JP7664129B2 - Aluminum alloy laminate and heat exchanger - Google Patents

Description

The present invention relates to an aluminum alloy laminate having excellent formability, corrosion resistance and brazing properties, and to an aluminum alloy laminate used in heat exchangers manufactured by a brazing method, such as aluminum heat exchangers for automobiles.
More specifically, the present invention relates to an aluminum alloy laminated material that uses an aluminum alloy material having a single layer thermal bonding function as a skin material and has excellent formability, brazing property and corrosion resistance.

The typical method for manufacturing aluminum alloy heat exchangers for automobiles and other uses is to use aluminum alloy brazing sheets, form the brazing sheets into the desired part shapes, combine the various parts, assemble them into a heat exchanger core, and then integrate them through a brazing process.

When the brazing sheet is to be largely processed into the component shape, O-tempered brazing sheets are used to ensure formability, but it is difficult to achieve formability, brazing ability, and corrosion resistance with O-tempered brazing sheets.

As an aluminum alloy brazing sheet that achieves both brazeability and corrosion resistance, for example, Patent Document 1 describes an aluminum alloy brazing sheet including an aluminum alloy core material, a first brazing filler metal clad on one side of the core material, and a second brazing filler metal clad on the other side, in which the core material is made of an aluminum alloy containing 0.05 to 1.50 mass% Fe, 0.30 to 2.00 mass% Mn, the balance being Al and unavoidable impurities, and the first brazing filler metal is made of 1.50 to 4.00 mass% Si, The present invention discloses an aluminum alloy brazing sheet, characterized in that the first brazing material is made of an aluminum alloy having a sacrificial anode function and a brazing function, the second brazing material containing 4.00 to 13.00 mass% Si and 0.03 to 1.00 mass% Fe, the balance being Al and unavoidable impurities, and the second brazing material contains 2000 pieces/ ^mm2 or less of Al-Si-Fe-based intermetallic compounds having a circle equivalent diameter of 0.5 to 80.0 μm.

JP 2017-145463 A

In the case of brazing sheets that use aluminum alloy brazing filler metal such as 4343 alloy or 4045 alloy on one or both sides of the core material to make the formed brazing sheet assembled to the heat exchanger core into an integral structure, the processing strain introduced during the forming process should disappear by recrystallization before the brazing filler metal melts during the brazing heating process. However, if the processing strain remains until the brazing filler metal melts, the molten brazing filler metal tends to diffuse using the processing strain of the core material as a route, making erosion more likely to occur, resulting in poor brazing properties and reduced corrosion resistance.

In particular, in recent years, there has been a demand for lighter heat exchangers, and when components are thinned to reduce the weight of the heat exchanger, it is necessary to increase the strength of the components. For this reason, it has been proposed to add Cu to the aluminum alloy for the core material or to increase the Mn content. However, when Cu is added, if the Cu content is too high, the melting point of the core material decreases, making it easier for the core material to melt during brazing. In addition, when Mn is added, fine precipitates are generated in the core material, making it difficult for the core material to recrystallize, and strain accumulated in the formed part during brazing tends to remain during brazing, making it easier for erosion to occur.

Although the aluminum alloy brazing sheet disclosed in Patent Document 1 has excellent brazing properties and corrosion resistance, further improvements are required to simultaneously achieve formability, brazing properties, and corrosion resistance.

The object of the present invention is therefore to provide an aluminum alloy material for brazing that can simultaneously achieve formability, brazeability, and corrosion resistance.

The inventors of the present invention have conducted extensive research to solve the above problems, and as a result have discovered that by strictly controlling the alloy composition and the manufacturing conditions, such as the conditions for cold rolling and annealing, in order to improve all of the formability, brazability, and corrosion resistance, it is possible to heat-bond the skin material in a single layer and suppress the reduction in plate thickness due to brazing, and by making the intermetallic compounds in the core fine, optimizing their distribution, and adjusting the crystal grain structure, it is possible to obtain an aluminum alloy material with excellent formability, brazability, and corrosion resistance, and have completed the present invention.

That is, the present invention (1) has a core material and a skin material clad on one or both sides of the core material,
The core material is made of an aluminum alloy containing 0.30 to 0.70 mass% Fe, 0.03 to 0.20 mass% Cu, 1.00 to 1.50 mass% Mn, with the remainder being aluminum and unavoidable impurities;
The skin material is made of an aluminum alloy containing 2.00 to 3.00 mass% Si, 0.10 to 0.40 mass% Fe, 0.80 to 5.00 mass% Zn, with Cu restricted to 0.20 mass% or less, and the remainder being aluminum and unavoidable impurities;
The average crystal grain size of the core material is 25 to 125 μm,
In a heating test in which the temperature is increased from 300°C to 400°C at an average heating rate of 80°C/min or less and then held at 600±3°C for 5±3 minutes, the skin thickness retention rate ((skin thickness after heating test/skin thickness before heating test)×100) is 90.0% or more,
The temper is O material,
The present invention provides an aluminum alloy laminate characterized by the above.

The present invention (2) also provides an aluminum alloy laminate according to (1), which is characterized in that it is a two-layer material consisting of the core material and the skin material clad on one side of the core material.

The present invention (3) also provides an aluminum alloy laminate according to (1), which is a three-layer material consisting of the core material and the skin material that is clad on both sides of the core material.

The present invention (4) is a three-layer material comprising the core material, the skin material clad on one side of the core material, and a brazing material clad on the other side of the core material,
The brazing filler metal is made of an aluminum alloy containing 6.00 to 13.00 mass% Si, an Fe content of 0.80 mass% or less, and a Cu content of 0.25 mass% or less, with the remainder being aluminum and unavoidable impurities;
The present invention provides an aluminum alloy laminate characterized by the above (1).

