Joined body, joining method, and brazing material

Abstract

A joined body according to the present invention comprises: a first member and a second member that are joined, the first member and / or the second member comprising a 7000 series aluminum alloy; and a joining layer that comprises aluminum (Al), magnesium (Mg), and unavoidable impurities, and that joins the first member and the second member.

Description

Joined body, joining method and brazing material

[0001] The present invention relates to a joined body, a joining method, and a brazing filler metal.

[0002] Conventionally, as a technique for joining metals or alloys, a joining method using a brazing filler metal to join the objects to be joined has been known (see, for example, Patent Documents 1 and 2). The brazing filler metal used is an aluminum (Al)-silicon (Si) alloy or an alloy in which zinc (Zn) and magnesium (Mg) are added to aluminum (Al).

[0003] Furthermore, products manufactured as joined bodies and used as heat dissipation components for batteries and inverters are required to be high in strength and lightweight, and 7000 series aluminum alloys containing Zn and Mg are suitable materials for this purpose.

[0004] JP 2002-192337 A JP 2017-039157 A

[0005] However, since the melting point of a conventionally used Al-Si brazing filler metal is higher than that of a 7000 series aluminum alloy, when joining using this brazing filler metal, it is necessary to perform the joining process at a heating temperature higher than the melting point of the 7000 series aluminum alloy. In this case, there is a risk that the 7000 series aluminum alloy to be joined will melt during heating, making it impossible to join.

[0006] The present invention has been made in view of the above, and has an object to provide a joined body, a joining method, and a brazing filler metal that can join objects to be joined at low temperatures.

[0007] In order to solve the above-mentioned problems and achieve the object, a joined body according to the present invention is characterized by comprising: a first member and a second member to be joined, at least one of which is made of a 7000 series aluminum alloy; and a joining layer which is made of aluminum (Al), magnesium (Mg) and unavoidable impurities and joins the first member and the second member together.

[0008] In addition, the bonded body according to the present invention is characterized in that, in the above invention, the bonding layer further contains at least one of silver (Ag), antimony (Sb), tin (Sn), and zinc (Zn).

[0009] Furthermore, the joining method according to the present invention is characterized in that a brazing filler metal consisting of 30% by weight or more and 37% by weight or less of magnesium (Mg), with the remainder being aluminum (Al) and unavoidable impurities, is disposed between a first base material and a second base material, at least one of which is made of a 7000 series aluminum alloy, and a laminate in which the first base material, the second base material, and the brazing filler metal are stacked is heated at a temperature higher than the melting point of the brazing filler metal and lower than the lower of the melting points of the first base material and the second base material, thereby forming a joining layer that joins the first base material and the second base material.

[0010] In addition, the joining method according to the present invention is characterized in that, in the above invention, the brazing filler metal further contains at least one of silver (Ag), antimony (Sb), tin (Sn), and zinc (Zn).

[0011] Furthermore, in the bonding method according to the present invention, in the above invention, the laminate is heated at a temperature higher than the melting point of the brazing filler metal and lower than the melting point of the 7000 series aluminum alloy to form the bonding layer.

[0012] Moreover, in the bonding method according to the present invention, in the above invention, the laminate is heated at a temperature higher than 450° C. and not higher than 490° C. to form the bonding layer.

[0013] Furthermore, the brazing filler metal according to the present invention is a brazing filler metal for joining a first member and a second member to be joined, at least one of which is made of a 7000 series aluminum alloy, characterized in that the brazing filler metal contains 30% by weight or more and 37% by weight or less of magnesium (Mg), with the remainder being aluminum (Al) and inevitable impurities.

[0014] According to the present invention, an effect is achieved in that objects to be joined can be joined at a low temperature.

[0015] Fig. 1 is a plan view showing the structure of a bonded body according to one embodiment of the present invention, Fig. 2 is a diagram illustrating an Al-Mg phase diagram, and Fig. 3 is a diagram illustrating a bonding method according to one embodiment of the present invention.

[0016] In the following description, a brazing filler metal, a joined body, and a joining method will be described as a mode for carrying out the present invention (hereinafter referred to as "embodiment"). The present invention is not limited to this embodiment. Furthermore, in the drawings, the same parts are denoted by the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the relationship between the thickness and width of each member, the ratio of each member, and the like may differ from reality. Furthermore, the drawings also include parts with different dimensions and ratios.

[0017] 1 is a plan view showing the configuration of a bonded structure according to one embodiment of the present invention. The bonded structure 1 includes a first member 11 and a second member 12 to be bonded, and a bonding layer 13 that bonds the first member 11 and the second member 12. Note that, although the first member 11 and the second member 12 shown in FIG. 1 are plate-shaped, the shapes are not limited to this.

