JP2011007383A - Aluminum alloy heat exchanger and method for manufacturing refrigerant passage pipe used for the same - Google Patents

Abstract

[Purpose] By using an aluminum alloy refrigerant passage tube with excellent strength and corrosion resistance after brazing and improved extrudability, it has high corrosion resistance and can be further reduced in weight and cost, especially in automobiles. An aluminum alloy heat exchanger suitable as a heat exchanger for use is provided.
[Structure] An aluminum alloy heat exchanger in which a mixture containing Si powder and a fluoride-based flux is applied to the surface of an aluminum alloy refrigerant passage tube, and fins are assembled and brazed. And Mn 0.5 to 1.7%, and is composed of an extruded material of an aluminum alloy composed of the balance Al and inevitable impurities, and the fin is made of Zn: 0.3 to 4.0%, Mn 0.8 to 1 It is characterized in that it is made of an aluminum alloy containing the remaining Al and unavoidable impurities, and a Zn diffusion layer is formed in the surface layer portion of the refrigerant passage tube.
[Selection figure] None

Description

  The present invention relates to an aluminum alloy heat exchanger and a method for producing a refrigerant passage tube used in the heat exchanger.

  For heat exchangers for automobiles such as an evaporator and a condenser, an aluminum alloy having good lightness and heat conductivity is generally used. In these heat exchangers, for example, an aluminum alloy extruded tube is used as a refrigerant passage tube, and a fluoride-based flux is attached to the surface of the heat exchanger, and after a member such as a fin material is assembled in a predetermined structure, the inside of a heating furnace in an inert gas atmosphere is used. In general, a method of brazing and joining is employed.

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

In the future, further weight reduction of the heat exchanger is expected, and it is expected that the thinning of the tube will further progress accordingly. In this case, it is necessary to increase the strength of the tube material itself. In recent years, in order to prevent global warming, there has been a movement to use CO ₂ which is a natural refrigerant instead of CFC which is conventionally used as a refrigerant. CO ₂ refrigerant has a higher operating pressure than conventional CFC refrigerant. From the point of view, it is necessary to increase the strength of the tube material.

The 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 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 addition, in 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, and intergranular corrosion is reduced. If it occurs, the refrigerant leaks early and cannot function as a tube of the heat exchanger.

  Therefore, the policy for increasing the strength must be 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 increases from several hundred to several thousand like the extruded multi-hole tube. As far as this is concerned, the extrudability is extremely inferior compared to conventional pure Al-based 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 material or the lower the critical extrusion speed, the poorer the extrudability. In the alloy with Mn and Si added at a high concentration, the ram pressure rises and the die breaks and wears compared to the conventional pure Al material. It becomes easy to occur, and the limit extrusion speed is also lowered, so that productivity is lowered.

  As a policy for increasing the strength and extrudability of extruded alloys, for example, adding Si and Mn to increase strength, combining high-temperature homogenization processing and low-temperature homogenization processing to improve extrudability A method has been proposed to reduce the solid solution amount of the solute element in the matrix and to reduce the deformation resistance, but in this case, the amount of the original solute element added is high, so high strength can be aimed at However, there is a limit to improving the extrudability, in particular, the extrusion speed, and it is difficult to achieve both high strength and extrudability, that is, productivity.

  In addition, if the refrigerant passage pipe of the automobile heat exchanger is penetrated by corrosion during use, refrigerant leakage occurs and the function as the heat exchanger cannot be achieved. For this reason, conventionally, Zn is adhered to the surface of the extruded tube for refrigerant passage in advance by thermal spraying or the like, and Zn is diffused by brazing, and at that time, the Zn diffusion layer formed on the tube surface layer is deeper than that. It acts as a sacrificial anode and suppresses corrosion in the thickness direction, extending the penetration life. In this case, after the tube is extruded, a Zn deposition process such as Zn spraying is required, and then the entire process of the fluoride core flux application process necessary for brazing, or after being assembled to the heat exchanger core. Since a flux coating process is required, the manufacturing cost increases. Further, since no brazing material is applied to the tube, brazing fins clad with the brazing material are required for the fin material to be assembled. This also leads to an increase in cost compared to the case where a bare fin material in which the brazing material is not clad is used.

As a means for solving these difficulties, Si powder and fluoride-based flux are applied to the surface of an extruded refrigerant passage tube made of pure aluminum-based A1050 alloy or Al-0.4% Cu alloy, Although possible to produce a heat exchanger assembly has been proposed, when the refrigerant tube is pure aluminum-based alloy can not be ensured strength, we can not meet the demand for thinning, CO ₂ It cannot be applied to a heat exchanger that requires high strength, such as a heat exchanger using a refrigerant. Although the refrigerant tube is in the case of Al-0.4% Cu alloy high strength compared to pure aluminum-based alloy can be obtained, for containing Cu, high temperatures when applied to a heat exchanger using a CO ₂ refrigerant There is concern about intergranular corrosion.

  For a heat exchanger using a conventional refrigerant used at room temperature, in the Zn diffusion layer formed on the surface of the refrigerant passage tube by melting a part of the Zn-containing fin, the Zn concentration is low, and Cu is contained in the refrigerant passage tube. Therefore, the surface potential of the refrigerant passage tube is not sufficiently reduced, and therefore, in the thickness direction of the refrigerant tube, the surface layer is necessary to prevent corrosion of the refrigerant passage tube itself, and the surface layer is base and the deep portion is not deep. A sufficient potential gradient is not formed. This is because, when the Zn concentration is low and coexists with Cu, the potential noble effect by Cu works more significantly than the potential base effect by Zn. Furthermore, Si applied in advance on the surface layer of the refrigerant passage tube diffuses by brazing to form a diffusion layer, and this diffusion layer also works in a direction to make the surface layer potential noble, and additionally obstructs the formation of the potential gradient. To do.

