Patent Application
20250207226
The present disclosure relates to an aluminum alloy with high strength and high surface treatment properties.
Light alloy materials meet various needs and are widely used industrially. When considered as mechanical and structural materials, light alloy materials are increasingly used for, for example, automobiles, high-speed railway vehicles, and aerospace. Among lightweight alloys, aluminum alloys are used in major fields in most countries because aluminum alloys are materials which are inexpensive and easy to process. Hereinafter, an aluminum alloy will be referred to as an Al alloy. Improvement in mechanical strength of Al alloys is being studied by material manufacturers. However, the strength of Al alloys is low compared to steel, Ti-based alloys, Ni-based alloys, and so forth. Even A7075-T6 (JIS standard), which is a high-strength commercially available Al alloy, is considered insufficient in terms of mechanical strength for some applications. For this reason, an optimal metal composition for Al alloys has been continuously studied.
For example, in Patent Literature 1, the composition of an Al alloy is required to be set to Zn: 5-12 mass %, Mg: 2-4 mass %, and Cu: 1-2 mass %, and 0.01-0.1 mass % of Ag needs to be further added, so as to obtain a high-strength Al alloy.
Further, in Patent Literature 2, the composition is required to contain Zn: 3.2-8.0 mass %, Mg: 1.2-4.5 mass %, Cu: 0.2-1.5 mass %, Mn: 0.1-1.2 mass %, Cr: 0.1-0.5 mass %, B: 0.005-0.2 mass %, Be: 0.02-1.0 mass %, Ni and/or Co: 0.1-1.2 mass %, Zr and/or Hf: 0.05-1.2 mass %, and Ag: 0.05-2.0 mass %, so as to obtain a high-strength Al alloy.
Further, in Patent Literature 3, the composition is set to contain Zn: 5-11 mass %, Mg: 2-4.5 mass %, Cu: 0.5-2.0 mass %, Mn 2-6 mass %, and Ag 0.01-0.5 mass %, so as to obtain a high-strength Al alloy.
Al alloys are known as base metal following Mg alloys among utility metals, and are known to be easily corroded. Therefore, it is necessary to perform surface treatment such as plating and painting on Al alloy products to provide corrosion resistance. In particular, a machined metal surface develops a plastically deformed layer called a Beilby layer. For this reason, it is common to perform surface treatment after removing the plastically deformed layer by etching with alkali or acid.
When an Al alloy is etched with acid or alkali, a black deposit called smut is generated on the surface.
There has been a problem in that smut interferes with a surface treatment process and with adhesion of plating and painting.
An object of the present disclosure is to provide an Al alloy on which smut generation is suppressed during a surface treatment process and which is highly strong.
In an aluminum alloy according to the present disclosure,
According to the Al alloy of the present disclosure, an Al alloy with excellent surface treatment properties and high strength can be provided. Higher strength of an Al alloy can reduce product weight. Further, improvement in surface treatment properties can provide stable corrosion resistance and shorten product lead time.
An Al alloy according to Embodiment 1 will be described below. The following description includes an Al alloy which is a raw material alloy and an Al alloy which is finally produced from a raw material alloy. To distinguish between the two, these Al alloys are sometimes referred to as a raw material alloy, and a final alloy which is an Al alloy manufactured from a raw material alloy. Further, a final alloy is sometimes referred to as an “Al alloy (final alloy)”. The final alloy is an Al alloy whose powder is solidified in a solidifying step described later.
The Al alloy (final alloy) of Embodiment 1 is manufactured by cold solidification. The tensile strength of the Al alloy (final alloy) of Embodiment 1 is 650 MPa or greater. The Al alloy (final alloy) of Embodiment 1 has a smut film of 1 μm or less when immersed in 10 mass % or more of alkali or 10 mass % or more of acid.
The aluminum alloy which is the raw material alloy has the following composition.
Here, elements contained in the raw material alloy will be further described later.
Step S20 is a powder producing step. In Step S20, an inert gas such as nitrogen, argon, and helium is injected at high pressure through nozzle holes to produce rapidly solidified Al alloy powder.
A relation between the mass % of Zn, Mg, and Cu in the raw material alloy and the diameter of crystal particles of powder will be described below. Powder with a particle diameter greater than 300 μm is not rapidly solidified and therefore not employed.
