JP5632140B2 - Aluminum alloy automotive heat exchanger and method of manufacturing the same - Google Patents

Description

The present invention relates to an aluminum alloy automotive heat exchanger and a method for manufacturing the same.

  In heat exchangers for automobiles such as evaporators and condensers, refrigerant passage tubes made of aluminum alloy extruded tubes with good lightness and heat conductivity are generally used. In the production of these heat exchangers, for example, A method is generally adopted in which a fluoride-based flux is attached to the tube surface of an aluminum alloy extruded material, and after being assembled with a member such as a fin material in a predetermined structure, brazing is performed in a heating furnace in an inert gas atmosphere. Yes.

  In general, a multi-hole pipe having a plurality of hollow portions partitioned by a plurality of partitions as a refrigerant flow path is used for an extruded tube for a refrigerant passage pipe of an automotive heat exchanger. In recent years, from the viewpoint of reducing environmental impact, it has been required to reduce the weight of heat exchangers in order to improve the fuel efficiency of automobiles, and as a result, it has been required to reduce the thickness of tubes. The extrusion ratio (container cross-sectional area / extruded cross-sectional area) is several hundred to several thousand. Therefore, pure aluminum-based material having good extrudability is used as the refrigerant passage tube material in consideration of extrudability.

In the future, further weight reduction will be promoted, and it is expected that the thickness of the tube will be further reduced. In such a case, it is necessary to increase the strength of the tube material itself. In recent years, there has been a movement to use CO ₂ which is a natural refrigerant in place of CFCs conventionally used as a refrigerant in order to prevent global warming. The CO ₂ refrigerant has a higher operating pressure than the conventional chlorofluorocarbon refrigerant, and it is necessary to increase the strength of the tube material.

Addition of Si, Cu, Mn, Mg, etc. is effective for increasing the strength of the tube material. However, if Mg is contained in the material to be brazed, the fluoride-based flux melted during the heating process It reacts with Mg in the material to produce compounds such as MgF ₂ and KMgF _3, and the activity of the flux is lowered and the brazing property is remarkably lowered. In the case of a heat exchanger using a CO ₂ refrigerant, the operating temperature is as high as about 150 ° C. Therefore, if Cu is contained in the material, the intergranular corrosion sensitivity is remarkably increased. When intergranular corrosion occurs, refrigerant leaks at an early stage and cannot function as a heat exchanger tube.

  Therefore, the achievement of high strength is dependent on the addition of Si and Mn. However, in an alloy in which Mn and Si are added at a high concentration, Mn and Si dissolved in the matrix phase increase the deformation resistance. For example, the extrusion ratio ranges from several hundred to several thousand like the above-mentioned multi-hole pipe. However, the extrudability is extremely inferior to conventional pure aluminum materials. In this case, extrudability refers to the ram pressure required for extrusion and the maximum extrusion speed (limit extrusion speed) that can be obtained without causing the loss of the partition of the hollow part of the multi-hole tube. The higher the value or the lower the limit extrusion speed, the lower the extrudability. Compared to conventional pure aluminum materials, alloys with high concentrations of Mn and Si are more susceptible to ram pressure and die breakage and wear, and the lower limit extrusion speed reduces productivity. descend.

  To increase the strength of the extruded alloy and improve the extrudability, Si and Mn are added to increase the strength, and high temperature homogenization treatment and low temperature are combined to improve the extrudability. A method has been proposed in which the amount of solute elements in the matrix phase is reduced to reduce the deformation resistance. However, in this case, since the amount of the original solute element added is large, high strength can be aimed at, but there is a limit to improving the extrudability, especially the extrusion speed, and both high strength and extrudability, that is, productivity must be completely compatible. It is difficult.

  In addition, the extruded tube for the refrigerant passage tube of the automotive heat exchanger, when penetration occurs due to corrosion during use, the refrigerant leaks and cannot function as a heat exchanger. Zn is adhered to the surface of the substrate in advance by spraying or the like, and Zn is diffused during brazing to form a Zn diffusion layer on the tube surface layer. The Zn diffusion layer functions as a sacrificial anode deeper than that, and the plate thickness In this case, after the tube is extruded, a Zn deposition process such as Zn spraying is required, and in addition, the application of fluoride flux necessary for brazing is applied. Since a flux coating process is required for the entire core after the process or the heat exchanger core is assembled, the manufacturing cost is increased.