  Since the Si diffusion layer makes the potential of the refrigerant passage tube noble, there is also a corrosion resistance evaluation by the CASS test that can improve the corrosion resistance compared to the refrigerant passage tube without the Si diffusion layer. When the liquid is sprayed and the specimen is always covered with a liquid film having a high conductivity, the cathodic protection effect acts more widely. Since the passage tube can be subjected to cathodic protection, and in most cases, it becomes a dry and wet repetitive environment in an actual use environment, so the range in which the cathodic protection effect acts is limited to a very narrow range. It is difficult to prevent corrosion of the refrigerant passage tube only by cathodic protection by making the potential of the current higher than that of the fin. In particular, the evaporator is covered with condensed water due to condensation, and this condensed water has a very low conductivity compared to the CASS test solution, so that it acts on a wide range of the cathodic protection effect even if it is always covered. Therefore, it is difficult to cathodic-protect the refrigerant passage tube. In order to prevent corrosion of the refrigerant passage pipe even in these environments, it is necessary to give a sufficient potential gradient to the refrigerant passage pipe itself so that the surface layer is base and the deep portion is noble.

  The tube is coated with Si powder with a maximum particle size of 30 μm or less together with a flux that does not contain Zn and fins, and the potential of the tube after brazing is no less than 50 mV higher than the fins, improving the corrosion resistance of the fillet. Although a heat exchanger is proposed, there is a problem that self-corrosion of the fin is large because it relies on corrosion prevention by using a base fin. In addition, as described above, in the actual use environment, it becomes a repeated dry and wet environment, and in particular, the evaporator is covered with low-conductivity condensed water. It is not possible to cathodic-protect the refrigerant passage tube by itself.

Japanese Patent Laying-Open No. 2005-256166 JP 2000-351062 A JP 2009-58139 A

  The present invention uses a fin containing Zn as a technique for solving the above-mentioned conventional problems in a heat exchanger for an automobile and an aluminum refrigerant passage tube, and Zn evaporated from the fin surface during brazing adheres to the surface of the refrigerant passage tube. The pitting corrosion resistance of the refrigerant passage pipe was found to be remarkably improved when a Zn diffusion layer having a concentration gradient is formed in the surface portion of the refrigerant passage pipe by diffusing into the refrigerant passage pipe. An object of the present invention is to provide an aluminum alloy heat exchanger that has high corrosion resistance, can be further reduced in weight and cost, and is particularly suitable as a heat exchanger for automobiles. Moreover, the other object of this invention is to provide the manufacturing method of the refrigerant path pipe | tube for improving the extrudability of the aluminum alloy which comprises the refrigerant path pipe | tube used for the said heat exchanger.

  To achieve the above object, an aluminum alloy heat exchanger according to claim 1, a mixture containing Si powder and a fluoride-based flux is applied to the surface of an aluminum alloy refrigerant passage tube, and fins are assembled. In the aluminum alloy heat exchanger to be brazed, the refrigerant passage tube contains 0.5 to 1.7% (mass%, hereinafter the same) of Mn, and the extruded material of the aluminum alloy consisting of the balance Al and inevitable impurities The fin is composed of an aluminum alloy containing Zn: 0.3 to 4.0%, Mn 0.8 to 1.7%, the balance Al and unavoidable impurities, A Zn diffusion layer is formed in the surface layer portion.

  An aluminum alloy heat exchanger according to claim 2 is the heat exchanger made of aluminum alloy according to claim 1, wherein the refrigerant passage tube further includes one or more of Ti 0.30% or less, Sr 0.10% or less, Zr 0.30% or less. An aluminum alloy extruded material containing

  An aluminum alloy heat exchanger according to a third aspect is characterized in that, in the first or second aspect, the refrigerant passage tube is an aluminum alloy extruded material in which the Cu content is regulated to less than 0.10%.

  An aluminum alloy heat exchanger according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the refrigerant passage tube is an aluminum alloy extruded material in which the Si content is regulated to less than 0.10%. And

  An aluminum alloy heat exchanger according to claim 5 is the aluminum alloy heat exchanger according to any one of claims 1 to 4, wherein the fin contains 0.3 to 4.0% Zn, 0.8 to 1.7% Mn, and further contains Si0. 2 to 0.6%, Fe 0.1 to 0.7%, Mg 0.05 to 0.3%, Cu 0.5 or less, Cr 0.3% or less, Zr 0.3% or less, Ti 0.3% or less It contains seeds or two or more, and is composed of the balance Al and inevitable impurities.

  An aluminum alloy heat exchanger according to claim 6 is the heat exchanger made of aluminum alloy according to claims 1 to 5, wherein the fin material further contains one or two of In 0.001 to 0.10% and Sn 0.001 to 0.10%. It is characterized by doing.

  A method of manufacturing a refrigerant passage tube according to claim 7 is a method of manufacturing the refrigerant passage tube used in the aluminum heat exchanger according to any one of claims 1 to 6, wherein The aluminum alloy ingot constituting the refrigerant passage tube described above is subjected to a homogenization heat treatment at a temperature of 400 ° C. to 650 ° C. for 4 hours or more and then hot extrusion.

