High-strength heat-resistant aluminum alloy and preparation method thereof

Abstract

The invention relates to the technical field of aluminum alloy materials, in particular to a high-strength heat-resistant aluminum alloy and a preparation method thereof.The high-strength heat-resistant aluminum alloy comprises, by mass, 7%-12% of Si, 1%-1.5% of Ni, 0.4%-1.5% of Fe, 0.1%-1% of Mn, 0.2%-0.7% of Cu, 0.1%-0.6% of Mg, 0.01%-0.2% of Zr, 0.01%-0.2% of Ti and the balance Al and impurities; wherein the impurity element content is less than or equal to 0.1%, Ni + Fe is less than or equal to 2.5%, and Ni / (Fe + Mn) is more than or equal to 1 and less than or equal to 1.4. A fine multi-element eutectic phase is obtained by regulating and controlling the components of all the elements, the multi-element eutectic phase is combined with other phases, and the strength of the material at the normal temperature and the high temperature is effectively improved; meanwhile, the requirement of an application end for the heat resistance of alloy components, the requirement of a design end for the forming performance of complex components and the requirement of a production end for the high impurity tolerance of alloy components are met.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy materials, and in particular to a high-strength heat-resistant aluminum alloy and a preparation method thereof. Background Art

[0002] Al-Si alloys have become an ideal substitute for lightweight automotive parts such as engine cylinder blocks, cylinder heads and pistons due to their low density, high strength and excellent casting properties. However, in recent years, with the continuous improvement of automobile engine efficiency, engines tend to have higher operating temperatures and working pressures. Traditional heat-resistant cast Al-Si alloys such as ZL109 and ZL117 generally have a tensile strength of no more than 120MPa at 300°C, and high-temperature performance can hardly meet service requirements. At the same time, with the advancement of policies, the ceiling of electrolytic aluminum production capacity and the elasticity of raw aluminum supply have weakened, and foundries have a strong demand for the recycling of materials, which requires materials to have a higher impurity tolerance. Traditional heat-resistant cast aluminum alloys such as A356 have a low Fe impurity tolerance, which is difficult to meet the demand for material recycling.

[0003] Prior art 1: CN111304500A discloses a cast aluminum alloy for a high power density piston and a preparation method thereof, wherein the aluminum alloy comprises 11.0-12.6wt.% Si, 3.5-4.5wt.% Cu, 0.7-1.2wt.% Mg, 2.2-3.2wt.% Ni, 0.6-0.8wt.% Fe, 0.25-0.35wt.% Mn, 0.10-0.15wt.% Sc, 0.13-0.17wt.% Zr, 0.13-0.17wt.% Ti, 0.08-0.12wt.% V, the remainder being Al and unavoidable impurities, and the mass ratio of Fe / Mn in the aluminum alloy is 1.71-3.2. This technology mainly increases the heat-resistant phase by adding Fe, Ni, Cu, Sc and other elements to Al-Si alloy, and adds Ti, Zr, V and other elements to refine the grains and improve the stability of the structure. However, the addition of Sc and the higher content of Cu and Ni increase the cost of the alloy. At the same time, if the Cu element in the alloy exceeds 3%, it is easy to cause hot cracking defects in the casting process, which is not conducive to the preparation of large and complex castings.

[0004] Prior art 2: CN113789453A discloses a method for improving the high temperature strength of heat-resistant aluminum alloys by Mn microalloying, wherein the intermediate alloy ingot is weighed according to the required composition ratio, melted in a resistance furnace, and poured into a metal mold or sand mold for forming after standing and refining. This technology mainly improves the high temperature coarsening resistance of the precipitated phase by adding Mn elements on the basis of Al-Si-Cu alloy, inhibits the phase change that occurs during the high temperature process, and improves the high temperature resistance of the aluminum alloy; however, the Cu content of the alloy is relatively high, and the alloy is prone to hot cracking defects during the casting process, and the high temperature strengthening phase is single, and the high temperature strength improvement is limited, and the tensile strength at 300°C in the T6 state is only 95MPa.

