Aluminum alloy structure, thermal bonding method, and aluminum alloy extruded material and method for producing same

Abstract

Disclosed is an aluminum alloy structure which is obtained by thermally bonding one member to be bonded and the other member to be bonded, the aluminum alloy structure being characterized in that: the one member to be bonded contains 1.80-3.00 mass% of Si, 0.10-1.60 mass% of Mn, and 0.01-0.70 mass% of Fe, with the balance being made up of Al and unavoidable impurities; the average crystal grain size in the outermost layer of the one member to be bonded at the bonded part of the one member to be bonded and the other member to be bonded is 200 μm or less; and the average crystal grain size is 400 μm or more in a cross-section at a depth of 100 μm of a portion that has the smallest width in the one member to be bonded. The present invention makes it possible to provide an aluminum alloy structure, and an aluminum alloy extruded material and a method for producing the same, the aluminum alloy structure enabling simplification of the manufacturing process by being able to be bonded in the form of a single layer. The aluminum alloy structure exhibits good bondability and is able to be suppressed in deformation during thermal bonding.

Description

Aluminum alloy structure, heat bonding method, aluminum alloy extrusion material and manufacturing method thereof

[0001] The present invention relates to an aluminum alloy structure, a heat-bonding method, an aluminum alloy extrusion material, and a manufacturing method thereof, and more particularly to an aluminum alloy structure that can be joined to another member by its own action without using a joining member such as a brazing material or a filler material, an aluminum alloy extrusion material, and a manufacturing method thereof.

[0002] In the manufacture of structures such as heat exchangers that use aluminum alloy materials as components, it is necessary to join aluminum alloy materials together. Various methods are known for joining aluminum alloy materials, and among these, brazing is the most widely used method.

[0003] One method for manufacturing a heat exchanger or the like using a brazing method to join aluminum alloy materials is to use a brazing sheet of a clad material clad with a brazing material made of an Al-Si alloy (Patent Document 1). However, manufacturing a clad material requires a process in which each layer is manufactured separately and then overlapped and joined, which makes the manufacturing process complicated and problematic.

[0004] Other known methods for manufacturing heat exchangers and the like using a brazing method for joining aluminum alloy materials include a method using aluminum alloy materials coated with a powder brazing material, and a method in which a brazing material such as a brazing filler metal or brazing paste is separately installed or applied to portions that require joining after assembling the materials (Patent Documents 2 and 3). However, these methods also require a step of separately preparing and installing or applying the brazing material in addition to the aluminum alloy material, which makes the manufacturing process complicated and problematic.

[0005] Therefore, instead of the above-mentioned method of using a brazing sheet of clad material or a method of using an aluminum alloy material coated with a powder brazing material, which complicates the manufacturing process of an aluminum alloy material or an aluminum alloy structure, there is a method of using a single-layer brazing sheet, which simplifies the manufacturing process of an aluminum alloy material or an aluminum alloy structure (Patent Document 4).

[0006] JP 2008-303405 A JP 2011-136358 A JP 09-047892 A International Publication No. 2014 / 184880

[0007] However, since a single-layer brazing sheet can be bonded by partially melting itself, there is a concern that the material may be significantly deformed when heated.

[0008] Furthermore, since a single-layer brazing sheet joins to other components by its own action (the liquid phase seeping out from the base material) without using any joining materials such as brazing filler metal or filler metal, the amount of liquid phase used for brazing joining is smaller than in conventional methods using brazing sheets clad with brazing filler metal or methods using aluminum alloy material coated with powder brazing filler metal, and therefore there is a risk that the heat bonding ability will be poor.

[0009] Therefore, an object of the present invention is to provide an aluminum alloy structure and an aluminum alloy extrusion material that can be joined in a single layer, thereby simplifying the manufacturing process, and that have good joinability and can suppress deformation during thermal joining.

[0010] As a result of extensive research, the inventors have invented an aluminum alloy structure, an aluminum alloy extrusion material, and a method for manufacturing the same, which can be joined in a single layer by controlling the alloy composition and crystal structure of the joined members, thereby simplifying the manufacturing process, and which has good joinability and can suppress deformation during thermal joining.

[0011] That is, the present invention (1) provides an aluminum alloy structure in which one member to be joined, made of an aluminum alloy, and another member to be joined, made of either an aluminum alloy or pure aluminum, are thermally joined, wherein the one member to be joined contains 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, with the remainder being Al and unavoidable impurities, and the average crystal grain size in the outermost layer of the one member to be joined at the joining portion between the one member to be joined and the other member to be joined is 200 μm or less, and the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part of the one member to be joined is 400 μm or more.

[0012] The present invention (2) provides a method for heat-bonding an aluminum alloy structure according to (1), characterized in that the metal structure at 575°C during heat-bonding has an average crystal grain size of 200 μm or less in the outermost layer of the surface to be bonded, and an average crystal grain size of 400 μm or more in the cross section at a depth of 100 μm from the thinnest part of the wall.

[0013] The present invention (3) provides an aluminum alloy extrusion having a single-layer thermal bonding function, comprising 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, with the remainder being Al and unavoidable impurities, the width of the thinnest part in a cross section perpendicular to the extrusion direction being 0.6 mm or more, and after a heating test in which the temperature is raised from 450°C to 575°C over 4 to 15 minutes and then maintained at 575 to 615°C for 5 to 40 minutes, the average crystal grain size in the outermost layer on the surface to be bonded is 200 μm or less, and the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part is 400 μm or more.

[0014] The present invention (4) provides a method for producing an aluminum alloy extrusion material according to (3), comprising: a casting step of casting an ingot containing 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, with the balance being Al and unavoidable impurities; and a hot extrusion step of hot extruding the ingot while the temperature of the ingot is 400°C or higher and 550°C or lower, to form the ingot into a shape in which the width of the thinnest part in a cross section perpendicular to the extrusion direction is 0.6 mm or higher.

[0015] The present invention (5) also provides a method for producing an aluminum alloy extrusion material according to (4), further comprising a homogenization step of performing a homogenization treatment on the ingot after the casting step by holding the ingot at a temperature of 570°C or less.

[0016] According to the present invention, it is possible to provide an aluminum alloy structure and an aluminum alloy extrusion material that can be joined in a single layer, thereby simplifying the manufacturing process, and that has good joinability and can suppress deformation during thermal joining.

[0017] 1 is a schematic phase diagram of an Al-Si alloy, which is a typical binary eutectic alloy.

