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

Abstract

The invention discloses a Mg-Zn-La alloy with both high thermal conductivity and high strength and a preparation method thereof. The mass percentages of the alloy components are as follows: the content of Zn is 6.18-6.43wt.%, and the content of La is 0.32- 0.55wt.%, the balance is Mg and other inevitable impurities. After the alloy is added with a trace amount of rare earth element La, a micron-scale granular strengthening phase τ ₁ -Mg ₂₈ Zn ₂₀ La ₄ phase is formed, which is dispersed on the grain boundary; after solid solution + aging treatment, nano-scale rod-shaped β ₁ '- Mg ₄ Zn ₇ and disc-shaped β ₂ '-MgZn ₂ precipitates are distributed in the α-Mg matrix. These two will hinder dislocation slip, improve the yield strength of the alloy, reduce the solid solubility of Zn in the Mg matrix, reduce the effect of lattice distortion on the thermal conductivity, and improve the thermal conductivity of the alloy. The room temperature thermal conductivity of the obtained Mg-Zn-La alloy is 150.2-155.3 W/(m·K), and the yield strength of the alloy is 164.9-172.1 MPa. On the basis of high yield strength, the magnesium alloy has excellent thermal conductivity; meanwhile, it reduces product weight and production cost, and can be used for heat dissipation structural materials such as electronic devices.

Description

A kind of preparation method of Mg-Zn-La alloy with both high thermal 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 thermal conductivity and high strength and a preparation method thereof, which are applied to the technical field of magnesium alloys.

Background technique

With the continuous development of industries such as new energy vehicles, aerospace and electronic equipment, the number and density of high-power electronic components continue to increase, so that the equipment needs to release the heat generated in time during operation to ensure the reliability and stability of the equipment. . Magnesium and magnesium alloys have the advantages of low density, high specific strength and high thermal conductivity, and have great application potential in heat dissipation structural materials. The room temperature thermal conductivity of pure magnesium is about 158W/(m·K), and the room temperature thermal conductivity of pure aluminum is about 237W/(m·K). quite. However, the tensile strength of as-cast pure magnesium is only 98MPa, which is difficult to meet the needs of structural materials.

In order to improve the mechanical properties of magnesium, pure magnesium is often alloyed, but the addition of alloying elements will reduce the thermal conductivity of magnesium. It is generally believed that the addition of alloying elements will form a solid solution or a second phase with magnesium, and both the solid solution and the second phase will reduce the thermal conductivity of magnesium alloys. The reason is that: the solid solution atoms will cause lattice distortion, which will enhance the scattering effect of electrons, hinder the free movement of electrons in the lattice, and reduce the mean free path of electrons; the second phase boundary will hinder electrons and sound. The more the second phase, the more diffuse the distribution, the greater the interface density, and the greater the resistance to thermal diffusion. Different alloying elements are added, and the degree of reduction is also different. Among the commonly used alloying elements, Al element has the greatest influence on the thermal conductivity of magnesium alloys, while Zn element has little effect on the thermal conductivity of magnesium alloys, but the overall trend is decreasing, that is, With the increase of alloying element content, the thermal conductivity of magnesium alloys decreases significantly. For example, commercial magnesium alloys AM60B and AZ91D have good mechanical properties, but their room temperature thermal conductivity is low. The room temperature thermal conductivity of AM60B alloy is about 62W/(m K), and the room temperature thermal conductivity of AZ91D alloy is only The room temperature thermal conductivity of commercial ZM51 alloy is about 98W/(m·K), and the room temperature thermal conductivity of as-cast Mg-6Zn-Cu can reach 121.3W/(m·K). Therefore, in Mg-Zn alloys, adding alloying elements to improve the thermal conductivity of magnesium alloys has great application potential.

Compared with Mg-Al and Mg-RE alloys, Mg-Zn alloys have better thermal conductivity, but they have problems such as poor casting properties and poor mechanical properties. Generally speaking, adding alloying elements can improve the casting properties and mechanical properties of Mg-Zn alloys, but adding too much alloying elements will reduce the thermal conductivity of the alloys. Aiming at the contradiction between the mechanical properties and thermal conductivity of Mg-Zn alloys, adding appropriate alloying elements and optimizing the T6 heat treatment process can simultaneously improve the thermal conductivity and yield strength of Mg-Zn alloys. Existing literature 1, in 2013, "Research on Thermal Conductivity of Magnesium Alloys" by Pan Hucheng of Chongqing University, etc., doctoral dissertation, after T6 heat treatment of Mg-6Zn alloy, its thermal conductivity was increased from 114.3W/(m K) to 125.1 W/(m·K), after adding 1.5wt.%Cu and after T6 heat treatment, the thermal conductivity of the alloy can reach 132.9W/(m·K). Chinese Patent Publication No. CN107164672B discloses an ultra-high thermal conductivity magnesium alloy, the alloy contains 0.01-1.0 wt.% Zn, 0.01-0.2 wt.% Cu, 0.01-0.095 wt.% Ag, and the balance is 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 elements can effectively improve the thermal conductivity of Mg-Zn alloys, but due to the inclusion of Ag in the alloy, the material cost is high, and the addition of Ag will reduce the corrosion resistance of the alloy; in addition, this preparation method requires Using deformation processing, the process is complicated and the production efficiency is low.

