Medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet and preparation method thereof

Abstract

The invention provides 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. The preparation method specifically comprises the following steps: preparing a CoCrNi medium-entropy alloy / Q235B steel / CoCrNi medium-entropy alloy composite thick plate by adopting a two-time explosive welding method; and a blank is cut from the composite thick plate and sequentially subjected to multi-pass hot rolling, annealing, multi-pass cold rolling and annealing, and the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate is obtained. The composite thin plate obtained by the method is tight in interface bonding, uniform in thickness, simple in production process and suitable for industrial production.

Description

Technical Field

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

[0002] Q235B steel is one of the most common low-carbon steels and is widely used in vehicles, buildings, ships and other fields. However, the alloy is easily oxidized and corroded, and needs to be rust-proofed when used, such as hot-dip galvanizing, chrome plating, zinc plating or nickel plating. However, the coating treatment only improves the corrosion resistance of Q235B, but does not improve the strength of the material. Moreover, with the enhancement of environmental awareness, the highly polluting electroplating treatment is gradually banned. Therefore, it is urgent to develop a new technology to improve the surface corrosion resistance of Q235B steel. As a new type of high-performance metal structural functional integrated material, CoCrNi medium-entropy alloy has the advantages of high hardness, high strength, high-temperature oxidation resistance, corrosion resistance and radiation resistance, and even shows excellent corrosion resistance in HCl solution. The composite sheet with CoCrNi medium-entropy alloy and Q235B steel is prepared by compounding the surface layer of CoCrNi medium-entropy alloy and the middle layer of Q235B steel, which can not only significantly improve the service life of Q235B steel in the fields of vehicles and ships, but also further expand the scope of use to highly corrosive environments such as petroleum and chemical industry.

[0003] Combining explosive compounding and rolling is currently one of the most important methods for preparing layered metal composite materials. A large number of patents and literature have reported the technology of using explosive compounding + rolling to prepare heterogeneous metal layered composite materials. However, due to the great differences in the performance of different materials, both the explosive welding process and the rolling process need to match specific technical parameters, and the mutual influence between the two technologies also needs to be considered. Therefore, the process parameters of the existing technology are difficult to be universal.

[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 can meet the requirements of explosive welding + rolling to prepare thin plates of this composite material. Summary of the invention

[0005] In view of 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 thin plate. The medium entropy alloy / Q235B steel / medium entropy alloy three-layer composite thin plate provided by the present invention, the medium entropy alloy is an equiatomic ratio CoCrNi alloy, the thickness of the upper and lower layers of medium entropy alloy is equal, which is 0.12~0.3mm, and the total thickness of the composite thin plate is 1~3mm.

[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 scheme:

[0008] The 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, 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 are in equal atomic ratios.

[0009] The medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate 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, which can greatly improve the corrosion resistance of Q235B steel and broaden the scope of application.

[0010] According to a preferred embodiment, 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%.

[0011] The invention provides a method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate, comprising: 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, and then performing hot rolling to obtain a hot-rolled plate, performing a first annealing on the hot-rolled plate to obtain an annealed hot-rolled plate, and then performing cold rolling to obtain a cold-rolled plate, and finally performing a second annealing on the cold-rolled plate 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 amount 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, firstly, 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 is obtained by two explosion weldings, and in the subsequent rolling process, the excellent plastic deformation ability of CoCrNi medium entropy alloy and Q235B steel at high temperature is utilized during hot rolling, and a process of low speed + large deformation amount is adopted, which not only avoids cracking of the bonding surface but also improves production efficiency, and the excellent work hardening ability of the medium entropy alloy is utilized during cold rolling, and a process of high speed + small deformation amount is selected to increase the deformation passes, so that the medium entropy alloy is fully work hardened, and the overall mechanical properties of the composite plate are improved.

[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 the 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.

[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 has good plasticity, ensuring that the explosion process can easily achieve metallurgical bonding of the material without cracking.

