A low-melting-point alloy for phase change thermal energy storage and its preparation method

Abstract

This invention discloses a low-melting-point phase-change thermal energy storage alloy and its preparation method, belonging to the field of liquid alloy technology. The liquid alloy comprises Bi, In, Sb, Cu, Sn, Ga, Ge, Zn, Nd, and pretreated nano-graphite powder. The preparation method includes: adding the metal components Bi, In, Sb, Cu, Ge, and Nd into a melting furnace and stirring to obtain a basic alloy liquid; cooling and then adding the metal components Sn, Ga, and pretreated nano-graphite powder and stirring evenly; continuing to cool and then adding the metal component Zn; and finally, after holding at the temperature, stirring, and cooling, obtaining the melting-point alloy. This liquid alloy can improve problems such as poor interfacial wettability and bonding stability between Bi-based low-melting-point alloys and copper substrates under heat dissipation conditions in electronic devices, low heat dissipation efficiency under low-frequency micro-vibration, insufficient phase change stability during high-frequency melting and solidification cycles, easy interfacial reactions due to dynamic micro-friction, uneven liquid distribution, and interfacial fatigue caused by long-term micro-motion erosion, thus meeting the heat dissipation requirements of high power density and high-frequency operation of electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of liquid alloy technology, specifically a phase change thermal energy storage low-melting-point alloy and its preparation method. Background Technology

[0002] With the rapid development of modern electronic and industrial technologies, the performance of various electronic and industrial equipment has continuously improved, leading to a sharp increase in power density and heat generation during operation. This is particularly evident in core components of high-performance computers, such as central processing units (CPUs), graphics processing units (GPUs), and precision industrial control components. These core components continuously generate a large amount of heat when performing complex calculations or under high loads. If this heat cannot be dissipated in a timely and efficient manner, the component's operating temperature will become excessively high. This not only significantly reduces the efficiency of electronic components and accelerates thermal aging and fatigue, but in severe cases, it can even cause permanent damage, directly affecting the operational stability and lifespan of the equipment. Therefore, efficient heat dissipation systems have become crucial components in this field, and phase change materials are a core component of heat dissipation systems. Their performance directly determines the heat dissipation efficiency, response speed, and long-term service stability of the heat dissipation system.

[0003] Currently, the phase change materials used in electronic device heat dissipation are mainly paraffin-based organic phase change materials. Although these materials have a certain phase change heat storage capacity, they have problems such as extremely low thermal conductivity and poor wettability at the interface with the metal heat dissipation substrate. At the same time, they are prone to leakage, debonding from the substrate interface, and damage to the heat conduction network during long-term repeated melting and solidification cycles. They are difficult to adapt to the high-load and high-frequency operation requirements of electronic devices, and cannot meet the high reliability requirements of precision electronic components for heat dissipation systems.

[0004] Low-melting-point alloys, whose melting points can be controlled within the core heat dissipation range of electronic devices from room temperature to 100°C by adjusting their composition, and whose thermal conductivity is much higher than that of paraffin-based organic phase change materials, are the preferred alternative to traditional organic phase change materials in the field of electronic device heat dissipation. Among them, Bi-based multi-component low-melting-point alloys have become the most promising candidate materials in this field due to the ease of composition adjustment and the high compatibility of their melting point range with the heat dissipation conditions of electronic devices. However, in the actual operation of electronic devices, these Bi-based low-melting-point alloys still have some technical defects that restrict their large-scale engineering application in the field of electronic device heat dissipation, as follows: Firstly, the heat dissipation substrates of electronic devices are mostly made of high thermal conductivity metals such as copper and aluminum. Existing Bi-based low-melting-point alloys have poor wettability on aluminum substrates, and although they can wet copper substrates, the interfacial bonding is weak, resulting in only a simple physical adhesion. The poor interfacial bonding effect easily leads to the formation of tiny gaps at the contact surface, increasing the heat conduction resistance and reducing heat dissipation efficiency. At the same time, fans and water pumps in server rooms and industrial control cabinets, as well as the movement and bumps of portable electronic devices, can cause low-frequency micro-vibrations. Combined with the small volume changes during the alloy melting and solidification process, this can easily cause local debonding and widening of gaps at the interface, further exacerbating the problem of reduced heat conduction efficiency.

[0005] Secondly, during long-term operation, the workload of core components in electronic devices dynamically changes with usage demands. The phase change materials in the heat dissipation system must repeatedly undergo melting-heat absorption and solidification-heat release cycles. In some high-load devices, these phase change materials may even experience high-frequency melting-solidification cycles on the order of hours or minutes. For non-eutectic or heterogeneous Bi-based alloys, under the influence of high-frequency melting-solidification cycles, localized compositional segregation and microstructure coarsening are likely to occur. This may lead to a wider phase transformation temperature range, a decrease in the phase transformation enthalpy in localized areas, and a corresponding decline in the overall heat absorption and dissipation capacity, making it impossible to stably dissipate heat for electronic components over a long period.

