A high modulus die-casting aluminum alloy, preparation method and application thereof

Abstract

The invention belongs to the technical field of die-casting aluminum alloys, and specifically discloses a high modulus die-casting aluminum alloy, which is composed of the following elements in mass percentage: Ni: 3.5% to 8.3%, Mn: 2.5 to 5.6%, Cu: 0.5 to 4.2%, Si≤1.0%, Fe≤1.0%, Zr≤0.5%, and the balance is Al and inevitable impurities. The die-casting aluminum alloy includes a matrix and a second phase, and the second phase is a high modulus monoclinic AlNiMnCu quaternary phase that presents a petal-shaped radial shape in the matrix; the quaternary phase significantly increases the elastic modulus of the aluminum alloy, and the alloy regulates the content of each element, effectively reduces the generation of coarse primary metal compounds, increases the fluidity of the melt during the die-casting process, and inhibits the formation of coarse second phases, and significantly improves the yield strength of the material. It has excellent casting fluidity and thermal cracking resistance, and can be applied to thin-walled shells and frame parts that have special requirements for elastic modulus and strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of die-cast aluminum alloys. Specifically, the present invention relates to a high-modulus die-cast aluminum alloy, a preparation method thereof, and its application in thin-walled parts of mobile phone midframes. Background Art

[0002] Die-cast aluminum alloys have been widely used in the fields of automotive parts, electronic products, communications, home appliances, etc. Currently, the commonly used die-cast aluminum alloys are mainly Al-Si and Al-Mg systems. Among them, the die-cast aluminum alloys commonly used in the electronic communications industry are mainly Al-Si system alloys, such as ADC12, etc. These alloys have excellent die-casting fluidity and thermal cracking resistance, and are suitable for manufacturing parts such as housings and brackets. With the rapid development of the electronic communications industry, housings and frame parts are designed to be more lightweight and thin-walled complex structures. For this reason, die-cast aluminum alloy materials are required to have higher stiffness and strength to resist deformation such as bending and impact that may be caused during use, as well as excellent casting properties to meet the forming requirements of thin-walled complex structural parts. However, the stiffness of commonly used die-cast aluminum alloys is generally lower than 80GPa. For example, the elastic modulus of the ADC12 die-cast aluminum alloy commonly used in mobile phone frames is only 70GPa.

[0003] In order to improve the elastic modulus of cast aluminum alloys, existing technologies mainly use alloying and composite methods. For example, the document [Materials Science & Engineering A 788 (2020) 139567] reports an Al-8Ni-0.3Zr hypereutectic alloy. Due to the formation of a large amount of Al3Ni eutectic phase in the alloy structure, the elastic modulus can reach 80GPa, but its tensile strength is only 107Mpa. Chinese patent CN113699418A discloses a high modulus and high plasticity aluminum alloy for automotive parts. The composition by mass percentage is: Si: 14-18%, Cu: 0-0.4%, Mg: 0.20.5%, Mn: 00.5%, Cr: 0.10.5%, Zr: 00.25%, Zn: 00.5%, Ti: 0.050.25%, Re: 00.5%, and the balance is Al and unavoidable impurities. The maximum elastic modulus can reach 83.3GPa and the tensile strength is 261MPa. Chinese patent CN109868397A discloses a high-strength, high-toughness, high-modulus aluminum alloy and its die-casting process. The alloy composition by mass is as follows: Mg: 2.5% to 6.0%, one or both of the rare earth elements Ce and La: 0.01% to 1.2%, one or both of Mn, Cr, and V: 2.0% to 10.0%, with the balance being Al. Impurities are ≤ 0.45%. The material achieves an elastic modulus exceeding 90 GPa and a tensile strength exceeding 320 MPa. However, the high magnesium content and the formation of a large number of needle-shaped primary intermetallic compounds hinder die-casting of complex thin-walled components. Composite methods prepare aluminum-based composite materials by adding or in-situ generating high-elastic modulus ceramic particles, such as SiC and TiB2, into the aluminum alloy melt. Chinese patent CN109628788B discloses a method for preparing a high-elastic modulus, high-strength aluminum alloy by mixing multiphase ceramic particles. While this method achieves both high modulus and high strength, the process is complex, and the presence of a large number of ceramic particles hinders the casting of thin-walled components. Therefore, it is extremely important to develop an aluminum alloy with high elastic modulus, high strength, and suitable for die-casting of thin-walled parts. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a die-cast aluminum alloy material with high elastic modulus, high strength and good casting performance and a preparation method thereof.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] First, a high-modulus, high-strength aluminum alloy material is provided. The high-modulus, high-strength aluminum alloy material comprises a matrix phase and a secondary phase. The matrix phase is α-Al, and the secondary phase is a monoclinic AlNiMnCu quaternary phase. The AlNiMnCu quaternary phase exhibits a petal-like radial structure, has a cross-sectional diameter of 100 nm to 1000 nm, and a volume fraction of not less than 15%. The volume percentages of the elements in the quaternary phase are: Al: 65% to 80%, Ni: 15% to 30%, Mn: 4% to 10%, and Cu: 0.1% to 4%.

