Cooling structure and battery unit

Abstract

Provided is a cooling structure (1) having water-cooling medium flow paths (25) formed so as to be in contact with a bottom surface portion (10a) of a battery pack (10). The cooling structure (1) has a flow path formation part (21) that forms a portion of the water-cooling medium flow paths (25). The flow path formation part (21) is joined to an adherend member by an adhesion part (30). The adherend member is made of a steel sheet obtained by forming an inorganic coating or a resin coating as a chemical conversion coating on an Al-based plated steel sheet or a Zn-based plated steel sheet. The flow path formation part (21) is made of an aluminum alloy. The thickness of the adhesion part (30) is at least 0.0005 mm. The adhesion part (30) protrudes by at least 0.1 mm toward the water-cooling medium flow paths (25). The flow path interval between the water-cooling medium flow paths (25) is at most 20 mm. The width of the water-cooling medium flow paths (25) is at most 60 mm.

Description

Cooling structure and battery unit

[0001] The present disclosure relates to a cooling structure and a battery unit. This disclosure claims priority to Japanese Patent Application No. 2023-191328, filed on November 9, 2023, the contents of which are incorporated herein by reference.

[0002] In the automotive sector, CO ２ To reduce carbon emissions, electric vehicles (EVs) are becoming more common. Among the components used in EVs, battery packs, which house the battery cells that serve as the power source, require a cooling structure to prevent battery deterioration due to temperature rise. Until now, air-cooled cooling structures have been the norm, but in recent years, as battery capacities have increased, water-cooled structures with high cooling capacity have increasingly been adopted. Components in water-cooled battery packs are generally made of iron or aluminum. For example, Patent Document 1 discloses the use of adhesives to bond aluminum cooling plates.

[0003] Special Publication No. 2022-514223

[0004] Iron is superior to aluminum in terms of strength and cost, but is inferior in corrosion resistance. A flow path that combines iron and aluminum can provide a cooling flow path that combines the strength and cost benefits of iron with the high corrosion resistance of aluminum. However, because it is a combination of dissimilar metals, the contact points between the iron and aluminum pose issues such as contact corrosion due to dissimilar metals and distortion due to differences in thermal expansion coefficients. Furthermore, because the inside of the flow path is an environment where a water refrigerant such as a coolant flows, erosion resistance is required in addition to strength at the joints.

[0005] The present invention has been made in view of the above problems, and has as its object to provide a cooling structure which has excellent strength and erosion resistance at the joint between dissimilar metals.

[0006] To solve the above problems, the present disclosure employs the following measures. (1) A cooling structure according to one aspect of the present disclosure is a cooling structure having a water refrigerant flow path formed to contact a bottom surface of a battery pack, the cooling structure having a flow path-forming portion constituting a part of the water refrigerant flow path, the flow path-forming portion being joined to a joined member by an adhesive portion, the joined member being either the bottom surface or a flow path top cover covering the flow path-forming portion, the joined member being made of an Al-plated steel sheet or a Zn-plated steel sheet having an inorganic coating or a resin coating formed as a chemical conversion coating, the flow path-forming portion being made of an aluminum alloy, the adhesive portion having a thickness of 0.0005 mm or more, the adhesive portion extending 0.1 mm or more into the water refrigerant flow path, the flow path spacing between the water refrigerant flow paths being 20 mm or less, and the water refrigerant flow path having a width of 60 mm or less. (2) In the cooling structure described in (1) above, the plating layer of the Al-plated steel sheet may contain Si. (3) In the cooling structure described in (2) above, the Si content of the plating layer of the Al-plated steel sheet may be 2.0 mass% or more and 15 mass% or less. (4) In the cooling structure described in (1) or (2) above, a chemical conversion coating containing a Zr-based component, a Ti-based component, or a Si-based component as a main component may be formed on the surface of the Al-plated steel sheet. (5) In the cooling structure described in (1) above, the inorganic coating on the surface of the Zn-plated steel sheet may contain a Si-based component or a Zr-based component as a main component. (6) In the cooling structure described in (1) above, the inorganic coating on the surface of the Zn-plated steel sheet may contain at least one of a V component, a P component, and a Co component as a rust-preventive component. (7) In the cooling structure described in (6) above, the rust-preventive component may be one or more of vanadium oxide, phosphoric acid, and Co nitrate. (8) In the cooling structure described in (1) above, the inorganic coating on the surface of the Zn-based plated steel sheet may be composed of a compound phase containing one or more of Si—O bonds, Si—C bonds, and Si—OH bonds. (9) In the cooling structure described in (1) above, the inorganic coating may have a thickness of more than 0 μm and 1.5 μm or less. (10) In the cooling structure described in (1) above, the inorganic coating or the resin coating may be electrically conductive.(11) In the cooling structure described in (1) above, the resin film may contain a resin, an anti-rust pigment, and a conductive pigment. (12) In the cooling structure described in (11) above, the resin film may contain one or more conductive pigments selected from the group consisting of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles, and the conductive pigment may have a powder resistivity of 7.0 x 10 Ω cm or less at 23 to 27°C and may contain one or more constituent elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W. (13) In the cooling structure described in (11) or (12) above, the resin film may contain the conductive pigment in a proportion of 1.0 mass % to 30 mass %. (14) In the cooling structure described in (1) above, the adhesive portion may contain 10% or more of any of epoxy resin, silicone resin, acrylic resin, and urethane resin. (15) In the cooling structure described in (1) above, the adhesive portion may have a hardness of A15 or more and D90 or less. (16) A battery unit according to one aspect of the present disclosure includes the cooling structure described in (1) or (2) above and a battery pack.

[0007] According to the above-mentioned aspects of the present invention, it is possible to provide a cooling structure that has excellent strength and erosion resistance at the joint between dissimilar metals.

[0008] Fig. 1 is a schematic cross-sectional view showing a cooling structure according to an embodiment of the present disclosure; Fig. 2 is a schematic cross-sectional view showing another example of the cooling structure according to the embodiment; Fig. 3 is a schematic cross-sectional view showing another example of the cooling structure according to the embodiment; Fig. 4 is a schematic plan view for illustrating the shape of a water coolant flow path of the cooling structure according to the embodiment; Fig. 5 is a schematic cross-sectional view for illustrating one end of the cooling structure of Fig. 1 .

[0009] A cooling structure according to an embodiment of the present disclosure will be described with reference to the drawings. In the following description, common components will be designated by the same reference numerals, and duplicate descriptions thereof may be omitted. However, the present disclosure is not limited to the configuration disclosed in this embodiment, and various modifications are possible within the scope of the present disclosure.

[0010] 1, 2, 3, and 5, the direction perpendicular to the paper surface is the Y direction, the direction in which a plurality of flow path forming sections 21 (described later) are arranged is the X direction, and the direction perpendicular to both the X direction and the Y direction is the Z direction. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" are not included in the numerical range.

[0011] <1. Overall Configuration of Cooling Structure> First, the overall configuration of the cooling structure 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view (a cross-sectional view perpendicular to a bottom surface 10a of a battery pack 10) showing an overview of the cooling structure 1 according to this embodiment.

[0012] The cooling structure 1 according to this embodiment is provided, for example, on the outside (below) of the bottom surface of an automobile. Because an LLC (long life coolant) solution containing organic components flows as a coolant (water coolant) through the water coolant flow paths 25 of the cooling structure 1, high coolant corrosion resistance is required for the cooling structure 1. Furthermore, the cooling structure 1 is required to improve its cooling capacity by narrowing the flow path spacing of the water coolant flow paths 25 to increase the liquid area.

[0013] The cooling structure 1 has a water coolant flow path 25. The coolant flowing in the water coolant flow path 25 cools the battery pack 10 by coming into contact with the bottom surface 10a of the battery pack 10 directly or through a flow path upper cover 26 (described later). Battery cells (not shown) are housed in the battery pack 10. Inside the battery pack 10, the battery cells are arranged in close contact with the bottom surface 10a.

[0014] The cooling structure 1 has a flow path forming portion 21. The flow path forming portion 21, together with the bonded members described below, forms a water coolant flow path 25. That is, the flow path forming portion 21 constitutes a part of the water coolant flow path 25. In the cross-sectional view of the cooling structure 1 shown in FIG. 1 , multiple water coolant flow paths 25 appear to be lined up. The flow path forming portion 21, together with the bonded members described below, forms multiple water coolant flow paths 25 extending in the Y direction. Along the X direction, adjacent water coolant flow paths 25 are connected to each other via joint portions 22 of the flow path forming portion 21. The joint portions 22 are the portions between adjacent water coolant flow paths 25.

[0015] The flow path forming portion 21 is joined to a member to be joined by an adhesive portion 30. The member to be joined is either the bottom surface portion 10a of the battery pack 10 or the flow path upper lid 26 that covers the flow path forming portion 21. Either the bottom surface portion 10a of the battery pack 10 or the flow path upper lid 26 that covers the flow path forming portion 21 is joined to the flow path forming portion 21 by an adhesive portion 30. Here, "the flow path upper lid 26 covers the flow path forming portion 21" means that the flow path upper lid 26 is arranged on the battery pack 10 side in at least the portion of the flow path forming portion 21 that forms the water coolant flow path 25.

[0016] As in the example of FIG. 1 , when the cooling structure 1 has a flow path upper lid 26, the joined member is the flow path upper lid 26, and the flow path forming portion 21 and the flow path upper lid 26 are joined by an adhesive part 30. When the cooling structure 1 does not have the flow path upper lid 26, the joined member is the bottom surface 10a of the battery pack 10, and the flow path forming portion 21 and the bottom surface 10a of the battery pack 10 are joined by an adhesive part 30. The adhesive part 22 is joined to the bottom surface 10a of the battery pack 10 or the flow path upper lid 26 via the adhesive part 30. In this embodiment, as shown in FIG. 1 , the adhesive part 30 joins the flow path upper lid 26, which covers at least the water refrigerant flow path 25, and the flow path forming portion 21. Specifically, the flow path upper lid 26 is joined by the adhesive part 22 and the adhesive part 30.

[0017] In this embodiment, the water coolant flow path 25 is a space that has a rectangular shape when viewed from the Y direction, as shown in FIG.

[0018] 1, the cooling structure 1 according to this embodiment has a flow path upper lid 26 that covers the upper side of the flow path forming portion 21. In this case, the flow path upper lid 26 is disposed between the flow path forming portion 21 and the battery pack 10. The battery pack 10 is provided on the opposite side of the flow path upper lid 26 from the flow path forming portion 21.

[0019] The flow path upper cover 26 is made of a steel sheet in which an inorganic coating or a resin coating is formed as a chemical conversion coating on an Al (aluminum)-plated steel sheet or a Zn (zinc)-plated steel sheet. Hereinafter, "a steel sheet in which an inorganic coating or a resin coating is formed as a chemical conversion coating" may be referred to as "a chemically treated steel sheet."

[0020] When the cooling structure 1 does not have the flow path upper cover 26, the bottom surface 10a of the battery pack 10 is joined to the flow path forming portion 21, and a water refrigerant flow path 25 is formed by a portion of the bottom surface 10a of the battery pack 10 and a portion of the flow path forming portion 21. In this case, the water refrigerant flow path 25 is in direct contact with the bottom surface 10a of the battery pack 10. In this case, the bottom surface 10a of the battery pack 10 is made of a steel plate with an inorganic coating or a resin coating formed as a chemical conversion coating on an Al-based plated steel plate or a Zn-based plated steel plate. When the cooling structure 1 has the flow path upper cover 26, the bottom surface 10a does not necessarily have to be made of a steel plate with an Al-based plated steel plate or a Zn-based plated steel plate that has been chemically treated. This is because the bottom surface 10a does not come into contact with the coolant.

