Thorium-doped 7-series aluminum alloy and preparation method and application thereof

Abstract

The invention relates to a thorium-doped 7-series aluminum alloy and a preparation method and application thereof, the aluminum alloy not only has high strength and high toughness, but also has better corrosion resistance, and can be applied to preparation of aviation products, armored products, ships, motor vehicles, building products, electronic products, sports equipment, aerospace products and national defense products.

Description

Technical Field

[0001] The present invention relates to the technical field of 7 series aluminum alloys, and in particular to a thorium-doped 7 series aluminum alloy and a preparation method and application thereof. Background Art

[0002] 7 series aluminum alloy uses zinc as the main alloying element, and its composition is generally Mg: 0.50% ~ 4.00%, Cu: 0.05% ~ 2.60%, Zn: 0.90% ~ 7.00%, Cr: 0.05% ~ 0.35%, Mn: 0.05% ~ 0.60%, Ti: 0.02% ~ 0.20%, and the balance is Al. With its advantages of high strength, high modulus, easy electrical and thermal conductivity, low density, good plasticity and processing properties, 7 series aluminum alloy is widely used in aerospace, military, civilian and other fields. However, its corrosion resistance is poor, especially in specific environments, such as stress corrosion cracking and hydrogen embrittlement, which affects its safe use.

[0003] In order to solve this problem, researchers have explored the preparation process of high-strength and high-corrosion-resistant alloys, and aimed to improve the corrosion resistance of 7-series aluminum alloys by adjusting the alloy ratio and optimizing the heat treatment process. For example, by adjusting the Zn / Mg ratio, using different deformation methods and regression re-aging processes, the microstructure, mechanical properties and corrosion resistance of the alloy have been optimized to a certain extent, but the current materials still cannot guarantee the safety of 7-series aluminum alloys in special environments.

[0004] Therefore, it is very important to develop a high-strength, corrosion-resistant 7 series aluminum alloy. Summary of the invention

[0005] At present, the use of thorium in 7-series aluminum alloys has not been reported. The inventors tried to improve the performance of 7-series aluminum alloys by doping thorium in 7-series aluminum alloys. Through experiments, it was found that directly adding thorium to 7-series aluminum alloys could not successfully disperse thorium in aluminum alloys to obtain the target aluminum alloy through smelting. Thorium could not be dissolved at a lower temperature, resulting in thorium being unable to fuse with the aluminum alloy. Although thorium was dissolved at high temperature, it would cause the volatilization of the main components of Mg and Zn in 7-series aluminum alloys and destroy the structure of 7-series aluminum alloys, resulting in the alloy obtained not being a 7-series aluminum alloy. After many attempts, it was found that an aluminum-thorium (Al-Th) master alloy could be prepared by first using a molten salt electrolysis method, and then the Al-Th master alloy was mixed with a 7-series aluminum alloy for smelting, and finally a thorium-doped 7-series aluminum alloy was successfully prepared. After performance testing, the inventors were pleasantly surprised to find that the prepared thorium-doped 7-series aluminum alloy not only had high strength and high toughness compared to the original 7-series aluminum alloy, but also had good corrosion resistance. The present invention was completed on this basis.

[0006] One aspect of the present invention relates to a 7 series aluminum alloy doped with thorium.

[0007] In some embodiments, based on the total mass of the aluminum alloy, the 7 series aluminum alloy contains 0.01% or more, 0.02% or more, 0.03% or more, 0.04% or more, or 0.05% or more thorium in terms of mass percentage. In some embodiments, based on the total mass of the aluminum alloy, the 7 series aluminum alloy contains 1.50% or less, 1.00% or less, 0.80% or less, 0.70% or less, or 0.60% or less thorium in terms of mass percentage. In some embodiments, based on the total mass of the aluminum alloy, the 7 series aluminum alloy contains 0.05% to 1.00%, 0.10% to 0.80%, 0.20% to 0.40%, or 0.40% to 0.60%, preferably 0.50% to 0.60% thorium in terms of mass percentage. It has been found through experiments that within the above-mentioned dosage range, it is beneficial to obtain an aluminum alloy with better comprehensive performance, such as a significant increase in tensile strength and yield strength, while the hardness is basically the same, and the corrosion resistance is enhanced.

