A multifunctional aluminum-based nitrogen-doped titanium carbide master alloy and its preparation method

Abstract

The present invention discloses a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy and a preparation method thereof, wherein the master alloy comprises an aluminum matrix and TiC dispersed on the aluminum matrix. N Particles, the TiC N Formed when nitrogen atoms occupy carbon vacancies in TiC crystals, the process shares the same crystal structure as TiC. The method comprises nitriding titanium powder, preparing a mixed powder prefabricated block, melting a pure aluminum ingot, raising the temperature to 1000-1250°C, adding the prefabricated block, and fully melting and stirring it. A refining agent is then pressed into the melt for refining, followed by argon gas degassing and slag removal, and finally, casting it into a metal mold to produce an intermediate alloy. The method can produce high-content nitrogen-doped titanium carbide particles with fine particle size, uniform distribution, good wettability with aluminum melt, and high interfacial bonding strength, effectively refining and dispersing aluminum and aluminum alloys.

Description

Technical Field

[0001] The invention relates to a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy and a preparation method thereof, and relates to the technical field of metal materials. Background Art

[0002] Grain refinement is a very effective method to improve the mechanical properties of aluminum alloys and their plastic processing properties. Due to the coarse grains of cast aluminum and aluminum alloys, the industry generally refines the structure by adding grain refiners such as Al-Ti-B, Al-Ti-C and other intermediate alloys; however, traditional commercial refiners still have many problems during use; for example, the content of TiB2 and TiC particles that can induce grain refinement in intermediate alloys such as Al-Ti-B and Al-Ti-C is relatively low, and the grain refining effect is limited. Although more particles can be introduced by increasing the amount of intermediate alloys, excessive Ti will react with Zr and Si elements to generate Coarse, hard and brittle intermetallic compounds will deteriorate the plasticity of the alloy and reduce product quality. In addition, the TiB2 particles of the Al-Ti-B master alloy will aggregate and settle in the melt as the holding time increases, and will easily react with strengthening elements such as Zr and V in the aluminum alloy, causing grain refinement to fail and resulting in a refinement "poisoning" phenomenon. Although the TiC particles of the Al-Ti-C master alloy can avoid the "poisoning" effect on the strengthening elements in the melt, they will undergo certain chemical reactions with aluminum to form harmful phases such as Al4C3, resulting in signs of a decline in the refinement effect.

[0003] To improve the chemical stability of TiC particles in molten aluminum, Reference 1 found that the element Mo can reduce the reaction diffusion coefficient between TiC and Al and increase the activation energy of the reaction, significantly improving the stability of TiC in molten aluminum. However, Mo is introduced into the alloy, affecting its properties. Reference 2 reports that nitrogen doping can also improve the structural stability of TiC in molten aluminum. However, using Mg3N2 as a nitrogen source requires stringent experimental requirements, while using BN as a nitrogen source prevents precise control of the doping level to regulate the chemical stability of TiCx in molten aluminum. Chinese Patent Publication No. CN108149127B discloses an aluminum-based nano-titanium carbonitride (TiNC) master alloy and its preparation method. Nano-TiNC is generated by an in-situ reaction in a vacuum heating furnace using aluminum powder, titanium nitride powder, and graphene as raw materials. However, the use of graphene as a raw material in this process is costly and inconvenient for industrial production. Furthermore, the in-situ synthesis method in this patent produces a TiCN ceramic phase, which is fundamentally different from the TiCx modified with trace amounts of nitrogen atoms in the present invention. Summary of the Invention

[0004] The present invention aims to provide a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy, which comprises an aluminum matrix and TiC dispersed on the aluminum matrix.N Particles, the TiC N It is formed when N atoms occupy the C vacancies in TiC crystals and has the same crystal structure as TiC. This master alloy has multifunctional properties. It not only plays a role in grain refinement and dispersion strengthening of aluminum and aluminum alloys, but also can produce eutectic silicon phase modification on aluminum-silicon alloys, transforming the lamellar eutectic silicon phase into a dendritic one.

