A medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet and its preparation method

Abstract

The present invention provides a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet and a preparation method thereof, belonging to the field of metal material forming. The preparation method specifically comprises: preparing a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy composite thick plate using a double explosive welding method; cutting a blank from the composite thick plate, and sequentially performing multiple hot rolling, annealing, multiple cold rolling, and annealing to obtain a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet. The composite sheet obtained by this method has a tight interface, uniform thickness, and a simple production process, making it suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet and a preparation method thereof, and belongs to the field of metal material forming. Background Art

[0002] Q235B steel, a common low-carbon steel, is widely used in vehicles, construction, and shipbuilding. However, the alloy is highly susceptible to oxidation and corrosion, requiring rust-proof treatments such as hot-dip galvanizing, chromium plating, zinc plating, or nickel plating. However, plating treatments only improve the corrosion resistance of Q235B steel and do not enhance its strength. Furthermore, with increasing environmental awareness, highly polluting electroplating processes are gradually being phased out. Therefore, there is an urgent need to develop new technologies to enhance the surface corrosion resistance of Q235B steel. CoCrNi medium-entropy alloys, a novel high-performance metal structural and functional integrated material, offer advantages such as high hardness, high strength, and resistance to high-temperature oxidation, corrosion, and radiation. They also exhibit excellent corrosion resistance in HCl solutions. Composite sheets composed of a CoCrNi medium-entropy alloy surface layer and a Q235B steel intermediate layer can significantly extend the service life of Q235B steel in applications such as vehicles and ships and expand its use to highly corrosive environments such as the petroleum and chemical industries.

[0003] Combining explosive bonding and rolling is currently one of the most prevalent methods for producing layered metal composites. Numerous patents and literature reports describe the use of explosive bonding and rolling to produce dissimilar metal layered composites. However, due to the significant differences in the properties of different materials, both the explosive bonding and rolling processes require unique technical parameters, and the interaction between the two techniques must also be considered. Consequently, the process parameters of existing technologies are difficult to universally apply.

[0004] Since there is currently no reference for the preparation technology of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy three-layer composite thin plates, it is urgent to develop a technology that meets the requirements of explosive welding + rolling to prepare thin plates of this composite material. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the first object of the present invention is to provide a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet. The medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet provided by the present invention comprises a CoCrNi alloy with an equiatomic ratio, and the upper and lower medium-entropy alloy layers have equal thicknesses of 0.12 to 0.3 mm, resulting in a total composite sheet thickness of 1 to 3 mm.

[0006] The second object of the present invention is to provide a method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate. The present invention adopts the technology of explosive welding + rolling. The preparation method is simple and controllable and suitable for industrial production.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] The present invention provides a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate, wherein the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate consists of a medium-entropy alloy upper layer, a medium-entropy alloy lower layer, and a Q235B steel middle layer, wherein the thickness of the medium-entropy alloy upper layer and the medium-entropy alloy lower layer are both 0.12-0.3 mm, and the thickness of the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate is 1-3 mm, and the medium-entropy alloys in the medium-entropy alloy upper layer and the medium-entropy alloy lower layer are both CoCrNi alloys, wherein Co, Cr, and Ni have an equiatomic ratio.

[0009] The medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet provided by the present invention has medium-entropy alloy layers on both sides of the Q235B steel middle layer. The CoCrNi medium-entropy alloy has the advantages of high hardness, high strength, high-temperature oxidation resistance, corrosion resistance, and radiation resistance. It can greatly improve the corrosion resistance of Q235B steel and broaden its application range.

[0010] In a preferred embodiment, the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet has a room temperature yield strength greater than 450 MPa, a tensile strength greater than 550 MPa, and an elongation greater than 8%.

[0011] The present invention provides a method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate, comprising the following steps: performing two explosion welding operations on two CoCrNi medium-entropy alloy plates and a Q235B steel plate to obtain a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy three-layer composite thick plate; preheating the CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy three-layer composite thick plate; hot-rolling the plate to obtain a hot-rolled plate; annealing the hot-rolled plate to obtain an annealed hot-rolled plate; cold-rolling the plate to obtain a cold-rolled plate; and finally annealing the cold-rolled plate to obtain a second annealing to obtain the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate.

