JP2024064688A - Aluminum alloy brazing sheet - Google Patents

Abstract

[Problem] The present invention aims to provide an aluminum alloy brazing sheet with improved supply of brazing filler metal to required locations. [Solution] The aluminum alloy brazing sheet of the present invention is an aluminum alloy brazing sheet in which a brazing filler metal made of an Al-Si alloy is combined with at least one surface of an aluminum alloy core material, and is characterized in that, in a drop type fluidity test, when the brazing filler metal flow coefficient in an unprocessed state is Ks, the brazing filler metal has a flow coefficient of 1.5 x Ks or more in a state in which a processing strain of 1% or more is applied, the amount of brazing filler metal eroded after brazing from the brazing filler metal to the core material is less than 10% of the core material thickness, and the recrystallization rate of the core material is 90% or more at a temperature just before the brazing filler metal melts. [Selected Figure] Figure 1

Description

This invention relates to an aluminum alloy brazing sheet.

In the brazing process, a brazing material, an aluminum alloy with a low melting point, is melted to join many components in an automobile heat exchanger. The brazing material can be applied directly to the components or through a sheet.
As a method of supplying brazing material, brazing sheets are currently used because they are easy to handle and cost-effective. These sheets are made by bonding an aluminum alloy with a high melting point and high strength as the core material to an aluminum alloy with a low melting point as the brazing material.

Regarding brazing sheets, as described in the following Patent Document 1, a four-layer material of brazing material/intermediate material/core material/brazing material is known, in which the compositions of the intermediate material, core material, and brazing material are limited, and the ratio of the flow coefficient before and after the application of strain in a flow test is specified.
The brazing sheet described in Patent Document 1 is designed to effectively destroy the aluminum oxide film that hinders brazing and to adjust the diffusivity of Mg, which is added to ensure brazability, in the molten brazing material.

JP 2021-021106 A

In order to meet the demands of high performance, heat exchangers often have complex shapes, and the amount of brazing filler required for each joint varies depending on the location, for example, the joint between the fins and tubes or the joint between the tubes and header plate. The brazing filler material attached to the brazing sheet has a cladding rate and Si content determined to compensate for the joints in the areas of the heat exchanger that require the most brazing filler material. However, in areas where brazing is not required, the amount of brazing filler material is excessive, causing problems such as brazing erosion.

In addition, a phenomenon specific to brazing sheets is that when using tempered O material, if a strain of about 5 to 20% is applied during processing of the heat exchanger components, the brazing material can severely corrode the core material during brazing. Due to these problems, it has been difficult to suppress brazing corrosion of the core material while filling only the areas to be joined with brazing material.

The present invention was made to solve these problems, and aims to provide an aluminum alloy brazing sheet that suppresses the supply of solder to areas where no processing strain is applied, and promotes the supply of solder by applying strain to areas that require solder, allowing the solder to be filled sufficiently.

(1) The aluminum alloy brazing sheet of this embodiment is an aluminum alloy brazing sheet in which a brazing filler metal made of an Al-Si alloy is combined on at least one surface of a core material made of an aluminum alloy, and is characterized in that, in a drop type fluidity test, when the brazing filler metal flow coefficient in an unprocessed state is Ks, the brazing filler metal has a flow coefficient of 1.5 x Ks or more in a state in which a processing strain of 1% or more is applied, the amount of brazing filler metal eroded after brazing from the brazing filler metal to the core material is less than 10% of the core material thickness, and the recrystallization rate of the core material is 90% or more at the temperature just before the brazing filler metal melts.

(2) In the aluminum alloy brazing sheet according to (1) of this embodiment, it is preferable that the core material contains, by mass%, at least one of the elements Fe: 0.05% to 1.0%, Mn: 0.05% to 1.2%, and _Si : 0.05% to 1.0%, and that when the amounts of each element added are _CFe , _CMn , and _CSi , the amounts of each element added satisfy the relationship _CFe + _1.5CMn + 1.6CSi ≦ 3.0.

(3) In the aluminum alloy brazing sheet according to (1) or (2) of this embodiment, it is preferable that the brazing material contains Si: 5.0% or more and 10.0% or less.

