Heat-treatment-free high-strength Al-Zn series aluminum alloy and preparation method
By adjusting the composition and process of Al-Zn aluminum alloys, high-strength heat-treatment-free aluminum alloys are prepared, which solves the problem of insufficient strength of existing casting alloys and realizes high-strength and easy-to-form aluminum alloy materials suitable for aerospace and other fields.
Patent Information
- Application Number
- CN202511210047.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-27
- Publication Date
- 2025-10-10
AI Technical Summary
Existing Al-Zn casting alloys are insufficiently strong and cannot meet the high-strength requirements of aerospace and automotive safety structural parts. Traditional deformable aluminum alloys also have poor forming adaptability, resulting in high equipment costs.
By adjusting the Zn content and adding Cu and Mn elements, combined with Zr and La microalloying, a high-strength Al-Zn aluminum alloy that does not require heat treatment is prepared. Its composition is optimized to form a strengthening phase and stable structure, the impurity content is controlled, and a specific melting and casting process is adopted.
It has been achieved that aluminum alloys with high yield strength of 200-374MPa and tensile strength of 420-483MPa can be obtained without heat treatment, which significantly improves the strength, improves the melt fluidity, facilitates the forming of complex components, and reduces production costs.
Smart Images
Figure CN120758769A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of metal materials, in particular to a heat-treatment-free high-strength Al-Zn series aluminum alloy and a preparation method thereof. BACKGROUND
[0002] Aluminum alloys have become widely used lightweight structural materials in the fields of aerospace and the like due to their low density and high specific strength. Al-Zn series cast alloys take zinc (Zn) as a main alloying element, and can form a strengthening phase through natural aging of zinc atoms in an aluminum matrix in a cast state, so that good mechanical properties can be obtained without complex heat treatment, thereby significantly reducing production cost and process complexity, and being widely applied. The conventional ZL401 alloy (Zn: 9-13 wt%) has a tensile strength generally distributed in the range of 200-250 MPa and a yield strength of about 150-200 MPa. Although this strength range can meet the requirements of general structural components, with the increasing demand for lightweight and high performance of high-end equipment, the strength limit of the existing alloy has become a key bottleneck restricting the expansion of its application. In particular, load-bearing components in the field of aerospace usually require a tensile strength of not less than 500 MPa, and automotive safety structural components also need to reach a strength standard of more than 300 MPa. In comparison, the strength index of conventional Al-Zn series cast alloys still has a significant gap.
[0003] Taking key components such as heavy-duty vehicle load wheels and aviation supports as examples, due to the insufficient strength and toughness of the existing cast aluminum alloys, deformed aluminum alloys (such as 7075-T6) are often forced to be used in engineering applications to improve the density and mechanical properties through plastic processing means such as extrusion and rolling. However, the anisotropy and residual stress caused by rapid plastic deformation lead to fatigue failure in shaped thin-walled components, and the forming adaptability of the deformation process to complex components is poor, resulting in a sharp increase in equipment cost and difficulty in meeting the requirements of integrated design.
[0004] Therefore, it is a key problem to be solved at present to develop a new high-strength heat-treatment-free Al-Zn series aluminum alloy. SUMMARY
[0005] In view of the problem of insufficient strength of the existing Al-Zn series cast alloys, the application provides a heat-treatment-free high-strength Al-Zn series aluminum alloy and a preparation method thereof. The performance of the aluminum alloy is regulated by changing the Zn content, adding Cu and Mn elements, and micro-alloying Zr and La.
[0006] The application is realized by the following technical scheme: A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by mass percentage, 15% to 45% Zn, 2.5% to 4.1% Cu, 0.1% to 0.5% Mn, and the remainder being Al and unavoidable impurities, wherein the Fe content of the impurities is less than 0.05%, and the Si content is less than 0.1%.
[0007] Preferably, by mass percentage, it further includes 0.1% to 0.5% of Zr and / or 0.1% to 0.5% of La.
[0008] Preferably, the cast metallographic structure of the Al-Zn aluminum alloy is a dendritic structure, including a white matrix α phase and a granular β phase.
[0009] Preferably, the Al-Zn aluminum alloy has a yield strength of 200-374 MPa, a tensile strength of 420-483 MPa, and an elongation of 2-16.5%.
[0010] A method for preparing a high-strength Al-Zn aluminum alloy that does not require heat treatment comprises the following steps: Add metal raw materials at a temperature of 745-755℃, stir to melt the metal elements, then refine them, and then cool them to 50℃-80℃ above the liquidus of Al to cast them to obtain high-strength aluminum alloy.
