A high-elongation uniformity ultra-light magnesium-lithium alloy and a preparation method thereof

Abstract

This invention provides an ultralight magnesium-lithium alloy with high uniform elongation and its preparation method. The preparation method includes the following specific processes: Melting and preparation: The raw materials are mixed according to the following ratio: Li: 11-16 wt.%, Ag: 1-10 wt.%, with the remainder being Mg. The mixture is then melted and cast using vacuum induction melting to initially produce a cast magnesium-lithium alloy; Homogenization treatment: The riser of the ingot is removed using a diamond cutter, the oxide scale on the surface of the ingot is removed by turning, and homogenization treatment is performed by holding at 300-400℃ for 4 hours; Rolling and heat treatment: Hot rolling is performed at 300-350℃, followed by solution treatment at 300-350℃, then cryogenic forging, and finally aging treatment at 50-180℃ for 1-4 hours. An ultralight magnesium-lithium alloy with a uniform elongation of over 20% and an elongation after fracture exceeding 35% is obtained, which has significant advantages compared with similar alloys. This invention utilizes low-temperature deformation-induced phase transformation to simultaneously improve the strength and plasticity of the magnesium-lithium alloy.

Description

Technical Field

[0001] This invention relates to the field of magnesium-lithium alloy processing technology, and in particular to an ultralight magnesium-lithium alloy with high uniform elongation and its preparation method. Background Technology

[0002] Magnesium-lithium alloys are ultralight alloys (with a density typically between 1.35 and 1.65 g / cm³). 3 Magnesium-lithium alloys (MgL) possess advantages such as low density, high specific strength, good plasticity, and excellent electromagnetic shielding performance, making them promising for applications in high-tech industries such as aerospace, automotive, 3C (computers, communications, and consumer electronics), and medical devices. However, their low absolute strength and poor high-temperature stability limit their widespread industrial application. Therefore, it is necessary to develop a processing technology that can effectively improve the mechanical properties of magnesium-lithium alloys.

[0003] Magnesium-lithium alloys exhibit two crystal structures: hcp and bcc. As the Li content increases, the crystal structure gradually transforms from an hcp structure to a bcc structure. When the Li mass percentage is below 5.7%, it exhibits a single-phase hcp structure; between 5.7% and 10.3%, it exhibits a two-phase structure of hcp and bcc; and when the Li mass percentage exceeds 10.3%, the alloy displays a single-phase bcc structure. The hcp structure has fewer slip systems, resulting in poorer plasticity, while the bcc structure possesses better plasticity and formability compared to the hcp structure, thus enabling it to be formed at low temperatures.

[0004] Current research on the composition of magnesium-lithium alloys mainly focuses on the addition of Al and Zn, with representative alloys being LA-based and LZ-based alloys. This is because Al and Zn have relatively low densities, have little impact on alloy density, and provide relatively ideal strengthening effects. However, the strengthening phases Mg3Al or MgZnLi2 formed are metastable phases, which are prone to softening at high temperatures or after long-term service, resulting in poor thermal stability of the alloy. Ag, on the other hand, can improve the solid solution capacity of magnesium-lithium alloys and suppress over-aging. However, due to its high density and cost, it is generally added in small amounts to improve the performance of magnesium-lithium-based multi-element alloys. Research on magnesium-lithium-silver ternary alloys is still relatively limited. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an ultralight magnesium-lithium alloy with high uniform elongation that offers superior performance compared to traditional forging processes. Specifically, this invention utilizes low-temperature forging to design a Mg-Li-Ag ternary single-bcc phase alloy with high uniform elongation.

[0006] To achieve the objective of this invention, the technical solution adopted is as follows:

[0007] A method for preparing an ultralight magnesium-lithium alloy with high uniform elongation, wherein the alloy ratio used in the method is Li: 11-16 wt.%, Ag: 1-10 wt.%, and the remainder is Mg.

[0008] The specific steps include:

[0009] Step 1, smelting and preparation: After mixing the raw materials according to the above ratio, the materials are smelted and cast by vacuum induction melting to initially produce a cast magnesium-lithium alloy.

