KR20170061183A - Aluminum alloy having excellent extrudability and intergranular corrosion resistance for finely hollow shape, and process for producing same - Google Patents

Abstract

The present invention provides an aluminum alloy for a fine hole hollow member, which is capable of suppressing the content of Cu, which is problematic in the intergranular corrosion resistance, and which can keep the natural potential inactive, and is excellent in extrudability. 0.05 to 0.15 mass% of Fe, 0.10 mass% or less of Si, 0.03 to 0.07 mass% of Cu, 0.30 to 0.55 mass% of Mn, 0.03 to 0.06 mass% of Cr and 0.08 to 0.12 mass% of Ti, 0.08% by mass or less of V and 0.08% to 0.2% by mass of Ti + V in accordance with the following formula (1). The DC cast billet having the chemical composition is heated to 550 to 590 캜 at a rate of 80 캜 / hour or less, held for 0.5 to 6 hours, maintained at 450 to 350 캜 for 0.5 to 1 hour, or 50 캜 / And then extruded into a desired shape at a processing ratio of 30 or more and 1000 or less after reheating at 450 to 550 캜. Thereby producing a hollow shape member.

Description

Technical Field [0001] The present invention relates to an aluminum alloy for a hollow-hole hollow member having excellent extrusion resistance and intercalation corrosion resistance, and a method for manufacturing the aluminum alloy.

The present invention relates to an aluminum alloy excellent in extrudability and intergranular corrosion resistance, which is used for an extruded fine hole hollow flat pipe constituting an aluminum heat exchanger, for example, a condenser, an evaporator, an intercooler, etc., ≪ / RTI >

In general, an aluminum-made heat exchanger is a condenser for a car air conditioner as shown in FIG. 1, for example, a pipe (flat pipe) (see FIG. 2 (a)) through which refrigerant flows, (See Fig. 2 (b)), which is made of a non-corrosive flux, and has a means for brazing to a member in contact with each other.

Aluminum-made heat exchangers are required to have high durability, and an extruded flat pipe as a constituent member is naturally required to have corrosion resistance, strength, brazing property, extrudability and the like.

On the other hand, from the viewpoint of the demand for lightening of the heat exchanger and economical efficiency, there is a demand for an aluminum alloy having a complicated fine hole hollow structure and excellent extrudability which enables thinning and weight reduction.

Particularly, with regard to corrosion resistance, it is a problem to prevent occurrence of early penetration defects due to intergranular corrosion in which refrigerant sealed in a flat pipe flows out.

As a widely used sacrificial method, there is a method in which a Zn metal is applied to the flattened tube surface and a Zn diffusion layer is formed in the surface layer after heating. And the formed Zn diffusion layer is used as a sacrificial method (see FIG. 3).

However, in the effect of the sacrificial system in which Zn metal is combined, the Zn diffusion layer including the bonding portion with the pin is consumed prematurely, and the performance of the heat exchanger deteriorates.

Aluminum alloys for extruded flattening pipes, which require such functions, have been proposed many times, but they have not reached a solution satisfying any requirement.

For example, in Patent Documents 1 and 2, an aluminum alloy improved in extrusion resistance and corrosion resistance has been proposed. And the extrudability is improved by positively adding Cu element and Fe element based on pure aluminum as a base.

Japanese Patent Application Laid-open No. 60-238438 Japanese Patent Application Laid-Open No. 5-222480

The alloys proposed in Patent Documents 1 and 2 are certainly improved in extrudability, but are insufficient from the viewpoint of corrosion resistance.

As described above, generally, a sacrificial method is employed as a means for preventing corrosion of a flat tube of a heat exchanger. The aluminum alloys proposed in the above Patent Documents 1 and 2 are alloys which are potentially inactive and have a natural potential of about -0.7 VvsSCE or so, so there is no problem in the use of the aluminum alloy in the region where the sacrificial method is employed.

However, since Cu is added to pure Al and an intermetallic compound of Al-Cu is formed in accordance with the grain boundaries, the corrosion of the grain boundaries may be promoted. That is, there is a risk that corrosion of the flat tube itself may proceed at a portion of the heat exchanger where the measures for reducing the Zn diffusion layer and the sacrificial method are not formed.

