High-strength heat-resistant hypoeutectic aluminum-silicon casting aluminum alloy and preparation method thereof

Abstract

This invention relates to a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy and its preparation method. The purpose of this invention is to address the problems of low room-temperature mechanical properties and insufficient thermal strength of hypoeutectic aluminum-silicon cast aluminum alloys when the service temperature exceeds 200°C. The high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy is composed of Si, Cu, Mg, Ag, Mn, Ti, V, Be, Ca, Sr, B, and Al by mass fraction. The process involves melting, casting, three-stage solution treatment, quenching, pre-aging treatment, and aging treatment to obtain a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy with high tensile strength and yield strength, capable of long-term operation at 220°C without failure. This invention has applications in the manufacturing of cast aluminum alloys.

Description

Technical Field

[0001] This invention relates to the field of alloy preparation technology, specifically to a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy and its preparation method. Background Technology

[0002] Commonly used hypoeutectic aluminum-silicon cast aluminum alloys such as ZL101A and ZL114A are ideal for casting due to their good fluidity, narrow solid-liquid temperature range, low porosity, ease of feeding, and good weldability. They are suitable for various casting methods and can be used to produce products with complex structures, thin walls, high corrosion resistance, and high airtightness requirements. They are mainly used for structural components bearing medium loads and complex-shaped shell components. However, the room temperature mechanical properties of this material are generally poor (the tensile strength of a single cast sample is generally below 350 MPa). Furthermore, when the service temperature exceeds 200℃, the strengthening phase tends to coarsen, leading to material softening and failure, making it unsuitable for critical components. Additionally, its specific strength is lower than that of the commonly used ZM6 magnesium alloy, making it difficult to meet the requirements of lightweight design. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of low room temperature mechanical properties and insufficient thermal strength of hypoeutectic aluminum-silicon cast aluminum alloys when the service temperature exceeds 200°C, and to provide a high-strength heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy and its preparation method.

[0004] This invention discloses a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy, which is composed of 6.5–7.5% Si, 1–1.3% Cu, 0.70–0.80% Mg, 0.50–0.90% Ag, 0.10–0.25% Mn, 0.08–0.12% Ti, 0.04–0.10% V, 0.0015–0.0030% Be, 0.0030% Ca, 0.0070–0.030% Sr, 0.015% B, and the balance Al by mass fraction.

[0005] This invention discloses a method for preparing a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy, which comprises the following steps:

[0006] I. Weigh out refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, AlV4 master alloy, pure magnesium, pure silver, cathode copper, AlB3 master alloy, AlSr5 master alloy, and AlCa10 master alloy according to the following mass fractions: 6.5-7.5% Si, 1-1.3% Cu, 0.70-0.80% Mg, 0.50-0.90% Ag, 0.10-0.25% Mn, 0.08-0.12% Ti, 0.04-0.10% V, 0.0015-0.0030% Be, 0.0030% Ca, 0.0070-0.030% Sr, 0.015% B, and the balance Al.

[0007] 2. Place the refined aluminum ingot, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, and AlV4 master alloy into a crucible for melting. When the melt temperature reaches 755-765℃, stir the melt and remove slag.

[0008] 3. Immerse pure magnesium, pure silver, and cathode copper into the melt. After they are completely melted, stir evenly. Add AlB3 intermediate alloy to refine the grains. After they are completely melted, stir evenly and let stand for 5 to 10 minutes.

[0009] IV. When the melt temperature is 740-750℃, add AlSr5 master alloy and AlCa10 master alloy. After they are completely melted, let them stand for 5 minutes, then use them for degassing and refining, and then pour them to obtain aluminum alloy castings.

[0010] Fifth, the aluminum alloy castings are subjected to three stages of solution treatment, quenching, pre-aging treatment, and aging treatment to complete the process.

