Aluminum alloy extrusions

Abstract

To provide an aluminum alloy extrusion material excellent in both proof stress and crushability.SOLUTION: An aluminum alloy extrusion material including Si:0.25-0.39 mass%, Mg:0.65-0.95 mass%, Fe:0.35 mass% or less (including 0 mass%), Cu:more than 0 mass% and 0.65 mass% or less, Cr:0.10 mass% or less (including 0 mass%), Ti:more than 0 mass% and 0.10 mass% or less and the remainder consisting of Al and inevitable impurities has a proof stress of 195 MPa or more. In metallic structure observation by cross-sectional SEM observation, grain boundary deposits existing within a visual field of 90 μm×120 μm and having a size of 50 nm or more and 2 μm or less in a direction orthogonal to a grain boundary are 25 pieces or less.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present disclosure relates to aluminum alloy extrusions. [Background technology]

[0002] There has been a demand for improved occupant safety in vehicles, and for this purpose, the strength of vehicle bodies has been improved. On the other hand, against the backdrop of worsening issues such as global warming, efforts to improve the fuel efficiency of automobiles are accelerating. It is known that reducing the weight of vehicle bodies is an effective way to improve fuel efficiency.

[0003] For this purpose, high-strength 6000-series aluminum alloys are used for automotive components. For example, Patent Document 1 discloses a 6000-series (Al-Mg-Si) age-hardenable aluminum alloy that combines high mechanical properties with high storage stability at room temperature. The aluminum alloy comprises 0.6-1 wt.% magnesium (Mg), 0.2-0.7 wt.% silicon (Si), 0.16-0.7 wt.% iron (Fe), 0.05-0.4 wt.% copper (Cu), maximum 0.15 wt.% manganese (Mn), maximum 0.35 wt.% chromium (Cr), maximum 0.2 wt.% zirconium (Zr), maximum 0.25 wt.% zinc (Zn), maximum 0.15 wt.% titanium (Ti), 0.005-0.075 wt.% tin (Sn), the balance being aluminum and maximum 0.05 wt.% each of impurities, totaling at most 0.15 wt.%, which are unavoidable in manufacturing, wherein the weight percent ratio of Si / Fe is less than 2.5, and the Si content is determined according to a predetermined formula. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7208005 Specification Summary of the Invention [Problem to be solved by the invention]

[0005] In order to comply with recent exhaust gas regulations, electric vehicles (EVs) are being developed. EVs are equipped with large battery modules, and these electric modules are protected by a frame. To reduce vehicle weight, the use of 6000-series aluminum alloy extrusions for battery module frames is being considered. Extrusions used in frames are required to have high yield strength (220 MPa) and excellent crush resistance (no cracks when crushed) to protect battery modules from impacts such as side collisions. However, generally, as yield strength increases, crush resistance decreases, making it difficult to improve both.

[0006] The 6000 series aluminum alloy disclosed in Patent Document 1 is not intended for extruded materials, and therefore no consideration is given to a method for improving both the yield strength and crush resistance of the extruded material.

[0007] The present invention has been made in view of the above circumstances, and one of its objects is to provide an aluminum alloy extrusion material that is excellent in both yield strength and crush resistance. [Means for solving the problem]

[0008] Aspect 1 of the present invention is Si:0.25~0.39% by mass, Mg: 0.65~0.95% by mass, Fe: 0.35 mass% or less (including 0 mass%), Cu: more than 0 mass%, 0.65 mass% or less, Cr: 0.10 mass% or less (including 0 mass%), and Ti: more than 0 mass% and 0.10 mass% or less; the balance being Al and unavoidable impurities, The yield strength is 195 MPa or more, This aluminum alloy extrusion has, in cross-sectional SEM observation of the metal structure, 25 or fewer grain boundary precipitates with dimensions of 50 nm or more and 2 μm or less in the direction perpendicular to the grain boundaries within a field of view of 90 μm x 120 μm.

