TWI842360B - Joint - Google Patents

Abstract

The subject of this case: In a joint body using a steel material having an opening, the corrosion resistance of the opening and its surroundings is further improved, thereby achieving a longer life of the joint body. The solution of this case: The joint body of the present invention is formed by joining a first component and a second component; the first component is composed of a steel material having a surface treatment layer, and the first component has: an opening, and an exposed portion adjacent to the opening and exposing the steel base material; the second component is composed of a steel material having a coating layer, the coating layer contains a predetermined chemical composition, and the second component is arranged to cover at least the opening of the first component. The opening circumference length L, the exposed area _SS , and the average adhesion amount _Mm of the coating meet the specified conditions, and the ratio R calculated from the Mg, Al, and Zn contents of the entire coating and the Mg, Al, and Zn contents from the surface of the coating to a depth of 3µm meets the specified conditions.

Description

Joint

The present invention relates to a conjugate.

Even steel materials that have been surface treated often still have various openings, such as holes for fastening parts such as screws and bolts, holes for transportation, and holes for alignment. In addition, the parts adjacent to these openings often expose the steel base material.

When the surface treatment applied to steel is painting, corrosion will start from the exposed part of the steel substrate. When the surface treatment applied to steel is zinc plating, although the corrosion rate can be suppressed to a certain extent by the sacrificial corrosion resistance of zinc plating, it is not expected to prolong the service life. In addition, sometimes repairs are performed near the opening by painting, etc., but there is a problem of cost and time consumption.

On the other hand, when iron oxide (including rust) is generated on the exposed part of the steel substrate, the iron oxide is sometimes removed by physical methods such as scraping or bead blasting, and then repaired with paint or the like. However, scraping or bead blasting is not easy to perform on site. In addition, if it is not adequately treated, the iron oxide will remain and the effect of the repair at an early stage will be lost. Therefore, a technology has been proposed that can prevent further rusting by coating on the iron oxide without removing the iron oxide (for example, refer to the following patent document 1).

Prior art literature

Patent Literature

Patent document 1: Japanese Patent Publication No. 2020-70328

However, if the technology disclosed in the above-mentioned patent document 1 is used, multiple coating operations are required, which is very complicated, and the curing time required for drying may prolong the construction period. In addition, this kind of coating is not only expensive, but also loses the effect of early repair if it is not fully coated. As a result, the corrosion of the component with the opening or the component covering the opening will start from the periphery of the opening at an early stage, and the entire structure cannot be expected to have a long life. Based on the above situation, it is strongly required that the structure composed of steel with an opening can have better corrosion resistance and longer life.

Therefore, the present invention is made in view of the above-mentioned problems, and the purpose of the present invention is to further improve the corrosion resistance of the opening and its surroundings in a joint body using a steel material having an opening.

In order to solve the above problems, the inventors of this case have conducted intensive research and obtained the following idea: using a steel material with a coating layer to at least cover the opening, and when the opening and the exposed part of the steel substrate around it are exposed to a corrosive environment, the coating component is dissolved from the coating layer. In addition, the inventors of this case also obtained the following idea: allowing the dissolved coating component to reach the opening and the exposed part of the steel substrate, thereby further improving the corrosion resistance.

As a result of further research based on the above idea, the main purpose of the present invention is as follows.

(1) A joined body, comprising a first member and a second member; the first member is made of a steel material having a surface treatment layer, and the first member has: an opening portion penetrating the steel material; and an exposed portion adjacent to the opening portion and exposing a steel substrate; the second member is made of a steel material having a coating layer, and the second member is arranged to cover at least the aforementioned opening portion of the aforementioned first member; the aforementioned coating layer of the aforementioned second member contains, in mass %, the following: Al: greater than 15.0% and less than 30.0%, Mg: greater than 5.0% and less than 15.0%, 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%, and B: 0% to 0.5%, and the remainder is composed of Zn and impurities; the circumferential length of the opening of the first member on the side not in contact with the second member is L [mm], the area of the exposed portion of the first member not in contact with the second member is S _S [mm ² ], and the average adhesion amount of the coating layer on each side of the second member is M _m [g/m ² ], in this case, if L<100, then M _m / _SS ≧0.008 holds, and if L≧100, then L×M _m / _SS ≧1.300 holds; the contents of Mg, Al, and Zn (unit: mass %) in the entire aforementioned coating layer on the side of the aforementioned second component that is in contact with the aforementioned first component are recorded as [Mg]', [Al]', and [Zn]', respectively. In a cross section obtained by cutting the aforementioned first component and the aforementioned second component in the thickness direction at the position of the aforementioned opening of the aforementioned first component, the aforementioned coating layer on the side of the aforementioned second component that is in contact with the aforementioned first component is measured by energy dispersive X-ray diffraction using a field emission scanning electron microscope. A line analysis device (FE-SEM/EDX) is used to perform a surface analysis from the surface layer to a depth of 3 μm, and the obtained Mg, Al, and Zn contents (unit: mass %) are recorded as [Mg], [Al], and [Zn], respectively. The ratio R calculated based on the analysis results of the above-mentioned surface analysis is defined as the following formula (1); let the position of one end of the above-mentioned opening portion in the above-mentioned cross section as the starting point and the position 20 mm away from the center of the above-mentioned opening portion be position A, at this time, the value RA of the above-mentioned ratio R at the above-mentioned position _A falls within the range of 1.10 to 5.00; and let the position of one end of the above-mentioned opening portion in the above-mentioned cross section be position B, at this time, the value RB of the above-mentioned ratio R at the above-mentioned position _B is less than the value of _RA .

(2) The conjugate of (1), wherein the _RB is in the range of 0.30 to 5.00.

(3) A joint body as described in (1), wherein a chemical conversion treatment film exists on the surface of the aforementioned coating layer of the aforementioned second component, and the resistance of the chemical conversion treatment film when measured by a four-terminal four-probe method is less than 1×10 ^-3 Ω.

(4) A joint body as in (1), wherein the aforementioned surface treatment layer of the aforementioned first component contains Zn.

(5) A joint body as in (1), wherein the surface treatment layer of the first component is composed of one or more layers, and the outermost surface is a coating.

(6) A joint body as described in any one of (1) to (5), wherein iron oxide is attached to the aforementioned exposed portion of the aforementioned first component.

(7) A joint body as described in any one of (1) to (5), wherein the aforementioned opening of the aforementioned first component has burrs facing the side of the aforementioned second component.

As described above, according to the present invention, in a joint body using a steel material having an opening, the corrosion resistance of the opening and its surroundings can be further improved, thereby achieving a longer life of the joint body.

1: Joint body

3,11: Opening

10: Component 1

13: Exposed part

15: Rough edges

17:Iron oxide

20: Component 2

101,201: Base steel

103: Surface treatment layer

203: Plating layer

205: Chemical conversion treatment of membranes

p: point

r _A , r _B : Analysis target area

FIG1 is an explanatory diagram schematically showing an example of a joint body in an embodiment of the present invention.

Figure 2 is an explanatory diagram for explaining an example of the structure of a joint body of the same embodiment.

