Hypoeutectic die-casting aluminum alloy material with high toughness and high thermal conductivity as well as preparation method and heat treatment method thereof

Abstract

The invention provides a high-strength and high-conductivity hypo-eutectic die-casting aluminum alloy material and a preparation method and a heat treatment method thereof, and the high-strength and high-conductivity hypo-eutectic die-casting aluminum alloy material provided by the invention comprises the following components in percentage by mass: 6.0-8.0% of Si; 0.40% to 0.70% of Fe; 0.50% to 0.80% of Cu; 0.15% to 0.40% of Mn; 0.50% to 0.80% of Mg; zn: less than or equal to 0.1%; ti: 0.005 to 0.05%; b, 0.005% to 0.05%; 0.01% to 0.04% of Sr; less than or equal to 0.1% of Pb; sn: < = 0.1%; less than or equal to 0.01% of Cd; the adding amount of the submicron aluminum-titanium-carbon-boron seed crystal material is 0.2-1.0%; the single content of other inevitable common impurity elements is less than or equal to 0.05%, and the sum is less than or equal to 0.15 The balance is Al; in the high-strength and high-conductivity hypoeutectic die-casting aluminum alloy material, the mass ratio of Mg to Cu is 1: (0.8-1.4). According to a die casting formed after the high-strength and high-conductivity aluminum alloy material is subjected to die casting, on the basis that it is guaranteed that the heat conductivity coefficient is larger than or equal to 140 W / (m.k), the tensile strength is larger than or equal to 350 MPa, the yield is larger than or equal to 250 MPa, the ductility is larger than or equal to 5%, and the elasticity modulus is larger than or equal to 68 GPa.

Description

Technical Field

[0001] This invention belongs to the field of die-cast aluminum alloy technology, specifically relating to a high-strength, high-toughness, high-thermal-conductivity hypoeutectic die-cast aluminum alloy material and its preparation and heat treatment methods. Background Technology

[0002] With the rapid advancement of technology, 5G technology is developing at an unprecedented pace, leading to explosive growth in the 5G smartphone market. Compared to traditional 4G phones, 5G phones need to be compatible with more communication frequency bands and support more functional modules, such as Bluetooth, Wi-Fi, GPS, and navigation. This necessitates the integration of more components and antennas within the phone, resulting in a more complex mid-plate structure that requires more space to accommodate the new components. Simultaneously, the widespread adoption of full-screen displays in 5G phones, coupled with continuously increasing screen sizes, places increasingly stringent demands on the flatness of the mid-plate. This necessitates that the aluminum alloy material used in the mid-plate possess higher yield strength and elongation to ensure stable support of the circuit board, screen, and maintenance of the overall structural rigidity and toughness of the phone. To match the high speeds of 5G, the processing power of the phone's CPU has significantly increased, leading to a substantial increase in heat generation. Heat dissipation has become a critical aspect of 5G phone design. As a vital internal component, the mid-plate material requires not only high strength but also enhanced thermal conductivity.

[0003] Eutectic aluminum-silicon alloys have been extensively studied for achieving high strength, toughness, and thermal conductivity. Furthermore, eutectic aluminum-silicon alloys are easily die-cast, making them the primary material used for the mid-plates of current mobile phones. For example, patent publications CN 109457146 A, CN111254326A, and CN114908273A all disclose high-strength, high-toughness, and high-thermal-conductivity eutectic aluminum-silicon alloys for use in mobile phone mid-plates.

[0004] Hypoeutectic aluminum-silicon alloys have poorer fluidity and die-casting performance than eutectic aluminum-silicon alloys. However, hypoeutectic aluminum-silicon alloys are less sensitive to gases during die casting than eutectic aluminum-silicon alloys. Furthermore, due to the larger liquid-solid temperature difference in hypoeutectic aluminum-silicon alloys, they are particularly suitable for semi-solid die casting. Semi-solid die casting can eliminate most gases and inclusions, resulting in superior and more stable product quality. At the same time, hypoeutectic aluminum-silicon alloys have higher elongation and toughness than eutectic aluminum-silicon alloys. For some heat dissipation devices and high-strength and high-toughness devices, hypoeutectic aluminum-silicon alloys are generally the preferred choice. However, research on high thermal conductivity of hypoeutectic aluminum-silicon alloys is limited. Furthermore, the domestic standards GB / T15115 (Die-cast Aluminum Alloys) and GB / T15114 (Aluminum Alloy Die-castings) do not specify requirements for thermal conductivity in hypoeutectic die-cast aluminum-silicon alloys, only outlining mechanical properties. Consequently, domestically produced hypoeutectic die-cast aluminum alloys cannot meet the needs of high thermal conductivity applications and cannot be effectively used in the communications industry, particularly for manufacturing mobile phone mid-plates. To address this issue, patent publication number CN114318073B discloses a hypoeutectic die-cast aluminum-silicon alloy material that offers both good thermal conductivity and toughness. This breakthrough in thermal conductivity overtakes existing hypoeutectic die-cast aluminum-silicon alloys, enabling their application in the communications field and providing a new option for basic materials in this field. The die-cast samples of this material, after T5 heat treatment, exhibited the following properties: tensile strength ≥230MPa, yield strength ≥130MPa, elongation ≥10%, and thermal conductivity ≥185W / m·K. This represents a significant breakthrough for hypoeutectic die-cast aluminum-silicon alloy materials. However, achieving further improvements in other properties while maintaining all of the above-mentioned performance characteristics is extremely difficult.

