High thermal conductive low expansion magnesium-based composite material and preparation method thereof

Abstract

The application designs a preparation method of high-thermal-conductivity and low-expansion magnesium-based composite material, which comprises a smelting step, an additional method preparation step of introducing diamond and a solidification forming step; after semi-solid mixed melt stirring is completed, the melt is poured into a metal mold under a protection environment of inert gas, and is cooled to room temperature in air, so that a diamond / AlN / AZ91 magnesium-based composite material is obtained; the application also provides the high-thermal-conductivity and low-expansion magnesium-based composite material prepared by the preparation method; and the application fully utilizes the additional method to introduce high-volume-fraction reinforcing body particles, so that the composite material meets the requirements of high thermal conductivity and low expansion, and the operation is simple and easy to implement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging, in particular to a magnesium-based composite material for packaging and a preparation method thereof. BACKGROUND

[0002] In recent years, magnesium-based composite materials are widely used in the field of electronic packaging. Based on the characteristics of electronic devices, new requirements are proposed for the thermal expansion coefficient matching of packaging materials and the high thermal conductivity of packaging materials. Therefore, the traditional magnesium-based alloy is difficult to meet the stringent requirements of electronic packaging due to the high thermal expansion coefficient of magnesium itself and the poor thermal conductivity of magnesium alloy.

[0003] In view of the performance requirements of electronic packaging, some scholars have proposed a preparation method of magnesium-based composite materials. The published literature is "Nano-and micro- / meso-scale engineered magnesium / diamond composites: Novel materials for emerging challenges in thermal management" of "Acta Materialia". This technology mainly uses an external method to prepare the composite material. Low-expansion, high-thermal-conductivity reinforcing particles are used to realize the low-expansion, high-thermal-conductivity of the composite material through the low-expansion, high-thermal-conductivity of the reinforcing particles. The magnesium-based composite material prepared by this method has low-expansion, high-thermal-conductivity performance, which meets the requirements of electronic packaging materials, and can introduce a higher volume fraction of reinforcing particles to realize the reinforcing effect of the reinforcing particles on the composite material. The commonality of the above-mentioned external preparation method is that the selection range of the reinforcing particles is less limited, and reinforcing particles with different characteristics can be introduced according to needs. If the preparation technology of the magnesium-based composite material can be improved to synthesize the reinforcing particles in situ in the magnesium matrix, the performance of the composite material can be further improved and the cost can be reduced.

[0004] In recent years, the technology of in-situ preparation of magnesium-based composite materials has developed rapidly. In the articles published in "Materials Science and Engineering A" in 2009 and "Foundry Technology" in 2023, the preparation technology of in-situ particle reinforced magnesium matrix composites is discussed. This technology introduces the reinforcing particles into the magnesium alloy matrix in-situ, which is simpler than the external method and has lower cost. Due to the in-situ introduction of the reinforcing system, the reinforcing particles are tightly and effectively combined with the matrix compared with the external reinforcing particles, and the reinforcing particles are usually nanoscale and uniformly dispersed, which can fully act on the matrix and improve the performance of the matrix. In-situ technology is widely used in the preparation of magnesium-based composite materials with high damping performance, high wear resistance and high strength and toughness, but so far, there is no report on the direct application of this technology in the preparation of electronic packaging materials. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art by combining the external method with the in-situ method, making full use of the small limitation of the external method to introduce high volume fraction of reinforcing particles, and the characteristics of the in-situ method to generate uniform and small reinforcing particles, so as to obtain high thermal conductivity and low expansion magnesium-based composite materials with excellent performance.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a preparation method of high thermal conductivity and low expansion magnesium-based composite material, comprising the following steps:

[0007] Step one, melting step:

[0008] Under the protection of inert gas, 1-10 kg of AlN / AZ91 magnesium-based composite material is placed in a melting furnace, the melting temperature is 740-760℃, and the holding time is 20-30 min, to obtain an AlN / AZ91 magnesium-based composite material melt;

[0009] Step two, external method for introducing diamond:

[0010] Diamond particles are added to the AlN / AZ91 magnesium-based composite material melt to form a semi-solid mixed melt, wherein the volume fraction of diamond in the semi-solid mixed melt is not more than 25%, and then mechanical stirring is performed for at least 1 min to uniformly disperse the diamond particles in the AlN / AZ91 magnesium-based composite material melt;

[0011] Then, the stirred semi-solid mixed melt is cooled to 540-560℃, and stirred for at least 1 min, during which the AlN and diamond reinforcing bodies in the AlN / AZ91 magnesium-based composite melt do not react, and no by-products are generated;

[0012] Step three, solidification forming:

[0013] After the semi-solid mixed melt is stirred, the melt is poured into a metal mold under the protection of an inert gas, and cooled to room temperature in air to obtain the diamond / AlN / AZ91 magnesium-based composite material.