[0019] In a preferred solution, the Q235B steel plate is a Q235B hot-rolled steel plate. In the present invention, a 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 the explosive welding are composed, by mass percentage, of 60-65% antimony-free rock ammonium nitrate explosive, 8-10% calcium carbonate powder, 10-12% perlite powder, 5-8% wood chips, and 8-10% sodium chloride.

[0021] The explosive of the present invention uses antimony-free rock ammonium nitrate as a basic explosive. Adding calcium carbonate and sodium chloride into the basic explosive can reduce the detonation velocity of the explosive. Adding perlite powder and crushed wood chips can improve the fluffiness and facilitate 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, by mass percentage, of 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% wood chips, and 9% sodium chloride.

[0023] In the actual operation process, the parts with poor bonding around the explosive composite thick plate are removed, and the billet 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. After the preheating is completed, hot rolling is directly carried out.

[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 min.

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

[0028] In the present invention, the material is completely softened by the first annealing, so the temperature is preferably the upper limit of the recrystallization temperature, that is, as high a temperature as possible, but not so high as to cause 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 both recrystallization can be achieved and fine grains can be ensured.

[0029] In industrial production, the annealed cold-rolled thin plates 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 the three-layer composite thin plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy, and the composite plate has good interface bonding and uniform thickness. After multiple experiments, the present invention has explored an explosive composition that can realize the explosive welding of CoCrNi medium entropy alloy / Q235B steel, and the welding interface is well bonded. And two explosion weldings of the same process are adopted to prepare a three-layer composite thick plate, which provides a blank for later rolling. The hot rolling process utilizes the excellent plastic deformation ability of CoCrNi medium entropy alloy and Q235B steel at high temperature, and adopts the process of low speed + large deformation amount, which not only avoids the cracking of the bonding surface, but also improves the production efficiency. In the cold rolling process, the excellent work hardening ability of the medium entropy alloy is utilized, and the process of high speed + small deformation amount is selected to increase the deformation pass, so that the medium entropy alloy is fully work hardened, and the overall mechanical properties of the composite plate are improved.

[0032] Based on the above process and parameter selection, it is ensured 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 A schematic diagram of the structure of a 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 the process innovation, any equivalent process transformation made by using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, shall be deemed as the patent protection scope of the present invention.

[0037] Example 1

[0038] The CoCrNi medium entropy alloy plate and the commercially available hot-rolled Q235B steel plate which were completely softened and annealed at 1000℃ / 2h were selected as raw materials, and the following steps were followed:

[0039] S1. Select Q235B steel plate with length × width of 500mm × 800mm and thickness of 10mm as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 1.5mm as composite plate for the first explosion welding. Then use the composite plate obtained by the first explosion welding as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 1.5mm as composite plate for the second explosion welding, and the bonding surface is medium entropy alloy and steel. The explosive composition and volume ratio selected for explosive welding are: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% wood chips, and 9% sodium chloride. Add 5% water by volume before use, mix well and spread the explosive, and the thickness of the spreading is 55mm. After explosive welding, a three-layer composite thick plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy with a total thickness of 13mm is obtained.

[0040] S2. Cut the billet to be rolled with a length × width of 300mm × 500mm 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 warm for 60 minutes.

[0042] S4. After the insulation is completed, hot rolling is directly carried out, and the rolling speed is controlled to be 15m / min, the pass deformation is 30%, and the total variable is 81%, and a three-layer composite hot-rolled plate with a thickness of 2.5mm is obtained.

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

[0044] S6. The annealed composite plate is subjected to multiple cold rolling passes, with the rolling speed controlled to be 40 m / min and the deformation amount per pass being 10%. When the billet thickness is 1 mm, the rolling is stopped.

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

[0046] The total thickness of the composite sheet obtained by this method is 1mm, of which the thickness of the upper and lower layers of CoCrNi medium entropy alloy is 0.12mm, and the thickness of the middle layer of Q235B steel is 0.76mm. The yield strength of the composite sheet is 520MPa, the tensile strength is 615MPa, and the elongation after fracture is 8.6%.