[0005] Another example of prior art 3: CN114774741A discloses a heat-resistant high-strength cast aluminum alloy and a method for manufacturing the same, wherein the aluminum alloy comprises the following elements: 7.0-9.0wt.% Si, 1.0-2.0wt.% Cu, 0.3-0.4wt.% Mg, 0.12-0.16wt.% Mn, 0.1-0.15wt.% Ti, 0.08-0.2wt.% V, 0.08-0.2wt.% Zr, and the remainder is Al and unavoidable impurity elements, wherein Fe among the impurity elements is not more than 0.12%, and the sum of other impurity elements is not more than 0.2%. This technology is mainly based on Al-Si alloy, by adding Cu, Mg, Zr, V and other elements to obtain heat-resistant Q (Al5Mg8Si6Cu2) phase and dispersed Al3Zr, Al3 (Zr, V) nanoparticle phase, which significantly enhances the comprehensive mechanical properties of the alloy while ensuring the alloy casting performance; but the alloy has a low tolerance for the impurity element Fe, and the content does not exceed 0.12%, which limits the use of recycled aluminum.

[0006] In summary, it is difficult for existing technologies to simultaneously meet the application end's requirements for the heat resistance of alloy components, the design end's requirements for the formability of complex components, and the production end's requirements for the high impurity tolerance of alloy components. Summary of the invention

[0007] The present invention aims to provide a high-strength heat-resistant aluminum alloy and a preparation method thereof, so as to solve the technical problem that the prior art is difficult to simultaneously meet the comprehensive performance requirements of the mass production process for impurity tolerance, casting performance, thermal stability, etc.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme:

[0009] A high-strength heat-resistant aluminum alloy comprises the following components in percentage by mass: 7-12% Si, 1-1.5% Ni, 0.4-1.5% Fe, 0.1-1% Mn, 0.2-0.7% Cu, 0.1-0.6Mg, 0.01-0.2% Zr, 0.01-0.2% Ti, and the remainder is Al and impurities; wherein the content of impurity elements is ≤0.1%, Ni+Fe is ≤2.5%, and 1 is ≤Ni / (Fe+Mn) ≤1.4.

[0010] Invention concept:

[0011] In order to solve the problems existing in the above-mentioned background technology, the inventors of the present application have conducted a lot of research. By reasonably designing different Si / Fe / Ni / Mn ratios, when Ni+Fe≤2.5%, 1≤Ni / (Fe+Mn)≤1.4, the size, number density, morphology and distribution state of the precipitated phase can be effectively regulated to obtain a fine high thermal stability phase (that is, the heat-resistant eutectic phase or multi-electrotectic phase described below); that is, when the Al-Si-Ni-Fe near-eutectic composition alloy solidifies, a eutectic reaction Liquid→α-Al+Si+(Al,Si)5(Fe,Ni) occurs, and the existence of this multi-electrotectic phase effectively regulates the needle-shaped Fe-rich phase and improves the stability of the alloy.

[0012] In order to ensure the die-casting forming performance of the alloy, the Si addition amount close to the Al-Si eutectic composition is selected, and the addition amount of other strengthening alloy elements is adjusted so that the alloy composition is close to the multi-element eutectic composition point to ensure the flow performance of the alloy. In order to ensure the demoulding performance of the alloy and make the alloy have the advantage of recyclability, a higher content of Fe element is added. As the most common impurity element in Al-Si alloy, the solubility of Fe in Al at room temperature is only 0.02%. Generally, the excess Fe exists in the form of narrow needle-shaped iron-rich phase, which strongly splits the matrix and damages the plasticity of the alloy. The present invention obtains a multi-element eutectic phase, so that the Fe element exists in the form of a multi-element eutectic refinement phase, which significantly hinders the slip and dislocation movement of grain boundaries.