The present invention provides an aluminum alloy brazing sheet that does not supply solder to areas where processing strain is not applied, and allows solder to be filled in areas that require solder by applying strain.

1 is a partial cross-sectional view showing an example of a brazing sheet according to the present invention. 1 is a perspective view showing an example of a heat exchanger configured to which a brazing sheet according to the present invention is applied. 1 is a graph showing an example of a thermal history curve when a brazing-equivalent heat treatment is performed. FIG. 1 is an explanatory diagram showing a drop type fluidity test performed to measure the brazing flow coefficient, in which (A) is a perspective view showing a test piece before brazing-equivalent heat treatment, and (B) is a perspective view showing a test piece after brazing-equivalent heat treatment. 1 is a structural photograph showing an example of a core material having a recrystallization rate of 90% or more. 1 is a structural photograph showing an example of a core material having a recrystallization rate of less than 90%. 1 is a cross-sectional structure photograph showing an example of a brazing sheet having a brazing erosion rate of 7% after heat treatment equivalent to brazing. 1 is a cross-sectional structure photograph showing an example of a brazing sheet having a brazing erosion rate of 15% after heat treatment equivalent to brazing.

Hereinafter, the present invention will be described in detail based on embodiments.
As an example, the aluminum alloy brazing sheet 1 of this embodiment can adopt a three-layer structure in which a brazing material 3 made of an aluminum alloy is clad on both sides of a core material 2 made of an aluminum alloy as a clad layer, as shown in Fig. 1. Alternatively, a two-layer structure in which the brazing material 3 faces only one side of the core material 2 may be adopted.
In addition, since the brazing sheet 1 can have a multi-layer structure of brazing material, it can have, for example, a structure in which one or more layers of another brazing material 3A are provided between the core material 2 and the brazing material 3 as shown by the dotted line in Figure 1, or a multi-layer structure in which one or more layers of another material such as a sacrificial material 3B are provided between the core material 2 and the brazing material 3.

The aluminum alloy constituting the core material 2 of this embodiment is not particularly limited in composition, and may be an aluminum alloy of any composition. As an example, an aluminum alloy containing, in mass%, Fe: 0.05-1.0%, Mn: 0.05-1.2%, Si: 0.05-1.0%, with the balance being Al and unavoidable impurities may be used. In addition to the elements mentioned above, the aluminum alloy for the core material may contain at least one of Mg: 0.5% or less, Cu: 1.0% or less, and Zn: 3.0% or less, and in addition to these elements, may contain at least one of Cr, Ti, Zr, and Ni in an amount of 0.3% or less.

The brazing filler metal 3 (cladding layer) disposed on one or both surfaces of the core material 2 so as to be located at the outermost surface preferably contains, by mass%, 5.0 to 10.0% Si. The brazing filler metal 3 may contain at least one of the following elements in addition to Si: 6.0% or less Zn, 2.0% or less Mg, and 0.05% or less Sr. The brazing filler metal contains the above elements, with the remainder being Al and unavoidable impurities.
In addition, when the upper and lower limits of a numerical range described in the present specification are specified using "to", it means more than or equal to or less than the limit unless otherwise specified. Thus, for example, 5.0 to 10.0% means 5.0% or more and 10.0% or less.

"Composition of aluminum alloy for core material"
"Fe: 0.05 to 1.0%"
The aluminum alloy for the core material of this embodiment contains, for example, 0.05 to 1.0% Fe.
Fe is added together with Si to form an Al-Fe-Si compound and to coarsen the recrystallized grains of the core material immediately before melting the brazing material. It is also added to improve the material strength of the core material 2 through solid solution strengthening and the formation of Al-Fe compounds and Al-Fe-Si compounds. If the Fe content is less than 0.05%, it will be below the concentration contained as an impurity in the raw material, and the manufacturing cost will be high.
If the Fe content exceeds 1.0%, the amount of coarse Al--Fe compounds increases, and the recrystallized grains immediately before the brazing material melts become fine, which may cause the core material 2 to be eroded by the brazing material.
"Mn: 0.05 to 1.2%"
The aluminum alloy for the core material of this embodiment contains, for example, 0.05 to 1.2% Mn.
Mn is added to coarsen the recrystallized grains of the core material immediately before melting the brazing material, and to improve the material strength of the core material 2 by solid solution strengthening and the formation of Al-Mn compounds and Al-Mn-Si compounds. If the Mn content is less than 0.05%, the strength required to maintain the structure of the heat exchanger tends to be insufficient.
If the Mn content exceeds 1.2%, the amount of compounds increases and inhibits recrystallization during brazing, so that recrystallization does not complete at a temperature just before the braze melts, and there is a risk that the core material 2 will be eroded by the braze.

