JP7555766B2 - Aluminum alloy bare material and aluminum alloy brazing sheet with excellent thermal conductivity and erosion resistance - Google Patents

Description

The present invention relates to an aluminum alloy bare material and an aluminum alloy brazing sheet that have excellent thermal conductivity and erosion resistance.

In recent years, new heat exchangers such as inverter coolers are being installed in automobiles due to the trend toward electric vehicles. In order to reduce the size and weight of inverter coolers, it is necessary to improve the heat dissipation performance of the heat exchanger. For example, in inverter coolers that have a structure with a high bonding density of components, the higher the thermal conductivity of the aluminum used in the components, the better the heat dissipation performance of the inverter cooler.
Aluminum alloys used in automotive heat exchangers are generally Al-Mn alloys due to their strength and corrosion resistance. However, Mn added to Al tends to significantly reduce electrical conductivity when dissolved in the Al matrix. The thermal conductivity and electrical conductivity of Al are proportional, and a decrease in electrical conductivity leads to a decrease in thermal conductivity.
Therefore, in the case of an automobile heat exchanger using an Al alloy containing Mn, which has poor electrical conductivity, the heat dissipation performance is limited. On the other hand, if a 1000 series alloy without Mn is used, it can have high electrical conductivity, but its strength is low as a component of an automobile heat exchanger, and the structural strength of the heat exchanger cannot be maintained. In addition, elements such as Si and Cu that improve strength by dissolving in the Al matrix can suppress the decrease in electrical conductivity and improve strength compared to Mn when compared with the same amount of addition, but since the melting point of the material decreases with increasing amount of addition, excessive addition increases the possibility of being severely corroded during brazing, making it difficult to maintain the shape of the heat exchanger. For this reason, in order to improve the heat dissipation performance while maintaining the structure of the automobile heat exchanger, it is necessary to ensure strength and improve thermal conductivity by using an aluminum alloy other than the Al-Mn alloy.

Conventionally, an aluminum alloy material having a composition of 2.0 to 3.0 mass% Fe, 0.5 to 1.5 mass% Si, 0.05 mass% or less Ti, with the balance being Al and unavoidable impurities, has been known as an aluminum alloy material exhibiting high strength and high thermal conductivity (see Patent Document 1).
Also, as an aluminum alloy fin material for heat exchangers, an aluminum fin material is known which is composed of 0.010 to 0.4 mass% Fe, less than 0.005 mass% Cu, the remainder being Al and impurities, has an Al purity of 99.30 mass% or more, has an average grain size of subgrains of 2.5 μm or less, and has 2000 pieces/ ^mm2 or less of intermetallic compounds having a maximum length exceeding 3 μm (see Patent Document 2).

JP 2002-256365 A JP 2014-074198 A

In recent years, with the demand for further miniaturization and high heat dissipation performance of heat exchangers, there is a demand for aluminum alloys with high electrical conductivity (= high thermal conductivity). Therefore, the inventors have been developing various materials for Al alloys of systems other than Al-Mn alloys.
In conjunction with the development of this material, the present inventors have studied a composition system in which Fe, Si, and Cu are added to Al, and as a result, have found that by using an alloy containing Fe, which is hardly dissolved in the aluminum matrix, and Si, a material having high electrical conductivity and strength sufficient to maintain the structural strength of a heat exchanger can be obtained. However, if the amount of Si added is increased, the melting point of the base material decreases when a large amount of Si is dissolved in the base material, so that the base material is severely eroded by brazing and the shape of the heat exchanger cannot be maintained. Furthermore, if the distribution ratio of fine Al-Fe-Si compounds relative to coarse Al-Fe compounds is low, recrystallization occurs with the coarse Al-Fe compounds as nuclei, and the recrystallized grains become fine, so that excessive brazing erosion may occur during brazing. Therefore, a process was adopted in which the solid solubility of Si is reduced and the particle size and density of the Al-Fe compounds present in the Al matrix and the particle size and density of the Al-Fe-Si compounds are optimized. It was found that this prevents recrystallization grains from becoming fine, provides excellent erosion resistance, and also enables a dramatic improvement in electrical conductivity compared to Al--Mn alloys.

They also discovered that adding Cu, which does not affect the distribution of these compounds, to Al in a range that does not cause brazing erosion during brazing can be used to make heat exchangers for automobiles, which require greater strength.

The present invention was made in light of these circumstances, and aims to provide an aluminum alloy bare material and an aluminum alloy brazing sheet that have high electrical conductivity, can suppress the occurrence of brazing erosion, and have the strength and corrosion resistance required for heat exchangers.

