JPH08165539A - Heat treated type thin aluminum extruded shape and its production - Google Patents

Abstract

PURPOSE: To produce a high strength aluminum extruded shapes excellent in corrosion resistance and weldability and capable of high speed hot extrusion. CONSTITUTION: This shape has a composition, which contains 2.1-2.9% Mg, 0.8-1.5% Si, 0.51-0.8% Cu, 0.3-0.8% Mn, and 0.05-0.4% Cr and in which the contents of Fe, Pb, Ti, and B are limited to <=0.15%, <=0.03%, 0.006-0.03%, and 0.0001-0.005%, respectively, and extruded at high speed into a shape having a thin and complicated shape. The blonk for extrusion is prepared by subjecting an ingot, prepared by DC casting, to heating at 460-540 deg.C for 1-10hrs for homogenizing treatment and then to forced air cooling. At the time of extrusion, the ingot is preheated to 350-520 deg.C and then subjected to forced air cooling or water-quenching at >=100 deg.C/min cooling rate at the outlet of a platen. When artificial aging treatment consisting of heating at 140-200 deg.C for 1-12hr is applied, strength required of a structural material can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength aluminum extruded shape material which is used as a thin structural material for ships, vehicles and the like and has excellent extrudability and corrosion resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Al-Mg alloys and Al-Mg-Mn alloys such as 5083 and 5086 have excellent corrosion resistance in seawater or air, and exhibit high strength without heat treatment. It is used as a structural material for various facilities and equipment. This type of alloy has good weldability and few weld crack defects. It also has the advantage that the strength after welding, that is, the yield strength in the annealed state is large. Al-Mg-based alloys, Al-Mg-Mn-based alloys, and the like have higher strength as the Mg content increases, but stress corrosion cracking and peel corrosion are more likely to occur. In this regard, in the Al-Mg-Mn-based alloy introduced in JP-A-4-32534, by controlling the contents and ratios of Fe and Si and adding Cu, the weld crack resistance, Improves resistance to stress corrosion cracking.

[0003]

However, the conventional Al-
In order to secure sufficient strength with a Mg type or an Al-Mg-Mn type, a Mg content of 4% by weight or more is required.
When such a large amount of Mg is contained, the hot extrudability is deteriorated, and it becomes difficult to manufacture not only a hollow material but also a solid thin-walled material having a thickness of 3 mm or less. Extrudability is 5052,51
It is improved by reducing the Mg content as seen in alloy systems such as 54 and 5454. However, this type of alloy lacks strength and cannot be used as a structural material like 5083. Also, 5083, 5086, 5056
Since alloys such as Mn contain a large amount of transition metals such as Mn and Cr in addition to Mg, a high pressure is required at the time of extrusion, and cracks are easily generated on the surface of the obtained extruded profile.

As an alloy other than the 5000 series alloy, there is a 6N01 alloy which is excellent in extrudability and obtains strength by air quenching after extrusion. The 6N01 alloy can be extruded into a thin and complex shape (enameled material), and is used as a vehicle material or the like. However, the corrosion resistance and the strength after welding are inferior to the 5000 series structural alloys such as 5083 and 5086. The present invention has been devised to solve such problems, and by adding Si, Cu or the like in an alloy system in which the Mg content is kept low in order to improve the extrudability, It is an object of the present invention to obtain an aluminum alloy extruded shape member which exhibits a strength comparable to that of the 5083 alloy by artificial aging treatment and is excellent in extrudability, corrosion resistance, weldability and the like.

[0005]

The heat-treatable thin-walled aluminum extruded profile of the present invention has the following object.
g: 2.1 to 2.9 wt%, Si: 0.8 to 1.5 wt%, Cu: 0.51 to 0.8 wt%, Mn: 0.3 to
0.8 wt% and Cr: 0.05 to 0.4 wt%, Fe: Pb, Ti and B: Fe: 0.15
% By weight, Pb: 0.03% by weight or less, Ti: 0.0
06-0.03% by weight and B: 0.0001-0.00
It is characterized by being regulated to 5% by weight. This extruded shape material was obtained by subjecting a molten aluminum alloy to DC casting, subjecting the obtained ingot to homogenization treatment by heating at 460 to 540 ° C for 1 to 10 hours, and then forcibly air cooling and ingot at 350 to 520 ° C. Preheat, hot extrude, cooling rate 100 at platen exit
It is manufactured by subjecting the solute element to a solid solution by forced air cooling or water quenching at a temperature of not less than ° C / min, then subjecting it to an artificial aging treatment of heating at 140 to 200 ° C for 1 to 12 hours, and air cooling to room temperature.

