JP5431046B2 - Manufacturing method of brazing structure made of aluminum alloy for heat exchanger excellent in high temperature durability - Google Patents

Description

The present invention relates to the production how of the aluminum alloy brazing structure excellent in high-temperature durability for use in heat exchangers.

  Generally, an automotive heat exchanger is configured by brazing and joining aluminum alloy members such as fins, tubes, and headers. As a material of this brazing structure, an Al—Mn alloy is often used. This includes both a case where it is used alone and a case where it is used as a core material of a clad material, and examples of the material form include an extruded material and a plate material.

In recent years, development of heat exchangers (intercoolers, air conditioners using CO ₂ refrigerant, etc.) used at 150 to 250 ° C., which is higher than conventional ones, has been progressing due to the need for improving fuel economy and environmental measures. Along with this, it is important to maintain the function of the heat exchanger for each member to which higher temperatures and higher stresses are applied, especially for flow passage members such as tubes through which gas and liquid pass, to suppress creep deformation during use. . Therefore, an improvement in creep resistance in this temperature range is also required for Al—Mn alloy materials suitable for brazing.

  However, there are few examples of effective prior art relating to the improvement of creep resistance of the flow path member of the heat exchanger.

  In Patent Document 1, as an Al alloy extruded material for a heat exchanger excellent in high-temperature strength, the components are Mn: 0.7 to 1.5 mass%, Cu: 0.3 to 1.0 mass%, Si: 0.00. It is disclosed that the content is less than 10% by mass, Fe: less than 0.20% by mass, and the electrical conductivity after brazing is 37.0% IACS or less. This is interpreted as a technique for increasing the amount of the solid solution element by selecting the alloy composition and improving the high temperature strength by solid solution strengthening. However, in Patent Document 1, there is no mention of improvement in creep resistance, and it is difficult to say that durability is ensured when stress is applied at a high temperature for a long time. This alloy contains a large amount of Cu that lowers the solidus temperature. If the brazing temperature is higher than 605 ° C., which is the brazing temperature of the example of Patent Document 1, local melting may occur. Further, the addition of high concentration of Cu has a problem of increasing the sensitivity of intergranular corrosion.

JP 2001-207231 A

The present invention has been made in view of such problems, and is an aluminum alloy brazing structure for a heat exchanger having a flow path member having excellent creep resistance at a temperature of 150 to 250 ° C. when the heat exchanger is used. an object of the present invention is to provide a manufacturing how. In particular, the creep resistance is improved on the premise that Cu that reduces intergranular corrosion resistance and the like, and Mg that lowers brazeability are not added, or the addition amount is suppressed, even though it is effective for improving high temperature strength. That was the issue.

In order to solve the above problems, a method for producing an aluminum alloy brazing structure for heat exchangers having excellent high temperature durability according to the first aspect of the present invention,
A method for producing an aluminum alloy brazing structure for heat exchangers having excellent high-temperature durability, comprising a flow path member that forms a gas or liquid flow path,
Mn: 0.7 to 1.6% by mass, Fe: 0.05 to 0.7% by mass, Si: 0.05 to 0.3% by mass, with the balance being composed of Al and inevitable impurities Brazing using Al-Mn alloy material for at least a part of the flow path member,
Control so that the ultimate temperature of the Al-Mn alloy material at the time of the brazing joining exceeds 610 ° C and is 628 ° C or less;
It is characterized by that.

In the aluminum alloy brazing structure for a heat exchanger described above, the Al—Mn alloy material further includes one or more of Cu, Mg, Ti, Cr, Zr, V, and Ni in amounts of 0.05 to 0.00. Including 2% by weight,
It is good as well.

  According to the present invention, in the Al-Mn alloy material used for the flow path member, both the Mn solid solution amount and the Fe solid solution amount after brazing can be increased. It becomes possible to improve the creep resistance at a temperature of 150 to 250 ° C.

It is a front view which shows the minicore for evaluation in the Example of this invention. It is a front view which shows the other minicore for evaluation in the Example of this invention.

  The present inventors have attempted to improve the creep resistance of Al-Mn alloy materials by controlling the alloy composition and brazing conditions without using any additional process, and the composition and brazing suitable for this purpose. The conditions were studied and the present invention was reached. Hereinafter, embodiments of the present invention will be specifically described.