[0011] In Al-Si-Cu-Mg alloys, the precipitate sequence is largely influenced by the Cu / Mg mass ratio. When the Cu / Mg mass ratio is below 2.1, the microstructure consists of a quaternary phase (α-Al, eutectic silicon, β phase (Mg₂Si), and Q phase (Al₅Cu₂Mg₈Si₆). When the Cu / Mg mass ratio is 2.1, the β phase (Mg₂Si) completely disappears, and the microstructure consists of a ternary phase (α-Al, eutectic silicon, and Q phase (Al₅Cu₂Mg₈Si₆)). When the Cu / Mg mass ratio is greater than 2.1, the microstructure includes α-Al, eutectic silicon, Q phase (Al₅Cu₂Mg₈Si₆), and a θ phase (Al₂Cu). At room temperature, the strengthening effect of the β phase (Mg₂Si) is greater than that of the θ phase (Al₂Cu).

[0012] Therefore, by controlling the Cu / Mg mass ratio between 1.6 and 1.7, a dual-strengthening phase of β phase (Mg2Si) and Q phase (Al5Cu2Mg8Si6) is formed, which yields excellent tensile properties at room temperature. The Q phase exhibits excellent thermal stability, and its strengthening effect does not diminish at 200℃.

[0013] Furthermore, Ag is typically added to Al-Mg-Si and Al-Cu-Mg alloys for alloying to improve performance. This invention involves adding an appropriate amount of Ag to an Al-Si-Cu-Mg alloy. During the aging process, Ag atoms replace some Mg atoms, acting as nucleation sites to form Si-Mg-Ag vacancy clusters. This increases the number of nucleation sites in the alloy, ultimately promoting the precipitation of the β'' phase. Additionally, Ag accumulates on the surface of the β'' phase, inhibiting its growth and improving strength.

[0014] Adding 0.0030% Ca can transform the coarse Mg2Si phase into fine particles, thereby increasing the solid solution degree of the β phase during the solid solution process and transforming it into more β'' phase during the aging process, thus improving the strength of the alloy.

[0015] Adding an appropriate amount of Mn can form intermetallic compounds with Cu, which are distributed at grain boundaries to hinder grain boundary slip and improve the heat resistance of aluminum alloys. Adding Ti, V, and B elements is used for α-Al grain refinement. For aluminum alloys with Si content exceeding 5%, if the Ti content is too high, Si will segregate in the reacting TiAl3 and react, thus diminishing the grain refinement effect of Ti. Therefore, the Ti content should be controlled between 0.08% and 0.12%. Sr transforms coarse, lamellar eutectic silicon into fine, fibrous structures, reducing the cutting effect of eutectic silicon on the matrix and improving alloy elongation. Trace amounts of Be can reduce the oxidation loss of Mg and promote the precipitation of the β'' phase during alloy aging treatment, increasing the amount of the strengthening phase β'' and thus improving the mechanical properties of the alloy.

[0016] In the preparation process of this invention, non-oxidizable refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, and AlBe5 master alloy are first placed into a melting furnace. Be is configured at 0.0015 to 0.0030% of the total furnace charge. The AlBe5 master alloy is melted first before pure magnesium is added. In this way, Be can be added in a timely and effective manner to avoid the oxidation and burning loss of Mg element.

[0017] Cu (Cu) is typically added to cast aluminum alloys in the form of AlCu50 master alloy, primarily because AlCu50 dissolves faster than pure copper. However, Cu is an inverse segregation element in aluminum alloys, and the copper content in AlCu50 master alloy can only be controlled between 48% and 52%, making it difficult to precisely control the copper content in cast aluminum alloys. Therefore, this invention cuts a 1cm thick high-purity cathode copper plate into small pieces (5cm × 5cm × 1cm), significantly accelerating copper dissolution (the use of fine silver particles for pure silver also accelerates dissolution and facilitates precise control of the addition amount). These small copper pieces are then immersed below the molten metal surface using a slag-removing spoon to dissolve, thus preventing Cu oxidation (similarly, pure magnesium and silver particles are also immersed below the molten metal surface to prevent oxidation and burn-off).