  Further, since no brazing material is applied to the tube, a brazing fin material clad with a brazing material is required as a fin material to be assembled. This also increases the cost compared to the case of using a bare fin material in which the brazing material is not clad. Therefore, in general, a mixture of Si powder and fluoride flux is pre-adhered to the surface of the extruded tube and brazed in combination with bare fins with a low potential containing Zn to manufacture a heat exchanger and sacrifice the fins. Means for corrosion protection have been employed as the anode.

  In this case, the step of attaching Zn can be omitted, and an inexpensive bare fin can be used, so the cost can be reduced. However, there is no fin in the vicinity of the header, or there is no fin even if there is a fin. It becomes difficult to prevent corrosion. As a means to solve this problem, a tube is produced using a brazing sheet in which 0.5% or more of Cu is added to the core material and the core material ingot is not homogenized, and the surface layer is formed during brazing heating. A method is proposed in which a layer containing a compound containing Al, Mn, and Si is formed in a layer in which Si is diffused from a clad brazing material, and the tube plate is used as a sacrificial anode to prevent corrosion of the tube plate. .

  However, in actuality, the Cu concentration in the plate surface layer portion decreases due to the diffusion and flow of Cu in the core material into the brazing material. It has become clear that the part has enhanced the anticorrosion effect as a sacrificial anode, and cannot be applied to an extruded material that cannot be clad with a brazing material. In a plate material, it is difficult to form a complicated refrigerant flow path like an extruded material, and there is a problem that heat exchange performance is lowered. When Cu is added to the extruded material as described above, the grain boundary at high temperature Corrosion sensitivity increases. In the case of an extruded material, extrudability is extremely reduced unless the ingot is subjected to a homogenization treatment.

  To improve corrosion resistance by applying Si powder and Zn fluoride to the surface of aluminum extruded multi-hole flat tube for heat exchanger, and forming Zn diffusion layer by substitution reaction with Zn fluoride and aluminum of tube material Although the Zn diffusion layer portion is effectively exhibited as a sacrificial anode layer, there is a problem that the sacrificial anode portion is preferentially corroded.

  By reducing the amount of Si in the Al-Mn alloy, an extruded tube has been proposed that forms a potential gradient that becomes noble as the surface enters the base with a lower base, but the inventors have examined, It has been found that proper homogenization conditions are necessary to obtain such properties.

Japanese Patent Laying-Open No. 2005-256166 Japanese Patent Laid-Open No. 61-202772 Japanese National Patent Publication No. 8-508542 JP 2003-094165 A JP 2009-58167 A

The present invention has been made to solve the above-described conventional problems in the refrigerant passage material of an automobile heat exchanger, and its purpose is to improve strength and corrosion resistance, and to improve productivity and reduce costs. Another object of the present invention is to provide an aluminum alloy automobile heat exchanger in which the refrigerant passage pipe is incorporated, and a method for manufacturing the same.

To achieve the above object, an aluminum alloy automotive heat exchanger according to claim 1 adds a binder to a mixture of Si powder and fluoride flux powder on the surface of a refrigerant passage tube made of an aluminum alloy extruded material. A heat exchanger for automobiles that is assembled by brazing and applying the above-mentioned coating agent, the refrigerant passage tube containing Mn: 0.5 to 1.7% (mass%, the same applies hereinafter), Cu : Less than 0.10%, Si: less than 0.20%, Fe: less than 0.15% , Mg: less than 0.10% , ingot of aluminum alloy having a composition consisting of the balance Al and inevitable impurities Is made of an aluminum alloy extruded material produced by hot extrusion after being subjected to a homogenization treatment at a temperature of 350 ° C. to 580 ° C. for 4 hours or more, and a refrigerant passage tube after brazing heating An Si-diffusion layer is formed in the surface layer part of this, and a precipitation zone of an Al-Mn-Si intermetallic compound is formed in the Si diffusion layer.

The aluminum alloy automotive heat exchanger according to claim 2 is the aluminum alloy extruded material constituting the refrigerant passage pipe according to claim 1, further comprising: Ti: 0.30% or less, Sr: 0.10% or less, Zr : One or more of 0.30% or less are contained .

