Aluminum alloy forging stock

Abstract

The present invention provides an aluminium alloy forging stock having an alloy composition that contains Cu in an amount of 0.3 mass% to 0.80 mass%, Mg in an amount of 0.65 mass% to 1.05 mass%, Si in an amount of 0.95 mass% to 1.25mass%, Mn in an amount of 0.44 mass% to 0.56 mass%, Fe in an amount of 0.15 mass% to 0.50 mass%, Zn in an amount of 0.25 mass% or less, Cr in an amount of 0.10 mass% to 0.35 mass%, Ti in an amount of 0.01 mass% to 0.1 mass%, B in an amount of 0.0010 mass% to 0.030 mass%, the balance being Al and unavoidable impurities, and has an average amount of Cr dissolved in AlFeSi crystalized constituents present at grain boundaries in the range of 0.30 mass% to 0.95 mass%.

Description

Aluminum alloy forging stock

[0001] The present invention relates to an aluminum alloy forging stock. This application claims priority based on Japanese Patent Application No. 2025-068723 filed in Japan on April 18, 2025, the content of which is incorporated herein by reference.

[0002] In recent years, aluminum alloys, taking advantage of their light weight, have seen expanding applications as structural members for various products. For example, high-tensile steel has conventionally been used for automotive undercarriage and bumper components, but in recent years, high-strength aluminum alloy materials have come into widespread use. Iron-based materials have been exclusively used for automotive parts such as suspension components, but they are increasingly being replaced with aluminum materials or aluminum alloy materials mainly for the purpose of weight reduction.

[0003] In automotive suspension systems, suspension arms are one of the important components, and are required to have excellent corrosion resistance, high strength, and excellent workability. For this reason, Al-Mg-Si based alloys, particularly A6061, are frequently used as aluminum alloy materials. In addition, in order to improve the strength of such automotive parts, they are manufactured by performing forging, which is a type of plastic working, using an aluminum alloy material as a working stock.

[0004] For forged products using such 6000-series aluminum alloys, there is a tendency for the worked structure to recrystallize and generate coarse crystal grains during hot forging in the manufacturing process and the subsequent solution treatment. When coarse crystal grains are generated due to such recrystallization, there is a concern that strength and corrosion resistance will decrease.

[0005] For this reason, it is known to add elements having a crystal grain refining effect such as Mn, Zr, and Cr in order to suppress recrystallization and the generation of coarse crystal grains caused by recrystallization (for example, refer to Patent Document 1).

[0006] Japanese Unexamined Patent Application Publication No. 2015-189993

[0007] However, the aluminum alloy forged material disclosed in Patent Document 1 has a limited effect in suppressing the generation of coarse crystal grains due to recrystallization, and there was a need for an aluminum alloy forging material that could effectively prevent a decrease in strength and corrosion resistance even after hot forging or solution treatment.

[0008] This invention has been made in view of the above technical background, and provides an aluminum alloy forging material that can suppress recrystallization due to forging and effectively prevent a decrease in strength and corrosion resistance even after hot forging or solution treatment.

[0009] To solve the above problems, the aluminum alloy forging material of one embodiment of the present invention proposes the following means. (1) The aluminum alloy forging material according to Embodiment 1 of the present invention is an aluminum alloy forging material having an alloy composition in which Cu is contained in a range of 0.3 mass% to 0.80 mass%, Mg in a range of 0.65 mass% to 1.05 mass%, Si in a range of 0.95 mass% to 1.25 mass%, Mn in a range of 0.44 mass% to 0.56 mass%, Fe in a range of 0.15 mass% to 0.50 mass%, Zn in a range of 0.25 mass%, Cr in a range of 0.10 mass% to 0.35 mass%, Ti in a range of 0.01 mass% to 0.1 mass%, and B in a range of 0.0010 mass% to 0.030 mass%, with the remainder being Al and unavoidable impurities, wherein the average amount of Cr solidly dissolved in AlFeSi-based precipitates present at grain boundaries is in the range of 0.30 mass% to 0.95 mass%.

