Method for forming rare earth oxide film on surface of rare earth-containing magnesium alloy and material

Abstract

The present application relates to a kind of rare earth magnesium alloy surface heat treatment forming rare earth oxide film method and material, belong to magnesium alloy surface treatment technical field, including: after the surface of rare earth-containing magnesium alloy sample is pretreated, short-time heating treatment is carried out in oxygen-containing atmosphere, so that the sample surface quickly forms a layer with rare earth oxide as main dense protective film, then cooling to room temperature.The rare earth-containing magnesium alloy contains one or more rare earth elements, the total content of rare earth element in the rare earth-containing magnesium alloy is 8-15 wt.%, and the rare earth element is selected from one or several of Gd, Y, Nd, Ce, Er.The method is simple, short processing time, film forming speed is fast, without additional coating raw material or complex equipment, the rare earth oxide film formed has better density and protection, can effectively improve the corrosion resistance and flame resistance of rare earth-containing magnesium alloy, and is suitable for the rapid surface protection treatment of rare earth-containing magnesium alloy sample or component.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy surface treatment technology, specifically to a method and materials for forming a rare earth oxide film on the surface of a rare earth-containing magnesium alloy through heat treatment. Background Technology

[0002] Magnesium alloys possess advantages such as low density, high specific strength, high specific stiffness, and good vibration damping performance, making them promising for applications in aerospace, rail transportation, electronics and information technology, and high-end equipment manufacturing, particularly in lightweight structural components. However, magnesium and magnesium alloys exhibit high chemical reactivity and are prone to oxidation at high temperatures, potentially leading to violent combustion, severely limiting their application in high-safety service environments. Furthermore, magnesium alloys are susceptible to surface damage and matrix degradation in corrosive media, demonstrating insufficient corrosion resistance. The naturally formed oxide film on magnesium alloy surfaces is typically thin, with limited density and stability, making it difficult to effectively prevent corrosive media from penetrating the matrix over long periods. Therefore, their high-temperature oxidation resistance, flame retardancy, and corrosion resistance generally require improvement.

[0003] Existing methods for improving the surface protection properties of magnesium alloys mainly include chemical conversion, anodizing, micro-arc oxidation, and coating deposition. While these methods can improve the surface protection properties of magnesium alloys to some extent, they typically suffer from problems such as long process flows, high equipment requirements, high processing costs, or insufficient adaptability to component sizes and shapes. For magnesium alloy samples or components requiring rapid surface treatment, the above methods still have certain limitations in practical applications. Existing research indicates that the key to improving the flame retardancy and high-temperature oxidation resistance of magnesium alloys lies in forming a surface oxide film with good protective properties. Magnesium alloys typically undergo a protective oxidation stage and an accelerated oxidation stage during high-temperature oxidation. The oxide film formed during the protective oxidation stage is relatively continuous and dense, which can hinder oxygen diffusion into the matrix to a certain extent. As the oxidation reaction proceeds, the oxide film thickness increases, internal stress gradually increases, cracks and pores form, the protective ability of the oxide film decreases, ultimately leading to accelerated oxidation or even ignition. Therefore, extending the protective oxidation stage and promoting the formation of a denser and more stable oxide film on the material surface is an effective way to improve the oxidation resistance and flame retardancy of magnesium alloys.

[0004] On the other hand, the surface oxide film also plays an important role in improving the corrosion resistance of magnesium alloys. A dense and continuous surface oxide film can effectively reduce the direct contact between the corrosive medium and the magnesium alloy substrate, hindering the corrosion of Cl-. -Corrosion-related media such as H2O and O2 are transported to the substrate surface, thereby slowing down the anodic dissolution process and localized corrosion of the magnesium alloy substrate. Simultaneously, a stable surface oxide film can reduce surface microcouple effects and susceptibility to localized corrosion, improving the surface stability of the material in corrosive environments. Therefore, constructing a dense, stable, and well-adhered surface oxide film not only helps improve the high-temperature oxidation resistance and flame retardancy of magnesium alloys but also enhances their corrosion resistance.

[0005] Further research indicates that rare earth elements have a significant impact on the formation of oxide films on magnesium alloy surfaces. Magnesium alloys containing rare earth elements such as Gd, Y, Nd, Ce, and Er can accumulate these elements on the surface under high-temperature conditions, forming corresponding rare earth oxides within the oxide film. Compared to ordinary MgO films, rare earth oxides are beneficial in improving the density, stability, and protective properties of the oxide film, thereby inhibiting oxygen diffusion inward, slowing magnesium volatilization outward, and enhancing the barrier effect of the oxide film against corrosive media, thus improving the high-temperature stability and corrosion resistance of magnesium alloys. Summary of the Invention

[0006] To address the problems in the prior art, the purpose of this invention is to provide a method and material for forming a rare earth oxide film on the surface of rare earth magnesium alloys through heat treatment. By forming a dense rare earth oxide film on the material surface in situ in a short time, the corrosion resistance and flame retardancy of rare earth magnesium alloys are simultaneously improved. It features simple process, rapid film formation and significant protective effect, and solves the problems of complex surface treatment processes, long processing cycles and insufficient protection of ordinary MgO oxide films in existing magnesium alloys.