[0033] FIG. 1 is an explanatory diagram showing the mechanism of liquid phase generation in the aluminum alloy forming the aluminum alloy extrusion material of the present invention, when joining is performed using the aluminum alloy extrusion material of the present invention.

[0034] FIG. 1 is an explanatory diagram showing the mechanism of liquid phase generation in the aluminum alloy forming the aluminum alloy extrusion material of the present invention, when joining is performed using the aluminum alloy extrusion material of the present invention.

[0035] FIG. 1 is a schematic phase diagram of an Al-Si alloy, which is a typical binary eutectic crystal.

[0036] FIG. 1 is a cross-sectional microstructure observation result in the thickness direction after a heating test simulating thermal bonding of an aluminum alloy extrusion material of the present invention.

[0037] FIG. 1 is a microstructure observation result in a cross-section perpendicular to the depth direction of the outermost layer after a heating test simulating thermal bonding of an aluminum alloy extrusion material of the present invention.

[0038] FIG. 1 is a combination diagram of an inverted T-shaped joining test.

[0018] The aluminum alloy structure of the present invention is an aluminum alloy structure in which one member to be joined, made of an aluminum alloy, and another member to be joined, made of either an aluminum alloy or pure aluminum, are thermally joined, wherein the one member to be joined contains 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, with the remainder being Al and unavoidable impurities, and the average crystal grain size in the outermost layer of the one member to be joined at the joining portion between the one member to be joined and the other member to be joined is 200 μm or less, and the average crystal grain size in the cross section at a depth of 100 μm in the thinnest part of the one member to be joined is 400 μm or more.

[0019] The aluminum alloy structure of the present invention is an aluminum alloy structure in which one member to be joined made of an aluminum alloy and the other member to be joined made of either an aluminum alloy or pure aluminum are thermally joined.

[0020] The one of the members to be joined in the aluminum alloy structure of the present invention is made of an aluminum alloy, that is, the one of the members to be joined is an aluminum alloy material and is formed from an aluminum alloy.

[0021] The aluminum alloy forming one of the members to be joined contains 1.80 to 3.00 mass % Si, 0.10 to 1.60 mass % Mn, 0.01 to 0.70 mass % Fe, with the remainder being Al and unavoidable impurities.

[0022] Si is an element that generates an Al-Si liquid phase during thermal bonding and contributes to bonding. If the Si content of the aluminum alloy is less than 1.80 mass%, a sufficient amount of liquid phase cannot be generated, resulting in reduced bondability. Furthermore, if the Si content exceeds 3.00 mass%, a large amount of elemental Si is contained, raising concerns about significant tool wear during the manufacturing process of the aluminum alloy material. Therefore, the Si content of the aluminum alloy forming one of the members to be bonded is specified to be 1.80 to 3.00 mass%. The lower limit of the Si content of the aluminum alloy forming one of the members to be bonded is preferably 2.00 mass%. Furthermore, the upper limit of the Si content of the aluminum alloy forming one of the members to be bonded is preferably 2.80 mass%. The Si content can be within a range that combines the above upper and lower limits.

[0023] Mn is an element that adjusts the crystalline structure of an aluminum alloy material, contributing to improving thermal bondability and suppressing deformation during thermal bonding. If the Mn content of the aluminum alloy is less than 0.10 mass%, the crystal grain size according to the present invention will not be obtained, resulting in significant deformation during thermal bonding. Furthermore, if the Mn content exceeds 1.60 mass%, the deformation resistance of the aluminum alloy material will increase, potentially making processing difficult during the manufacturing process of the aluminum alloy material. Therefore, the Mn content of the aluminum alloy forming one of the members to be joined is specified to be 0.10 to 1.60 mass%. The lower limit of the Mn content of the aluminum alloy forming one of the members to be joined is preferably 0.20 mass%, more preferably 0.30 mass%. Furthermore, the upper limit of the Mn content of the aluminum alloy forming one of the members to be joined is preferably 1.40 mass%, more preferably 1.20 mass%, more preferably 1.00 mass%, and more preferably 0.80 mass%. The Mn content can be within a range that combines the above upper and lower limits.

[0024] Fe is an element that contributes to improving the strength of aluminum alloy materials. If the Fe content of the aluminum alloy is less than 0.01% by mass, it is necessary to use extremely high-purity aluminum ingots to manufacture the aluminum alloy, which increases costs. Furthermore, if the Fe content exceeds 0.70% by mass, Al-Fe-Si compounds are formed, reducing the amount of Si that contributes to the formation of a liquid phase during thermal bonding, thereby reducing thermal bondability. Therefore, the Fe content of the aluminum alloy forming one of the members to be joined is specified to be 0.01 to 0.70% by mass. The lower limit of the Fe content of the aluminum alloy forming one of the members to be joined is preferably 0.05% by mass, more preferably 0.10% by mass, and more preferably 0.15% by mass. Furthermore, the upper limit of the Fe content of the aluminum alloy forming one of the members to be joined is preferably 0.60% by mass, more preferably 0.50% by mass, and more preferably 0.40% by mass. The Fe content can be within a range that combines the above upper and lower limits.

[0025] The other member to be joined in the aluminum alloy structure of the present invention is made of an aluminum alloy or pure aluminum. That is, the other member to be joined is an aluminum alloy material or pure aluminum material and is formed from an aluminum alloy or pure aluminum. When the other member to be joined is made of an aluminum alloy, the other member to be joined may have the same alloy composition as the aluminum alloy material forming the one member to be joined, or a different alloy composition.

[0026] Next, the metal structure of the aluminum alloy structure of the present invention will be described.

[0027] The metallographic structure of one of the joined members of the aluminum alloy structure of the present invention has fine grains at the joining surface to improve thermal bonding, and coarse grains inside the material to suppress deformation during thermal bonding. These metallographic structures should actually be achieved just before the formation of a liquid phase. However, since the metallographic structure is usually maintained after the completion of thermal bonding, the metallographic structure can be confirmed using either the structure after thermal bonding, a material subjected to a heating test simulating thermal bonding, or a material heated to just before the formation of a liquid phase and then cooled. One form of heat treatment involves heating to 580°C to 620°C at an average heating rate of 5 to 100°C / min, holding at 580°C to 620°C for approximately 0 to 20 minutes, and then cooling.