  The flow path portion of the heat exchanger targeted in the present invention is a portion through which gas and liquid necessary for heat exchange flow. Since the flow path portion becomes high temperature and pressure is applied during operation of the heat exchanger, a component member of the flow path portion (hereinafter referred to as a flow path member) requires creep resistance. Usually, the entire flow path is formed by combining a plurality of flow path members such as a header and a tube, and is formed as an integral brazing structure together with the fins. In this embodiment, it is assumed that an Al—Mn alloy material is used in at least a part of the flow path member. As a raw material form of the Al—Mn alloy material, for example, an extruded material or a plate material can be used. The extruded material is typically an extruded multi-hole tube having a flow channel shape. As the plate material, a so-called bare material composed entirely of one kind of Al—Mn alloy may be used, or a core material of a clad material composed of multiple layers may be used.

  In the manufacturing method of the present invention, control is performed so that the ultimate temperature at the time of brazing of the Al—Mn alloy material forming the flow path portion is higher than 610 ° C. and lower than 628 ° C. Such control makes it possible to increase the solid solution amount of Mn and Fe in the alloy. According to the study by the inventors, it has been confirmed that when both Mn and Fe are dissolved in a certain amount or more, the effect of improving the creep resistance is large.

  Mn and Fe in the Al—Mn alloy before brazing form a large amount of intermetallic compound particles, and the amount of solid solution is small. By brazing and heating this under the above specific conditions, it is possible to effectively dissolve the intermetallic compound particles.

  Specifically, the brazing temperature at the time of manufacturing the heat exchanger is typically around 600 to 605 ° C., but in the present invention, the ultimate temperature of the Al—Mn alloy material used for the flow path member is 610 higher than this. It controls so that it may exceed 620 degreeC and may be 628 degrees C or less. By setting it as such a high ultimate temperature, the amount of solid solution Mn and the amount of solid solution Fe in an Al-Mn type alloy material can be made high, and creep deformation can be suppressed by these solid solution elements.

  When the temperature reached by the material is 610 ° C. or less, no particular improvement in creep resistance occurs as compared with the case of the usual brazing treatment. If the ultimate temperature exceeds 628 ° C., local melting may occur in the extruded material. As a result, deformation of the fins to be combined occurs, and a normal structure cannot be obtained. In the present embodiment, in particular, it is more effective to improve the creep resistance by setting the material temperature to exceed 620 ° C. and not more than 628 ° C.

  It is desirable that the Al—Mn alloy material is held for 1 to 8 minutes in a temperature range exceeding 610 ° C. and not more than 628 ° C. during brazing. Further, in order to prevent precipitation of solid solution elements during cooling after brazing, the cooling rate is preferably 80 ° C./min or more, and more preferably 160 ° C./min or more.

  It is not necessary to take a heating time longer than usual in brazing by the production method of the present invention, and the time during which the material temperature is 500 ° C. or higher is within 25 min from the viewpoint of process productivity.

  Next, the composition of an Al—Mn alloy suitable for the above brazing conditions will be described. First, the addition amount and the solid solution amount of basic effective elements Mn and Fe will be described.

  Mn in the composition of the Al—Mn alloy used for the flow path member is an element effective for improving the creep resistance of the flow path member after brazing. If the amount added is less than 0.70% by mass, sufficient creep resistance cannot be obtained. On the other hand, if the addition amount exceeds 1.6% by mass, a coarse crystallized product is produced during normal DC (Direct Chill) casting, and a homogeneous structure cannot be obtained, which is inappropriate.

  Fe is a typical inevitable impurity of an aluminum alloy, but it is an element that contributes to improving the creep resistance of the tube material when appropriately added and controlled together with Mn. If Fe is contained in an amount exceeding 0.70% by mass, a coarse crystallized product is produced during DC casting, and a homogeneous structure cannot be obtained. Moreover, it is not appropriate to make this less than 0.05% by mass because it is necessary to use an expensive high-purity aluminum ingot, which is disadvantageous in terms of creep resistance.

