Aluminum alloy and preparation method and application thereof

Abstract

The invention belongs to the field of alloys, and particularly discloses an aluminum alloy and a preparation method and application thereof. The aluminum alloy is composed of, by mass, 0.95%-1.3% of Mn, 0.45%-0.75% of Fe, 0.15%-0.3% of Si, 0.06%-0.15% of Cu, 0.015%-0.03% of Ti, 0.01%-0.1% of Zr, smaller than or equal to 0.02% of Mg, smaller than or equal to 0.02% of Zn, smaller than or equal to 0.02% of B, smaller than or equal to 0.12% of inevitable impurities and the balance Al. By optimizing the composition proportion of the aluminum alloy, a large number of dispersively distributed iron-rich strengthening phases are formed in the aluminum alloy, and the high-temperature strength and the elastic modulus of the aluminum alloy can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of alloys, and in particular relates to an aluminum alloy and a preparation method and application thereof. Background Art

[0002] 3xxx series aluminum alloys are rust-resistant aluminum alloys based on the aluminum-manganese system. They are non-heat-toughenable aluminum alloys and offer advantages such as corrosion resistance, excellent weldability, high thermal conductivity, and superior processability. They are widely used in packaging and heat exchange materials. 3003 alloy is a commonly used 3xxx series aluminum alloy. 3003 aluminum alloy ingots, produced using a vertical semi-continuous casting process, are then extruded and drawn into square hollow profiles. They are widely used as the cell housing for blade batteries in new energy vehicles. The room temperature and high temperature mechanical properties of the cell housing are crucial to the safety and service life of blade batteries. To achieve lighter batteries and increase the range of new energy vehicles, the wall thickness of the cell housing is becoming increasingly thinner. This places higher demands on the room temperature and high temperature mechanical properties of 3003 aluminum alloy to ensure battery safety.

[0003] Currently, the tensile strength of conventional 3003 aluminum alloy ingots after homogenization is generally less than 130 MPa, and the elongation is less than 20%. After extrusion and drawing hardening, the room temperature tensile strength of thin-walled hollow profiles is difficult to reach 140 MPa. At 300°C, the tensile strength is generally less than 30 MPa, and the elastic modulus is less than 25 GPa, which cannot meet the requirements of further lightweighting and higher safety performance of battery cell shells. Summary of the Invention

[0004] In order to overcome at least one technical problem existing in the above-mentioned prior art, one of the objectives of the present invention is to provide an aluminum alloy.

[0005] A second object of the present invention is to provide a method for preparing an aluminum alloy.

[0006] A third object of the present invention is to provide a battery cell shell for an automotive blade battery.

[0007] A fourth object of the present invention is to provide a battery.

[0008] A fifth object of the present invention is to provide a new energy vehicle.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] The first aspect of the present invention provides an aluminum alloy composed of the following components in mass percentage: Mn 0.95-1.3%, Fe 0.45-0.75%, Si 0.15-0.3%, Cu 0.06-0.15%, Ti 0.015-0.03%, Zr 0.01-0.1%, Mg ≤ 0.02%, Zn ≤ 0.02%, B ≤ 0.02%, unavoidable impurities ≤ 0.12%, and the balance being Al. By optimizing the ratio of manganese, iron, silicon, and copper, the present invention facilitates the formation of a fine, dispersed, iron-containing, high-temperature strengthening phase, thereby improving the high-temperature strength and high-temperature elastic modulus of the aluminum alloy. Furthermore, by adding trace amounts of Ti and Zr to the aluminum alloy, α-Al is refined and a secondary phase is precipitated.

[0011] In some embodiments of the present invention, the aluminum alloy is composed of the following components in mass percentage: Mn 1.1-1.28%, Fe 0.6-0.62%, Si 0.21-0.29%, Cu 0.08-0.11%, Ti 0.018-0.022%, Zr 0.04-0.06%, Mg≤0.012%, Zn≤0.012%, B≤0.003%, unavoidable impurities≤0.12%, and the balance is Al.

[0012] In some embodiments of the present invention, the mass percentage of Mn can be selected from any one of 0.95%, 0.97%, 1.0%, 1.02%, 1.05%, 1.07%, 1.09%, 1.10%, 1.12%, 1.14%, 1.15%, 1.17%, 1.19%, 1.20%, 1.22%, 1.24%, 1.25%, 1.27%, 1.29%, 1.3%, or a range formed by any two of them. Mn is a main alloying element. In addition to improving the strength of aluminum alloys, it can also increase the recrystallization temperature of the alloy and avoid the formation of coarse recrystallized structure during extrusion. The diffusion coefficient of Mn element in aluminum alloys is small, and dendrite segregation is serious during solidification, so homogenization heat treatment is required. If the Mn content exceeds 1.3% or the temperature of the homogenization heat treatment is too low (for example, below 600°C), a large amount of brittle A l6 Mn or Al6(Fe,Mn) compounds can easily cause microcracks or cracking in profiles during extrusion. If the Mn content is less than 0.95%, brittle iron-containing compounds such as Al5(Fe,Si) will form in the casting structure, reducing the mechanical properties of the alloy.

