Magnesium / copper composite plate for electromagnetic shielding and preparation method thereof

Abstract

The present invention discloses a preparation method of a magnesium / copper composite plate for electromagnetic shielding, comprising the following steps: 1) riveting a copper plate / magnesium plate / copper plate together in sequence, and adding aluminum foil between the magnesium plate / copper plate to obtain a composite plate; 2) placing the composite plate into a heating furnace for single-pass rolling to obtain a copper / magnesium / copper composite plate; 3) after annealing the copper / magnesium / copper composite plate, flattening and straightening the copper / magnesium / copper composite plate and cutting it into the required size, performing cumulative lamination rolling to obtain a superimposed composite plate; 4) annealing and straightening the superimposed composite plate to obtain a magnesium / copper composite plate for electromagnetic shielding. The magnesium / copper composite plate of the present invention has an electromagnetic shielding effectiveness of 105-110DB, a tensile strength of 350-425MPa, and an elongation of 10%-16% at 1500Hz. That is, the magnesium / copper composite plate obtained by the preparation method has both light weight, high strength and high conductivity, and can be widely used in aerospace, 3C electronics, military and other fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of layered metal composite plates, and in particular relates to a magnesium / copper composite plate for electromagnetic shielding and a preparation method thereof. Background Art

[0002] Lightweight EMI (electromagnetic interference) shielding materials are particularly needed for aerospace electronic equipment and portable electronic devices. Magnesium alloys, which are lightweight and have good electrical conductivity, show great potential in reducing EMI, making them promising to become important electromagnetic shielding materials. However, due to various complex influencing factors, strategies used to improve the strength of magnesium alloys (such as alloying) often lead to a decrease in their EMI shielding effect (SE). The main EMI shielding mechanism of most magnesium alloys is surface reflection (SER), which usually depends on the conductivity of the magnesium alloy; higher conductivity will cause more electromagnetic waves to be reflected from the surface of the magnesium alloy. Therefore, the key to improving the EMI shielding performance of magnesium-based materials lies in improving their conductivity.

[0003] Cu, as the most widely used conductor material, has better electrical and thermal conductivity than magnesium, as well as better strength and ductility. By combining it with low-density magnesium, it can achieve even better functional properties. By controlling the thickness ratio of the two, a magnesium / copper composite plate with both strength and excellent electromagnetic shielding performance can be achieved.

[0004] However, magnesium and copper have different crystal structures, and there is a very large deformation difference between the two during thermal deformation. This makes the rolling process prone to lateral bending and curling, and even at large deformations (>50%), they cannot be combined. Moreover, even after the surface of the copper layer is polished, a thick oxide film forms on the surface during the high-temperature hot rolling process without atmosphere protection or vacuum protection, making it impossible for the two to be combined together. It is very difficult to prepare a magnesium / copper composite plate with good bonding and multiple heterogeneous interfaces by controlling the rolling process. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the main purpose of the present invention is to provide a magnesium / copper composite plate for electromagnetic shielding and a preparation method thereof, aiming to solve the problem that the strength and electromagnetic shielding performance of magnesium alloys cannot be improved simultaneously, and its strength and electromagnetic shielding performance can be greatly improved by layered composite with copper; aiming to solve the problem that magnesium / copper composites are difficult to combine due to interface oxidation and the like during rolling, by adding aluminum foil to the interface to achieve good bonding of the composite plate, and by introducing electric pulse heating to achieve low-temperature cumulative rolling preparation of the composite plate. The present invention also provides a preparation method for the electromagnetic shielding magnesium / copper composite plate.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] In a first aspect, a method for preparing a magnesium / copper composite plate for electromagnetic shielding comprises the following steps:

[0008] 1) The copper plate / magnesium plate / copper plate are riveted together in sequence, and aluminum foil is added between the magnesium plate / copper plate to obtain a composite plate;

[0009] 2) placing the composite slab into a heating furnace for single-pass rolling to obtain a copper / magnesium / copper composite plate;

[0010] 3) After annealing the copper / magnesium / copper composite plate, the copper / magnesium / copper composite plate is flattened and straightened, and then cut into a desired size, and then cumulatively laminated and rolled to obtain a laminated composite plate;

[0011] 4) Annealing and straightening the stacked composite plates to obtain magnesium / copper composite plates for electromagnetic shielding.

