JP2009215643A - Aluminum alloy laminated plate excellent in fatigue characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy laminated plate and a laminated plate subjected to heating corresponding to brazing, each of which is excellent in fatigue characteristics and capable of reducing thickness of laminated plate subjected to heating corresponding to brazing, such as an aluminum alloy radiator tube, or a laminated plate such as an aluminum alloy brazing sheet. <P>SOLUTION: The aluminum alloy laminated plate or a laminated plate subjected heating corresponding to brazing is composed of at least a core aluminum alloy sheet 2 and an anticorrosive aluminum alloy sacrifice material 3 cladded thereon. The core aluminum alloy sheet 2 has a specified 3000-series composition, and the average number density of specifically sized dispersed particles of the core aluminum alloy sheet 2 is regulated so as to impart better fatigue characteristics dominated by crack formation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aluminum alloy laminate (hereinafter, aluminum is also referred to as Al) having excellent fatigue characteristics for an aluminum alloy heat exchanger. In the present invention, a laminated plate in which at least a core material aluminum alloy plate and an aluminum alloy sacrificial anticorrosive material are clad, and a heat exchanger material that is made into a heat exchanger by brazing is also called an aluminum alloy laminated plate or simply a laminated plate. . In addition, a laminated plate that is clad with at least a core material aluminum alloy plate and an aluminum alloy sacrificial anticorrosive material and subjected to a heat treatment equivalent to brazing is obtained after the aluminum alloy laminated plate after brazing equivalent heating or simply after brazing equivalent heating. Also called a laminate.

  In order to reduce the weight of automobile bodies, the application of aluminum alloy materials to heat exchange members is increasing in place of copper alloy materials that have been used conventionally. And as these aluminum alloy materials for heat exchange members, corrosion-resistant aluminum alloy materials made of multilayered laminates (also referred to as clad plates or clad materials) are used.

  When the laminated plate is assembled as a heat exchanger by brazing, as a brazing sheet clad with an aluminum alloy sacrificial anticorrosive material (plate) on one side and an aluminum alloy brazing material (plate) on the other side Composed.

  FIG. 4 shows an example of an aluminum alloy automobile heat exchanger (radiator). As shown in FIG. 4, the radiator 100 is generally formed by integrally forming a corrugated aluminum alloy radiating fin 112 between a plurality of flat tubular aluminum alloy tubes 111. Both ends of the tube 111 are configured to open into spaces formed by a header 113 and a tank (not shown). In the radiator 100 having such a configuration, the refrigerant having a high temperature passes from the space of one tank through the inside of the tube 111 to the space on the other tank side, and heat exchange is performed at the portions of the tube 111 and the radiation fins 112 so that the temperature decreases. Recirculate the refrigerant again.

  The tube 111 made of this aluminum alloy material is composed of an aluminum alloy brazing sheet 101 whose cross section is shown in FIG. In FIG. 5, a brazing sheet 101 is formed by laminating (cladding) an aluminum alloy sacrificial anode material (also referred to as a skin material) 103 on one side surface of an aluminum alloy core material 102, and an aluminum alloy material on the other side surface of the core material 102. A brazing material 104 is laminated (clad). In FIG. 5, the clad sheet made of aluminum alloy is configured as a laminated plate in which only one aluminum alloy sacrificial anticorrosive material 103 is clad on one surface.

  Then, the brazing sheet 101 made of aluminum alloy is formed into a flat tubular shape by a forming roll or the like, and the brazing sheet 101 itself is brazed by electro-welding or heating by brazing. The fluid passages of the four tubes 111 are formed.

  The refrigerant (coolant) of the radiator is mainly composed of a water-soluble medium, and a refrigerant appropriately containing a commercially available rust preventive agent or the like is used. However, there is a problem that when a rust preventive agent or the like deteriorates with time, an acid is generated, and the aluminum alloy material such as the sacrificial material or the core material is easily corroded by these acids. For this reason, it is essential to use an aluminum alloy material having high corrosion resistance against a water-soluble medium.

  Therefore, as an aluminum alloy used for a laminated sheet of a brazing sheet or a clad sheet, the core material 102 is defined in JISH4000 from the viewpoint of corrosion resistance and strength, for example, Al-0.15 mass% Cu-1.1 mass%. An Al—Mn-based (3000-based) alloy such as 3003 having a composition such as Mn is used. In addition, for the skin material 103 that is always in contact with the refrigerant, an Al—Zn system such as 7072 made of a composition of Al-1 mass% Zn, etc., for the purpose of anti-corrosion and high strength by Mg diffusion to the core material 102, or Al—Zn—Mg (7000 series) alloys are used. Further, for the brazing filler metal 104, an Al—Si based (4000 based) alloy such as 4045 having a composition such as Al-10 mass% Si having a low melting point is used.

  The radiator 100 is integrally assembled by brazing using a tube 111 formed using such a brazing sheet 101, a heat dissipation fin 112 subjected to corrugation, and other members. Examples of the brazing method include a flux brazing method and a nocolok brazing method using a non-corrosive flux, and brazing by heating to a high temperature of about 600 ° C.

  In the radiator 100 assembled in this way, in particular in the tube 111, the above-described liquid refrigerant from high temperature to low temperature and from high pressure to normal pressure is always circulated and circulated. That is, the tube 111 is repeatedly subjected to stress over a long period of time including (in addition to) these repeated internal pressure fluctuations and vibrations of the automobile itself, so that it is required to have fatigue characteristics that can withstand these. If fatigue characteristics are low and fatigue failure occurs, cracks in the tube 111 are generated and propagated, and if the tube 111 is penetrated, liquid leakage from the radiator is caused. For this reason, improvement of these fatigue characteristics of the radiator tube is regarded as an important issue.

