ALUMINUM ALLOY COMPOSITION, ALUMINUM EXTRUSION TUBE AND FIN MATERIAL WITH IMPROVED CORROSION DURABILITY COMPRISING SAME, AND HEAT EXCHANGER CONSTRUCTED OF SAME

Info

Publication number: 20160237527
Type: Application
Filed: Sep 26, 2014
Publication Date: Aug 18, 2016
Applicant: RESEARCH & BUSINESS FOUNDATION SUNGKYUNKWAN UNIVERSITY (Suwon-si, Gyeonggi-do)
Inventors: Jung Gu KIM (Seongnam-si), In Jun PARK (Anyang-si)
Application Number: 15/025,166

Abstract

The present disclosure provides an aluminum alloy with enhanced penetration resistance for a heat exchanger, the alloy containing copper (Cu), and iron (Fe), whose contents are controlled to be equal to or smaller than predetermined contents respectively, and further containing zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof and the remainder being aluminum (Al). Further, the present disclosure provides an aluminum extruded tube and/or an aluminum fin with enhanced penetration resistance made of the alloy respectively. Further, the present disclosure provides a heat exchanger comprising the tube and/or fin. Addition and content-control of the alloy element may spread corrosion initiations and suppress intergranular corrosion to create uniform corrosion. In this manner, the present alloy have superior corrosion resistance compared to pitting corrosion of a previous alloy for a heat exchanger, and, at the same time, have an extrusion rate equal to that of the previous A1070.

Description

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims a priority to a Korean patent application number 2014-0018389 filed on Feb. 18, 2014, which claims a priority to a Korean patent application number 2013-0115043 filed on Sep. 27, 2013, the entire disclosures of which are incorporated herein in its entirety by reference.

BACKGROUND

1. Technical Field

The present disclosure generally relates to an aluminum alloy with enhanced penetration resistance for a heat exchanger, an aluminum alloy extruded tube and an aluminum alloy fin for a heat exchanger, the tube and fin being made of the alloy, and a heat exchanger comprising the tube and fin. More particularly, the present disclosure relates to an aluminum alloy extruded tube and an aluminum alloy fin for a heat exchanger, and a heat exchanger comprising the tube and fin, where the tube and fin have enhanced penetration and corrosion resistances to prevent the tube and fin from penetration and damage, which otherwise occur due to corrosion caused by internal refrigerant and external condensed water in the heat exchanger, for example, in an air-conditioner, refrigerator, radiator, etc.

2. Discussion of Related Arts

Recently, a material for a heat exchanger has changed from copper to aluminum in terms of costs, workability, corrosion resistance, etc. This is because that aluminum is weight-light, inexpensive, and highly thermal conductive.

Aluminum-based materials for a heat exchanger includes pure aluminum-based formulations (A1XXX) with a high extrusion rate, high thermal conductance, and a low cost, and aluminum manganese-based formulations (A3XXX) with a lower extrusion rate compared to the pure aluminum-based formulations, a relatively high strength, and relatively high corrosion resistance.

A following Table 1 describes respective compositions of A1070 and A3003 alloys as the previous aluminum-based formulations for a heat exchanger. The A1070 belongs to the pure aluminum-based formulations, while the A3003 belongs to the aluminum manganese-based formulations.

TABLE 1 name Cu Si Fe Zn Mg Mn Ti Al. A1070 0.03 0.20 0.25 0.04 0.03 0.03 0.03 Remainder A3003 0.158 0.084 0.421 0.034 0.001 1.021 0.014 Remainder

The A1070 may be employed for a tube and a fin, for example, in a condenser in home appliances such as an air-conditioner, a refrigerator, etc. where a high strength of the Al based material is not demanded but economical aspects such as a low material cost, and a low extrusion cost of the Al based material are demanded. To the contrary, the A3003 has a higher strength and corrosion resistance, but more expensive extrusion cost compared to the A1070, and, thus may be employed for a tube and a fin of a heat exchanger in an intercooler, radiator, etc. in an automobile.

Aluminum may have a high chemical activation, and may form an oxidized film at a surface thereof in an air space to have high corrosion resistance. However, when aluminum undergoes corrosion, there may occur a pitting corrosion where corrosion may occur only at a local area in which the oxidized film is damaged. Further, the corrosion may propagate and concentrate on a certain area due to electrochemical reaction with various impurities in the aluminum alloy. This corrosion mechanism may cause an aluminum heat exchanger to be locally penetrated, leading to a leak of internal refrigerant or hot fluids. Therefore, there is a need for an aluminum alloy with enhanced penetration resistance for the heat exchanger.

