US20200173740A1

US20200173740A1 - Highly corrosion-resistant heat exchanger system using control of alloy composition and alloy potential

Info

Publication number: US20200173740A1
Application number: US16/614,059
Authority: US
Inventors: Hee Sik Sohn
Original assignee: Sp Tech Co ltd
Current assignee: Sp Tech Co ltd
Priority date: 2017-05-25
Filing date: 2017-05-25
Publication date: 2020-06-04
Also published as: EP3633310A1; EP3633310A4; WO2018216832A1

Abstract

Disclosed is a technology for improving corrosion resistance of aluminum tubes, aluminum fins, and aluminum headers of a heat exchanger. The heat exchanger includes one or more tubes made of aluminum alloy, one or more headers made of aluminum alloy, one or more brazing header clads, one or more fins (or heat sinks) made of aluminum alloy, and one or more brazing fin clads. The corrosion potential of the tube ranges from −950 mV to −650 mV, the corrosion potential of the header has a difference of 0 mV to 150 mV with respect to the corrosion potential of the tube, and the corrosion potential of the header clad has a difference of −20 mV to 100 mV with respect to the corrosion potential of the tube.

Description

TECHNICAL FIELD

The present invention relates to a heat exchanger system and, more particularly, to a technology capable of improving corrosion resistance of components of a heat exchanger such as tubes, fins and headers made of aluminum. More particularly, the present invention relates to a technology capable of improving corrosion resistance of components of a heat exchanger through selection of an appropriate corrosion potential or addition of a specific element for each of the components of a heat exchanger.

BACKGROUND ART

In general, aluminum or an aluminum alloy being lightweight and highly thermally conductive is used for heat exchangers for evaporators, condensers, and pipes. A typical heat exchanger is composed of a condenser tube, fins (or heat sinks), a header pipe, and various pipes that are made of an aluminum alloy extrusion material. A heat exchanger is generally constructed by assembling a tube and fins (each being composed of a fin core and a coating or clad that is formed on the surface of the core through coating or cladding of a brazing plate) into a predetermined structure, and then brazing the assembled structure in a heating furnace in an inert gas atmosphere.
For heat exchangers, A 1XXX series and A 3XXX (series are widely used Al alloys. A 6XXX series are used for strength-improved products. On the other hand, brazing dads for joining tubes and header pipes or for joining fins and tubes, A 4XXX series are widely used.
Since extrusion tubes and pipes are used as coolant passage pipes in heat exchangers, there is a risk that holes are generated due to severe corrosion. If such a case occurs, coolant leaks, resulting in the heat exchanger malfunctioning. For this reason, conventionally, zinc (Zn) is affixed on the surface of an extrusion tube through spraying or the like, and Zn is then diffused into the extrusion tube during brazing. As a result, a Zn diffusion layer formed on the surface of the extrusion tube acts as a sacrificial anode, thereby protecting the core part, suppressing corrosion of the extrusion tube in the thickness direction, and extending the service time of the extrusion tube which lasts until occurrence of corrosion holes. In this case, after an extrusion tube is produced through extrusion, a Zn affixing process such as Zn coating (or spraying) is required, resulting in an increase in manufacturing cost.
In particular, in terms of corrosion resistance of a tube, Japanese Patent Application Publication No. 11-21649 discloses an aluminum alloy having a composition of 0.15% to 0.35% by weight of iron, 0.15% or less by weight of silicon, less than 0.03% by weight of zinc, 0.55% by weight of copper, 0.02% to 0.05% by weight of zirconium, 0.003% to 0.010% by weight of titanium, and the remainder of aluminum and inevitably added impurities, in which a ratio of iron to silicon is equal to or greater than 2.5.
However, in the alloy of the patent document, copper is contained as an additive to ensure corrosion resistance of the alloy. However, since a large amount (0.55% by weight) of copper is added, a large number of Al—Cu-based intermetallic compounds are formed, thereby reducing extrusion characteristics. Due to the precipitation of the intermetallic compounds, there is a problem that corrosion potential is lowered in local regions of the base material and thus the corrosion resistance is deteriorated.
In order to solve this problem, Korean Patent Application Publication No. 10-2011-0072237 discloses a method of eliminating a process of spraying Zn on the surface of a tube by adding Zr and B to an aluminum alloy containing 0.15 to 0.45% of copper. This document discloses the technical idea that due to the addition of Zr or B, the crystals of an aluminum alloy become finer and thus corrosion resistance of the aluminum alloy is increased. However, when the content of copper is more than 0.1% by weight, copper precipitates at grain boundaries during the operation of a heat exchanger, resulting in the susceptibility to intergranular corrosion being increased. Therefore, intergranular corrosion of the tube occurs, which shortens the service time that lasts until occurrence of corrosion penetration holes in the tube.
The documents disclose a technology in which copper (Cu) is added as a main element to improve corrosion resistance. However, this technology does not provide a solution to the disadvantages of Cu addition.
In order to overcome the disadvantages (for example, insufficient corrosion resistance) of Cu addition, Korea Patent Application Publication No. 10-2014-0000406 discloses later a technology in which 0.05 to 0.15% by weight of zirconium (Zr) is added to a composition of 0.50 to 1.0% by weight of manganese (Mn) and 0.2% by weight of silicon (Si) and the content of copper (Cu) is minimized to 0.01% or less. However, in this case, the advantage of the increase in the corrosion potential of Cu is sacrificed due to the removal of Cu. In addition, the flexibility in designing the potential attributable to the contact between parts during assembling of the parts of a heat exchanger is limited. Therefore, it is difficult for a heat exchanger system to employ this technology.
Therefore, the present disclosure is intended to compensate for the shortcomings of the related art. To this end, a cathodic protection principle is applied to the individual parts of a heat exchanger to maximize the corrosion resistance of the heat exchanger.