[0018] In step two of this invention, the heating temperature is 760°C, which can accelerate the dissolution of silver particles and small copper flakes; in step three, the heating temperature is 745°C, which has a good refining and dehydrogenation effect. At the same time, this temperature is close to the casting temperature, which shortens the time from deterioration to casting and controls the hydrogen absorption of the melt.

[0019] Generally, aluminum-titanium-boron master alloys (containing TiAl3 and TiB2 particles as nuclei) are used to refine the grains of aluminum alloys. However, for aluminum-silicon cast aluminum alloys, the grain refining effect is far less than that of aluminum-boron master alloys. In addition, Sr elements tend to agglomerate and precipitate with TiB2, affecting both the modification and grain refining effects. This invention uses a filamentous AlB3 master alloy, which can quickly dissolve into the aluminum alloy melt. By controlling the alloy boron element at 0.015%, a large number of finely dispersed AlB2 particles can be formed in the aluminum melt as nuclei to refine the grains, without agglomerating with Sr and affecting the modification effect.

[0020] Adding AlSr5 master alloy allows it to dissolve rapidly into the aluminum alloy melt. For casting methods with faster cooling rates, such as metal mold casting, controlling the Sr element at 0.0075% yields the best modification effect; for casting methods with slower cooling rates, such as sand casting, controlling the Sr element at 0.025% yields the best modification effect.

[0021] The beneficial effects of this invention are:

[0022] After heat treatment, the room temperature tensile strength of the single-cast specimens of this alloy in the metal mold ranges from 380 MPa to 410 MPa, the yield strength ranges from 325 MPa to 360 MPa, and the elongation ranges from 4% to 6%.

[0023] At 220℃, the tensile strength is between 290MPa and 320MPa, the yield strength is between 275MPa and 290MPa, and the elongation is between 5% and 7%.

[0024] When subjected to 220℃ for 150 hours, the endurance strength can reach 180MPa.

[0025] This invention provides a high-strength cast aluminum alloy for lightweight component design in aerospace, automotive and other fields. Attached Figure Description

[0026] Figure 1 The DSC curve of the alloy prepared in Example 1;

[0027] Figure 2 Enhanced phase morphology for HRTEM observation. Detailed Implementation

[0028] Specific Implementation Method 1: In this implementation method, a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy is composed of 6.5-7.5% Si, 1-1.3% Cu, 0.70-0.80% Mg, 0.50-0.90% Ag, 0.10-0.25% Mn, 0.08-0.12% Ti, 0.04-0.10% V, 0.0015-0.0030% Be, 0.0030% Ca, 0.0070-0.030% Sr, 0.015% B, and the balance Al.

[0029] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the hypoeutectic aluminum-silicon cast aluminum alloy is composed of 7.3% Si, 1.3% Cu, 0.75% Mg, 0.8% Ag, 0.2% Mn, 0.1% Ti, 0.07% V, 0.0025% Be, 0.0030% Ca, 0.0075-0.025% Sr, 0.015% B, and the balance Al by mass fraction. Other steps are the same as in Specific Implementation Method One.

[0030] Specific Implementation Method 3: This implementation method describes a method for preparing a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy, which is carried out according to the following steps:

[0031] I. Weigh out refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, AlV4 master alloy, pure magnesium, pure silver, cathode copper, AlB3 master alloy, AlSr5 master alloy, and AlCa10 master alloy according to the following mass fractions: 6.5-7.5% Si, 1-1.3% Cu, 0.70-0.80% Mg, 0.50-0.90% Ag, 0.10-0.25% Mn, 0.08-0.12% Ti, 0.04-0.10% V, 0.0015-0.0030% Be, 0.0030% Ca, 0.0070-0.030% Sr, 0.015% B, and the balance Al.

[0032] 2. Place the refined aluminum ingot, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, and AlV4 master alloy into a crucible for melting. When the melt temperature reaches 755-765℃, stir the melt and remove slag.

[0033] 3. Immerse pure magnesium, pure silver, and cathode copper into the melt. After they are completely melted, stir evenly. Add AlB3 intermediate alloy to refine the grains. After they are completely melted, stir evenly and let stand for 5 to 10 minutes.