[0006] Third, the heat dissipation structure of electronic devices and the phase change material will have dynamic micro-friction contact due to the micro-vibration of the device operation and the thermal expansion and contraction of electronic components. The mechanical action of dynamic micro-friction will accelerate the diffusion of interfacial atoms, causing the Sn element contained in the existing Bi-based low melting point alloy to slowly undergo thermal diffusion reaction with the copper substrate at the interface, generating some brittle intermetallic compounds, reducing the interfacial bonding strength and long-term reliability.

[0007] Fourth, when electronic devices are in standby, startup, or low-load to high-load states, the phase change material in the heat dissipation system is in a solid state at room temperature. When the components generate heat under high load, the ambient temperature rises to near the theoretical melting point of the alloy, and the components need to melt and absorb heat, some single-phase / non-eutectic Bi-based alloys are prone to having a large melting lag temperature. The actual melting start temperature is lower than the theoretical melting point, which slows down the start-up response speed of the phase change material melting and absorbing heat. It cannot match the heat generation demand of the components in time, which can easily cause temperature spikes at the moment of component startup or during sudden load changes, affecting the operational stability of the equipment.

[0008] Fifth, during actual long-term service, Bi-based low-melting-point alloys melt into a free-flowing liquid state. Under the combined effects of equipment vibration, thermal convection, and changes in usage posture, uneven distribution, local enrichment, or local deficiencies are likely to occur in the heat dissipation cavity, leading to a decrease in heat dissipation uniformity and difficulty in effectively controlling local hot spots. At the same time, the long-term reciprocating flow of the liquid alloy may also cause fretting erosion and interface fatigue effects on the heat dissipation cavity and interface, further affecting the long-term service reliability of the heat dissipation system.

[0009] Based on this, developing a novel low-melting-point phase change thermal energy storage alloy that can simultaneously improve interfacial bonding, cycle stability, interfacial reaction, melting hysteresis response, and service uniformity to meet the high-efficiency heat dissipation requirements of high-performance electronic and industrial equipment is of great practical significance. Summary of the Invention

[0010] The purpose of this invention is to provide a low-melting-point alloy for phase change thermal energy storage and its preparation method, so as to effectively improve the problems of poor interfacial wettability and bonding stability between Bi-based low-melting-point alloys and copper / aluminum metal substrates under the heat dissipation conditions of electronic devices, low heat dissipation efficiency under low-frequency micro-vibration, insufficient phase change stability during high-frequency melting and solidification cycles, easy interfacial reaction due to dynamic micro-friction, large melting hysteresis temperature at room temperature, uneven liquid distribution, and interfacial fatigue caused by long-term micro-motion erosion. This invention is suitable for the heat dissipation requirements of high power density and high-frequency operation of electronic devices. The objective of this invention is achieved through the following technical solution: A low-melting-point alloy for phase change heat storage comprises the following components in parts by weight: Bi 70-73 parts, In 20-23 parts, Sb 2-2.5 parts, Cu 1-1.2 parts, Sn 2-2.5 parts, Ga 0.8-1.2 parts, Ge 0.2-0.3 parts, Zn 0.5-0.8 parts, Nd 0.05-0.07 parts, and pretreated nano-graphite powder 0.05-0.08 parts; The preparation steps of the pretreated nano-graphite powder are as follows: The nano-graphite powder is immersed in a GaCl3 anhydrous ethanol dispersion with a concentration of 0.5-0.8 wt% at a solid-liquid ratio of 1 g: (15-20) mL, ultrasonically dispersed, and then dried.

[0011] In the above scheme, Bi and In, as basic components, can control the melting point of the alloy within the 70-90℃ range for heat dissipation in electronic devices, ensuring the core phase transformation heat absorption capacity of the alloy; Sb and Cu, as basic components, can further optimize the phase transformation thermal performance of the alloy, while improving the directional migration and phase separation phenomena of elements that are prone to occur in traditional Bi-based alloys under long-term high-frequency melting and solidification cycles, reducing the widening of the phase transformation temperature range and the decrease in phase transformation enthalpy.

[0012] Secondly, the synergistic effect of Sn and Zn can improve the problems of poor interfacial wettability and insufficient liquid fluidity between the alloy and the copper and aluminum heat dissipation substrate in the background technology. At the same time, it can alleviate the problem of reduced heat dissipation efficiency caused by the superposition of low-frequency vibration and small volume change of electronic devices. Sn can improve the liquid fluidity of the alloy and reduce the interfacial gap between the alloy and the copper and aluminum substrate. Zn can improve the interfacial wettability of the alloy on the copper and aluminum surface and fully mix with liquid Ga to form a Ga-Zn binary alloy phase. Ge atoms achieve atomic-level diffusion in this alloy phase to form a Ga-Zn-Ge ternary alloy phase, which is deposited on the copper and aluminum surface to form a dense protective layer. This not only improves the interfacial wettability but also effectively blocks the diffusion of Sn atoms to the copper and aluminum substrate, effectively avoiding the formation of brittle intermetallic compounds by interfacial reaction between Sn and copper and aluminum under dynamic micro-friction and thermal action.