DISCLOSURE

Technical Problem

The present invention has been made to solve the problems occurring in the related art, and an objective of the present invention is to provide a highly corrosion resistant heat exchanger system. Another objective of the present invention is to provide a highly corrosion resistant heat exchanger system in which the corrosion resistance of a heat exchanger is improved so that the airtightness of the heat exchanger can be maintained even in harsh environments, thereby preventing coolant from leaking, resulting in the service life of the heat exchanger system being increased.

Technical Solution

In order to accomplish one of the objectives, there is provided a highly corrosion resistant heat exchanger system in which an alloy composition and an alloy potential of the heat exchanger system are differently set for each component of the heat exchanger system, the heat exchanger system including:
one or more tubes made of an aluminum alloy; one or more headers made of an aluminum alloy; one or more brazing header clads; one or more fins (heat sinks) made of an aluminum alloy; and one or more brazing fin dads,
wherein: a corrosion potential of the tube ranges from −950 mV to −650 mV;
a corrosion potential of the header is in a range of +0 mV to +150 mV with respect to the corrosion potential of the tube;
a corrosion potential of the header clad is in a range of −20 mV to +100 mV with respect to the corrosion potential of the tube;
a Cu content in the aluminum alloy ranges from 0.001% to 0.50% by weight;
a Zn content in the aluminum alloy ranges from 0.001% to 5.00% by weight, and
the tube, the header, and the fin are joined through brazing of the header clad and the fin clad.
According to a feature of the invention,
the corrosion potential of the fin (heat sink) may be set to have a difference of −20 mV to −170 mV with respect to the corrosion potential of the tube.
According to another feature of the invention,
the corrosion potential of the fin clad may be set to have a difference of −40 mV to +80 mV with respect to the corrosion potential of the tube.
According to a further feature of the invention,
in the aluminum alloy, the content of one or more elements selected from Cu, Zn, Mn, Si, Fe, and Mg is a main factor to control a corrosion potential.
According to a further feature of the invention,
the aluminum alloy may contain at least rare earth metal selected from rare earth metals ranging from La of atomic number 57 to Lu of atomic number 71 in an amount of 0.005% to 1.00% by weight.
According to a further feature of the invention,
the aluminum alloy may contain Zr, B, or both in an amount of 0.005% to 0.25% by weight.
According to a further feature of the invention,
any one process selected from among aging heat treatment, zinc coating, conversion coating, resin coating, and any combination thereof may be performed on the tube, the fin (or heat sink), the header, or any combination thereof.
In order to achieve another objective of the invention,
there is provided a highly corrosion resistant heat exchanger system in which an alloy composition and an alloy potential are differently set for each component of the heat exchanger system, the heat exchanger system including a tube made of an aluminum alloy that satisfies the following conditions:
a content of Cu ranges from 0.001% to 0.50% by weight;
a content of Zn ranges from 0.001% to 5.00 wt %;
a content of at least one selected from among Zr and B is 0.001% to 0.25% by weight;
a content of at least one rare earth metal selected from rare earth metals ranging from La (atomic number 57) to Lu (atomic number 71) ranges from 0.001% to 1.00% by weight; and
S % in equations described below ranges from 0.05% to 0.30% by weight,
Equations:
Z %=the content of one or more elements selected from among Zr and B;
R %=the content of at least one element selected from elements ranging from La (atomic number 57) to Lu (atomic number 71); and
S %=((R %/M)+Z %)
wherein:
the content of Cu is 0.001% to 0.12% by weight;
the content of Zn is 0.001% to 3.00% by weight;
a content of Fe is 0.001% to 0.25% by weight;
the content of at least one metal selected from rare earth metals ranging from La (atomic number 57) to Lu (atomic number 71) is 0.05% to 0.50% by weight; and
the content of one or more element selected from Zr and B is 0.01% to 0.07% by weight.
According to one feature of the invention,
the aluminum alloy may contain Fe in a proportion of 0.40% to 0.70% by weight.
According to a further feature of the invention,
the aluminum alloy may further contain at least one element selected from Mn, Mg, Si, Fe, Ti, Cr, V, Ni, Co, In, Pb, Bi, Ca, Be, Ag, Pd, Sb, Sc, Nb, Hf, and Y.

