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

Abstract

The invention provides a preparation method of a high-strength and high-thermal-conductivity magnesium alloy plate, and relates to the technical field of magnesium alloy processing. The method comprises the following steps: carrying out annealing treatment on a rare earth magnesium alloy plate at 170 DEG C; the annealed rare earth magnesium alloy plate is rolled, in the rolling process, the preheating temperature of a roller is 120 DEG C, the linear speed of the roller is 5 m / min, the rolling reduction is 70%, and the rare earth magnesium alloy plate with the thickness of 1.8 mm is obtained; the rare earth magnesium alloy plate is subjected to quenching treatment and taken out after being cooled to the room temperature; and the quenched rare earth magnesium alloy plate is subjected to aging treatment at the temperature of 90 DEG C for 24-48 h, and the high-strength and high-thermal-conductivity magnesium alloy plate is obtained after the rare earth magnesium alloy plate is air-cooled to the room temperature. According to the magnesium alloy plate prepared through the method, the tensile strength can reach up to 456 MPa, the yield strength is 408 MPa, the ductility is 13%, and the heat conductivity is 125-134 (W / (m.K)).

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloys, and specifically relates to a forming process of a high-thermal-conductivity and high-strength magnesium alloy plate. Background Art

[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 a good development prospect 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, it is usually alloyed and deformed. The widely used commercial magnesium alloys such as AM60 and AZ31 have good forming and room temperature mechanical properties, but their heat dissipation capacity is not ideal. Their thermal conductivity values ​​are only 61W / (m·K)) and 96.4W / (m·K), which is far lower than the thermal conductivity of pure magnesium. On the other hand, rolling is a common magnesium alloy deformation process. The magnesium alloy sheet after rolling has high mechanical properties. However, rolling will greatly reduce its thermal conductivity, making it difficult to further apply. This contradiction between mechanical properties and thermal conductivity limits the research and development and design of high-strength and high-thermal-conductivity magnesium alloys. Summary of the invention

[0003] The main purpose of the present invention is to overcome the deficiencies in the prior art, solve the problem that the comprehensive mechanical properties and thermal conductivity of the existing magnesium alloys are not compatible, and develop a method for preparing a low-rare earth magnesium alloy plate with excellent mechanical and thermal conductivity. The present invention performs vertical die hot extrusion and rolling deformation treatment on the magnesium alloy material and then performs aging heat treatment to refine the dynamic recrystallization grain size while increasing the dispersion of the second phase, so that the strength of the alloy is at the 450MPa level and the thermal conductivity reaches above 130 (W / (m·K)).

[0004] The present invention is implemented by the following technical scheme: A preparation process of a high-strength and high-thermal-conductivity magnesium alloy sheet comprises the following steps:

[0005] (1) annealing the rare earth magnesium alloy plate, wherein the annealing temperature is 170° 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 sheet, wherein the preheating temperature of the roll is 120° C., the linear speed of the roll is 5 m / min, and the reduction is 70%, to obtain a rare earth magnesium alloy sheet with a thickness of 1.8 mm;

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

[0008] (4) The quenched rare earth magnesium alloy sheet is subjected to aging treatment at a temperature of 90° C. for 24 to 48 h, and then air-cooled to room temperature to obtain a high-strength and high-thermal-conductivity magnesium alloy sheet.

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

[0010] S1. Preparation of magnesium alloy ingots

[0011] The magnesium ingot, zinc particles, Mg-Gd master alloy, Mg-Mn master alloy and Mg-Y master alloy are removed from the surface and then heated and melted in a protective atmosphere, and then the mixed melt is poured into a mold, and the mold is demolded after cooling to obtain a magnesium alloy ingot with a low rare earth content;

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

[0013] S2-1, placing the magnesium alloy ingot in a heat treatment furnace for graded solution treatment, the first stage is a heating temperature of 420-480°C, a holding time of 6-8h, and the second stage is a heating temperature of 500-520°C, a holding time of 10-12h;

[0014] S2-2, after the graded solid solution treatment, the magnesium alloy ingot is polished and smooth, placed in a mold, heated to 300°C, kept warm for 40 minutes, and hot pressed at a loading speed of 10 KN / s. When the magnesium alloy ingot is hot pressed to 60 mm, the pressure is maintained for 100 seconds;

[0015] S2-3, processing the magnesium alloy ingot after hot pressing in step S2-2 into a standard sample size, and grinding it to a smooth surface; then placing the ingot in a heat treatment furnace for heating at a temperature of 300° C. for 30 minutes, and preheating the indenter, the die, the upper pad and the extrusion die for subsequent use;

[0016] S2-4, extruding the magnesium ingot after hot pressing in step 2-3, flipping the hot pressed block 90°, taking the PD-TD surface after hot pressing as the extrusion direction, a total of three steps of extrusion, the extrusion ratio is 25:1, the initial rate is 5m / min, the extrusion pressure is 2900KN, the initial extrusion temperature is 300-310℃, cutting and sampling are performed after the first section of plate extrusion, and then the extrusion temperature is reduced by 10-20℃ in each step, and the corresponding rate is increased by 2m / min, and the extrusion pressure is always maintained at 2700-3000KN, the second section extrusion temperature is 280-300℃, the rate is 7m / min, the third section extrusion temperature is 260-280℃, and the corresponding extrusion rate is 9m / min;

[0017] S2-5, quenching the slab after extrusion in step 2-4, cooling the slab to room temperature, chamfering the slab, and polishing the surface to obtain a magnesium alloy sheet.