[0011] Preferably, the adding of the metal raw material at a temperature of 745-755° C. comprises: First, Al and Al-Mn master alloy are added and melted at 745-755°C; Then, Zn and Al-Cu master alloy were added and melted at 730°C.
[0012] Preferably, the process further comprises the following steps: after Zn and Al-Cu master alloy are melted, Al-Zr master alloy and pure La are added to obtain aluminum alloy solution.
[0013] Preferably, the refining method of the aluminum alloy solution is as follows: The aluminum alloy solution was refined under argon and stirring conditions for 20 minutes.
[0014] Preferably, the casting temperature is 700°C-730°C.
[0015] The application of a high-strength Al-Zn aluminum alloy that does not require heat treatment in load-bearing components in the aerospace field.
[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This application provides a heat-treatment-free, high-strength Al-Zn aluminum alloy. A high Zn content of 15% to 45% is key to improving strength. Compared to the 9% to 13% Zn content of the traditional ZL401 alloy, this significantly enhances the solid solution strengthening effect of zinc atoms in the aluminum matrix, allowing the alloy to form a large number of strengthening phases through natural aging in the cast state. This allows for excellent mechanical properties without the need for complex heat treatment, significantly reducing production process complexity and costs. Furthermore, the addition of 2.5% to 4.1% Cu synergizes with Zn, distributing it in clusters within the matrix, further enhancing the alloy's overall strength. The addition of 0.1% to 0.5% Mn refines the grains, and its segregation at the eutectic phase interface effectively inhibits eutectic phase coarsening, stabilizing the alloy's microstructure and ensuring the stability of its mechanical properties. Furthermore, strict control of impurity content (Fe < 0.05%, Si < 0.1%) is crucial to this solution. This prevents impurities like Fe and Si from forming brittle phases (such as Al-Si and Al-Fe phases) that could reduce the alloy's strength and toughness, ensuring consistent material properties. The alloy boasts a yield strength of 200-374 MPa and a tensile strength of 420-483 MPa, far exceeding the 200-250 MPa tensile strength of conventional Al-Zn casting alloys. This even meets the high-strength requirements of load-bearing components in the aerospace industry (tensile strength of at least 500 MPa), addressing the strength bottleneck of conventional alloys. Furthermore, the high Zn content improves the alloy's melt fluidity, making it easier to cast and form complex, irregularly shaped components. This overcomes the shortcomings of deformed aluminum alloys (such as 7075-T6) in complex component forming, which often result in fatigue failure, broadening its application. In summary, this technical solution achieves synergistic improvements in strength enhancement, process simplification, formability optimization, and impurity control through a scientific composition ratio, providing a new type of aluminum alloy material with the advantages of high strength, easy processing, and low cost for high-end fields such as aerospace. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.
[0018] Figure 1 This is a metallographic image of the cast high-strength Al-Zn aluminum alloy obtained in Example 8 of the present invention without heat treatment; Among them, Figure a is the 100um cast metallographic image, and Figure b is the 20um cast metallographic image. DETAILED DESCRIPTION
[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.
[0020] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.
[0021] A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by mass percentage, 15% to 45% Zn, 2.5% to 4.1% Cu, 0.1% to 0.5% Mn, and the remainder being Al and unavoidable impurities, wherein the Fe content of the impurities is less than 0.05%, and the Si content is less than 0.1%.
[0022] The cast metallographic structure of the heat-treatment-free high-strength Al-Zn aluminum alloy is a dendritic structure, including a white matrix α phase and a granular β phase.
[0023] The yield strength of the heat-treatment-free high-strength Al-Zn aluminum alloy is 200-374 MPa, the tensile strength is 420-483 MPa, and the elongation is 2-16.5%.
[0024] In some embodiments, the heat treatment-free high-strength Al-Zn aluminum alloy further comprises, by mass percentage, 0.1% to 0.5% Zr and / or 0.1% to 0.5% La.
[0025] The heat-treatment-free high-strength Al-Zn aluminum alloy fully exerts the solid solution strengthening effect by increasing the Zn content to the above range and adding an appropriate amount of Cu element. The Cu element exists in the matrix in the form of clusters, further producing a synergistic strengthening effect. In addition, some Zn and Cu elements form a eutectic phase. The appropriate addition of Mn element can refine the grains, and the Mn element is concentrated at the eutectic phase interface, which can inhibit the coarsening of the eutectic phase and stabilize the microstructure of the alloy. Compared with traditional ZL401 and ZL402 alloys, the strength of the above-mentioned Al-Zn-Cu-Mn alloy is doubled. Compared with ordinary cast aluminum alloys, the high Zn content also significantly improves the melt fluidity of the alloy, which is beneficial to the forming of complex components. In addition, by adding Zr and La elements for microalloying, the grain size is refined and the yield strength of the alloy is improved. This Al-Zn alloy can achieve a comprehensive performance matching of yield strength of 200MPa~374MPa, tensile strength of 420MPa~483MPa, and elongation of 2%~16.5% without the need for heat treatment.
