KR20210091443A - Aluminum alloy extrudate having excellent formability and its production method - Google Patents

Abstract

The present invention relates to an aluminum alloy extrusion material having strength and excellent formability, which is suitable for a member requiring strength after welding and is capable of forming members of various shapes such as a frame of an LED lighting, and a manufacturing method thereof. According to the present invention, in an Al-Zn-Mg-based aluminum alloy, by adjusting contents of other elements, particularly Cu, Si, and Fe, without containing Mn and Cr, which are the structure-strengthening elements, and adjusting a homogenization condition or an extrusion condition, the Al-Zn-Mg-based aluminum alloy can easily extrude and process a tubular body having thickness of 2mm or less. Moreover, the present invention can manufacture the aluminum alloy extrusion material which can demonstrate preferrable mechanical strength while maintaining weldability.

Description

Aluminum alloy extrudate having excellent formability and its production method

The present invention relates to an aluminum alloy extruded material having strength and good formability, suitable for a member requiring strength after welding, which is capable of forming members of various shapes, such as a frame of an LED lighting, and a method for manufacturing the same.

As an aluminum alloy with good formability, an Al-Mg-Si-based, so-called 6000-series aluminum alloy is known. Since this alloy has good strength and corrosion resistance, it is widely used as various structural materials. However, the 6000 series aluminum alloy is not suitable for welding because it has a problem in strength after welding.

However, the 7000 series aluminum alloy having a large Zn content and containing Mg, Mn, Cr and Cu is the highest-strength alloy among aluminum alloys, but since it contains Mg, extrusion workability is relatively poor.

For example, a material containing a large amount of Mg and Cu has a high strength exceeding 600 MPa after aging treatment, but has a high deformation resistance in hot and is industrially extruded and molded into a tubular body with a thickness of 2 mm or less. It is very difficult to do.

On the other hand, since the material with the Cu content suppressed has lower strength, the intended mechanical properties cannot be obtained when used as a component material bearing a large load.

In this way, when an existing technique is attempted to manufacture an extruded material for application to structural materials (LED lighting premi), vehicle parts, etc. requiring mechanical properties after welding, product productivity is poor and production cost is high.

The present invention has been devised to solve this problem, and in particular, provides an aluminum alloy extruded material having high strength after welding and good formability.

The aluminum alloy extruded material having good formability according to the present invention, in order to achieve its purpose, Zn: 4.5-7 mass%, Mg: 0.2-0.38 mass%, Cu: 0.25-0.4 mass%, Zr: 0.1-0.3 mass% %, and older Si: 0.05-0.3 mass% and Fe: 0.05-0.3 mass%, including Al and unavoidable impurities.

Here, you may make it contain 1 type or 2 types among Ti:0.001-0.2 mass %, and B:0.0001-0.01 mass %.

In addition, an aluminum alloy extruded material having good moldability can be obtained by subjecting an aluminum alloy material having the above component composition to homogenization under predetermined conditions and then extruding under predetermined conditions.

According to the present invention, in the Al-Zn-Mg-based aluminum alloy, by adjusting the content of other elements, particularly Cu, Si and Fe, without containing Mn and Cr, which are the structure-strengthening elements, further homogenization conditions and extrusion By adjusting the conditions and the like, it is possible to easily extrude a tubular body having a thickness of 2 mm or less as an Al-Zn-Mg-based aluminum alloy. Moreover, it is possible to manufacture an aluminum alloy extruded material capable of exhibiting desirable mechanical strength while maintaining weldability.

Therefore, an extruded material for application to structural materials requiring mechanical properties after welding can be manufactured at a low cost.

Hereinafter, the present invention will be described in detail.

First, the action and content of the components constituting the Al-Zn-Mg-based aluminum alloy of the present invention will be described.

Manganese (Mn) or chromium (Cr) contained in a typical 7000 series alloy forms precipitates and inhibits recrystallization, thereby contributing to improvement of mechanical properties and prevention of cracking during welding.

However, Mn and Cr are not contained in the alloy of the present invention in order to increase the hot deformation resistance and deteriorate the extrusion workability.

However, Mn and Cr, which are unavoidably mixed as impurities from aluminum alloy scrap, which are raw materials, were not considered. If both are less than 0.05 mass %, extrusion moldability is hardly affected.