FIG3 is an explanatory diagram schematically showing an example of the structure of the first component in the joint body of the same embodiment.

FIG. 4A is an explanatory diagram schematically showing an example of the structure of the second component in the joint body of the same embodiment.

FIG. 4B is an explanatory diagram schematically showing an example of the structure of the second component in the joint body of the same embodiment.

Figure 5 is an illustrative diagram for explaining the coating layer in the joint body of the same embodiment.

Figure 6 is an explanatory diagram for explaining the coating layer in the joint body of the same embodiment.

The form used to implement the invention

Below, the preferred implementation form of the present invention is described in detail with reference to the attached drawings. In addition, in this specification and drawings, the same symbols will be attached to the components with substantially the same functional structure to omit repeated descriptions.

(About the joint body)

Below, the joint body of the embodiment of the present invention is described with reference to FIG1. FIG1 is an explanatory diagram schematically showing an example of the joint body of the embodiment of the present invention.

As described in detail below, the joint body of this embodiment is formed by joining a plurality of steel materials. In FIG. 1, a joint body 1 having a box-shaped appearance is schematically illustrated as an example of the joint body. Such a joint body 1 having a box-shaped appearance can be, for example, a switchboard, an outdoor unit, a water heater, etc. As mentioned earlier, such a joint body 1 is mostly provided with openings 3 of various shapes at various locations, such as holes for setting fastening parts such as screws and bolts, holes for transportation, holes for alignment, etc.

From the perspective of corrosion resistance, when manufacturing the above-mentioned various joints, surface-treated steel that has been subjected to various surface treatments is generally used as the steel of the blank. When the above-mentioned opening 3 is formed on the surface-treated steel of the blank, the surface treatment layer applied to the steel will be partially peeled off, thereby exposing the steel substrate. If the joint with the exposed steel substrate is exposed to a corrosive environment, the steel substrate will become the starting point and begin to corrode. Therefore, the joint 1 of this embodiment adopts a structure such as the one described in detail below at least near the opening 3, thereby further improving the corrosion resistance of the opening 3 and its surroundings, thereby achieving a longer life of the joint.

In addition, the joint body 1 of this embodiment is not limited to the box-shaped object mentioned above. The joint body 1 of this embodiment can be, for example, a plate-shaped joint body using plate-shaped steel such as a roof or wall of a building, a joint body using various shapes of steel such as a solar panel stand, a joint body using various H-shaped steels or corner columns such as a frame of a structure, or a joint body using various steel pipes such as a signal, a traffic light, a guardrail, etc.

<About the structure of the joint>

Next, refer to FIG. 2 and explain in detail what kind of steel material is used to form the joint body 1 of this embodiment. In addition, for convenience, the following example is used to explain the joint body 1 using a plate-shaped steel material (i.e., a steel plate). FIG. 2 is an explanatory diagram for explaining an example of the structure of the joint body of this embodiment, and FIG. 2 schematically shows a part of the cross section obtained by cutting the joint body of this embodiment in the thickness direction of the steel material of the blank.

As shown in FIG. 2 , the joint body 1 of this embodiment is formed by joining a first component 10 and a second component 20. The first component 10 has an opening 11 that passes through the steel material, and the second component 20 is arranged to at least cover the opening 11 of the first component 10.

<<About the composition of the first component 10>>

FIG3 is an explanatory diagram schematically showing an example of the structure of the first component 10 in the joint 1 of the present embodiment. As shown in FIG3, the first component 10 of the present embodiment has: a base steel 101 as an example of a steel base material, and a surface treatment layer 103 located on the surface of the base steel 101. Various openings as shown in FIG1 and FIG2 are provided on at least a portion of the first component 10. In addition, although FIG3 shows that the surface treatment layer 103 is provided on both sides of the base steel 101, the surface treatment layer 103 may be provided only on one surface of the base steel 101.

◇Base steel 101

The base steel material 101 that can be used as the base material of the first component 10 of this embodiment is not particularly limited, and various steel materials can be used in accordance with the mechanical strength (e.g., tensile strength) required for the joint body 1. The base steel material 101 can be, for example: various aluminum deoxidized steels; ultra-low carbon steels containing Ti, Nb, etc.; high-strength steels containing strengthening elements such as P, Si, and Mn in ultra-low carbon steels, etc.

In addition, the thickness of the base steel material 101 is not particularly limited, and can be appropriately set according to the mechanical strength required by the joint body 1.

◇Surface treatment layer 103

The surface treatment layer 103 of this embodiment is a layer provided to improve the corrosion resistance of the base steel 101 in the first component 10. The surface treatment used to form the surface treatment layer 103 is not particularly limited, and various known treatment methods can be applied, such as various plating treatments, coating treatments using various anti-rust coatings (including powder coating), etc. In addition, as the surface treatment used to form the surface treatment layer 103, a combination of multiple treatment methods can also be used.

Here, the surface treatment layer 103 of this embodiment is preferably a surface treatment layer containing Zn. By providing a surface treatment layer containing Zn, the corrosion resistance of the first component 10 can be further improved by utilizing the sacrificial corrosion resistance brought by Zn. The specific example of the surface treatment layer containing Zn is not particularly limited. The surface treatment layer containing Zn can be, for example, various zinc-based plating layers, or a layer that has been chemically converted on the surface of the plating layer (i.e., plating layer + chemical conversion treatment film), or a coating using a coating containing Zn.

Furthermore, the surface treatment layer 103 may be made into a multi-layer structure composed of multiple layers. In this case, the outermost surface of the surface treatment layer 103 may also be a coating film formed using various coatings. For example, by using a coating containing various coloring pigments to form a coating film as the outermost surface of the surface treatment layer 103, the design of the joint body 1 can be improved. Furthermore, by using other various coatings as coatings for forming the coating film, various functions exhibited by the additives contained in the coating can be applied to the joint body 1. Furthermore, a pre-painting treatment such as phosphate treatment may be performed before painting, and then the desired painting may be performed.

<<About the composition of the second component 20>>

FIG. 4A and FIG. 4B are explanatory diagrams schematically showing an example of the structure of the second component 20 in the joint 1 of this embodiment. As shown in FIG. 4A, the second component 20 of this embodiment has: a base steel material 201 as an example of a steel substrate, and a coating layer 203 located on the surface of the base steel material 201. Moreover, as shown in FIG. 4B, the second component 20 of this embodiment may also further have a chemical conversion treatment film 205 on the surface of the coating layer 203.

In addition, although FIG. 4A and FIG. 4B illustrate the case where the coating layer 203 and the chemical conversion treatment film 205 are provided on both surfaces of the base steel material 201, the coating layer 203 and the chemical conversion treatment film 205 may also be provided on only one surface of the base steel material 201.

◇Base steel 201

The base steel material 201 that can be used as the base material of the second component 20 of this embodiment is not particularly limited, and various steel materials can be used in accordance with the mechanical strength (e.g., tensile strength) required by the joint body 1. The base steel material 201 can be, for example: various aluminum deoxidized steels; ultra-low carbon steels containing Ti, Nb, etc.; high-strength steels that further contain strengthening elements such as P, Si, and Mn in ultra-low carbon steels, etc.

