A method for preparing an al-50si alloy by multistage sintering

Abstract

This invention provides a method for preparing Al-50Si alloy through multi-stage sintering. The specific steps of the method are as follows: Powder mixing: Aluminum powder and silicon powder are mixed in a three-dimensional powder mixer to obtain a mixed powder; the silicon powder has a particle size of 40-80 μm and exhibits a normal particle size distribution; Molding: The mixed powder is cold-pressed into a blank to be sintered in a hydraulic press, with carbon paper separating the mixed powder from the mold cavity to prevent aluminum powder from penetrating into the mold steel and adsorbing onto the mold; Multi-stage sintering: The blank to be sintered is placed under non-vacuum conditions, first undergoing low-temperature sintering, and then high-temperature sintering to obtain the Al-50Si alloy. This invention, through multi-stage temperature sintering, avoids the growth of the silicon phase and the precipitation of eutectic silicon under completely liquid phase conditions, reduces the size of eutectic silicon particles, thereby improving the mechanical properties and density of high-silicon aluminum alloys, and overcoming the disadvantage of metal matrix composites being difficult to process and form.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, and specifically to a method for preparing Al-50Si alloy by multi-stage sintering. Background Technology

[0002] High-silicon aluminum alloys, due to their advantages such as light weight, low coefficient of thermal expansion, good thermal conductivity, high strength and rigidity, ease of precision machining, non-toxicity, and the ability to be plated with thin layers of metals such as gold, silver, copper, and nickel to further optimize surface properties, as well as the ability to be welded to substrates, meet the requirements of electronic packaging technology towards miniaturization, lightweighting, and high-density assembly. They are widely used in military, aerospace, optoelectronics, and satellite communications fields. Si, as a common high thermal conductivity, low expansion material, possesses high thermal conductivity and a very low coefficient of thermal expansion. Al and its alloys are commonly used metallic materials with excellent thermal conductivity, low specific gravity, and excellent mechanical properties, but a relatively large coefficient of thermal expansion. Therefore, combining the characteristics of both, compositing high-volume-content Si particles with Al can yield high thermal conductivity, low expansion, and lightweight thermal control materials with broad application prospects.

[0003] Traditional methods for preparing high-silicon aluminum alloys include melting and casting, melt infiltration, powder metallurgy, and spray deposition. High-silicon aluminum alloys prepared using these traditional methods suffer from various problems, including low density, compositional segregation, uneven silicon particle distribution, coarse microstructure of primary and eutectic Si, needle-like eutectic Si cutting into the matrix and reducing material properties, poor toughness and plasticity, difficulty in processing and forming, complex operation, and high cost. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to provide a preparation method to improve the uneven distribution of silicon particles in Al-50Si alloy and increase the density of the alloy.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] This invention provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific steps of which are as follows:

[0007] Powder mixing: Aluminum powder and silicon powder are mixed in a three-dimensional powder mixer to obtain a mixed powder; the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0008] Pressing: The mixed powder is cold-pressed into a blank to be fired in a hydraulic press. The mixed powder and the mold cavity are separated by carbon paper to prevent aluminum powder from penetrating into the mold steel and adsorbing onto the mold.

[0009] Multi-stage sintering: The blank to be sintered is placed under non-vacuum conditions, first sintered at low temperature, and then sintered at high temperature to obtain Al-50Si alloy.

[0010] Beneficial effects: The selection of silicon powder particle size is crucial in this invention; it cannot be too large or too small. Too small particles are prone to oxidation, while too large particles are difficult to mold. This invention, by mixing aluminum powder and silicon powder before cold pressing, achieves a more uniform silicon distribution in the Al-50Si alloy, solving the problem of poor wettability between silicon particles and the aluminum matrix in traditional melt infiltration processes, making it difficult to incorporate silicon particles into the melt.

