A grain refining method for A356 cast aluminum alloy based on secondary stirring of Al-Nb-B-Ce refiner

Abstract

The application relates to an A356 casting aluminum alloy grain refining method based on secondary stirring of an Al-Nb-B-Ce refiner, and belongs to the aluminum alloy casting technical field. The grain refining method comprises the following steps: (1) adding an Al-Nb-B-Ce refiner into A356 casting aluminum alloy melt at a certain temperature in an argon atmosphere, and performing first stirring; after the first stirring in the step (1) is completed, the melt is subjected to standing and heat preservation; after the standing and heat preservation in the step (2), the melt temperature is kept unchanged, second stirring is performed, and after the stirring is completed, the A356 casting aluminum alloy grain refining is completed. By adding the refiner which has the functions of resisting silicon poisoning, grain refining and good modification into the A356 casting aluminum alloy and combining the secondary stirring process, the A356 casting aluminum alloy grain refining effect is remarkably improved.

Description

Technical Field

[0001] This invention relates to a method for refining the grain size of A356 cast aluminum alloy based on secondary stirring with an Al-Nb-B-Ce grain refiner, belonging to the field of aluminum alloy casting technology. Background Technology

[0002] A356 cast aluminum alloy is widely used in transportation, aerospace, and other fields due to its excellent casting properties, good corrosion resistance, low casting manufacturing cost, and ease of forming. Examples include automotive parts such as aluminum alloy wheels, engine parts, and chassis, as well as aircraft pumps and components, and aircraft connectors. Grain refinement, as a way to improve the mechanical properties of cast aluminum alloys, can simultaneously improve the material's strength, toughness, and ductility.

[0003] Currently, the common practice is to add Al-TCB seed alloys and Al-Sr master alloys to cast aluminum alloy A356 to achieve grain refinement. However, the grain refinement effect is limited, and there is still room and necessity for further improvement. Furthermore, since A356 cast aluminum alloy contains Si and Al-TCB refiners contain Ti, during the heat treatment process, Si separates to the surface of TiB2 particles and dissolves into TiAl3, forming Ti-Si covalent bonds in TiAl3. This makes it difficult for α-Al grains to nucleate on Si-doped TiAl3, leading to silicon poisoning.

[0004] Therefore, it is necessary to provide a method for refining the grains of A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce refining agent, so as to improve the grain refining effect of A356 cast aluminum alloy while avoiding the problem of silicon poisoning. Summary of the Invention

[0005] To overcome the problems in the prior art, this invention proposes a grain refinement method for A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce grain refiner. By employing a secondary stirring process, the number density of effective nucleation particles in the A356 cast aluminum alloy melt is increased, thereby improving the grain refinement effect of the A356 cast aluminum alloy. By using Nb element instead of Ti element, it not only resists silicon poisoning but also fully utilizes the heterogeneous nucleation effect of Al3Nb and NbB2, resulting in good grain refinement effect of A356 cast aluminum alloy.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] The grain refinement method includes the following steps:

[0008] (1) In an argon atmosphere, Al-Nb-B-Ce refining agent is added to the A356 cast aluminum alloy melt at a certain temperature and stirred for the first time.

[0009] (2) After the first stirring in step (1) is completed, the melt is kept still and kept warm.

[0010] (3) After standing and keeping warm in step (2), keep the melt temperature unchanged and stir for the second time. After stirring, the grain refinement of A356 cast aluminum alloy is completed.

[0011] Adding an Al-Nb-B-Ce grain refiner to the A356 cast aluminum alloy melt releases Al3Nb, NbB2, and CeO2 particles, resulting in the formation of second-phase nucleation particles Al3Nb and NbB2 in the melt. However, since the densities of Al3Nb and NbB2 are greater than those of Al, these particles tend to settle at the bottom of the melt during the holding process, reducing the number of nucleation-active second-phase particles and affecting the grain refinement of the A356 cast aluminum alloy. Therefore, secondary stirring allows the second-phase nucleation particles settled at the bottom of the melt to be resuspended, increasing the number and density of effective nucleation particles in the melt. Furthermore, secondary stirring also breaks down and disperses the second-phase nucleation particles in the melt, thereby improving the grain refinement of the A356 cast aluminum alloy.

