JP5977640B2 - Aluminum pipe joint - Google Patents

Description

  The present invention relates to an aluminum tube joined body having improved corrosion resistance of a joined portion.

  Aluminum heat exchangers for automobiles such as radiators, condensers and evaporators have been manufactured and used for the purpose of weight reduction. In air conditioning equipment such as air conditioners, copper pipes have been used from the viewpoint of heat exchanger performance. However, in recent years, the price of copper has soared that aluminum has become more cost-effective than copper, and heat exchangers for air conditioning equipment that use aluminum instead of copper for piping are drawing attention.

  The fin-and-tube heat exchanger joins a copper heat transfer tube and an aluminum fin material by mechanical expansion, expands the end of the heat transfer tube by flaring, and pipes the other U-shaped part called an R-bend. Is inserted into the expanded portion and joined by torch brazing.

  The heat exchanger in which the heat transfer tube is replaced with an aluminum alloy has a problem of pitting corrosion that occurs under high temperature and high humidity, as compared with a conventional copper heat exchanger. There is no concern about corrosion on the inner surface of the tube part of the straight part of the heat transfer tube, the R bend part that is not in contact with the fins, or the bent part of the tube. When exposed, pitting corrosion occurred on the surface, and as it progressed, there was a possibility of leading to a problem of penetration.

  In automotive heat exchangers, etc., there are two-layer clad materials with a surface coated with a pure aluminum material having a purity of 99.0 mass% or higher, clad materials with an Al-1 mass% Zn material, and thermal spray materials with a surface sprayed with pure Zn. Used. As a result, pure aluminum, Al-1 mass% Zn, and pure Zn coated on the surface act as a sacrificial anode layer to prevent penetration due to corrosion. By applying these to a heat exchanger for a domestic air conditioner, it has been found that penetration due to corrosion of the straight portion of the heat transfer tube, the R bend portion not in contact with the fins, and the bent portion of the heat transfer tube can be prevented.

  However, in a clad tube or a thermal spray tube using a sacrificial anode material on the surface, there arises a problem that penetration leakage due to corrosion occurs at a torch brazed joint portion between the heat transfer tube and the R bend portion. As shown in FIG. 5, such penetration due to corrosion occurs when the sacrificial anode layer provided on the surface corrodes preferentially over the brazing filler fillet of the torch brazing part. Further, in the case of a Zn spray tube, penetration due to corrosion occurs due to Zn concentration in the brazing filler fillet. In FIG. 5, 1 is a flare portion of the pipe material whose end is expanded, 2 is a straight portion of the pipe material inserted into the flare portion, 3 is a sacrificial anode material preferentially corroded in the brazing portion, 4 is an inner tube, Reference numeral 5 denotes a brazing filler fillet, and reference numeral 6 denotes a pipe joint joined by the fillet 5.

  As means for preventing such corrosion of the joint portion, Patent Document 1 describes that the joint portion of the aluminum tube body is surrounded by a sleeve provided with a brazing filler metal layer or a solder layer and then heat-joined. ing. In this method, although the length of the joint portion is increased, the time until the penetration leakage can be extended, but the preferential corrosion of the sacrificial material cannot be completely prevented. In addition, when this method is used, the sleeve is connected to the joint portion, which leads to an increase in the number of parts and man-hours, resulting in an increase in cost.

  As another means for preventing corrosion of the joint portion, in Patent Documents 2 and 3, aluminum pipes are joined to each other by torch brazing using a brazing material added with 1.0 to 2.0 mass% of Zn, and joined. Describes a method of preventing preferential corrosion by integrating the brazing filler fillet and Al-Zn sacrificial layer. However, even if the preferential corrosion of the Al—Zn sacrificial layer can be prevented, the corrosion rate of the braze filler fillet itself is also increased, which may not contribute to the improvement of the corrosion resistance of the joint itself.

JP 58-163572 A JP 2010-212256 A JP 2010-240696 A

  The present invention was made as a result of diligent research in view of the above problems, and provides an aluminum tube joined body excellent in corrosion resistance that prevents preferential corrosion of the brazed part and does not cause penetration leakage of the brazed part. With the goal.