[0012] In some specific embodiments, the thickness of the aluminum foil is 0.005-0.1 mm.

[0013] In some specific embodiments, the process parameters of the single-pass rolling in step 2) are: after preheating at 350-450° C. for 10-20 minutes, the pass reduction is 50-60%.

[0014] In some specific embodiments, the annealing process parameters in step 3) are annealing at a temperature of 300-350° C. for 10-15 minutes.

[0015] In some specific embodiments, the cumulative rolling in step 4) adopts electric pulse heating rolling, and the process parameters of the electric pulse heating rolling are: current density is 50-80A / mm 2 , the rolling temperature is 200-250℃, and the pass reduction is 40-60%.

[0016] In some specific embodiments, the annealing and straightening process parameters in step 4) are: keeping the temperature at 200-250° C. for 15-20 minutes and then straightening.

[0017] In some specific embodiments, the magnesium plate is AZ31 or AM60 magnesium alloy; and the copper plate is a pure copper plate.

[0018] In the second aspect, a magnesium / copper composite plate for electromagnetic shielding is prepared according to the aforementioned preparation method, wherein the ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer in the magnesium / copper composite plate for electromagnetic shielding is 0.53 to 1.22, and its cross section includes at least five magnesium and copper heterogeneous interfaces.

[0019] In certain specific embodiments, the magnesium / copper composite plate for electromagnetic shielding has an electromagnetic shielding effectiveness of 105-110 DB at 1500 Hz, a tensile strength of 350-425 MPa, and an elongation of 10%-16%.

[0020] Compared with the prior art, the present invention has at least the following advantages:

[0021] The present invention provides a method for preparing magnesium / copper for electromagnetic shielding. The method introduces an aluminum foil heterogeneous interface, utilizing the back stress strengthening effect of the heterogeneous interface and the reflection of electromagnetic waves. Simultaneously, by controlling the initial rolling process, a copper / magnesium / copper composite plate free of intermetallic compounds and with good strength-ductility matching is prepared. Furthermore, by introducing electric pulse rolling and cumulatively laminating at low temperature, a magnesium / copper composite plate containing multiple heterogeneous interfaces and coupled with enhanced strength and electromagnetic shielding performance is prepared. The composite plate exhibits an electromagnetic shielding effectiveness of 105-110 dB at 1500 Hz, a tensile strength of 350-425 MPa, and an elongation of 10%-16%. The magnesium / copper composite plate obtained by this preparation method combines lightness, high strength, and high conductivity, and can be widely used in aerospace, 3C electronics, military, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention, the following briefly introduces the drawings required for the specific embodiments or the description of the prior art.

[0023] Figure 1 is an SEM image of the interface of the magnesium / copper composite plate in Example 2 of the present invention;

[0024] Figure 2 is the EBSD micrograph of the magnesium / copper composite plate in Example 2 of the present invention;

[0025] Figure 3 is the tensile curve of the magnesium / copper composite plate in Example 2 of the present invention;

[0026] Figure 4 1 is a flow chart of the preparation process of Example 2 and Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are merely illustrative and non-restrictive, and should not be used to limit the scope of protection of the present invention.

[0028] When expressing a certain amount, concentration or other value or parameter in the form of a range, preferred range, or preferred upper and lower numerical limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, without considering whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within the range.

[0029] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0030] The materials, methods, and examples herein are illustrative and, unless otherwise indicated, are not to be construed as limiting.

[0031] In the following embodiments, the magnesium plate is purchased from Shanxi Yinguang Magnesium Industry; the magnesium plate is made of AZ31 magnesium alloy; and the copper plate is a pure copper plate.

[0032] The test methods used in the following examples include:

[0033] The mechanical properties and electromagnetic shielding properties of the magnesium / copper composite plate are reflected by testing the main properties of each test sample respectively; the main properties tested in this application include tensile strength, elastic modulus and interface strength test, electromagnetic shielding performance test, etc.

