CN114318097A

CN114318097A - Preparation method of Mg-Zn-La alloy with high heat conductivity and high strength

Info

Publication number: CN114318097A
Application number: CN202111478117.7A
Authority: CN
Inventors: 罗群; 刘权; 谢天赐; 李谦
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2021-12-06
Filing date: 2021-12-06
Publication date: 2022-04-12
Anticipated expiration: 2041-12-06
Also published as: CN114318097B

Abstract

The invention discloses a Mg-Zn-La alloy with high heat conductivity and high strength and a preparation method thereof, wherein the Mg-Zn-La alloy comprises the following alloy components in percentage by mass: the Zn content is 6.18-6.43 wt.%, the La content is 0.32-0.55 wt.%, and the balance is Mg and other unavoidable impurities. After the alloy is added with trace rare earth element La, a micron-sized granular strengthening phase tau is formed₁‑Mg₂₈Zn₂₀La₄The phase is dispersed and distributed on the crystal boundary; after solid solution and aging treatment, nano-scale rod-like beta is generated₁’‑Mg₄Zn₇And disc-like beta₂’‑MgZn₂Precipitated phase is distributed in an alpha-Mg matrix. Both of these can hinder dislocation glide and improve the alloyThe yield strength is improved, the solid solubility of Zn in the Mg matrix is reduced, the influence of lattice distortion on the thermal conductivity is reduced, and the thermal conductivity of the alloy is improved. The obtained Mg-Zn-La alloy has the room temperature thermal conductivity of 150.2-155.3W/(m.K) and the alloy yield strength of 164.9-172.1 MPa. The magnesium alloy has excellent heat-conducting property on the basis of higher yield strength; meanwhile, the product weight is reduced, the production cost is reduced, and the material can be used as a heat dissipation structure material for electronic devices and the like.

Description

Preparation method of Mg-Zn-La alloy with high heat conductivity and high strength

Technical Field

The invention relates to the technical field of non-ferrous metal materials, in particular to a Mg-Zn-La alloy with high heat conductivity and high strength and a preparation method thereof, which are applied to the technical field of magnesium alloys.

Background

With the continuous development of industries such as new energy automobiles, aerospace and electronic equipment, the number and density of high-power electronic components are continuously increased, so that the generated heat needs to be timely released when the equipment runs, and the reliability and stability of the equipment are ensured. The magnesium and the magnesium alloy have the advantages of small density, high specific strength, high thermal conductivity and the like, and have great application potential in heat-radiating structural materials. The pure magnesium has a room temperature thermal conductivity of about 158W/(m.K), the pure aluminum has a room temperature thermal conductivity of about 237W/(m.K), and the specific thermal conductivity (thermal conductivity per unit mass) of magnesium is comparable to that of aluminum. However, the tensile strength of the as-cast pure magnesium is only 98MPa, and it is difficult to satisfy the use requirements of the structural material.

In order to improve the mechanical properties of magnesium, pure magnesium is often alloyed, but the addition of alloying elements reduces the thermal conductivity of magnesium. It is believed that the addition of alloying elements forms a solid solution or second phase with magnesium, and both the solid solution and the second phase reduce the thermal conductivity of the magnesium alloy. The reason for this is that: solid solution atoms can cause lattice distortion, so that the scattering effect of the solid solution atoms on electrons is enhanced, the free movement of the electrons in the crystal lattice is blocked, and the mean free path of the electrons is reduced; the second phase boundary can block the movement of electrons and phonons, the more the second phase, the more dispersive the distribution, the higher the interface density, and the greater the resistance to thermal diffusion. The reduction degree of the added alloy elements is different, among the common alloy elements, Al element has the largest influence on the thermal conductivity of the magnesium alloy, Zn element has smaller influence on the thermal conductivity of the magnesium alloy, but the thermal conductivity of the magnesium alloy is generally in a descending trend, namely, the thermal conductivity of the magnesium alloy is obviously reduced along with the increase of the content of the alloy elements. For example, commercial magnesium alloys AM60B and AZ91D have good mechanical properties, but have low room temperature thermal conductivity, the AM60B alloy has the room temperature thermal conductivity of about 62W/(m.K), and the AZ91D alloy has the room temperature thermal conductivity of only 51W/(m.K); while the room temperature thermal conductivity of the commercial ZM51 alloy is about 98W/(m.K), and the room temperature thermal conductivity of the as-cast Mg-6Zn-Cu can reach 121.3W/(m.K). Therefore, the Mg-Zn alloy has great application potential in improving the heat conductivity of the magnesium alloy by adding alloy elements.

Compared with Mg-Al alloy and Mg-RE alloy, the Mg-Zn alloy has better heat conductivity, but has the problems of poor casting performance, poor mechanical property and the like. Generally, the addition of alloying elements can improve the casting performance and mechanical properties of Mg-Zn alloy, while the addition of excessive alloying elements can reduce the thermal conductivity of the alloy. Aiming at the contradiction between the mechanical property and the heat conductivity of the Mg-Zn alloy, the heat conductivity and the yield strength of the Mg-Zn alloy can be simultaneously improved by adding proper alloy elements and optimizing the T6 heat treatment process. In prior literature 1, 2013, a research on thermal conductivity of magnesium alloy, such as panhu cheng, Chongqing university, a doctor paper, the thermal conductivity of Mg-6Zn alloy is improved from 114.3W/(m.K) to 125.1W/(m.K) after the Mg-6Zn alloy is subjected to T6 heat treatment, 1.5 wt.% of Cu is added, and the thermal conductivity of the alloy can reach 132.9W/(m.K) after the Mg-6Zn alloy is subjected to T6 heat treatment. Chinese patent publication No. CN107164672B discloses an ultrahigh thermal conductivity magnesium alloy, which contains 0.01-1.0 wt.% Zn, 0.01-0.2 wt.% Cu, 0.01-0.095 wt.% Ag, and the balance Mg. After deformation processing and T6 heat treatment, the thermal conductivity of the alloy can reach 140-148W/(m.K). Therefore, the addition of Cu and Ag can effectively improve the heat-conducting property of the Mg-Zn alloy, but the material cost is higher due to the Ag contained in the alloy, and the addition of Ag can reduce the corrosion resistance of the alloy; in addition, the preparation method needs deformation processing, and has complex process and low production efficiency.