[0028] In the aluminum alloy structure of the present invention, at the joint between one of the joined members and the other of the joined members, the average crystal grain size of the outermost layer of the one of the joined members is 200 μm or less. The average crystal grain size of the outermost layer is measured at a cross section along the surface of one of the joined members at a depth of 0 to 10 μm (i.e., a cross section perpendicular to the depth direction at a depth of 0 to 10 μm), with the surface of the one of the joined members used for joining as the depth reference (zero position). However, due to the presence of a liquid phase generated from one of the joined members at the joint, the position of the surface of one of the joined members may not be clearly identified. In such cases, the average crystal grain size of the outermost layer can also be measured at a cross section along the surface of one of the joined members at a depth of 0 to 10 μm, with the surface of one of the joined members used as the depth reference, in a region near the joint that can be considered equivalent to the joining surface of one of the joined members.

[0029] The average crystal grain size of the outermost layer affects the thermal bondability during the fabrication of an aluminum alloy structure. If the average crystal grain size in the outermost layer is greater than 200 μm, the thermal bondability during the fabrication of the aluminum alloy structure is reduced. Specifically, during thermal bonding, an Al-Si liquid phase is generated at the grain boundaries of one of the members to be joined, and this liquid phase is supplied to the joint via the grain boundaries. The liquid phase fills the joint and solidifies, thereby achieving bonding. However, if the average crystal grain size in the outermost layer of one of the members to be joined is large, the amount of liquid phase supplied to the joint is reduced due to the small number of grain boundaries, which may result in insufficient bonding. For these reasons, the average crystal grain size of the outermost layer of one of the members to be joined is specified to be 200 μm or less. The average crystal grain size of the outermost layer of one of the members to be joined is preferably 180 μm or less, more preferably 160 μm or less, and more preferably 140 μm or less.

[0030] In the aluminum alloy structure of the present invention, the average grain size in the cross section at a depth of 100 μm in the thinnest part of one of the members to be joined is 400 μm or more. The average grain size in the cross section at a depth of 100 μm in the thinnest part is measured in a cross section at a depth of 100 μm along the surface of one of the members to be joined (i.e., a cross section perpendicular to the depth direction at a depth of 100 μm), with the surface of one of the members to be joined as the depth reference (zero position).

[0031] The average crystal grain size in the cross section at a depth of 100 μm from the thinnest part affects deformation during thermal bonding. If the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part is smaller than 400 μm, deformation during thermal bonding becomes significant. That is, when an Al-Si liquid phase is generated at the grain boundaries during thermal bonding, a small average crystal grain size causes a lot of grain boundary sliding. However, the thinnest part is particularly affected by this because of its low rigidity, resulting in a large amount of deformation and a concern that the dimensional specifications will not be met. For these reasons, the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part is specified to be 400 μm or more.

[0032] The joining surface of one of the members to be joined in the aluminum alloy structure of the present invention and the portion with the thinnest wall thickness may be located at the same position or at different positions.

[0033] In view of deformation resistance, the shape of one of the members to be welded in the aluminum alloy structure of the present invention is preferably such that the width of the thinnest part is 0.6 mm or more. If the width is less than 0.6 mm, the rigidity of the material will decrease and there is a concern that the metal structure according to the present invention will not be obtained.

[0034] The heat-bonding method of the present invention is a heat-bonding method for an aluminum alloy structure of the present invention, characterized in that the metal structure at 575°C during heat-bonding has an average crystal grain size of 200 μm or less in the outermost layer of the surface to be bonded, and an average crystal grain size of 400 μm or more in the cross section at a depth of 100 μm in the thinnest part of the wall.

[0035] In other words, the heat-bonding method of the present invention is a heat-bonding method in which one member to be joined and another member to be joined are heated to bond them together in order to obtain the aluminum alloy structure of the present invention, and in the heating for heat-bonding the one member to be joined and the other member to be joined, when the temperature of the one member to be joined reaches 575°C, the metal structure of the one member to be joined is a heat-bonding method in which the average crystal grain size of the outermost layer of the surface to be joined is 200 μm or less and the average crystal grain size of the cross section at a depth of 100 μm from the thinnest part is 400 μm or more.

[0036] In the heat-bonding method of the present invention, 575°C is the temperature immediately before the liquid phase is generated in one of the workpieces. Therefore, the heat-bonding method of the present invention is a heat-bonding method in which, for the metallographic structure immediately before the liquid phase is generated, the average crystal grain size of the outermost layer of the surface to be bonded is set to 200 μm or less, thereby forming multiple liquid phase supply paths in the surface layer and improving brazability. Furthermore, by setting the average crystal grain size in the cross section at a depth of 100 μm in the thinnest part to 400 μm or more, grain boundary sliding within the material is prevented and deformation is reduced. Furthermore, the metallographic structure formed at 575°C is substantially maintained even after subsequent heating and cooling.

[0037] In the heating and bonding method of the present invention, for example, one of the members to be bonded, which has been manufactured by the manufacturing method of one of the members to be bonded described below, is heated to 580°C to 620°C at an average heating rate of 5 to 100°C / min, and then held at 580°C to 620°C for approximately 0 to 20 minutes, thereby making it possible to change the metal structure of the one of the members to be bonded so that the average crystal grain size of the outermost layer of the surface to be bonded is 200 μm or less, and the average crystal grain size of the cross section at a depth of 100 μm from the thinnest part is 400 μm or more.

[0038] The aluminum alloy extrusion of the present invention is an aluminum alloy extrusion having a thermal bonding function in a single layer, characterized in that it contains 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, with the remainder being Al and unavoidable impurities, the width of the thinnest part in a cross section perpendicular to the extrusion direction being 0.6 mm or more, the average crystal grain size of the outermost layer on the surface to be bonded being 200 μm or less after a heating test in which the temperature is raised from 450°C to 575°C over 4 to 15 minutes and then maintained at 575 to 615°C for 5 to 40 minutes, and the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part being 400 μm or more.

[0039] The aluminum alloy extrusion material of the present invention is made of an aluminum alloy. That is, the aluminum alloy extrusion material of the present invention is an aluminum alloy material and is formed from an aluminum alloy.

[0040] The aluminum alloy extrusion material of the present invention has a thermal bonding function in a single layer. That is, the aluminum alloy extrusion material of the present invention enables bonding by utilizing a liquid phase generated inside the aluminum alloy material by heating, and therefore is an aluminum alloy extrusion material that can be bonded to other members despite being a single layer without using a bonding material such as a pre-heated brazing filler metal (hereinafter also referred to as a single-layer bonded aluminum alloy extrusion material). In detail, the aluminum alloy extrusion material of the present invention is an aluminum alloy extrusion material that has a thermal bonding function in a single layer at a temperature at which the liquid phase fraction is 5.0% or more and 35.0% or less (an aluminum alloy extrusion material having a single-layer thermal bonding function).