[0009] Aspect 2 of the present invention is The aluminum alloy extrusion material according to aspect 1 has a Si content of 0.27 to 0.37 mass %.

[0010] Aspect 3 of the present invention is moreover, Mn: 1.0 mass% or less (including 0 mass%), Zr: 0.2 mass% or less (including 0 mass%), V: 0.2% by mass or less (including 0% by mass), Zn: 0.5 mass% or less (including 0 mass%), Ag: 0.1% by mass or less (including 0% by mass), and Sn: 0.15 mass% or less (including 0 mass%) 3. The aluminum alloy extrusion of claim 1 or 2, comprising: [Effects of the Invention]

[0011] According to an embodiment of the present invention, it is possible to provide an aluminum alloy extrusion material that is excellent in both yield strength and crush resistance. [Brief explanation of the drawings]

[0012] [Figure 1A] 1 is a cross-sectional SEM image (×10,000 magnification) of the sample of Example Test No. 2. [Figure 1B] 1 is a cross-sectional SEM image (×2000 magnification) of a sample of Example Test No. 2. [Figure 2] FIG. 2 is a schematic diagram for explaining the dimensions of grain boundary precipitates. [Figure 3A] 1 is a cross-sectional view of an extruded material produced in an example, taken along a cross section perpendicular to the extrusion direction. [Figure 3B] 1 is a cross-sectional view of an extruded material produced in an example, taken along a cross section perpendicular to the extrusion direction. [Figure 4A] FIG. 3B is a schematic perspective view for explaining a lateral crushing test using the extruded material shown in FIG. 3A. [Figure 4B]It is a schematic perspective view for explaining a transverse crushing test using the extruded material shown in Fig. 3B.

Embodiments for Carrying out the Invention

[0013] The inventors have studied from various angles in order to realize an extruded material of 6000 - series aluminum alloy with excellent strength and crushability. As a result, by restricting the contents of Si and Mg to a narrower range than those of the conventional 6000 - series aluminum alloy and reducing the number of grain - boundary precipitates existing at the grain boundaries, it has been found that an aluminum alloy extruded material capable of achieving high strength and high crushability can be realized, and the present invention has been completed.

[0014] The details of each requirement defined by the embodiments of the present invention are shown below.

[0015] <1. Component Composition> The aluminum alloy extruded material according to the embodiment of the present invention has a component composition containing Si: 0.25 to 0.39% by mass, Mg: 0.65 to 0.95% by mass, Fe: 0.35% by mass or less (including 0% by mass), Cu: more than 0% by mass and 0.65% by mass or less, Cr: 0.10% by mass or less (including 0% by mass), and Ti: more than 0% by mass and 0.10% by mass or less. Further, the balance is preferably Al and unavoidable impurities. Each element will be described in detail below.

[0016] <Si: 0.25 to 0.39% by mass> Si can form a compound phase such as Mg2Si with Mg and precipitate, thereby increasing the strength of the aluminum alloy. Note that Mg2Si precipitates at the grain boundaries to become grain - boundary precipitates. When the content of Si is less than 0.25% by mass, it becomes difficult to obtain sufficient strength, so it is set to 0.25% by mass or more. The content of Si is preferably 0.26% by mass or more, more preferably 0.27% by mass or more. On the one hand, when the Si content exceeds 0.39% by mass, the number of grain boundary precipitates of Mg2Si increases and the crushing property decreases, so it should be 0.39% by mass or less. The Si content is preferably 0.38% by mass or less, more preferably 0.37% by mass or less, and particularly preferably 0.36% by mass or less.