"Si: 0.05 to 1.0%"
The aluminum alloy for the core material of this embodiment contains, for example, 0.05 to 1.0% Si.
Silicon is added to coarsen the recrystallized grains of the core material immediately before melting the brazing material, and to improve the material strength of the core material 2 by solid solution strengthening and the formation of Al-Fe-Si compounds or Al-Mn-Si compounds. If the silicon content is less than 0.05%, the strength required to maintain the structure of the heat exchanger tends to be insufficient.
If the Si content exceeds 1.0%, the melting point of the core material decreases, so there is a risk of the core material 2 being corroded by the brazing filler metal. Also, braze erosion is more likely to occur due to Si diffusion from the brazing filler metal.
"Mg: 0.5% or less"
The aluminum alloy for the core material of this embodiment may contain, for example, 0.5% or less of Mg.
Mg is an optional component, but is added to improve the material strength of the core material 2 by solid solution strengthening and the formation of Mg-Si compounds. If Mg is not contained, the desired strength improvement effect cannot be obtained. If the Mg content exceeds 0.5%, it reacts with the flux used during brazing to form compounds, which may reduce brazeability. The Mg content is preferably in the range of 0.05 to 0.5%.

"Cu: 1.0% or less"
The aluminum alloy for the core material of this embodiment may contain, for example, 1.0% or less of Cu.
Cu is an optional component, but is added to improve the material strength of the core material 2 by solid solution strengthening. If the aluminum alloy for the core material does not contain Cu, the desired strength improvement effect cannot be obtained. If the Cu content exceeds 1.0%, the parent phase melting point decreases, and there is a risk of local melting during brazing. In addition, there is a risk of corrosion resistance decreasing after brazing. The Cu content is preferably in the range of 0.05 to 1.0%.
"At least one of Cr, Ti, Zr, and Ni is 0.3% or less"
The aluminum alloy for the core material of this embodiment may contain, for example, 0.3% or less of at least one of Cr, Ti, Zr, and Ni.
Cr, Ti, Zr, and Ni are all optional components, but are added to improve the material strength of the core material 2. If these elements are not included, the desired strength improvement effect cannot be obtained. If at least one of Cr, Ti, Zr, and Ni is contained in an amount exceeding 0.3%, giant intermetallic compounds may be generated during casting, which may reduce rollability.

"Zn: 3.0% or less"
The aluminum alloy for the core material of this embodiment may contain, for example, 3.0% or less of Zn.
Zn is an optional component, but is added to protect the object to be protected from corrosion by its sacrificial anode action when the object to be protected is brazed to the sacrificial anode body. If Zn is not included, the desired sacrificial anode action cannot be obtained, and there is a risk that corrosion of the object to be protected will be accelerated. If the Zn content exceeds 3.0%, there is a risk that the self-corrosion resistance will decrease.

The amounts of each element contained in the aluminum alloy for the core have been explained above. When the amounts of Fe, Mn and Si added are expressed as _CFe , _CMn and _CSi , it is preferable that these amounts satisfy the relationship _CFe + _1.5CMn + 1.6CSi _≦ 3.0.
When the Fe content, the Mn content and the Si content satisfy the above-mentioned relational expression, recrystallization easily proceeds during the brazing heat treatment, which is effective in preventing braze erosion.

