JP7332978B1 - zygote - Google Patents

Abstract

An object of the present invention is to improve the corrosion resistance of an opening and its surroundings in a joined body using steel materials provided with an opening, thereby achieving a longer life of the joined body. A joined body according to the present invention comprises a first member made of steel materials having a surface treatment layer, and having an opening and an exposed portion where a steel substrate is exposed adjacent to the opening. and a second member provided to cover at least the opening of the first member. The peripheral length L of the opening, the area SS of the exposed portion, and the average deposition amount Mm of the plating layer satisfy specific conditions, and the Mg, Al, and Zn contents of the entire plating layer, and the The ratio R calculated from the Mg, Al, and Zn contents up to 3 μm deep satisfies specific conditions. [Selection drawing] Fig. 5

Description

The present invention relates to a conjugate.

Even steel materials that have undergone surface treatment are provided with various openings, such as holes for fastening parts such as screws and bolts, holes for transportation, holes for alignment, etc. There are many things. In addition, the steel substrate is often exposed in the portions adjacent to these openings.

If the surface treatment applied to the steel material is painting, corrosion progresses from the exposed portion of the steel substrate. When the surface treatment applied to the steel material is zinc-based plating, the corrosion rate can be suppressed to some extent due to the sacrificial anti-corrosion ability of the zinc-based plating, but a longer service life cannot be expected. In addition, although the vicinity of the opening may be repaired by painting or the like, there is a problem that costs and man-hours are required.

On the other hand, if iron oxide (including iron rust) occurs on the exposed part of the steel substrate, it may be repaired with paint after physically removing the iron oxide by scraping or shot blasting. . However, keren and shot blasting are not easy to work on site. In addition, if the treatment is inadequate, iron oxides will remain and the effectiveness of the repair will be lost prematurely. Therefore, a technique has been proposed to prevent further generation of rust by painting over the iron oxide without removing the iron oxide (see, for example, Patent Document 1 below).

Japanese Patent Application Laid-Open No. 2020-70328

However, the technique proposed in Patent Literature 1 requires a plurality of painting operations, which is complicated, and there is concern that the construction period may be prolonged due to the curing time for drying. In addition, such paints are not only expensive, but also quickly lose their effectiveness in repairing if the paint is insufficient. As a result, starting from the periphery of the opening, the corrosion of the member having the opening and the member closing the opening proceeds at an early stage, and the entire structure cannot be expected to have a long life. Under these circumstances, there is a demand for structures that are constructed using steel materials that have openings and that have better corrosion resistance and longer life.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to further improve the corrosion resistance of the opening and its surroundings in a joined body using steel materials provided with an opening. It is to let

In order to solve the above-mentioned problems, the present inventors conducted intensive studies, and as a result, at least the opening was covered with a steel material having a plating layer, and the opening and the exposed portion of the steel base existing around the opening were corroded. The inventors have come up with the idea of eluting the plating components from the plating layer when exposed to the environment. In addition, the present inventor has come up with the idea that the corrosion resistance can be further improved by allowing the eluted plating components to reach the openings and exposed portions of the steel base.
The gist of the present invention, which was completed as a result of further studies based on this idea, is as follows.

(1) It is composed of a steel material having a surface treatment layer, and has an opening that penetrates the steel material and an exposed part that is adjacent to the opening and where the steel base is exposed. 1 member and a second member made of a steel material having a plating layer and provided so as to cover at least the opening of the first member; The plating layer of the member is, in mass%, Al: more than 15.0% and 30.0% or less, Mg: more than 5.0% and 15.0% or less, Sn: 0% to 0.70%, Ca: 0.03% to 0.60%, Si: 0.01% to 0.75%, Ti: 0% to 0.25%, Ni: 0% to 1.00%, Co: 0% to 0.25 %, Fe: 0% to 5.0%, B: 0% to 0.5%, the balance being Zn and impurities, and the first material on the side not in contact with the second member L [mm] is the peripheral length of the opening of the member, _SS [mm ² ] is the area of the exposed portion of the first member that is not in contact with the second member, and one side of the second member M _m [g/m ² ] is the average _adhesion amount of the plating layer per unit _. L×M _m /S _S ≧1.300 is established, and in the plated layer of the second member on the side in contact with the first member, the total content of Mg, Al, and Zn (unit: :% by mass) are represented as [Mg]', [Al]', and [Zn]', respectively, and the first member and the second member are placed at the position of the opening of the first member. In the cross section obtained by cutting in the thickness direction, the plating layer of the second member on the side in contact with the first member is analyzed by an energy dispersive X-ray spectrometer (FE) of a field emission scanning electron microscope. -SEM/EDX), the contents of Mg, Al, and Zn obtained by surface analysis from the surface to a depth of 3 μm (unit: mass%) are denoted as [Mg], [Al], and [Zn], respectively. Then, the ratio R calculated based on the analysis result of the surface analysis is defined as the following formula (1), and in the cross section, starting from one end of the opening, from the center of the opening _RA , which is the value of the ratio R at the position A, is in the range of 1.10 to 5.00 when the position 20 mm away is the position A, and in the cross section, the opening A joined body, wherein RB, which is the value of the ratio R at the position B, is equal to or less than the value of the _RA when the position of one end of the portion is a position _B.
(2) The conjugate according to (1), wherein the R _B is in the range of 0.30 to 5.00.
(3) on the surface of the plating layer of the second member, there is a chemical conversion coating having a resistance of less than 1×10 ⁻³ Ω when measured by a four-terminal four-probe method; The described conjugate.
(4) The joined body according to (1), wherein the surface treatment layer of the first member contains Zn.
(5) The joined body according to (1), wherein the surface treatment layer of the first member is composed of one or more layers, and the outermost surface is a coating film.
(6) The joined body according to any one of (1) to (5), wherein iron oxide adheres to the exposed portion of the first member.
(7) The joined body according to any one of (1) to (5), wherein the opening of the first member has a burr facing the second member.

As described above, according to the present invention, it is possible to further improve the corrosion resistance of the opening and its surroundings in a joined body using steel materials provided with an opening, thereby realizing a longer life of the joined body. becomes.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which showed typically an example of the joined body which concerns on embodiment of this invention. It is an explanatory view for explaining an example of the structure of the joint body concerning the embodiment. FIG. 4 is an explanatory diagram schematically showing an example of the structure of the first member in the joined body according to the same embodiment; FIG. 4 is an explanatory diagram schematically showing an example of the structure of a second member in the joined body according to the same embodiment; FIG. 4 is an explanatory diagram schematically showing an example of the structure of a second member in the joined body according to the same embodiment; It is an explanatory view for explaining a plated layer in a bonded body according to the same embodiment. It is an explanatory view for explaining a plated layer in a bonded body according to the same embodiment.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

(Regarding zygotes)
A bonded body according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1 is an explanatory view schematically showing an example of a joined body according to this embodiment.

