High-toughness low-heat-cracking Al-Zn-Mg-Cu series semi-solid die-casting aluminum alloy and preparation method thereof

Abstract

The application belongs to the technical field of metal materials, and particularly discloses a high-strength and high-toughness low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-casting aluminum alloy and a preparation method thereof; the alloy comprises the following components in percentage by weight: Zn: 4-10%; Mg: 2-6%; Cu: 1-4%; Mn: 0.3-0.5%; Zr: 0.01-0.20%; rare earth element RE: 0.01-0.25%; Ti: 0.01-0.20%; B: 0.01-0.20%; Be: 0.01-0.10%, total amount of other impurities is ≤0.30%, and the balance is Al; the mass ratio of the Zr element to the RE element is 1:1; and the rare earth element is one or a combination of multiple of Sc, Er, Ce, Y and La. The alloy can have high strength, high toughness, low thermal cracking capacity and low process cost under the premise of ensuring good casting performance, and meets the application requirements of complex structural parts in the lightweight industry.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, specifically to a high-strength, high-toughness, low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy and its preparation method. Background Technology

[0002] The rapid development of new energy vehicles has placed higher demands on automotive components, making "larger size, greater complexity, thinner walls, and higher performance" important directions for lightweight development. 7xxx series Al-Zn-Mg-Cu alloys, due to their high specific strength, toughness, and good machinability, have been widely used in transportation and other fields. However, Al-Zn-Mg-Cu alloys have a wide solidification range and poor casting performance. Castings often contain numerous defects such as hot cracks, porosity, and segregation, which reduce casting performance and thus greatly limit their application in large, thin-walled, complex structural components.

[0003] Chinese patent application CN102127665A discloses an Al-Zn-Mg-Cu-Sc-Zr-RE alloy and its preparation method that can be used as an ultra-high strength cast aluminum alloy. The chemical composition of this alloy, by mass percentage, includes the following elements: Zn 7.0-8.0%, Mg 1.5-2.5%, Cu 1.4-2.0%; Mn 0.2-0.5%; Sc 0.15-0.25%; Zr 0.10-0.20%; Er and / or Yb 0.1-0.3%, with the balance being Al. This aluminum alloy reduces the tendency for hot cracking by adopting higher Zn and Mg contents, composite microalloying of Sc and Zr, and the addition of trace amounts of rare earth elements Er and / or Yb. However, it has the following drawbacks: it requires long-term temperature-controlled homogenization, strengthening solution treatment, and aging treatment to obtain high strength and toughness properties, making the process relatively complex and unsuitable for industrial mass production.

[0004] Therefore, how to develop aluminum alloy materials that balance low thermal cracking tendency, high toughness, and low processing cost has become a problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength, high-toughness, low-hot-cracking semi-solid die-cast aluminum alloy and its preparation method. While ensuring good casting performance, it solves the problem that existing aluminum alloys cannot simultaneously achieve high strength, high toughness, low hot-cracking ability, and low processing cost. This broadens the application scenarios of die-cast aluminum alloys, allowing them to be used in structural or heat-resistant components, replacing traditional steel or die-cast aluminum alloys (such as A380), and improving my country's lightweight technology level.

[0006] To achieve this objective, this invention, in its research on 7xxx series aluminum alloys, discovered that the composite addition of Zr and RE elements to the alloy causes compositional supercooling during the solidification process of the aluminum alloy melt, refines the grains, improves fluidity, and reduces the tendency of ingots to hot crack. Furthermore, the addition of Zr and RE elements forms more low-melting-point phases, which form a liquid film at the end of solidification, enhancing the alloy's ability to resist intergranular segregation. These factors reduce the alloy's tendency to hot crack and improve its casting performance. Under similar testing conditions, the high-strength and high-toughness cast aluminum alloy prepared by this invention exhibits 40-80% higher fluidity and a 60-80% lower hot crack sensitivity index compared to traditional high-strength cast aluminum alloys such as ZL201A and ZL205A.

[0007] Furthermore, by adding a small amount of Al-Ti-B master alloy to the above-mentioned aluminum alloy, the present invention prolongs the existence time of nucleation particles in the aluminum melt, improves the sedimentation behavior of particles, significantly refines the ingot grains, and improves the alloy casting performance.