"Composition of aluminum alloys for brazing filler metals"
"Si: 5.0 to 10.0%"
The aluminum alloy for brazing material of this embodiment contains Si in a range of 5.0% to 10.0%. In the aluminum alloy for brazing material, Si lowers the melting point of Al, so Si is added to melt during brazing and braze to other members. If the Si content is less than 5.0%, sufficient molten brazing material cannot be obtained, and brazing defects may occur. If the Si content exceeds 10.0%, the amount of molten brazing material increases, and the amount of molten brazing material supplied increases more than necessary, so that brazing material may be supplied to places other than the intended location.
"Zn: 6.0% or less"
The aluminum alloy for brazing material of this embodiment can contain 6.0% or less Zn. In the aluminum alloy for brazing material of this embodiment, Zn is an optional added component, and Zn is added to protect the core material 2 or the object to be protected from corrosion by sacrificial anode action when the core material 2 or the object to be protected from corrosion is brazed and joined to the brazing material. If Zn is not added, the desired sacrificial anode action cannot be obtained, and corrosion resistance may decrease. However, if Zn is added in an amount exceeding 6.0%, self-corrosion resistance may decrease.

"Mg: 2.0% or less"
The aluminum alloy for brazing material of this embodiment may contain 2.0% or less of Mg.
In the aluminum alloy for brazing filler metal of this embodiment, Mg is an optional added component. By adding Mg, it forms a compound with Si contained in the brazing filler metal, and the material strength can be increased.
Furthermore, since Mg destroys the aluminum oxide film on the material surface during brazing, it can be used in brazing methods that do not use flux.
In an aluminum alloy for brazing material, if the Mg content exceeds 2.0%, a Mg oxide film is formed on the surface, which may deteriorate the brazeability.

"Sr: 0.05% or less"
The aluminum alloy for brazing material of this embodiment may contain 0.05% or less of Sr.
In the aluminum alloy for brazing material of this embodiment, Sr is an optional component, but adding Sr can promote the refinement of eutectic Si during casting. If Sr is not added, there is a risk that the desired refinement of eutectic Si cannot be promoted. If the Sr content exceeds 0.05%, giant intermetallic compounds are generated during casting, and rollability may be reduced.

"Manufacturing conditions"
[Preparation of brazing material]
The brazing filler metal can be produced by, for example, semi-continuous casting an ingot of a molten alloy having a desired composition, homogenizing the ingot, machining the surface, and then hot rolling the ingot to produce a brazing filler metal plate having a desired thickness.
[Heartwood preparation]
The core material can be obtained by, for example, obtaining an ingot from a molten alloy of a desired composition by semi-continuous casting, and then subjecting it to homogenization treatment and facing to obtain a plate-shaped core material preform of a desired thickness.

"Homogenization treatment"
The obtained ingot or preliminary core material can be subjected to homogenization treatment at a temperature of 400°C or higher and lower than 600°C for a treatment time of 3 hours or higher and lower than 12 hours. This allows for a suitable dispersion state of intermetallic compounds to obtain desired properties. If conditions below the desired temperature are applied, the desired dispersion state of intermetallic compounds cannot be obtained, and the core material may not recrystallize during brazing heat treatment, which may cause brazing erosion. If the temperature is heated to a temperature exceeding the above-mentioned range, the amount of dispersed intermetallic compounds that inhibit the growth of recrystallized grains during brazing is small, and recrystallization is completed early, resulting in fine crystal grains, which may cause brazing erosion of the core material during brazing heat treatment. The homogenization treatment temperature is more preferably in the range of 450°C to 550°C.
The brazing material may be subjected to homogenization treatment at 400° C. to 550° C. for 1 hour to 10 hours in order to improve machinability.

"Pasting"
The brazing material preform processed into a plate shape is combined with a core material preform processed into a plate shape, and a brazing sheet with the desired cladding ratio is obtained by hot rolling and cold rolling as described below.
The cladding ratio when bonding can be set, for example, in the range of brazing material: core material=5-20%:80-95%.
However, the thickness of the brazing filler metal in the final plate thickness must be set to 80 μm or more. If the brazing filler metal thickness is less than 80 μm, the desired properties of the brazing filler metal cannot be obtained.

"Hot rolling"
The brazing material aluminum alloy or the clad material made by combining the core material and brazing material is hot-rolled into a plate material. In hot rolling, the reduction rate per pass and the finishing temperature at the end can be set. Hot rolling is performed at a temperature of about 500°C, and after rolling, the laminated plate material is coiled and cooled to room temperature.
"Cold rolling"
The conditions of the cold rolling up to the intermediate annealing are not particularly limited, but it is preferable to carry out the cold rolling at a reduction rate of 20 to 50% per pass.