[0008] In some embodiments, the 7 series aluminum alloy further includes, based on the total mass of the aluminum alloy, in mass percentage, Mg: 2.10% to 4.00%, Cu: 1.70% to 2.50%, Zn: 5.10% to 6.10%, Cr: 0.10% to 0.30%, Mn: 0.05% to 0.15%, and Ti: 0.01% to 0.10%.

[0009] In addition to the above-mentioned components, the balance of the 7 series aluminum alloy is generally aluminum. However, the 7 series aluminum alloy may also contain conventional unavoidable trace impurity components. In addition, for the purpose of further modifying the 7 series aluminum alloy, the 7 series aluminum alloy may further add trace amounts of other modifying components, such as zirconium, iron, cobalt, silicon, scandium, lithium, silver, cadmium, tin, indium, rare earth elements, etc., but not limited thereto.

[0010] On the other hand, the present invention provides a method for preparing the above-mentioned 7 series aluminum alloy, the method comprising:

[0011] S1: Obtain aluminum-thorium master alloy;

[0012] S2: The aluminum-thorium master alloy is mixed with other components for forming a 7 series aluminum alloy and melted.

[0013] In step S1, the aluminum-thorium master alloy can be commercially available, or can be prepared by any suitable method without particular limitation, for example, it can be prepared by referring to the preparation method of metal alloys with known large melting point differences, for example, by referring to the preparation method of rare earth-aluminum alloy, but is not limited thereto.

[0014] In some embodiments, the aluminum-thorium master alloy is prepared by molten salt electrolysis. The specific operation method of the molten salt electrolysis has been described in detail in the prior art, so the present invention does not specifically describe this. The molten salt electrolyte system can be selected from cryolite system, chloride system, chloride and fluoride mixed system, etc., but is not limited thereto.

[0015] In some embodiments, the aluminum-thorium master alloy can be prepared by referring to the preparation method of the aluminum-thorium alloy disclosed in CN116426983A, but the present invention is not limited thereto.

[0016] In some embodiments, the mass percentage of Th in the Al-Th master alloy is 10% to 20% based on the total mass of the alloy. Within this dosage range, it is beneficial to add the Al-Th master alloy to the 7-series aluminum alloy without affecting its basic properties. If the Th content is too high, the corresponding Al-Th master alloy is not easy to prepare; and if the Th content is too low, when the Al-Th master alloy is added to the 7-series aluminum alloy, its basic properties are easily affected, resulting in the alloy being unusable for its original purpose.

[0017] In step S2, other components used to form the 7 series aluminum alloy refer to other components except aluminum and thorium in the aluminum-thorium master alloy, such as Mg, Cu, Zn, Cr, Mn, Ti, etc., and the balance of aluminum.

[0018] The other components used to form the 7 series aluminum alloy can be added in the form of single elements, alloys or a combination thereof, and the present invention does not impose any particular restrictions on this. The amount of the other components used to form the 7 series aluminum alloy can be calculated based on the preset composition of the 7 series aluminum alloy and the content of aluminum and thorium in the aluminum-thorium master alloy.

[0019] In some embodiments, other components used to form the 7-series aluminum alloy may be added in the form of single elements. In this case, the required amount of each single element may be calculated based on the preset composition of the 7-series aluminum alloy and the content of aluminum and thorium in the aluminum-thorium master alloy, and then the ingredients may be proportioned and added according to the calculated amount.

[0020] In some embodiments, other components for forming the 7 series aluminum alloy are added in the form of an alloy, which may be an alloy of two or more components among the other components, or an alloy of all other components.