In addition, the thickness of the base steel material 201 is not particularly limited, and can be appropriately set according to the mechanical strength required by the joint body 1.

◇Coating layer 203

Regarding the coating layer 203 in the second component 20 of this embodiment, the layer not only improves the corrosion resistance of the second component 20, but also functions to ensure the corrosion resistance around the opening 11 of the first component 10 when the joint body 1 is exposed to a corrosive environment.

The coating 203 of this embodiment is a Zn-Al-Mg alloy coating, and its chemical composition contains, by mass%, Al: greater than 15.0% and less than 30.0%, Mg: greater than 5.0% and less than 15.0%, Ca: 0.03%~0.60%, Si: 0.01%~0.75%, and the remainder is composed of Zn and impurities.

Below, the ingredients and their contents are described in detail.

[Al: greater than 15.0 mass% and less than 30.0 mass%]

Al is an essential element required for constituting the main phase (Zn-Al-Mg alloy phase) of the coating layer 203 of this embodiment. If the Al content in the coating layer 203 is less than 15.0 mass%, the corrosion resistance of the joint body 1 cannot be ensured. Therefore, in the coating layer 203 of this embodiment, the Al content is greater than 15.0 mass%. The Al content is preferably greater than 17.0 mass%. Since the Al content falls within the above range, the corrosion resistance of the joint body 1 can be further improved.

On the other hand, if the Al content in the coating layer 203 is greater than 30.0 mass%, when placed in a corrosive environment, the Al phase that functions as a cathode will increase excessively, making it easier for the base steel 201 to corrode, and thus the corrosion resistance of the joint 1 cannot be ensured. Therefore, in the coating layer 203 of the present embodiment, the Al content is 30.0 mass% or less. The Al content is preferably 25.0 mass% or less.

[Mg: greater than 5.0 mass% and less than 15.0 mass%]

Mg is an essential element required to constitute the main phase (Zn-Al-Mg alloy phase) of the plating layer 203 of this embodiment. Therefore, in the plating layer 203 of this embodiment, the Mg content is greater than 5.0 mass%. Since the Mg content falls within the above range, the corrosion resistance of the joint body 1 can be ensured.

On the other hand, if the Mg content in the coating layer 203 is greater than 15.0 mass%, the anodic dissolution of the coating layer is easy to proceed when placed in a corrosive environment, so the corrosion resistance of the joint body 1 cannot be ensured. Therefore, in the coating layer 203 of the present embodiment, the Mg content is 15.0 mass% or less. The Mg content is preferably 13.0 mass% or less. Since the Mg content falls within the above range, the corrosion resistance of the joint body 1 can be further improved.

[Ca: 0.03~0.60 mass%]

The element Ca is contained in the coating layer 203, thereby forming an intermetallic compound phase with Al and Zn. In addition, Si and Ca are contained in the coating layer 203, thereby Ca also forms an intermetallic compound phase with Si. By forming such intermetallic compound phases, the corrosion resistance of the joint 1 can be ensured. The effect of forming the intermetallic compound phase is exhibited when the Ca content is set to 0.03 mass% or more. The Ca content in the coating layer 203 is preferably 0.05 mass% or more.

On the other hand, when the Ca content in the coating layer 203 is greater than 0.60 mass%, the corrosion resistance of the joint 1 will decrease. From the above viewpoint, the Ca content in the coating layer 203 is 0.60 mass% or less. The Ca content in the coating layer 203 is preferably 0.40 mass% or less.

[Si: 0.01~0.75 mass %]

The element Si inhibits the excessive growth of the Fe-Al intermetallic compound phase formed at the interface between the coating layer 203 and the base steel 201, thereby improving the adhesion between the coating layer 203 and the base steel 201. The effect of inhibiting the formation of the Fe-Al intermetallic compound phase is exhibited when the Si content is set to 0.01 mass % or more. The Si content in the coating layer 203 is preferably 0.03 mass % or more.

On the other hand, when the Si content in the plating bath used to manufacture the coating layer 203 is too high, the viscosity of the plating bath may increase beyond the required level, resulting in reduced plating workability. Therefore, the Si content in the plating bath can be adjusted from the perspective of plating workability, so the Si content in the coating layer 203 is 0.75 mass % or less. The Si content in the coating layer 203 is preferably 0.65 mass % or less.

In the coating layer 203, the remainder of the above-mentioned Al, Mg, Ca, and Si is Zn and impurities.

Zn is an essential element required for constituting the main phase (Zn-Al-Mg alloy phase) of the plating layer 203 of this embodiment, and is an important element for improving the corrosion resistance of the joint body 1.

Furthermore, the chemical composition of the coating layer 203 of the present embodiment may also replace part of the remaining Zn and selectively contain: Sn: 0%~0.70%, Ti: 0%~0.25%, Ni: 0%~1.00%, Co: 0%~0.25%, Fe: 0%~5.0%, B: 0%~0.5%. That is, the coating layer 203 of the present embodiment may also contain at least one element of Sn, Ti, Ni, Co, Fe, and B as an optional additive element. In addition, since the coating layer 203 of the present embodiment may not contain such optional additive elements, the lower limit of the content of such optional additive elements is 0%.

[Sn: 0~0.70 mass%]

When the Zn, Al, and Mg-containing coating 203 is placed in a corrosive environment, the element Sn increases the Mg dissolution rate. If the Mg dissolution rate increases, Mg ions are supplied to the portion of the exposed base steel 201, which can further improve the corrosion resistance. On the other hand, adding too much Sn will excessively promote the Mg dissolution rate, which may cause the corrosion resistance of the joint 1 to decrease. The increase in the Mg dissolution rate is very obvious when the Sn content is greater than 0.70 mass%, so the Sn content is 0.70 mass% or less. The Sn content is preferably 0.50 mass% or less. On the other hand, the lower limit of the Sn content is not specifically specified and can be 0 mass%, but if Sn is to be contained, the Sn content is preferably set to 0.005 mass% or more. In this way, the corrosion resistance of the coating layer 203 can be further improved.

[Ti: 0~0.25 mass%]

[Ni: 0~1.00 mass%]

If the coating layer 203 contains at least one of Ti and Ni, when the second component 20 having the coating layer 203 is welded, the Al-Fe alloy layer generated by welding will incorporate these elements into it, which can improve the corrosion resistance of the welded portion. The effect of improving corrosion resistance will be exhibited when the content of either Ti or Ni in the coating layer 203 is 0.005 mass% or more. Therefore, if the coating layer 203 is to contain at least one of Ti and Ni, the content of these elements should be set to 0.005 mass% or more respectively.

On the other hand, when forming a coating layer 203 with a Ti content greater than 0.25 mass% or a Ni content greater than 1.0 mass%, these elements will form various intermetallic compound phases in the plating bath used to form the coating layer 203, causing the viscosity of the plating bath to increase, so that the second component 20 with good plating characteristics cannot be manufactured. Therefore, the Ti content in the coating layer 203 is set to 0.25 mass% or less, and the Ni content in the coating layer 203 is set to 1.0 mass% or less. The Ti content is preferably 0.20 mass% or less. In addition, the Ni content is preferably 0.85 mass% or less.