  Conventionally, various improvements in the fatigue characteristics of the radiator tube have been proposed. For example, in Patent Document 1, the core material in the aluminum alloy brazing sheet is an aluminum alloy containing Cu, Ti, Mn and restricting Si, Fe, and Mg, and an average crystal grain size L in the rolling direction in the longitudinal section of the core material. Is set to 150 to 200 μm, the corrosion resistance of the welded portion of the tube 1 is improved, and fatigue resistance due to repeated bending of the tube 1 = vibration fatigue resistance characteristics under the vibration of an automobile is to be improved. In Patent Document 2, the average crystal grain size in the thickness direction on the sacrificial anticorrosive material side is set to be less than the thickness of the sacrificial anticorrosive material, and the corrosion resistance of the sacrificial anticorrosive material is improved. = Trying to improve fatigue properties.

  In addition, it is generally known that fatigue characteristics are related to static tensile strength. In order to improve the tensile strength of a material even in a heat exchanger, for example, as disclosed in Patent Document 3, Cu Materials with added are also proposed. And in patent document 4, it is going to improve a vibration fatigue-resistant characteristic by systematic improvement. That is, in a heat exchanger using a three-layer aluminum alloy brazing sheet clad with an aluminum alloy core material containing Cu, an aluminum alloy brazing material, and an aluminum alloy sacrificial material containing Zn and Mg, the brazing sheet after brazing It has been proposed to distribute specific Al—Cu—Mg—Zn-based precipitates at the core material side interface near the interface between the core material and the sacrificial material. This is intended to improve the fatigue fracture property = fatigue characteristics due to repeated internal pressure loading by increasing the strength of the core side interface portion by age hardening with Al—Cu—Mg—Zn based precipitates.

  Further, in Patent Document 5, an Al—Mn alloy core material, a skin material such as an Al—Zn alloy alloy clad on one side surface of this core material, and an Al—Si alloy alloy alloy clad on the other side surface of this core material are disclosed. The texture of the aluminum alloy brazing sheet composed of the material is defined by the X-ray diffraction intensity ratio. In Document 5, it is easy to uniformly generate plastic deformation in a direction parallel to the rolling direction of the brazing sheet. As a result, even when repeated tensile or compressive stress is applied in the rolling direction of the brazing sheet, the deformation does not concentrate locally, delays the growth of cracks in the thickness direction, and includes fatigue in the plastic region. The aim is to improve lifespan.

In addition, although not a brazing sheet, in order to improve the corrosion resistance of the heat radiation fin 112 made of the same 3000 series aluminum alloy provided in this brazing sheet, the shape and number density of crystallized substances and intermetallic compounds in the structure were specified. There are some (see, for example, Patent Documents 6, 7, and 8). In such a heat radiating fin, corrosion resistance that leads to disappearance of the fin itself is important when corroded. For this reason, the specifications of the shape and number density of crystallized substances and intermetallic compounds in the structure described in the above-mentioned patent documents are also associated with technical problems unique to the heat radiation fin 112, namely, improvement of momentum and corrosion resistance.
JP 2003-82427 A Japanese Patent Laid-Open No. 11-100608 JP-A-10-53827 JP-A-9-95749 JP 2006-291111 A JP-A-9-78168 JP 2000-119783 A JP 2005-139505 A

  However, these conventional automobile radiator tubes are relatively thick. For example, referring to the thickness (total thickness) of the brazing sheet that is the subject of fatigue resistance evaluation in the examples of the above-mentioned patent documents, 0.4 mm in Patent Document 1, 0.25 mm in Patent Document 2, In Patent Documents 4 and 5, the thickness is 0.20 mm, and the plate thickness is 0.20 mm or more. On the other hand, the weight of the radiator is reduced by reducing the weight of the automobile for improving the fuel efficiency caused by the global environmental problem. For this reason, further thinning of the radiator tube, that is, the aluminum alloy brazing sheet has been studied.

  When the radiator tube is relatively thick with a thickness of about 0.4 mm, the rigidity of the tube itself is relatively high. On the other hand, when the thickness of the radiator tube, mainly a laminated plate such as a brazing sheet, is reduced, the rigidity of the tube itself is lowered. On the other hand, the pressure of the refrigerant used is often set higher than before. Therefore, when the thickness of a laminated board such as a brazing sheet is thinned by these synergistic effects, the sensitivity to fatigue failure due to the repeated stress increases, and the fatigue characteristics tend to deteriorate.

  When such fatigue failure occurs, cracks (cracks) occur in the radiator tube. In the case of a radiator tube having a reduced thickness, the occurrence of such a crack is likely to penetrate the tube and lead to leakage of the radiator, resulting in more serious damage.

  However, no effective improvement measures have been found so far for the fatigue characteristics of the radiator tube thus thinned. If this effective improvement measure is not found, a radiator tube, that is, a laminated plate such as an aluminum alloy brazing sheet, cannot be thinned, resulting in a great limitation on the weight reduction of the radiator and the weight reduction of the automobile.

  In view of such problems, an object of the present invention is to provide an aluminum alloy laminated plate excellent in fatigue characteristics for an aluminum alloy heat exchanger capable of reducing the thickness of a radiator tube, that is, an aluminum alloy brazing sheet. It is in.

In order to achieve this object, the gist of the aluminum alloy laminate having excellent fatigue characteristics according to the present invention is that aluminum is clad at least with a core aluminum alloy plate and an aluminum alloy sacrificial anticorrosive, and is used as a heat exchanger by brazing. It is an alloy laminated board, The said core material aluminum alloy board is mass%, Si: 0.2-1.5%, Cu: 0.2-1.2%, Mn: 0.2-1.4% Ti: 0.03 to 0.3% respectively, Fe: regulated to not more than 1.0%, the balance having an aluminum alloy composition consisting of Al and unavoidable impurities, and this core aluminum alloy It has a structure in which the average number density of dispersed particles having an average value of the center-of-gravity diameter observed by SEM of 500 times at the surface layer portion of the rolled surface of the plate is 1 μm or more is 7000 particles / mm ² or less.