  The present invention according to claim 1 uses a plurality of aluminum pipes having either a straight part or a flare part at both ends, and fits the straight part of one adjacent aluminum pipe and the flare part of the other aluminum pipe. A joined aluminum tube brazed by placing an Al-Si brazing material between the straight part and the flare part, and the aluminum pipe provided with at least the straight part has Mn: 0.8 to 1 .3 mass%, Cu: 0.4 to 0.8 mass%, balance Al and the outer surface of the core of the Al alloy made of inevitable impurities, Zn: 0.5 to 1.5 mass%, balance Al and unavoidable This is an aluminum clad tube in which an Al—Zn sacrificial layer made of impurities is clad, and the Al—Si brazing material is sacrificed at the straight portion of the junction. A melt diffusion part composed of a hemispherical solidified structure eroded is formed, and the maximum thickness of the melt diffusion part is 0.5 to 2.0 times the clad thickness of the Al-Zn sacrificial layer. An aluminum tube joined body was obtained.

  According to a second aspect of the present invention, in the first aspect, the Zn concentration in the thinnest portion of the straight portion in contact with the melt diffusion portion is 0.7 mass% or less.

  According to the present invention, the preferential corrosion of the brazed portion is prevented as compared with the conventional joined body of aluminum pipe, and the joined body of aluminum pipe excellent in corrosion resistance of the joined portion is obtained.

It is sectional drawing which shows the joined body of the aluminum tube which concerns on this invention. It is sectional drawing of the junction part which shows the electric potential state at the time of the priority corrosion of a sacrificial anode layer generating. It is sectional drawing of the junction part which shows progress of the priority corrosion of a sacrificial anode layer typically. It is sectional drawing of the conjugate | zygote which shows a junction part typically. It is sectional drawing of the junction part which shows the preferential corrosion of the sacrificial anode layer in a prior art.

A. Mechanism of Through Leakage Phenomenon The present inventors have described the phenomenon in which when an aluminum tube provided with an Al—Zn sacrificial layer is joined by brazing, the Al—Zn sacrificial layer preferentially corrodes at the joint and leads to through leakage. The mechanism was examined. Here, the aluminum pipe refers to both a pipe made of pure aluminum and a pipe made of an aluminum alloy. Specifically, as shown in FIG. 1, a straight part 2 of the other aluminum clad tube is inserted into a flare part 1 of one aluminum clad pipe whose end is expanded by flaring, and a torch brazing material is used as a brazing method. The case where both pipes were joined using the torch brazing method using No. 5 was examined. Here, the layer 3 formed on the outer surface of the flare portion 1 and the outer surface of the straight portion 2 represents an Al—Zn sacrificial layer.

  In the aluminum tube provided with the Al—Zn sacrificial layer, as shown in FIG. 2, the phenomenon that the pitting corrosion potential of the Al—Zn sacrificial layer 3 occurs in the junction 6 and the inside of the torch brazing material 5 and the aluminum tube, as shown in FIG. This is because it is more basic than tube 4. In FIG. 2, the vertical axis of the graph represents an arbitrary distance in the radial direction from the axial center of the straight portion 2 of the aluminum tube, and the pitting corrosion potential represents a relative potential of each part. As schematically shown in FIG. 3, in the middle stage of corrosion in which corrosion has progressed, the Al—Zn sacrificial layer 31 other than the joint 6 in the straight portion 2 of the aluminum tube disappears. Further, in the later stage of corrosion where corrosion has progressed, the Al—Zn sacrificial layer 32 in the joint 6 of the straight portion 2 of the aluminum tube is preferentially corroded by the action of the pitting corrosion potential difference between the torch brazing material 5 and the Al—Zn sacrificial layer 3. Turned out to be.

  As a method of preventing the preferential corrosion of the Al—Zn sacrificial layer generated in the torch brazing portion as a result of intensive studies, the present inventors have studied the Al heating condition of the brazing portion to control the Al existing in the joint portion 6. It has been found that it is effective to eliminate the Al—Zn sacrificial layer by eroding the —Zn sacrificial layer with the molten brazing filler metal 5.

B. Form of joined body These are joined using a plurality of aluminum tubes each having a straight portion 2 at both ends or a straight portion 2 at one end. As an example, as shown in FIG. 4, a plurality of aluminum tubes each having one end portion as a flare portion 1 and the other end portion as a straight portion 2 are used, and the straight portion 2 of the first aluminum tube is used as a second aluminum tube. Then, the straight portion 2 of the second aluminum tube is fitted to the flare portion 1 of the third aluminum tube. This is sequentially repeated, and the straight portion 2 is fitted to the flare portion 1 for all of the plurality of aluminum tubes to produce a fitting body. And a fitting part is joined by brazing, such as a torch brazing, sequentially or at once, and it is set as a joined body (1st form). When joining two aluminum tubes, the straight portion 2 of the first aluminum tube is fitted to the flare portion 1 of the second aluminum tube, and the fitting portion is brazed by torch brazing or the like. Join to make a joined body.

