Aluminum alloy extruded material

Abstract

The present invention addresses the problem of providing an extruded material of 6000 series alloy having higher ultra-high strength.　The present invention solved the problem by configuring such that: a component composition of the extruded material contains 0.4 to 1.5 mass% of Si, 0.3 to 1.1 mass% of Mg, and 0.3 to 0.7 mass% of Cu, further contains one or more of 0.4 mass% or less of Cr and 0.7 mass% or less of Mn where the total of Cr and Mn is 0.1 to 0.7 mass%, and contains unavoidable impurities, the remainder being Al; and in addition, the metal structure of the extruded material is such that the number density of precipitates having an equivalent circle diameter of 20 nm or less is 2100 pieces / μm2 or more, or the width of the precipitate-free zone (PFZ) is 81 nm or less.

Description

Aluminum alloy extrusions

[0001] The present invention relates to an extruded material of an ultra-high strength 6000 series aluminum alloy.

[0002] Regarding 6000 series aluminum alloy extrusions, Non-Patent Document 1, page 31, states the following: "Alloys of this series have excellent strength and corrosion resistance and are widely used as structural materials. 6063 alloy, which is used in large quantities in aluminum sashes, and 6005C (6N01) alloy, which is used in railway vehicles and automobile parts, have excellent extrusion processability and can be used to obtain shapes with complex cross-sectional shapes. There are also many types, such as 6061 alloy, which contains a small amount of Cu and has a strength equivalent to that of structural steel." In recent years, the concept of carbon neutrality has been accepted and promoted worldwide as a measure against global warming. Japan has also declared its intention to achieve carbon neutrality by 2050, and reducing CO2 emissions is a major goal.

[0003] Japan Aluminum Association, "What is Aluminum?", URL: https: / / www.aluminum.or.jp / basic / aluminumtoha / pdf / AboutAluminum.pdf

[0004] In this environment, automobile collision safety standards are becoming stricter every year, and vehicle weights are tending to increase as electrification progresses. Lighter vehicle body weight leads to improved fuel efficiency and contributes to reducing CO2 emissions, so high-strength aluminum alloy materials are required as materials for further lightening vehicle bodies. An object of the present invention is to provide an extruded 6000 series alloy with even higher ultra-high strength.

[0005] In one aspect of the present invention, the component composition includes 0.4 to 1.5 mass% of Si, 0.3 to 1.1 mass% of Mg, and 0.3 to 0.7 mass% of Cu, and further includes at least one of 0.4 mass% or less of Cr and 0.7 mass% or less of Mn, with the total of Cr and Mn being 0.1 to 0.7 mass%, and the number density of precipitates is 2100 / μm 2 The problem was solved by providing an aluminum alloy extrusion material characterized by the above.

[0006] In another embodiment of the present invention, the problems are solved by providing an extruded aluminum alloy material characterized in that the component composition includes 0.4 to 1.5 mass% of Si, 0.3 to 1.1 mass% of Mg, and 0.3 to 0.7 mass% of Cu, and further includes at least one of 0.4 mass% or less of Cr and 0.7 mass% or less of Mn, the total of Cr+Mn being 0.1 to 0.7 mass%, and unavoidable impurities, the balance being Al, and the width of the precipitate-free zone (PFZ) is 81 nm or less.

[0007] The present invention provides an extruded material of an ultra-high strength 6000 series alloy.

[0008] FIG. 1 is a TEM (transmission electron microscope) image. FIG. 2 is a TEM image of precipitate 1 in Example 5, Example 4, Comparative Example 4, and Comparative Example 5. FIG. 3 is a TEM image of precipitate-free zone (PFZ) 2 in Example 5, Example 4, Comparative Example 4, and Comparative Example 5. FIG. 4 is a graph in which the tensile strength of Examples 1 to 6 (E1 to E6) and Comparative Examples 1 to 7 (C1 to C7) is plotted on the X-axis, precipitate-free zone (PFZ) 2 on the right Y-axis, and the number density of precipitates on the left Y-axis.

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts with the same function, and duplicated explanations in each drawing will be omitted as appropriate. [First Embodiment] The purpose of the first embodiment is to study the composition. The examples and comparative examples shown below were performed by adding elements mainly Fe, Cu, Mn, and Cr in varying ratios, including Si and Mg, which are the main components of 6000 series aluminum alloys.