[0013] In some embodiments of the present invention, the mass percentage of Fe can be selected from any one of 0.45%, 0.47%, 0.5%, 0.52%, 0.55%, 0.57%, 0.6%, 0.62%, 0.65%, 0.67%, 0.7%, 0.72%, 0.75%, or a range formed by any two of them. Fe can reduce the solid solubility of Mn in the aluminum alloy, reduce the degree of dendritic segregation of the Mn element, and form a high-temperature strengthening phase. If the Fe content exceeds 0.75%, coarse Al6 (Fe, Mn) compounds will be generated, reducing the strength and plasticity of the aluminum alloy. If the Fe content is lower than 0.45%, the high-temperature strength of the aluminum alloy will be affected.

[0014] In some embodiments of the present invention, the mass percentage of Si is any one of 0.15%, 0.17%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, or a range formed by any two of them. Si can improve the fluidity of the aluminum alloy melt, improve the casting performance of the aluminum alloy, and also play a role in solid solution strengthening. If the Si content is lower than 0.15%, the solid solution strengthening effect on the aluminum alloy is small. If the Si content is higher than 0.3%, needle-shaped silicon and Al6(Fe,Mn)Si compounds will precipitate in the casting structure, affecting the toughness of the alloy.

[0015] In some embodiments of the present invention, the mass percentage of Cu is any one of 0.06%, 0.08%, 0.10%, 0.12%, 0.14%, and 0.15%, or a range formed by any two of the above. The Cu element can increase the tensile strength of the aluminum alloy, but when the Cu content exceeds 0.15%, the corrosion resistance of the aluminum alloy decreases.

[0016] The present invention requires that the B content be controlled to ≤ 0.003%, for example, any value selected from 0%, 0.001%, 0.002%, 0.003%, or a range formed by any two of these. If the B content exceeds 0.003%, the B element tends to aggregate in the aluminum alloy, causing microcracks to form at the aggregated locations during subsequent extrusion processing, significantly degrading the mechanical properties of the aluminum alloy.

[0017] In some embodiments of the present invention, the sum of the mass percentage of Mg and the mass percentage of Zn is ≤ 0.03%. The present invention strictly controls the Mg and Zn contents so that the sum of their mass percentages does not exceed 0.03%, thereby improving the weldability of the aluminum alloy. If the individual or total content of Mg or Zn exceeds the range specified in the present invention, Mg and Zn are easily volatilized in the weld pool during welding, forming microbubble defects that easily lead to pinholes in the weld, thereby affecting weld strength and appearance.

[0018] In some embodiments of the present invention, the mass percentage of Ti is any one of 0.015%, 0.017%, 0.020%, 0.022%, 0.024%, 0.026%, 0.028%, or 0.03%, or a range formed by any two of these. Trace amounts of Ti promote nucleation in aluminum alloys and refine α-Al dendrites. A Ti content exceeding 0.03% increases the viscosity of the weld pool during welding, degrading weld quality.

[0019] In some embodiments of the present invention, the mass percentage of Zr is any one of 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, and 0.1%, or a range formed by any two of these. Zr refines and modifies the precipitated phase in the aluminum alloy, while also improving the weldability of the aluminum alloy.

[0020] A second aspect of the present invention provides a method for preparing the aluminum alloy according to the first aspect of the present invention, comprising the following steps:

[0021] S1: Melting and mixing raw materials for preparing aluminum alloy to obtain an aluminum alloy melt;

[0022] S2: Then, the aluminum alloy melt is cast into a shape by a vertical semi-continuous casting method, with a cooling rate of 40 to 60° C. / s during the casting process to obtain a cast rod;

[0023] S3: performing homogenization heat treatment on the cast rod and cooling it;

[0024] The homogenization heat treatment steps are: first, keep the temperature at 600-610° C. for 6-8 hours, then heat to 625-635° C. and keep the temperature for 1-2 hours, and then cool with air or water mist.

[0025] In some embodiments of the present invention, the preparation method further includes performing step S4 after step S3, and the step S4 is: extruding into a hollow profile after heating, and then drawing to the H14 state to obtain; in some embodiments of the present invention, the step S4 is: heating to 450-500°C and then extruding into a hollow profile, and then drawing to the H14 state to obtain the aluminum alloy.