Advantageous Effects

According to the present invention, in order to improve corrosion resistance of a heat exchanger, the composition of the aluminum alloy used for the heat exchanger is adjusted to vary from component to component of the heat exchanger. In addition, special elements such as rare earth metals are added to the composition of the base material of each component to improve corrosion resistance and strength. According to the present invention, it is possible to prolong the service life of each component of a heat exchanger and to simplify the manufacturing process of a heat exchanger by not requiring a zinc coating process and some post-treatment processes, resulting in reduction of the manufacturing cost.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a preferred corrosion potential distribution of heat exchanger tubes, fins, headers, and dads according to the present invention;

FIG. 2 is a diagram showing a more preferred corrosion potential distribution of heat exchanger tubes, fins, headers, and dads according to the present invention; and

FIG. 3 is a schematic perspective view of a heat exchanger system according to an embodiment of the present invention.

BEST MODE

Hereinafter, selections of materials for components of a heat exchanger and the construction of the heat exchanger system, according to the present invention, will be described with reference to the accompanying drawings. The terms and words used in the specification and claims should not be construed only in a conventional or dictionary sense but should be construed in a sense and concept consistent with the technical idea of the present invention, on the basis that the inventor can properly define the concept of a term to describe its invention in the best way possible. The exemplary embodiments described in the specification and the configurations illustrated in the drawings are merely examples and do not exhaustively present the technical spirit of the present invention. Accordingly, it should be appreciated that there may be various equivalents and modifications that can replace the exemplary embodiments and the configurations at the time at which the present application is filed.
A heat exchanger system 1 includes pipe-shaped headers 3 as a support structure, multiple tubes 5 that are configured with pipes thinner than the headers 3 to connect the headers 3 to each other, and multiple fins (or heat sinks) 7 interposed between the tubes 5 to increase a heat transfer rate. The fins 7 may take a corrugated form to increase the heat exchange area as illustrated in the drawings. A heat medium may circulate through the headers 3 and the tubes 5. Each of the headers 3 and each of the tubes 5 may be joined through brazing and each of the tubes 5 and each of the fins 7 may be joined through brazing. Hereinafter, it is noted that the term “fin” used herein includes a heat sink.
When the aluminum tubes 5 of the heat exchanger system 1 are corroded to have a leakage hole, coolant flows out. This means that the service life of the heat exchanger system 1 ends. Since aluminum alloys are susceptible to pitting corrosion, intensive effort has been made to prevent pitting corrosion. One approach to prevent pitting corrosion is controlling the composition of an aluminum alloy. That is, the content of Si, Fe, and Cu, which form precipitates (serving as a local cathode) having a high corrosion potential, such as Si, FeAl3, Cu, CuAl2, and the like, is lowered, and Mn or Mg that forms a phase with low potential by combining with Si or Fe is alloyed with aluminum. In terms of heat treatment, there is a method of avoiding heat treatment in the vicinity of 500° C. at which precipitates acting as a cathode are largely generated.
A macroscopic approach is a cathode protection process in which the material to be protected is controlled to have a higher corrosion potential than other contact materials. In the present invention, the cathode protection method and the alloy composition method are used in combination.
The effects of main alloying elements such as Cu, Zn, Mn, Fe, Si, and Mg in an aluminum alloy will be described below.
(1) Cu
Cu as an alloying element has a disadvantage of significantly reducing the extrudability compared to Mn while having an advantage of increasing the strength of the aluminum alloy by being dissolved in the matrix (Matrix). The addition of Cu is known to increase the corrosion potential. When Zn and Cu coexist, especially when a Zn content is small, the electric potential raising effect of Cu is predominant. That is, when the content of Cu is high, the electric potential raising effect of Cu is stronger than the electric potential lowering effect of Zn. When the content is less than 0.12% by weight, the effect of adding copper (Cu), for example, an increase in corrosion resistance, is difficult to realize. On the other hand, when the content is more than 0.45% by weight, the extrudability and the corrosion resistance are both lowered. Here, the content of Cu refers to a percentage of the weight of Cu with respect to the total weight of the aluminum alloy. The term “content” used in the description and claims have the same meaning. When the content of Cu is higher than an optimum content, precipitates tend to form at the grain boundaries, thereby increasing susceptibility to Intergranular corrosion and local corrosion.