[0010] [Embodiment] Regarding 6000-series alloys, JIS H 4100:2015 indicates that the highest strength was 310 MPa, a value consistent with the 6082 alloy. This embodiment was developed with the goal of achieving an aluminum alloy with a tensile strength of 400 MPa or greater. The added elements were selected for the following reasons: Mg contributes to increased strength through its own solid solution and, in conjunction with Si, to increased strength through aging precipitation hardening. Cu contributes to increased strength through its own solid solution and the formation of aging precipitates, θ'-CuAl2. The increased strength of the alloy is not only due to the formation of Mg-Si precipitates, but also to the formation of dense, fine θ'-CuAl2 through the addition of Cu. Fe is an element that affects the recrystallized grain size and alloy strength. Cr has the effect of suppressing recrystallization in extruded materials, thereby increasing strength. Mn, like Cr, has the effect of suppressing recrystallization in extruded materials, thereby increasing strength.

[0011] Below is a description of the evaluation methods and treatments used in the Examples and Comparative Examples.

[0012] The elements to be added were determined with the goal of obtaining a 6000 series aluminum alloy having a tensile strength of 400 MPa or more, and experiments were repeated.

[0013] (Experiment 1) The extruded material of the example used in Experiment 1 was manufactured by the following method. A cast aluminum ingot (billet) was homogenized for 10 hours or less at a temperature below the melting point of the aluminum alloy. The billet was then heated to 500°C or higher but below the melting point, and the heated billet was loaded into an extrusion tool (container, die, etc.) heated to 500-600°C, and then extruded. The extruded aluminum alloy material was water-cooled immediately after extrusion and subjected to artificial aging treatment. The artificial aging treatment was performed by holding the material at 160-200°C for 1-30 hours. The artificial aging treatment time was longer at lower temperatures and shorter at higher temperatures. If the artificial aging temperature was lower than 160°C, the time to reach maximum strength was significantly longer. On the other hand, if the artificial aging temperature exceeded 200°C, fine precipitates 1 could not be obtained. Furthermore, high strength cannot be obtained if the aging treatment is performed for less than 1 hour, and if the aging treatment is performed for more than 30 hours, the precipitates 1 of the Mg—Si compound may become coarse, which may result in a decrease in strength. The particularly preferred aging temperature is 165 to 185° C., and the particularly preferred treatment time is 3 to 25 hours.

[0014] Comparative Example The extruded shape of the comparative example used in Experiment 1 had an aluminum alloy composition that was not significantly different from that of the example, but the billet temperature, extrusion tool temperature, and artificial aging treatment time were different from those of the example.

[0015] (Evaluation Method - Tensile Strength) After the aging treatment, the tensile strength, 0.2% yield strength, and elongation at break of each extruded material were measured based on the tensile test method for metallic materials of JIS Z2241.

[0016] (Evaluation method: width of precipitate-free zone and number density of precipitates) Figure 1 shows a TEM (transmission electron microscope) observation image. Precipitates 1 were classified based on the arrangement of bright spots in the TEM observation image. As a result, it was found that precipitates 1 were classified into β'' phase 11, parallelogram type 12, and random type 13, which do not have a specific shape. The precipitates 1 counted in the observation included β'' phase 11, parallelogram type 12, random type 13, etc. Measurement samples were prepared by polishing each extruded material after aging treatment using a twin-jet electrolytic polishing method. The measurement samples were observed with a TEM (transmission electron microscope) to measure the width of the precipitate-free zone (PFZ) 2 near the grain boundary and the number density count of precipitates 1. The number density count of precipitates 1 was performed using image analysis software Winroof (Mitani Corporation, version 2018). In addition, the number density (particles / μm 2 The area equivalent diameter of precipitates 1 was determined by counting the number of dot-like precipitates 1 having a circle-equivalent diameter of 20 nm or less in a dark-field image observed by a TEM and converting the number of dots into a number per unit area. The circle-equivalent diameter of precipitates in the present invention is defined as the area equivalent diameter = circle-equivalent diameter in JIS Z 8827-1 "Particle size analysis - Image analysis method - Part 1, static image analysis method."

[0017] (Extrusion conditions and artificial aging conditions) The billets used to prepare the extruded shapes were aluminum alloy billets with a diameter of 60 mm and a length of 60 mm, and the alloy composition shown in Table 1 below. The billets were then extruded into round bars with a diameter of 18 mm at a ram speed of 5 mm / s using a 400-ton vertical extrusion press, with the billet temperature and die temperature varied as shown in Table 1 below. The obtained round bars were water-cooled immediately after extrusion. The extruded round bars were then subjected to an artificial aging treatment. The artificial aging treatment conditions were as shown in Table 1 below. (Results of Experiment 1)

[0018]

[0019]

[0020] Examples 1 to 6 clearly had higher tensile strengths than Comparative Examples 1 to 7. The tensile strengths of Examples 1 to 6 were 495 MPa to 421 MPa, which achieved the target of obtaining an aluminum alloy with a tensile strength of 400 MPa or more according to the embodiment, but Comparative Examples 1 to 7 did not achieve this. Note that the Comparative Examples were extruded at lower billet and / or die temperatures than the Examples, as shown in Table 1. The alloy compositions of the Comparative Examples and Examples include those that are nearly identical. Comparing the Comparative Examples and Examples, which have similar compositions, it was found that the number density of precipitates and the width of the precipitate-free zone (PFZ) 2 have a significant effect on tensile strength.