[0018] More preferably, the protective gas in step S1-2 is a mixed gas 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 invention has the following beneficial effects:

[0021] The present invention regulates the amount and distribution of phases in the rare earth magnesium alloy by low rare earth microalloying and multi-step deformation, thereby solving the problems of high cost of rare earth magnesium alloy and difficulty in matching strength and thermal conductivity. The alloy plate is single-pass rolled after annealing at 170°C for 30 minutes, and then low-temperature aging is performed. The tensile strength of the plate can reach 456MPa, the yield strength is 408MPa, the elongation is 13%, and the thermal conductivity is 125-134 (W / (m·K)). BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0024] Figure 3 The microstructure morphology of the extruded Mg-5Zn-1Gd-1Y-1Mn magnesium alloy;

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

[0026] Figure 5 The microstructure morphology of Mg-5Zn-1Gd-1Y-1Mn magnesium alloy after aging at 90℃ for 24h;

[0027] Figure 6 Tensile curves of Mg-5Zn-1Gd-1Y magnesium alloy in cast, extruded, rolled, and aged state after rolling.

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

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the preferred embodiments of the present invention are further described in detail in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

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

[0032] S1-1 soaks the pure Mg prepared in advance in an acidic solution to remove the oxide on the surface, and then polishes 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 with a grinder and an angle grinder to make the surface bright, so as to remove the influence of oxide scale and impurities on material preparation. After polishing, the raw materials are wrapped with aluminum foil and sealed for storage.

[0033] S1-2 Preheat the stainless steel crucible in a pit furnace, take it out when it is preheated to 500℃, and apply talcum powder coating and zinc oxide coating on its surface to prevent the Mg melt from directly contacting the crucible wall and introducing impurities. Then put the crucible in a pit furnace for heating, put pure Mg in when the temperature reaches 720℃, and introduce a mixed gas of CO2 and SF6 (the volume ratio of CO2 and SF6 is 100:1) as the protective gas during the smelting process.

[0034] S1-3 After the pure Mg is completely melted, let it stand for 15 minutes, add zinc particles, and stir for 1 minute. At the same time, wrap the Mg-30Gd and Mg-30Y intermediate alloys with aluminum foil, place them on the furnace for preheating, then increase the crucible temperature to 760°C, put in the preheated Mg-30Gd, Mg-30Y and Mg-30Mn intermediate alloys, stir rapidly for 3 minutes, keep warm for 10 minutes, lower the crucible temperature to 720°C, cast the molten alloy into a mold preheated to 250°C, and then naturally air cool to room temperature to obtain an 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 graded solution treatment. The first stage is a heating temperature of 430°C and a holding time of 6 hours. The second stage is a heating temperature of 500°C and a holding time of 10 hours.

[0037] S2-2, polish the surface of the magnesium alloy ingot homogenized in step 2-1 until the surface is smooth, put it into the mold, preheat it to 300°C with the furnace, keep it warm for 40 minutes, and perform hot pressing at a loading speed of 10KN / s. When the sample is hot pressed to 60mm, keep the pressure for 100s.

[0038] S2-3, process the magnesium alloy ingot after hot pressing in step S2-2 into a standard sample size and polish it until the surface is smooth. Then put the ingot into a heat treatment furnace for heating at a temperature of 300°C for 30 minutes, and preheat the pressure head, the concave die, the upper pad and the extrusion die for subsequent use;

[0039] S2-4, extruding the magnesium ingot after hot pressing in step 2-3, flipping the hot pressed block 90 degrees, taking the PD-TD surface after hot pressing as the extrusion direction, a total of three steps of extrusion, the extrusion ratio is 25:1, the initial rate is 5m / min, the extrusion pressure is 2900KN, the initial extrusion temperature is 300℃, cutting and sampling are performed after the first section of plate extrusion, and then the extrusion temperature is reduced by 20℃ in each step, and the corresponding rate is increased by 2m / min, and the extrusion pressure is always maintained at 2900KN, the second section extrusion temperature is 280℃, the rate is 7m / min, the third section extrusion temperature is 260℃, and the corresponding extrusion rate is 9m / min;

[0040] S2-5. Put the slab extruded in step 2-4 into 60°C warm water for quenching treatment. After the slab is cooled to room temperature, take it out, chamfer the slab, and polish the surface for subsequent use.

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

[0042] S3-1, placing the slab obtained in step 2 into a heat treatment furnace for annealing at a temperature of 170° C. for 30 minutes;

[0043] S3-2, put the slab obtained in step 3-1 into the BKD Ф350×400 test rolling mill, and quickly feed the sample into the roller for rolling. During the rolling process, the roller preheating temperature is 120°C, the roller linear speed is 5m / min, the reduction is 70%, and a plate with a thickness of 1.8mm is obtained;

[0044] S3-3, placing the slab obtained in step 3-2 into 60°C warm water for quenching, and taking it out after the slab is cooled to room temperature.

