A low-cost corrosion-resistant wrought magnesium alloy with ultrahigh thermal conductivity and a preparation method thereof

Abstract

The application discloses a low-cost corrosion-resistant deforming magnesium alloy with super-high thermal conductivity and a preparation method thereof. The magnesium alloy comprises Mg, Zn, Mn and Ca, and the molar ratio of Mg:Zn is (99.4-99.7):(0.1-0.2), and the molar ratio of Zn:Mn:Ca is 1:1:1. The preparation method comprises the following steps: preparing a micro-alloyed preform, preparing an alloy net-dense ingot, and plastic forming to obtain the low-cost super-high thermal conductivity corrosion-resistant deforming magnesium alloy. The low-cost super-high thermal conductivity corrosion-resistant deforming magnesium alloy is obtained by adding Zn, Mn and Ca alloy elements with similar valence electron structures to Mg in high-purity Mg, and has the characteristics of high thermal conductivity, high corrosion resistance and guaranteed mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of deformable magnesium alloys, and in particular to a low-cost, corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity and a preparation method thereof. Background Art

[0002] Magnesium alloy is the lightest metal structural material (ρ=1.8g / cm 3 ), which is comparable to the density of commonly used engineering plastics, and is 1 / 3 and 3 / 4 lower than the density of aluminum alloys and steel, respectively. It is very suitable for the lightweight development of the new generation of communication equipment (such as mobile base stations) and has a broad application market. According to reports, as of July 2023, China has built a total of 3.055 million 5G base stations, accounting for 26.9% of the total number of mobile base stations. Unfortunately, there is a large gap between the thermal conductivity (λ = 50-100W / (m·K)) of ordinary commercial magnesium alloys (such as Mg-Al magnesium alloys) and mainstream aluminum alloy materials (such as 6082 and 7075, λ = 130-160W / (m·K), and the latter has excellent formability, higher mechanical properties and good corrosion resistance than ordinary commercial magnesium alloys. In summary, lower thermal conductivity and lower corrosion resistance hinder the release of the lightweight advantages of magnesium alloys in the field of communication equipment.

[0003] While existing magnesium alloy preparation processes offer some good performance, their thermal conductivity remains lower than that of mainstream aluminum alloys, generally below 150W / (m·K), when applied to the technical requirements of thermal management components for communications equipment. This makes it difficult to meet the demands of lightweight, high-heat dissipation devices. Furthermore, their corrosion resistance is generally low, hindering the application and development of magnesium alloys in communications equipment. The current magnesium alloy preparation processes are as follows:

[0004] 1. The performance of the composite reinforcement design with high thermal conductivity particles is poor, and the cost of using rare and precious metals is high.

[0005] This type of method generally adopts the addition of an appropriate amount of non-metal with high thermal conductivity, such as Si (λ~150W / (m·K)) or metallic copper (λ~400W / (m·K)), metallic silver (λ~430W / (m·K)), to achieve a high thermal conductivity magnesium alloy with a thermal conductivity of 120-140W / (m·K). The patent application number is [CN202110201544.4], entitled "A high-strength and high-thermal conductivity magnesium alloy for ultra-thin-walled components for die casting and its preparation method". The addition of Cu obtains a 200MPa yield strength magnesium alloy of 130W / (m·K) level, and the elongation of the die-cast alloy can reach 10%. However, since Cu, Si, etc. are strictly controlled impurity elements in magnesium alloys, the addition of Cu in particular significantly deteriorates the corrosion resistance of the alloy, which is undoubtedly a huge safety hazard to the safe service of magnesium alloy heat dissipation devices. Ag is a rare and precious metal with high cost. It has poor economic efficiency in the civilian field and is not suitable for promotion.

[0006] 2. The design cost of heavy rare earth alloying is relatively high and is not suitable for promotion in the civilian field.

[0007] This type of alloy generally adds a relatively high content of rare earth alloying elements represented by Gd, Y, Nd, Ce, La, etc. The patent application number is [CN201911215432.3], and the name is “A low rare earth high thermal conductivity magnesium alloy and its preparation method”. It discloses a Mg-Zn-Gd-Er-Zr alloy with up to 10wt.% of rare earth elements Gd, Er, and Zr added. The room temperature thermal conductivity can reach 137W / (m·K) and the elongation can reach 24%. However, such rare earth elements and their intermediate alloys are relatively expensive and have poor economic efficiency, making them unsuitable for large-scale civilian promotion. At the same time, such alloys generally contain a large amount of brittle rare earth-containing intermetallic compounds, which are generally suitable for casting processing (die casting, sand casting, etc.). The thermoplastic forming performance and welding performance are poor. They are not suitable for plastic forming methods such as extrusion and forging, and the application scenarios of the technology are limited.