  In the Al—Mn alloy used for the flow path member, the Mn solid solution amount is 0.40 mass% or more and the Fe solid solution amount is 0.010 mass% or more after brazing heating in order to improve creep resistance. It is prescribed. This is achieved by employing the material composition and brazing heating conditions of the present invention. The upper limit of the solid solution amount is not particularly specified, but it is obvious that the amount is less than the addition amount. If the Mn solid solution amount is less than 0.40% by mass, the creep resistance of the flow path member is lowered, which is inappropriate. Moreover, the amount of solid solution of Fe in an aluminum alloy is usually very small, but the present inventors are effective in improving the creep resistance of an Al-Mn alloy even with a small amount of solid solution Fe that satisfies the specified amount. I found out. Note that if the Fe solid solution amount is less than 0.010% by mass, the creep resistance is not sufficiently improved, which is inappropriate.

  Here, the analysis of the solid solution amount of Mn and Fe shall be based on the hot phenol dissolution filtrate method. This analysis method is described in the document “Matsuo et al .: Light Metal, Vol. 47 (1997), 15.”, and is carried out according to this.

  Below, the component prescription | regulation of Si added as an essential element in this embodiment other than Mn and Fe is demonstrated.

  Si is an unavoidable impurity element and affects the state of Mn. If this is regulated to less than 0.05% by mass, an expensive high-purity metal is required, and it does not lead to a special improvement in characteristics. On the other hand, if the Si content exceeds 0.30% by mass, the precipitation of Mn is remarkably promoted, and as a result, the effect of improving the creep resistance is impaired. Furthermore, if the Si content exceeds the specified value and other selective elements are added, local melting in the material may occur under the brazing conditions specified in the present invention, which is inappropriate.

  Further, in addition to the above essential elements, 0.05 to 0.20 mass% of Cu, Mg, Ti, Cr, Zr, V, or Ni may be included as effective elements that can be selectively added. Good. Hereinafter, the reason for limitation of each component is demonstrated.

  Cu is an element that contributes to the improvement of creep resistance after brazing of the flow path member when added in a specified range. As described above, excessive addition of Cu has problems of causing local melting during high-temperature brazing due to a decrease in the solidus temperature and promoting intergranular corrosion. For this reason, addition exceeding 0.20 mass% is unsuitable. Moreover, addition of Cu less than 0.05% by mass does not lead to improvement in creep resistance.

  However, when a particularly high brazing temperature of 620 ° C. or higher and 628 ° C. or lower is employed, an alloy composition not containing Cu is desirable. In other words, in the case of an alloy composition (less than 0.05%) with substantially no addition of Cu due to concerns such as intergranular corrosion, the alloy composition is resistant to high temperature brazing above 620 ° C and below 628 ° C. The creep property can be supplemented.

  Addition of Mg within a specified range also contributes to improvement of creep resistance after brazing of the flow path member. However, addition exceeding 0.20% by mass is unsuitable because it lowers the bondability in Nocolok brazing using a flux. Further, excessive addition of Mg may cause local melting during high temperature brazing due to a decrease in the solidus temperature. On the other hand, when the amount is less than 0.05% by mass, a special strength improvement effect cannot be obtained.

  Moreover, when there are more addition amounts of Cu and Mg than regulation, the hot workability of material will fall. For this reason, when an extruded multi-hole tube is a target, extrudability productivity may be reduced, or a tube having a normal shape may not be obtained in some cases.

  Ti, Cr, Zr, V, and Ni are also elements that contribute to the strength of the flow path member after brazing. If the addition amount is less than the specified range, the strength improvement effect is insufficient. Unlike Cu and Mg, these do not cause a significant decrease in the solidus temperature, but if added beyond the specified range, a coarse crystallized product is formed during casting, so a homogeneous material structure cannot be obtained. Not appropriate.

  In addition, in the present invention, Ti: 0.005 to 0.10% by mass, or Ti: 0.005 to 0.00, which is a component of a finer agent added to the flow path member by ordinary casting of an aluminum alloy. 10 mass% and B: 0.001-0.01 mass% may be included. Note that Ti derived from the micronizing agent is effective as a solidified structure by being present as intermetallic compound particles at the time of casting, and is added separately from Ti as the reinforcing element.