[0021] An example of an Al-based plated steel sheet is an Al-9% by mass Si-plated steel sheet. Examples of a Zn-based plated steel sheet are a Zn-0.2% by mass Al-plated steel sheet, a Zn-0.09% by mass Al-plated steel sheet, a Zn-6% by mass Al-3% by mass Mg-plated steel sheet, and a Zn-11% by mass Al-3% by mass Mg-0.2% by mass Si-plated steel sheet. A particularly preferred material among the Zn-based plated steel sheets is a zinc (Zn)-aluminum (Al)-magnesium (Mg)-based alloy-plated steel sheet.

[0022] Chemically treated aluminum-based plated steel sheets and zinc-based plated steel sheets have high corrosion resistance to coolants. In particular, chemically treated aluminum-based plated steel sheets and zinc-based plated steel sheets have excellent corrosion resistance to LLC aqueous solutions.

[0023] The shape of the cross section perpendicular to the extension direction of the water coolant flow path 25 is not limited to a rectangular shape, but may be, for example, a trapezoidal shape as shown in FIG. 2, a semicircular shape as shown in FIG. 3, or other shapes.

[0024] In this embodiment, the water refrigerant flow path 25 extends in the Y direction (e.g., a direction parallel to or perpendicular to the longitudinal direction of the bottom surface 10a of the battery pack 10). The extension direction of the water refrigerant flow path 25 is not limited to this example and may extend in the X direction. The water refrigerant flow path 25 may have not only straight portions but also curved portions when viewed in a plan view perpendicular to the surface of the bottom surface 10a. As illustrated in FIG. 4 , the water refrigerant flow path 25 may have a U-shaped portion when viewed in a plan view perpendicular to the plate surface of the bottom surface 10a. The U-shaped portion may be provided by folding back the straight portion. For example, adjacent straight portions may be connected by these portions. FIG. 4A illustrates a schematic shape of the water refrigerant flow path 25 in which a straight portion 25a extending in the Y direction is folded back at a U-shaped folding portion 25b. FIG. 4B illustrates a schematic shape of an exemplary water coolant flow path 25 in which a similar straight portion 25a is folded back at a U-shaped folded back portion 25b.

[0025] The water refrigerant flow path 25 is connected to a circulation path (not shown). For example, a supply pipe flow path (not shown) that supplies the water refrigerant and a drain pipe flow path (not shown) that drains the water refrigerant are connected to the water refrigerant flow path 25. The supply pipe and the drain pipe may be connected to the flow path forming portion 21 at approximately both ends of the water refrigerant flow path 25. Alternatively, they may be arranged based on a cooling design, such as by positioning the supply pipe approximately in the middle of the water refrigerant flow path 25 and providing multiple or more drain pipes at both ends of the water refrigerant flow path 25. The water refrigerant supplied from the supply pipe flows through the water refrigerant flow path 25 and is drained from the drain pipe. The water refrigerant is cooled by a cooling device (not shown) and then supplied again from the supply pipe to the water refrigerant flow path 25.

[0026] In this manner, the coolant, which is a water refrigerant, flows through the circulation path and the water refrigerant flow path 25. After being cooled in the circulation path, the coolant flows through the water refrigerant flow path 25. The coolant absorbs heat from the battery pack 10 while flowing through the water refrigerant flow path 25. The coolant is then introduced back into the circulation path. That is, the coolant repeatedly flows through the circulation path and the water refrigerant flow path 25, thereby repeatedly absorbing heat from the battery pack 10.

[0027] Therefore, the material of the flow path forming portion 21 that forms the water coolant flow path 25 is required to be resistant to corrosion by the coolant. In this embodiment, the flow path forming portion 21 is made of an aluminum alloy. Examples of the aluminum alloy include 3000 series and 6000 series aluminum alloys. Because the flow path forming portion 21 is made of an aluminum alloy, it is possible to obtain a cooling structure 1 that has high corrosion resistance to the coolant and is lighter than a cooling structure that employs a steel flow path. The flow path forming portion 21 may be an Al alloy plate having a composition similar to that of the above-mentioned plating layer.

[0028] When the cooling structure 1 has the flow path upper lid 26, the flow path forming portion 21 is joined to the flow path upper lid 26 by an adhesive portion 30. When the cooling structure 1 does not have the flow path upper lid 26, the flow path forming portion 21 is joined to the bottom surface portion 10a of the battery pack 10 by an adhesive portion 30. The thickness (length in the Z direction) D30 of the adhesive portion 30 formed by the above-mentioned joining is 0.0005 mm or more.

[0029] In this embodiment, as shown in Fig. 5 , the thickness D30 of the adhesive portion 30 is the distance in a direction perpendicular to the surfaces of the joined members (Z direction in the example of Fig. 5 ) between the opposing surfaces of the flow path upper cover 26 and the joining portion 22 of the flow path forming portion 21, which are the joined members. If the cooling structure 1 does not have the flow path upper cover 26, the thickness D30 of the adhesive portion 30 is the distance in a direction perpendicular to the surfaces of the joined members (Z direction in the example of Fig. 5 ) between the opposing surfaces of the bottom surface portion 10a of the battery pack 10 and the joining portion 22 of the flow path forming portion 21, which are the joined members.

[0030] Since the distance (D30) between the flow path forming portion 21 and the joined member is ensured to be 0.0005 mm or more, contact corrosion due to dissimilar metals and distortion due to differences in thermal expansion coefficients can be suppressed even in the joining of dissimilar metals between the joined member made of a chemically treated Al-based plated steel sheet or Zn-based plated steel sheet and the flow path forming portion 21 made of an aluminum alloy. If the thickness D30 of the adhesive portion 30 is too large, the joining strength decreases, so it is preferably 10 mm or less, more preferably 5 mm or less.

[0031] The thickness D30 of the adhesive portion 30 can be controlled by including a filler or spacer in the adhesive that becomes the adhesive portion 30. Common materials can be used as the filler or spacer. There are no particular restrictions on the particle size of the filler or spacer, and it may be equal to or smaller than the desired thickness D30.

[0032] The thickness D30 of the adhesive portion 30 can be measured as follows. A sample is prepared by cutting out the flow path forming portion 21 along the Z direction so as to include the adhesive portion 30. This sample is observed using an optical microscope or an SEM (scanning electron microscope), and the thickness D30 of the adhesive portion 30 in the direction perpendicular to the surface of the joined members is measured using the captured image (photograph) and a scale bar. In this case, the arithmetic mean value of five points obtained from five fields of view is taken as the thickness D30.

[0033] Generally, the adhesive is applied within the width (X direction) of the joint 22. That is, the adhesive is applied so as not to spill out of the joint 22. This is because it is believed that spilling adhesive increases the amount of adhesive used, resulting in increased costs. In contrast, in this embodiment, the adhesive has a spill-out portion 23 that spills out from the joint 22 into the water refrigerant flow path 25. That is, the spill-out portion 23 is configured to spill out from the joint 22 toward the water refrigerant flow path 25 in the X direction. Specifically, the spill-out portion 23 spills out 0.1 mm or more toward the water refrigerant flow path 25.

[0034] The protruding portion 23 is a portion (cured adhesive portion) formed by the hardening of the adhesive, similar to the adhesive portion 30, and therefore has the same chemical composition as the adhesive portion 30. In the protruding portion 23, the material constituting the protruding portion 23 is in contact with the joined members, but is not in contact with other members on the water coolant flow path 25 side. Alternatively, there are portions of the protruding portion 23 that are not in contact with the joined members but are in contact with the flow path forming portion 21. Therefore, the protruding portion 23 does not have the function of adhering other members to each other.

[0035] FIG. 5 shows an example of the shape of the protruding portion 23. As shown in FIG. 5, the protruding portion 23 protruding toward the water refrigerant flow path 25 has a rounded shape. In the width direction of the water refrigerant flow path 25 (the X direction in the example of FIG. 5), the distance between the end of the protruding portion 23 and the point P (the boundary between the water refrigerant flow path 25 and the joint 22) on the inner surface of the side surface 21b of the flow path forming portion 21 (the surface constituting the water refrigerant flow path 25) closest to the joint 22 is defined as the protruding length L23. Protruding the protruding portion 23 toward the water refrigerant flow path 25 by 0.1 mm or more ensures a scraping allowance for the adhesive portion 30 due to erosion, improving the bonding strength. The protruding length L23 is preferably 0.2 mm or more. If the overhang length L23 is too large, it will hinder heat exchange between the water coolant and the bottom surface of the battery pack, reducing cooling performance and preventing a significant improvement in bonding strength, so the overhang length L23 is preferably 1 mm or less, and more preferably 0.8 mm or less. Here, the end of the overhang portion 23 refers to the point on the interface between the overhang portion 23 and the joined member that is farthest from the point P along the width direction of the water coolant flow path 25 (the X direction in the example of Figure 5).

[0036] The protruding portions 23 are preferably arranged on both sides of the joint portion 22 in the width direction, but may be arranged on only one side of the joint portion 22 in the width direction.

[0037] The protrusion length L23 can be measured as follows. A sample is prepared by cutting out a cross section of the flow path forming portion 21 that includes the adhesive portion 30 and is perpendicular to the extension direction (the Y direction) of the water coolant flow path 25. The sample is observed using an optical microscope, and the protrusion length L23 is measured from the captured image (photograph) and a scale bar. The arithmetic mean value of five points obtained from five fields of view is defined as the protrusion length L23.

[0038] There are no particular limitations on the means for applying the adhesive that constitutes the adhesive portion 30 and the protruding portion 23, and it is preferable to apply the adhesive so that the amount of adhesive applied is uniform. For example, a method that can apply a constant amount at a constant speed (for example, a method in which a robot applies adhesive from a gun while moving) results in a uniform amount of adhesive and good quality.

[0039] It is more preferable that there be no welded or brazed portion between the joined members and the joint 22, and that only the adhesive portion 30 be present. For example, if high-temperature treatment such as spot welding or brazing is performed on an Al-based plated steel sheet or a Zn-based plated steel sheet on which an inorganic or resin coating is formed as a chemical conversion coating, the plated layer, inorganic or resin coating may be damaged. However, by using adhesive bonding, as in the cooling structure 1 according to this embodiment, such damage problems do not occur, and erosion resistance can be ensured.

[0040] The channel spacing w between the water refrigerant channels 25 is 20 mm or less. In other words, the channel spacing w is the distance between the ends of adjacent water refrigerant channels 25 in the width direction (X direction). In the example shown in FIG. 1 , the cross-sectional shape of the water refrigerant channels 25 is rectangular, so the widthwise end-to-end distance (channel spacing) w of the water refrigerant channels 25 is the distance between the side surfaces 21b of the channel-forming portions 21 that form adjacent water refrigerant channels 25. In the example shown in FIGS. 2 and 3 , the boundary between the water refrigerant channels 25 and the joints 22 corresponds to the widthwise end of the water refrigerant channels 25. For example, joining components by spot welding requires a certain area of ​​joining surface to form the spot welds. If the cooling structure according to this embodiment were to be fabricated using spot welding instead of adhesive portions 30, the spot welds would exceed the channel spacing, preventing proper joining. Furthermore, ensuring sufficient channel spacing in order to properly form spot welds would undesirably narrow the channel width, as described below.