A joined body according to the present embodiment is formed by joining a plurality of steel materials, as described in detail below. FIG. 1 schematically shows a bonded body 1 having a box-like outer shape as an example of such a bonded body. Examples of the joint 1 having such a box-like outer shape include a switchboard, an outdoor unit, a water heater, and the like. As mentioned above, such a joined body 1 has openings 3 having various shapes, such as holes for providing fastening parts such as screws and bolts, holes for transportation, holes for alignment, and the like. are often located in various locations.

When manufacturing various types of joined bodies as described above, it is common to use surface-treated steel materials that have undergone various surface treatments as raw material steel materials from the viewpoint of corrosion resistance. When forming the above-described openings 3 in the surface-treated steel material that is the raw material, the surface-treated layer applied to the steel material is partially peeled off, thereby exposing the steel base. If the joined body with the steel base exposed is exposed to a corrosive environment, the corrosion reaction proceeds starting from the steel base. Therefore, in the joined body 1 according to the present embodiment, at least in the vicinity of the opening 3, by adopting a structure as described in detail below, the corrosion resistance of the opening 3 and its surroundings is further improved, and the joined body to achieve longer life.

Note that the joined body 1 focused on in the present embodiment is not limited to the box-shaped one as described above. The bonded body 1 focused on in the present embodiment may be, for example, a plate-shaped bonded body using plate-shaped steel materials, such as a roof or a wall of a building, or a solar panel mount. It may be a jointed body using various shaped steels, a jointed body using various H-shaped steels or square columns such as the framework of a structure, signs, traffic lights, guardrails, etc. It may be a joined body using various kinds of steel pipes.

<Regarding the structure of the joined body>
Next, with reference to FIG. 2, what kind of steel material is used to form the joined body 1 according to the present embodiment will be described in detail. In the following, for the sake of convenience, a case in which the joined body 1 is configured using a plate-shaped steel material (that is, a steel plate) will be described as an example. FIG. 2 is an explanatory diagram for explaining an example of the structure of the joined body according to the present embodiment, and is a part of a cross section of the joined body according to the present embodiment cut in the thickness direction of the steel materials that are the raw materials. is schematically shown.

As shown in FIG. 2, the joined body 1 according to the present embodiment includes a first member 10 having an opening 11 penetrating the steel material, and a member provided to cover at least the opening 11 of the first member 10. and the second member 20 are joined together.

<<Regarding the configuration of the first member 10>>
FIG. 3 is an explanatory diagram schematically showing an example of the structure of the first member 10 in the joined body 1 according to this embodiment. As shown in FIG. 3, the first member 10 according to the present embodiment has a base steel material 101 as an example of a steel base material, and a surface treatment layer 103 located on the surface of the base steel material 101. . At least part of the first member 10 is provided with various openings as illustrated in FIGS. 1 and 2 . Although FIG. 3 illustrates the case where the surface treatment layer 103 is provided on both surfaces of the base steel material 101 , the surface treatment layer 103 may be provided only on one surface of the base steel material 101 .

◇Base steel 101
The base steel material 101 used as the base material of the first member 10 according to the present embodiment is not particularly limited, and various of steel can be used. As such base steel material 101, for example, various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength ultra-low-carbon steel further containing strengthening elements such as P, Si, Mn, etc. Various steel materials such as steel can be mentioned.

Moreover, the thickness of the base steel material 101 is not particularly limited, and may be appropriately set according to the mechanical strength required for the joined body 1 and the like.

◇Surface treatment layer 103
The surface treatment layer 103 according to this embodiment is a layer provided to improve the corrosion resistance of the base steel material 101 of the first member 10 . The surface treatment for forming the surface treatment layer 103 is not particularly limited, and examples thereof include various plating treatments and painting treatments using various antirust paints (including powder coating). It is possible to apply various known processing methods such as Moreover, as the surface treatment for forming the surface treatment layer 103, a plurality of treatment methods may be used in combination.

Here, the surface treatment layer 103 according to this embodiment is preferably a surface treatment layer containing Zn. By providing the surface treatment layer containing Zn, it becomes possible to utilize the sacrificial anti-corrosion ability of Zn, and it becomes possible to further improve the corrosion resistance of the first member 10 . A specific example of the surface treatment layer containing Zn is not particularly limited. The Zn-containing surface treatment layer may be, for example, various zinc-based plating layers, or the surface of the plating layer may be subjected to chemical conversion treatment (that is, plating layer + chemical conversion treatment film). Alternatively, it may be a coating film using a paint containing Zn.

Also, the surface treatment layer 103 may have a multi-layer structure composed of a plurality of layers. At this time, the outermost surface of the surface treatment layer 103 may be a coating film formed using various paints. For example, the design of the joined body 1 can be improved by forming a coating film that becomes the outermost surface of the surface treatment layer 103 using a paint containing various color pigments. Further, by using various other paints as the paint for forming the coating film, various functions expressed by the additives contained in the paint can be applied to the joined body 1. In addition, the desired coating may be performed after performing a pre-coating treatment such as phosphating before coating.

<<Regarding the configuration of the second member 20>>
4A and 4B are explanatory diagrams schematically showing an example of the structure of the second member 20 in the joined body 1 according to this embodiment. As shown in FIG. 4A, the second member 20 according to the present embodiment has a base steel material 201 as an example of a steel base and a plating layer 203 located on the surface of the base steel material 201 . Moreover, as shown in FIG. 4B, the second member 20 according to this embodiment may further have a chemical conversion coating 205 on the surface of the plating layer 203 .

4A and 4B illustrate the case where the plating layer 203 and the chemical conversion coating 205 are provided on both sides of the base steel material 201, the plating layer 203 and the chemical conversion coating 205 are formed on one side of the base steel material 201. may be provided only on the surface of the

◇Base steel 201
The base steel material 201 used as the base material of the second member 20 according to the present embodiment is not particularly limited, and various of steel can be used. As such base steel material 201, for example, various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength ultra-low-carbon steel further containing strengthening elements such as P, Si, Mn, etc. Various steel materials such as steel can be mentioned.

Moreover, the thickness of the base steel material 201 is not particularly limited, and may be appropriately set according to the mechanical strength required for the joined body 1 and the like.

◇Plating layer 203
The plating layer 203 in the second member 20 according to this embodiment not only improves the corrosion resistance of the second member 20, but also prevents the opening of the first member 10 when the joined body 1 is exposed to a corrosive environment. It is a layer that functions to ensure corrosion resistance around the portion 11 .

The plating layer 203 according to the present embodiment has a chemical composition in mass% of Al: more than 15.0% and 30.0% or less, Mg: more than 5.0% and 15.0% or less, Ca: 0.03 % to 0.60%, Si: 0.01% to 0.75%, the balance being Zn and impurities.