  The manufacturing method of the refrigerant path pipe | tube by Claim 8 is a method of manufacturing the said refrigerant | coolant path pipe | tube used for the aluminum heat exchanger in any one of Claims 1-6, Comprising: Any of Claims 1-3 First-stage heat treatment in which the aluminum alloy ingot constituting the refrigerant passage tube is kept at a temperature of 570 ° C. to 650 ° C. for 2 hours or more, and then lowered to a temperature of 400 ° C. to 550 ° C. for 3 hours or more. A hot-extrusion process is performed after the homogenization heat treatment including the second-stage heat treatment to be held.

  A method of manufacturing a refrigerant passage pipe according to claim 9 is a method of manufacturing the refrigerant passage pipe used in the aluminum heat exchanger according to any one of claims 1 to 6, wherein The first-stage heat treatment in which the aluminum alloy ingot constituting the refrigerant passage tube is kept at a temperature of 570 ° C. to 650 ° C. for 2 hours or more, and then the temperature is lowered to room temperature, and then the temperature of 400 ° C. to 550 ° C. The material is characterized by being subjected to hot extrusion after being subjected to a homogenization heat treatment comprising a second-stage heat treatment for 3 hours or more.

  According to the present invention, by using a refrigerant passage tube made of an aluminum alloy having excellent strength and corrosion resistance after brazing and improved extrudability, it is possible to achieve high corrosion resistance and further reduce weight and cost. In particular, an aluminum alloy heat exchanger suitable as an automotive heat exchanger is provided. Moreover, the manufacturing method of the refrigerant path pipe | tube for improving the extrudability of the aluminum alloy which comprises the refrigerant path pipe | tube used for the said heat exchanger is provided.

The significance and reasons for limitation of the alloy components in the aluminum alloy extruded material constituting the refrigerant passage tube of the aluminum alloy heat exchanger of the present invention will be described.
Mn:
Mn is solid-dissolved in the parent phase after brazing and heat-bonding the heat exchanger, and it becomes possible to increase the strength compared to a pure aluminum alloy that constitutes a conventional extruded multi-hole tube for an automobile heat exchanger. Further, when Mn is added, the decrease in extrudability, particularly the limit extrusion speed, is remarkably small as compared with the case where 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 addition of Mn has the smallest decrease in the limit extrusion speed, and is an alloy component that can achieve both high strength and extrudability, that is, productivity. . The preferable content is in the range of 0.5 to 1.7%, and if it is less than 0.5%, the effect of increasing the strength is small, and if it exceeds 1.7%, a decrease in extrudability is observed. A more preferable content range is 0.6% to 1.5%.

Si:
Si is limited to less than 0.10%. As a result, the following effects are obtained. The Si powder applied to the surface of the refrigerant passage tube diffuses into the refrigerant passage tube by brazing heating, and forms and precipitates Mn in the aluminum alloy constituting the refrigerant passage tube and an Al-Mn-Si intermetallic compound. . Due to this precipitation, the solid solubility of Mn and Si decreases in the Si diffusion layer of the refrigerant passage tube, and the potential of the Si diffusion layer is lower than that of a portion deeper than the Si diffusion layer, that is, a portion where Si is not diffused. Turn into. As a result, from the surface to the depth of the Si diffusion layer, it acts as a sacrificial anode layer for deeper portions, and the corrosion penetration life in the depth direction can be improved.

  When the amount of Si is 0.10% or more, since an Al—Mn—Si based metal compound is present in the aluminum alloy constituting the refrigerant passage tube from the beginning, the Mn solid solubility in the alloy also decreases. In this case, even if the Si powder applied to the surface by brazing heating diffuses into the alloy, the precipitation of Al-Mn-Si intermetallic compounds is reduced, and the potential in the Si diffusion layer becomes lower. Therefore, 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 amount of Si for obtaining the above effect is in the range of 0.05% or less.

Cu:
Cu is limited to less than 0.10%. Thereby, the following effects (1) to (3) are obtained. (1) It is possible to suppress intergranular corrosion during use of a heat exchanger for automobiles that has been brazed and heat-joined, particularly during use at high temperatures. When the amount of Cu is 0.10% or more, particularly when used in a CO ₂ refrigerant cycle, the operating temperature becomes a high temperature of around 150 ° C., and precipitation of Cu or the like occurs remarkably at the grain boundaries, and the intergranular corrosion sensitivity. Becomes larger. (2) Addition of Cu significantly reduces the extrudability as compared with Mn as described above. From this point as well, the amount added must be limited.

  (3) Generally, it is known that when Zn is added, the potential is reduced, and when Cu is added, the potential becomes noble. It has been found that when the amount is small, the potential noble effect due to Cu acts more remarkably. In the present invention, the Zn diffusion layer formed by the adhesion and diffusion of Zn evaporated from the fin during brazing to the surface of the refrigerant passage tube is compared with the Zn diffusion layer formed on the surface of the refrigerant passage tube by conventional Zn spraying or the like. The surface Zn concentration is low. For this reason, if Cu is contained in the refrigerant passage tube by 0.10% or more, the potential noble effect of Cu contained in the potential diffusion effect due to the Zn diffusion layer formed by Zn evaporated from the fin is offset. Thus, despite the presence of the Zn diffusion layer, the potential of the surface layer of the refrigerant passage tube does not become lower, and a potential gradient is formed in which the surface layer is lower and the deep portion is noble with respect to the thickness direction of the refrigerant passage tube. It is not possible to prevent the deep portion from being corroded by using the surface layer as a sacrificial anode in the refrigerant passage tube itself, and the penetration life cannot be improved. In practice, there is a Si diffusion layer on the surface of the refrigerant passage tube due to the applied Si powder, and this also works in the direction of making the surface potential noble. In addition, when the Cu content is large, the potential nomination effect due to Cu is completely more dominant than the potential neutralization effect due to the Zn diffusion layer, and coupled with the potential noble effect due to the Si diffusion layer, A potential gradient is formed in which the surface layer is noble and the deep part is base in the thickness direction. In this case, since the deeper part becomes the anode with respect to the surface layer of the refrigerant passage pipe, the penetration becomes earlier. On the other hand, when the Cu content is limited to less than 0.10%, the surface layer of the refrigerant passage tube is obscured even in the low-concentration Zn diffusion layer, the surface layer is base and the deep portion is noble, and the surface of the refrigerant passage tube is used as a sacrificial anode. It is possible to form a potential distribution in the thickness direction sufficient to prevent corrosion at the deep part. A more preferable Cu content range is 0.05% or less, and more preferably 0.03% or less.

