Low-thermal-expansion aluminum-silicon alloy and preparation method thereof

Abstract

The invention discloses a low-thermal-expansion aluminum-silicon alloy and a preparation method thereof. The alloy comprises the following components in percentage by weight: 19.0-21.0 wt% of Si, 2-4.5 wt% of Cu, less than or equal to 0.4 wt% of Mg, 0.05-0.20 wt% of Ti, 0.1-0.2 wt% of Fe, 0.65-0.75 wt% of Mn, 0.01-0.1 wt% of Zr, 0.05-0.15 wt% of Sn, less than or equal to 0.01 wt% of other impurity elements in total, and the balance of Al. The preparation method comprises the steps of two-time sequential smelting, refining, degassing and deslagging, heat preservation and casting. Through the specific component design, the solid solution strengthening and phase change effects of the elements such as Cu and Mg are utilized, and the grain refinement effect of the elements such as Ti and Zr is cooperated, so that the good casting performance of the alloy is guaranteed, meanwhile, the thermal expansion coefficient is remarkably reduced, and the hardness and the tensile strength are improved. The method is suitable for structural members such as precise instruments and electronic product shells with high requirements on size thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, and relates to aluminum-silicon alloys, their preparation methods, and applications. Background Technology

[0002] Low thermal expansion aluminum-silicon alloys are aluminum alloy materials with a low coefficient of thermal expansion, primarily used in fields with stringent requirements for thermal expansion characteristics, such as precision instruments, aerospace, semiconductor manufacturing equipment, and automotive engine components. Under high-temperature operating environments, conventional aluminum-silicon alloys suffer from thermal deformation due to their high coefficient of thermal expansion, which impacts certain high-precision applications. To overcome this problem, researchers have aimed to manufacture hypereutectic aluminum-silicon alloy materials with lower thermal expansion properties by adjusting alloy composition, optimizing alloy ratios, and employing alloying modification techniques.

[0003] Several manufacturers and research institutions have disclosed some aluminum-based composite materials with low coefficients of thermal expansion. These include patents CN111663059A and CN111321329A using powder molding technology, and patent CN1531072 which uses rapid solidification spraying to form a molten alloy. However, powder molding is a complex process that increases alloy production costs, energy consumption, and the requirements for raw materials. Rapid solidification spraying, on the other hand, requires sophisticated production equipment. Summary of the Invention

[0004] The purpose of this invention is to provide a low thermal expansion aluminum-silicon alloy, which reduces the thermal expansion rate of the aluminum alloy and increases its hardness by solid solution atoms.

[0005] This invention is achieved through the following technical solution.

[0006] The low thermal expansion aluminum-silicon alloy of this invention comprises, based on the total weight of the low thermal expansion aluminum-silicon alloy: Si: 19.0–21.0 wt%, Cu: 2–4.5 wt%, Mg ≤ 0.4 wt%, Ti: 0.05–0.20 wt%, Fe: 0.1–0.2 wt%, Mn: 0.65–0.75 wt%, Zr: 0.01–0.1 wt%, Sn: 0.05–0.15 wt%, other impurity elements ≤ 0.01 wt%, and the balance being Al.

[0007] The present invention discloses a method for preparing a low thermal expansion aluminum-silicon alloy, comprising the following steps;

[0008] S1: Place Al in a melting furnace to melt and add Si, Cu and Fe raw materials. Melt at a melting temperature of 740-750℃ for the first melting and hold for 15 min to obtain the first melt.

[0009] S2: After cooling the first melt to 710-720℃, it is transferred to the intermediate furnace, and then the first material is placed in the first melt for a second melting and a first degassing, refining and slag removal to obtain the second melt.

[0010] The first material is composed of Ti raw material, Zr raw material, Mn element and Sn raw material, or the first material is composed of Mg raw material, Ti raw material, Zr raw material, Mn element and Sn raw material.

[0011] The first degassing, refining, and slag removal includes: adding refining agent powder into the converter furnace body under an inert gas atmosphere or nitrogen atmosphere; the inert gas is argon.

[0012] S3: After cooling the second melt, it is transferred to a holding furnace and held at 690-710℃ for 30 minutes. Then, the composition is tested. After the composition is qualified, it is cast to obtain a low thermal expansion aluminum-silicon alloy.

[0013] Optionally, the Cu raw material is an Al-Cu alloy; the Fe raw material is an Al-Fe alloy; the Mn raw material is an Al-Mn alloy; the Ti raw material is an Al-Ti alloy; the Zr raw material is an Al-Zr alloy; the Sn raw material is an Al-Sn alloy; and the Mg raw material has a purity ≥99.99 wt.%.