  Alternatively, a plurality of aluminum tubes whose both end portions are flared portions and a plurality of aluminum tubes whose both end portions are straight portions can be used. In this case, one straight portion of the fifth aluminum tube is fitted into one flare portion of the fourth aluminum tube, and then the other straight portion of the fifth aluminum tube is connected to the sixth aluminum tube. It fits into one flare part of a pipe, and this is repeated sequentially, and straight part 2 is fitted to flare part 1 about all of a plurality of aluminum pipes, and a fitting object is produced. And a fitting part is joined by brazing, such as a torch brazing, one by one or at a time (second form). When joining two aluminum alloy tubes, one straight portion of the fifth aluminum alloy tube is fitted to one flare portion of the fourth aluminum alloy tube, and the fitting portion is brazed torch. Joined by brazing or the like to make a joined body. Moreover, it is good also as a form with which the 1st form and the 2nd form were mixed.

C. Next, the form of the joint will be described.
As shown in FIG. 4, an aluminum clad tube in which an Al—Zn sacrificial layer 3 is provided on the outer surface of the straight portion 2 is used. The straight portion 2 is fitted to the flare portion 1 and brazing addition heat is performed using the Al—Si alloy brazing material 5. By heating, the brazing material 5 is melted into a liquid phase, and the Al—Zn sacrificial layer 3 that contacts the molten brazing on the outer surface of the straight portion 2 is also melted. While the molten braze erodes the molten Al—Zn sacrificial layer 3, the components of the molten Al—Zn sacrificial layer 3 diffuse into the molten braze. When the brazing heat is insufficient, such erosion does not proceed sufficiently, and the thick Al—Zn sacrificial layer 3 remains in the lower portion of the fillet, and the corrosion resistance at the joint cannot be sufficiently improved. In the present invention, the eroded portion of the Al—Zn sacrificial layer 3 caused by the above-described melting brazing is referred to as “melting diffusion portion (51)”.

  The melt diffusion part 51 has a hemispherical solidified structure. The melt diffusion portion 51 has a maximum thickness not less than 0.5 times and not more than 2.0 times the cladding thickness of the Al—Zn sacrificial layer 3 before brazing in the thickness direction from the outer surface of the straight portion 2. It is necessary to have. Since the amount of Zn contained in the Al—Zn sacrificial layer 3 decreases due to diffusion into the molten solder, it is not always necessary to completely melt the Al—Zn sacrificial layer 3 in order to prevent preferential corrosion due to the presence of Zn. However, when the ratio is less than 0.5 times, a thick Al-Zn sacrificial layer with a high Zn concentration still remains in the lower part of the fillet 5 after brazing, preferential corrosion occurs, and the inner tube is brought to an early stage. It penetrates. When the ratio of the melt diffusion portion 51 is 1.0, the Al—Zn sacrificial layer 3 is almost completely eroded by the melted solder. When this ratio exceeds 1.0, the Al—Zn sacrificial layer 3 is almost completely eroded by the molten brazing, and a part of the core material of the inner tube 4 is also eroded by the molten brazing. When the ratio exceeds 2.0 times, even the Al—Zn sacrificial layer 3 in the portion other than the joint is melted, and the corrosion resistance in the portion other than the joint is deteriorated. In addition, since the fusion | melting spreading | diffusion part 51 comprises a hemispherical solidification structure | tissue, the thickness is not uniform.

  During brazing addition heat, the Zn component contained in the Al—Zn sacrificial layer diffuses into the molten braze according to the Zn concentration gradient between the molten brazing and the Al—Zn sacrificial layer. For example, when brazing addition heat is applied using JIS 4047 for the brazing material and JIS7072 alloy for the Al—Zn sacrificial layer, the fillet after brazing has a Zn content of 0.05 to 0.2 mass% (hereinafter simply referred to as “%”). To be included). Thus, it is unavoidable that Zn is contained in the fillet, but the Zn concentration contained in the fillet 5 in contact with the thinnest portion of the straight portion in the formed joint portion is less than 1.0%. desirable. When the concentration of Zn contained in the fillet is 1.0% or more, the corrosion rate of the fillet is increased, the corrosion resistance is deteriorated, and the joint portion may penetrate early.