[0041] Single-layer bonded aluminum alloy extrusions must be bonded at a temperature where the ratio of the mass of the liquid phase generated within the aluminum alloy material to the total mass of the aluminum alloy material (hereinafter referred to as the "liquid phase ratio") is 5% or more and 35% or less. If the liquid phase ratio exceeds 35%, the amount of liquid phase generated is too large, making the aluminum alloy material unable to maintain its shape and resulting in significant deformation. On the other hand, if the liquid phase ratio is less than 5%, bonding becomes difficult. A preferred liquid phase ratio is 5 to 30%, and a more preferred liquid phase ratio is 10 to 20%.

[0042] The mechanism of liquid phase formation will be explained. Figure 1 shows a schematic diagram of an Al-Si alloy, a typical binary eutectic alloy. When an aluminum alloy material with a Si concentration of c1 is heated, liquid phase formation begins at a temperature T1 near the eutectic temperature (solidus temperature) Te. Below the eutectic temperature Te, as shown in Figure 2(a), crystal precipitates are distributed in a matrix separated by grain boundaries. When liquid phase formation begins, as shown in Figure 2(b), the grain boundaries with high segregation of crystal precipitate distribution melt and become liquid, as shown in Figure 2(c). Next, as shown in Figure 2(c), the peripheries of Si crystal precipitate particles and intermetallic compounds, which are the main additive element components dispersed in the aluminum alloy matrix, melt into spherical liquid phases. Furthermore, as shown in Figure 2(d), these spherical liquid phases formed in the matrix redissolve in the matrix over time and with increasing temperature due to interfacial energy, and migrate to the grain boundaries and surfaces by solid-phase diffusion. Next, as the temperature increases to T2 as shown in Figure 1, the amount of liquid phase increases according to the phase diagram. As shown in FIG. 1 , when the Si concentration of one aluminum alloy material is c2, which is lower than the maximum solubility limit, liquid phase formation begins near the solidus temperature Ts2. However, unlike the case of c1, the structure immediately before melting may not contain any crystal precipitates in the matrix, as shown in FIG. 3( a). In this case, as shown in FIG. 3( b), the material first melts and becomes liquid at the grain boundaries, and then, as shown in FIG. 3( c), liquid phases emerge from localized areas of high solute element concentration in the matrix. As shown in FIG. 3( d ), the spherical liquid phases formed in the matrix, as in the case of c1, redissolve into the matrix over time and with increasing temperature due to interfacial energy, and then migrate to the grain boundaries and surfaces by solid-phase diffusion. When the temperature rises to T3, the amount of liquid phase increases according to the phase diagram. Thus, the bonding method of the present invention utilizes the liquid phase generated by partial melting within the single-layer bonded aluminum alloy extrusion, thereby achieving both bonding and shape retention.

[0043] The behavior of the metallurgical structure from the time of liquid phase formation to the time of joining is explained below. A single-layer bonded aluminum alloy extrusion that generates a liquid phase is combined with the aluminum alloy mating material to be joined, and they are heated to a temperature at which the liquid phase ratio is 5.0% to 35.0%. Microscopic observation of the joint reveals that, as mentioned above, a very small amount of liquid phase formed on the surface of the single-layer bonded aluminum alloy extrusion fills the gap between the single-layer bonded aluminum alloy extrusion and the aluminum alloy mating material, where the oxide film has been destroyed by the action of flux or the like. Next, the liquid phase near the joining interface between the two alloy materials migrates into the aluminum alloy mating material, and as a result, the solid α-phase crystal grains of the single-layer bonded aluminum alloy extrusion that contact the joining interface grow toward the aluminum alloy mating material. Meanwhile, the crystal grains of the aluminum alloy mating material also grow toward the single-layer bonded aluminum alloy extrusion. Finally, the single-layer bonded aluminum alloy extrusion is joined to form a structure in which the structure of the single-layer bonded aluminum alloy extrusion penetrates into the aluminum alloy mating material near the joining interface. Therefore, no metallurgical structure other than that of the single-layer bonded aluminum alloy extrusion and the aluminum alloy mating material is generated at the joining interface.

[0044] On the other hand, when a brazing sheet clad with a brazing filler metal is used to join an aluminum alloy mating material by brazing heat, a fillet is formed at the joint, and a eutectic structure is observed, resulting in a joint structure that is different from that formed when a single-layer bonded aluminum alloy extrusion is used to join an aluminum alloy mating material by brazing heat. In other words, when a brazing sheet clad with a brazing filler metal is used to join an aluminum alloy mating material by brazing heat, the liquid phase brazing fills the joint and forms a fillet, resulting in a eutectic structure at the joint that is different from the surrounding area. Furthermore, when welding is used, the joint is locally melted, resulting in a metal structure that is different from that of other parts.

[0045] For this reason, when a single-layer bonded aluminum alloy extrusion is used to heat-bond to an aluminum alloy mating material, the metal structure of the bonded portion is composed only of those of both bonded members, or is composed of both bonded members integrated together, which means that the bonded structure is different from when a brazing sheet clad with a filler metal is used or when welding is used.

[0046] Because of this joining behavior, when a single-layer bonded aluminum alloy extrusion is heat-joined to an aluminum alloy mating material, almost no shape change occurs near the joint after the joining process. That is, when a single-layer bonded aluminum alloy extrusion is heat-joined to an aluminum alloy mating material, almost no shape change occurs near the joint after joining, such as a bead in a welding method or a fillet in a brazing method.

[0047] In the present invention, it is extremely difficult to measure the actual liquid phase ratio during heating of a single-layer bonded aluminum alloy extrusion. Therefore, the liquid phase ratio specified in the present invention is determined by equilibrium calculation. Specifically, it is calculated from the alloy composition and the maximum temperature reached during heating using thermodynamic equilibrium calculation software such as Thermo-Calc (registered trademark) manufactured by Thermo-Calc Software AB.

[0048] The relationship between the liquidus fraction and temperature will be explained based on the phase diagram shown in Figure 4. Figure 4 is a modified version of Figure 1. In Figure 4, a line extending parallel to the horizontal axis through temperature Te (hereinafter referred to as "solidus 1") and a line extending from the left end of solidus 1 to 660°C on the vertical axis, defining the boundary with the α phase, both represent solidus lines. In addition, a line extending downward and right from 660°C on the vertical axis and tangent to solidus 1 (hereinafter referred to as "liquidus 1") and a line extending upward and right from the tangent position, defining the boundary with the (Si + liquid phase), both represent liquidus lines.