[0005] Preferably, the nitrogen-doped TiC N By TiC x N y Indicates that, among them, 0.68 <x<0.73,0.05<y<0.25。

[0006] Preferably, the TiC N The particle size is submicron, less than 1μm, TiC N The mass percentage of the particles is 5 wt.% to 20 wt.%.

[0007] Preferably, the content of Ti in the master alloy of the present invention is 3.8wt.% to 16.5wt.%, the content of C is 0.8wt.% to 4.2wt.%, the content of N is 0.03wt.% to 1.2wt.%, and the rest is Al and unavoidable impurity elements.

[0008] Another object of the present invention is to provide a method for preparing the multifunctional aluminum-based nitrogen-doped titanium carbide master alloy. The nitrogen-doped TiC particles prepared by this method are small in size and uniformly distributed, and can produce significant grain refinement, eutectic silicon modification, and dispersion strengthening effects on aluminum-silicon alloys. The method specifically comprises the following steps:

[0009] (1) Nitriding treatment of titanium powder: Place the titanium powder in an atmosphere furnace, introduce nitrogen into the furnace for 10 minutes, then raise the furnace temperature to 480-650°C, control the nitrogen flow rate to 0.1-1.0 L / min, keep warm for 0.5-2 hours, and then cool to room temperature to obtain titanium powder with nitrogen atoms solid dissolved in a close-packed hexagonal titanium matrix.

[0010] (2) Preparation of mixed powder preforms: The titanium powder, graphite powder and pure aluminum powder obtained in step (1) are fully mixed in a mixer, and then pressed into preforms on a briquetting machine at a pressure of 20 to 70 MPa.

[0011] (3) Preparation of intermediate alloy: pure aluminum ingot is melted, and then the temperature is raised to 1000-1250℃. Prefabricated blocks are added and fully melted and stirred. Then, a refining agent is pressed into the melt for refining and argon gas is introduced for degassing and slag removal. Finally, the intermediate alloy is cast into a metal mold to obtain the intermediate alloy.

[0012] Preferably, in step (2) of the present invention, the size of the titanium powder is less than 50 μm, and the particle size of the pure aluminum powder is less than 50 μm.

[0013] Preferably, in step (2) of the present invention, the mass of pure aluminum powder is m1, the mass of titanium powder is m2, and the mass of graphite powder is m3, and the weight percentage of aluminum powder to titanium powder + graphite powder is m1 / (m1+m2+m3)=60~90.

[0014] Preferably, the graphite powder in step (3) of the present invention has a purity greater than 99.9% and a particle size less than 20 μm.

[0015] The present invention uses titanium powder that has been nitrided to introduce a nitrogen source. When the titanium powder is added to the aluminum melt, the titanium powder can quickly react with the graphite powder to form TiC. At the same time, since the nitrogen atoms dissolved in the titanium matrix come into contact with the titanium atoms, the nitrogen atoms easily occupy the vacancies of TiC to form nitrogen-doped TiC. N The present invention avoids the problems of slow doping reaction, high raw material cost, and easy formation of impurity phases caused by using nitrides such as TiN and BN as nitrogen sources, and the obtained intermediate alloy has less impurity phases and TiC N The particles are small and evenly distributed, which can produce good grain refinement and dispersion strengthening effects on pure aluminum and aluminum alloys.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The production process of the aluminum-based nitrogen-doped master alloy of the present invention is easy to control, low in cost, has a good and stable refinement effect, and is easy to carry out large-scale industrial production.

[0018] (2) The present invention can obtain high-content nitrogen-doped titanium carbide particles with small particle size, uniform distribution, good wettability with aluminum melt, and high interface bonding strength, which can play a good role in grain refinement and dispersion strengthening of aluminum and aluminum alloys.