[0026] In some embodiments of the present invention, the cooling rate during casting can be selected from any one of 40°C / s, 42°C / s, 44°C / s, 46°C / s, 48°C / s, 50°C / s, 52°C / s, 54°C / s, 56°C / s, 58°C / s, and 60°C / s, or a range formed by any two of them. The prior art generally uses a low cooling rate (cooling rate ≤ 30°C / s) during vertical semi-continuous casting of 3xxx series aluminum alloys. The present invention increases the cooling rate during casting (the cooling rate refers to the cooling rate of the aluminum alloy melt from the casting temperature to the solidus, based on the cooling rate at the core of the cast rod). This not only refines the grain size and second-phase particle size of the aluminum alloy ingot, but also increases the solubility of the Mn element within the crystal, laying the foundation for adjusting the second-phase compound type during subsequent homogenization heat treatment. The present invention adjusts the cooling rate during casting by adjusting parameters such as the casting temperature, casting speed, and cooling water volume, cooling water temperature, and cooling water pressure.

[0027] In some embodiments of the present invention, the homogenization heat treatment step is: first at 600 ~ 610 ℃ (for example: 600 ℃, 602 ℃, 604 ℃, 606 ℃, 608 ℃ or 610 ℃) keep warm for 6 ~ 8h (for example: 6h, 6.5h, 7h, 7.5h or 8h), then raise the temperature to 625 ~ 635 ℃ (for example: 625 ℃, 628 ℃, 630 ℃, 632 ℃, 634 ℃ or 635 ℃) keep warm for 1 ~ 2h (for example 1h, 1.5h or 2h), then air cooling or water mist cooling. The present invention adopts the above-mentioned homogenization heat treatment to make the Al precipitated in the aluminum alloy material 12 The average particle size of the second phase (Fe, Mn) 3Si is ≤ 1 μm, and Al 12 (Fe,Mn)3Si has excellent high-temperature stability and self-lubricates during extrusion and drawing, preventing the formation of orange peel defects on the profile surface. Furthermore, the homogenization heat treatment achieves an elongation of over 40% for the aluminum alloy, which facilitates subsequent extrusion and drawing. Although strength decreases during the homogenization heat treatment and extrusion stages, drawing significantly increases the strength after work hardening.

[0028] When producing 3003 aluminum alloy rods using a vertical semi-continuous casting method, the existing technology suffers from the problem of severe Mn dendrite segregation in Al-Mn aluminum alloys due to the slow diffusion rate of the Mn element. During solidification, the alloy is supersaturated and dissolved in the aluminum alloy. This results in a serious problem of Mn dendrite segregation in Al-Mn aluminum alloys. This requires a long (typically about 20 hours) single-stage homogenization heat treatment (single-stage refers to heat treatment performed at a fixed temperature) homogenization heat treatment before extrusion, which consumes a lot of energy. During research and development, the inventors discovered that single-stage homogenization heat treatment cannot both increase the number of precipitated second phases and reduce the size of second-phase particles. The single-stage homogenization heat treatment takes a long time, and the generated second phase gradually grows during the long homogenization heat treatment, forming a coarse second phase. This coarse second phase easily causes local stress concentration during the drawing process of hollow profiles formed by aluminum alloy extrusion, causing the hollow profile to break, making effective drawing impossible. Furthermore, the elongation of aluminum alloys after single-stage homogenization heat treatment is generally ≤20%, resulting in reduced strength and elongation after subsequent extrusion. This can easily cause problems such as orange peel and profile breakage during drawing. Therefore, after repeated attempts to overcome the shortcomings of single-stage homogenization heat treatment, the inventors finally found that a dual-stage homogenization heat treatment method (dual-stage means first performing heat treatment at a fixed temperature and then performing heat treatment at another fixed temperature) is adopted. The first stage homogenization heat treatment is first performed at a lower temperature, and then the temperature is increased to perform the second stage homogenization heat treatment. This can significantly shorten the homogenization time (the homogenization heat treatment can be completed in 7 to 10 hours). The temperature of the second stage homogenization heat treatment is higher, which is conducive to the dissolution of coarse second phases, thereby avoiding the presence of coarse second phases in the aluminum alloy. In addition, the homogenization heat treatment time is shorter, which avoids the gradual growth of the precipitated second phase during the long homogenization heat treatment process.

[0029] In some embodiments of the present invention, the temperature of the aluminum alloy melt is 730-760°C.

[0030] In some embodiments of the present invention, the casting speed during the casting is 160 to 200 mm / min.

[0031] In some embodiments of the present invention, the aluminum alloy melt is prepared by a preparation method comprising the following steps:

[0032] Heating part of the raw materials for preparing the aluminum alloy to 730-760° C. to melt, then sequentially adding an aluminum-titanium master alloy and an aluminum-zirconium master alloy, melting and mixing, refining, and skimming to obtain the aluminum alloy melt;

[0033] The raw materials used to prepare the aluminum alloy include aluminum ingots, aluminum-manganese master alloy or manganese agent, aluminum-iron master alloy or iron metal, aluminum-copper master alloy or copper metal, aluminum-silicon master alloy or silicon particles.