Ti, Sr, Zr:
The addition of Ti forms a high-concentration region and a low-concentration region in the alloy, and these regions are distributed alternately in the thickness direction of the material, and the low-concentration region is a high-concentration region. Since corrosion preferentially compared to the region, the corrosion form is layered and progress of corrosion in the thickness direction is suppressed, thereby improving pitting corrosion resistance and intergranular corrosion resistance. Further, the addition of Ti improves the strength at normal temperature and high temperature. The preferable Ti content 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 healthy refrigerant passage tube.

  The addition of Sr is caused by the fact that the Si powder previously applied to the surface of the refrigerant passage tube reacts with Al of the base material during brazing heating to form an Al-Si alloy liquid phase brazing and crystallizes when solidified during cooling. Functions to refine and disperse the crystal structure. When the eutectic structure serving as 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 preferred Sr content is in the range of 0.10% or less, and if it exceeds 0.10%, the Al—Si—Sr compound is crystallized and the eutectic structure is not refined.

  The addition of Zr coarsens the recrystallized grains when the refrigerant passage tube alloy is recrystallized by brazing heating. By coarsening, the grain boundary density of the base material can be reduced, and the Al-Si alloy liquid phase brazing generated by the Si powder previously applied to the surface of the refrigerant passage tube penetrates into the crystal grain size of the base material. It can suppress and it can suppress that the preferential corrosion to a grain boundary arises. 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 generated at the time of casting, making it difficult to produce a sound refrigerant passage tube. In addition, when the elements of Ti, Sr, and Zr are added in combination, the effect can be obtained in combination.

  The preferred production conditions of the aluminum alloy extruded material constituting the refrigerant passage tube of the aluminum alloy heat exchanger of the present invention will be described. The aluminum alloy having the above composition is melted and cast, and the obtained ingot is 400 ° C. A hot extrusion process is performed after performing the homogenization process hold | maintained at the temperature of -650 degreeC for 4 hours or more. By this homogenization treatment, a coarse crystallized product formed during casting solidification can be decomposed or granulated, and a non-uniform structure such as a segregation layer generated during casting can be homogenized. If coarse crystals remain during hot extrusion, or if a heterogeneous structure such as a segregation layer formed during casting remains, these will become resistance during extrusion and reduce extrudability. This leads to a reduction in the surface roughness of the subsequent product. If the homogenization treatment temperature is less than 400 ° C, the above effect is difficult to obtain. The higher the homogenization treatment temperature, the more the above effect is promoted, but if the temperature is too high, the upper limit may be 650 ° C or less. And A more preferable homogenization temperature is 430 to 620 ° C. In addition, since a longer treatment time is more effective, the homogenization treatment time should be 10 hours or more. However, even if the treatment is performed for more than 24 hours, it is difficult to obtain a further effect, and conversely, Since it becomes economical, it is preferable to set it as 10 to 24 hours.

  The ingot may be combined with a high-temperature homogenization treatment and a low-temperature homogenization treatment, which makes it possible to further improve the hot extrudability and reduce the generation of aluminum debris. The aluminum residue refers to a defect that is discharged from the die when the aluminum pieces accumulated in the die during extrusion become a certain size and adheres to the surface of the extruded aluminum material for refrigerant passage tube. The high-temperature homogenization process (first stage heat treatment) is a process of holding at 570 to 650 ° C. for 2 hours or more. By this process, the coarse crystallized product formed at the time of casting solidification is decomposed or granulated. And can be dissolved again. If it is less than 570 ° C., re-dissolution does not proceed easily. The higher the homogenization treatment temperature is, the more effective, but if the temperature is too high, there is a risk of melting, so the temperature is set to 650 ° C. or lower. A more preferable homogeneous treatment temperature is 580 to 620 ° C. Further, the treatment time is preferably longer, but even if the treatment is performed for more than 24 hours, it is difficult to obtain a further effect and, on the contrary, it becomes uneconomical. Therefore, the treatment is preferably performed for 5 to 24 hours.

  After performing the high-temperature homogenization treatment (first-stage heat treatment) and then performing the homogenization treatment at a lower temperature (second-stage heat treatment) than this, Mn dissolved in the matrix phase is precipitated, Since the solid solubility of Mn can be reduced, the deformation resistance in the subsequent hot extrusion can be reduced and the extrudability can be improved. The temperature range of the homogenization treatment (second stage heat treatment) at a low temperature is 400 to 550 ° C. When the temperature is lower than 400 ° C., the amount of precipitation is small, and the effect of reducing deformation resistance is insufficient. When the temperature exceeds 550 ° C., precipitation hardly occurs, and the effect of reducing deformation resistance is insufficient. The processing time is 3 hours or more. If it is less than 3 hours, such precipitation does not occur sufficiently, so that the effect of reducing deformation resistance is insufficient. In addition, a longer treatment time is more effective, but even if the treatment is performed for more than 24 hours, it is difficult to obtain a further effect, which is uneconomical. The treatment is preferably performed for 5 to 15 hours. The above-mentioned two-stage homogenization treatment is for precipitating Mn sufficiently homogeneously dissolved by the first-stage heat treatment by the second-stage heat treatment, and whether or not to perform these two-stage homogenization processes continuously? There is no particular limitation. That is, the second-stage heat treatment may be performed continuously after the first-stage heat treatment, or after the first-stage heat treatment, the ingot is once cooled to 200 ° C. or lower and then reheated to perform the second-stage heat treatment. Also good.