[Co: 0~0.25 mass%]

When Co is contained in the coating layer 203, the coating workability can be improved. The effect of improving the coating workability will be shown when the Co content is 0.003 mass% or more. Therefore, when Co is to be contained, its content should be set to 0.003 mass% or more.

On the other hand, if the Co content in the coating layer 203 is greater than 0.25 mass%, the corrosion resistance of the coating layer 203 may be reduced. Therefore, the Co content is 0.25 mass% or less.

[Fe: 0~5.0 mass%]

Elements constituting the steel may be mixed into the coating layer 203 from the base steel 201 as the parent material. In particular, in the melt coating method, the elements constituting the base steel 201 are easily mixed into the coating layer 203 due to the mutual diffusion of elements caused by the solid-liquid reaction between the base steel 201 and the coating layer 203. Due to the mixed elements, a fixed amount of Fe may be contained in the coating layer 203. If the above mutual diffusion is promoted, the adhesion between the base steel 201 and the coating layer 203 can be further improved. From the perspective of improving the adhesion between the base steel 201 and the coating layer 203, the Fe content in the coating layer 203 is preferably 0.05 mass% or more.

Furthermore, when manufacturing the coating layer 203, Fe can be deliberately added to the coating bath used within the range that does not damage the effect of the present invention. However, when the Fe content in the coating layer 203 is 5.0 mass% or more, a high-melting-point intermetallic compound of Fe and Al will be formed in the coating bath, and the high-melting-point intermetallic compound will adhere to the coating layer in the form of scum, which significantly reduces the appearance grade, so it is not good. The Fe content in the coating bath can be adjusted from the above viewpoint, so the Fe content in the coating layer 203 is 5.0 mass% or less. The Fe content in the coating layer 203 is preferably 3.5 mass% or less.

[B: 0~0.5 mass%]

If the coating 203 contains B, it can have the effect of inhibiting liquid metal embrittlement cracking (Liquid Metal Embrittlement: LME). It can be inferred that the reason is that if the coating 203 contains B, B will combine with at least one of Zn, Al, Mg, and Ca to form various intermetallic compound phases. These improvement effects will be shown when the content of B is 0.03 mass% or more. Therefore, the B content in the coating 203 is preferably 0.03 mass% or more.

On the other hand, if too much B is contained in the plating bath in order to make the plating layer 203 contain B, the plating melting point will rise sharply, resulting in a decrease in plating workability, and it will not be possible to produce a plated steel plate with excellent plating properties. The above-mentioned decrease in plating workability is very obvious when the B content is greater than 0.5 mass%, so the B content is less than 0.5 mass%.

[Measurement methods for chemical components]

The chemical composition of the above-mentioned coating 203 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). In addition, chemical composition analysis up to 0.1 mass% is performed using ICP-AES, and trace chemical composition analysis less than 0.1 mass% is performed using ICP-MS. The second component 20 is immersed in a 10% HCl aqueous solution with an inhibitor for about 1 minute, the coating portion is peeled off, and a solution in which the coating is dissolved is prepared. The obtained solution is analyzed by ICP-AES or ICP-MS to obtain the average chemical composition of the entire coating layer 203.

In the coating layer 203 of the second component 20 of this embodiment, Mg in the above chemical composition is already concentrated in the surface layer of the coating layer 203. The concentration state of Mg will be described again below.

In addition, the average adhesion amount per single side of the coating layer 203 in the second member 20 of this embodiment preferably meets the conditions described below and preferably falls within the range of 20-600 g/m ^2. The average adhesion amount per single side of the coating layer 203 is preferably 40-400 g/m ² .

The coating layer 203 having the above-described composition has an excellent hardness of 150 Hv or more in Vickers hardness specified by JIS Z2244-1:2009 (more specifically, the Vickers hardness when the load is 10 gf (1 gf is 9.8 mN)). Therefore, when the opening 11 is formed in the first member 10, burrs may sometimes be generated from the first member 10 side toward the second member 20 side. However, since the coating layer 203 itself is hard, the coating layer 203 can be prevented from being damaged by burrs and partially peeled off.

◇Chemical conversion treatment film 205

The chemical conversion treatment film 205 of the second component 20 of this embodiment is a film having a resistance of less than 1×10 ^-2 Ω when measured by a four-terminal four-probe method. The resistance can be measured using various resistivity meters (for example, Loresta-GX MCP-T700, probe: MCP-TP03P: both manufactured by Nittoseiko Analytech Co., Ltd.). Since the chemical conversion treatment film 205 exhibits the above-mentioned resistance, the chemical conversion treatment film 205 can exhibit a sacrificial anti-corrosion effect, and can further improve the corrosion resistance of the joint 1. In addition, there is no special regulation for the lower limit value of the resistance when measuring the chemical conversion treatment film 205 by the four-terminal four-probe method, and the lower the resistance, the better.

The specific components of the chemical conversion treatment film 205 of this embodiment are not particularly limited as long as they can exhibit the above-mentioned resistance. Various known chemical conversion treatment agents can be used to form the chemical conversion treatment film 205. The chemical conversion treatment agent can be, for example, the PALCOAT E300 series chemical conversion treatment agent manufactured by Nihon Parkerizing Co., Ltd., etc.

The thickness of the chemical conversion treatment film 205 of this embodiment is not particularly limited, and is preferably set within the range of 0.2~3.0μm, for example.

◇Surface concentration state of Mg in coating layer 203

Below, referring to FIG. 5 and FIG. 6, the surface concentration state of Mg in the coating layer 203 of this embodiment is described in detail. FIG. 5 and FIG. 6 are explanatory diagrams for describing the coating layer 203 in the joint body of this embodiment.

Before the following description, the contents of Mg, Al, and Zn in the entire coating layer 203 (unit: mass %) have been determined by the method described previously. In the following description, particular attention is paid to the contents of each component in the coating layer 203 on the side in contact with the first component 10. The reason is that the surface concentration of Mg in the coating layer 203 as described below contributes to the corrosion resistance of the joint 1 (especially the corrosion resistance near the opening 11), and in terms of the above-mentioned contribution to corrosion resistance, the coating layer 203 on the side in contact with the first component 10 plays an important role.

Here, the contents of Mg, Al, and Zn (unit: mass %) in the entire coating layer 203 on the side in contact with the first component 10 are recorded as [Mg]', [Al]', and [Zn]', respectively.

Next, we should pay attention to Figure 5. The upper part of Figure 5 is a top view of the first component 10 in the joint body 1 when it is viewed from above near the position where the opening 11 is formed. The lower part of Figure 5 is a cross-sectional view after the top view shown in the upper part is cut along the A-A cutting line in the thickness direction of the first component 10 and the second component 20.

As shown in the top view of the upper part of FIG. 5 , an opening portion 11 exists in a part of the first member 10 of the present embodiment, and the opening portion 11 has a hole portion penetrating the base steel 101. In addition, in the first member 10, an exposed portion 13 exists adjacent to the opening portion 11 (more specifically, adjacent to the hole portion), and the exposed portion 13 is a portion where the steel substrate (i.e., the base steel 101) is exposed. Here, burrs 15 facing the side of the second member 20 may exist in the opening portion 11. In addition, various iron oxides 17 may be attached to the surface of the exposed portion 13.

