JPH08251B2 - Aluminum alloy extruded material for welded structure with improved weld cracking and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy extruded material for a welded structure which is used by being welded as a tank structural material such as LNG, or a hull structural material for LNG tankers, fishing boats, etc. More particularly, the present invention relates to an Al alloy extruded material for welded structure with improved weld cracking and a method for producing the same.

[0002]

2. Description of the Related Art Aluminum alloy materials, particularly Al-Mg type alloy extruded materials used for the above-mentioned applications,
Not only is it lightweight, it has excellent corrosion resistance, low-temperature mechanical properties, and excellent weldability. It is generally recognized that welding cracks do not occur except during special welding. .

However, even in the case of such an Al-Mg alloy extruded material, if the thickness of the surface recrystallized structure layer produced in the manufacturing process is too thick, particularly when the general welding is performed, the welding distortion is caused. It was found by the study of the inventors that when the value is large, minute cracks occur in the heat affected zone (HAZ section).

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an Al alloy extruded material for a welded structure with improved weld cracking and a method for producing the same.

[0005]

For the above object, one of the present invention relates to the extruded material itself, and the thickness of the surface recrystallized structure layer is specified to be 0.05 to 0.15 mm. The gist is an Al alloy extruded material for welded structure, which has improved weld cracking.

The other one relates to a manufacturing method, and referring to the reference numerals in FIG. 1, Mg: 3.0-6.
When an Al-Mg alloy billet containing 0 wt% is extruded from an extrusion die, a molding hole (5) is formed in the bearing portion (11) over a length of 3 mm toward the extruding side.
For extruding an Al alloy extruded material for welded structure with improved weld cracking, characterized by extruding using an extrusion die (1) provided with a choked portion (12) having a continuously small height Is the gist.

First, Al for welded structure which is the object of the present invention
The alloy extruded material is preferably an Al-Mg alloy extruded material containing Mg: 3.0 to 6.0 wt%. Where Mg
The content of Al is regulated to 3.0 to 6.0% by weight, because it is contained in such a range, the Al-Mg alloy has superior corrosion resistance, good mechanical properties at low temperature, and weldability. This is because when Mg is less than 3.0 wt%, these effects are poor, and when it exceeds 6.0 wt%, extrudability deteriorates.

Further, the thickness of the surface recrystallized structure layer of the extruded material is regulated to 0.05 to 0.15 mm because welding is performed when the thickness of the recrystallized structure layer exceeds 0.15 mm. This is because there is a high risk that welding cracks will occur in the heat affected zone. On the other hand, if the thickness of the recrystallized structure layer is less than 0.05 mm, the effect of suppressing weld cracks is saturated, and further suppression of the recrystallized structure layer is meaningless.

Next, the manufacturing method will be described. The above Al-Mg alloy is manufactured into a billet by a conventional method, and if necessary, homogenized and then extruded with an extrusion die.

In the present invention, as the extrusion die, as shown in FIG. 1, a bearing having a choked portion is used. In FIG. 1, (1) is a die, (2) is a container, (3) is a billet, and (4) is a backer. The bearing (11) of the die (1) has a molding hole (5). A taper processing portion, that is, a choke processing portion (12) whose height is continuously reduced from the end on the container (2) side toward the extrusion side is formed. The choked portion (12) is provided to suppress surface recrystallization of the extruded material (A) extruded from the molding hole (5). That is, by forming the chalk processing part (12),
The strain distribution from the surface of the extruded material passing through the forming hole (5) to the thickness direction becomes gentle, and local plastic working is suppressed, so that recrystallization of the extruded material surface is suppressed. Here, the length (L) of the choked portion (12) must be set to 3 mm or more. When the length (L) is less than 3 mm, the effect of suppressing recrystallization on the surface of the extruded material is poor, and consequently, weld cracking during welding cannot be prevented. Further, the opening angle (θ) of the choked portion (12) is preferably set to 0.5 to 10 degrees.
If it is less than 0.5 degrees, the effect of suppressing recrystallization of the extruded material may be reduced. On the other hand, if the angle exceeds 10 degrees, the extrusion pressure may increase and the productivity may be impaired. Most preferably, θ is set to 1 to 3 degrees. When the length of the bearing part (11) is long, a part of the bearing part may be choked, or the entire length of the bearing part may be choked. FIG.
(13) is a relief portion. Other extrusion conditions are not particularly limited, but are 0.
It is also possible to suppress recrystallization of the surface of the extruded material by extruding at a product speed of 5 m / min or less, or by setting the billet heating temperature at the time of extrusion to be low.
However, the method of lowering the extrusion speed has a disadvantage that the yield productivity is reduced. In addition, in the method of lowering the billet heating temperature, the total length of the billet must be shortened, which also has the disadvantage that the production efficiency is not good. On the other hand, when the bearing die is provided with the choked portion over a length of 3 mm as in the invention of the present application, the extrusion speed and the billet length are not required to be reduced without the need to reduce the extrusion speed. The thickness of the recrystallized structure layer on the extruded material surface is 0.05 to
It can be said to be suppressed to about 0.15 mm.