[0049] Here, the point at temperature T2 is designated as P0, and a line parallel to the horizontal axis of the diagram is drawn through P0. The intersection with liquidus 1 is designated as P1, and the intersection with solidus 2 is designated as P2. An Al-Si alloy with a Si concentration of C1 is in a state where the liquid phase and solid phase coexist at temperature T2, and the Si concentration in the liquid phase is the concentration C at point P1. Ｐ１ and the Si concentration in the solid phase is the concentration C Ｐ２ The ratio of the mass of the liquid phase to the total mass at temperature T2, i.e., the liquid phase ratio, is the ratio of the length of the line segment P0 to P2 to the length of the line segment P1 to P2.

[0050] As described above, the liquid fraction can be determined by drawing a diagram from the alloy components and temperature based on the phase diagrams of binary alloys such as those shown in Figures 1 and 4. Similarly, for ternary or higher component systems, the liquid fraction can also be determined by drawing a diagram from the alloy components and temperature based on the phase diagram. It is difficult to represent the phase diagram of a ternary or higher component system as a simple X-Y plane diagram like that of Figure 4, but the liquid fraction can be obtained by computer calculation using Thermo-Calc's thermodynamic equilibrium calculation software.

[0051] The members to be joined that are combined with the aluminum alloy extrusion material of the present invention are made of an aluminum alloy or pure aluminum. That is, the members to be joined that are combined with the aluminum alloy extrusion material of the present invention are aluminum alloy materials or pure aluminum materials, and are formed from an aluminum alloy or pure aluminum. When the aluminum alloy material that forms the members to be joined that are combined with the aluminum alloy extrusion material of the present invention is made of an aluminum alloy, the aluminum alloy material that forms the members to be joined that are combined with the aluminum alloy extrusion material of the present invention may have the same alloy composition as the aluminum alloy material that forms the aluminum alloy extrusion material of the present invention, or a different alloy composition.

[0052] The aluminum alloy forming the aluminum alloy extrusion material of the present invention contains 1.80 to 3.00 mass % Si, 0.10 to 1.60 mass % Mn, 0.01 to 0.70 mass % Fe, with the remainder being Al and unavoidable impurities.

[0053] Si is an element that generates an Al-Si liquid phase during thermal bonding and contributes to bonding. If the Si content of the aluminum alloy is less than 1.80 mass%, a sufficient amount of liquid phase cannot be generated, resulting in reduced bondability. Furthermore, if the Si content exceeds 3.00 mass%, a large amount of elemental Si is contained, raising concerns about significant tool wear during the manufacturing process of the aluminum alloy material. Therefore, the Si content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is specified to be 1.80 to 3.00 mass%. The lower limit of the Si content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is preferably 2.00 mass%. Furthermore, the upper limit of the Si content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is preferably 2.80 mass%. The Si content can be within a range that combines the above upper and lower limits.

[0054] Mn is an element that adjusts the crystalline structure of an aluminum alloy material, contributing to improving heat bondability and suppressing deformation during heat bonding. If the Mn content of the aluminum alloy is less than 0.10% by mass, the crystal grain size according to the present invention cannot be obtained, resulting in significant deformation during heat bonding. Furthermore, if the Mn content exceeds 1.60% by mass, the deformation resistance of the aluminum alloy material increases, potentially making processing difficult during the manufacturing process of the aluminum alloy material. Therefore, the Mn content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is specified to be 0.10 to 1.60% by mass. The lower limit of the Mn content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is preferably 0.20% by mass, more preferably 0.30% by mass. Furthermore, the upper limit of the Mn content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is preferably 1.40% by mass, more preferably 1.20% by mass, more preferably 1.00% by mass, and more preferably 0.80% by mass. The Mn content can be within a range that combines the above upper and lower limits.

[0055] Fe is an element that contributes to improving the strength of aluminum alloy materials. If the Fe content of the aluminum alloy is less than 0.01% by mass, it is necessary to use extremely high-purity aluminum ingots to produce the aluminum alloy, which increases costs. Furthermore, if the Fe content exceeds 0.70% by mass, Al-Fe-Si compounds are formed, reducing the amount of Si that contributes to the formation of a liquid phase during thermal bonding, thereby reducing thermal bondability. Therefore, the Fe content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is specified to be 0.01 to 0.70% by mass. The lower limit of the Fe content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is preferably 0.05% by mass, more preferably 0.10% by mass, and more preferably 0.15% by mass. Furthermore, the upper limit of the Fe content of the aluminum alloy forming the aluminum alloy extrusion material of the present invention is preferably 0.60% by mass, more preferably 0.50% by mass, and more preferably 0.40% by mass. The Fe content can be within a range that combines the above upper and lower limits.

[0056] The width of the thinnest part of the aluminum alloy extrusion material of the present invention in a cross section perpendicular to the extrusion direction is 0.6 mm or more. If the width is less than 0.6 mm, the rigidity of the material will decrease and there is a concern that the metal structure according to the present invention will not be obtained.

[0057] Next, the metal structure of the aluminum alloy extrusion material of the present invention will be described.

[0058] The metallographic structure of the aluminum alloy extrusion material of the present invention has fine grains at the joining surface to improve thermal bondability, and coarse grains within the material to suppress deformation during thermal bonding. These metallographic structures should actually be achieved just before the formation of a liquid phase. However, since the metallographic structure is typically maintained after thermal bonding is completed, the metallographic structure can be confirmed in any of the following ways: a structure after thermal bonding, a material subjected to a heating test simulating thermal bonding, or a material heated to just before the formation of a liquid phase and then cooled. One form of heat treatment in which the material is heated to just before the formation of a liquid phase and then immediately cooled involves heating to 580°C to 620°C at an average heating rate of 5 to 100°C / min, holding at 580°C to 620°C for approximately 0 to 20 minutes, and then cooling.

[0059] The aluminum alloy extrusion of the present invention has an average crystal grain size of 200 μm or less in the outermost layer of the surface to be joined after a heating test in which the temperature is increased from 450° C. to 575° C. over 4 to 15 minutes and then maintained at 575 to 615° C. for 5 to 40 minutes. The average crystal grain size of the outermost layer is measured in a cross section at a depth of 0 to 10 μm along the surface of the surface to be joined (i.e., a cross section perpendicular to the depth direction at a depth of 0 to 10 μm), with the surface of the surface to be joined as the depth reference (zero position).