[0008] 3. Rare earth-free (trace) design has controllable costs and better economy, but the thermal conductivity of the published or reported thermally conductive magnesium alloys is still lower than that of pure magnesium and the corrosion resistance is poor.

[0009] This type of alloy uses Zn and Mn, two alloying elements that have minimal impact on the thermal conductivity attenuation of the magnesium matrix, as the primary elements. This Mg-Zn-based Mg-Zn-Mn alloy is designed. Patent application number [CN201410564789.3], titled "High Thermal Conductivity Mg-Zn-Mn Wrought Magnesium Alloy and Preparation Method Thereof," further enhances the alloy's mechanical properties by adding microalloying elements such as Ca, Mn, Sn, La, Zr, and Ce. However, when the Zn content is high, the corrosion rate is generally higher than 1 mm / a, resulting in poor corrosion resistance. Summary of the Invention

[0010] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity and a preparation method thereof. By adding Zn, Mn, and Ca alloy elements having a similar valence electron structure to Mg to high-purity magnesium, a low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity is obtained, which has the characteristics of high thermal conductivity, high corrosion resistance, applicable yield strength and elongation at break.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity. The magnesium alloy comprises Mg, Zn, Mn and Ca. In a molar ratio, Mg:Zn=(99.4-99.7):(0.1-0.2), and Zn:Mn:Ca=1:1:1.

[0013] The Zn, Mn and Ca are micro-alloying elements and have a similar valence electron structure to Mg.

[0014] A method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity comprises the following steps:

[0015] Step 1, preparing a microalloyed preform: adding high-purity magnesium, magnesium-calcium master alloy, and magnesium-manganese master alloy into a container, heating to 200-300° C. and holding for 1-2 hours, further heating to 650-700° C. and holding for 1-2 hours, heating to 750-800° C. and holding for 1-2 hours, until all the materials are melted, and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = (96-98):(1-2), and calcium:manganese = 1:1;

[0016] Step 2, preparing a net dense alloy ingot: preheating the high-purity magnesium, high-purity zinc, and the microalloyed preform prepared in step 1 to 300-350° C. in argon and keeping the temperature for 1-2 hours, then heating the preform to 750-800° C. and keeping the temperature for 1-2 hours, performing physical slag removal using a flux-free porous baffle, and casting to complete the preparation of the net dense alloy ingot; the net dense alloy ingot has a molar ratio of magnesium:zinc = (99.4-99.7):(0.1-0.2), and zinc:manganese:calcium = 1:1:1;

[0017] Step 3, plastic forming: homogenize the alloy net dense ingot prepared in step 2 under an argon protective atmosphere at a homogenization temperature of 400-450°C for a homogenization time of 6-56 hours, and water quench to obtain a homogenized alloy ingot. The obtained homogenized alloy ingot is subjected to thermomechanical treatment to obtain a low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity.

[0018] The magnesium-calcium master alloy in step 1 is one of Mg-10wt.%Ca, Mg-15wt.%Ca, Mg-20wt.%Ca or Mg-30wt.%Ca.

[0019] The magnesium-manganese master alloy in step 1 is Mg-5wt.%Mn or Mg-10wt.%Mn.

[0020] The thermomechanical treatment in step 3 is one of extrusion, forging, rolling and drawing.

[0021] The extrusion forming process has the following characteristics: the preheating temperature of the billet is 300-350°C, the temperature of the extrusion die is 350-400°C, the extrusion feed speed is 0.3-1mm / s, the temperature of the extrusion barrel is set to 300-350°C, the extrusion ratio is set to 10-30, and the extruded material is pulled by a traction machine with a traction force of 100-500N.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The ultra-high thermal conductivity, low-cost, corrosion-resistant deformable magnesium alloy prepared by the present invention selects atoms with a similar valence electron structure to magnesium atoms as microalloying elements. According to the periodic table, the valence electron configuration of Zn is 3d 10 4s 2 The valence electron configurations of Ca are 4s 2 The valence electron configuration of Mn is 3d 5 4s 2 , which are all arranged in the same way as the valence electrons of Mg element 3s 2 There is a certain similarity between them, so a small amount of solid solution of Zn, Ca and Mn elements into Mg alloy has little effect on the electronic thermal conductivity, and it has the characteristics of high thermal conductivity.