[0021] In some embodiments, the other composition used to form the 7 series aluminum alloy is a 7 series aluminum alloy that does not contain thorium, such as 7005, 7039, 7049, 7050, 7072, 7075, 7175, 7175, 7475, 7A03, 7A04 aluminum alloys.

[0022] In step S2, smelting can be performed using appropriate smelting temperature, heating rate and smelting time.

[0023] In some embodiments, the melting temperature may be 720-780°C, or 720-760°C, such as 725, 730, 735, 740, 745, 750, 755°C, etc. Within this temperature range, the aluminum-thorium alloy is conducive to the fusion with other alloy components. If the temperature is too low, the fusion may not be sufficient, and if the temperature is too high, it is not conducive to the stability of the alloy components.

[0024] The heating rate of smelting can be determined by a person skilled in the art by conventional methods. Generally speaking, if the heating rate is too slow, the time, energy and equipment cost of the operation will increase, which is not economical, while if the heating rate is too high, it may cause defects in the product. In some embodiments, the heating rate of smelting is 1°C / min or more, 2°C / min or more, or 5°C / min or more. In some embodiments, the heating rate of smelting can be less than 20°C / min, less than 15°C / min, or less than 10°C / min.

[0025] The melting time can be determined by a person skilled in the art by conventional methods. Generally speaking, if the melting time is too short, the fusion may be insufficient, while if the melting time is too long, the operation time, energy and equipment costs increase, which is not economical. In some embodiments, the melting time is more than 5 minutes or more than 10 minutes, or less than 2 hours, less than 1 hour, or less than 30 minutes.

[0026] The melting is carried out in an inert atmosphere (eg argon).

[0027] The method for preparing the 7 series aluminum alloy of the present invention may further include a degassing and slag removal step. For example, pure argon gas may be introduced to perform degassing and slag removal to remove surface slag inclusions.

[0028] The method for preparing the 7 series aluminum alloy of the present invention may further include a casting step. By casting the alloy solution into a mold, a 7 series aluminum alloy casting may be obtained.

[0029] The casting temperature may be 680-710°C, for example, 685, 690, 695, 700, 705°C, etc.

[0030] Another aspect of the present invention relates to an aluminum alloy material, which is made of the 7 series aluminum alloy according to the present invention. The aluminum alloy material can be a plate (such as a thin plate, a medium plate, a thick plate, etc.), a wire, a rod, a pipe, a profile, a component or a forging product.

[0031] The aluminum alloy material of the present invention can be connected with itself or other alloys to form new products, and can also be processed into final components through various processing methods, such as surface treatment, stamping, machining, etc.

[0032] The 7 series aluminum alloy according to the present invention not only has high strength and high toughness, but also has good corrosion resistance. The new 7 series aluminum alloy can be used for a variety of product applications, including aviation products (for example, aircraft structural parts, medium and thick plates for aircraft structural parts, extrusions, free forgings and die forgings, fuselage sheets, fuselage partitions, other damage-resistant double curvature plates requiring complex forming operations, aircraft skins, screws, and load-bearing components such as beam girders, bulkheads, wing ribs, landing gear, etc.), armor products (for example, armor plates, used for vehicle parts such as hulls, doors, tops, windows and hatches, etc.), ships (for example, used for water vehicles such as hulls, decks, bulkheads, superstructures and other structural parts, etc.), motor vehicles (such as trusses, rods, containers of transportation vehicles; doors or other parts of motor vehicles), building products (such as structural parts such as doors and windows), sports equipment (such as tennis rackets and softball bats, etc.), electronic products (for the casing and front of portable electronic devices, etc.), aerospace products (such as rockets, satellites, space shuttles, structural parts of space stations) and defense products (such as military equipment, missile devices, guns, cannons, tanks, armored vehicles, submarines, and warships). Structural parts), etc.

