WO2022231148A1 - Method for manufacturing aluminum alloy for heat exchanger - Google Patents

Abstract

The present invention relates to a method for manufacturing an aluminum alloy for a heat exchanger. The present invention pertains to a heat treatment process method for simultaneously achieving excellent perforation corrosion resistance and mechanical properties in an aluminum alloy material used in a heat exchanger. More specifically, proposed are: conditions for homogenization heat treatment which is divided into two stages, that is, a high-temperature stage and a low-temperature stage, and is for the uniform formation of fine precipitated phases; and conditions for annealing heat treatment for obtaining excellent tensile strength and elongation.

Description

Manufacturing method of aluminum alloy for heat exchanger

The present invention relates to a method of manufacturing an aluminum alloy for a heat exchanger, and the present invention relates to a heat treatment process method for simultaneously satisfying excellent penetration corrosion resistance and mechanical properties, targeting an aluminum alloy material used for a heat exchanger, and more particularly presents homogenization heat treatment conditions divided into two stages, high temperature and low temperature for uniform formation of fine precipitated phases, and annealing heat treatment conditions to obtain excellent tensile strength and elongation.

The aluminum alloy tube of the existing registered patent KR 10-1465389 maintains the extrusion speed and strength at the A1XXX series level while improving the corrosion propagation form and corrosion resistance. to be. However, the mechanical properties of the above alloy are at the level of the A1XXX series, and there is a possibility of damage due to the stress generated during the heat exchanger manufacturing process. Therefore, in the present invention, in order to improve the mechanical properties while maintaining the penetration resistance of the existing alloy, research on the alloy design and heat treatment process was conducted. A heat treatment process method showing

(1) Optimization of temperature and time for homogenization treatment

Homogenization is a process that removes fine segregation of cast billets through precipitation phase decomposition and re-precipitation, and removes residual internal stress to prevent product cracking. It is an essential process to achieve uniform distribution of solute atoms in aluminum alloy. to be.

Among the developed alloys, the Zr element not only improves the strength by refining the grain size in the Al matrix, but also generates a potential difference inside the material and finely disperses the precipitates that act as the starting point of corrosion, so that the narrow and deep shape is difficult to predict. It has the effect of suppressing the occurrence of pitting corrosion, a form of corrosion, and inducing uniform corrosion. However, Zr is an atom with severe segregation in the Al matrix, and in order to induce a uniform distribution of the solute atoms, heat treatment at a higher temperature (500°C or higher) is required than a general process. On the other hand, for fine dispersion of intermetallic compounds including Fe element that adversely affects corrosion resistance, heat treatment conditions that maximize the generation of Al3Zr phase are required. Therefore, optimization of temperature and time for homogenization heat treatment divided into two stages of high temperature and low temperature is required to remove microsegregation of the intermetallic compound, homogenize the macroscopic composition, and induce optimal grain size and distribution of the intermetallic compound.

(2) Strength of the developed alloy

In the case of mechanical properties of the alloy developed by KR 10-1465389, the tensile strength is lower than that of the A3XXX series aluminum alloy at the level of A1XXX series. Accordingly, there is a risk of deformation, cracking, and destruction due to external forces (fin bonding, bending, internal pressure caused by fluid) applied to the product during the manufacturing process.

The strength of a material can be increased by the disturbance of dislocation movement due to precipitation phases, impurities, defects, etc. present inside the material. The above defects can increase the strength by making it difficult to operate the slip system in which the material is deformed, but conversely, the ductility is reduced. Therefore, it is required to secure appropriate strength and ductility to prevent product damage.

In the present invention, heat treatment conditions that have excellent penetration corrosion resistance through annealing heat treatment after cold working and at the same time satisfy the mechanical properties of aluminum A3XXX series alloys were selected.

The present invention relates to an aluminum alloy material used in a heat exchanger, and relates to a heat treatment process step for simultaneously satisfying high corrosion resistance and excellent mechanical properties. Intermetallic compound (IMC) formation and dispersion through the addition of Mn and Zr It is a material with improved mechanical properties as well as resistance to penetration corrosion by inducing .

