Joint and joining method

Abstract

To provide a joined body of aluminum-based material and different material which has sufficient joint strength and is formed by high pressure die casting.SOLUTION: Provided is a joined body in which a first member made of an aluminum-based material formed by high-pressure die casting (HPDC) and a second member made of material different from that of the first member are joined to each other, in which the first member has a melted and solidified portion which is solidified after melting and has a gas content lower than that of an unmelted portion, and the first member has a joint portion to be joined to the second member on one end side of the melted and solidified portion.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a joined body and a joining method.

Background Art

[0002] In recent years, reduction of CO2 emissions and improvement of energy efficiency have been demanded. As one of the means, reduction of the weight of various members can be cited. As a means for reducing the weight of a member, for example, a means of adopting a dissimilar material joined member in which a part of a member made of a relatively high-strength and high-weight material such as a steel plate is replaced with a relatively lightweight material such as aluminum or magnesium can be cited.

[0003] As a technique for joining dissimilar materials, a method of composite welding an aluminum-based weldment and an iron-based weldment without using a brazing material and a flux has been disclosed (see Patent Document 1). Further, a laser welding method has been disclosed in which a plurality of metal plates including at least one metal plate having a surface treatment layer formed thereon are overlapped, and a laser that scans along the welding shape of each metal plate is irradiated to each metal plate to melt each metal plate and vaporize the surface treatment layer to join each metal plate (see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, aluminum-based materials formed by high-pressure die casting (HPDC) (hereinafter sometimes referred to as "HPDC aluminum") are known as materials to be welded. High-pressure die casting is a manufacturing process in which molten metal is supplied to a mold and solidified to obtain the desired part. It is widely used because it has advantages such as the ability to realize complex shapes and high production efficiency. On the other hand, HPDC aluminum generally has a high gas (hydrogen, etc.) content, so a large number of blowholes (pores) occur in the welded area. Therefore, there is a problem in that sufficient joint strength cannot be obtained when joining dissimilar materials.

[0006] Reference 1 discloses a method using a first heat source that heats the surface of an iron-based welded material by irradiating it from the aluminum-based welded material side, and a second heat source that heats the surface of the aluminum-based welded material in the overlapping section. The first heat source melts only the zinc-based coating layer near the end of the overlapping section, and then the second heat source melts the zinc-based coating layer and the aluminum-based welded material in the overlapping section. However, when this method is applied to HPDC aluminum material, the heat source that melts the zinc-based coating layer cannot melt the HPDC aluminum material, and the gas-rich state cannot be resolved. If a heat source capable of melting HPDC aluminum material is used, the melting point of aluminum decreases as the HPDC aluminum material and the zinc-based coating layer melt near the overlapping section. This may lead to the inflow of aluminum into the newly formed surface, potentially generating an excessive amount of intermetallic compounds.

[0007] The technology described in reference 2 describes a method for removing blowholes that occur when the plating layer vaporizes during welding, but it does not describe a means for removing gases present in the substrate.

[0008] The present invention has been made in view of the above, and aims to provide a joint between an aluminum-based material formed by high-pressure die casting and a dissimilar material that has sufficient joint strength. [Means for solving the problem]

[0009] (1) A joint comprising a first member made of an aluminum-based material formed by high-pressure die casting (HPDC) and a second member made of a different material from the first member, wherein the first member has a molten and solidified portion that is solidified after melting and has a lower gas content than the unmolten portion, and the first member has a joint portion that is joined to the second member on one end side of the molten and solidified portion.

[0010] According to the invention of (1), it is possible to provide a joint between an aluminum-based material formed by high-pressure die casting and a dissimilar material that has sufficient joint strength.

[0011] (2) The joint according to (1), wherein the second member is made of iron and comprises a base material and a plating layer formed on the surface of the base material, the boiling point of the plating layer is higher than the melting point of the base material, and the joint is joined to a solid solution layer in which at least a portion of the material constituting the plating layer is solidly dissolved in the base material.

[0012] According to invention (2), since the HPDC aluminum material is joined to the solid solution layer, it becomes a weld between aluminum and iron, and therefore a joined body can be easily formed compared to the case of direct welding to the plating layer.

[0013] (3) The joint according to (1) or (2), wherein the first member and the second member are separated at least a portion on the joint side of the portion other than the joint.