[0012] After the grain refiner releases Al3Nb, NbB2, and CeO2 particles dispersed in the melt, Al3Nb coats the surface of NbB2 particles, forming Al3Nb / NbB2 composite particles. Because Al3Nb particles have a lower lattice mismatch with α-Al compared to NbB2 particles, they promote α-Al nucleation on the Al3Nb particle surface. Furthermore, the reaction between liquid aluminum and Al3Nb generates Al, thus achieving grain refinement. Simultaneously, CeO2 particles dispersed in the melt are reduced by Al to Ce. Due to the selective adsorption properties of Ce atoms, they can adsorb onto the surface of the Al3Nb / NbB2 composite particles, forming Nb2Al. 20 Ce / NbB2 composite particles, due to Nb2Al 20 Ce / NbB2 composite particles can act as a heterogeneous nucleation substrate for α-Al during the solidification of molten aluminum, thereby further refining the grain size.

[0013] In unmodified A356 cast aluminum alloys, twins with a certain angle often exist in the silicon phase. In modified alloys, modified atoms are adsorbed in the twin grooves of the silicon phase and do not completely migrate with the solid-liquid interface. A considerable number of modified atoms are embedded in the silicon phase lattice, causing lattice distortion. This distortion transforms the eutectic silicon from a coarse needle-like or lamellar structure to a fine granular structure. Therefore, in the production process of A356 cast aluminum alloys, modification treatment can improve and refine the microstructure. Atomic radius is the primary condition for measuring the modifying ability of the modifier. i / r si≈1.65 (where r) i r is the radius of the atom that has undergone metamorphism. si The modifier's modifying ability is optimal when the ratio of the modifier's atomic radius to the silicon atomic radius is close to 1.65. Ce has an atomic radius of 0.188 nm, and Si has an atomic radius of 0.143 nm. The ratio of their atomic radii is approximately 1.31, which is close to 1.65. The addition of Ce can achieve the modification treatment of A356 cast aluminum alloy.

[0014] When a Ti-containing refining agent is added to A356 cast aluminum alloy, TiAl3 undergoes a dissolution reaction, and TiB2 becomes a heterogeneous nucleation particle of α-Al. As the temperature decreases, TiAl3 regenerates on the surface of TiB2. At this time, Si in the melt becomes free and migrates to the surface of the TiB2 particles coated with TiAl3, forming Ti-Si covalent bonds with TiAl3. This makes it difficult for α-Al grains to nucleate and grow on the Si-doped TiAl3. Therefore, the addition of a Ti-containing refining agent can easily lead to silicon poisoning in A356 cast aluminum alloy. However, since Nb is more stable than Ti in Al-Si melt, Nb will not react with Si. Therefore, using Nb instead of Ti allows the heterogeneous nucleation effects of Al3Nb and NbB2 to be fully utilized.

[0015] Preferably, in step (1), the amount of Al-Nb-B-Ce refining agent added is 0.5wt% of the A356 cast aluminum alloy melt, the first stirring speed is 500r / min, the stirring time is 5min, and the temperature of the A356 cast aluminum alloy melt is 700℃.

[0016] Preferably, in step (2), the static heat preservation temperature is 700℃ and the heat preservation time is 10-60min.

[0017] Preferably, in step (3), the second stirring speed is 500-700 r / min and the stirring time is 25-35 s.

[0018] Preferably, the Al-Nb-B-Ce refining agent is prepared by in-situ reaction of high-energy ball milling, ball milling mixing, cold pressing, and hot extrusion. The specific preparation method includes the following steps:

[0019] S1: Al powder and Nb powder are mixed and Al3Nb powder is prepared by in-situ reaction through high-energy ball milling.

[0020] S2: Take Al powder, NbB2 powder, CeO2 powder and Al3Nb powder prepared in step S1 and ball mill them together to obtain a mixed powder.

[0021] S3: The mixed powder obtained in step S2 is cold-pressed to obtain a cold-pressed blank.

[0022] S4: The cold-pressed billet obtained in step S3 is hot-extruded to obtain rod-shaped Al-Nb-B-Ce refining agent.

[0023] Hot extrusion can effectively break up the agglomeration of the grain refiner, improve the uniformity of the matrix structure, and make the second phase nucleation particles in the Al-Nb-B-Ce grain refiner fine and dispersed, thereby improving the dispersibility of the second phase nucleation particles Al3Nb and NbB2 in the melt and refining the grains.

[0024] Preferably, in step S1, the mass ratio of Al powder to Nb powder is 46.6:53.4, the particle size of Al powder is 10 μm, the particle size of Nb powder is 5 μm, the ball-to-material ratio of the high-energy ball mill in-situ reaction is 20:1, the rotation speed of the high-energy ball mill is 300 r / min, and the in-situ reaction time of the high-energy ball mill is 10 h.