These components and their contents will be described in detail below.

[Al: more than 15.0% by mass and 30.0% by mass or less]
Al is an element necessary for forming the main phase (Zn--Al--Mg alloy phase) of the plating layer 203 according to this embodiment. If the Al content in the plating layer 203 is 15.0% by mass or less, the corrosion resistance of the joined body 1 cannot be ensured. Therefore, in the plating layer 203 according to this embodiment, the Al content is over 15.0% by mass. The Al content is preferably 17.0% by mass or more. When the Al content falls within the above range, the corrosion resistance of the joined body 1 can be further improved.

On the other hand, when the Al content in the plating layer 203 exceeds 30.0% by mass, the Al phase that functions as a cathode increases excessively when placed in a corrosive environment, and the corrosion of the base steel material 201 progresses. Therefore, the corrosion resistance of the joined body 1 cannot be ensured. Therefore, in the plating layer 203 according to this embodiment, the Al content is 30.0% by mass or less. The Al content is preferably 25.0% by mass or less.

[Mg: more than 5.0% by mass and 15.0% by mass or less]
Mg is an element necessary for forming the main phase (Zn--Al--Mg alloy phase) of the plating layer 203 according to this embodiment. Therefore, in the plating layer 203 according to this embodiment, the Mg content is over 5.0% by mass. When the Mg content falls within the above range, the corrosion resistance of the joined body 1 can be ensured.

On the other hand, when the Mg content in the plating layer 203 exceeds 15.0% by mass, anodic dissolution of the plating layer is likely to proceed when placed in a corrosive environment. can't Therefore, in the plating layer 203 according to this embodiment, the Mg content is 15.0% by mass or less. The Mg content is preferably 13.0% by mass or less. When the Mg content falls within the above range, the corrosion resistance of the joined body 1 can be further improved.

[Ca: 0.03 to 0.60% by mass]
Ca is an element that forms an intermetallic compound phase with Al and Zn by being contained in the plating layer 203 . In addition, since the plating layer 203 contains Si together with Ca, Ca forms an intermetallic compound phase together with Si. By forming these intermetallic compound phases, the corrosion resistance of the joined body 1 can be ensured. The effect of forming such an intermetallic compound phase is exhibited by setting the Ca content to 0.03% by mass or more. The Ca content in the plating layer 203 is preferably 0.05% by mass or more.

On the other hand, when the Ca content in the plating layer 203 exceeds 0.60% by mass, the corrosion resistance of the joined body 1 is lowered. From this point of view, the Ca content in the plating layer 203 is 0.60% by mass or less. The Ca content in the plating layer 203 is preferably 0.40% by mass or less.

[Si: 0.01 to 0.75% by mass]
Si is an element that suppresses excessive growth of the Fe—Al intermetallic compound phase formed at the interface between the plating layer 203 and the base steel material 201 and improves the adhesion between the plating layer 203 and the base steel material 201 . The effect of suppressing the formation of such an Fe—Al intermetallic compound phase is exhibited by setting the Si content to 0.01% by mass or more. The Si content in the plating layer 203 is preferably 0.03% by mass or more.

On the other hand, when the Si content in the plating bath for producing the plating layer 203 is too high, the viscosity of the plating bath increases more than necessary, which may reduce the plating workability. Therefore, by adjusting the Si content in the plating bath from the viewpoint of plating workability, the Si content in the plating layer 203 is 0.75% by mass or less. The Si content in the plating layer 203 is preferably 0.65% by mass or less.

In the plating layer 203, the balance of Al, Mg, Ca, and Si is Zn and impurities.
Zn is an element necessary for forming the main phase (Zn—Al—Mg alloy phase) of the plating layer 203 according to the present embodiment, and is an important element for improving the corrosion resistance of the joined body 1. .

In addition, the chemical composition of the plating layer 203 according to the present embodiment is such that instead of part of the remaining Zn, Sn: 0% to 0.70%, Ti: 0% to 0.25%, Ni : 0% to 1.00%, Co: 0% to 0.25%, Fe: 0% to 5.0%, B: 0% to 0.5%. That is, the plated layer 203 according to this embodiment may contain at least one of Sn, Ti, Ni, Co, Fe, and B as an optional additive element. Since the plating layer 203 according to the present embodiment may not contain these optional additive elements, the lower limit of the content of these optional additive elements is 0%.

[Sn: 0 to 0.70% by mass]
Sn is an element that increases the Mg elution rate when the plating layer 203 containing Zn, Al, and Mg is placed in a corrosive environment. As the Mg elution rate increases, Mg ions are supplied to the exposed portions of the base steel material 201, further improving sacrificial corrosion resistance. On the other hand, the addition of excessive Sn excessively accelerates the Mg elution rate, possibly reducing the corrosion resistance of the joined body 1 . Since such an increase in the Mg elution rate becomes remarkable when the Sn content exceeds 0.70% by mass, the Sn content is 0.70% by mass or less. The Sn content is more preferably 0.50% by mass or less. On the other hand, the lower limit of the Sn content is not particularly defined, and may be 0% by mass, but when Sn is contained, the Sn content may be 0.005% by mass or more. preferable. This makes it possible to further improve the sacrificial corrosion resistance of the plating layer 203 .

[Ti: 0 to 0.25% by mass]
[Ni: 0 to 1.00% by mass]
When at least one of Ti and Ni is contained in the plating layer 203, when the second member 20 having such a plating layer 203 is welded, these elements are added to the Al—Fe alloy layer generated by welding. It is possible to improve the corrosion resistance of the weld that is incorporated and formed. Such an effect of improving corrosion resistance is exhibited when the content of either Ti or Ni in the plating layer 203 is 0.005% by mass or more. Therefore, when at least one of Ti and Ni is contained in the plating layer 203, the content of these elements is preferably 0.005% by mass or more independently.

On the other hand, when forming the plating layer 203 with a Ti content exceeding 0.25% by mass or a Ni content exceeding 1.0% by mass, the plating bath for forming the plating layer 203 These elements form various intermetallic compound phases, which causes an increase in the viscosity of the plating bath, making it impossible to manufacture the second member 20 with good plating properties. Therefore, the Ti content in the plating layer 203 is set to 0.25% by mass or less, and the Ni content in the plating layer 203 is set to 1.0% by mass or less. The Ti content is more preferably 0.20% by mass or less. Also, the Ni content is more preferably 0.85% by mass or less.

[Co: 0 to 0.25% by mass]
When Co is contained in the plating layer 203, it becomes possible to improve plating workability. The effect of improving the plating workability is exhibited when the Co content is 0.003% by mass or more. Therefore, when Co is contained, the content is preferably 0.003% by mass or more.

On the other hand, when the Co content in the plating layer 203 exceeds 0.25% by mass, the corrosion resistance of the plating layer 203 may be lowered. Therefore, the Co content is 0.25% by mass or less.