[0012] During the hot rolling, the rolling speed is controlled to be 10-15 m / min, and the deformation per pass is 20-30%;

[0013] During the cold rolling, the rolling speed is controlled to be 30-40 m / min, and the deformation amount per pass is 8-10%.

[0014] The preparation method of the present invention adopts the technology of explosive welding + rolling. First, two explosive weldings are performed to obtain a three-layer composite thick plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy with good welding interface bonding and uniform thickness. In the subsequent rolling process, during hot rolling, the excellent plastic deformation ability of CoCrNi medium entropy alloy and Q235B steel at high temperature is utilized, and a low speed + large deformation amount process is adopted, which not only avoids cracking of the bonding surface but also improves production efficiency. During cold rolling, the excellent work hardening ability of the medium entropy alloy is utilized, and a high speed + small deformation amount process is selected to increase the number of deformation passes, so that the medium entropy alloy is fully work hardened, thereby improving the overall mechanical properties of the composite plate.

[0015] As a preferred solution, a Q235B steel plate is first used as a substrate and a CoCrNi medium entropy alloy plate is used as a composite plate for a first explosive welding to obtain a CoCrNi medium entropy alloy / Q235B steel composite plate. Then, the CoCrNi medium entropy alloy / Q235B steel composite plate is used as a substrate and a CoCrNi medium entropy alloy plate is used as a composite plate. The Q235B steel layer in the CoCrNi medium entropy alloy / Q235B steel composite plate is controlled to contact the CoCrNi medium entropy alloy plate, and a second explosive welding is performed to obtain a CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy three-layer composite thick plate.

[0016] As a preferred solution, the thickness of the two CoCrNi medium entropy alloy plates is 1.5-5 mm, and the thickness of the Q235B steel plate is 10-50 mm.

[0017] As a preferred solution, the two CoCrNi medium entropy alloy plates are first subjected to annealing treatment, the annealing temperature is 1000-1100° C., and the annealing time is 1-2 hours.

[0018] By completely softening and annealing the medium entropy alloy plate within the above parameters, the alloy is given good plasticity, ensuring that the explosion process can easily achieve metallurgical bonding of the material without cracking.

[0019] In a preferred embodiment, the Q235B steel plate is a Q235B hot-rolled steel plate. In the present invention, commercially available Q235B hot-rolled steel plate is used, which has good plasticity and medium strength and can be metallurgically bonded with the softened CoCrNi medium entropy alloy plate through explosive compounding.

[0020] As a preferred embodiment, the explosives used for explosive welding are composed of the following by mass percentage: 60-65% antimony-free rock ammonium nitrate explosive, 8-10% calcium carbonate powder, 10-12% perlite powder, 5-8% sawdust, and 8-10% sodium chloride.

[0021] The explosive of the present invention uses antimony-free rock ammonium nitrate as a basic explosive. Calcium carbonate and sodium chloride are added to the basic explosive to reduce the detonation velocity of the explosive. Perlite powder and wood chips are added to increase the fluffiness, which is beneficial for detonation. With the cooperation of the above explosive components, explosive welding of CoCrNi medium-entropy alloy / Q235B steel can be achieved, and the welding interface is well bonded. The three-layer composite thick plate of CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy obtained by explosive welding is rolled to obtain a thin plate with a flat interface, uniform layer thickness, good quality, and excellent mechanical properties.

[0022] Further preferably, the explosive used for the explosive welding is composed of the following by mass percentage: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% sawdust, and 9% sodium chloride.

[0023] During the actual operation, the parts with poor bonding around the explosively composite thick plate are removed, and the blank with good interface bonding in the middle is cut for rolling.

[0024] As a preferred solution, the preheating temperature is 880-900°C and the holding time is 60-120 minutes. Hot rolling is carried out directly after preheating.

[0025] As a preferred solution, the total variable of the hot rolling is ≥80%.

[0026] As a preferred solution, the temperature of the first annealing is 750-780° C., and the holding time is 60-90 minutes.

