A composite coating preparation process for eliminating liquid metal embrittlement in the forming process of galvanized high-strength steel and application thereof

Abstract

The application discloses a composite coating preparation process method for eliminating liquid metal embrittlement in the forming process of galvanized high-strength steel and application thereof, and relates to the field of high-strength steel and hot galvanizing technology for automobiles, and provides a composite new coating process for eliminating liquid metal embrittlement (LME) in the forming process of galvanized high-strength steel. The method comprises the following steps: preheating and immersion plating an Al layer before hot galvanizing of high-strength steel, and then oxidizing the Al layer through heat treatment to generate an Al2O3 layer on the surface of the high-strength steel base material, so that a composite coating of the high-strength steel base material surface-Al2O3 layer-galvanized layer structure is formed, the Al2O3 layer serves as a protective layer to hinder the invasion of Zn in the high-strength steel base body in the forming process of the galvanized high-strength steel, and the liquid metal embrittlement phenomenon in the forming process of the galvanized high-strength steel is eliminated.

Description

Technical Field

[0001] This invention relates to the fields of high-strength steel for automobiles and hot-dip galvanizing processes, and provides a method for preparing a composite coating that eliminates the embrittlement of liquid metal during the forming process of galvanized high-strength steel. Background Technology

[0002] The research and application of lightweight automotive materials are related to many aspects of vehicle energy conservation, emission reduction, safety, and cost, and are of great significance to saving global energy, natural resources, and protecting the environment. This has become the leading direction in automotive materials development. High-strength materials, represented by advanced high-strength steel (AHSS), have fully demonstrated their enormous potential to achieve energy conservation by reducing vehicle weight.

[0003] With the advancement of automotive lightweighting, the automotive industry's demand for ultra-high-strength steel is increasing. Hot forming technology has significant advantages in solving problems such as shape defects and high forming loads that easily occur when cold-working high-strength steel sheets. To prevent oxidation of the steel sheet surface during heating and to obtain better corrosion resistance, galvanizing processes, including hot-dip galvanizing and electro-galvanizing, are widely used. The application of galvanized high-strength steel in the automotive field inevitably requires joining technology. However, liquid metal embrittlement (LME) is prone to occur during subsequent hot working of galvanized high-strength steel, such as hot stamping and resistance spot welding, becoming one of the main obstacles to the application of galvanized high-strength steel in the automotive field.

[0004] Light metal ore (LME) occurs during resistance spot welding of typical galvanized high-strength steels such as DP, TRIP, TWIP, and QP steels, covering three generations of automotive high-strength steels. TWIP and QP steels exhibit higher LME crack susceptibility. This undoubtedly has a significant negative impact on the safety of galvanized automotive steel sheets during application. Therefore, researching the formation mechanism of LME cracks in the spot welding process of galvanized high-strength steel and developing countermeasures is urgently needed. While reasonable adjustments to the spot welding process and element control can mitigate LME cracking in galvanized high-strength steel to some extent, they do not fundamentally solve the LME problem.

[0005] This invention involves preheating and immersing a layer of Al before the existing hot-dip galvanizing process, followed by heat treatment to oxidize the Al layer, thereby generating a continuous, dense Al2O3 layer on the surface of the high-strength steel substrate that is not easily cracked during subsequent forming processes. The presence of the Al2O3 layer on the surface of the high-strength steel effectively prevents the intrusion of liquid Zn into the steel matrix during the forming process, thus eliminating the formation of LME (Liquid Metallic Electrode) during the high-strength steel forming process. Summary of the Invention