[0041] By setting the flow path spacing w between the water coolant flow paths 25 to 20 mm or less, the width of the water coolant flow paths 25 can be increased, thereby increasing the contact area between the water coolant flow paths 25 and the bottom surface 10a, i.e., the contact area between the coolant and the battery pack 10. Therefore, in this embodiment, the cooling efficiency of the battery pack 10 can be improved. In particular, in this embodiment, the flow path upper cover 26 or the bottom surface 10a of the battery pack 10 is made of a steel plate that has been chemically treated with an Al-based plated steel plate or a Zn-based plated steel plate. The heat transfer characteristics of the Al-based plated steel plate or the Zn-based plated steel plate include the fact that heat is easily absorbed by the coolant in the portion of the flow path upper cover 26 or the bottom surface 10a of the battery pack 10 directly above the portion that contacts the coolant. Therefore, by increasing the contact area between the coolant and the flow path upper cover 26 or the battery pack 10, the area through which heat is transferred can be increased, thereby improving cooling efficiency. Although there are no particular limitations on the materials for the side surface portion 10b and the top surface portion 10c of the battery pack 10, they are preferably made of an Al-based plated steel sheet or a Zn-based plated steel sheet that has been subjected to a chemical conversion treatment, similar to the bottom surface portion 10a. In particular, since the side surface portion 10b is exposed to the external environment, it is preferably made of an Al-based plated steel sheet or a Zn-based plated steel sheet that has been subjected to a chemical conversion treatment, similar to the bottom surface portion 10a.

[0042] The channel spacing w between the water refrigerant channels 25 is preferably 1 mm or more and 15 mm or less. Setting the channel spacing w between the water refrigerant channels 25 to 1 mm or more ensures the width (length in the X direction) of the joint 22 and facilitates ensuring the joint strength with the bottom surface 10a of the battery pack 10 or the channel top cover 26. Setting the channel spacing w between the water refrigerant channels 25 to 15 mm or less increases the contact area between the coolant and the battery pack 10, thereby improving cooling efficiency. Narrowing the channel spacing w is necessary to increase the area ratio of the water refrigerant channels 25 without excessively increasing the channel width L and shorten the distance between the water refrigerant channels 25 and the non-contact areas with the coolant. To satisfy the shape of the water refrigerant channels 25, it is suitable to bond the water refrigerant channels 25 with an adhesive. Bonding with an adhesive allows the channel spacing w to be equivalent to the joint area.

[0043] The flow path spacing w in the water refrigerant flow paths 25 is measured using a vernier caliper. The flow path spacing w is determined by cutting out any 10 locations from the flow path forming portion 21, measuring the flow path spacing w at the cut-out locations using a vernier caliper, and calculating the average of the maximum and minimum values ​​of the measurements at the 10 locations. Note that the flow path spacing w refers to the flow path spacing w in the range where multiple water refrigerant flow paths 25 are lined up and where joints 22 are provided between the water refrigerant flow paths 25, as exemplified in FIG. 1 and other figures. Therefore, as described above, the locations where the flow paths turn back, such as in a U-shape, V-shape, or U-shape when viewed in a plan view perpendicular to the plate surface of the bottom surface portion 10a, are excluded from the measurement positions of the flow path spacing w.

[0044] To efficiently cool the battery pack 10, it is necessary to increase the area ratio of the water coolant flow channels 25 in contact with the battery pack 10. When viewed in a plan view perpendicular to the surface of the bottom surface 10a (e.g., the plan view shown in FIG. 4 ), the ratio of the area occupied by the water coolant flow channels 25 to the area of ​​the bottom surface 10a is preferably 0.23 or greater, and more preferably 0.40 or greater. This increases the contact area between the coolant and the battery pack 10, thereby improving the cooling efficiency of the battery pack 10. While the upper limit of this ratio is not particularly limited, it may be 0.80 because it is preferable to ensure a certain level of bonding strength between the joint 22 and the bottom surface 10a. From the perspective of balancing bonding strength and cooling efficiency, the ratio is more preferably 0.23 to 0.71. In other words, the cooling performance of the cooling structure 1 improves as the ratio increases, but it is also preferable to consider the bonding strength with the battery pack 10. From this perspective, the ratio is preferably 0.23 to 0.71.

[0045] The ratio of the area occupied by the water refrigerant flow path 25 to the area of ​​the bottom surface portion 10a can be increased by increasing the flow path width L. As shown in FIG. 1 , the flow path width L is the length of the water refrigerant flow path 25 in the X direction, i.e., the distance between the outer surfaces of the side portions 21b of the flow path forming portion 21 that form the water refrigerant flow path 25. In the example shown in FIGS. 2 and 3 , the boundary between the flow path forming portion 21 and the joint portion 22 is the widthwise end of the flow path forming portion 21, and the flow path width L is the distance between the widthwise ends of the water refrigerant flow path 25. If the flow path width L is too wide, the stress applied to the joint portion 22 will be large, or the flow of the coolant will not be limited to the longitudinal direction of the flow path and will be unstable. Therefore, the flow path width L is 60 mm or less. The lower limit of the flow path width is preferably 6 mm or more to ensure a stable flow of the coolant. To further stabilize the flow of the coolant, the flow path width L is more preferably 6 mm or more and 30 mm or less, and even more preferably 6 mm or more and 20 mm or less. The flow path width L of the water coolant flow path 25 is measured using a vernier caliper. The flow path width L is determined by cutting out any 10 locations from the flow path forming portion 21, measuring the flow path width L at the cut-out locations using the vernier caliper, and calculating the average of the maximum and minimum values ​​of the measurements at the 10 locations. Note that, as described above, the measurement positions for the flow path width L exclude the folding locations of the flow path that form a U-shape, V-shape, U-shape, or the like when viewed in a plan view in a direction perpendicular to the plate surface of the bottom surface portion 10a.

[0046] As shown in FIG. 1 and other figures, there is a region at the outer edge 27 of the flow path forming portion 21 where the water refrigerant flow paths 25 are not formed. If the region without the water refrigerant flow paths 25 is too large, the cooling effect of the coolant is reduced. Therefore, it is preferable to shorten the length of the end of the water refrigerant flow path 25 that does not come into contact with the coolant. Specifically, as shown in FIG. 1 and other figures, it is preferable to shorten the distance D in the X direction from the end of the flow path forming portion 21 to the nearest water refrigerant flow path 25, a region on the bottom surface 10a of the battery pack 10 where no water refrigerant flow paths 25 are present. Distance D is the widthwise distance of the water refrigerant flow path 25 from the end of the water refrigerant flow path 25 to the nearest water refrigerant flow path 25. This distance is preferably 10 mm or less, more preferably 7.5 mm or less. The distance D from the end of the flow path forming portion 21 to the start of the cavity in the nearest water refrigerant flow path 25 is measured using a vernier caliper. The distance D is determined by cutting out any 10 locations including the outer edge 27 of the flow path forming portion 21 and the water refrigerant flow path 25 closest to the outer edge 27, measuring the widthwise distance D of the water refrigerant flow path 25 at the cut-out locations using a vernier caliper, and calculating the average of the maximum and minimum measured values ​​at the 10 locations.

[0047] The height of the water refrigerant flow path 25, i.e., the distance h in the thickness direction (Z direction) of the water refrigerant flow path 25 from the bottom surface portion 21a of the flow path forming portion 21 (the lower end portion 21a-1 of the flow path forming portion 21 in the example of FIG. 3 ) to the joint portion 22, is not particularly limited, but is preferably 1 mm to 10 mm from the viewpoint of the cooling efficiency of the battery pack 10. From the viewpoint of processability for flow path formation, the upper limit of the distance h is preferably 8 mm. By setting the height (distance h) of the water refrigerant flow path 25 to 1 mm to 8 mm, both the cooling efficiency of the battery pack 10 and the processability for flow path formation can be better achieved. The distance h is measured using a vernier caliper. The distance h is determined by cutting out 10 arbitrary locations on the flow path forming portion 21, measuring the distance h at the cutout locations using a vernier caliper, and calculating the average of the maximum and minimum measured values ​​at the 10 locations.

[0048] The main resin component of the adhesive portion 30 is preferably one of epoxy resin, silicone resin, acrylic resin, and urethane resin. The adhesive portion 30 preferably contains at least 10%, more preferably at least 20%, of any of these main resin components. The adhesive portion 30 containing such a main component can suppress deterioration of the adhesive portion 30 and corrosion of the joint 22 due to water as a cooling medium, thereby ensuring watertightness. The content of the main resin component in the adhesive portion 30 is measured using a thermogravimetric analyzer.

[0049] At the outer edge of the cooling structure 1, the flow path forming portion 21 is also joined to the joined member by adhesive 30. Specifically, the outer edge 27 of the flow path forming portion 21 is joined to the outer edge 42 of the flow path upper lid 26 by adhesive 30. The outer edge 27 of the flow path forming portion 21 and the outer edge 42 of the flow path upper lid 26 are joined (watertightly joined) to form a watertight joint 70. A watertight joint is a joint that seals out water and prevents leakage even when water pressure is applied. When the cooling structure 1 does not have a flow path upper lid 26, the outer edge 11 of the bottom surface portion 10a of the battery pack 10 is joined to the outer edge 42 of the flow path upper lid 26 by adhesive 30 to form the watertight joint 70. By watertightly joining the outer edge of the cooling structure 1 in this manner, leakage of the coolant can be prevented and watertightness can be ensured.

[0050] The flow path forming portion 21 is manufactured, for example, by processing (e.g., bending, drawing, casting, etc.) a single sheet of aluminum alloy. The thickness of the aluminum alloy constituting the flow path forming portion 21 is not particularly limited, but is preferably, for example, 0.4 mm or more and 10.0 mm or less, and more preferably 0.4 mm or more and 5.0 mm or less. In this case, the strength of the flow path forming portion 21 can be increased. The manufacturing method of the flow path forming portion 21 is not limited to this example. For example, the flow path forming portion 21 may be manufactured using a die casting method. The thickness of the aluminum alloy is determined by cutting out a portion of the flow path forming portion 21, measuring the thickness of the cut-out portion at 10 locations using a vernier caliper, and calculating the average of the maximum and minimum values ​​measured at the 10 locations.

[0051] The thickness of the steel plate constituting the bottom surface portion 10a of the battery pack 10 is not particularly limited, but is preferably 0.4 mm to 1.2 mm, and more preferably 0.4 mm to 1.0 mm. In this case, the bottom surface portion 10a of the battery pack 10 can be formed thin while maintaining its strength. This reduces the distance between the coolant and the battery cells in the battery pack 10, thereby improving the cooling efficiency and cooling responsiveness of the battery pack 10. The thickness of the flow path upper cover 26 is also not particularly limited, but is preferably 0.4 mm to 1.2 mm, and more preferably 0.4 mm to 1.0 mm. The thickness of the steel plate is determined by cutting out a portion of the bottom surface portion 10a or the flow path upper cover 26 of the battery pack 10, measuring the thickness of the cut-out portion at 10 locations using a vernier caliper, and calculating the average of the maximum and minimum values ​​measured at the 10 locations.