[0026] Based on the above-mentioned high-strength Al-Zn aluminum alloy, the present application also provides a method for preparing a high-strength Al-Zn aluminum alloy without heat treatment, comprising the following steps: Metal raw materials are added at a temperature of 745-755°C, stirred to melt the metal elements, and then refined. The temperature is then lowered to 50-80°C above the liquidus of Al and cast to obtain a high-strength aluminum alloy.
[0027] In some embodiments, the metal feedstock includes Al, Zn, Mn, Cu, Zr, and La.
[0028] In some embodiments, the metal raw material includes Zn, Al-Cu master alloy, Al-Mn master alloy, Al-Zr master alloy, and pure La.
[0029] Optionally, the metal raw material is added as follows: First, add Al and Al-Mn master alloy and melt them at 745-755℃; Then, Zn and Al-Cu master alloy were added and melted at 730°C; Then, Al-Zr master alloy and pure La are added to the obtained mixed metal solution to obtain an aluminum alloy solution.
[0030] In some embodiments, the aluminum alloy solution is refined as follows: The aluminum alloy solution was refined under argon and stirring conditions for 20 minutes.
[0031] In some embodiments, the temperature 50°C-80°C above the liquidus of the Al is 700°C-730°C.
[0032] In some embodiments, a water-cooled copper mold is used in the casting process.
[0033] Embodiment 1 A heat-treatment-free high-strength Al-Zn series aluminum alloy, by mass percentage, includes Zn: 10.1%, Cu: 2.9%, Mn: 0.2%, Zr: 0.2%, and the rest is Al and inevitable impurities.
[0034] The preparation method of the heat-treatment-free high-strength Al-Zn series aluminum alloy is as follows: Step 1, prepare raw materials according to alloy composition: including pure Al, pure Zn, Al-Cu intermediate alloy, Al-Mn intermediate alloy, and Al-Zr intermediate alloy, and Al ingots with a purity of 99.99% are selected. The raw materials should be clean, rust-free, and oil-free to avoid bringing in gas during smelting and causing spattering.
[0035] Step 2, melting-refining-slag removal-casting; Heat the smelting furnace to 745℃, add pure Al and Al-Mn intermediate alloy; after complete melting, reduce the temperature to 730℃, add pure Zn and Al-Cu intermediate alloy; after complete melting, add Al-Zr intermediate alloy; after complete melting, introduce high-purity argon with a purity of ≥99.9% and fully stir the melt for refining, and after 20 minutes of standing, remove the slag from the melt; the casting temperature is controlled at 50℃ above the liquidus, the furnace temperature is reduced to 700℃ after slag removal treatment, and the melt is poured into a water-cooled copper mold to obtain a heat-treatment-free high-strength Al-Zn series aluminum alloy casting.
[0036] Embodiment 2 A heat-treatment-free high-strength Al-Zn series aluminum alloy, by mass percentage, includes Zn: 10.1%, Cu: 2.9%, Mn: 0.2%, Zr: 0.2%, and the rest is Al and inevitable impurities.
[0037] The preparation method includes the following steps: Step 1, prepare raw materials according to alloy composition: including pure Al, pure Zn, Al-Cu intermediate alloy, Al-Mn intermediate alloy, and Al ingots with a purity of 99.99% are selected. The raw materials should be clean, rust-free, and oil-free to avoid bringing in gas during smelting and causing spattering.
[0038] Step 2, melting-refining-slag removal-casting: Heat the melting furnace to 750°C, add pure Al and Al-Mn master alloy; after they are completely melted, reduce the temperature to 730°C, add pure Zn and Al-Cu master alloy; after they are completely melted, introduce high-purity argon gas with a purity of ≥99.9% and stir thoroughly to refine the melt, let it stand for 20 minutes, and then skim the melt; the casting temperature should be controlled at 60°C above the liquidus, so after skimming, the furnace temperature is reduced to 710°C, and the melt is poured into a water-cooled copper mold to obtain a casting.
[0039] Example 3 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 17% Zn, 3.2% Cu, 0.4% Mn, and the remainder being Al and unavoidable impurities.