[0011]

[Function] The thickness of the surface recrystallized structure layer is 0.05 to 0.15.
Since it is regulated to mm, welding cracks in the heat affected zone during welding are suppressed.

Further, since the bearing portion is extruded using an extrusion die provided with a choked portion in which the height of the forming hole is continuously reduced toward the extruding side over a length of 3 mm or more, the extruding die is extruded. The frictional force between the extruded material passing through the gap and the bearing portion is reduced, the temperature rise of the extruded material surface due to frictional heat is suppressed, and the surface recrystallization of the extruded material after extrusion is suppressed.

[0013]

EXAMPLE Two homogenizing treatments were carried out under the same conditions on two billets having a diameter of 202 mm, which were produced using an A5083 alloy containing Mg: 4.5 wt%. The billet lengths were 400 mm and 610 mm.

Next, for a billet having a length of 610 mm, the billet heating temperature is 480 ° C. and the extrusion product speed is 1.2.
It was extruded into a flat bar having a width of 100 mm and a thickness of 12 mm under the extrusion condition of m / min. The extrusion was performed using a die having a choked portion with a length L of 5 mm and an opening angle θ of 1 degree. Temperature of extruded material at this time (temperature of platen outlet)
Was 470 ° C. When the thickness of the surface recrystallized structure layer of this extruded material (product of the present invention) was measured, it was 0.05-0.
It was 15 mm.

For a billet having a length of 400 mm, the billet heating temperature is 450 ° C. and the extrusion product speed is 1.
It was extruded into a flat bar having the same shape as above under an extrusion condition of 0 m / min. Extrusion was performed using the same die as above except that the choked portion was not formed. The temperature of this extruded material was 420 ° C. Further, the thickness of the surface recrystallized structure layer of this extruded material (comparative product) was measured to be 0.8-1.
It was 2 mm.

Next, for each extruded material, MIG under the same conditions.
When butt welding by welding was performed, for the product of the present invention using a die having a choked portion,
No weld cracking was observed, whereas a comparative product using a die without a choked portion had fine cracks in the heat-affected zone.

Therefore, according to the present invention, it was confirmed that surface recrystallization can be suppressed and weld cracks can be improved.

[0018]

According to the present invention, since the thickness of the surface recrystallized structure layer is regulated to 0.05 to 0.15 mm depending on the above, the thickness of the surface recrystallized structure layer is large. Weld cracks in the heat affected zone that had occurred can be eliminated,
The advantage of the extruded material such as Al-Mg alloy as a welded structural material can be fully exerted.

In the method of the present invention, Mg: 3.0-6.
When an Al-Mg alloy billet containing 0 wt% is extruded from an extrusion die, a choked portion in which the height of the molding gap continuously decreases toward the extruding side over a length of 3 mm or more in the bearing portion. Since it is characterized by extruding using an extrusion die provided with, it is possible to reduce the frictional force between the extruded material passing through the forming hole and the bearing portion, and the temperature of the extruded material surface due to frictional heat. As a result of suppressing the rise, surface recrystallization can be suppressed, and an extruded material in which the thickness of the surface recrystallized structure layer is defined in the above range can be reliably manufactured. Moreover, since the surface recrystallization of the extruded material is suppressed by using a die provided with a predetermined choked portion, extruding is performed without the need to reduce the extrusion speed or shorten the billet length. It is possible to avoid a decrease in yield productivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an extrusion device including an extrusion die used in the present invention.

[Explanation of symbols]

 A ... Extruded material 1 ... Extrusion die 5 ... Molding hole 11 ... Bearing 12 ... Choke processing

Front page continuation (72) Inventor Masami Sudo 6-224 Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminum Co., Ltd. JP, A) Japanese Patent Publication Sho 53-36812 (JP, B2)

Claims (3)

[Claims] 1. The thickness of the surface recrystallized structure layer is from 0.05 to
An Al alloy extruded material for a welded structure with improved weld cracking characterized by being regulated to 0.15 mm. 2. A containing Mg: 3.0 to 6.0 wt%.
When extruding the 1-Mg alloy billet from the extrusion die, the bearing part (11) is choked so that the height of the forming hole (5) continuously decreases toward the extruding side over a length of 3 mm or more. A method for manufacturing an Al alloy extruded material for a welded structure with improved weld cracking, which comprises extruding using an extrusion die (1) provided with a portion (12). 3. The method for producing an Al alloy extruded material for a welded structure with improved weld cracking according to claim 2, wherein the opening angle (θ) of the choked portion (12) is 0.5 to 10 degrees.