CN106906388B - A kind of preparation method of silumin - Google Patents

Abstract

The invention discloses a method for preparing a high-silicon aluminum alloy. The silicon powder, aluminum powder or aluminum-silicon alloy powder is uniformly mixed according to a metering ratio with a silicon weight content of not less than 30%, and then loaded into a sealed graphite or alloy mold. , apply an axial pressure of 5~10MPa or more for pre-compression; then put the device into a vacuum hot-press furnace with a water cooling device at the bottom and raise the temperature to 580~900°C, and keep the vacuum in the furnace at 10~100Pa; After the temperature is uniform, apply an axial pressure not greater than 10 MPa and keep the pressure for 10-30 minutes, and then cool down at a rate of 1-10°C/min; during the cooling process, the water-cooling device continues to pass water from the bottom to accelerate the cooling of the mold; The high-silicon-aluminum bulk alloy with high density, uniform structure, silicon particle size below 100 microns and excellent performance can be obtained when it is lowered to the operable temperature.

Description

A kind of preparation method of high silicon aluminum alloy

technical field

The invention relates to the field of aluminum alloys, in particular to a method for preparing high-silicon aluminum alloys.

Background technique

With the rapid development of the core integrated circuit technology of microelectronics technology, the degree of integration has increased rapidly, and the current passing through has become larger and larger, resulting in a rapid increase in chip heating, which seriously affects the reliability and service life of the chip. As a new type of lightweight electronic packaging material, high-silicon aluminum alloy not only has light weight, excellent thermal conductivity, and low thermal expansion coefficient, but also can well adapt to the thermal management requirements of chips. Compared with other similar materials such as aluminum silicon carbide, high-silicon aluminum alloy has better weldability and easy processing shape, and has broad application prospects.

At present, the preparation methods of high-silicon aluminum alloys are mainly spray deposition + hot isostatic pressing, pressure infiltration, powder metallurgy liquid phase/hot pressing sintering method, powder preform solid phase hot extrusion, etc. Spray deposition + hot isostatic pressing is the main method to obtain high-density high-silicon aluminum alloy at home and abroad. This method can obtain an ideal microstructure with fine and uniform grains and no sharp edges and corners of silicon particles. However, the process parameters of spray deposition are difficult. control. Solid-phase hot extrusion of powder preforms can also obtain an ideal microstructure with fine and uniform grains and no sharp edges and corners of silicon particles. The above two technical solutions require several tons of pressure per square centimeter in the process of densification, which puts forward extremely high requirements on the pressurization equipment and supporting molds, and at the same time, both face the heat caused by the increase in silicon content and material size. A bottleneck where densification is increasingly difficult. Compared with aluminum silicon carbide packaging materials, the most obvious disadvantages of high-silicon aluminum alloys are their low strength and greater brittleness, which leads to the material being prone to jumping edges and corners when the silicon content reaches about 70% and higher, resulting in High scrap rate. When preparing high-silicon aluminum alloys by pressure infiltration and powder metallurgy, the combination of coarse and fine silicon particles is generally used to increase the bulk density of silicon. The coarse silicon particles inside the prepared high-silicon aluminum alloys have sharp edges and corners, which can be processed The property is obviously lower than the high silicon aluminum alloy obtained by spray deposition process.

Contents of the invention

The purpose of the present invention is to address the respective advantages and disadvantages of the above-mentioned processes, and propose a combination of the advantages of pressure infiltration and powder metallurgy, which can be liquid-solid (liquid aluminum-silicon alloy droplet-solid silicon powder mixture) under vacuum conditions. Dual isothermal extrusion scheme. Compared with spray deposition + hot isostatic pressing and powder preform solid-phase hot extrusion technology, the thermal densification pressure of the technical method provided by the invention is only 1/100 to 1/10, and the process flow is short, and the manufacturing The cost is lower.