[0013] By controlling the addition amount of Cu element to be less than 0.7%, the excessive Cu content is avoided to aggravate the tendency of the alloy to heat crack; and the existence of the heat-resistant eutectic phase obtained by the present invention enhances the high-temperature heat resistance of the alloy on the one hand, avoids the splitting of the needle-shaped Fe phase from the matrix, and on the other hand improves the tolerance of the alloy to Fe impurities, thereby improving the recyclability of the alloy. At the same time, by adding appropriate amounts of Cu, Mg and Zr elements and forming β phase (Mg2Si), Q phase (Al5Mg8Si6Cu2) and Al3Zr and Al3Ti phases with L12 structure through solid solution + artificial aging, the nano-scale precipitation phase is pinned in the matrix to hinder the movement of dislocations, and a multi-dimensional and multi-scale "heat-resistant eutectic phase + nano-precipitation phase" strengthening and toughening organization is constructed, thereby further improving the high-temperature performance.

[0014] Technical principles and beneficial effects:

[0015] 1. The role of Si element:

[0016] The Si addition amount of 7-12% is selected to utilize its large latent heat of solidification to ensure the die-casting performance of the alloy, so that the alloy has good fluidity and can fill complex mold cavities, which is crucial for manufacturing complex-shaped parts such as engine pistons. At the same time, Si is one of the key elements in the formation of multi-element eutectic structure. It participates in the eutectic reaction with other elements during the solidification process, which helps to build a stable microstructure.

[0017] 2. Multiple effects of Fe element:

[0018] A higher content of Fe element (0.4-1.5%) is added, and it exists in the form of a multi-element eutectic phase, rather than the traditional narrow needle-shaped iron-rich phase. This multi-element eutectic refinement phase can significantly hinder the slip and dislocation movement of the grain boundaries. This is because the eutectic phase forms a physical barrier at the grain boundary, increasing the resistance to dislocation movement, thereby improving the strength of the alloy; at the same time, the existence of this eutectic phase avoids the needle-shaped Fe phase from cutting the matrix, protecting the plasticity of the alloy, making it less likely for the alloy to undergo brittle fracture when subjected to external forces, thereby improving the comprehensive mechanical properties of the alloy. In addition, the rational use of the Fe element increases the alloy's tolerance to Fe impurities, allowing the alloy to use recycled aluminum as raw material, achieving recyclability and reducing production costs.

[0019] 3. Synergistic effect of Ni and Mn elements:

[0020] By introducing transition elements Ni (1-1.5%) and Mn (0.1-1%) and through a specific Si / Fe / Ni / Mn ratio (Ni+Fe≤2.5%, 1≤Ni / (Fe+Mn)≤1.4), effective regulation of the precipitate phase is achieved. Ni and Mn interact with other elements to promote the formation of uniform and fine precipitate phases during solidification. They can participate in the formation of complex intermetallic compounds. These compounds act as heterogeneous crystal nuclei, refine the grain structure, further hinder dislocation movement, and improve the strength of the alloy. At the same time, this ratio design helps to optimize the size, number density, morphology and distribution state of the precipitate phase, so that the precipitate phase can more effectively enhance the performance of the alloy.

[0021] 4. Control of Cu element:

[0022] Controlling the addition of Cu element between 0.2-0.7% avoids the aggravation of the alloy's thermal cracking tendency caused by excessive Cu content. Although Cu can play a certain strengthening role in aluminum alloys, excessive Cu content will cause the alloy to produce greater thermal stress during the solidification process, which is easy to cause cracks. By limiting the Cu content, the stability of the alloy during the casting process is guaranteed, ensuring the molding quality of complex structural parts.