[0060] The average crystal grain size of the outermost layer affects the heat bondability during the production of an aluminum alloy structure. If the average crystal grain size in the outermost layer is larger than 200 μm, the heat bondability during the production of an aluminum alloy structure is reduced. That is, during heat bonding, an Al-Si liquid phase is generated at the grain boundaries of the surfaces to be bonded, and this liquid phase is supplied to the bonded portion via the grain boundaries, filling the bonded portion and solidifying, thereby achieving bonding. However, if the average crystal grain size in the outermost layer of the surfaces to be bonded is large, the amount of liquid phase supplied to the bonded portion will be reduced due to the small number of grain boundaries, which may result in insufficient bonding. For these reasons, the average crystal grain size of the outermost layer of the surfaces to be bonded is specified to be 200 μm or less. The average crystal grain size of the outermost layer of the surfaces to be bonded is preferably 180 μm or less, more preferably 160 μm or less, and more preferably 140 μm or less.

[0061] The aluminum alloy extrusion of the present invention has an average crystal grain size of 400 μm or more in a cross section at a depth of 100 μm in the thinnest portion after a heating test in which the temperature is increased from 450° C. to 575° C. over 4 to 15 minutes and then maintained at 575 to 615° C. for 5 to 40 minutes. The average crystal grain size in the cross section at a depth of 100 μm in the thinnest portion is measured in a cross section at a depth of 100 μm along the surface of the surface to be joined (i.e., a cross section perpendicular to the depth direction at a depth of 100 μm), with the surface of the surface to be joined as the depth reference (zero position).

[0062] The average crystal grain size in the cross section at a depth of 100 μm from the thinnest part affects deformation during thermal bonding. If the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part is smaller than 400 μm, deformation during thermal bonding becomes significant. That is, when an Al-Si liquid phase is generated at the grain boundaries during thermal bonding, a small average crystal grain size causes a lot of grain boundary sliding. However, the thinnest part is particularly affected by this because of its low rigidity, resulting in a large amount of deformation and a concern that the dimensional specifications will not be met. For these reasons, the average crystal grain size in the cross section at a depth of 100 μm from the thinnest part is specified to be 400 μm or more.

[0063] Furthermore, the surface to be joined of the aluminum alloy extrusion material of the present invention and the portion with the thinnest wall thickness may be at the same position or at different positions.

[0064] As an example of the metal structure of the aluminum alloy extrusion material of the present invention, the microstructure of the portion to be joined and the portion with the thinnest wall thickness of the aluminum alloy extrusion material after a heating test simulating thermal bonding is shown in Figures 5 to 7. Figure 5 shows the microstructure of a cross section parallel to the extrusion direction and the wall thickness direction. The surface vicinity to be joined has a fine recrystallized structure, while the interior of the material has a coarse recrystallized structure. Figure 6 shows the microstructure of a cross section perpendicular to the depth direction of the outermost layer. The fine recrystallized structure is suitable for thermal bonding. Figure 7 shows the microstructure of a cross section perpendicular to the depth direction at a depth of 100 μm. The coarse recrystallized structure is effective in suppressing deformation during thermal bonding.

[0065] The average crystal grain size in the present invention is an average crystal grain size measured by a cutting method in accordance with JIS G 0551.

[0066] Thus, the aluminum alloy extrusion material of the present invention has a metal structure in which, when heated by raising the temperature from 450°C to 575°C in 4 to 15 minutes and holding at 575 to 615°C for 5 to 40 minutes, the average crystal grain size of the outermost layer of the surface to be joined is 200 μm or less, and the average crystal grain size of the cross section at a depth of 100 μm from the thinnest part is 400 μm or more. Since the aluminum alloy extrusion material of the present invention has the metal structure described above, it can be subjected to a heat treatment in which it is heated to just before the formation of a liquid phase and then immediately cooled, for example, by heating to 580°C to 620°C at an average heating rate of 5 to 100°C / min, holding at 580°C to 620°C for about 0 to 20 minutes, and then cooling. This heat treatment forms a structure in which, during heat bonding, the average crystal grain size of the outermost layer of the surface to be bonded is 200 μm or less and the average crystal grain size of the cross section at a depth of 100 μm from the thinnest part is 400 μm or more. Therefore, it can be bonded in a single layer, has good bondability, and can suppress deformation during heat bonding.

[0067] The aluminum alloy material as one of the joined members used in the aluminum alloy structure of the present invention and the aluminum alloy extrusion material of the present invention can be produced by an appropriate combination of continuous casting, DC casting, extrusion, and rolling. The aluminum alloy material as the other of the joined members used in the aluminum alloy structure of the present invention and the pure aluminum material can be produced by an appropriate combination of continuous casting, DC casting, extrusion, and rolling. As the casting raw materials, virgin aluminum ingots, recycled aluminum ingots, intermediate alloys, and aluminum waste can be used.

[0068] The aluminum alloy material as one of the members to be joined used in the aluminum alloy structure of the present invention and the method for producing the aluminum alloy extrusion material of the present invention are characterized by comprising: a casting step of casting an ingot containing 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, the balance being Al and unavoidable impurities; and a hot extrusion step of hot extruding the ingot while the temperature of the ingot is 400°C or higher and 550°C or lower, to form the ingot into a shape having a thinnest width of 0.6 mm or higher in a cross section perpendicular to the extrusion direction. Furthermore, the aluminum alloy material as one of the members to be joined used in the aluminum alloy structure of the present invention and the method for producing the aluminum alloy extrusion material of the present invention can further comprise a homogenization step of performing a homogenization treatment on the ingot at a temperature of 570°C or lower after the casting step and before the hot extrusion step.

[0069] The casting step is a step of casting an ingot containing 1.80 to 3.00 mass% Si, 0.10 to 1.60 mass% Mn, 0.01 to 0.70 mass% Fe, with the remainder being Al and unavoidable impurities, by DC casting, continuous casting, or the like. The lower limit of the Si content of the ingot is preferably 2.00 mass%, and the upper limit of the Si content of the ingot is preferably 2.80 mass%. The lower limit of the Mn content of the ingot is preferably 0.20 mass%, more preferably 0.30 mass%, and the upper limit of the Mn content of the ingot is preferably 1.40 mass%, more preferably 1.20 mass%, more preferably 1.00 mass%, and more preferably 0.80 mass%. The lower limit of the Fe content of the ingot is preferably 0.05 mass%, more preferably 0.10 mass%, more preferably 0.15 mass%, and the upper limit of the Fe content of the ingot is preferably 0.60 mass%, more preferably 0.50 mass%, more preferably 0.40 mass%. The contents of Si, Mn, and Fe can be within a range that combines the above upper and lower limits.

