Vacuum degassing method and device for aluminum matrix composite melt and composite material

Abstract

The present application belongs to the technical field of aluminum matrix composite material, and particularly relates to a vacuum degassing refining method and device for aluminum matrix composite melt and a composite material, which comprises two-stage refining, the first stage is to make the inside of a smelting device reach a first vacuum degree, and make the aluminum matrix composite material melt to obtain a melt under the first vacuum degree, then make the inside of the smelting device reach a second vacuum degree, and stir the melt for a certain time under the second vacuum degree; the second stage is to introduce a protective gas into the smelting device to a first pressure, and stir the melt for a certain time, then introduce the protective gas to a second pressure, and remove the surface dross and bubbles of the melt under the second pressure, the present application uses the way of vacuum extraction to make the gas in the composite material overflow, and the adsorption and agglomeration between the particle reinforcement and the gas is broken at the same time, which is beneficial to the uniform distribution of the particle reinforcement, and the synergistic effect of the protective atmosphere control and the design of stirring vortex is used to further purify the composite melt.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of aluminum matrix composites, and particularly relates to a vacuum degassing refining method and device for aluminum matrix composite melt and a composite material. BACKGROUND

[0002] Aluminum matrix composites have become a hot spot in recent years due to their high specific strength, specific stiffness, wear resistance, low thermal expansion coefficient, and excellent performance such as good thermal conductivity and dimensional stability. Among them, the particle reinforced aluminum matrix composite represented by SiC enables low-cost aluminum matrix composites to optimize performance through particle content, size, etc., and has achieved breakthroughs in the fields of aerospace, electronic packaging, automobile manufacturing, and high-speed trains.

[0003] The main processes for preparing aluminum matrix composites at present include stir casting, powder metallurgy, and pressure infiltration, etc. Among them, the stir casting method is to melt the matrix metal, form a vortex through mechanical or electromagnetic stirring, and then add the particle reinforcement under the action of the vortex to be rolled into the molten metal to obtain a uniformly distributed melt, which is then cast under certain conditions to obtain a composite material. Compared with powder metallurgy and pressure infiltration, this method has the advantages of simple equipment and process, high production efficiency, low cost, and the ability to mass-produce complex-shaped components, making it one of the most promising processes for industrial large-scale production. However, during the stir casting process, the wettability of the reinforcing phase and the matrix is poor, and the particle reinforcement is prone to agglomeration and gas adsorption, which causes the melt to absorb gas and lack of purity, further leading to poor density and low performance of the final composite material. Currently, the refining and degassing of aluminum alloys are mainly achieved by adding refining agents and skimming slag, for example, CN110016572A discloses a device for online purification of aluminum alloy melt, which adds refining agents in the melt through a biased rotating powder spraying device and a bottom gas blowing device, efficiently solving the problem of aluminum alloy deslagging. The added refining agent is mainly used to adsorb inclusions and gas and be removed by flotation. CN115572853A discloses an aluminum matrix composite refining device and preparation method, which includes a refining furnace with a multi-stage stirring mechanism, a driving mechanism connected to the shaft above the refining furnace, and a multi-stage stirring rotor connected to the shaft below. The multi-stage stirring rotor is a three-stage structure rotor refining furnace, and a vacuum system is provided above the refining furnace, and an electromagnetic valve is provided below the refining furnace; the aluminum alloy melt is sent into the refining furnace after gas blowing, and then aluminum alloy casting is performed after stirring by the multi-stage stirring rotor.

[0004] Unlike aluminum alloy refining, adding refining agents to the composite melt will adsorb both impurities and particle reinforcements, causing the loss of reinforcing phases in the composite material, and ultimately failing to obtain qualified composite material products. Therefore, the degassing and refining method for particle reinforced aluminum matrix composites without adding refining agents has become a new research point. SUMMARY

[0005] In view of the problems in the prior art, the present application provides an aluminum matrix composite melt vacuum degassing refining method and device and a composite material.