[0024] 2. The ultra-high thermal conductivity, low-cost, corrosion-resistant deformable magnesium alloy prepared by the present invention selectively adds solid solution atoms larger and smaller than the Mg atomic radius at the same time, which is easy to form segregation at the grain boundaries. The Zn atomic radius is 133pm, the Mn atomic radius is 136pm, and the Mg atomic radius is 160pm, all smaller than the Mg atomic radius. The Ca atomic radius is 197ppm, larger than the Mg atomic radius, and the two types of atoms (Zn+Ca) with atomic radius smaller than the Mg atomic radius and atomic radius larger than the Mg atomic radius are easy to form periodic co-segregation at the tensile stress and compressive stress positions of the magnesium alloy grain boundaries, reducing grain boundary energy to achieve grain boundary stability, thereby facilitating the formation of fine and uniform grain structure during subsequent thermomechanical processing and improving its room temperature strength and plasticity.

[0025] 3. In the alloy net dense ingot prepared in step 2 of the present invention, the molar ratio is: magnesium: zinc = (99.4-99.7): (0.1-0.2), zinc: manganese: calcium = 1:1:1, and the added zinc, manganese and calcium are relatively small. Therefore, the prepared low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity is low in cost, and the room temperature thermal conductivity of the deformed alloy can reach more than 160 W / (m·K), and can reach up to 175 W / (m·K). The yield strength and total elongation at break mechanical properties are better than those of the AZ31B deformed alloy prepared under the same processing parameters. At the same time, the corrosion rate can be reduced to below 0.5 mm / a and presents uniform corrosion characteristics, which has the characteristics of high corrosion resistance.

[0026] 4. In step 2 of the present invention, physical slag removal with a flux-free porous baffle is performed before casting to avoid a) chloride ions (Cl - ) residues affect the subsequent corrosion resistance; b) introduce low melting point impurities such as Na, sodium ions (Na + ) is easily reduced by calcium to introduce low-melting-point impurities such as Na, which increases the alloy's tendency to hot brittleness and deteriorates subsequent plastic forming properties. It has the characteristics of suitable yield strength and elongation at break.

[0027] In summary, the present invention obtains a low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity by adding Zn, Mn, and Ca alloy elements with similar valence electron structures to Mg to high-purity magnesium. The alloy has the characteristics of high thermal conductivity, high corrosion resistance, applicable yield strength and elongation at break. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the preparation method of the present invention.

[0029] Figure 2 This is a grain boundary segregation analysis diagram of the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, wherein: Figure 2 (a) Schematic diagram of focused ion beam (FIB) slice morphology; Figure 2 (b) is the TEM bright field image of the corresponding observation position; Figure 2 (c) TEM dark field image of the corresponding observation position and the observation area of ​​grain boundary segregation marked ROI-1 and ROI-2; Figure 2 (d) is the EDS spectrum of the area adjacent to the grain boundary of ROI-1. In this area, Figure 2 (e) is Mn, Figure 2 (h) is Zn, Figure 2 (i) is Ca; Figure 2 (f) is the EDS spectrum of the area adjacent to the grain boundary of ROI-2. In this area, Figure 2 (g) is Mn, Figure 2 (j) is Zn, Figure 2 (k) is Ca.

[0030] Figure 3 Optical microstructure diagram of the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention.

[0031] Figure 4 This is a comparison chart of the room temperature thermal conductivity of the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention and other alloys.

[0032] Figure 5 This is a comparison diagram of the corrosion-resistant deformable magnesium alloy prepared by performing physical slag removal with a flux-free porous baffle in step 3 and not performing physical slag removal with a flux-free porous baffle.

[0033] Figure 6 This is a comparison of the corrosion morphologies of the low-cost, corrosion-resistant, deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention after physical deslagging with a flux-free porous baffle and without. Figure 6 (a) is the corrosion morphology of the sample without physical deslagging by flux-free porous baffle (Highpurity, HP). Figure 6(b) is the corrosion morphology of physical deslagging (Highpurity, HP) after flux-free porous baffle.