[0005] The eternal theme of mobile phone design is "lighter, thinner, and higher screen-to-body ratio." To reduce weight and thickness without sacrificing structural rigidity, materials must possess higher specific strength. Using higher-strength materials allows for thinner designs while maintaining the same or even higher structural strength. For example, further thinning the mid-plate requires a significant leap in material strength. Furthermore, higher-strength materials can support larger spans of suspended structures, finer and denser reinforcing ribs, and more complex snap-fit ​​and stud designs. This allows engineers to directly integrate more functions onto the mid-plate, reducing auxiliary support components and driving the mid-plate towards a higher degree of structural and functional integration.

[0006] However, in existing technologies, the development of eutectic and hypoeutectic die-cast aluminum-silicon alloys that maintain high thermal conductivity while also possessing high yield strength and tensile strength has reached its limit, making further breakthroughs difficult. This is especially true for hypoeutectic die-cast aluminum-silicon alloys, where achieving both high thermal conductivity and increased strength simultaneously is extremely challenging. The microstructure of hypoeutectic alloys (typically with less than 10% silicon content) consists of primary α-Al dendrites + (α-Al + Si) eutectic structure. This structure leads to a fundamental contradiction: the primary α-Al dendrites are relatively soft, and the alloy's strength largely depends on solid solution strengthening elements (such as Mg, Cu, Zn, etc.) within the α-Al dendrites. However, the addition of these elements severely disrupts the periodicity of the aluminum lattice, significantly reducing the material's thermal conductivity. Therefore, while patent publication number CN114318073B has achieved a breakthrough in the high thermal conductivity and high strength properties of hypoeutectic die-cast aluminum-silicon alloys, further improvements in strength while maintaining high thermal conductivity remain extremely difficult. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, comprising the following components by mass percentage: Si: 6.0-8.0%; Fe: 0.40-0.70%; Cu: 0.50-0.80%; Mn: 0.15-0.40%; Mg: 0.50-0.80%; Zn: ≤0.1%; Ti: 0.005-0.05%; B: 0.005-0.05%; Sr: 0.01-0.04%; Pb: ≤0.1%; Sn: ≤0.1%; Cd: ≤0.01%; submicron-sized aluminum-titanium-carbon-boron seed material: 0.2-1.0%; other unavoidable common impurity elements, individually ≤0.05%, total common impurities: ≤0.15%; the remainder being Al.

[0008] In the high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, the mass ratio of Mg to Cu is 1:(0.8-1.4).

[0009] Preferably, Cu is 0.60-0.80%.

[0010] Preferably, the content of Mg is 0.50-0.62%.

[0011] Preferably, the mass ratio of Mg to Cu is 1:(1-1.35).

[0012] Preferably, the amount of submicron-sized aluminum-titanium-carbon-boron seed material added is 0.2-0.98%, and the main composition of the submicron-sized aluminum-titanium-carbon-boron seed material is, by mass percentage: Ti: 0.45-0.55%, C: 0.05-0.10%, B: 0.70-0.9%, RE: 2.0-2.5%, Fe: ≤1.2%, with the balance being Al.

[0013] Preferably, Fe is 0.40-0.55%.

[0014] Preferably, Mn is 0.20-0.30%.

[0015] Preferably, Sr is 0.02-0.036% and B is 0.005-0.03%.

[0016] This invention also provides a method for preparing a high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, comprising the following steps:

[0017] S1. After adding some aluminum ingots and all the metallic silicon, heat the mixture to melt it and raise the temperature to 800-850℃;

[0018] S2. Add the preheated iron additive in two batches;

[0019] S3. Add the preheated manganese additive, stir until melted, and let stand for 10-20 minutes.

[0020] S4. When the temperature is 800-850℃, add copper agent, stir and melt, and let stand for 10-20 minutes.

[0021] S5. Add the remaining aluminum ingots and adjust the temperature of the molten aluminum to 740-760℃;

[0022] S6. Use argon or nitrogen as the carrier gas and add 0.1-0.3% of the total amount of aluminum liquid as a refining agent for refining and purification.

[0023] S7. Add the preheated magnesium metal, melt and stir evenly, and let stand for 5-10 minutes.

[0024] S8. The aluminum liquid temperature is 720-760℃. After degassing with argon or nitrogen for 20-30 minutes, the slag is removed.

[0025] S9, aluminum liquid temperature 720-760℃, add preheated aluminum-boron master alloy;

[0026] S10, aluminum liquid temperature 720-760℃, with preheated aluminum-strontium master alloy added;

[0027] S11. Sample and test the components. If the components are qualified, proceed to the next step.

[0028] S12. Add preheated aluminum-titanium-carbon-boron seed material at a temperature of 720-760℃;

[0029] S13, aluminum liquid is poured at a temperature between 720±10℃.

[0030] The present invention also provides a heat treatment method for a high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, wherein the initial temperature of the heat treatment is 25-30℃; the process temperature is 165-175℃; the heating rate is 5-10℃ / minute; the holding time is 2-8 hours; and the cooling method is natural cooling in air.