[Fe: 0 to 5.0% by mass]
The plated layer 203 may contain elements that constitute the steel material from the base steel material 201 that is the base material. In particular, in the hot-dip plating method, elements forming the base steel material 201 are likely to mix into the plating layer 203 due to interdiffusion of elements due to solid-liquid reaction between the base steel material 201 and the coating layer 203 . A certain amount of Fe may be contained in the plating layer 203 due to such contamination of elements. If the interdiffusion is promoted, the adhesion between the base steel material 201 and the plating layer 203 is further improved. From the viewpoint of improving the adhesion between the base steel material 201 and the plating layer 203, the Fe content in the plating layer 203 is preferably 0.05% by mass or more.

In addition, Fe may be intentionally added to the plating bath used for manufacturing the plating layer 203 within a range that does not impair the effects of the present invention. However, when the Fe content in the plating layer 203 is 5.0% by mass or more, a high-melting intermetallic compound of Fe and Al is formed in the plating bath, and the high-melting intermetallic compound is dross. As such, it adheres to the plating layer and significantly deteriorates the appearance quality, which is not preferable. From this point of view, the Fe content in the plating layer 203 is 5.0% by mass or less by adjusting the Fe content in the plating bath. The Fe content in the plating layer 203 is more preferably 3.5% by mass or less.

[B: 0 to 0.5% by mass]
When B is contained in the plating layer 203, it has an effect of suppressing Liquid Metal Embrittlement (LME). It is presumed that this is because when B is contained in the plating layer 203, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compound phases. These improvement effects are exhibited by containing 0.03% by mass or more of B. Therefore, the content of B in the plating layer 203 is more preferably 0.03% by mass or more.

On the other hand, if an excessive amount of B is added to the plating bath in order to contain B in the plating layer 203, the melting point of the plating will rise sharply and the workability of the plating will decrease, producing a plated steel sheet with excellent plating properties. Can not do it. Since the deterioration of the plating workability becomes remarkable when the B content exceeds 0.5% by mass, the B content is 0.5% by mass or less.

[Method for measuring chemical composition]
The chemical composition of the plating layer 203 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). In addition, when analyzing chemical components up to 0.1% by mass, ICP-AES is used, and when analyzing trace chemical components of less than 0.1% by mass, ICP-MS shall be used. The second member 20 is immersed in an inhibitor-added 10% HCl aqueous solution for about 1 minute to peel off the plated layer portion, and prepare a solution in which the plated layer is dissolved. The resulting solution can be analyzed by ICP-AES or ICP-MS to obtain the overall average chemical composition of the plating layer 203 .

In the plated layer 203 of the second member 20 according to the present embodiment, Mg among the chemical components as described above is concentrated in the surface layer of the plated layer 203 . This Mg concentration state will be explained again below.

Further, the average adhesion amount per side of the plating layer 203 in the second member 20 according to the present embodiment is preferably within the range of 20 to 600 g/m ² while satisfying the conditions described below. . More preferably, the average deposition amount per side of the plating layer 203 is 40 to 400 g/m ² .

The plating layer 203 having the components as described above has a Vickers hardness specified by JIS Z2244-1:2009 (more specifically, when the load is 10 gf (1 gf is about 9.8 mN) Vickers hardness) is 150Hv or more, which is an excellent hardness. Therefore, when forming the opening 11 in the first member 10, burrs may be generated from the first member 10 side toward the second member 20 side. Therefore, it is possible to prevent a situation in which the plating layer 203 is damaged by burrs and partially peeled off.

◇Chemical conversion coating 205
The chemical conversion treatment film 205 in the second member 20 according to the present embodiment is a film having a resistance of less than 1×10 ⁻² Ω as measured by the four-terminal four-probe method. Such resistance can be measured using various resistivity meters (for example, Loresta-GX MCP-T700, probe: MCP-TP03P: both manufactured by Nitto Seiko Analytic Tech Co., Ltd.). Since the chemical conversion treatment film 205 exhibits the resistance as described above, the chemical conversion treatment film 205 exhibits a sacrificial anti-corrosion action and can further improve the corrosion resistance of the joined body 1 . The lower limit of the resistance of the chemical conversion treatment film 205 measured by the four-terminal four-probe method is not particularly specified, and the lower the resistance, the better.

The specific components of the chemical conversion treatment film 205 according to the present embodiment are not particularly limited as long as they exhibit the above resistance. It is possible to form Examples of such a chemical conversion treatment agent include Palcoat E300 series chemical conversion treatment agents manufactured by Nihon Parkerizing Co., Ltd., and the like.

The film thickness of the chemical conversion coating 205 according to this embodiment is not particularly limited, but is preferably within the range of 0.2 to 3.0 μm, for example.

◇ Surface Concentration State of Mg in Plating Layer 203 The surface concentration state of Mg in the plating layer 203 according to the present embodiment will be described in detail below with reference to FIGS. 5 and 6 . 5 and 6 are explanatory diagrams for explaining the plating layer 203 in the joined body according to this embodiment.

Prior to the following description, it is assumed that the contents of Mg, Al, and Zn (unit: mass %) in the entire plating layer 203 have been measured by the method described above. In the following description, the content of each component in the plating layer 203 on the side in contact with the first member 10 is particularly focused. The surface concentration of Mg in the plating layer 203 as described below contributes to the corrosion resistance of the joined body 1 (especially the corrosion resistance in the vicinity of the opening 11). This is because the plated layer 203 on the side in contact with the member 10 plays a major role.

Here, in the plated layer 203 on the side in contact with the first member 10, the total content of Mg, Al, and Zn (unit: mass %) is expressed as [Mg]', [Al]', [ Zn]'.

Next, attention is paid to FIG. The upper part of FIG. 5 is a plan view of the vicinity of the position where the opening 11 of the first member 10 is formed in the joined body 1 when viewed from above. The lower part of FIG. 5 is a cross-sectional view obtained by cutting the top view shown in the upper part along the line AA in the thickness direction of the first member 10 and the second member 20 .

As shown in the upper top view of FIG. 5, the first member 10 according to the present embodiment has an opening 11 having a hole penetrating through the base steel material 101 in a part thereof. In addition, the first member 10 has an exposed portion 13, which is a portion where the steel base (that is, the base steel material 101) is exposed so as to be adjacent to the opening 11 (more specifically, the hole). are doing. Here, the opening 11 may have a burr 15 facing the second member 20 side. Moreover, various iron oxides 17 may adhere to the surface of the exposed portion 13 .

Here, the size of the burr 15 (the size of the projection from the surface position of the base steel material 101) depends on the plate thickness of the base steel material 101, the drilling conditions for forming the opening 11, and the like, but is, for example, 0.5 mm. It is preferably 2 mm or less. If the size of the burr 15 is 0.2 mm or less, the surface of the second member 20 can be prevented from being excessively damaged by the burr 15, and the corrosion resistance of the second member 20 can be ensured.