In view of the above problems, rare earth elements can be added as alloying elements to Mg-Zn alloys because they can improve the fluidity of the magnesium alloy melt to improve the castability of the magnesium alloy and also enhance the corrosion resistance of the alloy. Chinese patent publication No. CN107043880A discloses a rare earth heat-conducting magnesium alloy and a preparation method thereof, wherein the alloy comprises the following components: mn content of 0.2-1.0 wt.%, Zn content of 0.5-3.0 wt.%, Nd content of 0.5-2.0 wt.%, and Mg residue by smelting, casting, homogenizing, hot extrusion and agingAfter treatment, the rare earth heat conduction magnesium alloy with the tensile strength of 250-350MPa and the heat conductivity of 110-120W/(m.K) is obtained. The rare earth magnesium alloy has low heat conductivity which is only equivalent to that of the Mg-6Zn alloy subjected to T6 heat treatment, and the main reason is that the content of the rare earth element Nd is high, so that a large amount of Mg can be formed in the alloy₃Nd phase and T₂-(Mg,Zn)₉₂Nd₈An equal second phase with increased phase boundaries, not conducive to heat diffusion; on the other hand, after the alloy is subjected to hot extrusion deformation processing, a large number of textures exist in the alloy, the scattering probability of electrons and phonons is increased, and the thermal conductivity of the alloy is reduced. Chinese patent with patent publication number CN 110819863B discloses a low rare earth high heat conduction magnesium alloy and a preparation method thereof, and the alloy comprises the following components: 5.0-7.0 wt.% Gd, 0.5-2.0 wt.% Er, 3.0-7.0 wt.% Zn, 0.5-1.0 wt.% Zr, the balance being Mg. The rare earth magnesium alloy with the thermal conductivity of 136.9W/(m.K) can be obtained by carrying out solid solution and aging treatment at a certain temperature and time. However, the rare earth element content of the alloy exceeds the Zn content, and the alloy actually belongs to a high rare earth magnesium alloy. On one hand, the maximum solid solubility of Gd in a magnesium matrix is 23.5 wt.%, the content of Gd is too high, the solid solubility of Gd in the matrix is higher, and meanwhile, a second phase is increased, so that the Gd does not contribute to the movement of phonons and electrons and the improvement of the thermal conductivity of the alloy; on the other hand, Gd and Zr have high density and high cost, and are not beneficial to reducing the weight of the magnesium alloy.

As described above, in the prior patent publications, the content of rare earth added to Mg — Zn alloys is high, the alloy has a large amount of second phases and phase boundaries, and thermal diffusion is inhibited; gd. The solid solubility of Nd and Er is larger, the maximum solid solubility of Gd and Nd in a magnesium matrix is 23.5 wt.% and 3.63 wt.%, solute atoms with larger solid solubility can cause larger lattice distortion, and further the thermal conductivity of the alloy is reduced. These rare earth magnesium alloys have good mechanical properties, but their thermal conductivity is not excellent, mainly because the increase of the second phase and solid solubility can realize solid solution strengthening and second phase strengthening, but at the same time, it can also obstruct the movement of phonons and electrons, and reduce the thermal conductivity of the alloy. Therefore, under the use requirement of the mechanical property of the alloy, in order to improve the heat conductivity of the Mg-Zn alloy, the following technical problems need to be solved:

(1) the solid solution amount of Zn and rare earth elements in the Mg matrix is reduced so as to reduce the influence of lattice distortion on the thermal conductivity;

(2) reducing the generation of a second phase in the Mg-Zn system to reduce the inhibition of the phase interface on the thermal movement;

(3) the number of nano-sized precipitates is increased to increase the inhibition of the dislocation glide relative to the precipitates.

These problems become an urgent technical problem to be solved.

Disclosure of Invention

In order to solve the problems of the prior art, the invention aims to overcome the defects in the prior art and provide a preparation method of the Mg-Zn-La alloy with high heat conductivity and high strength. The method is simple and reduces the use cost.

In order to achieve the purpose, the invention adopts the following inventive concept:

the invention needs to design a Mg-Zn-La alloy which reduces the content of rare earth to improve the thermal conductivity of the alloy:

first, in order to reduce the solid solubility of solute atoms in the magnesium matrix, on the one hand, a rare earth element having low solid solubility is added as light rare earth element La whose maximum solid solubility in the magnesium matrix is only 0.07 wt.%, and La can be used as an additive element of Mg — Zn-based alloy to reduce the influence of solid solubility on thermal conductivity.