"Intermediate annealing"
The intermediate annealing is performed to recrystallize the core material and the brazing material.
The intermediate annealing can be performed at a heating rate of 20 to 100° C./hour to 250 to 400° C. for a treatment time of 3 to 10 hours. If the intermediate annealing temperature is less than 250° C., recrystallization may not be completed, whereas if the temperature exceeds 400° C., abnormal grain growth may occur, resulting in non-uniform recrystallized grains.
"Final cold rolling"
Final cold rolling is performed after intermediate annealing with a reduction in the range of 6 to 13%.
If final cold rolling is not performed after intermediate annealing, microstrain accumulates in the area processed into a plate shape, causing erosion. More preferably, cold rolling is performed in two or more passes, with the first pass being 5% or more and the second and subsequent passes being 2% or less. This causes the recrystallization of the brazing material to become coarse, decreasing the brazing material fluidity of the unprocessed area.
In manufacturing, the aluminum alloy cannot be stably rolled down at a reduction rate of less than 6%, and manufacturing is impossible. In addition, there is a risk of erosion of the core material during brazing at a reduction rate of less than 6%. If the reduction rate is greater than 13%, the processing strain applied to the brazing material during rolling increases, promoting recrystallization grains of the brazing material during brazing, and the recrystallized grains become finer, which promotes brazing fluidity and increases the amount of brazing fluidity of the unprocessed part during molding, making it impossible to obtain the desired characteristics.

"Brazil flow coefficient: K"
In the brazing sheet 1 described above, when the brazing flow coefficient K in a drop type fluidity test when not processed is Ks, the brazing flow coefficient K at a point where a processing strain of 1% or more has been applied is 1.5 x Ks or more.

In the brazing sheet 1 of this embodiment, the brazing material erosion from the brazing material 3 to the core material 2 after brazing is less than 10% of the thickness of the core material 2 .
Moreover, in the brazing sheet 1 of this embodiment, the recrystallization rate of the core material 2 is 90% or more at a temperature immediately before the brazing material melts during brazing.
In the brazing sheet 1 described above, the supply of solder is suppressed or almost nonexistent in areas where no processing strain has been applied, but by applying processing strain to areas where it is desired to fill the solder, it is possible to fill the necessary areas with solder.

For example, the present invention can be applied to a heat exchanger that is constructed by partially applying strain to plate materials such as cooling plates for automobile batteries by forming depressions in the plate materials and brazing only the depressions.
Alternatively, the present invention can be applied to a heat exchanger having a structure in which only the portions of the tube material of the heat exchanger to which brazing material is to be supplied are processed, and brazing material is supplied only to the necessary portions for joining.

Figure 2 shows an aluminum heat exchanger 4. This heat exchanger 4 has corrugated fins 5 and incorporates aluminum alloy tubes 6, reinforcing members 7, and a header plate 8, which are integrated by brazing.

In the case of a heat exchanger 4 having the configuration shown in Fig. 2, a header plate 8 is formed by processing a brazing sheet 1. A through hole is formed in the header plate 8 at the portion where the tube 6 passes through, and the portion around this through hole has a larger brazing material flow coefficient than other portions due to processing strain. As a result of the molten brazing material flowing well around the portion where the tube 6 passes through, a fillet of sufficient size can be formed, and good brazing can be achieved.
Therefore, with the structure of this embodiment, an excellent heat exchanger 4 having excellent brazing properties and high joint strength can be obtained.

2 shows an example of a header plate 8, and it has been explained that the flow of molten brazing filler metal around the through hole of the header plate 8 and in its vicinity can be promoted to promote the generation of a fret of sufficient size. However, the configuration of this embodiment is widely applicable to heat exchangers having objects to be brazed of various other shapes, and is significant in that it can promote the flow of molten brazing filler metal in portions of the objects to be brazed that have processing strain.
There are various known structures for heat exchangers, and the shapes of the components vary depending on the structure of the heat exchanger. However, when a brazing structure is adopted in any of them, the gaps and spaces for the flow of molten brazing material tend to become smaller in parts with complex shapes. Therefore, increasing the fluidity of the molten brazing material in areas where processing strain is applied in the components of the heat exchanger made of brazing sheet is an important indicator for ensuring good brazing properties.

