JP5660011B2 - Sandwich panel - Google Patents

Description

  The present invention relates to a sandwich panel in which a core material is interposed between a pair of surface plates, and the surface plate and the core material are joined together by brazing.

In general, as a panel material used for building materials such as a roof material and an outer wall material, a so-called sandwich panel including a pair of upper and lower surface plates and a large number of core materials arranged between these surface plates is known. This sandwich panel has the characteristics of high rigidity and light weight.
In addition, there are adhesive and brazing for joining the face material and core material in sandwich panels, but for sandwich panels used outdoors, brazing joints are often used from the viewpoint of weather resistance. ing.

As a method for manufacturing a sandwich panel by brazing, that is, a method for manufacturing a brazed sandwich panel, the present inventors have proposed the technique of Patent Document 1.
In general, when Cu is added to an Al alloy, the mechanical strength increases, but the corrosion resistance decreases. Therefore, the technology of Patent Document 1 is a brazed sandwich panel that uses an aluminum plate material that reduces the addition amount of Cu, which causes a decrease in corrosion resistance and has improved strength, as a face material, is light in weight, has little distortion, and has excellent strength and corrosion resistance. Is to provide.

JP 2010-120216 A

According to the method disclosed in Patent Document 1, it is possible to produce a brazed sandwich panel that is lightweight, has little distortion, and has excellent strength and corrosion resistance.
However, when a sandwich panel is installed in an area where a load is generated on the structure itself due to snow or the like, the sandwich panel manufactured in Patent Document 1 is still insufficient in strength. It is necessary to increase further.

However, when Cu is added, the Al-Cu compound is precipitated at the grain boundary in the brazing process, and a Cu-deficient layer is formed in the vicinity of the grain boundary. Due to the potential difference between the Cu-deficient layer and the grain boundary, there arises a problem of grain boundary corrosion in which the grain boundary is selectively corroded. As described above, the corrosion resistance is lowered.
The present invention has been devised to solve such problems, and is made of an aluminum plate that has improved corrosion resistance while adding Cu to improve strength, and is lightweight, less distorted and strong. The object is to provide a brazed sandwich panel with excellent corrosion resistance.

In order to achieve the object, the sandwich panel of the present invention is made of two aluminum alloy face materials arranged facing each other up and down and made of aluminum or aluminum alloy arranged between the two face materials. Each of the face materials and the core material are joined to each other by brazing, and the face materials are composed of Si: 0.4 to 1.2% by mass, Fe: 1.0% by mass. %, Mn: 1.0 to 2.0% by mass, Cu: 0.2 to 1.0% by mass, with the balance being Al and inevitable impurities, and 3 × 10 ⁶ / mm ² precipitates of 1 μm or less after brazing It is characterized by being comprised from the aluminum alloy plate which has the above and has a yield strength of 60 MPa or more.

Each of the face materials is obtained by cold rolling a slab cast at a cooling rate of 10 ° C./sec or more, preferably 30 ° C./sec or more of the molten metal having the above composition, and A sandwich panel is preferably cooled after brazing the face material with the core material at a rate of 200 ° C./h or more.
In consideration of the productivity and quality of the slab, the face material cast at the above cooling rate and then cold-rolled includes a pair of rotating belt portions provided with endless belts, and a pair of rotating belt portions. Manufactured by a twin-belt casting machine comprising a cavity formed therebetween and a cooling means provided inside the rotating belt portion, and a molten metal is supplied into the cavity to continuously cast a slab. What was obtained by cold-rolling the thin slab made is preferable.
Moreover, it is preferable that the said brazing joining is made | formed by the brazing material which contains Cu: 27-37 mass%, Si: 5-10 mass%, and the remainder consists of Al and an unavoidable impurity.

The sandwich panel provided by the present invention uses an aluminum alloy plate having a Cu content of 0.2 to 1.0%, a Mn content of 1.0% by mass or more, and a Si content of 0.4% by mass or more as a face material. ing. Furthermore, the structure is adjusted so that the precipitates of 1 μm or less become 3 × 10 ⁶ pieces / mm ² or more after brazing. For this reason, it not only has excellent mechanical strength, but also does not deteriorate the corrosion resistance even after brazing.

Further, the sandwich panel provided by the present invention, which uses a plate material continuously cast by a twin belt type casting machine as a face material, brazes Cu, Mn and Si, which are dissolved in a large amount during casting. High strength is achieved by depositing finely and finely in the process.
Furthermore, by performing low-temperature brazing with a ternary eutectic alloy consisting of Al, Si and Cu and having a low melting point, even when using thin-walled face materials, the face materials are not softened or deformed by heating during brazing. A panel having an excellent surface appearance without distortion can be produced with high productivity. Therefore, an excellent quality sandwich panel is provided at low cost.