[0018] At least one of the first member 11 and the second member 12 is a plate made of a 7000 series aluminum alloy, which is an aluminum (Al)-magnesium (Mg)-zinc (Zn) alloy. For example, the first member 11 is made of a non-heat-treatable alloy, which is a 1000 series aluminum alloy. The second member 12 is made of a heat-treatable alloy, which is a 7000 series aluminum alloy.

[0019] For example, when the first member 11 is made of a 1000 series aluminum alloy and the second member 12 is made of a 7000 series aluminum alloy, the joined body 1 is used as a heat dissipation fin for a battery or an inverter. In this case, the second member 12 is attached to the housing side, and the first member 11 functions as a fin.

[0020] The bonding layer 13 is made of aluminum (Al), magnesium (Mg), and inevitable impurities. The bonding layer 13 is formed using a brazing filler metal. In this embodiment, the brazing filler metal is an Al-Mg brazing filler metal containing aluminum (Al) and magnesium (Mg). This brazing filler metal contains 30% by weight or more and 37% by weight or less of Mg, with the remainder being Al and inevitable impurities. In addition to the inevitable impurities, the brazing filler metal may further contain at least one of silver (Ag), antimony (Sb), tin (Sn), and zinc (Zn). The brazing filler metal contains a total of up to 5% by weight of Ag, Sb, Sn, and Zn. By adding these metals, the bonding layer 13 contains the added metals as components.

[0021] 2 is a diagram illustrating an Al-Mg phase diagram (source: Thaddesu B. Massalski et al., Binary Alloy Phase Diagrams Second Edition, USA, ASM International, (1990), 170). According to the Al-Mg phase diagram shown in FIG. 2, the maximum solid solubility on the Al side, which corresponds to the melting point, is the eutectic temperature of 450°C, and the weight percentage of Mg at this eutectic temperature is approximately 37% by weight. Therefore, the melting point of the brazing filler metal according to this embodiment is approximately 450°C.

[0022] Next, a joining method according to this embodiment will be described with reference to FIG. 3 . FIG. 3 is a diagram illustrating a joining method according to one embodiment of the present invention. First, a brazing filler metal 130 is disposed between a first base material 110 corresponding to the first member 11 and a second base material 120 corresponding to the second member 12 (see FIG. 3A). For example, the brazing filler metal 130 is placed on the second base material 120, and the first base material 110 is placed on the brazing filler metal 130. At this time, the first base material 110 has a base material portion 111 made of a 1000 series aluminum alloy and an oxide film 112 formed on the surface of the first base material 110 on the side where the brazing filler metal 130 is disposed. Furthermore, the second base material 120 has a base material portion 121 made of a 7000 series aluminum alloy and an oxide film 122 formed on the surface of the second base material 120 on the side where the brazing filler metal 130 is disposed. Then, the laminate 100 in which the brazing material 130 is disposed between the first base material 110 and the second base material 120 is placed in a furnace, and the air inside the furnace is evacuated to create a vacuum inside the furnace.

[0023] Thereafter, the laminate 100 is heated in a vacuum atmosphere. The heating temperature is set to a temperature higher than 450°C, which is the melting point of the brazing filler metal, and lower than the melting point of the lower of the first base material 110 and the second base material 120 (here, the members made of 7000-series aluminum alloys). For example, for aluminum alloy 7050 (melting point 524°C), the heating temperature is set to 490°C. When the laminate 100 is heated, the base material portions 111 and 121 expand, and cracks occur in the oxide films 112 and 122 (see FIG. 3B).

[0024] As the heating continues, Mg in the base materials 111 and 121 and the brazing material 130 and Zn in the base materials 111 and 121 volatilize (see FIG. 3(c)). Also, the brazing material 130 melts.

[0025] The molten brazing material 130 then spreads, and the oxygen, moisture, and aluminum oxide in the furnace react with the Mg, respectively, to remove the oxide films 112 and 122. The main reactions that occur at this time are as follows: Mg + (1 / 2)O → MgO Mg + H O → MgO + H Mg + (1 / 3)Al O → MgO + (2 / 3)Al

[0026] Thereafter, the temperature in the furnace is lowered to, for example, room temperature, and the joining process is completed. As a result, a joined body 1 in which the first member 11 and the second member 12 are joined by the joining layer 13 is obtained (see FIG. 3(d)). The obtained joined body 1 may be subjected to a solution treatment or an aging treatment.