[0034] 1) Mechanical properties test;

[0035] Use universal tensile testing machine to test mechanical properties and elastic modulus according to the tensile test method for metal materials specified in GB / T 228;

[0036] 2) Electromagnetic shielding performance test

[0037] Use vector network test equipment to test the electromagnetic shielding performance of samples according to GB / T 30142-2013 method;

[0038] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0039] Example 1

[0040] The method for preparing the magnesium / copper composite plate for electromagnetic shielding provided in this embodiment includes the following steps:

[0041] (1) AZ31 magnesium plate and T2 pure copper plate were selected, the surface was roughened to remove surface oxides and impurities; then, the blanks were riveted together in the order of copper plate / magnesium plate / copper plate, and aluminum foil (thickness of 0.05 mm) was added between the magnesium plate and the copper plate to obtain a composite blank;

[0042] (2) Preheating the composite slab at 400°C for 15 minutes and then pressing it with a 50% reduction to obtain a copper / magnesium / copper composite plate;

[0043] (3) After annealing the copper / magnesium / copper composite plate at 350°C for 10 min, the copper / magnesium / copper composite plate is flattened and straightened and then cut into the required size;

[0044] (4) Take three copper / magnesium / copper composite plates cut in step (3), polish their surfaces, and then perform cumulative rolling using an electric pulse heating rolling process. The process parameters of the electric pulse heating rolling process are: current density 70A / mm 2 , the rolling temperature is 200℃, the pass reduction is 50%, and a superimposed composite plate is obtained;

[0045] (5) The stacked composite plate obtained in step (4) is kept at 250° C. for 20 minutes and then straightened to obtain a magnesium / copper composite plate for electromagnetic shielding containing six magnesium and copper heterogeneous interfaces.

[0046] The ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer in the magnesium / copper composite plate of this embodiment is 0.68;

[0047] This application tests the mechanical properties and electromagnetic shielding performance of the prepared magnesium / copper composite plate for electromagnetic shielding. The mechanical properties are tested using the GB / T 228.1-2021 standard on a universal testing machine, and the electromagnetic shielding performance is tested using the GB / T 30142-2013 standard on a vector network tester. The results show that the electromagnetic shielding effectiveness of the magnesium / copper composite plate at 1500Hz is 105DB, the tensile strength is 420MPa, and the elongation is 16%.

[0048] Example 2

[0049] The preparation method of the magnesium / copper composite plate for electromagnetic shielding provided in this embodiment is as follows: Figure 4 As shown, the following steps are included:

[0050] (1) AZ31 magnesium plate and T2 pure copper plate were selected, the surface was roughened to remove surface oxides and impurities; then, the blanks were riveted together in the order of copper plate / magnesium plate / copper plate, and aluminum foil (thickness of 0.01 mm) was added between the magnesium plate and the copper plate to obtain a composite blank;

[0051] (2) Preheating the composite slab at 350°C for 15 minutes and then pressing it with a 50% reduction to obtain a copper / magnesium / copper composite plate;

[0052] (3) After annealing the copper / magnesium / copper composite plate at 300°C for 15 minutes, the copper / magnesium / copper composite plate is flattened and straightened and then cut into the required size;

[0053] (4) Take four copper / magnesium / copper composite plates cut in step (3), polish their surfaces, and then perform cumulative rolling using an electric pulse heating rolling process, wherein the process parameters of the electric pulse heating rolling are: current density 50A / mm 2 , the rolling temperature is 250℃, the pass reduction is 55%, and a superimposed composite plate is obtained;

[0054] (5) The stacked composite plate obtained in step (4) is kept at 200° C. for 20 minutes and then straightened to obtain a magnesium / copper composite plate for electromagnetic shielding comprising eight magnesium and copper heterogeneous interfaces.

[0055] In the magnesium / copper composite plate of this embodiment, the ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer is 1;

[0056] In this embodiment, the interface and organization of the composite plate are characterized and the mechanical properties are tested. The SEM results are shown in FIG. Figure 1 As shown in the figure, it can be seen that the copper / magnesium composite plates are tightly bonded and the aluminum foil is distributed at the interface between copper and magnesium. Figure 2 The EBSD results show that both magnesium and copper components are recrystallized structures, with the grain size of magnesium component being about 4.5μm and that of copper component being about 7.1μm. Figure 3 The mechanical property curves show that the maximum tensile strength of the Mg / Cu layered composite plate along the TD direction is 425 MPa, and the maximum tensile strength of the Mg / Cu layered composite plate along the RD direction is 365 MPa, and the elongation difference is small.