(1) The aluminum alloy bare material of this embodiment contains, by mass%, Fe: 0.6% or more and 0.8% or less, Si: more than 0.7% and 1.4% or less, Cu: 0.6% or less, Mn: 0.2% or less, Zn: 0.3% or less, the balance being Al and unavoidable impurities, has an electrical conductivity of 55% IACS or more, and is characterized in that the number of Al-Fe based compound particles or Al-Fe-Si based compound particles having a circle equivalent diameter of 0.5 to 2.0 μm distributed in a matrix is 1.0 x ¹⁰ to 3.0 x ¹⁰ particles/ ^mm2 .

(2) The aluminum alloy bare material of this embodiment has an electrical conductivity of 44% IACS or more after being subjected to a heat treatment equivalent to that for brazing a heat exchanger, which comprises heating to 600°C, holding the temperature for 5 minutes, and then cooling to 300°C at 60°C/min , and preferably has a number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having an equivalent circle diameter of 0.5 to 2.0 μm distributed in the matrix of ^1.0 x 104 to 3.0 x ¹⁰⁴ particles/ ^mm2 .

(3) The aluminum alloy brazing sheet of this embodiment is characterized in that the core material is an aluminum alloy for heat exchangers having the composition described in (1) or (2), and an aluminum alloy layer containing 3.0 to 12.0% Si by mass as a brazing material, with the remainder being Al and unavoidable impurities, is bonded to one or both surfaces of the core material.

(4) In the aluminum alloy brazing sheet of the present embodiment, it is preferable that the brazing material further contains, by mass%, Zn: 0.1 to 4.0%.
(5) In the aluminum alloy brazing sheet according to (3) or (4) of this embodiment, it is preferable that the aluminum alloy brazing sheet has an electrical conductivity of 53% IACS or more, and the number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having an equivalent circle diameter of 0.5 to 2.0 μm distributed in the core matrix is 0.1 x 10 ⁴ to 3.0 x 10 ⁴ particles/mm ² .

(6) In the aluminum alloy brazing sheet according to any one of (3) to (5) of this embodiment, after subjecting the sheet to a heat exchanger brazing-equivalent heat treatment of heating to 600°C, holding the temperature for 5 minutes, and then cooling to 300°C at 60°C/min, it is preferable that the sheet has an electrical conductivity of 43% IACS or more, and the number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having a circle equivalent diameter of 0.5 to 2.0 μm distributed in the core matrix is 1.0 x ¹⁰⁴ to 3.0 x ¹⁰⁴ particles/ ^mm2 .

(7) In the aluminum alloy brazing sheet according to any one of (3) to (6) of this embodiment, after a heat treatment equivalent to heat exchanger brazing is applied, which comprises heating to 600°C, holding the same for 5 minutes, and then cooling to 300°C at 60°C/min, the pitting potential difference between the surfaces of the core material and the brazing material is preferably 80 mV or more.

The present invention can provide an aluminum alloy bare material or an aluminum alloy brazing sheet for heat exchangers that has excellent electrical conductivity and excellent erosion resistance.
The aluminum alloy bare material or brazing sheet according to the present invention has excellent electrical conductivity while suppressing braze erosion, and can therefore be applied as an aluminum alloy bare material and brazing sheet suitable for use in automotive heat exchangers, which have been required to be further miniaturized and have high heat dissipation performance in recent years.

FIG. 1 is a cross-sectional view showing an example of an aluminum alloy bare material according to the present invention. 1 is a partial cross-sectional view showing an example of a brazing sheet according to the present invention. FIG. 4 is a partial cross-sectional view showing another example of the brazing sheet according to the present invention. FIG. 2 is a side view for explaining a joining state between the brazing sheet according to the present invention and a member to be brazed. 1 is a perspective view showing a heat exchanger configured to which a brazing sheet according to the present invention is applied.

Embodiments of the present invention will be described in detail below with reference to the attached drawings. Note that the drawings used in the following description may show enlarged characteristic parts for the sake of convenience in order to make the features easier to understand.

Figure 1 shows an example of an aluminum alloy bare material according to the present invention, and Figure 2 shows the cross-sectional structure of an aluminum alloy brazing sheet for heat exchangers of the first embodiment, which has a core material made of the same components as the aluminum alloy bare material shown in Figure 1. The aluminum alloy brazing sheet A of this embodiment is in the form of a plate or sheet, and has a three-layer structure in which a first brazing material layer 2 is laminated on both the top and bottom surfaces of a core material 1 made of the same components as the aluminum alloy bare material shown in Figure 1. The brazing material layer 2 may be laminated on only one side of the core material 1, as in other forms described below.