[0027] Here, the melting point (eutectic temperature) of the conventionally used Al-Si brazing filler metal is 577°C, which is higher than the melting points of the 2000 and 7000 series aluminum alloys, which are heat-treatable alloys. Therefore, when an Al-Si brazing filler metal is used, if the heating temperature is increased to the melting point of the brazing filler metal during the heat treatment for joining, the base materials to be joined may melt.

[0028] In the above-described embodiment, a brazing filler metal 130 containing 30% by weight to 37% by weight of magnesium (Mg), with the remainder being aluminum (Al) and unavoidable impurities, is disposed between a first base material 110 and a second base material 120, at least one of which is made of a 7000-series aluminum alloy, and a laminate 100 in which the first base material 110, the second base material 120, and the brazing filler metal 130 are stacked is heated at a temperature higher than the melting point of the brazing filler metal 130 and lower than the lower of the melting points of the first base material 110 and the second base material 120, thereby forming a bonding layer 13 that bonds the first base material 110 and the second base material 120. Because the brazing filler metal has a lower melting point than the objects to be bonded, the objects can be bonded at a low temperature.

[0029] Examples of the bonded structure according to the present invention will be described below, but the present invention is not limited to these examples.

[0030] Example 1 In Example 1, two base materials (base materials A and B) to be joined were used, with base material A (first member, first base material) being A1050, a 1000 series aluminum alloy, and base material B (second member, second base material) being A7050, a 7000 series aluminum alloy. A brazing filler metal having a composition consisting of 30 wt % Mg and the remainder Al and unavoidable impurities was used as the brazing filler metal. A joined body was produced by joining the base materials in a vacuum atmosphere for one hour at a contact pressure (brazing contact pressure) of 0.05 MPa and a heating temperature (brazing temperature) of 490° C. Note that in Example 1, the joined body was not subjected to solution treatment or aging treatment.

[0031] The bonded body of Example 1 was also evaluated for surface component-depleted zones and weldability. The weldability evaluation was performed visually, with a ◯ indicating a bonded body (if bonded) and an × indicating no bond. Images obtained using a microscope or the like can be used for this evaluation. Furthermore, the bond strength of Example 1 was measured. For the measurement, a sample of A7050 subjected to a vacuum heat treatment equivalent to brazing was used. Line analysis was performed using an EPMA within a range from the surface to a depth of 1 mm of the heat-treated sample. The average value of the peak intensity observed at a depth of 0.5 mm to 1.0 mm from the sample surface was defined as the Mg, Zn 100% peak intensity of A7050. In this example, the range where the peak intensity was below 90% was defined as the surface component-depleted zone.

[0032] The materials, joining conditions and properties in Example 1 are shown in Table 1.

[0033] Example 2 In Example 2, a joined body was produced in the same manner as in Example 1, except that A7050 was used as the base material A. The materials, joining conditions, and properties in Example 2 are shown in Table 1.

[0034] Example 3 In Example 3, a joined body was produced in the same manner as in Example 1, except that the brazing time was set to 5 hours. The materials, joining conditions, and properties in Example 3 are shown in Table 1.

[0035] Example 4 In Example 4, a joined body was produced in the same manner as in Example 2, except that the brazing time was set to 5 hours. The materials, joining conditions, and properties in Example 4 are shown in Table 1.

[0036] Example 5 In Example 5, a joined body was produced in the same manner as in Example 1, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 5 are shown in Table 1.

[0037] Example 6 In Example 6, a joined body was produced in the same manner as in Example 2, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 6 are shown in Table 1.

[0038] Example 7 In Example 7, a joined body was produced in the same manner as in Example 3, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 7 are shown in Table 1.

[0039] Example 8 In Example 8, a joined body was produced in the same manner as in Example 4, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 8 are shown in Table 1.

[0040] In Example 9, a joined body was produced in the same manner as in Example 2, except that the brazing filler metal was 30 wt % Mg, 3 wt % Ag, and the remainder was Al and unavoidable impurities. The materials, joining conditions, and properties in Example 9 are shown in Table 1.

[0041] Example 10 In Example 10, a joined body was produced in the same manner as in Example 9, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 10 are shown in Table 1.

[0042] In Example 11, a joined body was produced in the same manner as in Example 2, except that the brazing filler metal was 30 wt % Mg, 3 wt % Sb, and the remainder Al and unavoidable impurities. The materials, joining conditions, and properties in Example 11 are shown in Table 1.

[0043] Example 12 In Example 12, a joined body was produced in the same manner as in Example 11, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 12 are shown in Table 1.

[0044] In Example 13, a joined body was produced in the same manner as in Example 2, except that the brazing filler metal was 30 wt % Mg, 3 wt % Sn, and the remainder Al and unavoidable impurities. The materials, joining conditions, and properties in Example 13 are shown in Table 1.