[0014] According to the invention of (3), it is possible to suppress the decrease in joint strength caused by the formation of excessive intermetallic compounds during manufacturing, which occurs when a portion of the molten and solidified part flows into the solid solution layer.

[0015] (4) The joint according to any one of (1) to (3), wherein the first member has a stepped shape formed such that the cross-sectional area of ​​one end is smaller than the cross-sectional area of ​​the other end.

[0016] According to the invention of (4), it is possible to suppress the decrease in joint strength caused by the formation of excessive intermetallic compounds during manufacturing, which occurs when a portion of the molten and solidified portion flows into the solid solution layer.

[0017] (5) A joining method for joining a first member which is an aluminum-based material formed by high-pressure die casting (HPDC) and a second member which is made of a different material from the first member, comprising: a first step of melting one end of the first member; and a second step of melting the end of the first member further toward the end of the first member than the first molten portion melted in the first step, wherein the second molten portion melted in the second step of the first member is joined to the second member.

[0018] According to the invention of (5), it is possible to manufacture a joint between an aluminum-based material formed by high-pressure die casting and a dissimilar material that has sufficient joint strength.

[0019] (6) The joining method according to (5), wherein the second member is made of iron and comprises a base material and a plating layer formed on the surface of the base material, the boiling point of the plating layer is higher than the melting point of the base material, the first step is to form a solid solution layer by solid dissolving at least a portion of the material constituting the plating layer in the base material, and the second step is to join the second molten part with the solid solution layer.

[0020] According to the invention of (6), the HPDC aluminum material is joined to the solid solution layer, resulting in a weld between aluminum and iron. This makes it easier to create a joined body compared to welding to a plating layer. Furthermore, by simultaneously melting the plating layer and forming the first molten section in the first step, dissimilar welding between a high-melting-point plating material and an HPDC aluminum material, which is difficult to weld, can be performed in just two melting steps.

[0021] (7) The joining method according to (6), wherein the second step is to join the second molten portion with the solid solution layer after the surface temperature of the solid solution layer has fallen below its melting point.

[0022] According to the invention of (7), it is possible to suppress the excessive formation of intermetallic compounds between the iron material and the aluminum material.

Brief Description of the Drawings

[0023] [Figure 1] It is a cross-sectional view showing an overview of the joined body according to the first embodiment. [Figure 2] It is a cross-sectional view showing an overview of the joined body according to the second embodiment. [Figure 3] It is a view showing the manufacturing process of the joined body according to the first embodiment. [Figure 4] It is a view showing the manufacturing process of the joined body according to the first embodiment.

Modes for Carrying Out the Invention

[0024] <Joined body> [First Embodiment] As shown in FIG. 1, the joined body 1 according to the present embodiment is a joined body in which a first member 3 made of an aluminum-based material formed by high-pressure die casting (HPDC) and a second member 2 made of a material different from the first member 3 are joined. The first member 3 has a melt-solidified portion 32a having a lower gas content than the unmelted portion after melting and solidifying. The first member 3 has a joining portion 32b joined to the second member 2 at an end portion on one end side of the melt-solidified portion 32a. In the manufacturing process of the HPDC aluminum material, hydrogen or the like may exist as gas inside. However, since the first member 3 is joined to the second member 2 on the end side rather than the melt-solidified portion 32a with a low gas content, the joined body 1 has favorable joint strength.

[0025] (First member) As shown in FIG. 1, the first member 3 includes a base material 31 and one end portion 32. One end portion 32 includes a melt-solidified portion 32a and a joining portion 32b. As shown in FIG. 1, the joining portion 32b is formed on one end side (the side of the second member 2 of the first member 3) rather than the melt-solidified portion 32a.

[0026] The molten and solidified portion 32a is a part in which the internal gas content is reduced by being melted again after the component has been formed by high-pressure die casting (HPDC). The gas content of the molten and solidified portion 32a is lower than that of the unmelted portion (base material 31), and may be less than 5 cc per 100 g of aluminum weight, for example.

[0027] The joint portion 32b is the area that is melted and joined to the second member 2. By providing the joint portion 32b on one end side of the molten and solidified portion 32a, which has a low gas content, the strength of not only the joint portion 32b but also the surrounding area can be improved, thereby obtaining a desirable joint strength for the joined body 1. It is preferable that the joint portion 32b is joined to the solid solution layer 23 of the second member 2, which will be described later.