[0034] The aluminum-zirconium master alloy in the present invention needs to be added after the aluminum-titanium master alloy. If the order of addition is reversed, the refining effect of Ti will be significantly reduced.

[0035] In the present invention, Mg, Zn and B are impurity elements in the raw materials. There is no need to add Mg source, Zn source and B source during the preparation process. However, it is necessary to control the content range of Mg, Zn and B in the aluminum alloy so that the content of these three elements does not exceed the range specified by the present invention, otherwise the performance of the aluminum alloy will be reduced.

[0036] In some embodiments of the present invention, some of the raw materials used to prepare aluminum alloys include aluminum ingots, aluminum-manganese master alloys, aluminum-iron master alloys, aluminum-copper master alloys, and aluminum-silicon master alloys.

[0037] In some embodiments of the present invention, the refining uses high-purity nitrogen

[0038] The third aspect of the present invention provides a battery cell shell for an automotive blade battery, comprising the aluminum alloy described in the first aspect of the present invention.

[0039] A fourth aspect of the present invention provides a battery comprising the battery cell shell according to the third aspect of the present invention, or the aluminum alloy according to the first aspect of the present invention.

[0040] A fifth aspect of the present invention provides a new energy vehicle, comprising the battery described in the fourth aspect of the present invention, or the aluminum alloy described in the first aspect of the present invention.

[0041] The beneficial effect of the present invention is that the present invention optimizes the composition ratio of the aluminum alloy to form a large amount of dispersed Al 12 Iron-rich strengthening phases such as (Fe,Mn)3Si are beneficial to improving the strength and elastic modulus of aluminum alloys at room temperature and high temperature. Specifically, after extrusion and drawing, the room temperature tensile strength of H14 thin-walled hollow profiles can reach above 145MP, and the elongation is ≥5.6%; at 300°C, the tensile strength can reach above 50MPa, and the elastic modulus can reach 38Gpa.

[0042] In addition, the preparation method of the present invention adopts a high cooling rate and a two-stage homogenization heat treatment process during casting, which can regulate the grain size, density and size of the grain boundary and intragranular precipitation phase, on the one hand, inhibiting the formation of coarse second phase and avoiding material failure due to stress concentration; at the same time, forming a large amount of dispersed Al 12 Iron-rich strengthening phases such as (Fe,Mn)3Si are beneficial to improving the high-temperature strength and elastic modulus of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1This is a SEM image of the cast rod obtained in step (2) of Example 1, magnified 1000 times.

[0044] Figure 2 This is a SEM image of the cast rod obtained in step (2) of Example 1, magnified 5000 times.

[0045] Figure 3 This is a SEM image of the aluminum alloy prepared in Example 1 magnified 1000 times.

[0046] Figure 4 This is a SEM image of the aluminum alloy prepared in Example 1 magnified 5000 times.

[0047] Figure 5 This is a SEM image of the cast rod obtained in step (2) of Comparative Example 3, magnified 5000 times.

[0048] Figure 6 This is a SEM image of the cast rod obtained in step (2) of Comparative Example 5, magnified 2000 times.

[0049] Figure 7 This is a SEM image of the weld of a hollow profile in a drawn state made of the aluminum alloy in Example 1 after high-frequency welding. DETAILED DESCRIPTION

[0050] The specific implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are any processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be purchased commercially.

[0051] The raw material information used in the following examples and comparative examples is as follows:

[0052] In the AlMn10 master alloy, the mass percentage of Mn is 10% and the mass percentage of Al is 90%;

[0053] In the AlFe10 master alloy, the mass percentage of Fe is 10% and the mass percentage of Al is 90%;

[0054] In AlCu50 master alloy, the mass percentage of Cu is 50% and the mass percentage of Al is 50%;

[0055] In the AlTi10 master alloy, the mass percentage of Ti is 10% and the mass percentage of Al is 90%;

[0056] In the AlZr10 master alloy, the mass percentage of Zr is 10% and the mass percentage of Al is 90%;

[0057] In the AlSi20 master alloy, the mass percentage of Si is 20% and the mass percentage of Al is 80%.

[0058] Example 1

[0059] This example provides an aluminum alloy, which is composed of the following components in percentage by mass:

[0060] Mn 1.1%, Fe 0.6%, Si 0.22%, Cu 0.1%, Ti 0.02%, Zr 0.05%, Mg 0.01%, Zn 0.012%, B 0.002%, the total amount of other impurities ≤ 0.12%, the balance is Al.