Diagram showing differences in intergranular corrosion due to differences in cooling rate after brazing

The inventors of the present invention have made extensive studies on means for obtaining a brazed sandwich panel that is lightweight, has little distortion, and has excellent strength and corrosion resistance. One of them is proposed in Patent Document 1 described above, but in this technique, the Cu content is reduced in order to improve corrosion resistance. For this reason, although the intended purpose can be achieved regarding corrosion resistance, it is unsatisfactory in terms of mechanical strength.
Therefore, the present inventors have sought the existence form of Cu that does not deteriorate the corrosion resistance even when the Cu content is increased, and have arrived at the present invention.

In other words, by maintaining a relatively large amount of Cu forcibly dissolved by casting in a solid solution state until the brazing step, by adjusting the cooling rate after brazing and appropriately controlling the precipitate density, It was confirmed that the addition of a relatively large amount of Cu does not affect the intergranular corrosion sensitivity.
Below the predetermined cooling rate, the precipitate density decreases to the same level as in the conventional DC method, and the precipitate grows in the vicinity of the grain boundary, thus worsening the intergranular corrosion. Furthermore, a predetermined yield strength cannot be obtained by crystal grain growth. Therefore, the cooling rate after brazing was made fast so that the precipitates could be properly controlled and operated.
Details will be described below.

First, the component composition of the aluminum alloy to be used will be described.
Si: 0.4 to 1.2% by mass
Si dissolves in supersaturation at the time of casting, and precipitates as a fine Al- (Fe · Mn) -Si intermetallic compound in the brazing process together with Fe and Mn that are also supersaturated, thereby improving the strength. Present. In order to exhibit this action, the content of at least 0.4% by mass is required. However, if it is contained in a large amount, the solidus temperature is lowered, which causes softening and deformation of the face material at the time of brazing.

Fe: 1.0% by mass or less
Fe also has the effect of improving strength by precipitating fine Al- (Fe · Mn) -Si intermetallic compounds in the brazing process in the presence of Mn and Si. However, if it is contained in a large amount, the intermetallic compound that crystallizes during casting becomes coarse, and the castability and rollability are deteriorated. Therefore, the content is set to 1.0% by mass or less.

Mn: 1.0-2.0 mass%
Mn also has the effect of improving strength by precipitating fine Al- (Fe · Mn) -Si intermetallic compounds in the brazing process in the presence of Si and Fe. If the Mn content is less than 1.0% by mass, the desired strength cannot be obtained. On the contrary, if it is contained in a large amount so as to exceed 2.0% by mass, the crystallized intermetallic compound is coarsened and castability and rollability are lowered.

Cu: 0.20 to 1.0 mass%
Cu exhibits the effect of improving the strength by dissolving in the matrix. In order to obtain a desired strength, a content of 0.2% by mass or more is required. However, if it is contained in a large amount, the solidus temperature is lowered, which causes softening and deformation of the face material at the time of brazing, so the upper limit of its content is 1.0 mass%.

In addition, a minute amount of Ti or Ti + B may be contained in order to refine the crystal structure of the slab. However, if the content of the crystal grain refining agent is too large, a coarse intermetallic compound such as TiAl ₃ may be generated during casting to lower the formability. Therefore, when they are contained, the upper limit is Ti for 0.10% by mass and B for 0.01% by mass.
In addition, Zn, Mg, Ni, Ca, V, etc. may be mixed from aluminum ingots, return materials, or fluxes, all of which are unavoidable impurities. It is preferable to reduce as much as possible.

Next, the mechanical characteristics of the face material used for the sandwich panel of the present invention will be described.
Conventionally, a relatively high strength 3N33 alloy, which is often used as a low-temperature brazing face material, is sometimes used as a face material for sandwich panels. The yield strength after brazing of this 3N33 alloy is about 55 MPa. However, since this 3N33 material is a material containing a relatively large amount of Cu, there is a difficulty in corrosion resistance. Further, recent sandwich panels are required to use materials having a strength of 60 MPa or more after brazing and excellent corrosion resistance.

This proof stress of 60 MPa or more is a slab obtained by casting a molten alloy containing a relatively large amount of Cu at a cooling rate of 10 ° C./sec or more, preferably 30 ° C./sec or more, preferably a twin belt type continuous casting machine. A thin slab obtained by continuous casting by using a thin slab as a raw material, and a thin plate obtained by direct cold rolling without homogenization treatment is heated to a low temperature brazing temperature, and then cooled to 200 ° C / h or more It is manifested by cooling at a speed to form a structure in which precipitates of 1 μm or less are dispersed at 3 × 10 ⁶ pieces / mm ² or more. Even if it anneals in the middle of cold rolling or at the end as needed, an effect is not impaired.