[0040] The preparation method of the alloy is the same as that of Example 2.
[0041] Example 4 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 24.8% Zn, 2.7% Cu, 0.3% Mn, 0.34% Zr, and the remainder being Al and unavoidable impurities.
[0042] The preparation method of the alloy is the same as that of Example 1.
[0043] Example 5 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 28.0% Zn, 2.1% Cu, 0.5% Mn, 0.2% Zr, and the remainder being Al and unavoidable impurities.
[0044] The preparation method of the alloy is the same as that of Example 1.
[0045] Example 6 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 35.2% Zn, 3.5% Cu, 0.25% Mn, and the remainder being Al and unavoidable impurities.
[0046] The preparation method of the alloy is the same as that of Example 2.
[0047] Example 7 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 33.9% Zn, 4.1% Cu, 0.1% Mn, 0.17% La, and the remainder being Al and unavoidable impurities.
[0048] The preparation method of the alloy comprises the following steps: Step 1. Prepare raw materials according to the alloy composition: pure Al, pure Zn, Al-Cu master alloy, Al-Mn master alloy, and pure La. Select Al ingots with a purity of 99.99%. Raw materials must be clean, rust-free, and oil-free to prevent the introduction of gases and splashing during smelting.
[0049] Step 2: melting - refining - slag removal - casting; The melting furnace is heated to 755°C, and pure Al and Al-Mn master alloy are added; after they are completely melted, the temperature is lowered to 730°C, and pure Zn and Al-Cu master alloy are added; after they are completely melted, pure La is added; after they are completely melted, high-purity argon gas with a purity of ≥99.9% is introduced and fully stirred to refine the melt. After standing for 20 minutes, the melt is skimmed; the casting temperature should be controlled at 80°C above the liquidus, so after the skimming treatment, the furnace temperature is reduced to 730°C, and the melt is poured into a water-cooled copper mold to obtain a casting.
[0050] Example 8 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 43.5% Zn, 3.3% Cu, 0.5% Mn, 0.3% La, and the remainder being Al and unavoidable impurities.
[0051] The preparation method of the alloy is the same as that of Example 7.
[0052] Example 9 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 15% Zn, 3% Cu, 0.3% Mn, 0.1% Zr, 0.5% La, and the remainder being Al and unavoidable impurities.
[0053] The preparation method of the alloy is the same as that of Example 7.
[0054] Example 10 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 45% Zn, 2.8% Cu, 0.35% Mn, 0.5% Zr, 0.2% La, and the remainder being Al and unavoidable impurities.
[0055] The preparation method of the alloy is the same as that of Example 7.
[0056] Comparative Example 1 A high-strength Al-Zn aluminum alloy that does not require heat treatment comprises, by weight percentage, 9.1% Zn, 7.0% Si, 0.2% Mg, and the remainder being Al and unavoidable impurities.
[0057] The preparation method of the alloy comprises the following steps: Step 1, prepare raw materials according to alloy composition: including pure Al, pure Zn, Al-Si master alloy, Al-Mg master alloy, and select Al ingot with purity up to 99.99%. The raw materials should be clean, rust-free, and oil-free to avoid bringing in gas during smelting and producing spatter.
[0058] Step 2, melting-refining-slagging-casting; Heat the smelting furnace to 755℃, add pure Al; after it is completely melted, lower the temperature to 730℃, add Al-Si master alloy and pure Zn; after it is completely melted, add Al-Mg master alloy; after it is completely melted, introduce high-purity argon gas with purity ≥99.9% and fully stir the melt for refining, and after 20 minutes of standing, perform slagging on the melt; the casting temperature should be controlled at 70℃ above the liquidus, therefore after slagging treatment, the furnace temperature is lowered to 720℃, the melt is poured into a water-cooled copper mold, and the casting is obtained.
[0059] Comparative Example 1 is a control ZL401 aluminum alloy sample, and the ZL401 aluminum alloy sample corresponding to Comparative Example 1 is subjected to room temperature tensile testing according to the GB / T228.1-2021 “Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature” standard, and the corresponding mechanical property values are shown in Table 1.
[0060] Comparative Example 2 A heat-treatment-free high-strength Al-Zn series aluminum alloy, with Zn: 5.5%, Mg: 0.5%, Ti: 0.2% by weight, and the rest being Al and unavoidable impurities.
[0061] The preparation method of the alloy comprises the following steps: Step 1, prepare raw materials according to alloy composition: including pure Al, pure Zn, Al-Si master alloy, Al-Mg master alloy, and select Al ingot with purity up to 99.99%. The raw materials should be clean, rust-free, and oil-free to avoid bringing in gas during smelting and producing spatter.