Here, the size of the burr 15 (the protruding size from the surface position of the base steel 101) may vary depending on the plate thickness of the base steel 101 or the conditions for opening the opening 11, but the size of the burr is preferably less than 0.2 mm. If the size of the burr 15 is less than 0.2 mm, the surface of the second component 20 can be prevented from being excessively damaged by the burr 15, thereby ensuring the corrosion resistance of the second component 20.

In addition, various iron oxides 17 that may be attached to the surface of the exposed portion 13 include, for example, α-FeOOH, β-FeOOH, γ-FeOOH, Fe(OH) ₂ , Fe(OH) ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , FeO, and the like.

The base steel 101 is exposed in the exposed portion 13 of the first component 10, so the corrosion resistance of the exposed portion 13 is reduced compared to other portions where the surface treatment layer 103 exists. Therefore, when the exposed portion 13 is exposed to a corrosive environment, there will be a difference in 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 joint body 1 of the present embodiment, the coating component is appropriately dissolved in the form of ions from the coating 203 of the second component 20, so that it functions as a protective film for the exposed portion 13. Zn or Mg constituting the coating 203 will exhibit sacrificial anti-corrosion performance, and therefore is suitable as the main component of the protective film. In addition, it has been confirmed that even when a chemical conversion treatment film 205 is provided as an upper layer of the coating layer 203, the above-mentioned coating component elution will still occur.

In the Zn-Al-Mg coating composition of the coating layer 203 of the present embodiment, Mg exists in the coating layer 203 as an intermetallic compound. Compared with Al, Mg exhibits better sacrificial corrosion resistance, and the mobility of Mg ions after dissolution is high, so Mg is a particularly useful element as the main component of the protective film. Therefore, in the coating layer 203 of the present embodiment, Mg is deliberately concentrated near the surface of the coating layer 203 to make Mg easy to dissolve.

In the coating layer 203 of the present embodiment, the surface concentration state of Mg is as shown in the lower part of FIG. 5. The first component 10 and the second component 20 are cut in the thickness direction at the position of the opening 11 of the first component 10, and in the obtained cross section, the coating layer 203 on the side connected to the first component 10 is analyzed and evaluated using an energy dispersive X-ray spectroscopy (EDX) of a field emission scanning electron microscope (FE-SEM) (hereinafter referred to as "FE-SEM/EDX").

In the above evaluation, this implementation form focuses on two locations in the cross section of the coating layer 203 to perform FE-SEM/EDX surface analysis. That is, focus on two locations, position A and position B, in the cross section of the lower section of Figure 5. In the cross section shown in the lower section of Figure 5, position A is defined as a position 20 mm away from the center of the opening 11 from one end of the opening 11. In addition, in the cross section shown in the lower section of Figure 5, position B is defined as the position of one end of the opening 11.

Three test pieces as samples were taken out from the joint body 1 of interest, and each of them was buried in resin and then polished to prepare the cross-sections shown in the lower part of FIG. 5 as the observation object. Each cross-section was observed by FE-SEM/EDX, and the element analysis of the coating components at positions A and B was performed. When performing the surface analysis at positions A and B, as shown in FIG. 6, "the range from the surface of the coating layer 203 (which can also be understood as the interface between the first component 10 and the coating layer 203) to the depth direction of the coating layer 203 to 3μm" × "the range of 100μm in the direction perpendicular to the normal direction of the coating layer 203 surface (the direction of surface expansion)" was defined as the analysis object area _rA , _rB . Then, the average composition of each element of Zn, Mg, and Al is analyzed for each position. In addition, regarding the direction of surface development, it is preferable to set the range of 50 μm to the left and right with position A or position B as the center as shown in FIG6.

Here, the cross-sectional observation was performed by using FE-SEM/EDX such as JSM-7800F/EDX manufactured by JEOL Ltd., with an accelerating voltage of 15kV, an emission current of 65μA, and a working distance of 10mm, and five consecutive analyses were performed in a width of 20μm from a depth of 3μm.

The contents of Mg, Al, and Zn (unit: mass %) in the region from the surface to a depth of 3 μm obtained in the above manner are recorded as [Mg], [Al], and [Zn], respectively. Then, for positions A and B, the ratio R shown in the following formula (101) is determined based on the analysis results of the surface analysis. More specifically, the ratio R at position A is recorded as _RA , and the ratio R at position B is recorded as _RB . The ratio _RA and the ratio _RB of the above three samples are calculated in the above manner. The average value of the three ratios _RA obtained is defined as the ratio _RA of the joint 1 concerned. Similarly, the average value of the three ratios _RB obtained is defined as the ratio _RB of the joint 1 concerned.

In the coating layer 203 of the present embodiment, the value of the above ratio _RA is 1.10~5.00. That is, at position A, the Mg content of the area from the surface of the coating layer 203 to a depth of 3μm is 1.10~5.00 times the Mg content in the entire coating layer 203. Position A is a position 20mm away from the center of the opening 11 with one end of the opening 11 as the starting point, so it can be considered that position A is sufficiently far away from the position that will become the starting point of corrosion when the joint body 1 is exposed to a corrosive environment. Therefore, the above ratio _RA can be said to be a value reflecting the original surface concentration state of Mg in the coating layer 203.

Since the ratio _RA is the above value, the effect of forming a protective film accompanying Mg dissolution when exposed to a corrosive environment as mentioned above can be achieved. When the ratio _RA value is less than 1.10, the effect of forming a protective film accompanying Mg dissolution as mentioned above cannot be achieved. The value of the ratio _RA is preferably 1.50 or more. On the other hand, the above-mentioned Mg concentration state has a limit, so the upper limit of the actual ratio _RA is 5.00. In addition, if the value of the ratio _RA is too high, the amount of Mg dissolved from the coating 203 will become too much, resulting in a decrease in the corrosion resistance (more specifically, the long-term corrosion resistance) of the coating 203 itself. Therefore, the value of the ratio _RA is preferably 4.00 or less.

On the other hand, in the coating layer 203 of the present embodiment, the ratio _RB at position B is a value lower than the ratio _RA . For example, when the joint body 1 is just manufactured and the joint body 1 is not exposed to a corrosive environment, Mg and the like will not be dissolved from the coating layer 203, and therefore the value of the ratio _RB at position B is equal to the value of the ratio _RA at position A. However, if the joint body 1 is exposed to a corrosive environment and Mg and the like begin to be dissolved, the value of the above ratio _RB will become smaller than the ratio _RA , and at the time when the protective film is formed on the exposed portion 13, Mg and the like will stop dissolving, and the value of the ratio _RB will settle on a certain value. In the coating layer 203 of the present embodiment, the value of the ratio _RB is preferably lower than the ratio _RA , and the value of the ratio _RB is preferably within the range of 0.30 to 5.00. When the value of the ratio _RB is less than 0.30, the effect of the protective film formed by the Mg dissolution may be reduced. In addition, since the surface concentration state of Mg is limited, the upper limit of the actual ratio _RB is 5.00. The value of the ratio _RB is preferably less than the ratio _RA , and the value of the ratio _RB is preferably in the range of 0.50~4.00.