[0014] The Al-Cu alloy is an Al-50Cu master alloy; the Al-Fe alloy is an Al-5Fe master alloy; the Al-Mn alloy is an Al-20Mn master alloy; the Al-Ti alloy is an Al-5Ti master alloy; the Al-Zr alloy is an Al-5Zr master alloy; and the Al-Sn alloy is an Al-12Sn master alloy.

[0015] Optionally, the preparation method further includes: drying the aluminum, silicon, magnesium, Cu, Mn, Ti, Zr and Sn raw materials before proceeding with the subsequent melting or smelting steps; the drying temperature is 150-200°C.

[0016] The addition of Si to the low thermal expansion aluminum alloy of this invention not only increases the alloy's strength but also ensures its casting fluidity. The addition of Cu, under casting conditions, results in some Cu dissolving into the matrix to increase its strength, while the remaining Cu precipitates as an intermediate phase in the eutectic region, enhancing the bonding strength of the eutectic structure. Utilizing the smaller atomic volume of Cu compared to Al, the solvent atoms and solute atoms form a substitutional solid solution, reducing the lattice constant of the solid solution. As the lattice constant of the substitutional solid solution decreases, the volume of the solid solution decreases, leading to a decrease in the alloy's coefficient of thermal expansion.

[0017] In aluminum-silicon alloys, Cu can combine with Al to form the Al₂Cu phase. This Al₂Cu phase increases the interfacial thermal stress at the alloy interface due to the difference in thermal expansion coefficients between the Al matrix and the second phase as the temperature rises. This leads to both elastic and plastic deformation in the alloy. Furthermore, as the solid solubility of Si increases with temperature, more Si atoms enter the aluminum matrix. Both the plastic deformation of the matrix and the presence of the Si phase within it inhibit the alloy's thermal expansion behavior, resulting in a slower rate of increase in the coefficient of thermal expansion.

[0018] The magnesium element is dissolved in the aluminum matrix, resulting in solid solution strengthening, which increases the hardness of the aluminum alloy.

[0019] The Ti and Zr elements added to the heat-free die-cast aluminum alloy of the present invention act as heterogeneous nucleation particles, increasing the nucleation of primary (Al) grains and achieving grain refinement.

[0020] In low thermal expansion aluminum-silicon alloys, the silicon content is 20%, and this high silicon content gives the alloy good casting properties and wear resistance.

[0021] The low thermal expansion aluminum-silicon alloy provided by this invention has significantly improved tensile strength and hardness compared with existing hypereutectic aluminum-silicon alloys, and its thermal expansion rate is reduced, making it suitable for use in thin-walled structural components for electronic product housings. Attached Figure Description

[0022] Figure 1 This diagram illustrates the effect of solute atoms on the lattice constant. In the diagram, (a) represents the absence of impurity elements; (b) represents a solvent atom radius greater than the solute atom radius; and (c) represents a solvent atom radius smaller than the solute atom radius. When the lattice constant of a substitutional solid solution decreases, the volume of the solid solution decreases, leading to a decrease in the coefficient of thermal expansion of the alloy.

[0023] Figure 2 The effect of Cu on the microstructure of the alloy. Among them, (a) is Comparative Example 1; (b) is Comparative Example 2; (c) is Example 1; (d) is Example 2; (e) is Example 3.

[0024] Figure 3 The effect of Mg on the microstructure of the alloy. Among them, (a) is Example 4; (b) is Example 5; (c) is Example 6; and (d) is Comparative Example 5. Detailed Implementation

[0025] The present invention will be further described in conjunction with the accompanying drawings and through the following embodiments.

[0026] Example 1

[0027] The low thermal expansion aluminum-silicon alloy prepared in this embodiment has the following chemical composition: 20 wt.% Si, 2 wt.% Cu, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0028] The preparation and die-casting process of a low thermal expansion aluminum-silicon alloy according to this embodiment includes the following steps:

[0029] 1) Material preparation: Weigh the alloy raw materials according to the alloy composition and dry them. The raw materials used include Al, Si, Al-50Cu master alloy, Al-5Ti master alloy, Al-5Fe master alloy, Al-5Zr master alloy, Al-20Mn master alloy and Al-12Sn master alloy.

[0030] 2) Melting: The melting furnace is heated to 750℃ to melt Al, followed by the addition of Si, Al-50Cu master alloy, and Al-5Fe master alloy. After the master alloys melt, the molten liquid is transferred to a constant-temperature transfer furnace at 730℃, where Al-5Ti master alloy, Al-5Zr, Al-20Mn master alloy, and Al-12Sn master alloy are added. After the alloys melt, high-purity nitrogen gas is introduced into the melt, along with refining agent powder, and the gas is purged for 15 minutes to remove gas and slag. The mixture is then allowed to stand for 12 minutes, and then transferred to a holding furnace at 690℃ for 30 minutes. Afterward, pre-furnace composition analysis is performed.

