JP2002069559A - Aluminum alloy extruded material having excellent intergranular corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy extruded material having excellent intergranular corrosion resistance and substituted for a 6063 alloy extruded material. SOLUTION: This aluminum alloy extruded material has a composition containing, by mass, 0.2 to 1.5% Si, 0.2 to 1.5% Mg, 0.001 to 0.2% Ti and 0.2 to 1.0% Zn, and the balance Al with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extruded aluminum alloy having excellent intergranular corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, extruded JIS6262 alloys containing Pb and Bi to ensure cutting properties have been used as materials for heat exchanger members manufactured by using a lot of cutting. However, this alloy has corrosion resistance. Because of its inferiority, the member has been subjected to alumite treatment to ensure corrosion resistance, and there has been a problem that the manufacturing cost is high.

[0003]

In order to omit this alumite treatment, a JIS6063 alloy extruded material having excellent corrosion resistance and machinability may be used instead of the 6262 alloy extruded material having poor corrosion resistance. When the member is combined with a dissimilar metal member, for example, stainless steel, brass, etc., and is used in a severe corrosive environment such as at a high temperature, electric corrosion based on a potential difference between dissimilar metals usually results in 6 members.
There is a possibility that intergranular corrosion hardly occurs in the 063 alloy. When intergranular corrosion occurs in the refrigerant passage etc. of the heat exchanger member, crystal grains float at the intergranular corrosion portion and fall off the surface, the corrosion loss increases, the original surface is lost, and the refrigerant However, there is a risk of leaking, so that it is desired to prevent intergranular corrosion. The present invention has been made in view of such a problem, and an object of the present invention is to obtain an aluminum alloy extruded material having excellent intergranular corrosion resistance in place of the 6063 alloy extruded material.

[0004]

The aluminum alloy extruded material according to the present invention has an Si content of 0.2 to 1.5% and a Mg content of 0.2%.
2 to 1.5%, Ti: 0.001 to 0.2%, Zn:
It is characterized by containing 0.2 to 1.0%, the balance being Al and unavoidable impurities, having excellent intergranular corrosion resistance, and suitable as, for example, a heat exchanger member having a refrigerant passage.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for adding each component of the above-mentioned extruded aluminum alloy will be described below. Si, Mg Si and Mg have an effect of improving strength and machinability by precipitation of Mg ₂ Si. However, if the content of either Si or Mg is less than 0.2%, the effect is not sufficient, while if the content of either Si or Mg exceeds 1.5%, the extrusion productivity is greatly reduced. I do. Therefore, the contents of both Si and Mg are in the range of 0.2 to 1.5%. Ti Ti has an effect of refining the cast structure of the aluminum alloy. However, if the content is less than 0.001%, the effect is not sufficient. On the other hand, if the content exceeds 0.2%, the crystal grain refining effect is saturated and the extrusion productivity is greatly reduced. Therefore, the content of Ti is set in the range of 0.001 to 0.2%.

[0006] Zn Zn is added for the purpose of controlling the potential, and if its content is less than 0.2%, its effect cannot be obtained. Intergranular corrosion occurs when the intragranular potential or the difference between the potential of intergranular precipitates and the intergranular potential (low intergranular potential) increases to some extent. The potential of the precipitate decreases, and the difference from the grain boundary potential decreases. Thereby, intergranular corrosion is suppressed. On the other hand, if the content exceeds 1.0%, not only extrusion productivity is greatly reduced, but also self-depletion due to a decrease in potential is increased, and corrosion resistance is significantly reduced. From the viewpoint of extrusion productivity, the content is preferably 0.2 to 0.6%.

Inevitable impurities Fe is the most inevitable impurity contained in aluminum ingots. If it exceeds 0.50% in the alloy, coarse intermetallic compounds are crystallized during casting, and the mechanical properties of the alloy are reduced. Impair the nature. Therefore, the content of Fe is 0.50
% Or less. Further, when casting an aluminum alloy, impurities are mixed from various routes such as a base metal and an intermediate alloy of an additive element. There are various elements to be mixed, but impurities other than Fe alone have 0.05% or less, and if the total amount is 0.15% or less, it hardly affects the properties of the alloy. Therefore, these impurities are set to 0.05% or less in a simple substance, and 0.15% or less in total. In addition, B among impurities is mixed into the alloy in an amount of about 1/5 of the Ti content with the addition of Ti, but a more preferable range is 0.02% or less.
Further, it is desirably 0.01% or less.