[0045] Example 14 In Example 14, a joined body was produced in the same manner as in Example 13, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 14 are shown in Table 1.

[0046] In Example 15, a joined body was produced in the same manner as in Example 2, except that the brazing filler metal was 30 wt % Mg, 3 wt % Zn, and the remainder Al and unavoidable impurities. The materials, joining conditions, and properties in Example 15 are shown in Table 1.

[0047] Example 16 In Example 16, a joined body was produced in the same manner as in Example 15, except that solution treatment and aging treatment were performed. The materials, joining conditions, and properties in Example 16 are shown in Table 1.

[0048] In Comparative Example 1, a joined body was produced in the same manner as in Example 1, except that the brazing filler metal was one having a composition consisting of 12 wt % Si and the remainder consisting of Al and unavoidable impurities. The materials, joining conditions, and properties in Comparative Example 1 are shown in Table 1.

[0049] Comparative Example 2 In Comparative Example 2, a joined body was produced in the same manner as in Comparative Example 1, except that the base material A was A7050 and the brazing temperature was 600° C. The materials, joining conditions, and properties in Comparative Example 2 are shown in Table 1.

[0050] It was confirmed that in all of Examples 1 to 16, in which joining was performed using a brazing filler metal containing 30 wt % Mg and the remainder consisting mainly of Al and unavoidable impurities, joining was performed at a heating temperature of 490°C, which is lower than the melting point of 7000 series aluminum alloys. On the other hand, in Comparative Examples 1 and 2, in which joining was performed using a brazing filler metal containing 12 wt % Si and the remainder consisting mainly of Al and unavoidable impurities, joining was not possible at either the heating temperatures of 490°C or 600°C.

[0051] Furthermore, among Examples 1 to 16, Examples 3, 4, 7, and 8 tended to have thicker surface element-depleted layers, where the Mg and Zn concentrations at the base metal surface were reduced, compared to Examples 1, 2, 5, 6, and 9 to 16, which were not solution-treated or aging-treated. This is thought to be due to the length of brazing time. Here, as the surface element-depleted layer thickens, the solid solution strengthening mechanism of Mg and the precipitation strengthening mechanism of Zn are lost, which may result in a decrease in strength at the surface element-depleted layer. Furthermore, the corrosion resistance-improving effect of Zn is also impaired, potentially affecting corrosion resistance. These problems can be eliminated by surface machining. They can also be suppressed by devising a jig setup during joining.

[0052] As such, the present invention may include various embodiments not described here, and various design changes may be made within the scope of the technical idea specified by the claims.

[0053] As described above, the joined body and joining method according to the present invention are suitable for obtaining a joined body in which the joined portions are joined with high strength even when the weight is reduced.

[0054] REFERENCE SIGNS LIST 1 Bonded body 11 First member 12 Second member 13 Bonding layer 110 First base material 120 Second base material 130 Brazing material

Claims

1. A joined body comprising: a first member and a second member to be joined, at least one of which is made of a 7000 series aluminum alloy; and a joining layer made of aluminum (Al), magnesium (Mg) and unavoidable impurities, which joins the first member and the second member.

2. The bonded body according to claim 1, wherein the bonding layer further contains at least one of silver (Ag), antimony (Sb), tin (Sn) and zinc (Zn).

3. A joining method comprising: disposing a brazing filler metal consisting of 30% by weight to 37% by weight of magnesium (Mg), with the remainder being aluminum (Al) and unavoidable impurities, between a first base material and a second base material, at least one of which is made of a 7000 series aluminum alloy; and heating a laminate comprising the first base material, the second base material, and the brazing filler metal at a temperature higher than the melting point of the brazing filler metal and lower than the lower of the melting points of the first base material and the second base material, to form a joining layer that joins the first base material and the second base material.

4. The joining method according to claim 3, wherein the brazing material further contains at least one of silver (Ag), antimony (Sb), tin (Sn) and zinc (Zn).

5. The joining method according to claim 3, characterized in that the joining layer is formed by heating the laminate at a temperature higher than the melting point of the brazing filler metal and lower than the melting point of the 7000 series aluminum alloy.

6. The bonding method according to claim 4, wherein the laminate is heated at a temperature higher than 450°C and not higher than 490°C to form the bonding layer.

7. A brazing filler metal for joining a first member and a second member to be joined, at least one of which is made of a 7000 series aluminum alloy, characterized in that the brazing filler metal is composed of 30% by weight to 37% by weight of magnesium (Mg), with the remainder being aluminum (Al) and unavoidable impurities.

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