  Here, the core material aluminum alloy plate in the laminated plate is further in mass%, Cr: 0.03-0.3%, Zn: 0.2-1.0%, Zr: 0.03-0.3. It is preferable to contain 1 type or 2 types or more of%. Moreover, it is preferable that the core material aluminum alloy plate in the laminated plate further regulates Mg to 0.5% by mass or less. Moreover, it is preferable that the thickness of the core material aluminum alloy plate in the laminated plate is less than 0.25 mm. Moreover, it is preferable that the board thickness of the said laminated board is less than 0.3 mm.

In order to achieve the above object, another gist of the aluminum alloy laminate having excellent fatigue characteristics according to the present invention is that at least a core material aluminum alloy plate and an aluminum alloy sacrificial anticorrosive material are clad, and the core material aluminum alloy plate is , Si: 0.2-1.5%, Cu: 0.2-1.2%, Mn: 0.2-1.4%, Ti: 0.03-0.3% In addition, Fe is controlled to not more than 1.0%, the balance has an aluminum alloy composition composed of Al and inevitable impurities, and the core aluminum alloy sheet is rolled as a structure after heating equivalent to brazing. The average crystal grain size in the rolling direction in the longitudinal section of the direction is 200 μm or less, and the average value of the center of gravity diameter observed by SEM of 500 times in the surface layer portion of the rolled surface of the core material aluminum alloy plate is 1 μm. And have an average number density of 6000 / mm ² or less is tissue or of the dispersed particles.

  Here, the core material aluminum alloy plate in the laminated plate is further in mass%, Cr: 0.03-0.3%, Zn: 0.2-1.0%, Zr: 0.03-0.3. It is preferable to contain 1 type or 2 types or more of%. Moreover, it is preferable that the core material aluminum alloy plate in the laminated plate further regulates Mg to 0.5% by mass or less. Moreover, it is preferable that the thickness of the core material aluminum alloy plate in the laminated plate is less than 0.25 mm. Moreover, it is preferable that the board thickness of the said laminated board is less than 0.3 mm.

  The present inventors have sought a mechanism of fatigue failure in fatigue characteristics when the thickness of the laminate is reduced. As a result, according to the knowledge of the present inventors, there are two types of fatigue fracture mechanisms in the fatigue characteristics when the thickness is reduced, which is a problem of the present invention. In other words, the generation of cracks is more dominant than the propagation (speed) of cracks (cracks, cracks) due to fatigue failure and the propagation (speed) of cracks (cracks, cracks) due to fatigue failure. Case.

  The present inventors have found that metallurgically effective means for improving fatigue characteristics differ from these two mechanisms of fatigue fracture. That is, when the crack propagation (speed) is more dominant than the occurrence of cracks (cracks, cracks) due to fatigue failure, the fatigue fracture propagation (speed) is determined by the laminated plate constituting the heat exchanger. The structure of the core aluminum alloy plate, that is, the average crystal grain size and the average number density of relatively fine precipitates are greatly affected.

  On the other hand, when the crack generation is more dominant than the propagation (velocity) of the crack (crack, crack) due to fatigue failure, the ease of crack generation constitutes a heat exchanger. The structure of the core aluminum alloy plate of the laminated plate, that is, the average crystal grain size and the average number density of relatively coarse dispersed particles are greatly affected.

  In the present invention, the fatigue characteristics in the case where the generation of cracks is more dominant than the propagation (speed) of cracks (cracks, cracks) due to fatigue failure are improved. Therefore, as described above, the propagation (velocity) of this fatigue fracture is determined by brazing the structure of the core aluminum alloy plate of the laminated plate as the heat exchanger material before constituting the heat exchanger, or brazing the laminated plate. The structure of the core material aluminum alloy plate after considerable heating is suppressed by controlling the structure of the average crystal grain size and the average number density of relatively coarse dispersed particles.

  In the present invention, this control regulates the average number density of fine precipitates while miniaturizing the average crystal grain size of the core aluminum alloy plate. As in the present invention, the average crystal grain size of the core aluminum alloy plate is refined and the number density of relatively coarse dispersed particles is regulated, thereby suppressing the occurrence of fatigue fracture itself. As a result, the fatigue life (fatigue characteristics) in the case where the generation of cracks is more dominant than the propagation (speed) of cracks (cracks, cracks) due to fatigue failure is improved.

  Here, the dispersed particles referred to in the present invention are intermetallic compounds of elements such as alloy elements such as Si, Cu, Mn, and Ti, or Fe, Mg, and intermetallic compounds of these elements and Al. Thus, it is a general term for intermetallic compounds that can be identified from the above-mentioned size by structural observation, regardless of the forming element (composition).

  The best mode for carrying out the laminate of the present invention, the laminate after brazing equivalent heating (thermal history), and these core aluminum alloy plates will be described with reference to FIGS. FIG. 1 is a cross-sectional view of an aluminum alloy laminated plate for a heat exchanger according to the present invention, and FIG. 2 shows a laminated plate (for automobiles) using the laminated plate (aluminum alloy tube for heat exchanger) of FIG. It is principal part sectional drawing of a radiator tube. 1 and 2 are the same as those shown in FIGS. 4 and 5 described above.

(Laminated board)
The laminated board of the present invention is first manufactured in advance as an aluminum alloy laminated board 1 shown in FIG. 1 before being assembled into a heat exchanger. When the laminated plate 1 is brazed, an aluminum alloy sacrificial anticorrosive material (plate) 3 is clad on one surface of the core material aluminum alloy plate 2, and an aluminum alloy brazing material (plate) 4 is clad on the other surface. Configured as a brazing sheet.

  The core material aluminum alloy plate 2 is made of a JIS 3000 series aluminum alloy having a characteristic structure and composition to be described later. Moreover, as the brazing sheet, on the side that is always in contact with the refrigerant inside the core material 2 (upper side in FIG. 1), as a sacrificial anticorrosive material (sacrificial material, lining material, skin material) 3 described later, For example, an aluminum alloy such as JIS 7000 series having an Al—Zn composition is clad. Furthermore, an aluminum alloy brazing material 4 such as a JIS4000 series having an Al—Si composition is clad on the outer side (lower side in FIG. 1) of the core material 2.