[0028] The joint 32b may be part of the base material 31, but it may also be made of a different material from the base material 31. The joint 32b may be, for example, a brazing material (such as an aluminum wire).

[0029] (Second component) The second member 2 is made of a different material from the first member 3. The second member 2 is, for example, an iron material having a plating layer 22 on the surface of a base material 21. The plating layer 22 is not particularly limited, but it is preferably a high-melting-point plating layer having a boiling point higher than the melting point of the base material 21. As a result, the plating layer 22 does not melt in the second step described later. This prevents, for example, when the plating layer 22 is Zn plating, the components constituting the plating layer 22 and the components constituting the first member 3 from mixing and the decrease in the melting point of the aluminum constituting the first member 3 due to a eutectic reaction. If the melting point of aluminum decreases, aluminum may flow into the solid solution layer 23 formed in the second step, and there is a risk of excessive generation of intermetallic compounds.

[0030] An example of the plating layer 22 is an Fe-Al layer. An example of an iron material having an Fe-Al layer is a high-tensile steel sheet with an aluminum-based plating (such as an Al-Si alloy) applied to its surface. The aluminum-based plating formed on the surface of the high-tensile steel sheet is heated by hot stamping or the like, which forms the Fe-Al layer on the surface.

[0031] The Fe-Al layer may contain an intermetallic compound. The intermetallic compound is not particularly limited, but examples include Al-Si-Fe intermetallic compounds. The Fe-Al layer may also contain an alloy in addition to the intermetallic compound, for example, an Fe-Al alloy. The thickness of the plating layer 22 other than the joint in the second member 2 is not particularly limited. The thickness of the plating layer 22 may be, for example, 10 to 50 μm or 20 to 40 μm.

[0032] The melting point of the Fe-Al layer is not particularly limited, but is, for example, around 1280 to 1480°C. The melting point of the Fe-Al layer is close to the melting point of iron (base material 21) (approximately 1560°C) compared to, for example, the melting point of zinc-based plating. Therefore, when attempting to melt only the Fe-Al layer and join it with the first member 3, it is necessary to adjust the melting temperature to a temperature between the melting point of the Fe-Al layer and the melting point of the base material 21, making temperature control difficult. In this embodiment, the Fe-Al layer is melted together with the base material 21 to form a solid solution layer 23, and the solid solution layer 23 is joined to the first member 3. Thus, temperature control during the manufacturing of the joined body 1 becomes easier.

[0033] The solid solution layer 23 is a layer in which at least a portion of the material constituting the plating layer 22 is dissolved in the base material 21. For example, it is a layer in which aluminum contained in the Fe-Al layer as the plating layer 22 is dissolved. When the HPDC aluminum material is joined to the solid solution layer 23, it becomes a weld between the HPDC aluminum material and the surface layer of the iron material that does not have the plating layer 22, so the joint 1 can be easily formed compared to when the plating layer 22 and the first member 3 are directly welded. The solid solution layer 23 is a layer that reaches the position where the base material 21 is present in the thickness direction of the second member 2. The proportion of aluminum dissolved in iron in the solid solution layer 23, that is, the ratio of aluminum to iron in the solid solution layer 23, is preferably within 10% by mass. By keeping the proportion of aluminum in the solid solution layer 23 within the above range, it is possible to suppress the formation of intermetallic compounds due to the aluminum not being able to dissolve, which would reduce the strength of the second member.

[0034] When the joint 32b is joined to the solid solution layer 23, a thin intermetallic compound 4 can be formed between the first member 3 and the second member 2. The thickness of this intermetallic compound 4 is thinner than the thickness of the plating layer 22 in areas other than the joint. This characteristic of thickness difference is strongly evident at the toe 32c and root 32d of the joint 32b in Figure 1. From the above, it can be inferred that the material (aluminum) contained in the plating layer 22 has solid-solved in the base material 21.

[0035] As shown in Figure 1, it is preferable that only a thin intermetallic compound layer 4 exists at the interface between the solid solution layer 23 and the joint 32b. In other words, it is preferable that the joint 32b and the solid solution layer 23 are diffusion-bonded by a diffusion reaction. If a plating layer 22 of the same thickness as the rest of the solid solution layer exists at the interface between the joint 32b and the solid solution layer 23, the diffusion reaction (movement of atoms) will be inhibited, making diffusion bonding difficult.