[0052] In this embodiment, the joined members (bottom surface portion 10a of battery pack 10 or flow path upper cover 26) are made of aluminum-based plated steel sheet or zinc-based plated steel sheet with a chemical conversion treatment, and flow path forming portion 21 is made of an aluminum alloy. These different metals are joined with adhesive 30, and the thickness of adhesive 30 formed by joining is 0.0005 mm or more, which suppresses contact corrosion between dissimilar metals and distortion due to differences in thermal expansion coefficients. Furthermore, because protrusion portion 23 protrudes 0.1 mm or more toward water coolant flow path 25, a scraping allowance for adhesive 30 due to erosion can be secured, improving joint strength.

[0053] The hardness of the adhesive joint 30 is preferably A15 or more and D90 or less. The hardness of the adhesive joint 30 refers to the hardness of the adhesive joint 30 after the adhesive constituting the adhesive joint 30 has hardened. This prevents the adhesive from wearing away in an environment where cooling water circulates, and provides high erosion resistance. The hardness of the adhesive joint 30 is measured using a durometer hardness tester. Specifically, 10 random locations are cut out, and the hardness of the cut-out locations is measured based on JIS K 7215 "Durometer Hardness Test Method for Plastics," and the hardness is determined by calculating the average of the maximum and minimum values ​​measured at the 10 locations.

[0054] The cooling structure 1 according to this embodiment may be provided inside (above) the bottom surface of the automobile battery unit. In this case, the cooling structure 1 is housed inside the battery pack 10 together with the battery cells, and the battery cells are disposed above the cooling structure 1.

[0055] 2. Configuration of Al-based plated steel sheet Next, an example of an Al-based plated steel sheet constituting the members to be joined will be described in detail.

[0056] An Al-based plated steel sheet is a steel sheet on which a plating layer containing Al is formed. The plating layer of the Al-based plated steel sheet preferably contains Si. The Si content is, for example, 2.0 mass% or more and 15 mass% or less. The plating layer of the Al-based plated steel sheet is preferably a two-component or multi-component plating having an Al content of 70 mass% or more, an Al content of 70 to 98 mass%, and a Si content of 2.0 mass% or more and 15 mass% or less. A more preferable range for the Si content is 3.0 mass% or more and 15 mass% or less. By keeping the Si content within the above range, the workability and corrosion resistance of the Al-based plated steel sheet can be improved. The chemical composition of the plating layer may include, in addition to Al and Si, 15 mass% or less of Zn, 5 mass% or less of Mg, and the balance being Fe. The plating layer may be formed on only one side of the steel sheet, but is preferably formed on both sides.

[0057] Furthermore, trace amounts of Fe, Ni, Co, etc. may be present as impurity elements in the plating layer. Furthermore, Mg, Sn, misch metal, Sb, Zn, Cr, W, V, Mo, etc. may be added as necessary. There are no particular restrictions on the method for producing the aluminum-plated steel sheet, but hot-dip flux plating, hot-dip plating by the Sendzimir method, all-radiant method, etc., electroplating, and vapor deposition plating are preferred.

[0058] The composition of the base steel used for the Al-based plated steel sheet is not limited, but examples of the steel type include IF steel with added Ti, Nb, B, etc., Al-k steel, Cr-added steel, stainless steel, high-tensile steel, low-carbon steel, medium-carbon steel, high-carbon steel, and alloy steel.

[0059] In order to further improve the external corrosion resistance and coolant corrosion resistance of the Al-based plated steel sheet, it is preferable that a chemical conversion coating containing a Zr-based component, a Ti-based component, or a Si-based component as a main component (for example, 50 mass % or more) is formed on the surface (which may be on only one side, but preferably on both sides) of the Al-based plated steel sheet. The coating may also contain an organic component.

[0060] Examples of chemical conversion treatment films are listed in, for example, JP 2008-115442 A, JP 2013-7108 A, JP 2004-232040 A, Japanese Patent No. 3302676 A, Japanese Patent No. 4776458 A, and Japanese Patent No. 5336002 A. Therefore, the chemical conversion treatment films listed in these publications can be suitably used as the chemical conversion treatment film of this embodiment. Here, an overview of the chemical conversion treatment film will be described.

[0061] The first example of the chemical conversion coating is an example of a coating containing a Zr-based component as the main component, consisting only of Zr, F, P, C, O, N, and H, and containing no organic substances with a number average molecular weight of 200 or more. The components of the chemical conversion coating are adjusted so that the mass ratio of Zr to F, Zr / F, is 1.0 to 10.0, the mass ratio of Zr to P, Zr / P, is 8.5 to 18.0, and the Zr content in the chemical conversion coating is 23.0 mass% to 48.0 mass%. The sources of each component of the chemical conversion coating are one or more inorganic acids and / or ammonium salts thereof selected from the group consisting of carbonic acid, phosphoric acid, and hydrofluoric acid, and zirconium-containing complex compounds excluding zirconium hydrofluoric acid.

[0062] The second example of the chemical conversion coating is an example of a coating containing a Zr-based component as a primary component, and contains (A) at least one of titanium compounds and zirconium compounds, (B) at least one of myo-inositol phosphate esters having 2 to 6 bonds and their alkali metal salts, alkaline earth metal salts, and ammonium salts, and (C) silica. In this chemical conversion coating, the mass ratio of the metal equivalent amounts of (A) (Zr+Ti):(B):(C) is 1:0.2-1.7:0.2-5.

[0063] Examples of titanium compounds include potassium titanium oxalate, titanyl sulfate, titanium chloride, titanium lactate, titanium isopropoxide, isopropyl titanate, titanium ethoxide, titanium 2-ethyl-1-hexanolate, tetraisopropyl titanate, tetra-n-butyl titanate, titania sol, and the like.

[0064] Examples of the zirconium compound include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0065] Examples of the 2- to 6-linked phosphate ester of myo-inositol include myo-inositol diphosphate ester, myo-inositol triphosphate ester, myo-inositol tetraphosphate ester, myo-inositol pentane phosphate ester, and myo-inositol hexane phosphate ester.

[0066] Examples of silica include water-dispersible silica compounds. Water-dispersible silica compounds include liquid-phase colloidal silica and gas-phase silica. Examples of liquid-phase colloidal silica include, but are not limited to, Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex PS-L, Snowtex 20, Snowtex 30, and Snowtex 40 (all manufactured by Nissan Chemical Industries, Ltd.), Adelite AT-20N, Adelite AT-20A, and Adelite AT-20Q (all manufactured by Asahi Denka Kogyo Co., Ltd.).

[0067] The vapor phase silica is not particularly limited, but examples thereof include Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, and Aerosil MOX170 (all manufactured by Nippon Aerosil).

[0068] The third example of the chemical conversion coating is an example of a coating containing a Zr-based component as the main component, and is a composite coating made of a zirconium compound, a vanadium compound, a silica compound, a phosphate compound, and an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, and a carboxyl group. This chemical conversion coating contains 2 to 1200 mg / m of zirconium per side of the Al-based plated steel sheet. ２ , vanadium 0.1 to 300 mg / m ２ , 0.3 to 450 mg / m of phosphate compounds calculated as PO4 ２ Furthermore, the content of chromium or chromium compounds in the chemical conversion coating film is 0.1 mg / m ２ Hereinafter, the content of fluorine or fluorine compounds is 0.1 mg / m ２ The following is the list.

[0069] Examples of the zirconium compound include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0070] Examples of vanadium compounds include vanadium pentoxide, metavanadic acid, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, phosphovanadomolybdic acid, vanadium sulfate, vanadium dichloride, and vanadium oxide.

[0071] Examples of silica compounds include water-dispersible silica compounds, such as colloidal silica and gas-phase silica, and examples of colloidal silica include, but are not limited to, Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex PS-L, Snowtex 20, Snowtex 30, and Snowtex 40 (all manufactured by Nissan Chemical Industries, Ltd.), Adelite AT-20N, Adelite AT-20A, and Adelite AT-20Q (all manufactured by Asahi Denka Kogyo Co., Ltd.).

[0072] The vapor phase silica is not particularly limited, but examples thereof include Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, and Aerosil MOX170 (all manufactured by Nippon Aerosil).

[0073] The phosphate compound may contain phosphate ions, and examples of the phosphate compound include orthophosphoric acid (phosphoric acid), metaphosphoric acid, pyrophosphoric acid, and salts of these substances in which some or all of the hydrogen ions have been replaced, such as ammonium salts, sodium salts, calcium salts, and potassium salts, which can be used alone or in combination.

[0074] Examples of organic compounds having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, and a carboxyl group include alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; carbonyl compounds such as formaldehyde, acetaldehyde, furfural, acetylacetone, ethyl acetoacetate, dipivaloylmethane, and 3-methylpentanedione; organic acids such as formic acid, acetic acid, propionic acid, tartaric acid, ascorbic acid, gluconic acid, citric acid, and malic acid; monosaccharides such as glucose, mannose, and galactose; oligosaccharides such as maltose and sucrose; natural polysaccharides such as starch and cellulose; aromatic compounds such as tannic acid, humic acid, lignosulfonic acid, and polyphenols; and synthetic polymers such as polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyethyleneimine, and water-soluble nylon.

[0075] The chemical conversion coating may contain, as an additional component, a lubricity-imparting component made of at least one of polyolefin wax and paraffin wax.

[0076] A fourth example of a chemical conversion coating is a coating containing a Ti-based component as the main component, in which an oxide or hydroxide of a valve metal and a fluoride coexist. Examples of valve metals include Ti and V. Among these, tetravalent compounds of Ti are preferred because they are stable compounds and can form coatings with excellent properties. Examples of coatings containing a Ti-based component as the main component include oxides [TiO ２ ] and hydroxide [Ti(OH) ４ ] and the like. ６ (X: alkali metal, alkaline earth metal or NH4, n=1 or 2), TiF ４ Fluorides such as these coexist.

[0077] A fifth example of a chemical conversion coating is an example of a coating containing a silicon-based component as its primary component, specifically a chemical conversion coating containing an organosilicon compound (silane coupling agent) as its primary component. The organosilicon compound is obtained by blending a silane coupling agent (A) containing one amino group in its molecule with a silane coupling agent (B) containing one glycidyl group in its molecule at a solids mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound contains two or more functional groups (a) represented by the formula -SiRRR (wherein R, R, and R each independently represent an alkoxy group or a hydroxyl group, with at least one representing an alkoxy group), and one or more hydrophilic functional groups (b) selected from a hydroxyl group (different from those that may be contained in functional group (a)) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0078] The sixth example of the chemical conversion coating is an example of a coating containing a silicon-based component as the main component, that is, a chemical conversion coating containing an organosilicon compound (silane coupling agent) as the main component. The organosilicon compound has a cyclic siloxane structure within its structure. Here, the term "cyclic siloxane bond" refers to a cyclic structure having a continuous Si-O-Si bond, consisting only of Si and O bonds, with 3 to 8 Si-O repeating units.