[0017] <Mg: 0.65 - 0.95% by mass> Mg forms a compound phase such as Mg2Si with Si and precipitates, enhancing the strength of the aluminum alloy. When the Mg content is less than 0.65% by mass, it becomes difficult to obtain sufficient yield strength, so it should be 0.65% by mass or more. The Mg content is preferably 0.67% by mass or more, more preferably 0.70% by mass or more. On the other hand, when the Mg content exceeds 0.95% by mass, the number of grain boundary precipitates of Mg2Si increases and the crushing property decreases, so it should be 0.95% by mass or less. The Mg content is preferably 0.93% by mass or less, more preferably 0.90% by mass or less, still more preferably 0.88% by mass or less, and particularly preferably 0.80% by mass or less.

[0018] <Fe: 0.35% by mass or less (including 0% by mass)> Fe is a major inevitable impurity in the aluminum alloy. In order not to degrade the various properties of the aluminum alloy extrusion, the Fe content should be 0.35% by mass or less. The Fe content is preferably 0.30% by mass or less, more preferably 0.27% by mass or less, and particularly preferably 0.25% by mass or less. Since Fe is an inevitable impurity, the lower its content, the better. Therefore, the lower limit of the Fe content is 0% by mass, but reducing it to less than 0.05% by mass places a large burden in terms of cost. Therefore, the lower limit of the Fe content may be 0.05% by mass, may be 0.10% by mass, may be 0.15% by mass, or may be 0.18% by mass.

[0019] <Cu: more than 0% by mass, 0.65% by mass or less> Cu is an element that improves the strength of aluminum alloy extruded materials. To exhibit its effect, the content of Cu is more than 0 mass%. The content of Cu is preferably 0.05 mass% or more, more preferably 0.10 mass% or more, and particularly preferably 0.12 mass% or more. On the other hand, when the content of Cu exceeds 0.65 mass%, it causes a decrease in extrusion properties and corrosion resistance, so it is set to 0.65 mass% or less. The content of Cu is preferably 0.30 mass% or less, more preferably 0.20 mass% or less, and particularly preferably 0.18 mass% or less.

[0020] <Cr: 0.10 mass% or less (including 0 mass%)> Cr is an inevitable impurity in aluminum alloys. When the content of Cr is high, sticking is likely to occur in the extrusion process, so it is set to 0.10 mass% or less. Since Cr is an inevitable impurity, the lower its content, the more preferable. Therefore, the lower limit of the content of Cr is 0 mass%, but reducing it to less than 0.01 mass% places a large burden in terms of cost. Therefore, the lower limit of the content of Cr may be 0.01 mass%, may be 0.03 mass%, or may be 0.05 mass%.

[0021] <Ti: More than 0 mass%, 0.10 mass% or less> Ti has the effect of improving the formability of extruded materials. To exhibit its effect, the content of Ti is more than 0 mass%. The content of Ti is preferably 0.01 mass% or more, more preferably 0.02 mass% or more. On the other hand, when the content of Ti exceeds 0.10 mass%, its effect saturates, so it is set to 0.10 mass% or less. The content of Ti is preferably 0.08 mass% or less, more preferably 0.06 mass% or less, and particularly preferably 0.05 mass% or less.

[0022] <Inevitable impurities> [[ID= twenty-three]] In one embodiment of the present invention, the balance is preferably aluminum and inevitable impurities. Elements introduced due to the conditions of raw materials, materials, manufacturing equipment, etc. are permitted as inevitable impurities. The content of inevitable impurity elements other than the above elements is controlled within the range specified by JIS standards for 6000 series alloys. Specific examples of inevitable impurity elements include Ni, In, Ga, B, Na, Ca, and Sc. The content of these elements is preferably 0.05% by mass or less individually and 0.15% by mass or less in total. In addition, for example, there are elements such as Fe, whose content is usually preferably as small as possible and therefore is an inevitable impurity, but whose composition range is separately defined as described above. Therefore, in this specification, the term "unavoidable impurities" does not include elements whose composition range is separately defined.

