Aluminum alloy components for laser welding

Abstract

[Problem] To provide a laser welding-use aluminum alloy member for firmly joining an aluminum alloy and copper, which are materials of different types, by laser welding. [Solution] The foregoing is achieved by a laser welding-use aluminum alloy member which has a nickel-plating layer on an aluminum alloy, and in which the arithmetic average roughness Sa of the nickel plating layer surface is 100 nm or greater.

Description

[Technical field]

[0001] The present invention relates to an aluminum alloy member for laser welding and a welded structure of a metal member using the same. In this specification and claims, an alloy of a certain metal type M includes a pure metal M. For example, an aluminum alloy includes pure aluminum (aluminum with a purity of 99.00% or more) as defined by the JIS standard. A copper alloy includes pure copper (copper with a purity of 99.90% or more) as defined by the JIS standard. [Background technology]

[0002] A clad material made by pressing an aluminum (Al) alloy and copper (Cu) together has been used as a bus bar for connecting the positive electrode tab (aluminum alloy) and negative electrode tab (copper) of a battery. The clad material is the same metal as each electrode tab, so it is easy to laser weld, but a method has been proposed in which the positive electrode tab and negative electrode tab are welded to a bus bar made of an aluminum alloy in order to reduce costs (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2019-514694 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of the welding method described in Patent Document 1, it was found that the negative electrode tab (copper) and the aluminum alloy bus bar are different materials, and laser welding is difficult. Specifically, the aluminum alloy and copper do not melt and mix, and strength is not obtained. In addition, in the case of large members such as bus bars, it was found that melting and mixing is more difficult because gaps are formed between the mutually facing surfaces of the aluminum alloy member and the copper member (negative electrode tab) at the welding point due to material tolerances.

[0005] Therefore, an object of the present invention is to provide an aluminum alloy member for laser welding for firmly joining dissimilar materials, that is, an aluminum alloy and copper, by laser welding. [Means for solving the problem]

[0006] The aluminum alloy member for laser welding of the present invention is characterized in that a nickel plating layer is formed on an aluminum alloy, and the arithmetic mean roughness Sa of the surface of the nickel plating layer is set to 100 nm or more. Effect of the Invention

[0007] According to the present invention, nickel (also written as Ni) has a higher laser absorption rate than aluminum in the base material to be irradiated with the laser, and by roughening the surface, the absorption rate can be improved more than that of a smooth surface. Therefore, it is possible to efficiently melt and mix the aluminum alloy and dissimilar metals other than the aluminum alloy, and obtain a strong joint structure. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing how, in a conventional aluminum alloy member for laser welding, the material temperature increases due to laser irradiation, and excessive energy is input into the alloy member. [Diagram 2] FIG. 2 is a schematic diagram showing how, in the laser-welded aluminum alloy member of the present invention, the surface of the nickel plating layer is roughened so that most of the incident light and reflected light upon laser irradiation is absorbed inside the plating layer. [Diagram 3]3A and 3B are schematic diagrams showing the arithmetic mean roughness Sa of the surface of the nickel plating layer of the laser-welded aluminum alloy member of the present invention measured using an optical interference microscope. Figures 3A and 3B are black-and-white color images (two-dimensional and three-dimensional images) showing the roughness of the plating layer surface by different hues (concave side: purple → blue → green → yellow → convex side: red). Figures 3C and 3D are black-and-white color images (two-dimensional and three-dimensional images) of one area of ​​20 μm × 40 μm cut out by masking the color images (two-dimensional and three-dimensional images). [Figure 4] 1 is a diagram showing the state where the thickness of the nickel plating layer of the laser-welded aluminum alloy member of the present invention was measured using a field emission scanning electron microscope (FE-SEM). [Diagram 5] 5A and 5B are diagrams showing the state where the particle size of nickel particles in the nickel plating layer of the laser-welded aluminum alloy member of the present invention is measured using a field emission scanning electron microscope (FE-SEM). In micrographs shown in JIS G0551:2020 "Steel - Microscopic test method for grain size", Fig. 5A is a diagram showing the number of grains crossed by lines, and Fig. 5B is a diagram showing the number of grain boundaries crossed by lines. [Figure 6] 1 is a diagram showing how the gloss of a nickel plating layer of a laser-welded aluminum alloy member of the present invention is measured using a densitometer. [Figure 7] 1 is a diagram showing a schematic diagram of a laser welding aluminum alloy member and a metal member different from the aluminum alloy being melted and mixed and solidified to form a weld. [Figure 8] 1 is a diagram illustrating a schematic view of how the strength (tensile stress) of a welded structure of metal members is measured. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. In addition, the dimensional ratios of the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

[0010] <Aluminum alloy member for laser welding; First embodiment> One embodiment (first embodiment) of the laser welding aluminum alloy member according to the present invention is characterized in that the aluminum alloy has a nickel plating layer on it, and the arithmetic mean roughness Sa of the surface of the nickel plating layer is 100 nm or more. By having such a configuration, the above-mentioned effects can be effectively exhibited.