[0034] Figure 7 This is a comparison chart of the low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity prepared by the present invention and the commercial AZ31B wrought magnesium alloy, wherein: Figure 7 (a) is a comparison diagram of engineering stress-strain curves, Figure 7 (b) is a comparison chart of yield strength.

[0035] Figure 8 This is a comparison chart of the tangent modulus of the low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity prepared by the present invention and the commercial AZ31B wrought magnesium alloy as a function of loading stress. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings.

[0037] Example 1

[0038] See also Figure 1 , a low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity, the magnesium alloy includes Mg, Zn, Mn, and Ca, and the molar ratio is Mg:Zn=99.7:0.1, Zn:Mn:Ca=1:1:1.

[0039] A method for preparing a low-cost, corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity comprises the following steps:

[0040] Step 1, preparing a microalloyed preform: adding high-purity magnesium (99.99%), Mg-10wt.%Ca, and Mg-5wt.%Mn into a high-purity, high-density graphite crucible, heating to 300°C and holding for 1 hour, further heating to 750°C and holding for 1 hour, heating to 780°C and holding for 2 hours, until all the materials are melted, tilting the melted materials into the graphite crucible, pouring the melt into a rod-shaped graphite mold with a feeding riser, and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = 98:1, and calcium:manganese = 1:1;

[0041] Step 2, preparing a net dense alloy ingot: high-purity magnesium (99.99%), high-purity zinc (99.99%), and the microalloyed preform prepared in step 1 are preheated to 300° C. in argon and kept for 2 hours, then heated to 780° C. and kept for 2 hours. Before casting, physical slag removal is performed using a flux-free porous baffle to complete the preparation of a net dense alloy ingot; the net dense alloy ingot has a molar ratio of magnesium:zinc = 99.7:0.1, and zinc:manganese:calcium = 1:1:1;

[0042] Step 3, plastic forming: homogenize the alloy net dense ingot prepared in step 2 under an argon protective atmosphere, the homogenization temperature is 450°C, the homogenization time is 20 hours, and water quenching is performed to obtain a homogenized alloy ingot. The obtained homogenized alloy ingot is extruded to obtain a low-cost, ultra-high thermal conductivity, and corrosion-resistant deformable magnesium alloy; extrusion forming, the billet preheating temperature is 350°C, the extrusion die temperature is 400°C, the extrusion feed speed is 0.3 mm / s, the extrusion barrel temperature is set to 350°C, the extrusion ratio is set to 18, and the extruded material is pulled by a traction machine with a traction force of 200N.

[0043] Example 2

[0044] A low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity. The magnesium alloy comprises Mg, Zn, Mn and Ca. In a molar ratio, Mg:Zn=99.4:0.2, and Zn:Mn:Ca=1:1:1.

[0045] A method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity comprises the following steps:

[0046] Step 1, preparing a microalloyed preform: adding high-purity magnesium, Mg-20wt.%Ca, and Mg-10wt.%Mn into a high-purity, high-density graphite crucible, heating to 200°C and holding for 2 hours, further heating to 650°C and holding for 2 hours, heating to 800°C and holding for 1 hour, until all the materials are melted, tilting the melted materials into the graphite crucible, pouring the melt into a rod-shaped graphite mold with a feeding riser, and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = 96:2, and calcium:manganese = 1:1;

[0047] Step 2, preparing an alloy net dense ingot: high-purity magnesium (99.99%), high-purity zinc (99.99%), and the microalloyed preform prepared in step 1 are preheated to 350° C. in argon and kept for 1 hour, then heated to 800° C. and kept for 1 hour. Before casting, physical slag removal is performed using a flux-free porous baffle to complete the preparation of the alloy net dense ingot; the alloy net dense ingot has a molar ratio of magnesium:zinc = 99.4:0.2, and zinc:manganese:calcium = 1:1:1;

[0048] Step 3, plastic forming: homogenize the alloy net dense ingot prepared in step 2 under a protective atmosphere, the homogenization temperature is 400°C, the homogenization time is 56 hours, and water quenching is performed to obtain a homogenized alloy ingot, and the obtained homogenized alloy ingot is extruded to obtain a low-cost, ultra-high thermal conductivity, and corrosion-resistant deformable magnesium alloy; in extrusion forming, the billet preheating temperature is 300°C, the extrusion die temperature is 350°C, the extrusion feed speed is 1 mm / s, the extrusion barrel temperature is set to 300°C, the extrusion ratio is set to 30, and the extruded material is pulled by a traction machine with a traction force of 300N.