(2) Zn
When Zn as an alloying element coexists with Mg, mechanical properties of the alloy are improved. In general, the addition of Zn lowers the corrosion potential, but the change in corrosion potential is relatively small compared with the addition of Cu.
(3) Mn
Mn as an alloying element increases the strength of the aluminum alloy. The strength increasing effect is insufficient when the content of Mn is less than 0.5% by weight. On the other hand, when the content of Mn exceeds a proper range of 1.2% to 1.7% by weight, extrudability is deteriorated. The addition of Mn has a less influence on the deterioration in the extrudability (particularly, the decrease in the maximum extrusion speed) than the case where the same amount of Si, Cu or Mg is added. The addition of Mn also has an effect of increasing the corrosion potential of the alloy by precipitating as a fine intermetallic compound of Al6Mn. When the content of Mn is less than 0.6% by weight, the effect of adding manganese (for example, improvement in corrosion resistance) is insignificant. In addition, the addition of Mn has effects of eliminating the negative effect of Fe addition and refining grains. In addition, Mn forms a compound that does not deteriorate corrosion resistance. Therefore, the addition of Mn can improve the strength of the aluminum alloy without deteriorating the corrosion resistance. However, care should be taken because excess manganese can lower the mechanical strength of the aluminum alloy.
(4) Fe
Fe as an alloying element precipitates as an intermetallic compound in an Al alloy and improves abrasion resistance of the Al alloy. When the content of Fe is less than 0.1% by weight, nearly no improvement in abrasion resistance is exhibited. On the other hand, when the content exceeds 0.3% by weight, the grain size is increased, resulting in poor processability.
In addition, when even a very small amount of Fe exists, Al3Fe easily forms and combines easily with Si to form an Al—Fe—Si intermetallic compound which deteriorates the mechanical properties of the Al alloy. Even a very small amount of Fe deteriorates surface gloss and reduces the corrosion resistance and ductility. In addition, it is possible to prevent recrystallization crystal grains from being coarsened. That is, a grain refinement effect can be obtained. When Fe is added in a proportion of 0.5% by weight or less in a die casting process, there is an effect of preventing sticking to a mold.
(5) Si
Si as an alloying element is precipitated as an Al—Mn—Si-based intermetallic compound, thereby suppressing grain growth through interfering grain boundary movement and improving the extrudability by reducing the deformation resistance during extrusion. When the content of Si is less than 0.05% by weight, the casting cost is increased. On the other hand, when the content of Si is 0.10% or more by weight, an Al—Mn—Si-based intermetallic compound is formed in the alloy, thereby reducing the Mn solid solubility in the alloy. This can lead to a corrosion potential drop. In addition, when the content exceeds 0.2% by weight, the strength of the alloy is increased and thus the extrudability is deteriorated.
(6) Mg
Mg as an alloying element has an advantage of increasing the strength of the alloy by causing solid solution hardening in the matrix but has a disadvantage of reducing the extrudability. The reduction in the extrudability increases with the increasing content of Mg. When the content is more than 2.0% by weight, a compound having a high melting point is formed due a reaction with the flux, which tends to significantly reduce the bonding property in a brazing process. In addition, when the content exceeds 3.5% by weight, Mg2Al3 precipitates to increase the susceptibility to grain boundary corrosion and stress corrosion.
In addition, aging reinforcement may occur depending on whether Si and Zn coexist. In addition, machinability is improved, corrosion resistance especially against seawater is improved, and shrinkage during solidification is reduced. In addition, the fluidity of a molten metal is weakened. In particular, since the bonding force with oxygen is strong, caution against the inflow of oxide is required.
The composition of an aluminum alloy for each of a heat exchanger can be appropriately selected in consideration of the characteristics of the main alloying elements and the effects of the alloying elements on the corrosion resistance. Widely used alloys in heat exchangers are A 1XXX series and A 3XXX series alloys. Table 1 below shows the composition of typical alloy types.

TABLE 1

Alloy name	Zn	Mn	Si	Cu	Fe	etc.	Al

A1070	0.04max	0.03max	0.2max	0.04max	0.25max	0.15max	Rem
A3003	0.1max	1.0-1.5	0.6max	0.05-0.20	0.7max	0.15max	Rem