Zn, Mg, and Cu form a coarse intermetallic compound and accordingly,
Here, the notation “5.0-6.5 mass %” in Zn means “from 5.0 mass % to 6.5 mass % inclusive”. Further, the same is applied to the notations Mg: 2.0-3.0 mass %, Cu: 1.2-2.0 mass %, and the like.
When the addition concentration of Ni, Ag, and Li is low, the tensile strength of 650 MPa or greater cannot be obtained. On the other hand, when the addition concentration of Ni, Ag, and Li is high, coarse intermetallic compounds are easily formed, and hot cracking easily occurs during solidification.
Therefore, the raw material alloy contains at least one element in the following range of mass % for each of the three elements:
For example, when only Ni is contained, Ni: 2.0-5.0 mass %. When two elements, Ni and Ag, are contained, Ni: 2.0-5.0 mass % and Ag: 0.5-3.5 mass %. When three elements, Ni, Ag, and Li, are contained, respective elements are in the three ranges shown above. When two or more elements among Ni, Ag, and Li are contained, one of these elements may be at the lower limit of the allowable mass % range.
In the raw material alloy, contained Si is 0.25 mass % or less and contained Mn is 0.5 mass % or less. The contents of Si and Mn will be described later in relation to smut.
Step S30 is a solidifying step. The rapidly solidified powder of the raw material alloy produced in the powder producing step was densified and solidified by hot extrusion processing. Then, the rapidly solidified powder which was solidified was subjected to solution treatment and aging treatment under tempering conditions equivalent to T6 of A7075 in the JIS standard. Thus, a high-strength Al alloy was obtained as a final alloy
In
On the other hand, as shown in
In
To obtain the tensile strength of 650 MPa or greater, an appearance area, which represents a total area of an intermetallic compound appearing in the Al alloy (final alloy), is preferably 2% or less and more preferably 1% or less in observation with a scanning electron microscope with the field of view of 300 μm×300 μm.
Step S40 is a cleaning step. The manufactured Al alloy (final alloy) is degreased and cleaned to remove organic matters to which oil and the like are attached. Subsequently, alkaline cleaning is performed.
In alkaline cleaning, the surface is etched by performing immersion in an aqueous solution containing 10 mass % to 20 mass % inclusive of sodium hydroxide or potassium hydroxide at a temperature of 50° C. or higher for 10 to 30 seconds, revealing a clean surface.
In addition to sodium hydroxide, any strong alkaline aqueous solution such as potassium hydroxide may be adopted for alkaline cleaning.
The thickness of smut formed during alkaline cleaning was measured by spectroscopic ellipsometry. If smut is thin and reflected light from underlying metal can be measured, the smut thickness can be measured. When measurement was possible, a measurement result of the smut thickness was 1 μm or less. On the other hand, smut that is thick and exhibits a black color is difficult to measure. When measurement was difficult, the smut thickness was 1 μm or greater. Poor surface treatment properties can be visually determined based on change to a black color caused by thick smut.
In acid cleaning, the degreased and cleaned final alloy was immersed in an aqueous solution containing 10 mass % to 20 mass % inclusive of nitric acid. Smut was examined by immersion at a temperature of 50° C. or higher for 10 to 30 seconds, employing the same method as the alkaline cleaning. The surface treatment properties were determined based on the smut film thickness and blackening. Here, strong acids such as sulfuric acid and hydrochloric acid may be used or mixed acids may be used for acid cleaning in addition to nitric acid. Further, for mixed acids, weak acids such as phosphoric acid and carbonic acid can be mixed with strong acids. In particular, mixed acids of phosphoric acid and nitric acid and mixed acids of phosphoric acid and sulfuric acid are known as chemical polishing fluids. These are used for improving surface smoothness.
Amounts of Si and Mn largely affect thickening and blackening of smut.
The examination found that the followings are desirable:
Using a raw material alloy having the above-described composition, an Al alloy with excellent surface treatment properties and high strength can be manufactured by the manufacturing method described in
Further, the improvement in the surface treatment properties can provide stable corrosion resistance and shorten product lead time.
Supplementary information regarding Embodiment 1 will be given.
In order to suppress smut generation due to alkali or acid and to improve surface treatment properties, the smut thickness needs to be set to 1 μm or less. To achieve this, it has been necessary to set the Si content in the Al alloy to 0.25 mass % or less and the Mn content to 0.5 mass % or less. Patent Literature 1 and Patent Literature 2 allow the Si content to be up to 0.25 mass % or greater, and Patent Literature 3 allows the Mn content to be up to 2-6 mass %. Therefore, Patent Literature 1 and Patent Literature 2 cannot achieve the 1 μm or less of smut thickness.