[0014] Further, the inert gas protection environment is a mixed gas of sulfur hexafluoride and carbon dioxide in a ratio of (20:1) to (5:1), and the total flow rate of the mixed gas is 100-500 mL / min.

[0015] Further, the size and volume fraction of the diamond particles in step two are the same as the properties of the reinforcing body particles in the finally prepared material.

[0016] Further, the semi-solid mixed melt is cooled to 550℃ in step two, which is the optimal semi-solid stirring temperature of the AlN / AZ91 magnesium-based composite melt, and the preparation is preferably kept within the range of 550℃.

[0017] Further, the volume fraction of the diamond in the semi-solid mixed melt is 10-20%

[0018] The application also provides a high-thermal-conductivity and low-expansion magnesium-based composite material prepared by the preparation method, wherein the magnesium-based composite material is composed of reinforcing body particles and a matrix, the volume fraction of the reinforcing body particles is 10.5-22%, and the balance is the matrix, the matrix is a Mg-Al alloy, and the reinforcing body is AlN particles and diamond particles.

[0019] Further, the Mg-Al alloy matrix comprises, by weight percentage, 6.5-7 wt% of Al, 0.45-0.90 wt% of Zn, 0.17-0.4 wt% of Mn, less than or equal to 0.05 wt% of Si, and the balance of Mg.

[0020] The AlN particles and diamond particles have a size of 500 nm-50 μm and a volume fraction of 0.5-2%, and the diamond particles have a size of 40-230 μm and a volume fraction of not more than 25%.

[0021] Further, the volume fraction of the diamond is 10-20%.

[0022] The AlN / AZ91 magnesium-based composite material used in the application is prepared, produced and sold by Xi'an Ao Xiang Magnesium Industry Technology Co., Ltd. according to the invention patent (ZL201510882938.5).

[0023] The application has the following beneficial effects: the application fully utilizes the external method to introduce high-volume-fraction reinforcing particles, so that the composite material meets the requirements of high thermal conductivity and low expansion; and the operation is simple and easy. Meanwhile, the in-situ method is used to directly generate reinforcing particles in the magnesium matrix, and the reinforcing particles are fine and dispersed, and are combined with the matrix closely, and fully act on the matrix; the two methods are combined successfully, and on the basis of the in-situ AlN reinforced magnesium-based composite material, higher-volume-fraction diamond particles are further introduced externally, so that the magnesium-based composite material with ideal performance is obtained.

[0024] Meanwhile, in order to meet the requirements of electronic packaging materials, the volume fraction of the reinforcing bodies of the magnesium-based composite material prepared by the traditional external method is usually greater than 70%. However, the application can obtain the performance required by the electronic packaging materials under the condition that the volume fraction of the reinforcing bodies is not more than 25% through the combination of the in-situ method and the external method, so that the preparation cost of the composite material is reduced, and the lightweight of the electronic packaging material is realized without increasing the density of the composite material. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a structure schematic diagram of the high-thermal-conductivity and low-expansion magnesium-based composite material prepared by the application after electronic packaging.

[0026] In the figure: 1, magnesium alloy matrix; 2, AlN reinforcing body particle; 3, diamond reinforcing body particle. DETAILED DESCRIPTION

[0027] The principles and characteristics of the application are described below in combination with the drawings, and the examples are only used to explain the application, and are not used to limit the scope of the application.