[0007] The method for forming a rare earth oxide film on the surface of a rare earth-containing magnesium alloy according to the present invention includes the following steps: Step S1: Perform surface pretreatment on the rare earth magnesium alloy sample; Step S2: The pretreated sample is placed in an oxygen-containing atmosphere for heating treatment to form a rare earth oxide film on the sample surface; Step S3: After the processing is completed, the sample is cooled to room temperature to obtain a rare earth magnesium alloy material with an oxide film formed on the surface.

[0008] Preferably, the total rare earth element content in the rare earth magnesium alloy is 8-15 wt.%, and the rare earth element is selected from one or more of Gd, Y, Nd, Ce, and Er.

[0009] Preferably, the temperature of the short-time heating treatment is 450–800°C, and the treatment time is 5–10 min.

[0010] Preferably, the surface pretreatment includes one or more of mechanical grinding, polishing, ultrasonic cleaning, and drying.

[0011] Preferably, the oxygen-containing atmosphere is air, oxygen, or a mixture of oxygen and an inert gas.

[0012] Preferably, the heating treatment employs a continuous heating method or a rapid heating method by directly placing the sample into a preheating furnace.

[0013] Preferably, the cooling method is air cooling or furnace cooling.

[0014] Preferably, the oxide film comprises MgO and one or more rare earth oxides.

[0015] Preferably, the rare earth oxide includes one or more of Gd2O3, Y2O3, Nd2O3, CeO2, and Er2O3.

[0016] The rare earth magnesium alloy material obtained by the method described in this invention is characterized in that the surface of the material has an oxide film containing MgO and rare earth oxides.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes the inherent compositional characteristics of rare earth magnesium alloys to rapidly form a dense oxide film containing rare earth oxides on the surface through short-time heat treatment, without the need for additional surface coating materials, making the process simple.

[0018] 2. The present invention has a short processing time, requiring only a short heating time to achieve surface film formation, making it suitable for rapid surface treatment of samples or components.

[0019] 3. In addition to MgO, the surface oxide film formed by the present invention also contains rare earth oxides, which have better density and protection than ordinary MgO film and can effectively prevent oxygen and corrosive media from further diffusing into the substrate.

[0020] 4. The dense rare earth oxide film formed by the present invention can improve the corrosion resistance and flame retardancy of rare earth magnesium alloys.

[0021] 5. This invention is particularly applicable to magnesium alloy systems containing rare earth elements such as Gd, Y, Nd, Ce, and Er. By utilizing the surface enrichment and preferential oxidation of rare earth elements during heat treatment, a surface protective layer can be quickly constructed. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort. Other features, objects, and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The images show the surface and cross-sectional morphology of the oxide film on the surface of the rare earth magnesium alloy after short-time heat treatment in Example 1 of the present invention, where (a) is the surface morphology of the oxide film, and (b) and (c) are the cross-sectional morphology of the oxide film. Figure 2 The results are obtained by elemental line scan analysis of the cross-section of the oxide film on the surface of the rare earth magnesium alloy in Example 1 of the invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific 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 various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0024] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0026] The technical solutions of the present invention and how they solve the above-mentioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0027] Example 1

[0028] The rare earth magnesium alloy sample GWZ941-Ca was selected. Its actual composition is: Mg-8.93Gd-4.12Y-0.87Zn-0.30Zr-0.13Ca, with the balance being Mg. The total rare earth element content in this sample is 13.05wt.%, classifying it as a magnesium alloy containing Gd and Y rare earth elements.

[0029] First, the sample surface is pretreated. Specifically, the sample surface is mechanically polished and cleaned to remove surface contaminants and original oxidation residues. Preferably, the process may involve sanding, polishing, ultrasonic cleaning, and drying in sequence.

[0030] The pretreated sample is placed in an oxygen-containing atmosphere for short-term heat treatment. The oxygen-containing atmosphere can be air, oxygen, or a mixture of oxygen and an inert gas. The short-term heat treatment temperature is 450°C, and the treatment time is 6 minutes. The heat treatment can be performed using a continuous heating method or a rapid heating method by directly placing the sample in a preheating furnace. After treatment, the sample is cooled to room temperature using air cooling or furnace cooling.

[0031] After the above treatment, a dense rare earth oxide film was formed on the sample surface. In related magnesium alloys containing Gd and Y, after medium- and high-temperature oxidation, the oxide film formed on the sample surface mainly consisted of MgO, Gd₂O₃, and Y₂O₃, with rare earth elements showing significant enrichment in the inner layer of the oxide film. This result indicates that during heat treatment, rare earth elements can migrate to the surface and preferentially oxidize, thereby forming a protective layer containing rare earth oxides on the surface.

[0032] Furthermore, at approximately 600℃, a thin and continuous oxide film can form on the sample surface; at higher temperatures, if the rare earth oxide film is sufficiently dense, it can still provide good protection for the substrate. Compared to ordinary MgO films, the rare earth oxide-containing oxide films formed are more dense, effectively improving the high-temperature protection capability of the sample surface and enhancing its barrier effect against corrosive media.