"Aluminum alloy bare material and core material"
The bare material M and the core material 1 are made of an aluminum alloy containing, by mass%, Fe: 0.6% or more and 0.8% or less, Si: 0.7% or more and 1.4% or less, Cu: 0.6% or less, Mn: 0.2% or less, Zn: 0.3% or less, and the balance being Al and unavoidable impurities.
The aluminum alloy bare material M can be rolled into a plate shape as shown in Fig. 1 and used as a fin for a heat exchanger, or the aluminum alloy and the double-sided clad material can be processed into a cup shape and used as a member to be brazed by stacking them alternately. One example of the use of the aluminum alloy bare material M of this embodiment is the brazing sheet A shown in Fig. 2, in which an alloy of the same composition is used as the core material 1, but it is of course possible to use it for other purposes.

The reasons for limiting the composition of the component elements contained in the aluminum alloy constituting the bare material M and the core material 1 will be explained below.
Fe: 0.6% or more and 0.8% or less Fe is added to Al to precipitate Al-Fe or Al-Fe-Si compound particles in the aluminum alloy matrix, and to improve the material strength by particle dispersion strengthening. If the Fe content is less than the lower limit, the Al-Fe compound particles or Al-Fe-Si compound particles cannot obtain the desired dispersion state (required number per unit area). If the Fe content exceeds the upper limit, the number of dispersed Al-Fe compound particles or Al-Fe-Si compound particles increases more than necessary, so that when a corrosive solution adheres to the bare material or the core material itself, the cathodic reaction on the surface is promoted, and the self-corrosion resistance is reduced.

Si: 0.7% or more and 1.4% or less Si improves the material strength of Al by dissolving in Al or by precipitating in the aluminum alloy matrix as compound particles such as Al-Fe-Si system. If the Si content exceeds the upper limit, the melting point of the aluminum alloy is lowered more than necessary, so that the core material melts during brazing, which may cause poor brazing. If the Si content exceeds the upper limit, the electrical conductivity after brazing may decrease. If the Si content is less than the lower limit, the desired dispersion state of the compound particles is not obtained, the recrystallized grains become fine, and the bare material and the core material are excessively eroded by brazing during brazing, so that the shape of the heat exchanger may not be maintained.

Cu: 0.6% or less Cu is added to dissolve in Al to improve the material strength of Al. If the Cu content is less than the lower limit, the strength required to maintain the structure of the heat exchanger cannot be obtained. If the Cu content is more than the upper limit, the electrical conductivity after brazing decreases. In addition, if the Cu content increases, Cu may precipitate on the surface during corrosion of the Al alloy, which may reduce the self-corrosion resistance. In addition, when used as a brazing sheet, Cu is diffused from the core material to the brazing material during brazing, making the potential of the brazing material more noble, and the potential difference between the brazing material and the core material becomes smaller, so that the sacrificial corrosion protection by the brazing material may not work effectively.

Mn: 0.2% or less It is difficult to completely avoid the inclusion of Mn in the production of an aluminum alloy, and therefore a small amount is included for the sake of convenience of production. Even if a small amount of Mn is included, it significantly reduces the electrical conductivity when it dissolves in Al. However, if the Mn content is 0.2% or less, the amount of Mn dissolved in Al can be minimized by carrying out a predetermined homogenization treatment, thereby suppressing the decrease in electrical conductivity. The Mn content is more preferably 0.1% or less.
Zn: 0.3% or less Zn is an element that contributes to ensuring corrosion resistance, and if the Zn content exceeds 0.3%, the self-corrosion resistance decreases. The Zn content is more preferably 0.2% or less.

"Brazing material"
The reasons for limiting the composition of the component elements contained in the brazing material 2 will be explained below.
Si: 3.0-12.0%
Silicon is added to form a molten braze during brazing and to form a fillet at the brazed joint.
If the Si content is less than the lower limit, the amount of molten brazing material is reduced, and the brazing bondability is reduced.If the Si content is more than the upper limit, the amount of molten brazing material produced during brazing is excessive, and the core material 1 or the member to be brazed is melted so violently that the shape of the heat exchanger cannot be maintained, and there is a risk of performance degradation and damage to the appearance.
In addition, when a range of mass% or a numerical range is expressed using "to", the lower limit and the upper limit are included unless otherwise specified. Thus, as an example, 3.0 to 12.0% means that the content is 3.0 mass% or more and 12.0 mass% or less.

Zn: 0.1-4.0%
Zn is added to the brazing filler metal to obtain the sacrificial corrosion protection effect of the core material by the brazing filler metal. If Zn is added in excess of 4.0%, the corrosion rate increases, and the brazing filler metal corrodes early, making it impossible to protect the core material from corrosion. This results in a decrease in corrosion resistance.

"Particle size of Al-Fe based compound particles or Al-Fe-Si based compound particles"
0.5-2.0μm (0.5μm or more and 2.0μm or less)
If the particle size (circle equivalent diameter) of the compound particles is less than 0.5 μm, the compound particles are redissolved in the matrix during brazing, and the electrical conductivity of the material after brazing decreases. If the particle size exceeds 2.0 μm, particle dispersion strengthening cannot be effectively achieved, and the material strength decreases, so that the structural strength of the heat exchanger cannot be maintained. In addition, if a large number of compound particles exceeding 2.0 μm are distributed, recrystallization progresses with the compound particles as nuclei, and the recrystallized grains become fine, so that the aluminum alloy bare material and core material are severely eroded, and the shape of the heat exchanger cannot be maintained.