  The laminated plate such as the brazing sheet of the present invention is the above-described three-layer rolled clad material (plate) centering on the core material aluminum alloy plate 2. When the thickness of the core aluminum alloy plate is 0.16 to 0.24 mm which is less than 0.25 mm, the thickness of both the brazing material and the sacrificial anticorrosive material is usually about 20 to 30 μm. However, the coverage varies depending on the thickness of the heat exchanger member used (specification of application), and is not limited to these values.

  However, the thickness of the laminated plate 1 such as a brazing sheet (mainly the thickness of the core aluminum alloy plate) is the key to reducing the weight of the heat exchanger as described above. Therefore, it is preferable that the thickness of the laminated plate is a thin plate of about 0.16 to 0.29 mm which is less than 0.3 mm, and the core material is a thin plate of about 0.16 to 0.24 mm which is less than 0.25 mm.

  These brazing sheets are hot-rolled with a sacrificial anticorrosive material (plate) or brazing material (plate) superimposed on one side of a homogenized heat-treated core aluminum alloy plate (ingot), then cold-rolled, intermediate Annealing and cold rolling are sequentially performed to produce a sheet such as H14 tempered material. Here, the homogenization heat treatment may be performed before hot rolling.

(Heat exchanger)
The aluminum alloy laminated plate 1 such as a brazing sheet is bent in the width direction by a forming roll or the like, and formed into a flat tube so that the skin material 3 is disposed on the inner surface side of the tube. A flat tubular tube is formed. That is, the flat tubular tube (laminated member) 11 shown in FIG.

  Such a flat tubular tube (laminated member) 11 is a heat exchanger such as the radiator 10 shown in FIG. 2 integrally with other members such as the corrugated radiating fins 12 and the header 13 by brazing. Made (assembled). A portion where the tube (laminated member) 11 and the heat radiation fin 12 are integrated is also referred to as a core of the heat exchanger. At this time, the brazing is performed by heating to a high temperature of 585 to 620 ° C., preferably 590 to 600 ° C., which is equal to or higher than the solidus temperature of the brazing material 4. If this heating temperature exceeds 620 ° C. and is too high, excessive melting, erosion, etc. will occur. As this brazing method, a flux brazing method, a noclock brazing method using a non-corrosive flux, etc. are generally used.

  In the heat exchanger of FIG. 2, both ends of the flat tube (laminated member) 11 are open to spaces formed by a header 13 and a tank (not shown). Then, the high-temperature refrigerant is sent from the space on one tank side through the flat tube 11 to the space on the other tank side, heat is exchanged between the tube 11 and the fins 12, and the low-temperature refrigerant is circulated again.

(Core material aluminum alloy sheet structure)
Here, the core material aluminum alloy plate in the laminated plate or the laminated plate after brazing equivalent heating (heat history) is made of a 3000 series aluminum alloy composition. In the present invention, in order to improve the fatigue fracture resistance in fatigue when cracking due to fatigue fracture of the core aluminum alloy sheet is dominant, the average grain size in the rolling direction in the longitudinal section of the aluminum alloy sheet is determined. The diameter (only the laminate after brazing equivalent heating is defined) and the average number density of the above dispersed particles of 1 μm or more (laminate and laminate after brazing equivalent heating) are defined.

(Crystal grains)
When the average crystal grain size of the core aluminum alloy plate is coarsened as a laminated plate after brazing equivalent heating or as a material laminated plate before assembly (thermal history), cracking due to fatigue failure is dominant. Fatigue fracture resistance against excessive fatigue is reduced. Therefore, the average crystal grain size in the rolling direction in the longitudinal section in the rolling direction of the core aluminum alloy plate in the laminated plate after brazing equivalent heating is refined to 200 μm or less, preferably 150 μm or less. In order to make the core material aluminum alloy plate in the laminated plate after brazing equivalent heating finer in this way, naturally, the average crystal grain size of the core material aluminum alloy plate of the material laminated plate is 200 μm or less, preferably 150 μm or less. It is necessary to prepare in advance. However, even if the average grain size of the core aluminum alloy plate of the material laminate is specified, the laminate after heating equivalent to brazing may have an average grain size depending on the heating conditions such as brazing treatment at the time of manufacturing the heat exchanger. The diameter changes (coarse). For this reason, even if the average crystal grain size of the core aluminum alloy plate is defined at the stage of the material laminate, depending on the heating conditions, there is a possibility that the above-mentioned regulation may be coarsened. Not specified.

  In addition, the crystal grain size said here is a crystal grain of the rolling direction in the longitudinal section (cross section of the board cut | disconnected along the rolling direction) of the rolling direction. This crystal grain size is 50 times higher after pre-processing the longitudinal section in the rolling direction of the core material aluminum alloy plate (sampled sample) in the material laminated plate or the laminated plate after brazing equivalent heating by mechanical polishing and electrolytic etching. Observe with an optical microscope. At this time, a straight line is drawn in the rolling direction, and a section length of each crystal grain positioned on the straight line is measured by a cutting method (line intercept method) in which each crystal grain size is measured. This is measured at 10 arbitrary locations, and the average crystal grain size is calculated. At this time, the length of one measurement line is 0.5 mm or more, and three measurement lines per one visual field are observed, and five visual fields are observed per one measurement point. The average crystal grain size measured sequentially for each measurement line is averaged sequentially per field of view (three measurement lines), per field of view per 1 measurement point, and 10 measurement points, and the average crystal referred to in the present invention. The particle size.

(Dispersed particles)
When the core material aluminum alloy plate is assembled (incorporated) into a laminated plate after brazing equivalent heating, whether it is a brazing sheet, it is inevitably heated to a temperature around 600 ° C. during brazing. Even if such a heating history is received, the above-described chemical component composition defined in the present invention does not change. However, the number density of the above-mentioned dispersed particles of 1 μm or more as defined in the present invention changes to a smaller number in the laminated plate after the brazing equivalent heating due to solid solution or coarsening than the raw material laminated plate. To do.