[0011] Although the details of why the aluminum alloy member for laser welding of the present embodiment provides the above-mentioned effects are unclear, the following mechanism of action is considered. Note that the following mechanism of action is based on speculation, and the present embodiment is not limited to the following mechanism of action in any way.

[0012] For example, when welding dissimilar metals such as Al-Cu, thermal energy is required to raise the material to its melting point. However, because the intermetallic compounds that form when dissimilar metals react are brittle, excessive energy input reduces the weld strength and increases the electrical resistance, resulting in a low-quality electrical connection. When welding dissimilar metals such as Al and Cu, the main intermetallic compounds that form are AlCu, Al2Cu, and Al4Cu9.

[0013] In addition, as shown in Figure 1, when using aluminum alloy 11, a material with low absorption rate like existing aluminum alloy components for laser welding, laser irradiation 12 causes surface reflection 13 at the starting point of welding, allowing the targeted energy 14 to be input. However, when the material temperature of aluminum alloy 11 rises during welding, the laser absorption rate increases, resulting in the input of excessive energy 15 that is greater than the targeted value.

[0014] In response to the above problem, in this embodiment, the nickel in the nickel plating layer is a material that absorbs surface energy, and nickel has a higher laser absorption rate than aluminum, which is the base material for irradiating the laser, and by roughening the surface of the nickel plating layer, the absorption rate can be improved compared to a smooth surface. That is, as shown in FIG. 2, by roughening the surface 21 of the nickel plating layer, when the roughened surface 21 is irradiated with laser light 22, the incident light 22a is refracted and absorbed in the nickel plating layer on the surface, and the reflected light 22b is also reabsorbed by the nickel plating layer, and most of the incident light 22a and the reflected light 22b are absorbed. On the other hand, in the case of a smooth surface (not shown), even if the surface is irradiated with a laser, the incident light is absorbed by the nickel plating layer on the surface, but the reflected light is reflected on the surface of the nickel plating layer in the opposite direction (toward the light source) from the incident (irradiation) direction, and is hardly reabsorbed by the nickel plating layer. Therefore, by roughening the surface of the nickel plating layer, the absorption rate can be improved compared to a smooth surface. Therefore, it is believed that it is possible to efficiently melt and mix the aluminum alloy with dissimilar metals other than the aluminum alloy, such as copper (negative electrode tab, etc.), and obtain a strong joint structure.

[0015] Hereinafter, the aluminum alloy member for laser welding of this embodiment (hereinafter also simply referred to as an aluminum alloy member) will be described in detail with respect to each of its constituent elements.

[0016] [Base material] (Base material) The base material of the aluminum alloy member of this embodiment may be any aluminum alloy. That is, because of the effect of improving the energy absorption rate by plating, the effect can be enjoyed by all alloy systems, although there are some differences in melting points depending on the additives. Therefore, alloys with low weldability are also included. Generally, international aluminum alloy names are used for aluminum alloys, and even in JIS (Japanese Industrial Standards), the international aluminum alloy names consisting of four digits are incorporated into part of the names of aluminum alloys. Each No. 1000 contains different substances mixed in, and the number allows you to determine what substances the alloy is made of. Examples of the aluminum alloy include, but are not limited to, A1050-H24, A1100-O, A1100-H24, A2011-T3, A2011-T8, A2017-T4, A2024-T3, A2024-T4, A2024-T6, A2024-T81, A5052-O, A5052-H34, A5052-H112, A5056-H34, A5056-H112, A5083-O, A6061-T6, A6061-T651, A6063-T5, A6082-T6, A6101-T6, and A7075-T651. In all cases, the first A stands for aluminum, the four digits following the A are the material code, and the code after the slash indicates the quality code. The melting point of the aluminum alloy base material itself varies little depending on its type (material). Therefore, the type of aluminum alloy base material (6101, 1100, etc.) does not affect the amount of energy absorbed by the nickel (plated layer) that melts the base material and the dissimilar metal parts that are joined to the base material. Therefore, the type (material) of aluminum alloy base material can be selected appropriately according to the required performance for each application other than the melting characteristics (melting point), such as vibration and impact resistance.

[0017] (Material, shape and size of base material) Regarding the material, shape, and size of the base material, the same material, shape, and size as those of existing aluminum alloy members for laser welding can be applied as they are. That is, a structural member having an existing aluminum alloy member as the base material and a nickel plating layer formed by surface roughening (arithmetic mean roughness Sa=100 nm or more) on the base material can be the aluminum alloy member for laser welding of this embodiment. However, the base material of this embodiment may have the same material, shape, and size as those of existing aluminum alloy members for laser welding, but may have one or more of the material, shape, and size changed from the viewpoint of weight reduction, etc.

[0018] (Shape of the aluminum alloy base material) The shape of the aluminum alloy base material may be the same as that of existing aluminum alloy members for laser welding, and in this case, a flat plate shape is generally used.

[0019] (Thickness of aluminum alloy base material) In addition, the size of the aluminum alloy base material can be the same as that of existing aluminum alloy members for laser welding. When the aluminum alloy base material has a thickness such as a flat plate shape, the thickness of the aluminum alloy is preferably in the range of 0.2 mm to 1 mm. If the thickness of the aluminum alloy is 0.2 mm or more, it is preferable that the tolerance with the counterpart member during welding can be sufficiently absorbed. On the other hand, if the thickness of the aluminum alloy is 1 mm or less, it is preferable that the aluminum alloy is easily melted by the absorbed energy, and can be made lighter and less expensive.