[0006] To address the existing technical problem of liquid metal embrittlement (LME) during the forming process of galvanized high-strength steel, this invention aims to overcome the shortcomings of existing technologies and provide a composite coating preparation process and its application that eliminates liquid metal embrittlement during the forming process of galvanized high-strength steel. Before the existing hot-dip galvanizing process, a layer of Al is preheated and deposited, followed by heat treatment to oxidize the Al layer, forming a continuous, dense Al2O3 layer on the surface of the high-strength steel substrate that is not easily cracked during subsequent forming processes. The presence of the Al2O3 layer on the surface of the high-strength steel effectively prevents the intrusion of liquid Zn into the steel substrate during the forming process, thus achieving the goal of eliminating LME formation during the high-strength steel forming process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel is disclosed. In the existing hot-dip galvanizing process, a layer of Al is preheated and dipped, and then the Al layer is oxidized by heat treatment to generate an Al2O3 layer on the surface of the high-strength steel substrate. This forms a composite coating with a structure of high-strength steel substrate surface-Al2O3 layer-galvanized layer. The Al2O3 layer acts as a protective layer to prevent Zn from penetrating into the high-strength steel substrate during the forming process, thereby eliminating the liquid metal embrittlement phenomenon during the forming process of galvanized high-strength steel.

[0008] Preferably, the thickness of the Al and Al2O3 layers formed on the surface of the high-strength steel is 0.01-5 μm.

[0009] Preferably, the Al2O3 layer formed on the surface of the high-strength steel is continuous, dense, and not easily cracked during subsequent forming processes.

[0010] Preferably, the aluminum plating solution used in the hot-dip aluminum plating process is mainly Al, and the aluminum solution may contain oxides, Si, rare earth elements and other substances or elements that are beneficial to Al plating.

[0011] Preferably, after hot-dip aluminizing, the obtained Al layer is further annealed to obtain high-strength steel containing an Al2O3 layer, and then hot-dip galvanized.

[0012] Preferably, the high-strength steel includes, but is not limited to, QP steel, TWIP steel, and other steel types.

[0013] Preferably, the composite coating preparation process of the present invention for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel includes the following steps: a. Clean the surface of the high-strength steel to be galvanized and set aside; b. Hot-dip Al is applied to high-strength steel, and the aluminum coating parameters are adjusted according to the actual situation; c. Heat-treat the high-strength steel with an Al layer to generate an Al2O3 layer on the surface of the high-strength steel substrate; d. Hot-dip galvanize the high-strength steel and adjust the galvanizing parameters according to the actual situation to form a composite coating with a high-strength steel substrate surface-Al2O3 layer-galvanized layer structure; Preferably, in step d, the parameters for controlling the hot-dip galvanizing parameters include at least one of the following: galvanizing temperature, galvanizing time, and dew point temperature.

[0014] The present invention relates to a new composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel. The process assesses the sensitivity of galvanized high-strength steel to liquid metal embrittlement during forming and adjusts spot welding and hot forming parameters according to actual conditions. Then, by comparing the sensitivity data of liquid metal embrittlement during resistance spot welding and hot forming of galvanized high-strength steel prepared by existing hot-dip galvanizing processes, a quantitative assessment result of the sensitivity to liquid metal embrittlement is obtained.

[0015] Preferably, the resistance spot welding parameter control includes at least one of the following parameters: welding current, welding voltage, holding time, cooling time, and number of pulses. Preferably, the thermoforming parameter control includes at least one parameter among thermoforming temperature and thermoforming time.

[0016] Preferably, the quantitative assessment result of the sensitivity to liquid metal embrittlement includes at least one conclusion: LME crack location and crack length. Preferably, by evaluating the LME sensitivity of galvanized high-strength steel forming process under different parameters, the test results show that the liquid metal embrittlement information of galvanized steel during the forming process can be effectively eliminated.