[0062] Step 2, melting-refining-slagging-casting; Heat the smelting furnace to 745℃, add pure Al; after it is completely melted, lower the temperature to 730℃, add pure Zn; after it is completely melted, lower the temperature to 680℃, add Al-Mg master alloy; after it is completely melted, raise the temperature to 730℃, add Al-Ti master alloy; after it is completely melted, introduce high-purity argon gas with purity ≥99.9% and fully stir the melt for refining, and after 20 minutes of standing, perform slagging on the melt; the casting temperature should be controlled at 50℃ above the liquidus, therefore after slagging treatment, the furnace temperature is lowered to 700℃, the melt is poured into a water-cooled copper mold, and the casting is obtained.
[0063] Comparative Example 2 is a control ZL402 aluminum alloy sample. The ZL402 aluminum alloy sample corresponding to Comparative Example 2 is subjected to room temperature tensile test in accordance with GB / T228.1-2021 "Tensile Test of Metallic Materials Part 1: Room Temperature Test Method" standard, and the corresponding mechanical property values are shown in Table 1.
[0064] The mechanical properties of Comparative Examples 1-2 and Examples 1-9 are shown in Table 1.
[0065] Tensile performance test: According to GB / T 228.1-2021 "Tensile tests on metallic materials - Part 1: Room temperature test method".
[0066] Table 1 Yield strength, tensile strength and elongation of each alloy in the examples and comparative examples
[0067] Table 1 shows the yield strength, tensile strength, and elongation of the alloys of Comparative Examples 1-2 and Examples 1-8. According to the data in Table 1, compared with existing ZL401 and ZL402 samples, the alloy strength of the present invention is significantly improved with increasing Zn content. The combined addition of Cu and Mn further increases the alloy strength, reaching a yield strength of 363 MPa, a tensile strength of 483 MPa, and an elongation of 12%. The alloy exhibits excellent overall mechanical properties, far exceeding those of existing ZL401 and ZL402. However, the addition of La reduces ductility and has a limited effect on improving strength.
[0068] Figure 1 The as-cast metallographic structure of the high-strength Al-Zn-based heat-treatment-free aluminum alloy obtained in Example 8 is shown. It can be seen that it presents a typical dendritic structure, mainly composed of a white matrix α phase and a granular β phase.
[0069] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.
Claims
1. A high-strength Al-Zn aluminum alloy that does not require heat treatment, characterized in that: Calculated by mass percentage, it includes 15% to 45% Zn, 2.5% to 4.1% Cu, 0.1% to 0.5% Mn, and the rest is Al and unavoidable impurities, and the Fe content in the impurities is less than 0.05%, and the Si content is less than 0.1%.
2. The high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 1, characterized in that: Calculated by mass percentage, it also includes 0.1% to 0.5% of Zr and / or 0.1 to 0.5% of La.
3. The high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 1, characterized in that: The cast metallographic structure of the Al-Zn aluminum alloy is a dendritic structure, including a white matrix α phase and a granular β phase.
4. The high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 1, characterized in that: The Al-Zn aluminum alloy has a yield strength of 200-374 MPa, a tensile strength of 420-483 MPa, and an elongation of 2-16.5%.
5. A method for preparing a high-strength Al-Zn aluminum alloy that does not require heat treatment according to any one of claims 1 to 4, characterized in that: The following steps are involved: Add metal raw materials at a temperature of 745-755℃, stir to melt the metal elements, then refine them, and then cool them to 50℃-80℃ above the liquidus of Al to cast them to obtain high-strength aluminum alloy.
6. The method for preparing a high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 5, wherein: The step of adding the metal raw material at a temperature of 745-755° C. comprises: First, Al and Al-Mn master alloy are added and melted at 745-755°C; Then, Zn and Al-Cu master alloy were added and melted at 730°C.
7. The method for preparing a high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 6, wherein: The method further comprises the following steps: after Zn and Al-Cu master alloy are melted, Al-Zr master alloy and pure La are added to obtain aluminum alloy solution.
8. The method for preparing a high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 5, wherein: The refining method of the aluminum alloy solution is as follows: The aluminum alloy solution was refined under argon and stirring conditions for 20 minutes.
9. The method for preparing a high-strength Al-Zn aluminum alloy that does not require heat treatment according to claim 5, wherein: The casting temperature is 700°C-730°C.
10. Use of the heat-treatment-free high-strength Al-Zn aluminum alloy according to claims 1 to 4 in load-bearing components in the aerospace field.