Incidentally, in the brazing sheet 1 of this embodiment, a configuration may be adopted in which an intermediate layer that functions as a brazing material is provided between the brazing material 3 and the core material 2 .
Furthermore, a sacrificial anticorrosion layer may be provided by cladding an aluminum alloy containing Zn onto the surface of the core material that is not clad with a brazing filler metal.
The brazing sheet that can be applied to this embodiment may have a four-layer structure of brazing material/core material/sacrificial material/brazing material, or a five-layer structure of brazing material/sacrificial material/core material/sacrificial material/brazing material, or a four-layer structure of first brazing material/second brazing material/core material/brazing material, or a six-layer structure of first brazing material/second brazing material/sacrificial material/core material/sacrificial material/brazing material, and the clad structure is not particularly limited.

Aluminum alloy brazing sheets were produced having core materials and brazing materials having the compositions shown in the following Tables 1 to 11. Ingots were obtained from the aluminum alloys having the compositions shown in Tables 1 to 11 by semi-continuous casting, and then each ingot was subjected to homogenization treatment at the temperatures and times shown in Tables 12 to 22.
The homogenized core preform and the plate-shaped brazing filler preform were stacked together and subjected to hot rolling and cold rolling, with the final cold rolling reductions set to those shown in Tables 12 to 22, to obtain brazing sheets No. 1 to No. 326. The brazing sheets had a thickness of 1.0 mm.
Moreover, these brazing sheets have a one-sided brazing material construction with a cladding ratio of 10%.
Each brazing sheet was subjected to a heat treatment equivalent to brazing in a nitrogen gas atmosphere under the conditions shown below.

The brazing-equivalent heat treatment was carried out in a nitrogen gas atmosphere, with the temperature rising at an average rate of 100-400°C/min until it exceeded 400°C, as shown in the temperature history in Figure 3, and then the temperature was raised to 600°C over a period of 10-15 minutes, and the material was held in the temperature range of 585°C-630°C for 2-10 minutes. The material was then air-cooled to 300°C at a rate of 50-100°C/min.

"Recrystallization rate of core material just before wax melts"
The recrystallization rate of the core material just before the braze melting was measured by removing the material at the temperature just before the braze melting, mechanically polishing the cross section, anodizing it with Barker's solution ( _HBF4 : _H2O = 1:30), and observing it with an optical microscope. The recrystallization rate of each brazing sheet sample was judged according to the following criteria, and the evaluation results are shown in Tables 12 to 22 below. Figure 5 shows a structural photograph of a sample with a recrystallization rate of 90% or more, and Figure 6 shows a structural photograph of a sample with a recrystallization rate of less than 90%.
As is clear from a comparison of Fig. 5 and Fig. 6, the sample shown in Fig. 5 shows a structure in which recrystallized grains of a different size from the recrystallized grains after final rolling are dominant as a result of the completion of recrystallization, whereas the sample shown in Fig. 6 shows a structure in which recrystallized grains during intermediate annealing can be observed.
×…Less than 90% ○…90% to less than 95% ◎…95% or more

"Brazing erosion rate to core material after brazing"
It is preferable that the thickness of the core material observed by mechanical polishing in cross section is reduced by 10% or less after brazing compared to the thickness before brazing. If the reduction exceeds 10%, the strength of the component is reduced and the structural strength of the heat exchanger cannot be maintained.
An example of a sample in which the braze erosion rate was 7% as a result of cross-sectional observation is shown in Fig. 7, and an example of a sample in which the braze erosion rate was 15% as a result of cross-sectional observation is shown in Fig. 8. The samples shown in Figs. 7 and 8 are reference samples for explaining the cross-sectional observation conditions.

"Flow coefficient when 1% strain is applied"
For the brazing sheet after the heat treatment equivalent to brazing, the brazing fluidity coefficient K was determined by the following drop type fluidity test.
The brazing sheet was subjected to a 1% strain using a tensile tester, and cut to a width of 22 mm and a length of 60 mm to prepare test pieces (see FIG. 4(A)). These test pieces were held vertically and charged into a heating furnace, where they were subjected to the above-mentioned brazing-equivalent heat treatment. A round hole for hanging was formed in the top of each test piece, and the test pieces were hung using the round hole and charged into the heating furnace.