[0023] <Other elements> The aluminum alloy sheet according to this embodiment may further contain, for example, the following elements as elements other than those described above. The allowable amounts of these elements contained in the melted raw materials of the ingot, such as scrap, are set to the following upper limits, and even if they are actively added within these ranges, the effects of the present invention are not impaired. There is no lower limit for each content, and the case of 0% is also included. Mn: 1.0 mass% or less, Zr: 0.2 mass% or less, V: 0.2 mass% or less, Zn: 0.5 mass% or less, Ag: 0.1 mass% or less, Sn: 0.15 mass% or less

[0024] <2. Yield strength> The aluminum alloy extrusion material according to the embodiment of the present invention has a yield strength (average yield strength) of 195 MPa or more. This corresponds to a yield strength of 220 MPa or more (220±25 MPa). Due to such high yield strength, when used as a frame material for a battery module, the battery module can be protected from impact. In order to achieve the desired yield strength, it is important to control the component composition (particularly, to set the Si content to 0.25 mass % or more and the Mg content to 0.65 mass % or more).

[0025] The proof stress is measured as follows. A tensile test piece according to JIS No. 13B or JIS No. 5 is taken from the aluminum alloy extrusion material, and a tensile test is carried out at room temperature to measure the 0.2% yield strength. Prepare multiple test pieces (e.g., 2 to 5 pieces) so that the tensile direction of the test piece is parallel to the extrusion direction (L direction). The tensile test is performed in accordance with the metallic material testing method specified in JIS Z 2241:2011. The arithmetic average of the measured values ​​of the yield strength obtained from multiple tensile tests (e.g., 2 to 5 times) is used as the yield strength (average yield strength) of the aluminum alloy extrusion material.

[0026] <3. Number of grain boundary precipitates> The aluminum alloy extrusion material according to the embodiment of the present invention can exhibit excellent crush resistance by reducing the number of grain boundary precipitates of a predetermined size. The present inventors have conducted extensive research and found that grain boundary precipitates 10 having a dimension of 2 μm or less in the direction perpendicular to the grain boundaries 20 (see FIG. 2 ) affect the crushability of an aluminum alloy extrusion. Based on this finding, further research was conducted, and the inventors have found for the first time that crushability can be improved by limiting the number of grain boundary precipitates 10 having a dimension of 50 nm or more and 2 μm or less in the direction perpendicular to the grain boundaries 20 within a field of view of 90 μm × 120 μm in cross-sectional SEM observation of the metal structure to 25 or less.

[0027] Hereinafter, the term "the size of the grain boundary precipitate 10" refers to the size of the grain boundary precipitate 10 in a direction perpendicular to the grain boundary 20.

[0028] In order to control the size and number of the grain boundary precipitates 10 within the desired range, it is important to control the composition of the aluminum alloy (in particular, to set the Si content to 0.39 mass% or less and the Mg content to 0.95 mass% or less), and also to control the cooling rate after extrusion during manufacturing.

[0029] The number of grain boundary precipitates is counted by cross-sectional SEM observation within a field of view of 90 μm × 120 μm (Fig. 1B, magnification × 2000). Grain boundary precipitates 10 usually have an elongated shape extending along the grain boundaries 20 (Fig. 1A). The grain boundary precipitates 10 to be measured are limited to those having a dimension of 2 μm or less in the direction perpendicular to the grain boundaries 20 (FIG. 2). In other words, grain boundary precipitates 10 having a dimension exceeding 2 μm are not measured (they are not counted in the number of grain boundary precipitates 10). In addition, due to the resolution of the SEM device, the lower limit of the dimension of the grain boundary precipitates 10 to be measured in the direction perpendicular to the grain boundaries 20 is set to 50 nm.