For realizing the purpose described in the present invention, take following technical scheme:

A method for preparing a high-silicon aluminum alloy, comprising the following steps:

(1) Mix silicon powder and aluminum powder or aluminum-silicon alloy powder evenly according to the weight ratio of silicon weight not less than 30%, then put them into a sealed graphite or alloy mold, and apply an axial pressure of 5-10MPa Preload;

(2) Then put the device into a vacuum hot-press furnace with a water-cooling device at the bottom and raise the temperature to 580-900°C, and keep the vacuum degree in the furnace at 10-100Pa; after the temperature inside and outside the mold is uniform, apply an axial pressure not greater than 10 MPa Keep the pressure for 10-30 minutes, and then cool down at a rate of 1-10°C/min;

(3) During the cooling process, the water cooling device continues to flow water from the bottom to accelerate the cooling of the mold;

(4) After the furnace temperature drops to the operable temperature, a high-silicon-aluminum bulk alloy with high density, uniform structure, silicon particle size below 100 microns and excellent performance can be obtained.

The preparation method of a kind of high-silicon aluminum alloy is characterized in that it operates according to the following steps:

Step 1, powder preparation. Weigh silicon powder and aluminum powder, or aluminum-silicon alloy powder according to the proportion of silicon content of 30-70%, and mix them;

Step two, the preparation of the mold. Spray or coat a boron nitride-containing barrier agent on the inner wall of the female die and the pressure-applying end faces of the upper and lower dies;

Step 3, powder molding. Place the female mold vertically and put it into the lower die punch, then place the flexible graphite paper for compaction, then put the mixed powder into the cavity of the female die; then put the flexible graphite paper, and press the upper die punch into the female die from the upper end Inside, finally compress the upper and lower die punches along the axial direction;

Step 4, liquid aluminum alloy-solid silicon particle dual-phase hot extrusion. Put the pre-compressed mold, including the female mold, upper and lower die punches, and the powder loaded in the female mold, into a vacuum hot-press furnace with a water cooling device at the bottom to raise the temperature to 580-900°C, and keep the vacuum degree in the furnace at 10 ~100Pa, after the temperature inside and outside the mold is uniform, slowly apply an axial pressure not greater than 10 MPa and keep the pressure for 10-30 minutes;

Step five, cooling and sampling. After the pressure holding is completed, the water cooling device at the bottom of the vacuum furnace immediately and continuously feeds cooling water to speed up the cooling of the mold from the lower end of the extrusion die. While feeding the cooling water, the furnace temperature is controlled to cool down at a rate of 1-10°C/min. Keep the extrusion pressure stable during the process; when the temperature drops below 570°C, remove the pressure and stop heating, and further cool down to the operable temperature. The sample is released together with the mold. Dense high-silicon aluminum alloy block.

The preparation method of the high-silicon aluminum alloy is characterized in that, in the first step, the particle size of the silicon powder, aluminum powder or aluminum-silicon alloy powder used is not greater than 20 microns.

The preparation method of the high-silicon aluminum alloy is characterized in that, in the step 4, the hot extrusion temperature and pressure corresponding to the mixed powder in each silicon content interval are respectively: the silicon content is 30-55%, and the silicon content is 580-580. 700°C and 0.1-4MPa, silicon content of 55-65% is 650-800°C and 1-8MPa, silicon content greater than 65% is 700-900°C and 2-10MPa.

In the first step, the raw material powder is preferably silicon powder, aluminum powder or aluminum-silicon alloy powder with high purity, so as to improve the thermal conductivity of the material. No matter which batching scheme is adopted, the maximum particle size of various powders should be controlled below 20 microns. The mixing method can be dry mixing, or wet mixing with organic solvents such as ethanol and acetone.

In the second step, the mold material can be made of alloy or graphite, preferably graphite; the barrier agent containing boron nitride can be prepared by itself, or can be directly purchased from the market for die-casting aluminum alloy and hot extruded aluminum All kinds of high temperature resistant mold release lubricant products for alloys.

In the third step, the flexible graphite paper placed between the powder in the mold and the upper and lower die punches plays a sealing role. Single-layer or multi-layer graphite paper can be used, and other high-temperature-resistant and effective sealing materials can also be used. Flexible materials or powder materials.