SUMMARY OF THE INVENTION The present invention has been conceived in order to solve such a problem, and it is an object of the present invention to provide an aluminum alloy for microhole hollow members capable of suppressing the content of Cu, which is problematic in intercalation corrosion resistance, And an object of the present invention is to provide an aluminum alloy excellent in extrudability.

In order to attain the object, the aluminum alloy for fine hole hollow members having excellent extrudability and intergranular corrosion resistance according to the present invention comprises 0.05 to 0.15% by mass of Fe, 0.10% by mass or less of Si, 0.03 to 0.07% by mass of Cu, : 0.30 to 0.55 mass%, Cr: 0.03 to 0.06 mass%, and Ti: 0.08 to 0.12 mass%, with the balance being Al and inevitable impurities.

In addition, V may be contained in an amount of 0.08 mass% or less in relation to Ti + V in an amount of 0.08 to 0.2 mass%.

The aluminum alloy for the fine hole hollow member is heated at 550 to 590 캜 for 0.5 to 6 hours at a rate of 80 캜 / hour or less, and then heated at 450 to 350 Deg.] C for 0.5 to 1 hour or a cooling process at a cooling rate of 50 [deg.] C / hour to 200 [deg.] C or lower.

Then, the homogenized billet is reheated at 450 to 550 占 폚 and extruded into a desired shape at an extrusion ratio of 30 or more and 1000 or less to obtain an aluminum alloy microporous hollow member having excellent intercalation corrosion resistance.

The aluminum alloy for fine hole hollow members having excellent extrudability and intergranular corrosion resistance according to the present invention is basically made of pure aluminum and has a low content of Fe, Cu, Mn and Cr so that the extrudability is good. Although it is suppressed to a low level, it contains the required amount of Fe, Cu, Mn, Cr, and the like. Therefore, it has strength and corrosion resistance as a hollow hole material constituting the heat exchanger.

Particularly, in the alloy of the present invention, since the Cu content is suppressed to 0.07 mass% or less, the formation of the Al-Cu intermetallic compound is suppressed, and the possibility of grain boundary corrosion is extremely reduced. Further, by containing an appropriate amount of Ti, dispersion of the Ti element in the grain boundary or in the matrix (matrix) inhibits the progress of intergranular corrosion and improves the corrosion resistance.

1 schematically illustrates a general structure of a capacitor for a car air conditioner.
2 is a view for explaining a schematic structure of a flat pipe and a heat exchanger incorporating it.
3 is a view for explaining a sacrificial mode action of the Zn diffusion layer.
4 is a view showing a cross-sectional shape of a hollow flat pipe for a heat exchanger manufactured in the embodiment.
Fig. 5 is a diagram comparing the pressure-time curves at the time of extrusion of the homogenized billets in the examples. Fig.

As described above, the aluminum alloy for extrusion molding, which is proposed in Patent Document 2, is excellent in extrusion moldability, while the alloy containing Cu forms an Al-Cu-based intermetallic compound in grain boundaries to cause intergranular corrosion to be.

Therefore, in order to find an aluminum alloy having a reduced Cu content and having extrusion moldability and mechanical properties equivalent to those of the aluminum alloy for extrusion molding proposed in Patent Document 2 and the like, and there is no possibility of causing grain boundary corrosion, come.

As a result, it has been found that the above problems can be solved by suppressing the Cu content to 0.07 mass% or less and appropriately adjusting the content of other Fe, Si, Mn, Cr and the like and adding an appropriate amount of Ti.

The details will be described below.

The aluminum alloy for microporous hollow members having excellent extrudability and intergranular corrosion resistance according to the present invention comprises 0.05 to 0.15% by mass of Fe, 0.10% by mass or less of Si, 0.03 to 0.07% by mass of Cu, 0.30 to 0.55% by mass of Mn, : 0.03 to 0.06 mass%, Ti: 0.08 to 0.12 mass%, and if necessary, 0.08 mass% or less of V and 0.08 to 0.2 mass% of Ti + V, and the balance of Al and inevitable impurities Chemical composition.

First, the action of each component and the reason for limitation will be described. The following "%" marks are all% by mass.

Fe: 0.05 to 0.15%

Fe has an effect of improving the strength of the aluminum alloy. This action is exhibited by the content of not less than 0.05%, but if it is contained in an amount exceeding 0.15%, an Al-Fe compound may be formed to adversely affect the intercalation corrosion, and at the same time, the extrudability may be deteriorated. The upper limit value was 0.15%.