[0021] 2 shows TEM images of precipitates 1 in Example 5, Example 4, Comparative Example 4, and Comparative Example 5. It can be seen that the number of precipitates 1 (bright spots) in Example 5 and Example 4 is greater than in Comparative Example 4 and Comparative Example 5. This suggests that the number of precipitates 1 may affect the tensile strength.

[0022] 3 shows TEM images of the precipitate-free zones (PFZ) 2 of Example 5, Example 4, Comparative Example 4, and Comparative Example 5. It was suggested that the width of the precipitate-free zones (PFZ) 2 may affect the tensile strength.

[0023] (Summary of Experiment 1) Comparing Examples 1 to 6, the number density of precipitates 1 affects the tensile strength, and the higher the number density of precipitates 1, the higher the tensile strength of the alloy. The boundary of the number density of precipitates 1 that results in an aluminum alloy with a tensile strength of 400 MPa or more is 2052 precipitates / μm in Comparative Example 1. 2 The tensile strength was 397 MPa and the number of pieces / μm in Comparative Example 2 was 1882. 2 392 MPa, whereas Example 6 was 2262 pieces / μm 2 When statistical variations (errors) are taken into consideration, the 2 Therefore, it was found that the number density of the precipitates 1 was 2100 / μm 2 If this is the case, an aluminum alloy having a tensile strength of 400 MPa or more according to the embodiment can be obtained.

[0024] Comparing Examples 1 to 6, it was found that the width of the precipitate-free zone (PFZ) 2 of the precipitate 1 affected the tensile strength, with the narrower the width of the precipitate-free zone (PFZ) 2, the higher the tensile strength of the alloy. The boundary of the width of the precipitate-free zone (PFZ) 2 at which an aluminum alloy with a tensile strength of 400 MPa or more is obtained is as follows: Comparative Example 1 has a precipitate-free zone (PFZ) 2 width of 85.1 nm and a tensile strength of 397 MPa; Comparative Example 2 has a PFZ 2 width of 82.1 nm and a tensile strength of 392 MPa; while Example 6 has a PFZ 2 width of 80.8 nm and a tensile strength of 421 MPa. Taking into account statistical variation (error), etc., it was found that the boundary is 81.0 nm. Therefore, if the width of the precipitate-free zone (PFZ) 2 is 81.0 nm or less, an aluminum alloy of the embodiment having a tensile strength of 400 MPa or more can be obtained.

[0025] (Number Density and Precipitate-Free Zone) A combined analysis of Examples 1 to 6 and Comparative Examples 1 to 7 revealed that the number density of precipitate 1 affected tensile strength, with the higher the density of precipitate 1, the higher the tensile strength of the alloy. This indicates a positive correlation between tensile strength and the density of precipitate 1. Furthermore, the narrower the width of precipitate-free zone (PFZ) 2, the higher the tensile strength of the alloy. Table 2 also reveals that tensile strength is negatively correlated with the width of precipitate-free zone (PFZ) 2. Figure 4 is a graph of Examples 1 to 6 (E1 to E6) and Comparative Examples 1 to 7 (C1 to C7), with the tensile strength on the X-axis, the width of precipitate-free zone (PFZ) 2 on the right Y-axis, and the number density of precipitates on the left Y-axis. In Figure 4, ■ indicates the width of the precipitate-free zone (PFZ), and ● indicates the number density of precipitates. The graph shows Examples 1 to 6 (E1 to E6) and Comparative Examples 1 to 7 (C1 to C7) with ● indicating the number density of precipitates. The precipitate-free zone (PFZ)2 widths corresponding to Examples 1 to 6 (E1 to E6) and Comparative Examples 1 to 7 (C1 to C7) indicated by ● are shown as ■, connected by a two-dot chain line. The precipitate-free zone (PFZ)2 widths (■) and precipitate number densities (●) for Examples 1 to 6 (E1 to E6) and Comparative Examples 1 to 7 (C1 to C7) are distributed so that the two-dot chain lines connecting each example are perfectly parallel, revealing an inverse correlation between the precipitate-free zone (PFZ)2 width and the precipitate number density. In other words, the larger the precipitate-free zone (PFZ)2 width, the smaller the precipitate number density. Figure 4 clearly shows a clear relationship between the tensile strength, increasing with increasing precipitate number density and decreasing with decreasing precipitate-free zone (PFZ)2 width.