[0013] In practical applications, the vapor pressure of Ga is higher than that of other alloy components in the 220℃-280℃ melting range, and the high-temperature environment during melting can easily cause trace amounts of Ga to volatilize. To address this, the introduction of Ge can effectively improve the situation: based on the well-known Ga-Ge binary phase diagram, during the cooling process of the base alloy liquid from 275-285℃ to 235-245℃, liquid Ga can encapsulate Ge powder and achieve atomic-level diffusion, forming a Ga-Ge alloy phase. This restricts the high fluidity of Ga at low temperatures, reduces Ga yield loss due to splashing and wall adhesion during melting, and improves the uniformity of Ga dispersion in the alloy matrix. Furthermore, Ge fully integrates with Cu and Sb in the high-temperature melting environment, effectively improving the uniformity of the Cu-Sb eutectic phase distribution in the Bi-In matrix, avoiding Cu-Sb segregation during the melting and solidification cycle, and ensuring the overall uniformity of the alloy composition.

[0014] In addition, in the Ga-Ge alloy phase formed by Ga and Ge, Ge is a brittle semiconductor. If it does not diffuse completely and forms local elemental segregation, it is easy to accumulate at the alloy grain boundaries, which leads to a slight increase in brittleness of the alloy at room temperature (25°C), posing a potential risk for long-term service. Therefore, the introduction of Nd can suppress the local aggregation of the Ge-Ga alloy phase inside the alloy and promote its uniform dispersion in the Bi-In matrix, thereby reducing the brittleness of the Ge-Ga alloy phase, avoiding the decrease in interfacial bonding force caused by cracking of the brittle phase, and improving the long-term service stability of the alloy interface with copper and aluminum substrates.

[0015] Furthermore, low-melting-point Ga readily adheres to the surface of copper and aluminum heat dissipation substrates, simultaneously carrying trace solid impurities and incompletely dispersed graphite powder from the alloy, forming a paste-like "metal sludge" that adsorbs Sn and deposits together. This not only causes uneven thermal resistance on the heat dissipation surface but may also affect the operational stability of precision electronic components due to the shedding of the deposited layer. To address this issue, this alloy incorporates pretreated nano-graphite powder, which can be uniformly dispersed in the alloy matrix. Utilizing the self-lubricating properties of graphite, under dynamic micro-friction conditions, a discontinuous physical lubrication zone is formed at the interface between copper / aluminum and the alloy, reducing direct Ga adhesion. This alleviates the problems of "metal sludge" formation, component loss, and protective layer damage. It also reduces direct metal contact between the alloy and the heat dissipation cavity, lowering shear damage to the Ga-Zn protective layer. Simultaneously, through its synergistic effect with Ga and Zn, the alloy's liquid fluidity is appropriately regulated, avoiding uneven distribution within the heat dissipation cavity caused by excessive fluidity. This also reduces the micro-erosion effect of the liquid alloy on the heat dissipation cavity, mitigating interface fatigue effects and improving the stability of lubrication and heat dissipation.

[0016] In summary, the alloy provided by this invention can significantly improve the problems of poor interfacial bonding, phase separation, and performance degradation in the prior art, and can meet the heat dissipation requirements of high power density and high frequency operation of electronic devices.

[0017] Furthermore, in practical applications, directly adding nano-graphite powder to the alloy can easily lead to poor adhesion with the metal matrix, resulting in decreased dispersibility and reduced lubrication effects during long-term use. This application improves the adhesion of nano-graphite powder to the metal matrix through pretreatment, reducing problems such as agglomeration and delamination. Preferably, it also includes 0.02-0.03 parts by weight of Sc. Sc and Nd form a synergistic effect, further suppressing the local aggregation of the Ge-Ga alloy phase within the alloy and reducing its brittleness.

[0018] Preferably, the mass percentage of Ge is not less than 1 / 4 of the mass percentage of Ga; and the mass percentage of Nd is not less than 1 / 3 of the mass percentage of Ge.

[0019] Furthermore, to achieve the above objectives, this application also provides a method for preparing a low-melting-point alloy for phase change thermal energy storage, comprising the following steps: S1, the metal components Bi, In, Sb, Cu, Ge and Nd are added to a melting furnace and stirred to obtain a basic alloy liquid; S2, after cooling, add the metal components Sn, Ga and pretreated nano-graphite powder, and stir evenly; S3, after continuing to cool down, add the metal component Zn and stir until homogeneous; S4, after being kept warm, stirred, and cooled, yields a low-melting-point alloy.