[0020] [Nickel plating layer] (Location of nickel plating layer) The nickel plating layer of the aluminum alloy member is provided on the aluminum alloy base material. More specifically, the nickel plating layer is provided on one surface of the aluminum alloy base material. With this member structure, the nickel plating layer is arranged on the base material surface side facing the welded portion where the base material and a metal member different from the base material are melted and solidified during welding, and the following effects can be effectively achieved. That is, nickel, which is a component of the nickel plating layer, is a material that absorbs surface energy, and nickel can have a higher laser absorption rate than aluminum, which is a component of the base material to which a laser is irradiated. In addition, the nickel plating layer may be provided at least on the surface portion facing the welded portion. For example, the nickel plating layer may be provided on the surface portion facing the welded portion and its vicinity (for example, in a range of about 5 to 10 mm outside from the outer edge of the surface portion facing the welded portion) of the base material surface on the side facing the welded portion. It may be provided in a wider range, and the widest range is the entire surface of the base material surface on the side facing the welded portion. From the viewpoints of ease of forming the nickel plating layer and of not having to strictly align the members with each other during welding (a certain degree of misalignment can be tolerated), the nickel plating layer is preferably provided on the entire surface of the base material facing the welded portion. In order to form a member structure having a nickel plating layer on a portion of the base material surface facing the welded portion, for example, a peelable insulating film is attached to and covered on the surface portion on which the nickel plating layer is not provided before plating. A method of plating the base material partially covered with the insulating film and then peeling the insulating film from the base material is exemplified, but is not limited to such a method. In addition, it is preferable that the nickel plating layer is provided on one surface of the aluminum alloy of the base material, and nothing is provided on the other surface of the aluminum alloy of the base material. Therefore, a method of attaching a peelable insulating film to cover the entire other surface of the aluminum alloy before plating, plating the base material covered with the insulating film, and then peeling the insulating film from the base material can be used.

[0021] (Arithmetic mean roughness Sa of the surface of the nickel plating layer) The nickel plating layer has a surface with an arithmetic mean roughness Sa of 100 nm or more. With this configuration, the energy absorption rate (laser absorption efficiency) of the surface is increased, and by avoiding the input of more energy than necessary, it is possible to suppress the generation of brittle intermetallic compounds generated by the reaction of dissimilar metals due to excessive energy input. This prevents the weld from becoming weak (reduced in strength), and improves (stabilizes) the weld strength. In addition, since the larger the arithmetic mean roughness Sa of the surface, the higher the energy absorption rate of the surface, it is preferable that the arithmetic mean roughness Sa of the surface is 185 nm or more. With this configuration, the absorption efficiency is further increased in the Sa region, so welding can be performed with less energy input. In other words, the energy absorption rate (laser absorption efficiency) of the surface is further increased, and welding can be performed with less energy input, so the generation of intermetallic compounds can be further suppressed, and the weld strength is further improved (stabilized). The upper limit of the arithmetic mean roughness Sa of the surface is preferably 500 nm or less, more preferably 300 nm or less, and more preferably 250 nm or less. This is because the aluminum alloy base material of the alloy member melts and penetrates into the dissimilar metal (copper, etc.) member due to the absorption of energy, but to roughen (increase) the arithmetic mean roughness Sa, the thickness of the nickel plating layer also tends to increase. However, if the arithmetic mean roughness Sa is equal to or less than the above upper limit (500 nm), it is possible to effectively prevent energy from accumulating only in the nickel (plating layer) (the volume of the nickel (plating layer) that absorbs energy becomes large). Therefore, it is possible to avoid the input of more energy than necessary, to suppress the generation of intermetallic compounds, and to improve (stabilize) the welding strength.

[0022] (Method of measuring the arithmetic mean roughness Sa of the nickel plating layer surface) The arithmetic mean roughness Sa of the surface of the nickel plating layer can be measured and calculated by the following method.

[0023] The roughness of the plating layer surface is observed (measured) with a 115x lens of a Bruker optical interference microscope, and an image of the surface roughness is obtained. Specifically, the optical interference microscope measures the roughness (unevenness) of the plating layer surface, and color images (2D and 3D images) are obtained in which the roughness (unevenness) of the plating layer surface is expressed by different hues (concave side: purple → blue → green → yellow → convex side: red). These color images are shown in black and white in Figures 3A and 3B. For these color images, the surface is masked to eliminate the effect of waviness, and three areas of 20 μm × 40 μm are cut out, and the Sa (arithmetic mean roughness of the surface) is measured and the average is calculated. This average value is the arithmetic mean roughness Sa of the nickel plating layer surface. The color images (2D and 3D images) are shown in black and white in Figures 3C and 3D for one area of ​​20 μm × 40 μm cut out by masking. In the above, an example was shown in which a Bruker microscope was used as the optical interference microscope, but this embodiment is not limited to Bruker microscopes. That is, an optical interference microscope equipped with an image analyzer equipped with software capable of measuring the surface roughness as described above and analyzing the arithmetic mean roughness Sa of an image obtained by masking an arbitrary 20 μm×40 μm area can be appropriately used.