At the same time, it has been necessary to limit the addition amounts of Si and Mn to determine an optimal composition ratio of elements added to the Al alloy.
In order to obtain a high-strength Al alloy whose tensile strength is 650 MPa or higher,
The added elements are preferably dissolved as a solid solution in Al matrix. In addition, higher tensile strength is obtained when inhibiting generation of precipitates, which are coarse intermetallic compounds. Therefore, rapid solidification was employed for manufacturing.
As a modification of Embodiment 1, an application to a 3D printer 40 will be described. Referring to
On the XY plane and the ZX plane, a diameter φd of a crystal particle 20 is shown. The diameter of the crystal particle 20 is sometimes referred to as the particle diameter.
The powder particle size distribution of the atomized powder produced in the powder producing step in Step S20 is adjusted as follows.
In the solidifying step of Step S30-1, by adjusting particle diameters, an Al alloy (final alloy) product can be directly manufactured by additive manufacturing using the 3D printer 40.
Step S30-1 will be described with reference to
The powder 31 produced in Step S20 is easily oxidized and nitrided because the temperature can be raised and lowered in a short time by irradiation with the laser light 11. Therefore, it is important to control oxygen and nitrogen concentrations. In particular, oxidation causes brittle fracture and therefore, products are preferably manufactured with the 3D printer 40 in a non-oxygen atmosphere, and products are more preferably manufactured in an Ar gas atmosphere. Oxygen contained in a manufactured object manufactured with the 3D printer 40 in the non-oxygen atmosphere is preferably 0.1 mass % or less, and more preferably 0.05 mass % or less.
Nitrogen contained in a manufactured object by the 3D printer 40 is preferably 0.01 mass % or less, and more preferably 0.001 mass % or less.
When the laser wavelength of the laser light 11 used for melting the powder 31, which is produced in Step S20, is 700 nm or less, the light absorption rate by Al is reduced. Therefore, the range of the laser wavelength is preferably from 700 nm to 1100 nm inclusive. The Si content of the powder 31 produced in Step S20 is low, whereby the melting temperature is high. Accordingly, it is more preferable to irradiate it at a laser wavelength from 800 nm to 1100 nm inclusive, which is a wavelength range where light is easily absorbed.
<Diameter φd of Crystal Particle 20 after Irradiated with Laser Light 11>
As the diameter φd of the crystal particle 20 of the powder 31 which is rapidly solidified is smaller, the tensile strength is higher. When a product is manufactured with the 3D printer 40, the manufactured product has anisotropy in the diameter φd of the crystal particles 20 due to the characteristics of the 3D printer 40. When the laser light 11, which is a heat source, is radiated in the Z direction, the diameter φd of the crystal particle 20 is elongated in the Z direction. The Z direction is assumed to be the height direction.
As shown in the XY plane of
As shown in the ZX plane of
As shown in the perspective view of the XYZ coordinates in
A product made of high-strength Al alloy can be obtained by implementing one or both of aging treatment and stress relaxation heat treatment to the product without performing solution treatment of the product, after manufacturing with the 3D printer 40.
In Step S40-1 which is a surface treatment, cleaning is performed by using alkali and acid which are the same conditions as in
As described above, an Al alloy (final alloy) manufactured by solidification is irradiated with a heat source from a direction along the Z axis in the solidifying step, and the diameter φd of the crystal particle 20 has anisotropy with respect to the laser light 11 which is a heat source. The diameter φd is 30 μm or less in a cross section parallel to the XY plane, and 200 μm or less in a cross section parallel to the ZX plane. In the Al alloy (final alloy) manufactured by solidification, the contained oxygen is 0.1 mass % or less and the contained nitrogen is 0.01 mass % or less.
According to the product production with the 3D printer 40 described in
The Al alloy (final alloy) of Embodiment 1 described above is as the following.
In the Al alloy (final alloy),
Further, an appearance area, which represents a total area of an intermetallic compound appearing in the Al alloy (final alloy), is 2% or less in observation with a scanning electron microscope with a field of view of 300 μm×300 μm.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/014160 | 3/24/2022 | WO |