[0020] In actual implementation, the melting points of each alloy component differ. If the feeding sequence is not appropriate, problems such as premature melting and splashing of low-melting-point components and incomplete melting of high-melting-point components may occur, resulting in uneven mixing of components and phase separation, while also affecting the formation of the alloy phase between Ga and Ge. This application designs a step-by-step feeding process based on the differences in the melting points of each component to achieve uniform melting and mixing of each component and ensure the uniformity of the alloy composition.

[0021] Preferably, in step S1, argon or nitrogen is introduced into the melting furnace as an inert protective gas, the temperature is raised to 1100-1150℃, and after melting and stirring, the temperature is lowered to 275-285℃ and held.

[0022] Preferably, in step S2, the temperature is lowered to 235-245℃, and the addition rate of the metal components Sn and Ga is 0.4-0.6 g / s, based on 100 g of base alloy liquid.

[0023] Preferably, in step S3, the temperature is lowered to 215-225℃, and the Zn addition rate is 0.1-0.3 g / s.

[0024] Preferably, in step S4, the holding and stirring temperature is 215-225℃, the stirring speed is 180-270 r / min, and the holding and stirring time is 4-6 min. Cooling is achieved using a reverse temperature gradient cooling method, i.e., a temperature gradient is achieved by placing a water-cooled copper plate at the bottom of the melting furnace and a resistance heating strip at the top, with the temperature at the top of the melting furnace being 4-9℃ higher than the bottom temperature. This reverse temperature gradient cooling process can further ensure the uniformity of alloy composition, improve the density uniformity of the alloy in its liquid state, and reduce the risk of uneven distribution within the heat dissipation cavity.

[0025] Compared with the prior art, the beneficial effects of the present invention are: The low-melting-point phase-change thermal energy storage alloy for heat dissipation in electronic devices provided by this invention, through the synergistic design of Bi, In, Sb, Cu, Sn, Ga, Ge, Nd and pretreated nano-graphite powder, effectively adapts to the heat dissipation requirements of high power density and high frequency operation of electronic devices. Testing shows that the alloy has a phase change temperature range of 70–90℃, a contact angle with the copper substrate of ≤35.8°, a heat dissipation coefficient of ≥532.6 W·m⁻²·K⁻¹ under low-frequency micro-vibration, a phase change temperature range offset of ≤+0.3 / -0.2℃ during high-frequency melting and solidification cycles, a phase change enthalpy retention rate of ≥93.8%, a phase change enthalpy per unit volume before cycling of ≥260 J / cm³, a melting hysteresis temperature of ≤2.2℃, a Cu-Sb segregation degree of ≤2.8%, a relative deviation of liquid composition of ≤2.5%, and an interfacial bonding strength retention rate of ≥88%. These data indicate that the alloy provided by the present invention can effectively improve the technical problems of existing Bi-based low-melting-point alloys, such as poor interfacial wettability and bonding stability with copper and aluminum metal substrates, phase transformation performance degradation after high-frequency melting and solidification cycles, easy interfacial reaction with copper and aluminum substrates to form brittle intermetallic compounds, large melting hysteresis temperature leading to sluggish heat dissipation response, uneven liquid flow distribution, and interfacial fatigue caused by long-term fretting erosion. Detailed Implementation

[0026] Example 1 (1) Liquid alloy composition and weight parts used.

[0027] Bi 73 parts, In 20 parts, Sb 2 parts, Cu 1 part, Sn 2.5 parts, Ga 0.8 parts, Ge 0.2 parts, Zn 0.6 parts, Nd 0.05 parts, and pretreated nano-graphite powder 0.05 parts.

[0028] The above-mentioned pretreated nano-graphite powder preparation method is as follows: nano-graphite powder is immersed in 0.5wt% GaCl3 anhydrous ethanol dispersion at a solid-liquid ratio of 1 g: 20 mL, placed in an ultrasonic disperser and ultrasonically dispersed at 300W power for 10 min, and then the dispersed mixture is placed in a vacuum drying oven at 60℃ and dried to constant weight. After sieving, pretreated nano-graphite powder with a particle size of 100-300 nm is obtained.

[0029] (2) Alloy preparation method.