"Number of Al-Fe based compound particles or Al-Fe-Si based compound particles: 1.0×10 ⁴ to 3.0×10 ⁴ particles/mm ² (1.0×10 ⁴ particles/mm ² or more and 3.0×10 ⁴ particles/mm ² or less)"
When the number of compound particles is less than 1.0 × 10 ⁴ , if the amount of the element added to the material is large, the added element is almost in a solid solution state in the matrix, and the electrical conductivity is greatly reduced. Conversely, if the amount of the element added is small, the solid solubility is low, so the electrical conductivity is high, but the material strength is low, so the structural strength for applications such as heat exchangers cannot be maintained.
If the number of compound particles exceeds 3.0 × 10 ⁴ , the number of compounds exposed to the surface increases. The increase in the number of compound particles increases the cathodic reaction occurring on the material surface, and the self-corrosion resistance of the Al alloy decreases.
The number of Al-Fe based compound particles or Al-Fe-Si based compound particles is more preferably in the range of 1.0×10 ⁴ to 3.0×10 ⁴ particles/mm ² .

"Number of Al-Fe based compound particles or Al-Fe-Si based compound particles after brazing: 1.0×10 ⁴ to 3.0×10 ⁴ particles/mm ² (1.0×10 ⁴ particles/mm ² or more and 3.0×10 ⁴ particles/mm ² or less)"

"Potential difference between core potential and brazing material potential"
When the potential difference between the core material potential and the brazing material potential is 80 mV or more, the sacrificial corrosion protection ability (corrosion resistance) of the core material by the brazing material is improved. When the potential difference is 80 mV or less, the sacrificial corrosion protection does not work effectively, and the core material corrodes significantly. The fact that the corrosion resistance is improved at a potential difference of 80 mV or more can be confirmed by the corrosion test described below, as an example.

In the corrosion test, a brazed test sample in which the brazing filler metal and the core metal are overlapped so that the core metal is exposed is immersed in OY water, which is an aqueous solution containing 195 ppm Cl ^- , 60 ppm SO ₄ ^2- , 1 ppm Cu ²⁺ , and 30 ppm Fe ³⁺ .
The test cycle is 8 hours at 88°C, followed by 16 hours at room temperature. The corrosive solution is stirred using a magnetic stirrer while heating to 88°C. The sample size is processed so that the specific liquid volume is 16.7 ml/ ^cm2 .
For those with a potential difference of 80 mV or more, after a four-week test in OY water, the number of pits in the core material with a depth of 0.1 mm or less is less than 0.1 pits/ ^mm2 , indicating good corrosion resistance.
Therefore, if the potential difference between the core material and the brazing material is 80 mV or more, the brazing sheet is less susceptible to pitting corrosion and can be provided as a brazing sheet with excellent corrosion resistance.

"Manufacturing method"
For example, aluminum alloys for bare materials and core materials, and aluminum alloys for brazing materials are cast by semi-continuous casting.
As an aluminum alloy for the core material, an aluminum alloy containing, by mass%, Fe: 0.6% or more and 0.8% or less, Si: more than 0.7% and 1.4% or less, Cu: 0.6% or less, Mn: 0.2% or less, Zn: 0.3% or less, with the balance being Al and unavoidable impurities can be applied, and bare material and core material can be manufactured from this aluminum alloy.
An aluminum alloy for brazing filler metal can be used that contains, by mass%, 3.0 to 12.0% Si, and can further contain 0.1 to 4.0% Zn as necessary, with the balance being Al and unavoidable impurities. Brazing filler metal can be produced from this aluminum alloy.

"Homogenization treatment"
The resulting core material can be subjected to a homogenization treatment at 400° C. to 600° C. for a treatment time ranging from 3 to 12 hours. By selecting the appropriate temperature and time, the desired properties of high electrical conductivity and optimal dispersion of the compound particles in the matrix can be obtained.

To improve machinability, the brazing material may be subjected to homogenization treatment at a temperature of 400°C to 500°C for a treatment time of 1 to 10 hours.

"Pasting"
When used as a brazing sheet, it can be produced by combining brazing material on one or both sides of a sheet or plate-shaped core material with an appropriate cladding ratio of brazing material:core material=5-15%:85-95%. When used on both sides, the brazing sheet can be produced by combining cladding ratios of skin material:core material:skin material=5-15%:70-90%:5-15%.
There are no particular limitations on the preparation of the brazing material, and it can be prepared under the conditions for preparing the brazing material when manufacturing a general brazing sheet. After homogenization, the surface is machined, rolled to the desired thickness by hot rolling, cut to a specified length, and bonded to the core material.

