JP2001026832A - Extruded tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tube capable of securing compressive strength required even after brazing heat treatment without deteriorating its extrudability and corrosion resistance and used for a heat exchanger of an automotive air conditioner by adding specified amounts of Fe, Cu and Mn to Al. SOLUTION: This extruded tube is composed of, by weight, 0.25 to 0.70% Fe, 0.30 to 0.50% Cu, 0.10 to 0.20% Mn, and the balance Al. Moreover, this compsn. may be incorporated with one or more kinds of 0.05 to 0.25% Ti and 0.05 to 0.25% Zr. In this way, a fine crystal structure in which the average crystal grain size after brazing heat treatment is <=150 μm, more desirably <=100 μm can be obtd. Furthermore, in this extruded tube, impurity elements are included in addition to the above elements, but, in the case of the ranges of <=0.10 % Si, <=0.02% Mg, <=0.02% Zr, <=0.01% V and <=0.002% B, the purpose is not checked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extruded tube used for a heat exchanger of an air conditioner for an automobile.

[0002]

2. Description of the Related Art Al or an Al alloy is used as an extruded material for various uses because of its excellent extrudability as compared with other metal materials. In addition, Al or an Al alloy is used for a heat exchanger of an air conditioner for an automobile because it has excellent thermal conductivity, light specific gravity, and excellent lightweight. More specifically, it is used as an extruded material in a tube through which a refrigerant passes in a heat exchanger.

[0003] The extruded tube is made of a pure Al material (pure Al having a purity of 99.5% or more) such as JIS1050 or an Al-M
An n-type alloy or an improved alloy containing 0.4 to 0.6% of Cu in the pure Al material is mainly used.

[0004]

In recent years, in order to reduce the weight and size of automotive heat exchangers, the cross-sectional shape of extruded tubes has become smaller and more complicated. Therefore, it is required that the alloy used for the extruded tube has better extrudability. In order to improve the extrudability, it is ideal to reduce the additive elements in the alloy as much as possible, that is, to use pure Al. However, since these additional elements are generally added to secure the strength, the reduction leads to a decrease in the strength of the extruded tube. Therefore, there has been a demand for an extruded tube capable of ensuring extrudability without lowering the strength and corrosion resistance.

A heat exchanger of the type using an extruded tube is formed by bending the extruded tube in a meandering shape, inserting fins between the extruded tubes, or laminating the fins and tubes, and then placing the tubes in a heating furnace and brazing the tubes. And fins are joined. However, when this brazing heat treatment is performed, the crystal grains of the Al alloy constituting the extruded tube are coarsened and the strength is reduced. In other words, after the extruded tube is extruded, after the coiling step of once winding it into a coil shape, the roll is usually subjected to a process (resize) for adjusting the height and width to predetermined dimensions using a roll. Bending and tension based on resizing and strain due to compression and tension based on resizing occur in the material, and the crystal grains grow abnormally due to recrystallization during brazing heat treatment based on the strain. A decrease in the strength after the brazing heat treatment is a practical problem because the strength against pressure as the heat exchanger is reduced.

Accordingly, an object of the present invention is to provide an extruded tube which can ensure good extrudability and necessary pressure resistance even after heat treatment for brazing.

[0007]

In order to solve the above-mentioned problems, studies have been made to find that the strength of the tube can be improved by adding an appropriate amount of one or two of Fe, Ti and Zr. At the same time, it was found that the coarsening of crystal grains due to recrystallization during brazing heat treatment can be suppressed.
Further, by adding an appropriate amount of Cu, it is possible to improve the strength of the tube while suppressing a decrease in corrosion resistance.
It was found that by adding an appropriate amount of, it was possible to improve the strength of the tube while ensuring the extrudability.

[0008] The present invention is based on the above findings,
By weight%, Fe: 0.25 to 0.70%, Cu: 0.3
0 to 0.50%, Mn: 0.10 to 0.20%, balance A
1 and an extruded tube consisting of unavoidable impurities.
Further, the present invention provides the above composition in which Ti: 0.05 to 0.25%
And an extruded tube containing one or two of Zr: 0.05 to 0.25%. According to the present invention, a fine crystal structure having an average crystal grain size after brazing heat treatment of 150 μm or less, more preferably 100 μm or less can be obtained.

The components of the present invention and other reasons for limitation will be described below. <Fe: 0.25 to 0.70%> Fe is crystallized or precipitated in the alloy as an Al-Fe-based intermetallic compound to improve the strength after brazing. Further, the Al-Fe-based intermetallic compound functions to suppress crystal grain coarsening during brazing heat treatment. If it is less than 0.25%, the above effects cannot be sufficiently obtained, so the lower limit is set to 0.25%. Also,
If the Al-Fe-based intermetallic compound is present in a large amount, the extrudability is reduced, so the upper limit is set to 0.70%. Desirable Fe content is 0.4 to 0.6%.

<Cu: 0.30 to 0.50%> Cu is an element that contributes to improvement in strength after brazing by forming a solid solution in the alloy matrix. In order to obtain this effect, 0.30% or more is added in the present invention. However, if added in a large amount, the corrosion resistance of the tube is reduced, so the present invention sets the upper limit to 0.50%. Desirable Cu content is 0.35
0.45%.