[0008] In terms of process, this invention employs a semi-solid die casting process. Semi-solid die casting can significantly reduce the shrinkage of molten metal in the casting cavity, while simultaneously refining the alloy's grain structure, transforming it from coarse columnar crystals to fine equiaxed crystals or even spherical crystals. This improves the alloy's feeding ability and reduces its tendency to hot cracking. Therefore, using semi-solid die casting to prepare Al-Zn-Mg-Cu alloys can yield aluminum alloy materials with both good formability and excellent mechanical properties, helping to solve the "forming" and "property" problems in the production process of complex, large, thin-walled die-cast aluminum alloy parts.

[0009] More specifically, this invention employs an eccentric rotation semi-solid die-casting process. During the semi-solid process, the eccentric rotation in the rotational thermal equilibrium method can force convection and shearing of the aluminum alloy melt, thereby making the temperature field and solute distribution inside the slurry more uniform. Furthermore, when the shearing effect generated by the eccentric rotation is strong enough, it can break dendrites in the aluminum alloy melt, resulting in a more rounded semi-solid slurry. At relatively high rotational speeds, although the nucleation generated by rapid cooling can be distributed relatively uniformly inside the slurry through convection, the heat dissipation of the aluminum alloy melt is rapid at lower casting temperatures. The semi-solid slurry easily forms a solidified layer on the inner wall surface of the crucible, thereby reducing convection within the slurry and preventing heterogeneous nucleation on the crucible wall. Therefore, the number of primary crystal nuclei in the slurry will be reduced to a certain extent. As a result, during the subsequent slow cooling process, there is more space for grain growth and the intensity of competition decreases, thus merging and growing into larger rosettes. This effectively avoids the problems of decreased mechanical properties and increased brittleness of the alloy that may be caused by dendrites, which would affect its performance and safety. This gives the alloy better strength and toughness.

[0010] Accordingly, the technical solution adopted by the present invention is as follows:

[0011] In a first aspect, the present invention provides a high-strength, high-toughness, low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy, wherein the weight percentages of each component in the die-cast aluminum alloy are as follows: Zn: 4-10%; Mg: 2-6%; Cu: 1-4%; Mn: 0.3-0.5%; Zr: 0.01-0.20%; rare earth element RE: 0.01-0.25%; Ti: 0.01-0.20%; B: 0.01-0.20%; Be: 0.01-0.10%; the total amount of other impurities is ≤0.30%; and the balance is Al.

[0012] Preferably, the mass ratio of Zr to RE elements is 1:1; the rare earth elements are one or more combinations of Sc, Er, Ce, Y, and La. A Zr to RE mass ratio of 1:1 provides the best strength-toughness match. A mass ratio greater than 1 results in increased strength but decreased plasticity; a ratio less than 1 results in insignificant grain refinement.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy, the method comprising the following steps:

[0014] S1. Material preparation: Prepare the aluminum alloy according to the composition and weight percentage of claim 1; wherein Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg, and Cu, Mn, Zr, RE, Ti, B, and Be are prepared in the form of aluminum-containing master alloys.

[0015] S2. Melting: First, melt pure aluminum, then heat to 740-780℃ and add Al-Zr, Al-Be and Al-RE master alloys, stirring until the melt is clear; cool the melt to 720-750℃, then add Al-Mn and Al-Cu master alloys for melting; after melting, cool to 710-720℃, add pure Zn, and stir until the melt is clear; then, when the melt cools to 670-690℃, add pure Mg and press it into the bottom area of ​​the crucible for melting;

[0016] S3, Refining: Heat the melt from step S2 to 740-760℃, introduce gas containing refining agent powder into the melt for powder spraying refining and slag removal treatment, let it stand for 15-30 minutes, and skim off the slag on the surface of the melt; then, when the melt temperature is 710-720℃, add Al-Ti-B master alloy for refining and modification treatment, and immediately prepare for the die casting process after treatment;

[0017] S4. Die Casting: This is a semi-solid die casting process performed by eccentrically rotating the melt after refining and slag removal in step S3, ultimately producing the semi-solid die casting. Step S4 can also be replaced by casting alloy ingots to produce alloy ingots.

[0018] Preferably, step S1 further includes a step of preheating the prepared raw materials to 180-240°C for drying.

[0019] Preferably, step S2 further includes the following steps: after the melt is stirred evenly, it is allowed to stand and a pre-furnace composition analysis is performed to detect the composition content of the alloy melt. For melts with deviations in content, additional material is added or diluted to bring the composition to a qualified range.

[0020] Preferably, in step S3, the refining agent is a salt flux that does not contain Na ions.