[0010] (2) The aluminum alloy forging material of embodiment 2 of the present invention is characterized in that, in embodiment 1, the average value of the measured potential of the precipitates measured by a surface potential microscope is 0.50 V or less.

[0011] (3) In the aluminum alloy forging material of embodiment 3 of the present invention, in embodiment 1 or 2, the measured potential difference between the precipitate and the matrix phase, as measured by a surface potential microscope, is 0.68 V or less.

[0012] According to the present invention, the potential of the Al-Fe-Si precipitate is reduced by solid-solving Cr in the Al-Fe-Si precipitate. This suppresses the electrochemical corrosion between the Al-Fe-Si precipitate and the matrix phase, making it possible to provide an aluminum alloy forging material with improved corrosion resistance without reducing the strength of aluminum alloys such as 6000 series aluminum alloys.

[0013] This graph shows the measurement results of the average potential of the AlFeSi-based precipitates in the examples. This graph shows the measurement results of the potential difference between the AlFeSi-based precipitates and the matrix phase in the examples. This graph shows the measurement results of the amount of Cr dissolved in the precipitates in the examples. This is an explanatory diagram showing an example of the method for measuring the potential difference in the examples.

[0014] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for the sake of clarity, the drawings used in the following description may show enlarged versions of key features, and the dimensional ratios of each component may not be the same as those in reality. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not necessarily limited to them. It can be implemented with appropriate modifications without altering its effects.

[0015] The following describes an aluminum alloy forging material according to one embodiment of the present invention. The aluminum alloy forging material of this embodiment is a material for manufacturing forged products, such as suspension arms, through a forging process. The aluminum alloy forging material of this embodiment has an alloy composition in which Cu is contained in the range of 0.3 mass% to 0.80 mass%, Mg in the range of 0.65 mass% to 1.05 mass%, Si in the range of 0.95 mass% to 1.25 mass%, Mn in the range of 0.44 mass% to 0.56 mass%, Fe in the range of 0.15 mass% to 0.50 mass%, Zn in the range of 0.25 mass%, Cr in the range of 0.10 mass% to 0.35 mass%, Ti in the range of 0.01 mass% to 0.1 mass%, and B in the range of 0.0010 mass% to 0.030 mass%, with the remainder being Al and unavoidable impurities, and the average amount of Cr dissolved in the AlFeSi-based precipitates present at the grain boundaries is in the range of 0.30 mass% to 0.95 mass%.

[0016] The aluminum alloy in this embodiment corresponds to the 6000 series aluminum alloy in that it contains Mg and Si.

[0017] (Cu: 0.3% by mass or more, 0.80% by mass or less) Cu has the effect of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys by precipitating as Al-Cu-Mg-Si compounds, including the Q phase. The Cu content is in the range of 0.30% by mass or more and 0.80% by mass or less, and may also be in the range of 0.35% by mass or more and 0.70% by mass or 0.45% by mass or less.

[0018] By keeping the Cu content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved. Furthermore, when the Cu content exceeds 0.80 mass%, Mg occurs at the grain boundaries. ２ Since the amount of Cu coexisting with Si increases, the potential difference between the matrix phase and the compound at the grain boundaries becomes larger, impairing corrosion resistance and stress corrosion cracking resistance. Therefore, it is preferable that the amount remains within the above range.

[0019] (Mg: 0.65% by mass or more, 1.05% by mass or less) Mg has the effect of improving the tensile strength of aluminum alloys. Mg is dissolved in the aluminum matrix, or Mg-Si compounds such as the β'' phase (Mg ２ By precipitating as Si, or as Al-Cu-Mg-Si compounds including the Q phase, it contributes to strengthening the aluminum alloy. The Mg content is in the range of 0.65% by mass or more and 1.05% by mass or less, and may also be in the range of 0.75% by mass or more and 1.00% by mass or more than 0.85% by mass and 0.95% by mass or less. By having the Mg content within the above range, the corrosion resistance of the aluminum alloy can be improved along with the mechanical properties at room temperature.