[0049] Example 3

[0050] A low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity. The magnesium alloy comprises Mg, Zn, Mn and Ca. In a molar ratio, Mg:Zn=99.6:0.13, and Zn:Mn:Ca=1:1:1.

[0051] A method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity comprises the following steps:

[0052] Step 1, preparing a microalloyed preform: adding high-purity magnesium, Mg-15wt.%Ca and Mg-10wt.%Mn into a high-purity, high-density graphite crucible, heating to 230°C and holding for 1.4 hours, further heating to 660°C and holding for 1.2 hours, heating to 780°C and holding for 1.5 hours, until all the materials are melted, pouring the melted materials into a graphite mold with a feeding riser and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = 97:1.5, and calcium:manganese = 1:1;

[0053] Step 2, preparing an alloy net dense ingot: high-purity magnesium (99.99%), high-purity zinc (99.99%), and the microalloyed preform prepared in step 1 are heated to 330° C. and kept for 1.5 hours in argon gas for preheating, then heated to 780° C. and kept for 1.5 hours. Before casting, physical slag removal is performed using a flux-free porous baffle to complete the preparation of the alloy net dense ingot; the alloy net dense ingot has a molar ratio of magnesium:zinc = 99.6:0.13, and zinc:manganese:calcium = 1:1:1;

[0054] Step 3, plastic forming: homogenizing the alloy net dense ingot prepared in step 2 under a protective atmosphere, the homogenization temperature is 420°C, the homogenization time is 30 hours, and water quenching is performed to obtain a homogenized alloy ingot, and the obtained homogenized alloy ingot is extruded to obtain a low-cost, ultra-high thermal conductivity, and corrosion-resistant deformable magnesium alloy; extrusion forming, the billet preheating temperature is 330°C, the extrusion die temperature is 380°C, the extrusion feed speed is 0.5 mm / s, the extrusion barrel temperature is set to 330°C, the extrusion ratio is set to 15, and the extruded material is pulled by a traction machine with a traction force of 300N.

[0055] Example 4

[0056] A low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity. The magnesium alloy comprises Mg, Zn, Mn and Ca. In a molar ratio, Mg:Zn=99.55:0.15, and Zn:Mn:Ca=1:1:1.

[0057] A method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity comprises the following steps:

[0058] Step 1, preparing a microalloyed preform: adding high-purity magnesium, Mg-30wt.%Ca, and Mg-10wt.%Mn into a high-purity, high-density graphite crucible, heating to 250°C and holding for 1.5 hours, further heating to 680°C and holding for 1.5 hours, heating to 790°C and holding for 1.7 hours, until all the materials are melted, pouring the melted materials into a graphite mold with a feeding riser and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = 96.4:1.8, and calcium:manganese = 1:1;

[0059] Step 2, preparing an alloy net dense ingot: high-purity magnesium (99.99%), high-purity zinc (99.99%), and the microalloyed preform prepared in step 1 are preheated to 340° C. in argon and kept warm for 1.7 hours, then heated to 790° C. and kept warm for 1.7 hours. Before casting, physical slag removal is performed using a flux-free porous baffle to complete the preparation of the alloy net dense ingot; the alloy net dense ingot has a molar ratio of magnesium:zinc = 99.55:0.15, and zinc:manganese:calcium = 1:1:1;

[0060] Step 3, plastic forming: homogenizing the alloy net dense ingot prepared in step 2 under a protective atmosphere, the homogenization temperature is 430°C, the homogenization time is 40h, and water quenching is performed to obtain a homogenized alloy ingot, and the obtained homogenized alloy ingot is extruded to obtain a low-cost, ultra-high thermal conductivity, and corrosion-resistant deformable magnesium alloy; extrusion forming, the billet preheating temperature is 340°C, the extrusion die temperature is 390°C, the extrusion feed speed is 0.7mm / s, the extrusion barrel temperature is set to 340°C, the extrusion ratio is set to 20, and the extruded material is pulled by a traction machine with a traction force of 400N.