Zn forms Mg-Zn type precipitates and is the most important component for improving the strength of an aluminum alloy, and its preferable content range is 4.5-7 mass %. If the Zn content is less than 4.5 mass%, the effect of improving the strength is not sufficient. Even if it exceeds 7% by mass, further improvement in strength cannot be expected and, conversely, corrosion resistance is lowered.

The preferable content range of Mg is 0.2-0.38 mass %. Mg forms Mg-Zn-based precipitates and disperses them in the parent phase to improve the mechanical strength of the extruded material. This effect is effective when 0.2 mass % or more of Mg is contained. Conversely, when it is added in an amount exceeding 0.38% by mass, hot deformation resistance increases, moldability and extrusion processability deteriorate, and productivity decreases. Therefore, 0.2-0.38 mass % is suitable for content of Mg, Preferably 0.30-0.35 mass % is more preferable.

Cu is dissolved in the parent phase to improve mechanical strength. This effect becomes remarkable when Cu content is 0.25 mass % or more. Conversely, when it contains exceeding 0.4 mass %, corrosion resistance will fall. Therefore, as for Cu content, 0.25-0.4 mass % is preferable, and it is more preferable to set it as 0.25-0.35 mass %.

The preferable content range of Zr is 0.1-0.3 mass %. Zr forms an Al-Zr-based compound and disperses it in the parent phase, suppresses coarsening of recrystallized grains by pin fixing effect, increases strength, and prevents cracking during welding. This effect becomes remarkable when the Zr content is 0.1 mass% or more. However, when it contains more than 0.3 mass %, a coarse Al-Zr type compound is produced|generated, and hot workability is reduced. In addition, when the precipitates are excessively generated, the hot deformation resistance increases and the extrusion processability is impaired.

The preferable content range of Si is 0.05-0.3 mass %. Si forms an Al-Si-Fe-based compound and is finely dispersed in the matrix to suppress coarsening of crystal grains, thereby improving mechanical strength. This effect is remarkable when Si content is made into 0.05 mass % or more. However, when the content exceeds 0.3% by mass, the formation of the Mg-Zn-based compound is inhibited in order to form the Mg-Si-based compound. For this reason, natural aging hardenability deteriorates and sufficient strength cannot be obtained after welding. Preferably, it is made to contain in 0.05-0.15 mass %.

The preferable content range of Fe is 0.05-0.3 mass %. Fe improves mechanical strength by forming an Al-Si-Fe compound and finely dispersed in the matrix to suppress coarsening of crystal grains. This effect becomes remarkable when Fe content is made into 0.05 mass % or more. However, when the content exceeds 0.3% by mass, the Al-Si-Fe-based compound is dispersed in a large amount, so that the surface properties and state of the extruded material are impaired. Preferably, it is made to contain in 0.10-0.20 mass %.

As for the ratio of Fe mass %/Si mass %, 1-3 are preferable. In order to obtain the effect of preventing grain coarsening after extrusion, Fe and Si are contained. In addition, although there is an effect of suppressing casting breakage, as described above, when the content of both is too large, mechanical properties are reduced and extrusion processability is impaired. Therefore, in order to efficiently form an Al-Si-Fe-based compound, the Fe/Si ratio is regulated to 1-3. If the Fe/Si ratio is less than 1, the excess Si forms a compound with Mg and inhibits the formation of the Mg-Zn-based compound, and the mechanical properties deteriorate. However, when the Fe/Si ratio exceeds 3, the excess Fe forms an Al-Fe-based compound to deteriorate the extrusion processability.

The preferred content range of Ti is 0.001 to 0.2 mass% and the preferred content range for B is 0.0001 to 0.01 mass%, and one or two of these are used. Ti and B work to refine the crystal grains of the cast material to prevent cracking during casting and improve extrusion processability. For this reason, within the range of Ti:0.001-0.2 mass % and B:0.0001-0.01 mass %, 1 type or 2 types of these can be contained in an alloy. When the content of Ti and B exceeds the upper limit, respectively, a coarse compound is formed, which deteriorates the surface properties and state of the extruded material.

However, the extruded material of the Al-Zn-Mg-based aluminum alloy is generally manufactured by hot extrusion processing of a cast mass subjected to homogenization heat treatment and press quenching or separate solution treatment.

The aluminum alloy extruded material of the present invention can also achieve the intended purpose by limiting the temperature conditions and processing time conditions in each step, and the manufacturing conditions thereof will be described below.