[0020] (Si: 0.95% by mass or more, 1.25% by mass or less) Like Mg, Si improves the corrosion resistance of aluminum alloys as well as their mechanical properties at room temperature. However, if Si is added in excess to an aluminum alloy, coarse primary Si grains may crystallize, which may reduce the tensile strength of the aluminum alloy.

[0021] The Si content is in the range of 0.95% by mass or more and 1.25% by mass or less, and may also be in the range of 0.95% by mass or more and 1.20% by mass or less, or 1.00% by mass or more and 1.18% by mass or less. By having the Si content within the above range, it is possible to suppress the crystallization of primary Si while improving the corrosion resistance as well as the mechanical properties at room temperature of the aluminum alloy.

[0022] (Mn: 0.44% by mass or more, 0.56% by mass or less) Mn improves the tensile strength of aluminum alloys by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy. The Mn content is in the range of 0.44% by mass or more and 0.56% by mass or less, and may also be in the range of 0.45% by mass or more and 0.5% by mass or less and 0.45% by mass or less. By having a Mn content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0023] (Fe: 0.15% by mass or more, 0.50% by mass or less) Fe crystallizes in aluminum alloys as fine precipitates containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe, thereby improving the tensile strength of the aluminum alloy. The Fe content is in the range of 0.15% by mass or more and 0.50% by mass or less, and may also be in the range of 0.20% by mass or more and 0.50% by mass or less, or in the range of 0.20% by mass or more and 0.40% by mass or more and 0.22% by mass or more. By having an Fe content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0024] (Cr: 0.10% by mass or more, 0.35% by mass or less) Cr improves the tensile strength of aluminum alloys by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr, which are AlFeSi-based precipitates, in the aluminum alloy. The Cr content is in the range of 0.10% by mass or more and 0.35% by mass or less, and may also be in the range of 0.15% by mass or more and 0.35% by mass or less, or in the range of 0.20% by mass or more and 0.35% by mass or less, or 0.25% by mass or more and 0.35% by mass or less. By having a Cr content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0025] (Ti: 0.01% by mass or more, 0.1% by mass or less) Ti has the effect of refining the crystal grains of aluminum alloy and improving its wroughtability. If the Ti content is less than 0.01% by mass, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.1% by mass, coarse precipitates may form, which may reduce the wroughtability. In addition, if a large amount of coarse precipitates containing Ti are mixed into the aluminum alloy, the toughness may decrease. Therefore, the Ti content should be 0.01% by mass or more, and 0.1% by mass or less. Preferably, the Ti content is 0.015% by mass or more, and 0.080% by mass or less.

[0026] (B: 0.0010% by mass or more, 0.030% by mass or less) B has the effect of refining the crystal grains of aluminum alloy and improving its wroughtability. By adding B to aluminum alloy together with the above-mentioned Ti, the effect of refining the crystal grains is improved.

[0027] If the B content is less than 0.001% by mass, the grain refinement effect may not be sufficiently obtained. On the other hand, if the B content exceeds 0.030% by mass, coarse precipitates may form and be mixed into the aluminum alloy forging as inclusions. Furthermore, if a large amount of coarse precipitates containing B are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the B content should be 0.001 to 0.030% by mass. Preferably, the B content is 0.0015 to 0.025% by mass.

[0028] (Unavoidable Impurities) Unavoidable impurities are impurities that inevitably become mixed into the aluminum alloy from the raw materials or manufacturing process. Examples of unavoidable impurities include Zn, Zr, Ni, Sn, and Be. It is preferable that the content of these unavoidable impurities does not exceed 0.1% by mass.

[0029] Furthermore, the aluminum alloy forging material of this embodiment has an average amount of Cr dissolved in the AlFeSi-based precipitates present at the grain boundaries after forging that is in the range of 0.30% by mass or more and 0.95% by mass or less.