[0027] As a preferred solution, the temperature of the second annealing is 550-600° C., and the holding time is 60-70 minutes.

[0028] In the present invention, the material is brought into a completely soft state through the first annealing, so the temperature is preferably the upper limit of the recrystallization temperature, that is, as high a temperature as possible without causing excessive grain growth. The purpose of the second annealing is to regulate the performance, and the lower limit of the recrystallization temperature is selected, so that recrystallization can be achieved while ensuring fine grains.

[0029] In industrial production, the annealed cold-rolled sheets need to be trimmed and slit to obtain the required size of the final product.

[0030] Beneficial effects

[0031] The present invention optimizes the explosive composition and controls the rolling process, and adopts the technology of explosive welding + rolling to realize the preparation of a three-layer composite thin plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy. The composite plate has good interface bonding and uniform thickness. After multiple experiments, the present invention has explored an explosive composition that can realize explosive welding of CoCrNi medium entropy alloy / Q235B steel, and the welding interface is well bonded. And two explosive weldings using the same process are used to prepare a three-layer composite thick plate, providing a blank for subsequent rolling. The hot rolling process utilizes the excellent plastic deformation ability of CoCrNi medium entropy alloy and Q235B steel at high temperature, and adopts a process of low speed + large deformation amount, which not only avoids cracking of the bonding surface, but also improves production efficiency. The excellent work hardening ability of the medium entropy alloy is utilized in the cold rolling process, and a process of high speed + small deformation amount is selected to increase the deformation pass, so that the medium entropy alloy can fully undergo work hardening, thereby improving the overall mechanical properties of the composite plate.

[0032] The above process and parameter selection ensure that the room temperature yield strength of the CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy three-layer composite thin plate prepared by the present invention is greater than 450 MPa, the tensile strength is greater than 550 MPa, and the elongation is greater than 8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of the three-layer composite material sheet of the present invention;

[0034] Figure 2 The three-layer composite material sheet sample in Example 1 of the present invention;

[0035] Figure 3 The cross-sectional view of the composite sheet along the thickness direction in Example 1 of the present invention shows that the obtained interface is a straight interface. DETAILED DESCRIPTION

[0036] The following are preferred embodiments of the present invention, but not all embodiments. Without departing from the principle of this process innovation, any equivalent process transformation made by utilizing the contents of the present invention specification, or directly or indirectly applied in other related technical fields, shall be deemed to be within the scope of patent protection of this invention.

[0037] Example 1

[0038] CoCrNi medium entropy alloy plates and commercially available hot-rolled Q235B steel plates that had been fully softened and annealed at 1000°C for 2 hours were selected as raw materials and the following steps were followed:

[0039] S1. A Q235B steel plate measuring 500 mm × 800 mm in length, 10 mm in thickness, and a CoCrNi medium-entropy alloy plate measuring 520 mm × 820 mm in length, 1.5 mm in thickness were selected for the first explosive welding. The composite plate obtained from the first explosive welding was then used as the base plate, and a CoCrNi medium-entropy alloy plate measuring 520 mm × 820 mm in length, 1.5 mm in thickness was used for the second explosive welding. The bonding surface was the medium-entropy alloy and the steel. The explosive composition and volume ratio used for the explosive welding were: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% sawdust, and 9% sodium chloride. 5% water was added by volume before use, mixed thoroughly, and then the explosive was applied to a thickness of 55 mm. After explosive welding, a three-layer composite plate of CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy with a total thickness of 13 mm was obtained.

[0040] S2. Cut a 300mm x 500mm long x wide billet to be rolled from the center of the explosively welded thick plate.

[0041] S3. Place the billet to be rolled in a heating furnace at 880°C and keep it at this temperature for 60 minutes.

[0042] S4. After the insulation, hot rolling was performed directly at a controlled rolling speed of 15 m / min, a pass deformation of 30%, and a total deformation of 81%, to obtain a three-layer composite hot-rolled plate with a thickness of 2.5 mm.

[0043] S5. Place the hot-rolled plate in an annealing furnace at 750°C for 60 minutes and then air-cool.