The present invention (5) also provides an aluminum alloy composite material according to (4), characterized in that the brazing filler metal further contains 4.00 mass% or less of Zn and the Mn content is restricted to 0.30 mass% or less.

The present invention (6) also provides an aluminum alloy laminate according to any one of (1) to (5), characterized in that the skin material further contains one or more of the following: 1.50% by mass or less Mn, 0.20% by mass or less Ti, 0.20% by mass or less Zr, 0.20% by mass or less Cr, 0.20% by mass or less V, and 0.10% by mass or less Bi.

The present invention (7) also provides an aluminum alloy composite material according to any one of (1) to (6), characterized in that the core material further contains one or more of 0.20% by mass or less of Si, 0.30% by mass or less of Mg, 0.30% by mass or less of Zn, 0.30% by mass or less of Ti, 0.30% by mass or less of Zr, and 0.30% by mass or less of Cr.

The present invention (8) also provides a heat exchanger obtained by combining two or more molded bodies of any one of the aluminum alloy composite materials (1) to (7) and heating them for brazing.

The present invention provides an aluminum alloy composite material for brazing that has both formability, brazeability, and corrosion resistance.

FIG. 2 is a schematic cross-sectional view showing a state in which formed bodies of an example of an aluminum alloy laminate material of the present invention are combined. FIG. 2 is a schematic cross-sectional view showing a state in which formed bodies of another embodiment of the aluminum alloy laminate of the present invention are combined. 1 is a microstructure photograph of a cross section of a core material of an embodiment (0.5 mm material). 1 is a microstructure photograph of a cross section of a core material of an embodiment (1.0 mm material). FIG. 1 is a schematic diagram showing a drop test. 13 is a photograph showing the cross-sectional structure of the joint after an inverted T-shaped test in an embodiment (0.5 mm material) and an embodiment (1.0 mm material). 1 is a photograph of the microstructure of a cross section of an aluminum alloy laminate of an example (0.5 mm material). 1 is a photograph of the microstructure of a cross section of an aluminum alloy laminate of an example (1.0 mm material).

The aluminum alloy laminate of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing an example of the aluminum alloy laminate of the present invention formed into the shape of each part, and then combining the formed bodies to produce a combined body. Also, Figure 2 is a schematic cross-sectional view showing another example of the aluminum alloy laminate of the present invention formed into the shape of each part, and then combining the formed bodies to produce a combined body. In Figure 1, the combined body 1 is formed into the shape of each part that forms a flow path by forming a two-layer aluminum alloy laminate 4a consisting of a core material 2a and a skin material 3a clad on one side of the core material 2a, and a two-layer aluminum alloy laminate 4b consisting of a core material 2b and a skin material 3b clad on one side of the core material 2b, to produce a formed body 6a and a formed body 6b, and then the skin material 3a of the formed body 6a and the skin material 3b of the formed body 6b are opposed to each other and combined. When this combination 1 is heated for brazing, a liquid phase is generated in the skin materials 3a and 3b during the brazing heating process, and volume expansion occurs when the solid phase changes to liquid phase, so the liquid phase generated in the skin materials seeps out to the surface of the skin materials. The aluminum alloy composite material 4a and the aluminum alloy composite material 4b are joined by the liquid phase that has seeped out to the surface of the skin materials 3a and 3b. At this time, the skin materials 3a and 3b do not melt because they contain a small amount of Si, so even after brazing heating, the parent phase remains and the original shape is maintained, and the skin material containing Zn remains, so after brazing heating, the skin materials 3a and 3b function as sacrificial anti-corrosion materials.

In FIG. 2, the combined body 11 is formed by forming a three-layer aluminum alloy composite material 14a consisting of a core material 12a, a skin material 13a clad on one side of the core material 12a, and a skin material 15a clad on the other side of the core material 12a, and a three-layer aluminum alloy composite material 14b consisting of a core material 12b, a skin material 13b clad on one side of the core material 12b, and a skin material 15b clad on the other side of the core material 12b, into the respective component shapes that form a flow path to produce formed body 16a and formed body 16b, and then combining the skin material 13a of formed body 16a and the skin material 13b of formed body 16b, and the skin material 15a of formed body 16a and the skin material 15b of formed body 16b, respectively, in an opposing relationship. When this combined body 11 is heated for brazing, a liquid phase is generated in the skin materials 13a, 13b, 15a, and 15b during the brazing heating process, and volume expansion occurs when the solid phase changes to the liquid phase, so the liquid phase generated in the skin materials seeps out to the surface of the skin materials. The aluminum alloy composite material 14a and the aluminum alloy composite material 14b are joined by the liquid phase that has seeped out to the surfaces of the skin materials 13a, 13b, 15a, and 15b. At this time, the skin materials 13a, 13b, 15a, and 15b do not melt because they contain a small amount of Si, so even after brazing heating, the parent phase remains and the original shape is maintained, and the skin materials containing Zn remain, so the skin materials 13a, 13b, 15a, and 15b function as sacrificial anti-corrosion materials after brazing heating.