[0021] Preferably, in step S3, the amount of refining agent added is 0.3-1.2% of the total weight of the melt.

[0022] Preferably, in step S4, when using the semi-solid die casting process to produce semi-solid die castings, the pouring temperature is 640-660℃.

[0023] Preferably, in step S4, when using the semi-solid die-casting process to produce semi-solid die-cast parts, the rotational speed range of the eccentric rotation is 80-180 r / min. -1 .

[0024] Preferably, in step S4, when using the semi-solid die casting process to produce semi-solid die castings, the rotation time range of the eccentric rotation is 60-120s.

[0025] Preferably, in step S4, when using the semi-solid die casting process to produce semi-solid die castings, the injection speed range is 2.5-5 m / s.

[0026] Preferably, in step S4, when using the semi-solid die casting process to produce semi-solid die castings, the casting pressure range is 60-150 MPa.

[0027] The present invention has the following beneficial effects:

[0028] 1. The aluminum alloy described in this invention, through the composite addition of Zr and RE elements, causes compositional supercooling during the solidification process of the aluminum alloy melt, refines the grains, improves fluidity, and reduces the tendency of ingot hot cracking. By adding an Al-Ti-B master alloy, the existence time of nucleation particles in the aluminum melt is prolonged, the sedimentation behavior of particles is improved, and the ingot grains are significantly refined, thereby improving the alloy casting performance.

[0029] 2. The semi-solid die casting process with eccentric rotation described in this invention is used to produce aluminum alloy die castings, which further reduces the tendency of ingots to hot crack. Compared with the prior art, it can obtain high strength and toughness without the need for long-term temperature homogenization, strengthening solution treatment and aging treatment. The process is simpler, the production cost is reduced, and it is suitable for industrial mass production.

[0030] 3. The aluminum alloy obtained by this invention has high toughness and low hot cracking performance. The yield strength of the die-cast aluminum alloy in the semi-solid die-cast state is 420-430MPa, the tensile strength is 470-480MPa, the elongation is 8-11%, and the crack sensitivity index (CSI) is 1000-6100. Attached Figure Description

[0031] Figure 1 The SEM structure of the semi-solid die-cast aluminum alloy part in Embodiment 1 of the present invention.

[0032] Figure 2 These are micrographs of die-cast aluminum alloy parts from Examples 1, 3, 5, and Comparative Example 1 of the present invention. (a)-(d) correspond to Examples 1, 3, 5, and Comparative Example 1, respectively.

[0033] Figure 3 Examples 1-8 of this invention illustrate the hot cracking tendency of alloy 1 in Comparative Example 1. Wherein, 1# is a comparative example, and 2-8# correspond to Examples 1-8 respectively. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0035] Example 1

[0036] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are: Zn: 4%; Mg: 2%; Cu: 2%; Mn: 0.4%; Zr: 0.1%; RE(La): 0.1%; Ti: 0.1%; B: 0.1%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0037] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0038] S2. Preheat the crucible to 150℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0039] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0040] S4. After refining, the melt is allowed to stand for 10 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃, with an eccentric rotation time of 80 seconds and a rotation speed of 120 r / min. -1 Then, die casting is carried out at an injection speed of 4 m / s and a casting pressure of 90 MPa.

[0041] Example 2

[0042] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are as follows: Zn: 6%; Mg: 4%; Cu: 4%; Mn: 0.3%; Zr: 0.15%; RE(La): 0.15%; Ti: 0.15%; B: 0.15%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0043] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0044] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0045] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0046] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃, with an eccentric rotation time of 60 seconds and a rotation speed of 80 r / min. -1 Then, die casting is carried out, with an injection speed of 4m / s and a casting pressure of 150MPa.

[0047] Example 3

[0048] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are as follows: Zn: 10%; Mg: 6%; Cu: 4%; Mn: 0.5%; Zr: 0.2%; RE (Er): 0.2%; Ti: 0.2%; B: 0.2%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0049] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0050] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0051] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0052] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃, with an eccentric rotation time of 120 seconds and a rotation speed of 180 r / min. -1 Then, die casting is carried out at an injection speed of 5 m / s and a casting pressure of 60 MPa.

[0053] Example 4

[0054] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are as follows: Zn: 10%; Mg: 2%; Cu: 1%; Mn: 0.3%; Zr: 0.1%; RE(La): 0.1%; Ti: 0.1%; B: 0.1%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0055] S1. Prepare the materials according to the aluminum alloy composition and weight percentage. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. Preheat the raw materials to 200℃ and dry them.