[0010] Step 2, homogenization treatment: The cast alloy with the ingot riser removed and the surface oxide layer removed is homogenized at 300-400℃ for about 4 hours to eliminate possible component segregation in the alloy.

[0011] Step 3: Hot rolling. After removing the oxide layer, hot rolling is carried out at 300-350℃, and multiple rolling processes are performed. The reduction in each pass is 10%, and finally, a plate with a thickness of about 20mm is rolled out.

[0012] Step four, solution treatment, perform solution treatment at 300-350℃ for 10-60 minutes, followed by quenching treatment.

[0013] Step 5: Forging in liquid nitrogen. After removing the oxide layer, the raw material is cut into samples with dimensions of 20*20*30mm. The samples are immersed in liquid nitrogen for 10 minutes to bring the sample temperature to the liquid nitrogen temperature. After removing the samples from the liquid nitrogen, wide-face bidirectional forging is quickly performed. Each forging pass achieves 5-8% of the engineering strain. Before each change in forging direction, the samples are immersed in liquid nitrogen to ensure that the sample temperature is maintained before forging. Finally, after multiple forging passes, a long rod-shaped sample is obtained.

[0014] Step 6, aging treatment: The cryogenically forged sample is aged at 50-180℃ for 1-4 hours.

[0015] Compared with the prior art, the advantages of the present invention include:

[0016] 1. High plasticity: The cryogenic forged magnesium-lithium alloy of the present invention has a uniform elongation of over 20%, while the elongation of similar alloys is generally below 15%, and the elongation after fracture is as high as over 35%, and the tensile strength also reaches 150 MPa, which is more than 10% higher than that of similar alloys, and has better mechanical properties.

[0017] 2. Simple process: The preparation method of this invention is simple and reliable, suitable for processing large-scale magnesium-lithium alloy industrial samples, with high efficiency and easy to promote.

[0018] 3. Uniform and refined microstructure: After cryogenic forging under liquid nitrogen, BCC-based ordered phases are precipitated, and the microstructure is greatly refined, making it very suitable for preparing magnesium-lithium alloy plates with excellent mechanical properties, and it has important practical value. Attached Figure Description

[0019] To better illustrate the practical application of the present invention, the accompanying drawings used in the description of the examples or prior art will be briefly introduced below.

[0020] Figure 1 This is a schematic diagram of the liquid nitrogen cryogenic forging of magnesium-lithium alloy according to the present invention.

[0021] Figure 2 These are the stress-strain curves of the magnesium-lithium alloy in the as-cast state and after liquid nitrogen forging according to the present invention.

[0022] Figure 3 The image shows the metallographic structure of the magnesium-lithium alloy after liquid nitrogen forging according to the present invention.

[0023] Figure 4 The image shows the metallographic structure of the magnesium-lithium alloy after room temperature forging according to the present invention.

[0024] Figure 5 The images show the XRD patterns of the magnesium-lithium alloy of this invention in the as-cast state, after room temperature forging, and after liquid nitrogen forging. Detailed Implementation

[0025] The invention will be further described with reference to the accompanying drawings.

[0026] Magnesium-lithium alloys exhibit different matrix structures depending on the Li content. As the Li content increases, the alloy transforms from a single-phase hcp structure to a bcc structure. When the Li mass ratio exceeds 10.3 wt.%, the alloy exhibits a single-phase bcc structure. The alloy matrix of this invention has a single-phase bcc structure, which offers higher plasticity and easier processing compared to single-phase hcp and dual-phase hcp+bcc structures. Furthermore, the higher Li content significantly reduces the alloy's density. Ag has a certain solid solubility in magnesium-lithium alloys, which decreases with decreasing temperature, leading to the precipitation of AgLi and MgLi2Ag phases. Small amounts of precipitation can form pinning structures within the matrix, refining the grain size. When the silver content is less than 10%, the alloy's strength increases linearly with increasing silver content, but the increase is small. Simultaneously, because Ag can refine the grain size, the alloy's plasticity also increases with increasing Ag content.

[0027] Specifically as follows:

[0028] After removing the oxide scale and washing the weighed raw materials, they are initially melted into a cast alloy in a vacuum induction melting furnace. The specific ratio is: Li: 11-16wt%, Ag: 1-10wt%, and the remainder is Mg.