[0011] This invention avoids the growth of silicon phase and the precipitation of eutectic silicon under completely liquid conditions by using a multi-stage temperature sintering method, thereby reducing the size of eutectic silicon particles, improving the mechanical properties of high-silicon aluminum alloys, increasing the density of the alloys, and overcoming the disadvantage of metal matrix composites being difficult to process and form.

[0012] Preferably, the aluminum powder has a particle size of 2-10 μm, exhibits a normal particle size distribution, and the mass percentage of aluminum powder to silicon powder in the mixed powder is 1:1.

[0013] Preferably, the mixing time in the powder mixture is 6-8 hours.

[0014] Preferably, the cold pressing pressure is 100-200 MPa.

[0015] Preferably, the blank to be fired is wrapped in carbon paper and placed in a sintering boat, and the blank wrapped in carbon paper is completely covered with carbon powder.

[0016] Beneficial effects: This invention uses carbon paper to wrap the blank to be sintered and cover it with carbon powder under non-vacuum conditions to create oxygen-free conditions. Compared with vacuum sintering, the process is simpler, more efficient, easier to operate, and has lower production costs.

[0017] Preferably, the temperature of the low-temperature sintering is 700°C.

[0018] Preferably, the low-temperature sintering time is 1 hour.

[0019] Preferably, the high-temperature sintering temperature is 900-1000℃.

[0020] Preferably, the high-temperature sintering time is 10-30 minutes.

[0021] Preferably, the silicon phase size of the Al-50Si alloy exhibits a bimodal distribution.

[0022] The advantages of this invention are:

[0023] The selection of silicon powder particle size is crucial in this invention; it cannot be too large or too small. Too small particles are prone to oxidation, while too large particles are difficult to mold. This invention, by mixing aluminum powder and silicon powder before cold pressing, achieves a more uniform silicon distribution in the Al-50Si alloy, solving the problem of poor wettability between silicon particles and the aluminum matrix in traditional melt infiltration processes, making it difficult to incorporate silicon particles into the melt.

[0024] This invention avoids the growth of silicon phase and the precipitation of eutectic silicon under completely liquid conditions by using a multi-stage temperature sintering method, thereby reducing the size of eutectic silicon particles, improving the mechanical properties of high-silicon aluminum alloys, increasing the density of the alloys, and overcoming the disadvantage of metal matrix composites being difficult to process and form.

[0025] This invention creates an oxygen-free environment by wrapping the blank to be sintered with carbon paper and covering it with carbon powder under non-vacuum conditions. Compared with vacuum sintering, the process is simpler, more efficient, easier to operate, and has lower production costs. Attached Figure Description

[0026] Figure 1 This is a metallographic diagram of the Al-50Si alloy from Example 1;

[0027] Figure 2 This is a metallographic diagram of the Al-50Si alloy from Example 2;

[0028] Figure 3 This is a metallographic diagram of the Al-50Si alloy in Example 3;

[0029] Figure 4 This is a metallographic diagram of the Al-50Si alloy from Example 4;

[0030] Figure 5 This is a metallographic diagram of the Al-50Si alloy from Example 5;

[0031] Figure 6 This is a metallographic diagram of the Al-50Si alloy in Example 6;

[0032] Figure 7 This is a metallographic diagram of the Al-50Si alloy in Comparative Example 1.

[0033] Figure 8 This is a metallographic diagram of the Al-50Si alloy in Comparative Example 2.

[0034] Figure 9 This is the metallographic structure of the Al-50Si alloy in Comparative Example 3.

[0035] Figure 10 This is the metallographic structure of the Al-50Si alloy in Comparative Example 4.

[0036] Figure 11This is the metallographic diagram of the Al-50Si alloy in Comparative Example 5. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0039] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0040] Example 1

[0041] This embodiment provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific method is as follows:

[0042] Powder mixing: Weigh aluminum powder and silicon powder in a mass ratio of 1:1, put the raw materials into a sealed container, and mix them in a three-dimensional powder mixer for 6 hours to obtain a mixed powder; the aluminum powder has a particle size of 2-10μm and the particle size is normally distributed, and the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0043] Pressing: The mixed powder is loaded into a steel mold, and the powder and the mold cavity are separated by carbon paper. After the mixed powder is filled, it is cold-pressed by a hydraulic press at a pressure of 150MPa to obtain the blank to be fired.