[0007] In the present invention, according to the interatomic interaction model, the elastic modulus is a direct reflection of the interatomic bonding force. Ni and Mn in the quaternary phase are transition elements, and the d-shell electrons of the Ni and Mn atoms are not filled, which significantly increases the interatomic bonding force. This makes the AlNiMnCu phase theoretically have a higher elastic modulus. According to the Voigt model or the Reuss model of the composite material, the macroscopic elastic modulus of the material directly depends on the elastic modulus and volume fraction of the second phase. By regulating the content of alloying elements and introducing a large volume fraction of the AlNiMnCu phase, the elastic modulus of the aluminum alloy can be significantly increased.

[0008] In one embodiment, the present invention discloses a high modulus, high strength aluminum alloy material composed of the following elements by mass percentage: Ni: 3.5% to 8.3%, Mn: 2.5 to 5.6%, Cu: 0.5 to 4.2%, Si≤1.0%, Fe≤1.0%, Zr≤0.5%, with the balance being Al and unavoidable impurities. Preferably, the high modulus, high strength aluminum alloy material comprises the following chemical composition by mass content: Ni: 5.0% to 6.5%, Mn: 3.2 to 4.8%, Cu: 1.8 to 2.4%, Si: 0.3 to 0.8%, Fe: 0.15 to 0.62%, Zr: 0.2 to 0.35%, with the balance being Al and unavoidable impurities.

[0009] Furthermore, the aluminum alloy material using the above components also includes a matrix phase and a second phase. The second phase is a high modulus orthorhombic AlNiMnCu quaternary phase, which appears petal-shaped and radial in the matrix. The cross-sectional diameter of the phase is 100nm to 1000nm, and the volume fraction of the second phase is not less than 15%.

[0010] The die-casting process of the above-mentioned high modulus and high strength aluminum alloy material includes the following steps:

[0011] (1) Ingredients: Industrial pure aluminum, aluminum nickel, aluminum manganese, aluminum copper, aluminum iron and aluminum zirconium master alloy are used as raw materials for batching, and dried to remove moisture;

[0012] (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 760-850℃, then add aluminum zirconium, aluminum manganese, aluminum iron, aluminum nickel, aluminum silicon and aluminum copper master alloy in sequence, and keep it warm for 30min-1h after it is completely melted;

[0013] (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 10 to 20 minutes;

[0014] (4) Cool down to 710-760℃ for die casting.

[0015] Furthermore, the obtained alloy has excellent casting fluidity and can be used to form complex thin-walled parts by die casting, and the thickness of the thin-walled parts is less than 0.5 mm.

[0016] Furthermore, the high modulus die-cast aluminum alloy is used in the fields of communications, 3C electronics, and automotive products.

[0017] The beneficial effects of the present invention compared with the prior art are:

[0018] (1) Al, Ni, Mn, and Cu were selected as the main alloying elements, and a large volume fraction of petal-shaped radial AlNiMnCu eutectic phase was obtained in the structure. This phase, as the main strengthening phase, significantly increased the elastic modulus of the aluminum alloy.