Secondly, aiming at the generation of a second phase, on one hand, the addition amount of alloy elements is reduced, and the La content in the designed Mg-Zn-La alloy is less than 0.55 wt.%; on the other hand, the phase variety in the alloy is reduced, and the designed Mg-Zn-La alloy only contains tau₁+ α -Mg two phases. On the other hand, by aging treatment, β is promoted₁’-Mg₄Zn₇Phase and beta₂’-MgZn₂The solid solubility of Zn in the magnesium matrix is reduced by the precipitation of the phase, and the desolventization of Zn is realized;

finally, as the aging progresses, the beta of the nanometer scale₁’-Mg₄Zn₇And beta₂’-MgZn₂The number of precipitated phases is increased, dislocation sliding movement is hindered, precipitation strengthening is realized, and the alloy yield strength is improved.

According to the inventive concept, the invention adopts the following technical scheme:

the Mg-Zn-La alloy with high heat conductivity and high strength comprises the following components in percentage by mass: the Zn content is 6.18-6.43 wt.%, the La content is 0.32-0.55 wt.%, and the balance is Mg and other inevitable impurities; the Mg-Zn-La alloy is subjected to solid solution and aging treatment to form nano rod-like beta₁’-Mg₄Zn₇Phase and nanoscale discotic beta₂’-MgZn₂And a micron-sized particulate reinforcing phase tau distributed in an alpha-Mg matrix₁-Mg₂₈Zn₂₀La₄The phase is dispersed and distributed in alpha-Mg crystal boundary.

Preferably, the Mg-Zn-La alloy of the present invention has a mid-edge [ 0001%]_MgRod-like beta of direction₁’-Mg₄Zn₇The average length and average diameter of the precipitated phase were 236.2. + -. 76.5nm and 15.7. + -. 4.5nm, respectively.

Preferably, the Mg-Zn-La alloy of the present invention has a disk-like beta₂’-MgZn₂The average diameter of the precipitated phase was 25.7. + -. 8.4 nm.

Preferably, the Mg-Zn-La alloy of the invention has a reinforcing phase tau in the form of micron-sized particles₁-Mg₂₈Zn₂₀La₄The average diameter of the phases is 1.2. + -. 0.3. mu.m.

Preferably, the Mg-Zn-La alloy of the invention is beta after heat treatment₁’-Mg₄Zn₇And beta₂’-MgZn₂Reducing the solid solubility of Zn in the alpha-Mg matrix to 3.62-3.80 wt.%.

Preferably, the Mg-Zn-La alloy of the present invention has a grain size of 61.6 to 69.8 μm.

Preferably, the thermal conductivity of the Mg-Zn-La alloy of the invention at room temperature is 150.2-155.3W/(m.K), and the yield strength of the Mg-Zn-La alloy is 164.9-172.1 MPa.

The invention discloses a preparation method of a Mg-Zn-La alloy with high heat conductivity and high strength, which comprises the following steps:

(1) preparing Mg-17La intermediate alloy:

preparing Mg-17La intermediate alloy by using pure Mg with the purity not lower than 99.99%, pure La with the purity not lower than 99.99% and pure Ce with the purity not lower than 99.99% as raw materials and adopting a vacuum induction melting method;

(2) smelting Mg-Zn-La alloy:

taking pure Mg with the purity not lower than 99.99 percent, pure Zn with the purity not lower than 99.99 percent and the Mg-La intermediate alloy prepared in the step (1) as alloy raw materials, and smelting the alloy raw materials by adopting a well-type resistance furnace as a smelting furnace;

the magnesium alloy comprises the following raw materials in percentage by mass:

the content of Zn is 6.18-6.43 wt.%, the content of La is 0.32-0.55 wt.%, and the balance is Mg, wherein La is added in the form of Mg-17La intermediate alloy, and the smelting process is as follows:

firstly, setting the temperature of a resistance furnace to be not lower than 600 ℃, preheating the polished raw materials to be not lower than 300 ℃, and removing water vapor; after the temperature of the resistance furnace is raised to be not lower than 600 ℃, pure magnesium is put into a corundum crucible in the furnace, and simultaneously SF is introduced into the furnace₆And CO₂Mixing protective gas, adding pure Zn and Mg-17La intermediate alloy after pure magnesium in the furnace is completely melted and the temperature of the melt is stabilized at 700 ℃, continuously stirring the melt for at least 1min, heating to be not lower than 720 ℃, and preserving heat for at least 30min to ensure that alloy elements fully react;

then opening a furnace cover, slowly scattering a refining agent, continuously stirring for 1-2min, continuously heating to a temperature not lower than 740 ℃, and refining for at least 30 min; after refining, powering off the well type resistance furnace, cooling the melt to be not higher than 720 ℃, removing slag on the surface of the melt by using a slag spoon, and casting the melt into a low-carbon steel mold with the mold temperature not higher than 300 ℃ to obtain an Mg-Zn-La alloy cast ingot;

(3) solution treatment:

wrapping an Mg-Zn-La alloy cast ingot by using an aluminum foil to reduce alloy oxidation, then putting the cast ingot into a box-type resistance furnace, raising the temperature along with the furnace, wherein the solid solution temperature is not lower than 400 ℃, the solid solution time is at least 6h, and finally carrying out water quenching treatment on the alloy;

(4) aging treatment:

and (3) putting the Mg-Zn-La subjected to the solution treatment into tetramethylglycerol, and putting the Mg-Zn-La into a box type resistance furnace for aging treatment, wherein the aging temperature is not lower than 200 ℃, and the aging time is 5-20h, so that the high-heat-conductivity Mg-Zn-La alloy is prepared.