  Next, each member manufacturing method in the brazing structure for a heat exchanger according to the present invention will be described.

  The flow path member including the prescribed Al—Mn alloy material is appropriately brazed to another member using an Al—Si alloy brazing material to form a structure for a heat exchanger. As the brazing sheet, a bare material or one having a brazing material layer on the surface can be used. As a brazing method, nocollock brazing which uses a flux in a non-oxidizing atmosphere is preferable. The Al—Si based alloy brazing is generally supplied as a skin material for the brazing sheet, but brazing powder or foil may be installed at the joint.

  As one embodiment of the present invention, an extruded multi-hole tube made of an Al-Mn alloy whose components are defined as described above is used as a flow path member, and a heat exchanger structure is combined with fins and headers made of a brazing sheet. What constitutes is preferable. Of these, brazing sheet fins having a thickness of 0.04 to 0.12 mm having an Al—Mn alloy as a core and Al—Si brazing filler metal layers on both sides are suitable. Brazed to the road member. In addition, a fin is a thin member and is a part where the temperature rises fastest in the heat exchanger during brazing. When the brazing temperature is raised, buckling deformation of the corrugated fin is likely to occur, and a normal-shaped structure may not be obtained. In order to prevent this, it is preferable to use a brazing sheet fin having a sag amount of 18 mm or less in a sag test carried out by protruding 30 mm with holding at 615 ° C. × 3 min. In addition, about a sag test, it shall be implemented according to light metal welding structure association standard LWST8801.

  As a manufacturing process of the extruded multi-hole tube which is one form of the flow path member, a method of producing an Al—Mn alloy billet having a prescribed composition by DC casting, appropriately homogenizing, and hot extruding is suitable. The sacrificial anode layer can be formed on the surface of the extruded material by Zn spraying as usual. The tube after hot extrusion is cut into a predetermined length and incorporated into a structure for a heat exchanger.

  A clad material having an Al—Mn alloy as a core can also be produced by pressure bonding an Al—Si alloy material to one side or both sides of a slab by hot rolling in the above process.

  Moreover, as a manufacturing method of the board | plate material used as a flow-path member, the thing by the process shown below, for example is suitable. That is, it is preferable to produce an Al-Mn alloy slab by ordinary DC casting, appropriately homogenizing, and then hot rolling and combining the cold rolling and annealing to obtain a plate material having a predetermined thickness. is there. In general, the plate member as the flow path member is brazed and joined after forming with a roll or a mold in order to give a flow path shape.

  The aluminum alloy brazing structure for a heat exchanger according to the present invention can also be used as a part of the flow path member. As such an embodiment, for example, use in a tube such as a condenser or an evaporator of a car air conditioner can be mentioned. Since deformation due to creep can be suppressed while reducing the thickness of the tube, the technique of the present invention is most effective. In this case, the other flow path member such as the header tank is thicker, and therefore, a design that does not cause creep deformation is possible even if the flow path member is not defined in the present invention. Of course, these other flow path members can also be made thinner by using the material defined in the present invention.

  Next, examples of the aluminum alloy brazing structure for heat exchanger according to the present invention will be specifically described in comparison with comparative examples that are out of the scope of the claims, but the present invention is not limited thereto. is not.

  First, an 80 mm thick slab of an Al—Mn alloy having the composition shown in Table 1 was produced by a DC casting method. This was subjected to hot rolling preheating that also served as a homogenization treatment after slab face milling under the condition of 450 ° C. × 3 h, and hot rolled to obtain a hot rolled plate having a thickness of 4.5 mm. Next, this hot-rolled plate was cold-rolled to a plate thickness of 1.5 mm, subjected to intermediate annealing under conditions of 390 ° C. × 3 h, and further cold-rolled to produce a plate material having a plate thickness of 0.7 mm. In the column of the alloy composition in Table 1, “Remainder” includes inevitable impurities (the same applies to Table 2 described later), and “−” indicates that it is below the detection limit.