Based on the above problems, rare earth elements can be added to Mg-Zn alloys as alloying elements because they can not only improve the melt fluidity of magnesium alloys to improve the casting properties of magnesium alloys, but also enhance the corrosion resistance of alloys. The patent publication number is CN107043880A Chinese patent document discloses a rare earth thermal conductive magnesium alloy and its preparation method, the alloy composition is: Mn content is 0.2-1.0wt.%, Zn content is 0.5-3.0wt.%, Nd content is 0.5 -2.0wt.%, the balance is Mg, after smelting, casting, homogenization, hot extrusion and aging treatment, the tensile strength is 250-350MPa and the thermal conductivity is 110-120W/(m·K ) of rare earth thermally conductive magnesium alloys. The thermal conductivity of the rare earth magnesium alloy is relatively low, which is only comparable to the Mg-6Zn alloy heat treated by T6. The main reason is that the content of rare earth element Nd is relatively high, and a large amount of Mg ₃ Nd phase and T ₂ -(Mg, Zn) ₉₂ Nd ₈ is the second phase, and its phase boundary increases, which is not conducive to thermal diffusion; on the other hand, after the alloy is processed by hot extrusion, there are a lot of textures in the alloy, which will also increase the scattering of electrons and phonons Chances of reducing the thermal conductivity of the alloy. Patent publication number CN110819863 B Chinese patent discloses a low rare earth high thermal conductivity magnesium alloy and its preparation method, the alloy composition is: 5.0-7.0wt.% Gd, 0.5-2.0wt.% Er, 3.0-7.0wt.% Zn, 0.5-1.0 wt.% Zr, balance Mg. The rare earth magnesium alloy with a thermal conductivity of 136.9W/(m·K) can be obtained by performing solid solution + aging treatment at a certain temperature and time. However, the rare earth element content of the alloy exceeds the Zn content, and it is actually a high rare earth magnesium alloy. On the one hand, the maximum solid solubility of Gd in the magnesium matrix is 23.5wt.%, the content of Gd is too high, its solid solubility in the matrix is high, and the second phase is also increased, both of which are not conducive to sound The movement of particles and electrons is not conducive to improving the thermal conductivity of the alloy; on the other hand, the high density and high cost of Gd and Zr are not conducive to reducing the weight of magnesium alloys.

To sum up, in the current published patent documents, in Mg-Zn alloys, the rare earth content is high, the second phase of the alloy is high, and the phase boundary is high, which hinders thermal diffusion; Gd, Nd, Er solid solution The maximum solid solubility of Gd and Nd in the magnesium matrix is 23.5wt.% and 3.63wt.%, respectively. The higher the solid solubility of solute atoms can lead to greater lattice distortion, thereby reducing the thermal conductivity of the alloy. . These rare earth magnesium alloys have good mechanical properties, but their thermal conductivity is not excellent. The main reason is that the increase of the second phase and solid solubility can achieve solid solution strengthening and second phase strengthening, but it also hinders phonons and electrons. The movement of the alloy reduces the thermal conductivity of the alloy. Therefore, under the requirements of the mechanical properties of the alloy, in order to improve the thermal conductivity of Mg-Zn alloys, the following technical problems must be solved:

(1) Reduce the solid solution amount of Zn and rare earth elements in the Mg matrix to reduce the effect of lattice distortion on thermal conductivity;

(2) Reduce the generation of the second phase in the Mg-Zn system to reduce the hindering effect of the phase interface on thermal motion;

(3) Increase the number of nanoscale precipitates to increase the hindering effect of precipitation relative to dislocation slip.

The above problems have become technical problems that need to be solved urgently.

SUMMARY OF THE INVENTION

In order to solve the problems of the prior art, the object of the present invention is to overcome the deficiencies of the prior art, and to provide a preparation method of a Mg-Zn-La alloy with both high thermal conductivity and high strength. The alloy of the present invention has better thermal conductivity, With more nanoscale precipitates, less secondary phases, fewer phase boundaries, higher quality, and increased application range. The method of the invention is simple, and the use cost is reduced.

To achieve the above object, the present invention adopts the following inventive concept:

The present invention needs to design a Mg-Zn-La alloy that reduces the rare earth content 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, rare earth elements with low solid solubility are added. As a light rare earth element La, its maximum solid solubility in the magnesium matrix is only 0.07wt.%, La can be used as an additive element in Mg-Zn alloys to reduce the effect of solid solubility on thermal conductivity.