A method for producing an aluminum alloy automobile heat exchanger according to claim 3 is a method for producing an aluminum alloy automobile heat exchanger according to claim 1 or 2 , wherein the Si powder and fluoride in the mixture are produced. The mixing ratio of the system flux powder is in the range of 10:90 to 40:60, the binder is added so as to be 5 to 40% of the entire coating agent, and the total amount of Si powder and fluoride system flux powder is 5 The outer surface of the refrigerant passage tube is coated to ˜30 g / m ² and brazed and heated to form a Si diffusion layer on the surface layer of the refrigerant passage tube, and Al— It is characterized by forming a precipitation zone of Mn-Si intermetallic compound.

According to the present invention, in an automotive heat exchanger, aluminum formed by brazing and joining a refrigerant passage tube made of an aluminum alloy extruded material that has improved strength and corrosion resistance , and has improved productivity and reduced cost. An alloy automotive heat exchanger and a method of manufacturing the same are provided. The aluminum alloy automotive heat exchanger has good corrosion resistance, and can exhibit good durability even when exposed to a severe corrosive environment as an automotive heat exchanger.

The significance and reason for limitation of the alloy component of the aluminum alloy extruded material for the refrigerant passage tube of the automotive heat exchanger of the present invention will be described.
Mn:
When Mn is added, the decrease in extrudability, particularly the limit extrusion rate, is significantly smaller than when the same amount of Si, Cu or Mg is added. Compared to the case where Si, Cu or Mg is added so as to have the same strength, the decrease in the limit extrusion speed is the smallest when Mn is added, and Mn is an additive component that can achieve both high strength and extrudability, that is, productivity. is there.

  Mn is a pure aluminum alloy that is an alloy for extruded multi-hole pipes that dissolves in the matrix phase and is applied as a refrigerant passage for conventional automotive heat exchangers when joining automotive heat exchangers by brazing heating. Higher strength can be achieved. The preferable content of Mn is in the range of 0.5 to 1.7%. If it is less than 0.5%, the effect of increasing the strength is small, and if it exceeds 1.7%, the extrudability decreases. A more preferable content range of Mn is 0.6% to 1.5%.

Cu:
Cu is limited to a range of less than 0.10%. In an automotive heat exchanger, particularly when used in a CO ₂ refrigerant cycle, etc., the operating temperature becomes a high temperature of around 150 ° C., so that the precipitation of Cu at the grain boundaries of the aluminum alloy extruded material for refrigerant passage pipes is noticeably generated. It becomes easy, and it becomes easy to produce intergranular corrosion sensitivity by precipitation of Cu to a grain boundary. By setting the amount of Cu to less than 0.10%, intergranular corrosion can be suppressed. Moreover, since addition of Cu significantly reduces the extrudability as compared with Mn as described above, the content needs to be limited also from this point. The more preferable content range of Cu for obtaining these more effectively is 0.05% or less.

Si:
Si is limited to less than 0.20%. The Si powder applied to the surface of the refrigerant passage tube melts the surface portion of the refrigerant passage tube by brazing heating to produce an Al—Si eutectic brazing material and also solid-phase diffuses in the refrigerant passage tube. The diffused Si is precipitated by forming a solid solution Mn and an Al—Mn—Si intermetallic compound in the aluminum alloy for the refrigerant passage tube. For this reason, the Si diffusion layer of the aluminum alloy extruded material for refrigerant passage tubes has a lower solid solubility of Mn and Si, and the potential is lower than that of a portion deeper than the Si diffusion layer, that is, a portion where Si is not diffused. Thereby, the Si diffusion layer on the surface layer of the refrigerant passage tube acts as a sacrificial anode layer, and the corrosion penetration life in the depth direction can be improved.

  If the Si content is 0.20% or more, it precipitates as an Al—Mn—Si intermetallic compound at the time of casting, so that the Mn solid solubility decreases. For this reason, even if Si diffuses into the extruded material during brazing heating, precipitation of Al-Mn-Si intermetallic compounds due to this hardly occurs, and from the surface layer of the refrigerant passage tube to the depth of the Si diffusion layer. Not only is the change in potential small, but the amount of Si dissolved increases, so that the potential of the Si diffusion layer becomes noble. Accordingly, the depth from the surface to the depth of the Si diffusion layer does not act as a sacrificial anode layer, and the corrosion penetration life is not improved. A more preferable range of Si is less than 0.10%, and a more preferable range is 0.05% or less.