[0006] The present application adopts the technical solution for solving the above technical problems:

[0007] An aluminum matrix composite melt vacuum degassing refining method, the vacuum degassing refining process does not add a refining agent, and includes a first-stage refining and a second-stage refining. The first-stage refining is as follows: the inside of a smelting device is brought to a first vacuum degree, and the aluminum matrix composite is melted to obtain a melt under the first vacuum degree; then the inside of the smelting device is brought to a second vacuum degree, and the melt is stirred for a certain time under the second vacuum degree. The second-stage refining is as follows: after the first-stage refining is completed, protective gas is introduced into the smelting device to a first pressure, and the melt is stirred for a certain time; then the protective gas is introduced to a second pressure, and the surface dross and bubbles of the melt are removed under the second pressure. The aluminum matrix composite includes an aluminum alloy matrix and a SiC particle reinforcement, the SiC particle reinforcement is a mixture of micron-level particles and sub-micron-level particles, the addition amount of the sub-micron-level particles accounts for 0.1% to 2% of the total mass of the composite material, the SiC particle reinforcement is subjected to a pre-oxidation process, and the surface is covered with an oxide layer. The micron-level particle surface oxide layer is distributed in a dotted manner, and the thickness is 50-500 nm. The sub-micron-level particle surface oxide layer completely covers the sub-micron-level particles, and the thickness is 20-200 nm.

[0008] Further, the first vacuum degree is 20-100 KPa, the second vacuum degree is 0.1-10 KPa, and the stirring time of the melt under the second vacuum degree is 10-20 min.

[0009] Further, the protective gas is argon or nitrogen, the first pressure is 50-100 KPa, the stirring time of the melt under the first pressure is 5-20 min, and the second pressure is one atmosphere.

[0010] Further, the degassing refining process is repeated 2-5 times in the second stage.

[0011] Further, after the second stage is repeated, the melt is caused to flow out, and pressure casting or gravity casting is performed for forming.

[0012] Further, the thickness of the micron-level particle surface oxide layer is greater than the thickness of the sub-micron-level particle surface oxide layer.

[0013] Further, an aluminum matrix composite based on vacuum degassing refining is subjected to vacuum degassing refining by using the method, the melt is caused to flow out, and pressure casting or gravity casting is performed for forming to obtain the aluminum matrix composite.

[0014] Further, the aluminum-based composite melt degassing refining device for the vacuum degassing refining method, the refining device is provided with a heating mechanism in the wall, the inner cavity of the refining device is a ceramic crucible for containing the aluminum-based composite melt, a rotating shaft is arranged in the refining device, the rotating shaft is connected with a driving mechanism, and a stirring rotor is connected below the rotating shaft; a vacuum system is arranged on the refining device, and a valve for controlling the melt outflow is arranged below the refining device.

[0015] Further, the stirring rotor comprises one to three stirring blades, and the angle between the blade and the horizontal plane is 25-80°; through the stirring of the rotor, a vortex is formed in the composite melt, the melt in the center of the vortex flows from top to bottom, and the melt in the periphery of the vortex flows from bottom to top.

[0016] Preferably, the stirring rotor is a primary rotor, and the blade is a spiral blade with an angle of 45-70° with the horizontal plane.

[0017] Preferably, the maximum diameter of the stirring rotor is 1 / 2 of the diameter of the crucible of the refining device, and the height from the bottom of the crucible is 5-20 cm. The height of the rotor is 1 / 4-1 / 3 of the height of the melt.

[0018] Further, the refining device is provided with a protective atmosphere system, the protective gas is argon or nitrogen, and the gas is introduced into the device through a pipeline to complete the atmosphere control. The pipeline gas outlet is 1-8, which is uniformly distributed at a radius of 1 / 4-3 / 4 of the crucible center and along the circumference.