A method of manufacturing an aluminum alloy for a heat exchanger according to an embodiment of the present invention, 0.30 to 0.70 wt% of Mn; 0.10 to 0.20 wt % of Zr; the remainder of aluminum; and preparing an aluminum alloy molten metal including other additives; casting the aluminum alloy molten metal; Including the step of heat-treating the aluminum alloy formed through the casting step in two steps, wherein the heat treatment in the two steps is heat-treated at a temperature of 500 to 580° C. for 7 to 10 hours and thereafter at a temperature of 370 to 390° C. 7 to heat treatment for 10 hours.

The aluminum alloy molten metal is 0.01wt% or less of Cu; 0.3 wt% or less of Fe; and 0.15 wt% or less of Si.

It further includes the step of air cooling after the step of heat treatment in the two steps.

After the air cooling step, the method further comprises cold rolling or extruding the aluminum alloy.

The method further comprises annealing the extruded aluminum alloy at a temperature of 390 to 410° C. for 0.5 to 2 hours. The annealing heat treatment temperature is 395 to 405 ℃.

By the two-step heat treatment, the Al3Zr phase, which is an intermetallic compound, is uniformly distributed, so that penetration corrosion resistance and mechanical properties are improved.

A method of manufacturing an aluminum alloy for a heat exchanger according to an embodiment of the present invention, 0.30 to 0.70 wt% of Mn; 0.10 to 0.20 wt % of Zr; the remainder of aluminum; and preparing an aluminum alloy molten metal including other additives; casting the aluminum alloy molten metal; heat-treating the aluminum alloy formed through the casting step in two steps; air cooling after the heat treatment in the two steps; cold rolling or extruding the aluminum alloy after the air cooling step; and annealing the extruded aluminum alloy at a temperature of 390 to 410° C. for 0.5 to 2 hours, wherein the heat treatment in the two steps is heat treatment at a temperature of 500 to 580° C. for 7 to 10 hours, and then and heat treatment at a temperature of 370 to 390° C. for 7 to 10 hours.

The aluminum alloy molten metal is 0.01wt% or less of Cu; 0.3 wt% or less of Fe; and 0.15 wt% or less of Si.

The annealing heat treatment temperature is 395 to 405 ℃.

By the two-step heat treatment, the Al3Zr phase, which is an intermetallic compound, is uniformly distributed, so that penetration corrosion resistance and mechanical properties are improved.

Previously developed alloys were aluminum alloys for heat exchangers with improved penetration corrosion resistance. The present invention is an aluminum alloy for a tube and fin material for a heat exchanger that maintains the properties for penetration corrosion resistance through appropriate control of the content of Zr, Mn, etc. and an optimized heat treatment process, and has mechanical properties equivalent to the existing A3XXX series.

Figure 1 shows the microstructure and the distribution shape of the intermetallic compound (lower left) after cold rolling (reduction ratio 87.5%) according to the heat treatment temperature in the low temperature section.

Figure 2 shows the area ratio of the intermetallic compound to the matrix for each temperature condition after cold rolling (reduction ratio 87.5%) according to the heat treatment temperature in the low temperature section.

3 shows the grain size distribution and average after cold rolling (reduction ratio 87.5%) of the alloy subjected to the optimized two-step homogenization heat treatment.

Figure 4 shows the tensile curve according to the annealing heat treatment time at 380 ℃.

Figure 5 shows the tensile curve according to the annealing heat treatment time at 400 ℃.

Figure 6 shows the tensile curve according to the annealing heat treatment time at 420 ℃.

7 shows mechanical properties (tensile strength, elongation) after 2 hours of treatment at each annealing heat treatment temperature.

8 shows a potential polarization curve for corrosion characteristic evaluation before and after annealing heat treatment in an acid rain simulation environment.

9 shows a cross-section (AA3003, developed alloy [before/after annealing heat treatment]) after an acid rain simulation environment potentiostatic corrosion acceleration experiment.