In said step 4, the isothermal extrusion temperature increases with the increase of the silicon content, and the raw material powder with the same silicon content will increase in silicon particle size or grain size in the alloy as the extrusion temperature increases, The preferred hot extrusion temperature is as follows: the hot extrusion temperature and pressure corresponding to the mixed powder in each silicon content range are: 580-700°C and 0.1-4MPa for silicon content of 30-55%, and 650-4MPa for silicon content of 55-65%. 800°C and 1~8MPa, silicon content greater than 65% is 700~900°C and 2~10MPa. The extrusion temperature used in the technical solution provided by the present invention is lower than the temperature of the aluminum-silicon alloy liquid-solid phase transition line corresponding to the nominal composition of the mixed powder, that is, with the prolongation of the holding time at the extrusion temperature, even if the mixed powder All the aluminum elements are melted, and even form numerous dispersed aluminum-silicon binary saturated solution droplets, and the entire extrusion object is still liquid (aluminum alloy)-solid (silicon particles) two-phase coexistence. At this time, by applying a pressure below 10Mpa, these droplets can be extruded into the solid silicon particles in their respective adjacent regions, and the required pressure is only 1/100 to 1/10 of that of the full-solid thermal densification. With the increase of silicon content, although the hot extrusion temperature is increasing, the content of solid silicon particles in the liquid-solid two-phase mixture is still increasing, and the required hot extrusion force needs to increase accordingly. On the other hand, excessive pressure will lead to the aggregation and growth of solid silicon particles in the extrusion object, which is detrimental to the final performance of the alloy.

In the fifth step, it is necessary to control the matching of the water cooling speed at the bottom of the sample and the cooling speed of the entire vacuum furnace, and ensure that the water cooling speed at the bottom of the sample is faster than the cooling speed of the entire vacuum furnace, so that a temperature gradient is formed in the height direction of the sample. The cooling rate should be slow near the temperature of the aluminum-silicon eutectic point, that is, the cooling rate between 590°C and 560°C is preferably controlled at 1°C/min.

Principle of the present invention is:

Use the mixed powder of fine silicon, aluminum or aluminum-silicon alloy powder as the raw material, and after a short heat preservation between the aluminum-silicon eutectic temperature and the solidus temperature of the aluminum-silicon nominal composition corresponding to the mixed powder, apply a pressure similar to that of pressure infiltration (pressure Not more than 10 MPa), the liquid small aluminum droplets dispersed in the mixed powder, together with its dissolved silicon, are slowly extruded into the gaps between adjacent solid silicon particles to prepare high-silicon aluminum alloys. The preparation method of high-silicon aluminum alloy provided by the present invention has a short process flow, does not require high-pressure equipment and high-temperature and high-pressure-resistant supporting molds, has lower manufacturing costs, and its microstructure is similar to that obtained by spray deposition + hot isostatic pressing The structure is similar, that is, the silicon grains are fine, evenly distributed, and have no sharp edges and corners, which is convenient for machining.

The present invention has the following advantages:

1. The process flow of the present invention is short, and liquid-solid two-phase hot extrusion can be carried out after mixing materials, and high-silicon aluminum alloy powder consistent with the final composition can also be used for direct liquid-solid two-phase hot extrusion;

2. The pressure required for liquid-solid two-phase hot extrusion is only 1/100-1/10 of that of conventional solid-state thermal densification, and the requirements for equipment and molds are not high, and it is easy to obtain large-sized high-silicon aluminum alloys;

3. The silicon phase in the high-silicon aluminum alloy obtained by the present invention has no obvious straight edges and sharp edges and corners, which is conducive to improving the toughness and machinability of the material;

4. The high-silicon aluminum alloy obtained in the present invention has good properties: the density is 2.4-2.6g·cm ^-3 , the bending strength is 110-230MPa, and the thermal conductivity at room temperature is 110-170w. m ^-1 ·°C ^-1 , thermal expansion coefficient 7～17×10 ^-6 °C ^-1 .

Description of drawings

Figure 1 is a 50Si50Al sample with a size of Φ62mm×18mm obtained under hot extrusion conditions of 10 micron silicon powder and 20 micron aluminum powder at 650°C and 1MPa;

Fig. 2 is the microstructure diagram of the 50Si50Al sample described in Fig. 1;

Figure 3 is a microstructure diagram of 70Si30Al alloy obtained under hot extrusion conditions of 20 micron silicon powder and 10 micron aluminum powder at 800°C and 6MPa.