Si: not more than 0.10%

Si is inevitable impurities incorporated from the Al base material, but the upper limit value is also set to 0.10% in order to suppress the generation of Al-Fe-Si compounds adversely affecting the workability.

Cu: 0.03 to 0.07%

Cu is an effective element for suppressing deep fitting of Al paper. The effect is recognized by the content of 0.03% or more. However, when the content is increased, an Al-Cu compound is formed in the grain boundary, and corrosion from the grain boundary is promoted. For this reason, the Cu content was 0.03 to 0.07%.

Mn: 0.30 to 0.55%

Mn has an action of improving corrosion resistance and strength, particularly high temperature strength. Their action is effectively expressed by the content of 0.30% or more. In order to increase the strength at high temperature, Mn does not cause significant softening at the time of brazing, and thus has a great role in maintaining the rigidity of the structure. On the other hand, since the high-temperature strength is high, the processing pressure at the time of extrusion is increased and the extrudability is lowered. Further, Al-Mn-based intermetallic compounds are formed depending on the grain boundaries, which may adversely affect intercalation corrosion. Therefore, the upper limit of the Mn content was 0.55%.

Cr: 0.03 to 0.06%

Cr has an action of suppressing coarsening of the extruded structure. This action is effectively expressed by the content of 0.03% or more. However, if it is contained in a large amount, the extrudability is deteriorated, so the upper limit is set to 0.06%.

Ti: 0.08 to 0.12%

Ti has a function of refining the casting structure, and the distribution of the Ti element has an action to suppress intergranular corrosion of the extruded material. This action is effectively expressed by the content of 0.08% or more. However, when the content is large, a coarse intermetallic compound is produced to deteriorate the extrudability, so that the upper limit is set to 0.12%.

V: 0.08% or less

Since the V and V compounds formed at the time of casting are dispersed in a layer form by extrusion to prevent the progress of intergranular corrosion, they are contained if necessary. However, when the content thereof is increased, the extrudability is deteriorated. Therefore, the upper limit is set to 0.08%.

Ti + V: 0.08 to 0.2%

The combined addition of Ti and V enhances the effect of suppressing intergranular corrosion, but if the content thereof is excessively large, the extrudability is deteriorated. Therefore, the upper limit of the total amount thereof is set to 0.2%.

Others are inevitable impurities.

The aluminum alloy for fine hole hollow members having excellent extrudability and intergranular corrosion resistance according to the present invention is dissolved by a conventional means and is provided as a billet having a desired shape by a semi-continuous casting method which is a general casting method.

In order to effectively utilize the contained components of the alloy in the obtained aluminum alloy billet, it is necessary to heat the billet after casting at a high temperature to reuse the matrix constituting the intermetallic compound crystallized at the time of casting, It is necessary to perform a homogenization treatment to remove the distribution. As the homogenization treatment, it is preferable to carry out the heat treatment at 550 to 590 DEG C for 0.5 to 6 hours.

The aluminum alloy of the present invention is an alloy containing Fe, Si, and Cu, Mn, Cr, and Ti based on pure Al.

If the billet obtained by casting is not maintained at 550 DEG C or higher for 0.5 hours or more, the Al-Fe-Si compound can not be finely dispersed and defects are produced when the billet is extruded at a high processing rate. In order to allow compounds such as Cu, Cr and Mn, which are other elements, to penetrate into Al paper or to exist as a fine compound, it is necessary to maintain the temperature at 550 DEG C or more for 0.5 hours or more.

On the other hand, if heating is carried out at a temperature exceeding 590 占 폚 for 0.5 hour or more, penetration of Fe, Si and Cu is favorable, but the amount of penetration of Mn and Cr increases and the processing pressure at the subsequent extrusion is increased, Further, there is a tendency to make the structure of the extruded material into a recrystallized structure.

In addition, economically, it is preferably 6 hours or less, and the homogenization treatment for a long time increases the billet cost, and the oxidation of the billet surface proceeds, so that the desired quality is not obtained. The suitable temperature for the homogenization treatment is 570 ° C ± 10 ° C. Economically, it is preferable to rapidly increase the temperature and rapidly cool the alloy. However, when the temperature of the alloy containing Mn and Cr increases to 80 ° C / h (Al-Fe, Al-Fe-Al, Fe-Al, Fe-Co, and Fe-Co) Si or the like. On the other hand, Cr and Mn, which have been employed, are precipitated as Al- (Fe, Mn, Cr) -Si compound and Al-Mn compound to improve the texture of the billet.