[0006]

[Operation] For the structural materials such as the deck material of a ship, the lightness of aluminum alloy is utilized, and the thickness of 2mm or less
A wide material of 0 to 500 mm is desired. In addition, a ribbed shape is required in order to omit or save welding points and improve the strength of the rigid body. In order to manufacture a structural material having such a shape by extrusion, it is necessary that the aluminum alloy to be used is more excellent in extrudability than ever and is extruded at a high extrusion speed. Further, from the use as a structural material, it is required that the yield strength σ _0.2 after heat treatment is 180 N / mm ² or more and that the corrosion resistance is excellent. The present invention
The alloy design satisfying these requirements has been established. That is, by reducing the Mg content as compared with the conventional 5000 series alloy, it was possible to extrude a thin wall. As a result, for example, when obtaining an extruded profile having a wall thickness of 2 mm and a width of 450 mm, the extrusion rate was 2 m / min in the conventional 5083 alloy, whereas the extrusion rate was 5 m / min in the alloy system according to the present invention. Can be raised up to.
In this respect, the Al-Mg-Mn-based alloy introduced in Japanese Patent Laid-Open No. 4-32534 also has a large Mg content, and therefore the extrusion rate cannot be set high. The lack of strength associated with a low Mg content is recovered by compensating with age hardening of Si, Cu and the like. The strength is improved by Mg ₂ Si, CuAl _{2 and the} like precipitated by the aging treatment, and the yield strength σ _0.2 required as a structural material becomes 180 N / mm ² or more.

The alloying elements and contents contained in the aluminum alloy according to the present invention will be described below. Mg: 2.1 to 2.9 wt% It is an alloying element effective for improving strength, ductility and corrosion resistance.
When the Mg content is 2.1% by weight or more, sufficient strength and corrosion resistance can be obtained. However, if the Mg content exceeds 2.9% by weight, the extrudability is inferior and an extruded profile having a thin and complicated shape cannot be obtained. Si: 0.8 to 1.5 wt% Improves the strength of the alloy by combining with Mg during the aging treatment and precipitating as Mg ₂ Si. The precipitation hardening of Mg ₂ Si becomes remarkable at a Si content of 0.8% by weight or more,
Effectively improve strength. However, when a large amount of Si exceeding 1.5% by weight is contained, the amount of solid solution Mg decreases as the amount of Mg ₂ Si precipitation increases, and the corrosion resistance deteriorates.

Cu: 0.51 to 0.8% by weight An alloying element effective for improving strength and ductility. Also, M
improves age hardening of g ₂ Si, Cu itself, CuAl _2, Al-Cu-based, increase the age hardening properties become Al-Mg-Cu system or the like of the precipitates. Such Cu
The effect of is remarkable when the content is 0.51% by weight or more.
However, when a large amount of Cu exceeding 0.8% by weight is contained, the Al-Mg-Cu-based compound increases, and the corrosion resistance and extrudability deteriorate. For example, if a large amount of Cu is contained, intergranular corrosion is likely to occur. Mn: 0.3 to 0.8% by weight It is an effective alloying element that improves the strength and corrosion resistance by making the extruded shape structure fibrous, and the effect of Mn is remarkable at a content of 0.3% by weight or more. become. However, when a large amount of Mn is contained in excess of 0.8% by weight, a huge intermetallic compound is generated and extrudability and corrosion resistance are deteriorated.

Cr: 0.05 to 0.4% by weight Like Mn, it is an effective alloying element which improves the strength and corrosion resistance by making the extruded shape structure into a fibrous structure. Cr is 0.
When the content is 05% by weight or more, a remarkable effect is exhibited. However, if the Cr content exceeds 0.4% by weight, a huge intermetallic compound is generated, and extrudability and corrosion resistance are deteriorated. Fe: 0.15 wt% or less FeAl ₃ , Al-, which is an element mixed as an impurity.
A compound such as Fe-Si system is crystallized to deteriorate the corrosion resistance. In this respect, it is necessary to keep the Fe content as low as possible,
In the present invention, the upper limit of the Fe content is regulated to 0.15% by weight. Pb: 0.03 wt% or less An element mixed in as an impurity, which causes intergranular corrosion, stress corrosion cracking, and the like. Therefore, in the present invention,
The upper limit of the Pb content was restricted to 0.03% by weight.