[0024] (Thickness of nickel plating layer) The thickness of the nickel plating layer is preferably 3 μm or more, more preferably 5 μm or more. This is because the thicker the nickel plating layer, the larger the surface roughness of the surface layer = plating particle size (particle size of nickel particles) becomes, and the easier it is to obtain the laser absorption improvement effect due to the surface roughening. Due to such laser absorption improvement effect, the welding strength is improved (stabilized). From this viewpoint, the thickness of the nickel plating layer is more preferably 8 μm or more. In addition, the thickness of the nickel plating layer is preferably 16 μm or less, more preferably 14 μm or less. The aluminum alloy member is melted by absorbing energy and penetrates into the dissimilar metal (copper) member that is the welding partner member, so that the aluminum alloy and the dissimilar metal (copper) can be melted and mixed, and a strong welding structure with good welding strength (stable) can be obtained. If the thickness of the nickel plating layer is the upper limit value (16 μm) or less, energy is stored only in the nickel (plating layer), and the volume of the nickel (plating layer) that absorbs energy can be effectively prevented from increasing. Therefore, it is possible to avoid the input of more energy than necessary, to suppress the generation of brittle intermetallic compounds, and to improve (stabilize) the weld strength.

[0025] (Method for measuring thickness of nickel plating layer) The thickness of the nickel plating layer can be measured by the following method.

[0026] The cross-section of an aluminum alloy sample, which has been machined using a cross-section grinder, is observed using a field emission scanning electron microscope (FE-SEM) to obtain an image of the cross-section. The thickness of the nickel plating layer is measured from this cross-sectional image. In more detail, as shown in Figure 4, the thickness of the nickel plating layer can be measured using an image analyzer installed in the FE-SEM from a cross-sectional image at a magnification of 3000 times. The surface of the nickel plating layer is counted as the minimum value during measurement = film thickness (the concave part of the surface unevenness).

[0027] (Particle size of nickel particles in nickel plating layer) The particle size of the nickel particles in the nickel plating layer is preferably 0.5 μm or more, more preferably 0.8 μm or more. This is because when the particle size of the nickel particles is coarsened within the above range, the surface roughness increases, resulting in an improved laser absorption rate and improved (stabilized) welding strength. The upper limit of the particle size of the nickel particles in the nickel plating layer is not particularly limited, but is preferably 1.0 μm or less in terms of the relationship with the film thickness of the nickel plating layer.

[0028] (Method for measuring the particle size of nickel particles in a nickel plating layer) The particle size of the nickel particles in the nickel plating layer can be measured by the following method.

[0029] The cross section of a sample of an aluminum alloy member, the cross section of which has been processed by a cross section grinder, is observed with a field emission scanning electron microscope (FE-SEM) to obtain an image of the cross section. Specifically, a backscattered electron image with a magnification of 10,000 times is obtained. From the obtained backscattered electron image, the number of nickel grain boundaries P in the nickel plating layer is measured to obtain the number of grains N. Specifically, the number of nickel grains N can be considered to be the number of grain boundaries P by counting the number of grains with the ends of a line segment inside as 1 / 2 as shown in Figures 5A and 5B according to JIS G0551:2020 "Steel - Microscopic test method for grain size", where Figures 5A and 5B show the number of grains crossed by a line segment in the same micrograph. Here, Figures 5A and 5B show the number of grains crossed by a line segment in the same micrograph. From the above, the number of grains crossed by a line segment can be considered to be the number of grain boundaries P measured from the backscattered electron image. Next, the average grain size is calculated by the section method described in Takayama, Light Metals, 44, p. 48, "Method of evaluating grain size" (1994). In detail, by the section method, a line segment with a total length L is drawn on the cross section (backscattered electron image) of the target sample, and the number of grains that the line segment crosses is calculated by the number n. L (N) ≒ Number of grain boundaries P, and from the following formula (1), the average grain size l ave Calculate the average grain size l ave is the particle size of the nickel particles in the nickel plating layer.

[0030]

number

[0031] (Glossiness of nickel plating layer) The gloss of the nickel plating layer is preferably 0.40 or less, and more preferably 0.38 or less. This is because a lower gloss causes light to be scattered, leading to increased absorption within the surface (improved laser absorptivity). This improves (stabilizes) the welding strength. Since a lower gloss of the nickel plating layer is more preferable, the lower limit of the gloss is not particularly limited, but is preferably 0.2 or more in practice.

[0032] (Method for measuring the gloss of nickel plating layer) The gloss of the nickel plating layer can be measured by the following method.

[0033] The measurement can be performed using a densitometer ND-11 manufactured by Nippon Denshoku Industries Co., Ltd. In more detail, as shown in FIG. 6, the light source incidence angle is set to 0°, the light source 61 is a white light source having the spectral characteristics of a CIE standard light source, and the opening angle of the light receiver 62 is 45°. The gloss level is measured by measuring a φ3 mm point on the work surface (measurement point) in the center of the specimen (nickel plating layer surface of an aluminum alloy member) 63 three times and calculating the average value. This average value is regarded as the gloss level of the nickel plating layer. The gloss level is expressed as Log(I in / I out )(I in is the intensity of the light emitted from the light source (incident light), I out is calculated as the intensity of the reflected light detected by the receiver out of the light reflected by the specimen.