[0019] (2) Regulating the content of each element effectively reduces the formation of coarse primary intermetallic compounds, including Al6Mn phase and Al 60 Mn 11 Ni4 is equal, which significantly increases the fluidity of the melt during the die casting process.

[0020] (3) Controlling the amount of Si added can effectively improve the fluidity of the alloy and inhibit the formation of coarse second phase.

[0021] (4) The addition of Cu and Mn elements effectively increased the solid solution strengthening effect of the matrix and significantly improved the yield strength of the material.

[0022] (5) On the one hand, the addition of Zr element is beneficial to grain refinement and increase the yield strength of the material. On the other hand, the addition of Zr can also significantly refine the coarse second phase and further improve the casting performance of the material.

[0023] The high modulus die-cast aluminum alloy of the present invention has an elastic modulus of not less than 91 GPa, a yield strength of not less than 200 MPa, a tensile strength of not less than 350 MPa, an elongation of not less than 5.9%, and has excellent casting fluidity and thermal cracking resistance. It can be applied to thin-walled shells and frame parts that have special requirements for elastic modulus and strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 These are diagrams of high modulus die-cast aluminum alloy samples in Examples 1 to 4 of the present invention.

[0025] Figure 2 TEM bright field phase and EDS analysis results of the high modulus die-cast aluminum alloy in Example 1 of the present invention.

[0026] Figure 3 This is the EDS element distribution diagram of the high modulus die-cast aluminum alloy in Example 2 of the present invention.

[0027] Figure 4 This is the electron selected area diffraction spot of the high modulus die-cast aluminum alloy AlNiMnCu phase in Example 1 of the present invention.

[0028] Figure 5 This is the SEM image of the high modulus die-cast aluminum alloy in Example 3 of the present invention.

[0029] Figure 6 This is the SEM image of the high modulus die-cast aluminum alloy in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only for illustration and are not intended to limit this application.

[0031] The high modulus die-cast aluminum alloy of the present invention is composed of the following elements in mass percentage: Ni: 3.5% to 8.3%, Mn: 2.5 to 5.6%, Cu: 0.5 to 4.2%, Si≤1.0%, Fe≤1.0%, Zr≤0.5%, and the balance is Al and unavoidable impurities.

[0032] The preferred chemical composition consists of the following elements in mass percentage: Ni: 5.0% to 6.5%, Mn: 3.2 to 4.8%, Cu: 1.8 to 2.4%, Si: 0.3 to 0.8%, Fe: 0.15 to 0.62%, Zr: 0.2 to 0.35%, and the remainder is Al and unavoidable impurities.

[0033] The present invention also provides a method for preparing the high modulus die-cast aluminum alloy, which specifically comprises the following steps:

[0034] (1) Ingredients: Industrial pure aluminum, aluminum nickel, aluminum manganese, aluminum copper, aluminum iron and aluminum zirconium master alloy are used as raw materials for batching, and dried to remove moisture;

[0035] (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 760-850℃, then add aluminum zirconium, aluminum manganese, aluminum iron, aluminum nickel, aluminum silicon and aluminum copper master alloy in sequence, and keep it warm for 30min-1h after it is completely melted;

[0036] (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 10 to 20 minutes;

[0037] (4) Cool down to 710-760℃ for die casting.

[0038] In order to describe the preparation method of the high modulus die-cast aluminum alloy in the present invention in more detail, further explanation is given through the following examples.

[0039] Example 1:

[0040] The high modulus die-cast aluminum alloy of the present invention is composed of the following elements by mass percentage: Ni: 5.4%, Mn: 3.6%, Cu: 2.1%, Si: 0.7%, Fe: 0.5%, Zr: 0.2%, with the balance being Al and unavoidable impurities. The high modulus die-cast aluminum alloy is prepared as follows:

[0041] (1) Ingredients: Industrial pure aluminum, Al-20Ni, Al-20Mn, Al-50Cu and Al-5Zr master alloy are prepared according to the above ratios as raw materials and dried to remove moisture;

[0042] (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 830℃, then add Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy in sequence, and keep it warm for 45 minutes after it is completely melted;

[0043] (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 20 minutes;

[0044] (4) Cool down to 750℃ and perform die casting.

