JPH108172A - Production of high strength aluminum-magnesium-silicon base alloy for structural material excellent in extrudability and extruded material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an alloy high in the extruding rate and having high strength by prescribing the alloy components and melting starting temp. SOLUTION: This alloy contains, by weight, 0.2 to 0.9% Cu, 0.6 to 1.1% Si, 0.4 to 1.0% Mg, and prescribed amounts of Fe, Mn, Cr, Ti and B. Then, the components are set so as to regulate the melting starting temp. T defined by T( deg.C)=667-21%Cu-42×%Si-38×Mg to >=585 deg.C. Furthermore, by suitably regulating the casting conditions, homogenizing treatment to a billet and the conditions of extruding and aging treatment, the material strength of >=350N/mm<2> tensile strength and >=330N/mm<2> 0.2% proof stress can be obtd. Thus, it is usable instead of steels, and the remarkable lightening of various apparatus and structural bodies is made possible. Furthermore, the material extrudable at the extruding rate equivalent to that in 6061 alloys good in extrudabilidty can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a structural material for building materials, vehicles, and the like, and has a high extrudability and high strength.
The present invention relates to a method for producing a Si-based alloy and an extruded profile.

[0002]

2. Description of the Related Art In order to reduce the weight of structures such as joists and girders for trucks, pillars and beams for buildings, cubicles for curtain walls, fasteners and cross members, aluminum is used instead of conventional steel. The tendency to use wood is increasing. In order to use an aluminum material as a structural material, an aluminum alloy that can obtain a complicated cross-sectional shape by extrusion and can be designed in consideration of rigidity is required. Common extrusion aluminum alloys such as 6063 and 6061 have excellent extrudability and can be extruded into a complicated cross-sectional shape. However, since the strength is inferior to that of the steel material SS400, a thick and large cross-sectional shape is inevitable, resulting in a high cost product. In a 6000 series alloy, Mg ₂ Si, excess Si, Cu
Some of them have increased their strength by increasing the amount or by adding fiber elements such as Mn, Cr, Zr, etc. However, roughening and tearing are likely to occur on the profile surface during extrusion.
Therefore, the extrusion speed must be set low. In addition, the extrusion pressure is high, and the life of the die is shortened. In addition, the cross-sectional shape that can be manufactured may be restricted. By increasing the heating temperature of the billet before extrusion, the extrusion pressure can be reduced and the extrusion speed can be increased. But,
Since the temperature of the extruded material rises, the material is partially melted, and roughening, tearing, and the like are likely to occur. Therefore, there is a limit in setting the material temperature high and increasing the extrusion speed.

[0003]

The steel SS400 used for general structures has an actual tensile strength of 400-5.
10 N / mm ² , and the yield point is 245 N / mm ² or more. Therefore, in a structure using SS400 as a structural material, the reference strength of the material is designed to be 245 N / mm ² from the results of various calculations in determining the design values. When this is applied to an aluminum material, the material strength of the aluminum material is 305 N / mm ² or more in tensile strength and 245 N / m in 0.2% proof stress.
m ² or more. When an aluminum material that satisfies such mechanical properties is obtained as the minimum guaranteed value, it is possible to replace the structural material designed in SS400 with a lightweight aluminum material, and the structure can be significantly reduced in weight. Can be The present invention has been devised to meet such a demand, and can be extruded at a high extrusion speed which cannot be obtained with a conventional high-strength aluminum alloy.
An object of the present invention is to obtain an aluminum alloy having a strength equal to or higher than a structural design standard strength of 400.

[0004]

SUMMARY OF THE INVENTION The high-strength Al-Mg-Si alloy for structural materials of the present invention has a Cu content of 0.2 to 0.9% by weight and a Si content of 0.6. ~ 1.
1% by weight, Mg: 0.4 to 1.0% by weight, Fe: 0.1
To 0.3% by weight, Mn: 0.2 to 0.5% by weight, Cr:
0.1 to 0.3% by weight, Ti: 0.005 to 0.05% by weight, B: 0.001 to 0.01% by weight,
(° C) = 667-21 ×% Cu-42 ×% Si-38 ×
It is characterized by having a composition designed so that the melting start temperature T defined by% Mg is 585 ° C. or higher.
This Al-Mg-Si alloy further has a Zr: 0.05-
0.2% by weight. Si content and Mg
The content is represented by a point A (0.8, 1.0), a point B (0.6, 0.4), and a point C (1.1, 0.4) in a coordinate system of Si content-Mg content. It is preferable to be within the area ABCD defined by the points A and D (1.1, 0.8). M
It is preferable that the total content of n, Cr and Zr is adjusted in the range of 0.3 to 0.8% by weight. The extruded high-strength Al-Mg-Si alloy for structural materials is DC-cast within 120 minutes after the addition of the refining agent, and is heated at a rate of 200 ° C / hour or less and maintained at a high temperature of 500 to 580 ° C x 1 ~ 12
Time, cooling rate 200-500 ° C / hour, homogenization treatment, preheating 430-520 ° C x 1-60 minutes, extruding under the condition of profile surface temperature 500-555 ° C immediately after extrusion, surface temperature of profile It is manufactured by quenching a press end that is water-cooled from 430 ° C. or higher, then holding at 170 to 200 ° C. × 1 to 12 hours, and then performing an aging treatment of air cooling.