[0057] This application tests the mechanical properties and electromagnetic shielding performance of the prepared magnesium / copper composite plate for electromagnetic shielding. The mechanical properties are tested using the GB / T 228.1-2021 standard on a universal testing machine, and the electromagnetic shielding performance is tested using the GB / T 30142-2013 standard on a vector network tester. The results show that the electromagnetic shielding effectiveness of the magnesium / copper composite plate at 1500Hz is 110DB, the tensile strength is 425MPa, and the elongation is 14%.

[0058] Example 3

[0059] The method for preparing the magnesium / copper composite plate for electromagnetic shielding provided in this embodiment includes the following steps:

[0060] (1) AZ31 magnesium plate and T2 pure copper plate were selected, the surface was roughened to remove surface oxides and impurities; then, the blanks were riveted together in the order of copper plate / magnesium plate / copper plate, and aluminum foil (thickness of 0.05 mm) was added between the magnesium plate and the copper plate to obtain a composite blank;

[0061] (2) Preheating the composite slab at 400°C for 15 minutes and then pressing it with a 50% reduction to obtain a copper / magnesium / copper composite plate;

[0062] (3) After annealing the copper / magnesium / copper composite plate at 300°C for 15 minutes, the copper / magnesium / copper composite plate is flattened and straightened and then cut into the required size;

[0063] (4) Take five copper / magnesium / copper composite plates cut in step (3), polish their surfaces, and then perform cumulative rolling using an electric pulse heating rolling process, wherein the process parameters of the electric pulse heating rolling are: current density 75A / mm 2 , the rolling temperature is 230℃, the pass reduction is 50%, and a superimposed composite plate is obtained;

[0064] (5) The stacked composite plate obtained in step (4) is kept at 240° C. for 15 minutes and then straightened to obtain a magnesium / copper composite plate for electromagnetic shielding containing ten magnesium and copper heterogeneous interfaces.

[0065] The ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer in the magnesium / copper composite plate of this embodiment is 1.2;

[0066] This application tests the mechanical properties and electromagnetic shielding performance of the prepared magnesium / copper composite plate for electromagnetic shielding. The mechanical properties are tested using the GB / T 228.1-2021 standard on a universal testing machine, and the electromagnetic shielding performance is tested using the GB / T 30142-2013 standard on a vector network tester. The results show that the electromagnetic shielding effectiveness of the magnesium / copper composite plate at 1500Hz is 105DB, the tensile strength is 380MPa, and the elongation is 10%.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing a magnesium / copper composite plate for electromagnetic shielding. The preparation method is basically the same as that of Example 2, except that no aluminum foil is added between the magnesium plate and the copper plate in step (1). Specifically,

[0069] (1) AZ31 magnesium plate and T2 pure copper plate were selected, the surface was roughened, and the surface oxides and impurities were removed; then, the blanks were riveted together in the order of copper plate / magnesium plate / copper plate to obtain a composite blank;

[0070] (2) After the composite slab was preheated at 350°C for 15 minutes, a copper / magnesium / copper composite plate was obtained after 55% reduction. The copper / magnesium / copper composite plate was partially not composited and the copper plate had severe lateral bending.

[0071] Comparative Example 2

[0072] This comparative example provides a method for preparing a magnesium / copper composite plate for electromagnetic shielding, and its preparation method is basically the same as that of Example 2, except that the superimposed rolling process in step (4) is different, specifically: four copper / magnesium / copper composite plates cut in step (3) are taken, the surface of which is polished, and then kept in a heating furnace at 250°C for 10 minutes with a pass reduction of 55% to obtain a superimposed composite plate; the superimposed composite plate is not composited.