[0023] The present invention also provides a method for preparing a high-strength heat-resistant aluminum alloy, comprising the following steps:

[0024] S1. Ingredients: industrial pure aluminum, magnesium metal, Al-Si master alloy, Al-Ni master alloy, Al-Cu master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Zr master alloy, Al-Fe master alloy, and sorted, cleaned, and preheated waste aluminum materials are mixed as raw materials, and the raw materials are calculated, weighed, and prepared to obtain alloy raw materials;

[0025] S2, smelting: adding the raw materials in S1 into the smelting furnace in order, adjusting the components to meet the design requirements, and obtaining an alloy melt;

[0026] S3, refining: cooling down and degassing and refining the alloy melt;

[0027] S4, casting: feeding the alloy melt obtained in S3 into a casting machine, and obtaining a casting after casting;

[0028] S5. Heat treatment: heat treatment of castings.

[0029] Preferably, in step S1, the raw material is subjected to drying pretreatment at a drying temperature of 150-200° C. for 1-2 hours.

[0030] Preferably, in step S2, the temperature of the alloy melt is 740-780°C.

[0031] Preferably, in step S3, the refining temperature is 710-720°C, and the alloy melt density is ≥2.65g / cm3.

[0032] Preferably, in step S4, the casting method is one of gravity casting and high pressure casting, wherein the gravity casting temperature is 710-720°C and the mold temperature is 150-200°C.

[0033] Preferably, in step S5, the heat treatment includes solution treatment at a temperature of 520-580°C for 4-8 hours, after which the alloy is rapidly cooled in water to room temperature, with a quenching transfer time of less than 30 seconds; and artificial aging at an aging temperature of 150-200°C for 2-8 hours.

[0034] Technical principles and beneficial effects:

[0035] 1. Formation and function of β phase (Mg2Si) and Q phase (Al5Mg8Si6Cu2)

[0036] Adding appropriate amounts of Mg (0.1-0.6%) and Cu (0.2-0.7%) elements, they will interact to form β phase (Mg2Si) and Q phase (Al5Mg8Si6Cu2) during the solid solution + artificial aging treatment. These phases are evenly distributed in the alloy, playing a role in precipitation strengthening. The formation of β phase and Q phase increases the number of second phase particles in the alloy. These particles interact with dislocations and hinder the movement of dislocations, thereby increasing the strength of the alloy; at the same time, their presence also helps to improve the stability of the alloy at high temperatures, because these phases are not prone to coarsening and decomposition at high temperatures, and can continuously and effectively strengthen the alloy.

[0037] 2. Strengthening mechanism of Al3Zr and Al3Ti phases with L12 structure

[0038] Trace amounts of Zr (0.01-0.2%) and Ti (0.01-0.2%) elements combine with Al atoms in the alloy, and after solid solution + artificial aging treatment, form Al3Zr and Al3Ti phases with L12 structure. These nanoscale precipitates have high stability and good coherence with the matrix. They are dispersed in the alloy and become a strong obstacle to dislocation movement, pinning dislocations and making them difficult to move, thereby significantly improving the strength of the alloy; moreover, these nano-precipitates can also maintain their strengthening effect at high temperatures, which helps to improve the high-temperature performance of the alloy. This multi-element and multi-scale "heat-resistant eutectic phase + nano-precipitate phase" strengthening and toughening organization design enables the alloy to have good performance at different scales. On a macro level, the eutectic phase ensures the stability and heat resistance of the overall structure, and on a micro level, the nano-precipitate phase further enhances the local strength and toughness, thereby achieving an improvement in the overall performance of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the metallographic structure under the heat treatment conditions of 540°C*6h+170°C*4h in Example 1 of the present invention.

[0040] Figure 2 This is a schematic diagram of the metallographic structure under the heat treatment conditions of 540°C*6h+170°C*8h in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The present invention avoids the use of expensive rare earth elements, and the addition ratio of Ni and Cu elements is low. At the same time, it has a higher Fe impurity tolerance, so that the alloy has good economic applicability. At the same time, the design of the multi-element eutectic phase and the lower Cu content make the alloy have good die-casting forming performance, achieving a balance between mechanics, casting performance and cost.