[0070] After the casting process, if necessary, a homogenization treatment can be performed by holding the ingot at a temperature of 570°C or less, preferably 450 to 570°C. The holding time for the homogenization treatment is selected appropriately, but is preferably 2 hours or more, more preferably 2 to 24 hours. The homogenization treatment has the effect of eliminating microsegregation in the ingot structure of the billet and homogenizing the structure. If the homogenization treatment temperature is higher than 570°C, there is a risk of the billet partially melting. Furthermore, if the homogenization treatment time is shorter than 2 hours, there is a risk of insufficient diffusion energy, and the microsegregation in the ingot structure of the billet will not be eliminated. Furthermore, from the viewpoint of productivity, the homogenization treatment time is preferably 24 hours or less.

[0071] The hot extrusion process is a process in which the ingot is hot extruded while its temperature is between 400°C and 550°C, and the ingot is formed into a shape in which the narrowest part of the cross section perpendicular to the extrusion direction has a width of 0.6 mm or more. The hot extrusion temperature is preferably between 400°C and 550°C. If the extrusion temperature is lower than 400°C, the extrusion pressure increases, which may make extrusion difficult. If the extrusion temperature is higher than 550°C, strain defects are likely to occur in the extruded aluminum alloy pipe during extrusion. In this case, the extrusion ratio in the hot extrusion is preferably between 20 and 1000. By having an extrusion ratio in the hot extrusion of between 20 and 1000, sufficient processing strain is applied to the surface by hot extrusion, and the metal structure according to the present invention is obtained. Here, the extrusion ratio is the ratio of the cross-sectional area of ​​the container into which the billet is inserted before extrusion to the cross-sectional area of ​​the extruded material. If the extrusion ratio is less than 20, the processing strain applied by hot extrusion will be insufficient, and there is a concern that the metal structure according to the present invention will not be obtained. On the other hand, if the extrusion ratio is more than 1000, the load during extrusion processing will be large, and extrudability will be impaired. The lower limit of the extrusion ratio is preferably 20 or more, more preferably 40 or more, and even more preferably 60 or more.

[0072]

[0013] The aluminum alloy material as one of the joined members used in the aluminum alloy structure of the present invention and the aluminum alloy extrusion of the present invention can be produced by producing a billet by continuous casting, DC casting, etc., subjecting the billet to a homogenization treatment as necessary, and then hot rolling. The hot rolling conditions can be appropriately selected so as to distort the surface of the billet to an extent that the metal structure according to the present invention can be obtained.

[0073] The present invention provides a joining method for manufacturing an aluminum alloy structure, and a method for joining an aluminum alloy extrusion material of the present invention to another member. Joining is preferably performed at a temperature at which the ratio of the mass of the liquid phase generated within the aluminum alloy material to the total mass of the aluminum alloy material forming one of the joined members or the aluminum alloy material forming the present aluminum alloy extrusion material (hereinafter referred to as the "liquid phase ratio") is 5% to 35%. If the liquid phase ratio exceeds 35%, the amount of liquid phase generated is too large, causing the aluminum alloy material to be unable to maintain its shape and undergo significant deformation. On the other hand, if the liquid phase ratio is less than 5%, joining becomes difficult. It is extremely difficult to measure the actual liquid phase ratio during heating. Therefore, the liquid phase ratio is determined by equilibrium calculation. Specifically, it is calculated from the alloy composition and the maximum temperature reached during heating using thermodynamic equilibrium calculation software such as Thermo-Calc.

[0074] In addition, in order to ensure that the liquid phase is sufficiently filled in the joint, it is preferable to consider the filling time, and the time during which the liquid phase rate is 5% or more is preferably 30 seconds or more and 3600 seconds or less. More preferably, the time during which the liquid phase rate is 5% or more is 60 seconds or more and 1800 seconds or less, which allows for more sufficient filling and reliable joining. If the time during which the liquid phase rate is 5% or more is less than 30 seconds, the liquid phase may not be sufficiently filled in the joint. On the other hand, if it exceeds 3600 seconds, deformation of the aluminum material may progress. Note that in the joining method of the present invention, the liquid phase moves only in the very vicinity of the joint, so the time required for this filling does not depend on the size of the joint.

[0075] Specific examples of desirable joining conditions include a joining temperature of 580°C to 620°C and a holding time at the joining temperature of approximately 0 to 20 minutes. The average rate of temperature rise to the joining temperature is 5 to 100°C / min. A holding time of 0 minutes means that cooling begins immediately after the temperature of the members reaches the predetermined joining temperature. Furthermore, the heating conditions may be adjusted depending on the composition in order to bring the metal structure of the joining portion into a suitable state, as described below.

[0076] An oxide film is formed on the surface of aluminum alloy material, which inhibits joining. Therefore, it is necessary to destroy the oxide film during joining. In order to destroy the oxide film, it is preferable to apply flux to at least the joining area. The flux is KAlF, which is used for brazing aluminum alloys. ４ and CsAlF ４ Fluoride-based fluxes such as fluoride-based fluxes or chloride-based fluxes such as KCl or NaCl are used. These fluxes melt before a liquid phase is formed or before the joining temperature is reached, and react with and destroy the oxide film. Furthermore, in this method, joining is performed in a non-oxidizing atmosphere such as nitrogen gas or argon gas to suppress the formation of an oxide film. In particular, when using a fluoride-based flux, it is preferable to join in a non-oxidizing gas atmosphere with an oxygen concentration of 250 ppm or less and a dew point of -25°C or less.

[0077] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples shown below.

[0078] (Examples and Comparative Examples) <Production of Aluminum Alloy Extrusions> First, ingots having the chemical compositions (alloy symbols A1 to A7) shown in Table 1 were cast by DC casting. The ingots were cylindrical with a diameter of 90 mm. The ingots were then heated and subjected to a homogenization treatment. The holding temperature and holding time in the homogenization treatment were 530°C for 8 hours. After the homogenization treatment was completed, the ingots were inserted into a preheated container with a diameter of 97 mm while the temperature of the ingots was 520°C, and hot extrusion was performed to form flat bars with a width of 35 mm and a thickness of 3.0 mm. Aluminum alloy extrusions were obtained by the above method.

