JPS6250452A - Manufacture of aluminum alloy material - Google Patents

Abstract

PURPOSE:To prevent the intergranular corrosion of an alloy material and to improve the reliability of a structure using the alloy material by homogenizing and heat treating an alloy contg. prescribed percentages of Mg, Ti, B, Mn, Cr and Al under prescribed conditions. CONSTITUTION:An alloy consisting of, by weight, 3-6% Mg, 0.001-0.3% Ti, 0.0001-0.005% B, 0.1-1% Mn, 0.05-0.3% Cr and the balance Al is manufactured. An ingot of the alloy is homogenized at 400-570 deg.C, rolled, heat treated at 400-550 deg.C and cooled at >=3 deg.C/min cooling rate. The resulting alloy material does not undergo intergranular corrosion and the reliability of a structure using the alloy material is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing an A1-Mg alloy material used for structures, particularly structures used in corrosive atmospheres.

(Prior Art) A1-Mg alloys have a proven track record as structural materials with excellent strength and weldability. These alloy thick plates are generally used as they are after hot rolling, or after being annealed to improve workability. Further, after hot rolling, the material may be work-hardened by cold rolling.

(Problem to be solved by the invention) However, even if the manufacturing method is used, A11~Mg
When these alloys are used for long periods of time in seawater or other corrosive atmospheres, corrosion may occur and progress along grain boundaries. This tendency is particularly noticeable in the case of materials that have been subjected to hot-rolling, where processing strains introduced during rolling remain, or materials that have been cold-worked and then stabilized at high temperatures. Therefore, it has been desired to develop a material that does not generate corrosion holes, particularly along grain boundaries, even in a corrosive atmosphere, but no material has been developed that satisfies this requirement.

Note that AfLMg (
- In order to increase the stress corrosion cracking resistance R of Zn) alloys, a method of rapid cooling immediately after hot rolling is described, but this method does not disclose anything about improving general corrosion in a state where no stress is applied. There is no.

By the way, corrosion holes that occur at grain boundaries are caused by compounds of Mg and AQ (Mg2A, Q) that are continuously precipitated at one grain boundary.
It has been pointed out that this is caused by. That is,
The precipitation of Mg2An3 is approximately 70 to 200 from the metal phase diagram.
This is promoted when the material is held in the :/ section of the C range. Because material #1 produced by the conventional method is often left to cool after hot rolling, Mg2A
If n3 is continuously precipitated at grain boundaries and welding is involved during use, the precipitation will further progress due to the influence of the heat generated during welding, inducing corrosion.

In order to prevent this, a method of cooling the rolled plate immediately after hot rolling is considered (for example, the method described in the above-mentioned Japanese Patent Publication No. 59-19987), but since cooling is performed in the rolling line, the cooling rate is It is difficult to make −・ constant,
It is actually difficult to manufacture a board that is uniform over the entire surface of the board.

Therefore, an object of the present invention is to provide an A-Mg alloy material for use in structures, especially structures used in corrosive atmospheres, which has improved corrosion resistance, particularly intergranular corrosion, and
An object of the present invention is to provide a method for manufacturing an AfL-Mg alloy material that improves the reliability of structures.

(Means for Solving the Problems) As a result of various studies to achieve the above object, the inventors of the present invention found that the process of cooling Mg2A text 31 after hot rolling or after annealing the rolled plate. Not only does Mg precipitate at the grain boundaries during ingot production, but unless the homogenization treatment conditions are appropriately selected, Mg2AM will not dissolve sufficiently at the grain boundaries and will become Mg2AM during rolling.

We obtained the knowledge that the formation of As a result of further investigation based on this knowledge, we found that i! I! Control of hot rolling conditions or selection of annealing treatment conditions alone is not sufficient to prevent continued precipitation.In addition to homogenizing the ingot and selecting hot rolling conditions, it is necessary to Furthermore, it is necessary to perform heat treatment, which promotes the solid solution of Mg. We have discovered that scales can reduce the precipitation of corrosion and suppress the occurrence of corrosion. The present invention has been made based on this knowledge.

That is, in the present invention, Mg3-6t4%, Ti0.001
~0.3% by weight, B 0.0001~0.005 tonpu%
, M n 0.1-1.0 Nail 1% and Cr 0.05
~0.3 weight j5% (hereinafter, % is simply abbreviated as %)
After homogenizing a lump of alloy tJ' consisting of impurities and A text, the remainder of which is unavoidably contained, at 400 to 570°C,
The present invention provides a method for producing an aluminum alloy material having excellent corrosion resistance, which comprises rolling the material, heat-treating the material at 400 to 550"0, and cooling at a rate of 3 DEG C./min or more.

The method of the present invention will be explained in more detail.

Mg in the aluminum alloy used in the method of the present invention
is a curing element, but if it is less than 3% it is not sufficiently effective;
If it exceeds 6%, workability deteriorates and stress corrosion cracking is likely to occur.

Ti has the effect of refining crystal grains, but at 0.001%
If it is less than 0.3%, refinement will not be promoted, and if it exceeds 0.3%, it will be A.
Forms coarse compounds with I, impairing toughness.

B coexists with Ti and has the effect of refining crystal grains, but
There is no effect if it is less than 0.0001%. Also, the miniaturization is 0.
Even if it exceeds 0.005%, it will not be promoted.

Conversely, if it exceeds 0.005%, the toughness of the material will be impaired.