Secondly, for the formation of the second phase, on the one hand, reducing the amount of alloying elements added, the La content in the designed Mg-Zn-La alloy is less than 0.55wt.%; on the other hand, reducing the types of phases in the alloy, the designed The Mg-Zn-La alloy contains only τ ₁ +α-Mg two phases. On the other hand, through aging treatment, the precipitation of β ₁ '-Mg ₄ Zn ₇ phase and β ₂ '-MgZn ₂ phase is promoted, the solid solubility of Zn in the magnesium matrix is reduced, and the desolubilization of Zn is realized;

Finally, with the progress of aging, the number of nano-scale β ₁ '-Mg ₄ Zn ₇ and β ₂ '-MgZn ₂ precipitates increases, which hinders dislocation slip motion, realizes precipitation strengthening, and improves alloy yield strength.

According to the above-mentioned inventive concept, the present invention adopts the following technical solutions:

A Mg-Zn-La alloy with both high thermal conductivity and high strength, the Mg-Zn-La alloy composition and composition mass percentage are as follows: the content of Zn is 6.18-6.43wt.%, and the content of La is 0.32-0.55wt .%, the balance is Mg and other unavoidable impurities; after the Mg-Zn-La alloy undergoes solid solution and aging treatment, nano-scale rod-like β ₁ '-Mg ₄ Zn ₇ phase and nano-scale disc-like β ₂ '- The MgZn ₂ phase is distributed in the α-Mg matrix, and the micron granular strengthening phase τ ₁ -Mg ₂₈ Zn ₂₀ La ₄ phase is dispersed in the α-Mg grain boundary.

Preferably, the average length and average diameter of the rod-shaped β ₁ '-Mg ₄ Zn ₇ precipitates along the [0001] _Mg direction in the Mg-Zn-La alloy of the present invention are 236.2±76.5 nm and 15.7±4.5 nm, respectively.

Preferably, the average diameter of the discoid β ₂ '-MgZn ₂ precipitates in the Mg-Zn-La alloy of the present invention is 25.7±8.4 nm.

Preferably, the micron-sized granular strengthening phase τ ₁ -Mg ₂₈ Zn ₂₀ La ₄ phase in the Mg-Zn-La alloy of the present invention has an average diameter of 1.2±0.3 μm.

Preferably, after the heat treatment of the Mg-Zn-La alloy of the present invention, the precipitation of β ₁ '-Mg ₄ Zn ₇ and β ₂ '-MgZn ₂ reduces the solid solubility of Zn in the α-Mg matrix to 3.62-3.80 wt.%.

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

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

A preparation method of the Mg-Zn-La alloy having both high thermal conductivity and high strength of the present invention, comprising the following steps:

(1) Preparation of Mg-17La master alloy:

Using pure Mg with a purity of not less than 99.99%, pure La with a purity of not less than 99.99% and pure Ce with a purity of not less than 99.99% as raw materials, a Mg-17La master alloy is prepared by a vacuum induction melting method;

(2) Smelting Mg-Zn-La alloy:

Using pure Mg with a purity of not less than 99.99%, pure Zn with a purity of not less than 99.99%, and the Mg-La master alloy prepared in the step (1) as alloy raw materials, using a pit-type resistance furnace as a melting furnace for alloying raw material smelting;

The magnesium alloy raw material composition and mass percentage are:

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

First, set the temperature of the resistance furnace to not less than 600 °C, and preheat the polished raw materials to not less than 300 °C to remove the water vapor; after the temperature of the resistance furnace rises to not less than 600 °C, the pure The magnesium is put into the corundum crucible in the furnace, and the mixed protective gas of SF ₆ and CO ₂ is introduced into the furnace at the same time. When the pure magnesium in the furnace is completely melted and the melt temperature is stable at 700 ℃, pure Zn and Mg-17La are added in the middle Alloy, continue to stir the melt for at least 1min, heat up to not less than 720°C, and keep the temperature for at least 30min to make the alloy elements fully react;

Then open the furnace cover, slowly sprinkle the refining agent, and continue to stir for 1-2 minutes, continue to heat up to not less than 740 ° C, and carry out refining for at least 30 minutes; after refining is completed, power off the pit type resistance furnace and reduce the melt temperature to When the temperature is not higher than 720°C, remove the slag on the surface of the melt with a slag spoon, and cast it into a low-carbon steel mold with a mold temperature not higher than 300°C to obtain a Mg-Zn-La alloy ingot;

(3) Solution treatment:

Use aluminum foil to wrap the Mg-Zn-La alloy ingot to reduce the oxidation of the alloy, then put it into a box-type resistance furnace, and heat up with the furnace, the solution temperature is not lower than 400 ℃, and the solution time is at least 6h. water quenching;

(4) Aging treatment:

Put the solution-treated Mg-Zn-La into tetramethylglycerol, and put it into a box-type resistance furnace for aging treatment. -Zn-La alloy.