[0033] Therefore, another aspect of the present invention relates to the use of the 7 series aluminum alloy according to the present invention or the aluminum alloy material according to the present invention in the preparation of aviation products, armor products, ships, motor vehicles, construction products, electronic products, sports equipment, aerospace products and defense products. The 7 series aluminum alloy according to the present invention or the aluminum alloy material according to the present invention can be used alone or together with other materials to prepare these products or components of these products.

[0034] In the present invention, by adding Th element, the obtained 7 series aluminum alloy not only has high strength and high toughness, but also has good corrosion resistance.

[0035] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples.

[0036] Unless otherwise expressly stated, the numerical ranges throughout the application documents include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value therein. Unless otherwise expressly stated, the numerical values ​​throughout the application documents represent approximate measurements or limitations of the range of embodiments including slight deviations from the given values ​​and having approximately the values ​​mentioned and having the exact values ​​mentioned. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this application document (including the appended claims) should be understood in all cases as modified by the term "approximately", regardless of whether "approximately" actually appears before the numerical value. "Approximately" means that the numerical value described allows for slight imprecision (some close to precision in the value; approximately or reasonably close to the value; approximately). If the imprecision provided by "approximately" is not understood in this ordinary sense in the art, the "approximately" used herein at least represents the variation that can be produced by ordinary methods of measuring and using these parameters. For example, "approximately" can include a variation of less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1% or less than or equal to 0.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the dimension drawing for sampling of national standard GB / T 228.1-2010.

[0038] Figure 2 The Tafel polarization curves of the samples of Comparative Example 1 and Examples 1-4 are shown (upper figure) and local magnified figures (lower figure). DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0040] Reagents

[0041] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0042] The raw material cast 7075 aluminum alloy was purchased from Dongwan Ruhr Metal Materials Co., Ltd., and its element distribution was: Mg: 2.10%-2.90%, Cu: 1.20%-2.00%, Zn: 5.10%-6.10%, Cr: 0.18%-0.28%, Mn: 0.05%-0.15%, Ti: 0.01%-0.20%, Fe<0.51%, Si<0.41%, and the balance was Al.

[0043] The Al-18%Th master alloy (i.e., the Th content is 18% based on the total mass of the alloy) was provided by the Institute of Materials and Chemistry, Ganjiang Innovation Institute, Chinese Academy of Sciences, and was prepared according to the molten salt electrolysis method disclosed in CN116426983A.

[0044] Physical properties test

[0045] (1) Alloy composition measurement

[0046] The alloy composition was analyzed by X-ray fluorescence spectrometer (XRF, EXPLORER5000).

[0047] (2) Vickers hardness

[0048] Use an EDM wire cutting machine to take out a block sample of 5mm×5mm×5mm in size from the middle part of the cast aluminum alloy, use resin for cold mounting, and grind the sample on a grinder and polisher. The sample grinding is carried out in sequence using sandpaper of 240-1200 mesh, and the sample is rotated 90° clockwise each time; polishing uses diamond polishing liquid for rough polishing for 5-10 minutes, alumina polishing liquid for medium polishing, and 0.08μm silica polishing liquid for fine polishing on a damping polishing cloth. The polished sample is soaked in anhydrous ethanol for ultrasonication for 5 minutes and blown dry.

[0049] The hardness of the aluminum alloy specimens was tested using a Vickers microhardness tester (Leroyt, SCV-10A / T), with a load of 1000 g and a holding time of 15 s. Five locations of the alloy specimens were randomly selected for Vickers hardness measurement, and the average value was taken.

[0050] (3) Room temperature tensile properties

[0051] Use wire-cut EDM to take samples at different locations of cast aluminum alloy according to the Chinese national standard GB / T 228.1-2010. The sizes are as follows: Figure 1 shown.

[0052] The samples were polished with 240-mesh, 400-mesh, 800-mesh, and 1200-mesh sandpapers in sequence to remove traces and oxide layers from the processing process. The polished samples were immersed in acetone for 10 minutes for ultrasonic treatment to remove surface oil stains, and then rinsed with anhydrous ethanol and blown dry.