Preferably, in the step (1), the raw material composition and weight percentage of the Mg-17La master alloy are as follows: the content of La is not higher than 17 wt.%, and the balance is Mg; the smelting process of the Mg-17La intermediate alloy comprises the following steps:

firstly, cutting pure Mg into cuboid blocks with the volume of not more than 3 multiplied by 4 multiplied by 5cm, cutting pure La into blocks with the size of not more than 0.5 multiplied by 0.5cm, polishing oxide skins on all pure metal surfaces to avoid introducing oxide inclusions in the smelting process, and putting the pure Mg and the pure La into a vacuum induction smelting furnace;

before smelting, performing at least three times of gas washing on a cavity of the smelting furnace, and vacuumizing by using a mechanical pump each time until the absolute pressure is not higher than 0.3 MPa; after the last washing, filling Ar gas into the cavity until the pressure in the cavity is 10-20Pa higher than the atmospheric pressure so as to prevent external air from entering the cavity and being oxidized; adjusting the current to be not less than 200A, preserving heat for at least 5min, after the crucible is heated to be red, adjusting the current to be not less than 220A, preserving heat for 4-5min until the metal in the crucible is completely melted, adjusting the current to 230-240A, preserving heat for at least 2min, and after the fluidity is observed to meet the casting requirement, casting the alloy melt into a copper mold; and repeatedly reversing and smelting for at least three times in the whole process of smelting and casting to ensure that the components are uniform, and removing an oxide film on the surface of the cast ingot by using sand paper after each reversing and smelting to prepare the Mg-17La intermediate alloy.

Preferably, in the step (2), the refining agent comprises the following components in percentage by mass: BaCl₂The content is 35-43 wt.%, CaF₂The content is 2-5 wt.%, and the balance is KCl.

The technical scheme of the invention has obvious effect and can be verified.

1. An isothermal section phase diagram under 400 ℃ is calculated through an Mg-Zn-La system thermodynamic database, and two isothermal section phase diagrams positioned at 400 ℃ are designedτ₁The experimental distribution points marked in the phase diagram of the Mg-Zn-La heat-conducting alloy in the + alpha-Mg two-phase region are the design components of the Mg-Zn-La alloy, as shown in figure 1. Tau of Mg-6.18Zn-0.55La alloy calculated based on thermodynamic phase diagram₁Phase fraction was 2.27 wt.%, solid solubility of Zn in magnesium matrix was 5.73 wt.%; for the Mg-6.18Zn-0.55La alloy, τ₁The phase is precipitated at about 177 ℃ and can stably exist in the temperature range of 177-400 ℃. Therefore, the Mg-Zn-La alloy of the invention is subjected to solution treatment at 400 ℃ and aging treatment at 200 ℃. Age hardening curves were determined by aging at different times, as shown in figure 2, providing experimental evidence for the choice of age treatment time.

2. In order to obtain the Mg-Zn-La alloy with high heat conductivity and high strength and the preparation method thereof, firstly, a vacuum induction melting method is adopted to prepare a Mg-17La intermediate alloy, then the Mg-Zn-La alloy is melted and cast for molding, and finally, the solid solution and aging treatment are carried out at a certain temperature and time, so that the Mg-Zn-La alloy with high heat conductivity and high strength can be obtained.

According to the invention, the component range of the Mg-Zn-La system heat-conducting alloy is designed by constructing an Mg-Zn-La phase diagram and a heat conductivity thermodynamic database, and meanwhile, under the condition of calculating the same phase composition according to the thermodynamic database, the rare earth content is further reduced to improve the heat conductivity of the alloy, and effective verification is carried out on the alloy with two alloy components of Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55 La.

The Mg-Zn-La alloy with high heat conductivity and high strength comprises the following components in percentage by mass: the Zn content is 6.18-6.43 wt.%, the La content is 0.32-0.55 wt.%, and the balance is Mg and other unavoidable impurities. After the alloy is added with trace rare earth element La, a micron-sized granular strengthening phase tau is formed₁-Mg₂₈Zn₂₀La₄The phase is dispersed and distributed on the crystal boundary; after solid solution and aging treatment, nano-scale rod-like beta is generated₁’-Mg₄Zn₇And disc-like beta₂’-MgZn₂Precipitated phase is distributed in an alpha-Mg matrix. The two can hinder dislocation slippage, improve the yield strength of the alloy, simultaneously reduce the solid solubility of Zn in the Mg matrix, reduce the influence of lattice distortion on the thermal conductivity, and improveHigh alloy thermal conductivity. The obtained Mg-Zn-La alloy has the room temperature thermal conductivity of 150.2-155.3W/(m.K) and the alloy yield strength of 164.9-172.1 MPa. The magnesium alloy has excellent heat-conducting property on the basis of higher yield strength; meanwhile, the product weight is reduced, the production cost is reduced, and the material can be used as a heat dissipation structure material for electronic devices and the like.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. the invention reduces the content of rare earth to improve the thermal conductivity of the alloy, and designs the high-performance Mg-Zn-La alloy;

2. the invention carries out solid solution and aging treatment process on the as-cast Mg-Zn-La alloy, and improves the yield strength of the alloy through precipitation strengthening; by rod-like beta₁’-Mg₄Zn₇Phase and bulk beta₂’-MgZn₂The solid solubility of Zn in an alpha-Mg matrix is reduced from 5.58-5.73 wt.% to 3.62-3.80 wt.% by the precipitation of the phase, so that the desolventization of Zn is realized, the influence of the solid solution of Zn on the thermal conductivity of the alloy is reduced, and the thermal conductivity of the alloy is further improved. The designed Mg-Zn-La alloy has the room temperature thermal conductivity of 150.2-155.3W/(m.K) and the alloy yield strength of 164.9-172.1 MPa. On the basis of meeting the use requirement of mechanical properties, obtaining the Mg-Zn-La alloy with high thermal conductivity;