Various iron oxides 17 that can adhere to the surface of the exposed portion 13 include, for example, α-FeOOH, β-FeOOH, γ-FeOOH, Fe(OH) ₂ , Fe(OH) ₃ and Fe ₂ O _{3 .} , Fe ₃ O ₄ , FeO, and the like.

Since the base steel material 101 is exposed at the exposed portion 13 of the first member 10, the corrosion resistance is lower than that of the other portion where the surface treatment layer 103 is present. Therefore, when the exposed portion 13 is exposed to a corrosive environment, a difference occurs between the corrosion resistance of the exposed portion 13 and the corrosion resistance of the portion where the surface treatment layer 103 exists. Therefore, in the joined body 1 according to the present embodiment, the components of the plating layer are appropriately eluted as ions from the plating layer 203 of the second member 20 to function as a protective film for the exposed portion 13 . Zn and Mg forming the plating layer 203 exhibit sacrificial anti-corrosion properties and are suitable as main components of the protective film. It has already been confirmed separately that even when the chemical conversion treatment film 205 is provided as the upper layer of the plating layer 203, the above-described elution of plating components occurs.

Among the Zn—Al—Mg-based plating components that the plating layer 203 according to this embodiment has, Mg exists as an intermetallic compound in the plating layer 203 . Mg exhibits superior sacrificial anti-corrosion performance compared to Al and has high mobility of Mg ions after elution, making it a particularly useful element as the main component of protective coatings. Therefore, in the plating layer 203 according to the present embodiment, Mg is intentionally concentrated in the vicinity of the surface of the plating layer 203 so that Mg is easily eluted.

In the plating layer 203 according to the present embodiment, the surface concentration of Mg as described above affects the first member 10 and the second member 20 as shown in the lower part of FIG. In the cross section obtained by cutting in the thickness direction at the position of the opening 11, the plating layer 203 on the side in contact with the first member 10 is observed with a Field Emission Scanning Electron Microscope (FE- SEM) energy dispersive X-ray spectroscopy (EDX) (hereinafter abbreviated as “FE-SEM/EDX”) for surface analysis.

For this evaluation, in the present embodiment, two points on the cross section of the plating layer 203 are focused on and surface analysis is performed by FE-SEM/EDX. That is, there are two positions, A and B, in the cross-sectional view in the lower part of FIG. The position A is a position 20 mm away from the center of the opening 11 from one end of the opening 11 in the cross section shown in the lower part of FIG. Position B is the position of one end of the opening 11 in the cross section shown in the lower part of FIG.

Three specimens to be samples are taken out from the joined body 1 of interest, and each specimen is embedded in resin and then polished to prepare a cross section to be observed as shown in the lower part of FIG. Each of the cross sections is observed by FE-SEM/EDX to perform elemental analysis of plating components at positions A and B. When carrying out the surface analysis of the positions A and B, as schematically shown in FIG. ) to 3 μm in the depth direction of the plating layer 203”דthe range of 100 μm in the direction orthogonal to the surface normal direction of the plating layer 203 (the direction in which the surface expands)” is the analysis target area r _A , _rB . Then, the average composition of each element of Zn, Mg, and Al is analyzed for each position. In addition, as shown in FIG. 6, it is preferable that the direction in which the surface spreads is within a range of up to 50 μm to the left and right of the position A or the position B as the center.

Here, the above cross-sectional observation uses FE-SEM/EDX such as JSM-7800F/EDX manufactured by JEOL Ltd., with an acceleration voltage of 15 kV, an emission current of 65 μA, a working distance of 10 mm, and a range up to a depth of 3 μm. A size of 20 μm wide is performed by analyzing 5 tethers.

The contents of Mg, Al, and Zn (unit: % by mass) in the region from the surface layer to a depth of 3 μm obtained in this way are denoted by [Mg], [Al], and [Zn], respectively. Then, at each of the positions A and B, a ratio R is defined as shown in the following formula (101) based on the results of the surface analysis. More specifically, the ratio R at location A is denoted _RA and the ratio R at location B is denoted _RB . For the above three samples, the ratio R _A and the ratio R _B are calculated as described above. The average value of the three ratios _RA obtained is taken as the ratio _RA in the conjugate 1 of interest. Similarly, the average value of the three obtained ratios _RB is taken as the ratio _RB in the joined body 1 of interest.

In the plating layer 203 according to this embodiment, the value of the ratio _RA is 1.10 to 5.00. That is, at the position A, the Mg content in the region from the surface of the plating layer 203 to a depth of 3 μm is 1.10 to 5.00 times the Mg content in the entire plating layer 203. there is Position A is a position 20 mm away from the center of the opening 11 with one end of the opening 11 as the starting point, and thus the position becomes the starting point of corrosion when the joined body 1 is exposed to a corrosive environment. , can be considered to be sufficiently spaced apart. Therefore, it can be said that the ratio _RA is a value reflecting the surface concentration of Mg that the plating layer 203 originally has.

By setting the ratio _RA to the value described above, it is possible to realize the protective film forming effect associated with the elution of Mg when exposed to a corrosive environment, as mentioned above. When the value of the ratio _RA is less than 1.10, it is not possible to achieve the protective film-forming effect associated with the elution of Mg as described above. The value of ratio _RA is preferably greater than or equal to 1.50. On the other hand, since there is a limit to the concentration state of Mg, the practical upper limit of the ratio _RA is 5.00. If the value of the ratio _RA becomes too high, the amount of Mg eluted from the plating layer 203 becomes too large, and the corrosion resistance (more specifically, long-term corrosion resistance) of the plating layer 203 itself decreases. . Therefore, the value of ratio _RA is preferably 4.00 or less.

On the other hand, in the plating layer 203 according to this embodiment, the ratio RB at the position _B is a value equal to or less than the ratio _RA . For example, when the bonded body 1 is not exposed to a corrosive environment, such as immediately after manufacturing the bonded body 1, Mg or the like does not elute from the plating layer 203. Therefore, the value of the ratio _RB at the position B is equal to the value of the ratio _RA at position A. However, when the joined body 1 is exposed to a corrosive environment and the elution of Mg or the like starts, the value of the ratio _RB becomes less than the ratio _RA , and when the protective film is formed on the exposed portion 13, the Mg or the like begins to dissolve. Elution will stop and the value of ratio _RB will settle to a certain value. In the plating layer 203 according to this embodiment, the value of the ratio R _B is preferably equal to or less than the ratio R _A and within the range of 0.30 to 5.00. When the value of the ratio _RB is less than 0.30, there is a possibility that the effect of forming a protective film accompanying the elution of Mg as described above will be reduced. Further, since there is a limit to the surface concentration state of Mg, the practical upper limit of the ratio _RB is 5.00. The value of the ratio R _B is more preferably less than or equal to the ratio R _A and within the range of 0.50 to 4.00.