[0061] See also Figure 2 , which is a grain boundary segregation analysis diagram of the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, Figure 2 (a) is a schematic diagram of the focused ion beam (FIB) slice morphology and the observation position marking. The observation position is marked with a yellow dotted line. Figure 2 (b) is the TEM bright field image of the corresponding observation position; Figure 2 (c) TEM dark field image of the corresponding observation position and the observation area of ​​grain boundary segregation marked ROI-1 and ROI-2;

[0062] Figure 2 (d) Figure 2 (e) Figure 2 (h) and Figure 2(i) is the EDS spectrum of the area near the grain boundary of ROI-1. It can be seen that Zn and Ca are distributed in a concentrated manner at the grain boundary, while Mn is mainly distributed in the form of nanoparticles; Figure 2 (f) Figure 2 (g) Figure 2 (j) and Figure 2 (k) is the EDS energy spectrum of the ROI-2 grain boundary vicinity. It can be seen that Zn and Ca are segregated at the grain boundaries, while Mn is mainly distributed in the form of nanoparticles. The above results prove that in the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, the Zn atomic radius is 133pm, the Mn atomic radius is 136pm, and the Mg atomic radius is 160pm, all of which are smaller than the Mg atomic radius. The Ca atomic radius is 197ppm, which is larger than the Mg atomic radius. The two types of atoms (Zn+Ca) with atomic radius smaller than the Mg atomic radius and atomic radius larger than the Mg atomic radius are easy to form periodic co-segregation at the tensile stress and compressive stress positions of the magnesium alloy grain boundaries, reduce grain boundary energy and achieve grain boundary stability, thereby facilitating the formation of fine and uniform grain structure during subsequent thermomechanical processing, and improving its room temperature strength and plasticity.

[0063] See also Figure 3 , which is the optical microstructure of the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention. It can be seen that the low-cost corrosion-resistant deformable magnesium alloy prepared by the present invention has a uniform and refined grain structure, which confirms Figure 2 The grain boundary segregation design is beneficial to the formation of fine and uniform grain structure during subsequent thermomechanical processing.

[0064] See also Figure 4 The low-cost, corrosion-resistant, deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention had test results of 171.23 W / (m·K), 167.71 W / (m·K), and 174.72 W / (m·K) for three randomly selected samples, respectively. The average value was 9% higher than the theoretical room-temperature thermal conductivity of pure magnesium (156 W / (m·K)), and nearly 200% higher than the room-temperature thermal conductivity of commercial AZ31B magnesium alloy. This confirms that the selection of atoms with similar valence electron structures to magnesium atoms as microalloying elements, such as Zn, Ca, and Mn, to be dissolved in a small amount into the Mg alloy has little effect on the electronic thermal conductivity, thereby achieving high thermal conductivity.

[0065] According to JB / T 7901-2001 - Laboratory Uniform Corrosion Full Immersion Test Method for Metal Materials, samples of low-cost corrosion-resistant wrought magnesium alloy extruded sheets with ultra-high thermal conductivity were placed in a 3.5% sodium chloride solution at 25°C for 7 days. The corrosion rate results are shown in Table 1:

[0066] Table 1

[0067]

[0068]

[0069] Table 1 compares the corrosion rates of the low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity prepared by the present invention, namely the alloy of the present invention (HP), and the existing ingot alloy (LP). Under the conditions of the same homogenization treatment, extrusion rate, extrusion ratio and similar extrusion temperature, the corrosion rate of the low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity prepared by the present invention, namely the alloy of the present invention (HP), is significantly lower than the corrosion rate of the ingot alloy (LP) in the prior art, and the corrosion rate is lower than 0.5 mm / a, which is a general corrosion-resistant magnesium alloy.

[0070] See also Figure 5 The low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention undergoes physical deslagging with a flux-free porous baffle (High purity, HP) in step 3 of the present invention, and the hydrogen evolution rate is significantly reduced compared with the group without physical deslagging with a flux-free porous baffle (Low purity, LP). Therefore, it can be concluded that the corrosion rate of the alloy of the present invention is significantly lower than the corrosion rate of the alloy prepared by extrusion after general semi-continuous casting, indicating that the alloy prepared by the present invention has excellent corrosion resistance.