[0026] (Amount of each component added) Si cooperates with Mg to form Mg-Si precipitates, imparting strength to the alloy through precipitation hardening. The Si concentration is preferably 0.4 to 1.5 mass%. A preferred Si concentration is 0.8 to 1.2 mass%, with a more preferred range being 1.0 to 1.2 mass%. If the Si concentration is less than 0.4 mass%, a sufficient number of Mg-Si precipitates cannot be formed, while if the Si concentration exceeds 1.5 mass%, it will not form a solid solution during homogenization or extrusion processing, and will not contribute to the formation of Mg-Si precipitates.

[0027] Mg contributes to an increase in strength through its own solid solution and, in cooperation with Si, through aging precipitation hardening. The Mg concentration is set to 0.3 to 1.1 mass%. A preferred Mg concentration is 0.6 to 0.9 mass%, with a more preferred range being 0.7 to 0.8 mass%. If the Mg concentration is less than 0.3 mass%, a sufficient number of Mg-Si-based precipitates cannot be formed, while if the Mg concentration exceeds 1.1 mass%, Mg will not be solid-dissolved during homogenization treatment or extrusion processing, and will not contribute to the formation of Mg-Si-based precipitates.

[0028] Cu is an element that imparts strength to alloys by increasing strength through its own solid solution and by forming θ'-CuAl2, an aging precipitate. The increase in alloy strength is not only due to the formation of Mg-Si precipitates, but also due to the formation of dense and fine θ'-CuAl2 by adding Cu. The Cu concentration should be 0.3 to 0.7 mass%. The preferred Cu concentration is 0.3 to 0.6 mass%. If the Cu concentration is less than 0.3 mass%, the strength-increasing effect due to solid solution cannot be fully obtained, and if it exceeds 0.7 mass%, corrosion resistance decreases.

[0029] Cr and Mn have the effect of suppressing recrystallization and increasing the strength of the extruded material. However, if the total content of one or more of Cr and Mn is less than 0.1 mass%, this effect is not fully achieved. On the other hand, if the content exceeds 0.7 mass%, coarse intermetallic compounds such as Al-Fe-Si-Cr and Al-Fe-Si-Mn intermetallic compounds are likely to form. The presence of such coarse intermetallic compounds in the extruded material deteriorates the external roughness of the extruded material. It is recommended that the total content of one or more of Cr and Mn be 0.1 to 0.7 mass%. The preferred total content is 0.2 to 0.6 mass%, with a more preferred range being 0.2 to 0.4 mass%.

[0030] With reference to the drawings and tables, it has been explained that the number density of precipitates 1 and the precipitate-free zone (PFZ) 2 correlate with tensile strength in the embodiments of the present invention. This correlation is extremely clear as shown in Figure 4. Figure 4 strongly supports the present invention. The present invention is the first to clarify the relationship between tensile strength, number density, and precipitate-free zone (PFZ) 2, and the specific composition of the components can be changed as appropriate as long as these relationships are not violated. It goes without saying that unavoidable impurities may be included in the practice of the present invention.

[0031] 1 Precipitates 11 β'' phase 12 Parallelogram type 13 Random type 2 Precipitation-free zone (PFZ)

Claims

1. The chemical composition includes 0.4 to 1.5 mass% of Si, 0.3 to 1.1 mass% of Mg, and 0.3 to 0.7 mass% of Cu; and further includes at least one of 0.4 mass% or less of Cr and 0.7 mass% or less of Mn, with the total of Cr and Mn being 0.1 to 0.7 mass%, and unavoidable impurities, with the balance being Al; and the number density of precipitates with a circle equivalent diameter of 20 nm or less is 2100 / μm 2 An aluminum alloy extrusion material characterized by the above.

2. An aluminum alloy extrusion material characterized in that its chemical composition includes 0.4 to 1.5 mass% Si, 0.3 to 1.1 mass% Mg, and 0.3 to 0.7 mass% Cu, and further includes at least one of 0.4 mass% or less Cr and 0.7 mass% or less Mn, with the total of Cr and Mn being 0.1 to 0.7 mass%, and also includes inevitable impurities, the balance being Al, and the width of the precipitate-free zone (PFZ) is 81 nm or less.

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