[0045] The sample of the high modulus die-cast aluminum alloy in this embodiment is as follows Figure 1 As shown, the thickness of the sample is 0.52mm and no thermal cracking occurs. The modulus of the die casting was tested by ultrasonic method, and the tensile properties were tested by universal mechanical testing machine. Table 1 lists the mechanical properties data of the die casting samples of this embodiment. It can be seen that the yield strength of the die casting aluminum alloy of the present invention reaches 230MPa, and its elastic modulus also reaches 93.5GPa. This is because the alloy designed by the present invention forms a large number of petal-shaped eutectic phases (such as Figure 2 shown), Figure 4 This is the electron selected area diffraction spot image of the AlNiMnCu phase of the alloy. Figure 4 (a) is the

[010] crystal direction, Figure 4 (b) is the

[001] crystal orientation. These eutectic phases can significantly increase the elastic modulus and strength of the material while improving the die-casting properties of the material.

[0046] Example 2:

[0047] The high modulus die-cast aluminum alloy of the present invention is composed of the following elements by mass percentage: Ni: 4.1%, Mn: 4.3%, Cu: 3.0%, Zr: 0.4%, with the balance being Al and unavoidable impurities. The high modulus die-cast aluminum alloy is prepared as follows:

[0048] (1) Ingredients: Industrial pure aluminum, Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy are used as raw materials for batching, and dried to remove moisture;

[0049] (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 835℃, then add Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy in sequence, and keep it warm for 30 minutes after it is completely melted;

[0050] (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 20 minutes;

[0051] (4) Cool down to 730℃ for die casting.

[0052] The sample of the high modulus die-cast aluminum alloy in this embodiment is as follows Figure 1 As shown, the thickness of the sample is 0.48 mm and no thermal cracking occurs. Figure 3 The SEM and EDS element distribution images of the die-cast alloy show that it is primarily composed of an aluminum matrix and a petal-shaped AlNiMnCu eutectic phase. Table 1 lists the mechanical properties of the die-cast samples of this embodiment, demonstrating that the die-cast aluminum alloy of the present invention achieves a yield strength of 210 MPa and an elastic modulus of 91.2 GPa.

[0053] Example 3:

[0054] The high modulus die-cast aluminum alloy of the present invention is composed of the following elements by mass percentage: Ni: 4.0%, Mn: 5.0%, Cu: 2.5%, Si: 0.3%, Fe: 0.45%, Zr: 0.3%, with the balance being Al and unavoidable impurities. The high modulus die-cast aluminum alloy is prepared as follows:

[0055] (1) Ingredients: Industrial pure aluminum, Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy are used as raw materials for batching, and dried to remove moisture;

[0056] (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 840℃, then add Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy in sequence, and keep it warm for 30 minutes after it is completely melted;

[0057] (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 20 minutes;

[0058] (4) Cool down to 725℃ for die casting.

[0059] The sample of the high modulus die-cast aluminum alloy in this embodiment is as follows Figure 1 As shown, the sample thickness is 0.52 mm and no thermal cracking occurs. Figure 5 Table 1 lists the mechanical properties of the die-casting samples of this embodiment. It can be seen that the yield strength of the die-casting aluminum alloy of the present invention reaches 208MPa, and its elastic modulus also reaches 91.7GPa. The structure of the die-casting alloy is as follows Figure 3 As shown, it can be found that this embodiment has less coarse phase in the structure than the embodiment 1, which also makes the die-cast alloy of this composition have better elongation.

[0060] Example 4:

[0061] The high modulus die-cast aluminum alloy of the present invention is composed of the following elements by mass percentage: Ni: 4.2%, Mn: 5.2%, Cu: 1.5%, Si: 0.6%, Zr: 0.4%, with the balance being Al and unavoidable impurities. The high modulus die-cast aluminum alloy is prepared as follows:

[0062] (1) Ingredients: Industrial pure aluminum, Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy raw materials are prepared and dried to remove moisture;

[0063] (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 835℃, then add Al-20Ni, Al-20Mn, Al-50Cu, and Al-5Zr master alloy in sequence, and keep it warm for 30 minutes after it is completely melted;

[0064] (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 20 minutes;

[0065] (4) Cool down to 715℃ for die casting.