Mixture containing Si powder and fluoride flux powder:
In the present invention, the mixture containing Si powder and fluoride flux powder applied to the surface of the refrigerant passage tube extrusion 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 A preferable range of the maximum particle size of the Si powder is 30 μm or less, and a more preferable range is 15 μm or less. Fluoride fluxes include potassium fluoroaluminate fluxes such as KAlF ₄ , K ₂ AlF ₆ , 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, even when a flux not containing Zn is used, the same sacrificial anode effect can be obtained by forming the Zn diffusion effect by Zn evaporated from the fin.

The mixing ratio of the Si powder and the fluoride-based flux powder is a mass ratio (Si powder: fluoride-based flux = 10: 90 to 40:60). When the Si powder ratio is less than 10%, sufficient brazing is not generated at the time of brazing, and bonding failure is likely to occur. On the other hand, when the Si powder ratio exceeds 40%, the ratio of the fluoride-based flux powder decreases, and the brazing property is inferior. Moreover, when applying these mixed powders, a binder such as an acrylic resin may be added and applied as a coating agent in order to improve adhesion. 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, peeling of the adhering mixture tends to occur. When the binder ratio exceeds 40% of the entire coating agent, the brazing property is lowered. The coating amount is appropriately 5 to 30 g / m ² as a mixture of Si powder and fluoride flux powder. If it is less than 5 g / m ² , the bondability will be reduced, and if it exceeds 30 g / m ² , the amount of wax produced will increase, and fins and base metals will be easily melted and dissolved.

  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. 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 of 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, a mixture containing Si powder and fluoride-based flux is applied to the surface of the refrigerant passage tube and joined to the fin material, so that compared with the case where conventional Zn spraying is applied to the surface of the refrigerant passage tube. 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 significance and reasons for limitation of the alloy components in the aluminum alloy constituting the fin of the aluminum alloy heat exchanger of the present invention will be described.
Zn:
In the present invention, when a mixture of Si powder and fluoride-based flux powder is applied to the refrigerant passage tube and the fin containing Zn is assembled and brazed, Zn evaporates from the fin surface during brazing and the surface of the refrigerant passage tube The adhered Zn diffuses in the thickness direction of the refrigerant passage tube to form a Zn diffusion layer having a concentration gradient in the surface layer portion of the refrigerant passage tube. This Zn diffusion layer lowers the surface potential of the refrigerant passage tube, and forms a potential gradient in which the surface layer is base and the deep portion is noble with respect to the plate thickness direction. Thus, the deep portion can be cathodic-proofed and penetration due to corrosion can be suppressed. The amount of Zn evaporated from the fins and adhering to the refrigerant passage tube is affected by the shape of the fins to be combined. When the distance from the surface of the refrigerant passage tube to the fin surface is short, more Zn is deposited than when the distance is long. Therefore, it is more preferable to use corrugated fins in order to efficiently attach Zn to the refrigerant passage tube. When corrugated fins are used, the amount of Zn attached to the refrigerant passage tube varies depending on the fin pitch and fin height.

  The preferable Zn content in the aluminum alloy constituting the fin is in the range of 0.3 to 4.0%. When the Zn content is less than 0.3%, the fin pitch is made as small as possible or the fin height is made low. However, the amount of Zn adhering to the surface of the refrigerant passage tube is small, and the surface of the refrigerant passage tube is formed by diffusion of the Si powder previously applied to the surface of the refrigerant passage tube in the thickness direction of the refrigerant passage tube during brazing. There is also a potential nobleening effect, and a sufficient potential lowering effect on the surface of the refrigerant passage tube cannot be expected. If the amount of Zn in the fin exceeds 4.0%, the amount of Zn adhering to the refrigerant passage tube will be sufficient if the fin shape is normally used as a heat exchanger, but the potential of the fin itself is extremely low. In the use environment where the fins and self-corrosion resistance decrease, the potential difference between the fins and the refrigerant passage pipe increases, and the liquid is constantly exposed to high conductivity liquid, the anode fins are quickly corroded and consumed. End up. The more preferable Zn content range of the fin is 0.5 to 2.5%.

Mn:
Mn increases the strength of the fin material. A preferable content of Mn is in the range of 0.8 to 1.7%. If it is less than 0.8%, the effect is small, and if it exceeds 1.7%, giant crystals are produced during casting, making it difficult to produce a sound fin material. A more preferable content range of Mn is 0.6 to 1.5%.

Si, Fe, Cu, Mg, Cr, Zr, Ti:
Si improves the strength of the fin material. A preferable content of Si is in the range of 0.2 to 0.6%. If it is less than 0.2%, the effect is small, and if it exceeds 0.6%, the melting point of the fin material is lowered, and local melting is likely to occur during brazing heating.

  Fe improves the strength. The preferable content of Fe is in the range of 0.1 to 0.7%. If the content is less than 0.1%, the effect is small. If the content exceeds 0.7%, the amount of the Al—Fe noble compound increases, so that the self-corrosion resistance of the fin material decreases.

