KR20210006749A - Aluminum alloys for heat exchanger, and heat exchanger made of the same - Google Patents

Abstract

The present invention relates to an aluminum alloy for a heat exchanger, a tube for a heat exchanger and a pin material for a heat exchanger using the alloy, and a heat exchanger manufactured thereby. The tube and pin material aluminum alloy for a heat exchanger is a material inducing the formation of residual Fe and an intermetallic compound (IMC) through addition of Mn to improve penetrating resistance and corrosion resistance against uniform corrosion and has strength and productivity comparable to existing AA3003 through Mn and Zr content control and optimized homogenization treatment.

Description

Aluminum alloy for heat exchanger and heat exchanger manufactured therefrom {ALUMINUM ALLOYS FOR HEAT EXCHANGER, AND HEAT EXCHANGER MADE OF THE SAME}

The present invention relates to an aluminum alloy for a heat exchanger, and to a heat exchanger tube, a heat exchanger fin material, and a heat exchanger manufactured thereby using such an alloy.

The aluminum alloy tube of the registered patent KR 10-1465389 is a material that improves the durability against penetration corrosion than the existing 1XXX series and 3XXX series aluminum alloy tubes by improving the shape and corrosion resistance of corrosion propagation while maintaining the extrusion speed and strength at the level of 1XXX. . However, as the penetration resistance improved, the uniform corrosion rate was increased, and the strength of the above alloy is at the level of 1XXX, and there is a possibility that the product may be damaged due to external stress generated during the heat exchanger manufacturing process or the use of the finished product.

Through additional research, this research group further improved the corrosion resistance while maintaining penetration resistance of the KR 10-1465389 aluminum alloy tube, and discovered a composition having similar strength compared to the existing A3003 alloy, and this technology development was carried out for this purpose.

(1) Homogenization temperature and time optimization

Homogenization treatment is a process to prevent product cracking by removing micro-segregation of cast billets through precipitation phase decomposition and re-precipitation, and removing residual internal stress.It is an essential process to achieve uniform distribution of solute atoms in aluminum alloys. to be.

KR 10-1465389 With the addition of Mn to improve the strength of the developed alloy and improving the chemical composition, this developed alloy not only the existing intermetallic compounds (Al ₃ Zr) but also new metals such as Al ₆ (Mn, Fe) and Al ₆ Mn. Liver compounds are formed. Therefore, optimization of the temperature and time of the homogenization treatment is required to remove the microsegregation of the intermetallic compound, homogenize the macroscopic composition, and induce the optimum grain size and distribution of the intermetallic compound.

(2) Increased corrosion rate by inducing uniform corrosion

Zr not only improves strength by minimizing the grain size in the Al matrix, but also generates a potential difference inside the material, finely dispersing the precipitates acting as the initiation point of corrosion, a form of narrow and deep form that is difficult to predict. It has the effect of suppressing the occurrence of pitting corrosion and inducing uniform corrosion.

In the case of the KR 10-1465389 developed alloy, the penetration resistance was improved by the effect of Zr as described above, but there is a problem that the rate of uniform corrosion increases due to the initiation point of dispersed corrosion.

Such an increase in the rate of uniform corrosion can be judged as a better result than the penetration of the tube, but since it is a factor that affects the life of the product, it is necessary to reduce the rate of uniform corrosion by additional research.

(3) Strength of the developed alloy

The KR 10-1465389 development alloy of this research group is an alloy developed with the aim of 1XXX-based alloy, and its strength is lower than that of 3XXX-based aluminum alloy. However, during the manufacturing process of the aluminum heat exchanger tube, there is a process (Fin bonding, bending, internal pressure due to fluid) that applies pressure to the product, and the product is deformed or cracked due to the stress applied to the product depending on the usage environment after the product is shipped. , Destruction, etc. may occur. Therefore, existing developed alloys show excellent performance in terms of penetration resistance, but additional research is required in terms of the mechanical properties of the material.

Zr is an element that improves strength by making it difficult to move dislocations through miniaturization of intermetallic compounds, and Mn also forms an Al ₆ Mn phase in Al to increase the energy required for dislocation movement, thereby improving the strength of the alloy. Known as. The A3003 material is a material containing 1.0 to 1.5 wt.% of Mn, whereas the developed alloy of this research group reduces the Mn content to secure workability and dislocation stability, and at the same time add Zr to obtain similar strength to the existing AA3003 material. have.