[0017] Compared with the prior art, the present invention has the following obvious and prominent substantive features and significant advantages: 1. The method of this invention can prepare a composite zinc coating that eliminates liquid metal embrittlement (LME) during the forming process of galvanized high-strength steel. Before hot-dip galvanizing the high-strength steel, a layer of Al is preheated and dip-coated, and then the Al layer is oxidized by heat treatment to generate an Al2O3 layer on the surface of the high-strength steel substrate. This forms a composite coating with a high-strength steel substrate surface-Al2O3 layer-galvanized layer structure. The Al2O3 layer acts as a protective layer to prevent Zn from penetrating into the high-strength steel substrate during the forming process, thus eliminating the liquid metal embrittlement phenomenon during the forming process of galvanized high-strength steel. 2. Compared with the traditional hot-dip galvanizing process, the present invention pre-plats an Al layer before hot-dip galvanizing. After hot-dip Al plating, annealing can be carried out to obtain high-strength steel containing an Al2O3 layer, and then conventional hot-dip galvanizing is performed. This method can meet the needs of composite zinc coatings for different high-strength steel varieties. 3. This invention provides a new composite coating process that eliminates LME during the forming process of high-strength steel. It can statistically analyze the LME sensitivity of galvanized high-strength steel under different forming conditions, providing reference data for improving the new composite coating process. This provides high-quality surface engineering solutions for the application of high-strength steel in automobiles and offers big data support for the development of new galvanized steel products. Attached Figure Description

[0018] Figure 1 This diagram compares the traditional and new hot-dip galvanizing processes. In the diagram, 1 represents the high-strength steel substrate, 2 represents the Al2O3 layer, and 3 represents the zinc plating layer. Detailed Implementation

[0019] The above solution will be further described below with reference to specific embodiments. The preferred embodiments of the present invention are described in detail below: Example 1

[0020] In this embodiment, a composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel involves preheating and immersing a layer of Al before hot-dip galvanizing the high-strength steel. Then, the Al layer is oxidized through heat treatment to generate an Al2O3 layer on the surface of the high-strength steel substrate, forming a composite coating structure of high-strength steel substrate surface - Al2O3 layer - galvanized layer. The Al2O3 layer acts as a protective layer, preventing the intrusion of Zn into the high-strength steel substrate during the forming process, thus eliminating the liquid metal embrittlement phenomenon during the forming process of galvanized high-strength steel.

[0021] In this embodiment, the method for preparing a new composite coating that eliminates the embrittlement of liquid metal during the forming process of galvanized high-strength steel includes the following steps: a. Clean the surface of the QP980 high-strength steel to be galvanized and set aside; b. Hot-dip Al is applied to high-strength steel at a temperature of about 700℃, and the Al layer thickness is adjusted to about 2μm based on the actual situation. c. Heat-treat the high-strength steel with an Al layer to generate an Al2O3 layer on the surface of the high-strength steel substrate; d. Hot-dip galvanize the high-strength steel at a temperature of 455-460℃, and adjust the galvanizing parameters according to the actual situation to form a composite coating structure of QP980 steel substrate surface-Al2O3 layer-galvanized layer.

[0022] Experimental test analysis

[0023] QP980 high-strength steel obtained by traditional hot-dip galvanizing and the new hot-dip galvanizing process were selected respectively, and corresponding spot welded joints were obtained under resistance spot welding process conditions. At least three spot welded joints under the same process conditions were selected to ensure the reliability of the test data. The resistance spot welding sample was wire-cut to cut out the sample containing all the welding feature areas of the spot weld joint. The cut sample was then surface-washed to prevent foreign matter from interfering with the test results. The washed sample was then dried. The dried sample was polished, and then high-resolution panoramic images of the polished surface were taken under a metallographic microscope. Comparison of LME cracking in resistance spot welded joints of QP980 steel under traditional hot-dip galvanizing and new hot-dip galvanizing processes.

[0024] This embodiment provides a novel composite coating process to eliminate liquid metal embrittlement (LME) during the forming process of galvanized high-strength steel. Figure 1 This diagram illustrates traditional and novel hot-dip galvanizing processes. In the diagram, 1 represents a high-strength steel substrate, 2 represents an Al2O3 layer, and 3 represents a galvanized layer. In this embodiment, the Al2O3 layer formed on the high-strength steel surface is continuous, dense, and resistant to cracking during subsequent forming processes. The beneficial effect of this embodiment is that it eliminates liquid metal embrittlement (LME) during the forming process of galvanized high-strength steel. It is applicable to the hot-dip galvanizing process of various automotive high-strength steels. By evaluating the LME sensitivity of galvanized high-strength steel forming processes under different parameters, the test results show that this invention can effectively eliminate LME in galvanized steel during the forming process, and the entire testing process is simple and efficient. Example 2