In FIG. 2, the combined body 21 is formed by forming a three-layer aluminum alloy composite material 24a consisting of a core material 22a, a skin material 23a clad on one side of the core material 22a, and a brazing material 25a clad on the other side of the core material 22a, and a three-layer aluminum alloy composite material 24b consisting of a core material 22b, a skin material 23b clad on one side of the core material 22b, and a brazing material 25b clad on the other side of the core material 22b, into the respective part shapes that form a flow path to produce the formed body 26a and the formed body 26b, and then combining the skin material 23a of the formed body 26a and the skin material 23b of the formed body 26b with the brazing material 25a of the formed body 26a and the brazing material 25b of the formed body 26b, respectively, facing each other. When the combined body 21 is heated for brazing, a liquid phase is generated in the skin materials 23a and 23b during the brazing heating process, and volume expansion occurs when the solid phase changes to the liquid phase, so that the liquid phase generated in the skin materials seeps out onto the skin material surface. The skin material 23a side of the aluminum alloy laminated material 24a and the skin material 23b side of the aluminum alloy laminated material 24b are joined by the liquid phase that has seeped out onto the surfaces of the skin materials 23a and 23b. In addition, the brazing material 25a and the brazing material 25b melt during the brazing heating process to generate a liquid-phase braze, and the brazing material 25a side of the aluminum alloy laminated material 24a and the brazing material 25b side of the aluminum alloy laminated material 24b are joined by the generated liquid-phase braze. At this time, since the Si content of the skin materials 23a and 23b is low, they do not melt, so even after the brazing heat, the parent phase remains and the original shape is maintained, and since the skin material containing Zn remains, the skin materials 23a and 23b function as sacrificial anti-corrosion materials after the brazing heat.

The aluminum alloy laminate of the present invention has a core material and a skin material clad on one or both sides of the core material,
The core material is made of an aluminum alloy containing 0.30 to 0.70 mass% Fe, 0.03 to 0.20 mass% Cu, 1.00 to 1.50 mass% Mn, with the remainder being aluminum and unavoidable impurities;
The skin material is made of an aluminum alloy containing 2.00 to 3.00 mass% Si, 0.10 to 0.40 mass% Fe, 0.80 to 5.00 mass% Zn, with Cu restricted to 0.20 mass% or less, and the remainder being aluminum and unavoidable impurities;
In a heating test in which the temperature is increased from 300°C to 400°C at an average heating rate of 80°C/min or less and then held at 600±3°C for 5±3 minutes, the skin thickness retention rate ((skin thickness after heating test/skin thickness before heating test)×100) is 90.0% or more,
The average crystal grain size of the core material is 25 to 125 μm,
The temper is O material,
This is an aluminum alloy laminate characterized by the above.

The aluminum alloy laminate of the present invention has a core material and a skin material clad on one or both sides of the core material. That is, the aluminum alloy laminate of the present invention has at least one side of the core material of the aluminum alloy laminate of the present invention clad with the skin material of the aluminum alloy laminate of the present invention, and the other side of the core material may not be clad with anything, or may be clad with the skin material of the aluminum alloy laminate of the present invention or the brazing material of the aluminum alloy laminate of the present invention. The form of the aluminum alloy laminate of the present invention includes (1) a two-layer aluminum alloy laminate consisting of a core material and a skin material clad on one side of the core material, (2) a three-layer aluminum alloy laminate consisting of a core material and a skin material clad on both sides of the core material, and (3) a three-layer aluminum alloy laminate consisting of a core material, a skin material clad on one side of the core material, and a brazing material clad on the other side of the core material. In addition, when the aluminum alloy laminate of the present invention has skin materials on both sides of the core material, the two skin materials may have the same composition or different compositions as long as they are within the specified range of the skin materials related to the aluminum alloy laminate of the present invention.

The core material of the aluminum alloy composite material of the present invention is an aluminum alloy containing 0.30 to 0.70 mass% Fe, 0.03 to 0.20 mass% Cu, 1.00 to 1.50 mass% Mn, with the remainder being aluminum and unavoidable impurities.

The Fe in the core material has the effect of forming intermetallic compounds in the aluminum alloy and refining the recrystallized grains, and in the present invention, the recrystallized grains of the core material are refined to improve formability. The Fe content in the core material is 0.30 to 0.70 mass%, preferably 0.45 to 0.70 mass%. By having the Fe content in the core material within the above range, the formability of the aluminum alloy composite material is improved. On the other hand, if the Fe content in the core material is less than the above range, the crystal grains formed during O material treatment become coarse, and the size of the crystal grains does not fall within the range specified in the present invention. In addition, if the Fe content in the core material exceeds the above range, coarse intermetallic compounds are formed, which are likely to cause cracks during forming.

Cu in the core material is an element added to improve the strength of the aluminum alloy, and to make the potential of the alloy more noble, thereby protecting it from the sacrificial corrosion protection effect of the alloy with a less noble potential, and to improve the corrosion resistance of the material. The Cu content in the core material is 0.03 to 0.20 mass%, preferably 0.05 to 0.18 mass%. By having the Cu content in the core material within the above range, the corrosion resistance of the aluminum alloy composite material is increased. On the other hand, if the Cu content in the core material is less than the above range, the effect of adding Cu is insufficient, and if it exceeds the above range, the Cu added to the core alloy during annealing or brazing heat diffuses into the skin material, the amount of Cu in the skin material increases, and the potential becomes more noble, so the sacrificial corrosion protection effect of the skin material does not work.

Mn in the core material is an element added to improve the strength of the aluminum alloy. The Mn content in the core material is 1.00 to 1.50 mass%, preferably 1.00 to 1.40 mass%. When the Mn content in the core material is within the above range, the strength of the aluminum alloy composite material is increased. On the other hand, if the Mn content in the core material is less than the above range, the strength improvement effect is insufficient, and if it exceeds the above range, fine precipitates are formed in the aluminum alloy, causing the recrystallized grains to become coarse, so that the crystal grain size does not fall within the range specified in the present invention.

The core material may contain one or more of the following elements: 0.20% by mass or less Si, 0.30% by mass or less Mg, 0.30% by mass or less Zn, 0.30% by mass or less Ti, 0.30% by mass or less Zr, and 0.30% by mass or less Cr. These elements have the effect of improving strength, etc.