[0030] S1: Argon gas is introduced into the melting furnace as an inert protective gas (gas flow rate 0.8L / min, based on an effective cavity volume of 1L in the melting furnace). The metal components Bi, In, Sb, Cu, Ge, and Nd are added to the melting furnace, heated to 1100℃, and stirred at a constant temperature of 300r / min for 20min. Then, the temperature is slowly lowered to 280℃ and held for 3min to obtain the basic alloy liquid. S2: Cool the base alloy liquid to 240℃, and add the metal components Sn, Ga and pretreated nano-graphite powder simultaneously at an addition rate of 0.5g / s (based on 100g base alloy liquid). Maintain 240℃ and stir at 300r / min for 10min. After stirring evenly, keep warm for 5min. S3: Continue cooling to 220℃, add the metal component Zn at a rate of 0.2 g / s (based on 100 g of product in S2), and stir at 250 r / min for 8 min; S4: Maintain a holding and stirring temperature of 220℃, adjust the stirring speed to 220r / min, and hold and stir for 5min; then use reverse temperature gradient cooling (reverse temperature gradient cooling is achieved by setting a water-cooled copper plate at the bottom of the melting furnace and a resistance heating belt at the top), control the temperature at the top of the melting furnace to be 6℃ higher than the temperature at the bottom, and maintain a cooling rate of 2℃ / min while maintaining a stirring speed of 150r / min until the alloy liquid cools down to 200℃, then stop stirring, and continue to maintain the temperature gradient until the alloy is completely solidified, to obtain a low melting point alloy with phase change heat storage.

[0031] Example 2 (1) Liquid alloy composition and weight parts used.

[0032] Bi 70 parts, In 22 parts, Sb 2.5 parts, Cu 1.2 parts, Sn 2.5 parts, Ga 1.2 parts, Ge 0.3 parts, Zn 0.8 parts, Nd 0.07 parts, and pretreated nano-graphite powder 0.06 parts.

[0033] The above-mentioned pretreated nano-graphite powder preparation method is as follows: nano-graphite powder is immersed in 0.8wt% GaCl3 anhydrous ethanol dispersion at a solid-liquid ratio of 1 g: 15 mL, placed in an ultrasonic disperser and ultrasonically dispersed at 300W power for 10 min, and then the dispersed mixture is placed in a vacuum drying oven at 60℃ and dried to constant weight. After sieving, pretreated nano-graphite powder with a particle size of 100-300 nm is obtained.

[0034] (2) Alloy preparation method.

[0035] S1: Argon gas is introduced into the melting furnace as an inert protective gas (gas flow rate 1.0L / min, based on an effective cavity volume of 1L in the melting furnace). The metal components Bi, In, Sb, Cu, Ge, and Nd are added to the melting furnace, heated to 1150℃, and stirred at a constant temperature of 350r / min for 15min. Then, the temperature is slowly lowered to 280℃ and held for 3min to obtain the basic alloy liquid. S2: Cool the base alloy liquid to 235℃, and add the metal components Sn, Ga and pretreated nano-graphite powder simultaneously at an addition rate of 0.4g / s (based on 100g base alloy liquid). Maintain 235℃ and stir at 280r / min for 12min. After stirring evenly, keep warm for 6min. S3: Continue cooling to 215℃, add the metal component Zn at a rate of 0.1 g / s (based on 100 g of product in S2), and stir at 200 r / min for 10 min; S4: Maintain a holding and stirring temperature of 215℃, adjust the stirring speed to 180r / min, and hold and stir for 6min; then use reverse temperature gradient cooling (reverse temperature gradient cooling is achieved by setting a water-cooled copper plate at the bottom of the melting furnace and a resistance heating strip at the top), control the temperature at the top of the melting furnace to be 4℃ higher than the temperature at the bottom, maintain the stirring speed of 150r / min until the alloy liquid cools down to 200℃ and then stop stirring, continue to maintain the temperature gradient until the alloy is completely solidified, and obtain a low melting point alloy with phase change heat storage.

[0036] Example 3 (1) Liquid alloy composition and weight parts used.

[0037] Bi 72.8 parts, In 20 parts, Sb 2 parts, Cu 1 part, Sn 2.5 parts, Ga 0.8 parts, Ge 0.2 parts, Zn 0.55 parts, Nd 0.05 parts, Sc 0.02 parts, and pretreated nano-graphite powder (preparation method same as in Example 1) 0.05 parts.

[0038] (2) Alloy preparation method.

[0039] Based on Example 1, in step S2, Sn, Ga, Sc and pretreated nano-graphite powder were added simultaneously at an addition rate of 0.5 g / s. The other unmentioned process steps, parameters, stirring and heat preservation conditions were the same as in Example 1, resulting in a Sc-containing phase change heat storage low melting point alloy.

[0040] Comparative Example 1 Compared to Example 1, the metal component Ge was removed, while the remaining components, amounts, and preparation processes were the same as in Example 1.

[0041] Comparative Example 2 Compared to Example 1, the metal component Nd was removed, while the remaining components, dosages, and preparation processes were the same as in Example 1.

[0042] Comparative Example 3 Compared to Example 1, the pretreated nano-graphite powder was replaced with an equal mass of commercially available untreated nano-graphite powder of the same particle size, while the remaining components, dosages, and preparation processes were the same as in Example 1.