Further, the home appliances have been widely used in China, India etc. suffering from heavy air pollution. In these countries, the aluminum heat exchanger in the home appliances may be susceptible to such a leak therefrom due to the corrosion. This may be true of a seashore area. This leak may cause economical loss such as a component replacement, and may lead to deterioration of the home appliances.

FIG. 1 shows a mechanism for pitting corrosion and intergranular corrosion of a previous aluminum formulation. A left side drawing in FIG. 1 shows a grain-boundary distribution of a cathodic site. To be specific, a protective passive film is formed on an aluminum surface, and Al₂Cu, Al₃Fe, etc. are distributed along and in the grain boundary in an intermetallic phase. Upon a start of corrosion, pitting corrosion is initiated, such that, as shown in a middle drawing in FIG. 1, there may be generated a potential difference between a base material and the intermetallic phase materials Al₂Cu, and Al₃Fe, and, thus, a local circuit may be created. This may lead to the passive film damage, which may confirm the pitting corrosion initiation. Then, as shown in a right side drawing in FIG. 1, the pitting corrosion propagates. In this connection, a propagation rate of the pitting corrosion along the grain boundary may be higher than an initiation rate of new pitting corrosion at the surface of the alloy. This causes a larger penetration depth relative to an actual corrosion amount. This aluminum corrosion mechanism may cause a local penetration through the aluminum heat exchanger, and, thus, a leak of an internal refrigerant or hot fluid from the exchanger.

FIG. 2 illustrates corrosion propagation behavior in a previous aluminum alloy for a heat exchanger. As shown in the figure, a penetration depth becomes gradually larger due to the propagation of the pitting corrosion as time goes by.

SUMMARY

The present disclosure may provide an aluminum alloy for a tube and a fin in a heat exchanger, the alloy having enhanced penetration resistance and corrosion resistance and, at the same time, a non-lowered extrusion rate, which are not the case in the previous A1070 and A3003 aluminum alloys. This may be achieved by adding zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof into the alloy and adjusting composition ratios thereof to suppress corrosion concentration and thus allow uniform corrosion.

Further, the present disclosure may provide an aluminum alloy extruded tube and an aluminum alloy fin for a heat exchanger, the tube and fin being made of the above-defined aluminum alloy, and, thus, having enhanced penetration resistance. Further, the present disclosure may provide a heat exchanger comprising the above-defined tube and fin.

In one aspect of the present disclosure, there is provided an aluminum alloy comprising: copper (Cu); iron (Fe); zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof; and the remainder being aluminum (Al), and unavoidable impurities, wherein the zirconium (Zr), titanium (Ti), or hafnium (Hf), or the mixture thereof has a content from 0.05 wt % to 0.2 wt % relative to a total weight of the alloy; wherein contents of the copper and iron are adjusted such that a PHI (penetration hazard index) value defined by following equations (1) and (2) is equal to or smaller than 1.5:

$\begin{matrix} X = \frac{0.4 \times Cu % + 0.5 \times \exp (Fe % - 0.3)}{{1.24}^{(6 \times Zr %)}} & (1) \\ PHI = 0.1559 \times \exp (X \div 0.1226) - 3.7492 . & (2) \end{matrix}$

In one embodiment, the alloy may further comprises silicon (Si), wherein a content of the silicon may be adjusted to be equal to or smaller than 0.2 wt % relative to a total weight of the alloy.

In one embodiment, the alloy may further comprises magnesium (Mg), wherein a content of the magnesium is adjusted to be equal to or smaller than 0.05 wt % relative to a total weight of the alloy.

In one aspect of the present disclosure, there is provided an aluminum tube with enhanced corrosion resistance for a heat exchanger, the tube being made of the above-defined aluminum alloy.

In one aspect of the present disclosure, there is provided an aluminum fin with enhanced corrosion resistance for a heat exchanger, the fin being made of the above-defined aluminum alloy.

In one aspect of the present disclosure, there is provided a heat exchanger with enhanced corrosion resistance, the exchanger comprising the above-defined aluminum tube.