[0005]

In order to satisfy the design strength standard strength of the rolled steel for general structure SS400, the minimum guaranteed value of the aluminum material is a tensile strength of 305 N / mm ² or more and 245 N / mm ^2.
The above 0.2% proof stress is required. Further, from the viewpoint of production cost, it is set that the extrudability is required to be comparable to that of the 6000 series 6061 alloy having good extrudability. Under such a premise, the present inventors, in order to replace the aging material of the extruded aluminum alloy with the same shape as SS400, the strength after T6 treatment has a tensile strength of 350 N / mm ² or more, 0.2% proof stress. 330 N / mm ² or more and 606
Materials that can be extruded at the same extrusion speed as one alloy were investigated and studied. As a result, while specifying the alloy components, 667-21 ×% Cu-42 ×% Si-38 ×% M
It has been found that when the composition is adjusted so that the melting start temperature T defined by g becomes 585 ° C. or higher, an aluminum alloy extruded profile excellent in both strength and extrudability can be obtained. With respect to the extrudability, the limit extrusion speed at which an extruded profile having no defects such as pickup, rough skin, tearing and the like on the surface was obtained was used as a criterion. By the way, 606
The extrusion speed equal to or higher than that of one alloy differs depending on the shape of the shape material, but is, for example, 150 mm in height, 50 mm in width,
With a hollow rectangular hollow material having a thickness of 2 mm, the extrusion speed is 8 m / min or more.

Hereinafter, alloy components, contents, production conditions, and the like of the aluminum alloy of the present invention will be described. Cu: 0.2 to 0.9% by weight S'-CuMgAl or an Al-Cu-based compound is formed, and has an effect of improving the strength of the Al-Mg-Si-based alloy by precipitation hardening. In particular, when the strength imparted by the addition of Mg and Si cannot satisfy the strength required for the member, it is added as an effective alloy component. Such an effect becomes remarkable at a Cu content of 0.2% by weight or more. However, if the Cu content exceeds 0.9% by weight, the melting start temperature of the billet at the time of extrusion is reduced and the hot deformation resistance is increased, and it is necessary to reduce the extrusion speed to obtain a good product. . In addition, the corrosion resistance decreases as the Cu content increases. Si: 0.6 to 1.1% by weight Mainly binds to Mg, and increases the strength by precipitation hardening of β′-Mg ₂ Si. Further, in the present invention, Si is added in an amount more than necessary for the generation of Mg ₂ Si. This excess Si
Reduces the hot deformation resistance during extrusion and effectively increases the extrusion speed. This effect is caused by the fact that at least 0.6% by weight of Si
It becomes remarkable in the content. However, when a large amount of Si exceeding 1.1% by weight is contained, the melting start temperature of the billet must be lowered and the extrusion speed must be reduced in order to obtain a product having good surface properties.

Mg: 0.4-1.0% by weight While strengthening the solid solution of the matrix, combining with Si or Cu and precipitating as β'-Mg ₂ Si or S'-CuMgAl ₂ , improving the strength by precipitation hardening. Let it. The precipitation hardening effect by Mg becomes remarkable at a Mg content of 0.4% by weight or more. However, even if Mg is added in excess of 1.0% by weight,
Heat treatment after extrusion processing cannot provide strength, but rather increases the hot deformation resistance value and lowers the melting start temperature of the billet, and causes roughening of the extruded profile. Fe: 0.1 to 0.3% by weight At the time of casting, an Al-Fe-Si crystallized substance is formed, and after the subsequent billet homogenization treatment, it is divided during extrusion processing to be refined and recrystallized. Pinning the movement of grain boundaries,
Strength is improved by preventing coarsening of recrystallized grains. The effect of Fe becomes remarkable at a content of 0.1% by weight or more, but when a large amount of Fe exceeding 0.3% by weight is contained, a coarse Al—Fe—Si compound is generated, and the surface of the extruded material is formed. The surface is likely to be rough. Al (Fe,
M) Produces Si-based crystallization (M represents Mn and Cr)
There is a tendency to inhibit the effect of suppressing recrystallization of Mn, Cr, etc.

Mn: 0.2-0.5% by weight An Al-Mn intermetallic compound having a submicron size is formed by homogenization treatment, and the movement of recrystallized grain boundaries generated during extrusion is pinned, and recrystallization is performed. By improving the strength, the strength is improved. The effect of Mn becomes remarkable at a content of 0.2% by weight or more, but when the content of Mn exceeds 0.5% by weight, Mn acts as a precipitation site of Mg ₂ Si, thereby increasing quenching sensitivity. , Reduce the effect of quenching. In addition, the Al (Fe, M) Si crystallized material is coarsened, and the surface condition of the extruded material is deteriorated. Cr: 0.1-0.3% by weight Subhomogeneous Al after homogenization as in Mn
-Improve the strength of the aluminum alloy by forming a Cr-based compound and preventing recrystallization. Such an effect becomes remarkable at a Cr content of 0.1% by weight or more. However, when Cr is contained in a large amount exceeding 0.3% by weight, it acts as a precipitation site of Mg ₂ Si like Mn, so that quenching sensitivity is increased and the effect of quenching is reduced. In addition, the Al (Fe, M) Si crystallized material is coarsened, and the surface condition of the extruded material is deteriorated.