[0029] The as-cast alloy with its riser removed and surface oxide layer removed is homogenized at 300–400°C for about 4 hours to eliminate component segregation and ensure uniform alloy composition.

[0030] After removing the oxide layer, hot rolling is carried out at 300-350℃, with multiple rolling passes and a reduction of 10% in each pass, finally rolling into a plate with a thickness of about 20mm. This process not only further homogenizes the composition and structure of the alloy material, but also refines the grains and enhances the various mechanical properties of the alloy material.

[0031] After removing the oxide scale that may exist during hot rolling, the alloy is solution treated at 300-350℃ for 10-60 minutes and then quenched to preserve the structure at high temperature. At this time, most of the small amount of uneven precipitate phases are dissolved into the matrix, preparing for subsequent aging treatment.

[0032] After removing the oxide scale, the alloy material sheet is cut into samples with dimensions of 20*20*30mm and placed in liquid nitrogen for cooling. The sheet temperature is uniformly cooled to -196℃. The sheet is then removed and cryogenically forged with an engineering strain of 5% to 8%. After forging, the sheet is placed in liquid nitrogen for recooling for 3 to 5 minutes. The cooled sheet is then cryogenically forged again. The above steps are repeated multiple times, with the forging temperature controlled at the liquid nitrogen temperature. The final total reduction is approximately 20%.

[0033] After removing any possible oxide scale, the alloy material is aged at 50–180°C for 1–4 hours. This process causes recovery, slightly softening the alloy and improving its plasticity. Figure 2 It can be seen that the strength of the alloy after a series of heat treatments is improved to a certain extent compared with the as-cast state, and its uniform elongation reaches more than 20%, and its elongation after fracture reaches more than 35%.

[0034] Example 1

[0035] A high-uniform-elongation ultralight magnesium-lithium alloy material, the mass percentage of each component is: Li: 15wt.%, Ag: 4wt.%, with the balance being magnesium and unavoidable impurities, the total amount of impurities being less than 0.02wt.%.

[0036] The preparation method of the above-mentioned ultralight magnesium-lithium alloy with high uniform elongation includes the following steps:

[0037] (1) Mix pure Mg, pure Li and pure Ag according to the mass percentage of each component in the magnesium-lithium alloy, place them in a crucible in a vacuum induction furnace, and evacuate to 10 °C. -3Pa, and then argon gas is introduced. Vacuum melting is carried out under the protection of argon gas. Subsequently, the as-cast alloy with the ingot riser removed and the surface oxide layer removed is homogenized at 350°C for about 4 hours to eliminate the component segregation in the alloy and initially obtain as-cast magnesium-lithium alloy plate with a thickness of about 30 mm;

[0038] (2) After removing the oxide layer, hot rolling is carried out at 300°C, and multiple rolling processes are performed. The reduction in each pass is 10%, and finally the plate is rolled into a thickness of about 20 mm.

[0039] (3) After removing the oxide scale that may exist during the hot rolling process, the alloy is solution treated at 320°C for 30 min and then quenched.

[0040] (4) After removing the oxide scale, the alloy material plate is placed in liquid nitrogen for cooling, so that the plate temperature is uniformly cooled to the liquid nitrogen temperature. The plate is taken out and wide-face bidirectional forging is performed with a reduction of 6%. After rolling, the rolled plate is placed in liquid nitrogen for cooling again for 5 minutes. The cooled plate is then subjected to deep cryogenic forging. The above steps are repeated for multiple forgings. The final total reduction is about 20%.

[0041] (5) Remove any possible oxide scale and age the material at 100°C for 2 hours.

[0042] Comparative Example 1

[0043] This comparative example relates to an ultralight magnesium-lithium alloy with high uniform elongation. The composition of the magnesium-lithium alloy is the same as that of Example 1, and the preparation method of the magnesium-lithium alloy is basically the same as that of Example 1, except that the forging temperature is room temperature.

[0044] It can be seen that the grains are completely broken after room temperature forging, the surface is covered with deformation bands, and no complete grain boundaries can be seen. Furthermore, XRD shows that no phase transformation has occurred and no ordered phase has precipitated.