[0034] (Method of forming nickel plating layer) The following method can be used to form a nickel plating layer having an arithmetic mean roughness Sa of 100 nm or more on an aluminum alloy. However, the method of forming the nickel plating layer in this embodiment is not limited to the following method, and the nickel plating layer can be formed by appropriately using any conventionally known matte nickel plating technique for roughening the surface.

[0035] The nickel plating layer of this embodiment can be formed by electrolytic nickel plating under the following conditions.

[0036] <Conditions for electrolytic nickel plating> Bath solution: Sulfamic acid bath, pH 3.5-4.8, 445-645ml / L (60% nickel sulfamate) Impurities: Sulfur content 0.1wt% or less ·Current density 2~10A / dm 2 .

[0037] The sulfamate bath, mentioned above, is basically composed of nickel sulfamate, boric acid, and nickel chloride (or nickel bromide), and is characterized by being more flexible than a Watts bath, being able to use a higher current density, and having less internal stress.

[0038] The sulfamic acid bath is composed of 445 to 645 ml / L (60% nickel sulfamate), 20 to 40 g / L of boric acid, and 5 to 20 g / L of nickel chloride (or nickel bromide). In the sulfamic acid bath, plating is often performed using only these three base components, and since the purpose of this embodiment is to roughen the surface without gloss, it is preferable not to use a glossing agent or the like. However, additives may be added within a range that does not affect the effects of this embodiment. In addition, the film formation time may be appropriately determined according to the target film thickness (for example, 3 to 15 μm) (for example, about 3 to 20 minutes). In addition, the bath temperature may also be appropriately determined in relation to the film formation speed, etc. (for example, about 35 to 45° C.). However, these conditions may be outside the above ranges as long as a nickel plating layer with the above-mentioned predetermined surface roughness can be formed by the non-glossy nickel plating method. It is sensitive to concentration changes, pH changes, and impurities, and the desired surface roughness (roughness) can be obtained by adjusting these.

[0039] (Welding partner for aluminum alloy components) The aluminum alloy member is preferably welded to a member made of a copper alloy. The ability to weld different types of materials leads to cost reduction. Furthermore, the ability to stably weld different types of materials that previously had insufficient welding strength leads to improved (stable) welding strength. In principle, all metals including aluminum are effective as the material (type of material) of the member to be welded to the aluminum alloy member, and may be appropriately selected depending on the intended use.

[0040] The aluminum alloy member is preferably spaced apart from the welding partner member except for the welded portion. If there is a gap between the aluminum alloy member and the welding partner member, the material vaporized during welding can be secured to escape, blowholes can be prevented, strength reduction can be prevented, and the welding strength can be improved (stabilized). The distance apart from the welded portion can be, for example, a thin plate (about 0.2 mm thick) made of iron or the like having an opening only at the portion corresponding to the welded portion. This thin plate member is preferably cut into two or more members on the left and right (front and back) with the welded portion (opening) as the center so that it can be easily removed after welding. In addition, each divided thin plate preferably has a portion (portion to be a handle) protruding from the aluminum alloy member so that the divided thin plates can be easily removed.

[0041] (Thickness of the welded part) The thickness of the member to be welded (copper plate, etc.) may be appropriately determined depending on the intended use (electrode tab or use other than electrode tab).

[0042] (Surface of the welded part) The counterpart member to be welded (copper plate, etc.) may have a bright nickel plating layer on the side of the welded part with the aluminum alloy member, as long as the effect of the present invention is not impaired. This is for the purpose of preventing oxidation of the surface of the counterpart member to be welded (copper plate, etc.), and since nickel is less susceptible to oxidation than the base material such as copper plate, various environmental negative effects can be avoided.

[0043] <Welded structure of metal members; second embodiment> One embodiment (second embodiment) of a welded structure of a metal member according to the present invention is a welded structure of a metal member having a welded portion in which an aluminum alloy member for laser welding and a metal member other than the aluminum alloy are melted and solidified, The aluminum alloy member has a nickel plating layer on the side facing the welded portion, and the arithmetic mean roughness Sa of the surface of the nickel plating layer is 100 nm or more. With this configuration, nickel has a higher laser absorption rate than aluminum in the base material of the aluminum alloy member to which the laser is irradiated. Therefore, the energy absorption rate in the nickel plating layer on the surface of the alloy member increases, and by avoiding the input of more energy than necessary, it is possible to suppress the generation of brittle intermetallic compounds. Furthermore, by roughening the surface, the absorption rate can be improved more than on a smooth surface. Therefore, it is possible to efficiently melt and mix the aluminum alloy and a dissimilar metal other than the aluminum alloy, and a strong welded structure with improved (stable) welding strength can be obtained.