"Hot rolling, cold rolling, annealing"
The bare aluminum alloys and the combination of the core and skin materials can be produced by hot rolling (or clad rolling) using a hot rolling mill.
After the hot rolling, the steel sheet can be cold-rolled to a desired thickness, and annealing may be performed as many times as necessary during the cold rolling to continue the rolling.
The thickness of the final material is not particularly limited, but the reduction ratio from the thickness finished by hot rolling and the thickness annealed for further rolling to the final thickness is preferably 20 to 99%. In addition, annealing may be performed after cold rolling to achieve an O temper. The annealing may be performed by performing a heat treatment at 200°C to 500°C for 1 to 10 hours using, for example, a batch annealing furnace.

The aluminum alloy bare material M produced according to the process described above or the aluminum alloy brazing sheet A having the configuration shown in FIG. 2 is used for the purpose of brazing by placing it for about 1 to 30 minutes in an inert gas atmosphere at a brazing temperature in the range of, for example, about 590 to 620° C. when producing a heat exchanger or the like.
For example, it is used in assembling a heat exchanger by laminating it with brazing target components such as fins and tubes of various heat exchangers or cup-shaped bodies, and after assembling the fins, tubes, or cup-shaped bodies, the whole is heated to the brazing temperature to melt the brazing material 2 of the aluminum alloy brazing sheet A, and then cooled to room temperature to form a fillet and complete the brazing. Alternatively, components such as fins and tubes of a heat exchanger can be directly formed from the brazing sheet and used for brazing.
The workpiece to be brazed may be a bare aluminum alloy material M shown in FIG.

FIG. 3 shows a brazing sheet B obtained by cladding and rolling a brazing material 2 on only one side of a core material 1, and FIG. 4 is an explanatory diagram showing the state in which this brazing sheet B is used to braze a brazing target member 3 such as a fin.
The brazing is completed by brazing the brazing sheet B and the brazing target member 3 shown in FIG. 4 under the above-mentioned brazing conditions.

The bare material M and the brazing sheets A and B have high electrical conductivity, excellent erosion resistance, and the strength and corrosion resistance required for heat exchangers, and therefore can be provided as brazing sheets suitable for use in automotive heat exchangers, which have been required in recent years to be further miniaturized and have high heat dissipation performance.
The brazing material 2 may have a multi-layer structure, such as a two-layer structure including a first brazing material 2A and a second brazing material 2B as shown by the two-dot chain line in FIG. 4, or another multi-layer structure.

5 shows an aluminum heat exchanger 5 in which fins 6 are formed using the brazing sheet A or brazing sheet B, and an aluminum alloy tube 7 is used as the brazing target member. The fins 6 and tubes 7 are combined with a reinforcing material 8 and a header plate 9, and brazed to obtain the aluminum heat exchanger 5 for automotive use, etc.
The brazing sheets A and B described above have excellent electrical conductivity, excellent erosion resistance, and the strength and corrosion resistance required for heat exchangers, and therefore can be used in automotive heat exchangers, which have been required to be further miniaturized and have high heat dissipation performance in recent years, and can provide automotive heat exchangers, which are being further miniaturized and have high heat dissipation performance.

In addition to being used to form fins in heat exchangers, brazing sheets can also be used to form tubes, header pipes, and other heat exchanger components. In these cases, various laminated structures can be used depending on the application, such as single-sided brazing material types, double-sided brazing material types, and even structures in combination with sacrificial materials and structures that are multi-layered by combining with intermediate materials.

Aluminum alloys were produced by semi-continuous casting so as to have the compositions of Alloy Nos. A1 to A28 shown in Tables 1 and 2. The resulting aluminum alloy ingots were subjected to homogenization annealing (homogenization treatment) under the conditions (temperature (°C) x time (h)) shown in Tables 1 and 2, and then hot rolled. Then, the ingots were cold rolled to a thickness of 1.0 mm so as to give a rolling reduction of 85%, and annealed at 350°C for 5 hours to produce the desired aluminum alloy bare materials.
Additionally, sample brazing sheets were prepared by using the aluminum alloys of each alloy number listed in Tables 1 and 2 as core materials and combining them with brazing filler metals of the compositions shown in Tables 3 and 4 by clad rolling. In this process, the brazing filler metal was bonded to one side of the core material by clad rolling so that the clad ratio was 10%, and then hot-rolled and cold-rolled to a thickness of 1.0 mm so that the reduction ratio was 85%, followed by annealing at 350°C for 5 hours to prepare brazing sheet samples of each number.