[0079] The organosilicon compound is obtained by blending a silane coupling agent (A) containing at least one amino group in the molecule with a silane coupling agent (B) containing at least one glycidyl group in the molecule in a solids mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound (W) thus obtained preferably contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 each independently represent an alkoxy group or a hydroxyl group, and at least one of R1, R2, and R3 represents an alkoxy group) and one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (if the functional group (a) contains a hydroxyl group, this is separate from the hydroxyl group) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0080] Of course, examples of the chemical conversion coating of this embodiment are not limited to those described above, and for example, the chemical conversion coatings listed in the examples described below can also be suitably used.

[0081] The method for forming the above-mentioned chemical conversion coating is not particularly limited, and it is sufficient to apply a chemical conversion solution (coating solution) corresponding to each of the above compositions to an Al-based plated steel sheet by a known method, followed by baking and drying.

[0082] 3. Configuration of Zn-based plated steel sheet> Next, an example of the Zn-based plated steel sheet that constitutes the members to be joined will be described in detail.

[0083] A zinc-based plated steel sheet is a steel sheet on which a zinc-containing plating layer is formed. The plating layer may be formed on only one side of the steel sheet, but is preferably formed on both sides. Examples of zinc-based plated steel sheets include zinc-plated steel sheets, zinc-nickel-plated steel sheets, zinc-iron-plated steel sheets, zinc-chromium-plated steel sheets, zinc-aluminum-plated steel sheets, zinc-titanium-plated steel sheets, zinc-magnesium-plated steel sheets, zinc-manganese-plated steel sheets, zinc-aluminum (Al)-magnesium (Mg)-plated steel sheets, and zinc-aluminum-magnesium-silicon-plated steel sheets. Furthermore, zinc-based plated steel sheets containing small amounts of different metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic in the plating layer, or zinc-based plated steel sheets with inorganic substances such as silica, alumina, and titania dispersed therein, can also be used. Furthermore, the above plating can be combined with other types of plating, and for example, multi-layer plating can be applied by combining it with iron plating, iron-phosphorus plating, nickel plating, cobalt plating, etc. The plating method is not particularly limited, and any of the known methods such as electroplating, hot-dip plating, vapor deposition plating, dispersion plating, and vacuum plating can be used.

[0084] Furthermore, an inorganic coating or a resin coating is formed as a chemical conversion coating on the surface of the Zn-based plated steel sheet (it may be on one side only, but preferably on both sides). The inorganic coating contains a Si-based component or a Zr-based component as a main component (for example, 50 mass % or more). The inorganic coating may also contain an organic component.

[0085] The inorganic coating or resin coating preferably has electrical conductivity. In this case, the electrodeposition coatability of the zinc-based plated steel sheet can be improved. Furthermore, the inorganic coating is preferably composed of a compound phase containing one or more of Si—O bonds, Si—C bonds, and Si—OH bonds. Furthermore, the compound phase preferably contains an acrylic resin, as described below. When these requirements are satisfied, the adhesion of the chemical conversion coating can be improved, thereby improving the external corrosion resistance and coolant corrosion resistance of the processed portion of the zinc-based plated steel sheet. Furthermore, the inorganic coating preferably contains at least one of a vanadium component, a phosphorus component, and a cobalt component as a rust-preventing component. The rust-preventing component of the inorganic coating is preferably one or more of vanadium oxide, phosphoric acid, and cobalt nitrate. Furthermore, the thickness of the inorganic coating is preferably greater than 0 μm and less than or equal to 1.5 μm. In this case, the electrical conductivity or adhesion of the above-mentioned chemical conversion coating can be further improved.

[0086] The resin coating preferably contains a resin, an anti-rust pigment, and a conductive pigment. Furthermore, the resin coating preferably contains one or more conductive pigments selected from the group consisting of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles. The conductive pigment preferably has a powder resistivity of 7.0 × 10 Ω cm or less at 23 to 27°C and contains one or more constituent elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W. Furthermore, the resin coating preferably contains the conductive pigment in a proportion of 1.0 mass % to 30 mass %. Furthermore, the average thickness of the resin coating is preferably 1.0 μm to 15 μm. Furthermore, the average particle size of the conductive pigment is preferably 0.5 to 1.5 times the average thickness of the resin coating. When any one or more of these requirements are satisfied, the external corrosion resistance and coolant corrosion resistance of the zinc-based plated steel sheet can be further improved.

[0087] Examples of chemical conversion coatings are listed in, for example, Japanese Patent No. 4776458, Japanese Patent No. 5336002, Japanese Patent No. 6191806, Japanese Patent No. 6263278, International Publication No. WO 2020 / 202461, and Japanese Patent No. 4084702. Therefore, the chemical conversion coatings listed in these publications can be suitably used as the chemical conversion coating of this embodiment. Here, an overview of the chemical conversion coating will be described.

[0088] The first example of the chemical conversion coating is an inorganic coating, and is a chemical conversion coating containing an organosilicon compound (silane coupling agent) as a primary component. The organosilicon compound is obtained by blending a silane coupling agent (A) containing one amino group per molecule with a silane coupling agent (B) containing one glycidyl group per molecule in a solids mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 each independently represent an alkoxy group or a hydroxyl group, with at least one representing an alkoxy group), and one or more hydrophilic functional groups (b) selected from a hydroxyl group (different from those that may be contained in functional group (a)) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0089] In a first example, the Zr-based component is contained in the chemical conversion coating as zirconium hydrofluoric acid. The V component is contained in the chemical conversion coating as a vanadium compound, the P component is contained in the chemical conversion coating as phosphoric acid, and the Co component is contained in the chemical conversion coating as at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate. Examples of vanadium compounds include vanadium pentoxide (V). ２ O ５ , metavanadate HVO ３ , ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl ３ , vanadium trioxide V ２ O ３ , vanadium dioxide VO ２ , vanadium oxide, vanadium oxysulfate VOSO ４, vanadium oxyacetylacetonate VO(OC(=CH ２ ) CH ２ COCH ３ )) ２ , vanadium acetylacetonate V(OC(=CH ２ ) CH ２ COCH ３ )) ３ , vanadium trichloride VCl ３ Examples include phosphovanadomolybdic acid, etc. Also usable are those obtained by reducing a pentavalent vanadium compound to a tetravalent to divalent form with an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphoric acid group, and a phosphonic acid group.

[0090] A second example of a chemical conversion coating is an inorganic coating, which contains an organosilicon compound (silane coupling agent) as its main component. The organosilicon compound has a cyclic siloxane structure within its structure. Here, "cyclic siloxane bond" refers to a cyclic structure having a continuous Si-O-Si bond, composed only of Si and O bonds, with 3 to 8 Si-O repeating units.

[0091] The organosilicon compound is obtained by blending a silane coupling agent (A) containing at least one amino group in the molecule with a silane coupling agent (B) containing at least one glycidyl group in the molecule in a solids mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound (W) thus obtained preferably contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 each independently represent an alkoxy group or a hydroxyl group, and at least one of R1, R2, and R3 represents an alkoxy group) and one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (if the functional group (a) contains a hydroxyl group, this is separate from the hydroxyl group) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0092] In a second example, the Zr-based component is contained in the chemical conversion coating as a zirconium compound. Examples of zirconium compounds include zirconium hydrofluoric acid, zirconium ammonium fluoride, zirconium sulfate, zirconium oxychloride, zirconium nitrate, and zirconium acetate. Among these, zirconium compounds are preferably zirconium hydrofluoric acid. When zirconium hydrofluoric acid is used, better corrosion resistance and paintability can be obtained.

[0093] The V component is a vanadium compound, the P component is a phosphate compound, and the Co component is at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate, and is contained in the chemical conversion coating. Examples of vanadium compounds include vanadium pentoxide V ２ O ５ , metavanadate HVO ３ , ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl ３ , vanadium trioxide V ２ O ３ , vanadium dioxide VO ２ , vanadium oxide, vanadium oxysulfate VOSO ４ , vanadium oxyacetylacetonate VO(OC(=CH ２ ) CH ２ COCH ３ ) ２ , vanadium acetylacetonate V(OC(=CH ２ ) CH ２ COCH ３ ) ３ , vanadium trichloride VCl ３ Examples include phosphovanadomolybdic acid, etc. Also usable are those obtained by reducing a pentavalent vanadium compound to a tetravalent to divalent vanadium compound with an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphoric acid group, and a phosphonic acid group.

[0094] Examples of the phosphate compound include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate. Among these, phosphoric acid is more preferable as the phosphate compound. When phosphoric acid is used, better corrosion resistance can be obtained.

[0095] The third example of the chemical conversion coating is an inorganic coating, and contains an acrylic resin, zirconium, vanadium, phosphorus, and cobalt. More specifically, the chemical conversion coating contains particulate acrylic resin (resin particles) and an inhibitor phase. The acrylic resin is preferably a resin containing a polymer of a (meth)acrylic acid alkyl ester, and may be a polymer obtained by polymerizing only a (meth)acrylic acid alkyl ester, or a copolymer obtained by polymerizing a (meth)acrylic acid alkyl ester with other monomers. "(Meth)acrylic" means "acrylic" or "methacrylic." The inhibitor phase contains zirconium, vanadium, phosphorus, and cobalt. The zirconium forms a crosslinked structure with the acrylic resin.

[0096] A fourth example of the chemical conversion coating is an inorganic coating, and includes a zirconium carbonate compound, an acrylic resin, a vanadium compound, a phosphorus compound, and a cobalt compound. Examples of the zirconium carbonate compound include zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, and sodium zirconium carbonate, and one or more of these can be used. Among these, zirconium carbonate and ammonium zirconium carbonate are preferred due to their excellent corrosion resistance.

[0097] The acrylic resin is a water-soluble resin or water-based emulsion resin obtained by copolymerizing monomer components containing at least styrene (b1), (meth)acrylic acid (b2), a (meth)acrylic acid alkyl ester (b3), and acrylonitrile (d4), in which the amount of acrylonitrile (b4) is 20 to 38 mass % based on the solid mass of all monomer components of the resin, and which has a glass transition temperature of −12 to 15° C. That is, the acrylic resin is present in the chemical conversion coating in the form of resin particles.

[0098] Examples of vanadium compounds include divalent to tetravalent vanadium compounds, more specifically, vanadium pentoxide (V ２ O ５ ), metavanadic acid (HVO ３ ), ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl ３ ), which are pentavalent vanadium compounds such as vanadium trioxide (V), which are reduced to divalent, trivalent or tetravalent vanadium compounds with a reducing agent, ２ O ３ ), vanadium dioxide (VO ２ ), vanadium oxysulfate (VOSO ４ ), vanadium oxyoxalate [VO(COO) ２ ], vanadium oxyacetylacetonate [VO(OC(CH ３ ) = CHCOCH ３ )) ２ ], vanadium acetylacetonate [V(OC(CH ３ ) = CHCOCH ３ )) ３ ], vanadium trichloride (VCl ３ ), phosphovanadomolybdic acid {H １５ -X [PV １２ -xM ｏｘ O ４０ ]・nH ２ O (6<x<12, n<30)}, vanadium sulfate (VSO ４ ・8H ２ O), vanadium dichloride (VCl ２ and vanadium compounds having an oxidation number of 4 to 2, such as vanadium oxide (VO).

[0099] Examples of phosphorus compounds include inorganic acid anions having an acid group containing phosphorus, and organic acid anions having an acid group containing phosphorus. Examples of inorganic acid anions having an acid group containing phosphorus include inorganic acid anions in which at least one hydrogen atom of an inorganic acid such as orthophosphoric acid, metaphosphoric acid, condensed phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetraphosphoric acid, and hexametaphosphoric acid is liberated, and salts thereof.