  In the present invention, the melt diffusion part 51 is formed on the outer surface of the straight part 2 existing below the fillet 5. The melt diffusion part 51 is at least one of the outer surfaces of the straight part 2 existing below the fillet 5. What is necessary is just to be formed in the part. That is, even if it forms over the whole outer surface of the straight part 2 which exists in the lower part of the fillet 5, it may be formed discontinuously.

D. Bonding interface between melt diffusion portion and straight portion The Zn concentration in the thinnest portion of the straight portion 2 of the inner tube 4 in contact with the melt diffusion portion 51 having a hemispherical solidified structure is preferably 0.7% or less. When the Zn concentration exceeds 0.7%, preferential corrosion occurs in the inner pipe 4 in this portion and penetrates early. Here, “the thinnest portion of the inner tube” refers to a portion where the inner tube thickness shows the minimum value in the cross section along the tube longitudinal direction of the joint. The melt diffusion part 51 is composed of a number of hemispherical parts, and these are aggregated to form a composite hemispherical shape as a whole. Therefore, the surface of the straight portion 2 of the inner tube 4 in contact with the melt diffusion portion 51 has a shape complementary to the hemispherical shape of the melt diffusion portion 51, and the thickness thereof is not uniform. The Zn concentration in the thinnest portion of the straight portion 2 is more preferably 0.5% or less.

E. Aluminum tube The aluminum tube having a straight portion used in the present invention is a clad tube made of an aluminum alloy in which an Al-Zn sacrificial layer having a predetermined composition is clad on an aluminum core material having a predetermined composition.

E-1. Core Material An Al alloy containing Mn: 0.8 to 1.3% and Cu: 0.4 to 0.8% and the balance Al and inevitable impurities is used for the core material.

Mn:
Mn is a main additive element that improves the strength of the 3000 series alloys. It dissolves in Al and partly precipitates to provide an effect of imparting strength. If the amount of Mn added is less than 0.8%, the strength is insufficient. On the other hand, if it exceeds 1.3%, the effect of improving the strength is saturated, and the amount of coarse intermetallic compounds formed increases, causing problems such as cracks in the production process. Therefore, the amount of Mn added is in the range of 0.8 to 1.3%. A preferable Mn addition amount is 1.0 to 1.2%.

Cu:
Cu is an element that does not impair workability even though it has the effect of further improving the strength by solid solution in Al. Moreover, Cu has a function of making the pitting corrosion potential noble, can increase the pitting corrosion potential difference between the Zn diffusion layer and the central portion of the tube where Zn is not diffused, and can enhance the sacrificial anticorrosive action. If the amount of Cu added is less than 0.4%, the strength is insufficient and the crushing of the groove due to mechanical expansion cannot be prevented, and furthermore, no sufficient sacrificial anticorrosive action can be obtained due to insufficient pitting corrosion potential. When the amount of Cu added exceeds 0.8%, processability such as extrudability and drawability, and corrosion resistance are inferior. Therefore, the amount of Cu added is in the range of 0.4 to 0.8%. A preferable Cu addition amount is 0.55 to 0.75%.

  Examples of inevitable impurities present in the Al alloy include Fe, Mg, and Zn. If Fe: 0.6% or less, Mg: 0.2% or less, and Zn: 0.3% or less, the effects of the present invention are not inhibited.

  Further, Ti, Cr, and Zr may be contained because they have an effect of uniformly refining the ingot structure. However, if the content of each of these elements exceeds 0.2%, a giant intermetallic compound is formed and the extrudability also decreases. Is preferred. If content of each element of Ti, Cr, and Zr is 0.2% or less, the effect of this invention will not be inhibited. In addition, content of each said element becomes like this. Preferably it is 0.1% or less, More preferably, it is 0.05% or less.

E-2. Al—Zn Sacrificial Layer An aluminum alloy clad tube having a straight portion used in the present invention is obtained by clad a core material with an Al—Zn alloy as a sacrificial layer, and drawing it. Since the sacrificial layer has a lower pitting potential than the core material, the sacrificial anticorrosive action prevents the core material and improves the durable life of the pipe material. For the sacrificial layer, an Al alloy containing Zn: 0.5 to 1.5% and the balance Al and inevitable impurities is used.