"Heat treatment equivalent to brazing"
In order to evaluate the bare material and brazing sheet used in the brazed heat exchanger alone, each bare material and brazing sheet sample was subjected to a brazing-equivalent heat treatment in a batch furnace. The brazing-equivalent heat treatment was performed under the following conditions: heating from room temperature to 600°C, holding at 600°C for 5 minutes, and then cooling to 300°C at 60°C/min. After reaching 300°C, each sample was quickly cooled to room temperature using a fan. The obtained bare material and brazing sheet samples were subjected to the evaluation described below.

"Evaluation Method"
<Electrical Conductivity>
The measurement was performed by a four-terminal method. A current of 500 mA was applied to the sample in a room temperature environment of 20 to 25° C., and the resistance was calculated from the voltage value, and then the electrical conductivity was calculated.
<Compound particle distribution state>
The cross sections parallel to the rolling direction were observed for the produced aluminum alloy bare material and brazing sheet core material, and for the aluminum alloy bare material and brazing sheet core material that had been subjected to heat treatment equivalent to brazing. The observation was performed using a field emission scanning electron microscope (FE-SEM) on the cross sections that had been subjected to CP processing (cross-section polishing) based on the ion milling method. The circle equivalent diameter and distribution density of the compound particles were calculated by image analysis based on the observed images.

<Electrochemical polarization measurement>
A 2.67% _AlCl3 aqueous solution thoroughly deaerated with high-purity _N2 gas and an electrochemical measurement cell were used, Pt was used as the working counter electrode, and the Luggin capillary and reference electrode Ag/AgCl were bypassed. The liquid temperature during the measurement was maintained at 40°C.
The brazing material surface and core of the sample that had been subjected to heat treatment equivalent to brazing were exposed to light, ^and the rest was masked with insulating paint. As a pretreatment for the measurement area, the sample was immersed in 5% NaOH at 50°C for 30 seconds, rinsed with water, and then immersed in 30% _HNO3 at room temperature for 1 minute and rinsed with water.
After holding at the natural potential for about 5 minutes, the potential was swept from the natural potential at a rate of 0.5 mV/s. The bending point (the region where the current suddenly stops flowing (passivation region) and the region where the current suddenly starts flowing) observed after a certain sweep from the polarization curve was taken as the pitting potential. In addition, since no bending point appears in the sample containing a large amount of Zn, the potential of 0.1 mA/ ^cm2 was taken as the pitting potential (brazing material potential).

<Observation of recrystallized grains and measurement of grain size>
The cross section of the brazed aluminum alloy parallel to the rolling direction was mechanically polished and anodized using Barker's solution. The recrystallized grains were photographed using an optical microscope, and the grain size was calculated by the formula: "grain size = length of line drawn on photograph / number of grains cut by line x photograph magnification."
<Waste corrosion assessment>
For aluminum alloys brazed into a heat exchanger shape, erosion depths of 1/100 or less of the bare plate thickness before brazing or the core plate thickness of the brazing sheet were rated as excellent (◎), erosion depths of more than 1/100 and 1/20 or less were rated as good (○), and erosion depths of more than 1/20 to 1/10 of the plate thickness were rated as fair (△).

The following Tables 1 and 2 show the composition of the bare aluminum alloy materials No. A1 to A28 used in the evaluation of each test, the temperature (°C) and time (h) of the homogenization treatment, the electrical conductivity (% IACS) before and after brazing, the number of compound particles (× ¹⁰⁴ particles/ ^mm2 ) before and after brazing, the recrystallized grain size (μm) after brazing, and the results of the braze erosion evaluation.
Tables 3 and 4 show the brazing sheets of alloys No. B1 to B31 used in the evaluation of each test, the applied core alloy No. (corresponding to the aluminum alloy No. shown in Tables 1 and 2), the results of measuring the electrical conductivity of the brazing sheets before and after brazing, the results of measuring the number of compound particles before and after brazing, the recrystallized grain size of the core material after brazing, the results of the brazing erosion assessment, the core material potential (mV vs Ag/AgCl), the brazing material potential (mV vs Ag/AgCl), and the potential difference between the brazing material and the core material.
In addition, in each column of Tables 1 and 2, the notation "-" indicates that the corresponding component is not contained (less than the measurement limit).

The aluminum alloy bare materials of Alloy Nos. A1 to A19 shown in Table 1 are aluminum alloys containing, by mass%, Fe: 0.6% or more and 0.8% or less, Si: more than 0.7% and 1.4% or less, Cu: 0.6% or less, Mn: 0.2% or less, Zn: 0.3% or less, the balance being Al and unavoidable impurities, having an electrical conductivity of 55% IACS or more, and the number of Al-Fe based compound particles or Al-Fe-Si based compound particles having a circle equivalent diameter of 0.5 to 2.0 μm distributed in the matrix is 1.0 x 10 ⁴ to 3.0 x 10 ⁴ particles/mm ² .