(4) Extrusion force and production speed

The increase in strength of a material can be explained as a phenomenon in which dislocation movement becomes difficult due to precipitation phases, impurities, defects, etc. existing inside the material. The above defects make it difficult to operate the slip system in which the material is deformed, thereby increasing the strength, but conversely, the workability decreases.

For commercialization of materials, production efficiency must be considered in the mass production process. The production process of aluminum tubes for heat exchangers can be divided into extrusion and drawing, and the main process variables are extrusion force and production speed. This research group has developed an alloy having excellent strength and productivity required for mass production through additional research on the composition of the developed alloy.

According to the present invention, by inducing the formation and dispersion of intermetallic compounds (IMC) through the addition of Mn and Zr, it provides a material that improves not only penetration resistance but also corrosion resistance against uniform corrosion, and control and optimization of Mn and Zr contents. Through the homogenization treatment, we intend to provide an aluminum alloy for heat exchanger tubes and fins with strength and productivity comparable to that of the existing AA3003.

Aluminum alloy for a heat exchanger according to an embodiment of the present invention, 0.20 to 0.50% by weight of manganese (Mn); 0.05 to 0.20% by weight of zirconium (Zr); More than 0 and 0.01% by weight or less of the copper (Cu); More than 0 and 0.1% by weight or less of the iron (Fe); More than 0 and 0.15% by weight or less of the silicon (Si); And the remainder of aluminum (Al) and indispensable impurities.

The aluminum alloy for a heat exchanger according to the present invention has improved penetration resistance and improved corrosion resistance against uniform corrosion.

The aluminum alloy is obtained by homogenizing the billet produced through the casting process in a range of 425 to 490° C. for 7 to 10 hours, followed by air-cooling the 6 inch billet, and the heating rate is 10 to 50° C. per minute. The billet was preheated at 475~490℃ and extruded by direct extrusion.

The existing alloy developed by this research group was an aluminum alloy for heat exchangers with improved penetration resistance. This research group developed a material with improved penetration resistance as well as corrosion resistance against uniform corrosion through additional research on the composition, and for heat exchangers with strength and productivity comparable to the existing AA3003 through control of Mn and Zr content and optimized homogenization treatment. Tube and fin material aluminum alloy.

1 shows the corrosion potential and potential stability (10H) according to the homogenization treatment temperature of the developed alloy billet.
2 shows the corrosion potential and potential stability (475°C) according to the homogenization treatment time of the developed alloy billet.
Figure 3 shows the results of a polarization experiment (240H) of an aluminum alloy coincidence by Mn composition in an SWAAT environment.
4 shows a cross-section (A3003, KR 10-1465389, developed alloy) after a SWAAT environment constant current corrosion acceleration experiment.
5 shows the extrusion force and extrusion speed for each composition of Zr and Mn of the developed alloy.
Various embodiments are now described with reference to the drawings, in which like reference numbers are used to indicate like elements throughout the drawings. In this specification for purposes of explanation, various descriptions are presented to provide an understanding of the invention. However, it is clear that these embodiments may be implemented without this specific description. In other instances, well-known structures and devices are presented in block diagram form to facilitate description of the embodiments.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present invention, various modifications may be made and various forms may be applied, and specific embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific form of disclosure, it is to be understood as including all changes, equivalents, or substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar elements.

The terms used in the present application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the existence of features, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features or steps It is to be understood that it does not preclude the possibility of addition or presence of, operations, components, parts, or combinations thereof.

Registered patent KR 10-1465389 of this research group was developed through additional research on the composition of'aluminum alloy composition, aluminum extruded tube and fin material with improved penetration resistance, and a heat exchanger composed of the same'. About. The developed alloy improved the penetration resistance of the aluminum alloy due to the effect of Zr, but the uniform corrosion rate was increased. This developed alloy is a material that induces the formation of the balance Fe and intermetallic compounds (IMC) through the addition of Mn to improve not only penetration resistance but also corrosion resistance against uniform corrosion. It is an aluminum alloy for heat exchanger tubes and fins with strength and productivity comparable to the existing AA3003.