[0061] This example provides a method for preparing an aluminum alloy, which specifically includes the following steps:

[0062] (1) According to the composition and proportion of the alloy in Example 1 in Table 1, aluminum ingots with a purity of 99.8%, AlSi20 master alloy, AlMn10 master alloy, AlFe10 master alloy, and AlCu50 master alloy are added to a gas-heated melting furnace for melting. B, Mg, and Zn are impurity elements in the raw materials and do not need to be added separately. Their contents only need to be controlled within the scope of the present invention. When the melt temperature reaches 750°C, AlTi10 alloy is added to the melting furnace for melting. The electromagnetic stirring device at the bottom of the melting furnace is then activated to stir the melt evenly. AlZr10 alloy is then added, and after stirring evenly again, the melt is refined using high-purity nitrogen and a commercially available aluminum alloy refining agent. After refining, the slag is removed and the melt is allowed to stand for 30 minutes before semi-continuous casting begins.

[0063] (2) During casting, the melt temperature in the furnace was 740°C, the cooling water pressure was 120 kPa, the cooling water temperature was 5°C, the casting speed was 180 mm / min, and the cooling rate of the core of the cast rod was measured to be 50°C / s by burying a thermocouple in the cast rod. A cast rod with a diameter of 127 mm was prepared.

[0064] (3) The cast rod prepared in step (2) is subjected to a two-stage homogenization heat treatment. The specific process is as follows: first, the temperature is raised to 605°C and kept at this temperature for 7 hours; then, the cast rod is heated to 630°C and kept at this temperature for 1.5 hours, and then cooled by water mist cooling to obtain the aluminum alloy in this example.

[0065] Examples 2 to 12

[0066] The only difference between the preparation methods of the aluminum alloys in Examples 2 to 12 and Example 1 is that the composition ratios of the aluminum alloys are different. Examples 2 to 12 respectively adopt the composition ratios of the aluminum alloys corresponding to Examples 2 to 12 in Table 1.

[0067] Comparative Examples 1 to 9

[0068] The only difference between the preparation methods of the aluminum alloys in Comparative Examples 1 to 9 and Example 1 is that the composition ratios of the aluminum alloys are different. Comparative Examples 1 to 9 respectively adopt the composition ratios of the aluminum alloys corresponding to Comparative Examples 1 to 9 in Table 1.

[0069] Table 1 Composition ratio of the aluminum alloys in Examples 1 to 12 and Comparative Examples 1 to 9

[0070]

[0071] Comparative Example 10

[0072] The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that in step (2) of this example, the cooling rate of the core of the cast rod is 65°C / s by adjusting the cold water pressure, temperature, and casting speed. The specific parameters are: adjusting the cold water pressure to 135kPa, the cold water temperature to 3.2°C, and the casting speed to 197mm / min.

[0073] Comparative Example 11

[0074] The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that in step (2) of this example, the cooling rate of the core of the cast rod is 35°C / s by adjusting the cold water pressure, temperature, and casting speed. The specific parameters are: adjusting the cold water pressure to 96 kPa, the cold water temperature to 15.4°C, and the casting speed to 155 mm / min.

[0075] Comparative Example 12

[0076] The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that step (3) of this example adopts a single-stage homogenization process, and the specific process is: keeping the temperature at 600°C for 20 hours, and then cooling it by water mist cooling.

[0077] Comparative Example 13

[0078] The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that the cast rod in step (3) of this example adopts a two-stage homogenization process, and the specific process is: first, keep it at 630℃ for 1.5h, then cool it to 605℃ and keep it for 7h, and then cool it down by water mist cooling.

[0079] Comparative Example 14

[0080] The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that in step (1) of this example, when the melt temperature reaches 750°C, the AlZr10 master alloy is added to the melting furnace for melting, and then the electromagnetic stirring device at the bottom of the melting furnace is started to stir the melt uniformly. Then the AlTi10 master alloy is added,

[0081] Performance Testing

[0082] (1) Room temperature mechanical properties test

[0083] Samples were taken from the cast rods with a diameter of 127 mm (i.e., as-cast) obtained in step (2) of Examples 1 to 12 and Comparative Examples 1 to 14, and the aluminum alloy obtained in step (3) (i.e., homogenized state), and then subjected to room temperature mechanical property tests. The test standards for tensile strength and yield strength were referred to "GB / T16865-2013", and the test standard for elongation after fracture was referred to "GB / T16865-2013". The specific test results are shown in Table 2.