Zn:
Zn lowers the potential of the sacrificial layer so that it acts as a sacrificial anode, thereby improving the corrosion resistance. If the amount of Zn added is less than 0.5%, the potential difference from the core material is insufficient and the sacrificial anticorrosive effect cannot be improved. On the other hand, if the Zn addition amount exceeds 1.5%, Zn is concentrated at the joint and the corrosion resistance of the joint is deteriorated. Therefore, the Zn addition amount is in the range of 0.5 to 1.5%. The preferable addition amount of Zn is 0.7 to 1.0%.

  Examples of impurities present in the Al—Zn sacrificial layer include Si, Fe, Cu, and Mn. If Si: 0.5% or less, Fe: 0.6% or less, Cu: 0.2% or less, and Mn: 0.8% or less, the effect of the present invention is not inhibited.

  Further, Ti, Cr, and Zr may be contained because they have an effect of uniformly refining the ingot structure. However, if the content of each of these elements exceeds 0.2%, a giant intermetallic compound is formed and the extrudability also decreases. Is preferred. If content of each element of Ti, Cr, and Zr is 0.2% or less, the effect of this invention will not be inhibited. In addition, content of each said element becomes like this. Preferably it is 0.1% or less, More preferably, it is 0.05% or less.

  The thickness of the Al—Zn sacrificial layer is not particularly limited, but is preferably 5 to 30% of the total thickness of the core material + Al—Zn sacrificial layer. When this ratio is less than 5%, the period of effective action as a sacrificial anticorrosive layer becomes insufficient, and when it exceeds 30%, the strength decreases.

  The joined body according to the present invention is obtained by joining two or more aluminum tubes. An aluminum alloy clad tube made of the core material and the Al—Zn sacrificial material is used as an aluminum tube having at least a straight portion. For example, in a joined body obtained by alternately joining a plurality of aluminum tubes, one end of which is a straight portion and the other end of which is a flare portion, all of these aluminum tubes are made of an aluminum alloy clad tube made of the core material and an Al-Zn sacrificial material. To do.

  On the other hand, in a joined body in which both ends are composed of a plurality of aluminum tubes each having a flare portion and a plurality of aluminum tubes having both ends are straight portions, and these are alternately joined, a plurality of aluminum tubes each having both ends are straight portions The tube is an aluminum alloy clad tube made of the core material and an Al—Zn sacrificial material. In this case, it is not always necessary to use an aluminum alloy clad tube made of the core material and the Al—Zn sacrificial material for the plurality of aluminum tubes having both ends formed of flare portions.

F. In the present invention, the alloy composition of the brazing material used for brazing is not particularly limited, but an Al-Si based alloy containing Si: 9 to 14% is preferably used. When brazing heat is applied using these brazing materials, Zn diffuses from the high concentration side Al—Zn sacrificial layer to the low concentration side brazing material side due to the Zn concentration gradient in the brazing material and the Al—Zn sacrificial layer. To do. When Zn is added to the brazing material, since the Zn concentration gradient in the Al—Zn sacrificial layer and the brazing material is small, the diffusion of Zn to the brazing material side during brazing is suppressed. If it is 0.0% or less, the brazing material may contain Zn. However, if the Zn addition amount in the brazing material exceeds 1.0%, the Zn concentration gradient in the Al—Zn sacrificial layer and the brazing material is too small, and Zn diffusion to the brazing material side during brazing It is greatly suppressed. As a result, a large amount of Zn remaining in the Al—Zn sacrificial layer without being diffused may deteriorate the corrosion resistance of the inner tube.

G. Production of Aluminum Alloy Clad Tube Hereinafter, a method for producing an aluminum alloy clad tube used in the present invention will be described, but the present invention is not limited thereto. Here, a manufacturing method of an aluminum alloy clad tube using an Al—Zn sacrificial layer as a clad layer will be described.

  First, a combination billet is manufactured by covering the outer surface of a cylindrical inner tube with a skin sleeve serving as a cladding layer. The thickness of the skin sleeve is selected so as to obtain a desired cladding layer thickness. Next, the combined billet is soaked at 350 to 600 ° C. in a heating furnace. Next, the combination billet is inserted between the die and the ramnose and inserted into the container, and a mandrel having an outer diameter larger than the inner diameter of the core material is press-fitted while the die and the ramnose are fixed, and the inner diameter of the inner pipe is expanded. Expel the air between the tube and skin. Further, the mandrel is fixed at a predetermined position, the hollow system is advanced, the combination billet is pushed out through a die, and a seamless hollow tube material is obtained. Finally, an aluminum alloy clad pipe having a predetermined outer diameter and inner diameter is obtained through a drawing process.