[0019] The degassing refining method specifically comprises the following steps:

[0020] Step a: place the aluminum-based composite material master ingot or return material in the crucible, close the furnace door, and start the vacuum system to vacuum to 20-100 KPa;

[0021] Step b: after the vacuum degree reaches the preset requirement, close the vacuum system, start heating, melt the composite material to obtain a melt;

[0022] Step c: start stirring at a stirring speed of 100-500 r / min, further vacuumize to 0.1-10 KPa by starting the vacuum system, and keep stirring for 10-20 min, then close the vacuum system;

[0023] Step d: open the protective atmosphere control, introduce the protective gas to 50-100 KPa, and continue stirring for 5-20 min;

[0024] Step e: after the stirring is completed, close the stirring system, introduce the protective gas to 1 atm, open the furnace door, use a slag scoop to remove the dross and bubbles, and close the furnace door;

[0025] Step f: Repeat steps c-e for 2-5 times to degas the melt, and open the lower valve to control the melt flow out for pressure casting or gravity casting.

[0026] Preferably, the stirring speed in step c is 50-100 r / min, and the vacuum is extracted to 0.1-1 KPa.

[0027] Preferably, the protective gas is introduced to 80 KPa in step d, and the stirring is performed for 10 min.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] 1. The present application uses the vacuum extraction to make the gas in the composite overflow, and the adsorption and agglomeration between the particle reinforcement and the gas are broken at the same time, which is beneficial to the uniform distribution of the particle reinforcement. At the same time, the particle reinforcement is prevented from being adsorbed and floated out due to the addition of the conventional refining agent into the aluminum-based composite, and the loss of the particle reinforcement is reduced.

[0030] 2. The present application uses the protective atmosphere control and the vortex design of the stirring to further purify the composite melt. The stirring rotor achieves a stable melt vortex, and the melt flow direction in the center of the vortex is from top to bottom, and the melt flow direction on the periphery of the vortex is from bottom to top. At the same time, the protective gas is introduced into the melt from the center of the vortex and is diffused out of the melt from the periphery. In this process, the movement of the protective gas in the melt helps to carry out the dross and impurity gas to further purify the composite melt. The prepared SiC particle aluminum-based composite has good wear resistance and good heat cycle resistance at room temperature-300℃. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the content of the present application and the specific implementation cases, the drawings required in the description process are introduced. The following drawings are only for the purpose of facilitating the description of the subject matter of the present application. For those skilled in the related art, other similar drawings can be easily obtained according to the drawings provided in the present application without creative labor.

[0032] Figure 1 It is a schematic diagram of the refining device of the present application as a whole structure;

[0033] Figure 2 It is a metallographic photo of the particle reinforced aluminum-based composite material of the embodiment of the present application. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the embodiments and accompanying drawings. However, it should be understood that the embodiments and accompanying drawings are merely exemplary descriptions of the present invention and do not constitute any limitation on the scope of protection of the present invention. All reasonable variations and combinations within the scope of the inventive concept of the present invention fall within the scope of protection of the present invention.

[0035] like Figure 1 As shown, this embodiment discloses an aluminum-based composite material refining device, comprising a refining furnace 1, a heating mechanism 2 disposed within the wall of the refining furnace 1, a ceramic crucible within the refining furnace cavity, and a stirring mechanism disposed within the refining furnace. The stirring mechanism comprises a rotating shaft 3 connected to a driving mechanism 4 above the refining furnace, and a stirring rotor 5 connected below the rotating shaft 3. To ensure sufficient stirring and dispersing of particles and discharging scum, the stirring rotor structure is specifically designed, preferably a primary structure rotor 5. Further preferably, the rotor blades are spiral blades with an angle of 45-70° with the horizontal plane; the maximum diameter of the stirring rotor is 1 / 2 the diameter of the refining furnace 1, and the height from the bottom of the crucible is 5-20 cm. The rotor height is 1 / 4-1 / 3 the height of the melt.

[0036] Refining furnace 1 is equipped with a vacuum system 6 to achieve vacuum environment control. Refining furnace 1 is also equipped with a protective atmosphere control system. The protective gas is argon or nitrogen stored in a gas tank 7. This gas is introduced into the device through a pipe outlet 8 to complete the atmosphere control system. Preferably, there are two pipe outlets 8, located at a radius of 1 / 2 from the center of the crucible and evenly distributed along the diameter. A valve 9 is installed below refining furnace 1. After degassing and refining are completed, valve 9 is opened, allowing the melt to flow out of refining furnace 1 by gravity for subsequent casting processes.