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

First, cut pure Mg into cuboid blocks with a volume of no more than 3 × 4 × 5 cm, cut pure La into blocks with a size of no more than 0.5 × 0.5 × 0.5 cm, and clean the oxide scale on all pure metal surfaces to avoid Oxide inclusions are introduced in the smelting process, and pure Mg and pure La are put into the vacuum induction melting furnace;

Before smelting, the cavity of the smelting furnace should be purged at least three times, and the absolute pressure should not be higher than 0.3MPa by using a mechanical pump each time; after the last purge, Ar gas was filled into the cavity until the cavity was The pressure is higher than atmospheric pressure by 10-20Pa to prevent oxidation from outside air entering the furnace cavity; adjust the current to not less than 200A and keep it warm for at least 5min. All the metal in the melt is melted, and then the current is adjusted to 230-240A, and the temperature is kept for at least 2 minutes. After observing that the fluidity meets the casting requirements, the alloy melt is poured into the copper mold; To ensure uniform composition, after each inversion smelting, sandpaper was used to remove the oxide film on the surface of the ingot to prepare Mg-17La master alloy.

Preferably, in the step (2), the mass percentage of the refining agent components is composed of: the content of BaCl ₂ is 35-43 wt.%, the content of CaF ₂ is 2-5 wt.%, and the balance is KCl.

To solve the above technical problems, the technical solution of the present invention has obvious effects and can be verified.

1. Calculate the isothermal cross-sectional phase diagram at 400 °C through the thermodynamic database of the Mg-Zn-La system, and design two Mg-Zn-La thermally conductive alloys located in the τ ₁ +α-Mg two-phase region. The experiments marked in the phase diagrams The layout is the design composition of the Mg-Zn-La alloy, as shown in Figure 1. Based on the thermodynamic phase diagram calculation, the τ ₁ phase fraction of the Mg-6.18Zn-0.55La alloy is 2.27wt.%, and the solid solubility of Zn in the magnesium matrix is 5.73wt.%; for the Mg-6.18Zn-0.55La alloy, the In other words, the τ ₁ phase precipitates around 177°C and can exist stably in the temperature range of 177-400°C. Therefore, the Mg-Zn-La alloy of the present invention is solution-treated at 400°C and aged at 200°C. Through different aging times, the aging hardening curve is measured, as shown in Figure 2, which provides an experimental basis for the selection of aging treatment time.

2. In order to obtain a Mg-Zn-La alloy with both high thermal conductivity and high strength and a preparation method thereof, a vacuum induction melting method is used to prepare a Mg-17La master alloy, and then the Mg-Zn-La alloy is smelted and cast into shape, Finally, by solid solution + aging treatment at a certain temperature and time, a Mg-Zn-La alloy with both high thermal conductivity and high strength can be obtained.

The invention designs the composition range of the Mg-Zn-La system thermally conductive alloy by constructing the Mg-Zn-La phase diagram and the thermal conductivity thermodynamic database, and at the same time calculates the same phase composition according to the thermodynamic database, and further reduces the rare earth content to improve the alloy. The thermal conductivity was effectively verified for two alloy compositions of Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La alloys.

The mass percentage of the Mg-Zn-La alloy composition having both high thermal conductivity and high strength in the present invention is as follows: the content of Zn is 6.18-6.43wt.%, the content of La is 0.32-0.55wt.%, and the balance is Mg and other inevitable impurities. After the alloy is added with a trace amount of rare earth element La, a micron-sized granular strengthening phase τ ₁ -Mg ₂₈ Zn ₂₀ La ₄ phase is formed, which is dispersed on the grain boundary; after solid solution + aging treatment, nano-scale rod-shaped β ₁ '- Mg ₄ Zn ₇ and discotic β ₂ '-MgZn ₂ precipitates, distributed in the α-Mg matrix. These two will hinder dislocation slip, improve the yield strength of the alloy, reduce the solid solubility of Zn in the Mg matrix, reduce the effect of lattice distortion on the thermal conductivity, and improve the thermal conductivity of the alloy. The room temperature thermal conductivity of the obtained Mg-Zn-La alloy is 150.2-155.3 W/(m·K), and the yield strength of the alloy is 164.9-172.1 MPa. On the basis of higher yield strength, the magnesium alloy has excellent thermal conductivity; meanwhile, it reduces product weight and production cost, and can be used for heat dissipation structural materials such as electronic devices.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