The aluminum alloy bare materials of Alloy Nos. A1 to A19 exhibited excellent electrical conductivity of 55% IACS or more (55 to 63% IACS) before brazing and 44% IACS or more (44 to 64% IACS) after brazing.
In the bare aluminum alloy materials of Alloy Nos. A1 to A19, the number of compound particles before brazing was in the range of 1.2×10 ⁴ to 3.0×10 ⁴ particles/mm ² , and the number of compound particles after brazing was in the range of 1.1×10 ⁴ to 2.9×10 ⁴ particles/mm ² .
The aluminum alloy bare materials of Alloy Nos. A1 to A19 had recrystallized grain sizes in the range of 37 to 65 μm, which was sufficiently large, and therefore these alloys were capable of providing excellent evaluation results for brazing corrosion evaluation when brazed.

The bare aluminum alloy material of Alloy No. A20 shown in Table 2 had a small Fe content, and therefore the number of compound particles before and after brazing was small, the recrystallized grain size was fine, and excessive erosion occurred.
The aluminum alloy bare material of Alloy No. A21 had too much Fe content, so the number of compounds after brazing was too large, the cathodic reaction was promoted, and the self-corrosion resistance was reduced.

The aluminum alloy bare material of Alloy No. A22 had a low Si content, and therefore the ratio of Al-Fe based compounds to Al-Fe-Si based compounds increased, resulting in an excessively small recrystallized grain size after brazing, and excessive erosion.
The aluminum alloy bare material of Alloy No. A23 had a high Si content, which lowered the melting point of the base material, and was excessively eroded by brazing during brazing. As a result, the shape of the heat exchanger could not be maintained, and therefore it was not possible to evaluate it.
The aluminum alloy bare material of Alloy No. A24 had an excessively high Cu content, and therefore the electrical conductivity after brazing was reduced.

The aluminum alloy bare material of Alloy No. A25 had too high a Mn content and Zn content, and therefore had low electrical conductivity both before and after brazing.
In the case of the bare aluminum alloy material of Alloy No. A26, the homogenization temperature was too low, so that the number of compound particles was reduced both before and after brazing, and the electrical conductivity after brazing was reduced.
In the case of the bare aluminum alloy material of Alloy No. A27, the homogenization treatment time was too short, so that the number of compound particles was reduced both before and after brazing, and the electrical conductivity after brazing was reduced.
In the case of the bare aluminum alloy material of Alloy No. A28, the homogenization temperature was too high, so that the number of compound particles was reduced both before and after brazing, and the electrical conductivity after brazing was reduced.

The brazing sheets of alloy Nos. B1 to A25 shown in Table 3 are brazing sheets containing, by mass%, Fe: 0.6% or more and 0.8% or less, Si: more than 0.7% and 1.4% or less, Cu: 0.6% or less, Mn: 0.2% or less, Zn: 0.3% or less, the balance being Al and unavoidable impurities, having an electrical conductivity of 53% IACS or more, and having a core material in which the number of Al-Fe compound particles or Al-Fe-Si compound particles having an equivalent circle diameter of 0.5 to 2.0 μm distributed in the matrix is 1.0 x 10 ⁴ to 3.0 x 10 ⁴ particles/mm ^2. Furthermore, these brazing sheets are brazing sheets in which an aluminum alloy layer is laminated, which contains, by mass%, Si: 3.0 to 12.0% as a brazing material, the balance being Al and unavoidable impurities.

The brazing sheets Nos. B1 to B25 have high electrical conductivity before and after brazing, the number of compound particles before and after brazing is in a suitable range, and the recrystallized grain size is also within a good range (37 to 65 μm).
The brazing sheets No. B1 to B25 exhibited excellent electrical conductivity of 53% IACS or more (54 to 62% IACS) before brazing and 43% IACS or more (43 to 59% IACS) after brazing.

The brazing sheets No. B1 to B25 showed a range of compound particle counts of 1.0×10 ⁴ to 3.0×10 ⁴ particles/mm ² (1.2×10 ⁴ to 3.0×10 ⁴ particles/mm ² ) before brazing, and a range of compound particle counts of 1.0×10 ⁴ to 3.0×10 ⁴ particles/mm ² (1.1×10 ⁴ to 2.9×10 ⁴ particles/mm ² ) after brazing.
The brazing sheets No. B1 to B25 have a potential difference between the core material potential after brazing and the brazing filler metal potential after brazing of 80 mV or more (81 to 268 mV), and the core material also has excellent corrosion resistance due to the sacrificial anode effect of the brazing filler metal.