[0044] (Aluminum alloy parts) The aluminum alloy member for laser welding of this embodiment can be applied to the aluminum alloy member for laser welding of the above-mentioned first embodiment. Therefore, the aluminum alloy member for laser welding of this embodiment is explained as in the above-mentioned first embodiment, and in order to avoid repetitive explanation, the explanation will be omitted here.

[0045] In the present embodiment, the aluminum alloy member is preferably a bus bar to be joined to an electrode tab. By using the aluminum alloy member of the present embodiment as a bus bar, it is possible to connect the electrode tabs to ensure conductivity while ensuring strength as necessary.

[0046] (Welding partner of aluminum alloy component; metal component different from aluminum alloy) The metal member different from the aluminum alloy is preferably a copper alloy member, which is suitable as a welding mating member for the aluminum alloy member (bus bar) for automotive applications and conductive applications, such as a negative electrode tab for an on-board storage battery for an electric vehicle (EV) or the like.

[0047] (Materials of the parts to be welded, etc.) As the material of the metal member other than the aluminum alloy, the copper alloy is preferable as described above.

[0048] (Weld shape) It is preferable that the plurality of welding counterpart members each have the welded portion and are welded to the aluminum alloy member. With such a configuration, it is not necessary to prepare a plurality of aluminum alloy members corresponding to the plurality of welding counterpart members, so the number of parts is reduced, costs are reduced, and parts management is also made easier. In addition, since it is not necessary to weld a plurality of welding counterpart members using a plurality of aluminum alloy members, the welding work can be easily performed without being complicated, resulting in low costs.

[0049] (Method of forming welded joints; Welding method) Examples of a method for forming a weld by melting and mixing an aluminum alloy member for laser welding with a metal member different from the aluminum alloy and solidifying the mixture include, but are not limited to, the following methods.

[0050] As shown in FIG. 7, welding is performed by irradiating a laser 74 from the nickel plating layer 71b side of an aluminum alloy member 71, which is the upper plate, under the conditions described below.

[0051] <Laser welding conditions> The laser was irradiated from the nickel-plated layer side of the upper aluminum alloy component under the following conditions: Laser type: YAG laser Welding speed: 100±20mm / sec - The laser wobble (moves in circles) The bead length is determined by the length of the part to be welded (in this example, 21mm x 2).

[0052] Advances in laser welding technology have also contributed to the problem of dissimilar material welding of aluminum alloy (bus bar) and copper (negative electrode tab) and gaps between materials caused by manufacturing variations (tolerance range). That is, in the past, linear welding caused excessive heat input and small welding strength, which was not possible at all, but by performing circular welding called wobbling, a technology has been developed that can avoid excessive heat input and melt the material. Therefore, it is preferable to use circular welding called wobbling in laser welding. This is because, in order to address the problem of dissimilar material welding and gaps between materials, by using the aluminum alloy member for laser welding of this embodiment and performing wobbling (circular welding), it is possible to melt and mix dissimilar materials with lower energy while closing the gaps between the materials. As a result, a stronger joint structure can be obtained. In addition, it is preferable to use a YAG laser as the laser type in laser welding. By using a YAG laser, the light energy absorption by metals is superior to that of a CO2 laser. Therefore, processing can be performed with less energy. As a result, a stronger joint structure can be obtained. EXAMPLES

[0053] The present embodiment will be described in detail below with reference to examples, but the present invention is not limited to the following examples. Each example and comparative example was carried out under atmospheric pressure, at room temperature (25°C ± 3°C), and at a relative humidity of 50% ± 5% RH, unless otherwise specified.

[0054] (Examples 1 to 5 and Comparative Examples 1 to 3) (Preparation of aluminum alloy components for laser welding) Aluminum alloys A1100-H24 or A6101-T6 were used as the base material for the aluminum alloy components for laser welding. The thickness of the base alloy was 0.6 mm, and the shapes were rectangular plate materials for measuring the arithmetic mean roughness Sa of the surface of the nickel plating layer, glossiness, and film thickness, and the particle size of nickel particles on the plating layer surface, and plate materials with an L-shaped cross section were used for measuring the strength (tensile stress) (see Figure 8).

[0055] In Comparative Example 2, without forming a plating film, the aluminum alloy A1100-H24 of the base material was directly used as an aluminum alloy member for laser welding. The thickness of the alloy member was 0.6 mm, and for measuring strength (tensile stress), a plate material with an L-shaped cross-section (see Fig. 8) was used as the shape.

[0056] In Comparative Example 3, without forming a plating film, the aluminum alloy A6101-T6 of the plate-shaped base material was directly used as an aluminum alloy member for laser welding. The thickness of the alloy member was 0.6 mm, and for measuring strength (tensile stress), a plate material with an L-shaped cross-section (see Fig. 8) was used as the shape.

[0057] On one surface of the aluminum alloy of the base materials of Examples 1 to 5 and Comparative Example 1, a nickel plating layer was formed to obtain an aluminum alloy member for laser welding. The conditions for Ni plating for forming such a nickel plating layer were as follows. Note that the other surface of the aluminum alloy of the base material was coated with a release-type insulating film so that no plating film was formed, and then plating was performed. After the plating was completed, the insulating film was peeled off.