[0044] S6. The annealed composite plate is subjected to multiple cold rolling passes at a controlled rolling speed of 40 m / min and a pass deformation of 10%. Rolling is stopped when the billet thickness reaches 1 mm.

[0045] S7. The cold-rolled sheet was subjected to stress relief annealing at 550°C for 60 min and then naturally cooled to obtain a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy three-layer composite sheet.

[0046] The resulting composite sheet has a total thickness of 1 mm, with the upper and lower layers of CoCrNi medium-entropy alloy measuring 0.12 mm thick and the middle layer of Q235B steel 0.76 mm thick. The composite sheet has a yield strength of 520 MPa, a tensile strength of 615 MPa, and an elongation of 8.6%.

[0047] Example 2

[0048] CoCrNi medium entropy alloy plates and commercially available hot-rolled Q235B steel plates that had been fully softened and annealed at 1000°C for 2 hours were selected as raw materials and the following steps were followed:

[0049] S1. A Q235B steel plate measuring 500 mm x 800 mm and 50 mm thick was selected as the base plate, and a CoCrNi medium-entropy alloy plate measuring 520 mm x 820 mm and 5 mm thick was selected as the secondary plate for the first explosive welding. The secondary explosive welding was then performed using the secondary plate obtained from the first explosive welding as the base plate, and a CoCrNi medium-entropy alloy plate measuring 520 mm x 820 mm and 5 mm thick was selected as the secondary plate. The bonding surface was the medium-entropy alloy and the steel. The explosive composition and volume ratio used for the explosive welding were: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% sawdust, and 9% sodium chloride. Before use, 5% water was added by volume, mixed thoroughly, and then the explosive was applied to a thickness of 65 mm. After explosive welding, a three-layer composite plate of CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy with a total thickness of 60 mm was obtained.

[0050] S2. Cut a 300mm x 500mm long x wide billet to be rolled from the center of the explosively welded thick plate.

[0051] S3. Place the billet to be rolled in a heating furnace at 900°C and keep it at this temperature for 120 minutes.

[0052] S4. After the insulation, hot rolling was directly carried out at a controlled rolling speed of 10 m / min, a pass deformation of 20%, and a total deformation of 85%, to obtain a three-layer composite hot-rolled plate with a thickness of 9 mm.

[0053] S5. Place the hot-rolled plate in an annealing furnace at 780°C for 90 minutes and then air-cool.

[0054] S6. The annealed composite plate is subjected to multiple cold rolling passes at a controlled rolling speed of 30 m / min and a pass deformation of 8%. Rolling is stopped when the billet thickness reaches 3 mm.

[0055] S7. The cold-rolled sheet was subjected to stress relief annealing at 600°C for 60 min and then naturally cooled to obtain a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy three-layer composite sheet.

[0056] The resulting composite sheet has a total thickness of 3 mm, with the upper and lower layers of CoCrNi medium-entropy alloy being 0.3 mm thick and the middle layer of Q235B steel being 2.4 mm thick. The composite sheet has a yield strength of 458 MPa, a tensile strength of 552 MPa, and an elongation of 10.4%.

[0057] Example 3

[0058] CoCrNi medium entropy alloy plates and commercially available hot-rolled Q235B steel plates that had been fully softened and annealed at 1000°C for 2 hours were selected as raw materials, and the following steps were followed:

[0059] S1. A Q235B steel plate measuring 500 mm × 800 mm in length, 40 mm in thickness, was selected as the base plate, and a CoCrNi medium-entropy alloy plate measuring 520 mm × 820 mm in length, 3 mm in thickness was selected for the first explosive welding. The composite plate obtained from the first explosive welding was then used as the base plate, and a CoCrNi medium-entropy alloy plate measuring 520 mm × 820 mm in length, 3 mm in thickness was selected for the second explosive welding. The bonding interface was the medium-entropy alloy and the steel. The explosive composition and volume ratio used for the explosive welding were: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% sawdust, and 9% sodium chloride. 5% water was added by volume before use, mixed thoroughly, and then the explosive was applied to a thickness of 65 mm. After explosive welding, a three-layer composite plate of CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy with a total thickness of 46 mm was obtained.