[0031] The high-strength, high-toughness, and high-thermal-conductivity aluminum alloy material provided by this invention can achieve a tensile strength of ≥360MPa, a yield strength of ≥255MPa, an elongation of ≥7%, and an elastic modulus of ≥70GPa, while ensuring a thermal conductivity of ≥155W / (mk). Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0033] This invention provides a high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, comprising the following components by mass percentage: Si: 6.0-8.0%; Fe: 0.40-0.70%; Cu: 0.50-0.80%; Mn: 0.15-0.40%; Mg: 0.50-0.80%; Zn: ≤0.1%; Ti: 0.005-0.05%; B: 0.005-0.05%; Sr: 0.01-0.04%; Pb: ≤0.1%; Sn: ≤0.1%; Cd: ≤0.01%; submicron-sized aluminum-titanium-carbon-boron seed material: 0.2-1.0%; other unavoidable common impurity elements: individual ≤0.05%, total: ≤0.15%; the remainder is Al. In this invention's high-strength, high-conductivity hypoeutectic die-cast aluminum alloy material, the mass ratio of Mg to Cu is 1:(0.8-1.4).

[0034] In a preferred embodiment, the mass ratio of Mg to Cu is 1:(1-1.35).

[0035] In a preferred embodiment, Cu is 0.60-0.80%.

[0036] In a preferred embodiment, Mg is 0.50-0.62%.

[0037] The copper content range of this invention is reasonable. Copper is a double-edged sword in the aluminum-silicon series. On the one hand, copper has a high solid solubility in aluminum, forming a supersaturated solid solution during die casting. In subsequent aging treatment, fine and dispersed strengthening phases precipitate. These nanoscale strengthening phases can effectively hinder dislocation movement and improve the room temperature strength, hardness, and wear resistance of the alloy. In addition, copper and magnesium can form more complex strengthening phases, such as the S (Al2CuMg) phase, which can provide a stronger strengthening effect than the Q phase (Al2Cu) phase alone. On the other hand, the electrode potential of the Al2Cu phase is different from that of the aluminum matrix, forming a micro-galvanic cell with the matrix. The Al matrix, acting as the anode, will be preferentially corroded. Furthermore, the solid solution of copper increases the lattice distortion of the Al matrix and the second phase interface, increasing electron scattering and thus reducing the thermal conductivity of the alloy.

[0038] When a suitable magnesium element is selected, its effect is no longer a simple additive when added to the hypoeutectic aluminum-silicon alloy containing copper (Cu) in this invention. Instead, it produces a complex interaction that significantly changes the strengthening mechanism and final properties of the alloy.

[0039] On one hand, when copper and magnesium are present in the alloy, a crucial S (Al₂CuMg) phase precipitates during aging. These phases disperse in the aluminum matrix as fine needle-like or rod-like precipitates. They more effectively hinder dislocation movement, thus providing much higher strength than the strengthening (θ or β phases) produced by copper or magnesium alone, which is key to achieving the alloy's highest strength. In the aluminum-silicon-copper-magnesium quaternary system, intermetallic compounds of the Q phase also form, which can form as a primary phase during solidification or precipitate during aging. The precipitated Q phase also contributes to some strengthening effect, but its morphology and distribution are crucial. If coarse primary Q phases form during solidification, they become brittle phases, impairing ductility. Uniform, fine, age-precipitated Q phases, on the other hand, are beneficial to both strength and ductility.

[0040] On the other hand, as the magnesium content increases, the plasticity of the material is further reduced. A large number of high-hardness reinforcing phases (especially coarse or discontinuously distributed S and Q phases) severely restrict dislocation movement, making the material brittle. The elongation of the alloy decreases significantly with increasing magnesium content. Secondly, multi-element alloying makes the solidification process more complex and widens the solidification temperature range, thus increasing the tendency for hot cracking. This places higher demands on casting processes, mold design, and pouring temperatures. Therefore, a reasonable ratio of magnesium and copper elements finds an optimal balance between strength and thermal conductivity, producing a significant age-hardening effect. This is the core mechanism for obtaining high yield strength (≥255MPa) and tensile strength (≥360MPa).

[0041] An improper ratio or content of copper and magnesium may lead to increased electron scattering in the solid solution, which in turn reduces thermal conductivity and increases the tendency for hot cracking, resulting in insufficient strength of the material.

[0042] The high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material provided by this invention has good flow properties and die-casting performance. It adopts a medium Si content to match the alloy's plasticity and thermal conductivity.

[0043] Silicon phase (especially after modification treatment) is a hard phase and one of the main sources of alloy strength. The silicon content within a reasonable range in this invention ensures castability while avoiding excessive silicon content that would lead to a significant increase in brittleness and a decrease in thermal conductivity.

[0044] In a preferred embodiment, Fe is 0.40-0.55% and manganese is 0.20-0.30%. The material contains an appropriate amount of iron, mainly to solve the problem of metal mold sticking during die casting, and to reduce the corrosion of the mold during die casting. The addition of a certain amount of manganese is to improve the morphology of the iron-rich phase, reduce the adverse effects of Fe on the material properties, ensure the overall performance of the material, and improve the material's flow properties.

[0045] In a preferred embodiment, the submicron-sized aluminum-titanium-boron-carbon (TCB) seed material is added at an amount of 0.2-0.98%. The main function of the TCB seed is to refine the α-Al phase by increasing heterogeneous nucleation sites, thereby refining the grain size and improving overall performance, particularly enhancing plasticity and thermal conductivity. The main composition of the TCB seed in this invention, by mass percentage, is: Ti: 0.45-0.55%, C: 0.05-0.10%, B: 0.70-0.9%, RE: 2.0-2.5%, Fe: ≤1.2%, with the balance being Al. It is suitable for aluminum-silicon alloys containing a suitable amount of iron.