  Mg improves the strength of the fin material. A preferable content of Mg is in the range of 0.05 to 0.3%. If the content is less than 0.05%, the effect is small, and if the content exceeds 0.3%, when heat brazing in an inert gas atmosphere using a fluoride-based flux, Mg becomes a fluoride-based flux during brazing. It reacts to produce Mg fluoride, which lowers the brazing property and makes the appearance of the brazed part unclear. A more preferable content range of Mg is 0.05 to 0.15%.

  Cu improves the strength. A preferable content of Cu is in the range of 0.5% or less. If the content exceeds 0.5%, the potential of the fin material becomes noble, and the corrosion resistance of the refrigerant passage tube is impaired. In addition, the self-corrosion resistance of the fin material also decreases.

  Cr and Zr have the effect of making the crystal grain size after brazing coarse and reducing the buckling of fins during brazing heating. The preferable contents of Cr and Zr are both in the range of 0.3% or less. When both contain more than 0.3%, a giant crystallized product is produced at the time of casting, which makes it difficult to produce a sound fin material.

  Ti forms a high-concentration region and a low-concentration region, and these regions are distributed alternately in the thickness direction of the material, and the Ti-concentration region corrodes preferentially over the high-concentration region. Therefore, the corrosion form becomes 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 0.3% or less. If the content exceeds 0.3%, a giant crystallized product is generated at the time of casting, which makes it difficult to produce a sound fin material.

In, Sn:
In and Sn lower the potential of the fin material by adding a small amount, exert a sacrificial anode effect on the refrigerant passage tube, and prevent pitting corrosion of the refrigerant passage tube. The preferred contents of In and Sn are both in the range of 0.001 to 0.10%, and if both are less than 0.001%, the effect is small, and if it exceeds 0.10%, the self-corrosion resistance of the fin material decreases. To do.

  Generally, the fin material is produced by semi-continuous casting to produce an ingot, and hot rolling-cold rolling-intermediate annealing-cold rolling is generally used, but intermediate annealing is omitted. You can also. Moreover, the method of producing a hot-rolled sheet directly from a molten metal by continuous casting rolling, and manufacturing by cold rolling is also possible.

  The heat exchanger of the present invention can be manufactured by assembling the refrigerant passage tube having the above composition and the fin material and brazing by a conventional method, and the manufacturing method is not particularly limited. The heat exchanger of the present invention has good corrosion resistance, and can exhibit good durability even when mounted on an automobile in a severe corrosive environment, for example. There is no particular limitation on the heating method and the structure of the heating furnace in the homogenization treatment of the aluminum alloy constituting the refrigerant passage tube. Moreover, the extrusion shape of the aluminum extrusion material which comprises a refrigerant path pipe | tube is not specifically limited, The extrusion shape is selected according to the use, for example, the shape of a heat exchanger. In extruding, since the extrudability of the material is good, it is possible to extrude well using a hollow porous die. For example, when a refrigerant passage tube for a heat exchanger is used as a heat exchanger component, it is assembled with other members (for example, fin material or header material) and is usually joined by brazing, but the atmosphere and heating temperature during brazing. The time is not particularly limited, and the brazing method is not particularly limited.

  In order to produce aluminum alloy extruded materials for refrigerant passage tubes, billets of aluminum alloys (alloys A to L) having the compositions shown in Table 1 and aluminum alloys (alloys MT) having the compositions shown in Table 2 were ingoted. . The alloy T is generally widely used as a conventional alloy. The following tests 1, 2, and 3 were carried out using these billets. In Table 2, those outside the conditions of the present invention are underlined.

(Test 1)
The ingot billet was homogenized at 600 ° C. for 10 hours, and then hot extruded into a multi-hole tube. At that time, the limit extrusion speed ratio at the time of extrusion (relative ratio with respect to the limit extrusion speed of the alloy T) was investigated. The results are shown in Tables 3 and 4. Those having a limit extrusion speed ratio exceeding 1.0 were evaluated as having good extrudability (◯), and those having less than 1.0 were evaluated as having poor extrudability (x).

(Test 2)
The multi-hole tube extruded in Test 1 was brazed and heated. The heating conditions were heating to 600 ° C. at a rate of temperature increase of 50 ° C./min on average in a nitrogen gas atmosphere, holding the temperature for 3 minutes, and then cooling to room temperature. Thereafter, a tensile test was performed at room temperature. Tables 3 and 4 show the tensile strength. When the tensile strength exceeded that of the alloy T, the strength property after brazing was good (◯), and when the tensile strength was less than the tensile strength of the alloy T, the strength property after brazing was evaluated as poor (×).

(Test 3)
The billets of aluminum alloys C and D were homogenized under the conditions shown in Table 5 and Table 6, and then hot-extruded into a multi-hole tube in the same manner, and the critical speed ratio (relative to the critical extrusion speed of alloy T) Ratio). The temperature increase rate was 50 ° C./h, the temperature decrease rate when the first-stage heat treatment and the second-stage heat treatment were continuously performed was 25 ° C./h, and the temperature decrease rate after the completion of the second-stage heat treatment was left in the furnace. Tables 5 and 6 show the results of investigation of the limit speed ratio. Those having a limit extrusion speed ratio exceeding 1.0 were evaluated as having good extrudability (◯), and those having less than 1.0 were evaluated as having poor extrudability (x).

  As shown in Tables 3 to 4, the refrigerant passage aluminum alloys A to L according to the present invention showed excellent results in both extrusion characteristics and brazing characteristics. On the other hand, the aluminum alloy MS for refrigerant passages outside the conditions of the present invention was inferior in either extrusion characteristics or brazing characteristics.