[0060] S2. Cut a 300mm x 500mm long x wide billet to be rolled from the center of the explosively welded thick plate.

[0061] S3. Place the billet to be rolled in a heating furnace at 900°C and keep it at this temperature for 80 minutes.

[0062] S4. After the insulation, hot rolling was performed directly at a controlled rolling speed of 12 m / min, a pass deformation of 25%, and a total deformation of 82.6%, resulting in a three-layer composite hot-rolled plate with a thickness of 8 mm.

[0063] S5. Place the hot-rolled plate in an annealing furnace at 780°C for 70 minutes and then air-cool.

[0064] S6. The annealed composite plate is subjected to multiple cold rolling passes at a controlled rolling speed of 35 m / min and a pass deformation of 10%. Rolling is stopped when the billet thickness reaches 2 mm.

[0065] S7. The cold-rolled sheet was subjected to stress relief annealing at 550°C for 60 min and then naturally cooled to obtain a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy three-layer composite sheet.

[0066] The resulting composite sheet has a total thickness of 2 mm, with the upper and lower layers of CoCrNi medium-entropy alloy being 0.15 mm thick and the middle layer of Q235B steel being 1.7 mm thick. The composite sheet has a yield strength of 515 MPa, a tensile strength of 603 MPa, and an elongation of 9.2%.

[0067] Example 4

[0068] CoCrNi medium entropy alloy plates that had been completely softened and annealed at 1000°C for 2 hours and commercially available hot-rolled Q235B steel plates were selected as raw materials, and the following steps were followed:

[0069] S1. A Q235B steel plate measuring 500 mm × 800 mm in length, 30 mm in thickness, and a CoCrNi medium-entropy alloy plate measuring 520 mm × 820 mm in length, 2.5 mm in thickness were selected for the first explosive welding. The composite plate obtained from the first explosive welding was then used as the base plate, and a CoCrNi medium-entropy alloy plate measuring 520 mm × 820 mm in length, 2.5 mm in thickness was used for the second explosive welding. The bonding surface was the medium-entropy alloy and the steel. The explosive composition and volume ratio used for the explosive welding were: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% sawdust, and 9% sodium chloride. Before use, 5% water was added by volume, mixed thoroughly, and then the explosive was applied to a thickness of 65 mm. After the explosive welding, a three-layer composite plate of CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy with a total thickness of 35 mm was obtained.

[0070] S2. Cut a 300mm x 500mm long x wide billet to be rolled from the center of the explosively welded thick plate.

[0071] S3. Place the billet to be rolled in a heating furnace at 890°C and keep it at this temperature for 70 minutes.

[0072] S4. After the insulation, hot rolling was directly carried out at a controlled rolling speed of 14 m / min, a pass deformation of 22%, and a total deformation of 82.9%, to obtain a three-layer composite hot-rolled plate with a thickness of 6 mm.

[0073] S5. Place the hot-rolled plate in an annealing furnace at 760°C for 80 minutes and then air-cool.

[0074] S6. The annealed composite plate is subjected to multiple cold rolling passes at a controlled rolling speed of 38 m / min and a pass deformation of 10%. Rolling is stopped when the billet thickness reaches 2 mm.

[0075] S7. The cold-rolled sheet was subjected to stress relief annealing at 550°C for 60 min and then naturally cooled to obtain a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy three-layer composite sheet.

[0076] The resulting composite sheet has a total thickness of 2.5 mm, with the upper and lower layers of CoCrNi medium-entropy alloy being 0.18 mm thick and the middle layer of Q235B steel being 2.14 mm thick. The composite sheet has a yield strength of 462 MPa, a tensile strength of 558 MPa, and an elongation of 9.4%.

[0077] Comparative Example 1

[0078] All other conditions were the same as in Example 1, except that the CoCrNi medium-entropy alloy was not annealed before explosive cladding, meaning the composite plate material was a hard CoCrNi medium-entropy alloy. Because hard medium-entropy alloys have high strength but poor plasticity, they cannot withstand strong plastic deformation during explosive cladding. Therefore, after the explosion, the strong impact force generated by the explosives caused the medium-entropy alloy composite plate to rupture, resulting in composite failure.