[0034] IV. When the melt temperature is 740-750℃, add AlSr5 master alloy and AlCa10 master alloy. After they are completely melted, let them stand for 5 minutes, then use them for degassing and refining, and then pour them to obtain aluminum alloy castings.

[0035] Fifth, the aluminum alloy castings are subjected to three stages of solution treatment, quenching, pre-aging treatment, and aging treatment to complete the process.

[0036] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that the cathode copper is a copper sheet cut from a 1cm thick cathode copper plate. All other steps are the same as in Specific Implementation Method Three.

[0037] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Three or Four in that the size of the copper sheet is 5cm × 5cm × 1cm. The other steps are the same as in Specific Implementation Method Three or Four.

[0038] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods Three to Five in that it employs gravity or anti-gravity casting methods. If casting is done using a metal mold, the mass fraction of Sr in the alloy is 0.0075%; if casting is done using a sand mold, the mass fraction of Sr in the alloy is 0.025%. The other steps are the same as in Specific Implementation Methods Three to Five.

[0039] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods Three to Six is ​​that the three-stage solution treatment involves holding at 503°C for 5 hours, heating to 525°C and holding for 5 hours, and heating to 530°C and holding for 15 hours. The other steps are the same as in Specific Implementation Methods Three to Six.

[0040] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods Three to Seven is that the quenching water temperature is 20℃~40℃. The other steps are the same as those in Specific Implementation Methods Three to Seven.

[0041] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods Three to Eight is that the pre-aging treatment is carried out at room temperature for 8 to 10 hours. The other steps are the same as those in Specific Implementation Methods Three to Eight.

[0042] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods Three to Nine is that the aging temperature for the aging treatment is 170℃~180℃, and the holding time is 8h~15h. The other steps are the same as those in Specific Implementation Methods Three to Nine.

[0043] The beneficial effects of the present invention are verified using the following embodiments:

[0044] Example 1: This example describes a method for preparing a high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy, which is carried out according to the following steps:

[0045] I. Weigh out refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, AlV4 master alloy, pure magnesium, pure silver, cathode copper, AlB3 master alloy, AlSr5 master alloy, and AlCa10 master alloy according to the following mass fractions: 7.3% Si, 1.3% Cu, 0.75% Mg, 0.8% Ag, 0.2% Mn, 0.1% Ti, 0.07% V, 0.0025% Be, 0.0030% Ca, 0.0075% Sr, 0.015% B, and the balance Al.

[0046] 2. First, place refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, and AlV4 master alloy into a crucible. When the melt temperature reaches 760℃, stir the melt and remove slag. Add pure magnesium blocks, pure silver particles, and cathode copper sheets using a strainer, ensuring they sink below the melt surface to prevent oxidation of Cu, Mg, and Ag elements. After they are completely dissolved, stir evenly. Add AlB3 master alloy to refine the grains. After it is completely dissolved, stir evenly and let it stand for 5 minutes. When the temperature is adjusted to 745℃, add filamentous AlSr5 master alloy and AlCa10 master alloy to achieve Sr and Ca contents of 0.0075% and 0.0030%, respectively. After they are completely melted, let it stand for 5 minutes. Then, use a refining mill for degassing and refining, and pour the metal mold casting.

[0047] Figure 1 The DSC curve for the alloy heating stage in this embodiment is shown. The endothermic peak temperature ② is 507.9℃. At this temperature, a low melting point phase melts. In order to avoid overheating, it is necessary to keep the temperature at this point for a period of time to allow the melting point phase to completely dissolve and diffuse into the matrix before continuing to heat up.

[0048] Therefore, the heat treatment process in this embodiment is as follows:

[0049] Solution treatment: Hold at 503℃ for 5 hours. Increase the temperature to 525℃ and hold for 5 hours, then increase the temperature to 530℃ and hold for 15 hours. Quench with water at room temperature, with a transfer time not exceeding 10 seconds.

[0050] After being placed at room temperature for 10 hours for pre-aging treatment, it is then placed in an aging furnace at 180℃ for 9 hours and then air-cooled after being removed from the furnace.