10 shows a flowchart of a method of manufacturing an aluminum alloy for a heat exchanger according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In this specification for purposes of explanation, various descriptions are presented to provide an understanding of the present invention. However, it will be apparent that these embodiments may be practiced without these specific descriptions. In other instances, well-known structures and devices are presented in block diagram form in order to facilitate describing the embodiments.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Since the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

The terms used in the present application are used only to describe specific embodiments and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, step, operation, component, part, or combination thereof described in the specification is present, and includes one or more other features or steps. , it should be understood that it does not preclude the possibility of the existence or addition of , operation, components, parts or combinations thereof.

In the present invention, research was conducted for the purpose of minimizing the grain size after processing of the aluminum developed alloy. This can be achieved by increasing the formation of the intermetallic Al ₃ Zr phase. Therefore, a homogenization heat treatment condition was developed for optimal conditions for the generation of the corresponding phase, and this will be described below.

10 shows a flowchart of a method of manufacturing an aluminum alloy for a heat exchanger according to an embodiment of the present invention.

As shown in FIG. 10 , the method for manufacturing an aluminum alloy for a heat exchanger according to an embodiment of the present invention includes the steps of: preparing a molten aluminum alloy (S110); casting the aluminum alloy molten metal (S 120); Heating the aluminum alloy formed through the casting step in two steps (S 130); air cooling after the heat treatment in the two steps (S 140); Cold rolling or extruding the aluminum alloy after the air cooling step (S 150); and annealing the extruded aluminum alloy at a temperature of 390 to 410° C. for 0.5 to 2 hours (S 160).

In step S 110, an aluminum alloy molten metal is prepared. Mn of 0.30 to 0.70 wt% of molten aluminum alloy; 0.10 to 0.20 wt % of Zr; the remainder of aluminum; and other additives. In the case of Zr of less than 0.10 wt%, the Zr content is low, so that the dispersion material (Al3Zr) is not sufficiently generated, making it difficult to induce uniform dispersion of the intermetallic compound. In addition, in the phase diagram, the solubility of Zr in Al is about 0.20 wt%, and Zr in excess of this exists as a precipitated phase to deteriorate the ductility of the alloy. In the case of Mn, attention was paid to the effect of suppressing Al3Fe acting as a local corrosion initiation point in the Al alloy so that the Mn/Fe content ratio was set to 1 or more.

By inducing the formation and dispersion of intermetallic compounds through the addition of Mn and Zr, not only penetration corrosion resistance but also mechanical properties are improved.

In addition, the aluminum alloy molten metal is 0.01wt% or less of Cu; 0.3 wt% or less of Fe; and 0.15 wt% or less of Si. In the case of Cu, it exists as an intermetallic compound at grain boundaries in Al and causes corrosion within grains, so it was suppressed. In addition, Fe also exists in the Al3Fe phase in Al, and acts as a local corrosion initiation point due to the potential difference with the base material (Al), so it was suppressed. Finally, in the case of Si, it was suppressed within the impurity content because it deteriorates the mechanical properties of the Al alloy.

In step S 120, an aluminum alloy molten metal is cast. Aluminum alloy specimens can be cast in the form of billets.

In step S 130, the aluminum alloy formed through the casting step is heat-treated in two steps. The heat treatment in two steps includes heat treatment at a temperature of 500 to 580° C. for 7 to 10 hours and then heat treating at a temperature of 370 to 390° C. for 7 to 10 hours. That is, by performing a high-temperature heat treatment in two steps first, and then performing a low-temperature heat treatment, the homogenization heat treatment is performed in two steps before the extrusion step. Through the two-step heat treatment, the Al ₃ Zr phase, which is an intermetallic compound, is uniformly distributed to improve penetration corrosion resistance and mechanical properties. That is, in order to uniformly generate a fine precipitated phase (meaning that the precipitated phase is maximally generated), a homogenization heat treatment divided into two stages, high temperature and low temperature, is performed. The temperature range of the two-step heat treatment will be explained to the reason for the limitation of the temperature range in the examples.

In step S 140, an air cooling step is performed.

In step S 150, cold rolling or extrusion of the aluminum alloy is performed after the air cooling step. A plate material may be formed by cold rolling or extruding an air-cooled aluminum alloy. The alloy can be processed at room temperature with a rolling reduction ratio of 80 to 90% through a double speed rolling mill to form a plate.