On the other hand, penetration of Mn and Cr compounds occurs due to the maintenance at a high temperature, and it is necessary to precipitate the Mn and Cr compounds reliably as an appropriate compound. For this, it is necessary to maintain the temperature at 450 to 350 ° C for 0.5 to 1 hour, Lt; RTI ID = 0.0 > C / hr. ≪ / RTI > When this condition is exceeded, Mn and Cr remain in a solid state in the matrix (matrix), and only a small amount of the Mn and Cr are precipitated at the time of heating before the extrusion processing, so that the extrusion pressure is high and the workability is lowered.

The material obtained by extruding the billet obtained by such a homogenization treatment can uniformize the surface and the internal structure of the extruded material and suppress coarsening of crystal grains by hot working.

The billet obtained by casting the alloy composition of the present invention is subjected to a predetermined homogenization treatment and heated at 450 캜 or higher and 550 캜 or lower so as to obtain an ultrafine extruded shape member having an extrusion ratio of 30 to 1000 It is necessary to perform extrusion processing.

If it is not satisfied at 450 캜, the extrusion ratio of the fine hollow shape member is high, so that the extrusion pressure exceeds the limit capability of the extrusion pressure of the extruder (normally, 210 kg / cm 2). Even if it can be extruded, defects such as tearing are formed on the inner surface of the fine hollow material, and the shape and size become out of tolerance. Further, in heating at a temperature as high as 550 占 폚, extrusion can be easily performed, but since the extrusion rate and the extrusion speed are high, the temperature of the mold during extrusion becomes high and tearing or local melting occurs on the surface and inside of the micro- And the desired shape can not be maintained. When the extrusion ratio is small enough not to satisfy the requirement of 30, it becomes difficult to obtain a Ti effect (a state in which Ti exists in the form of a layer along the extrusion direction inside the shape member), which is a feature of the present invention. On the contrary, if the extrusion ratio is set to exceed 1000, it becomes difficult to design the mold and select the extrusion condition, and the extrusion process itself becomes impossible.

(Example)

Flon-based refrigerant is used as a fluid for heat exchange. Therefore, as a material to be used in the heat exchanger, an alloy which is excellent in corrosion resistance, strength and brazing property and which can be extruded into a fine hole hollow shape member (flat pipe) of about 0.5 to 2 mm which is a main member of a heat exchanger assembly is required do.

Therefore, extrusion moldability, corrosion resistance, strength, and brazing property were verified for various aluminum alloys having the chemical compositions shown in Table 1.

First, various aluminum alloys having the chemical compositions shown in Table 1 were dissolved to prepare castings having a diameter of 6 to 10 inches and a length of 2 to 6 m.

The castings were subjected to a homogenization treatment at a temperature of 550 to 590 占 폚 for 0.5 to 6 hours and then heated to 460 to 550 占 폚 and molded into a thin die having an extrusion ratio of 30 to 1000 so as to have a sectional shape shown in Fig. , A width of 16.2 mm, a thickness of 1.93 mm, and a thickness of 0.35 mm was extruded from a hollow flat tube for a heat exchanger.

Then, the extruded samples were examined for corrosion resistance, strength, and brazing property.

The results are shown in Table 2.

The strength was determined from the room temperature strength of the annealing material, and the results were as follows: ⊚: exceeding 90 MPa on the basis of 65 MPa of pure Al; ◯: 60 to 90 MPa;

Corrosion resistance was evaluated by observing presence or absence of intergranular corrosion from the observation of microstructures after the corrosion test and observing progress of the intergranular corrosion. The results indicated that the intergranular corrosion was scarcely observed. The results were rated as?, Those having a layered corrosion of 100 占 퐉 or less, Respectively.

The extrudability was determined by the surface defects (tearing, surface roughness, tearing of the unevenness of the inner surface of the drawing) of the flattened pipe, no surface defects were found at all, Was evaluated as x.

Regarding the brazing property, both the present invention and the comparative example were almost equal and the difference was unknown.

As a comprehensive evaluation, acceptable products that can be used as hollow flat pipes for heat exchangers are indicated by o, and rejected products that can not be used are indicated by x.