  As shown in FIG. 1, a mini-core 10 as an experimental structure was assembled using the plate material of the Al—Mn alloy as a simulation material for the flow path member. That is, the Al—Mn-based alloy plate 11 had a width of 20 mm and a length of 128 mm, and was disposed vertically with a corrugated brazing sheet fin 12 having a width of 16 mm interposed therebetween. The central part of the Al-Mn alloy plate 11 was opened so that the fins were not joined, but this part (characteristic evaluation part 13 within the range indicated by the broken line in FIG. 1) is the length of the parallel part of the creep test piece described later. Was set to 30 mm. As the brazing sheet fin 12, one having a composition as shown in Table 2 was used. That is, among the brazing sheet fins 12, the core material is an Al—Mn alloy material containing 1.35% by mass of Mn, and the brazing material is an Al—Si alloy material containing 7.1% by mass of Si. It is. The symbol “Tr.” In Table 2 indicates that the content of the element is very small. The brazing material was disposed on both sides of the core material so as to have a cladding rate of 7%, and the overall thickness of the brazing sheet fin 12 was 0.08 mm. The corrugated peak height of the brazing sheet fin 12 was 7.5 mm, and the peak interval was 1.8 mm. Each member of the mini-core 10 was fixed with a stainless steel wire (not shown).

  Then, brazing heating was performed on the mini-core 10 configured as described above by general sawlock brazing. More specifically, after applying a fluoride-based non-corrosive flux to the surface of the mini-core 10, brazing and heating were performed under the conditions shown in Table 3. At the time of brazing heating, a thermocouple was attached to the Al—Mn alloy plate 11 and the ultimate temperature of the Al—Mn alloy plate 11 during brazing (hereinafter also simply referred to as ultimate temperature) was measured.

  Next, the brazing sheet fins 12 are removed from the mini-core 10 after brazing heating, and the length of the parallel part (characteristic evaluation part 13) is 30 mm and the width is 12.5 mm from the Al-Mn alloy plate 11. A dumbbell-shaped creep test piece having a grip width of 20 mm was produced.

The evaluation items for each test piece are shown below. The creep test was performed by applying various stresses to the test piece at 200 ° C., and the test stress at which the minimum strain rate was 10 ⁻⁷ / s was defined as the creep strength and evaluated. In addition, the high temperature tensile strength at 200 ° C. was measured at a tensile speed of 5 mm / min using the same test piece. Moreover, about the member of the same position as this characteristic evaluation part 13, the analysis of the Mn solid solution amount and the Fe solid solution amount was performed by the hot phenol extraction method.

  Table 4 shows various manufacturing conditions and measurement results of the evaluation items in the brazed structure using the mini-core 10 shown in FIG. 1, that is, the Al—Mn alloy plate. Table 4 shows alloy Nos. Each having a composition within the scope of the present invention. 1, 2 and 5 are used for structures formed by various brazing conditions.

  As shown in Table 4, when the brazing conditions defined in the present invention were taken for the same alloy having the composition of the present invention (Examples 1-1 to 1-3, 2-1 to 2-4, 3-1 3-3) and the examples (Comparative Examples 1-1 to 1-2, 2-1 to 2-3, 3-1 to 3-2) deviating from the brazing conditions in the specified range, It can be seen that the creep strength is increased for each alloy under the brazing conditions (examples) defined in the present invention. Moreover, also about the high temperature tensile strength, the result of the Example was higher than the comparative example about each alloy. As shown in Table 4, this is interpreted as an effect of increasing the solid solution amounts of both Mn and Fe as solid solution elements. Further, when Example 2-1 and Example 2-2 are compared, if the same alloy and the same ultimate temperature are obtained, Example 2-1 having a higher cooling rate as described above has higher creep strength and higher temperature tensile strength. Larger values were obtained for both strengths. Thus, it can be said that the creep strength can be improved by controlling the brazing conditions in any alloy composition within the specified alloy composition range. Even in the conditions within the scope of the present invention, particularly when the temperature reached during brazing exceeds 620 ° C., the improvement in creep resistance is significant.