<<Relationship between the perimeter of the opening, the area of the exposed part, and the average coating weight of the plating layer>>
In the joined body 1 according to the present embodiment, in order to properly form the protective coating on the exposed portion 13, attention should be paid not only to the elution rate of Mg, but also to the time until the protective coating is formed on the exposed portion 13. should.

For example, the farthest distance from the plated layer 203 to the exposed portion 13 is the maximum distance over which a component such as Mg that can be a protective film must move. For example, in the case of the exposed portion 13 of the first member 10 on the side in contact with the plating layer 203, the distance from the plating layer 203 is short. On the other hand, for example, point p in FIG. The longer the distance from the plating layer 203, the longer it takes to form the protective film, and the plating layer 203 continues to dissolve due to sacrificial corrosion protection until the protective film is formed. The sooner the protective film is formed, the less the elution of plating components such as Mg due to sacrificial corrosion protection, and the longer the life of the joined body 1 can be achieved.

In addition, if the area of the exposed portion 13 is too large, not only will the amount of plating layer (Mg, Zn, etc.) eluted due to sacrificial corrosion protection increase, but it will also take a long time to form a protective film on the exposed portion 13. turn into.

In this way, when considering the time required for the protective film to be formed on the exposed portion 13, the distance from the plating layer 203 to the exposed portion 13 and the width (area) of the exposed portion 13 itself should be considered. should. From this point of view, the present inventors have determined (a) the peripheral length L [mm] of the opening 11 of the first member 10 on the side not in contact with the second member 20, (b) the first area S _S [mm ² ] of the exposed portion 13 not in contact with the second member 20 in the member 10 , (c) the average deposition amount M _m [g/m ² ], we have come to the knowledge that three types of factors should be taken into consideration.

Here, (a) the peripheral length L of the opening 11 corresponds to the peripheral length of the ellipse in the case of the elliptical opening 11 as shown in the upper part of FIG. 5, for example. For such a peripheral length L, a design value described in a design drawing or the like when manufacturing the joined body 1 may be used. You may use the measured value measured using.

In addition, (b) the area _SS of the exposed portion 13 not in contact with the second member 20 is not only the area of the exposed portion 13 on the upper surface of the first member 10, but also exists as the wall surface of the opening 11. , the exposed portion of the base steel material 101 shall also be considered. For example, when focusing on a cylindrical opening 11 as shown in FIG. With respect to such an area _SS , a commercially available digital camera is used to capture an image of the exposed portion 13 so that the entire exposed portion 13 is within the field of view. Using an application, a boundary line is set so as to surround the exposed portion 13, and the area of the portion surrounded by the boundary line is specified. Also, from the plate thickness of the base steel material 101 and the peripheral length L of the opening 11, the area of the exposed portion of the base steel material 101 existing as the wall surface of the opening 11 is calculated. From these results, it is possible to identify the area _SS .

Also, (c) the average adhesion amount Mm of the plating layer 203 is measured as follows. That is, after removing the part corresponding to the second member 20 from the joined body 1, a sample of 30 mm × 30 mm was cut out (the back surface was tape-sealed so that the back surface was not dissolved). , its mass is measured in advance. After that, the sample is immersed in a 10% HCl aqueous solution to which an inhibitor has been added to remove the plating layer 203 by pickling, and the mass of the sample after pickling is measured. It is possible to determine the adhesion amount of the plating layer 203 per side from the change in mass of the sample before and after pickling.

As a result of intensive studies on the relationship between the above three factors, the present inventor found that in order to appropriately generate a protective film and improve the corrosion resistance of the opening 11 and its surroundings (that is, the exposed portion 13), , when L < 100 mm, M _m /S _S ≥ 0.008 must be established, and when L ≥ 100 mm, L × M _m /S _S ≥ 1.300. It was found that it is necessary to By establishing the above-described relationship, when the exposed portion 13 is exposed to a corrosive environment, a protective film is quickly formed to improve the corrosion resistance of the exposed portion 13, thereby realizing a long life of the joined body 1. can do.

Here, when L<100 mm, the value of (M _m /S _s ) is preferably 0.020 or more. On the other hand, the upper limit of (M _m /S _s ) is not particularly defined, and the smaller the denominator _SS and the larger the value of (M _m /S _s ), the better. However, considering the range that the average adhesion amount Mm of the plating layer 203 can take, the plate thickness of the base steel material 101, the drilling conditions, etc., about 100.000 is the substantial upper limit.

Also, when L≧100 mm, the value of (L×M _m /S _S ) is preferably 1.400 or more. On the other hand, the upper limit of (L×M _m /S _s ) is not particularly defined, and the smaller the denominator _SS and the larger the value of (L×M _m /S _s ), the better. However, considering the range that the average adhesion amount Mm of the plating layer 203 can take, the plate thickness of the base steel material 101, the drilling conditions, etc., the substantial upper limit is about 600.000.

The joined body 1 according to the present embodiment has been described in detail above with reference to FIGS. 1A to 6. FIG.

(Regarding the manufacturing method of the joined body)
Next, a method for manufacturing a joined body according to this embodiment will be described.
The method for manufacturing a joined body according to the present embodiment includes (a) a steel material having a surface treatment layer, an opening passing through the steel material, and an exposed steel base adjacent to the opening. and (b) a steel material having a plating layer, in which the specific Mg surface concentration as described above is applied to the plating layer. (c) bonding the prepared first and second members;

In addition, in the step of preparing the second member, _the ^second By controlling the average adhesion amount M _m [g/m ² ] of the plating layer per one side of the member, the peripheral length L, the area S _S of the exposed portion, and the average adhesion amount Mm of the plating layer are as described above. meet certain conditions.

In addition, in this description, it has been described that the average adhesion amount M _m [g/m ² ] is controlled according to the peripheral length L and the area S _S of the exposed portion. However, according to the design values of the peripheral length L and the average adhesion amount _Mm , the area _SS of the exposed portion can be reduced by performing the processing for forming the opening so that the area _SS of the exposed portion satisfies the conditions. may be controlled.

Here, in the steel material constituting the first member, the method of forming the surface treatment layer is not particularly limited, and various known methods can be used according to the type of the surface treatment layer to be formed. is possible. Also, prior to joining the second member, the first member may be processed in advance so as to have a desired shape.

Further, when forming a plated layer on the steel material forming the second member, in addition to the hot dipping method, a thermal spraying method, a cold spraying method, a sputtering method, a vapor deposition method, an electroplating method, or the like can be applied. However, the hot dip plating method is most preferable in terms of cost.

An example of a manufacturing method for obtaining a plate-shaped second member using hot dip plating will be described below in detail.
In this manufacturing process, first, a base steel sheet used as a base material is rolled by the Sendzimir method to a desired thickness, then coiled and installed in a hot-dip plating line.