[0073] Comparative Example 3

[0074] This comparative example provides a method for preparing a magnesium / copper composite plate for electromagnetic shielding. The only difference from Example 2 is that no cumulative rolling is performed, but a single large deformation rolling is performed. Figure 4 As shown, the specific steps include:

[0075] (1) Select AZ31 magnesium plate and T2 pure copper plate (wherein the total thickness of the magnesium plate and the total thickness of the copper plate are consistent with the total thickness of the magnesium plate and the copper plate of the four copper / magnesium / copper composite plates in Example 2, for example: the total thickness of the magnesium plate of the four copper / magnesium / copper composite plates in Example 2 is 4 mm, and the total thickness of the copper plate is 4 mm, while the single magnesium plate in the comparative example is 4 mm, and the single copper plate is 2 mm*2=4 mm), and the surface is roughened to remove surface oxides and impurities; then, the copper plate / magnesium plate / copper plate are riveted together in the order of copper plate / magnesium plate / copper plate, and aluminum foil (thickness of 0.01 mm) is added between the magnesium plate and the copper plate to obtain a composite plate blank;

[0076] (2) Preheating the composite slab at 350°C for 15 minutes and then pressing it with a reduction of 55% to obtain a copper / magnesium / copper composite plate;

[0077] (3) The copper / magnesium / copper composite plate was kept at 300°C for 15 minutes to obtain a magnesium / copper composite plate for electromagnetic shielding containing two magnesium and copper heterogeneous interfaces.

[0078] In the magnesium / copper composite plate of this embodiment, the ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer is 1;

[0079] This application conducts mechanical property and electromagnetic shielding performance tests on the prepared magnesium / copper composite plate for electromagnetic shielding. The mechanical properties are tested using the GB / T 228.1-2021 standard on a universal testing machine, and the electromagnetic shielding performance test is performed using the GB / T 30142-2013 standard on a vector network tester. The results show that the electromagnetic shielding effectiveness of the magnesium / copper composite plate at 1500Hz is 98DB, the tensile strength is 360MPa, and the elongation is 15%.

[0080] Comparative Example 4

[0081] This comparative example provides a method for preparing a magnesium / copper composite plate for electromagnetic shielding. Compared with Example 2, the method is different in that the cumulative rolling is performed at a high temperature, and the rolling process is a heat preservation at 400°C for 30 minutes. Specifically, the method comprises the following steps:

[0082] (1) AZ31 magnesium plate and T2 pure copper plate were selected, the surface was roughened to remove surface oxides and impurities; then, the blanks were riveted together in the order of copper plate / magnesium plate / copper plate, and aluminum foil (thickness of 0.01 mm) was added between the magnesium plate and the copper plate to obtain a composite blank;

[0083] (2) Preheating the composite slab at 350°C for 15 minutes and then pressing it with a 50% reduction to obtain a copper / magnesium / copper composite plate;

[0084] (3) After annealing the copper / magnesium / copper composite plate at 300°C for 15 minutes, the copper / magnesium / copper composite plate is flattened and straightened and then cut into the required size;

[0085] (4) taking four copper / magnesium / copper composite plates cut in step (3), polishing their surfaces, and then performing cumulative rolling, wherein the process parameters of the cumulative rolling are: rolling temperature of 400° C., holding time of 30 min, and pass reduction of 55%, to obtain a stacked composite plate;

[0086] (5) The stacked composite plate obtained in step (4) is kept at 200° C. for 20 minutes and then straightened to obtain a magnesium / copper composite plate for electromagnetic shielding comprising eight magnesium and copper heterogeneous interfaces.

[0087] In the magnesium / copper composite plate of this embodiment, the ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer is 1;

[0088] This application conducts mechanical property and electromagnetic shielding performance tests on the prepared magnesium / copper composite plate for electromagnetic shielding. The mechanical properties are tested using the GB / T 228.1-2021 standard on a universal testing machine, and the electromagnetic shielding performance is tested using the GB / T 30142-2013 standard on a vector network tester. The results show that the maximum electromagnetic shielding effectiveness is 100dB at 1500Hz, the tensile strength is 380MPa, and the elongation is 8%.