Mn is one of the hardening elements and has the effect of improving corrosion resistance, but if it is less than 0.1%, it has no effect;
%, a coarse intermetallic compound is formed with AM, impairing the workability and toughness of the material.

Cr has the effect of improving corrosion resistance, but if it is less than 0.05%, it has no effect, and if it exceeds 0.3%, it forms a huge intermetallic compound with An, reducing ductility and toughness.

In the method of the present invention, the homogenization treatment is performed to dissolve or finely precipitate the contained elements.
At temperatures below '0, the grain boundary segregation of Mg, which is a factor in the formation of corrosion holes, is not alleviated and solid solution within the grains is not promoted.5
At temperatures above 70° C., the quality of the material deteriorates due to the melting of low-melting compounds segregated at grain boundaries, and coarse compounds of A-texture, Mn, and Fe are formed, leading to a decrease in internal quality.

In the method of the present invention, it is necessary to heat-treat the homogenized aluminum alloy at 400 to 550°C after hot rolling or cold rolling.

By heat-treating after rolling, the compound of Mg and AM that precipitated at the grain boundaries during plate manufacturing can be dissolved in the grains, but it is not effective below 400°C, and solid solution is accelerated when the temperature exceeds 550°C. When a load is applied, stress tends to concentrate at the grain boundaries due to secondary growth and coarsening of the crystal grains, which leads to a decrease in strength and ductility and promotes intergranular corrosion.

As described above, by rapidly cooling the heat-treated aluminum alloy material, it is possible to prevent Mg2AM from continuously precipitating at the grain boundaries, but this effect cannot be expected at a cooling rate of less than 3°C/min.

According to the method of the present invention, an A-Mg alloy material with excellent corrosion resistance can be obtained, but the effects of the present invention are not affected by hot rolling conditions or cold rolling conditions. Further, after the quenching treatment, it will not be damaged even if it is subjected to mild cold working.

(Example) Next, the present invention will be explained in more detail based on examples.

Example 1 JIS5083 with thickness 600+nm and width 1400mm
Aluminum alloy ingot with equivalent composition (Mg4.6%, Ti
0.01%, B 0.0005%, Mn0.7%, C
r0.11%, balance A) was homogenized and then hot rolled into a plate with a thickness of 20 mm. After heat treatment, this was cooled to room temperature to produce samples Nos. 1 to 9, and a corrosion test was conducted. The results are shown in Table 1 together with the manufacturing conditions.

The corrosion test was performed by immersing a test piece machined into a 5% saline solution with a thickness of 20 mm and a width and length of 40 mm and 100 mm, respectively. Zero judgment was performed visually and with an optical microscope.

From the results in Table 1, sample No. manufactured by the method of the present invention
, 1 to 9 are samples j-4 No. 1 manufactured by the comparative method.
It was found that intergranular corrosion did not occur and excellent corrosion resistance was exhibited compared to Example 1 and fiTI, which had a thickness of 600 mm and a width of 1600 mm.
450-550 after homogenizing an aluminum alloy ingot with a composition equivalent to J155083 at 530°C for 2 hours.
Example 1 was hot-rolled to a thickness of 20 mm at a temperature of 20°C, then heat-treated at 470°C for 1 hour, and then cooled to 70°C at an average cooling rate of 3 to 100 ml. A corrosion test was conducted in the same manner. The results are shown in Table 2 together with the manufacturing conditions.

As is clear from the results in Table 2, sample Nos. 14 to 17
It can be seen that all of these have excellent corrosion resistance and do not cause intergranular corrosion regardless of the tensile bonding. That is, the properties of the plate material manufactured by the method of the present invention are not impaired even if the plate material is subjected to mild cold working after heat treatment.

Example 3 An aluminum alloy ingot having a composition equivalent to JIS 5083 similar to that used in Example 1 and having a thickness of 600 mm and a width of 1100 mm was homogenized at 550°C for 2 hours, and then
It was hot rolled at a temperature of 'C to form a plate with a thickness of 5 mm. Next, the plate was annealed at 350°C for 2 hours, cold-rolled to a thickness of 2 mm, subjected to a prescribed heat treatment, and then cooled to obtain sample No.

Nos. 18 to 23 were produced. Sample No. 18-23 (7) Corrosion resistance was tested in the same manner as in Example 1. The results of this corrosion test are shown in Table 3 together with the heat treatment and cooling treatment conditions.

From the results in Table 3, sample Nos. 18 to 21 according to the present invention
It can be seen that intergranular corrosion did not occur in the plate compared to Sample Nos., 22, and 23 shown as comparative examples, and the plate exhibited excellent corrosion resistance.

(Note to Table 3) O: No intergranular corrosion porosity occurs ×: Intergranular corrosion pores occur Intergranular corrosion of aluminum alloy materials can be prevented, improving the reliability of structures. At the same time, it expands the scope of use of aluminum alloys and is effective in reducing the weight of structures.

Claims (1)

[Claims] (1) Mg 3-6% by weight, Ti 0.001-0.3% by weight, B 0.0001-0.005% by weight, Mn 0.1-0.
1.0% by weight and 0.05-0.3% by weight of Cr,
An alloy ingot consisting of impurities and Al, the remainder of which is unavoidably included, is homogenized at 400 to 570°C, then rolled, then heat treated at 400 to 550°C, and then cooled at a rate of 3°C/min or more. A manufacturing method for aluminum alloy material with excellent corrosion resistance.