[0044] Multi-stage sintering: The blank to be sintered is wrapped with carbon paper and placed in a sintering boat. The carbon paper covering the blank is completely covered with carbon powder. Then it is placed in a sintering furnace and slowly heated. First, low-temperature sintering is carried out, the temperature is raised to 700℃ and held for 1 hour. Then, high-temperature sintering is carried out, the temperature is raised to 900℃ and held for 10 minutes to obtain Al-50Si alloy.

[0045] The Al-50Si alloy prepared in this embodiment has a packing density of 95.6% and a density of 2.39 g / cm³. 3 Its metallographic structure is as follows Figure 1 As shown, the silicon phase in the alloy exhibits a bimodal size distribution, with the largest being approximately 40 μm and the smallest approximately 2 μm.

[0046] Example 2

[0047] This embodiment provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific method is as follows:

[0048] Powder mixing: Weigh aluminum powder and silicon powder in a mass ratio of 1:1, put the raw materials into a sealed container, and mix them in a three-dimensional powder mixer for 7 hours to obtain a mixed powder; the aluminum powder has a particle size of 2-10μm and the particle size is normally distributed, and the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0049] Pressing: The mixed powder is loaded into a steel mold, and the powder and the mold cavity are separated by carbon paper. After the mixed powder is filled, it is cold-pressed by a hydraulic press at a pressure of 150MPa to obtain the blank to be fired.

[0050] Multi-stage sintering: The blank to be sintered is wrapped with carbon paper and placed in a sintering boat. The carbon paper covering the blank is completely covered with carbon powder. Then it is placed in a sintering furnace and slowly heated. First, low-temperature sintering is carried out, the temperature is raised to 700℃ and held for 1 hour. Then, high-temperature sintering is carried out, the temperature is raised to 900℃ and held for 20 minutes to obtain Al-50Si alloy.

[0051] The Al-50Si alloy prepared in this embodiment has a packing density of 95.2% and a density of 2.38 g / cm³. 3 Its metallographic structure is as follows Figure 2 As shown, the silicon phase in the alloy exhibits a bimodal size distribution, with the largest being approximately 40 μm and the smallest approximately 2 μm.

[0052] Example 3

[0053] This embodiment provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific method is as follows:

[0054] Powder mixing: Weigh aluminum powder and silicon powder in a mass ratio of 1:1, put the raw materials into a sealed container, and mix them in a three-dimensional powder mixer for 8 hours to obtain a mixed powder; the aluminum powder has a particle size of 2-10μm and the particle size is normally distributed, and the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0055] Pressing: The mixed powder is loaded into a steel mold, and the powder and the mold cavity are separated by carbon paper. After the mixed powder is filled, it is cold-pressed using a hydraulic press at a pressure of 100MPa to obtain the blank to be fired.

[0056] Multi-stage sintering: The blank to be sintered is wrapped with carbon paper and placed in a sintering boat. The carbon paper covering the blank is completely covered with carbon powder. Then it is placed in a sintering furnace and slowly heated. First, low-temperature sintering is carried out, the temperature is raised to 700℃ and held for 1 hour. Then, high-temperature sintering is carried out, the temperature is raised to 900℃ and held for 30 minutes to obtain Al-50Si alloy.

[0057] The Al-50Si alloy prepared in this embodiment has a packing density of 96% and a density of 2.4 g / cm³. 3 Its metallographic structure is as follows Figure 3 As shown, the silicon phase in the alloy exhibits a bimodal size distribution, with the largest being approximately 40 μm and the smallest approximately 2 μm.

