.1% and 71.8% of those of the welded joint prepared in Example 4, respectively.

[0122] The presence of the AlLi phase in magnesium-lithium alloys reduces the overall properties of the alloy. At a temperature of 150 °C, the AlLi phase is more likely to precipitate from the matrix, promoting the aging of the alloy and reducing the mechanical properties of magnesium-lithium alloy welded workpieces.

[0123] Comparative Example 6 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 4, except that: The accelerating voltage is 120kV.

[0124] In this embodiment, E=1.95.

[0125] After all the processes were completed, it was found that the weld seam was sunken, the forming effect was poor, and cracks appeared in the welded joint.

[0126] The main reason for these defects is that when the accelerating voltage is 120kV, the electron beam current is 6.5mA, and the welding speed is 400mm / min, the welding process parameters result in an excessively high heat input per unit length, which is not conducive to the formation of high-quality electron beam welded joints of Mg-12Li-3Al-2Zn-1Y magnesium-lithium alloy.

[0127] Comparative Example 7 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 5, except that: The focusing current is 900 mA, which makes the electron beam reach the under-focusing state (at which point the focal point is close to the lower surface of the workpiece).

[0128] After all the processes were completed, a depression was found on the upper surface of the weld, and nail-like protrusions and pores appeared at the root of the weld.

[0129] The main reason for these defects is that, under excessive focusing, the focal point of the electron beam is too deep, resulting in insufficient surface energy and excessive root energy. Therefore, the amount of surface metal melted is insufficient, and it is easy to form depressions after solidification. Meanwhile, the excessive concentration of energy at the root causes excessive melting depth and excessive metal vapor pressure at the bottom, preventing bubbles from escaping, thus forming nail-like protrusions and root pores.

[0130] Comparative Example 8 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 5, except that: The focusing current is 1400 mA, which enables the electron beam to reach the focusing state on the upper surface (at this time, the focal point is located above the upper surface of the workpiece). After all the processes were completed, it was found that the weld seam had excess height and porosity, and the penetration depth was insufficient.

[0131] The main reason for these defects is that, under the focused state on the upper surface, the energy of the electron beam begins to diverge upon reaching the workpiece surface, resulting in reduced energy density and excessive concentration in the surface area. This leads to excess surface energy and insufficient energy at the root. Consequently, the amount of surface metal melted and the metal vapor pressure are too high, resulting in excess thickness and porosity after solidification. At the same time, energy cannot be effectively transferred to the depth of the workpiece, leading to insufficient penetration.

[0132] Comparative Example 9 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 5, except that: After welding, no solution treatment or aging treatment is performed.

[0133] After all the processes were completed, hot cracks were found in the welding area, and the overall welding performance was poor.

[0134] Comparative Example 10 The material, structural dimensions, and welding parameters of the electron beam welded component in this comparative example are basically the same as those in Example 6, except that: The welding speed is 300 mm / min.

[0135] In this embodiment, E=1.

[0136] After all the processes were completed, it was found that the weld formation quality was poor, with some spatter, dents and a few hot cracks on the weld surface. At the same time, the weld width was very large, and there was a certain excess height at the bottom, resulting in poor overall welding performance.

[0137] The main reason for these defects is that when the accelerating voltage is 60 kV, the electron beam current is 5.0 mA, and the welding speed is 300 mm / min, the welding process parameters result in an excessively high heat input per unit length, which is not conducive to the formation of high-quality electron beam welded joints of Mg-14Li-1Al-1Zn-0.5Y magnesium-lithium alloy.

[0138] In summary, this invention utilizes a high-energy electron beam generated in a vacuum, focused and accelerated, to weld ultralight, high-modulus magnesium-lithium alloy components. After welding, the components achieve complete penetration without porosity. Electron beam parameters significantly influence the final joint's microstructure and overall performance. The heat input during welding is primarily determined by the accelerating voltage, electron beam current, and welding speed. Excessive heat input can lead to lithium burn-out, weld zone collapse, and metal spatter, reducing the joint's forming quality and overall performance. Conversely, insufficient heat input can result in incomplete penetration, significantly weakening the joint's mechanical properties. Therefore, a reasonable combination of heat input and process parameters is crucial.

[0139] Furthermore, in this invention, the electron beam used in the welding process does not involve beam oscillation or other operations, making the welding method simpler, more convenient, and more universally applicable. Simultaneously, the welding process of this invention is carried out in a vacuum environment, resulting in extremely high electron beam thermal efficiency, concentrated heat input, and extremely fast welding and cooling rates. This not only significantly suppresses the oxidation, burn-off, and evaporation of magnesium and lithium elements, but also produces narrow and deep welds and extremely narrow heat-affected zones, greatly reducing the impact of heat input on the overall performance of the component and effectively maintaining the integrity of the joint.

[0140] Furthermore, under a reasonable combination of process parameters such as accelerating voltage, electron beam current, and welding speed, the weld grains of the welded components are significantly refined, resulting in excellent comprehensive mechanical properties. The weld and heat-affected zone exhibit high strength and plasticity (elongation). Simultaneously, under appropriate parameter combinations, the weld has good formability, a neat appearance without spatter or collapse, no component deformation, and no defects such as porosity or cracks inside the weld, achieving excellent formability and ensuring both welding quality and component performance.

[0141] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An electron beam welding method for magnesium-lithium alloy components, characterized in that, Includes the following steps: Under vacuum, the electron beam is controlled to be subsurface focused, with the focal point 0.5~2 mm away from the upper surface of the workpiece, the accelerating voltage 60~120kV, the electron beam current 4~8 mA, the welding speed 400~800mm / min, and single-sided welding is performed. After welding, the workpiece is heat-treated.

2. The welding method according to claim 1, characterized in that, Focusing current 1050~1300 mA.

3. The welding method according to claim 1, characterized in that, The heat treatment involves solution treatment followed by aging treatment.

4. The preparation method according to claim 3, characterized in that, The solution treatment is performed at 300-400 ℃ for 2-24 h, and the aging treatment is performed at 100-175 ℃ for 10-60 min.

5. The welding method according to any one of claims 1 to 4, characterized in that, The welding method described herein is applicable to the welding of magnesium-lithium alloys from Mg-6Li to Mg-14Li series.

6. The welding method according to claim 5, characterized in that, The welding method is applicable to welding between magnesium-lithium alloy forged workpieces, between rotary forged workpieces, and between forged and rotary forged workpieces.

7. The welding method according to claim 5, characterized in that, The welding method can achieve welding of one or more weld types, including straight welds, arc welds, curved surface welds, circumferential circumferential welds, and closed circumferential welds.

8. The magnesium-lithium alloy electron beam welded component prepared by the welding method according to any one of claims 1 to 7, characterized in that, The composition by mass fraction is Li 6~14 wt.%, Al 1~5 wt.%, Zn 1~5 wt.%, RE 0.2~3 wt.%, with the balance being Mg and unavoidable impurities.

9. The welded component according to claim 8, characterized in that, The RE element includes one or more of Yb, Gd, Dy, Er, Tb, Ho, and Y.

10. The welded component according to claim 8, characterized in that, The yield strength and tensile strength of the welded joint reach more than 97% of the base material, and the elongation reaches more than 66% of the base material.

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