[0045] Compared with liquid nitrogen forging, the microstructure of the material forged at room temperature was significantly refined, and a deformation-induced phase transformation occurred at low temperature. Figure 4 XRD analysis revealed that the matrix was BCC phase in all three treatment methods, but after low-temperature forging, a BCC-based ordered phase precipitated inside the matrix. Figure 2 After liquid nitrogen forging, the strength of the material increased from 110MPa to about 150MPa, the uniform elongation after forging increased from 17% to 22%, and the elongation after fracture also increased to more than 35%. Compared with similar magnesium-lithium alloy materials, the overall mechanical properties have been significantly improved.

Claims

1. A high-uniform-elongation ultralight magnesium-lithium alloy, characterized in that, The mass percentage of the magnesium-lithium alloy components is: Li: 11-16 wt.%, Ag: 1-10 wt.%, with the remainder being Mg. The preparation method of the ultralight magnesium-lithium alloy with high uniform elongation is as follows: S1: The raw materials washed with anhydrous ethanol are mixed according to the formula and then melted and cast by vacuum induction melting to initially produce a cast magnesium-lithium alloy. The cast alloy with the ingot riser removed and the surface oxide layer removed is homogenized to eliminate the component segregation in the alloy. In S1, the homogenization treatment is as follows: the cast alloy with the ingot riser removed and the surface oxide layer removed is homogenized at 300~400℃ for 4h. S2: After removing the oxide layer, hot rolling is performed, and multiple rolling processes are carried out to produce a 20mm thick plate. Then, solution treatment is performed, followed by quenching. S3: After removing the oxide scale, the plate is placed in liquid nitrogen for cooling, followed by multiple forgings, with the forging temperature controlled at the liquid nitrogen temperature, and then aging treatment is performed; In S3, liquid nitrogen forging is as follows: after removing the oxide scale, the plate is placed in liquid nitrogen for cooling, followed by multiple bidirectional forgings, with each forging amount reaching 5-8% of the engineering strain, and the temperature controlled at the liquid nitrogen temperature, and finally, after multiple forgings, a long rod-shaped sample is obtained.

2. A method for preparing an ultralight magnesium-lithium alloy with high uniform elongation, characterized in that, This method is S1: The raw materials washed with anhydrous ethanol are mixed according to the formula and then melted and cast by vacuum induction melting to initially produce a cast magnesium-lithium alloy. The cast alloy with the ingot riser removed and the surface oxide layer removed is homogenized to eliminate the component segregation in the alloy. In S1, the homogenization treatment is as follows: the cast alloy with the ingot riser removed and the surface oxide layer removed is homogenized at 300~400℃ for 4h. S2: After removing the oxide layer, hot rolling is performed, and multiple rolling processes are carried out to produce a 20mm thick plate. Then, solution treatment is performed, followed by quenching. S3: After removing the oxide scale, the plate is placed in liquid nitrogen for cooling, followed by multiple forgings, with the forging temperature controlled at the liquid nitrogen temperature, and then aging treatment is performed; In S3, the liquid nitrogen forging is as follows: after removing the oxide scale, the plate is placed in liquid nitrogen for cooling, followed by multiple bidirectional forgings, with each forging amount reaching 5-8% of the engineering strain, and the temperature controlled at the liquid nitrogen temperature, and finally, after multiple forgings, a long rod-shaped sample is obtained; The mass percentage of the magnesium-lithium alloy components is: Li: 11-16wt.%, Ag: 1-10wt.%, with the remainder being Mg.

3. The method for preparing the ultralight magnesium-lithium alloy with high uniform elongation according to claim 2, characterized in that, In S2, hot rolling is carried out at 300~350℃, with multiple rolling passes, each pass having a reduction of 10%, and finally rolling into a 20mm thick plate.

4. The method for preparing the ultralight magnesium-lithium alloy with high uniform elongation according to claim 2, characterized in that, In S2, the solution treatment is performed at 370℃ for 10~60min, followed by quenching.

5. The method for preparing the ultralight magnesium-lithium alloy with high uniform elongation according to claim 2, characterized in that, In S3, the aging treatment is performed at 50~180 ℃ for 1~4 h.

Images