[0042] A high-strength heat-resistant aluminum alloy comprises the following components in percentage by mass: 7-12% Si, 1-1.5% Ni, 0.4-1.5% Fe, 0.1-1% Mn, 0.2-0.7% Cu, 0.1-0.6Mg, 0.01-0.2% Zr, 0.01-0.2% Ti, and the remainder is Al and impurities; wherein the content of impurity elements is ≤0.1%, Ni+Fe is ≤2.5%, and 1 is ≤Ni / (Fe+Mn) ≤1.4.

[0043] The mass values ​​of the alloy components in the embodiments and comparative examples of the present invention are shown in Table 1.

[0044] A method for preparing a high-strength heat-resistant aluminum alloy comprises the following steps:

[0045] S1. Ingredients: industrial pure aluminum, magnesium metal, Al-Si master alloy, Al-Ni master alloy, Al-Cu master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Zr master alloy, Al-Fe master alloy and sorted, cleaned and preheated waste aluminum are mixed as raw materials, and calculation, weighing and material preparation are performed to obtain alloy raw material S1; wherein, the raw materials are dried before smelting, and the drying temperature is 150-200° C. and the drying time is 1-2 hours.

[0046] S2. Melting: Add the raw materials in S1 into the melting furnace in order, adjust the components to meet the design requirements, and obtain an alloy melt; the temperature of the alloy melt is 740-780°C.

[0047] S3. Refining: Cooling down and degassing and refining the alloy melt; the refining temperature is 710-720℃, and the density of the alloy melt is ≥2.65g / cm3.

[0048] S4, casting: the alloy melt obtained in S3 is fed into a casting machine, and a casting is obtained after casting; the casting method is one of gravity casting and high pressure casting, wherein the gravity casting temperature is 710-720°C, and the mold temperature is 150-200°C.

[0049] S5. Heat treatment: The casting is heat treated, including solution treatment, the solution temperature is 520-580℃, the time is 4-8h, after solution treatment, the alloy is quickly placed in water to cool to room temperature, the quenching transfer time is less than 30s; artificial aging, the aging temperature is 150-200℃, the time is 2-8h.

[0050] The various performance indicators of the alloy under different values ​​of the present invention are tested in combination with specific examples, see Table 2 for details.

[0051] Table 1: Alloy composition mass table in each embodiment and comparative example (mass percentage, wt%)

[0052]

[0053] Table 2: Processing technology and performance test indicators corresponding to different alloy components in various embodiments and comparative examples

[0054]

[0055]

[0056] According to Table 1-2, the following conclusions can be drawn:

[0057] According to Examples 1-3, due to the formation of a multi-element eutectic phase, such as Figure 1-2 As shown in the figure, a multi-scale strengthening phase distribution is formed, among which the coarser ones are Cu and Mg-containing phases, the finer ones are multi-element eutectic phases, and the dispersed strengthening phases precipitated after heat treatment are Al3Zr and Al3Ti phases; due to the existence and joint action of these eutectic phases, the high-temperature strength of the material is improved.

[0058] In addition, due to the presence of fine multi-element eutectic phases, the heat-resistant aluminum alloy in the present application improves the tolerance of the alloy to Fe impurities compared to existing aluminum alloys, avoids the cutting of the matrix by flake or needle-shaped Fe-containing phases, and improves the recyclability of the alloy; on the other hand, it can significantly hinder the slip and dislocation movement of grain boundaries, thereby enhancing the high-temperature heat resistance of the alloy.

[0059] According to the comparison between Comparative Example 1 and Example 1, it can be seen that in Comparative Example 1, Cu and Mg are not added, and its yield strength and tensile strength are greatly reduced, but the elongation is improved due to the reduction of coarse heat-resistant phases (containing Cu and Mg phases).

[0060] According to Comparative Example 2 compared with Example 1, the Cu and Mg contents are excessively added, resulting in a large number of coarse phases (containing Cu and Mg), which impairs the strength and elongation, especially the yield strength of the material.