Si is an element that is inevitably contained in aluminum alloys. When the core material contains 0.20 mass% or less of Si, the strength is increased. Si forms fine precipitates together with Mn, but if the Si content exceeds 0.20 mass%, the amount of precipitates increases too much, and the pinning effect of the precipitates during annealing makes the recrystallized grains prone to coarsening, and the size of the crystal grains does not fall within the range specified in this invention.

By containing 0.30% or less Mg by mass in the core material, the strength is improved by the precipitation of Mg-Si. Since Mg reacts with the flux during brazing heating and inhibits brazing, the upper limit of the Mg content is 0.30% by mass.

By containing 0.30% or less by mass of Zn in the core material, it becomes possible to utilize scrap material containing Zn. Since Zn makes the potential of the alloy more base, if the Zn content in the core material is too high, the core material will not be protected by sacrificial corrosion protection, so the upper limit of the Zn content is 0.30% by mass.

The core material contains one or more of 0.30% by mass or less Ti, 0.30% by mass or less Zr, and 0.30% by mass or less Cr, which improves strength through solid solution strengthening. Ti, Zr, and Cr are elements added to improve strength and control grain size, but if the content is high, coarse intermetallic compounds are generated during casting, reducing the formability of the aluminum alloy composite material. Therefore, the Ti content is 0.30% by mass or less, the Zr content is 0.30% by mass or less, and the Cr content is 0.30% by mass or less.

The unavoidable impurity elements contained in the core material other than the above elements are each contained in an amount of 0.05% by mass or less, with the total amount being 0.15% by mass or less.

The skin material of the aluminum alloy composite material of the present invention is an aluminum alloy containing 2.00 to 3.00 mass% Si, 0.10 to 0.40 mass% Fe, 0.80 to 5.00 mass% Zn, Cu is restricted to 0.20 mass% or less, and the remainder is aluminum and unavoidable impurities. In the brazing heating process in which two or more aluminum alloy composite materials of the present invention are combined so that the skin materials of the aluminum alloy composite material of the present invention face each other and the combined body is brazed and heated, a liquid phase is generated in the skin material, and volume expansion occurs when the solid phase changes to a liquid phase, so the liquid phase generated in the skin material seeps out to the surface of the skin material. The aluminum alloy composite materials of the present invention are then joined together by the liquid phase that has seeped out to the surface of the skin material. At this time, the skin material does not melt because it has a low Si content, so the parent phase remains and maintains its original shape even after brazing heating, and the skin material containing Zn remains, so the skin material functions as a sacrificial anti-corrosion material after brazing heating. In other words, in the aluminum alloy composite of the present invention, the skin material supplies the brazing material during brazing and functions as a sacrificial corrosion protection material after brazing. In other words, the skin material of the aluminum alloy composite of the present invention is a clad layer that has a sacrificial corrosion protection function and can be thermally bonded in a single layer.

The Si content in the skin material is 2.00 to 3.00 mass%, preferably 2.10 to 2.80 mass%. By having the Si content in the skin material within the above range, it is possible to achieve both brazing properties and corrosion resistance. On the other hand, if the Si content in the skin material is less than the above range, the molten brazing material generated during brazing is insufficient, resulting in poor brazing properties, and if it exceeds the above range, the skin material itself is reduced, its function as a sacrificial corrosion protection layer is reduced, and the corrosion resistance of the aluminum alloy composite material is reduced.

The Fe content in the sheath material is 0.10 to 0.40% by mass, preferably 0.10 to 0.30% by mass. When the Fe content in the sheath material is within the above range, the brazing property is good. On the other hand, if the Fe content in the sheath material is less than the above range, the aluminum ingot cost becomes too high, and if it exceeds the above range, too much Al-Fe-Si intermetallic compound is formed during brazing heating, which consumes the Si used to form the braze, inhibiting brazing property.

The Zn content in the skin material is 0.80 to 5.00 mass%, preferably 2.50 to 4.00 mass%. When the Zn content in the skin material is within the above range, the skin material exerts a sacrificial corrosion protection function, and the sacrificial corrosion protection effect of the aluminum alloy composite material is enhanced. On the other hand, if the Zn content in the core material is less than the above range, the sacrificial corrosion protection effect becomes insufficient, and if it exceeds the above range, the amount of wax generated from the skin material increases, and the sacrificial corrosion protection function of the skin material decreases.

In the aluminum alloy laminate of the present invention, the Fe content in the skin is 0.10 to 0.40 mass%, preferably 0.10 to 0.30 mass%, and the Zn content is 0.80 to 5.00 mass%, preferably 2.50 to 4.00 mass%, so that the skin provides a stable sacrificial corrosion protection effect. The Fe content in the above range generates intermetallic compounds, and the crystal grain size is stabilized during recrystallization associated with brazing heat. The liquid phase generated from the skin appears on the material surface along the grain boundaries, and the stable crystal grain size allows the liquid phase to be generated uniformly throughout the material. Zn diffuses into the liquid phase, so by exposing the liquid phase uniformly, Zn is present uniformly, and local corrosion is suppressed.

The Cu content in the cladding material is regulated to 0.20 mass% or less. Cu has almost the same function as Si in forming the wax that seeps out in the cladding material. Therefore, if the Cu content in the cladding material is too high, the cladding material itself will decrease, so the Cu content in the cladding material is regulated to 0.20 mass% or less. There is no particular lower limit for the Cu content in the cladding material, and it may be 0.00 mass%. Furthermore, if the Cu content in the cladding material exceeds 0.20 mass%, the sacrificial corrosion protection effect of the cladding material will be reduced.

The skin material may contain one or more of the following: 1.50% by mass or less Mn, 0.20% by mass or less Ti, 0.20% by mass or less Zr, 0.20% by mass or less Cr, 0.20% by mass or less V, and 0.10% by mass or less Bi. These elements are added to increase the strength of the skin material, thereby increasing the strength of the entire aluminum alloy laminate, and to control the crystal grains.