In step S 160, annealing the extruded aluminum alloy. The extruded aluminum alloy is annealed at a temperature of 390 to 410° C. for 0.5 to 2 hours, preferably the annealing heat treatment temperature is 395 to 405° C., 395 to 400° C., and most preferably about 400° C. Excellent tensile strength and elongation can be obtained by such annealing heat treatment.

An aluminum alloy for a heat exchanger is obtained by this method, and an aluminum tube for a heat exchanger, an aluminum fin material for a heat exchanger, and a heat exchanger including such a tube and a fin material can be manufactured using the obtained aluminum alloy.

Hereinafter, the content of the present invention will be further described along with specific examples.

[Example 1]

In this example, the annealing heat treatment conditions that can secure the strength of the A3XXX series at the same time as the recovery of the elongation, which is drastically reduced after cold working, were evaluated. In addition, through the electrochemical test, it was confirmed that the penetration corrosion property maintained effectively even after annealing heat treatment.

As a specific method, an aluminum alloy specimen containing Zr: 0.15 wt.%, Mn: 0.5 wt.%, Fe: 0.1 wt.% was produced through casting in the form of a 6-inch billet, followed by two steps (high temperature 10 hours, low temperature). 10 hours) was subjected to homogenization heat treatment. At this time, in order to optimize the low-temperature temperature condition in which Al ₃ Zr phase production is maximized, the temperature range from 320° C. to 440° C. was divided into 20° C. intervals to analyze the grain size after cold rolling for each condition. In addition, in order to evaluate the mechanical properties according to the annealing heat treatment, a tensile test piece was prepared and the tensile properties were measured. Finally, for the evaluation of the corrosion properties, the open circuit potential (OCP) was measured for 30 hours using a saturated calomel electrode (SCE) as a reference electrode in a solution simulating acid rain, and then the co-potential polarization was performed. Corrosion potential and corrosion rate were measured through the test, and the cross-section of the specimen was observed after performing a potentiostatic corrosion acceleration test to evaluate penetration resistance. Based on this result, it was confirmed that the penetration resistance characteristic effectively maintained even after annealing heat treatment.

(1) Manufacture of aluminum development alloy

The composition of the specimen used in the present invention is as follows [Table 1].

Composition (wt.%)
Cu	Fe	Si	Zr	Mn	Al
0.01 below	0.3 below	0.15 below	0.15	0.5	Rem.

Experimental Example 1: Evaluation of grain size after processing according to homogenization treatment conditions

A key technology in the development alloy is an Al ₃ Zr phase production optimization process. The Al ₃ Zr phase plays a role of refining the grain boundary by preventing the grain boundary movement of the Al alloy and suppressing the growth of grains according to the recrystallization treatment after cold working. In addition, the grain boundaries, which act as the main initiation of corrosion in the Al alloy, are also distributed in a uniform form by refining, so that the corrosion reaction occurs uniformly over the entire surface of the material rather than being concentrated in a local area, so the penetration corrosion resistance is greatly improved. .

However, since the temperature range of 425 to 490° C. used for the homogenization treatment of the aluminum alloy is not an optimal condition for the Al ₃ Zr phase precipitation, the two-step homogenization is performed to produce an Al ₃ Zr phase with small, uniform and high density particles. Heat treatment was performed. In the two-step homogenization heat treatment, heat treatment was performed at high temperature (540° C.) for 10 hours for uniform diffusion of Zr element with severe segregation in the Al matrix. Then, in order to optimize the low-temperature temperature condition in which the amount of Al ₃ Zr phase is maximized, the temperature range from 320°C to 440°C was divided into 20°C intervals and homogenized heat treatment was performed in the low-temperature section _. It was evaluated through comparison of the distribution shape of the compound. 1 is a distribution shape of the microstructure and intermetallic compound after cold rolling according to the heat treatment temperature in the low temperature section, and the area ratio of the intermetallic compound to the base material measured through this is shown in FIG. 2 . As a result of the analysis, it was confirmed that the intermetallic compound was most uniformly distributed at 380° C. in the case of the homogenization treatment in the low-temperature section as shown in FIGS. 1 and 2, which indicates that the amount of Al ₃ Zr phase was maximized. Therefore, after 10 hours of high temperature (540° C.), 10 hours of low temperature (380° C.) was selected as the optimized two-step homogenization heat treatment condition. The grain size distribution and average of the corresponding conditions are shown in FIG. 3, and the average grain size and the density of grains are shown in Table 2.