[0071] See also Figure 6 , which is a comparison of the corrosion morphology of the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention after physical deslagging with a flux-free porous baffle and without. Figure 6 (a) is the corrosion morphology of the high purity (HP) sample without physical deslagging by the flux-free porous baffle. Figure 6 (b) is the corrosion morphology of the HP after physical deslagging with a flux-free porous baffle. It can be seen that the HP is more uniformly corroded than the LP and has no obvious pitting. Figure 5 The results of hydrogen evolution rate were consistent.

[0072] See also Figure 7 The low-cost corrosion-resistant deformable magnesium alloy extruded sheet with ultra-high thermal conductivity prepared by the present invention was sampled and heated at 25°C for 10 -3 s -1 The engineering stress-strain curve is obtained by measuring the initial strain rate. Figure 7 (a) The total elongation at break of the alloy prepared by the present invention is 36%, while the total elongation at break of the most mature commercial extruded AZ31B is 33%. Figure 7 As shown in (b), the alloy prepared by the present invention and the AZ31B extruded alloy are 185MPa and 160MPa, respectively, which is 15.6% higher than that of AZ31B; this shows that the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, that is, the alloy of the present invention, has excellent mechanical properties.

[0073] See also Figure 8 The low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, that is, the alloy of the present invention, has a tangent modulus that maintains a relatively high modulus level (>42GPa) until the tensile stress is about 100MPa, while the tangent modulus of ordinary AZ31B extruded plate has decayed to below 42GPa under a tensile stress of less than 82MPa. It can be seen that the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, that is, the alloy of the present invention, has better high tangent modulus retention ability in the range of 0-160MPa than AZ31B. This indicates that the low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity prepared by the present invention, that is, the alloy of the present invention, has better stiffness retention performance when subjected to larger tensile stress loads than the AZ31B extruded magnesium alloy.

Claims

1. A low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity, characterized in that: The magnesium alloy comprises Mg, Zn, Mn, and Ca, with a molar ratio of Mg:Zn=(99.4-99.7):(0.1-0.2), and Zn:Mn:Ca=1:1:

1. The Zn, Mn, and Ca are microalloying elements and have similar valence electron structures to Mg. The preparation method comprises the following steps: Step 1, preparing a microalloyed preform: adding high-purity magnesium, magnesium-calcium master alloy, and magnesium-manganese master alloy into a container, heating to 200-300°C and holding for 1-2 hours, further heating to 650-700°C and holding for 1-2 hours, heating to 750-800°C and holding for 1-2 hours until all the materials are melted, and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = (96-98):(1-2), and calcium:manganese = 1:1; Step 2, preparing an alloy net dense ingot: preheating the high-purity magnesium, high-purity zinc, and the microalloyed preform prepared in step 1 to 300-350°C in argon and keeping the temperature for 1-2 hours, then heating the preform to 750-800°C and keeping the temperature for 1-2 hours, performing physical slag removal using a flux-free porous baffle, and casting to complete the preparation of the alloy net dense ingot; the alloy net dense ingot has a molar ratio of magnesium to zinc of (99.4-99.7): (0.1-0.2), and zinc to manganese to calcium of 1:1:1; Step 3, plastic forming: homogenize the alloy net dense ingot prepared in step 2 under an argon protective atmosphere at a homogenization temperature of 400-450°C for a homogenization time of 6-56 h, water quench, and obtain a homogenized alloy ingot. The obtained homogenized alloy ingot is subjected to thermomechanical treatment to obtain a low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity.

2. A low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity according to claim 1, characterized in that: The magnesium alloy includes Mg, Zn, Mn and Ca, and in a molar ratio, Mg:Zn=99.4:0.2, Zn:Mn:Ca=1:1:

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3. The low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity according to claim 1, characterized in that: The magnesium-calcium master alloy in step 1 is one of Mg-10 wt.%Ca, Mg-15 wt.%Ca, Mg-20 wt.%Ca or Mg-30 wt.%Ca.

4. The low-cost corrosion-resistant deformable magnesium alloy with ultra-high thermal conductivity according to claim 1, characterized in that: The magnesium-manganese master alloy in step 1 is Mg-5 wt.% Mn or Mg-10 wt.% Mn.