[0030] In Figure 2, the "direction perpendicular to the grain boundary 20" is determined on the assumption that the grain boundary 20 is linear, but in reality, the grain boundary 20 is often not linear (Figures 1A and 1B). In such cases, the "direction perpendicular to the grain boundary 20" is determined as follows. In the cross-sectional SEM image, a point is placed on the grain boundary near the center of the grain boundary precipitate 10 whose dimensions are to be measured, and a tangent line is drawn to the grain boundary at that point. The direction perpendicular to this tangent line is considered to be the "direction perpendicular to the grain boundary 20," and the dimensions of the grain boundary precipitate 10 are confirmed. If it is difficult to confirm the dimensions of the grain boundary precipitate 10 at the observation magnification (×2000) of FIG. 1B, the dimensions of the grain boundary precipitate 10 can be confirmed by performing cross-sectional SEM observation at a higher magnification (for example, ×10000) (FIG. 1A).

[0031] For cross-sectional SEM observation, a cross section parallel to the extrusion direction (L direction) and thickness direction (ST direction) is used as the observation surface, and three arbitrary fields of view are taken around 1 / 4t of the plate thickness. Within each field of view, the number of grain boundary precipitates 10 with dimensions of 50 nm or more and 2 μm or less in the direction perpendicular to the grain boundaries 20 is counted. When the observation surface is observed in BSE (Back Scattered Electron) mode, the grain boundary precipitates 10 are observed as black, elongated particles existing along the grain boundaries 20. The number of grain boundary precipitates 10 found in each field of view is summed up and divided by 3 to obtain the number (average number) of grain boundary precipitates 10 in that aluminum extrusion.

[0032] <4. Manufacturing method> In the method for producing an aluminum alloy extrusion according to an embodiment of the present invention, an aluminum alloy ingot having the above-described composition is cast, homogenized, and then extruded at an extrusion temperature. The extruded product is cooled and then artificially aged to obtain an aluminum alloy extrusion having desired characteristics.

[0033] Cooling after extrusion has generally been carried out by water cooling (average cooling rate of 5,000 to 30,000°C / min (83 to 500°C / sec)). The inventors have investigated fan cooling after extrusion (average cooling rate of 50 to 300°C / min (0.83 to 5°C / sec)) in order to reduce production costs, etc. However, there is concern that a slower cooling rate after extrusion will increase the number of grain boundary precipitates, which may result in a decrease in crushability. As a result of investigations by the inventors, it was found that by controlling the composition of the aluminum alloy to the composition specified in the embodiment of the present invention (in particular, the Si content is 0.39 mass% or less), an increase in the number of grain boundary precipitates can be suppressed even when air-cooled, and excellent crush resistance can be achieved.

[0034] This manufacturing method makes it possible to manufacture an aluminum alloy extrusion material having a proof stress of 195 MPa or more and excellent crush resistance. [Example]

[0035] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0036] <Sample Preparation> Aluminum alloy billets with the chemical compositions shown in Table 1 were cast and homogenized at 520°C for 4 hours. The billets were then heated to 500°C and extruded at 6 m / min. Fan cooling was used for post-extrusion cooling. The extrusion ratio was 44 for Tests 1 to 5 and 54 for Tests 6 and 7. The extrusion shapes (cross-sectional shapes) were as shown in Figure 3A for Tests 1 to 5 and as shown in Figure 3B for Tests 6 and 7. After fan cooling, the billets were subjected to artificial aging (T5 treatment). Tensile tests and lateral crush tests were performed using the artificially aged samples.

[0037] <Tensile test> Two JIS 13B test pieces were taken from designated locations on the artificially aged samples (the locations labeled "tensile test pieces" on specimens 31 and 32 shown in Figures 3A and 3B), and tensile tests were performed at room temperature. The test pieces were prepared so that the tensile direction was parallel to the extrusion direction (L direction). Tensile tests were performed in accordance with the metallic material testing method specified in JIS Z 2241:2011, and the tensile strength, yield strength, and elongation were measured. Measurements were performed twice, and the arithmetic mean of the measurement results was calculated. The average values ​​are shown in Table 2.