<Mn: 0.10 to 0.20%> Mn is
As an Al-Mn-based intermetallic compound, it has the effect of crystallizing or precipitating in the alloy and improving the strength after brazing. However, if it is less than 0.10%, this effect cannot be sufficiently obtained, while if it exceeds 0.20%, the extrudability decreases. Therefore, the present invention sets the Mn content to 0.10 to 0.20.
%. Desirable Mn content is 0.13 to 0.1.
7%. The Al-Mn-based intermetallic compound includes the above-mentioned Al-Fe-based intermetallic compound and Al-Ti, A
Since it is coarser than the l-Zr-based intermetallic compound, the function of suppressing the crystal grain coarsening is small as compared with these intermetallic compounds.

<Ti, Zr: 0.05-0.25%> T
i, Zr is crystallized or precipitated in the alloy as an Al-Ti, Al-Zr-based intermetallic compound to improve the strength after brazing. Further, the Al-Ti, Al-Zr-based intermetallic compound functions to suppress coarsening of crystal grains during brazing heat treatment. However, if the content is less than 0.05%, this effect is insufficient, and if it exceeds 0.25%, the effect corresponding to the content cost cannot be obtained. Therefore, in the present invention, the content is set to 0.05 to 0.25%. Desirable Ti, Zr
Is 0.1 to 0.2%.

<Other impurity elements> The extruded tube of the present invention contains impurity elements in addition to the above-mentioned elements. However, the following range does not impair the object of the present invention. Si: 0.10% or less Mg: 0.02% or less Zn: 0.02% or less V: 0.01% or less B: 0.002% or less

In order to obtain the extruded tube of the present invention, a conventionally known production method may be applied. For example, after obtaining an ingot by the DC casting method, a billet to be subjected to extrusion is prepared. This billet is subjected to a homogenizing heat treatment in a temperature range of 450 to 650 ° C. By this homogenization heat treatment, a part of Fe is dissolved, and Al-Fe-based intermetallic compound, Al-Mn-based intermetallic compound, Al-Ti, Al
-The Zr-based intermetallic compound precipitates uniformly and finely. Thereafter, extrusion is performed using a die having a predetermined shape.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. Billets were prepared under the alloy composition (wt.%) And homogenization treatment conditions shown in Table 1, and extruded tubes were prepared under normal conditions. The pushing force, extrusion speed and tube shape accuracy at this time were comprehensively evaluated as extrudability. Then, after performing coiling and resizing in the same manner as the actual product, a heat treatment of holding at 600 ° C. for 5 minutes assuming brazing was performed (hereinafter referred to as brazing). A tensile test was performed before and after the brazing to measure the tensile strength. Further, in order to confirm the corrosion resistance, a SWAAT test (test period: 20 days) according to ASTM was performed, and the maximum corrosion depth was measured. Table 2 shows the above evaluation and measurement results.

[0016]

[Table 1]

[0017]

[Table 2]

As is clear from Table 2, the extruded tube according to the present invention has excellent strength after brazing and excellent corrosion resistance. The extrudability is also at a level that does not cause any problem.
No. of the present invention. 1, 2, and 3 have the same Fe and Mn contents, but the Cu content increases in the order of 1-3. This N
o. Comparing the tensile strengths of 1 to 3, it is understood that the tensile strength improves as the Cu content increases. But,
It can be seen that when the Cu content increases, the maximum corrosion depth increases and the corrosion resistance deteriorates.

No. Nos. 4, 1, and 5 have the same Fe and Cu contents but have the same Mn content. Increase in the order of 4, 1, 5. Table 2 shows that the tensile strength is improved as the Mn content is increased. Where Mn
Extrudability tends to be inferior as the content increases.

No. Nos. 1, 6, and 7 have the same Cu and Mn contents, but have the Fe contents of Nos. 1, 6, and 7. It increases in the order of 1, 6, 7. Table 2 shows that the tensile strength is improved as the Fe content is increased. Where Fe
Extrudability tends to be inferior as the content increases.

No. Nos. 9 to 11 are examples containing one or two of Ti and Zr. In this case, too, it can be seen that an extruded tube having excellent extrudability, tensile strength and corrosion resistance can be obtained.

Table 2 shows the average grain size after brazing.
Each extruded tube according to the present invention has a fine crystal structure of 60 μm or less. On the other hand, No. 12,
Sample No. 13 had an average crystal grain size of about 200 μm and about 500 μm, and it was confirmed that recrystallization was coarsened by brazing.

[0023]

As described above, according to the present invention, Fe: 0.25 to 0.70%, Cu: 0.30% by weight.
-0.50%, Mn: 0.10-0.20%, balance Al
Further, since the composition is composed of unavoidable impurities, it is possible to obtain an extruded tube having improved tensile strength while ensuring extrudability.

Claims (3)

[Claims] 1. Fe: 0.25 to 0.70% by weight
%, Cu: 0.30 to 0.50%, Mn: 0.10 to
An extruded tube comprising 0.20%, the balance being Al and unavoidable impurities. 2. Ti: 0.05-0.25% and Z
The extruded tube according to claim 1, wherein one or more kinds of r: 0.05 to 0.25% are contained. 3. The average crystal grain size after the heat treatment for brazing is 150.
3. The extruded tube according to claim 1, which has a size of not more than μm.