Fe:
When the Fe content is 0.30% or more, an Al—Mn—Fe intermetallic compound or an Al—Mn—Fe—Si intermetallic compound is formed in the aluminum alloy for refrigerant passage tubes, and the solid solubility of Mn is increased. descend. For this reason, during brazing heating, precipitation of solute Mn by Si diffusion becomes insufficient. Further, when the amount of Fe is increased, the extrudability is lowered and the Al-Mn-Fe intermetallic compound having a noble potential is increased, so that the self-corrosion resistance is lowered. In the present invention, the Fe content is limited to a range of 0.15% or less.

Mg:
Mg is limited to less than 0.10%. If the Mg content is 0.10% or more, the molten fluoride flux reacts with Mg during the brazing heating process to produce compounds such as MgF ₂ and KMgF _3, and the activity of the flux decreases and brazing occurs. Remarkably deteriorates. Mg also significantly reduces extrudability. A more preferable content range of Mg is 0.05% or less.

Ti, Sr, Zr:
Ti forms a high-concentration region and a low-concentration region in the extruded material, and these regions are alternately distributed in the thickness direction of the material, and a low-concentration region is a high-concentration region. Therefore, the corrosion form is layered and the progress of corrosion in the thickness direction is suppressed. This improves pitting corrosion resistance and intergranular corrosion resistance. Further, the addition of Ti improves the strength at normal temperature and high temperature. The preferable content of Ti is in the range of 0.30% or less, and if it exceeds 0.30%, a giant crystallized product is produced during casting, and it becomes difficult to produce a sound extruded material.

  When Sr is added, the Si powder previously applied to the surface of the extruded material reacts with Al of the base material during brazing heating to produce an Al-Si alloy liquid phase brazing, and is co-crystallized when solidified during cooling. The crystal structure is refined and dispersed. Thereby, since the eutectic structure which becomes the anode site on the surface of the material is dispersed, the corrosion is uniformly dispersed to form a planar corrosion form and the corrosion resistance is improved. The preferable content of Sr is in the range of 0.10% or less, and if it exceeds 0.10%, the Al—Si—Sr-based compound crystallizes and the eutectic structure is difficult to refine.

  When Zr is added, the extruded material recrystallizes during brazing heating, but the recrystallized grains at that time become coarse. As a result, the grain boundary density of the extruded material can be reduced, and the Al-Si alloy liquid phase brazing generated by the Si powder previously applied to the surface of the extruded material can be prevented from penetrating into the crystal grain boundaries of the extruded material. It is possible to suppress the occurrence of preferential corrosion on the grain boundaries. The preferable content of Zr is in the range of 0.30% or less, and if it exceeds 0.30%, a giant crystallized product is produced at the time of casting, making it difficult to produce a sound extruded material. When Ti, Sr, and Zr are added in combination, the effect is also obtained in combination.

Manufacture of aluminum alloy extrusions for refrigerant passage tubes:
The manufacturing method of the aluminum alloy extrusion material for refrigerant passage pipes of the present invention is explained.
The aluminum alloy for refrigerant passage pipes having the above composition is melted, ingot is formed by ordinary semi-continuous casting, and the resulting ingot is subjected to a homogenization treatment at a temperature of 350 ° C. to 580 ° C. for 4 hours or more. Then, hot extrusion is performed. This treatment decomposes or granulates coarse crystals formed during casting solidification, homogenizes non-uniform structures such as segregation layers produced during casting, and improves extrudability. Al-Mn based intermetallic compounds can be precipitated. Since the Al—Mn intermetallic compound in the extruded material is fine, when brazed and heated, Mn re-dissolves in the extruded material, and the potential of the refrigerant passage tube can be made noble.