  In the present invention, in order to improve the fatigue fracture resistance against fatigue where the occurrence of cracks due to fatigue fracture is dominant, the core material aluminum alloy plate of the raw material laminated plate or the laminated plate after brazing equivalent heating has the above 1 μm or more. The average number density of dispersed particles is regulated so as not to increase more than necessary. In other words, the average number density of the dispersed particles as a heat exchanger member that has received a heating history at a temperature in the vicinity of 600 ° C. during brazing is regulated so as not to increase more than necessary.

When the average number density of the above dispersed particles in the core aluminum alloy sheet of the laminated sheet after brazing equivalent heating exceeds 6000 particles / mm ² , fatigue fracture resistance to fatigue, where cracking due to fatigue fracture is dominant Decreases. Accordingly, the average number density of dispersed particles having an average value of the center-of-gravity diameter of 1 μm or more observed by the SEM of 500 times in the rolled surface surface layer portion of the core aluminum alloy plate of the laminated plate after brazing equivalent heating is 6000 pieces / Regulate to be ² mm or less. The average number density of the dispersed particles is preferably 4000 particles / mm ² or less, more preferably 2000 particles / mm ² or less.

  On the other hand, in the present invention, in order to suppress the number density of the dispersed particles of the core aluminum alloy plate of the laminated plate after brazing equivalent heating, in the material laminated plate stage before receiving the heating history during brazing. The average number density of the dispersed particles of the core material aluminum alloy plate is defined.

That is, if the average number density of the above dispersed particles of the core aluminum alloy plate at the raw material laminated plate stage is not set to 7000 / mm ² or less, the number density of the dispersed particles is reduced by receiving the heating history at the time of brazing. Even if it decreases (decreases), the average number density of the above dispersed particles of the core aluminum alloy plate in the laminated plate after brazing equivalent heating cannot be guaranteed (secured). Accordingly, in the present invention, the average number density of dispersed particles having an average value of the center-of-gravity diameter of 1 μm or more observed by an SEM 500 times that of the core aluminum alloy plate at the material laminate stage is defined as 7000 particles / mm ² or less. . The average number density of the dispersed particles is preferably 5000 / mm ² or less, more preferably 3000 / mm ² or less.

  As described above, these dispersed particles are alloy elements such as Si, Cu, Mn, and Ti, intermetallic compounds of elements contained such as Fe and Mg, and intermetallic compounds of these elements and Al. In the present invention, as described above, the size and the number density define the dispersed particles regardless of the forming element (composition), and the size and number density are dominant in crack propagation (velocity). This is because it greatly influences the fatigue fracture resistance in fatigue.

In order to measure the size and average number density of these precipitates, the structure of the surface layer portion of the rolled aluminum alloy sheet is observed in 10 fields of view with an SEM (scanning electron microscope) at a magnification of 500 times. This is image-analyzed, and the average number density (particles / mm ² ) of dispersed particles having an average value of each centroid diameter of 1 μm or more is measured.

(Controlling number density of dispersed particles)
The control of the average number density of the dispersed particles is performed by not increasing the number density of the dispersed particles precipitated in the heating process of the soaking process more than necessary in the soaking process (homogenizing heat treatment). In order to prevent the average number density of the above dispersed particles from exceeding 7000 particles / mm ² at the stage of the core material aluminum alloy plate (ingot) as a raw material, the number density of precipitates of these sizes is equal. When the hot rolling is started after the heat temperature is reached and held for a certain time, the time from the end of soaking to the start of hot rolling is set to 30 minutes or less. The soaking temperature is 450 ° C. or higher and a relatively high temperature that does not cause burning. If this soaking temperature is less than 450 ° C., there is no effect of homogenization (soaking). However, since the soaking process for the core aluminum alloy plate (ingot) is relatively high, depending on the melting point of the sacrificial anticorrosive material (plate) and brazing material (plate), the sacrificial anticorrosive material (plate) and brazing material may be used as the core material. It may not be possible in a state where (plates) are overlapped. In such a case, the above-described relatively high temperature soaking is performed only on the core aluminum alloy ingot, and then the relatively low temperature soaking or hot rolling is performed on the laminated laminate. It is preferable to perform a reheating treatment for the purpose.

(Aluminum alloy composition)
Hereinafter, the aluminum alloy composition of each member constituting the laminate according to the present invention will be described. First, the core material aluminum alloy plate 2 is made of a 3000 series aluminum alloy composition as described above. However, the core material aluminum alloy plate 2 is not only used as a heat exchanger member such as a tube material and a header material, but also to have the structure of the present invention described later, and in addition to that, formability, brazing property or weldability, strength, Various characteristics such as corrosion resistance are required.

  For this reason, the core material aluminum alloy plate according to the present invention is in mass%, Si: 0.2 to 1.5%, Cu: 0.2 to 1.2%, Mn: 0.2 to 1.4%, Ti: 0.03 to 0.3% each is contained, Fe is regulated to 1.0% or less, and the balance is an aluminum alloy composition composed of Al and inevitable impurities. In addition,% display of content of each element means the mass% altogether.

  Here, the aluminum alloy plate further includes, in mass%, Cr: 0.03-0.3%, Zn: 0.2-1.0%, Zr: 0.03-0.3% It is preferable to contain 1 type (s) or 2 or more types. Moreover, it is preferable to regulate Mg to 0.5 mass% or less.

  Elements other than the above-described Fe, Mg, and the above-described elements are basically impurities. However, from the viewpoint of recycling aluminum alloy plates, not only high-purity aluminum bullion but also 6000 series alloys, other aluminum alloy scrap materials, and low-purity aluminum bullion are used as melting materials. These elements are mixed. And reducing these elements below the detection limit, for example, increases the cost itself, and a certain amount of allowance is required. Therefore, the content in the range which does not inhibit the object and effect of the present invention is allowed. For example, elements other than the above, such as B, may be contained if they are 0.05% or less.

Si: 0.2 to 1.5%
Si forms an intermetallic compound with Fe to increase the strength of the core aluminum alloy plate. For this reason, in order to ensure the required intensity | strength as a laminated board after the said laminated board and brazing equivalent heating, a lower limit is contained 0.2% or more. On the other hand, if the Si content is too large, a coarse compound is formed in the core material, and the corrosion resistance as the laminated plate or the laminated plate after brazing equivalent heating is lowered. Therefore, the upper limit is 1.5% or less. . Therefore, the Si content range is set to 0.2 to 1.5%.