[0079] Comparative Example 2

[0080] Other conditions were the same as in Example 1, except that the explosive composition was changed to 50% antimony-free rock ammonium nitrate explosive, 10% calcium carbonate powder, 15% perlite powder, 10% sawdust, and 10% sodium chloride. Reducing the main antimony-free rock ammonium nitrate explosive component and increasing the content of other ingredients resulted in a lower detonation velocity of the explosive, making it impossible to achieve interfacial metallurgical bonding during the explosion process, resulting in composite failure.

[0081] Comparative Example 3

[0082] Other conditions are the same as those in Example 1. Only during hot rolling, the rolling speed is modulated to 20 m / min. As the rolling speed increases, the rolling force increases, the friction between the plate surface and the roller also increases, and the shear stress between the layers of the composite plate increases, resulting in interface cracking during rolling and rolling failure.

[0083] Comparative Example 4

[0084] Other conditions were the same as those in Example 1. Only during cold rolling, the deformation per rolling pass was increased to 20%. The deformation per rolling pass increased, and the degree of uneven deformation of the Q235B steel and the entropy alloy in CoCrNi increased. During rolling, the plate underwent severe wavy bending, resulting in rolling failure.

Claims

1. A method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet, characterized by: First, a Q235B steel plate is used as a substrate and a CoCrNi medium entropy alloy plate is used as a composite plate for a first explosion welding to obtain a CoCrNi medium entropy alloy / Q235B steel composite plate, and then the CoCrNi medium entropy alloy / Q235B steel composite plate is used as a substrate and a CoCrNi medium entropy alloy plate is used as a composite plate, and the Q235B steel layer in the CoCrNi medium entropy alloy / Q235B steel composite plate is controlled to contact the CoCrNi medium entropy alloy plate, and a second explosion welding is performed to obtain a CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy three-layer composite thick plate, the CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy three-layer composite thick plate is preheated, and then hot rolled to obtain a hot-rolled plate, the hot-rolled plate is annealed for a first time to obtain an annealed hot-rolled plate, and then cold rolled to obtain a cold-rolled plate, and finally the cold-rolled plate is annealed for a second time to obtain a medium entropy alloy / Q235B steel / medium entropy alloy three-layer composite thin plate; During the hot rolling, the rolling speed is controlled to be 10-15 m / min, and the deformation per pass is 20-30%; During the cold rolling, the rolling speed is controlled to be 30-40 m / min, and the deformation per pass is 8-10%; Both CoCrNi medium entropy alloy plates are first annealed at a temperature of 1000-1100° C. for 1-2 h. The Q235B steel plate is a Q235B hot-rolled steel plate; The explosives used in the explosive welding are composed of the following by mass percentage: 60-65% antimony-free rock ammonium nitrate explosive, 8-10% calcium carbonate powder, 10-12% perlite powder, 5-8% sawdust, and 8-10% sodium chloride; The preheating temperature is 880-900°C and the holding time is 60-120 minutes; The total variable of the hot rolling is ≥80%; The first annealing temperature is 750-780°C, and the holding time is 60-90 minutes; The second annealing temperature is 550-600°C and the holding time is 60-70 minutes; The medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet consists of a medium-entropy alloy upper layer, a medium-entropy alloy lower layer, and a Q235B steel middle layer, wherein the thickness of the medium-entropy alloy upper layer and the medium-entropy alloy lower layer are both 0.12~0.3mm, the thickness of the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet is 1~3mm, and the medium-entropy alloys in the medium-entropy alloy upper layer and the medium-entropy alloy lower layer are both CoCrNi alloys, wherein Co, Cr, and Ni are in equal atomic ratios.

2. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 1, characterized in that: The thickness of the two CoCrNi medium entropy alloy plates is 1.5~5mm, and the thickness of the Q235B steel plate is 10~50mm.

3. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 1, characterized in that: The medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate has a room temperature yield strength greater than 450 MPa, a tensile strength greater than 550 MPa, and an elongation greater than 8%.

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