[0043] Comparative Example 4 Compared to Example 1, in step S4, the reverse temperature gradient cooling is cancelled and replaced with room temperature natural cooling, while the other heat preservation and stirring parameters are the same as in Example 1.

[0044] Comparative Example 5 Compared to Example 1, the metal component Ge was replaced with an equal mass of the metal component Sb, while the remaining components, amounts, and preparation processes were the same as in Example 1.

[0045] Comparative Example 6 Compared to Example 1, the pretreatment agent (GaCl3 anhydrous ethanol dispersion) for the pretreated nano-graphite powder was replaced with a pretreatment agent of equal concentration (0.5wt% anhydrous ethanol dispersion), while the remaining components, proportions, and preparation processes remained the same as in Example 1.

[0046] Comparative Example 7 Compared to Example 1, the pretreated nano-graphite powder was removed, while the remaining components, dosages, and preparation processes were the same as in Example 1.

[0047] Experimental Example Using the low-melting-point alloys prepared in Examples 1-3 (denoted as S1-S3) and Comparative Examples 1-7 (denoted as D1-D7) as samples, the following experimental tests were conducted (the test results are shown in Table 1): (1) Testing of interface wettability and heat transfer efficiency under low-frequency micro-vibration: ①Interfacial wettability: Using the seat drop method, in a constant temperature and sealed environment at 85℃, the T2 copper sample was preheated to 85℃, and 5μL of each alloy sample after melting was dropped onto the surface of the T2 copper sample. The contact angle between the alloy and the T2 copper was measured by a heated contact angle measuring instrument.

[0048] ② Heat dissipation efficiency under low-frequency micro-vibration: The T2 copper heat sink was immersed in the molten alloy (temperature 85℃), and vertical low-frequency micro-vibration (5-15Hz, amplitude 0.5~2mm, vibration direction perpendicular to the heat sink axis) was applied. The surface heat flux density Φ of the heat sink was measured by a heat flow meter (unit: W / m²). At the same time, the outer wall temperature T1 of the heat sink and the molten alloy temperature T2 (unit: ℃) were measured by a thermocouple. The steady-state heat dissipation coefficient (unit: W·m) was calculated according to the heat dissipation coefficient h=Φ / (T2-T1). -2 ·K -1 Each group of samples was tested continuously for 2 hours, and the average heat dissipation coefficient during the stable phase was recorded.

[0049] (2) Testing of phase change stability and heat storage capacity under long-term melting and solidification cycles: Each alloy sample was placed in a high and low temperature test chamber and subjected to 1,000 high-frequency melting and solidification cycle simulation experiments. The melting temperature was 90℃ and the holding time was 1 hour. The solidification temperature was 25℃ and the holding time was 1 hour.

[0050] ① Phase transformation stability test: Differential scanning calorimeter (DSC) was used to detect the phase transformation temperature range of each alloy sample before and after the cycle at a heating / cooling rate of 5℃ / min, and the shift of the phase transformation temperature range was calculated. ② Heat absorption and dissipation capacity test: The phase transformation enthalpy of each alloy sample before and after cycling is detected by DSC, and the phase transformation enthalpy retention rate is calculated as (phase transformation enthalpy after cycling / phase transformation enthalpy before cycling × 100%).

[0051] (3) Detection of interfacial reaction under dynamic friction: A pin-disc friction and wear test bench was constructed, using T2 copper as the grinding disc (20 mm in diameter and 5 mm in thickness) and various alloy samples as grinding pins. Under molten conditions at 85°C, the grinding disc was rotated at 300 r / min and subjected to a load of 5 N to simulate the dynamic micro-friction contact between the heat dissipation cavity of electronic equipment (made of T2 copper) and the alloy. The test bench was run continuously for 500 hours. Afterward, scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to observe whether intermetallic compounds formed on the surface of the T2 copper grinding disc. After the experiment, the T2 copper grinding disc was ultrasonically cleaned with anhydrous ethanol and dried to constant weight. The mass of the grinding disc before and after the experiment was measured using an electronic analytical balance (accuracy 0.01 mg), and the wear amount was calculated (wear amount = mass before experiment - mass after experiment).

[0052] (4) Detection of melting hysteresis temperature at room temperature: Use DSC to detect the melting hysteresis temperature (i.e. the difference between the theoretical phase transformation temperature and the actual melting initiation temperature) of each alloy sample after room temperature standby at a heating rate of 5℃ / min.

[0053] (5) Other tests: ① Cu-Sb segregation degree (uniformity of composition distribution): After melting each alloy sample, it is cooled according to the process. Two points, one above and one below, are taken along the height direction. The mass fractions of Cu and Sb are detected by ICP-OES. The relative difference between the mass fractions of Cu and Sb elements at the two points is calculated. The maximum value of the two is taken as the degree of Cu-Sb segregation, which characterizes the uniformity of the composition distribution of Cu and Sb elements inside the alloy.