The content of unavoidable impurity elements contained in the skin material other than the above elements is 0.05% by mass or less for each element, and 0.15% by mass or less in total.

The reason for disposing the brazing filler material on one side of the aluminum alloy composite material of the present invention in a form having a brazing filler material on one side is to ensure a supply of brazing filler material when manufacturing a heat exchanger that requires a certain amount of brazing filler material. For example, when bare corrugated fins are joined to the brazing filler material side or when an extruded multi-hole pipe is joined, the aluminum alloy composite material of the present invention having a brazing filler material on one side is used.

When the aluminum alloy composite material of the present invention has a brazing filler metal, the brazing filler metal for the aluminum alloy composite material of the present invention is an aluminum alloy containing 6.00 to 13.00 mass% Si, an Fe content of 0.80 mass% or less, and Cu content restricted to 0.25 mass% or less, with the remainder being aluminum and unavoidable impurities.

The Si content in the brazing filler metal is 6.00 to 13.00 mass%. When the Si content in the brazing filler metal is within the above range, the melting point of the brazing filler metal is lowered and a liquid phase is generated, thereby making brazing possible. The Fe content in the brazing filler metal is 0.80 mass% or less. When the Fe content in the brazing filler metal is within the above range, good brazing properties are achieved. The Si and Fe contents in the brazing filler metal are appropriately selected within the above ranges.

In the aluminum alloy sheet of the present invention, the Cu content in the brazing filler metal is restricted to 0.25 mass% or less so that the core material does not corrode preferentially due to the potential difference between the core material and the brazing filler metal. If the Cu content in the brazing filler metal exceeds 0.25 mass%, the core material corrodes preferentially due to the potential difference between the core material and the brazing filler metal.

The brazing filler metal may contain 4.00% by mass or less of Zn. When the brazing filler metal contains 4.00% by mass or less of Zn, the Zn in the brazing filler metal diffuses into the core material during brazing, forming a potential gradient from the surface of the core material toward the inside, improving the corrosion resistance of the core material. On the other hand, if the Zn content in the brazing filler metal exceeds 4.00% by mass, the brazing filler metal at the brazed joint corrodes preferentially, reducing the corrosion resistance of the heat exchanger as a whole.

The brazing filler metal may contain 0.30% by mass or less of Mn. The brazing filler metal is placed on one side of the core material for the purpose of brazing by supplying the brazing filler metal, but if the Mn content in the brazing filler metal exceeds 0.30% by mass, the fluidity of the brazing filler metal decreases, and the brazing properties decrease. Therefore, the Mn content in the brazing filler metal is set to 0.30% by mass or less.

The content of unavoidable impurity elements contained in the brazing material other than the above elements is 0.05 mass% or less for each element, and 0.15 mass% or less in total.

In a heating test in which the aluminum alloy composite of the present invention is heated from 300°C to 400°C at an average heating rate of 80°C/min or less and held at 600±3°C for 5±3 minutes, the skin thickness remaining rate ((thickness of skin after heating test (mm)/thickness of skin before heating test (mm)) x 100) is 90.0% or more. After brazing, the skin functions as a sacrificial corrosion inhibitor, but if the skin remaining rate in the heating test is less than the above range, the sacrificial corrosion inhibitor will be insufficient and the corrosion resistance of the aluminum alloy composite will be reduced.

In the present invention, the thickness of the skin material is measured by observing the cross section of the plate with an optical microscope. At this time, etching may be performed if necessary. In addition, the heating test is performed by heating from 300°C to 400°C at an average heating rate of 80°C/min or less and holding at 600±3°C for 5±3 minutes. First, the aluminum alloy composite material of the present invention, which is the test sample, is heated in an inert gas atmosphere to a holding temperature of 600±3°C, then held at 600±3°C for 5±3 minutes, and then cooled to room temperature. Then, the thickness of the skin material in the cross section (perpendicular to the rolled surface) cut in the thickness direction of the test sample before and after the heating test is measured. The heating conditions for the heating test are as follows: from 300°C to 400°C, the average heating rate is 80°C/min or less, then the temperature is raised to 600°C, preferably from 300°C to 400°C, the average heating rate is 75°C/min or less, preferably 70°C/min or less, from 400°C to 580°C in 8±3 minutes, and from 580°C to the holding temperature in 10 minutes or less. Also, the average heating rate from 300°C to 400°C is preferably 40°C/min or more.

In the aluminum alloy laminate of the present invention, the skin thickness retention rate in the above heating test is adjusted to 90% or more by setting the composition of the skin within the range specified in the present invention and by setting the Si content of the skin to 2.00 to 3.00 mass% when manufacturing the aluminum alloy laminate of the present invention.

The aluminum alloy composite material of the present invention is tempered as O material. By tempering the aluminum alloy composite material as O material, the formability of the aluminum alloy composite material is improved.

In the aluminum alloy laminate of the present invention, the average crystal grain size of the core material is 25 to 125 μm, preferably 40 to 120 μm. Usually, in the aluminum alloy laminate of O-type temper, the smaller the crystal grain size, the better the formability. However, if the crystal grain size is too small, the generated liquid phase diffuses into the core material along the grain boundaries, resulting in poor brazing (resistance to deformation during brazing). Therefore, in the aluminum alloy laminate of the present invention, the average crystal grain size of the core material is adjusted to the above range, so that the formability and brazing properties are good. On the other hand, if the average crystal grain size of the core material is less than the above range, the brazing properties are poor, and if it exceeds the above range, the crystal grain structure pattern of the core material becomes fine irregularities after forming and appears on the plate surface, which is called the rough skin phenomenon, becomes large, and as a result, the small amount of liquid phase generated in the skin material does not flow well to the joint, resulting in poor brazing properties.

