Preparation method of high-strength high-thermal-conductivity magnesium alloy plate

Abstract

The application provides a preparation method of high-strength and high-thermal-conductivity magnesium alloy plate and relates to the technical field of magnesium alloy processing. The rare earth magnesium alloy plate is annealed at 170 DEG C; the annealed rare earth magnesium alloy plate is rolled, the preheating temperature of the roller is 120 DEG C, the linear speed of the roller is 5 m / min, the reduction is 70%, and the rare earth magnesium alloy plate with a thickness of 1.8 mm is obtained; the rare earth magnesium alloy plate is quenched, and is taken out after cooling at room temperature; the quenched rare earth magnesium alloy plate is aged at 90 DEG C for 24-48 h, and is air-cooled to room temperature to obtain the high-strength and high-thermal-conductivity magnesium alloy plate. The tensile strength of the magnesium alloy plate prepared by the application can be up to 456 MPa, the yield strength is 408 MPa, the elongation is 13%, and the thermal conductivity is 125-134 (W / (m*K)).

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnesium alloy, and particularly relates to a forming process of high-thermal-conductivity high-strength magnesium alloy plate. BACKGROUND

[0002] With the continuous development of the field of electronic devices, there is a huge demand for heat dissipation in the field of electronic devices. Magnesium is the lightest high-thermal-conductivity metal, and has good development prospects in energy saving, energy efficiency improvement and emission reduction. However, the poor mechanical properties of pure magnesium restrict its production and application. On this basis, alloying and deformation treatment are usually performed. Although the currently widely used commercial magnesium alloys such as AM60 and AZ31 have good forming and room-temperature mechanical properties, their heat dissipation capacity is not ideal, and their thermal conductivities are only 61 W / (m·K) and 96.4 W / (m·K), which are far lower than that of pure magnesium. On the other hand, rolling is a common deformation process for magnesium alloys. The magnesium alloy plate formed by rolling has high mechanical properties, but rolling can greatly reduce the thermal conductivity, making it difficult to further apply. The contradiction between the mechanical properties and the thermal conductivity limits the research and design of high-strength high-thermal-conductivity magnesium alloys. SUMMARY

[0003] The main purpose of the present application is to overcome the shortcomings in the prior art, solve the problem of unsuitable combination of the comprehensive mechanical properties and the thermal conductivity of the existing magnesium alloy, and develop a low-rare-earth magnesium alloy plate preparation method with excellent mechanical and thermal conductivity. The magnesium alloy material is subjected to vertical concave die hot extrusion and rolling deformation treatment and then subjected to aging heat treatment, so as to refine the dynamic recrystallization grain size and increase the dispersion degree of the second phase, so that the thermal conductivity of the alloy reaches more than 130 (W / (m·K)) under the premise that the strength of the alloy is 450 MPa.

[0004] The present application is implemented by the following technical scheme: a preparation process of high-strength high-thermal-conductivity magnesium alloy plate, comprising the following steps:

[0005] (1) annealing the rare earth magnesium alloy plate, the annealing temperature is 170 DEG C, and the annealing time is 30 min; the rare earth magnesium alloy plate is Mg-5Zn-1Gd-1Y-1Mn;

[0006] (2) rolling the annealed rare earth magnesium alloy plate, the preheating temperature of the roller is 120 DEG C, the linear speed of the roller is 5 m / min, and the reduction is 70%, so as to obtain a rare earth magnesium alloy plate with a thickness of 1.8 mm;

[0007] (3) quenching the rare earth magnesium alloy plate, and taking it out after cooling at room temperature;

[0008] (4) the quenched rare earth magnesium alloy plate is aged at a temperature of 90 DEG C for 24-48 h, and the high-strength and high-thermal-conductivity magnesium alloy plate is obtained after air cooling to room temperature.

[0009] Preferably, the preparation method of the rare earth magnesium alloy plate in step (1) comprises the following steps:

[0010] S1, preparing a magnesium alloy ingot

[0011] After the magnesium ingot, zinc particles, Mg-Gd intermediate alloy, Mg-Mn intermediate alloy and Mg-Y intermediate alloy are surface-degreased, they are heated and melted in a protective atmosphere, then the mixed melt is poured into a mold, and after cooling, the low-rare earth content magnesium alloy ingot is obtained by demolding;

[0012] S2, extruding the low-rare earth content magnesium alloy ingot

[0013] S2-1, the magnesium alloy ingot is placed in a heat treatment furnace for hierarchical solid solution treatment, the first stage is heating at a temperature of 420-480 DEG C for 6-8 h, and the second stage is heating at a temperature of 500-520 DEG C for 10-12 h;