[0037] The method for refining aluminum-based composite materials using the above-mentioned refining device comprises the following steps:

[0038] Step a: placing a 20 wt.% SiC particle reinforced A359-based aluminum-based composite mother ingot prepared by stir casting and part return material into a crucible, closing the furnace door, and turning on the vacuum system to evacuate to 30 KPa;

[0039] Step b: After the vacuum degree reaches the requirement, the vacuum system is closed, and the heating is turned on to raise the temperature to 750°C and keep the temperature for 30 minutes to melt the composite material to obtain a melt;

[0040] Step c: Start stirring at a speed of 100 r / min, start the vacuum system and further evacuate to 1 KPa, keep stirring for 10 minutes, and then turn off the vacuum system;

[0041] Step d: Open the protective atmosphere control, introduce argon to 80KPa, and continue stirring for 10 minutes;

[0042] Step e: After stirring, turn off the stirring system, introduce protective gas to 1 atmosphere, open the furnace door, use a skimmer to remove the scum and bubbles, close the furnace door;

[0043] Step f: Repeat steps c-e for a total of 3 times to remove the gas from the melt, and then open the lower valve to control the flow of the melt into the metal mold for gravity casting.

[0044] The aluminum matrix composite includes an aluminum alloy matrix and a particle reinforcement, the particle reinforcement being one or more of SiC, Al2O3, TiC particles. Preferably, the SiC particle reinforcement is a mixture of micron-sized particles and sub-micron-sized particles, the micron-sized particles having a particle size of 10-100 μm, and the sub-micron-sized particles having a particle size of 0.3-0.8 μm. The sub-micron-sized particles have an addition amount of 0.1%-2% of the total mass of the composite material. The SiC particle reinforcement is subjected to a pre-oxidation process, and has an oxide layer on the surface, the thickness and morphology of the oxide layer on the micron-sized particles and the sub-micron-sized particles being different. The thickness of the oxide layer on the micron-sized particles is greater than the thickness of the oxide layer on the sub-micron-sized particles. The thickness of the oxide layer on the micron-sized particles is 50-500 nm, and is in a dot-like distribution. The thickness of the oxide layer on the sub-micron-sized particles is 20-200 nm, and is completely covered. The micron-sized particles improve the strength and hardness of the composite material through load transfer strengthening, and act as the main wear-resistant particles in the friction process to improve the wear resistance. The sub-micron-sized SiC, due to the difference in the thermal expansion coefficient between the sub-micron-sized SiC and the aluminum matrix, excites a large number of thermal mismatch dislocations in the primary aluminum phase through a thermal mismatch effect in the thermal cycle process, and the thermal mismatch dislocations are entangled to strengthen the primary aluminum phase, thereby inhibiting the performance degradation of the matrix in the thermal cycle process.

[0045] The aluminum alloy matrix composition, with the mass fraction of the aluminum alloy matrix being 100%, has the following mass percentages of each element: Si: 6.5%-12%, Cu: 2%-6%, Ni: 1%-3%, Mg: 0.5%-1.5%, Fe: 0.05%-0.2%, Ti: 0.01%-0.2%, Mn: 0.1%-0.5%, Cr: 0.01%-0.4%, Zr: 0.05%-0.2%, Y: 0.02%-0.2%, and V: 0.02%-0.1%; and the balance of Al and unavoidable impurities. The aluminum alloy matrix composition is a hypoeutectic aluminum-silicon alloy, and includes a primary aluminum phase and a micron-sized network strengthening structure. The network strengthening structure includes silicon carbide, eutectic Si, and one or more intermetallic compound strengthening phases, the intermetallic compound strengthening phases having a size of 5-40 μm and a volume percentage in the composite material of ≥4%. The room temperature nano-hardness value of the network strengthening structure is 6-12 GPa, and the nano-hardness value at 350°C is 4-8 GPa. The micron-sized particles are distributed in the eutectic structure, and the sub-micron-sized particles are distributed in the eutectic structure and the primary aluminum phase, thereby forming a synergistic strengthening effect.