[0031] 3) Casting: After the composition test is qualified, the melt at 690℃ is transferred to the tensile sample preparation mold. The mold temperature is 200℃. The mold used is a flat mold with a length of 35 cm and a width of 25 cm.

[0032] Example 2

[0033] The preparation and casting process of the low thermal expansion aluminum-silicon alloy in this embodiment are the same as in Embodiment 1. The difference is that the low thermal expansion aluminum-silicon alloy prepared in this embodiment has the following chemical composition: 20 wt.% Si, 3 wt.% Cu, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0034] Example 3

[0035] The preparation and casting process of the low thermal expansion aluminum-silicon alloy in this embodiment are the same as in Embodiment 1. The difference is that the low thermal expansion aluminum-silicon alloy prepared in this embodiment has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0036] Example 4

[0037] The low thermal expansion aluminum-silicon alloy prepared in this embodiment has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.1 wt.% Mg, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0038] The preparation and die-casting process of a low thermal expansion aluminum-silicon alloy according to this embodiment includes the following steps:

[0039] 1) Material preparation: Weigh the alloy raw materials according to the alloy composition and dry them. The raw materials used include Al, Si, Mg, Al-50Cu master alloy, Al-5Fe master alloy, and Al-20Mn master alloy.

[0040] 2) Melting: The melting furnace was heated to 750℃ to melt Al, followed by the addition of Si and Al-50Cu master alloy. After the master alloy melted, the molten liquid was transferred to a constant-temperature transfer furnace at 730℃, where commercially pure Mg, Al-5Ti master alloy, Al-5Zr, Al-20Mn master alloy, and Al-12Sn master alloy were added. After the alloy melted, high-purity nitrogen gas was introduced into the melt, along with refining agent powder, and the gas was purged for 15 minutes to remove gas and slag. The mixture was then allowed to stand for 12 minutes, and then transferred to a holding furnace and held at 690℃ for 30 minutes. Afterward, pre-furnace composition analysis was performed.

[0041] Example 5

[0042] The preparation and casting process of the low thermal expansion aluminum-silicon alloy in this embodiment are the same as those in Embodiment 4. The difference is that the low thermal expansion aluminum-silicon alloy prepared in this embodiment has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.2 wt.% Mg, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.%, and the balance Al.

[0043] Example 6

[0044] The preparation and casting process of the low thermal expansion aluminum-silicon alloy in this embodiment are the same as those in Embodiment 4. The difference is that the low thermal expansion aluminum-silicon alloy prepared in this embodiment has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.4 wt.% Mg, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.%, and the balance Al.

[0045] Comparative Example 1

[0046] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as in Example 1.

[0047] The low thermal expansion aluminum-silicon alloy performance test piece prepared in this comparative example has the following chemical composition: 20 wt.% Si, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0048] The preparation and casting process of the low thermal expansion aluminum-silicon alloy in this comparative example are the same as those in Example 1, except that Al-50Cu is not added during the preparation process, and it does not contain C compared to Example 1.

[0049] Comparative Example 2

[0050] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as in Example 1.

[0051] The low thermal expansion aluminum-silicon alloy performance test piece prepared in this comparative example has the following chemical composition: 20 wt.% Si, 1 wt.% Cu, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0052] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as those in Example 1, except that Al-50Cu is not added during the preparation process, and the Cu content is 1% compared with Example 1.

[0053] Comparative Example 3

[0054] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as in Example 3.

[0055] The low thermal expansion aluminum-silicon alloy performance test piece prepared in this comparative example has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.2 wt.% Mn, 0.12 wt.% Fe, 0.11 wt.% Sn, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0056] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as those in Example 1. The difference is that no Al-5Ti master alloy and Al-5Zr master alloy are added during the preparation process. Compared with Example 3, it does not contain Ti or Zr.

[0057] Comparative Example 4

[0058] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as in Example 3.

[0059] The low thermal expansion aluminum-silicon alloy performance test piece prepared in this comparative example has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.% and the balance Al.

[0060] The preparation and casting process of the low thermal expansion aluminum-silicon alloy in this comparative example are the same as those in Example 1. The difference is that no Al-20Mn master alloy is added during the preparation process, and it does not contain Mn compared with Example 3.

[0061] Comparative Example 5

[0062] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as in Example 4.

[0063] The low thermal expansion aluminum-silicon alloy performance test piece prepared in this comparative example has the following chemical composition: 20 wt.% Si, 4.1 wt.% Cu, 0.7 wt.% Mg, 0.2 wt.% Mn, 0.15 wt.% Ti, 0.12 wt.% Fe, 0.11 wt.% Sn, 0.04 wt.% Zr, other impurity elements less than or equal to 0.01 wt.%, and the balance Al.

[0064] The preparation and casting process of a low thermal expansion aluminum-silicon alloy in this comparative example are the same as those in Example 4, except that an excess of commercially pure Mg is added during the preparation process, and the Mg content is 0.7% compared with Example 3.