[0046] In a preferred embodiment, Sr is 0.02-0.036%. The purpose of adding an appropriate amount of Sr is to modify the eutectic silicon, change the morphology of the eutectic silicon, reduce the cutting of the matrix and the obstruction of electrons, and improve the overall mechanical properties of the material, especially the plasticity and thermal conductivity of the material.

[0047] In a preferred embodiment, B is 0.005-0.03%. The role of B is to remove transition elements, such as V, Ti, Cr, etc., to improve the thermal conductivity of the material.

[0048] The main challenge in this invention is to balance the interactions of the aluminum-silicon-copper-magnesium quaternary system, maximizing its strengths and minimizing its weaknesses to achieve our target high performance.

[0049] In summary, this invention achieves a tensile strength ≥360MPa and a yield strength ≥255MPa while maintaining a high thermal conductivity. This is mainly due to the aging strengthening of Mg and Cu, the strengthening of the Si phase, and the grain refinement strengthening brought about by TCB seed crystals.

[0050] Elongation ≥7%: This is mainly due to: Sr's modification treatment of eutectic silicon (eliminating stress concentration points); Mn's morphological modification of the Fe phase (eliminating brittle needle-like phase); TCB seed crystals bringing fine grain strengthening (improving plasticity); and extreme control of harmful impurities.

[0051] Thermal conductivity ≥155 W / (m·K): This is exceptionally high thermal conductivity for die-cast aluminum alloys of equivalent strength. The key to achieving this lies in: "purifying" the aluminum matrix: extremely low levels of harmful elements and impurities, reducing electron scattering by solid-solid atoms; optimizing the phase structure: through modification, refinement, and Fe phase transformation, the second phase (Si phase, intermetallic compounds) becomes finer, rounder, and more uniformly distributed, reducing obstacles to electron transport; and a dense, uniform microstructure: the grain refinement brought by TCB seed crystals and rapid solidification during die casting reduce microscopic shrinkage and segregation, creating more "unobstructed" heat conduction paths.

[0052] The high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material provided by this invention has a core advantage stemming from a systematic, multi-scale composition design concept. It does not pursue the limits of a single element in isolation, but rather achieves this through:

[0053] "Purification" (controlling impurities)

[0054] "Transformation" (converting the harmful Fe phase into a less harmful phase)

[0055] "Refinement" (using TCB to refine the grains to the extreme, and using Sr to refine the Si phase)

[0056] "Enhanced" (precise control of Cu / Mg to optimize aging precipitation)

[0057] This series of methods synergistically optimizes the microstructure of the alloy (matrix, grains, and second phase), thereby successfully reconciling the inherent contradictions among strength, toughness, and thermal conductivity on a macroscopic level. This results in an advanced die-cast aluminum alloy material with extremely excellent comprehensive performance, which is very suitable for fields that require lightweight, heat dissipation, and structural strength (such as new energy vehicles and communication electronic housings).

[0058] The high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material provided by this invention offers a raw material with excellent thermal conductivity and structural strength for the fabrication of mobile phone mid-plates, enabling the mid-plates to be made thinner and stronger. This breakthrough in raw material properties provides more possibilities for innovation in mobile phone design.

[0059] This invention also provides a method for preparing a high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, comprising the following steps:

[0060] S1. After adding 90-92% aluminum ingots and metallic silicon, heat the mixture to 800-850℃ and let it stand for 30-40 minutes. After confirming that the silicon has melted completely, remove the slag.

[0061] S2. When the temperature is 800-850℃, add the preheated iron additive in two batches, stirring and melting each time, and let it stand for 10-20 minutes after each batch.

[0062] S3. When the temperature is 800-850℃, add the preheated manganese additive, stir and melt it, and let it stand for 10-20 minutes.

[0063] S4. When the temperature is 800-850℃, add copper agent, stir and melt, then let stand for 10-20 minutes; take a sample to test the composition. If the composition is qualified, proceed to the next step.

[0064] S5. Add the remaining aluminum ingots and adjust the temperature of the molten aluminum to 740-760℃;

[0065] S6. Use argon or nitrogen as the carrier gas and add 0.1-0.3% of the total amount of aluminum liquid as a refining agent for refining and purification; remove the slag after the slag and liquid have been fully separated.

[0066] S7. Add the preheated magnesium metal, melt and stir evenly, and let stand for 5-10 minutes.

[0067] S8. The aluminum liquid temperature is 720-760℃. After degassing with argon or nitrogen for 20-30 minutes, remove the slag. The pinhole requirement is no higher than level 2.

[0068] S9. When the aluminum liquid temperature is 720-760℃, add the preheated aluminum-boron master alloy; stir gently to melt, and let stand for 20-30 minutes.

[0069] S10, with the aluminum melt temperature at 720-760℃, add the preheated aluminum-strontium master alloy; stir gently to melt, then let stand for 20-30 minutes.

[0070] S11. Sample and test the components. If the components are qualified, proceed to the next step.

[0071] S12. Add the preheated aluminum-titanium-carbon-boron seed material at a temperature of 720-760℃; stir gently until melted, then let stand for 5-10 minutes.