[0028] In order to achieve the above-mentioned purpose, the application provides the following specific implementation mode:

[0029] Embodiment 1: a preparation method of a high-thermal-conductivity and low-expansion magnesium-based composite material, comprising the following steps:

[0030] Step 1: melting step:

[0031] Under the protection of an inert gas, 1-10 kg of the AlN / AZ91 magnesium-based composite material is placed in a melting furnace, the melting temperature is 740-760 DEG C, the holding time is 20-30 min, and the AlN / AZ91 magnesium-based composite material melt is obtained;

[0032] Step 2: external method for introducing diamond:

[0033] The diamond particles are added to the AlN / AZ91 magnesium-based composite melt to form a semi-solid mixed melt, wherein the volume fraction of the diamond in the semi-solid mixed melt is not more than 25%, preferably 10% to 20%, and then mechanically stirred for at least 1 min for uniform dispersion of the diamond particles in the AlN / AZ91 magnesium-based composite melt; the diamond particle size, volume fraction and the final material are the same as the reinforcing particle properties.

[0034] Then, the stirred semi-solid mixed melt is cooled to 540 to 560°C and stirred for at least 1 min, during which the AlN / AZ91 magnesium-based composite melt does not react with the AlN and diamond reinforcing agents, and no by-products are generated;

[0035] Step 3: solidification forming:

[0036] After the semi-solid mixed melt is stirred, the melt is poured into a metal mold under the protection of an inert gas environment and cooled to room temperature in air to obtain a diamond / AlN / AZ91 magnesium-based composite material.

[0037] The inert gas protection environment is a mixed gas of sulfur hexafluoride and carbon dioxide in a ratio of 20:1 to 5:1, and the total flow rate of the mixed gas is 100 to 500 mL / min. The sulfur hexafluoride gas and the carbon dioxide gas effectively prevent the burning and oxidation of the magnesium alloy melt by their own large density and the formation of a protective film on the surface of the magnesium alloy melt.

[0038] In order to more clearly illustrate the present application, the present application provides a specific operation example:

[0039] A. batching: calculate the amount of composite raw materials and prepare 1 kg of AlN / AZ91 composite material according to the ratio, and add diamond raw materials to form a mixture, the volume fraction of diamond in the mixture is 10%;

[0040] B. smelting: smelt the AlN / AZ91 composite material in a smelting furnace, the smelting temperature is 740°C, the holding time is 20 min, and the whole process is protected by inert gas;

[0041] C. introduction of diamond: after the composite material in step B is completely melted, the diamond particles are poured into the composite melt and stirred for 1 min;

[0042] D. semi-solid stirring: the mixed melt is cooled to 550°C and stirred for 1 min;

[0043] E. solidification forming: after the semi-solid stirring is completed, the melt is poured into a metal mold and cooled to room temperature to obtain a diamond / AlN / AZ91 composite material.

[0044] Example 2: Same as example 1, except that in step two, the semi-solid mixed melt is cooled to 550℃, which is the optimal semi-solid stirring temperature for the AlN / AZ91 magnesium-based composite melt, and the temperature should be precisely controlled at this temperature during preparation, and the volume fraction of the added diamond in the mixture is 15%.

[0045] After the introduction of diamond into the AlN / AZ91 melt, semi-solid stirring of the mixture can effectively achieve uniform dispersion of the diamond in the melt, and the AlN / AZ91 melt is at the optimal semi-solid stirring temperature of 550℃, which is conducive to the uniform dispersion of diamond particles in the AlN / AZ91 melt, prevents agglomeration and sedimentation of the diamond, and avoids defects in the prepared composite material after cooling.

[0046] Example 3: Same as example 1, except that the volume fraction of the added diamond in the mixture is 20%.

[0047] The thermal diffusivity, thermal conductivity, density, and thermal expansion coefficient of the diamond / AlN / AZ91 composite material and AZ91 alloy obtained from examples 1-3 are shown in Table 1:

[0048] Table 1 Properties of the composite materials and base alloys obtained from examples 1-3

[0049]

[0050]

[0051] As can be seen from Table 1, the thermal expansion coefficient of the diamond / AlN / AZ91 composite material is significantly reduced compared to the base alloy AZ91, and the thermal expansion coefficient of example 3 is reduced to 8.1 ppm, which is 65.5% lower than that of AZ91 alloy; the thermal conductivity is 65.2 Wm - 1 K -1 , which is 29.1% higher than that of AZ91 alloy, achieving the preparation of high-thermal-conductivity and low-expansion magnesium-based composite material.

[0052] Example 4: As Figure 1 shown, the present application also provides a high-thermal-conductivity and low-expansion magnesium-based composite material prepared by the above preparation method, which is composed of reinforcing body particles and a base, and the volume fraction of the reinforcing body particles is 10.5-22%, and the balance is the base.