[0058] <Conditions for Ni plating> · Bath solution: Sulfamic acid bath · Component concentration in the bath solution (aqueous solution); Nickel sulfamate (60% nickel sulfamate) 545 ml / L, Nickel chloride 10 g / L, Boric acid 30 g / L · pH of the bath solution; 4.0 · Temperature of the bath solution; 40 °C · Impurities in the bath solution; Sulfur content 0.1 wt% or less · Current density: 3 A / dm 2 。

[0059] Note that in the bright electrolytic nickel plating of Comparative Example 1, in addition to the above three components, 0.1% by mass of sulfur was added as a brightener to the above sulfamic acid bath. Note that the pH and film formation time of the bath solutions of Examples 1 to 5 and Comparative Example 1 were the conditions shown in Table 1 below.

[0060] [Table 1]

[0061] <Measurement of the arithmetic mean roughness Sa of the nickel plating layer surface> The arithmetic mean roughness Sa of the surface of the nickel plating layer was measured and calculated by the above-mentioned method for the plate-shaped laser-welded aluminum alloy members of Examples 1 to 5 and Comparative Example 1 obtained above. The arithmetic mean roughness Sa of the surface of the obtained nickel plating layer is shown in Table 2 below.

[0062] <Measurement of thickness of nickel plating layer> The thickness of the nickel plating layer was measured by the above-mentioned method for each of the plate-shaped laser-welded aluminum alloy members obtained in Examples 1 to 5 and Comparative Example 1. The thicknesses of the obtained nickel plating layers are shown in Table 2 below.

[0063] <Measurement of the particle size of nickel particles in nickel plating layer> The particle size of the nickel particles in the nickel plating layer was measured by the above-mentioned method for the plate-shaped laser-welded aluminum alloy members obtained in Examples 1 to 5 and Comparative Example 1. The particle size of the nickel particles in the obtained nickel plating layer is shown in Table 2 below.

[0064] <Measurement of the gloss of nickel plating layer> The gloss of the nickel plating layer was measured by the above-mentioned method for the plate-shaped laser-welded aluminum alloy members obtained in Examples 1 to 5 and Comparative Example 1. The gloss of the obtained nickel plating layer is shown in Table 2 below.

[0065] (Production of welded structures of metal components) Using the plate-shaped aluminum alloy members for laser welding of Examples 1 to 5 and Comparative Examples 1 to 3 obtained above, the aluminum alloy members and a metal member different from the aluminum alloy were arranged as shown in Fig. 7 and laser welding was performed under the conditions shown below. As a result, a welded structure of a plate-shaped metal member was obtained, which had a welded part where the aluminum alloy member and the metal member different from the aluminum alloy were melted and solidified.

[0066] Specifically, pure copper (oxygen-free copper) C1020-O was used for the metal member different from the aluminum alloy. The thickness was 0.2 mm, and the shape was a rectangular plate material, and for measuring strength (tensile stress), a plate material with an L-shaped cross section (see FIG. 8) was used. The aluminum alloy member and the metal member different from the aluminum alloy used were plate materials of the same size and shape. The surface of this metal member was formed with a glossy nickel plating layer in the same manner as in Example 1.

[0067] Next, they were arranged as shown in Fig. 7 and laser welding was performed under the following conditions. In detail, a gap (73) of 0.2 mm was provided between the upper aluminum alloy member 71 and the lower copper plate 72, which is a metal member different from the aluminum alloy, by using a 0.2 mm thick SUS spacer (φ10 mm) (not shown). The upper aluminum alloy member 71 was arranged so that the side (upper side of the base material 71a = laser incident side) facing the side to be welded (side facing the copper plate 72) was a nickel plating layer 71b. The lower copper plate 72 was arranged so that the side to be welded was a glossy nickel plating layer (not shown).

[0068] The gap created by this spacer was intentional. In other words, gaps occur due to manufacturing variations (within the tolerance range) in each component. Between the bus bar and negative electrode tab of an in-vehicle storage battery, the median variation is 0.1 mm, and the maximum is 0.2 mm, so this spacer was intentionally created to confirm that even if a gap exists, it can be sufficiently closed by welding. Therefore, although it was used in this test, such spacers are not used in actual laser welding. In this test, the spacers were set before welding and removed after welding.

[0069] Next, as shown in Fig. 7, a laser 74 was irradiated from the nickel plating layer 71b side on the base material 71a of the upper aluminum alloy member 71 under the conditions shown below to perform welding. In practice, instead of a rectangular plate material, a plate material with an L-shaped cross section was used, and as shown in Fig. 8, the aluminum alloy member 81 was arranged so that a portion 81a bent by 90 degrees faced upward (the nickel plating layer side). Meanwhile, the copper plate 82 was arranged so that a portion 82a bent by 90 degrees faced downward (the back side not to be welded). The aluminum alloy member 81 and the copper plate 82 were welded at the points where they faced each other with a gap of 0.2 mm between them. The obtained welded part is indicated by the reference symbol 83. As a result, as shown in Figure 8, when measuring the strength (tensile stress), a welded structure 80 whose strength can be measured is obtained by grasping and fixing a 90° bent portion 81a on top of an aluminum alloy member 81 and a 90° bent portion 82a on top of a copper plate 82, and pulling each in the vertical direction (the direction of the arrow in Figure 8).