3. compared with heavy rare earth and high rare earth heat conduction magnesium alloy, the Mg-Zn-La alloy provided by the invention reduces the usage amount of rare earth elements and the second phase tau₁The generation of the phase reduces the phase boundary and greatly improves the thermal conductivity of the Mg-Zn-La alloy; compared with Mg-6Zn alloy, the addition of trace rare earth elements effectively improves the casting performance of the alloy and simultaneously improves the mechanical property and the heat-conducting property. In addition, La is a light rare earth element, and the addition amount of rare earth is small, so that the use cost can be effectively reduced;

4. the alloy components are designed based on the Mg-Zn-La phase diagram and the thermal conductivity thermodynamic database, so that the experiment cost generated by a trial-and-error method is effectively reduced; compared with the prior art, the invention has better heat-conducting property, reduces the use cost, improves the application range and has wide application prospect.

Drawings

FIG. 1 is a schematic view showing the isothermal cross-sectional composition distribution at 400 ℃ of a Mg-Zn-La alloy system according to a preferred embodiment of the present invention.

FIG. 2 is an age hardening curve for a preferred embodiment of the Mg-Zn-La alloy of the present invention.

FIG. 3 is a graph showing the room temperature thermal conductivity of Mg-Zn-La alloys in solid solution and aged in accordance with a preferred embodiment of the present invention.

FIG. 4 shows the room temperature yield strength of Mg-Zn-La alloy in solid solution state and aged state according to the preferred embodiment of the present invention.

FIG. 5 is a TEM and HRTEM image of Mg-Zn-La alloy in the aged state according to the preferred embodiment of the present invention.

FIG. 6 is a graph showing the trend of mechanical-thermal conductivity of various Mg alloy systems according to the present invention.

Detailed Description

The invention is further described in detail by the embodiment and the attached drawings in the specification. The alloy compositions and phase compositions thereof referred to in the respective examples and comparative examples are shown in Table 1.

TABLE 1 compositions of alloy compositions and their phases of examples and comparative examples

The middle edge [0001 ] of the Mg-Zn-La alloy of the invention]_MgRod-like beta of direction₁’-Mg₄Zn₇The average length and average diameter of the precipitated phase were 236.2. + -. 76.5nm and 15.7. + -. 4.5nm, respectively.

The disk-shaped beta in the Mg-Zn-La alloy of the invention₂’-MgZn₂The average diameter of the precipitated phase was 25.7. + -. 8.4 nm.

The micron-sized granular strengthening phase tau in the Mg-Zn-La alloy₁-Mg₂₈Zn₂₀La₄The average diameter of the phases is 1.2. + -. 0.3. mu.m.

Beta after heat treatment of the Mg-Zn-La alloy of the invention₁’-Mg₄Zn₇And beta₂’-MgZn₂Reducing the solid solubility of Zn in the alpha-Mg matrix to 3.62-3.80 wt.%.

The grain size of the Mg-Zn-La alloy is 61.6-69.8 mu m. As can be seen from FIG. 6, the comprehensive properties of the Mg-Zn-La alloy are superior to those of the existing La-free Mg-Zn alloy, Mg-Al alloy, Mg-Mn alloy and Mg-Ce-Zn alloy.

The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:

example 1

In this embodiment, an Mg-Zn-La alloy with high thermal conductivity and high strength comprises the following components in percentage by mass: the Zn content was 6.43 wt.%, the La content was 0.32 wt.%, and the balance Mg and other unavoidable impurities. The Mg-Zn-La alloy with the thermal conductivity and yield strength of 150.2W/(m.K) and 164.9MPa is prepared by adopting a solid solution and aging treatment process.

A preparation method of Mg-Zn-La alloy with high heat conductivity and high strength comprises the following steps:

(1) preparing Mg-17La intermediate alloy: pure Mg with the purity of 99.99 percent and pure La with the purity of 99.99 percent are taken as raw materials, and the Mg-17La intermediate alloy is prepared by adopting a vacuum induction melting method.

(2) Smelting Mg-Zn-La alloy: the raw materials comprise 99.99 percent of pure Mg, 99.99 percent of pure Zn and the Mg-17La intermediate alloy prepared in the step (1), and the smelting furnace is a well-type resistance furnace. The magnesium alloy comprises the following raw materials in percentage by mass: the Zn content was 6.43 wt.%, the La content was 0.32 wt.%, and the balance Mg, wherein La was added in the form of Mg-17La master alloy. The smelting process comprises the following steps: firstly, setting the temperature of a resistance furnace to 600 ℃ for the first time, preheating the polished raw materials to 300 ℃, and removing water vapor; after the temperature of the resistance furnace rises to 600 ℃, pure magnesium is put into a corundum crucible in the furnace, and simultaneously SF is introduced into the furnace₆And CO₂Mixing protective gas, adding pure Zn and Mg-17La intermediate alloy after pure magnesium in the furnace is completely melted and the temperature of the melt is stabilized at 700 ℃, continuously stirring the melt for 1min, heating to 720 ℃, and preserving the temperature for 30min to ensure that the alloy elements fully react. Then opening the furnace cover, slowly scattering a refining agent, continuously stirring for 1-2min, and continuously heating to 740 ℃ for refining for 30 min. Is refined completelyAnd after the alloy is formed, the well-type resistance furnace is powered off, when the temperature of the melt is reduced to 720 ℃, the slag on the surface of the melt is removed by a slag ladle, and the alloy is cast into a low-carbon steel mold preheated at 300 ℃ to obtain the Mg-Zn-La alloy cast ingot.