[0084] Table 2 Test results of mechanical properties of cast rods at room temperature

[0085]

[0086]

[0087] As shown in Table 2, the room temperature yield strength of the cast rod with a diameter of 127 mm (i.e., cast state) obtained in step (2) of Examples 1 to 12 of the present invention is 76-89 MPa, the room temperature tensile strength is 128-152 MPa, and the room temperature elongation is 20-27%; the room temperature yield strength of the aluminum alloy (i.e., homogenized state) obtained in step (3) is 71-84 MPa, the room temperature tensile strength is 123-135 MPa, and the room temperature elongation is 40-47%. By comparing the mechanical properties of the cast state and the homogenized state, it can be seen that the elongation of the aluminum alloy after the cast rod obtained in step (2) is subjected to a double-stage homogenization treatment is significantly improved, which is beneficial to subsequent extrusion and drawing processing, and avoids the occurrence of undesirable conditions such as orange peel, cracks, splitting, and breaking during the extrusion and drawing process.

[0088] The room temperature yield strength of the cast rod with a diameter of 127 mm (i.e., cast state) obtained in step (2) of comparative examples 1 to 14 is 52 to 72 MPa, the room temperature tensile strength is 108 to 128 MPa, and the room temperature elongation is 14.3 to 25%; the room temperature yield strength of the aluminum alloy (i.e., homogenized state) obtained in step (3) is 40 to 55 MPa, the room temperature tensile strength is 98 to 112 MPa, and the room temperature elongation is 29 to 39%. It can be seen that the performance of the aluminum alloy in the cast and homogenized states in comparative examples 1 to 14 are significantly inferior to those in examples 1 to 12, indicating that if the content of any component or the range of any parameter is not within the range specified by the present invention, the performance of the obtained aluminum alloy will be significantly reduced.

[0089] Compared to Example 1, the cooling rate of Comparative Example 10 was too high, making casting impossible. The cooling rate of Comparative Example 11 was too slow, resulting in significantly inferior properties of the aluminum alloy in both the as-cast and homogenized states compared to Example 1. This was due to the coarsening of the grain size and the precipitated second phase, and the decrease in the density of the precipitated phase. Comparative Example 12 employed a single-stage homogenization process, while Comparative Example 13 adjusted the temperature of the dual-stage homogenization process. The properties of the aluminum alloys in both Comparative Examples 12 and 13 were significantly inferior to those in Example 1 in both the as-cast and homogenized states, due to the coarsening of the precipitated second phase and the decrease in the density of the precipitated phase.

[0090] (2) Tissue characteristic test

[0091] Samples were taken from the 1 / 2 radius of the cross section of the cast rod (i.e., cast state) with a diameter of 127 mm obtained in steps (2) of Examples 1 to 12 and Comparative Examples 1 to 14, respectively. The average grain size was determined by electron backscatter diffraction (EBSD) with reference to GB / T38532-2020. The size of the second phase precipitated in the grains and grain boundaries of the aluminum alloy (i.e., homogenized state) obtained after the double-stage homogenization heat treatment in step (3) was then determined by scanning electron microscopy (SEM). The specific measurement method is as follows: a scanning electron microscope (SEM) was used to randomly photograph more than 10 fields of view of the sample at a magnification of 20,000 times, and the image was observed and analyzed. The maximum length of the second phase in the grain was taken as the diameter. More than 5 particles were randomly measured in the photos of each field of view, and the particle sizes of all measurements were averaged to obtain the average diameter of the particles in the grain. The number of the second phase was counted in the photos of each field of view, and the distribution density of the second phase was calculated by considering the field of view area of ​​the photo. A scanning electron microscope (SEM) was used to randomly photograph more than 10 fields of view of the sample at a magnification of 500 times. The images were observed and analyzed, and the maximum length of the second phase at the grain boundary was taken as the diameter. More than 5 particles were randomly measured in the photograph of each field of view, and then the sizes of all measured particles were averaged to obtain the average diameter of the grain boundary particles. The data of the cast grain size and the homogenized second phase measured according to the above test method are shown in Table 3 below.

[0092] Table 3 Microstructure characteristics of as-cast and homogenized states

[0093]

[0094]

[0095] As shown in Table 3, compared with Comparative Examples 1 to 14, the grain size of the aluminum alloys obtained in Examples 1 to 12 in the as-cast state (17.3 to 18.8 μm) is reduced, and the density of the second phase precipitated in the crystal in the homogenized state (1.15×10 8 ~1.35×10 8 mm 2) is increased, the average diameter of the second phase precipitated in the crystal (161-198nm) and the average diameter of the second phase precipitated at the grain boundary (1.76-1.93μm) are significantly reduced, the average grain size of the cast state is controlled below 20μm, and the particle size of the second phase precipitated on the grain boundary is controlled below 2μm, achieving the purpose of fine grains and strengthening the aluminum alloy. After the aluminum alloy in the present invention undergoes a two-stage homogenization heat treatment, the grain size is basically the same as that of the cast state, but the element distribution in the aluminum alloy is more uniform, the size of the second phase on the grain boundary is significantly smaller than that of the cast state, and at the same time, a large amount of Al is precipitated. 12 (Fe,Mn)3Si phase, this compound has higher high-temperature stability, and at the same time a large number of nano-sized precipitates are precipitated inside the grains, which plays a dispersion strengthening role on the aluminum alloy.