5. The method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity according to claim 1, characterized in that: The thermomechanical treatment in step 3 is one of extrusion, forging, rolling and drawing.

6. The method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity according to claim 5, characterized in that: The extrusion forming process has the following characteristics: the preheating temperature of the billet is 300-350°C, the extrusion die temperature is 350-400°C, the extrusion feed speed is 0.3-1 mm / s, the extrusion barrel temperature is set at 300-350°C, the extrusion ratio is set at 10-30, and the extruded material is pulled by a traction machine with a traction force of 100-500N.

7. The method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity according to claim 1, characterized in that: The following steps are involved: Step 1, preparing a microalloyed preform: adding high-purity magnesium, Mg-20 wt.% Ca, and Mg-10 wt.% Mn to a high-purity, high-density graphite crucible, heating to 200°C and holding for 2 hours, further heating to 650°C and holding for 2 hours, heating to 800°C and holding for 1 hour, until all the materials are melted, pouring the melted material into a graphite mold with a feeding riser and naturally cooling it to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = 96:2, and calcium:manganese = 1:1; Step 2, preparing an alloy net dense ingot: preheating high-purity magnesium, high-purity zinc, and the microalloyed preform prepared in step 1 to 350° C. in argon gas and holding for 1 hour, then heating to 800° C. and holding for 1 hour, and performing physical slag removal using a flux-free porous baffle before casting to complete the preparation of an alloy net dense ingot; the alloy net dense ingot has a molar ratio of magnesium to zinc of 99.4 to 0.2 and a molar ratio of zinc to manganese to calcium of 1 to 1. Step 3, plastic forming: homogenize the alloy net dense ingot prepared in step 2 under a protective atmosphere, the homogenization temperature is 400°C, the homogenization time is 56 h, and water quenching is performed to obtain a homogenized alloy ingot, and the obtained homogenized alloy ingot is extruded to obtain a low-cost ultra-high thermal conductivity and corrosion-resistant deformable magnesium alloy; in extrusion forming, the billet preheating temperature is 300°C, the extrusion die temperature is 350°C, the extrusion feed speed is 1 mm / s, the extrusion barrel temperature is set to 300°C, the extrusion ratio is set to 30, and the extruded material is pulled by a traction machine with a traction force of 300N.

8. The method for preparing a low-cost corrosion-resistant wrought magnesium alloy with ultra-high thermal conductivity according to claim 1, characterized in that: The preparation method thereof comprises the following steps: Step 1, preparing a microalloyed preform: adding high-purity magnesium, Mg-15 wt.% Ca and Mg-10 wt.% Mn to a high-purity, high-density graphite crucible, heating to 230°C and holding for 1.4 hours, further heating to 660°C and holding for 1.2 hours, heating to 780°C and holding for 1.5 hours, until all the materials are melted, pouring the melted material into a graphite crucible and pouring the melt into a rod-shaped graphite mold with a feeding riser and naturally cooling to obtain a microalloyed preform; the microalloyed preform has a molar ratio of magnesium:calcium = 97:1.5, and calcium:manganese = 1:1; Step 2, preparing a net dense alloy ingot: preheating high-purity magnesium, high-purity zinc, and the microalloyed preform prepared in step 1 to 330° C. in argon gas and holding the temperature for 1.5 hours, then heating the temperature to 780° C. and holding the temperature for 1.5 hours. Before casting, physical slag removal is performed using a flux-free porous baffle to complete the preparation of a net dense alloy ingot; the net dense alloy ingot has a molar ratio of magnesium to zinc of 99.6 to 0.13 and a molar ratio of zinc to manganese to calcium of 1 to 1. Step 3, plastic forming: homogenizing the alloy net dense ingot prepared in step 2 under a protective atmosphere, the homogenization temperature is 420°C, the homogenization time is 30 h, and water quenching is performed to obtain a homogenized alloy ingot, and the obtained homogenized alloy ingot is extruded to obtain a low-cost ultra-high thermal conductivity and corrosion-resistant deformable magnesium alloy; extrusion forming, the billet preheating temperature is 330°C, the extrusion die temperature is 380°C, the extrusion feed speed is 0.5 mm / s, the extrusion barrel temperature is set to 330°C, the extrusion ratio is set to 15, and the extruded material is pulled by a traction machine with a traction force of 300N.

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