  On the other hand, in the present invention, since the Si powder is preliminarily adhered to the surface of the aluminum alloy extruded material for the refrigerant passage tube before the brazing heating, the aluminum alloy extruded material and the Si powder are alloyed during the brazing heating, and the Al-Si alloy is melted. As the wax is formed, Si diffuses into the surface layer of the extruded material. In the Si diffusion layer, re-dissolved Mn and Si are bonded, and an Al—Mn—Si intermetallic compound is precipitated. For this reason, the solid solubility of Mn and Si decreases in the Si diffusion layer, and the potential becomes lower than that of the deep portion where Si does not diffuse and the Mn solid solubility is high, so that a sacrificial anode layer can be formed. By forming this sacrificial anode layer, the corrosion resistance can be improved when the brazed heat exchanger is used in an actual environment.

  If the homogenization temperature is less than 350 ° C., the decomposition and granulation of coarse crystals formed during casting solidification is insufficient, and if the temperature exceeds 580 ° C., precipitation of Al—Mn intermetallic compounds is sufficient. In addition, since the extrudability deteriorates and the Al—Mn intermetallic compound becomes coarse, re-dissolution during brazing hardly occurs, and the potential of the extruded material is difficult to be noble. A more preferable homogenization treatment temperature is 430 to 570 ° C. Further, the preferable homogenization treatment time is 10 hours or more, less effect is less than 10 hours, even if the treatment is performed for more than 24 hours, it is difficult to obtain further effects, and conversely, it becomes uneconomical. A preferred homogenization time is 10 to 24 hours.

Mixture of Si powder, fluoride flux powder and binder:
In this invention, the coating agent which added the binder to the mixture which consists of Si powder and fluoride system flux powder is apply | coated to the surface of an extrusion material. The purpose is as follows. The Si powder reacts with Al in the extruded material during brazing to produce an Al-Si liquid phase brazing, and the fin material or header material can be joined to the extruded material. Fluoride-based flux powder breaks the oxide film present on the surface of the extruded material during brazing, and enables brazing. The Si diffusion layer formed by melting the Si powder and diffusing into the surface layer of the refrigerant passage tube causes precipitation of the Al—Mn—Si intermetallic compound, thereby reducing the Mn solid solution amount. The potential base effect by reducing the amount of Mn solid solution can form a potential gradient in which the surface is base and the deep part is noble from the surface to the deep part of the extruded material, and the surface part becomes a sacrificial anode to prevent corrosion of the deep part. be able to.

In the present invention, the mixture containing Si powder and fluoride flux powder applied to the surface of the refrigerant passage tube extruded material has a maximum particle size of Si powder of 100 μm or less and a fluoride flux powder having an average particle size of about 5 μm. Configured using Fluoride fluxes include potassium fluoroaluminate fluxes such as KAlF ₄ , K ₂ AlF ₅ , K ₂ AlF ₅ .H ₂ O, K ₃ AlF ₆ , AlF ₃ , Cs ₈ AlF ₆ , CsAlF ₄ · 2H Examples thereof include cesium uroaluminate-based fluxes such as ₂ O and Cs ₂ AlF ₅ .H ₂ O. Compound fluxes containing Zn, such as ZnF ₂ and KZnF ₃ , diffuse Zn on the surface of the refrigerant passage tube during brazing to form a Zn diffusion layer, so that a refrigerant passage tube with a high sacrificial anode effect is obtained. However, in the present invention, the sacrificial anode effect can be obtained even when a flux containing no Zn is used. The smaller the Si powder particle size, the better the fluidity of the Al-Si liquid phase brazing that occurs during brazing heating, and the erosion of the extruded material is also suppressed. The maximum particle size of the Si powder is preferably 30 μm or less, and more preferably 15 μm or less.

  The mixing ratio of the Si powder and the fluoride-based flux powder is 10:90 to 40:60. When the Si powder ratio is less than 10:90, that is, less than 10%, a sufficient liquid phase brazing is not generated at the time of brazing, and bonding failure is likely to occur. When the Si powder ratio exceeds 40:60, that is, when it exceeds 40%, the brazing property decreases due to the decrease in the flux amount. Moreover, when applying these mixed powders, in order to improve adhesion, it is applied to the surface of the extruded material as a coating agent to which a binder such as an acrylic resin is further added. The binder ratio is 5 to 40% of the entire coating agent. When the binder ratio is less than 5% of the entire coating agent, the applied coating agent is easily peeled off. When the binder ratio exceeds 40% of the entire coating agent, the brazing property is lowered.