[0096] Comparative Example 8 does not contain titanium and Comparative Example 9 does not contain zirconium. The grain size of the obtained aluminum alloy is larger, the density of the precipitated second phase is reduced, and the size of the second phase is also larger. This shows that the synergistic effect of titanium and zirconium elements in the aluminum alloy plays a role in refining the α-Al grains and promoting the precipitation of the second phase.

[0097] (3) Room temperature mechanical properties of hollow profiles

[0098] The aluminum alloy cast rods obtained after the homogenization heat treatment in step (3) of Examples 1 to 12 and Comparative Examples 1 to 14 were heated to 470° C. and then extruded into hollow profiles with a wall thickness of 0.4 mm (i.e., extruded state). The hollow profiles were then drawn at room temperature to the H14 state (i.e., H14 state). Samples were taken from the hollow profiles after extrusion and drawing for room temperature mechanical property testing. The specific test results are shown in Table 4.

[0099] Table 4 Room temperature mechanical properties of hollow profiles

[0100]

[0101]

[0102] As can be seen from Table 4, the aluminum alloys obtained in Examples 1 to 12 have good extrusion and drawing effects. The room temperature yield strength of the extruded state is 69 to 78 MPa, the tensile strength is 124 to 133 MPa, and the elongation is 20 to 28%. The room temperature yield strength of the H14 state is 135 to 145 MPa, the tensile strength is 147 to 165 MPa, and the elongation is 5.6 to 6.7%. That is, the room temperature mechanical properties of the aluminum alloys in the extruded state and H14 state obtained in Examples 1 to 12 are significantly higher than those in Comparative Examples 1 to 14.

[0103] Samples were taken from the hollow profiles in the H14 state (i.e., H14 state) after drawing in Example 1, Example 5, Example 6, Example 8, Example 11, and Comparative Example 13, and the room temperature elastic modulus was tested. The test standard was based on GB / T 22315-2008. The specific test results are shown in Table 5.

[0104] Table 5 Room temperature elastic modulus data of hollow profiles

[0105] Elastic modulus (GPa) Example 1 69.9 Example 5 69.7 Example 6 69.8 Example 8 69.5 Example 11 69.4 Comparative Example 13 68.5

[0106] As can be seen from Table 5, the elastic modulus of the hollow profiles in the embodiment of the present invention and the comparative example at room temperature are not much different.

[0107] (4) High temperature mechanical properties test

[0108] Samples were taken from the hollow profiles in the H14 state (i.e., H14 state) after drawing in the above-mentioned Examples 1, 5, 6, 8, 11, and Comparative Example 13, and mechanical properties were tested at 300°C. The test standard was based on DIN EN ISO 6892-2. The specific test results are shown in Table 6.

[0109] Table 6 Mechanical properties data of hollow profiles

[0110]

[0111]

[0112] As can be seen from Table 6, after the aluminum alloys in Examples 1 to 12 of the present invention are drawn to the H14 state, at a high temperature of 300°C, the yield strength of the aluminum alloys is 36 to 42 MPa, the tensile strength is 43 to 49 MPa, and the elastic modulus is 38.2 to 39.5 GPa, which are significantly higher than the aluminum alloys prepared in Comparative Examples 1 to 14.

[0113] Compared with Example 1, Comparative Example 13 only changed the heat treatment temperature and heat treatment time of the two-stage homogenization heat treatment step, and the yield strength, tensile strength and elastic modulus of the obtained aluminum alloy at 300°C were significantly reduced.

[0114] (5) Weld quality evaluation test

[0115] Laser welding experiments were conducted on samples of hollow profiles in the H14 state (i.e., H14 state) after drawing in Examples 1, 10, and 11. Weld quality was evaluated based on weld uniformity, cracks, and holes. The welding parameters were: power 1500 W, welding speed 40 mm / s, defocusing distance -1 mm, shielding gas Ar, and gas flow rate 20 L / min. The test results are shown in Table 7 below.

[0116] Table 7 Weld quality evaluation

[0117] Weld uniformity Weld cracks Hole defects Example 1 Uniform appearance none none Example 10 Uniform appearance none none Comparative Example 11 Uniform appearance none A large number of pinholes

[0118] As can be seen from Table 7, compared with Comparative Example 11, the aluminum alloy prepared in the present invention has better weld appearance uniformity during laser welding, and there are no cracks or holes in the weld, which further indicates that the aluminum alloy in the present invention can be used for battery core shells.