(3) Solution treatment: wrapping an Mg-Zn-La alloy cast ingot by using an aluminum foil to reduce alloy oxidation, then putting the cast ingot into a box-type resistance furnace, raising the temperature along with the furnace, wherein the solid solution temperature is 400 ℃, the solid solution time is 6 hours, and finally carrying out water quenching treatment on the alloy.

(4) Aging treatment: and (3) putting the Mg-Zn-La alloy subjected to the solution treatment into tetramethylglycerol, and putting the Mg-Zn-La alloy and the tetramethylglycerol into a box type resistance furnace together for aging treatment, wherein the aging temperature is 200 ℃, and the aging time is 5 hours, so that the high-heat-conductivity Mg-Zn-La alloy can be prepared.

(5) Testing the heat conduction performance: the calculation formula of the thermal conductivity of the alloy is as follows: λ ═ α ρ C_pIn the formula, lambda is the thermal conductivity of the alloy, alpha is the thermal diffusion coefficient of the alloy, rho is the density of the alloy, and Cp is the specific heat capacity of the alloy. Because the error between the heat capacity measured by the experiment and the calculated heat capacity is not large, the heat capacity and the density of the alloy are both numerical values obtained by calculation of a thermodynamic database; and measuring the thermal diffusion coefficient of the Mg-Zn-La alloy subjected to heat treatment at room temperature by adopting a laser flash method, wherein the model of the laser thermal conductivity instrument is relaxation-resistant LFA 467. The sampling area of the thermal diffusion coefficient test sample is 5mm away from the bottom of the cast ingot, and firstly, a sample with the size of phi 10 multiplied by 3mm is cut by using linear cutting; then, using 800-mesh sand paper to polish and remove oxide skin on the surface of the sample; and then sequentially polishing with 1500-mesh and 2000-mesh abrasive paper to ensure that the sample has uniform thickness and smooth surface, and finally obtaining the cylindrical standard sample with the diameter of 10mm and the thickness of less than or equal to 3 mm.

(6) And (3) testing tensile property: according to the requirement of GB/T16865-2013, the tensile test sample is processed into a dog-bone-shaped rectangular standard sample, the gauge length is 25.0mm, the thickness is 4.0mm, and the width is 6.0 mm. The number of the crystal grains of the gauge length section is about 10000, which meets the requirement of tensile measurement. The tensile properties of the alloys in the solid solution state and in the aged state were measured using an Instron5982 universal tester at a tensile rate of 1 mm/min. To reduce experimental error, three replicates were tested per alloy.

Example 2

This embodiment is substantially the same as the first embodiment, and is characterized in that:

in this embodiment, an Mg-Zn-La alloy with high thermal conductivity and high strength comprises the following components in percentage by mass: the Zn content was 6.18 wt.%, the La content was 0.55 wt.%, and the balance Mg and other unavoidable impurities. The Mg-Zn-La alloy with the thermal conductivity and yield strength of 155.3W/(m.K) and 172.1MPa is prepared by adopting a solid solution and aging treatment process.

(2) Smelting Mg-Zn-La alloy: the raw materials comprise 99.99 percent of pure Mg, 99.99 percent of pure Zn and the Mg-17La intermediate alloy prepared in the step (1), and the smelting furnace is a well-type resistance furnace. The magnesium alloy comprises the following raw materials in percentage by mass: the Zn content was 6.18 wt.%, the La content was 0.55 wt.%, and the balance Mg, wherein La was added in the form of Mg-17La master alloy. The smelting process comprises the following steps: firstly, setting the temperature of a resistance furnace to 600 ℃ for the first time, preheating the polished raw materials to 300 ℃, and removing water vapor; after the temperature of the resistance furnace rises to 600 ℃, pure magnesium is put into a corundum crucible in the furnace, and simultaneously SF is introduced into the furnace₆And CO₂Mixing protective gas, adding pure Zn and Mg-17La intermediate alloy after pure magnesium in the furnace is completely melted and the temperature of the melt is stabilized at 700 ℃, continuously stirring the melt for 1min, heating to 720 ℃, and preserving the temperature for 30min to ensure that the alloy elements fully react. Then opening the furnace cover, slowly scattering a refining agent, continuously stirring for 1-2min, and continuously heating to 740 ℃ for refining for 30 min. And after refining is finished, powering off the well type resistance furnace, removing slag on the surface of the melt by using a slag spoon when the temperature of the melt is reduced to 720 ℃, and casting the melt into a low-carbon steel mold preheated at 300 ℃ to obtain the Mg-Zn-La alloy cast ingot.

(4) Aging treatment: and (3) putting the Mg-Zn-La alloy subjected to the solution treatment into tetramethylglycerol, and putting the Mg-Zn-La alloy into a box type resistance furnace together for aging treatment, wherein the aging temperature is 200 ℃, and the aging time is 20 hours, so that the high-heat-conductivity Mg-Zn-La alloy can be prepared.

(5) Testing the heat conduction performance: the test means and calculation method used were the same as in example 1, and the operation steps not specifically described were the same as in example 1.

(6) And (3) testing tensile property: the tensile test standards and test parameters were the same as in example 1, and the procedure not specifically described was the same as in example 1.

Comparative example

The Mg-Zn alloy without adding trace rare earth elements comprises the following components in percentage by mass: the Zn content was 6.25 wt.%, the balance Mg and other unavoidable impurities.

The preparation method of the Mg-Zn alloy without adding trace rare earth elements comprises the following steps:

(1) preparing raw materials: pure Mg with the purity of 99.99 percent and pure Zn with the purity of 99.99 percent are taken as raw materials, and the materials are mixed according to the alloy components.