<<Relationship between the circumference of the opening, the exposed area, and the average adhesion amount of the coating>>

In the joint body 1 of this embodiment, in order to properly form a protective film on the exposed portion 13, attention should be paid not only to the dissolution rate of Mg but also to the time until the protective film is formed on the exposed portion 13.

For example, the point where the distance between the coating layer 203 and the exposed portion 13 is the farthest is the maximum distance that the components such as Mg that can form the protective film must move. For example, in the case of the exposed portion 13 on the side of the first component 10 that is in contact with the coating layer 203, the distance from the coating layer 203 is very short. On the other hand, for example, point p in FIG. 5 is the point farthest from the coating layer 203 in the exposed portion 13 on the side that is not in contact with the coating layer 203. The farther the distance from the coating layer 203 is, the longer it takes until the protective film is formed, and during the period until the protective film is formed, the coating layer 203 will continue to dissolve at the expense of corrosion protection. The earlier the protective film is formed, the less the dissolution of plating components such as Mg at the expense of corrosion protection will be, and the longer the life of the joint body 1 can be achieved.

Furthermore, if the area of the exposed portion 13 is too large, not only will the amount of the plating layer (Mg, Zn, etc.) dissolved at the expense of corrosion protection increase, but the time required to form a protective film on the exposed portion 13 will also increase.

As described above, when considering the time required until the protective film is formed on the exposed portion 13, the distance from the coating layer 203 to the exposed portion 13 and the width (area) of the exposed portion 13 itself should be considered. From the above viewpoint, the inventors of the present case finally obtained the view that the following three main factors should be considered: (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 area _SS [mm ² ] of the exposed portion 13 of the first member 10 not in contact with the second member 20; (c) the average adhesion amount M _m [g/m ² ] of the coating layer 203 per single side of the second member 20.

Here, for example, in the case of the elliptical opening 11 shown in the upper part of FIG. 5 , the circumferential length L of the opening 11 (a) corresponds to the circumferential length of the ellipse. This circumferential length L can be a design value recorded in the design drawing when manufacturing the joint 1, or can be measured using a machine such as a curve meter that can measure the length of any curve and the actual measured value obtained can be used.

In addition, regarding (b) the area _SS of the exposed portion 13 not in contact with the second member 20, not only the area of the exposed portion 13 on the upper surface of the first member 10 but also the exposed portion of the base steel material 101 existing as the wall surface of the opening 11 should be considered. For example, when focusing on the cylindrical opening 11 shown in FIG. 5 , the exposed portion of the base steel material 101 corresponding to the side surface of the cylinder should also be considered as the exposed portion 13. Regarding the area _SS , the exposed portion 13 is photographed using a commercially available digital camera in such a manner that the entire exposed portion 13 is included in the field of view, and then a boundary line is set to surround the exposed portion 13 using a commercially available image editing application for the obtained photographic image, and the area of the portion surrounded by the boundary line is identified. In addition, the area of the exposed portion of the base steel material 101 existing as the wall surface of the opening 11 is calculated from the plate thickness of the base steel material 101 and the peripheral length L of the opening 11. From these results, the area S _S can be identified.

(c) The average adhesion amount M _m of the coating layer 203 is measured in the following manner. That is, after removing the portion corresponding to the second component 20 from the joint body 1, a sample of 30 mm × 30 mm in size (the back side has been sealed with tape to prevent the back side from dissolving) is cut out, and its mass is measured in advance. Then, the sample is immersed in a 10% HCl aqueous solution to which an inhibitor is added, and the coating layer 203 is pickled and peeled off, and the mass of the sample after pickling is measured. The adhesion amount of the coating layer 203 on each single side can be determined by the change in the mass of the sample before and after pickling.

The inventors of this case have conducted in-depth research on the relationship between the above three main factors, and have obtained the following insights: In order to appropriately generate a protective film to improve the corrosion resistance of the opening 11 and its surroundings (i.e., the exposed portion 13), if L<100mm, then M _m / _SS ≧0.008 must be established, and if L≧100mm, then L×M _m / _SS ≧1.300 must be established. By establishing the above relationship, when the exposed portion 13 is exposed to a corrosive environment, the protective film will be quickly generated to improve the corrosion resistance of the exposed portion 13, thereby achieving a longer life of the joint 1.

Here, if L<100 mm, the value of (M _m / _SS ) is preferably 0.020 or more. On the other hand, there is no particular upper limit for (M _m / _SS ), and the smaller the denominator S _S is, the larger the value of (M _m / _SS ) is, the better. However, if the range of the average adhesion amount Mm of the coating layer 203 that can be obtained, the plate thickness of the base steel material 101, the opening conditions, etc. are considered, then about 100.000 is the actual upper limit.

If L≧100 mm, the value of (L×M _m / _SS ) is preferably 1.400 or more. On the other hand, there is no particular upper limit for (L×M _m / _SS ), and the smaller the denominator S _S is, the larger the value of (L×M _m / _SS ) is, the better. However, if the range of the average adhesion amount Mm of the coating layer 203 that can be obtained, the plate thickness of the base steel material 101, the opening conditions, etc. are considered, about 600.000 is the actual upper limit.

The above has described in detail the joint body 1 of this embodiment with reference to Figures 1 to 6.

(Regarding the manufacturing method of the joint body)

Next, the manufacturing method of the joint body of this embodiment is described.

The manufacturing method of the joint body of this embodiment comprises: (a) a step of preparing a first component, wherein the first component is composed of a steel material having a surface treatment layer, and the first component has: an opening portion that penetrates the steel material; and an exposed portion that is adjacent to the opening portion and exposes the steel substrate; (b) a step of preparing a second component, wherein the second component is composed of a steel material having a coating layer, and the above-mentioned specific surface concentration state of Mg has been achieved in the coating layer; and (c) a step of bonding the prepared first component and the second component.

Furthermore, in the step of preparing the second component, the average adhesion amount M m [ _{g/m 2 ] of the coating layer on each side of the second component is controlled according to the peripheral length L [mm] of the opening of the first component and the exposed area S S} ^{[mm 2} _] ^of the first component, and the peripheral length L, the exposed area S _S and the average adhesion amount Mm of the coating layer meet the specific conditions described above.

In addition, in this description, the purpose of controlling the average adhesion amount M _m [g/m ² ] according to the peripheral length L and the exposed area _SS has been explained. However, the exposed area SS can also be controlled by performing the forming process of the opening portion in a manner such that the exposed area _SS meets the conditions according to the design values of the peripheral length L and the average adhesion amount _{M m} .

Here, the method for forming the surface treatment layer on the steel material constituting the first component is not particularly limited, and various known methods can be used according to the type of surface treatment layer to be formed. In addition, the first component can be processed into the desired shape before joining the second component.

Furthermore, when forming a coating layer on the steel material constituting the second component, in addition to the melt coating method, the spraying method, cold spray coating method, sputtering method, evaporation method, electroplating method, etc. can also be applied. However, in terms of cost, the melt coating method is the best.