[0038] <Lateral crushing test> The artificially aged samples were cut into 200 mm lengths in the extrusion direction (L direction) to prepare specimens 31 and 32 for the lateral crush test (Figures 4A and 4B). Using a 30-ton universal testing machine, specimens 31 and 32 were placed on a surface plate, and an indenter 40 was pressed against the top surfaces of specimens 31 and 32 to perform the lateral crush test. The displacement of the indenter 40 during the test was 27 mm (equivalent to 50% of the height of specimen 31) for Tests 1 to 5 (Figure 4A), and 35 mm (equivalent to 40% of the height of specimen 32) for Tests 6 and 7 (Figure 4B). After the test, specimens 31 and 32 were visually inspected for the presence or absence of crushing cracks. Those without cracks were evaluated as passing (◯), and those with cracks were evaluated as failing (×). The evaluation results are listed in the "Crushability" column of Table 2.

[0039] <Measurement of grain boundary precipitates> SEM observations of cross sections parallel to the extrusion direction (L direction) and thickness direction (ST direction) of the artificially aged samples were performed. Cross-sectional SEM observations were performed in BSE (backscattered electron) mode. Three fields of view were randomly selected at approximately 1 / 4 of the sheet thickness and observed at 2000x magnification (Fig. 1B). The observation area per field was 90 μm (ST direction) × 120 μm (L direction). Grain boundary precipitates 10 (Fig. 2) on grain boundaries 20 identified within the observation area were further observed at 10,000x magnification. Grain boundary precipitates 10 were observed as black, elongated particles along the grain boundaries 20 (Fig. 1A). The number of grain boundary precipitates 10 (indicated by arrows in Fig. 1B) with dimensions of 50 nm or more and 2 μm or less in the direction perpendicular to the grain boundaries 20 was counted. The lower limit of the size of the grain boundary precipitates 10 to be measured was determined based on the detection limit of the SEM device (approximately 50 nm). The number of grain boundary precipitates 10 found in each field of view was summed up and divided by 3 to obtain the number (average number) of grain boundary precipitates 10 for that sample. The results are shown in Table 3.

[0040] [Table 1]

[0041] [Table 2]

[0042] [Table 3]

[0043] Both the samples of Test Nos. 1 and 7 satisfied the requirements defined in the embodiment of the present invention, and had high yield strength (195 MPa or more) and excellent crush resistance. The samples of Test Nos. 2, 5 and 6 had too much Si content, so the average number of grain boundary precipitates within the field of view exceeded 25, and the crushability was unacceptable. The samples of Test Nos. 3 and 4 had an insufficient Si content, resulting in a yield strength lower than 195 MPa. [Explanation of symbols]

[0044] 10 Grain boundaries 20 Grain boundary precipitates 31, 32 Test specimens 40 indenter

Claims

1. Si: 0.25 to 0.39% by mass, Mg: 0.65 to 0.95% by mass, Fe: 0.35 mass% or less (including 0 mass%), Cu: more than 0 mass%, 0.20 mass% or less, Cr: 0.10% by mass or less (including 0% by mass), and Ti: more than 0 mass% and 0.10 mass% or less; the balance being Al and unavoidable impurities; The yield strength is 195 MPa or more and 245 MPa or less, An aluminum alloy extrusion material in which, in metal structure observation by cross-sectional SEM observation, there are 25 or less grain boundary precipitates with dimensions of 50 nm or more and 2 μm or less in a direction perpendicular to the grain boundaries present within a field of view of 90 μm x 120 μm.

2. The aluminum alloy extrusion material according to claim 1, wherein the Si content is 0.27 to 0.37 mass%.

3. moreover, Mn: 1.0 mass% or less (including 0 mass%), Zr: 0.2 mass% or less (including 0 mass%), V: 0.2% by mass or less (including 0% by mass), Zn: 0.5 mass% or less (including 0 mass%), Ag: 0.1% by mass or less (including 0% by mass), and Sn: 0.15 mass% or less (including 0 mass%) The aluminum alloy extrusion material according to claim 1 or 2, comprising:

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