[0056] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0057] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0058] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃, with an eccentric rotation time of 60 seconds and a rotation speed of 100 r / min. -1 Then, die casting is carried out at an injection speed of 5 m / s and a casting pressure of 70 MPa.

[0059] Example 5

[0060] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are as follows: Zn: 7%; Mg: 3%; Cu: 3%; Mn: 0.3%; Zr: 0.15%; RE (Er): 0.15%; Ti: 0.15%; B: 0.15%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0061] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0062] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0063] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0064] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃ with an eccentric rotation time of 100 seconds and a rotation speed of 120 r / min. -1 Then, die casting is carried out at an injection speed of 2.5 m / s and a casting pressure of 90 MPa.

[0065] Example 6

[0066] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are: Zn: 8%; Mg: 6%; Cu: 3%; Mn: 0.4%; Zr: 0.1%; RE(Sc): 0.1%; Ti: 0.1%; B: 0.1%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0067] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0068] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0069] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0070] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. If the composition is qualified, the pulping process is carried out at 650℃, with a rotation time of 100 seconds and a rotation speed of 100 r / min. -1 Then, die casting is carried out at an injection speed of 4 m / s and a casting pressure of 90 MPa.

[0071] Example 7

[0072] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are: Zn: 4%; Mg: 2%; Cu: 1%; Mn: 0.3%; Zr: 0.1%; RE(Ce): 0.1%; Ti: 0.1%; B: 0.1%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0073] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0074] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0075] S3. Heat the melt to 740°C, introduce a refining agent containing 1% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment, let it stand for 20 minutes, and skim off the slag on the surface of the melt; then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0076] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃, with an eccentric rotation time of 80 seconds and a rotation speed of 120 r / min. -1 Then, die casting is carried out, with an injection speed of 4m / s and a casting pressure of 120MPa.

[0077] Example 8

[0078] This embodiment provides a high-strength, high-toughness, low-hot-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy. The weight percentages of the components in this aluminum alloy are: Zn: 4%; Mg: 6%; Cu: 1%; Mn: 0.3%; Zr: 0.1%; RE(La): 0.1%; Ti: 0.1%; B: 0.1%; Be: 0.1%, with the total amount of other impurities ≤ 0.30%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0079] S1. Prepare materials according to the composition and weight percentage of the aluminum alloy. Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg. Cu, Mn, Zr, RE, Ti, B, and Be are prepared as aluminum-containing master alloys. The raw materials are preheated to 200℃ and dried.

[0080] S2. Preheat the crucible to 160℃, evenly coat the inner wall of the crucible with a coating, dry it, and then heat it to 460℃. Add pure aluminum, then raise the temperature to 750℃ and add Al-Zr, Al-Be, and Al-RE master alloys, stirring until the melt is clear. Cool the melt to 730℃, then add Al-Mn and Al-Cu master alloys to melt it. After melting, cool it to 710℃, add pure Zn, and stir until the melt is clear. Then, when the melt cools to 680℃, add pure Mg and press it into the bottom area of ​​the crucible to melt it. After melting and stirring evenly, let it stand and perform pre-furnace composition analysis to detect the composition content of the alloy melt. For melts with deviations in content, add material or dilute it to bring the composition to the qualified range.

[0081] S3. Heat the melt to 750°C, and introduce a refining agent containing 0.8% of the total weight of the melt into the melt for powder spraying refining and slag removal treatment. After standing for 20 minutes, skim off the slag on the surface of the melt. Then, when the melt temperature is 710°C, add Al-Ti-B master alloy for refining and modification treatment.

[0082] S4. After refining, the melt is allowed to stand for 15 minutes, and then a pre-furnace composition analysis is performed. Once the composition is deemed acceptable, the pulping process is carried out at 650℃, with an eccentric rotation time of 90 seconds and a rotation speed of 100 r / min. -1 Then, die casting is carried out at an injection speed of 2.5 m / s and a casting pressure of 90 MPa.

[0083] Comparative Example 1

[0084] This comparative example provides an Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy, which is basically the same as Example 1, except that Zr and RE are not added in this comparative example.

[0085] Comparative Example 2

[0086] This comparative example provides an Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy, which is basically the same as Example 1, except that Al-Ti-B is not added in this comparative example.