[0089] In summary, the magnesium / copper composite plate for electromagnetic shielding in the present application is prepared by adding aluminum foil at the interface, and then preparing the copper / magnesium / copper composite plate by an initial single-pass rolling, and then preparing the magnesium / copper composite plate by cumulative rolling, wherein the copper plate and the magnesium plate are distributed in alternating layers, and the heterogeneous interface is greater than five. The magnesium / copper composite plate obtained by the preparation method of the present invention can greatly improve the strength and conductivity of the magnesium alloy, and the conductive performance and strength coupling can be greatly improved through the layered structure design. By comparing Example 2 with Comparative Examples 1 and 2, it can be seen that by setting an aluminum foil heterogeneous interface and combining a specific electric pulse heating rolling process, cumulative rolling can be achieved at low temperature to achieve composite plate compounding; by comparing Example 2 with Comparative Example 3, it can be seen that the heterogeneous interface introduced by cumulative rolling can achieve back stress strengthening of the composite plate and improve the comprehensive performance of the copper / magnesium composite plate, while ordinary rolling cannot achieve similar effects. By comparing Example 2 with Comparative Example 4, it can be seen that a rapid rolling process can be achieved through electric pulse low-temperature rolling, and the electric pulse can achieve rapid stress relief and recrystallization of magnesium and copper, reduce deformation resistance, and achieve good comprehensive performance of the composite plate; while when rolling is carried out at 400°C for 30 minutes, the strength of the composite plate is weakened, and the copper layer is easily oxidized at high temperature, which further reduces its electromagnetic shielding performance.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A method for preparing a magnesium / copper composite plate for electromagnetic shielding, characterized in that: The steps include: 1) Rivet the copper plate / magnesium plate / copper plate together in sequence, and add aluminum foil between the magnesium plate / copper plate to obtain a composite plate; 2) placing the composite slab in a heating furnace for preheating and then performing single-pass rolling to obtain a copper / magnesium / copper composite plate; 3) After annealing the copper / magnesium / copper composite plate, the copper / magnesium / copper composite plate is flattened and straightened, then cut into the required size, and cumulatively laminated and rolled to obtain a laminated composite plate; 4) Annealing and straightening the stacked composite plates to obtain magnesium / copper composite plates for electromagnetic shielding; The cumulative rolling is performed by electric pulse heating rolling, and the process parameters of the electric pulse heating rolling are: the current density is 50-80A / mm 2 The rolling temperature is 200-250℃ and the pass reduction is 40-60%.

2. The method for preparing a magnesium / copper composite plate for electromagnetic shielding according to claim 1, characterized in that: The thickness of the aluminum foil is 0.005-0.1 mm.

3. The method for preparing a magnesium / copper composite plate for electromagnetic shielding according to claim 1, wherein: The process parameters of the single-pass rolling in step 2) are: preheating at 350-450° C. for 10-20 minutes and a pass reduction of 50-60%.

4. The method for preparing a magnesium / copper composite plate for electromagnetic shielding according to claim 3, characterized in that: The annealing process parameters in step 3) are annealing at a temperature of 300-350° C. for 10-15 minutes.

5. The method for preparing a magnesium / copper composite plate for electromagnetic shielding according to claim 1, wherein: The annealing and straightening process parameters in step 4) are: keeping the temperature at 200-250° C. for 15-20 minutes and then straightening.

6. The method for preparing a magnesium / copper composite plate for electromagnetic shielding according to claim 4, characterized in that: The magnesium plate is AZ31 or AM60 magnesium alloy; the copper plate is a pure copper plate.

7. A magnesium / copper composite plate for electromagnetic shielding prepared according to the preparation method according to any one of claims 1 to 6, characterized in that: The ratio of the total thickness of the magnesium plate layer to the total thickness of the copper plate layer in the magnesium / copper composite plate for electromagnetic shielding is 0.53-1.22, and its cross section includes at least five magnesium-copper heterogeneous interfaces.

8. The magnesium / copper composite plate for electromagnetic shielding according to claim 7, characterized in that: The magnesium / copper composite plate for electromagnetic shielding has an electromagnetic shielding effectiveness of 105-110 DB at 1500 Hz, a tensile strength of 350-425 MPa, and an elongation of 10%-16%.

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