[0058] Example 4

[0059] This embodiment provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific method is as follows:

[0060] Powder mixing: Weigh aluminum powder and silicon powder in a mass ratio of 1:1, put the raw materials into a sealed container, and mix them in a three-dimensional powder mixer for 6 hours to obtain a mixed powder; the aluminum powder has a particle size of 2-10μm and the particle size is normally distributed, and the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0061] Pressing: The mixed powder is loaded into a steel mold, and the mixed powder and the mold cavity are separated by carbon paper. After the mixed powder is filled, it is cold-pressed by a hydraulic press at a pressure of 200MPa to obtain the blank to be fired.

[0062] Multi-stage sintering: The blank to be sintered is wrapped with carbon paper and placed in a sintering boat. The carbon paper covering the blank is completely covered with carbon powder. Then it is placed in a sintering furnace and slowly heated. First, low-temperature sintering is carried out, the temperature is raised to 700℃ and held for 1 hour. Then, high-temperature sintering is carried out, the temperature is raised to 1000℃ and held for 10 minutes to obtain Al-50Si alloy.

[0063] The Al-50Si alloy prepared in this embodiment has a packing density of 97.2% and a density of 2.43 g / cm³. 3 Its metallographic structure is as follows Figure 4 As shown, the silicon phase in the alloy exhibits a bimodal size distribution, with the largest being approximately 60 μm and the smallest approximately 2 μm.

[0064] Example 5

[0065] This embodiment provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific method is as follows:

[0066] Powder mixing: Weigh aluminum powder and silicon powder in a mass ratio of 1:1, put the raw materials into a sealed container, and mix them in a three-dimensional powder mixer for 6 hours to obtain a mixed powder; the aluminum powder has a particle size of 2-10μm and the particle size is normally distributed, and the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0067] Pressing: The mixed powder is loaded into a steel mold, and the mixed powder and the mold cavity are separated by carbon paper. After the mixed powder is filled, it is cold-pressed using a hydraulic press at a pressure of 150MPa to obtain the blank to be fired.

[0068] Multi-stage sintering: The blank to be sintered is wrapped with carbon paper and placed in a sintering boat. The carbon paper covering the blank is completely covered with carbon powder. Then it is placed in a sintering furnace and slowly heated. First, low-temperature sintering is carried out, the temperature is raised to 700℃ and held for 1 hour. Then, high-temperature sintering is carried out, the temperature is raised to 1000℃ and held for 20 minutes to obtain Al-50Si alloy.

[0069] The Al-50Si alloy prepared in this embodiment has a packing density of 96.8% and a density of 2.42 g / cm³. 3 Its metallographic structure is as follows Figure 5 As shown, the silicon phase in the alloy exhibits a bimodal size distribution, with the largest being approximately 60 μm and the smallest approximately 2 μm.

[0070] Example 6

[0071] This embodiment provides a method for preparing Al-50Si alloy by multi-stage sintering, the specific method is as follows:

[0072] Powder mixing: Weigh aluminum powder and silicon powder in a mass ratio of 1:1, put the raw materials into a sealed container, and mix them in a three-dimensional powder mixer for 6 hours to obtain a mixed powder; the aluminum powder has a particle size of 2-10μm and the particle size is normally distributed, and the silicon powder has a particle size of 40-80μm and the particle size is normally distributed.

[0073] Pressing: The mixed powder is loaded into a steel mold, and the mixed powder and the mold cavity are separated by carbon paper. After the mixed powder is filled, it is cold-pressed using a hydraulic press at a pressure of 150MPa to obtain the blank to be fired.

[0074] Multi-stage sintering: The blank to be sintered is wrapped with carbon paper and placed in a sintering boat. The carbon paper covering the blank is completely covered with carbon powder. Then it is placed in a sintering furnace and slowly heated. First, low-temperature sintering is carried out, the temperature is raised to 700℃ and held for 1 hour. Then, high-temperature sintering is carried out, the temperature is raised to 1000℃ and held for 30 minutes to obtain Al-50Si alloy.