In the present invention, the average grain size of the core material is determined by polishing the test material to the center of the core material in the thickness direction, etching it by anodizing, observing the polarized image with an optical microscope, and determining the average grain size of the core material from the ASTM grain diagram based on the microstructure of the observed grain structure image.

In the aluminum alloy composite of the present invention, the average crystal grain size of the core material is adjusted to 25 to 125 μm, preferably 40 to 120 μm, by making the composition of the core material within the range specified in the present invention, and by homogenizing the core material at 570°C to 620°C when manufacturing the aluminum alloy composite of the present invention, performing a hot clad rolling process to a plate thickness of 6 mm or less, a cold rolling process to cold roll the hot clad rolled clad material, and one or more annealing processes to anneal the clad material either during the cold rolling process or after the cold rolling process, and by making the clad material into an O-material tempered material by setting the final annealing temperature at 330 to 420°C.

The thickness of the aluminum alloy laminate of the present invention is not particularly limited, but is usually 0.3 to 3.0 mm. If the thickness of the aluminum alloy laminate is less than 0.3 mm, the amount of liquid phase brazing material supplied from the skin material will be small, which may result in unjoined parts, and if it exceeds 3.0 mm, the final cold rolling rate before O material treatment cannot be sufficiently ensured, making it difficult to obtain the specified crystal grain size. The thickness of the aluminum alloy laminate of the present invention is preferably 0.4 to 2.0 mm.

The cladding ratio of the skin material of the aluminum alloy laminate of the present invention is not particularly limited, but is preferably 5 to 25%. If the cladding ratio of the skin material is less than 5%, the liquid phase brazing material supplied from the skin material will be small, which may result in unjoined parts, and if it exceeds 25%, the skin material will account for a large proportion of the plate material, which may result in reduced strength. In addition, the cladding thickness of the skin material of the aluminum alloy laminate of the present invention is selected appropriately in the range of 50 to 300 μm according to the plate thickness and the type of heat exchanger.

The following manufacturing method can be used to manufacture the aluminum alloy composite of the present invention. First, an aluminum alloy ingot having the composition of the core material of the aluminum alloy composite of the present invention is produced, and the aluminum alloy ingot for the core material is cut to a predetermined thickness. In addition, an aluminum alloy ingot having the composition of the skin material of the aluminum alloy composite of the present invention and, if necessary, an aluminum alloy ingot having the composition of the brazing material of the aluminum alloy composite of the present invention are produced, and cut to a predetermined thickness by hot rolling or the like.

The aluminum alloy ingot for the core material is made of an aluminum alloy containing 0.30 to 0.70 mass%, preferably 0.45 to 0.70 mass%, Fe, 0.03 to 0.20 mass%, preferably 0.05 to 0.18 mass%, Cu, 1.00 to 1.50 mass%, preferably 1.00 to 1.40 mass%, Mn, and optionally one or more of 0.20 mass% or less Si, 0.30 mass% or less Mg, 0.30 mass% or less Zn, 0.30 mass% or less Ti, 0.30 mass% or less Zr, and 0.30 mass% or less Cr, with the remainder being aluminum and unavoidable impurities. At this time, it is preferable to homogenize the aluminum alloy ingot for the core material at 570 to 620 ° C. By homogenizing in this temperature range, the grain size of the core material is made uniform, thereby suppressing the variation in the properties of the resulting product sheet. Homogenization at 570-620°C coarsens Mn-containing precipitates, reduces the pinning effect of recrystallization caused by the precipitates during final annealing, and adjusts the average crystal grain size of the core material to the range specified in the present invention. If the homogenization temperature is less than 570°C, the precipitates containing Mn become excessive, reducing the amount of dissolved Mn, and the pinning effect of the precipitates does not occur during final annealing, resulting in an excessively fine average crystal grain size. If the homogenization temperature is 620°C or higher, the core material may melt. After homogenization, the ingot is face-machined to a specified thickness. The thickness after face-machining is determined by the cladding ratio of the skin material and brazing material.

The aluminum alloy ingot for the skin material contains 2.00 to 3.00 mass%, preferably 2.10 to 2.80 mass%, Si, 0.10 to 0.40 mass%, preferably 0.10 to 0.30 mass%, Fe, 0.80 to 5.00 mass%, preferably 2.50 to 4.00 mass%, Zn, and optionally one or more of 1.50 mass% or less Mn, 0.20 mass% or less Ti, 0.20 mass% or less Zr, 0.20 mass% or less Cr, 0.20 mass% or less V, and 0.10 mass% or less Bi, with Cu restricted to 0.20 mass% or less, and the balance being aluminum and unavoidable impurities. The heating temperature before hot rolling of the aluminum alloy ingot for the skin material is 400 to 520°C, preferably 420 to 500°C. If the heating temperature is less than 400°C, the plastic workability is poor and cracks may occur during rolling. On the other hand, if the heating temperature exceeds 500°C, the energy required for heating is large, which is costly. In addition, the heating time before hot rolling is 0.5 to 30 hours, preferably 1 to 29 hours. If the heating time is less than 0.5 hours, the material temperature will be non-uniform, which may cause cracks. On the other hand, if the heating time exceeds 30 hours, productivity will decrease significantly.