In the hot-dip plating line, the steel sheet is continuously passed while being drawn out from the coil. At that time, the steel sheet is heat-reduced at 800° C. in an atmosphere of N ₂ -5% H ₂ gas in an environment with an oxygen concentration of 20 ppm or less, for example, by annealing equipment provided on the line, and then Air-cooled with _N2 gas to about +20°C of the bath temperature of the plating bath, and immersed in the plating bath.

Here, in the plating bath, a plating alloy in a molten state having the chemical components as described above is prepared. The temperature of the plating bath should be above the melting point of the plating alloy (for example, about 400 to 600° C.). When preparing the material for the plating alloy, it is preferable to use a pure metal (purity of 99% or more) as the alloy material. First, predetermined amounts of alloy metals are mixed so as to obtain the composition of the plating layer as described above, and the mixture is completely melted using a high-frequency induction furnace, an arc furnace, or the like to form an alloy. Furthermore, the alloy mixed with the predetermined components (the composition of the plating layer) is melted in the atmosphere, and the resulting melt is used as a plating bath.

It should be noted that there is no particular restriction on the use of pure metals in the production of the plating alloys as described above, and existing Zn alloys, Mg alloys, and Al alloys may be dissolved and used. In this case, there is no problem as long as an alloy with a predetermined composition containing few impurities is used.

After the steel sheet is immersed in the plating bath as described above, it is pulled up at a predetermined pulling speed. At this time, the plating amount is controlled by, for example, _N2 wiping gas so that the formed plating layer has a desired thickness. Here, for conditions other than the bath temperature, general plating operation conditions may be applied, and no special equipment or conditions are required.

Here, in order to realize the Mg surface concentration state as described above, for example, after the plating treatment as described above, the cooling rate until the plating solidifies is in the range of 10 to 50 ° C./sec. or at least either physically or chemically process the surface of the base steel material so that the surface roughness Ra specified in JIS B0601:2001 is 0.1 μm or more. should be implemented. Further, by controlling the cooling rate during solidification of the plating after the surface roughness of the base steel material is in the above state, the surface enrichment state of Mg can be made into a more preferable state.

Moreover, when forming a chemical conversion treatment film on the surface of the plating layer, the chemical conversion treatment agent may be applied using various known chemical conversion treatment agents.

A method for joining the first member and the second member is not particularly limited. For example, it is possible to use various known joining methods such as welding by various welding methods, joining using fasteners such as screws, bolts, caulks, etc., thermocompression bonding, adhesion using various adhesives, and the like. .

The method for manufacturing a joined body according to this embodiment has been briefly described above.
In addition, in such a method for manufacturing a joined body, for example, the opening of an existing article formed using steel materials is reinforced using the second member according to the present embodiment, and the joined body It is also possible to apply when forming

EXAMPLES Hereinafter, the joined body according to the present invention will be specifically described with reference to Examples. The examples shown below are merely examples of the joined body according to the present invention, and the joined body according to the present invention is not limited to the following examples.

<Preparation of the first member>
Below, as the first member, a steel plate (cold-rolled steel plate and hot-dip galvanized steel plate (GI)) with a thickness of 1.6 mm and 150 mm × 150 mm, as shown in Table 1 below, are both Nippon Steel Corporation company) was prepared. For the powder coating, V-PET #1340QD manufactured by Dainippon Toryo Co., Ltd. was used so that the film thickness was 50 μm. Palcoat E384 manufactured by Nihon Parkerizing Co., Ltd. was used as a non-chromate chemical conversion treatment agent.

An opening was formed by punching under the conditions shown in Table 2 below in the substantially central portion of the first member thus prepared. The peripheral length L of the opening and the area _SS of the exposed portion adjacent to the opening were measured by the method described above. In addition, around the formed opening, burrs existed toward the punching direction side in the punching process (in other words, the side where the second member is positioned).

In addition, No. shown in Table 4 below. In test examples 57 to 60, 62, 76, 77, 80, and 81, the first member was sprayed with salt water as specified in JIS Z2371:2015 before preparing the evaluation sample. It was subjected to a test (SST) for 6 hours, and red rust, which is an iron oxide, was generated in the exposed portion adjacent to the opening.

<Preparation of the second member>
A hot-dip plating bath having the chemical composition shown in Table 3 below was prepared. A cold-rolled steel sheet (manufactured by Nippon Steel Corporation) with a thickness of 0.8 mm is plated by an existing hot-dip plating process, and a second member (150 mm × 150 mm) is obtained by controlling the coating amount M _m per side. prepared. At this time, the following No. 1-15, No. 17, No. For Nos. 19 to 27, the cooling rate until the plating solidified was controlled within the range of 10 to 50°C/sec. Also, the following No. For Nos. 16 to 18, the cooling rate was controlled to over 50° C./sec until the plating solidified. For each of the prepared second members, the Mg, Al, and Zn contents in the entire plating layer were measured by the method described above, and the results are also shown in Table 3 below.

In addition, No. shown in Table 4 below. For Test Examples 61, 62, and 82, a chemical conversion film was formed on the surface of the plating layer using a non-chromate chemical conversion treatment agent (Palcoat E384 manufactured by Nihon Parkerizing Co., Ltd.). When the surface resistance value of the obtained chemical conversion film was measured by the four-terminal four-probe method, No. 61 and 62 are within the range of 1×10 ⁻⁴ to 1×10 ⁻³ Ω. 82 was in the range of 1×10 ⁻³ to 1×10 ⁻⁴ .

<Joining the first member and the second member>
By overlapping the second member so as to cover the opening provided in the first member and fastening the four corners with plastic bolts, the joints shown in Tables 4-1 and 4-2 below Two bodies were made for each example.

The two joints produced were subjected to 150 cycles of neutral salt spray cyclic corrosion testing as described below. One of the two joints was removed from the test after 50 cycles, and a sample for cross-sectional observation was prepared according to the method previously described. After 50 cycles, the contents of Mg, Al, and Zn were measured at positions A and B from the plating surface to a depth of 3 μm by FE-SEM/EDX. The measurement results of the content and the calculated ratios R _A and R _B are shown in Tables 4-1 and 4-2 below. It is separately confirmed that R _A =R _B holds true in the bonded body before being subjected to the neutral salt spray cycle corrosion test after fabrication.

<Neutral salt spray cycle corrosion test>
Each obtained evaluation sample was subjected to 150 cycles of a neutral salt spray cyclic corrosion test (CCT) specified in JIS H8502:1999, with the side where the opening can be seen as the evaluation surface. Prior to the test, the outer four sides of each evaluation sample were sealed.