The brazing sheet No. B26 shown in Table 4 has a core material of the aluminum alloy No. A20 with a low Fe content, so the number of compound particles before and after brazing is small, and the desired recrystallized grain size is not obtained, resulting in a poor brazing erosion evaluation result.
The brazing sheet No. B27 shown in Table 4 has a core material of the aluminum alloy No. A21 having too much Fe content, so that the number of compound particles after brazing was increased and the self-corrosion resistance was reduced.

The brazing sheet No. B28 shown in Table 4 has a core material of aluminum alloy No. A22, which has a low Si content, and as a result, the recrystallized grain size became smaller, resulting in excessive erosion and a poor brazing corrosion evaluation result.

The brazing sheet No. B29 shown in Table 4 has a core material of the aluminum alloy No. A23, which has a high Si content, so the base material was excessively eroded by the brazing material during brazing and the shape of the heat exchanger could not be maintained, and therefore it could not be evaluated.
The brazing sheet No. B30 shown in Table 4 had a core material of the aluminum alloy No. A24 having a high Cu content, and therefore had a reduced electrical conductivity before brazing.
The brazing sheet No. B31 shown in Table 4 had a core material of the aluminum alloy No. A25, which had too high a Mn content and Zn content, and therefore did not obtain the desired electrical conductivity and compound distribution, and the characteristics were not achieved.

Therefore, according to the present invention, it is possible to provide an aluminum alloy or an aluminum alloy brazing sheet for heat exchangers which has excellent electrical conductivity, the number of compounds before and after brazing is in an appropriate range, and has excellent brazing erosion evaluation properties.
Furthermore, the aluminum alloy or brazing sheet according to the present invention has excellent electrical conductivity and excellent corrosion resistance, and therefore can be used as an aluminum alloy and brazing sheet suitable for use in automotive heat exchangers, which have been required to be further miniaturized and have high heat dissipation performance in recent years.

A, B...aluminum alloy brazing sheet, M...aluminum alloy bare material, 1...core material, 2...filler material, 3...part to be brazed (fin), 5...heat exchanger, 6...fin, 7...tube.

Claims (7)

An aluminum alloy bare material for heat exchangers, characterized in that it contains, by mass%, Fe: 0.6% or more and 0.8% or less, Si: more than 0.7% and 1.4% or less, Cu: 0.6% or less, Mn: 0.2% or less, Zn: 0.3% or less, the balance being Al and unavoidable impurities, has an electrical conductivity of 55% IACS or more, and has a number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having a circle equivalent diameter of 0.5 to 2.0 μm distributed in a matrix of 1.0 x 10 ⁴ to 3.0 x 10 ⁴ particles/mm ² . The aluminum alloy bare material for heat exchangers according to claim 1, characterized in that after being subjected to a heat treatment equivalent to heat exchanger brazing, which involves heating to 600°C, holding for 5 minutes, and then cooling to 300°C at 60°C/min, the aluminum alloy bare material for heat exchangers has an electrical conductivity of 44% IACS or more, and the number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having a circle equivalent diameter of 0.5 to 2.0 μm distributed in the matrix is 1.0 x ¹⁰⁴ to 3.0 x ¹⁰⁴ particles/ ^mm2 . An aluminum alloy brazing sheet for heat exchangers, comprising a core material made of the aluminum alloy for heat exchangers according to claim 1 or 2, and an aluminum alloy layer containing 3.0 to 12.0% by mass of Si as a brazing material, with the remainder being Al and unavoidable impurities, laminated to one or both surfaces. The aluminum alloy brazing sheet for heat exchangers according to claim 3, characterized in that the brazing material further contains Zn: 0.1 to 4.0% by mass. The aluminum alloy brazing sheet for heat exchangers according to claim 3 or 4, characterized in that it has an electrical conductivity of 53% IACS or more, and the number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having a circle equivalent diameter of 0.5 to 2.0 μm distributed in the matrix of the core material is 1.0 x 10 ⁴ to 3.0 x 10 ⁴ particles/mm ² . The aluminum alloy brazing sheet for heat exchangers according to any one of claims 3 to 5, characterized in that after being subjected to a heat treatment equivalent to heat exchanger brazing, which involves heating to 600°C, holding for 5 minutes, and then cooling to 300°C at 60°C/min, the aluminum alloy brazing sheet for heat exchangers has an electrical conductivity of 43% IACS or more, and the number of Al-Fe-based compound particles or Al-Fe-Si-based compound particles having an equivalent circle diameter of 0.5 to ^2.0 μm distributed in the matrix of the core material is 1.0 x ¹⁰⁴ to 3.0 x 104 particles/ ^mm2 . 7. The aluminum alloy brazing sheet for heat exchangers according to claim 3, characterized in that after a heat treatment equivalent to heat exchanger brazing is applied, which comprises heating to 600°C, holding the temperature for 5 minutes, and then cooling to 300° C at 60°C/min, the pitting potential difference between the surfaces of the core material and the brazing material is 80 mV or more.

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