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

2. The present invention performs a solid solution + aging treatment process _on the as _- cast Mg _- Zn _- La alloy, and improves the yield strength of the alloy through precipitation strengthening _; The precipitation of Zn in the α-Mg matrix reduces the solid solubility of Zn in the α-Mg matrix from 5.58-5.73wt.% to 3.62-3.80wt.%, realizing the precipitation of Zn, thereby reducing the effect of the solid solution of Zn on the thermal conductivity of the alloy , thereby improving the thermal conductivity of the alloy. The thermal conductivity of the designed Mg-Zn-La alloy at room temperature is 150.2-155.3 W/(m·K), and the yield strength of the alloy is 164.9-172.1 MPa. On the basis of meeting the requirements of mechanical properties, a Mg-Zn-La alloy with high thermal conductivity is obtained;

3. Compared with heavy rare earths and high rare earth thermal conductivity magnesium alloys, the Mg-Zn-La alloy of the present invention reduces the amount of rare earth elements used, reduces the generation of the second phase τ ₁ phase, reduces phase boundaries, and greatly improves Mg-Zn-La alloys. Thermal conductivity of Zn-La alloy; compared with Mg-6Zn alloy, the addition of trace rare earth elements can effectively improve the casting properties of the alloy, while improving the mechanical properties and thermal conductivity. In addition, La is a light rare earth element, and the amount of rare earth added is small, which can effectively reduce the cost of use;

4. The present invention designs alloy compositions based on the Mg-Zn-La phase diagram and the thermal conductivity thermodynamic database, which effectively reduces the experimental cost generated by the trial-and-error method; The cost of use increases the scope of application and has broad application prospects.

Description of drawings

FIG. 1 is a distribution point diagram of isothermal cross-section at 400° C. of a Mg-Zn-La alloy system according to a preferred embodiment of the present invention.

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

FIG. 3 is the room temperature thermal conductivity of the solid solution state and aging state Mg-Zn-La alloy according to the preferred embodiment of the present invention.

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

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

FIG. 6 is a trend graph of the mechanical-thermal conductivity of different Mg alloy systems of the present invention.

Detailed ways

The present invention will further describe the content of the present invention in detail through embodiments and in conjunction with the accompanying drawings. The alloy components and their phase compositions involved in each embodiment and comparative example are shown in Table 1.

Table 1. Examples and comparative examples alloy composition and its phase composition

The average length and average diameter of the rod-shaped β ₁ '-Mg ₄ Zn ₇ precipitates along the [0001] _Mg direction in the Mg-Zn-La alloy of the present invention are 236.2±76.5 nm and 15.7±4.5 nm, respectively.

The average diameter of the discoid β ₂ '-MgZn ₂ precipitates in the Mg-Zn-La alloy of the present invention is 25.7±8.4 nm.

The micron-sized granular strengthening phase τ ₁ -Mg ₂₈ Zn ₂₀ La ₄ phase in the Mg-Zn-La alloy of the present invention has an average diameter of 1.2±0.3 μm.

After the heat treatment of the Mg-Zn-La alloy of the present invention, the precipitation of β ₁ '-Mg ₄ Zn ₇ and β ₂ '-MgZn ₂ reduces the solid solubility of Zn in the α-Mg matrix to 3.62-3.80wt.% .

The grain size of the Mg-Zn-La alloy of the present invention is 61.6-69.8 μm. It can be seen from Figure 6 that the comprehensive properties of the Mg-Zn-La alloy are better than those of the existing La-free Mg-Zn alloys, Mg-Al alloys, Mg-Mn alloys, and Mg-Ce-Zn alloys. performance.

The above scheme will be further described below in conjunction with specific embodiments, and preferred embodiments of the present invention are described in detail as follows:

Example 1

In this embodiment, a Mg-Zn-La alloy with both high thermal conductivity and high strength, the mass percentage content of the Mg-Zn-La alloy composition is: the content of Zn is 6.43wt.%, and the content of La is 0.32 wt.%, the balance is Mg and other inevitable impurities. A Mg-Zn-La alloy with thermal conductivity and yield strength of 150.2 W/(m·K) and 164.9 MPa was prepared by solution + aging treatment process, respectively.

A preparation method of a Mg-Zn-La alloy with both high thermal conductivity and high strength, comprising the following steps:

(1) Preparation of Mg-17La master alloy: Using pure Mg with a purity of 99.99% and pure La with a purity of 99.99% as raw materials, the Mg-17La master alloy was prepared by vacuum induction melting.