In one aspect of the present disclosure, there is provided a heat exchanger with enhanced corrosion resistance, the exchanger comprising the above-defined aluminum fin.

In one aspect of the present disclosure, there is provided a heat exchanger with enhanced corrosion resistance, the exchanger comprising an aluminum fin and an aluminum tube, wherein both the fin and tube are defined above.

In accordance with the present disclosure, the above-defined aluminum alloy may have superior penetration resistance and corrosion resistance, compared to the previous A1070 for a heat exchanger, and, thus, have superior corrosion and penetration resistances against external condensed water and internal refrigerant. To be specific, the addition of the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof may allow uniform corrosion of the alloy, and, thus, more enhanced penetration resistance relative to the pitting corrosion.

Furthermore, in accordance with the present disclosure, together with control of contents of the zirconium (Zr), titanium (Ti), or hafnium (Hf), control of contents of the copper (Cu) and iron (Fe) using the PHI may suppress intergranular corrosion, and, thus, may spread corrosion propagation, leading to enhanced penetration resistance of the alloy.

Furthermore, in accordance with the present disclosure, the above-defined aluminum alloy may exhibit an extrusion rate (about 90 m/min) similar to that of the previous A1070, and, thus, have good productivity and economy.

Furthermore, in accordance with the present disclosure, the above-defined heat exchanger may include components (for example, the fin and tube) thereof with enhanced corrosion resistance, such that the exchanger has a prolonged life span, good performance, and more energy-saving effect due to lack of leak of the refrigerant and, thus, improved heat-exchanging efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

A brief description of each drawing is provided to more fully understand the drawings, which is incorporated in the detailed description of the disclosure.

FIG. 1 shows a mechanism for pitting corrosion and intergranular corrosion of a previous aluminum alloy.

FIG. 2 illustrates corrosion propagation behavior in a previous aluminum alloy for a heat exchanger.

FIG. 3A and FIG. 3B illustrate cross-sectional views of a A1070 specimen as a previous 1XXX-based aluminum alloy for a heat exchanger, after being subjected to a potentiostatic polarization test.

FIG. 4A and FIG. 4B illustrate cross-sectional views of a A3003 specimen as a previous 3XXX-based aluminum alloy for a heat exchanger, after being subjected to a potentiostatic polarization test.

FIG. 5 is a schematic view illustrating a pitting corrosion and intergranular corrosion mechanism of an aluminum alloy of the present disclosure.

FIG. 6A and FIG. 6B illustrate cross-sectional views of specimens made of the aluminum alloy in accordance with one embodiment of the present disclosure, after being subjected to a potentiostatic polarization test.

FIG. 7 illustrates an aluminum heat exchanger in accordance with one embodiment of the present disclosure.

FIG. 8 illustrates a graph describing varying PHIs and varying extrusion rates of the present aluminum tube relative to varying zirconium contents.

FIG. 9 illustrates a graph describing varying PHIs relative to varying copper and iron contents.

FIG. 10 illustrates a graph describing a correlation between an X factor and a PHI value.

DETAILED DESCRIPTIONS

Examples of various embodiments are illustrated in the accompanying drawings and described further below. It will be understood that the discussion herein is not intended to limit the claims to the specific embodiments described. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the present disclosure as defined by the appended claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and “including” when used in this specification, specify the presence of the stated elements, and/or components, but do not preclude the presence or addition of one or more other elements, components, and/or portions thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Further, all numbers expressing dimensions, physical characteristics, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical values set forth in the following specification and claims can vary depending upon the desired properties sought to be obtained by the practice of the present disclosure. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.

As used herein, the term “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure.”

In one embodiment of the present disclosure, an aluminum alloy with enhanced penetration resistance includes copper (Cu); iron (Si); zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof; the remainder being aluminum (Al), and unavoidable impurities.

Hereinafter, a reason for content control of each component, and a property thereof will be first described, which, in turn, will be supported by a numerical-limitation example using experiment data for a numerical content of each component.

In one embodiment of the present disclosure, the aluminum alloy with enhanced penetration resistance contains zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof. The zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof may not only refine a grain size to improve strength of the alloy, but also suppress pitting corrosion and, thus, allow uniform corrosion. The suppression of pitting corrosion, and, thus, creation of the uniform corrosion may be achieved as follows: the addition of the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof may generate a potential difference in the alloy to finely spread precipitations serving as initiation points for corrosion, and thus, may suppress the pitting corrosion occurring locally and intensely and thus hard to predict corrosion locations. To achieve the uniform corrosion, respective optimal contents of the above components may be determined from a following Table 2.