Ti: 0.006 to 0.03% by weight It is added as a grain refiner to prevent casting cracks. In order to make the crystal grains finer, it is necessary to add 0.006% by weight or more of Ti. However, if a large amount of Ti exceeding 0.03% by weight is added, huge TiAl ₃ , T
It produces iB ₂ and deteriorates the surface of the profile. It also causes damage to the mold. B: 0.0001 to 0.005% by weight Like Ti, it is added as a grain refiner to prevent casting cracks. From the point of refining the crystal grains, 0.0
It is necessary to add B in an amount of 001% by weight or more. However, 0.
If a large amount of B exceeding 005 wt% is added, a huge T
forming a iB ₂ and Al-B-based compound, resulting in mold damage and frame members defects. In addition, Ti-
It has the effects of forming a B-based compound to refine the structure of the ingot, preventing cracks during DC casting, increasing ingot productivity and improving the quality of the extruded material.

DC casting The DC casting method is suitable for mass production as a method for producing ingots such as billets, and the molten metal that has passed through a water-cooled mold is directly water-cooled, so that the cell size of the ingot structure, crystal grains, Compounds are miniaturized to improve product quality. Homogenization treatment: heating at 460 to 540 ° C. for 1 to 10 hours A homogenization treatment is performed in order to sufficiently dissolve the intermetallic compounds crystallized in the ingot obtained by DC casting into a solid solution and to refine the ingot. Heating temperature 460 ° C or higher and heating time 1
After a lapse of time, the crystallized substances such as Al-Mg system and MgSi ₂ are completely dissolved, and a material having a homogeneous structure is obtained. However, at a heating temperature higher than 540 ° C, burning is likely to occur at grain boundaries. Further, the cast structure is sufficiently homogenized within 10 hours, and even if the casting structure is heated for a longer period of time, the effect corresponding to it cannot be obtained. The homogenized aluminum alloy is forcibly air-cooled so that solid solution elements do not precipitate.

Preheating temperature during hot extrusion: 350 to 520
The heating temperature of the ingot at the time of extrusion is preferably as low as possible so long as it can be extruded at a low temperature. However, 350 ° C. or higher is required for productivity and solid solution of the compound during extrusion.
Moreover, in order to prevent cracks due to local melting from occurring during extrusion, the temperature is preferably 520 ° C. or lower. Cooling after hot extrusion: Forced air cooling or water quenching at a cooling rate of 100 ° C / min or more The extruded shape is forced after hot extrusion to keep the solute elements in a solid solution state at room temperature. It is rapidly cooled at a cooling rate of 100 ° C./min or more by air cooling or water quenching. When the cooling rate is 100 ° C./minute or more, the solute element does not precipitate and is maintained in a solid solution state at room temperature.

Artificial aging treatment: 1-1 at 140-200 ° C
Heating for 2 hours 140 ~ 20 in aluminum alloy with solute element
When artificial aging is performed by heating at 0 ° C. for 1 to 12 hours, solute elements are precipitated as intermetallic compounds such as Mg ₂ Si and AlCu ₂ and the material strength is improved. The intermetallic compound is 140
Precipitation is promoted at a heating temperature of ℃ or more and a heating time of 1 hour or more. However, at a heating temperature exceeding 200 ° C., precipitates such as MgSi ₂ , AlCu _{2 and the} like, which are effective for strengthening, are likely to be coarsened, and overaging causes strength reduction. Also,
Even if heating is performed for more than 12 hours, the material improvement effect due to precipitation hardening saturates, and rather the heat consumption increases.

[0014]

[Example] DC casting of various aluminum alloys with a diameter of 6
A billet of 00 mm was obtained. The results of analysis of each billet are shown in Table 1 together with comparative examples.

[0015]

[Table 1]

After subjecting each billet to homogenization treatment,
Forced air cooling. Then, a blank for extrusion was cut out from the billet. After preheating each blank, it was housed in a container and extruded hot. At this time, both the container and the extrusion die were kept at 460 ° C. Then, it was extruded at a extrusion speed of 5 m / min into the shape of the shape shown in FIG. The extruded profile obtained was subjected to artificial aging treatment and then air-cooled to room temperature.
Table 2 shows the processing conditions from the homogenization treatment to the artificial aging treatment. In addition, in the comparative example of alloy number 13, the heating condition usually applied to the 6000 series alloy was adopted. Also,
As shown in FIG. 1, the extruded profile has a thickness of 2 mm and a width of 450 mm at its thinnest portion, which is extremely small compared to the width, and has a complicated shape in which a plurality of ribs are integrated. In the case of extruding a profile having such a shape, even a 6000 series alloy or the like, which has good extrudability, usually has a rustle at the left and right ends or deteriorates in shape at a high speed of about 10 m / min. In addition, in the conventional 5000 series alloy, 5052
Even in the system, defects such as cracks at the left and right ends and clogging in the die holes are likely to occur.