[0051] In this embodiment, the strengthening phases after heat treatment of the alloy are β'' phase (Mg2Si) and Q' phase (Al5Cu2Mg8Si6), a dual strengthening phase, see [link to documentation]. Figure 2 .

[0052] In this embodiment, the alloy casting single-cast specimens, after heat treatment, exhibited tensile strengths between 380 MPa and 410 MPa at room temperature, yield strengths between 325 MPa and 360 MPa, and elongation between 4% and 6%. At 220°C, the tensile strengths ranged from 290 MPa to 320 MPa, the yield strength from 275 MPa to 290 MPa, and the elongation from 5% to 7%. After continuous exposure to 220°C for 150 hours, the creep rupture strength reached 180 MPa.

[0053] The alloy of this embodiment exhibits good fluidity, with a solid-liquid temperature range of 549℃ to 613℃ and a temperature difference of 64℃. Its tendency to porous is slightly lower than that of the ZL114A alloy, while their fluidity is similar. Its tensile strength and yield strength are both more than 70 MPa higher than those of ZL114A. While the ZL114A alloy is used in environments below 150℃, the alloy of this invention can operate for extended periods at 220℃ without failure.

Claims

1. A high-strength, heat-resistant hypoeutectic aluminum-silicon cast aluminum alloy, characterized in that, The hypoeutectic aluminum-silicon cast aluminum alloy is composed of 7.3% Si, 1.3% Cu, 0.75% Mg, 0.8% Ag, 0.2% Mn, 0.1% Ti, 0.07% V, 0.0025% Be, 0.0030% Ca, 0.0075% Sr, 0.015% B, and the balance Al by mass fraction. The preparation method of the hypoeutectic aluminum-silicon cast aluminum alloy is carried out according to the following steps: I. Weigh out refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, AlV4 master alloy, pure magnesium, pure silver, cathode copper, AlB3 master alloy, AlSr5 master alloy, and AlCa10 master alloy according to the following mass fractions: 7.3% Si, 1.3% Cu, 0.75% Mg, 0.8% Ag, 0.2% Mn, 0.1% Ti, 0.07% V, 0.0025% Be, 0.0030% Ca, 0.0075% Sr, 0.015% B, and the balance Al.

2. First, place refined aluminum ingots, AlSi30 master alloy, AlMn20 master alloy, AlTi10 master alloy, AlBe5 master alloy, and AlV4 master alloy into a crucible. When the melt temperature reaches 760℃, stir the melt and remove slag. Add pure magnesium, pure silver, and cathode copper. After they are completely melted, stir evenly. Add AlB3 master alloy to refine the grains. After it is completely melted, stir evenly and let it stand for 5 minutes. When the temperature is adjusted to 745℃, add AlSr5 master alloy and AlCa10 master alloy to make the Sr and Ca contents reach 0.0075% and 0.0030% respectively. After they are completely melted, let it stand for 5 minutes. Then, use a refining machine to degas and refine the metal mold casting. Finally, perform heat treatment to complete the process. The heat treatment process is as follows: Solution treatment: hold at 503℃ for 5 hours, raise the temperature to 525℃ and hold for 5 hours, raise the temperature to 530℃ and hold for 15 hours, quench in water at room temperature, and transfer time not exceeding 10 seconds. After being placed at room temperature for 10 hours for pre-aging treatment, it is then placed in an aging furnace at 180℃ for 9 hours and then air-cooled after being removed from the furnace. The heat-treated hypoeutectic aluminum-silicon cast aluminum alloy has two strengthening phases: β'' phase Mg2Si and Q' phase Al5Cu2Mg8Si6. Its room temperature tensile strength is between 380 MPa and 410 MPa, its yield strength is between 325 MPa and 360 MPa, and its elongation is between 4% and 6%. At 220℃, its tensile strength is between 290 MPa and 320 MPa, its yield strength is between 275 MPa and 290 MPa, and its elongation is between 5% and 7%. After 150 hours at 220℃, its creep rupture strength is 180 MPa.

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