An example of a method for manufacturing a plate-shaped second member using a melt plating method is described in detail below.

In the manufacturing process, the base steel plate used as the parent material is first rolled by the Sendzimir method to produce the desired plate thickness, and then rolled into a coil and placed in a molten plating production line.

In the melt plating line, the steel sheet is continuously fed while being released from the coil. At this time, the steel sheet is heat-reduced at 800°C in an _N2-5 % _H2 gas environment with an oxygen concentration of less than 20ppm by the annealing equipment installed on the line. After that, the steel sheet is air-cooled to the bath temperature of the rear stage +20°C by _N2 gas, and then immersed in the bath.

Here, a plating alloy having the aforementioned chemical composition and in a molten state is prepared in advance in the plating bath. The plating bath temperature is set to be above the melting point of the plating alloy (for example, about 400~600℃). When making the material of the plating alloy, it is advisable to use pure metal (purity above 99%) as the alloy material for blending. First, a predetermined amount of alloy metal is mixed in a manner to form the above-mentioned plating layer composition, and a high-frequency induction furnace or arc furnace is used to completely melt it to form an alloy. Furthermore, the alloy mixed according to the predetermined composition (the above-mentioned plating layer composition) is melted in the atmosphere, and the resulting molten material is used as a plating bath.

In addition, the production of the above-described plating alloy is not particularly limited to using pure metals, and existing Zn alloys, Mg alloys, and Al alloys can also be dissolved for use. In this case, there is no problem as long as the predetermined composition alloy with less impurities is used.

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

Here, in order to achieve the surface concentration state of Mg described above, at least one of the following can be implemented: after the above-mentioned plating treatment, the cooling rate until the plating solidifies is within the range of 10~50℃/second; or the surface of the base steel is processed physically or chemically so that the surface roughness Ra of the base steel surface specified in JIS B0601:2001 is above 0.1μm. In addition, after the surface roughness of the base steel is made into the above state, the cooling rate during the solidification of the plating is controlled, thereby making the surface concentration state of Mg a better state.

Furthermore, when a chemical conversion treatment film is to be formed on the surface of the coating layer, it is sufficient to use various known chemical conversion treatment agents and apply the chemical conversion treatment agent.

The method for joining the first component and the second component is not particularly limited. Various known joining methods can be used, such as welding by various welding methods, joining using fastening parts such as screws and bolts, and fittings, and joining by hot pressing and various adhesives.

The above briefly describes the manufacturing method of the joint body of this embodiment.

In addition, this method of manufacturing a joint body can also be applied to the following situation, for example: the opening of an existing article formed using steel is reinforced using the second component of this embodiment to form a joint body.

Implementation example

The following examples are given to illustrate the conjugate of the present invention in detail. In addition, the following examples are only examples of the conjugate of the present invention, and the conjugate of the present invention is not limited to the following examples.

<Prepare the first component>

As the first component, a steel plate with a thickness of 1.6 mm and a thickness of 150 mm × 150 mm (cold-rolled steel plate and hot-dip galvanized steel plate (GI), both manufactured by Nippon Steel Corporation) was prepared as shown in Table 1 below. Powder coating was performed using V-PET#1340QD manufactured by Dainippon Coating Co., Ltd., and the film thickness was 50 μm. In addition, the chromate-free chemical conversion treatment agent was PALCOAT E384 manufactured by Nihon Parkerizing Co., Ltd.

The first component prepared in the above manner is punched at its approximate center under the conditions shown in Table 2 below to form an opening. In addition, the length L of the opening and the area S _S of the exposed portion adjacent to the opening are measured according to the method described above. In addition, burrs exist around the formed opening on the side facing the punching direction of the punching process (in other words, on the side where the second component is located).

In addition, in the test examples No. 57~60, 62, 76, 77, 80, and 81 shown in Table 4 below, the first component was subjected to the salt water spray test (SST) specified in JIS Z2371:2015 for 6 hours before the evaluation specimen was prepared, and red rust as iron oxide was generated in the exposed part adjacent to the opening in advance.

<Prepare the second component>

A molten plating bath having the chemical composition shown in Table 3 below was prepared. A cold rolled steel plate (manufactured by Nippon Steel Corporation) having a thickness of 0.8 mm was plated by the existing molten plating process, and the coating adhesion amount M _m per single side was controlled to prepare a second member (150 mm×150 mm). At this time, the cooling rate during the period until the coating solidified in No. 1 to 15, No. 17, and No. 19 to 27 below was controlled within the range of 10 to 50°C/sec. In addition, the cooling rate during the period until the coating solidified in No. 16 to 18 below was controlled to be greater than 50°C/sec. For the prepared second component, the Mg, Al, and Zn contents in the entire coating layer were measured according to the methods described above and are summarized in the following Table 3.

In addition, the test examples No. 61, 62, and 82 shown in Table 4 below used a chromate-free chemical conversion treatment agent (PALCOAT E384 manufactured by Nihon Parkerizing Co., Ltd.) to form a chemical conversion treatment film on the surface of the coating. The surface resistance of the obtained chemical conversion treatment film was measured by the four-terminal four-probe method. As a result, the surface resistance values of No. 61 and 62 fell within the range of 1×10 ^-4 ~1×10 ^-3 Ω, and the surface resistance value of No. 82 fell within the range of 1×10 ^-3 ~1×10 ^-4 .

<Joining the first component and the second component>

The second component is overlapped in a manner to cover the opening portion provided in the first component, and the four corners are fastened with plastic bolts to produce the joint bodies shown in the following Tables 4-1 and 4-2, and two joint bodies are produced for each example.

Each of the two joints produced was subjected to the 150-cycle neutral salt water spray cyclic corrosion test described below. After 50 cycles, one of the two joints was taken out of the test, and a sample for cross-section observation was produced according to the method described above. For the sample after 50 cycles, the Mg, Al, and Zn contents of the coating surface to a depth of 3μm were measured at position A and position B using FE-SEM/EDX. The results of the content measurements and the calculated values of the ratios _RA and _RB are summarized in the following Tables 4-1 and 4-2. In addition, it was confirmed that _RA = _RB was established for the joint after production and before being subjected to the neutral salt water spray cyclic corrosion test.

<Neutral salt water spray cycle corrosion test>

The evaluation samples were subjected to 150 cycles of the 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. In addition, the four outer sides of each evaluation sample were sealed before the test.

Bolts were removed from the evaluation specimens after the cyclic corrosion test, and 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. The evaluation was conducted according to the following evaluation criteria. Scores A and B were considered qualified.

[Evaluation Criteria]

Score A: The corrosion depth of the first and second components is 0mm

B: Among the corrosion depths of the first component and the second component, the greater corrosion depth is greater than 0mm and less than 0.2mm

C: The larger erosion depth of the first component and the second component is greater than 0.2mm and less than 0.5mm.

D: Among the corrosion depths of the first component and the second component, the greater corrosion depth is more than 0.5mm

It is clear from Table 4-1 and Table 4-2 that in the test examples that meet the present invention, the erosion depth is judged as qualified and shows excellent corrosion resistance. On the other hand, in the test examples that meet the comparative examples of the present invention, the erosion depth is judged as unqualified and the corrosion resistance is poor.