[0046] The intermetallic compound strengthening phase includes Al3CuNi, Al3Ni, Al7Cu4Ni, AlSi(FeMn)CuNi. The primary aluminum phase is strengthened by nano precipitates, the nano precipitates are selected from nano precipitates containing one or more of Al, Si, Mg, Fe, Mn, Cr, Zr, Y, V, the precipitates are in the form of needles and short rods, the size is 10-400nm, the size of the nano precipitates is coarsened by 8% or less after being kept at 350℃ for 30h.

[0047] The aluminum alloy matrix contains magnesium element, the percentage of SiC in the composite and the percentage of Mg content in the alloy matrix meet the following relationship: SiC / Mg=13~25, the pointy oxide layer on the surface of the micron grade particles is composed of SiO2, which reacts with aluminum and magnesium elements in the matrix melt to form micro rivet shaped MgAl2O4, so as to enhance the interfacial bonding force between the particles and the Al matrix; the surface of the submicron grade particles is completely covered with SiO2, which improves the wettability between the matrix melt and the particles, so as to reduce the difficulty of adding submicron particles. The 20 wt.% SiC particle reinforced A359 aluminum matrix composite prepared by the above degassing refining method has a metallographic photo as shown in Figure 2 The density of the composite can reach 99.5%, and the tensile strength can reach 250MPa.

[0048] The above application is only some embodiments of the application. For those skilled in the art, without departing from the concept created by the application, several variations and improvements can be made, which are all within the protection scope of the application.

Claims

1. A vacuum degassing and refining method for an aluminum-based composite material melt, characterized in that: No refining agent is added during the vacuum degassing refining process, and the process includes a first-stage refining and a second-stage refining. The first-stage refining comprises: making the interior of the smelting device reach a first vacuum degree, and melting the aluminum-based composite material under the first vacuum degree to obtain a melt, then making the interior of the smelting device reach a second vacuum degree, and stirring the melt under the second vacuum degree for a certain time; the second-stage refining comprises: after the first-stage refining is completed, introducing a protective gas into the smelting device to a first pressure, stirring the melt for a certain time, then introducing a protective gas to a second pressure, and removing slag and bubbles on the surface of the melt under the second pressure. The aluminum-based composite material comprises an aluminum alloy matrix and a SiC particle reinforcement. The SiC particle reinforcement is a mixture of micron-sized particles and submicron-sized particles. The amount of submicron-sized particles added accounts for 0.1% to 2% of the total mass of the composite material. The SiC particle reinforcement undergoes a pre-oxidation process, and the surface is covered with an oxide layer. The oxide layer on the surface of the micron-sized particles is distributed in a dotted manner with a thickness of 50-500nm. The oxide layer on the surface of the submicron-sized particles completely covers the submicron-sized particles with a thickness of 20-200nm.

2. The vacuum degassing and refining method for aluminum-based composite material melt according to claim 1, characterized in that: The first vacuum degree is 20-100 KPa; the second vacuum degree is 0.1-10 KPa, and the melt is stirred for 10-20 minutes under the second vacuum degree.

3. The vacuum degassing and refining method for aluminum-based composite material melt according to claim 2, characterized in that: The protective gas is argon or nitrogen, the first pressure is 50-100 KPa, and the melt stirring time under the first pressure is 5-20 minutes; the second pressure is one atmosphere.

4. The vacuum degassing and refining method for aluminum-based composite material melt according to claim 3, characterized in that: The degassing refining process and the second stage refining are repeated 2 to 5 times.

5. The vacuum degassing and refining method for aluminum-based composite material melt according to claim 4, characterized in that: The particle size of micron-sized particles is 10~100μm, and the particle size of submicron-sized particles is 0.3~0.8μm.

6. The vacuum degassing and refining method for aluminum-based composite material melt according to claim 5, characterized in that: The thickness of the oxide layer on the surface of micron-sized particles is greater than that on the surface of submicron-sized particles.

7. An aluminum-based composite material based on vacuum degassing and refining, characterized in that: After vacuum degassing and refining by the method according to any one of claims 1 to 6, the melt is allowed to flow out and is subjected to pressure casting or gravity casting to obtain the aluminum-based composite material.

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