Detailed ways

Implementation Example 1

1. Preparation of powder. Take by weighing 100 grams of 10-micron silicon powder and 100 grams of 20-micron aluminum powder at a ratio of 50% by silicon weight, and dry-mix for 4 hours with a small-sized drum mixer;

2. Preparation of the mold. Spray the commercially available Jiadan brand JD-3028 boron nitride release agent on the inner wall of the Φ62mm cylindrical female mold and the pressure-applying end faces of the upper and lower dies, and dry it.

3. Powder molding. Place the female mold vertically on the horizontal operating table, load the lower die punch, and then place multi-layer flexible graphite paper for compaction; weigh 100 grams of powder from the mixture obtained in step 1 and slowly pour it into the female mold Die cavity; then put flexible graphite paper, and lightly press the upper die punch from the upper end of the female die into the female die, and finally apply a pressure of 8Mpa in the axial direction on the small manual hydraulic press to pre-tighten the upper and lower die punches.

4. Two-phase hot extrusion of liquid aluminum alloy-solid silicon particles. Put the pre-compressed mold in step 3, including the female mold, upper and lower die punches, and the powder loaded in the female mold, together into a vacuum hot-press furnace with a water cooling device at the bottom to heat up to 650°C, and keep the inner vacuum at 10~ Between 20Pa. Keep warm for 30 minutes to make the temperature inside and outside the mold uniform, and then slowly apply axial pressure. When the pressure reaches 1 MPa, start to hold the pressure for 30 minutes.

5. Cooling and sampling. After the pressure holding is over, the water cooling device at the bottom of the vacuum furnace immediately and continuously feeds cooling water. While feeding cooling water, control the furnace temperature to cool down to 590°C at a rate of 5°C/min, and then cool to 560°C at a rate of 1°C/min. Remove the pressure, stop heating and continue to feed cooling water, wait for the furnace temperature to drop below 100°C, and start the furnace to take samples. After demoulding on a small manual hydraulic press, remove the shrinkage cavity layer with a thickness of 4 mm above the sample to obtain a high-density high-silicon aluminum alloy block.

The actual sample obtained is shown in Figure 1, and its microstructure is shown in Figure 2. The measured properties are as follows: the density is 2.49g·cm ^-3 , the flexural strength is 150-180MPa, and the thermal diffusivity at room temperature is 0.72cm ² ·s ^{- 1.} The thermal conductivity is 146W·m ^-1 ·℃ ^-1 , and the average thermal expansion coefficient from room temperature to 200℃ is 11～12×10 ^-6 ℃ ^-1 .

Implementation example 2

1. Preparation of powder. Take by weighing 140 grams of 20-micron silicon powder and 60 grams of 10-micron aluminum powder at a ratio of 50% by silicon weight, and dry-mix for 4 hours with a small-sized drum mixer;

2. Preparation of the mold. Spray the commercially available Jiadan brand JD-3028 boron nitride release agent on the inner wall of the Φ62mm cylindrical female mold and the pressure-applying end faces of the upper and lower dies, and dry it.

3. Powder molding. Place the female mold vertically on the horizontal operating table, load the lower die punch, and then place multi-layer flexible graphite paper for compaction; weigh 100 grams of powder from the mixture obtained in step 1 and slowly pour it into the female mold Die cavity; then put flexible graphite paper, and lightly press the upper die punch from the upper end of the female die into the female die, and finally apply a pressure of 6Mpa in the axial direction on the small manual hydraulic press to pre-tighten the upper and lower die punches.

4. Two-phase hot extrusion of liquid aluminum alloy-solid silicon particles. Put the pre-compressed mold in step 3, including the female mold, upper and lower die punches, and the powder loaded in the female mold, together into a vacuum hot-press furnace with a water cooling device at the bottom to raise the temperature to 850°C, and keep the vacuum degree in the furnace at 10 Between ~20Pa. Keep warm for 30 minutes to make the temperature inside and outside the mold uniform, and then slowly apply axial pressure. When the pressure reaches 6 MPa, start to hold the pressure for 30 minutes.