[0053] The base is a Mg-Al alloy, and the composition of the base by weight percentage is: 6.5-7wt% Al, 0.45-0.90wt% Zn, 0.17-0.4wt% Mn, less than or equal to 0.05wt% Si, and the balance is Mg.

[0054] The reinforcement consists of AlN particles and diamond particles. The AlN particles are 500 nm to 50 μm in size and have a volume fraction of 0.5% to 2%, while the diamond particles are 40 to 230 μm in size and have a volume fraction of no more than 25%.

[0055] like Figure 1 As shown, the high thermal conductivity, low expansion magnesium-based composite material prepared by this invention, when applied to electronic packaging, can dissipate heat promptly and maintain dimensional stability during service. In the figure, numbers 1, 2, and 3 represent the magnesium alloy matrix, AlN reinforcing particles, and diamond reinforcing particles in the high thermal conductivity, low expansion magnesium-based composite material prepared by this invention, respectively. AlN and diamond particles have low coefficients of thermal expansion, effectively suppressing the thermal expansion of the magnesium alloy matrix during temperature changes; furthermore, both reinforcing particles possess high thermal conductivity, further enhancing the thermal conductivity of the matrix and achieving high thermal conductivity in the composite material.

[0056] Example 5: Same as Example 4, except that the volume fraction of diamond is 10-20%. The added diamond particles work synergistically with the in-situ generated AlN particles to reduce the coefficient of thermal expansion of the composite material and improve its thermal conductivity. Furthermore, the in-situ synergistic addition method is more conducive to the reinforcement fully exerting its pinning effect on the thermal expansion of the matrix. The coefficient of thermal expansion of the composite material can be effectively reduced with a volume fraction not exceeding 25%, avoiding the damage to the plasticity, toughness, and processability of the composite material caused by the introduction of high volume fraction reinforcement, as well as the high raw material cost.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a high thermal conductive low expansion magnesium-based composite material, characterized by, Comprising the following steps: Step one, smelting step: Under the protection of inert gas environment, 1-10 Kg of AlN / AZ91 magnesium-based composite material is placed in a smelting furnace, the smelting temperature is 740-760℃, the holding time is 20-30 min, and the AlN / AZ91 magnesium-based composite melt is obtained; The inert gas protection environment is a mixed gas of sulfur hexafluoride and carbon dioxide in a ratio of (20:1) to (5:1), and the total flow rate of the mixed gas is 100-500 mL / min; Step two, external preparation of introducing diamond: Diamond particles are added to the AlN / AZ91 magnesium-based composite melt to form a semi-solid mixed melt, wherein the volume fraction of diamond in the semi-solid mixed melt is 10-20%, and then mechanical stirring is performed for at least 1 min to uniformly disperse the diamond particles in the AlN / AZ91 magnesium-based composite melt; Then, the stirred semi-solid mixed melt is cooled to 540-560℃, and stirred for at least 1 min, during which the AlN and diamond reinforcements in the AlN / AZ91 magnesium-based composite melt do not react and no by-products are generated; The magnesium-based composite material is composed of reinforcement particles and a matrix, the volume fraction of the reinforcement particles is 10.5-22%, and the balance is the matrix, the matrix is a Mg-Al alloy, and the reinforcement is AlN particles and diamond particles; The Mg-Al alloy matrix consists of 6.5-7wt% Al, 0.45-0.90wt% Zn, 0.17-0.4wt% Mn, and less than or equal to 0.05wt% Si, with the balance being Mg; The AlN particles are 500nm-50μm in size and have a volume fraction of 0.5-2%, and the diamond particles are 40-230μm in size and have a volume fraction of 10-20%; Step three, solidification forming: After the semi-solid mixed melt is stirred, the melt is poured into a metal mold under the protection of inert gas, and cooled to room temperature in air to obtain a diamond / AlN / AZ91 magnesium-based composite material.

2. The preparation method of the high thermal conductivity and low expansion magnesium-based composite material as described in claim 1, characterized in that, The diamond particle size and volume fraction in step two are the same as the properties of the reinforcement particles in the final material.

3. The method for preparing the high thermal conductivity, low expansion magnesium-based composite material as described in claim 1, characterized in that, In step two, the semi-solid mixed melt is cooled to 550℃.

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