TABLE 2 corrosion corrosion depth depth standard extrusion Cu Fe Zr Al average (μm) deviation PHI rate (m/min) 1 0.21 0.42 0.001 Remainder 175.59 154.7 27.171 90 2 0.19 0.38 0.06 Remainder 171.81 57.63 9.9021 90 3 0.22 0.4 0.13 Remainder 127.25 53.53 6.8121 90 4 0.19 0.39 0.21 Remainder 103.31 31.03 3.2058 84 5 0.20 0.41 0.41 Remainder 98.21 24.67 2.4225 32

In the above Table 2, a content of each component refers to a content in % by weight. In order to determine an optimal zirconium content, experiment conditions are set such that a content of zirconium is variable, while each of contents of copper, and iron is controlled to a given content. As shown from the Table 2, the results of the experiments indicate corrosion depth averages and corresponding corrosion depth standard deviations, and PHIs and extrusion rates, depending on the varying contents of the zirconium. In this connection, based on the Table 2, the PHIs and extrusion rates depending on the varying contents of the zirconium are graphically presented as shown in FIG. 8.

As used herein, a PHI refers to an acronym of a “penetration hazard index”. The PHI may be calculated by means of a corrosion penetration depth of an aluminum tube after being subjected to electrochemical corrosion acceleration. Thus, The PHI may serve as a measure of corrosion resistance of an aluminum alloy. A lower PHI value may mean superior corrosion resistance of an aluminum alloy.

The PHI may be expressed as follows:

PHI=(corrosion depth average)×(corrosion depth standard deviation)/1000.

In order to calculate the PHI, an aluminum alloy specimen is subjected to electrochemical corrosion acceleration in a synthetic acid rain, and, then, a cross-section of the resulting specimen is analyzed to measure a corrosion depth average and a corrosion depth standard deviation.

As seen from the above Table 2, in terms of the PHI and extrusion rate, an optimal Zr content may be 0.05 wt % to 0.2 wt %. This is due to following facts: an alloy composition of No. 1 in the Table 2 (whose Zr content is smaller than 0.05 wt %) may not suppress a crack in the alloy due to a much smaller Zr amount (this is confirmed from a remarkably high PHI value), while alloy compositions of No. 4 and No. 5 in the Table 2 (whose Zr content is larger than 0.2 wt %) may lower an extrusion rate of the alloy due to a much larger Zr amount. In this connection, in the present disclosure, it is desirable that the aluminum alloy should not only exhibit uniform corrosion, but also maintain an extrusion rate.

When the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof is added to the aluminum alloy, an intergranular corrosion mechanism of the alloy may be as follows:

FIG. 5 is a schematic view illustrating a pitting corrosion and intergranular corrosion mechanism of the present aluminum alloy. As shown in FIG. 5, in the aluminum alloy in accordance with the present disclosure, the addition of the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof may allow a decrease of a residence of Al₂Cu, Al₃Fe, etc. in the grain boundary in the intermetallic phase, and, thus, spread the residence of Al₂Cu, Al₃Fe, etc. For a comparison, in FIG. 1, the Al₂Cu, Al₃Fe, etc. mainly reside in the grain boundary, while in FIG. 5 (see a left side drawing therein), the residence of the Al₂Cu, Al₃Fe, etc. in the grain boundary may decrease.

Further, as shown in a middle drawing of FIG. 5, it is confirmed that upon start of pitting corrosion, corrosion initiation points are disperse. For a comparison, in FIG. 1, upon start of pitting corrosion, the corrosion occurs in a local and concentrated manner.

Finally, as shown in a right drawing of FIG. 5, it is confirmed that upon propagation of the pitting corrosion, the corrosion may not concentrate on a certain location, and, thus, may be suppressed in a deep and inwardly direction. As a result, upon the pitting corrosion propagation, inwardly penetration may be less probable. To the contrary, in FIG. 1 (see a right side drawing therein), the pitting corrosion may propagate along the grain boundary, and, thus, the inwardly penetration depth may be larger than that in the aluminum alloy of the present disclosure.