[0025] Preferably, in step S2, the mass ratio of Al powder, Al3Nb powder, NbB2 powder, and CeO2 powder is 86.3:7.7:4.5:1.5, the particle size of Al powder is 10 μm, the particle size of Al3Nb powder is 500 nm, the particle size of NbB2 powder is 500 nm, the particle size of CeO2 powder is 1 μm, the ball-to-particle ratio of the ball milling mixture is 5:1, the ball milling speed is 150 r / min, and the ball milling time is 1 h.

[0026] Preferably, in step S3, the cold pressing pressure is 500 MPa, and the pressure is maintained for 10 minutes.

[0027] Preferably, in step S4, the hot extrusion temperature is 500°C and the extrusion ratio is 30.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention addresses the characteristic of Al-Nb-B-Ce refining agents forming second-phase nucleation particles Al3Nb and NbB2. By secondary stirring of the melt after static holding, the second-phase nucleation particles in the melt are resuspended in the melt and broken down and dispersed in the melt, increasing the number density of effective nucleation particles in the melt and improving the grain refinement effect of A356 cast aluminum alloy. The grain size of A356 cast aluminum alloy can be refined to 91-178.9μm, and the eutectic silicon size can be modified to 3-5μm.

[0030] 2. By adding an Al-Nb-B-Ce grain refiner that has both anti-silicon poisoning, grain refinement, and good modification effects, the second-phase nucleation particles are not affected by silicon poisoning and can fully exert their heterogeneous nucleation effect, which helps to improve the grain refinement effect of A356 cast aluminum alloy.

[0031] 3. This invention obtains an Al-Nb-B-Ce refining agent with finely dispersed second-phase nucleation particles through hot extrusion. After the refining agent is added to the A356 aluminum alloy melt, the second-phase nucleation particles are better dispersed in the melt, further improving the crystal refining effect of the A356 aluminum alloy. Attached Figure Description

[0032] Figure 1 This is a flow chart of the Al-Nb-B-Ce grain refiner preparation and A356 cast aluminum alloy grain refinement process of the present invention.

[0033] Figure 2 This is a diagram showing the grain refinement effect of A356 cast aluminum alloy with different secondary stirring times according to the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments.

[0035] Example 1

[0036] In this embodiment, the Al-Nb-B-Ce refining agent was prepared by the following method:

[0037] (1) Al powder with a particle size of 10 μm and Nb powder with a particle size of 5 μm were selected and subjected to high-energy ball milling in situ reaction for 10 h at a mass ratio of 46.6:53.4. The ball-to-material ratio of the high-energy ball milling in situ reaction was 20:1 and the ball milling speed was 300 r / min. After the high-energy ball milling in situ reaction, Al3Nb powder was obtained.

[0038] (2) Select Al powder with a particle size of 10μm, Al3Nb powder with a particle size of 500nm, NbB2 powder with a particle size of 500nm, and CeO2 powder with a particle size of 1μm. Mix them by ball milling in a mass ratio of Al powder:Al3Nb powder:NbB2 powder:CeO2 = 86.3:7.7:4.5:1.5. The ball-to-material ratio of the ball milling mixture is 5:1. The ball milling speed is 150r / min and the ball milling time is 1h. After ball milling, Al-Nb-B-Ce mixed powder is obtained.

[0039] (3) The Al-Nb-B-Ce mixed powder obtained in step (2) is placed in a cold pressing mold, and Al-Nb-B-Ce cold pressing blank is obtained under the conditions of cold pressing pressure of 500MPa and holding time of 10min.

[0040] (4) The Al-Nb-B-Ce cold-pressed billet obtained in step (3) is hot-extruded at 500°C and an extrusion ratio of 30 to obtain rod-shaped Al-Nb-B-Ce refining agent.

[0041] In this embodiment, the Al-Nb-B-Ce grain refiner prepared by the above method is used to refine the grains of A356 cast aluminum alloy. The specific method is as follows:

[0042] (1) Under argon atmosphere, 0.5wt% of Al-Nb-B-Ce refining agent was added to the A356 cast aluminum alloy melt at 700℃, and then the mixture was stirred for the first time at a stirring speed of 500r / min for 5min.

[0043] (2) After the first stirring is completed, the melt is kept at 700℃ for 10 minutes.

[0044] (3) After the static heat preservation is completed, the melt temperature is kept at 700℃ and a second stirring is carried out. The stirring speed is 500r / min and the stirring time is 25s to obtain A356 cast aluminum alloy with an average grain size of 178.9μm and a eutectic silicon size of 5μm.

[0045] Example 2

[0046] This embodiment uses the same method as Example 1 to prepare the Al-Nb-B-Ce grain refiner and refine the grains of A356 cast aluminum alloy. The difference is that in this embodiment, the standing temperature holding time is 20 min, the second stirring speed is 550 r / min, and the second stirring time is 28 s. The average grain size of the A356 cast aluminum alloy obtained in this embodiment is 149.6 μm, and the eutectic silicon size is 4.5 μm.