(2) Alloy smelting: firstly, setting the temperature of a resistance furnace to 600 ℃ for the first time, preheating the polished raw materials to 300 ℃, and removing water vapor; after the temperature of the resistance furnace rises to 600 ℃, pure magnesium is put into a corundum crucible in the furnace, and simultaneously SF is introduced into the furnace₆And CO₂Mixing protective gas, adding pure Zn after pure magnesium in the furnace is completely melted and the temperature of the melt is stabilized at 700 ℃, continuously stirring the melt for 1min, heating to 720 ℃, and preserving heat for 30min to ensure that the alloy elements fully react. Then opening the furnace cover, slowly scattering a refining agent, continuously stirring for 1-2min, and continuously heating to 740 ℃ for refining for 30 min. After refining, the well type resistance furnace is powered off, when the temperature of the melt is reduced to 720 ℃, the slag on the surface of the melt is removed by a slag ladle and is cast into a low-carbon steel die preheated at 300 ℃ to obtain Mg-Zn alloyAnd (5) ingot casting.

(3) Solution treatment: wrapping an Mg-Zn alloy ingot by using an aluminum foil to reduce alloy oxidation, then putting the Mg-Zn alloy ingot into a box-type resistance furnace, raising the temperature along with the furnace, wherein the solid solution temperature is 400 ℃, the solid solution time is 6 hours, and finally carrying out water quenching treatment on the alloy.

(4) Aging treatment: and (3) putting the Mg-Zn alloy subjected to the solution treatment into tetramethyl glycerol, and putting the Mg-Zn alloy and the tetramethyl glycerol into a box type resistance furnace together for aging treatment, wherein the aging temperature is 200 ℃, and the aging time is 5 hours.

(5) Testing the heat conduction performance: the specific test means and calculation method are the same as those in example 1, and the operation steps not specifically described are the same as those in example 1.

By comparing the examples and comparative examples, the following conclusions can be drawn:

(1) the thermal conductivity of solid solution Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La alloys is 122.4 +/-0.4W/(m.K) and 124.4 +/-0.4W/(m.K) respectively, which is higher than 100.7 +/-0.2W/(m.K) of the Mg-6.25Zn alloy. After aging treatment, the thermal conductivity of the aged Mg-Zn-La alloy is obviously improved compared with that of the solid solution alloy, the thermal conductivity of the Mg-6.43Zn-0.32La and the Mg-6.18Zn-0.55La alloy is 150.2 +/-0.3W/(m.K) and 155.3 +/-0.6W/(m.K), and the increase range is 27.8-30.9W/(m.K), as shown in figure 3. The reason for this is that the rod-like beta is obtained after the aging treatment₁’-Mg₄Zn₇Phase and disk beta₂’-MgZn₂The phase is precipitated from the magnesium matrix, so that the solid solubility of Zn in the alpha-Mg matrix is reduced from 5.58-5.73 wt.% to 3.62-3.80 wt.%, the desolventization of Zn is realized, the influence of lattice distortion on the thermal conductivity is reduced, and the excellent thermal conductivity is further obtained.

(2) The yield strengths of solid solution Mg-6.25Zn, Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La are respectively 60.9MPa, 64.9MPa and 79.3 MPa. After addition of La element, although La has a limited solid solubility in the alpha-Mg matrix, tau still remains after solution treatment₁The alloy plays a role in strengthening the second phase, so that the yield strength of the alloy is improved to a certain extent. AgingAfter treatment for 5-20h, the grain sizes of Mg-Zn and Mg-Zn-La alloys are not obviously grown, the grain sizes are 67.4 +/-4.9 mu m, 69.8 +/-7.4 mu m and 61.6 +/-5.6 mu m respectively, the grain sizes are smaller, and the alloy yield strength is theoretically more excellent according to a Hall-Peltier formula. Experiments show that after aging treatment is carried out for 5-20h at 200 ℃, the maximum yield strengths of the aged Mg-6.25Zn, Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La can respectively reach 160.9MPa, 164.9MPa and 172.1MPa, as shown in figure 4. Compared with the alloy in a solid solution state, the yield strength of the alloy in an aging state is obviously improved, and the yield strength is respectively improved by 164%, 150% and 148%. The reason for this is the rod-like beta₁’-Mg₄Zn₇Phase and disk beta₂’-MgZn₂The phase is precipitated from the magnesium matrix, and the generation of the precipitated phase can hinder dislocation glide and improve the yield strength of the alloy.

(3) After aging treatment, Mg-Zn-La alloy exists along [0001 ]]_MgRod-like beta of direction₁' precipitated phase and discotic beta₂' precipitation phase, rod-like beta in Mg-Zn-La alloy₁' the average length and average diameter of the precipitated phase were 236.2nm and 15.7nm, respectively. In the course of aging,. beta.₁’-Mg₄Zn₇Phase and beta₂’-MgZn₂The phase formation is accompanied with the desolventizing of solute elements, and the thermal conductivity of the Mg-Zn-La alloy is improved. After aging treatment, in the Mg-Zn-La alloy,

and (0001)_MgThe degree of mismatch of (A) was 0.76%, as shown in FIG. 5. With the progress of aging,. beta.₁' phase and alpha-Mg matrix still have coherent relationship, the lattice distortion is improved, and the influence on the thermal conductivity is limited.