[0025] This embodiment is basically the same as Embodiment 1: In this embodiment, a composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel involves preheating and immersing a layer of Al before hot-dip galvanizing the high-strength steel. Then, the Al layer is oxidized through heat treatment to generate an Al2O3 layer on the surface of the high-strength steel substrate, forming a composite coating structure of high-strength steel substrate surface - Al2O3 layer - galvanized layer. The Al2O3 layer acts as a protective layer, preventing the intrusion of Zn into the high-strength steel substrate during the forming process, thus eliminating the liquid metal embrittlement phenomenon during the forming process of galvanized high-strength steel.

[0026] In this embodiment, the method for preparing a new composite coating that eliminates the embrittlement of liquid metal during the forming process of galvanized high-strength steel includes the following steps: a. Clean the surface of the TWIP high-strength steel to be galvanized and set aside; a. Clean the surface of the TWIP high-strength steel to be galvanized and set aside; b. Hot-dip Al is applied to high-strength steel at a temperature of about 700℃, and the Al layer thickness is adjusted to about 2μm based on the actual situation. c. Heat-treat the high-strength steel with an Al layer to generate an Al2O3 layer on the surface of the high-strength steel substrate; d. Hot-dip galvanize the high-strength steel at a temperature of 455-460℃, and adjust the galvanizing parameters according to the actual situation to form a composite coating with a structure of TWIP steel substrate surface-Al2O3 layer-galvanized layer.

[0027] Experimental test analysis

[0028] High-strength steel obtained by traditional hot-dip galvanizing and new hot-dip galvanizing processes were selected respectively, and tensile tests were conducted at 900-950℃ to obtain samples under the corresponding hot-dip galvanizing process. At least three samples under the same process conditions were selected to ensure the reliability of the test data. The thermoformed specimen is wire-cut to cut out a specimen containing all the characteristic areas. The cut specimen is then surface-washed to prevent foreign matter from interfering with the test results. The washed specimen is then dried. The dried sample was polished, and then high-resolution panoramic images of the polished surface were taken under a metallographic microscope. Comparing the LME cracking of high-strength steel during high-temperature tensile testing under traditional hot-dip galvanizing and new hot-dip galvanizing processes.

[0029] This embodiment provides a novel composite coating process to eliminate liquid metal embrittlement (LME) during the forming process of galvanized high-strength steel. The Al2O3 layer formed on the surface of the high-strength steel in this embodiment is continuous, dense, and resistant to cracking during subsequent forming processes. The beneficial effect of this embodiment is that it can eliminate the LME phenomenon during the forming process of galvanized high-strength steel. It is applicable to the hot-dip galvanizing process of various automotive high-strength steels. By evaluating the LME sensitivity of galvanized high-strength steel during the forming process under different parameters, the test results show that this invention can effectively eliminate LME in galvanized steel during the forming process, and the entire testing process is simple and efficient. Example 3

[0030] This embodiment is basically the same as the previous embodiments: In this embodiment, a novel composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel is applied. The sensitivity of the galvanized high-strength steel to liquid metal embrittlement during the forming process is evaluated, and spot welding parameters and hot forming parameters are adjusted according to the actual situation. Then, the sensitivity data of liquid metal embrittlement during resistance spot welding and hot forming processes of galvanized high-strength steel prepared by the existing hot-dip galvanizing process are compared to obtain a quantitative evaluation result of the sensitivity to liquid metal embrittlement.

[0031] In this embodiment, the resistance spot welding parameter control includes at least one of the following parameters: welding current, welding voltage, holding time, cooling time, and number of pulses. In this embodiment, the thermoforming parameter control includes at least one of thermoforming temperature and thermoforming time.