	average grain size [μm]	grain density [count/mm 2 ]	grain size Standard Deviation
After 10 hours of high temperature (540 o C), 10 hours of low temperature (380 o C)	87.57	34.3	37.6

Experimental Example 2: Evaluation of mechanical properties by annealing heat treatment conditions

This study is an evaluation of the mechanical properties according to the annealing heat treatment conditions (temperature, time) after cold rolling (reduction ratio 87.5%) of the material subjected to the two-step homogenization heat treatment. Annealing heat treatment is a process for removing residual stress after processing and removing the directionality of grains. In the case of annealing heat treatment, since the manufacturing method is different depending on the composition of the alloy, the grain size of the finished product, and the mechanical properties, characteristic evaluation under various conditions is required.

Experimental temperature was carried out in the range of 360 ~ 440 ℃, and the tensile curves for each annealing temperature and time conditions are shown in FIGS. 4 to 6 . In addition, the results of tensile strength and ductility after annealing heat treatment for each temperature for 2 hours are shown in FIG. 7 . As shown in FIG. 7 , the recovery of elongation by heat treatment was insignificant at less than 400° C., but it was confirmed that the workability of the alloy increased from 400° C. or higher. In addition, in the case of tensile strength, it can be seen that the annealing heat treatment temperature is significantly decreased as the temperature increases. Therefore, in order to optimize the mechanical properties similar to that of the A3XXX series, it was determined that the annealing heat treatment conditions of 395-405°C and 2 hours were suitable.

(2) Evaluation of corrosion resistance and penetration resistance

Experimental Example 3: Corrosion resistance evaluation after annealing heat treatment

This test was conducted by continuously changing the voltage in the range of +1 V based on the corrosion potential of the electrode in the three-electrode system at a rate of 10 mV/min, and measuring the current density at each voltage. Through this test, it is possible to know the corrosion characteristics of aluminum tube for heat exchanger.

For the aluminum tube, a specimen polished with #600 abrasive paper was used, and the electrolyte was OCP ( After measuring the open-circuit potential), a potential polarization test was performed, and the corrosion rates before and after heat treatment are shown in FIG. 8 .

8 is a graph schematically showing the results of the electrostatic polarization test before and after annealing heat treatment, indicating that the corrosion properties (corrosion potential, corrosion current density) of the material are maintained even after the annealing heat treatment, and the results are summarized in Table 3.

	corrosion potential [mV SCE ]	corrosion current density [μA/cm 2 ]
Before annealing heat treatment	-625	2.035
After annealing heat treatment	-636	2.393

Experimental Example 4: Evaluation of penetration resistance after annealing heat treatment

This test is a cross-section of a specimen for a corrosion reaction amount of 26.55 mAh/cm ² through a potential acceleration test at -530 mV _SCE based on a saturated red electrode in an environment simulating acid rain for the developed alloy before and after annealing heat treatment. This test is a test that accelerates corrosion of materials by applying an anode polarization potential rather than a corrosion potential after calculating the corrosion potential of a specimen in a three-electrode system. The electrostatic potential acceleration test was conducted for the purpose of identifying the corrosion form one year after use, and a cross-sectional view after the test is shown in FIG. 9 . 9 is a cross-sectional analysis result after a potentiostatic corrosion acceleration test in an environment simulating acid rain. As a result of the analysis, it can be confirmed that the developed alloy did not show penetration corrosion and showed a lower corrosion thinning depth than A3003. The respective corrosion thinning depths are shown in Table 4. The corrosion thinning depth of the developed alloy is 32.21 / 31.73 μm, respectively, before and after annealing heat treatment, confirming the corrosion resistance 3 times improved compared to 102.77 μm of A3003.