[0047] Example 2

[0048] The CoCrNi medium entropy alloy plate and the commercially available hot-rolled Q235B steel plate which were completely softened and annealed at 1000℃ / 2h were selected as raw materials, and the following steps were followed:

[0049] S1. Select Q235B steel plate with length × width of 500mm × 800mm and thickness of 50mm as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 5mm as composite plate for the first explosion welding. Then use the composite plate obtained by the first explosion welding as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 5mm as composite plate for the second explosion welding, and the bonding surface is medium entropy alloy and steel. The explosive composition and volume ratio selected for explosive welding are: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% wood chips, and 9% sodium chloride. Add 5% water by volume before use, mix well and spread the explosive, and the thickness of the spreading is 65mm. After explosive welding, a three-layer composite thick plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy with a total thickness of 60mm is obtained.

[0050] S2. Cut the billet to be rolled with a length × width of 300mm × 500mm 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 warm for 120 minutes.

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

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

[0054] S6. The annealed composite plate is subjected to multiple cold rolling passes, with the rolling speed controlled to be 30 m / min and the deformation amount per pass being 8%. When the billet thickness is 3 mm, the rolling is stopped.

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

[0056] The total thickness of the composite sheet obtained by this method is 3mm, of which the thickness of the upper and lower layers of CoCrNi medium entropy alloy is 0.3mm, and the thickness of the middle layer of Q235B steel is 2.4mm. The yield strength of the composite sheet is 458MPa, the tensile strength is 552MPa, and the elongation after fracture is 10.4%.

[0057] Example 3

[0058] The CoCrNi medium entropy alloy plate and the commercially available hot-rolled Q235B steel plate which were completely softened and annealed at 1000℃ / 2h were selected as raw materials, and the following steps were followed:

[0059] S1. Select Q235B steel plate with length × width of 500mm × 800mm and thickness of 40mm as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 3mm as composite plate for the first explosion welding. Then use the composite plate obtained by the first explosion welding as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 3mm as composite plate for the second explosion welding, and the bonding surface is medium entropy alloy and steel. The explosive composition and volume ratio selected for explosive welding are: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% wood chips, and 9% sodium chloride. Add 5% water by volume before use, mix well and spread the explosive, and the thickness of the spreading is 65mm. After explosive welding, a three-layer composite thick plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy with a total thickness of 46mm is obtained.

[0060] S2. Cut the billet to be rolled with a length × width of 300mm × 500mm 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 warm for 80 minutes.

[0062] S4. After the insulation is completed, hot rolling is directly carried out, the rolling speed is controlled to be 12m / min, the pass deformation is 25%, the total variable is 82.6%, and a three-layer composite hot-rolled plate with a thickness of 8mm is obtained.

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

[0064] S6. The annealed composite plate is subjected to multiple cold rolling passes, with the rolling speed controlled to be 35 m / min and the deformation amount per pass being 10%. When the billet thickness is 2 mm, the rolling is stopped.

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

[0066] The total thickness of the composite sheet obtained by this method is 2mm, of which the thickness of the upper and lower layers of CoCrNi medium entropy alloy is 0.15mm, and the thickness of the middle layer of Q235B steel is 1.7mm. The yield strength of the composite sheet is 515MPa, the tensile strength is 603MPa, and the elongation after fracture is 9.2%.