[0054] ② Liquid alloy distribution uniformity test: After melting the alloy into a liquid state, it is injected into a miniature cavity (material T2 copper) of the same proportion as the heat dissipation cavity of the electronic device. Simulate the low-frequency micro-vibration of the electronic device at 5-15Hz, the hot and cold convection at 80℃-25℃, and the cyclic change of the attitude at 0° / 90° / 180° (each attitude is maintained for 30 minutes, and the cycle is repeated 10 times). After being allowed to cool to room temperature, samples are taken at 5 positions along the top, bottom, left, right and center of the cavity. The mass ratio of the core alloy components (Bi / In / Ga) at each position is detected by ICP-OES, and the relative deviation of the composition is calculated.

[0055] ③ Anti-fretting erosion and interfacial fatigue performance test: A miniature erosion test bench was built, and the T2 copper heat dissipation substrate specimen was immersed in liquid alloy at 70-90℃ to simulate the long-term reciprocating flow of liquid alloy at 0.5m / s. After continuous operation for 1000h, the substrate surface was observed by SEM (to check for obvious erosion damage and interfacial fatigue cracks), and the interfacial bonding strength between the alloy and the substrate was tested by shear method. The interfacial bonding strength retention rate was calculated as (bonding strength after cycles / initial bonding strength × 100%). Table 1: Performance test results of each sample It is worth noting that the units for the relevant items in the table are as follows: Contact angle: °; Low-frequency vibration heat dissipation coefficient: W·m -2 ・K -1 ; Phase change temperature range offset after 1000 melting and solidification cycles: ℃; Phase change enthalpy retention rate after 1000 melting and solidification cycles: %; Wear amount: mg (representing wear amount after 500 hours of dynamic friction); Melting hysteresis temperature: ℃; Cu-Sb segregation degree: %; Relative deviation of liquid composition: %; Interfacial bonding strength retention rate: %.

[0056] As can be seen from Table 1: Examples 1-2 show that both have a contact angle ≤35.8°, improving the interface adhesion with the copper heat dissipation substrate; the heat dissipation coefficient under low-frequency micro-vibration is ≥532.6W・m⁻²・K⁻¹, ensuring the heat conduction efficiency of electronic devices under micro-vibration conditions; the phase change temperature range offset during high-frequency melting and solidification cycles is ≤+0.3 / -0.2℃, maintaining the stability of the phase change temperature after long-term high-frequency melting and solidification cycles; the phase change enthalpy retention rate during melting and solidification cycles is ≥93.8% [the phase change enthalpy per unit volume in Examples 1-3 is ≥260 J / cm³], maintaining good heat absorption and dissipation capabilities; only trace amounts of intermetallic compounds are generated on the surface of the copper substrate, which can suppress the dynamic micro-friction interface reaction between the alloy and the copper substrate; the wear amount of the copper substrate is ≤1.0mg, indicating that the alloy of this invention can effectively reduce the wear of hard crystals on the copper heat dissipation substrate; the room temperature standby melting hysteresis temperature is ≤2.2℃, reducing the hidden danger of delayed heat dissipation response after room temperature standby of electronic devices; Cu-Sb The degree of segregation was ≤2.8%, which alleviated the problems of element segregation and microstructure coarsening in high-frequency melting and solidification cycles; the relative deviation of liquid composition was ≤2.5%, which improved the uniformity of liquid distribution of the alloy in the heat dissipation cavity and avoided local hot spots caused by local enrichment or deficiency; after resisting fretting erosion, no obvious erosion damage or interface fatigue cracks were detected at the interfaces of Examples 1-3 (a small number of microcracks were visible inside Comparative Examples 1-2 due to their high brittleness). The interface bonding strength retention rate was ≥88%, which enhanced the alloy's resistance to fretting erosion and interface fatigue resistance, and ensured the long-term service reliability of the heat dissipation system.

[0057] Example 3: Based on Example 1, the Sc component was introduced to further optimize the overall performance of the alloy, making it more suitable for the stringent heat dissipation requirements of high power density and high frequency operation of electronic devices.