[0072] S13, aluminum liquid temperature is between 720±10℃;

[0073] S14. During the casting process, argon or nitrogen gas is used to degas online at the bottom of the filter box through a permeable brick with a pore size of 15-25μm.

[0074] The present invention also provides a heat treatment method for high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy materials. The initial temperature of the heat treatment is 25-30℃; the process temperature is 165-175℃; the heating rate is 5-10℃ / minute; the holding time is 2-8 hours; and the cooling method is natural cooling in air.

[0075] To provide a better understanding of the technical solution of the present invention, several preferred embodiments are listed below for further detailed description.

[0076] Example 1:

[0077] By weight percentage: Si: 6.41%; Fe: 0.43%; Cu: 0.77%; Mn: 0.28%; Mg: 0.58%; Zn: 0.008%; Ti: 0.012%; B: 0.006%; Sr: 0.023%; Pb: 0.001%; ​​Sn: 0.003%; Cd: 0.0002%; Aluminum-titanium-carbon-boron (TCB) seed crystals: 0.5%; the remainder is Al.

[0078] The aluminum alloy is prepared according to the above proportions, and the steps are as follows:

[0079] After adding 92% aluminum ingots and metallic silicon, heat the mixture to 800-850℃, let it stand for 35 minutes, and remove the slag after confirming that the silicon has melted completely.

[0080] At a temperature of 842℃, add the preheated iron additive in two batches, stirring and melting each time, and let it stand for 20 minutes after each addition.

[0081] At a temperature of 838℃, add the preheated manganese additive, stir until melted, and let stand for 15 minutes.

[0082] Add copper agent at 830℃, stir and melt, then let stand for 10 minutes; take a sample to test the composition. If the composition is qualified, proceed to the next step.

[0083] Add the remaining aluminum ingots and adjust the temperature of the molten aluminum to 745℃.

[0084] Argon or nitrogen is used as the carrier gas, and 0.2% of the total amount of refining agent is added for refining and purification. The slag is removed after the slag and liquid have been fully separated.

[0085] Add preheated magnesium metal, melt and stir evenly, let stand for 5 minutes, take a sample to test the composition, if the composition is qualified, proceed to the next step.

[0086] The aluminum liquid temperature is 740℃. After degassing with argon or nitrogen for 30 minutes, the slag is removed, resulting in pinhole level 1.

[0087] The aluminum liquid temperature is 737℃. Add the preheated aluminum-boron master alloy, stir gently until it melts evenly, and let it stand for 30 minutes.

[0088] The aluminum liquid temperature is 735℃. Add the preheated aluminum-strontium master alloy, stir gently until it melts evenly, and let it stand for 25 minutes.

[0089] Samples were taken and tested for components. If the components were found to be qualified, the next step was carried out.

[0090] Add preheated aluminum titanium carbon boron (TCB) seed material at 732℃, stir gently until melted, and let stand for 5 minutes.

[0091] The aluminum liquid was poured at a temperature between 720°C.

[0092] During the casting process, argon or nitrogen gas is used to degas online at the bottom of the filter box through a permeable brick with a pore size of 15-25μm.

[0093] Example 2

[0094] By weight percentage: Si: 7.88%; Fe: 0.55%; Cu: 0.64%; Mn: 0.21%; Mg: 0.52%; Zn: 0.010%; Ti: 0.031%; B: 0.027%; Sr: 0.035%; Pb: 0.005%; Sn: 0.003%; Cd: 0.009%; Aluminum-titanium-carbon-boron (TCB) seed material, added: 0.95%; the remainder is Al.

[0095] The aluminum alloy is prepared according to the above proportions, and the steps are as follows:

[0096] After adding 91% aluminum ingots and metallic silicon, heat the mixture to 800-850℃, let it stand for 35 minutes, and remove the slag after confirming that the silicon has melted completely.

[0097] When the temperature is 840℃, add the preheated iron additive in two batches, stirring and melting each time, and let it stand for 20 minutes after each addition.

[0098] At a temperature of 839℃, add the preheated manganese additive, stir until melted, and let stand for 15 minutes.

[0099] At a temperature of 836℃, add copper agent, stir and melt, then let stand for 10 minutes; take a sample to test the composition. If the composition is qualified, proceed to the next step.

[0100] Add the remaining aluminum ingots and adjust the temperature of the molten aluminum to 748℃.

[0101] Argon or nitrogen is used as the carrier gas, and 0.2% of the total amount of refining agent is added for refining and purification. The slag is removed after the slag and liquid have been fully separated.

[0102] Add preheated magnesium metal, melt and stir evenly, let stand for 5 minutes, take a sample to test the composition, if the composition is qualified, proceed to the next step.

[0103] The aluminum liquid temperature is 745℃. After degassing with argon or nitrogen for 30 minutes, the slag is removed, resulting in a pinhole level of 1.

[0104] The aluminum liquid temperature is 740℃. Add the preheated aluminum-boron master alloy, stir gently until it melts evenly, and let it stand for 30 minutes.

[0105] The aluminum liquid temperature is 737℃. Add the preheated aluminum-strontium master alloy, stir gently until it melts evenly, and let it stand for 25 minutes.

[0106] Samples were taken and tested for components. If the components were found to be qualified, the next step was carried out.

[0107] Add preheated aluminum titanium carbon boron (TCB) seed material at 730℃, stir gently until melted, and let stand for 5 minutes.

[0108] The aluminum liquid was poured at a temperature between 726°C.