[0053] The room temperature tensile properties (tensile strength, yield strength, and elongation) of the alloy samples were tested using a German Zwick / Roell-020 universal tensile test machine. The tensile rate was set to 1 mm / min and the strain rate was set to 10-3 s. -1 The sample gauge length is 15 mm. The parallel experiment is measured three times and the average value is calculated.

[0054] (4) Electrochemical experiments

[0055] Use an electric spark wire cutting machine to take out block samples of size 10mm×10mm×5mm from different parts of the cast aluminum alloy, use resin for cold mounting, and grind the samples on a grinder and polisher with the same grinding and polishing requirements as above.

[0056] The electrochemical corrosion test of the alloy sample was carried out using the Swiss Metrohm AUTOLAB electrochemical workstation. In the experiment of the present invention, a three-electrode system was used for testing, with the alloy sample as the working electrode, the Ag / AgCl electrode as the reference electrode, and the platinum sheet electrode (10×10×0.1mm) as the counter electrode, and the test was carried out in a 3.5wt% NaCl solution. First, an open circuit potential test (OCP) was carried out with a scanning rate of 1mV / s. After it stabilized, a dynamic potential polarization curve test (LSV) was carried out at a scanning rate of 1mV / s. The parallel experiment was measured three times and the average value was calculated.

[0057] Comparative Example 1 and Examples 1-4

[0058] In the designed aluminum alloy material, based on the total weight of the aluminum alloy, the Th content is 0.00%, 0.10%, 0.30%, 0.50%, and 0.60% by weight, respectively, as comparative example 1 and embodiments 1 to 4. In order to prepare an aluminum alloy ingot weighing about 130.00 g, the amount of each material required is calculated based on the design and is listed in the following Table 1.

[0059] Table 1 Amount of each raw material used in the examples

[0060]

[0061] Weigh the as-cast 7075 and Al-18% Th according to the amount in Table 1, mix them evenly and place them in a graphite crucible, and place them vertically in a vacuum melting furnace. Perform the pumping and filling operation, evacuate to below 10Pa, fill with high-purity argon to 0.05MPa, repeat the pumping and filling three times and stop, adjust the current, and start heating with the furnace. The temperature range is controlled at 720-760℃. When the metal in the crucible is completely melted, cast it into a water-cooled copper mold. After the furnace temperature drops to room temperature, open the mold and take out the cast aluminum alloy. It is measured to be a cylindrical alloy sample with a diameter of 25mm and a height of 90mm.

[0062] The alloy composition of the samples was tested and the results are shown in Table 2.

[0063] Table 2 Weight percentage content of each alloy component in the alloy sample of the embodiment

[0064]

[0065] There is a deviation between the content of each alloy component in the alloy sample and the designed content, which may be caused by weighing error, raw material purity, loss in the production process, etc.

[0066] Experimental Example 1 Mechanical Properties

[0067] The Vickers hardness, tensile strength, yield strength and elongation of the aluminum alloys of Comparative Example 1 and Examples 1-4 were tested. The results are shown in Table 3.

[0068] Table 3 Hardness and tensile properties of aluminum alloy

[0069]

[0070] The aluminum alloy of Example 1 contains 0.07% Th. Compared with Comparative Example 1 in which no Th is added, the tensile strength of the 7075 aluminum alloy with 0.07% Th added is increased by 80.61%, and the yield strength is increased by 85.40%.

[0071] The aluminum alloy of Example 3 contains 0.55% Th. Compared with Comparative Example 1 in which no Th is added, the hardness of the 7075 aluminum alloy with 0.55% Th added is increased by 2.87%, the tensile strength is increased by 171.76%, and the yield strength is increased by 112.84%.

[0072] In addition, the aluminum alloys of Examples 2 and 4 containing Th, compared with Comparative Example 1 without Th, have hardness increased by 2.74% and 0.1%, tensile strength increased by 150.57% and 101.59%, and yield strength increased by 89.35% and 72.33%, respectively.