[0032] In this embodiment, the quantitative assessment result of the sensitivity to liquid metal embrittlement includes at least one conclusion: LME crack location and crack length. In this embodiment, by evaluating the LME sensitivity of the forming process of galvanized high-strength steel under different parameters, the test results show that the liquid metal embrittlement information of galvanized steel during the forming process can be effectively eliminated.

[0033] This embodiment describes resistance spot welding and hot forming of hot-dip galvanized high-strength steel, adjusting the welding and hot forming parameters according to actual conditions. It compares the low surface area (LME) sensitivity of galvanized high-strength steel during resistance spot welding and hot forming with existing hot-dip galvanizing processes. This embodiment eliminates LME during the high-strength steel forming process with a novel composite coating process. It can statistically analyze the LME sensitivity of galvanized high-strength steel under different forming conditions, providing reference data for improving the novel composite coating process. This offers high-quality surface engineering solutions for the application of high-strength steel in automobiles and provides big data support for the development of new galvanized steel products, possessing significant industrial application value.

[0034] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent substitutions. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite coating that eliminates the embrittlement of liquid metal during the forming process of galvanized high-strength steel, characterized in that: Before hot-dip galvanizing high-strength steel, a layer of Al is preheated and then oxidized through heat treatment to form an Al2O3 layer on the surface of the high-strength steel substrate. This forms a composite coating with a structure of high-strength steel substrate surface - Al2O3 layer - zinc coating. The Al2O3 layer acts as a protective layer to prevent Zn from penetrating into the high-strength steel substrate during the forming process, thus eliminating the phenomenon of liquid metal embrittlement during the forming process of galvanized high-strength steel.

2. The method for preparing a composite coating to eliminate liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 1, characterized in that: Before hot-dip galvanizing high-strength steel, a layer of Al is preheated and dipped. The main component of the hot-dip aluminum galvanizing solution is Al, while the aluminum solution also contains oxides, Si, and rare earth substances or elements that are beneficial to Al plating.

3. The method for preparing a composite coating to eliminate liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 1, characterized in that: The thickness of the Al layer preheated and dip-coated on the surface of the high-strength steel is 0.01-5 μm.

4. The method for preparing a composite coating to eliminate liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 1, characterized in that: The Al2O3 layer formed on the surface of the high-strength steel is continuous, dense, and not easily broken in subsequent forming processes.

5. The method for preparing a composite coating to eliminate liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 1, characterized in that: The high-strength steel is either QP steel or TWIP steel.

6. The method for preparing a composite coating to eliminate liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 1, characterized in that, It includes the following steps: a. Clean the surface of the high-strength steel to be galvanized and set aside; b. Hot-dip Al is applied to high-strength steel, and the aluminum coating parameters are adjusted according to the actual situation; c. Heat-treat the high-strength steel with an Al layer to generate an Al2O3 layer on the surface of the high-strength steel substrate; d. Hot-dip galvanize the high-strength steel and adjust the galvanizing parameters to form a composite coating with a high-strength steel substrate surface-Al2O3 layer-galvanized layer structure.

7. The application of the composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel as described in claim 1, characterized in that: The sensitivity of galvanized high-strength steel to liquid metal embrittlement during the forming process was evaluated, and spot welding parameters and hot forming parameters were adjusted. Then, by comparing the sensitivity data of liquid metal embrittlement during resistance spot welding and hot forming of galvanized high-strength steel prepared by existing hot-dip galvanizing processes, quantitative assessment results of the sensitivity of liquid metal embrittlement were obtained.

8. The application of the composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 7, characterized in that: The spot welding parameter control includes at least one of the following parameters: welding current, welding voltage, holding time, cooling time, and number of pulses. The thermoforming parameter control includes at least one of thermoforming temperature and thermoforming time.

9. The application of the composite coating preparation process for eliminating liquid metal embrittlement during the forming process of galvanized high-strength steel according to claim 7, characterized in that: The quantitative assessment results of the sensitivity to liquid metal embrittlement include at least one conclusion: LME crack location and crack length.

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