[0047] Example 3

[0048] This embodiment uses the same method as Example 1 to prepare the Al-Nb-B-Ce grain refiner and refine the grains of the A356 cast aluminum alloy. The difference is that in this embodiment, the standing temperature holding time is 30 min, the second stirring speed is 600 r / min, and the second stirring time is 31 s. The average grain size of the A356 cast aluminum alloy obtained in this embodiment is 108.1 μm, and the eutectic silicon size is 4 μm.

[0049] Example 4

[0050] This embodiment uses the same method as Example 1 to prepare the Al-Nb-B-Ce grain refiner and refine the grains of the A356 cast aluminum alloy. The difference is that in this embodiment, the standing temperature holding time is 60 min, the second stirring speed is 700 r / min, and the second stirring time is 35 s. The average grain size of the A356 cast aluminum alloy obtained in this embodiment is 91 μm, and the eutectic silicon size is 3 μm.

[0051] In summary, adding Al-Nb-B-Ce grain refiners to A356 cast aluminum alloy, combined with secondary stirring, can achieve better grain refinement and modification effects in A356 cast aluminum alloy.

[0052] Finally, it should be noted that the above preferred 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 through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for refining the grain size of A356 cast aluminum alloy based on secondary stirring with an Al-Nb-B-Ce grain refiner, characterized in that: The grain refinement method includes the following steps: (1) In an argon atmosphere, Al-Nb-B-Ce refining agent is added to the A356 cast aluminum alloy melt at a certain temperature and stirred for the first time; In step (1), the amount of Al-Nb-B-Ce refining agent added is 0.5 wt% of the A356 cast aluminum alloy melt; (2) After the first stirring in step (1) is completed, the melt is kept still and kept warm. (3) After standing and keeping warm in step (2), keep the melt temperature unchanged and stir for the second time. After stirring, the grain refinement of A356 cast aluminum alloy is completed. In step (2), the static heat preservation temperature is 700℃ and the heat preservation time is 10-60min; In step (3), the second stirring speed is 500-700 r / min and the stirring time is 25-35 s; The Al-Nb-B-Ce refining agent is prepared by in-situ high-energy ball milling reaction, ball milling mixing, cold pressing, and hot extrusion. The specific preparation method includes the following steps: S1: Al powder and Nb powder are mixed and Al3Nb powder is prepared by in-situ reaction through high-energy ball milling. S2: Take Al powder, NbB2 powder, CeO2 powder and Al3Nb powder prepared in step S1 and ball mill them together to obtain a mixed powder; S3: The mixed powder obtained in step S2 is cold-pressed to obtain a cold-pressed blank; S4: Hot extrusion of the cold-pressed billet obtained in step S3 to obtain rod-shaped Al-Nb-B-Ce refining agent; In step S1, the mass ratio of Al powder to Nb powder is 46.6:53.4, the particle size of Al powder is 10 μm, and the particle size of Nb powder is 5 μm. In step S2, the mass ratio of Al powder, Al3Nb powder, NbB2 powder, and CeO2 powder is 86.3:7.7:4.5:1.

5. The particle size of Al powder is 10 μm, the particle size of Al3Nb powder is 500 nm, the particle size of NbB2 powder is 500 nm, and the particle size of CeO2 powder is 1 μm.

2. The method for grain refinement of A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce grain refiner according to claim 1, characterized in that: In step (1), the first stirring speed is 500 r / min, the stirring time is 5 min, and the temperature of the A356 cast aluminum alloy melt is 700℃.

3. The method for grain refinement of A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce grain refiner according to claim 1, characterized in that: In step S1, the ball-to-material ratio of the high-energy ball mill in-situ reaction is 20:1, the rotation speed of the high-energy ball mill is 300 r / min, and the in-situ reaction time of the high-energy ball mill is 10 h.

4. The method for grain refinement of A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce grain refiner according to claim 1, characterized in that: In step S2, the ball-to-material ratio of the ball mill is 5:1, the ball milling speed is 150 r / min, and the ball milling time is 1 h.

5. The method for grain refinement of A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce grain refiner according to claim 1, characterized in that: In step S3, the cold pressing pressure is 500 MPa, and the pressure is maintained for 10 minutes.

6. The method for grain refinement of A356 cast aluminum alloy based on secondary stirring with Al-Nb-B-Ce grain refiner according to claim 1, characterized in that: In step S4, the hot extrusion temperature is 500°C and the extrusion ratio is 30.

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