  Moreover, about what performed the homogenization process on the conditions shown in Table 5 and Table 6 using the aluminum alloys C and D for refrigerant paths according to this invention, the homogenization process on the conditions (condition shown in Table 5) according to this invention However, the extrusion characteristics were inferior when the homogenization treatment was performed under conditions outside the conditions of the present invention.

  Next, slabs of aluminum alloys (alloys a to l) having the compositions shown in Table 7 and aluminum alloys (alloys mx) having the compositions shown in Table 8 were ingoted as the aluminum alloy for the fin material. About the ingot slab, after performing a predetermined homogenization treatment, hot rolling, cold rolling to finish a fin material with a thickness of 0.1 mm, corrugation is performed on the dimensions shown in Table 9 and Table 10, The aluminum channel extruded multi-hole tube for refrigerant passage (shown as an alloy in Tables 9 and 10) and the corrugated fin (shown as a fin material alloy in Tables 9 and 10) 9 and Table 10 were combined and brazed to produce a heat exchanger core. In Tables 7 and 8, those outside the conditions of the present invention are underlined.

Regarding the production status of the heat exchanger core, those that could be produced without any defects were evaluated as good core production status (◯), and those with defects were evaluated as poor core production status (×), and the results are shown in Table 9 and Table 10. Show. In addition, the homogenization treatment of the extruded multi-hole tube is performed under the condition of holding at 600 ° C. for 10 hours in accordance with the present invention. A coating agent obtained by adding a binder to the mixed powder mixed at a ratio of 25:75 was previously applied at 15.5 g / m ² . The mass of the binder was added so as to be 20% of the entire coating agent. Brazing heating conditions were carried out under the conditions of heating to 600 ° C. at a temperature rising rate of 50 ° C./min on average in a nitrogen gas atmosphere, and lowering to room temperature after holding for 3 minutes. The following tests 4, 5, and 6 were carried out using the produced heat exchanger core.

(Test 4)
The heat exchanger core 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. The results are shown in Table 11 and Table 12.

(Test 5)
Zn concentration on the surface of the refrigerant passage tube of the heat exchanger core, Zn diffusion depth, surface-to-depth potential and surface-to-depth potential difference, fin material potential, refrigerant passage tube surface to fin material potential difference, refrigerant passage tube deep And the potential difference between the fin material was measured. The Zn concentration on the surface of the refrigerant passage tube and the Zn diffusion depth were determined from the results of EPMA line analysis in the thickness direction after filling the cross section of the core with resin. The Zn diffusion depth was a depth at which the Zn concentration became 0.01%. The electric potential was measured by grinding the surface of the refrigerant passage tube and the fin material as they were after brazing, the deep portion of the refrigerant passage tube from the surface to a depth of 150 μm, and the portion where Zn diffusion did not reach. 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. The results are shown in Table 13 and Table 14.

(Test 6)
About the heat exchanger core, the SWAAT test and CCT test prescribed | regulated to ASTM-G85-Annex A3 were each implemented for 1000 h. In the CCT test, 5% saline adjusted to pH 3 with acetic acid is used as a test solution, sprayed at an ambient temperature of 35 ° C. for 2 hours, dried at an ambient temperature of 60 ° C. for 4 hours, and then at a relative humidity of 95% RH or higher. The cycle of wetting for 2 hours at an ambient temperature of 50 ° C. was repeated. Tables 15 and 16 show the maximum corrosion depth of the refrigerant passage tube (tube) after the test and the corrosion state of the fins. The maximum corrosion depth of the refrigerant passage tube is 0.05 mm or less, ◯, 0.05 mm to 0.10 mm or less, 0.10 mm to 0.20 mm or less, Δ, 0.20 mm. Those that exceeded were evaluated as x. As for the corrosion of the fins, almost none was evaluated as ◎, minor was evaluated as ○, intermediate was evaluated as Δ, and remarkable was evaluated as ×.

  Although no intergranular corrosion was observed in the heat exchanger cores 1 to 24 produced according to the present invention, among the heat exchanger cores, a heat exchanger using an alloy T containing Cu as an aluminum alloy for the refrigerant passage. Intergranular corrosion occurred remarkably in the cores 38 to 43.

  In the heat exchanger cores 1 to 24 manufactured according to the present invention, a sufficient Zn diffusion layer is formed on the surface portion of the refrigerant passage tube, so that the surface of the refrigerant passage tube has a base potential with respect to the deep portion, and the refrigerant The potential difference between the surface of the passage tube and the deep portion was 95 to 100 mV. In addition, the potential of the fin material is also low with respect to the deep part of the refrigerant passage tube. On the other hand, in the heat exchanger cores 25 to 43 manufactured under conditions outside the conditions of the present invention, there may be cases where a sufficient Zn diffusion layer is not formed in the refrigerant passage tube surface layer portion, in which case A sufficient potential difference could not be obtained between the surface of the refrigerant passage tube and the deep part. In addition, even if a sufficient Zn diffusion layer is formed, the potential lowering effect of Zn is offset in the heat exchanger cores 38 to 43 using the alloy T containing Cu as the aluminum alloy for the refrigerant passage. The surface had the same or slightly lower potential than the deep part.

  In the SWAAT test, all of the heat exchanger cores 1 to 24 produced according to the present invention had a sufficient potential difference between the surface of the refrigerant passage tube and the deep portion, and thus the maximum corrosion depth was shallow and excellent corrosion resistance was exhibited. . In addition, since the sacrificial anode effect of the fin is obtained in the SWAAT test, a difference in the corrosion consumption of the fin material occurs due to the potential difference between the surface of the refrigerant passage tube and the fin material, but the heat exchanger cores 1 to 24 manufactured according to the present invention are used. In all cases, the potential difference was appropriate and the fin material was hardly or slightly corroded.