[0100] Examples of organic acid anions having a phosphorus-containing acid group include organic acid anions having at least one free hydrogen atom, such as 1-hydroxymethane-1,1-diphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-hydroxypropane-1,1-diphosphonic acid, 1-hydroxyethylene-1,1-diphosphonic acid, 2-hydroxyphosphonoacetic acid, aminotri(methylenephosphonic acid), ethylenediamine-N,N,N',N'-tetra(methylenephosphonic acid), hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic acid), diethylenetriamine-N,N,N',N'',N''-penta(methylenephosphonic acid), 2-phosphonic acid butane-1,2,4-tricarboxylic acid, inositol hexaphosphonic acid, and organic phosphonic acids such as phytic acid, and organic phosphoric acid, and salts thereof.

[0101] Examples of the cobalt compound include cobalt sulfate, cobalt nitrate, and cobalt carbonate.

[0102] A fifth example of the chemical conversion coating is an example of a resin coating, and contains at least one conductive pigment selected from the group consisting of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles. The conductive pigment has a powder resistivity of 7.0×10 at 23 to 27° C. ７ The alloy has a resistivity of Ωcm or less and contains at least one element selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W as a constituent element.

[0103] Examples of intermetallic compounds include ferrosilicon and ferromanganese. Examples of conductive oxide particles include doped conductive oxides, which are made conductive by doping impurities into the oxide crystal lattice, and oxide particles whose surfaces are modified with a conductive substance. Examples of the former include commonly known metal oxides doped with one or more metal elements selected from Al, Nb, Ga, Sn, etc. (e.g., Al-doped zinc oxide, Nb-doped zinc oxide, Ga-doped zinc oxide, Sn-doped zinc oxide, etc.). Examples of the latter include commonly known zinc oxides or silica modified with SnO2, which provides conductivity to the oxide. Doped conductive oxides are preferred as conductive oxides, and Al-doped zinc oxide is a preferred doped conductive oxide.

[0104] The conductive non-oxide ceramic particles are composed of ceramics made of oxygen-free elements or compounds. Examples of conductive non-oxide ceramic particles include boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics. Furthermore, boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics are non-oxide ceramics whose main non-metallic constituent elements are boron (B), carbon (C), nitrogen (N), and silicon (Si), respectively. These commonly known non-oxide ceramics may contain one or more elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, and W. Furthermore, the non-oxide ceramic particles are more preferably the following non-oxide ceramics in terms of availability as industrial products, stable distribution in domestic and international markets, price, electrical resistivity, and the like. For example, Mo ２ B, MoB, MoB ２ , Mo ２ B ５ , NbB ２ , VB, VB ２ , W ２ B ５ , ZrB ２ , Mo ２ C.V. ２ C, VC, WC, W ２ C, ZrC, Mo ２N, VN, ZrN, Mo ３ Si, Mo ５ Si ３ , MoSi ２ , NbSi ２ , Ni ２ Si, Ta ２ Si, TaSi ２ , TiSi, TiSi ２ , V ５ Si ３ , VSi ２ , W ３ Si, WSi ２ , ZrSi, ZrSi ２ , CrB, CrB ２ , Cr ３ C ２ , Cr ２ More preferred are particles of N, CrSi, and particles of a mixture of two or more selected from these.

[0105] The sixth example of the chemical conversion treatment film is a resin film, which includes a resin having urethane bonds and conductive particles (conductive pigments). The resin having urethane bonds is an organic resin obtained from a film-forming resin raw material that includes (a) a polyester polyol having at least three functional groups, and (b) a blocked product of an organic polyisocyanate or a blocked product of a prepolymer having NCO groups at its terminals, which is obtained by reacting an organic polyisocyanate with an active hydrogen compound.

[0106] (a) The polyester polyol having a functionality of at least 3 can be obtained by esterifying a dicarboxylic acid, a glycol, and a polyol having at least 3 OH groups.

[0107] Examples of dicarboxylic acids used in the production of polyester polyols include aliphatic dicarboxylic acids such as succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, dodecanoic diacid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, and dimer acid; and aromatic and alicyclic dicarboxylic acids such as phthalic acid, phthalic anhydride, isophthalic acid, isophthalic acid dimethyl ester, terephthalic acid, terephthalic acid dimethyl ester, 2,6-naphthalenedicarboxylic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, cyclohexanedicarboxylic acid, cyclohexanedicarboxylic acid dimethyl ester, methylhexahydrophthalic anhydride, himic anhydride, and methyl himic anhydride.

[0108] Examples of glycols include ethylene glycol, diethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, dipropylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, neopentyl glycol ester of hydroxydivalinic acid, triethylene glycol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,4-diethyl-1,5-pentanediol, polycaprolactone diol, and polypropylene glycol. Examples of the polyol include aliphatic ones such as glycol, polytetramethylene ether glycol, polycarbonate diol, 2-n-butyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol; and aliphatic or aromatic ones such as cyclohexanedimethanol, cyclohexanediol, 2-methyl-1,1-cyclohexanedimethanol, xylylene glycol, bishydroxyethyl terephthalate, 1,4-bis(2-hydroxyethoxy)benzene, hydrogenated bisphenol A, an ethylene oxide adduct of bisphenol A, and a propylene oxide adduct of bisphenol A.

[0109] Examples of polyols having at least three OH groups include glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, pentaerythritol, diglycerin, and ethylene oxide adducts, propionoxide adducts, and ε-caprolactone adducts using these polyols as initiators.

[0110] Examples of the blocked compounds of (b) include compounds having at least two NCO groups, such as aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, and 2,6-diisocyanatomethyl caproate. and, for example, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylhexyl isocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, cycloalkylene diisocyanates such as (methyl)cyclohexane and trans-cyclohexane-1,4-diisocyanate; and diisocyanates such as m-xylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, aromatic diisocyanates such as isocyanate, for example, ω,ω'-diisocyanato-1,3-dimethylbenzene, ω,ω'-diisocyanato-1,4-dimethylbenzene, ω,ω'-diisocyanato-1,4-diethylbenzene, α,α,α',α'-tetramethylmetaxylylene diisocyanate, and aromatic aliphatic diisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, ω-isocyanatoethyl-2,Examples of such blocked compounds include triisocyanates such as 6-diisocyanatocaproate, blocked compounds of tetraisocyanates such as 4,4'-diphenylmethylmethane-2,2',5,5'-tetraisocyanate, blocked compounds of derivatives of isocyanate compounds such as dimers, trimers, biurets, allophanates, carbodiimides, polymethylene polyphenyl polyisocyanates (crude MDI, c-MDI, polymeric MDI), and crude TDI, and blocked compounds of prepolymers having NCO groups at their terminals obtained by reacting these compounds with active hydrogen compounds.

[0111] The conductive particles are corrosion-resistant particles that are alloys or compounds containing 50% by mass or more of Si, or composites thereof. The conductive particles are preferably ferrosilicon. Anti-rust pigments may also be added to the chemical conversion coating. Examples of anti-rust pigments include well-known anti-rust pigments, such as hexavalent chromates such as strontium chromate and calcium chromate. If it is desired to avoid the use of hexavalent chromium compounds as anti-rust agents, those that release one or more of silicate ions, phosphate ions, and vanadate ions can be used.

[0112] Of course, examples of the chemical conversion coating of this embodiment are not limited to those described above, and for example, the chemical conversion coatings listed in the examples described below can also be suitably used.

[0113] The method for forming the above-mentioned chemical conversion coating is not particularly limited, and it is sufficient to apply a chemical conversion treatment solution (coating treatment solution) corresponding to each of the above compositions to a Zn-based plated steel sheet by a known method, followed by baking and drying. One example of a preferred combination of a Zn-based plated steel sheet and a chemical conversion coating is a combination of a Zn—Al—Mg plated steel sheet and an inorganic coating containing a Si-based component as a main component.

[0114] The present disclosure will be described in more detail below with reference to examples. Note that the examples described below are merely examples of the present disclosure and are not intended to limit the present disclosure.

[0115] <Material Preparation> Steel having the steel composition shown in Table 1 (the balance being iron and impurities) as an ultra-low carbon steel with excellent workability was hot-rolled, pickled, and cold-rolled to prepare a cold-rolled steel sheet with a thickness of 0.6 mm. Next, the cold-rolled steel sheet was subjected to hot-dip Al plating in a non-oxidation furnace type continuous hot-dip plating line to obtain an Al-based plated steel sheet. A non-oxidation furnace-reducing furnace type plating line was used, and annealing was also performed in this hot-dip plating line. The annealing temperature was 850°C.

[0116]

[0117] After plating, the plating thickness is reduced to approximately 40 g / m on both sides using the gas wiping method. ２ The temperature of the plating bath during hot dip plating was 660° C. The plating bath used was a molten Al bath to which Si was added as needed.

[0118] In the present examples, a steel sheet plated in a molten Al bath to which no Si has been added will also be referred to as a "pure Al-plated steel sheet," a steel sheet plated in a molten Al bath to which 2% by mass of Si has been added will also be referred to as an "Al-2% Si-plated steel sheet," a steel sheet plated in a molten Al bath to which 9% by mass of Si has been added will also be referred to as an "Al-9% Si-plated steel sheet," a steel sheet plated in a molten Al bath to which 15% by mass of Si has been added will also be referred to as an "Al-15% Si-plated steel sheet," and a steel sheet plated in a molten Al bath to which 20% by mass of Si has been added will also be referred to as an "Al-20% Si-plated steel sheet."

[0119] Next, a chemical conversion treatment solution was applied to the surface of the Al-plated steel sheet as needed using a roll coater. The amount of applied chemical conversion treatment solution was adjusted by adjusting the rotation speed of the roll coater and the pressure between the rolls (generally called nip pressure). The amount of applied chemical conversion treatment solution was 500 mg / m2 per side in dry weight. ２ After the chemical conversion treatment solution was applied, the chemical conversion treatment solution was dried in a hot air oven under conditions such that the ultimate sheet temperature became 80° C. The chemical conversion treatment was performed on both sides of the Al-based plated steel sheet.

[0120] The chemical conversion treatment solutions used for coating were three types: an aqueous solution containing 2.5 g / L of γ-aminopropyltriethoxysilane, which is a Si-based chemical conversion treatment solution; an aqueous solution containing 3 g / L of ammonium zirconium carbonate, which is a Zr-based chemical conversion treatment solution; and an aqueous solution containing 40 g / L of ammonium titanium (IV) fluoride, which is a Ti-based chemical conversion treatment solution. Details of the Al-based plated steel sheets produced are shown in Table 4.

[0121] Furthermore, the cold-rolled steel sheet that had undergone the above-described steps up to cold rolling was annealed in a continuous hot-dip galvanizing apparatus capable of annealing under conditions where the maximum sheet temperature reached was 820°C, and then hot-dip galvanized to prepare a hot-dip galvanized steel sheet (Zn-based coated steel sheet). Here, the gas atmosphere in the annealing furnace in the annealing step was 1.0% by volume of H ２ N including ２ The plating bath used in the plating step was composed of four different components: Zn-0.2% by mass Al (hereinafter also referred to as "GI"), Zn-0.09% by mass Al (hereinafter also referred to as "GA"), Zn-6% by mass Al-3% by mass Mg (hereinafter also referred to as "Zn-Al-Mg"), and Zn-11% by mass Al-3% by mass Mg-0.2% by mass Si (hereinafter also referred to as "Zn-Al-Mg-Si").