[0030] When casting aluminum alloy forging material, crystal grains are formed by heat treatment, and AlFeSi-based precipitates are formed at the grain boundaries between adjacent crystal grains. In this embodiment, the aluminum alloy forging material has an average amount of Cr dissolved in these AlFeSi-based precipitates within the range of 0.30 mass% to 0.95 mass%.

[0031] In this embodiment, by setting the Cr content in the aluminum alloy forging material to 0.10% by mass or more and 0.35% by mass or less, the average amount of Cr in the AlFeSi-based precipitates formed at the grain boundaries of the crystal grains can be set to within the range of 0.30% by mass or more and 0.95% by mass or less.

[0032] Furthermore, it is preferable that the aluminum alloy forging material of this embodiment has an average measured potential of AlFeSi-based precipitates measured by a surface potential microscope of 0.50 V or less. It is also preferable that the measured potential difference between the AlFeSi-based precipitates and the matrix phase measured by a surface potential microscope is 0.68 V or less.

[0033] The surface potential microscope (Kelvin Force Microscope: KFM) used for measurement evaluates the distribution of the surface potential of a sample by applying a voltage between the sample and the probe. More specifically, by keeping the distance between the probe and the sample constant to obtain a topographic image of the sample, a DC voltage is applied between the probe and the sample such that the sample side is positive, creating conditions that facilitate hole formation on the sample surface. When an AC voltage is then applied, the probe vibrates due to an electrical force of the same frequency. Since the angular frequency of the amplitude of this probe vibration is proportional to the surface potential of the sample, regions with a more positive surface potential are displayed as brighter images.

[0034] In this embodiment, the aluminum alloy forging material preferably has an average value of the KFM measurement potential of AlFeSi-based precipitates formed at grain boundaries between crystal grains of 0.50 V or less. By setting the Cr content to within the range of 0.10 mass% to 0.35 mass%, the potential of the precipitates is lower than that of an aluminum alloy material without added Cr.

[0035] Furthermore, in this embodiment, it is preferable that the measured potential difference between the AlFeSi-based precipitates and the matrix phase of the aluminum alloy forging material, as measured by KFM, is 0.68 V or less. Here, the matrix phase refers to the portion of the aluminum alloy forging material that constitutes the region other than the precipitates. By making the measured potential difference between the AlFeSi-based precipitates and the matrix phase 0.68 V or less, it is possible to suppress the occurrence of corrosion due to the potential difference at the grain boundaries between crystal grains, that is, to improve resistance to intergranular corrosion.

[0036] This makes it possible to prevent corrosion-induced deterioration of forged products obtained by forging aluminum alloy forging materials. Achieving a measurement potential difference of 0.68V or less between these AlFeSi-based precipitates and the matrix phase can be accomplished by limiting the Cr content in the aluminum alloy forging material to between 0.10% by mass and 0.35% by mass.

[0037] Although one embodiment of the present invention has been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0038] The effects of embodiments of the present invention were verified. Table 1 shows the actual compositions of the aluminum alloy forging materials for Examples 1-2 and Comparative Example 1-2 of the present invention. In Example 1-2 of the present invention, Cu was in the range of 0.3% by mass or more and 0.80% by mass or less, and Cr was in the range of 0.10% by mass or more and 0.35% by mass or less. On the other hand, Comparative Example 1 had a composition that did not contain Cr, and Comparative Example 2 had Cr at 0.49% by mass.

[0039]

[0040] The aluminum alloy forging materials (cast materials) with the compositions of the present invention examples 1-2 and comparative examples 1-2 were heated to 470°C, held for 7 hours, and then cooled to room temperature by air cooling (homogenization heat treatment). Next, each sample that had undergone this homogenization heat treatment was heated to 540°C, held for 3 hours (solution treatment), and then placed in a water bath (water temperature 50°C) (quenching treatment). Furthermore, each sample that had undergone the quenching treatment was held at 180°C for 6 hours and then air cooled (aging treatment process).