[0036] As shown in Figure 1, it is preferable that the first member 3 and the second member 2 are separated by a predetermined distance G at least on the side of the joint 32b, excluding the joint 32b. This prevents the first molten portion 32a1 from flowing into the solid solution layer 23 and the excessive generation of intermetallic compounds in the first step described later. As shown in Figure 1, the first member 3 and the second member 2 may be separated at all locations except for one end 32.

[0037] [Second Embodiment] Next, the configuration of the joint 1a according to the second embodiment will be described with reference to Figure 2. Components similar to those in the first embodiment may be denoted by the same reference numerals in the drawings and their descriptions may be omitted.

[0038] As shown in Figure 2, the joint 1a includes a first member 3 having a stepped shape 31a. The stepped shape 31a is formed such that the cross-sectional area of ​​one end (the side with the second member 2) is smaller than that of the other end (the side with the base material 31). This allows the first member 3 and the second member 2 to be separated by a predetermined distance G. The stepped shape 31a of the first member 3 makes it easy to maintain the separated state between the first member 3 and the second member 2 when joining them. To obtain the above effect, it is preferable that the stepped shape 31a has a flat surface that contacts the second member 2.

[0039] <Joining method> Next, a joining method for joining the first member 3 and the second member 2 to obtain a joined body 1 will be explained using Figures 3 and 4. The joining method according to this embodiment comprises a first step of melting one end of the first member, and a second step of melting the end further to the other end than the first molten portion melted in the first step, and joining the second molten portion melted in the second step with the second member.

[0040] In the first step, one end of the first member 3 is melted to form a first molten portion 32a1, thereby creating a blowhole for the gas present inside the HPDC aluminum material. The first molten portion 32a1 is cooled and solidified after the second step to become the molten and solidified portion 32a of the joined body 1. In the first step, the heat source for melting one end of the first member is not particularly limited, but it is preferably a laser beam B1, as shown in Figure 3. The laser beam B1 is irradiated onto one end of the first member from, for example, a laser beam irradiation device 51. In the following description, the heat source will be described as a laser beam, but the heat source is not limited to the above, and known heat sources used in welding, such as arcs and electron beams, can be used.

[0041] In the first step, it is preferable to melt one end of the first member 3 and at least a portion of the plating layer 22 on the surface of the second member 2. That is, in the first step, as shown in Figure 3, it is preferable to partially overlap the first member 3 and the second member 2 at the joint and heat them by irradiating them with a laser beam or the like so that heat is transferred from the first member 3 to a portion of the second member 2. This makes it possible to solid dissolve the plating layer 22 in the base material 21 with a single irradiation and form a solid solution layer 23. Moreover, since heat is not easily transferred to the portion of the plating layer 22 that overlaps with the first molten portion 32a1, melting is less likely to occur. Furthermore, because the plating layer 22 has a high melting point, melting is even less likely to occur. In addition, the first member 3 and the second member 2 are separated by a predetermined distance G. Therefore, the flow of the first molten portion 32a1 into the plating layer 22 can suppress the excessive generation of intermetallic compounds.

[0042] The amount of heat in the first step is preferably sufficient to melt the first member 3 and to form a solid solution layer 23. For example, if the plating layer 22 is an Fe-Al layer, it is preferable to adjust the volume of the molten plating layer 22 and the base material 21 so that the aluminum content derived from the Fe-Al layer in the solid solution layer 23 is within 10% by mass of Fe. This suppresses the formation of intermetallic compounds and improves the strength of the joint 1. The above adjustment can be made, for example, by adjusting the temperature and irradiation time of the laser beam B1. Even when using a single laser beam, a difference in heat absorption occurs due to the difference in materials between the first member 3 and the second member 2, so if the second member 2 is made of iron, the temperature of the iron material will rise more easily than that of the first member 3. The heating temperature of the first member 3 in the first step may be, for example, around 800°C, and the heating temperature of the second member 2 may be, for example, around 1500 to 2000°C.

[0043] In the first step, the cross-sectional area of ​​one end of the first member 3 may be made smaller than other parts so that it is easier to melt.