  On the other hand, in the heat exchanger cores 25 to 43 manufactured under conditions other than the conditions of the present invention, a sufficient potential difference between the surface of the refrigerant passage tube and the deep portion is not obtained, or the potential of the fin material is In the heat exchanger cores 25 and 37 to 43 that are noble from the deep part of the refrigerant passage pipe, the maximum corrosion depth of the refrigerant passage pipe was deep. About the heat exchanger core 31, since the aluminum alloy s with a large amount of Cu was used as the fin material, the potential of the fin was lower than the potential of the refrigerant passage tube, and the maximum corrosion depth of the refrigerant passage tube was deepened. As for the fin material, the core 35, 36, 38, 39, 40, 42, 43 in which the potential of the fin material is significantly lower than the potential of the refrigerant passage tube, and the aluminum alloy having a large amount of Zn, Fe, and Cu as the fin material The fins of the cores 26, 29, and 31 using n, q, and s were inferior in self-corrosion resistance, and corrosion was remarkable.

  In the CCT test, it becomes an evaluation close to the actual environment by entering the drying process, but conversely, despite the difficulty of obtaining the sacrificial anode effect of the fins, in the heat exchanger cores 1 to 24 manufactured according to the present invention, Since a sufficient potential difference was obtained between the surface of the refrigerant passage tube and the deep portion, the maximum corrosion depth of the refrigerant passage tube was shallow and showed excellent corrosion resistance as in the SWAAT test. There was almost no corrosion of the fin material.

  On the other hand, in the heat exchanger cores 25 to 43 produced under conditions other than the conditions of the present invention, the maximum corrosion of the refrigerant passage tube is caused by insufficient potential difference between the surface and the deep portion of the refrigerant passage tube. The depth was deep. Regarding the corrosion of the fin material, the tendency was the same as the result of the SWAAT test. In addition, among the heat exchanger cores 25 to 43, the cores 27, 28, 30, and 32 to 34 had good corrosion resistance evaluation results, but as shown in Table 12, problems occurred when the heat exchanger core was produced. Met.

Claims (9)

In the aluminum alloy heat exchanger, a mixture containing Si powder and fluoride-based flux is applied to the surface of the aluminum alloy refrigerant passage tube, and fins are assembled and brazed. It is composed of an extruded material of an aluminum alloy containing 5 to 1.7% and the balance being Al and inevitable impurities, and the fin is composed of Zn: 0.3 to 4.0%, Mn 0.8 to 1.7% A heat exchanger made of an aluminum alloy, characterized in that it is made of an aluminum alloy composed of the balance Al and inevitable impurities, and a Zn diffusion layer is formed in the surface layer portion of the refrigerant passage tube. 2. The refrigerant passage pipe is an aluminum alloy extruded material further containing one or more of Ti 0.30% or less, Sr 0.10% or less, and Zr 0.30% or less. The aluminum alloy heat exchanger as described. The aluminum alloy heat exchanger according to claim 1 or 2, wherein the refrigerant passage tube is an aluminum alloy extruded material in which a Cu content is regulated to less than 0.10%. The aluminum alloy heat exchanger according to any one of claims 1 to 3, wherein the refrigerant passage pipe is an aluminum alloy extruded material in which the Si content is regulated to less than 0.10%. The fin contains 0.3 to 4.0% Zn, 0.8 to 1.7% Mn, Si 0.2 to 0.6%, Fe 0.1 to 0.7%, Mg 0.05 to 0% 3%, Cu 0.5 or less, Cr 0.3% or less, Zr 0.3% or less, Ti 0.3% or less, one or two or more kinds, and the balance consisting of Al and inevitable impurities The heat exchanger made from aluminum alloy in any one of Claims 1-4. 6. The aluminum alloy according to claim 1, wherein the fin material further contains one or two of In 0.001 to 0.10% and Sn 0.001 to 0.10%. Heat exchanger. It is a method of manufacturing the said refrigerant | coolant passage tube used for the aluminum heat exchanger in any one of Claims 1-6, Comprising: The aluminum alloy which comprises the refrigerant | coolant passage tube in any one of Claims 1-3 A method for producing a refrigerant passage pipe, characterized by subjecting the ingot to a homogenization heat treatment at a temperature of 400 ° C. to 650 ° C. for 4 hours or more, followed by hot extrusion. It is a method of manufacturing the said refrigerant | coolant passage tube used for the aluminum heat exchanger in any one of Claims 1-6, Comprising: The aluminum alloy which comprises the refrigerant | coolant passage tube in any one of Claims 1-3 A first-stage heat treatment in which the ingot is kept at a temperature of 570 ° C. to 650 ° C. for 2 hours or more, and then a second-stage heat treatment in which the temperature is lowered to 400 ° C. to 550 ° C. and held for 3 hours or more. A method of manufacturing a refrigerant passage tube, characterized by performing hot extrusion after the application. It is a method of manufacturing the said refrigerant | coolant passage tube used for the aluminum heat exchanger in any one of Claims 1-6, Comprising: The aluminum alloy which comprises the refrigerant | coolant passage tube in any one of Claims 1-3 A first-stage heat treatment in which the ingot is kept at a temperature of 570 ° C. to 650 ° C. for 2 hours or more, and after that, the temperature is once lowered to room temperature and then held at a temperature of 400 ° C. to 550 ° C. for 3 hours or more. A method of manufacturing a refrigerant passage pipe, characterized by performing hot extrusion after a homogenizing heat treatment.