[0065] Table 1 shows the composition of the cast aluminum alloys prepared in Examples 1-6 and Comparative Examples 1-5.

[0066]

[0067] Table 2 shows the mechanical properties and thermal expansion coefficient of the aluminum alloy castings prepared in Examples 1-6 and Comparative Examples 1-5.

[0068]

[0069] As shown in Table 2, the aluminum alloy castings prepared in this embodiment have a significantly reduced coefficient of thermal expansion, while their hardness and tensile strength are also improved. In particular, under the premise that the amounts of other components are the same, Cu effectively improves the tensile strength and hardness of the castings and reduces their coefficient of thermal expansion. An appropriate amount of Mg can significantly improve the hardness and strength of the material while slightly increasing its coefficient of thermal expansion; however, excessive Mg will severely affect the coefficient of thermal expansion.

[0070] Through optical micrographs ( Figure 2 It was found that with the increase of copper content, the white Al2Cu phase in the alloy gradually increased. When the Cu content in the alloy increased from 0.5 wt.% to 4.1 wt.%, the Al2Cu phase content increased from 0.46% to 5.87%, and the shape gradually changed from needle-like to mesh-like. This was confirmed by optical microscopy. Figure 3 It was found that with the increase of Mg content, the Al2Cu phase in the alloy gradually decreased. When the Mg content in the alloy increased from 0 wt.% to 0.7 wt.%, the Al2Cu phase content decreased from 1.25% to 0.23%. Mg in the alloy promotes the gradual transformation of the Al2Cu phase into the Q-AlCuMgSi phase, so with the increase of Mg content, the Al2Cu in the alloy gradually decreases.

[0071] The low thermal expansion aluminum-silicon alloy provided by this invention has significantly improved tensile strength and hardness compared with existing hypereutectic aluminum-silicon alloys, and its thermal expansion rate is reduced, making it suitable for use in thin-walled structural components for electronic product housings.

Claims

1. A low thermal expansion aluminum-silicon alloy, characterized in that, Based on the total weight of the alloy, the components include the following mass percentages: Si: 19.0–21.0 wt%, Cu: 2–4.5 wt%, Mg ≤0.4 wt%, Ti: 0.05–0.20 wt%, Fe: 0.1–0.2 wt%, Mn: 0.65–0.75 wt%, Zr: 0.01–0.1 wt%, Sn: 0.05–0.15 wt%, other impurity elements ≤0.01 wt%, balance Al.

2. A method for preparing the low thermal expansion aluminum-silicon alloy according to claim 1, characterized in that, Includes the following steps: S1: Place Al in a melting furnace and melt it, then add Si, Cu and Fe raw materials. Perform the first melting at 740-750℃ and hold for 15 min to obtain the first melt. S2: After cooling the first melt to 710-720°C, it is transferred to a converter, and the first material is added to the first melt for a second melting and a first degassing, refining and slag removal to obtain the second melt. The first material is composed of Ti raw material, Zr raw material, Mn raw material and Sn raw material; or the first material is composed of Mg raw material, Ti raw material, Zr raw material, Mn raw material and Sn raw material. S3: After cooling the second melt, it is transferred to a holding furnace and held at 690-710℃ for 30 minutes. Then, the composition is tested. After the composition is qualified, it is cast to obtain the low thermal expansion aluminum-silicon alloy.

3. The preparation method according to claim 2, characterized in that, In step S2, the first degassing, refining and slag removal includes: adding refining agent powder into the converter furnace body under an inert gas atmosphere or a nitrogen atmosphere.

4. The preparation method according to claim 3, characterized in that, The inert gas is argon.

5. The preparation method according to claim 2, characterized in that, The Cu raw material is an Al-Cu master alloy; the Fe raw material is an Al-Fe master alloy; the Mn raw material is an Al-Mn master alloy; the Ti raw material is an Al-Ti master alloy; the Zr raw material is an Al-Zr master alloy; the Sn raw material is an Al-Sn master alloy; and the Mg raw material is commercially pure magnesium with a purity ≥99.99 wt.%.

6. The preparation method according to claim 5, characterized in that, The Al-Cu master alloy is an Al-50Cu master alloy; the Al-Fe master alloy is an Al-5Fe master alloy; the Al-Mn master alloy is an Al-20Mn master alloy; the Al-Ti master alloy is an Al-5Ti master alloy; the Al-Zr master alloy is an Al-5Zr master alloy; and the Al-Sn master alloy is an Al-12Sn master alloy.

7. The preparation method according to claim 2, characterized in that, Before step S1, the process includes drying the aluminum, silicon, magnesium, Cu, Mn, Ti, Zr and Sn raw materials; the drying temperature is 150-200°C.

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