The heating associated with the brazing heat treatment causes the brazing material to melt and spread, and the wetted and spread molten braze flows by gravity to the lower part of the test piece, forming a thick braze puddle as shown in FIG. 4(B).
Here, the weight ( _W0 ) of the entire brazing sheet and the weight ( _Wb ) of approximately 1/4 (1/4 of the total length = 15 mm) of the lower part of the test piece after the brazing heat treatment, including the above-mentioned brazing pool, were obtained, and the brazing flow coefficient (K) was calculated using the following formula.
K=(4W _b −W ₀ )/(3W ₀ × brazing material cladding ratio)

The flow coefficients calculated based on the above formula were evaluated according to the following criteria and are shown in Tables 12 to 22 below.
×...Less than 1.5 times ◯...1.5 times or more but less than 2.0 times ◎...2.0 times or more The core material composition and brazing material composition of each brazing sheet described above are shown in Tables 1 to 11 below, and the homogenization temperature, homogenization time, and final rolling reduction of each brazing sheet are shown in Tables 12 to 22 below. In addition, the core brazing material erosion rate, core recrystallization rate, and brazing material flow coefficient Ks of each brazing sheet are shown in Tables 12 to 22 below.

Samples No. 1 to No. 288 shown in Tables 1 to 11 are brazing sheets that, in a drop type fluidity test, have a flow coefficient of 1.5 x Ks or more when subjected to a processing strain of 1%, where Ks is the brazing flow coefficient in an unprocessed state.
These brazing sheets are brazing sheets in which the amount of brazing material eroded after brazing from the brazing material to the core material is less than 10% of the thickness of the core material, and the recrystallization rate of the core material is 90% or more at a temperature just before the brazing material melts.
Moreover, the brazing sheets No. 1 to No. 288 had a recrystallization rate of 90% or more after the heat treatment equivalent to brazing.

For the brazing sheets No. 1 to 288, the amount of brazing material eroded after brazing from the brazing material to the core material is less than 10% of the core material thickness, so even when brazing is performed using a brazing sheet, a brazing structure in which the core material is not eroded by the brazing material can be achieved.
Furthermore, when header plates of various shapes are constructed using these brazing sheets, the brazing material flow coefficient can be increased in the portion where processing strain has been applied. This means that when a header plate and a tube are brazed together to manufacture a heat exchanger, the fluidity of the molten brazing material can be increased in the region between the portion where processing strain has been applied and the tube adjacent to that portion, and the molten brazing material can be supplied sufficiently to the portion adjacent to the header plate and the tube.

Fins are processed into various shapes for use in heat exchangers, so the materials to be brazed to the fins come in a variety of configurations, and the shapes of the joints between the materials to be brazed and the fins also vary. However, by designating the area where the fin approaches the materials to be brazed as an area where processing strain is applied, good brazing between the materials to be brazed and the fins can be ensured.

Brazing sheets No. 289 to No. 299 shown in Table 10 are samples in which any of the components exceeds the upper limit of the desired content.
As shown in Table 21, brazing sheets No. 289 to No. 299 had a high core braze erosion rate of 11 to 20%, and the flow coefficient of the portion with processing strain was less than 1.5 times the flow coefficient of the portion without processing strain. Additionally, brazing sheets No. 291 to No. 293 and No. 296 to 299 also had a core recrystallization rate of less than 90%.

The brazing sheets No. 300 to No. 308 shown in Table 11 are samples whose Fe content, Mn content and Si content are within the desired ranges of Fe: 0.05% or more and 1.0% or less, Mn content: 0.05% or more and 1.2% or less, and Si content: 0.05% or more and 1.0% or less, but whose total amount of each additive, expressed as _CFe + _1.5CMn + _1.6CSi , exceeds 3.0.
The brazing sheets No. 300 to No. 308 shown in Table 11 had a high core braze erosion rate of 14 to 20%, as shown in Table 22, a core recrystallization rate of less than 90%, and a flow coefficient ratio of less than 1.5.
In addition, the brazing sheets Nos. 300 to 308 were not completely recrystallized during the heat treatment equivalent to brazing, and therefore suffered from severe braze erosion.