[0019] (3) The present invention easily introduces nitrogen into titanium carbide through the titanium powder nitriding process, and can well adjust the nitrogen doping content in titanium carbide, thereby improving the chemical stability of titanium carbide in aluminum melt. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD pattern (a) and metallographic structure (b) of Al-5TiC master alloy;

[0021] Figure 2 Effect of adding master alloys on the microstructure of ZL114 cast aluminum-silicon alloy: (a) and (c) A357; (b) and (d) A357+0.3wt.%TiC. DETAILED DESCRIPTION

[0022] To facilitate understanding of the present invention, the present invention lists the following embodiments; those skilled in the art should understand that the embodiments are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0023] Example 1

[0024] A multifunctional aluminum-based nitrogen-doped titanium carbide master alloy specifically comprises the following steps:

[0025] (1) Prepare the required raw materials according to the following mass percentages: titanium powder (size less than 50 μm) 4.00%, graphite powder (size less than 20 μm) 1.00%, pure aluminum powder (size less than 50 μm) 3.50%, and pure aluminum ingot 91.50%.

[0026] (2) The titanium powder was placed in a tubular atmosphere furnace and argon gas was introduced for 10 minutes. The furnace temperature was then raised to 520°C, the argon flow rate was controlled at 0.1 L / min, and the mixture was kept at this temperature for 1 hour and then cooled to room temperature to obtain nitrided titanium powder.

[0027] (3) The nitrided titanium powder, graphite powder and pure aluminum powder were fully mixed in a V-type mixer and then pressed into a preform on a briquetting machine at a pressure of 50 MPa.

[0028] (4) The pure aluminum ingot weighed in (1) is melted at 720°C, then the temperature is raised to 1000°C, and the prefabricated block is added and fully melted and stirred. Then, a refining agent is pressed into the melt for refining, and argon gas is introduced for degassing and slag removal. Finally, the melt is cast into a metal mold to obtain an Al-5TiC master alloy.

[0029] The XRD pattern of the Al-5TiC master alloy prepared in Example 1 is as follows: Figure 1 As shown in (a), in addition to the α-Al matrix, there is also an obvious TiC diffraction peak in the alloy; from the metallographic structure of Figure (b), it can be seen that the particles in the cast structure are mainly distributed at the grain boundaries, with a size of 10 to 250 nm. The energy spectrum results show that the particles contain Ti, C, and N elements, which are determined to be TiC N Phase; 0.15wt% TiC N Adding a certain amount of master alloy to Al-4.5Cu alloy can reduce the average grain size of the alloy from 500 μm to 53 μm.

[0030] Example 2

[0031] A multifunctional aluminum-based nitrogen-doped titanium carbide master alloy specifically comprises the following steps:

[0032] (1) Prepare the required raw materials according to the following mass percentages: titanium powder (size less than 50 μm) 8.00%, graphite powder (size less than 20 μm) 2.00%, pure aluminum powder (size less than 50 μm) 8.00%, and pure aluminum ingot 82.00%.

[0033] (2) The titanium powder was placed in a tubular atmosphere furnace and argon gas was introduced for 10 minutes. The furnace temperature was then raised to 650°C, the argon gas flow rate was controlled at 0.5 L / min, and the temperature was kept at that temperature for 0.5 hours before cooling to room temperature to obtain nitrided titanium powder.

[0034] (3) The nitrided titanium powder, graphite powder and pure aluminum powder were fully mixed in a V-type mixer and then pressed into a preform on a briquetting machine at a pressure of 20 MPa.

[0035] (4) The pure aluminum ingot weighed in (1) is melted at 720°C, then the temperature is raised to 1250°C, and the prefabricated block is added and fully melted and stirred. Then, a refining agent is pressed into the melt for refining, and argon gas is introduced for degassing and slag removal. Finally, the melt is cast into a metal mold to obtain an Al-10TiC master alloy.

[0036] The size of nitrogen-doped titanium carbide particles in the Al-10TiC master alloy prepared in Example 2 is 15 to 280 nm; N Adding an additional amount of master alloy to pure aluminum can reduce the average grain size of pure aluminum from ~800μm to ~120μm.

[0037] Example 3

[0038] A multifunctional aluminum-based nitrogen-doped titanium carbide master alloy specifically comprises the following steps:

[0039] (1) Prepare the required raw materials according to the following mass percentages: titanium powder (size less than 50 μm) 16.00%, graphite powder (size less than 20 μm) 4.00%, pure aluminum powder (size less than 50 μm) 13.50%, and pure aluminum ingot 71.50%.