[0073] In summary, adding trace amounts of Th elements can effectively improve the mechanical properties of cast 7075 aluminum alloy, among which 7075 aluminum alloy with 0.55% Th has the best mechanical properties.

[0074] Experimental Example 2 Electrochemical Performance Analysis

[0075] The samples of Comparative Example 1 and Examples 1-4 were subjected to electrochemical tests. The test results are as follows: Figure 2 As shown. Figure 2 In the figure, the samples of Comparative Example 1 and Examples 1-4 are respectively labeled as 7075, 7075-0.07% Th, 7075-0.30% Th, 7075-0.55% Th, and 7075-0.69% Th.

[0076] from Figure 2 It can be found that after adding Th, the corrosion potential of the aluminum alloy moves in the positive direction compared with the comparative example 1 without Th, indicating that the trace addition of Th element can improve the corrosion resistance of the alloy, and when the Th addition amount is about 0.55%, the corrosion potential moves in the positive direction to the maximum extent.

[0077] In addition, from Figure 2It can also be found that adding Th elements can reduce the corrosion current density of 7 series aluminum alloys, indicating that the corrosion rate of the alloy is lower under the same potential difference. It is also found that adding Th can widen the passivation zone of 7 series aluminum alloys. It can be seen that adding trace Th elements has a comprehensive improvement effect on the corrosion resistance of 7 series aluminum alloys. When the Th content is 0.55%, the corrosion resistance of the alloy sample is the best.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A 7 series aluminum alloy doped with thorium.

2. The 7 series aluminum alloy according to claim 1, wherein: Based on the total mass of the aluminum alloy, the 7 series aluminum alloy comprises, in terms of mass percentage, 0.01% or more, 0.02% or more, 0.03% or more, 0.04% or more, or 0.05% or more of thorium, and / or 1.50% or less, 1.00% or less, 0.80% or less, 0.70% or less, or 0.60% or less of thorium, Particularly, the 7 series aluminum alloy contains 0.05% to 1.00%, 0.10% to 0.80%, 0.20% to 0.40%, or 0.40% to 0.60%, preferably 0.50% to 0.60% thorium, in mass percentage, based on the total mass of the aluminum alloy.

3. The 7 series aluminum alloy according to claim 1, wherein: The 7 series aluminum alloy also contains, based on the total mass of the aluminum alloy, in mass percentage, Mg: 2.10% to 4.00%, Cu: 1.70% to 2.50%, Zn: 5.10% to 6.10%, Cr: 0.10% to 0.30%, Mn: 0.05% to 0.15%, and Ti: 0.01% to 0.10%.

4. A method for preparing the 7 series aluminum alloy according to any one of claims 1 to 3, the method comprising: S1: Obtain aluminum-thorium master alloy; S2: The aluminum-thorium master alloy is mixed with other components for forming a 7 series aluminum alloy and melted.

5. The method according to claim 4, wherein: Aluminum-thorium master alloy is prepared by molten salt electrolysis.

6. The method according to claim 4, wherein: The mass percentage of Th in the Al-Th master alloy is 10% to 20% based on the total mass of the alloy.

7. The method according to claim 4, wherein: The melting temperature is 720-780°C, or 720-760°C.

8. The method according to claim 4, further comprising a degassing and deslagging step and / or a casting step, in particular, introducing pure argon gas for degassing and deslagging; and the casting temperature is 680-710°C.

9. An aluminum alloy material, which is made of the 7 series aluminum alloy according to the present invention, in particular, the aluminum alloy material is a plate, wire, bar, tube, profile, component or forging product.

10. Use of the 7 series aluminum alloy according to any one of claims 1 to 3 or the aluminum alloy material according to claim 9 in the preparation of aviation products, armor products, ships, motor vehicles, construction products, electronic products, sports equipment, aerospace products and national defense products.

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