That is, a molten aluminum alloy having a Cu content of 0.20 to 1.0 mass%, an Mn content of 1.0 to 2.0 mass%, and an Si content of 0.4 to 1.2 mass% is 10 ° C./sec or more, preferably 30 ° C./sec. When casting at the above cooling rate, Cu, Mn, and Si are forcibly dissolved because of the high solidification and cooling rate. When the obtained slab is cold-rolled without being homogenized, it becomes a cold-rolled material in which Cu, Mn and Si are forcibly dissolved. Forcibly dissolved Cu precipitates uniformly and finely in the matrix together with Al- (Fe · Mn) -Si intermetallic compounds when heated and cooled to the brazing temperature. By forming a structure in which these fine precipitates are dispersed at a density of 3 × 10 ⁶ pieces / mm ² or more, it becomes a surface material having higher strength than that using a cold-rolled material made of a normal DC cast slab, Expresses a proof stress of 60 MPa or more. In addition, precipitation in the matrix can suppress grain boundary precipitation, and as a result, generation and progression of grain boundary corrosion can be suppressed.

If the cooling rate when casting a molten aluminum alloy having a prescribed composition is so slow that it is less than 10 ° C / sec, the amount of solid solution of Cu, Mn and Si is small, and the desired precipitation strengthening action is achieved during brazing. Not expressed. When cast at a cooling rate of 30 ° C./sec or more, precipitation strengthening is sufficient during brazing. In addition, when the cooling rate after brazing is so slow that it does not reach 200 ° C / h, the precipitate density decreases to the same level as in the conventional DC method, and the precipitate grows near the grain boundary. Worsen. Furthermore, a predetermined yield strength cannot be obtained by crystal grain growth.
A cold-rolled material obtained by directly cold-rolling a thin slab produced by a twin belt type continuous casting machine is subjected to final annealing as necessary.
As an aspect of annealing, a continuous annealing furnace or a batch annealing furnace is used, and both temperature and time may be set as appropriate.

Subsequently, a mode of low-temperature brazing using a low melting point brazing material will be described.
As a low-temperature brazing material, Cu: 27 to 37% by mass, Si: 5 to 10% by mass, and the balance of Al and inevitable impurities are used. By using a brazing material having such a component composition, the brazing temperature can be lowered to 540-560 ° C.
As the low-temperature brazing material, it is preferable to use a powdered aluminum alloy brazing material having an average particle diameter of 10 to 100 μm obtained by spraying molten metal in vacuum or in an inert gas and quenching. Furthermore, it is preferable to use a fluoride flux containing 11% by mass or more of CsF as a solid content.

As a practical brazing mode, a mixed slurry containing a powdered aluminum alloy brazing material and a CsF-containing fluoride flux is applied to the face plate and, as necessary, the brazing surface of the core material, and then the mixed slurry is applied. In a state where the core material is disposed between the brazing surfaces of the face plates so that the side surfaces thereof are in contact with each other, it is preferable to braze the both by heating the face plate and the core material in an inert gas.
After brazing, it is necessary to cool at a cooling rate of 200 ° C./h or more as described above.
By low-temperature brazing, each member to be joined at the time of brazing is not deformed or the strength is not lowered, and a sandwich panel having an excellent surface appearance can be obtained. Moreover, since low temperature brazing becomes possible, the production speed can be increased, and as a result, a sandwich panel can be manufactured at low cost.

Preparation of test specimens For the two types of aluminum alloys shown in Table 1, test specimens were prepared by changing the cooling rate after brazing.
The aluminum alloy sheet used is formed between a pair of rotating belt portions that are provided with an endless belt and are vertically opposed to each other by filtering the molten alloy melted in a melting furnace through an ceramic filter. And a cooling means provided inside the rotating belt part, and a thickness of 10 mm in a double belt casting machine in which molten metal is supplied into the cavity to continuously cast a slab. The slab was manufactured and wound on a coil. The obtained thin slab was then cold-rolled to a final thickness of 1.5 mm without homogenization and intermediate annealing. In addition, it was annealed at 330 ° C for 3 hours in a batch annealing furnace to make H24 tempered material.

Sandwich panels were made using these cold-rolled annealed materials as upper and lower face materials, and a cylindrical body with a diameter of 25mm and height of 37.0mm made of 300mm alloy plate of 0.5mm thickness.
As a flux, a brazing material containing Cu: 30.9% by mass and Si: 9.3% by mass, the balance of which is an aluminum alloy composed of Al and inevitable impurities and having an average particle diameter of 40 μm, is used as a flux. using an aqueous solution containing 30% solids fluoride based flux consisting of KF-AlF ₃ based complex fluoride cesium (CsF) containing 16 mass%, respectively, at a coverage of ^{100g / m 2, 130g / m} 2 Applied. And it brazed at the temperature of 550 degreeC, and cooled at the cooling rate shown in Table 1 after that. The cooling rate was controlled by changing the number of cooling fans and the distance from the specimen.