[0033] Example 2

[0034] The rare earth magnesium alloy sample GWZ941 was selected. Its actual composition is Mg-9.47Gd-3.84Y-0.85Zn-0.26Zr, with the balance being Mg. The total rare earth element content in this sample is 13.31 wt.%, and it also belongs to the magnesium alloy containing Gd and Y rare earth elements.

[0035] After surface pretreatment of the sample in the same manner as in Example 1, it was subjected to short-term heat treatment at 450°C for 6 minutes in an oxygen-containing atmosphere, and then cooled to room temperature after treatment.

[0036] The results show that a surface oxide film containing MgO and rare earth oxides can also be formed on the sample surface, indicating that the method of the present invention is applicable to general rare earth magnesium alloys. In particular, for magnesium alloys containing rare earth elements such as Gd and Y, short-time heat treatment can utilize the enrichment and oxidation of rare earth elements on the surface to form a dense oxide film, thereby improving surface protection performance.

[0037] Example 3

[0038] Based on Example 1, the heat treatment method was changed to a rapid heating method in which the sample was directly placed in a preheating furnace for short-time heat treatment. The treatment temperature was controlled in the range of 450 to 800°C and the treatment time was controlled in the range of 5 to 10 minutes. Subsequently, the sample was cooled by air cooling.

[0039] The results show that this method can also form a rare earth oxide film on the surface of rare earth magnesium alloy samples, indicating that the present invention is not only applicable to continuous heating heat treatment, but also to direct rapid heating methods, and has good process flexibility.

[0040] The mechanism of action of this invention is as follows: During short-time heat treatment, an MgO film first forms on the surface of the rare-earth magnesium alloy; as the temperature rises, the rare-earth elements in the alloy accumulate on the surface and preferentially react with oxygen to form a rare-earth oxide layer in the oxide film. Because rare-earth oxides have good density and stability, the composite oxide film composed of MgO and rare-earth oxides has superior protective performance compared to a simple MgO film, effectively preventing further diffusion of oxygen and corrosive media into the substrate, thereby improving the corrosion resistance and flame retardancy of the rare-earth magnesium alloy.

[0041] For magnesium alloy systems containing Gd and Y, previous observations have shown that Gd and Y are significantly enriched in the oxide film, and the Gd₂O₃ and Y₂O₃ formed in the oxide film are key components for improving the protective properties of the film. For related systems containing trace amounts of Ca, Ca can also promote the enrichment of rare earth elements on the surface, thereby further enhancing the density and protection of the film. However, the method of the present invention is not limited to magnesium alloys that must contain Ca.

[0042] As can be seen from the above embodiments, the short-time heat treatment method for rare-earth magnesium alloy surfaces proposed in this invention can rapidly form a dense oxide film containing rare-earth oxides on the material surface in a short time. This method is simple, has a short processing time, and a fast film formation rate. It requires no additional surface coating materials, and the resulting oxide film has good density and protective properties, making it suitable for improving the corrosion resistance and flame retardancy of rare-earth magnesium alloy materials.

[0043] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0044] 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. A method for forming a rare earth oxide film on the surface of a rare earth-containing magnesium alloy by heat treatment, characterized in that, Includes the following steps: Step S1: Perform surface pretreatment on the rare earth magnesium alloy sample; Step S2: The pretreated sample is placed in an oxygen-containing atmosphere for heating treatment to form a rare earth oxide film on the sample surface; Step S3: After the processing is completed, the sample is cooled to room temperature to obtain a rare earth magnesium alloy material with an oxide film formed on the surface.

2. The method according to claim 1, characterized in that, The total rare earth element content in the rare earth magnesium alloy is 8-15 wt.%, and the rare earth element is selected from one or more of Gd, Y, Nd, Ce, and Er.

3. The method according to claim 1 or 2, characterized in that, The short-time heating treatment is performed at a temperature of 450–800°C for 5–10 minutes.

4. The method according to any one of claims 1 to 3, characterized in that, The surface pretreatment includes one or more of mechanical grinding, polishing, ultrasonic cleaning, and drying.

5. The method according to any one of claims 1 to 4, characterized in that, The oxygen-containing atmosphere is air, oxygen, or a mixture of oxygen and an inert gas.

6. The method according to any one of claims 1 to 5, characterized in that, The heating treatment employs a continuous heating method or a rapid heating method by directly placing the sample into a preheating furnace.

7. The method according to any one of claims 1 to 6, characterized in that, The cooling method is air cooling or furnace cooling.

8. The method according to any one of claims 1 to 7, characterized in that, The oxide film comprises MgO and one or more rare earth oxides.

9. The method according to claim 8, characterized in that, The rare earth oxides include one or more of Gd2O3, Y2O3, Nd2O3, CeO2, and Er2O3.

10. A rare-earth magnesium alloy material obtained by the method according to any one of claims 1 to 9, characterized in that, The surface of the material has an oxide film containing MgO and rare earth oxides.

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