[0058] In Comparative Example 1, the removal of the Ge component made it difficult to alleviate Cu-Sb segregation, leading to an increased degree of Cu-Sb segregation, a larger shift in the phase transformation temperature range, a higher relative deviation in liquid composition, and a lower retention rate of interfacial bonding strength. In Comparative Example 2, the removal of the Nd component failed to improve the brittleness of the Ge-Ga alloy phase, causing the alloy phase to easily aggregate locally, resulting in increased low-temperature brittleness, a larger room-temperature standby melting hysteresis temperature, decreased interfacial bonding stability, and a lower retention rate of interfacial bonding strength. In Comparative Example 3, the use of untreated nano-graphite powder resulted in poor compatibility with the metal matrix, leading to agglomeration, reduced lubrication and interfacial protection, increased formation of intermetallic compounds on the copper substrate surface, and a certain impact on heat dissipation efficiency. Simultaneously, it weakened resistance to fretting erosion, resulting in a low retention rate of interfacial bonding strength. In Comparative Example 4, the elimination of reverse temperature gradient cooling caused uneven composition distribution during alloy solidification, exacerbating Cu-Sb segregation, increasing the shift in the phase transformation temperature range, and raising the relative deviation of liquid composition. In Comparative Example 5, replacing Ge with Sb failed to alleviate Cu-Sb segregation. In Comparative Example 6, replacing the pretreatment agent in the nano-graphite powder resulted in poor pretreatment, decreased graphite powder dispersibility, weakened lubrication, increased wear, low interfacial bonding strength retention, and reduced resistance to fretting erosion. In Comparative Example 7, removing the pretreated nano-graphite powder led to Ga adhesion and the formation of metal sludge under dynamic micro-friction, resulting in decreased heat dissipation efficiency. Simultaneously, the fretting effect of the liquid alloy on the heat dissipation cavity was enhanced, leading to increased relative deviation of the liquid composition and decreased interfacial bonding strength retention.

Claims

1. A low-melting-point alloy for phase change heat storage, characterized in that, It consists of the following components in parts by weight: Bi 70-73 parts, In 20-23 parts, Sb 2-2.5 parts, Cu 1-1.2 parts, Sn 2-2.5 parts, Ga 0.8-1.2 parts, Ge 0.2-0.3 parts, Zn 0.5-0.8 parts, Nd 0.05-0.07 parts, and pretreated nano-graphite powder 0.05-0.08 parts; The preparation steps of the pretreated nano-graphite powder are as follows: the nano-graphite powder is immersed in an anhydrous ethanol dispersion of GaCl3 with a concentration of 0.5-0.8wt% at a solid-liquid ratio of 1 g: (15-20) mL, ultrasonically dispersed and then dried. The preparation method of the phase change thermal energy storage low-melting-point alloy includes the following steps: S1, the metal components Bi, In, Sb, Cu, Ge and Nd are added to a melting furnace and stirred to obtain a basic alloy liquid; S2, after cooling, add the metal components Sn, Ga and pretreated nano-graphite powder, and stir evenly; S3, after continuing to cool down, add the metal component Zn and stir until evenly mixed; S4, after being kept at a constant temperature, stirred and cooled, yields a low-melting-point alloy; In step S4, the holding and stirring temperature is 215-225℃, the stirring speed is 180-270r / min, and the holding and stirring is carried out for 4-6 minutes; the cooling adopts reverse temperature gradient cooling, that is, the temperature gradient is achieved by setting a water-cooled copper plate at the bottom of the melting furnace and a resistance heating belt at the top, and the temperature at the top of the melting furnace is 4-9℃ higher than the temperature at the bottom.

2. The low-melting-point alloy for phase change heat storage according to claim 1, characterized in that, The mass percentage of Ge is not less than 1 / 4 of the mass percentage of Ga; the mass percentage of Nd is not less than 1 / 3 of the mass percentage of Ge.

3. The low-melting-point alloy for phase change heat storage according to claim 1, characterized in that, It also contains 0.02-0.03 parts by weight of Sc.

4. A method for preparing a low-melting-point alloy for phase change thermal energy storage as described in any one of claims 1-2, characterized in that, Includes the following steps: S1, the metal components Bi, In, Sb, Cu, Ge and Nd are added to a melting furnace and stirred to obtain a basic alloy liquid; S2, after cooling, add the metal components Sn, Ga and pretreated nano-graphite powder, and stir evenly; S3, after continuing to cool down, add the metal component Zn and stir until homogeneous; S4, after being kept warm, stirred, and cooled, yields a low-melting-point alloy.

5. The method for preparing the low-melting-point alloy for phase change thermal energy storage according to claim 4, characterized in that, In step S1, argon or nitrogen is introduced into the melting furnace as a protective gas, the temperature is raised to 1100-1150℃, and after melting and stirring, the temperature is lowered to 275-285℃ and held.

6. The method for preparing a low-melting-point alloy for phase change thermal energy storage according to claim 4, characterized in that, In step S2, the temperature is lowered to 235-245℃, and the addition rate of the metal components Sn and Ga is 0.4-0.6 g / s, based on 100 g of base alloy liquid.

7. The method for preparing a low-melting-point alloy for phase change thermal energy storage according to claim 4, characterized in that, In step S3, the temperature is lowered to 215-225℃, and the Zn addition rate is 0.1-0.3 g / s, based on 100 g of the product in S2.

Images