In general, the corrosion potential of an aluminum alloy is most strongly affected by Cu. When the content of Cu is in a range of 0.01% to 0.5%, the corrosion potential varies in a range of −950 mV to −650 mV, depending on the content of the Cu. Therefore, when the influences of other alloying elements are neglected, the corrosion potential can be easily changed by increasing or decreasing a small amount of copper that is added to the composition of an aluminum alloy. On the other hand, zinc decreases the corrosion potential by about 30 mV to 40 mV per 1.0% by weight when it is added to a general aluminum alloy. That is, the change in the corrosion resistance caused by addition of zinc is smaller than that of Cu. Therefore, it is possible to control the corrosion potential only with the content of zinc. In addition, Mn has the effect of increasing the corrosion potential and Si has the effect of lowering the corrosion potential. Therefore, the corrosion potential of the aluminum alloy can be easily changed by changing the content of each of the alloying elements such as Cu, Zn, Mn, Si, Mg, and Fe.
For example, by adjusting the contents of copper and zinc with respect to A1070 and A3003, the corrosion potential of the alloy can be changed.
In the case of an aluminum alloy for a heat exchanger, the content of Zn is preferably 5.0% by weight or less, and the content of Cu is preferably 0.5% by weight or less. In the case of the tubes in a heat exchanger, it is preferable that the content of Cu is 0.5% by weight or less. That is, the corrosion potential of the tube is set to be preferably within a range of −950 mV to −650 mV and more preferably within a range of −850 mV to −650 mV.
On the other hand, as described above, the cathode protection method can be used to prevent occurrence of corrosion holes in the tubes. In this case, a suitable component serving as a sacrificial anode is the fin. This is because there is no risk that the coolant leaks through the fins even when the corrosion of the fins occurs. Therefore, in order to reduce the corrosion of the tubes through the cathode protection method, the corrosion potential of the fin must be lower than the corrosion potential of the tube, and it is preferably in a range of −20 mV to −170 mV and, more preferably, in a range of −20 mV to −100 mV. When the difference in the corrosion potential between the fin and the tube is too small, the effect of the cathode protection method is insignificant. On the contrary, when the difference is excessively large, the increase in the corrosion rate of the fins is undesirably high. Therefore, when the material of the fins is A3003, the corrosion potential decreases with a decrease in the copper content or an increase in the zinc content. For example, an A3003-based tube to which copper is added to increase the corrosion potential and an A3003-based fin to which Zn is added to decrease the corrosion potential are combined, the corrosion resistance of the tube is improved.
The location at which a coolant leakage easily occurs due to the corrosion of a heat exchanger is a joint portion between the tube 5 and the header 3. In particular, even though a corrosion hole is not formed in the header 3, when the tube-header joint is slightly eroded in a direction perpendicular to the surface of the header 3 due to corrosion, the coolant leakage easily occurs. Therefore, the corrosion potential of the header 3 must be carefully monitored. On the other hand, since the tube 5 has a sufficient tube thickness which is the dimension in the depth direction of the joint portion, the tube 5 does not suffer the coolant leakage until the entire thickness of the tube 5 is eroded due to the corrosion. Therefore, since improvement in the corrosion resistance of the header 3 is more urgently required than that of the tube 5, it is preferable that the corrosion potential of the header 3 is higher than the corrosion potential of the tube 5. The difference in the corrosion potential is preferably in a range of +0 mV to +150 mV and, more preferably in a range of +20 mV to +100 mV.
The heat exchanger system 1 is generally manufactured by first assembling the tubes 5, the fins 7, and the headers 3 and then joining the same through brazing. To this end, the fin is configured such that an aluminum alloy for a fin clad is provided on the surface of a fin core. The header 3 is also configured such that a clad is provided at an area to be joined with the tube 5. The clad is melted in the brazing process to securely join the parts (i.e., the header and the tube) to each other. The tube-fin joint and the tube-header joint are required to have high corrosion resistance for secure electrical contact retention and structural stability.
In the case of the tube-fin joint clad, since the corrosion potential of the fin 7 is low, it is preferable that the corrosion potential of the tube-fin joint clad is in a range of −40 to +80 mV with respect to the corrosion potential of the tube 5. The corrosion potential of the tube-fin joint clad is more preferably in a range of 0 to +80 mV with respect to the corrosion potential of the tube 5. In the case of the tube-header joint clad, since the corrosion potential of the header 3 is high, it is preferable that the corrosion potential of the tube-header joint clad is slightly higher than that of the tube-fin joint clad. The corrosion potential of the tube-header joint clad is preferably in a range of −20 mV to +100 mV and more preferably in a range of +10 mV to +90 mV when compared with the corrosion potential of the tube 5.