[0040] (2) The titanium powder was placed in a tubular atmosphere furnace and argon gas was introduced for 10 minutes. The furnace temperature was then raised to 480°C, the argon gas flow rate was controlled at 1.0 L / min, and the mixture was kept at this temperature for 2 hours and then cooled to room temperature to obtain nitrided titanium powder.

[0041] (3) The nitrided titanium powder, graphite powder and pure aluminum powder were fully mixed in a V-type mixer and then pressed into a preform on a briquetting machine at a pressure of 70 MPa.

[0042] (4) The pure aluminum ingot weighed in (1) was melted at 720°C, then the temperature was raised to 1200°C, and the prefabricated block was added and fully melted and stirred. Then, a refining agent was pressed into the melt for refining, and argon gas was introduced for degassing and slag removal. Finally, the melt was cast into a metal mold to obtain an Al-15TiC master alloy.

[0043] The size of nitrogen-doped titanium carbide particles in the structure of the Al-15TiC master alloy prepared in Example 3 is 10 to 270 nm; N Addition of master alloy to A357 cast aluminum silicon alloy, Figure 2 From the organizational comparison, it can be seen that the intermediate alloy can not only reduce the macro grain size of the alloy, but also refine the dendrites in the organization, and the morphology of the eutectic silicon phase changes from lamellar to dendritic.

[0044] Comparative Example 1

[0045] The method described in this embodiment is the same as that in embodiment 1, except that step (2) is omitted. The specific steps are:

[0046] (1) Prepare the required raw materials according to the following mass percentages: titanium powder (size ≤ 20 μm) 4.00%, graphite powder (size less than 20 μm) 1.00%, pure aluminum powder (size less than 50 μm) 3.50%, and pure aluminum ingot 91.50%.

[0047] (2) Titanium powder, graphite powder and pure aluminum powder were fully mixed in a V-type mixer and then pressed into a preform on a briquetting machine at a pressure of 50 MPa.

[0048] (3) The weighed pure aluminum ingot was melted at 720°C, and then the temperature was raised to 1000°C. The prefabricated block was added and fully melted and stirred. Then, a refining agent was pressed into the melt for refining, and argon gas was introduced for degassing and slag removal. Finally, the melt was cast into a metal mold to obtain an Al-5TiC master alloy.

[0049] Comparative Example 1 shows that although a large number of TiC particles are formed in the Al-5TiC master alloy prepared, since the TiC is not nitrogen-doped, by adding the master alloy with a TiC addition amount of 0.15wt% to the Al-4.5Cu alloy, it can be seen that the grain size is only reduced from 500μm to 480μm. This is because the TiC structure is unstable in the aluminum alloy melt, resulting in a decline in the refinement effect.

[0050] Comparative Example 2

[0051] The method described in this embodiment is the same as that in embodiment 1, except that step (3) is omitted and the nitrided titanium powder, graphite powder and pure aluminum powder are directly added to step (4). The specific steps are as follows:

[0052] (1) Prepare the required raw materials according to the following mass percentages: titanium powder (size less than 50 μm) 4.00%, graphite powder (size less than 20 μm) 1.00%, pure aluminum powder (size less than 50 μm) 3.50%, and pure aluminum ingot 91.50%.

[0053] (2) The titanium powder was placed in a tubular atmosphere furnace and argon gas was introduced for 10 minutes. The furnace temperature was then raised to 520°C, the argon flow rate was controlled at 0.1 L / min, and the mixture was kept at this temperature for 1 hour and then cooled to room temperature to obtain nitrided titanium powder.

[0054] (3) The pure aluminum ingot weighed in (1) is melted at 720°C, and then the temperature is raised to 1000°C. Nitrided titanium powder, graphite powder and pure aluminum powder are added and fully melted and stirred. Then, a refining agent is pressed into the melt for refining, and argon gas is introduced for degassing and slag removal. Finally, the melt is cast into a metal mold to obtain an Al-5TiC master alloy.

[0055] Comparative Example 2 shows that the Al-5TiC master alloy prepared has a large amount of needle-shaped Al3Ti phase in its structure. This is because the powders are not evenly mixed and pressed, which results in poor wettability between graphite and aluminum liquid. The amount of graphite participating in the reaction is very small, and TiC particles cannot be formed.