(1) Homogenization treatment

- Heating rate 200℃/h or less

If the heating rate is high, the Al-Zr-based precipitates are coarsened, reducing the recrystallization inhibitory effect, and thus mechanical properties are deteriorated. Also, the crack susceptibility during welding is increased. However, if it is too late, it is not economical, so it is preferably about 100°C/h.

- Homogenization temperature Ⅷ hours; 450~520℃/1~24 h

This is carried out to homogenize segregation of Mg, Zn, etc. generated during casting, to obtain a sufficient solid solution during extrusion, and to form an Al-Zr-based compound suitable for suppressing recrystallization of the extruded material. At a temperature lower than 450°C, even if treated for 24 hours, a sufficient tissue cannot be obtained. On the other hand, if the treatment exceeds 520°C or exceeds 24 hours, Mg and Zn are homogenized, but the Al-Zr-based compound coarsens, and the effect of inhibiting recrystallization of the extruded material cannot be sufficiently obtained. In a treatment of less than 1 hour, homogenization is insufficient. Therefore, the homogenization treatment is performed under the conditions of 450 to 520° C./1 to 24 h.

- Cooling rate: 150℃/h or more

Mg and Zn are homogenized by maintaining the above high temperature, but if the cooling rate is slow, coarse precipitates are formed and sufficient solutionization cannot be achieved during extrusion. Therefore, the cooling rate after homogenization is set to 150°C/h or more.

(2) Extrusion processing

- Extrusion processing temperature: 450~560℃

The billet heating temperature and the extrusion rate are adjusted so that the profile material temperature immediately after extrusion is 450 to 560°C. This makes it possible to sufficiently dissolve Mg and Zn in solid solution. 4 When the temperature is less than 50°C, the solid solution state is insufficient, and sufficient strength cannot be obtained even by subsequent aging treatment. On the other hand, when it is extruded to a temperature exceeding 560°C, it is easy to recrystallize and the strength is lowered, and the crack susceptibility during welding is increased. For this reason, in manufacture of a hollow material, it is preferable to set the billet temperature to 450 to 540°C, and to set the die temperature to 400 to 500°C, and to extrude at an extrusion rate of 3 to 20 m/min.

- Cooling temperature: 100℃/min or more

A standard tubular body with a thickness of 2 mm or more is difficult to deform even at high temperatures immediately after extrusion because of its high cross-sectional rigidity. For the purpose of preventing deformation, the shape member is actively cooled immediately after extrusion. Cooling to 150°C or less at an average cooling rate of 100°C/min or more is preferable to suppress deformation. It is preferable that a cooling rate shall be 200 degreeC/min or more.

As a cooling method, air cooling or liquid nitrogen spray cooling is preferable. In the case of water cooling, cooling is so strong that an imbalance in cooling is likely to occur, and deformation due to imbalance in cooling is likely to occur. Therefore, water cooling is not preferable.

The result of the present invention has excellent extrusion processability and high strength. However, it was confirmed that, when the cooling rate is slow after extrusion processing, the deformation during cooling is large and the dimensional accuracy is lowered.

In addition, when the Cu content is reduced, extrusion processing is possible, but the yield strength is lowered. In addition, when the Mn content is large and the Mg content is large, the hot deformation resistance is high, and when the extrusion processing is attempted, the extrusion force exceeds 2200t, and it is difficult to perform the extrusion processing.

Claims (3)

Zn: 4.5 to 7 mass%, Mg: 0.2 to 0.38 mass%, Cu: 0.25 to 0.4 mass%, Zr: 0.1 to 0.3 mass%, Si: 0.05 to 0.3 mass% and Fe: 0.05 to 0.3 mass% (Fe mass %/Si mass %) = 1 to 3, and the remaining part is an aluminum alloy extruded material having good formability, characterized in that it consists of Al and unavoidable impurities. According to claim 1,
An aluminum alloy extruded material having good moldability, characterized in that it further contains one or two of Ti: 0.001 to 0.2 mass% and B: 0.0001 to 0.01 mass%. A method for producing an aluminum alloy extruded material having good formability, characterized in that the aluminum alloy material having the component of claim 1 or 2 is subjected to a homogenization treatment under a predetermined condition and then extrusion-molded under a predetermined condition.