[0067] Example 4

[0068] The CoCrNi medium entropy alloy plate and the commercially available hot-rolled Q235B steel plate which were completely softened and annealed at 1000℃ / 2h were selected as raw materials, and the following steps were followed:

[0069] S1. Select Q235B steel plate with length × width of 500mm × 800mm and thickness of 30mm as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 2.5mm as composite plate for the first explosion welding. Then use the composite plate obtained by the first explosion welding as substrate, and CoCrNi medium entropy alloy with length × width of 520mm × 820mm and thickness of 2.5mm as composite plate for the second explosion welding, and the bonding surface is medium entropy alloy and steel. The explosive composition and volume ratio selected for explosive welding are: 63% antimony-free rock ammonium nitrate explosive, 9% calcium carbonate powder, 12% perlite powder, 7% wood chips, and 9% sodium chloride. Add 5% water by volume before use, mix well and spread the explosive, and the thickness of the spreading is 65mm. After the explosion welding machine, a three-layer composite thick plate of CoCrNi medium entropy alloy / Q235B steel / CoCrNi medium entropy alloy with a total thickness of 35mm is obtained.

[0070] S2. Cut the billet to be rolled with a length × width of 300mm × 500mm 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 warm for 70 minutes.

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

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

[0074] S6. The annealed composite plate is subjected to multiple cold rolling passes, with the rolling speed controlled to be 38 m / min and the deformation amount per pass being 10%. When the billet thickness is 2 mm, the rolling is stopped.

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

[0076] The total thickness of the composite sheet obtained by this method is 2.5mm, of which the thickness of the upper and lower layers of CoCrNi medium entropy alloy is 0.18mm, and the thickness of the middle layer of Q235B steel is 2.14mm. The yield strength of the composite sheet is 462MPa, the tensile strength is 558MPa, and the elongation after fracture is 9.4%.

[0077] Comparative Example 1

[0078] The other conditions are the same as those in Example 1, except that the CoCrNi medium entropy alloy is not annealed before the explosive composite, that is, the composite plate material is a hard CoCrNi medium entropy alloy. Since the hard medium entropy alloy has high strength and poor plasticity, it cannot withstand strong plastic deformation during the explosive composite process. Therefore, after the explosion, the medium entropy alloy composite plate is cracked due to the strong impact force generated by the explosives, and the composite fails.

[0079] Comparative Example 2

[0080] The other conditions were the same as those 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% wood chips, and 10% sodium chloride. Reducing the main explosive component of antimony-free rock ammonium nitrate and increasing the content of other components resulted in a decrease in the detonation velocity of the explosive, and the interface metallurgical bonding could not be achieved during the explosion process, resulting in composite failure.

[0081] Comparative Example 3

[0082] The 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] The other conditions are the same as those in Example 1. Only during cold rolling, the deformation amount per rolling pass is increased to 20%. The deformation amount per rolling pass increases, the degree of uneven deformation of the entropy alloy in Q235B steel and CoCrNi increases, and the plate undergoes severe wavy bending during rolling, resulting in rolling failure.

Claims

1. A medium entropy alloy / Q235B steel / medium entropy alloy three-layer composite sheet, characterized in that: 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 0.12~0.3mm, the thickness of the medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite thin plate 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 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%.

3. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 1 or 2, characterized in that: Two CoCrNi medium entropy alloy plates and a Q235B steel plate are explosively welded twice 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 the 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 the 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 amount per pass is 20-30%; During the cold rolling, the rolling speed is controlled to be 30-40 m / min, and the deformation amount per pass is 8-10%.

4. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3, characterized in that: First, a Q235B steel plate is used as a substrate and a CoCrNi medium entropy alloy plate is used as a composite plate for the first explosion 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 with 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.

5. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3 or 4, 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.

6. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3 or 4, characterized in that: The two 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.

7. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3 or 4, characterized in that: The explosive used for the explosive welding is 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% wood chips, and 8-10% sodium chloride.

8. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3 or 4, characterized in that: The preheating temperature is 880-900°C and the holding time is 60-120min; The total variation of the hot rolling is ≥80%.

9. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3 or 4, characterized in that: The temperature of the first annealing is 750-780° C., and the holding time is 60-90 minutes.

10. The method for preparing a medium-entropy alloy / Q235B steel / medium-entropy alloy three-layer composite sheet according to claim 3 or 4, characterized in that: The temperature of the second annealing is 550-600° C., and the holding time is 60-70 minutes.

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