5. Cooling and sampling. After the pressure holding is over, the water cooling device at the bottom of the vacuum furnace immediately and continuously feeds cooling water. While feeding cooling water, control the furnace temperature to cool down to 590°C at a rate of 5°C/min, and then cool to 560°C at a rate of 1°C/min. Relieve the pressure, stop heating and continue to feed cooling water. When the furnace temperature drops below 100°C, start the furnace to take samples. After demoulding on a small manual hydraulic press, remove the shrinkage cavity layer with a thickness of 6 mm above the sample to obtain a high-density high-silicon aluminum alloy block.

The microstructure of the obtained sample is shown in Figure 3, and the measured properties are as follows: the density is 2.392g·cm ^-3 , the flexural strength is 110-132MPa, and the thermal diffusivity at room temperature is 0.68cm ² . s ^-1 , thermal conductivity 124W·m ^-1 ·℃ ^-1 , average thermal expansion coefficient from room temperature to 200℃ 7.5～8.5×10 ^-6 ℃ ^-1 .

Claims (2)

1. a preparation method of high silicon aluminum alloy, is characterized in that, comprises the following steps: (1) Mix silicon powder and aluminum powder, or aluminum-silicon alloy powder, according to the weight ratio of silicon weight not less than 30%, and then put it into a sealed graphite or alloy mold, and apply an axial pressure of 5-10MPa Preload; (2) Then put the device into a vacuum hot-press furnace with a water-cooling device at the bottom and raise the temperature to 580-900°C, and keep the vacuum in the furnace at 10-100Pa; after the temperature inside and outside the mold is uniform, apply an axial pressure not greater than 10 MPa Keep the pressure for 10-30 minutes, and then cool down at a rate of 1-10°C/min; (3) During the cooling process, the water cooling device continues to flow water from the bottom to accelerate the cooling of the mold; (4) After the furnace temperature drops to the operable temperature, a high-silicon-aluminum bulk alloy with high density, uniform structure, silicon particle size below 100 microns and excellent performance can be obtained; Follow these steps: Step 1. Weigh silicon powder and aluminum powder or aluminum-silicon alloy powder according to the ratio of silicon content of 30% to 70%, and mix them; Step 2: Spray or coat a barrier agent containing boron nitride on the inner wall of the female mold and the pressing end faces of the upper and lower dies; Step 3. Place the female mold vertically and put it into the lower punch, then place the flexible graphite paper for compaction, then pour the mixed powder into the cavity of the female mold; then put in the flexible graphite paper, and put the upper punch from the The upper end is pressed into the female die, and finally the upper and lower die punches are pressed axially; Step 4. Put the pre-compressed mold, including the female mold, upper and lower die punches, and the powder loaded in the female mold, into a vacuum hot-pressing furnace with a water-cooling device at the bottom and raise the temperature to 580-900°C. Keep it at 10-100Pa, after the temperature inside and outside the mold is uniform, slowly apply an axial pressure not greater than 10 MPa and keep the pressure for 10-30 minutes; Step 5. After the pressure holding is completed, the water cooling device at the bottom of the vacuum furnace immediately and continuously feeds cooling water, accelerates the cooling of the mold from the lower end of the extrusion die, and controls the furnace temperature to cool down at a rate of 1-10°C/min while feeding the cooling water , keep the extrusion pressure stable during the cooling process; when the temperature drops below 570°C, remove the pressure and stop heating, and further cool down to the operable temperature, the sample is released together with the mold, and the loose area containing shrinkage cavities on the top is removed after demoulding A dense high-silicon aluminum alloy block can be obtained. 2. The preparation method of high-silicon aluminum alloy according to claim 1, characterized in that, in step 4, the hot-pressing temperature and pressure corresponding to the mixed powder in each silicon content interval are respectively: silicon content 30～ 55% is 580-700°C and 0.1-4MPa, the silicon content is 55-65% is 650-800°C and 1-8MPa, and the silicon content is greater than 65% is 700-900°C and 2-10MPa.