Aluminum alloy for a heat exchanger according to an embodiment of the present invention, 0.20 to 0.50% by weight of manganese (Mn); 0.05 to 0.20% by weight of zirconium (Zr); More than 0 and 0.01% by weight or less of the copper (Cu); More than 0 and 0.1% by weight or less of the iron (Fe); More than 0 and 0.15% by weight or less of the silicon (Si); And the remainder of aluminum (Al) and indispensable impurities.

The aluminum alloy for a heat exchanger according to the present invention has improved penetration resistance and improved corrosion resistance against uniform corrosion.

The aluminum alloy is obtained by homogenizing the billet produced through the casting process in a range of 425 to 490° C. for 7 to 10 hours, followed by air-cooling the 6 inch billet, and the heating rate is 10 to 50° C. per minute. The billet was preheated at 475~490℃ and extruded by direct extrusion.

Hereinafter, an aluminum alloy for a heat exchanger according to an embodiment of the present invention will be described in more detail.

In the present invention, the optimum composition was designed by measuring the corrosion rate, extrusion force, production rate, and tensile strength of each of the aluminum alloys by controlling the composition of Mn and Zr. These results are shown in FIGS. 1 to 5.

As a specific method, a test piece was prepared with 0.2 / 0.3 / 0.4 / 0.5 / 0.6 wt.% Mn as a variable for the 0.05 / 0.10 / 0.15 wt.% Zr alloy, and the extrusion force generated during the extrusion of the tube material of the 6 inch billet and The production rate was measured and evaluated. Corrosion rate measurement method was carried out after measuring OCP for 12 hours using a saturated calomel electrode (SCE) as a reference electrode in a SWAAT (salt water acetic-acid test) solution environment. Based on this result, an optimization design of the extrusion force and production rate according to the composition was carried out, and the corrosion rate for each alloy was plotted.

(1) Manufacture of aluminum development alloy billet

The composition of the specimen used in this experiment is shown in Table 1 below.

Composition (wt.%) Cu Fe Si Zr Mn Al One 0.01
max. 0.1
max. 0.15
max. 0.05 0.2 Rem. 2 0.3 3 0.4 4 0.5 5 0.6 6 0.01
max. 0.1
max. 0.15
max. 0.10 0.2 Rem. 7 0.3 8 0.4 9 0.5 10 0.6 11 0.01
max. 0.1
max. 0.15
max. 0.15 0.2 Rem. 12 0.3 13 0.4 14 0.5 15 0.6

* Experimental Example 1 (Evaluation of corrosion potential according to the homogenization treatment temperature)

The developed alloy billet, which was heat-treated for 10 hours at different homogenization temperatures, was measured for the average value and standard deviation of the corrosion potential for 48 hours in an SWAAT (salt water acetic-acid test) solution environment. At this time, a saturated calomel electrode (SCE) was used as the reference electrode. The potential stability was compared based on the standard deviation and shown in the graphs of [Table 2] and [Fig. 1].

The average corrosion potential is -0.780 V vs. the standard value. When it is combined with the pin when it is above SCE, corrosion acceleration due to potential reversal does not occur. When the homogenization temperature is between 425 and 475℃, the average potential is -0.780 V vs. It is maintained above SCE. Standard deviation is an item indicating the stability of potential. The lower the standard deviation, the closer the corrosion potential is to the average value, and if it is less than 0.01, the potential stability is high. Like the average potential, it was confirmed that the standard deviation was very low in the 425~475°C section of the homogenization treatment temperature compared to other sections.

The temperature range of 425~475°C is the temperature range where the nucleation rate is the maximum when Zr is precipitated into the Al ₃ Zr phase in a solid solution in the base material Al. In this section, the Al ₃ Zr particles are small, uniform and high density. Can be. The uniform distribution of the Al ₃ Zr phase, which plays a role in determining the corrosion potential of the aluminum alloy, can be seen as a factor stabilizing the corrosion potential of the aluminum alloy. On the other hand, when the temperature range for homogenization is higher than 500°C, the Al ₃ Zr phase transitions from the maximum nucleation period to the maximum growth period to form a coarse Al ₃ Zr phase. In this case, the agglomeration of Al ₃ Zr phases exists because the free energy is low, so the degree of dispersion decreases, and as a result, the stability of the corrosion potential also decreases.