[0122] In the case of hot-dip galvanizing using a hot-dip galvanizing bath containing Zn-0.09 mass% Al (GA), alloyed hot-dip galvanizing was performed by the following steps: The steel sheet was immersed in the hot-dip galvanizing bath. Then, while the steel sheet was being withdrawn from the bath, N ２ The coating weight was adjusted by gas wiping with gas spraying, and then alloying was carried out by heating the steel sheet at a sheet temperature of 480°C using an induction heater, thereby diffusing Fe in the steel sheet into the coating layer.

[0123] The coating weight of the plated steel sheet was 45 g / m2 per side of the steel sheet. ２ , 60g / m for plating other than GA ２ For comparison, a cold-rolled steel sheet was also prepared that was not plated but was only annealed in a continuous annealing line.

[0124] Next, a chemical conversion treatment solution (film treatment solution) was applied to the surface of the zinc-based plated steel sheet prepared in the above process using a roll coater, as needed. The amount of chemical conversion treatment solution applied (i.e., the film thickness of the chemical conversion treatment film) was controlled by adjusting the rotation speed of the roll coater and the pressure between the rolls (commonly called nip pressure). In this way, a chemical conversion treatment film of a predetermined film thickness was formed on the plated steel sheet.

[0125] When the chemical conversion coating was an inorganic coating, the chemical conversion coating solution was applied and then dried in a hot air oven under conditions where the ultimate sheet temperature reached 80°C. When the chemical conversion coating was a resin coating, Palcoat E200 (manufactured by Nippon Parkerizing Co., Ltd.) was applied to the plated steel sheet using a roll coater as a pretreatment to improve adhesion to the plated steel sheet before applying the chemical conversion coating solution to the plated steel sheet, and then dried in a hot air oven under conditions where the ultimate sheet temperature reached 80°C. Subsequently, the chemical conversion coating solution was applied to a predetermined film thickness using a roll coater, and then dried in a hot air oven under conditions where the ultimate sheet temperature reached 200°C. The chemical conversion coating was applied to both sides of the plated steel sheet. The film thickness after coating and drying of each coating was measured by embedding the coated steel sheet in resin, polishing it so that the vertical cross section could be observed, and observing it with a scanning electron microscope. The optimal magnification for observation with the scanning electron microscope was selected appropriately depending on the film thickness.

[0126] In addition, samples prepared with inorganic coatings having a thickness exceeding 1.5 μm after application and drying showed cracks or detachment in the coatings in all treatment solutions, making it impossible to obtain uniformly formed coatings, and therefore it was determined that it was difficult to produce inorganic coatings with a thickness exceeding 1.5 μm. Details of the steel sheets prepared by coating various plated steel sheets with coatings are shown in Table 4.

[0127] <Method for preparing inorganic chemical conversion treatment solution> An inorganic chemical conversion treatment solution (chemical conversion treatment solution for forming an inorganic coating) was prepared using the following process. That is, an aqueous solution containing 10 g / L of γ-aminopropyltriethoxysilane was prepared as an inorganic chemical conversion treatment solution containing a Si-based component as the main component. 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were further added to the prepared γ-aminopropyltriethoxysilane aqueous solution as needed to prepare an inorganic chemical conversion treatment solution.

[0128] Furthermore, an aqueous solution containing 3.0 g / L of ammonium zirconium carbonate was prepared as an inorganic chemical conversion treatment solution containing a Zr-based component as the main component. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added to the prepared aqueous solution of ammonium zirconium carbonate as needed to prepare an inorganic chemical conversion treatment solution. Details of the prepared inorganic chemical conversion treatment solution are shown in Table 2.

[0129] Furthermore, an aqueous solution containing 40 g / L of ammonium titanium (IV) fluoride, a Ti-based chemical conversion treatment solution, was prepared. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added to the prepared aqueous solution of ammonium zirconium carbonate as needed to prepare an inorganic chemical conversion treatment solution. Details of the inorganic chemical conversion treatment solutions prepared are shown in Table 2.

[0130]

[0131] Whether or not the inorganic coating contains Si—O bonds and the like was confirmed by the following method. That is, the prepared inorganic conversion treatment solution was applied to one of the plated steel sheets prepared above using a wire bar, and then dried under conditions that resulted in a sheet temperature of 80°C. In this way, an inorganic coating was formed on the plated steel sheet. Next, the coating surface was measured using an IRT-5200 manufactured by JASCO Corporation, and it was determined whether or not the inorganic coating contained one or more of Si—O bonds, Si—C bonds, and Si—OH bonds based on the assignment of observed peaks derived from resin components in the infrared absorption spectrum of the obtained inorganic coating. Specifically, －１ Near 1080-1020 cm －１ Near 500-300 cm －１ Near 900-700 cm －１ When a peak was observed in at least one of the vicinity, it was determined that the inorganic coating contained one or more of Si—O bonds, Si—C bonds, and Si—OH bonds. The determination results are shown in Table 2.

[0132] <Method for preparing a resin-based chemical conversion treatment solution> A resin-based chemical conversion treatment solution (a chemical conversion treatment solution for forming a resin film) was prepared using the following steps. Specifically, a polyester resin, "Vylon® 300" manufactured by Toyobo Co., Ltd., was dissolved in cyclohexanone as a solvent at 30% by mass. 20 parts by mass of melamine resin "CYMEL® 303" manufactured by Allnex Corporation was added to 100 parts by mass of the solid content of this solution and mixed. Furthermore, 5% by mass of curing catalyst "CYCAT® 600" manufactured by Allnex Corporation was added to the total solid content of the prepared mixture and mixed. In this way, a base treatment solution for obtaining a resin film was prepared.

[0133] Next, the particles shown below were mixed with the prepared base treatment liquid to prepare a resin-based chemical conversion treatment liquid. The amount of particles added was adjusted in the following manner. That is, the mass ratio of the solid content of the particles added to the base treatment liquid in the resin film (mass ratio to the solid content other than the particles) was determined, and the volume ratio was calculated from the specific gravity of the solid content of the resin film and the specific gravity of the particles. Next, the amount of particles added was adjusted so that the calculated volume ratio was the volume ratio listed in Table 3. The specific gravity was determined from the catalog value or literature value for each substance. Table 3 shows details of the resin-based treatment liquid.

[0134]

[0135] Vanadium boride: "VB" manufactured by Nippon Shinkinzoku Co., Ltd. ２ -O" was classified using a sieve to have an average particle size of 3.1 μm. ２". The average particle size was calculated based on the mass percentage of each classified particle size fraction. Al-doped zinc oxide: Conductive zinc oxide (Al-doped ZnO) "23-K" manufactured by Hakusui Tech Co., Ltd., with a primary particle size of 120 to 250 nm (catalog value), was used. Hereinafter, this will also be referred to as "Al-ZnO." Metallic zinc: Reagent zinc particles were sieved to an average particle size of 10 μm, and used. Hereinafter, this will also be referred to as "Zn." Ferrosilicon: Ferrosilicon manufactured by Marubeni Tetsugen Co., Ltd. was crushed into fine particles using a crusher, and then classified using a crusher to an average particle size of 3.5 μm, and used. Hereinafter, this will also be referred to as "Fe-Si." Ferromanganese: Ferrosilicon manufactured by Marubeni Tetsugen Co., Ltd. was crushed into fine particles using a crusher, and then classified using a crusher to an average particle size of 3.5 μm, and used. Hereinafter, this will also be referred to as "Fe-Mn." Zirconium boride: "ZrB" manufactured by Nippon Shinkinzoku Co., Ltd. ２ -O" was classified using a sieve to have an average particle size of 2 μm. ２ " Molybdenum silicide: "MoSi" manufactured by Nippon Shinkinzoku Co., Ltd. ２ "MoSi -F" was classified using a sieve to have an average particle size of 3.5 μm. ２ Chromium boride: "CrB" manufactured by Nippon Shinkinzoku Co., Ltd. ２ -O" was classified using a sieve to have an average particle size of 5 μm. ２ " Tungsten silicide: "WSi" manufactured by Nippon Shinkinzoku Co., Ltd. ２ -F" was classified using a sieve to have an average particle size of 2 μm. ２" Nickel: Reagent nickel powder was used, classified using a sieve to an average particle size of 5 μm. Hereinafter referred to as "Ni." Conductive titanium oxide: Sn-doped titanium oxide "ET-500W" manufactured by Ishihara Sangyo Kaisha, Ltd., with an average particle size of 2 to 3 μm (catalog value), was used. Hereinafter referred to as "conductive Ti." Alumina: Fine alumina "A-42-2" manufactured by Showa Denko K.K., with an average particle size (median diameter of particle size distribution) of 4.7 μm (catalog value), was used. Hereinafter referred to as "alumina." Titanium oxide: "Tipake(R) CR-95" manufactured by Ishihara Sangyo Kaisha, with an average particle size of 0.28 μm (catalog value), was used. Hereinafter referred to as "TiO2." Aluminum nitride: Aluminum nitride powder for filler manufactured by Tokuyama Corporation, with a particle size of 1 μm (catalog value), was used. Hereinafter referred to as "AlN."

[0136] The powder resistivity of the particles in Table 3 was determined as the resistance value when each powder was compressed at 25° C. under 10 MPa using a powder resistivity measurement system MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd.

[0137] <Evaluation of Prepared Metal Sheets> (1. Evaluation of Coolant Corrosion Resistance) The coolant corrosion resistance of the prepared steel sheets was investigated when used in a cooling structure (cooling device) for a battery unit. Specifically, the prepared Al-based plated steel sheets and Zn-based plated steel sheets were subjected to Erichsen processing to produce cup-shaped cylindrical processed products with a diameter of 50 mm and a drawing height of 40 mm. 30 mL of coolant was added to the inside of the cylindrical processed product, which was then sealed with a lid. The coolant used was an aqueous solution prepared by diluting a long-life coolant solution manufactured by Nissan Motor Co., Ltd. with water to 30% by mass. These were left in a constant temperature bath at 90°C for 1,000 hours to accelerate deterioration of the steel sheets immersed in the coolant. Additionally, assuming deterioration of the coolant, a similar test was also conducted using a deteriorated solution prepared by adding 800 ppm of formic acid to a 30% by mass aqueous solution of the long-life coolant solution. After the test, the coolant immersed in the cylindrical workpiece was removed and the cylindrical workpiece was dried. The corrosion state of the coolant immersed part was then observed, and the coolant corrosion resistance was evaluated according to the following criteria. The results are shown in Tables 4 and 5.

[0138] The coolant corrosion resistance in Tables 4 and 5 was rated as follows: 5 points: No change in appearance. 4 points: Discolored to black or dotted white rust has occurred. 3 points: White rust has occurred, but the area of ​​white rust in the coolant-immersed parts is less than 20% of the total area of ​​the coolant-immersed parts. 2 points: White rust occurrence rate is 20% or more but less than 80%. 1 point: White rust occurrence rate is 80% or more, or red rust has occurred.