(2) Smelting Mg-Zn-La alloy: the raw materials are 99.99% pure Mg, 99.99% pure Zn and the Mg-17La master alloy prepared in step (1), and the smelting furnace is a pit type resistance furnace. The magnesium alloy raw material composition and mass percentage content are as follows: the content of Zn is 6.43wt.%, the content of La is 0.32wt.%, and the balance is Mg, wherein La is added in the form of Mg-17La master alloy. The smelting process is as follows: first, set the temperature of the resistance furnace to 600 °C for the first time, and preheat the polished raw materials to 300 °C to remove water vapor; after the temperature of the resistance furnace rises to 600 °C, put pure magnesium into the furnace. In the corundum crucible in the furnace, the mixed protective gas of SF ₆ and CO ₂ was introduced into the furnace at the same time. When the pure magnesium in the furnace was completely melted and the melt temperature was stabilized at 700 ℃, pure Zn and Mg-17La master alloy were added for a continuous period of time. Stir the melt for 1 min, raise the temperature to 720 °C, and keep the temperature for 30 min to fully react the alloying elements. Then open the furnace cover, slowly sprinkle the refining agent, and continue stirring for 1-2 minutes, and continue to heat up to 740 ° C for refining for 30 minutes. After the refining is completed, power off the pit-type resistance furnace, and when the melt temperature drops to 720 °C, remove the slag on the surface of the melt with a slag spoon, and cast it into a low-carbon steel mold preheated at 300 °C to obtain Mg-Zn -La alloy ingot.

(3) Solution treatment: use aluminum foil to wrap the Mg-Zn-La alloy ingot to reduce the oxidation of the alloy, then put it into a box-type resistance furnace, and heat up with the furnace, the solution temperature is 400 ° C, and the solution time is 6h. Finally, the alloy is water quenched.

(4) Aging treatment: put the solution-treated Mg-Zn-La alloy into tetramethyl glycerin, and put it into a box-type resistance furnace for aging treatment. The aging temperature is 200°C and the aging time is 5h, that is High thermal conductivity Mg-Zn-La alloys can be prepared.

(5) Thermal conductivity test: The formula for calculating the thermal conductivity of the alloy is: λ=αρC _p , where λ is the thermal conductivity of the alloy, α is the thermal diffusivity of the alloy, ρ is the density of the alloy, and Cp is the specific heat capacity of the alloy . Since the error between the experimentally measured heat capacity and the calculated heat capacity is not large, the heat capacity and density of the alloy are calculated from the thermodynamic database; for the thermal diffusivity of the Mg-Zn-La alloy after heat treatment at room temperature, the Measured by the laser flash method, the model of the laser thermal conductivity meter is NETZSCH LFA467. The sampling area of the thermal diffusivity test sample is 5mm from the bottom of the ingot. First, use wire cutting to cut a sample with a size of Ф10 × 3mm; then, use 800-grit sandpaper to remove the oxide scale on the surface of the sample; then use 1500-grit and Grind with 2000-grit sandpaper to ensure uniform thickness and smooth surface of the sample, and finally obtain a cylindrical standard sample with a diameter of 10mm and a thickness of ≤3mm.

(6) Tensile performance test: The tensile test sample is processed into a dog-bone-shaped rectangular standard sample according to the requirements of GB/T16865-2013. The gauge length is 25.0mm, the thickness is 4.0mm, and the width is 6.0mm. . The number of grains in the gauge length section is about 10,000, which meets the requirements of tensile measurement. The tensile properties of the solid solution and aging alloys were measured by an Instron 5982 universal testing machine, and the tensile rate was 1 mm/min. To reduce experimental error, three parallel samples were tested for each alloy.

Example 2

This embodiment is basically the same as the first embodiment, and the special features are:

In this embodiment, a Mg-Zn-La alloy with both high thermal conductivity and high strength, the mass percentage content of the Mg-Zn-La alloy composition is: the content of Zn is 6.18wt.%, and the content of La is 0.55 wt.%, the balance is Mg and other inevitable impurities. A Mg-Zn-La alloy with thermal conductivity and yield strength of 155.3 W/(m·K) and 172.1 MPa was prepared by solution + aging treatment process.

A preparation method of a Mg-Zn-La alloy with both high thermal conductivity and high strength, comprising the following steps:

(1) Preparation of Mg-17La master alloy: Using pure Mg with a purity of 99.99% and pure La with a purity of 99.99% as raw materials, the Mg-17La master alloy was prepared by vacuum induction melting.

(2) Smelting Mg-Zn-La alloy: the raw materials are 99.99% pure Mg, 99.99% pure Zn and the Mg-17La master alloy prepared in step (1), and the smelting furnace is a pit type resistance furnace. The magnesium alloy raw material composition and mass percentage content are as follows: the content of Zn is 6.18wt.%, the content of La is 0.55wt.%, and the balance is Mg, wherein La is added in the form of Mg-17La master alloy. The smelting process is as follows: first, set the temperature of the resistance furnace to 600 °C for the first time, and preheat the polished raw materials to 300 °C to remove water vapor; after the temperature of the resistance furnace rises to 600 °C, put pure magnesium into the furnace. In the corundum crucible in the furnace, the mixed protective gas of SF ₆ and CO ₂ was introduced into the furnace at the same time. When the pure magnesium in the furnace was completely melted and the melt temperature was stabilized at 700 ℃, pure Zn and Mg-17La master alloy were added for a continuous period of time. Stir the melt for 1 min, raise the temperature to 720 °C, and keep the temperature for 30 min to fully react the alloying elements. Then open the furnace cover, slowly sprinkle the refining agent, and continue stirring for 1-2 minutes, and continue to heat up to 740 ° C for refining for 30 minutes. After the refining is completed, power off the pit-type resistance furnace, and when the melt temperature drops to 720 °C, remove the slag on the surface of the melt with a slag spoon, and cast it into a low-carbon steel mold preheated at 300 °C to obtain Mg-Zn -La alloy ingot.