[0044] A cooling step may be provided after the first step and before the second step to cool the first molten portion 32a1. The cooling step allows the blowholes formed in the first molten portion 32a1 in the first step to solidify (accumulate above the molten portion 32a1). This makes it easier for the blowholes to be released in the second step. In addition, by providing a cooling step, the melting range of the first member 3 due to heating in the second step can be reduced, and the generation of new blowholes can be suppressed. Therefore, the quality of the joined body 1 can be improved. The cooling step is performed by providing a time between the first step and the second step during which no heat is applied by a laser beam or the like, or the amount of heat applied is reduced (for example, by increasing the distance from the laser beam irradiation device).

[0045] The second step is to melt the end of the first member 3 further toward the end of the first molten portion 32a1 to form a second molten portion 32b1. The second molten portion 32b1 is cooled and solidified after the second step to become the joint portion 32b of the joined body 1. In this embodiment, the first molten portion 32a1 is provided at the end of the first member 3, and the second molten portion 32b1 is formed by introducing an aluminum wire to that end and melting it. However, the invention is not limited to the above, and the second molten portion 32b1 may also be formed by melting a part of the base material 31.

[0046] In the second step, the second molten section 32b1 is formed, and the gas inside the solidified blowhole B of the first molten section 32a1 is released to the outside. This reduces the gas content of the molten and solidified section 32a, thereby improving the joint strength.

[0047] The heat source for forming the second molten portion 32b1 is not particularly limited, but a laser beam B2 is preferred. The laser beam B2 is irradiated onto the second molten portion 32b1 from, for example, a laser beam irradiation device 52, similar to the laser beam B1. Instead of a laser beam, other known heat sources used in welding, such as arcs or electron beams, can also be used as the heat source.

[0048] In the second step, after forming the second molten portion 32b1, the second molten portion 32b1 is joined to the second member 2. The joining of the second molten portion 32b1 is preferably performed against the solid solution layer 23. Furthermore, the joining is preferably performed after the surface temperature of the solid solution layer 23 has fallen below its melting point. This suppresses the excessive formation of intermetallic compounds. The joining is preferably performed under a shielding gas to prevent oxidation of the surface of the second member 2.

[0049] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and any modifications or improvements that can achieve the objectives of the present invention are included in the present invention. [Explanation of Symbols]

[0050] 1, 1a Joint 2. Second member 21 Base material 22 Plating layer 23 Solid solution layer 3. First component 31a Stepped shape 32a Molten and solidified section 32a1 First molten section 32b Joint 32b1 Second molten section

Claims

1. A first component is an aluminum-based material formed by high-pressure die casting (HPDC), A jointed body formed by joining a second member, which is made of a different material from the first member, The first member has a molten and solidified portion that has solidified after melting and has a lower gas content than the unmelted portion. The first member has a joint portion that is joined to the second member at one end of the molten and solidified portion, The second member is made of iron and has a base material and a plating layer formed on the surface of the base material. The boiling point of the plating layer is higher than the melting point of the base material. The joint is a joint body in which the joint portion is joined to a solid solution layer in which at least a portion of the material constituting the plating layer is solid-solved in the base material.

2. The joint according to claim 1, wherein the first member and the second member are separated at least a portion on the joint side of the portion other than the joint.

3. The joint according to claim 2, wherein the first member has a stepped shape formed such that the cross-sectional area of ​​one end is smaller than the cross-sectional area of ​​the other end.

4. A first component is an aluminum-based material formed by high-pressure die casting (HPDC), A joining method for joining a second member, which is made of a different material from the first member, A first step of melting one end of the first member, The process comprises a second step of melting the end portion of the first member that is further toward one end than the first molten portion that was melted in the first step, The second molten portion of the first member that was melted in the second step is joined to the second member. The second member is made of iron and has a base material and a plating layer formed on the surface of the base material. The boiling point of the plating layer is higher than the melting point of the base material. The first step involves solid-solving at least a portion of the material constituting the plating layer with the base material to form a solid-solution layer. The second step is a joining method for joining the second molten portion with the solid solution layer.

5. The joining method according to claim 4, wherein the second step involves joining the second molten portion to the solid solution layer after the surface temperature of the solid solution layer has fallen below its melting point.

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