In summary, as can be seen from FIGS. 1 to 4, the above-mentioned embodiments of the present invention design the composition range of the Mg-Zn-La system heat-conducting alloy at τ by constructing the Mg-Zn-La phase diagram and the thermal conductivity thermodynamic database₁In the + alpha-Mg two phases, the content of rare earth is further reduced to improve the thermal conductivity of the alloy, and two alloy components are designed to be Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La alloy. Preparing materials according to the following alloy components in percentage by mass: zn content of 6.18-6.43 wt.%, La content of 6.18-6.43 wt.%0.32-0.55 wt.%, the balance being Mg and other unavoidable impurities. The smelting process comprises the steps of raw material preparation, Mg-La intermediate alloy preparation, Mg-Zn-La alloy smelting and casting molding. Then, carrying out solid solution and aging treatment on the as-cast Mg-Zn-La alloy, on one hand, improving the yield strength of the alloy through precipitation strengthening; on the other hand, by a rod-like beta₁’-Mg₄Zn₇Phase and bulk beta₂’-MgZn₂The precipitation of the phase reduces the solid solubility of Zn atoms in a magnesium matrix, realizes the desolventizing of Zn, and reduces the influence of the solid solution of Zn on the heat conductivity of the alloy, thereby improving the heat conductivity of the alloy. The designed Mg-Zn-La alloy has the room temperature thermal conductivity of 150.2-155.3W/(m.K) and the alloy yield strength of 164.9-172.1 MPa. On the basis of meeting the use requirement of mechanical properties, the Mg-Zn-La alloy with high thermal conductivity is obtained. Compared with heavy rare earth and high rare earth heat conduction magnesium alloy, the Mg-Zn-La alloy of the embodiment of the invention reduces the usage amount of rare earth elements and the second phase tau₁The generation of the phase reduces the phase boundary, is beneficial to thermal diffusion and greatly improves the thermal conductivity of the Mg-Zn-La alloy. Compared with Mg-6Zn alloy, the addition of the trace rare earth element La effectively improves the casting performance of the alloy, and simultaneously improves the mechanical property and the heat-conducting property. In addition, La is a light rare earth element, and the addition amount of rare earth is small, so that the use cost can be effectively reduced, and the method is easy for commercial popularization.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be replaced with equivalents as long as the object of the present invention is met, and the technical principle and the inventive concept of the present invention are not departed from the scope of the present invention.

Claims

1. An Mg-Zn-La alloy with high heat conductivity and high strength, which is characterized in that: the Mg-Zn-La alloy comprises the following components in percentage by mass: zn content of 6.18-6.43 wt.%, La content of 0.32-0.55 wt.%, and Mg and other inevitable impurities as balanceQuality; the Mg-Zn-La alloy is subjected to solid solution and aging treatment to form nano rod-like beta₁’-Mg₄Zn₇Phase and nanoscale discotic beta₂’-MgZn₂And a micron-sized particulate reinforcing phase tau distributed in an alpha-Mg matrix₁-Mg₂₈Zn₂₀La₄The phase is dispersed and distributed in alpha-Mg crystal boundary.

2. The Mg-Zn-La alloy of claim 1, which has both high thermal conductivity and high strength, characterized in that: Mg-Zn-La alloy middle edge [0001 ]]_MgRod-like beta of direction₁’-Mg₄Zn₇The average length and average diameter of the precipitated phase were 236.2. + -. 76.5nm and 15.7. + -. 4.5nm, respectively.

3. The Mg-Zn-La alloy of claim 1, which has both high thermal conductivity and high strength, characterized in that: discoid beta in Mg-Zn-La alloy₂’-MgZn₂The average diameter of the precipitated phase was 25.7. + -. 8.4 nm.

4. The Mg-Zn-La alloy of claim 1, which has both high thermal conductivity and high strength, characterized in that: micron-sized granular strengthening phase tau in Mg-Zn-La alloy₁-Mg₂₈Zn₂₀La₄The average diameter of the phases is 1.2. + -. 0.3. mu.m.

5. The Mg-Zn-La alloy of claim 1, which has both high thermal conductivity and high strength, characterized in that: beta of the Mg-Zn-La alloy after heat treatment₁’-Mg₄Zn₇And beta₂’-MgZn₂Reducing the solid solubility of Zn in the alpha-Mg matrix to 3.62-3.80 wt.%.

6. The Mg-Zn-La alloy of claim 1, which has both high thermal conductivity and high strength, characterized in that: the grain size of the Mg-Zn-La alloy is 61.6-69.8 mu m.

7. The Mg-Zn-La alloy of claim 1, which has both high thermal conductivity and high strength, characterized in that: the heat conductivity of the Mg-Zn-La alloy at room temperature is 150.2-155.3W/(m.K), and the yield strength of the Mg-Zn-La alloy is 164.9-172.1 MPa.

8. The method for preparing the Mg-Zn-La alloy with high heat conductivity and high strength according to claim 1, which comprises the following steps:

(1) preparing Mg-17La intermediate alloy:

(2) smelting Mg-Zn-La alloy:

(3) solution treatment:

(4) aging treatment:

9. The method for preparing Mg-Zn-La alloy with high thermal conductivity and high strength according to claim 8, wherein: in the step (1), the Mg-17La master alloy comprises the following raw materials in percentage by weight: the content of La is not higher than 17 wt.%, and the balance is Mg; the smelting process of the Mg-17La intermediate alloy comprises the following steps:

10. The method for preparing Mg-Zn-La alloy with high thermal conductivity and high strength according to claim 8, wherein: in the step (2), the refining agent comprises the following components in percentage by mass: BaCl₂The content is 35-43 wt.%, CaF₂The content is 2-5 wt.%, and the balance is KCl.