The aluminum alloy ingot for brazing material contains 6.00 to 13.00 mass% Si, optionally 4.00 mass% or less Zn, with an Fe content of 0.80 mass% or less, Cu restricted to 0.25 mass% or less, Mn restricted to 0.30 mass% or less, and the balance being aluminum and unavoidable impurities. The heating temperature before hot rolling of the aluminum alloy ingot for brazing material is 400 to 520°C, preferably 420 to 500°C. If the heating temperature is less than 400°C, the plastic workability is poor and cracks may occur during rolling. On the other hand, if the heating temperature exceeds 500°C, the energy required for heating is large and costs are high. In addition, the heating time before hot rolling is 0.5 to 30 hours, preferably 1 to 29 hours. If the heating time is less than 0.5 hours, the material temperature becomes non-uniform, which causes cracks. On the other hand, if the heating time exceeds 30 hours, productivity is significantly reduced.

Next, the aluminum alloy ingot for the core material is combined with an aluminum alloy hot-rolled plate for the skin material, and if necessary, an aluminum alloy hot-rolled plate for the brazing material, and then hot-rolled to obtain a composite material. The heating temperature of the composite material before hot rolling is 400 to 520°C, preferably 420 to 500°C. If the heating temperature is less than 400°C, the plastic workability is poor, so cracks may occur during rolling, and the composite material may not be sufficiently bonded, causing the skin material or brazing material to peel off, making it easy for clad material to not be obtained. On the other hand, if the heating temperature exceeds 500°C, the energy required for heating is large and costs are high. In addition, the heating time before hot rolling is 0.5 to 30 hours, preferably 1 to 29 hours. If the heating time is less than 0.5 hours, the material temperature becomes non-uniform, which causes cracks. On the other hand, if the heating time exceeds 30 hours, productivity is significantly reduced. The plate thickness of the composite material at the end of hot rolling is 6 mm or less, preferably 5 mm or less. If the plate thickness exceeds 6 mm, the number of cold rolling passes will increase, and manufacturability will deteriorate. There is no particular lower limit for the plate thickness, but it is preferably at least twice the final plate thickness. If the plate thickness is less than twice the final plate thickness, the amount of distortion during cold rolling will be small, and the temperature required for recrystallization in the final annealing process will be high, resulting in poor manufacturability.

Then, the resulting hot-rolled composite material is subjected to one or more cold rolling processes and at least a final annealing process after the final cold rolling process to obtain the aluminum alloy sheet of the present invention.

Since the aluminum alloy ingot used as the core material contains Mn, homogenization treatment at high temperatures is performed to coarsen the precipitates containing Mn, reducing the pinning effect of recrystallization caused by the precipitate particles that occurs during final annealing, and the average crystal grain size of the core material can be adjusted to the range specified in this invention.

In addition, intermediate annealing may be performed between hot rolling and final annealing. The intermediate annealing is performed to coarsen the fine precipitates that formed before hot rolling and to precipitate elements such as Mn that are in solid solution, thereby making the recrystallized grains finer during the final annealing.

By setting the rolling ratio of the cold rolling before the final annealing treatment to 50% or more, the amount of accumulated strain due to cold rolling becomes large, and the crystal grains become finer. On the other hand, if the amount of accumulated strain due to cold rolling is small, the crystal grains become less fine. In addition, by setting the heating temperature of the final annealing treatment to 330 to 420°C, a recrystallized structure is obtained, which prevents excessive refinement of recrystallized grains during the brazing heating process and suppresses brazing penetration. Then, by using an aluminum alloy ingot for the core material and an aluminum alloy ingot for the skin material having a predetermined composition, and further using an aluminum alloy ingot for the brazing material as necessary, and adopting the above-mentioned cold rolling and final annealing conditions in the manufacturing process for manufacturing the aluminum alloy composite material, the aluminum alloy composite material of the present invention that can simultaneously achieve formability, brazing ability, and corrosion resistance can be obtained.

In the aluminum alloy laminate of the present invention, the skin material is used as a joining layer to prevent diffusion of the solder into the core material. This is the most important point of the present invention.

In the case of Al-Si alloys normally used as brazing filler metals, the interfaces of the crystallized particles of Si, the main additive element component dispersed in the aluminum alloy matrix, and the intermetallic compounds melt into a spherical shape during brazing heating, and become liquid. Regular brazing filler metals contain a high amount of Si, at 5-13 mass%, and therefore have a large amount of Si crystallized particles and intermetallic compounds. During the brazing heating process, a liquid phase is generated at the interfaces of these Si crystallized particles and intermetallic compounds, and this liquid phase flows into the joint to form a joint fillet. As a result, the brazing filler metal no longer retains its original shape.

In contrast, in the aluminum alloy laminate of the present invention, the Si content in the skin is low, so the total amount of liquid phase generated is small, and the parent phase remains and maintains its original shape. The generated liquid phase diffuses through the parent phase and along the grain boundaries, but when it changes from solid to liquid, volume expansion occurs and it seeps out onto the unconstrained material surface, making it possible to bond even with a low Si content. Furthermore, in such skin materials, the amount of liquid phase formed during brazing heating is small, so even if the crystal grain size of the core material is fine, only a small amount of the brazing material diffuses into the grain boundaries of the core material. This makes brazing possible even with a fine crystal grain size of the core material, which was difficult with conventional brazing sheets.

The heat exchanger of the present invention is a heat exchanger obtained by forming two or more aluminum alloy composite materials of the present invention into the shapes of the respective parts, combining them, and subjecting the combined body to brazing heating. The heating temperature during brazing heating is preferably 580 to 620°C, and particularly preferably 590 to 610°C. The heating retention time during brazing heating is preferably 0 to 10 minutes. The atmosphere during brazing heating is an inert gas atmosphere such as nitrogen or argon.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the examples shown below.