(3) Solution treatment: use aluminum foil to wrap the Mg-Zn-La alloy ingot to reduce the oxidation of the alloy, then put it into a box-type resistance furnace, and heat up with the furnace, the solution temperature is 400 ° C, and the solution time is 6h. Finally, the alloy is water quenched.

(4) Aging treatment: put the solution-treated Mg-Zn-La alloy into tetramethylglycerol, and put it into a box-type resistance furnace for aging treatment. The aging temperature is 200°C and the aging time is 20h, namely High thermal conductivity Mg-Zn-La alloys can be prepared.

(5) Thermal conductivity test: the adopted test means and calculation method are the same as those in Example 1, and the operation steps that are not specifically described are the same as those in Example 1.

(6) Tensile performance test: the standard sample and test parameters of the tensile test are the same as those in Example 1, and the operation steps that are not specially described are the same as those in Example 1.

Comparative ratio

A Mg-Zn alloy without adding trace rare earth elements, the mass percentage content of the Mg-Zn alloy components is: the content of Zn is 6.25wt.%, and the balance is Mg and other inevitable impurities.

A preparation method of a Mg-Zn alloy without adding trace rare earth elements, comprising the following steps:

(1) Preparation of raw materials: pure Mg with a purity of 99.99% and pure Zn with a purity of 99.99% are used as raw materials, and the ingredients are prepared according to the above alloy components.

(2) Alloy smelting: First, set the temperature of the resistance furnace to 600 °C for the first time, and preheat the polished raw materials to 300 °C to remove water vapor; after the temperature of the resistance furnace rises to 600 °C, put the pure magnesium Put it into the corundum crucible in the furnace, and at the same time pass the mixed protective gas of SF ₆ and CO ₂ into the furnace. When the pure magnesium in the furnace is completely melted and the melt temperature is stable at 700 ℃, pure Zn is added, and the melt is continuously stirred for 1min. The temperature was raised to 720°C, and the temperature was kept for 30min, so that the alloy elements were fully reacted. Then open the furnace cover, slowly sprinkle the refining agent, and continue stirring for 1-2 minutes, and continue to heat up to 740 ° C for refining for 30 minutes. After the refining is completed, power off the pit-type resistance furnace, and when the melt temperature drops to 720 °C, remove the slag on the surface of the melt with a slag spoon, and cast it into a low-carbon steel mold preheated at 300 °C to obtain Mg-Zn Alloy ingots.

(3) Solution treatment: use aluminum foil to wrap the Mg-Zn alloy ingot to reduce the oxidation of the alloy, and then put it into a box-type resistance furnace to heat up with the furnace. The solution temperature is 400°C, and the solution time is 6h. The alloy is water quenched.

(4) Aging treatment: put the solution-treated Mg-Zn alloy into tetramethyl glycerin, and put it into a box-type resistance furnace for aging treatment. The aging temperature is 200°C and the aging time is 5h.

(5) Thermal conductivity test: the specific test means and calculation method are the same as those in Example 1, and the operation steps that are not specifically described are the same as those in Example 1.

(6) Tensile performance test: the standard sample and test parameters of the tensile test are the same as those in Example 1, and the operation steps that are not specially described are the same as those in Example 1.

Carry out comparative analysis with embodiment and comparative example, the following conclusions can be obtained:

(1) The thermal conductivities of the solid solution Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La alloys are 122.4±0.4W/(m·K) and 124.4±0.4W/(m·K), respectively, It is higher than 100.7±0.2W/(m·K) of Mg-6.25Zn alloy. After aging treatment, the thermal conductivity of aged Mg-Zn-La alloy is significantly improved compared with that of solid solution alloy, and the thermal conductivity of Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La alloys is 150.2±0.3W/( m·K) and 155.3±0.6W/(m·K), with an increase of 27.8-30.9W/(m·K), as shown in Figure 3. The reason is that the rod-shaped β ₁ '-Mg ₄ Zn ₇ phase and the disc-shaped β ₂ '-MgZn ₂ phase are precipitated from the magnesium matrix after the aging treatment, which makes the solid solubility of Zn in the α-Mg matrix from 5.58-5.73wt% .% is reduced to 3.62-3.80wt.% to realize the desolubilization of Zn, reduce the influence of lattice distortion on thermal conductivity, and obtain excellent thermal conductivity.