[0079]

[0080] <Grain size after heating test simulating thermal bonding> Using the same manufacturing method as above, ingots made of alloys A1 to A7 shown in Table 2 were hot extruded at the extrusion ratios shown in Table 2 to produce aluminum alloy extrusions B1 to B5 and C1 to C2 with a width of 35 mm and a thickness of 3.0 mm. Also, an ingot made of alloy A3 shown in Table 2 was hot extruded at the extrusion ratio shown in Table 2 to produce aluminum alloy extrusion C3 with a width of 60 mm and a thickness of 15 mm. Next, the temperature was raised from 450°C to 575°C over 4 to 15 minutes, and the extrusions were held at 575 to 615°C for 5 to 40 minutes. After that, the test materials B1 to B5 and C1 to C3 after the heating test were obtained by cooling to room temperature. The material surfaces parallel to the extrusion direction and width direction were assumed to be the surfaces to be used for bonding, and the outermost surface and a depth of 100 μm from the surface were machined and polished to adjust the surface. Further, etching was carried out, and an arbitrary field of view of each sample was photographed at 50x magnification using a polarizing microscope, and the average crystal grain size was measured by the intercept method in accordance with JIS G 0551.

[0081]

[0082] As shown in Table 2, test materials B1 to B5 had the average grain size specified in the present invention. On the other hand, test materials C1 and C2 had a low Mn content, so the average grain size at a depth of 100 μm was smaller than the range specified in the present invention. Therefore, there was a risk of significant deformation during thermal bonding. Furthermore, test material C3 had a small extrusion ratio, so the average grain size in the outermost layer was larger than the range specified in the present invention. In aluminum alloy materials that have thermal bonding function in a single layer, the grain boundaries serve as liquid phase supply paths. However, test material C3 had a very large average grain size in the outermost layer, so it is presumed that there were very few paths for liquid phase brazing material to be supplied. Therefore, there was a risk of test material C3 having reduced thermal bondability.

[0083] <Evaluation of Heat Bondability and High-Temperature Deformation Resistance> Materials were prepared using the same manufacturing method as above to obtain test materials B1 to B5 and test materials C1 and C2. To evaluate heat bondability, an inverted T-shaped joining test was performed using the test piece (reference numeral 1) shown in Figure 8. Each test material was cut to a length of 60 mm, and a fluoride-based flux was applied to the surface to be joined. A 1.0 mm thick A3003 aluminum alloy plate (reference numeral 2) was placed at the center of the width of the joining surface of each test material, and the test materials were combined in an inverted T-shape to undergo heat treatment for heat bonding. The heat treatment conditions were a temperature increase from 450°C to 575°C in 4 minutes, a hold at 600°C for 3 minutes, and then cooling to room temperature. The presence or absence of bonding was then confirmed by cross-sectional observation. Bonded specimens were rated as "pass," while unbonded specimens were rated as "fail." The results are shown in Table 3.

[0084] To evaluate high-temperature deformation resistance, a sag test was performed as follows. Each test piece was cut to a length of 130 mm, and the end was fixed with 100 mm of the cut piece protruding horizontally. Heat treatment for thermal bonding was performed. The heat treatment conditions were to raise the temperature from 450°C to 575°C in 6 minutes, hold at 600°C for 3 minutes, and then cool to room temperature. The sagging amount of each test piece was then measured, and a sagging amount of 2 mm or less was evaluated as "pass, excellent," a sagging amount of more than 2 mm and less than 5 mm was evaluated as "pass, good," a sagging amount of more than 5 mm and less than 20 mm was evaluated as "fail, poor," and a sagging amount of more than 20 mm was evaluated as "fail, very poor." The results are shown in Table 3.

[0085]

[0086] Test materials B1 to B5 had good heat bondability and high-temperature deformation resistance. On the other hand, test material C1 had poor heat bondability because its Si content was lower than the range specified in the present invention. Furthermore, test material C2 had a Mn content lower than the range specified in the present invention, so the average crystal grain size at a depth of 100 μm was smaller than the range specified in the present invention. As a result, deformation after heating was significant and high-temperature deformation resistance was poor.

[0087] Examples of the aluminum alloy structure of the present invention, and the aluminum alloy extrusion material of the present invention and the manufacturing method thereof have been described above based on the examples. However, the specific aspects of the aluminum alloy structure of the present invention, the aluminum alloy extrusion material of the present invention and the manufacturing method thereof are not limited to those of the examples, and the configurations can be changed as appropriate within the scope that does not impair the spirit of the present invention.

Claims

1. An aluminum alloy structure in which one member to be joined made of an aluminum alloy and the other member to be joined made of either an aluminum alloy or pure aluminum are thermally joined, the one member to be joined containing 1.80-3.00 mass% Si, 0.10-1.60 mass% Mn, 0.01-0.70 mass% Fe, with the remainder being Al and unavoidable impurities, the average crystal grain size in the outermost layer of the one member to be joined at the joining portion between the one member to be joined and the other member to be joined being 200 μm or less, and the average crystal grain size in the cross section at a depth of 100 μm in the part where the thickness of the one member to be joined is the thinnest being 400 μm or more.

2. A method for heat-bonding an aluminum alloy structure as described in claim 1, characterized in that the metal structure at 575°C during heat-bonding has an average crystal grain size of 200 μm or less in the outermost layer of the surface to be bonded, and an average crystal grain size of 400 μm or more in the cross section at a depth of 100 μm in the thinnest part.

3. An aluminum alloy extrusion having a single layer thermal bonding function, comprising 1.80-3.00 mass% Si, 0.10-1.60 mass% Mn, 0.01-0.70 mass% Fe, with the remainder being Al and unavoidable impurities, the width of the thinnest part in a cross section perpendicular to the extrusion direction being 0.6 mm or more, the average crystal grain size of the outermost layer on the surface to be bonded being 200 μm or less after a heating test in which the temperature is raised from 450°C to 575°C over 4-15 minutes and then maintained at 575-615°C for 5-40 minutes, and the average crystal grain size of the cross section at a depth of 100 μm from the thinnest part being 400 μm or more.

4. A method for producing an aluminum alloy extrusion product according to claim 3, comprising: a casting step of casting an ingot containing 1.80-3.00 mass% Si, 0.10-1.60 mass% Mn, 0.01-0.70 mass% Fe, with the remainder being Al and unavoidable impurities; and a hot extrusion step of hot extruding the ingot while the temperature of the ingot is between 400°C and 550°C, to form the ingot into a shape in which the width of the thinnest part in a cross section perpendicular to the extrusion direction is 0.6 mm or more.

5. A method for producing an aluminum alloy extrusion material according to claim 4, further comprising a homogenization step of holding the ingot at a temperature of 570°C or less after the casting step.

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