[0066] The sample of the high modulus die-cast aluminum alloy in this embodiment is as follows Figure 1 As shown, the sample thickness is 0.46 mm and no thermal cracking occurs. Figure 6This is a SEM image of the die-cast alloy of this embodiment. The secondary phase in the microstructure is primarily a quaternary phase of AlNiMnCu. Table 1 lists the mechanical properties of the die-cast samples of this embodiment. It can be seen that the yield strength of the die-cast aluminum alloy of the present invention reaches 213 MPa, and its elastic modulus also reaches 91.4 GPa.

[0067] Table 1 Room temperature tensile mechanical properties data of high modulus die-cast aluminum alloys of Examples 1-4

[0068] Yield strength / MPa Tensile strength / MPa Elongation / % Elastic modulus / GPa Example 1 230 410 6.0 93.5 Example 2 210 380 5.9 91.2 Example 3 208 400 7.3 91.7 Example 4 213 350 6.4 91.4

[0069] The above applications are only some embodiments of the present application. For those skilled in the art, without departing from the inventive concept of the present application, several modifications and improvements can be made, which all fall within the scope of protection of the present application.

Claims

1. A high modulus die-casting aluminum alloy, characterized in that: The invention comprises a matrix phase and a second phase, wherein the matrix phase is α-Al, and the second phase is a monoclinic AlNiMnCu quaternary phase, The die-cast aluminum alloy is composed of the following elements in mass percentage: Ni: 3.5% to 8.3%, Mn: 2.5 to 5.6%, Cu: 0.5 to 4.2%, Si≤1.0%, Fe≤1.0%, Zr≤0.5%, and the balance is Al and inevitable impurities. The elastic modulus of the die-cast aluminum alloy is not less than 91 Gpa, the yield strength is not less than 200 Mpa, the tensile strength is not less than 350 Mpa, and the elongation is not less than 5.9%.

2. A high modulus die-casting aluminum alloy according to claim 1, characterized in that: It is composed of the following elements in mass percentage: Ni: 5.0%-6.5%, Mn: 3.2-4.8%, Cu: 1.8-2.4%, Si: 0.3-0.8%, Fe: 0.15-0.62%, Zr: 0.2-0.35%, and the remainder is Al and inevitable impurities.

3. The high modulus die-casting aluminum alloy according to claim 2, characterized in that: The AlNiMnCu quaternary phase is radially petal-shaped in the matrix, the cross-sectional diameter of the AlNiMnCu quaternary phase is 100nm-1000nm, and the phase volume fraction is not less than 15%.

4. The high modulus die-casting aluminum alloy according to claim 3, characterized in that: The volume percentage content of each element in the AlNiMnCu quaternary phase is: Al: 65% to 80%, Ni: 15% to 30%, Mn: 4% to 10%, Cu: 0.1% to 4%.

5. A method for preparing a high modulus die-casting aluminum alloy according to any one of claims 1 to 4, characterized in that: The steps include: (1) Drying materials: Drying industrial pure aluminum, aluminum nickel, aluminum manganese, aluminum copper, aluminum iron and aluminum zirconium master alloy raw materials to remove moisture; (2) Melting: Add industrial pure aluminum into the melting furnace and heat it to make it completely melted, so that the aluminum liquid temperature reaches 760-850°C, then add aluminum zirconium, aluminum manganese, aluminum iron, aluminum nickel, aluminum silicon and aluminum copper master alloy in sequence, and keep warm for 30 minutes to 1 hour after melting; (3) Refining: Add refining agent for refining, purification and slag removal, and let the melt stand for 10 to 20 minutes; (4) Cool down to 710-760°C for die casting.

6. A high modulus die-casting aluminum alloy according to claim 1 or 2, characterized in that: The alloy has excellent casting fluidity and can be used to form complex thin-walled parts by die casting, and the thickness of the obtained complex thin-walled parts at the thin wall is less than 0.5 mm.

7. Application of the high modulus die-casting aluminum alloy according to any one of claims 1 to 6 in the fields of communications, 3C electronics, and automotive products.

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