The corrosion potential relationships among the components are shown in FIGS. 1 and 2. FIG. 1 is a graph illustrating preferable corrosion potential ranges of the fin 7, the header 3, and the clads compared with the corrosion potential of the tube 5, and FIG. 2 is a graph illustrating more preferable corrosion potential ranges.
In order to suppress occurrence of a corrosion hole of the tube 5, alloying elements described below may be added.
(7) Zirconium (Zr) and boron (B)
Zirconium (Zr) not only improves the strength of an aluminum ally by reducing the size of crystal grains, but also has the effect of suppressing local pitting corrosion by finely dispersing precipitates that cause a potential difference. This has an effect of enabling the corrosion to occur uniformly over the whole area. This also improves extrusion characteristics by reducing the deformation resistance during the extrusion process and improves the strength by suppressing grain coarsening after brazing. The effects are not sufficient when the content is 0.005% by weight or less. However, the content needs not exceed 0.25% by weight because of the difficulty of extrusion and the increase in economical cost. Boron has a similar effect to zirconium when added to aluminum alloys.
(8) Rare earth metal (RE)
According to the present invention, the effect of a rare earth metal added has advantages described below.
Rare earth metals ranging from La (atomic number 57) to Lu (atomic number 71) reduce a local corrosion cathodic reaction because of precipitates in the matrix, resulting in reduction in a local corrosion anodic reaction. Consequently, those rare earth metals have an effect of suppressing location corrosion.
In addition, those rare earth metals reduce Fe and Ni that are vulnerable to corrosion and are present in a molten metal at the time of preparing an aluminum alloy, thereby improving corrosion resistance of the aluminum alloy. Therefore, even with impurities such as Fe being present in an amount of 0.2% by weight or more in the aluminum alloy, rare earth metals help in maintaining good corrosion resistance.
In addition, since rare earth metals have an effect of raising the corrosion potential, the rare earth metal, when added, may minimize the use of Cu that is usually added to increase the corrosion potential or may replace Cu in terms of increase in the corrosion potential. Accordingly, the rare earth metals can improve the corrosion resistance while minimizing negative effects of an excessive amount of Cu that is added to increase the corrosion potential.
In addition, since the ductility and adhesion of an oxide film formed at the grain boundary or surface are improved, the lifetime of the oxide film is prolonged, resulting in improvement in corrosion resistance. In addition, the strength and fluidity of an aluminum alloy are improved, plastic workability of a metal is improved, and brazing characteristics are improved.
Since the effect of corrosion resistance improvement of the rare earth metal is only about 20% to 100% compared with Zr, a similar effect can be obtained with a dose of 1 to 5 times compared to Zr. However, the use of the rare earth metals instead of Zr may be preferable because Zr is expensive.
In the present invention, in order to prevent an aluminum alloy from becoming susceptible to local corrosion and intergranular corrosion, a rare earth metal is added to the aluminum alloy, resulting in the aluminum alloy having an improved corrosion resistance. In this case, the appropriate amount of a rare earth element is preferably in a range of 0.005% to 1.0% by weight, more preferably in a range of 0.01% to 0.60% by weight, and most preferably in a range of 0.05% to 0.50% by weight.
Because of the advantages of rare earth metals, research and development are being extensively performed on rare earth metals in terms of utilization thereof. However, the research and development have been focused on technology for increasing corrosion resistance of magnesium or magnesium alloys, technology for increasing the strength of some aluminum alloys for casting, and conversion coating technology for increasing corrosion resistance of the surface of an aluminum alloy.
However, no documents report that rare earth elements have been added directly to alloys to improve the corrosion resistance of 1XXX, 3XXX, and 6XXX (series of aluminum alloys and the corrosion resistance of 4XXX series that are used for brazing.
Only a few documents report a technology in which rare earth elements are used for A 1XXX series and A 4XXX series. For example, Korean Patent No. 10-1335680, Korean Patent No. 10-1349359, and Korean Patent No. 10-1194970 are those documents disclosing the technology. However, the technology of the present invention differs from those of the documents.
(9) Other elements [99] In all the above cases, aluminum alloys may further contain at least one alloying element among Ti, Cr, V, Ni, Co, In, Pb, Bi, Ca, Be, Ag, Pd, Sb, and Y that are widely used as allying elements in the aluminum industry and inevitable impurities.
On the other hand, according to the present invention, when a high corrosion resistance is required, zinc coating (spraying, etc.) may be performed on the tube 5, the fin 7, the header 3, or any combination thereof to obtain a sacrificial anode effect. Additionally, conversion coating also may be performed to increase the corrosion resistance. Additionally, according to the present invention, silicone coating or resin coating may be performed on the surface of the components of the heat exchanger to further improve the corrosion resistance, and heat treatment for aging hardening may also be performed to increase the strength.