After the bolts were removed from the evaluation samples after the cyclic corrosion test, the coating, plating layer, corrosion products, etc. were removed with a remover or hydrochloric acid, and then the corrosion depth of the base steel plate was measured. Evaluation was performed according to the following evaluation criteria. Rating A and rating B were regarded as passing.

[Evaluation criteria]
Rating A: Both the first member and the second member have an erosion depth of 0 mm
B: Among the erosion depths of the first member and the second member, the larger erosion depth is more than 0 mm and less than 0.2 mm C: Among the erosion depths of the first member and the second member , the larger erosion depth is 0.2 mm or more and less than 0.5 mm D: Among the erosion depths of the first member and the second member, the larger erosion depth is 0.5 mm or more

As is clear from Tables 4-1 and 4-2 above, in the test examples corresponding to the examples of the present invention, the determination of the corrosion depth was passed, indicating excellent corrosion resistance, while corresponding to the comparative examples of the present invention. In the test example, it was found that the determination of the corrosion depth was rejected, and the corrosion resistance was poor.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

The following configuration also belongs to the technical scope of the present invention.
(1) It is composed of a steel material having a surface treatment layer, and has an opening that penetrates the steel material and an exposed part that is adjacent to the opening and where the steel base is exposed. 1 member and a second member made of a steel material having a plating layer and provided so as to cover at least the opening of the first member; The plating layer of the member is, in mass%, Al: more than 15.0% and 30.0% or less, Mg: more than 5.0% and 15.0% or less, Sn: 0% to 0.70%, Ca: 0.03% to 0.60%, Si: 0.01% to 0.75%, Ti: 0% to 0.25%, Ni: 0% to 1.00%, Co: 0% to 0.25 %, Fe: 0% to 5.0%, B: 0% to 0.5%, the balance being Zn and impurities, the first on the side not in contact with the second member L [mm] is the peripheral length of the opening of the member, S [mm 2 ] is the area of the exposed portion of the first member that is not in contact with the second member, and _S [mm ² ] of the second member When the average deposition amount of the plating layer per one side is M _m [g/m ² ], when L < 100, M _m /S _S ≥ 0.008 holds, , L×M _m /S _S ≧1.300 holds, and the total content of Mg, Al, and Zn in the plated layer of the second member on the side in contact with the first member ( Unit: % by mass) are represented as [Mg]', [Al]', and [Zn]', respectively, and the first member and the second member are the positions of the openings of the first member. In the cross section obtained by cutting in the thickness direction, the plating layer of the second member on the side in contact with the first member is analyzed by an energy dispersive X-ray analyzer of a field emission scanning electron microscope ( FE-SEM/EDX), the contents of Mg, Al, and Zn obtained by surface analysis from the surface to a depth of 3 μm (unit: mass%) are respectively [Mg], [Al], and [Zn]. The ratio R calculated based on the analysis result of the surface analysis is defined as the following formula (1), and in the cross section, the center of the opening with one end of the opening as the starting point When a position 20 mm _away from the A joined body, wherein RB, which is the value of the ratio R at the position B, is equal to or less than the value of the _RA when the position of one end of the opening is a position _B.
(2) The conjugate according to (1), wherein the R _B is in the range of 0.30 to 5.00.
(3) on the surface of the plating layer of the second member, there is a chemical conversion coating having a resistance of less than 1×10 ⁻² Ω when measured by a four-terminal four-probe method; (1) or The conjugate according to (2).
(4) The joined body according to any one of (1) to (3), wherein the surface treatment layer of the first member contains Zn.
(5) The bonding according to any one of (1) to (4), wherein the surface treatment layer of the first member is composed of one or more layers, and the outermost surface is a coating film. body.
(6) The joined body according to any one of (1) to (5), wherein iron oxide adheres to the exposed portion of the first member.
(7) The joined body according to any one of (1) to (6), wherein the opening of the first member has a burr facing the second member.

Reference Signs List 1 joined body 3 opening 10 first member 11 opening 13 exposed portion 15 burr 17 iron oxide 20 second member 101 base steel 103 surface treatment layer 201 base steel 203 plating layer 205 chemical conversion coating

Claims (7)

A first member composed of a steel material having a surface treatment layer, and having an opening penetrating through the steel material and an exposed part adjacent to the opening and having the steel substrate exposed. and,
a second member made of a steel material having a plating layer and provided so as to cover at least the opening of the first member;
is joined with
The plating layer of the second member is mass %,
Al: more than 15.0% and 30.0% or less,
Mg: more than 5.0% and 15.0% or less,
Sn: 0% to 0.70%,
Ca: 0.03% to 0.60%,
Si: 0.01% to 0.75%,
Ti: 0% to 0.25%,
Ni: 0% to 1.00%,
Co: 0% to 0.25%,
Fe: 0% to 5.0%,
B: 0% to 0.5%,
and the balance consists of Zn and impurities,
L [mm] is the peripheral length of the opening of the first member on the side not in contact with the second member, and the exposed portion of the first member not in contact with the second member is When the area is S _S [mm ² ] and the average amount of the plating layer per side of the second member is M _m [g/m ² ], when L<100, M _m /S If _S ≥ 0.008 holds and L ≥ 100 then L x M _m /S _S ≥ 1.300 holds,
In the plated layer of the second member on the side in contact with the first member, the total content of Mg, Al, and Zn (unit: mass%) is [Mg]' and [Al], respectively. ', [Zn]',
In the cross section obtained by cutting the first member and the second member in the thickness direction at the position of the opening of the first member, the first member on the side in contact with the first member Mg, Al, Zn obtained by surface analysis of the plating layer of the member 2 from the surface layer to a depth of 3 μm with an energy dispersive X-ray analyzer (FE-SEM/EDX) of a field emission scanning electron microscope. The content (unit: mass%) of [Mg], [Al], [Zn] respectively,
The ratio R calculated based on the analysis result of the surface analysis is defined as in the following formula (1),
In the cross section, when a position 20 mm away from the center of the opening starting from one end of the opening is position A, the value of the ratio R at the position A is _RA , is in the range of 1.10 to 5.00, and
In the cross section, when the position of one end of the opening is position B, _RB , which is the value of the ratio R at the position B, is equal to or less than the value of _RA .

The conjugate of claim 1, wherein said R _B is in the range of 0.30 to 5.00. The joining according to claim 1, wherein a chemical conversion treatment film having a resistance of less than 1 × 10 ^-2 Ω when measured by a four-terminal four-probe method is present on the surface of the plating layer of the second member. body. 2. The joined body according to claim 1, wherein said surface treatment layer of said first member contains Zn. 2. The joined body according to claim 1, wherein said surface treatment layer of said first member is composed of one or more layers, and the outermost surface thereof is a coating film. The joined body according to any one of claims 1 to 5, wherein iron oxide adheres to said exposed portion of said first member. The joined body according to any one of claims 1 to 5, wherein the opening of the first member has a burr facing the second member.

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