JPH0523732A - Manufacture of aluminum alloy extruding material for welding structure improving against welding crack - Google Patents

Abstract

PURPOSE:To obtain an extruding Al-Mg based alloy material having no welding crack by restricting the surface recrystallization of the material. CONSTITUTION:The Al-Mg based alloy billet incorporating 3.0-6.0wt.% Mg is extruded from an extruding die. The die is provided with a choke working part having forming holes whose heights continuously are smaller over more than the length of 3mm toward the extruding-out side on a bearing part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an Al alloy extruded material for a welded structure which is welded and used as a material for a tank structure such as LNG or a hull structure material for LNG tankers, fishing boats and the like. In particular, the present invention relates to a method for manufacturing an Al alloy extruded material for a welded structure with improved weld cracking.

[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 with such an Al-Mg alloy extruded material, if the thickness of the surface recrystallized structure layer generated in the manufacturing process reaches about 0.3 mm or more and is too thick, general welding is performed. It has been found by the inventors' research that minute cracks occur in the heat-affected zone (HAZ section) when the welding strain is particularly large when applied.

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 in which weld cracking is improved by suppressing surface recrystallization.

[0005]

In order to achieve the above object, the present invention will be described with reference to the numerals in FIG.
When the Al-Mg alloy billet containing 3.0 to 6.0 wt% is extruded from the extrusion die, the bearing part (11)
Extruding using an extrusion die (1) provided with a choking portion (12) in which the height of the molding hole (5) continuously decreases toward the extrusion side over a length of 3 mm or more. In order to improve weld cracks by suppressing surface recrystallization of the extruded material.

First, in the Al-Mg alloy extruded material which is the subject of the present invention, the content of Mg is specified to be 3.0 to 6.0 wt% because the content of Mg is within this range.
This is because the advantages of the 1-Mg-based alloy such as corrosion resistance, good mechanical properties at low temperature, and weldability are sufficiently exhibited, and if Mg is less than 3.0 wt%, those effects are poor.
On the other hand, if it exceeds 6.0 wt%, the extrudability will deteriorate.

The Al-Mg alloy is formed 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 portion 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. Note that 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 leads to the drawback of lowering the yield productivity. In addition, the method of lowering the billet heating temperature inevitably shortens the entire length of the billet, which also leads to the drawback of poor production efficiency. 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 or less.

[0009]

[Function] Since the bearing portion is extruded by using the extrusion die provided with the choke portion where the height of the molding hole is continuously reduced toward the extrusion side over the length of 3 mm or more, the molding gap is formed. The frictional force between the extruded material passing through and the bearing part 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. Weld cracking in the heat affected zone is suppressed.

[0010]

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.

[0015]

As described above, according to the present invention, Mg: 3.
When the Al-Mg alloy billet containing 0 to 6.0 wt% is extruded from the extrusion die, the diameter of the bearing is 3 mm.
The molding hole is characterized by being extruded using an extrusion die provided with a choked portion in which the height of the molding gap continuously decreases toward the extrusion side over the above length. The frictional force between the extruded material passing through and the bearing can be reduced, and the temperature rise of the extruded material surface due to frictional heat can be suppressed.As a result, the surface recrystallization can be suppressed and the thickness of the surface recrystallized structure layer of the extruded material can be suppressed. Can be thinned. Therefore, it is possible to eliminate welding cracks in the heat-affected zone that have been conventionally generated due to the large thickness of the surface recrystallization texture layer.
-The advantages of the Mg-based alloy extruded material as a welded structural material can be fully exerted. 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]

1 ... Extrusion die 11 ... Bearing part 12 ... Chalk processing section

Continued front page    (72) Inventor Masami Sudo             Showa Al, 6-224, Kaiyamacho, Sakai City, Osaka Prefecture             Minium Corporation

Claims (2)

[Claims] 1. 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). 2. The method for producing an Al alloy extruded material for welded structure with improved weld cracking according to claim 1, wherein the opening angle (θ) of the choked portion (12) is 0.5 to 10 degrees.