[0070] <Laser welding conditions> The laser was irradiated from the nickel-plated layer side of the upper plate under the following conditions. Laser type: YAG laser Welding speed: 100mm / sec - The laser wobble (moves in circles) -Bead length is 21mm x 2.

[0071] By the above-mentioned laser welding, a welded structure of a plate-shaped metal member with an L-shaped cross section (see FIG. 8) was obtained, which has a welded portion (not shown) where the aluminum alloy member 71 and a copper plate 72, which is a metal member different from the aluminum alloy, were melted and solidified.

[0072] [evaluation] <Measurement of the strength (tensile stress) of welded structures> The strength (tensile stress) of the welded structures of the metal members of Examples 1 to 5 and Comparative Examples 1 to 3 was measured using a universal testing machine, an autograph, and a tensile tester. In detail, as shown in FIG. 8, a portion 81a of the welded structure bent at 90° above an aluminum alloy member 81 and a portion 82a of the welded structure bent at 90° below a copper plate 82 were fixed to a jig, and a tensile stress was applied in the peeling direction (the direction of the arrow in the figure). The maximum load at which the welded structure broke was recorded using the autograph, and the average -3σ value of the data of N50 (50 samples) was taken as the strength (N). The strength of the welded structure 80 thus obtained is shown in Table 2 below.

[0073] [Table 2] [Explanation of symbols]

[0074] 11 Aluminum alloy, 12 Laser irradiation, 13 Surface reflection, 14 Targeted energy, 15 Excessive energy, 21 surface of nickel plating layer; 22 laser light; 22a Incident light refracted and absorbed within the plating layer, 22b Reflected light reabsorbed in plating layer, 61 Light source, 62 Light receiver, 63 specimens, 71, 81 aluminum alloy parts (bus bars), 71a base material, 71b nickel plating layer, 72, 82 copper plate, 73 gap, 74 laser, 80 welded structure, 81a, 82a 90° bent parts, 83 welded parts.

Claims

1. A nickel plating layer is provided on an aluminum alloy, and the arithmetic mean roughness Sa of the surface of the nickel plating layer is 100 nm or more and 500 nm or less; The thickness of the nickel plating layer is 3 μm or more and 16 μm or less, An aluminum alloy member for laser welding, for firmly joining dissimilar materials, an aluminum alloy and a copper alloy, by laser welding by irradiating a laser from the nickel plating layer side.

2. 2. The aluminum alloy member for laser welding according to claim 1, wherein the arithmetic mean roughness Sa of the surface is 185 nm or more.

3. 3. The aluminum alloy member for laser welding according to claim 1, wherein the nickel plating layer has a thickness of 5 μm or more.

4. 4. The aluminum alloy member for laser welding according to claim 3, wherein the nickel plating layer has a thickness of 8 μm or more.

5. The laser welding aluminum alloy member according to any one of claims 1 to 4, wherein the nickel plating layer has a film thickness of 14 µm or less.

6. The laser welding aluminum alloy member according to any one of claims 1 to 5, wherein the nickel particles in the nickel plating layer have a particle size of 0.8 µm or more.

7. The laser welding aluminum alloy member according to any one of claims 1 to 6, wherein the nickel plating layer has a glossiness of 0.40 or less.

8. An aluminum alloy component for laser welding as described in any one of claims 1 to 7, wherein the thickness of the aluminum alloy is 0.2 mm or more and 1 mm or less.

9. 9. The aluminum alloy member for laser welding according to claim 1, wherein the aluminum alloy member is separated from a counterpart member other than the welded portion.

10. A welded structure of a metal member including an aluminum alloy member for laser welding, a metal member different from the aluminum alloy member as a welding partner, and a welded portion, The aluminum alloy member has a nickel plating layer, and the arithmetic mean roughness Sa of a surface of the nickel plating layer is 100 nm or more and 500 nm or less, The thickness of the nickel plating layer is 3 μm or more and 16 μm or less, A welded structure of metal members, wherein the welded portion is formed by melting and solidifying the aluminum alloy member and the metal member.

11. 11. The welded structure of metal members according to claim 10, wherein the aluminum alloy members are spaced apart from the counterpart member except for the welded portion.

12. 12. The welded structure of metal members according to claim 10, wherein a plurality of said welding counterpart members each have said welded portion and are welded to said aluminum alloy member.

13. The welded structure of metal members according to any one of claims 10 to 12, wherein the metal member different from an aluminum alloy is a metal member made of a copper alloy.

14. The welded structure of metal members according to any one of claims 10 to 13, wherein the aluminum alloy member is a bus bar joined to an electrode tab.

15. The welded structure of metal members according to any one of claims 10 to 14, wherein a laser type used to form the weld is a YAG laser.

16. The laser welding aluminum alloy member according to any one of claims 1 to 9, wherein the nickel plating layer has a glossiness of 0.38 or less.

17. The welded structure of the metal member according to any one of claims 10 to 15, wherein the nickel plating layer has a glossiness of 0.40 or less.

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