Example

Hereinafter, some examples will be described in order to help the understanding of the present invention. However, the following examples are merely or illustrative purpose, and the scope of the present invention is not limited thereto.
Exemplary compositions (% by weight) of aluminum alloys are shown in Table 2. The specifications of the compositions of A 3003 and A 4343 that are widely used aluminum alloys are shown in the table. Each alloy may further contain inevitable impurities.

TABLE 2

Alloy type	Zn	Mn	Si	Cu	Fe	Others	Al

A 3003 Spec.	0.1max	1.0-1.5	0.6max	0.05-0.20	0.7max	0.15max	Rem.
A 4343 Spec.	<0.20	<0.10	6.8-8.2	<0.25	<0.80	0.15max	Rem.

Table 3 shows alloy types used in the present invention. A 3003 was used as the base material (denoted by an alloy symbol of b) of tubes, fins, and headers, and A4343 was used as the base material (denoted by an alloy symbol of h) of the clads. In Table 3, in the case of A3003, an alloy prepared by adding copper to A3003 to increase a corrosion potential is referred to as High potential 1 (denoted by an alloy symbol of a), and an alloy prepared by adding zinc to A3003 to decrease a corrosion potential is referred to as Low corrosion potential 1 (denoted by an alloy symbol of c).
An alloy prepared by adding a rare earth material of La to the base material (an alloy symbol of b) is referred to as Modified alloy 1 (an alloy symbol of d). An alloy prepared by adding Zr to the base material (an alloy symbol of b) is referred to as Modified alloy 2 (an alloy symbol of e). An alloy prepared by adding both of La and Zr to the base material (an alloy symbol of b) is referred to as Modified alloy 3 (an alloy symbol of f). An alloy in which the content of copper is increased to increase a corrosion potential compared with the base material (an alloy symbol of h) of the dads is referred to as High corrosion potential 2 (an alloy symbol of g), and an alloy in which the content of copper is decreased to decrease a corrosion potential compared with the base material (an alloy symbol of h) of the dads is referred to as High corrosion potential 2 (an alloy symbol of i).

TABLE 3

Alloy	Corrosion	Alloy
type	potential	symbol	Zn	Mn	Si	Cu	Fe	etc.	La	Zr	Al

High	−670	a	0.05	1.20	0.30	0.25	0.40	0.15	—	—	Rem
corrosion								max
potential 1
Basic alloy	−720	b	0.05	1.20	0.30	0.12	0.40	0.15	—	—	Rem
(A3003)								max
Low	−770	c	1.50	1.20	0.30	0.12	0.40	0.15	—	—	Rem
corrosion								max
potential1
Modified	−700	d	0.05	1.20	0.30	0.10	0.40	0.15	0.15	—	Rem
alloy 1								max
Modified	−710	e	0.05	1.20	0.30	0.12	0.40	0.15	—	0.05	Rem
alloy 2								max
Modified	−700	f	0.05	1.20	0.30	0.10	0.40	0.15	0.15	0.05	Rem
alloy
3								max
High	−700	g	0.10	0.05	7.5	0.25	0.45	0.15	—	—	Rem
corrosion								max
potential 2
Clad	−720	h	0.10	0.05	7.5	0.20	0.45	0.15	—	—	Rem
(A4343)								max
Low	−740	i	0.10	0.05	7.5	0.15	0.45	0.15	—	—	Rem
corrosion								max
potential 2

Table 4 shows various heat exchangers in which aluminum alloys for tubes, fins, headers, and dads vary, in which the aluminum alloys used for the tubes, fins, headers, and dads are selected from the examples described above. For example, in the case of Sample No. 1, the material selected for the tubes, the fins, and the headers is an alloy denoted by an alloy symbol of b and the material selected for the clads is an alloy denoted by an alloy symbol of h. A total of 12 types of samples were constructed, with three sets for each type.
In order to evaluate the corrosion resistance of each heat exchanger system, a SWAAT test was performed for each set of the prepared heat exchangers in accordance with ASTM standard. The test results are shown in Table 4. In Table 4, each of the numerical values is the average of the test results of the three sets for each type of heat exchanger. The SWAAT test refers to a test according to ASTM standard G85. In the test, glacial acetic acid was added to 4.2% by weight of NaCl solution to maintain a pH of 2.8 to 3.0, and the solution mixture was sprayed at a pressure of 0.07 MPa and an ambient temperature of 49° C. to each heat exchanger to be tested. The amount of the solution mixture sprayed was maintained at 1 ml/hr to 2 ml/hr.

TABLE 4

Type of	Sample No.

Component	1	2	3	4	5	6	7

Alloy Symbol for tube	b	a	a	b	b	c	c
Alloy Symbol for Fin	b	b	c	a	c	a	b
Alloy Symbol for	b	c	b	c	a	b	a
Header
Alloy Symbol for	h	h	h	h	h	h	h
Clad
SWAAT Leak	504	645	1032	576	1416	432	528
Time (hr)

Type of

Sample No.