Cu: 0.2-1.2%
Cu exists in the aluminum alloy plate in a solid solution state, and improves the strength of the core material aluminum alloy plate. For this reason, in order to ensure the required intensity | strength as a laminated board after the said laminated board and brazing equivalent heating, a lower limit is contained 0.2% or more. On the other hand, if the Cu content is too high, the corrosion resistance of the laminated plate and the laminated plate after brazing equivalent heating is lowered, so the upper limit is made 1.2% or less. Therefore, the Cu content range is 0.2 to 1.2%.

Mn: 0.2 to 1.4%
Mn is an element for improving the strength without reducing the corrosion resistance of the core aluminum alloy plate by distributing intermetallic compounds such as prescribed dispersed particles in the aluminum alloy plate. In addition, the crystal grain size is refined, and there is an effect of improving vibration fatigue resistance and fatigue fracture resistance against fatigue in which cracking due to fatigue fracture is dominant. For this reason, in order to ensure the required strength as the laminated board or the laminated board after brazing equivalent heating and to improve the fatigue fracture resistance, the lower limit is 0.2% or more.

  On the other hand, if the Mn content is too high, the number density of the dispersed particles is too much higher than specified, and the fatigue resistance against vibration and fatigue resistance against fatigue in which cracking due to fatigue fracture is dominant are reduced. . In addition, the formability of the aluminum alloy laminate is reduced, and the aluminum alloy laminate may be broken during processing such as assembly to a part shape. For this reason, the upper limit of the Mn content is set to 1.4% or less. Therefore, the content range of Mn is made 0.2 to 1.4%. Further, the content range of Mn is preferably 0.2% or more and 1.0% or less, more preferably 0.2% or more and 0.6% or less.

Ti: 0.03-0.3%
Ti has the function of forming a fine intermetallic compound in the aluminum alloy plate and improving the corrosion resistance of the core aluminum alloy plate. For this reason, in order to ensure the required corrosion resistance as the laminated board or the laminated board after brazing equivalent heating, the lower limit is made 0.03% or more. On the other hand, when there is too much Ti content, the moldability of an aluminum alloy laminated board will fall, and there exists a possibility that an aluminum alloy laminated board may be cracked at the time of processes, such as an assembly | attachment to a component shape. For this reason, the upper limit of Ti content is made 0.3% or less. Therefore, the Ti content range is 0.03 to 0.3%.

Fe: 1.0% or less Fe is inevitably contained in the core aluminum alloy plate as long as scrap is used as an aluminum alloy melting raw material as an impurity. Fe has the effect of forming an intermetallic compound with Si as described above to increase the strength of the core aluminum alloy plate, refine the crystal grain size, and further increase the brazing properties of the core material. However, if the content is too large, the corrosion resistance of the core material aluminum alloy plate is significantly reduced. For this reason, Fe content is controlled to 1.0% or less.

Mg: 0.5% or less Mg increases the strength of the core material aluminum alloy plate, but if its content is large, brazing performance decreases in a Nocolok brazing method using a fluoride flux. For this reason, it is preferable to regulate the Mg content to 0.5% or less for a heat exchanger under brazing conditions in which the brazing property is lowered by Mg.

One or more of Cr: 0.03-0.3%, Zn: 0.2-1.0%, Zr: 0.03-0.3% Cr, Zn, Zr are core material aluminum It has the effect of enhancing the vibration fatigue resistance of the alloy sheet and the fatigue characteristics in which cracking due to fatigue failure is dominant. In order to exert this effect, Cr: 0.03 to 0.3%, Zn: 0.2 to 1.0%, Zr: 0.03 to 0.3%, one or two Contains more than seeds.

(Brazing alloy)
Next, as the brazing alloy 4 clad on the core material aluminum alloy plate 2, a known brazing aluminum alloy such as a 4000 series Al-Si based brazing material such as JIS4043, 4045, 4047 which has been widely used in the past is used. it can. The brazing material alloy is configured as a brazing sheet in which an aluminum alloy sacrificial anticorrosive material (plate) 3 is clad on one surface and an aluminum alloy brazing material (plate) 4 is clad on the other surface.

(Sacrificial anticorrosive material)
Furthermore, the sacrificial anticorrosive alloy 3 clad on the core material aluminum alloy plate 2 is a known sacrificial anticorrosive aluminum containing Zn, such as a 7000 series aluminum alloy such as JIS7072 of Al-1 mass% Zn composition which has been widely used conventionally. Alloys can be used. Such a sacrificial anticorrosive material is essential for a heat exchanger for automobiles in which cooling water is present on the inner surface side of the tube. That is, it is indispensable for preventing corrosion and ensuring corrosion resistance on the inner surface of the tube where the cooling water is present.

  Hereinafter, the present invention will be described more specifically with reference to examples. A laminate (brazing sheet) 1 having aluminum alloy core material 2 having the composition of A to J shown in Table 1 was prepared, and the structure of the core material 2 portion was examined. Further, the laminated plate 1 was heated and held at a temperature of 600 ° C. for 3 minutes, imitating brazing, and then cooled at an average cooling rate of 100 ° C./min. The structure of the core part of the later laminate was investigated. These results are shown in Table 2. In addition, the mechanical properties and fatigue properties of the laminate after the brazing equivalent heating were measured and evaluated. These results are shown in Table 3.

(Manufacture of laminates)
The production of the laminate was as follows. An aluminum alloy core material ingot was manufactured by melting and casting 3000 series aluminum alloy compositions having compositions A to J shown in Table 1. A JIS7072 aluminum alloy plate made of an Al-1 mass% Zn composition is used as a sacrificial anticorrosive material on one surface of the core ingot, and a JIS4045 aluminum alloy plate made of an Al-10 mass% Si composition is used as a brazing material on the other surface. Each was clad. Then, as shown in Table 2, the clad plate was subjected to the soaking temperature in each example, and the number of dispersed particles was controlled by variously changing the time from the end of soaking until the start of hot rolling. Then, the clad plate was hot-rolled. Further, it was cold-rolled with appropriate intermediate annealing to obtain a laminated board (brazing sheet) of H14 tempered material.