Three-layered aluminum alloy composites for brazing were manufactured with a plate thickness of 0.5 mm as shown in Table 1 and a plate thickness of 1.0 mm as shown in Table 2. The skin material in the table is clad on one side of the core material, and the brazing material is clad on the other side of the core material.
These composite materials were manufactured by the following process. The ingots for the skin material and the brazing material were DC cast and then surface-machined to produce the ingots for the skin material and the brazing material. The ingots for the core material were manufactured by the DC casting process, and then homogenized at 600°C for 10 hours, and then surface-machined to produce the ingots for the core material.
Next, the hot rolling process was performed to obtain a skin material rolled plate and a brazing material rolled plate having a plate thickness that would provide the target cladding ratio, which were then combined with the core ingot to obtain a thickness of 505 mm before lamination, and the clad rolling was performed in the hot rolling process. The final plate thickness of the hot rolling was 3.5 mm.
The obtained hot-rolled materials were cold-rolled to a plate thickness of 0.5 mm and 1.0 mm, respectively, and then subjected to a final annealing treatment at 365° C. for 2 hours to obtain O materials.
The mechanical properties of the obtained aluminum alloy laminate and the grain size of the core material are shown in Table 3. For the tensile test, a tensile test piece corresponding to JIS-13B was used.
The grain size of the core material was also measured. The microstructure photographs obtained are shown in Figure 3 (0.5 mm thick material) and Figure 4 (1.0 mm thick material). The grain size was determined from the ASTM grain diagram of the microstructure obtained by polishing the core material to the center in the thickness direction and then etching it.
As a result, the elongation of the 0.5 mm and 1.0 mm thick materials exceeded 30%, indicating excellent formability, and the tensile strength exceeded 110 MPa, indicating sufficient strength.

Next, for each of the 0.5 mm and 1.0 mm thick materials, in an inert gas atmosphere, the temperature was increased from 300°C to 400°C at a heating rate of 62°C/min, from 400°C to 580°C in 9.3 minutes, and from 580°C to 600°C in 1.6 minutes, heated to a holding temperature of 600±3°C, then held at 600±3°C for 3.6 minutes, and then cooled to room temperature, which is heating equivalent to brazing, and the bondability was evaluated by an inverted T-shaped test shown in Figure 5, and the corrosion resistance was evaluated by natural potential measurement. The heating equivalent to brazing was performed under the same heating conditions as the heating test for measuring the skin thickness remaining rate.
The results of the cross-sectional structure observation of the joint with the 3003 material by the inverted T-shaped test are shown in Figure 6. A uniform fillet was formed at the joint with the 3003 material for both the 0.5 mm thick material and the 1.0 mm thick material, and the material had sufficient brazing weldability.
The results of the spontaneous potential measurements are shown in Table 4, and the results of cross-sectional structure observations before and after brazing are shown in Figure 7 (0.5 mm thick material) and Figure 8 (1.0 mm thick material). The upper parts of Figure 7 (0.5 mm thick material) and Figure 8 (1.0 mm thick material) are before brazing heating, and the lower parts are after brazing heating. The lower part of each photograph is the skin material, and the upper part is the brazing alloy. Table 4 also shows the skin thickness remaining rate after heating equivalent to brazing.
It is clear that the potential of the skin material after heating equivalent to brazing is sufficiently lower than that of the core material, and the alloy layer is secured, providing excellent sacrificial corrosion protection. In addition, the skin material survival rate is 90% or more in all cases, indicating that sufficient skin material remains to function as a sacrificial corrosion protection material.

Claims (8)

A core material and a skin material clad on one or both sides of the core material,
The core material is made of an aluminum alloy containing 0.30 to 0.70 mass% Fe, 0.03 to 0.20 mass% Cu, 1.00 to 1.50 mass% Mn, with the remainder being aluminum and unavoidable impurities;
The skin material is made of an aluminum alloy containing 2.00 to 3.00 mass% Si, 0.10 to 0.40 mass% Fe, 0.80 to 5.00 mass% Zn, with Cu restricted to 0.20 mass% or less, and the remainder being aluminum and unavoidable impurities;
The average crystal grain size of the core material is 25 to 125 μm,
In a heating test in which the temperature is increased from 300°C to 400°C at an average heating rate of 80°C/min or less and then held at 600±3°C for 5±3 minutes, the skin thickness retention rate ((skin thickness after heating test/skin thickness before heating test)×100) is 90.0% or more,
The temper is O material,
An aluminum alloy laminate characterized by: The aluminum alloy laminate according to claim 1, characterized in that it is a two-layer material consisting of the core material and the skin material clad on one side of the core material. The aluminum alloy laminate according to claim 1, characterized in that it is a three-layer material consisting of the core material and the skin material that is clad on both sides of the core material. a three-layer material including the core material, the skin material clad on one side of the core material, and a brazing material clad on the other side of the core material;
The brazing filler metal is made of an aluminum alloy containing 6.00 to 13.00 mass% Si, an Fe content of 0.80 mass% or less, and a Cu content of 0.25 mass% or less, with the remainder being aluminum and unavoidable impurities;
The aluminum alloy laminate according to claim 1, The aluminum alloy composite material according to claim 4, characterized in that the brazing material further contains 4.00 mass% or less of Zn and Mn is restricted to 0.30 mass% or less. The aluminum alloy laminate according to any one of claims 1 to 5, characterized in that the skin material further contains one or more of the following: 1.50 mass% or less Mn, 0.20 mass% or less Ti, 0.20 mass% or less Zr, 0.20 mass% or less Cr, 0.20 mass% or less V, and 0.10 mass% or less Bi. The aluminum alloy composite material according to any one of claims 1 to 6, characterized in that the core material further contains one or more of the following: 0.20 mass% or less Si, 0.30 mass% or less Mg, 0.30 mass% or less Zn, 0.30 mass% or less Ti, 0.30 mass% or less Zr, and 0.30 mass% or less Cr. A heat exchanger obtained by combining two or more molded bodies of the aluminum alloy composite material according to any one of claims 1 to 7 and heating them for brazing.

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