[0045] S3-4, aging the magnesium alloy sheet after rolling in step S4-2 at an aging temperature of 90° C. for 24 hours, and then air-cooling to room temperature to obtain a high-strength and high-thermal-conductivity magnesium alloy sheet.

[0046] By comparing the microstructure of the magnesium alloy after extrusion and that after rolling, it can be seen that most of the second phase at the grain boundary after solid solution is dissolved into the matrix. After extrusion deformation, obvious dynamic recrystallization occurs around the second phase. The soft and hard structures of the deformed structure and the recrystallized structure cooperate with each other, which greatly improves the plastic deformation capacity of the plate. After annealing at 170°C for 30 minutes and single-pass rolling after annealing, the magnesium alloy plate has a tensile strength of 385MPa, a yield strength of 337MPa, and an elongation of 13% to 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 36 hours, and the others are the same as Example 1. After low-temperature aging, the tensile strength is as high as 416 MPa, the yield strength is 352 MPa, 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 48 hours, and the others are the same as Example 1. After low-temperature aging, the tensile strength is as high as 422 MPa, the yield strength is 338 MPa, the elongation is 14%, and the thermal conductivity is 127 (W / (m·K)).

[0052] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength and high-thermal-conductivity magnesium alloy sheet, characterized in that: The following steps are involved: (1) annealing the rare earth magnesium alloy plate, wherein the annealing temperature is 170° C. and the annealing time is 30 min; the rare earth magnesium alloy plate is Mg-5Zn-1Gd-1Y-1Mn; (2) rolling the annealed rare earth magnesium alloy sheet, wherein the preheating temperature of the roll is 120° C., the linear speed of the roll is 5 m / min, and the reduction is 70%, to obtain a rare earth magnesium alloy sheet with a thickness of 1.8 mm; (3) quenching the rare earth magnesium alloy plate, cooling it to room temperature and then taking it out; (4) The quenched rare earth magnesium alloy sheet is subjected to aging treatment at a temperature of 90° C. for 24 to 48 h, and then air-cooled to room temperature to obtain a high-strength and high-thermal-conductivity magnesium alloy sheet.

2. The preparation method according to claim 1, characterized in that: The method for preparing the rare earth magnesium alloy plate in step (1) comprises the following steps: S1. Preparation of magnesium alloy ingots S1-1, removing impurities from the surfaces of magnesium flakes, zinc particles, Mg-Gd master alloy, Mg-Mn master alloy, and Mg-Y master alloy, and then sealing and storing them; S1-2, heating and melting the magnesium flakes under a protective atmosphere to obtain a Mg melt; S1-3, adding zinc particles to the Mg melt and stirring evenly, adding Mg-Gd alloy and Mg-Y master alloy, heating and melting, and then adding Mg-Mn master alloy and heating and melting to obtain a mixed melt; S1-4, pouring the mixed melt into a mold, and demolding after cooling to obtain a magnesium alloy ingot with a low rare earth content; S2, extruding the magnesium alloy ingot with low rare earth content S2-1, placing the magnesium alloy ingot in a heat treatment furnace for graded solution treatment, the first stage is a heating temperature of 420-480°C, a holding time of 6-8h, and the second stage is a heating temperature of 500-520°C, a holding time of 10-12h; S2-2, after the graded solid solution treatment, the magnesium alloy ingot is polished and smooth, placed in a mold, heated to 300°C, kept warm for 40 minutes, and hot pressed at a loading speed of 10 KN / s. When the magnesium alloy ingot is hot pressed to 60 mm, the pressure is maintained for 100 seconds; S2-3, processing the magnesium alloy ingot after hot pressing in step S2-2 into a standard sample size, and grinding it to a smooth surface; then placing the ingot in a heat treatment furnace for heating at a temperature of 300° C. for 30 minutes, and preheating the indenter, the die, the upper pad and the extrusion die for subsequent use; S2-4, extruding the magnesium ingot after hot pressing in step 2-3, flipping the hot pressed block 90°, taking the PD-TD surface after hot pressing as the extrusion direction, a total of three steps of extrusion, the extrusion ratio is 25:1, the initial rate is 5m / min, the extrusion pressure is 2900KN, the initial extrusion temperature is 300-310℃, cutting and sampling are performed after the first section of plate extrusion, and then the extrusion temperature is reduced by 10-20℃ in each step, and the corresponding rate is increased by 2m / min, and the extrusion pressure is always maintained at 2700-3000KN, the second section extrusion temperature is 280-300℃, the rate is 7m / min, the third section extrusion temperature is 260-280℃, and the corresponding extrusion rate is 9m / min; S2-5, quenching the slab after extrusion in step 2-4, cooling the slab to room temperature, chamfering the slab, and polishing the surface to obtain a magnesium alloy sheet.

3. The preparation method according to claim 2, characterized in that: The protective gas in step S1-2 is a mixed gas of CO2 and SF6.

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

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