Homogenization
Temperature(℃) time Corrosion potential (V vs. SCE) electric potential
Stability Average Standard Deviation One 400 10 hours -0.7912 0.0149 △ 2 425 -0.7675 0.0062 O 3 450 -0.7724 0.0065 O 4 475 -0.7711 0.0071 O 5 500 -0.7782 0.0309 O 6 550 -0.8200 0.0412 X 7 600 -0.8432 0.0464 X

* Experimental Example 2 (Evaluation of corrosion potential according to homogenization treatment time)

When the homogenization temperature was 475°C, the corrosion potential of the developed alloy billet according to the heat treatment time was measured. The specific method is the same as above, and the results are shown in Table 3 and the graph of FIG. 2.

As a result of the experiment, when the homogenization treatment time is less than 5 hours, the average corrosion potential is -0.78 V vs. It is as low as less than SCE, and the standard deviation is more than 0.01. When the homogenization treatment time is between 7 and 10 hours, both the average corrosion potential and the standard deviation meet the standard values, and as it exceeds 15 hours, the average corrosion potential decreases and the standard deviation increases. If the homogenization treatment time is shorter than 7-10 hours, the concentration of the Al ₃ Zr precipitated phase is low, and if the time is longer, the possibility of Al ₃ Zr nucleation is increased because the nucleation of Al ₃ Zr has sufficiently occurred. It gets higher. Therefore, the homogenization treatment time is appropriate for 7-10 hours.

Homogenization
Temperature(℃) time Corrosion potential (V vs. SCE) electric potential
Stability Average Standard Deviation One 475 3 hours -0.8192 0.0212 X 2 5 hours -0.7927 0.0108 △ 3 7 hours -0.7724 0.0065 O 4 10 hours -0.7732 0.0052 O 5 15 hours -0.7789 0.0101 O 6 20 hours -0.8026 0.0174 △ 7 30 hours -0.8224 0.0207 X

(2) Evaluation of corrosion resistance and penetration resistance

* Experimental Example 3 (corrosion resistance evaluation)

This experiment was conducted by continuously changing the voltage in the range of +1 V based on the corrosion potential of the electrode in a three-electrode system at a rate of 10 mV/min and measuring the current density at each voltage. Through this experiment, the corrosion characteristics of aluminum tubes for heat exchangers can be found.

For the aluminum tube, a specimen polished with #600 abrasive paper was used, and the electrolyte was OCP (OCP) for 12 hours using a saturated calomel electrode (SCE) in an SWAAT (salt water acetic-acid test) solution environment. After measuring open-circuit potential), an electrokinetic polarization test was performed, and the corrosion rate according to the Mn composition is shown in FIG. 3.

3 is a graph schematically showing the results of an experiment on the coincidence polarization curve for each Mn composition. As the composition of Mn increases, the corrosion resistance of the material is improved. The increased amount of corrosion resistance tends to decrease in the width of 0.5 wt.% or more, and as shown in FIG. 5, since the productivity decreases as the Mn composition increases, 0.2 to 0.5 wt.% of Mn is appropriate.

* Experimental Example 4 (Evaluation of penetration resistance)

In this experiment, an aluminum tube was subjected to a constant current acceleration experiment for 12 hours at 1 mA/cm ² in a salt water acetic-acid test (SWAAT) environment, and then the cross section of the specimen was observed. This experiment is an experiment that accelerates the corrosion of the material by applying a current greater than the corrosion current density for a certain period of time after calculating the corrosion current density of the specimen in a three-electrode system. . The constant current acceleration experiment was conducted for the purpose of determining the corrosion pattern 2 years after use, and a cross-sectional view of the test piece after the experiment is shown in FIG. 4 is a cross-sectional analysis result after a constant current corrosion acceleration test in the SWAAT (salt water acetic-acid test) environment. As a result of the analysis, it can be confirmed that the intergranular corrosion did not appear in this developed alloy, and the corrosion thinning depth was lower than that of A3003. Table 4 shows the depth of each corrosion thinning. The average corrosion thinning depth of the developed alloy was 52.27 um, which was twice the corrosion resistance of A3003's 102.77 um.