Material name	Corrosion thinning depth (μm)		note
	Average	Standard Deviation
A3003	102.77	26.75	local corrosion
development alloy Before annealing heat treatment	32.21	8.24	uniform corrosion
development alloy After annealing heat treatment	31.73	7.86	uniform corrosion

Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that you can.

Claims (14)

1. 0.30 to 0.70 wt % Mn; 0.10 to 0.20 wt % of Zr; the remainder of aluminum; and preparing an aluminum alloy molten metal including other additives;

   casting the aluminum alloy molten metal;

   Comprising the step of heat-treating the aluminum alloy formed through the casting step in two steps,

   The step of heat treatment in the above two steps,

   Heat treatment at a temperature of 500 to 580 ° C. for 7 to 10 hours and then heat treatment at a temperature of 370 to 390 ° C. for 7 to 10 hours.

   A method of manufacturing an aluminum alloy for a heat exchanger.
2. The method of claim 1,

   The aluminum alloy molten metal is 0.01wt% or less of Cu; 0.3 wt% or less of Fe; and 0.15 wt% or less of Si,

   A method of manufacturing an aluminum alloy for a heat exchanger.
3. The method of claim 1,

   Further comprising the step of air cooling after the step of heat treatment in the two steps,

   A method of manufacturing an aluminum alloy for a heat exchanger.
4. 4. The method of claim 3,

   Further comprising the step of cold rolling or extruding the aluminum alloy after the step of air cooling,

   A method of manufacturing an aluminum alloy for a heat exchanger.
5. 5. The method of claim 4,

   Further comprising the step of annealing the extruded aluminum alloy at a temperature of 390 to 410 ℃ for 0.5 to 2 hours (annealing),

   A method of manufacturing an aluminum alloy for a heat exchanger.
6. 6. The method of claim 5,

   The annealing heat treatment temperature is 395 to 405 ℃,

   A method of manufacturing an aluminum alloy for a heat exchanger.
7. The method of claim 1,

   By the two-step heat treatment, the intermetallic compound Al ₃ Zr phase is uniformly distributed, so that penetration corrosion resistance and mechanical properties are improved,

   A method of manufacturing an aluminum alloy for a heat exchanger.
8. An aluminum alloy for a heat exchanger produced by the method for manufacturing an aluminum alloy for a heat exchanger according to any one of claims 1 to 7.
9. An aluminum tube for a heat exchanger, made of the aluminum alloy of claim 8.
10. Made of the aluminum alloy of claim 8, an aluminum fin material for a heat exchanger.
11. 0.30 to 0.70 wt % Mn; 0.10 to 0.20 wt % of Zr; the remainder of aluminum; and preparing an aluminum alloy molten metal including other additives;

    casting the aluminum alloy molten metal;

    heat-treating the aluminum alloy formed through the casting step in two steps;

    air cooling after the heat treatment in the two steps;

    cold rolling or extruding the aluminum alloy after the air cooling step; and

    Comprising the step of annealing the extruded aluminum alloy at a temperature of 390 to 410 ℃ for 0.5 to 2 hours,

    The step of heat treatment in the above two steps,

    Heat treatment at a temperature of 500 to 580 ° C. for 7 to 10 hours and then heat treatment at a temperature of 370 to 390 ° C. for 7 to 10 hours.

    A method of manufacturing an aluminum alloy for a heat exchanger.
12. 12. The method of claim 11,

    The aluminum alloy molten metal is 0.01wt% or less of Cu; 0.3 wt% or less of Fe; and 0.15 wt% or less of Si,

    A method of manufacturing an aluminum alloy for a heat exchanger.
13. 12. The method of claim 11,

    The annealing heat treatment temperature is 395 to 405 ℃,

    A method of manufacturing an aluminum alloy for a heat exchanger.
14. 12. The method of claim 11,

    By the two-step heat treatment, the intermetallic compound Al ₃ Zr phase is uniformly distributed, so that penetration corrosion resistance and mechanical properties are improved,

    A method of manufacturing an aluminum alloy for a heat exchanger.

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