An appropriate coating amount of the mixture of the Si powder and the fluoride-based flux powder is 5 to 30 g / m ² . If it is less than 5 g / m ² , the bondability is reduced, and if it exceeds 30 g / m ² , the amount of wax produced increases, and the fins and extruded materials are likely to melt and dissolve. In addition, since the thickness of the adhesion film between the extruded material and the fin material increases when assembled in a heat exchanger, when the film thickness decreases due to melting during brazing heating, the overall core size decreases. End up. These mixtures can be applied to the refrigerant passage tube by roll coating.

  When the heat exchanger is manufactured using the refrigerant passage pipe according to the present invention, it is possible to suppress the brazing failure of the fitting portion between the refrigerant passage pipe and the header material. That is, the fitting portion between the refrigerant passage tube and the header material is joined mainly by the brazing material applied to the header material, but the surface of the refrigerant passage tube is also attached with Si powder, and at the time of brazing, the Si powder and the refrigerant are bonded. Since the surface layer portion of the passage pipe is covered with the liquid phase wax generated by melting, the wax of the header material is connected to the liquid phase wax on the surface of the refrigerant passage pipe and can flow freely. The refrigerant passage pipe has a joint portion with fins on the opposite side of the header, and the solder of the header material travels along the surface of the refrigerant passage pipe and is pulled to the fin joint portion by surface tension. For this reason, brazing is insufficient at the header and the refrigerant passage pipe fitting portion, resulting in poor brazing. In particular, when a refrigerant passage pipe made of a conventional pure aluminum alloy or an alloy to which Cu is added is used, brazing failure occurs. On the other hand, when the refrigerant passage pipe is made of the aluminum alloy of the present invention, the refrigerant passage pipe and the header can be used even when the header material having the same amount of brazing material as that of the conventional alloy refrigerant passage pipe is used. There is no brazing failure at the fitting part of the material. This is because the Al—Mn-based precipitates exist on the surface of the aluminum alloy for refrigerant passage pipes according to the present invention, which becomes resistance, and pure aluminum-based alloy, which is a conventional alloy for refrigerant passage pipes, and Cu are added thereto. Compared with the alloy, the wetting and spreading of the liquid phase brazing on the surface can be suppressed, and the brazing of the header material can be suppressed from flowing along the surface of the refrigerant passage tube to the fin joint. Furthermore, in the present invention, since a coating agent obtained by adding a binder to a mixture of Si powder and fluoride-based flux powder is applied to the surface of the refrigerant passage tube and joined to the fin material, conventional Zn spraying or the like is applied to the refrigerant passage tube. Compared with the case where it is applied to the surface, the Zn concentration of the fin material joint fillet can be kept low. Therefore, preferential corrosion of the fin joint fillet can be suppressed, and fin peeling can be suppressed.

  The aluminum alloy heat exchanger according to the present invention can be manufactured by brazing according to a conventional method by combining refrigerant passage tubes made of an aluminum alloy having the above composition, and the manufacturing method is not particularly limited. Further, the heating method in the homogenization treatment of the refrigerant passage tube alloy, the structure of the heating furnace, and the like are not particularly limited. Furthermore, the extrusion shape of the aluminum alloy extruded material for the refrigerant passage tube is selected according to its use, for example, the shape of the heat exchanger. In extruding, since the extrudability of the material is good, it is possible to extrude well using a hollow porous die. When the refrigerant passage tube made of an aluminum alloy extruded material is used as a heat exchanger component, it is assembled with another member (for example, a fin material or a header material) and usually joined by brazing. A bare fin is preferably used as the fin material. The fin material manufacturing method is generally an ingot produced by semi-continuous casting and hot rolling-cold rolling-intermediate annealing-cold rolling, but the intermediate annealing can be omitted. Moreover, the method of manufacturing a hot-rolled sheet directly from a molten metal by continuous casting rolling, and cold-rolling this is also possible. Also, a brazing fin material in which a brazing material is clad on both surfaces of the core material can be used. In this case, the brazing failure between the fin and the refrigerant passage pipe can be surely reduced. The atmosphere, heating temperature, and time during brazing are not particularly limited, and the brazing method is not particularly limited.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. These examples show one embodiment of the present invention, and the present invention is not limited thereto.