[0017]

[Table 2]

Specimens were cut out from each of the alloy materials that had been subjected to artificial aging treatment and subjected to a tensile test. As can be seen from Table 3 showing the test results, the alloys of Examples 1 to 4 according to the present invention showed 0.2% proof stress comparable to that of the non-heat treated type 5083 alloy (alloy No. 11) and the structural materials. It turns out that it has the required strength.

[0019]

[Table 3]

Next, for each of the obtained extruded shape members,
The extrudability, weldability and corrosion resistance were investigated. The survey results are shown in Table 4. The extrudability was judged based on the surface texture and internal defects of the extruded profile extruded at an extrusion speed of 5 m / min, and those exhibiting a very good surface quality with no defects were extruded without any defects. The samples were evaluated in four grades, the ones with cracks at the corners being triangular, and the ones that could not be extruded with x. The weldability was determined by butt welding the cut portions of the extruded shape member, MIG welding, and measuring the strength of the weld portion. Then, those having a welding strength of 90% or more with respect to the T ₅ strength were evaluated as ⊚, 80% or more as ◯, and 70% or more as Δ. The occurrence of defects in the welded part was evaluated as Δ when microcracks were generated in the welded part and as x when visually cracked. Corrosion resistance is 35% NaC adjusted to pH ≈ 3 with acetic acid
A cycle of repeating 10 minutes in an aqueous solution for 10 minutes and then drying for 50 minutes was continued for 7 days, and judged by the average depth of pits generated at grain boundaries. And the pit depth is 10 on average
A grade of 0 μm or less was evaluated as “⊚”, an average of 100 to 500 μm was rated as “◯”, and an average of 500 μm or more was rated as “X”.

[0021]

[Table 4]

As is clear from Table 4, the alloys of Examples 1 to 4 according to the present invention show good results in terms of extrudability, weldability and corrosion resistance. On the other hand, in Comparative Examples of Alloy Nos. 5, 6, 9 to 13, any of the extrudability, weldability and corrosion resistance was inferior. Although the comparative examples of Alloy Nos. 7 and 8 have good extrudability, weldability and corrosion resistance,
As shown in Table 3, the tensile strength and the yield strength were insufficient, and it was not suitable for use as a structural material.

[0023]

As described above, the extruded aluminum profile of the present invention correlatively specifies the content of alloying components in an alloy system with a reduced Mg content, and Fe which is mixed as an impurity. , Pb, etc. are restricted. As a result, a good extrudability is ensured, and an extruded profile having high strength and excellent weldability and corrosion resistance is obtained. In this way, the extruded profile obtained according to the present invention is used in a wide range of fields as structural materials such as ships and vehicles, land structures, agricultural members, and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional shape of an extruded shape member manufactured in an example.

[Procedure amendment]

[Submission date] January 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

[0015]

[Table 1]

Claims (2)

[Claims] 1. Mg: 2.1 to 2.9% by weight, Si:
0.8-1.5 wt%, Cu: 0.51-0.8 wt%, Mn: 0.3-0.8 wt% and Cr: 0.05-
0.4% by weight, Fe, Pb, Ti and B are respectively Fe: 0.15% by weight or less, Pb: 0.03% by weight or less, Ti: 0.006 to 0.03% by weight and B: 0. .0
A heat-treatable thin-walled aluminum extruded shape material that has an excellent extrudability controlled to 001 to 0.005% by weight. 2. An aluminum alloy melt having the composition specified in claim 1 is DC-cast, and the obtained ingot is 460-460.
After homogenizing treatment by heating at 540 ° C for 1 to 10 hours, forced air cooling, preheating the ingot to 350 to 520 ° C, extruding hot, forced air cooling at a cooling rate of 100 ° C / min or more at the platen outlet. Alternatively, a method for producing a heat-treatable thin-walled aluminum extruded profile, in which a solute element is solid-dissolved by water quenching, then artificial aging treatment is performed by heating at 140 to 200 ° C. for 1 to 12 hours, and air cooling is performed to room temperature.