[0075] The Al-50Si alloy prepared in this embodiment has a packing density of 96% and a density of 2.4 g / cm³. 3 Its metallographic structure is as follows Figure 6 As shown, the silicon phase in the alloy exhibits a bimodal size distribution, with the largest being approximately 60 μm and the smallest approximately 2 μm.

[0076] Comparative Example 1

[0077] This comparative example uses a melting and casting method. Pure aluminum blocks and pure silicon blocks are weighed in a mass ratio of 1:1. The aluminum blocks are first placed in a crucible resistance furnace and heated to 670°C. After the aluminum blocks are completely melted, silicon blocks are added and the temperature is raised to 900°C for melting. Al-10Si-4P alloy blocks are added to refine the silicon phase. Finally, the completely molten metal is slowly poured into a metal mold for cooling and solidification to obtain the cast Al-50Si alloy.

[0078] The metallographic structure of the Al-50Si alloy prepared in this comparative example is as follows: Figure 7 As shown, silicon in the alloy precipitates in the form of relatively large needle-like and blocky shapes, with a maximum size of 150-200 μm, and there are a large number of defects.

[0079] Comparative Example 2

[0080] This comparative example uses the melt infiltration method. Aluminum powder and silicon powder are uniformly mixed in a mass ratio of 1:1 and then cold-pressed into shape. The green billet is placed in a sintering boat, and the aluminum block to be infiltrated is placed on the top of the billet. The surrounding area is filled with nano-sized alumina powder, and then placed in a high-temperature atmosphere tube furnace for slow heating at a heating rate of 5-8℃ / min. The temperature is raised to 800℃ and held for 1.5h. Subsequently, the furnace is cooled with argon gas at a flow rate of 1-2L / h. After the tube furnace cools down, the Al-50Si alloy with good melt infiltration is obtained.

[0081] The Al-50Si alloy prepared in this comparative example has a packing density of 90.0% and a density of 2.25 g / cm³. 3 Its metallographic structure is as follows Figure 8 As shown, the silicon phase in the alloy has a size of 30–150 μm and is irregularly distributed.

[0082] Comparative Example 3

[0083] The method used to prepare Al-50Si in Comparative Example 1 is the same as that in Example 1, except that the blank to be fired was placed directly into the sintering boat without being wrapped with carbon paper, and the blank to be fired was not covered with carbon powder.

[0084] The Al-50Si alloy prepared in this embodiment has a packing density of 90.8% and a density of 2.27 g / cm³. 3 Its metallographic structure is as follows Figure 9 As shown, without external force, molten aluminum at high temperature flows along the pores to the material surface, resulting in severe aluminum loss in the alloy. The liquid phase does not fill the pores of silicon particles sufficiently, and the alloy cannot be sintered densely.

[0085] Comparative Example 4

[0086] The comparative example uses the same method as Example 3 to prepare Al-50Si, except that the blank to be fired is sintered at high temperature only, heated to 900°C and held for 30 minutes to obtain Al-50Si alloy.

[0087] The Al-50Si alloy prepared in this embodiment has a packing density of 91.2% and a density of 2.28 g / cm³. 3 Its metallographic structure is as follows Figure 10 As shown, the silicon phase in the alloy is unevenly distributed in size, ranging from 60 μm to 20 μm, and the presence of defects in the large silicon blocks reduces the alloy density.

[0088] Comparative Example 5

[0089] The comparative example uses the same method as Example 1 to prepare Al-50Si, except that the blank to be fired is sintered at a low temperature, heated to 700°C and held for 1 hour to obtain the Al-50Si alloy.

[0090] The Al-50Si alloy prepared in this embodiment has a packing density of 93.6% and a density of 2.34 g / cm³. 3 Its metallographic structure is as follows Figure 11 As shown, the low-temperature sintered alloy silicon particles are not fully bonded to the aluminum matrix, resulting in many gaps and a low alloy density.