[0056] Comparative Example 3

[0057] The method described in this embodiment is the same as that in embodiment 1, except that the titanium powder is replaced with titanium nitride powder, which is directly mixed with graphite powder and pure aluminum powder, pressed and added to step (4). The specific steps are as follows:

[0058] (1) Prepare the required raw materials according to the following mass percentages: titanium nitride powder (size less than 1 μm) 4.00%, graphite powder (size less than 20 μm) 1.00%, pure aluminum powder (size less than 50 μm) 3.50%, and pure aluminum ingot 91.50%.

[0059] (2) Titanium nitride powder, graphite powder and pure aluminum powder were fully mixed in a V-type mixer and then pressed into a preform on a briquetting machine at a pressure of 50 MPa.

[0060] (3) The pure aluminum ingot weighed in (1) is melted at 720°C, and then the temperature is raised to 1000°C. The pressed block prepared in (2) is added and fully melted and stirred. Then, a refining agent is pressed into the melt for refining, and argon gas is introduced for degassing and slag removal. Finally, the melt is cast into a metal mold to obtain an Al-5TiC master alloy.

[0061] Compared with the Al-5TiC master alloy prepared in Example 3, TiC and unreacted TiN coexist in the structure; by adding the master alloy with a TiC addition amount of 0.15wt% to the Al-4.5Cu alloy, the grain size is reduced from 500μm to 260μm, which is weaker than the grain refinement effect of the master alloy prepared in Example 1.

Claims

1. A method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy, characterized in that: The specific steps include: (1) Nitriding treatment of titanium powder: Place the titanium powder in an atmosphere furnace, introduce nitrogen into the furnace for 10 min, then raise the furnace temperature to 480-650°C, control the nitrogen flow rate to 0.1-1.0 L / min, keep the temperature for 0.5-2 h, and then cool to room temperature to obtain titanium powder with nitrogen atoms solid dissolved in a close-packed hexagonal titanium matrix; (2) Preparation of mixed powder preforms: The titanium powder, graphite powder and pure aluminum powder obtained in step (1) are fully mixed in a mixer, and then pressed into a preform on a briquetting machine at a pressure of 20-70 MPa; (3) Preparation of master alloy: pure aluminum ingot is melted, then the temperature is raised to 1000-1250℃, prefabricated blocks are added and fully melted and stirred, then a refining agent is pressed into the melt for refining and argon gas is introduced for degassing and slag removal, and finally cast into a metal mold to obtain a master alloy; The master alloy includes an aluminum matrix and TiC dispersed on the aluminum matrix. N particles, the TiC N It is formed when N atoms occupy the C vacancies in TiC crystals, and has the same crystal structure as TiC.

2. The method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy according to claim 1, characterized in that: In step (2), the size of the titanium powder is less than 50 μm, and the particle size of the pure aluminum powder is less than 50 μm.

3. The method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy according to claim 1, characterized in that: In step (2), the mass of pure aluminum powder is m1, the mass of titanium powder is m2, and the mass of graphite powder is m3. The percentage of aluminum powder in the total weight of the powder is m1 / (m1+m2+m3)*100%=60~90%.

4. The method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy according to claim 1, characterized in that: The purity of the graphite powder in step (3) is greater than 99.9% and the particle size is less than 20 μm.

5. The method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy according to claim 1, characterized in that: TiC N By TiC x N y Indicates that, among them, 0.68 <x<0.73,0.05<y<0.25。 6. The method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy according to claim 1, characterized in that: The TiC N The particle size is submicron, less than 1µm, TiC N The mass percentage of the particles is 5wt.%~20wt.%.

7. The method for preparing a multifunctional aluminum-based nitrogen-doped titanium carbide master alloy according to claim 1, characterized in that: The content of Ti in the master alloy is 3.8wt.%~16.5wt.%, the content of C is 0.8wt.%~4.2wt.%, the content of N is 0.03wt.%~1.2wt.%, and the rest is Al and unavoidable impurity elements.

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