The above has referred to the attached drawings and described in detail the preferred embodiments of the present invention, but the present invention is not limited to the above examples. And obviously, anyone with general knowledge of the technical field to which the present invention belongs can think of various changes or amendments within the scope of the technical ideas recorded in the scope of the patent application, and know that these should also belong to the technical scope of the present invention.

In addition, for example, the following structures also fall within the technical scope of the present invention.

(1) A joint body, which is formed by joining a first member and a second member; the first member is composed of a steel material having a surface treatment layer, and the first member has: an opening portion which penetrates the steel material; and an exposed portion which is adjacent to the opening portion and exposes the steel base material; the second member is composed of a steel material having a coating layer, and the second member is arranged to cover at least the aforementioned opening portion of the aforementioned first member; the aforementioned coating layer of the aforementioned second member contains, by mass%, Al: greater than 15.0% and less than 30.0%, Mg: greater than 5.0% and less than 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%, and B: 0% to 0.5%, and the remainder is composed of Zn and impurities; the circumference length of the opening of the first member on the side not in contact with the second member is L [mm], and the area of the exposed portion of the first member not in contact with the second member is S _S [mm ² ], and the average adhesion amount of the aforementioned coating layer on each side of the second member is M _m [g/m ² ], then, if L<100, then M _m /S _S ≧0.008 holds, and if L≧100, then L×M _m /S _S holds ≧1.300; the contents of Mg, Al and Zn (unit: mass %) in the entire aforementioned coating layer on the side of the aforementioned second component that is in contact with the aforementioned first component are recorded as [Mg]', [Al]', [Zn]', respectively. In a cross section obtained by cutting the aforementioned first component and the aforementioned second component in the thickness direction at the position of the aforementioned opening of the aforementioned first component, the aforementioned coating layer on the side of the aforementioned second component that is in contact with the aforementioned first component is measured by energy dispersive X-ray diffraction using a field emission scanning electron microscope. A line analysis device (FE-SEM/EDX) is used to perform a surface analysis from the surface layer to a depth of 3 μm, and the obtained Mg, Al, and Zn contents (unit: mass %) are recorded as [Mg], [Al], and [Zn], respectively. The ratio R calculated based on the analysis results of the above-mentioned surface analysis is defined as the following formula (1); let the position of one end of the above-mentioned opening portion in the above-mentioned cross section as the starting point and the position 20 mm away from the center of the above-mentioned opening portion be position A, at this time, the value RA of the above-mentioned ratio R at the above-mentioned position _A falls within the range of 1.10 to 5.00; and let the position of one end of the above-mentioned opening portion in the above-mentioned cross section be position B, at this time, the value RB of the above-mentioned ratio R at the above-mentioned position _B is less than the value of _RA .

(2) The conjugate of (1), wherein the _RB is in the range of 0.30 to 5.00.

(3) A joint body as described in (1) or (2), wherein a chemical conversion treatment film exists on the surface of the aforementioned coating layer of the aforementioned second component, and the resistance of the chemical conversion treatment film when measured by a four-terminal four-probe method is less than 1×10 ^-2 Ω.

(4) A joint body as described in any one of (1) to (3), wherein the aforementioned surface treatment layer of the aforementioned first component contains Zn.

(5) A joint body as described in any one of (1) to (4), wherein the surface treatment layer of the first component is composed of one or more layers, and the outermost surface is a coating.

(6) A joint body as described in any one of (1) to (5), wherein iron oxide is attached to the aforementioned exposed portion of the aforementioned first component.

(7) A joint body as described in any one of (1) to (6), wherein the aforementioned opening of the aforementioned first component has burrs facing the side of the aforementioned second component.

10: Component 1

11: Opening

13: Exposed part

15: Rough edges

17:Iron oxide

20: Component 2

p: point

Claims (7)

A joint body is formed by joining a first component and a second component; the first component is composed of a steel material having a surface treatment layer, and the first component has: an opening portion that penetrates the steel material; and an exposed portion that is adjacent to the opening portion and exposes the steel substrate; the second component is composed of a steel material having a coating layer, and the second component is configured to cover at least the aforementioned opening portion of the aforementioned first component; the aforementioned coating layer of the aforementioned second component contains, by mass%, Al: greater than 15.0% and less than 30.0%, Mg: greater than 5.0% and less than 15.0%, Sn: 0%~0.70%, Ca: 0.03%~0.60%, Si: 0.01%~0.75%, Ti: 0%~0.25%, Ni: 0% to 1.00%, Co: 0% to 0.25%, Fe: 0% to 5.0%, and B: 0% to 0.5%, and the remainder is composed of Zn and impurities; Let the circumferential length of the opening of the first member on the side not in contact with the second member be L [mm], let the area of the exposed portion of the first member not in contact with the second member be S _S [mm ² ], and let the average adhesion amount of the plating layer on each side of the second member be M _m [g/m ² ], at this time, if L<100, then M _m /S _S ≧0.008 holds, and if L≧100, then L×M _m /S _S ≧1.300 holds; The contents of Mg, Al and Zn (unit: mass %) in the entire coating layer on the side of the second member that is in contact with the first member are respectively recorded as [Mg]', [Al]', [Zn]'. In a cross section obtained by cutting the first member and the second member in the thickness direction at the position of the aforementioned opening of the first member, the coating layer on the side of the second member that is in contact with the first member is subjected to a surface analysis from the surface layer to a depth of 3 μm using an energy dispersive X-ray analyzer of a field emission scanning electron microscope (FE-SEM/EDX), and the obtained contents of Mg, Al and Zn (unit: mass %) are respectively recorded as [Mg], [Al], [Zn]. The ratio R calculated based on the analysis result of the surface analysis is defined as the following formula (1); Let the position of one end of the aforementioned opening in the aforementioned cross section be the starting point, and the position 20 mm away from the center of the aforementioned opening be position A, at which point the value RA of the aforementioned ratio R at the aforementioned position _A falls within the range of 1.10 to 5.00; and let the position of one end of the aforementioned opening in the aforementioned cross section be position B, at which point the value RB of the aforementioned ratio _R at the aforementioned position B is less than the value of _RA ; [Mathematical formula 1] ···Formula 1). The conjugate of claim 1, wherein the aforementioned R _B falls within the range of 0.30~5.00. A joint body as claimed in claim 1, wherein a chemical conversion treatment film exists on the surface of the aforementioned coating layer of the aforementioned second component, and the resistance of the chemical conversion treatment film when measured by a four-terminal four-probe method is less than 1×10 ^-2 Ω. A joint body as claimed in claim 1, wherein the aforementioned surface treatment layer of the aforementioned first component contains Zn. In the joint body of claim 1, the surface treatment layer of the first component is composed of one layer or a plurality of layers, and the outermost surface is a coating. A joint body as in any one of claims 1 to 5, wherein iron oxide is attached to the aforementioned exposed portion of the aforementioned first component. A joint body as in any one of claims 1 to 5, wherein a burr facing the side of the second component exists in the aforementioned opening portion of the aforementioned first component.