  In common with each example, the laminated plate has a core aluminum alloy plate thickness of 0.18 mm, and the thickness of both the brazing material and the sacrificial anticorrosive material laminated on each side of the core material is 20 to 20 mm. The range was 30 μm.

(Organization)
Using each of the measurement methods described above, the structure of the core material portion of the laminated plate, which is the cold-rolled clad plate, and the core material portion of each laminated plate after the heating is observed, and the rolling direction in the longitudinal section in the rolling direction is observed. The average crystal grain size (μm) and the average number density (particles / mm ² ) of dispersed particles having an average value of the center-of-gravity diameter of 1 μm or more observed by a 500-fold SEM in the surface layer portion of the rolled surface were measured. These results are shown in Table 2. Here, although the average crystal grain size of the core aluminum alloy plate of the laminated plate before the brazing equivalent heating, which is the raw material, is not shown in Table 2, it hardly changes in the above-mentioned short brazing equivalent heating. The average grain size of the core material aluminum alloy plate in the laminated plate after brazing equivalent heating shown in FIG.

(Mechanical properties)
Tensile tests were performed on each of the laminated plates after heating, and tensile strength (MPa), 0.2% proof stress (MPa), elongation (%), drawing (%), and n value were measured. These results are shown in Table 3. As test conditions, JISZ2201 No. 5 test piece (25 mm × 50 mmGL × plate thickness) perpendicular to the rolling direction was sampled from each laminated plate and subjected to a tensile test. The tensile test was conducted at room temperature of 20 ° C. based on JISZ2241 (1980) (metal material tensile test method). The crosshead speed was 5 mm / min, and the test was performed at a constant speed until the test piece broke. The n value is calculated by calculating the true stress and true strain from the end point of yield elongation, plotted on a logarithmic scale with the abscissa as the strain and the ordinate as the stress, and the slope of the straight line represented by the measurement point is measured. did.

(Fatigue properties)
The evaluation of the fatigue properties of each laminated board after the heating was performed at room temperature using a known single swing type flat bending fatigue tester described in Patent Document 5 shown in FIG. That is, a test piece having a thickness of 10 mm × 60 mm × plate thickness was cut out from each of the laminated plates after heating so as to be parallel to the rolling direction. One end of the test piece was attached to the fixed side of a single swing plane bending fatigue tester as shown on the right side of FIG. And the other end of this test piece was clamped with the knife edge on the drive side as shown on the left side of FIG.

  In the bending fatigue test, by moving the position of the knife edge, the test piece is subjected to plane bending so that the swing width is constant (5 mm in the vertical direction in FIG. 3) while changing the test piece set length. Repeatedly. At this time, in order to reproduce the fatigue, which is the subject of the present invention, cracking is dominant, the length of the test piece set is set so that the additional bending stress is about 0.005 which is a relatively high strain amount at the fracture portion. Adjusted. Under such conditions, the number of repetitions of plane bending until each test piece broke was determined. These results are shown in Table 3.

  Since the strain gauge cannot be applied directly to the fracture site, the strain gauge is affixed to two or three predetermined positions slightly apart from the fracture site, and the strain gauge for each test piece length. The strain amount at the fracture site was estimated by interpolating the strain amount at the fracture site from the strain value, and the load stress, that is, the test piece set length was adjusted based on this.

(Fracture surface observation)
Furthermore, the rolling surface in the vicinity of the fatigue failure of each laminate (after the brazing equivalent heating) after the bending fatigue test was observed with a 100-fold SEM, and the mechanism of fatigue failure was investigated from the degree of occurrence of cracks. When the degree of occurrence of this crack is relatively large, the crack generation that is the subject of the present invention is dominant fatigue, and when the degree of occurrence of crack is relatively small, crack propagation is the dominant fatigue. . Therefore, with regard to the same type of aluminum alloy sheet, the difference in the degree of crack initiation from the reference sample, in which fatigue is intentionally (typically) dominant in crack initiation and fatigue dominant in crack propagation. Check in advance. Compared with this reference sample, crack propagation is dominant fatigue when the crack generation is relatively large, and crack propagation is dominant when the crack generation is relatively small. Determined to be fatigued. These results are shown in Table 3.

As shown in Table 2, in Invention Examples 1 to 13, the core material aluminum alloy plate is produced within the composition range of the present invention component and in a preferable soaking condition range. For this reason, as shown in Table 2, the core material aluminum alloy plate of the laminated plate (brazing sheet) is an average of dispersed particles having an average value of the center-of-gravity diameter of 1 μm or more observed by SEM of 500 times on the rolled surface layer portion. It has a structure whose number density is 7000 pieces / mm ² or less. Therefore, even as a laminated plate (brazing sheet) after brazing equivalent heating, the core material aluminum alloy plate has an average crystal grain size in the rolling direction in a longitudinal section in the rolling direction of 200 μm or less, and a surface layer portion of the rolled surface. The average number density of dispersed particles having an average value of the center-of-gravity diameter of 1 μm or more observed by SEM of 500 times is 6000 / mm ² or less.

  As a result, as shown in Table 3, Invention Examples 1 to 13 have excellent properties such as drawing and n value after having a predetermined strength, and the number of repetitions until the brazing equivalent material in the bending fatigue test is broken. Many have a long fatigue life. Therefore, it can be seen from the observation results of the surface in the vicinity of the fracture surface that the degree of occurrence of cracks is large, Inventive Examples 1 to 13 are excellent in fatigue in which cracks are the subject of the present invention.

  In other words, in comparison with each comparative example to be described later, as in Invention Examples 1 to 13, if the aperture is 85% or more and the n value is 0.32 or more, the occurrence of cracks, which is a problem of the present invention, is dominant. It turns out that it is excellent in fatigue.