[0041] For the samples of Invention Examples 1-2 and Comparative Examples 1-2 subjected to the series of treatments as described above, a surface potential microscope (Dimension XR Nanomechanics: manufactured by Bruker Corporation) was used to measure the average potential of AlFeSi-based crystallized products at grain boundaries, and calculate the potential difference between the average potential of these crystallized products and the average potential of the parent phase. The average potential of the crystallized products is shown as a graph in Figure 1, and the potential difference from the parent phase is shown as a graph in Figure 2, respectively.

[0042] Note that an example of the potential difference measurement method is shown using Comparative Example 1. For example, in the potential distribution map of Comparative Example 1 shown in Figure 4, the potential difference between the bright portion (the region where the surface potential is on the more positive side: the region of the crystallized product) and the dark portion (the region where the surface potential is on the negative side: the region of the parent phase) is calculated. In the case of this Comparative Example 1, the potential difference was set to 0.702, calculated as (0.549 V (potential of the crystallized product)) - (-0.153 V (potential of the parent phase)).

[0043] Further, an electron probe microanalyzer (Electron Probe Micro Analyzer: EPMA) was used to measure the average amount of Cr dissolved in solid solution in the crystallized products in Invention Examples 1-2 and Comparative Examples 1-2. The results are shown as a graph in Figure 3.

[0044] According to the measurement results shown in Figures 1 and 2, in Invention Examples 1-2, by adding Cr in the range of 0.10 mass% to 0.35 mass%, the average potential of the crystallized products was lower than that of the sample with no Cr added (Comparative Example 1) and the sample with Cr added in an amount greater than 0.35 mass% (Comparative Example 2).

[0045] Thereby, it was confirmed that the samples of Invention Examples 1-2 can make the potential difference between the average potential of the crystallized products and the average potential of the parent phase smaller than the samples of Comparative Examples 1-2, and improve the intergranular corrosion resistance.

[0046] Further, according to the measurement results shown in Figure 3, it was confirmed that the amount of Cr dissolved in solid solution in the crystallized products also increases in accordance with the added amount of Cr.

[0047] According to the aluminum alloy forging material of the present invention, by solid-solving Cr in the Al-Fe-Si precipitates, the potential of the precipitates is lowered, thereby suppressing electrochemical corrosion between the Al-Fe-Si precipitates and the matrix phase. This improves the corrosion resistance of aluminum alloys such as 6000 series aluminum alloys without reducing their strength. Furthermore, it is possible to obtain an aluminum alloy forging material that suppresses recrystallization due to forging and effectively prevents a decrease in strength and corrosion resistance even after hot forging or solution treatment. This makes it possible to manufacture forged products such as suspension components for vehicles that have high strength and improved corrosion resistance. Therefore, it has industrial applicability.

Claims

1. An aluminum alloy forging material having an alloy composition in which Cu is contained in an amount of 0.3 mass% to 0.80 mass%, Mg in an amount of 0.65 mass% to 1.05 mass%, Si in an amount of 0.95 mass% to 1.25 mass%, Mn in an amount of 0.44 mass% to 0.56 mass%, Fe in an amount of 0.15 mass% to 0.50 mass%, Zn in an amount of 0.25 mass%, Cr in an amount of 0.10 mass% to 0.35 mass%, Ti in an amount of 0.01 mass% to 0.1 mass%, and B in an amount of 0.0010 mass% to 0.030 mass%, with the remainder being Al and unavoidable impurities, wherein the average amount of Cr dissolved in the AlFeSi-based precipitates present at the grain boundaries is in the range of 0.30 mass% to 0.95 mass%.

2. The aluminum alloy forging material according to claim 1, wherein the average value of the measured potential of the precipitates measured by a surface potential microscope is 0.50 V or less.

3. The aluminum alloy forging material according to claim 1 or 2, wherein the measured potential difference between the precipitate and the matrix phase, as measured by a surface potential microscope, is 0.68 V or less.

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