[0109] During the casting process, argon or nitrogen gas is used to degas online at the bottom of the filter box through a permeable brick with a pore size of 15-25μm.

[0110] Example 3

[0111] By weight percentage: Si: 7.15%; Fe: 0.48%; Cu: 0.68%; Mn: 0.25%; Mg: 0.55%; Zn: 0.011%; Ti: 0.013%; B: 0.012%; Sr: 0.031%; Pb: 0.004%; Sn: 0.003%; Cd: 0.004%; Aluminum titanium carbon boron (TCB) seed crystals: 0.7%; the remainder is Al.

[0112] 2. Prepare the aluminum alloy according to the above proportions, following these steps:

[0113] (1) After adding 92% aluminum ingots and metallic silicon, heat the furnace to melt and raise the temperature to 800-850℃. Let it stand for 36 minutes to ensure that the silicon is completely melted and remove the slag.

[0114] (2) When the temperature is 846℃, add the preheated iron additive in two batches, and let it stand for 20 minutes after each stirring and melting.

[0115] (3) When the temperature is 843℃, add the preheated manganese additive, stir and melt it, and let it stand for 15 minutes.

[0116] (4) When the temperature is 840℃, add copper agent, stir and melt, and let stand for 10 minutes; take a sample to test the composition. If the composition is qualified, proceed to the next step.

[0117] (5) Add the remaining aluminum ingots and adjust the temperature of the molten aluminum to 750°C.

[0118] (6) Use argon or nitrogen as the carrier gas and add 0.2% of the total amount of refining agent to the aluminum liquid for refining and purification. Remove the slag after the slag and liquid have been fully separated.

[0119] (7) Add preheated magnesium metal, melt and stir evenly, let stand for 5 minutes, take a sample to test the composition, if the composition is qualified, proceed to the next step.

[0120] (8) The aluminum liquid temperature is 743℃. After degassing with argon or nitrogen for 30 minutes, the slag is removed and the pinhole is grade 1.

[0121] (9) When the aluminum liquid temperature is 740℃, add the preheated aluminum-boron intermediate alloy, stir gently until it melts evenly, and let it stand for 30 minutes.

[0122] (10) When the aluminum liquid temperature is 736℃, add the preheated aluminum-strontium intermediate alloy, stir gently until it melts evenly, and let it stand for 25 minutes.

[0123] (11) Take samples to test the components. If the components are qualified, proceed to the next step.

[0124] (12) Add the preheated aluminum titanium carbon boron (TCB) seed material at 735℃, stir gently until it melts, and let it stand for 5 minutes.

[0125] (13) The aluminum liquid is poured at a temperature between 724℃.

[0126] (14) Argon or nitrogen gas is used to degas the filter box online through a permeable brick with a pore size of 15-25μm.

[0127] The main composition of the titanium boron carbon (TCB) seed materials in Examples 1-3 is as follows, by mass percentage: Ti: 0.45-0.55%, C: 0.05-0.10%, B: 0.70-0.9%, RE: 2.0-2.5%, Fe: ≤1.2%, with the balance being Al.

[0128] Example 4: The aluminum alloy ingot (casting) prepared in Example 1 was die-cast using the following die-casting process requirements to finally obtain the mobile phone mid-plate. It can be seen that the high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material provided by this invention can be well used in the preparation of mobile phone mid-plates.

[0129] The main process parameters and requirements for die casting are as follows:

[0130] The temperature of the aluminum melt before die casting (remelting temperature) is ≤740℃.

[0131] The temperature of the die-cast aluminum melt is 685±5℃. The wall thickness is closer to the lower limit, and the wall thickness is closer to the upper limit.

[0132] The die-casting mold temperature is 200±10℃. The lower limit is for thicker walls, and the upper limit is for thinner walls.

[0133] Before die casting, the molten aluminum is degassed with argon or nitrogen for 20-30 minutes. After degassed, the slag is removed.

[0134] When the Mg content in the die-cast aluminum melt drops below the lower limit due to burn-off, metallic magnesium needs to be added.

[0135] When the Sr content in the die-cast aluminum melt drops below the lower limit due to burn-off, aluminum-strontium master alloy needs to be added.

[0136] During the die casting process, cold materials such as return materials are not added to the furnace to avoid the melt absorbing air and increasing impurities.

[0137] Iron tools need to be coated and dried to prevent the aluminum melt from adding iron and absorbing air during the die-casting process.

[0138] Comparative Example 1: The only difference between this comparative example and Example 1 is that the silicon content in the comparative example is 5.0%;

[0139] Comparative Example 2: The only difference between this comparative example and Example 1 is that the silicon content of the comparative example is 9.0%;

[0140] Comparative Example 3: The only difference between this comparative example and Example 1 is that the iron content in the comparative example is 0.80%;

[0141] Comparative Example 4: The only difference between this comparative example and Example 1 is that the copper content in the comparative example is 1.0%;

[0142] Comparative Example 5: The only difference between this comparative example and Example 1 is that the magnesium content in the comparative example is 0.95%;

[0143] Comparative Example 6: The only difference between this comparative example and Example 1 is that the strontium content in the comparative example is 0.08%;

[0144] Comparative Example 7: The only difference between this comparative example and Example 1 is that no aluminum-boron intermediate alloy was added to the comparative example;

[0145] Comparative Example 8: The only difference between this comparative example and Example 1 is that submicron-sized aluminum-titanium-carbon-boron seed material is added to the comparative example. Its composition is: Ti: 1.8-2.2%, C: 0.28-0.35%, B: 0.28-0.35%, and the remainder is Al.