In contrast, in Comparative Examples 14 and 15, although the core material aluminum alloy plate is within the composition range (B) of the present invention, the soaking temperature is too low. For this reason, as shown in Table 2, in the core material aluminum alloy plate of the laminated plate, the average number density of the precipitates exceeds 7000 pieces / mm ² . Therefore, each of the laminated plates after the heating also has an average crystal grain size of the core aluminum alloy plate of 150 μm or less, but the average number density of the dispersed particles exceeds 6000 / mm ² .

  As a result, as shown in Table 3, although Comparative Examples 14 and 15 have a predetermined strength, these characteristics are inferior because the aperture is less than 85% and the n value is less than 0.32. For this reason, the number of repetitions until fracture of the brazing equivalent material in the bending fatigue test is small, and the fatigue life is short. Therefore, it can be seen from the observation result that the degree of occurrence of cracks on the surface near the fractured portion is large, Comparative Examples 14 and 15 are inferior to fatigue in which cracks are dominant.

  Comparative Examples 16 to 20 have component compositions N, O, P, Q, and R (Table 1) in which the core aluminum alloy plate departs from the scope of the present invention. That is, the contents of Si, Cu, Mn, Ti, and Fe each exceed the upper limit and are too much. As a result, each of the laminated plates after heating has a small number of repetitions until the brazing equivalent material in the bending fatigue test is broken and has a short fatigue life.

  Therefore, from the results of the above-described examples, the mechanical properties as a heat exchanger laminated plate or a laminated plate after brazing equivalent heating, and each requirement of the present invention for excellent fatigue due to crack generation are excellent. The critical significance and effect of this are supported.

  According to the present invention, it is possible to reduce the thickness of a laminated plate after heating equivalent to brazing, such as an aluminum alloy radiator tube, or a laminated plate such as an aluminum alloy brazing sheet. A laminated sheet after heating can be provided. Therefore, the present invention is suitable for use in aluminum alloy heat exchangers for automobiles and the like that are required to have excellent fatigue characteristics as well as thin radiator tubes.

It is sectional drawing which shows this invention laminated board. It is sectional drawing which shows the heat exchanger made from aluminum alloy. It is explanatory drawing which shows a bending fatigue test. It is sectional drawing which shows the general heat exchanger made from an aluminum alloy. It is sectional drawing which shows laminated sheets, such as a general brazing sheet.

Explanation of symbols

1: Aluminum alloy laminated plate for heat exchanger, 2: Core material, 3: Skin material, 4: Brazing material, 10: Radiator (heat exchanger), 11: Tube (laminated member), 12: Radiation fin, 13: Header

Claims (10)

At least a core material aluminum alloy plate and an aluminum alloy sacrificial anticorrosive material are clad, and are made into a heat exchanger by brazing, wherein the core material aluminum alloy plate is in mass%, Si: 0.2- 1.5%, Cu: 0.2 to 1.2%, Mn: 0.2 to 1.4%, Ti: 0.03 to 0.3%, respectively, and Fe: 1.0% or less The balance has an aluminum alloy composition consisting of Al and unavoidable impurities, and the average value of the center-of-gravity diameter observed by SEM of 500 times at the surface layer portion of the rolled surface of the core aluminum alloy sheet is 1 μm or more An aluminum alloy laminate having excellent fatigue characteristics, characterized by having a structure with an average number density of dispersed particles of 7000 particles / mm ² or less.   The core material aluminum alloy plate in the laminate is further in mass%, Cr: 0.03-0.3%, Zn: 0.2-1.0%, Zr: 0.03-0.3% The aluminum alloy laminated board excellent in the fatigue characteristics of Claim 1 containing 1 type, or 2 or more types of these.   The aluminum alloy laminated plate excellent in fatigue characteristics according to claim 1 or 2, wherein the core material aluminum alloy plate in the laminated plate further regulates Mg to 0.5 mass% or less.   The aluminum alloy laminated plate excellent in fatigue characteristics according to any one of claims 1 to 3, wherein a thickness of the core aluminum alloy plate in the laminated plate is a thin wall of less than 0.25 mm.   The aluminum alloy laminate having excellent fatigue characteristics according to any one of claims 1 to 4, wherein the laminate has a thin thickness of less than 0.3 mm. At least a core material aluminum alloy plate and an aluminum alloy sacrificial anticorrosive material are clad, and the core material aluminum alloy plate is in mass%, Si: 0.2 to 1.5%, Cu: 0.2 to 1.2%, Mn An aluminum alloy composition containing 0.2 to 1.4% and Ti: 0.03 to 0.3%, respectively, and Fe: 1.0% or less, with the balance being Al and inevitable impurities. Furthermore, as a structure after heating equivalent to brazing, the average grain size in the rolling direction in the longitudinal section in the rolling direction of the core material aluminum alloy sheet is 200 μm or less, and the rolled surface surface layer of the core material aluminum alloy sheet Characterized by having a structure in which the average number density of dispersed particles having an average value of the center-of-gravity diameter of 1 μm or more observed by SEM of 500 times in the part is 6000 particles / mm ² or less. Aluminum alloy laminate with excellent properties.   The core material aluminum alloy plate in the laminate is further in mass%, Cr: 0.03-0.3%, Zn: 0.2-1.0%, Zr: 0.03-0.3% The aluminum alloy laminated board excellent in the fatigue characteristics of Claim 6 containing the 1 type (s) or 2 or more types of these.   The aluminum alloy laminated plate excellent in fatigue characteristics according to claim 6 or 7, wherein the core aluminum alloy plate in the laminated plate further regulates Mg to 0.5% by mass or less.   The aluminum alloy laminated plate excellent in fatigue characteristics according to any one of claims 6 to 8, wherein a thickness of the core aluminum alloy plate in the laminated plate is a thin wall of less than 0.25 mm.   The aluminum alloy laminate having excellent fatigue characteristics according to any one of claims 6 to 9, wherein the laminate has a thin wall thickness of less than 0.3 mm.

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