Next, an experiment for measuring the PHI values, and the PHI values depending on aluminum alloy compositions may be as follows:

In order to calculate the PHI, an aluminum alloy specimen is subjected to electrochemical corrosion acceleration in a synthetic acid rain, and, then, a cross-section of the resulting specimen is analyzed to measure a corrosion depth average and a corrosion depth standard deviation. Details about an experimental procedure are as follows: first, a surface of the aluminum alloy specimen is polished using a #600 SiC paper, and, then, an exposure area thereof is controlled to be 1 cm×1 cm. Then, the specimen is immersed for 4 hours in a test solution (synthetic acid rain) of pH 5 containing 4 ppm SO4²⁻, 1.5 ppm NO²⁻, and 2 ppm Cl⁻ to stabilize a surface state of the specimen. Thereafter, the specimen has a constant potential of 0.25 V applied thereto for 6 hours, the potential being relative to SCE (saturated calomel electrode), to accelerate corrosion in a constant rate. The synthetic acid rain simulates a corrosion environment to which a heat exchanger including an aluminum tube is exposed in an air space. The electrochemical acceleration method simulates a corrosion mechanism identical with an actual corrosion environment purely in an electrochemical manner. The electrochemical acceleration method may be more similar to the actual corrosion environment than an existing chemical acceleration method. Further, in the electrochemical acceleration method, since the same acceleration energy is applied to all specimens, differences in corrosion resistances between the specimens may be evaluated in a more reliable manner. A following Table 3 indicates chemical compositions, corrosion penetration depths after the electrochemical acceleration, and the PHI values for 11 aluminum specimens. In the Table 3, a No. 11 specimen is made in accordance with one embodiment of the present disclosure. As seen from the Table 3, when a PHI value is smaller than or equal to 1.5, corrosion resistance of the alloy is superior. From comparison of the PHI values between previous alloys (No. 1 to No. 10 specimens) and the present alloy (No. 11 specimen), it is confirmed that when the PHI value of the alloy is smaller than or equal to 1.5, the alloy exhibits a relatively low average corrosion depth and standard deviation, which means that corrosion of the alloy occurs and propagates substantially uniformly, and, thus, the alloy has sufficient corrosion resistance enhancement.

Corrosion Corrosion penetration penetration depth depth average standard Cu Fe Zr Al (μm) deviation PHI 1 0.006 0.098 0 Remainder 64.74 28.01 1.813 2 0.003 0.246 0 Remainder 75.29 65.84 4.957 3 0.005 0.46 0 Remainder 156.81 92.56 14.514 4 0.158 0.421 0 Remainder 190.97 150.31 28.705 5 0.2 0.51 0 Remainder 265.59 143.72 38.171 6 0.5 0.07 0 Remainder 236.97 65.22 15.455 7 0.21 0.42 0.001 Remainder 175.59 154.7 27.171 8 0.19 0.38 0.06 Remainder 171.81 57.63 9.9021 9 0.22 0.4 0.13 Remainder 127.25 53.53 6.8121 10 0.19 0.39 0.21 Remainder 103.31 31.03 3.2058 11(present 0.005 0.2 0.1 Remainder 40.68 14.41 0.586 alloy)

As seen from the Table 3, when the present alloy (No. 11 specimen) has the PHI value smaller than or equal to 1.5, and, thus, exhibits a relatively low average corrosion depth and standard deviation, which means that corrosion of the alloy occurs and propagates substantially uniformly. Although the previous alloy (No. 1 specimen) has a low PHI value, contents of the copper and iron may not be adjusted to low levels as in the No. 1 specimen due to technical difficulty and economical aspects.

Hereinafter, descriptions will be made about controls of contents of the copper and iron in connection with the above-described PHI value and the optimal content of the zirconium.

Regarding an alloy formation, when a metal has a different element injected intentionally thereto, the element is referred to as an alloy element. Meanwhile, impurities are unavoidably injected into the alloy due to a technical limitation and an economical aspect during the alloy formation. The impurities may be limited in contents thereof by contents equal to or smaller than acceptable amounts, and, thus, presences thereof in the alloy may be acceptable. The acceptable contents of the impurities may depend on what extent of harm the impurities give the metal.