[0014] S2-2, after the magnesium alloy ingot after hierarchical solid solution treatment is polished smooth, it is placed in a mold, heated to 300 DEG C, and heat-pressed for 40 min, the loading speed is 10 KN / s, and when the magnesium alloy ingot is hot-pressed to 60 mm, the pressure is maintained for 100 s;

[0015] S2-3, the magnesium alloy ingot after hot pressing in step S2-2 is processed into a standard sample size and polished to be smooth; then the ingot is placed in a heat treatment furnace for heating at a temperature of 300 DEG C for 30 min, and a pressure head, a concave die, and an upper cushion block are preheated for subsequent use;

[0016] S2-4, the magnesium ingot after hot pressing in step 2-3 is extruded, the hot-pressed block is placed after 90 DEG C turning over, the hot-pressed PD-TD surface is used as the extrusion direction, a total of three extrusions are performed, the extrusion ratio is 25:1, the initial speed is 5 m / min, the extrusion force is 2900 KN, the initial extrusion temperature is 300-310 DEG C, the first section of the plate is cut after extrusion, then the extrusion temperature is reduced by 10-20 DEG C for each step, the corresponding speed is increased by 2 m / min, the extrusion force is always maintained at 2700-3000 KN, the second section of the extrusion temperature is 280-300 DEG C, the speed is 7 m / min, and the third section of the extrusion temperature is 260-280 DEG C, the corresponding extrusion speed is 9 m / min;

[0017] S2-5, the plate blank after extrusion in step 2-4 is quenched, the plate blank is cooled to room temperature, the plate blank is chamfered, and the surface is polished clean, and the magnesium alloy plate is obtained.

[0018] More preferably, the protective gas in step S1-2 is a mixture of CO2 and SF6.

[0019] Further preferably, the volume ratio of CO2 to SF6 is 100:1.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The present application solves the problem of high cost, difficult matching of strength and thermal conductivity of rare earth magnesium alloy by regulating the phase quantity and distribution of rare earth magnesium alloy through low rare earth micro-alloying and multi-step deformation. After annealing at 170 DEG C for 30 min, single pass rolling, and then low temperature aging, the tensile strength of the plate material can reach 456 MPa, the yield strength is 408 MPa, the elongation is 13%, and the thermal conductivity is 125-134 (W / (m*K)). BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of hot pressing and extrusion direction;

[0023] Figure 2 is a microstructure morphology diagram of Mg-5Zn-1Gd-1Y-1Mn magnesium alloy after solid solution;

[0024] Figure 3 is a microstructure morphology diagram of Mg-5Zn-1Gd-1Y-1Mn magnesium alloy after extrusion;

[0025] Figure 4 is a microstructure morphology diagram of Mg-5Zn-1Gd-1Y-1Mn magnesium alloy after rolling;

[0026] Figure 5 is a microstructure morphology diagram of Mg-5Zn-1Gd-1Y-1Mn magnesium alloy after aging at 90 DEG C for 24 h;

[0027] Figure 6 is a tensile curve of as-cast, extruded, rolled, and aged after rolling Mg-5Zn-1Gd-1Y magnesium alloy.

[0028] Figure 7 is a data diagram of yield strength and thermal conductivity of Mg-5Zn-1Gd-1Y after aging. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application more clear, the preferred embodiments of the present application are further described in detail below in combination with examples. All other examples obtained by those skilled in the art without creative labor on the basis of the examples in the present application belong to the scope of protection of the present application.

[0030] Example 1

[0031] S1, Preparation of Mg-5Zn-1Gd-1Y-1Mn low rare earth content magnesium alloy ingot, comprising the following steps:

[0032] S1-1, the prepared pure Mg is immersed in an acidic solution to remove the surface oxides, and then the treated pure Mg, pure Zn, Mg-Gd intermediate alloy containing 30% (wt%) Gd, Mg-Mn intermediate alloy containing 30% (wt%) Mn, and Mg-Y intermediate alloy containing 30% (wt%) Y are polished with a grinder and an angle grinder to remove the influence of the oxide scale and impurities on the material preparation. After polishing, the raw materials are wrapped with aluminum foil and sealed for storage.

[0033] S1-2, the stainless steel crucible is preheated in the pit furnace, and when it is preheated to 500℃, it is taken out, and talc paint and zinc oxide paint are coated on the surface, which can prevent the Mg melt from directly contacting the crucible wall and thus introducing impurities. Then the crucible is placed in the pit furnace for heating, and when the temperature reaches 720℃, pure Mg is put in, and a mixed gas of CO2 and SF6 (volume ratio of CO2 to SF6 is 100:1) is introduced as the protective gas during smelting.