[0061] According to Comparative Example 3 compared with Example 2, although the same amount of Cu and Mg elements were added, due to excessive addition of Fe+Ni, the fine quaternary eutectic composition of α-Al+Si+(Al,Si)5(Fe,Ni) was not completely formed, and a coarse Fe-containing primary phase appeared. The presence of the coarse phase impaired the strength and elongation of the alloy.

[0062] In summary, by controlling the composition of each element within the composition range of the present invention, a good coordination of multi-element and multi-scale reinforcement phases can be achieved, so that the heat-resistant aluminum alloy of the present application achieves effective improvement in room temperature mechanical properties and high temperature strength compared with similar alloys.

[0063] In addition, the aluminum alloy of the present invention has the following advantages compared with the several aluminum alloys mentioned in the background technology:

[0064] Compared with the prior art 1, the Cu element content is low, the casting performance is excellent, and the preparation of large and complex castings can be realized; compared with the prior art 2, the alloy strength is higher; compared with the prior art 3, the Fe impurity tolerance is high, and recycled aluminum can be used as raw material for smelting.

[0065] That is, the present invention can simultaneously meet the application end's requirements for the heat resistance of alloy components, the design end's requirements for the forming performance of complex components, and the production end's requirements for the high impurity tolerance of alloy components, and has good market potential.

[0066] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A high-strength heat-resistant aluminum alloy, characterized in that: The invention comprises the following components in percentage by mass: 7-12% Si, 1-1.5% Ni, 0.4-1.5% Fe, 0.1-1% Mn, 0.2-0.7% Cu, 0.1-0.6Mg, 0.01-0.2% Zr, 0.01-0.2% Ti, and the remainder is Al and impurities; wherein the content of impurity elements is ≤0.1%, Ni+Fe≤2.5%, and 1≤Ni / (Fe+Mn)≤1.

4.

2. A method for preparing a high-strength heat-resistant aluminum alloy, used to prepare a high-strength heat-resistant aluminum alloy as claimed in claim 1, characterized in that: The steps include: Step S1, batching: industrial pure aluminum, magnesium metal, Al-Si master alloy, Al-Ni master alloy, Al-Cu master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Zr master alloy, Al-Fe master alloy, and sorted, cleaned, and preheated waste aluminum materials are mixed as raw materials, and the raw materials are calculated, weighed, and prepared to obtain alloy raw materials; Step S2, smelting: adding the raw materials in S1 into the smelting furnace in order, adjusting the components to meet the design requirements, and obtaining an alloy melt; Step S3, refining: cooling the alloy melt and performing a degassing and refining treatment; Step S4, casting: feeding the alloy melt obtained in S3 into a casting machine, and obtaining a casting after casting; Step S5, heat treatment: heat treatment is performed on the casting.

3. The method for preparing a high-strength heat-resistant aluminum alloy according to claim 2, characterized in that: In step S1, the raw material is pre-treated by drying at a temperature of 150-200° C. for 1-2 hours.

4. The method for preparing a high-strength heat-resistant aluminum alloy according to claim 3, characterized in that: In step S2, the temperature of the alloy melt is 740-780°C.

5. The method for preparing a high-strength heat-resistant aluminum alloy according to claim 4, characterized in that: In step S3, the refining temperature is 710-720°C, and the alloy melt density is ≥2.65g / cm3.

6. The method for preparing a high-strength heat-resistant aluminum alloy according to claim 5, characterized in that: In step S4, the casting method is one of gravity casting and high pressure casting, wherein the gravity casting temperature is 710-720°C and the mold temperature is 150-200°C.

7. The method for preparing a high-strength heat-resistant aluminum alloy according to claim 6, characterized in that: In step S5, the heat treatment includes solution treatment at a temperature of 520-580°C for 4-8 hours, the alloy is rapidly placed in water to cool to room temperature after solution treatment, and the quenching transfer time is less than 30 seconds; artificial aging at a temperature of 150-200°C for 2-8 hours.

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