Evaluation of Corrosion Resistance From each of the four types of sandwich panel face materials obtained, 70 mm × 150 mm specimens were cut out, the cut surfaces were sealed, and an intergranular corrosion susceptibility test was conducted.
In addition, evaluation of intergranular corrosion sensitivity was performed by optically analyzing the cross-section of the face material after an acetic acid acidic saline alternate immersion test (5% NaCl + acetic acid 6 ml / l, 35 ° C., 10 minutes immersion → 50 minutes drying, 168 cycles). The observation was made with a microscope. The observation results are shown in Table 2 and FIG.
In the comparative specimens Nos. 2 and 3, intergranular corrosion was observed to a slight extent. On the other hand, no significant intergranular corrosion was observed in specimen No. 1 which is an example of the present invention.
As a result, it was found that even if the Cu content increases, the corrosion resistance can be suppressed by increasing the cooling rate after brazing.

Tissue observation Tissue observation pieces were cut out from the upper and lower surfaces of the four types of sandwich panels prototyped above, and the cross-sectional structure was observed with a transmission electron microscope. As a result, in the specimens No. 2 and 3 which are comparative examples, the precipitates are coarsened, whereas in the specimen No. 1 which is an example of the present invention, the precipitates are uniformly dispersed in the grain boundaries. I found out. Then, the number of fine precipitates having a size of 1 μm or less was measured. The results are also shown in Table 2.
From Table 2, it was found that the number of fine precipitates was increased by increasing the cooling rate after brazing.

Evaluation of mechanical properties In addition, three test pieces each having a length of 200 mm and a width of 30 mm were cut out from the upper and lower surfaces of the four types of sandwich panels prototyped above, and the core was deleted. It processed into the piece and the tension test was done.
The tensile test is performed using a precision universal testing machine of 50 kN class manufactured by Shimadzu Corporation with a tensile strength of 0.2 mm and a tensile strength of 0.2 mm. The tensile strength is 0.2 mm. % Proof stress and elongation were measured. The results are also shown in Table 2. The numerical values in the table are average values of six numerical values, three each on the upper and lower sides.

  Summing up the above results, even if it is a sandwich panel using aluminum alloy plates with increased Cu and improved mechanical properties as face materials, if the cooling rate after brazing is increased, the contained Cu will be In the cooling process after brazing, it precipitates uniformly and finely in the matrix together with the Al- (Fe · Mn) -Si intermetallic compound, and does not cause intergranular corrosion. In other words, even if it contains a large amount of Cu that tends to precipitate near the grain boundary and cause intergranular corrosion if it is contained in a large amount, precipitation near the grain boundary can be suppressed by increasing the cooling rate after brazing. It can be seen that the corrosion can be suppressed and the intended strength improvement of Cu can be achieved.

Claims (5)

A sandwich panel composed of two aluminum alloy face materials arranged facing each other vertically and an aluminum or aluminum alloy core material arranged between the two face materials,
Each of the face materials and the core material are joined together by brazing joining,
Each of the face materials contains Si: 0.4 to 1.2% by mass, Fe: 1.0% by mass or less, Mn: 1.0 to 2.0% by mass, Cu: 0.2 to 1.0% by mass, and the balance is composed of Al and inevitable impurities. A sandwich panel characterized by being composed of an aluminum alloy plate having a precipitate of 1 μm or less after brazing at 3 × 10 ⁶ pieces / mm ² or more and exhibiting a proof stress of 60 MPa or more.   Each of the face materials is obtained by cold rolling a slab cast from a molten metal having the above composition at a cooling rate of 10 ° C./sec or more, and brazing each of the face materials to the core material. The sandwich panel according to claim 1, wherein the sandwich panel is subsequently cooled at a rate of 200 ° C / h or more.   Each of the face materials is obtained by cold rolling a slab cast from a molten metal having the above composition at a cooling rate of 30 ° C./sec or more, and brazing each of the face materials to the core material. The sandwich panel according to claim 1, wherein the sandwich panel is subsequently cooled at a rate of 200 ° C / h or more.   Each of the face materials includes an endless belt and a pair of rotating belt portions opposed to each other, a cavity formed between the pair of rotating belt portions, and a cooling means provided inside the rotating belt portion. A thin slab produced by a twin-belt casting machine in which a molten metal is supplied into the cavity and continuously casts the slab is obtained by cold rolling. The described sandwich panel.   The said brazing joining contains Cu: 27-37 mass%, Si: 5-10 mass%, The remainder is made | formed by the brazing material which consists of Al and an unavoidable impurity. The described sandwich panel.