[0034] S1-3, after the pure Mg is completely melted, it is left for 15 minutes, zinc particles are added, and stirring is performed for 1 minute. Meanwhile, the Mg-30Gd and Mg-30Y intermediate alloys are wrapped with aluminum foil and preheated at the side of the furnace. Then the temperature of the crucible is raised to 760℃, the preheated Mg-30Gd, Mg-30Y and Mg-30Mn intermediate alloys are put in, rapid stirring is performed for 3 minutes, and the temperature is kept for 10 minutes. The temperature of the crucible is lowered to 720℃, and the molten alloy is poured into a preheated 250℃ mold. Then it is naturally air cooled to room temperature to obtain the alloy ingot.

[0035] S2, magnesium alloy ingot extrusion forming, comprising the following steps:

[0036] S2-1, first, the magnesium alloy ingot is placed in a heat treatment furnace for hierarchical solid solution treatment. The first stage is heating at 430℃ for 6h, and the second stage is heating at 500℃ for 10h.

[0037] S2-2, the magnesium alloy ingot after step 2-1 is polished until the surface is smooth. It is placed in a mold and preheated to 300℃ in the furnace for 40 minutes for hot pressing at a loading speed of 10KN / s. When the sample is hot pressed to 60mm, it is kept for 100s.

[0038] S2-3, the magnesium alloy ingot after hot pressing in step S2-2 is processed into a standard sample size and polished to be smooth. Then the ingot is placed in a heat treatment furnace for heating, the temperature is 300 DEG C, the holding time is 30 minutes, the pressure head, the concave die, the upper cushion block and the extrusion die are preheated, and are used subsequently;

[0039] S2-4, the magnesium ingot after hot pressing in step 2-3 is extruded, the hot pressing block is placed after 90 DEG turning, the PD-TD surface after hot pressing is used as the extrusion direction, a total of three extrusions, the extrusion ratio is 25:1, the initial speed is 5 m / min, the extrusion force is 2900KN, the initial extrusion temperature is 300 DEG C, the first section of the plate is cut after extrusion for sampling, then the extrusion temperature is reduced by 20 DEG C for each step, the corresponding speed is increased by 2 m / min, the extrusion force is always kept at 2900KN, the second section extrusion temperature is 280 DEG C, the speed is 7 m / min, the third section extrusion temperature is 260 DEG C, and the corresponding extrusion speed is 9 m / min;

[0040] S2-5, the plate blank after extrusion in step 2-4 is placed in 60 DEG C warm water for quenching treatment, and then taken out after the plate blank is cooled to room temperature, the plate blank is chamfered and the surface is polished for subsequent use.

[0041] S3, magnesium alloy single pass rolling forming and heat treatment, comprising the following steps:

[0042] S3-1, the plate blank obtained in step 2 is placed in a heat treatment furnace for annealing treatment, the temperature is 170 DEG C, and the annealing time is 30 minutes;

[0043] S3-2, the plate blank obtained in step 3-1 is placed on a BKDФ350x400 test rolling mill, and the sample is quickly sent to the roller for rolling. The preheating temperature of the roller is 120 DEG C, the roller linear speed is 5 m / min, and the reduction is 70%, and the plate with a thickness of 1.8 mm is obtained;

[0044] S3-3, the plate blank obtained in step 3-2 is placed in 60 DEG C warm water for quenching treatment, and then taken out after the plate blank is cooled to room temperature.

[0045] S3-4, the magnesium alloy plate after rolling in step S4-2 is aged, the aging temperature is 90 DEG C, the aging time is 24h, and then air cooling to room temperature, and a high-strength high-thermal-conductivity magnesium alloy plate is prepared.

[0046] Comparing the microstructure of the magnesium alloy after extrusion with the microstructure of the magnesium alloy after rolling, it can be seen that most of the second phase at the grain boundary after solid solution is dissolved into the matrix, and after extrusion deformation, dynamic recrystallization occurs obviously around the second phase, the soft and hard structures of the deformed and recrystallized structures cooperate with each other, which greatly improves the plastic deformation ability of the plate. After annealing at 170℃ for 30min and single-pass rolling, the tensile strength of the magnesium alloy plate is 385MPa, the yield strength is 337MPa, and the elongation is 13%-17%.