[0008]

Next, examples of the extruded aluminum alloy according to the present invention will be described in comparison with comparative examples. An Al-Mg-Si-based aluminum alloy having the chemical composition shown in Table 1 was melted by a conventional method, cast into a billet having a diameter of 200 mm by semi-continuous casting, and the billet was homogenized to obtain a 20 mm × 5 mm.
It was extruded hot with a 0 mm square bar, water-cooled press quenching was performed immediately after extrusion, and aging treatment was further performed. In addition, No.
5 is a 6063 alloy.

Each extruded material after the aging treatment was used as a test material, and a hardness measurement and a corrosion form judgment test were performed in the following manner. The results are shown in Table 1. Hardness measurement: A cross section perpendicular to the extrusion axis of each test material was polished with emery paper (# 2400), and the cross-sectional hardness was measured using a micro Vickers meter (load: 19.6) in accordance with JIS 2244.
N). Corrosion form judgment test: Both sides of each test material were milled to a thickness of 10 mm, degreased with acetone, and sealed with tape leaving a connection part a and a test part b (20 mm × 50 mm × 10 mm) as shown in FIG. Then, the middle part or less of the seal part c was immersed in the test solution, and a current was passed between the electrode d and the electrode d to perform a corrosion test. As test conditions, the test solution was 5% NaCl, the specific solution volume was 150 cc / cm ² , the test temperature was room temperature, and the current density was 3
mA / cm ² and the test time were set to 24 hours. After the corrosion test, the test portion was cut perpendicular to the extrusion direction, and the cross-sectional structure was observed with a stereoscopic microscope to examine the form of corrosion. The evaluation criteria are shown in the footnote of Table 1. As an extrudability test, the same diameter 2
A billet of 00 mm is extruded for 30 m at an extrusion temperature of 470 ° C.
Extrude hot into a square bar of mx 30 mm, change the extrusion speed, find the speed just before extrusion defects (wrinkles) occur on the surface of the extruded material, and extrude each alloy according to the evaluation criteria shown in the footnote in Table 1. Productivity was evaluated.

[0010]

[Table 1]

As shown in Table 1, No. 1 containing a predetermined amount of Zn. Alloys 1 to 4 are generally shallowly corroded on the surface,
Almost no intergranular corrosion has occurred. No. FIG. 2 shows a microstructure photograph of Sample No. 2. Extrusion productivity was the same for No. 2 having a Zn content in the range of 0.2 to 0.6%. Nos. 1 and 2 are particularly excellent. 3 and 4 are also within the practical range. In contrast, Zn
Containing no or low content of No. In Nos. 5 and 6, grain boundary corrosion occurred deep in the cross section. No. 5 is shown in FIG. No. 1 having a large Zn content. In No. 7, no intergranular corrosion occurred, but the extrusion productivity was poor. There was also a large amount of corrosion. In addition, No. Looking at the hardness of Nos. 1 to 4, No. 6063 alloy is No. 1; A value of 5 or more was obtained, and it is presumed that both the strength and the machinability were as good as the 6063 alloy. As described above, N which is an example of the present invention
o. Nos. 1 to 4 are generally excellent in intergranular corrosion resistance, extrudability and strength, and machinability.

[0012]

According to the present invention, it is possible to obtain an aluminum alloy extruded material having excellent intergranular corrosion resistance in place of the 6063 alloy extruded material.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a test piece and a test used in a corrosion form determination test.

FIG. 2 is a photograph of a microstructure of Invention Example 2 (Example).

FIG. 5 is a photograph of a microstructure of Comparative Example 5 (Comparative Example).

Claims (1)

[Claims] 1. Si: 0.2 to 1.5% (mass%, the same applies hereinafter), Mg: 0.2 to 1.5%, Ti: 0.001 to
Extruded aluminum alloy containing 0.2%, Zn: 0.2 to 1.0%, and excellent in intergranular corrosion resistance consisting of balance Al and inevitable impurities.