  In Table 5, the effectiveness of the present invention is shown by evaluating each test piece when the mini-core 10 is manufactured by changing the alloy composition. Table 5 shows alloy no. For each of the alloys 3, 4, and 6 to 11, the results of Examples 4 to 11 and the corresponding Comparative Examples 4 to 11 under different brazing conditions were listed side by side. In addition, Alloy No. having a composition outside the scope of the present invention. The results for 20-30 are also shown in Table 5 as Comparative Examples 12-22. In Table 5, the item “***” indicates that the test piece was formed normally but some evaluation items were not measured. In Table 5, items indicated by “---” indicate that the measurement could not be performed because the test piece was not normally created.

  As shown in Table 5, in each of the above alloys, Examples 4 to 11 are improved in both creep strength and high temperature tensile strength as compared with Comparative Examples 4 to 11. As in the case of Table 4, this is interpreted because both the solid solution amounts of Mn and Fe after brazing were larger in the example than in the comparative example. In addition, about the solid solution amount of Mn and Fe in Example 5 and Comparative Example 5, considering the results of Table 4, it is almost equivalent to other examples of the same brazing conditions (C, E) Inferred. In Comparative Example 12, since the Mn content was less than the specified range, the high temperature tensile strength and creep strength were low. Furthermore, as shown in the remarks column of Table 5 for Comparative Examples 13 to 22, the content of each element was greater than the specified range, so that a test piece was formed normally for the reason described above in the description of each element. There wasn't. Therefore, the item indicated by “---” in Table 5 in the test piece could not be measured.

  The above results were obtained when the flow path member was a plate material. In addition, the extruded material was also evaluated. Hereinafter, the manufacturing method and evaluation of a test piece are demonstrated.

Alloy No. 1 in Table 1 For No. 1, a billet having a diameter of 200 mm was DC-cast, and subjected to hot extrusion at 500 ° C. after homogenization at 600 ° C. for 5 hours. Thereby, an Al—Mn alloy extruded tube 21 having a multi-hole tube shape of 11 holes with a width of 16 mm and a thickness of 1.6 mm was formed. Subsequently, this Al—Mn alloy extruded tube 21 and the brazing sheet fin 22 having the composition shown in Table 2 were combined to form a mini-core 20 as shown in FIG. Thereafter, the brazing sheet fins 22 were removed from the mini-core 20, and the characteristic evaluation unit 23 shown in FIG. 2 was collected from the Al—Mn alloy extruded tube 21 to obtain a test piece. And the collected test piece was fixed with the chuck | zipper of the creep test machine, various stress was applied at 200 degreeC, and the test stress from which the minimum strain rate became 10 ^<-7 > / s was calculated and evaluated as creep strength. The evaluation results are shown in Table 6.

  As shown in Table 6, the results of Examples 12 and 13 that the creep strength was improved as compared with Comparative Examples 23 and 24 were obtained. This result can be explained by the fact that the amount of solid solution of Mn and Fe after brazing is larger in the example than in the comparative example, as in the case of the plate material described above. Thus, it was demonstrated that even when brazing was performed using an Al—Mn alloy extruded material, the creep resistance could be improved by brazing under the conditions of the present invention.

DESCRIPTION OF SYMBOLS 10 Minicore 11 Al-Mn type alloy plate 12 Brazing sheet fin 13 Characteristic evaluation part 20 Minicore 21 Al-Mn type alloy extruded tube 22 Brazing sheet fin 23 Characteristic evaluation part

Claims (2)

A method for producing an aluminum alloy brazing structure for heat exchangers having excellent high-temperature durability, comprising a flow path member that forms a gas or liquid flow path,
Mn: 0.7 to 1.6% by mass, Fe: 0.05 to 0.7% by mass, Si: 0.05 to 0.3% by mass, with the balance being composed of Al and inevitable impurities Brazing using Al-Mn alloy material for at least a part of the flow path member,
Control so that the ultimate temperature of the Al-Mn alloy material at the time of the brazing joining exceeds 610 ° C and is 628 ° C or less;
A method for producing an aluminum alloy brazing structure for heat exchangers having excellent high-temperature durability. The Al-Mn alloy material further includes one or more of Cu, Mg, Ti, Cr, Zr, V, and Ni, each 0.05 to 0.2 mass%.
The manufacturing method of the aluminum alloy brazing structure for heat exchangers of Claim 1 characterized by the above-mentioned.

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