Brazing sheets No. 309 to No. 311 shown in Table 11 are samples whose Si content, Fe content, and Mn content are higher than the desired ranges, and whose total amount of each additive ( _CFe + _1.5CMn + _1.6CSi ) exceeds 3.0.
As shown in Table 22, the brazing sheets No. 309 to No. 311 shown in Table 11 had a high core braze erosion rate of 12 to 13%, and the flow coefficient ratio was also lower than 1.5 times.
Brazing sheet No. 310 was subject to severe braze erosion due to its fine crystal grains.
In the brazing sheets No. 309 and No. 311, the recrystallization rate of the core material was less than 90%.

Brazing sheets No. 312 to No. 314 have core material and brazing material components within the desired range, but brazing sheet No. 312 has a low homogenization temperature as shown in Table 22, brazing sheet No. 313 has a high final rolling reduction, and brazing sheet No. 314 is a sample with a low final rolling reduction.
These brazing sheets were samples having a flow coefficient ratio lower than 1.5 times and a high core braze erosion rate or a low core recrystallization rate.
The brazing sheets Nos. 311, 312 and 314 were not completely recrystallized during the heat treatment equivalent to brazing, and therefore suffered from severe braze erosion.

Brazing sheet No. 315 is a sample with a low Si content in the brazing material as shown in Table 11, while brazing sheet No. 316 is a sample with a high Si content in the brazing material, and as shown in Table 22, the flow coefficient ratio was lower than 1.5 times.
Brazing sheets No. 317 to No. 323 are samples in which the core material contains any one of Mg, Cu, Cr, Ti, Zr, Ni, and Zn in a content greater than the desired content of each element, as shown in Table 11.
Brazing sheet No. 317 had poor brazing properties, brazing sheet No. 318 had an increased braze erosion rate due to a decrease in the core melting point, and brazing sheets No. 319 to 322 produced large intermetallic compounds during casting, causing problems during rolling.
The No. 323 brazing sheet had reduced self-corrosion resistance of the core material, the No. 324 brazing sheet had reduced self-corrosion resistance of the filler metal, the No. 325 brazing sheet had reduced brazeability, and the No. 326 brazing sheet produced large intermetallic compounds during casting, causing problems during rolling.
The brazing sheet No. 327 had a high rolling reduction in the second pass and a flow coefficient of less than 1.5 times, while the brazing sheet No. 328 had a low rolling reduction in the first pass and a flow coefficient of less than 1.5 times.

From the above explanation, it has been found that in the case of a brazing sheet made by combining an aluminum alloy core material and a brazing material and applying processing strain, if the ratio of the brazing flow coefficient before and after the brazing process in the area without strain to the area with processing strain is 1.5 times or more, and the recrystallization rate at the temperature just before the brazing melting point is 90% or more, the desired brazing sheet can be provided.

Reference Signs List 1: aluminum alloy brazing sheet, 2: core material, 3: brazing material, 3A: brazing material, 3B: sacrificial material, 4: heat exchanger, 5: fin, 5a: bent portion, 6: tube.

Claims (3)

An aluminum alloy brazing sheet in which a brazing material made of an Al-Si alloy is combined with at least one surface of a core material made of an aluminum alloy,
An aluminum alloy brazing sheet characterized in that, in a drop-type fluidity test, when the brazing material has a brazing material flow coefficient Ks in an unprocessed state, the brazing material has a flow coefficient of 1.5 x Ks or more when a processing strain of 1% or more is applied, the amount of brazing material eroded after brazing from the brazing material to the core material is less than 10% of the core material thickness, and the recrystallization rate of the core material is 90% or more at a temperature just before the brazing material melts. The core material is, in mass %,
Fe: 0.05% or more and 1.0% or less,
Mn: 0.05% or more and 1.2% or less,
Si: Contains at least one element in an amount of 0.05% or more and 1.0% or less;
In addition, when the amounts of each added are _CFe , _CMn , and _CSi ,
2. The aluminum alloy brazing sheet according to claim 1, characterized in that the amounts of the elements added satisfy the relationship: _CFe + _1.5CMn +1.6CSi _≦ 3.0. The brazing material is
3. The aluminum alloy brazing sheet according to claim 1, further comprising: Si: 5.0% or more and 10.0% or less.

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