  Alternatively, an inner tube is produced by extrusion molding, and a Zn sprayed layer is formed on the outer surface by thermal spraying, a Zn plated layer is formed by plating, or a Zn substituted treated layer is formed by a Zn substituted treated layer. May be formed.

H. Brazing Brazing heating is performed at a temperature higher than the solidus temperature. Heating below the solidus temperature cannot be brazed because no liquid phase is generated in the brazing material. Furthermore, both the melting of the brazing material and the erosion of the Al—Zn sacrificial layer are more likely to occur at a temperature higher than the solidus temperature. The solidus temperature here refers to an Al—Si—Zn alloy in which Zn diffuses into the brazing material. For example, the solidus temperature of Al-12% Si-1% Zn is 575 ° C. .

  A torch brazing method is suitably used as the brazing method. The other aluminum tube with the flux applied to the joint is inserted into the flare portion of one aluminum tube having one end expanded. Next, a torch brazing material is disposed at the joint, and both pipes are brazed and joined by torch brazing using a torch such as propane, air, or torch. As the flux, a fluoride-based flux or a cesium-based flux can be used. Thus, a general torch brazing method can be used.

  The torch brazing conditions are a brazing addition heat temperature of 575 to 660 ° C., and a heating time for brazing is a heating time to the brazing addition heat temperature of 16 to 20 seconds, a holding time at the brazing addition heat temperature. Is preferably 3 to 8 seconds, and the temperature lowering time from the brazing addition heat temperature to 200 ° C. is preferably 16 to 20 seconds. The brazing addition heat temperature is more preferably 600 to 635 ° C.

  In the case of torch brazing, brazing heating may be used in which the strength of the flame, the distance between the flame and the object, the holding time, and the like are adjusted. When the clad thickness of the Al—Zn sacrificial layer is d and brazing is performed under the condition that the maximum melt diffusion thickness is less than 0.5 d, a thick Al—Zn sacrificial layer is formed between the fillet and the outer surface of the straight portion. It remains, preferential corrosion occurs, and the inner pipe penetrates early. When all conditions of brazing addition heat temperature of less than 600 ° C., heating time to brazing addition heat temperature of less than 16 seconds, and retention time at brazing addition heat temperature of less than 3 seconds are satisfied, maximum melt diffusion thickness Is likely to be less than 0.5d.

  On the other hand, when brazing under conditions where the maximum melt diffusion thickness exceeds 2d, even the Al—Zn sacrificial layer other than the joint is melted and the corrosion resistance is poor. When all conditions of brazing addition heat temperature exceeding 635 ° C., heating time to brazing addition heat temperature exceeding 20 seconds and holding time at brazing addition heat temperature exceeding 8 seconds are satisfied, maximum melt diffusion thickness Is likely to exceed 2d.

  EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not restrict | limited to this.

  First, invention examples and comparative examples will be described. For various evaluations, a double-layer clad tube having an outer diameter φ of 7 mm, a total thickness t of 0.8 mm, and a cladding ratio of a skin material to be an Al—Zn sacrificial layer: 10%, that is, a clad thickness of 80 μm was used.

  Hereinafter, a method for producing a two-layer clad tube used in Examples will be described. An aluminum alloy skin material having the composition shown in Table 1 is used as the Al—Zn sacrificial layer, and a cylindrical core material (outer diameter 370 mm, inner diameter 80 mm, length 900 mm) made of the aluminum alloy having the composition shown in Table 2 is used as the inner tube. A certain 148 mmφ core material hollow billet was used to form a two-layer clad tube having the combinations shown in Table 3. First, after heating the skin material to 495 ° C., the skin material was covered on the outside of the core hollow billet at room temperature to obtain a two-layer clad hollow billet. A two-layer clad hollow billet is indirectly extruded at 460 ° C. to form an extruded tube having an outer diameter of 45 mm and a wall thickness of 4.0 mm, and this extrusion tube is repeatedly subjected to drawing to form two layers having an outer diameter of 7 mm and a wall thickness of 0.8 mm. An aluminum clad tube was obtained.