(2) The yield strengths of Mg-6.25Zn, Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La in solid solution state are 60.9MPa, 64.9MPa and 79.3MPa, respectively. After adding La element, although the solid solubility of La in the α-Mg matrix is limited, the τ ₁ that still exists after solution treatment plays a role in the second phase strengthening of the alloy, so that the yield strength of the alloy is improved to a certain extent. After aging for 5-20h, the grain size of Mg-Zn and Mg-Zn-La alloys did not grow significantly. The size is small, and according to the Hall-Page formula, the yield strength of the alloy is theoretically superior. Experiments show that the maximum yield strength of aged Mg-6.25Zn, Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La can reach 160.9MPa, 164.9MPa and 172.1MPa, respectively, after aging at 200℃ for 5-20h. MPa, as shown in Figure 4. Compared with the solid solution alloy, the yield strength of the aged alloy is significantly improved, and its yield strength is increased by 164%, 150% and 148%, respectively. The reason is that the rod-shaped β ₁ '-Mg ₄ Zn ₇ phase and the disc-shaped β ₂ '-MgZn ₂ phase are precipitated from the magnesium matrix, and the formation of the precipitation phase will hinder the dislocation slip and improve the yield strength of the alloy.

和(0001)_Mg的错配度为0.76％，如图5所示。随着时效的进行，β₁’相与α-Mg基体仍然呈共格关系，晶格畸变提升，对热导率影响有限。(3) After aging treatment, there are rod-shaped β ₁ ' precipitates and disc-shaped β ₂ ' precipitates along the [0001] _Mg direction in Mg-Zn-La alloys. The rod-shaped β ₁ ' precipitates in Mg-Zn-La alloys The average length and average diameter were 236.2 nm and 15.7 nm, respectively. During the aging process, the formation of β ₁ '-Mg ₄ Zn ₇ phase and β ₂ '-MgZn ₂ phase was accompanied by the desolubilization of solute elements, which improved the thermal conductivity of Mg-Zn-La alloys. After aging treatment, in Mg-Zn-La alloy,

and (0001) _Mg have a mismatch of 0.76%, as shown in Figure 5. With the progress of aging, the β ₁ ' phase is still in a coherent relationship with the α-Mg matrix, and the lattice distortion increases, which has a limited impact on the thermal conductivity.

To sum up, as can be seen from Figures 1 to 4, the above-mentioned embodiments of the present invention design the composition range of the thermally conductive alloy of the Mg-Zn-La system by constructing the Mg-Zn-La phase diagram and the thermal conductivity thermodynamic database, at τ ₁ + In the two phases of α-Mg, the rare earth content was further reduced to improve the thermal conductivity of the alloy. Two alloy compositions were designed: Mg-6.43Zn-0.32La and Mg-6.18Zn-0.55La alloys. The materials are prepared according to the mass percentage of the following alloy components: the content of Zn is 6.18-6.43wt.%, the content of La is 0.32-0.55wt.%, and the balance is Mg and other inevitable impurities. The smelting process includes raw material preparation, preparation of Mg-La intermediate alloy, Mg-Zn-La alloy smelting and casting molding. Then, the as-cast Mg _- Zn _- La alloy is subjected to solid solution ₊ aging treatment. _On the one hand, the yield strength of the alloy is improved through precipitation strengthening; -The precipitation of MgZn ₂ phase reduces the solid solubility of Zn atoms in the magnesium matrix, realizes the precipitation of Zn, reduces the influence of the solid solution of Zn on the thermal conductivity of the alloy, and improves the thermal conductivity of the alloy. The thermal conductivity of the designed Mg-Zn-La alloy at room temperature is 150.2-155.3 W/(m·K), and the yield strength of the alloy is 164.9-172.1 MPa. On the basis of meeting the requirements of mechanical properties, a Mg-Zn-La alloy with high thermal conductivity is obtained. Compared with heavy rare earths and high rare earth thermal conductivity magnesium alloys, the Mg-Zn-La alloys of the above embodiments of the present invention reduce the usage of rare earth elements, reduce the generation of the second phase τ ₁ phase, reduce phase boundaries, and facilitate thermal diffusion. , which greatly improves the thermal conductivity of Mg-Zn-La alloys. Compared with Mg-6Zn alloy, the addition of trace rare earth element La can effectively improve the casting properties of the alloy, while improving the mechanical properties and thermal conductivity. In addition, La is a light rare earth element, and the amount of rare earth added is small, which can effectively reduce the use cost and is easy to commercialize.

The embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and various changes can also be made according to the purpose of the invention and creation of the present invention. Changes, modifications, substitutions, combinations or simplifications should be equivalent substitution methods, as long as they meet the purpose of the present invention, as long as they do not deviate from the technical principles and inventive concepts of the present invention, all belong to the protection scope of the present invention.

Claims (10)

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:

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.

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:

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.

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.

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