[0119] (6) Surface morphology test

[0120] The SEM image of the cast rod obtained in step (2) of Example 1 was tested using a scanning electron microscope. The specific test results are as follows: Figure 1 and Figure 2 As shown. Among them, Figure 1 The SEM image is magnified 1000 times. Figure 2 The SEM image is magnified 5000 times. Figure 1 and Figure 2 It can be seen that the grains (α aluminum) are uniform and fine, and the second phase (e.g. Al 12 (Fe, Mn)3Si, etc.) precipitate on the grain boundaries and are distributed discontinuously.

[0121] The SEM image of the aluminum alloy obtained in step (3) of Example 1 was tested using a scanning electron microscope. The specific test results are as follows: Figure 3 and Figure 4 As shown. Among them, Figure 3 The SEM image is magnified 1000 times. Figure 4 The SEM image is magnified 5000 times. Figure 3 and Figure 4 It can be seen that after the two-stage homogenization heat treatment, the second phase on the grain boundary of the cast rod becomes finer, and a large amount of nano-scale second phase precipitates in the crystal.

[0122] The SEM image of the cast rod obtained in step (2) of comparative example 3 was magnified 5000 times using a scanning electron microscope. Figure 5 As shown by Figure 5 It can be seen that coarse iron-rich compounds exist in the aluminum alloy in Comparative Example 3.

[0123] The SEM image of the cast rod obtained in step (2) of comparative example 5 was magnified 2000 times using a scanning electron microscope. Figure 6 As shown by Figure 6 It can be seen that a large amount of silicon phase is precipitated in the aluminum alloy in Comparative Example 5, and microcracks exist between the silicon phase and the aluminum matrix.

[0124] The SEM images of the hollow profiles in the drawn state made of the aluminum alloy in Example 1 after laser welding were measured by scanning electron microscopy. Figure 7 As shown by Figure 7 It can be seen that the weld has uniform structure and is free of defects such as pores and inclusions.

[0125] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. An aluminum alloy, characterized in that: It is composed of the following components in mass percentage: Mn 0.95-1.3%, Fe 0.45-0.75%, Si 0.15-0.3%, Cu 0.06-0.15%, Ti 0.015-0.03%, Zr 0.01-0.1%, Mg≤0.02%, Zn≤0.02%, B≤0.02%, unavoidable impurities≤0.12%, and the balance is Al.

2. The aluminum alloy according to claim 1, wherein: The aluminum alloy is composed of the following components in mass percentage: Mn 1.1-1.28%, Fe 0.6-0.62%, Si 0.21-0.29%, Cu 0.08-0.11%, Ti 0.018-0.022%, Zr 0.04-0.06%, Mg≤0.012%, Zn≤0.012%, B≤0.003%, unavoidable impurities≤0.12%, and the balance is Al.

3. The aluminum alloy according to claim 1 or 2, characterized in that: The sum of the mass percentage of Mg and the mass percentage of Zn is ≤0.03%.

4. The method for preparing the aluminum alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Melting and mixing raw materials for preparing aluminum alloy to obtain an aluminum alloy melt; S2: Then, the aluminum alloy melt is cast into a shape by a vertical semi-continuous casting method, with a cooling rate of 40 to 60° C. / s during the casting process to obtain a cast rod; S3: performing homogenization heat treatment on the cast rod and cooling it; The homogenization heat treatment comprises the following steps: firstly keeping the temperature at 600-610° C. for 6-8 hours, then heating to 625-635° C. for 1-2 hours.

5. The method for preparing the aluminum alloy according to claim 4, wherein: The temperature of the aluminum alloy melt is 730-760°C; And / or, the casting speed during the casting is 160-200 mm / min.

6. The method for preparing the aluminum alloy according to claim 4, wherein: The preparation method further includes performing step S4 after step S3; step S4 is: extruding into a hollow profile after heating, and then drawing to an H14 state.

7. The method for preparing the aluminum alloy according to claim 4, wherein: The aluminum alloy melt is prepared by a preparation method comprising the following steps: Heating part of the raw materials for preparing the aluminum alloy to 730-760° C. to melt, then sequentially adding an aluminum-titanium master alloy and an aluminum-zirconium master alloy, melting and mixing, refining, and skimming to obtain the aluminum alloy melt; The raw materials for preparing the aluminum alloy include aluminum metal, aluminum-manganese master alloy or manganese metal, aluminum-iron master alloy or iron metal, aluminum-copper master alloy or copper metal, aluminum-silicon master alloy or silicon particles.

8. A battery cell shell for a car blade battery, characterized by: The aluminum alloy comprises the aluminum alloy according to any one of claims 1 to 3.

9. A battery, characterized in that: The battery cell shell comprises the battery cell shell according to claim 8, or the aluminum alloy according to any one of claims 1 to 3.

10. A new energy vehicle, characterized by: The battery according to claim 9 or the aluminum alloy according to any one of claims 1 to 3.

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