  Using two aluminum alloy clad tubes, one aluminum tube was expanded by flaring, and the straight portion of the other aluminum tube was inserted into this flared portion. Next, the Al—Si based alloy brazing material and the Al—Si—Zn based alloy brazing material (D1 to D6) shown in Table 4 formed in a wire shape are disposed between the flare portion and the straight portion, which serve as joint portions. Torch brazing was performed under the conditions shown in Tables 5 and 6 to produce a joined body test piece.

  Thus, the characteristic of each test piece produced was evaluated by the following tests (a) to (c), respectively. In each example, 10 specimens were tested.

(A) Joining state The joining state was judged by confirming the melt diffusion state of the fillet and the joining length. After bonding and polishing the bonding test piece, the cross section of the bonded portion was observed with a metal microscope. In all of the 10 test pieces, the melt diffusion part has a hemispherical solidified structure “◯” (passed), and in at least one of the 10 test pieces, not the hemispherical solidified structure but the Al—Zn sacrificed The thing with the layer remaining was set as "x" (failed). Also, by observing the cross section of the joint with a metal microscope, the maximum melt diffusion thickness is measured to obtain an average value, and the ratio of the maximum melt diffusion thickness (the above average value) to the cladding thickness of the Al—Zn sacrificial layer is determined. Asked. Furthermore, the joining length (fillet length) was measured as brazing joining evaluation. When the length of the fillet in the longitudinal direction of the tube is 1 mm or more, ◯ is less than 1 mm, 0.5 mm or more is Δ, and less than 0.5 mm is x. ○ and Δ were accepted and x was rejected. The results are shown in Tables 7 and 8.

(B) Corrosion resistance of non-joining part SWAAT according to ASTM G85 which simulated the atmospheric exposure environment was performed for 1500 hours. In the evaluation method, the maximum pitting corrosion depth of a non-joined portion such as an inner tube straight portion not in contact with a fillet is measured by optical microscope observation after the test, and all of the ten test pieces penetrated in 2000 hours. No and the maximum pitting depth is 80 μm or less as “◯” (passed), and all of the 10 specimens have not penetrated in 1500 hours, but the maximum pitting depth exceeds 80 μm. The thing was set as "(triangle | delta)" (pass), and the thing penetrated in at least one of 10 test pieces was set as "x" (failed). The results are shown in Tables 7 and 8. In addition, the maximum pitting corrosion depth is an average value of 10 test pieces.

(C) Corrosion resistance of joint part SWAAT according to ASTM G85 which simulated atmospheric exposure environment was performed for 1500 hours. In the evaluation method, after the test, a pressure resistance test of the bonding test piece was performed, and a cross section of the bonded portion was observed. “X” means that leakage occurs in the pressure test and / or the cross section of the inner pipe straight part of the joint is corroded by one of the 10 test pieces. It was. If all 10 test pieces are leak-free in the pressure resistance test, and the inner pipe straight portion of the joint is not penetrating through cross-sectional observation, the corrosion portion is more than half of the thickness. All of the 10 test pieces were leak-free in the pressure test, and the inner pipe straight part of the joint part was not penetrated by cross-sectional observation, and the corroded part was 1/4 or less of thickness and less than half. In some cases, “◯” indicates that all of the ten test pieces have no leak leakage in the pressure resistance test, and the inner pipe straight portion of the joint portion does not penetrate through the cross-sectional observation. The case of less than 4 was designated as “◎”. ◎, ○, and Δ were accepted, and x was rejected.

(D) Comprehensive evaluation According to the evaluation of the tests of (a) to (c), all evaluations consisted of “◎” and “○”, and the comprehensive evaluation was “◎”, and all evaluations consisted of “○”. Items with a comprehensive evaluation of “○”, all evaluations with “◎” and “○” and having one or more “△”, those with a comprehensive evaluation of “△” and one or more “×” The overall evaluation was “x”. The overall evaluations were “◎”, “◯”, and “△” as acceptable, and “×” as unacceptable.
Tables 7 and 8 also show the Zn concentration in the thinnest part of the straight part in contact with the melt diffusion part and the Zn concentration of the fillet in contact with the thinnest part of the straight part.