[0047] After low-temperature aging, the tensile strength is as high as 456MPa, the yield strength is 408MPa, the elongation is 13%, and the thermal conductivity is 135(W / (m·K)).

[0048] Example 2

[0049] Compared with Example 1, the aging time in Step 3 is 36h, and the others are the same as Example 1. After low-temperature aging, the tensile strength is as high as 416MPa, the yield strength is 352MPa, the elongation is 12%, and the thermal conductivity is 125(W / (m·K)).

[0050] Example 3

[0051] Compared with Example 1, the aging time in Step 3 is 48h, and the others are the same as Example 1. After low-temperature aging, the tensile strength is as high as 422MPa, the yield strength is 338MPa, the elongation is 14%, and the thermal conductivity is 127(W / (m·K)).

[0052] The above-described examples are part of the embodiments of the present application, but not all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

Claims

1. A method for preparing a high-strength, high-thermal-conductivity magnesium alloy sheet, characterized in that, Includes the following steps: (1) The rare earth magnesium alloy plate is annealed at a temperature of 170°C for 30 minutes; the rare earth magnesium alloy plate is Mg-5Zn-1Gd-1Y-1Mn. (2) The annealed rare earth magnesium alloy plate is rolled. During the rolling process, the preheating temperature of the roll is 120℃, the roll linear speed is 5m / min, and the reduction is 70%, resulting in a rare earth magnesium alloy plate with a thickness of 1.8mm. (3) The rare earth magnesium alloy plate is quenched and then cooled to room temperature before being taken out; (4) The quenched rare earth magnesium alloy plate is aged at 90°C for 24-48 hours and then air-cooled to room temperature to obtain a high-strength and high-thermal-conductivity magnesium alloy plate. The preparation method of the rare earth magnesium alloy plate in step (1) includes the following steps: S1. Preparation of magnesium alloy ingots S1-1. After removing impurities from the surface of magnesium sheets, zinc granules, Mg-Gd master alloy, Mg-Mn master alloy, and Mg-Y master alloy, seal and store them. S1-2. The magnesium sheet is heated and melted under a protective atmosphere to obtain molten Mg. S1-3. Add zinc granules to the molten Mg and stir evenly. Add Mg-Gd alloy and Mg-Y master alloy, heat and melt, and then add Mg-Mn master alloy and heat and melt again to obtain a mixed melt. S1-4. Pour the mixed molten liquid into a mold, and after cooling, demold to obtain a magnesium alloy ingot with low rare earth content. S2. The magnesium alloy ingot with low rare earth content is extruded and formed. S2-1. The magnesium alloy ingot is placed in a heat treatment furnace for graded solution treatment. The first stage is a heating temperature of 420~480℃ and a holding time of 6-8h. The second stage is a heating temperature of 500~520℃ and a holding time of 10-12h. S2-2. After the magnesium alloy ingot after graded solution treatment is polished smooth, it is placed in a mold, heated to 300℃, held for 40 minutes, and then hot-pressed at a loading speed of 10kN / s. When the magnesium alloy ingot is hot-pressed to 60mm, it is held for 100s. S2-3. Process the magnesium alloy ingot after hot pressing in step S2-2 into standard sample size and grind it until the surface is smooth. Then put the ingot into a heat treatment furnace for heating at 300℃ and holding for 30 minutes. Preheat the pressure head, die, upper pad block and extrusion die for subsequent use. S2-4. Extrude the magnesium ingots hot-pressed in step 2-3. Flip the hot-pressed block 90° and place it with the PD-TD surface after hot pressing as the extrusion direction. Extrusion is carried out in three steps with an extrusion ratio of 25:1, an initial speed of 5m / min, an extrusion pressure of 2900kN, and an initial extrusion temperature of 300-310℃. After the first section of the plate is extruded, it is cut and sampled. Then, the extrusion temperature decreases by 10-20℃ for each subsequent step, and the corresponding speed increases by 2m / min. The extrusion pressure is always maintained at 2700~3000kN. The second extrusion temperature is 280-300℃ and the speed is 7m / min. The third extrusion temperature is 260-280℃ and the corresponding extrusion speed is 9m / min. S2-5. The slab extruded in step 2-4 is quenched and cooled to room temperature. The slab is then chamfered and the surface is cleaned to obtain a magnesium alloy sheet.

2. The preparation method according to claim 1, characterized in that, The protective gas mentioned in step S1-2 is a mixture of CO2 and SF6.

3. The preparation method according to claim 2, characterized in that, The volume ratio of CO2 to SF6 is 100:1.

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