[0146] Comparative Example 9: The only difference between this comparative example and the embodiment is that submicron-sized aluminum-titanium-carbon-boron seed material is added to the comparative example. Its composition is as follows: Ti: 4.5-5.5%, C: 0.1-0.2%, B: 0.15-0.25%, Ce: 0.4-0.6%, Mn: ≤0.1%, Fe: ≤0.4%, Si: ≤0.1%, V: ≤0.1%, and the remainder is Al.

[0147] The aluminum alloy ingots (castings) obtained from Examples 1-3 and Comparative Examples 1-9 were die-cast to obtain die castings. The resulting die castings were then subjected to heat treatment under the following conditions. The main process parameters and requirements for die casting are as described in Example 4.

[0148] T5 heat treatment process conditions: Equipment: heat treatment furnace (temperature accurate to 0.1℃).

[0149] Initial temperature: 25-30℃.

[0150] Process temperature: 165-175℃.

[0151] Heating rate: 5-10℃ / minute.

[0152] Insulation time: 2-8 hours.

[0153] Cooling method: Natural cooling in the air.

[0154] The performance tests of die-cast parts from Examples 1-3 and Comparative Examples 1-9 after T5 heat treatment are as follows:

[0155] Table 1

[0156]

[0157] As can be seen from the data in Table 1, the high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy materials prepared in Examples 1-3 of this invention, after heat treatment, exhibit good thermal conductivity and strength in the resulting die-cast parts. While ensuring a thermal conductivity ≥155 W / (mk), they also possess tensile strength ≥360 MPa, yield strength ≥255 MPa, elongation ≥7%, and elastic modulus ≥70 GPa.

[0158] The high-strength, high-conductivity hypoeutectic die-cast aluminum alloy materials prepared in Examples 1-3 of this invention have a thermal conductivity greater than 180 W / (mk) before die casting. For example, the thermal conductivity of the casting in Example 1 was measured to be 180.907 W / (mk). After die casting and heat treatment, the thermal conductivity of the die-cast parts can be guaranteed to be ≥155 W / (mk), and the strength has been greatly improved.

[0159] In Comparative Example 1, the silicon content was reduced, making the composition outside the scope of this invention. This resulted in poorer die-casting performance and die-casting molding performance, and the tensile strength and yield strength did not meet the requirements.

[0160] The increased silicon content in Comparative Example 2 resulted in a composition outside the scope of this invention, leading to a significant decrease in thermal conductivity, with a value of only 110 W / (mk), which fails to meet the requirements for high thermal conductivity.

[0161] The iron content in Comparative Example 3 is relatively high, which means that the composition is outside the scope of this invention. It has good die-casting performance, but its thermal conductivity and strength do not meet the requirements.

[0162] The copper content in Comparative Example 4 is relatively high, which means that the composition is not within the scope of this invention. Furthermore, the ratio of copper to magnesium is also not within the scope of this invention, resulting in low thermal conductivity, which cannot meet the requirements for high thermal conductivity. Additionally, the elongation is low, making it prone to cracking during machining.

[0163] The magnesium content in Comparative Example 5 is relatively high, which means that the composition is not within the scope of this invention. This results in low thermal conductivity, which cannot meet the requirements for high thermal conductivity, and low elongation, making it prone to cracking during machining.

[0164] The high strontium content in Comparative Example 6 means that the composition is outside the scope of this invention, and the product has more pores, resulting in its strength not meeting the requirements.

[0165] In Comparative Example 7, no aluminum-boron master alloy was added, resulting in mediocre overall performance; its thermal conductivity and strength did not meet the requirements.

[0166] The composition of the submicron-sized aluminum-titanium-carbon-boron seed materials in Comparative Examples 8 and 9 is different from that of the present invention, and their thermal conductivity and elongation do not meet the requirements.

[0167] Comparative Examples 10, 13, 16 and 19 used aluminum alloy ingots (castings) obtained from Example 1 for die casting to obtain die castings. The main process parameters and requirements for die casting are as in Example 4. Then, the obtained die castings were heat treated under the following heat treatment process conditions.

[0168] Comparative Examples 11, 14, 17 and 20 used aluminum alloy ingots (castings) obtained from Example 2 for die casting to obtain die castings. The main process parameters and requirements for die casting are as in Example 4. Then, the obtained die castings were heat treated under the following heat treatment process conditions.

[0169] Comparative Examples 12, 15, 18 and 21 used aluminum alloy ingots (castings) obtained from Example 3 for die casting to obtain die castings. The main process parameters and requirements for die casting are the same as those in Example 4. The obtained die castings were then subjected to heat treatment under the following heat treatment process conditions.

[0170] Processing conditions: Equipment: Heat treatment furnace (temperature accurate to 0.1℃).

[0171] Initial temperature: 25-30℃.

[0172] Process temperature: as shown in Table 2.

[0173] Heating rate: 5-10℃ / minute.

[0174] Insulation time: 2-8 hours.

[0175] Cooling method: Natural cooling in the air.

[0176] The performance data obtained from the test are shown in Table 2.