Specifically, the copper (Cu) may react with the aluminum and hence be precipitated into Al₂Cu promoting the cathodic reaction of corrosion. The copper may mainly reside in a continuous or networking manner along the grain boundary of the aluminum, and, thus, may be a factor for intergranular corrosion where the corrosion damage propagates along the grain boundary. This intergranular corrosion may cause the aluminum alloy for a heat exchanger to be susceptible to the penetration. In order to avoid the intergranular corrosion, the copper should be controlled in a content thereof by a content smaller than a high content at a room temperature.

The iron (Fe) may react with the aluminum and silicon to generate precipitations acting as initiation points of cathodic reactions in corrosion environment, thereby to play a considerable role for the aluminum corrosion. Thus, the iron content should be minimized. However, the precipitations derived from the irons may reside in a non-continuous or isolated manner and, thus, be less susceptible to the interganular corrosion compared to the copper. Further, in order to reduce the content of the iron below a low concentration, a high cost may occur. Therefore, the iron (Fe) content should be controlled from considerations of the above.

The copper and iron may play a significant role in aluminum corrosion in a corrosion environment based on a content correlation between there. Thus, in the present disclosure, the content correlation is determined to suppress intergranular corrosion.

Not only the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof, but also the copper (Cu) and iron (Fe) may affect the intergranular corrosion. FIG. 9 illustrates a graph describing varying PHIs relative to varying copper and iron contents. It is confirmed that when a content of copper is equal to or larger than 0.01 wt %, the intergranular corrosion may occur, and, thus, the PHI may increase. When a content of copper is equal to or larger than 0.01 wt %, the copper may precipitate along the grain boundary of the aluminum in a continuous or networking manner. This continuous or networking manner of the precipitation may allow the corrosion of the aluminum alloy, for example, an aluminum tube to propagate along the grain boundary and, thus, be susceptible to penetration. Therefore, it is observed that when a content of copper is equal to or larger than 0.01 wt %, the content of the copper and the PHI have a linear correlation. Meanwhile, it is confirmed that when a content of iron is equal to or larger than 0.2 wt %, the PHI may increase exponentially. The iron may act as a highly corrosive impurity. However, the iron may be individually spread in a form of islands in the aluminum in a low concentration thereof, and, thus, may not cause intergranular corrosion. This is not true of the copper. When the iron content increases, precipitations thereof which are individually spread in the low concentration of the iron may increase and thus form a continuous form thereof to allow the corrosion to occur in a continuous manner as in the intergranular corrosion. In this way, it is confirmed that when a content of iron is equal to or larger than 0.2 wt %, the PHI may increase exponentially. From the considerations of the above facts, a relationship between the contents of the iron and copper and the PHI value is that a sum of the contents of the copper and iron equal to or larger than critical amounts respectively may increase the PHI value. In addition to this, as indicated in the Table 2, the zirconium content may also affect the intergranular corrosion (the larger the Zr content is, the lower the PHI is; the optimal Zr content may be 0.05 to 0.2 wt %). Thus, the zirconium content should be taken into account.

From comprehensive considerations of the above facts, the PHI may be expressed as follows:

$\begin{matrix} PHI = f (X); where \\ X = \frac{0.4 \times Cu % + 0.5 \times \exp (Fe % - 0.3)}{{1.24}^{(6 \times Zr %)}}; & (1) \end{matrix}$

where the X factor refers to concentrations of alloy elements. That is, the PHI may be expressed as a function of the X factor.

In this connection, FIG. 10 illustrates a graph describing a correlation between the X factor and the PHI value. It may be seen from this graph that the X factor and the PHI value have an exponential relationship, which may be expressed as follows:

PHI=0.1559×exp(X÷0.1226)−3.7492 (2).

When the PHI is adjusted to be equal to or smaller than 1.5 (as addressed above) based on the above equations (1) and (2), and the Zr content is adjusted to be 0.05 to 0.2 wt % (as addressed above), a relationship about the Cu and Fe contents is as follows:

Although the PHI value may be adjusted to be equal to or smaller than 1.5, the PHI value is fixed to 1.5 for the sake of an exemplary simplified calculation. In this connection, the PHI 1.5 may suffice to suppress the intergranular corrosion and thus obtain enhanced corrosion resistance of the aluminum alloy for a fin and a tube of a heat exchanger. Of course, the PHI value smaller than 1.5 may be more preferable. The PHI value 1.5 may be employed to define a maximum numerical range.