Material name Corrosion thinning depth (um) Remark Average Standard Deviation A3003 102.77 26.75 Intergranular/local corrosion KR 10-1465389 32.21 8.24 Oral/uniform corrosion Development alloy 26.27 5.17 Oral/uniform corrosion

(3) Evaluation of strength of the developed alloy

* Experimental Example 5 (evaluation of yield, tensile strength and elongation)

This experiment is an experiment in which the manufactured aluminum tube for a heat exchanger is cut to a certain size and the yield, tensile strength and elongation of the tube are evaluated through a tensile tester. As the Mn content increased, the strength of the material increased and the elongation decreased. Table 5 shows the yield, tensile strength, and elongation results of A3003 and the developed alloy. Depending on the degree of work hardening, the developed alloy has a maximum yield strength of 166.6 MPa and a maximum tensile strength of 119.8 ~ 220.2 MPa, and the elongation at this time is 31 ~ 3.3%. As a result of analyzing the mechanical properties of the material, it was confirmed that the developed alloy has superior properties than A3003 in terms of strength, and has similar elongation.

Yield strength
[MPa] The tensile strength
[MPa] Elongation
[1.6mm %] A3003 39.2 ~ 186.3 107.8 ~ 201.0 30 to 4 KR 10-1465389 16.1 ~ 72.8 48.0 ~ 87.2 42 to 8 Development alloy 30.4 ~ 166.6 119.8 ~ 220.2 31 ~ 3.3

(4) Evaluation of process variables in the production process

* Experimental Example 6 (evaluation of pressure output and extrusion speed)

This experiment is an experiment on optimizing the alloy composition that can be mass-produced by measuring process variables (pressing power, extrusion speed) occurring in extrusion during the production process of aluminum tubes for heat exchangers according to Mn content. The extrusion process was performed by direct extrusion after preheating a 6-inch billet and an extrusion mold at 490°C, and the measurement results are shown in FIG. 5.

5 is a result of measuring process variables (pressure output, extrusion speed) occurring in the extrusion process during the production process of an aluminum tube for a heat exchanger according to the Mn content. As the addition amount of Zr and Mn increases, the extrusion force required for extrusion increases, and the extrusion speed tends to decrease. Compared to the current mass-produced A3003 aluminum alloy (press output 240 MPa, extrusion speed 2.8 to 3.1 m/s), 0.1 to 0.15 wt.% Zr and 0.2 to 0.5 wt.% Mn alloys of this development group have excellent corrosion resistance. At the same time, it can be seen that it has similar productivity to the A3003 material.

The description of the presented embodiments is provided to enable any person skilled in the art to use or implement the present invention. Various modifications to these embodiments will be apparent to those of ordinary skill in the art, and the general principles defined herein can be applied to other embodiments without departing from the scope of the present invention. Thus, the present invention is not to be limited to the embodiments presented herein, but is to be interpreted in the widest scope consistent with the principles and novel features presented herein.

Claims (7)

0.20 to 0.50% by weight of manganese (Mn);
0.05 to 0.20% by weight of zirconium (Zr);
More than 0 and 0.01% by weight or less of the copper (Cu);
More than 0 and 0.1% by weight or less of the iron (Fe);
More than 0 and 0.15% by weight or less of the silicon (Si); And
Including the balance of aluminum (Al) and indispensable impurities,
Aluminum alloy for heat exchanger.
The method of claim 1,
Penetration resistance is improved, corrosion resistance to uniform corrosion is improved,
Aluminum alloy for heat exchanger.
An aluminum tube for a heat exchanger made of the aluminum alloy for a heat exchanger according to claim 1.
An aluminum fin material for a heat exchanger made of the aluminum alloy for a heat exchanger according to claim 1. A heat exchanger comprising an aluminum tube according to claim 3 or an aluminum fin material according to claim 4.
The method of claim 1,
The aluminum alloy,
It is obtained by homogenizing the billet produced through the casting process for 7 to 10 hours at 425 to 490°C for 7 to 10 hours and then air cooling after homogenizing
The heating rate is 10~50℃ per minute,
Aluminum alloy for heat exchanger.
The method of claim 6,
The billet was preheated at 475~490℃ and extruded by direct extrusion,
Aluminum alloy for heat exchanger.

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