Component	1	5	8	9	10	11	12

Alloy Symbol for	b	b	d	e	f	f	f
Tube
Alloy Symbol for Fin	b	c	c	c	c	c	c
Alloy Symbol for	b	a	a	a	a	a	a
Header
Alloy Symbol for	h	h	h	h	h	g	i
Clad
SWAAT Leak	504	1416	1824	1704	2160	2304	1320
Time (hr)

As shown in Table 4, when the same clad material (alloy symbol h) is used for the tube 5, the fin 7, and the header 3 and the corrosion potentials of the tube 5, the fin 7, and the header 3 differ from each other (Samples 1 to 7), Sample 5 shows the best corrosion resistance. This is the case where the corrosion potentials of the header, the tube, and the fin are in descending order (i.e., header>tube>fin). Sample 8 is the case where La is added to the aluminum alloy, Sample 9 is the case where Zr is added to the aluminum alloy, and Sample 10 is the case where La and Zr are added to the aluminum alloy. That is, the addition of rare earth metal and zirconium enhances corrosion resistance. In the case of Samples 10 to 12, the corrosion potential of the dads are changed with the corrosion potential of Sample 10 being the base potential. It is shown that when the potential of the clad is lower than that of the tube (Sample 12), the corrosion resistance is reduced.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A highly corrosion resistant heat exchanger system in which an alloy composition and an alloy potential are differently set for each component of the heat exchanger system, the heat exchanger system comprising:

one or more tubes made of an aluminum alloy;

one or more headers made of an aluminum alloy;

one or more brazing header clads; and

one or more fins (or heat sinks); and

one or more brazing fin clads,

wherein a corrosion potential of the tube ranges from −950 mV to −650 mV,

a corrosion potential of the header has a difference of +0 mV to +150 mV with respect to the corrosion potential of the tube,

a corrosion potential of the header cladding has a difference of −20 mV to +100 mV with respect to the corrosion potential of the tube,

a Cu content in the aluminum alloy ranges from 0.001% to 0.50% by weight,

a Zn content in the aluminum alloy ranges from 0.001% to 5.00% by weight, and the tubes, the headers, and the fins are joined by brazing the header clads and the fin clads.

2. The heat exchanger system of claim 1, wherein the corrosion potential of the fin (or heat sink) has a difference of −20 mV to −170 mV with respect to the corrosion potential of the tube.

3. The heat exchanger system of claim 1, wherein the corrosion potential of the fin clad has a difference of −40 mV to +80 mV with respect to the corrosion potential of the tube.

4. The heat exchanger system of claim 1, wherein in the aluminum alloy, a change in the content of at least one element selected from Cu, Zn, Mn, Si, Fe, and Mg is a major control factor of the corrosion potential.

5. The heat exchanger system of claim 1, wherein the aluminum alloy contains at least one rare earth metal selected from rare earth metals ranging from La of atomic number 57 to Lu of atomic number 71 in a proportion of 0.005% to 1.00% by weight.

6. The heat exchanger system of claim 1, wherein the aluminum alloy contains at least 0.005% to 0.25% by weight of at least one element selected from Zr and B.

7. The heat exchanger system of claim 1, wherein at least one process selected from aging heat treatment, zinc coating, conversion coating, resin coating, and any combination thereof is additionally performed on at least one of the tube, the fin (or heat sink), the header, and any combination thereof.

8. A highly corrosion resistance heat exchanger system in which an alloy composition and an alloy potential are differently set for each component of the heat exchanger system, the heat exchanger system comprising a tube made of an aluminum alloy satisfying conditions specified below (wherein M in a formula below is 1 to 5):

a content of Cu ranges from 0.001% to 0.50% by weight;

a content of Zn ranges from 0.001% to 5.00 wt %;

a content of at least one selected from among Zr and B is 0.001% to 0.25% by weight;

a content of at least one rare earth metal selected from the group consisting of rare earth metals ranging from lanthanum atoms (La, atomic number 57) to lutetium (Lu, atomic number 71) ranges from 0.001% to 1.00% by weight; and

S % in the following equations ranges from 0.05% to 0.30% by weight,

Equations:

where Z % is the content of one or more elements selected from among Zr and B;

R % is the content of at least one element selected from elements ranging from La (atomic number 57) to Lu (atomic number 71); and

S %=((R %/M)+Z %)

9. The heat exchanger system of claim 8, wherein:

the content of Cu is 0.001% to 0.12% by weight;

the content of Zn is 0.001% to 3.00% by weight;

a content of Fe is 0.001% to 0.25% by weight;

the content of at least one metal selected from rare earth metals ranging from La (atomic number 57) to Lu (atomic number 71) is 0.05% to 0.50% by weight; and

the content of at least one element selected from Zr and B ranges from 0.01 to 0.07% by weight.

10. The heat exchanger system of claim 8, wherein the aluminum alloy contains Fe in a proportion of 0.40% to 0.70% by weight.

11. (canceled)