Based on the equation (2), when the PHI is 1.5, X is 0.4311. In this case, the Zr content of 0.05 to 0.2 wt % is applied to the equation (1). The result is as follows:

0.4598≦0.4×Cu %+0.5×exp(Fe %−0.3)≦0.5580 (3).

In this connection, since the lowest contents of the copper and iron may be ideal, a minimum value, that is, the left side value in the equation (3) is not meaningful, and, thus is ignored. In addition to, the right side value is rounded off. Hence, a final relationship about the Cu and Fe contents is as follows:

0.4×Cu %+0.5×exp(Fe %−0.3)≦0.56 (4).

Therefore, in order to suppress intergraular corrosion, the Cu and Fe contents may be adjusted as in the equation (4).

The aluminum alloy composition of one embodiment of the present disclosure may contain silicon and magnesium impurities beside the copper and iron. Thus, the silicon and magnesium impurities should be limited in contents thereof as follows.

The magnesium (Mg) may react with the silicon (Si) to form precipitations to improve alloy strength. However, the magnesium (Mg) may create an oxide film to deteriorate brazing bonding ability. Thus, the Mg content should be minimized. In the present disclosure, the Mg content may be controlled to be as follows: 0 wt %<Mg≦0.05 wt %. When the Mg content exceeds 0.05 wt %, the brazing bonding ability may be deteriorated, leading to poor brazing process. Thus, the Mg content should be adjusted to be equal to or smaller than 0.05 wt %. Further, because of an economical aspect, the alloy may avoidably contain the impurity Mg, and, thus, the Mg content has no choice but to exceed zero %.

The silicon (Si) may react with unavoidable impurities (magnesium) to generate precipitations, which may promote cathodic reaction in corrosion environment. Thus, the silicon content should be minimized. In the present disclosure, the silicon (Si) content may be controlled to be greater than 0% by weight and equal to or smaller than about 0.2% by weight.

Although, in order to reduce the corrosion, it is preferable that contents of the above-mentioned impurities, namely, copper, iron, silicon and magnesium should be minimized, the contents thereof may be controlled to the above-defined contents due to the economical aspect. The above-defined contents thereof may suffice to provide the good aluminum alloy for a heat exchanger as illustrated below.

FIG. 3A and FIG. 3B illustrate cross-sectional views of a A1070 specimen as a previous 1XXX-based aluminum alloy for a heat exchanger, after being subjected to a potentiostatic polarization test. FIG. 4A and FIG. 4B illustrate cross-sectional views of a A3003 specimen as a previous 3XXX-based aluminum alloy for a heat exchanger, after being subjected to a potentiostatic polarization test. FIG. 6A and FIG. 6B illustrate cross-sectional views of specimens made of the aluminum alloy in accordance with one embodiment of the present disclosure, after being subjected to a potentiostatic polarization test.

In the potentiostatic polarization test, a constant voltage is applied and maintained to the specimen to accelerate corrosion. This test may be useful to evaluate a corrosion resistance of the alloy. In the present disclosure, the alloy specimen is subjected to the potentiostatic polarization test for 6 hours using the synthetic acid rain simulating the external condensed water, and a cross-section of the resulting specimen is measured in terms of a corrosion depth.

Referring to FIG. 3A, FIG. 3B, FIG. 4A, FIG. 4B, FIG. 6A and FIG. 6B, a comparison between the present and previous alloys will be made in terms of the penetration depth. In this comparison, the penetration depth may be relative to the reference line (red line). In case of previous A1070 and A3003 specimens, corrosion is concentrated on a certain region, and propagate inwardly along the grain boundary, to form a large penetration depth. To the contrary, in case of the present specimen, corrosion is spread along the reference line, that is, a surface line of the alloy, and an intergranular corrosion may not occur and, thus, create a uniform corrosion, to form a small penetration depth. Hence, it is confirmed that the present specimen has a greater decrease in the corrosion propagation than in the A1070 and A3003 specimens.

The following Table 4 indicates corrosion depth measurements of the previous A1070 and A3003 specimens, and the present specimens made of the aluminum alloy of one embodiment of the present disclosure, after being subjected to the potentiostatic polarization test.