Example 1 and Comparative Example 1
For refrigerant passage pipes, billets of aluminum alloys AK having the compositions shown in Table 1 as invention materials and billets of aluminum alloys LV having compositions shown in Table 2 as comparative materials were cast. Aluminum alloy V is generally widely used as a conventional alloy. The following tests 1, 2, and 3 were carried out using these billets.

(Test 1)
About the invention material and the comparative material, the billet was hot-extruded into a multi-hole tube after homogenization treatment at 500 ° C. for 10 hours. At that time, the limit extrusion speed ratio at the time of extrusion (ratio with the limit extrusion speed of the aluminum alloy V) was investigated. The results are shown in Tables 3 and 4. When the limit extrusion speed ratio exceeds 1.0, the extrudability is evaluated as good, and when the ratio is 1.0 or less, the extrudability is evaluated as poor.

(Test 2)
The multi-hole tube hot-extruded in Test 1 was brazed and heated. The heating conditions were heating to 600 ° C. at a temperature increase rate of 50 ° C./min on average in a nitrogen gas atmosphere, and holding down for 3 minutes followed by cooling to room temperature. Thereafter, a tensile test was performed at room temperature. The results are shown in Tables 3 and 4. Those having a tensile strength exceeding the aluminum alloy V are considered good, and those having an aluminum alloy V or less are evaluated as poor.

(Test 3)
The billets of the inventive materials C and D were homogenized under the conditions shown in Tables 5 and 6 and hot-extruded into a multi-hole tube in the same manner, and the limit extrusion speed ratio during extrusion (limit of the aluminum alloy V) The ratio to the extrusion speed) was investigated. The temperature rising rate was 50 ° C./h, and the temperature decreasing rate was left in the furnace. The results are shown in Tables 5 and 6. When the limit extrusion speed ratio exceeds 1.0, the extrudability is evaluated as good, and when the ratio is 1.0 or less, the extrudability is evaluated as poor.

  As shown in Tables 3 and 4, the inventive materials AK obtained excellent results in both the limit extrusion speed ratio and the strength, but in the comparative materials L to U having compositions outside the conditions of the present invention. Was inferior in either the limit extrusion speed ratio or the strength.

  As shown in Tables 5 and 6, the billets of the inventive materials C and D having the composition of the present invention were homogenized under the conditions of the present invention according to Table 5, and an excellent limit extrusion rate ratio was obtained. However, those subjected to homogenization under conditions outside the conditions of the present invention had a poor limit extrusion rate ratio.

Example 2 and Comparative Example 2
Using the slabs of aluminum alloys A to K having the composition shown in Table 1 as the inventive material and aluminum alloys C and V having the composition shown in Table 2 as the comparative material, the homogenization treatment shown in Table 5 and Table 6 was performed and applied. Extruded into a hole tube.

  Using the obtained multi-hole tube as a test material, coating agents obtained by adding an acrylic resin binder to a mixture of Si powder and Noclock flux powder mixed at the ratios shown in Table 7 and Table 8 are shown in Table 7 and Table 8. The surface was coated with a roll coat in an amount and brazed and heated. Thereafter, the following tests 4 to 6 were performed. The evaluation results are shown in Table 7 and Table 8. In addition, it carried out on the conditions which heat to brazing heating and 600 degreeC by the temperature increase rate of 50 degreeC / min on average in nitrogen gas atmosphere, and temperature-fall to room temperature after hold | maintaining for 3 minutes.

(Test 4)
The extruded multi-hole tube after brazing heating was subjected to heat treatment at 150 ° C. for 120 hours simulating high temperature use, and then subjected to intergranular corrosion test by the method specified in ISO11846 method B. Those in which intergranular corrosion did not occur were evaluated as good, and those in which intergranular corrosion occurred were evaluated as poor.

(Test 5)
The potential of the extruded multi-hole tube surface and the deep part after brazing heating and the potential difference between them were measured. The potential was measured by grinding the surface as it was brazed, the deep part from the surface to a depth of 150 μm, and the site where Si and Zn did not diffuse. The measurement was performed by immersing in a 5% NaCl aqueous solution adjusted to pH 3 with acetic acid for 24 hours, and the average of stable measurement values after 10 hours was adopted. A saturated calomel electrode was used as the reference electrode.