[0177] Table 2

[0178]

[0179] As can be seen from the data in Table 2, the die castings of the high-strength and high-conductivity hypoeutectic die-cast aluminum alloy provided by the present invention, after undergoing appropriate heat treatment process conditions, have a tensile strength ≥360MPa, yield strength ≥255MPa, elongation ≥7%, elastic modulus ≥70GPa, and thermal conductivity ≥155W / (mk).

[0180] In summary, the high-strength, high-toughness, and high-thermal-conductivity hypoeutectic die-cast aluminum alloy material formulation and preparation method provided by this invention are reasonable. By simultaneously coordinating the content of each element and preparing aluminum alloy die-casting parts under aging heat treatment, the resulting castings possess excellent comprehensive properties, with tensile strength ≥360MPa, yield strength ≥255MPa, elongation ≥7%, elastic modulus ≥70GPa, and thermal conductivity ≥155W / (mk). The high thermal conductivity provides good thermal conductivity, the high elongation provides good machinability, and the high tensile and yield strengths provide good strength, making it suitable as a base material for preparing mobile phone mid-plates. While ensuring thermal conductivity, it further breaks through the strength performance of the material.

[0181] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-toughness high-thermal-conductivity hypoeutectic die-cast aluminum alloy material, characterized by comprising: Si: 6.0-8.0% by mass; Fe: 0.40-0.70%; Cu: 0.50-0.80%; Mn: 0.15-0.40%; Mg: 0.50-0.80%; Zn: ≤0.1%; Ti: 0.005-0.05%; B：0.005-0.05%； Sr：0.01-0.04%； Pb: ≤0.1%; Sn: ≤0.1%; Cd: ≤0.01%; the addition amount of sub-micron aluminum titanium carbon boron seed material: 0.2-1.0%; other inevitable common impurity elements: ≤0.05% each, and ≤0.15% in total; and the rest is Al. The mass ratio of Mg to Cu in the high-strength and high-ductility high-thermal-conductivity hypoeutectic die-casting aluminum alloy material is 1:(0.8-1.4).

2. The high-strength high-thermal-conductivity hypoeutectic die casting aluminum alloy material according to claim 1, wherein Cu is 0.60-0.80%.

3. The high-strength high-thermal-conductivity hypoeutectic die casting aluminum alloy material according to claim 1, wherein Mg is 0.50-0.62%.

4. The high-strength, high-ductility, high-thermal-conductivity hypoeutectic die casting aluminum alloy material of claim 1, wherein, The mass ratio of Mg to Cu is 1:(1-1.35).

5. The high-strength, high-ductility, high-thermal-conductivity hypoeutectic die casting aluminum alloy material of claim 1, wherein, The addition amount of sub-micron aluminum titanium carbon boron seed material is 0.2-0.98%, and the main components of the sub-micron aluminum titanium carbon boron seed material are, by mass: Ti: 0.45-0.55%, C: 0.05-0.10%, B: 0.70-0.9%, RE: 2.0-2.5%, Fe: ≤1.2%, and the rest is Al.

6. The high-strength, high-ductility, high-thermal-conductivity hypoeutectic die casting aluminum alloy material of claim 1, wherein, Fe is 0.40-0.55%.

7. The high strength, high thermal conductivity, hypoeutectic, die casting aluminum alloy material of claim 1, wherein, Mn is 0.20-0.30%.

8. The high strength, high thermal conductivity, hypoeutectic, die casting aluminum alloy material of claim 1, wherein, Sr is 0.02-0.036%; and B is 0.005-0.03%.

9. The method of producing a high-strength high-conductivity hypoeutectic die casting aluminum alloy material according to any one of claims 1 to 8, characterized by, The method comprises the following steps: S1, after adding part of aluminum ingots and all of the metallic silicon, start melting and heating to 800-850℃; S2, add the preheated iron additive in two times; S3, add the preheated manganese additive, after melting and stirring, stand for 10-20 minutes; S4, when the temperature is 800-850℃, add the copper additive, after melting and stirring, stand for 10-20 minutes; S5, add the remaining aluminum ingots, and adjust the temperature of the aluminum liquid to 740-760℃; S6, use argon or nitrogen as the carrier gas, add 0.1-0.3% of the total amount of the aluminum liquid as the refining agent to perform refining and purification; S7, add the preheated metallic magnesium, melt and stir uniformly, and stand for 5-10 minutes; S8, when the temperature of the aluminum liquid is 720-760℃, remove the slag after 20-30 minutes of argon or nitrogen degassing; S9, when the temperature of the aluminum liquid is 720-760℃, add the preheated aluminum boron intermediate alloy; S10, when the temperature of the aluminum liquid is 720-760℃, add the preheated aluminum strontium intermediate alloy; S11, take a sample to test the composition, and if the composition is qualified, proceed to the next step; S12, when the temperature is 720-760℃, add the preheated aluminum titanium carbon boron seed material; S13, cast when the temperature of the aluminum liquid is 720±10℃.

10. The heat treatment method of the high-strength high-conductivity hypoeutectic die casting aluminum alloy material according to any one of claims 1 to 8, characterized by, The initial temperature of the heat treatment is 25-30℃; the process temperature is 165-175℃, the heating speed is 5-10℃ / min, the holding time is 2-8h, and the cooling mode is natural cooling in air. The initial temperature of the heat treatment is 25-30℃; the process temperature is 165-175℃, the heating speed is 5-10℃ / min, the holding time is 2-8h, and the cooling mode is natural cooling in air.

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