Next, the homogenization treatment conditions were verified.

An aluminum alloy having the chemical composition shown in Table 1 was sprayed and subjected to a predetermined molten treatment such as degassing, refining, filtration, and then a billet having a diameter of 210 mm at a temperature of 680 캜 or higher was cast Respectively.

Thereafter, the resultant was held at a temperature of 590 캜 for 4 hours, and then subjected to cooling homogenization treatment to obtain a billet having a length of 4000 mm. This billet is referred to as the current treatment billet.

In the present invention, when the cast billet is cooled at a homogenization temperature of 590 占 폚 and maintained at a homogenization temperature of 80 占 폚 / hour or less for 4 hours at a homogenization temperature (450 占 폚 to 350 占 폚 Was cooled at a cooling rate of 50 DEG C / hour, and then cooled outside the furnace. This billet will be referred to as the inventive billet.

Observation of the microstructure of the present treated billet and the inventive method billet revealed that the present treated billet had no remarkable compound other than the diluted product of the billet before treatment. On the other hand, the structure of the billet of the present invention is not limited to the precipitate Al-Mn system) was finely dispersed.

Next, these two kinds of billets were made to have a length of 500 mm, and a flat pipe having an extrusion ratio of 150 and a shape as shown in Fig. 4 was produced at an extrusion rate of 500 rpm at a rate of 15 m / min. At this time, the extrusion pressure at the time of extrusion was measured.

The results are shown in Table 3.

5 shows a comparison of the pressure-time curve at the time of extrusion.

Compared with the existing method, the present invention method has a small maximum pressure and a high pressure drop. It can be seen that the area in the curve is small and the energy required for extrusion is small.

Further, the extrusion ratio at the time of extrusion processing was verified.

The billet of the present invention used for the verification of the homogenization treatment conditions was heated to 480 DEG C and then a flat pipe having an extrusion ratio of 150 and a flat bar material having an extrusion ratio of 20 were extruded at a speed of 20 m / min.

The microstructure of these two kinds of extruded materials was observed, and the dispersion state of the Ti compound was compared. The results are shown in Table 4.

According to the present invention, as an aluminum alloy for a fine hole hollow member, it is possible to suppress the content of Cu, which is problematic in the intergranular corrosion resistance, and to keep the natural potential inactive, thereby providing an aluminum alloy excellent in extrudability.

Claims (3)

Wherein the alloy contains 0.05 to 0.15 mass% of Fe, 0.10 mass% or less of Si, 0.03 to 0.07 mass% of Cu, 0.30 to 0.55 mass% of Mn, 0.03 to 0.05 mass% of Cr and 0.08 to 0.12 mass% of Ti, And a balance of Al and inevitable impurities, is heated to 550 to 590 占 폚 at a rate of 80 占 폚 / hour or less, held for 0.5 to 6 hours, maintained at 450 to 350 占 폚 for 0.5 to 1 hour, Having a microstructure including Al-Mn-based precipitates finely dispersed in the crystallized product by performing homogenization treatment at a cooling rate of 50 占 폚 / hour to 200 占 폚 or less and then extruding by heating at 450 to 550 占 폚 Features aluminum alloy for fine hole hollow material with excellent extrudability and intergranular corrosion resistance. A DC cast billet of an aluminum alloy having the chemical composition according to claim 1 is heated to 550 to 590 캜 at a rate of 80 캜 / hour or less, held for 0.5 to 6 hours, and then heated at 450 to 350 캜 for 0.5 to 1 hour Or a homogenization treatment in which the mixture is cooled to a temperature of 200 ° C or less at a cooling rate of 50 ° C / hour, and then the mixture is extruded by heating at 450 to 550 ° C. A method for producing an aluminum alloy. A DC cast billet of an aluminum alloy having the chemical composition according to claim 1 is heated to 550 to 590 캜 at a rate of 80 캜 / hour or less, held for 0.5 to 6 hours, and then heated at 450 to 350 캜 for 0.5 to 1 hour Or a homogenization treatment in which the homogenization treatment is carried out at a cooling rate of 50 ° C / hour or less to 200 ° C or less is reheated to 450 to 550 ° C and then extruded into a desired shape at an extrusion ratio of 30 to 1000 , A method of manufacturing a fine hole hollow shape member made of an aluminum alloy excellent in corrosion resistance in the intergranular system.

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