[0087] Performance testing

[0088] 1. Characterization

[0089] The microstructure of the die-cast aluminum alloy part obtained in the example is shown in the figure below. Figure 1-2 As shown, the structure is dense with no obvious defects. In contrast, Comparative Example 1, which did not contain Zr and RE elements, has significantly coarser grains.

[0090] 2. Tendency to thermal cracking

[0091] Examples 1-8, Comparative Example 1 alloy hot cracking tendency test results are as follows: Figure 3As shown, compared with Comparative Example 1, the thermal cracking tendency CSI values ​​of Examples 1-8 are significantly reduced, and the addition of Zr and RE elements effectively reduces the thermal cracking tendency.

[0092] 3. Strength and toughness

[0093] The performance test results of the die-cast aluminum alloy parts obtained in each embodiment and comparative example are summarized in Table 1. The room temperature tensile properties were tested according to the methods in GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature". It can be seen that the addition of Zr, RE, and Al-Ti-B all improve both strength and toughness.

[0094] Table 1

[0095]

[0096]

[0097] In summary, the alloy of this invention, through optimized formulation design and preparation methods, successfully reduces the tendency for hot cracking, making it more suitable for use in high-temperature environments. The alloy of this invention utilizes a semi-solid die-casting process to achieve more precise casting shapes and superior mechanical properties, while simultaneously reducing production costs and energy consumption. It possesses excellent mechanical properties, meeting the application requirements of complex structural components in the lightweight industry.

[0098] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A high-strength, high-toughness, low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy, characterized in that, The weight percentages of each component in the die-cast aluminum alloy are as follows: Zn: 4-10%; Mg: 2-6%; Cu: 1-4%; Mn: 0.3-0.5%; Zr: 0.01-0.20%; rare earth element RE: 0.01-0.25%; Ti: 0.01-0.20%; B: 0.01-0.20%; Be: 0.01-0.10%; the total amount of other impurities is ≤0.30%, and the balance is Al; in the composition of the die-cast aluminum alloy, the mass ratio of Zr to RE is 1:1; the rare earth element is one or more combinations of Sc, Er, Ce, Y, and La; The aluminum alloy in the die-cast state has a yield strength of 420-430MPa, a tensile strength of 470-480MPa, an elongation of 8-11%, and a crack sensitivity index of 1000-6100. The preparation method of this aluminum alloy includes the following steps: S1. Material preparation: Prepare materials according to the aluminum alloy composition and weight percentage; among them, Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg, while Cu, Mn, Zr, RE, Ti, B, and Be are prepared in the form of aluminum-containing master alloys. S2. Melting: First, melt pure aluminum, then heat to 740-780℃ and add Al-Zr, Al-Be and Al-RE master alloys, stirring until the melt is clear; cool the melt to 720-750℃, then add Al-Mn and Al-Cu master alloys for melting; after melting, cool to 710-720℃, add pure Zn, and stir until the melt is clear; then, when the melt cools to 670-690℃, add pure Mg and press it into the bottom area of ​​the crucible for melting; S3, Refining: Heat the melt from step S2 to 740-760℃, introduce gas containing refining agent powder into the melt for powder spraying refining and slag removal treatment, let it stand for 15-30 minutes, and skim off the slag on the surface of the melt; then, when the melt temperature is 710-720℃, add Al-Ti-B master alloy for refining and modification treatment, and immediately prepare for the die casting process after treatment; S4. Die Casting: The semi-solid die casting process involves eccentric rotation of the melt after refining and slag removal in step S3 to finally complete the production of semi-solid die castings. When using the semi-solid die casting process to produce semi-solid die castings, the pouring temperature is 640-660℃, the rotation speed range of the eccentric rotation is 80-180r / min, the rotation time range of the eccentric rotation is 60-120s, the injection speed range is 2.5-5m / s, and the casting pressure range is 60-150MPa.

2. The high-strength, high-toughness, low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy according to claim 1, characterized in that, Step S1 also includes a step of preheating the prepared raw materials to 180-240°C and then drying them.

3. The high-strength, high-toughness, low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy according to claim 1, characterized in that, Step S2 further includes the following steps: after the melt is stirred evenly, it is allowed to stand and a pre-furnace composition analysis is performed to detect the composition content of the alloy melt. For melts with deviations in content, additional material is added or diluted to bring the composition to the qualified range.

4. The high-strength, high-toughness, low-thermal-cracking Al-Zn-Mg-Cu semi-solid die-cast aluminum alloy according to claim 1, characterized in that, In step S3, the refining agent is a salt flux that does not contain Na ions.

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