  Inventive Examples 1 to 29 were within the scope of the present invention, and were excellent in the joined state, the corrosion resistance of the non-joined part, and the corrosion resistance of the joined part, and the overall evaluation was “◎” or “Δ”. In Invention Examples 25 and 26, since the Zn concentration of the brazing material is high, melt diffusion hardly occurs, the Zn concentration in the thinnest portion of the straight portion is slightly high, and further, the corrosion resistance of the joint is slightly inferior because the Zn concentration of the fillet is high. . In Invention Examples 27 and 29, since the brazing temperature is lower and the heating time is shorter, the maximum melt diffusion thickness becomes the specified lower limit, and the joining length is slightly inferior. Also, the corrosion resistance of the joint is slightly inferior. In Invention Example 28, since the brazing temperature is high and the heating time is long, the Al—Zn sacrificial layer other than the joint is affected, and the corrosion resistance of the non-joint is slightly inferior.

On the other hand, in Comparative Example 1, since the Zn concentration of the Al—Zn sacrificial layer was low, the sacrificial anticorrosive action was inferior, the corrosion resistance of the non-joined part was rejected, and the comprehensive evaluation was rejected.
In Comparative Example 2, since the Zn concentration of the Al—Zn sacrificial layer was high, high-concentration Zn remained in the joint portion, the corrosion resistance of the joint portion failed, and the overall evaluation failed.
In Comparative Example 3, the sacrificial anticorrosive action was inferior because the Mn concentration of the core material was low, the corrosion resistance of the non-joined part was rejected, and the overall evaluation was rejected.
In Comparative Example 4, the corrosion rate increased because the Mn concentration of the core material was high, the corrosion resistance of the non-joined part was rejected, and the overall evaluation was rejected.
In Comparative Example 5, the sacrificial anticorrosive action was inferior because the Cu concentration of the core material was low, and the corrosion resistance of the non-joined part was rejected. Further, since the holding time during brazing was short, the thickness of the melt diffusion portion was reduced, and the solidified structure, the joining length, and the corrosion resistance of the joining portion were rejected. As a result, the overall evaluation was rejected.
In Comparative Example 6, since the Cu concentration of the core material was high, the corrosion rate was fast, the corrosion resistance of the non-joined part was rejected, and the comprehensive evaluation was rejected.
In Comparative Example 7, since the heating time was short, the thickness of the melt diffusion portion was thin. As a result, high-concentration Zn remained in the joint and the corrosion resistance of the joint was rejected, the solidified structure and the joint length were also rejected, and the overall evaluation was rejected.
In Comparative Example 8, the thickness of the melt diffusion part was increased due to the long heating time. As a result, the corrosion resistance of the joint part was rejected, and the comprehensive evaluation was rejected.

  According to the present invention, it is possible to obtain good jointability of a joint portion by brazing such as torch brazing and good corrosion resistance in a joint portion and a non-joint portion.

DESCRIPTION OF SYMBOLS 1 ... Flare part 2 ... Straight part 3 .... Al-Zn sacrificial layer, clad layer 31 ... Al-Zn sacrificial layer, clad layer 32 ... Al-Zn sacrificial layer, clad layer 4 .... -Inner pipe 5 ... Torch brazing filler metal, brazing filler metal fillet 51 ... Melt diffusion part 6 ... Joining part

Claims (2)

  Using a plurality of aluminum pipes having either a straight part or a flare part at both ends, the straight part of one adjacent aluminum pipe and the flare part of the other aluminum pipe are fitted, and the straight part and the flare part An aluminum tube joined by brazing with an Al—Si brazing material disposed between them, and the aluminum tube provided with at least the straight part is Mn: 0.8 to 1.3 mass%, Cu: 0.00. Al: Zn sacrificial layer containing Zn: 0.5-1.5 mass% and comprising the balance Al and unavoidable impurities on the outer surface of the Al alloy core material comprising 4 to 0.8 mass% and the balance Al and unavoidable impurities An aluminum clad pipe clad with a hemispherical solidified assembly in which the Al-Si brazing material erodes the Al-Zn sacrificial layer at the straight part of the joint Is melted diffusions formed consisting conjugate of aluminum tube to the maximum thickness of the molten diffusion portion is characterized in that 0.5 to 2.0 times the cladding thickness of the Al-Zn sacrificial layer.   The joined body of aluminum pipes according to claim 1 whose Zn concentration in the thinnest part of the straight part which touches said melt diffusion part is 0.7 mass% or less.

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