[0139] (2. External Corrosion Resistance Test) An external corrosion resistance test was conducted to evaluate the external corrosion resistance of the battery unit (including the cooling structure) at the portion exposed to the outside air. Since electrodeposition coating is generally applied to the portion exposed to the outside air, in the present disclosure, the external corrosion resistance after electrodeposition coating was evaluated.

[0140] Specifically, the prepared steel plate was cut into a size of 70 mm wide x 150 mm long, and the resulting steel billets were degreased, surface-conditioned, zinc phosphate-treated, and then electrodeposited. Specifically, the steel billets were degreased by immersing them in a degreasing agent "Fine Cleaner E6408" manufactured by Nippon Parkerizing Co., Ltd. at 60°C for 5 minutes. The degreased steel billets were surface-conditioned by immersing them in "Preparen X" manufactured by Nippon Parkerizing Co., Ltd. at 40°C for 5 minutes. Subsequently, the steel billets were zinc phosphate-treated by immersing them in a zinc phosphate conversion agent "Palbond L3065" manufactured by Nippon Parkerizing Co., Ltd. at 35°C for 3 minutes. After the zinc phosphate treatment, the steel billets were washed with water and dried in an oven at 150°C. Subsequently, the steel billets were electrodeposited with an electrodeposition paint "Power Float 1200" manufactured by Nippon Paint Co., Ltd. at a thickness of 15 μm per side and baked in an oven at 170°C for 20 minutes. The electrodeposition coated steel pieces prepared by the above steps were cut with a cutter knife to prepare test pieces.

[0141] A cyclic corrosion test (CCT) was carried out using the prepared test specimens. The CCT mode was carried out in accordance with the automotive industry standard JASO-M609. The surface of the electrodeposition coating film with cut scratches was used as the evaluation surface, and the test specimens were placed in a testing machine so that salt water was sprayed onto the evaluation surface, and the cyclic corrosion test was carried out.

[0142] The test was carried out for 120 cycles (one cycle lasting 8 hours), and the state of corrosion from the cut was observed to evaluate the external corrosion resistance according to the following criteria. The results are shown in Tables 4 and 5. The external corrosion resistance in Tables 4 and 5 was evaluated as follows: 5 points: When the paint film blister width from the cut was 15 mm or less and no red rust occurred. 4 points: When the paint film blister width from the cut was more than 15 mm but not more than 20 mm and no red rust occurred. 3 points: When the paint film blister width from the cut was more than 20 mm and no red rust occurred. 2 points: When slight red rust occurred from the cut. 1 point: When red rust occurred over the entire cut area.

[0143] (3. Workability Evaluation) Bending tests were performed using the prepared Al-based plated steel sheets and Zn-based plated steel sheets. In particular, if cracks occur on the surface when the plated steel sheets are processed, the plating layer breaks and the iron base is exposed to the outside air. Therefore, depending on the processed shape, corrosion may be more likely to occur from the processed area, so workability was evaluated. Specifically, the prepared Al-based plated steel sheets were subjected to 180° close bending, and the processed area was checked with a 20x magnifying glass to visually evaluate the workability. Specifically, the workability was evaluated based on whether or not cracks occurred on the surface. The results are shown in Tables 4 and 5. In Tables 4 and 5, "-" indicates that this evaluation was not performed because the steel sheets were Zn-based plated.

[0144]

[0145]

[0146] <Evaluation of Cooling Characteristics and Adhesion Durability in Battery Pack> (1. Preparation of Battery Pack) A battery unit was prepared using the prepared steel sheet (Steel Sheet No. 4 in Table 4) and A6063 aluminum alloy. Specifically, this steel sheet was cut into flat plates to form the battery pack case top cover (top surface) 10c and the above-mentioned flow path top cover 26. A separately prepared steel sheet was deep-drawn into a square cylinder using a press, and the flanges were cut off after processing to form the other parts of the battery pack (bottom surface and side surface). The bottom surface of the battery pack was also processed to have a width of 375 mm and a length of 1060 mm. Rust-preventive oil was applied to the Al-plated steel sheet during processing, and the oil was removed by alkaline degreasing after processing.

[0147] The cooling structure was fabricated by die-casting A6063 aluminum to form a flow path. The number of flow paths, the flow path width (L), and the distance between flow paths (w) in the cooling structure were set to the values ​​shown in Tables 7 and 8.

[0148] Next, adhesive was applied to the joint of the cooling structure, and the cooling structure and the channel upper cover were overlapped. The adhesives used were "ThreeBond 2249G" (manufactured by ThreeBond Fine Chemical Co., Ltd.) for the epoxy adhesive, "ThreeBond 1207B" (manufactured by ThreeBond Fine Chemical Co., Ltd.) for the silicone adhesive, "Metal Grip" (manufactured by 3M Japan Ltd.) for the acrylic adhesive, and "ThreeBond 1539" (manufactured by ThreeBond Fine Chemical Co., Ltd.) for the urethane adhesive. After bonding, the adhesive was applied and bonded to the thickness (D30) and overhang length (L23) shown in Tables 7 and 8. The adhesive was then cured according to the curing conditions of each adhesive. Table 6 shows the main resin content and hardness after curing of each adhesive.

[0149]

[0150] Next, rubber heaters were placed inside the battery pack as a substitute for the battery cells, and the case was then covered with a lid. When the lid was closed, a sealant was applied to the case flange to seal the case. The sealant used was "Sealant 45N" manufactured by Shin-Etsu Silicone Co., Ltd.

[0151] (2. Battery Pack Cooling Characteristic Evaluation Test) The battery pack was heated by passing a current through the rubber heater of the fabricated battery pack. The current value at which the surface temperature of the rubber heater reached 50°C was determined in advance, and this current value was set as a fixed value and passed through the rubber heater. Next, a coolant was passed through the water coolant flow path. The coolant was an aqueous solution prepared by diluting Nissan Motor Co.'s long-life coolant liquid with water to 30% by mass. Hoses, pumps, and chillers were attached to the ends of the flow paths on both sides of the cooling structure to form a circulation path, and the coolant was circulated through this circulation path. The chiller was controlled to maintain the coolant temperature at 25-30°C. The surface temperature of the rubber heater inside the case, directly above the midpoint between the cooling flow paths, was measured one hour after the start of the coolant circulation. In the "cooling capacity" category, a temperature drop of 8°C or more compared to when coolant was not circulating was evaluated as "A," a temperature drop of 2°C or more but less than 8°C was evaluated as "B," and a temperature drop of less than 2°C was evaluated as "C." The battery pack cooling characteristic evaluation test was conducted in an air-conditioned room maintained at 25°C. The results are shown in Tables 7 and 8. In Tables 7 and 8, "-" indicates a level where the flow path was not established due to insufficient bonding strength.

[0152]

[0153]

[0154] (3. Battery Pack Bonding Strength Evaluation Test) To evaluate the bonding strength of the battery pack, the bonding portion of the cooling structure was cut out and subjected to a peel tensile test. In the category of "bonding strength," a peel tensile strength of 1.0 kN / m or more was rated "A," 0.2 kN / m or more but less than 1.0 kN / m was rated "B," and less than 0.2 kN / m was rated "C."

[0155] Furthermore, after circulating cooling water through the fabricated cooling structure for 1,000 hours, the bonded portion of the cooling structure was cut out and subjected to a peel tensile test. In the "bond strength retention" category, a bond strength retention of 60% or more before and after cooling water circulation was rated "A," 60% or more but less than 20% was rated "B," and less than 20% was rated "C." The results are shown in Tables 7 and 8. In Table 8, "-" indicates a level where the bond strength was insufficient and the structure was not viable as a flow path.

[0156] As shown in Tables 4, 5, 7, and 8, the examples of the present invention that met the requirements of this embodiment achieved excellent results in all evaluation items. Therefore, it was found that the cooling structure according to this embodiment has excellent strength and erosion resistance at the joint between dissimilar metals.

[0157] In contrast, in comparative examples that do not satisfy the requirements of this embodiment, such as those that are not plated, poor results were obtained in some of the evaluation items.

[0158] 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 these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0159] The cooling structure and battery unit according to the present disclosure can provide a cooling structure that has excellent strength and erosion resistance at the joints between dissimilar metals, and is therefore extremely useful industrially.

[0160] REFERENCE SIGNS LIST 1 Cooling structure 10 Battery pack 21 Flow path forming portion 22 Joint portion 23 Protruding portion 25 Water coolant flow path 26 Flow path upper cover 30 Adhesion portion

Claims

1. A cooling structure having a water refrigerant flow path formed to contact a bottom surface of a battery pack, the cooling structure having a flow path forming portion constituting a part of the water refrigerant flow path, the flow path forming portion being joined to a joined member by an adhesive portion, the joined member being either the bottom surface or a flow path top cover covering the flow path forming portion, the joined member being made of a steel plate having an inorganic coating or a resin coating formed as a chemical conversion coating on an Al-based plated steel plate or a Zn-based plated steel plate, the flow path forming portion being made of an aluminum alloy, the adhesive portion having a thickness of 0.0005 mm or more and protruding 0.1 mm or more into the water refrigerant flow path side, the flow path spacing between the water refrigerant flow paths is 20 mm or less, and the water refrigerant flow path has a width of 60 mm or less.

2. The cooling structure according to claim 1, characterized in that the plating layer of the Al-based plated steel sheet contains Si.

3. The cooling structure described in claim 2, characterized in that the Si content of the plating layer of the Al-based plated steel sheet is 2.0 mass % or more and 15 mass % or less.

4. A cooling structure as described in claim 1 or 2, characterized in that a coating containing a Zr-based component, a Ti-based component or a Si-based component as a main component is formed on the surface of the Al-plated steel sheet as a chemical conversion coating.

5. The cooling structure according to claim 1, wherein the inorganic coating on the surface of the Zn-based plated steel sheet contains a Si-based component or a Zr-based component as a main component.

6. The cooling structure according to claim 1, wherein the inorganic coating on the surface of the Zn-based plated steel sheet contains at least one of V, P and Co as an anti-rust component.

7. The cooling structure according to claim 6, wherein the rust-preventive component is at least one of vanadium oxide, phosphoric acid, and cobalt nitrate.

8. The cooling structure according to claim 1, wherein the inorganic coating on the surface of the Zn-based plated steel sheet is composed of a compound phase containing one or more of Si-O bonds, Si-C bonds, and Si-OH bonds.

9. The cooling structure according to claim 1, characterized in that the thickness of the inorganic coating is greater than 0 μm and not greater than 1.5 μm.

10. The cooling structure according to claim 1, wherein the inorganic film or the resin film is electrically conductive.

11. The cooling structure according to claim 1, wherein the resin coating contains a resin, an anti-rust pigment, and a conductive pigment.

12. The cooling structure according to claim 11, wherein the resin coating contains at least one of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles as the conductive pigment, and the conductive pigment has a powder resistivity of 7.0 x 107 Ω cm or less at 23 to 27°C and contains at least one element selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W.

13. A cooling structure as described in claim 11 or 12, characterized in that the resin coating contains the conductive pigment in a proportion of 1.0 mass % or more and 30 mass % or less.

14. The cooling structure according to claim 1, characterized in that the adhesive portion contains 10% or more of any one of epoxy resin, silicone resin, acrylic resin and urethane resin.

15. The cooling structure according to claim 1, characterized in that the hardness of the adhesive joint is not less than A15 and not more than D90.

16. A battery unit comprising the cooling structure according to claim 1 or 2 and a battery pack.