[0091] Summary: Through Examples 1-6 and Comparative Examples 1-5, combined with the appendix... Figure 1-11 It can be seen that:

[0092] The microstructure of Al-50Si alloy prepared by melting and casting method has severe compositional segregation. The size and distribution of silicon phase are very uneven, and silicon in the eutectic structure precipitates in the form of coarse needle-like precipitates with a maximum size of 150-200 μm. This structure cuts the aluminum matrix, reduces the toughness of the material, and seriously affects the thermal conductivity and mechanical properties of high silicon aluminum alloy.

[0093] The microstructure of Al-50Si alloy prepared by melt infiltration shows a much more uniform distribution of silicon particles compared to that prepared by melting and casting. However, the problem of excessively large silicon particles, with the maximum size reaching 100-150 μm, still exists. Furthermore, due to the lack of wetting between the reinforcing silicon particles and the molten aluminum matrix, the infiltration is incomplete, resulting in many obvious pores in the microstructure. This defect reduces the material density and is very detrimental to the mechanical and thermodynamic properties of high-silicon aluminum alloys.

[0094] Compared to this invention, the three methods—not using carbon paper wrapping, high-temperature sintering only, and low-temperature sintering only—all suffer from numerous alloy defects and non-dense samples. Specifically, the Al-50Si alloy sintered directly without carbon paper wrapping exhibits severe aluminum loss and insufficient liquid phase filling of silicon particle pores, resulting in extremely low alloy density. In the Al-50Si alloy sintered only at high temperatures, the lack of low-temperature holding during sintering causes silicon particles to grow and passivate directly at higher temperatures. The grown silicon phase obstructs the communication channels of the molten aluminum during liquid phase sintering, leading to the formation and enlargement of pores within the material structure. Finally, in the Al-50Si alloy sintered only at low temperatures, the loose defects between powder particles are not completely eliminated even after remelting and liquid phase filling, resulting in insufficient aluminum filling of pores and the presence of partial defect distribution in the sample.

[0095] The Al-50Si alloy prepared by the multi-stage sintering method of the present invention has a bimodal distribution of silicon phase size in its microstructure, with the largest being about 50 μm and the smallest being about 2 μm. It is uniformly dispersed on the aluminum alloy matrix, contains few defects, improves the density of the alloy, solves the problem of poor wettability between silicon particles and aluminum matrix and difficulty in adding silicon particles into the melt, and the material can be formed in one step with less machining, overcoming the disadvantage of difficult processing of metal matrix composites.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing Al-50Si alloy by multi-stage sintering, characterized in that, The specific steps of the method are as follows: Powder mixing: Aluminum powder and silicon powder are mixed in a three-dimensional powder mixer to obtain a mixed powder; the silicon powder has a particle size of 40-80μm and the particle size is normally distributed. Compression molding: The mixed powder is loaded into the mold, and carbon paper is used to separate the mixed powder from the mold cavity. Then, it is cold-pressed in a hydraulic press to obtain the blank to be fired. The cold pressing pressure is 100-200MPa. Multi-stage sintering: The blank to be sintered is placed in a non-vacuum environment, wrapped with carbon paper and placed in a sintering boat. The blank wrapped with carbon paper is then completely covered with carbon powder. Low-temperature sintering is performed first at 700℃, followed by high-temperature sintering at 900-1000℃ to obtain Al-50Si alloy.

2. The method according to claim 1, characterized in that, The aluminum powder has a particle size of 2-10 μm and exhibits a normal distribution. The mass percentage of aluminum powder to silicon powder in the mixed powder is 1:

1.

3. The method according to claim 1, characterized in that, The mixing time for the powder is 6-8 hours.

4. The method according to claim 1, characterized in that, The low-temperature sintering time is 1 hour.

5. The method according to claim 1, characterized in that, The high-temperature sintering time is 10-30 minutes.

6. The method according to claim 1, characterized in that, The silicon phase size of the Al-50Si alloy exhibits a bimodal distribution.

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