(Test 6)
The SWAAT test defined in ASTM-G85-Annex A3 was performed for 1000 h on the extruded multi-hole tube after brazing heating. The maximum corrosion depth of 0.05 mm or less is excellent (◎), 0.05 mm to 0.10 mm or less ○, 0.10 mm to 0.20 mm or less △, 0.20 mm or more to bad (x) evaluated.

  As shown in Table 7, intergranular corrosion was not observed in the test materials 1 to 13 according to the present invention. On the other hand, as shown in Table 8, in the test materials 14 to 23 produced under conditions other than the conditions of the present invention, the test material 23 (using a refrigerant passage tube containing Cu) is markedly grained. Boundary corrosion occurred.

  In the test materials 1 to 13 according to the present invention, sufficient Al—Mn—Si intermetallic compound is precipitated in the Si diffusion layer, so that the surface has a base potential with respect to the deep portion, and the surface and the deep portion. The potential difference was 25 mV.

  On the other hand, in the test materials 14 to 23 manufactured under conditions other than the conditions of the present invention, the test material 14 to 23 having a homogenization temperature higher than the range of the present invention (test material 16) The precipitation of the AlMnSi-based intermetallic compound was insufficient, and the diffusion of Si in the solid solution caused the surface potential to be noble from the deeper part. Even when homogenized according to the present invention, when Cu is contained (test material 23), the surface becomes deeper due to the potential nomination due to solid solution of diffusion Si and the offset of the potential lowering effect of Zn due to Cu. The electric potential was equivalent to that.

  In the SWAAT test, since all of the test materials 1 to 13 according to the present invention had a sufficient potential difference between the surface and the deep portion, the maximum corrosion depth was shallow and excellent corrosion resistance was exhibited. On the other hand, in the test materials 14 to 23 manufactured under conditions other than the conditions of the present invention, those having the same potential at the surface and in the deep portion (test material 23), the surface potential is more noble. The maximum corrosion depth of the sample (test material 16) was large. In addition, among the test materials 14 to 23 produced under conditions other than the conditions of the present invention, the test materials 14, 15, and 17 to 22 had good corrosion resistance evaluation results, but the extrusion failure, the coating film peeling failure, Or, problems such as poor brazing occurred.

Claims (3)

A heat exchanger for an automobile that is assembled by applying a coating agent in which a binder is added to a mixture of Si powder and fluoride-based flux powder to the surface of a refrigerant passage tube made of an aluminum alloy extruded material and brazing. The refrigerant passage tube contains Mn: 0.5 to 1.7% (mass%, the same shall apply hereinafter), Cu: less than 0.10%, Si: less than 0.20%, Fe: 0.15% or less Mg: After being subjected to a homogenization treatment in which an ingot of aluminum alloy having a composition composed of the balance Al and unavoidable impurities is held at a temperature of 350 ° C. to 580 ° C. for 4 hours or longer. The Si diffusion layer is formed in the surface layer portion of the refrigerant passage tube after brazing and heating, and is formed of an aluminum alloy extruded material manufactured by hot extrusion, and the Si diffusion layer is formed of Al-Mn-Si. Intermetallic A heat exchanger for an automobile made of an aluminum alloy, wherein a precipitation zone of a compound is formed. The extruded aluminum alloy material constituting the refrigerant passage tube further contains one or more of Ti: 0.30% or less, Sr: 0.10% or less, Zr: 0.30% or less. The aluminum alloy automotive heat exchanger according to claim 1. The mixing ratio of the Si powder to the fluoride-based flux powder in the mixture is in the range of 10:90 to 40:60, and the binder is added so as to be 5 to 40% of the entire coating agent. The outer surface of the refrigerant passage tube is coated so that the total amount of the fluoride-based flux powder is 5 to 30 g / m ² , brazed and heated, and a Si diffusion layer is formed on the surface layer portion of the refrigerant passage tube. together, according to claim 1 or 2 manufacturing method of an aluminum alloy automotive heat exchanger according to and forming a deposition zone of the Si diffusion layer on the Al-Mn-Si-based intermetallic compound.