TABLE 4 Corrosion depth (thinning) (μm) A1070 A3003 Present alloy 1 236.03 184.25 41.56 2 262.82 58.41 30.86 3 240.00 97.25 28.34 4 37.47 49.51 39.06 5 245.58 48.54 30.86 6 57.48 124.31 34.01 7 98.27 88.41 51.64 8 42.62 157.52 62.97 9 23.78 121.24 23.30 10 147.32 35.45 64.24 Average 139.14 96.49 40.68 Standard deviation 98.63 50.07 14.40

Referring to the Table 4, the A1070 specimens exhibit an average corrosion depth of 139.14 μm, and a standard deviation of 98.63 μm. The A3003 specimens exhibit an average corrosion depth of 94.49 μm, and a standard deviation of 50.07 μm. To the contrary, the present specimens made of the aluminum alloy of one embodiment of the present disclosure exhibit an average corrosion depth of 40.68 μm, and a standard deviation of 14.4 μm. In other words, the present specimens made of the aluminum alloy of one embodiment of the present disclosure exhibit about 3.5 times corrosion resistance improvement compared to the A1070 specimens. Further, the present specimens made of the aluminum alloy of one embodiment of the present disclosure exhibit an overall lowered corrosion depth deviation which means that a uniform corrosion occurs, leading to enhanced penetration resistance.

Furthermore, the present specimens made of the aluminum alloy of one embodiment of the present disclosure exhibit a good extrusion rate of about 90 m/min. This rate may be substantially equal to an extrusion rate of the previous A1070, and may be higher than an extrusion rate of the previous A3003 which is about 60-70 m/min. That is, the present specimens made of the aluminum alloy of one embodiment of the present disclosure may have a superior extrusion rate compared to the previous A3003.

The aluminum alloy of one embodiment of the present disclosure may be employed for not only an extruded tube but also for a fin in a heat exchanger.

FIG. 7 illustrates an aluminum heat exchanger in accordance with one embodiment of the present disclosure. The heat exchanger comprising those extruded tube and fin may be classified into a stack type, a tube type, draw-on cap type, etc. in terms of a structure.

In particular, the tube type heat exchanger may increase heat dissipation via a fin internally attached thereto or a pipe having multiple holes formed therein. Specifically, the heat exchanger may be manufactured by provisionally assembling the extruded tube with a fin, a plate and a side tank, etc. and fixing one another via a clamp, and applying a flux treatment to the fixed structure, and passing the structure through a brazing furnace.

In this way, the aluminum alloy of the present disclosure for the heat exchanger has greatly enhanced corrosion resistance, and, thus, the heat exchanger made of the alloy has enhanced penetration resistance, leading to a prolonged life span and improved performance.

The above description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of exemplary embodiments, and many additional embodiments of this disclosure are possible. It is understood that no limitation of the scope of the disclosure is thereby intended. The scope of the disclosure should be determined with reference to the Claims. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic that is described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

Claims

1. An aluminum alloy comprising:

copper (Cu);

iron (Fe);

zirconium (Zr); and

the remainder being aluminum (Al), and unavoidable impurities,

wherein the zirconium (Zr) comprises a content from 0.05 wt % to 0.2 wt % relative to a total weight of the alloy, and

contents of the copper and iron are adjusted such that a PHI (penetration hazard index) value is equal to or smaller than 1.5, in accordance with equations (1) and (2), in which: X=0.4×Cu %+0.5×exp(Fe %−0.3)/1.24(×Zr %) (1) PHI=0.1559×exp(X÷0.1226)−3.7492 (2).

2. The alloy of claim 1, further comprising silicon (Si), wherein a content of the silicon is adjusted to be equal to or smaller than 0.2 wt % relative to a total weight of the alloy.

3. The alloy of claim 1, further comprising magnesium (Mg), wherein a content of the magnesium is adjusted to be equal to or smaller than 0.05 wt % relative to a total weight of the alloy.

4. The alloy of claim 2, further comprising magnesium (Mg), wherein a content of the magnesium is adjusted to be equal to or smaller than 0.05 wt % relative to a total weight of the alloy.

5. An aluminum tube with enhanced corrosion resistance for a heat exchanger, the tube being made of the aluminum alloy of claim 1.

6. An aluminum fin with enhanced corrosion resistance for a heat exchanger, the fin being made of the aluminum alloy of claim 1.

7. A heat exchanger with enhanced corrosion resistance, the exchanger comprising an aluminum tube and an aluminum fin, the tube and fin both being made of the alloy of claim 1.