Ti: 0.005 to 0.05% by weight An alloy component effective for refining the crystal grains of an ingot, which prevents casting cracks, reduces hot deformation resistance, and increases extrusion speed. . Such an effect becomes remarkable at a Ti content of 0.005% by weight or more, and is further enhanced by the combined addition with B. However, when a large amount of Ti exceeding 0.05% by weight is contained, coarse particles of Al-Ti system are generated, and surface defects of the shaped material easily occur during extrusion. B: 0.001 to 0.01% by weight Similar to Ti, it has the effect of refining the crystal grains of the ingot and preventing casting cracks. Such an effect becomes remarkable at a B content of 0.001% by weight or more. However, when a large amount of B exceeding 0.01% by weight is contained, Al-B and Ti-
B-type coarse particles are generated, and surface defects of the shaped material are easily generated at the time of extrusion.

Zr: 0.05-0.2% by weight An alloy component added as necessary. After homogenizing the billet, it has a submicron size (0.05 μm or less).
By forming an Al-Zr-based compound (Al ₃ Zr) and preventing recrystallization during extrusion, a fibrous structure is formed in the extruded material, and strength and stress corrosion cracking resistance are improved. Such an effect becomes remarkable when Zr is contained in an amount of 0.05% by weight or more. However, when it contains a large amount of Zr in excess of 0.2 wt%, Mn, similarly to Cr, Mg ₂
The quenching sensitivity is increased and the quenching effect is reduced due to the Al-Zr-based compound acting as a Si deposition site. In addition, the Al-Zr-based crystallized product is coarsened, and the surface state of the extruded material is deteriorated. In the aluminum alloy of the present invention, recrystallization is firmly prevented by the complex addition of Mn, Cr, Zr, etc., and the strength is improved. The recrystallization inhibiting action of these added components becomes remarkable when the total content of Mn, Cr, Zr, etc. is 0.3% by weight or more, but when the total content exceeds 0.8% by weight, huge crystallization occurs during casting. A product is generated, which causes surface defects in the profile during extrusion. In addition, quenching sensitivity is increased, and press quenching property is significantly impaired. For this reason, it is preferable to adjust the total content of Mn + Cr or Mn + Cr + Zr to a range of 0.3 to 0.8% by weight.

Relationship between Mg Content and Si Content The aluminum alloy of the present invention has β ′
High material strength is imparted by the precipitation hardening of -mg ₂ Si. At this time, the calculated value of Mg ₂ Si amount [Mg ₂ Si = M
g% (1 / 1.73 + 1)], it is necessary to add Si in excess. Excess Si lowers the hot deformation resistance during extrusion and increases the extrusion speed. However, S
If i is added excessively, the melting start temperature of the material decreases, and the surface state of the extruded shape material deteriorates. The present inventors,
As a result of examining the Si content in relation to the Mg content, FIG.
It has been found that when the Si content and the Mg content are adjusted in the ABCD region of the above, an extruded profile having a good surface condition can be produced at a high extrusion rate. ABC-
When the Si content and the Mg content are in the D region, the target tensile strength and 0.2% proof stress can be obtained, and the limit extrusion speed (the highest production rate at which the surface of the extruded profile does not have a rough surface). Speed) can be set to a speed equal to or higher than 6061, and an extruded profile can be manufactured with high productivity. AB-
The inside of the CD region is determined from the results of many experiments by the present inventors, but if it is outside this region, an extruded profile having the desired mechanical properties cannot be obtained at a high extrusion speed. That is, in the region on the left side of the line AB, the amount of excess Si is small, Mg ₂ Si is not finely and uniformly deposited, and the strength is not sufficient. In the region below the straight line BC, Mg
Insufficient amount and a small amount of Mg ₂ Si deposited cannot provide sufficient strength. In the region on the right side of the straight line CD, there is too much excess Si, the melting temperature during extrusion is lowered, and the skin is likely to be rough. In the region above the straight line AD, Mg
If the content is too large, the extrusion pressure rises, which makes it difficult to extrude a shaped member having a complicated shape, and the melting temperature during the extrusion decreases, so that the skin becomes rough.

Melting start temperature: T ≧ 585 ° C. Generally, the higher the material temperature, the higher the extrusion speed can be set. However, when the raw material temperature is high, the surface of the raw material further heated by the processing heat generated during the extrusion may be partially melted. Surface defects such as pick-up, rough skin, tearing and the like are likely to occur in the profile extruded in this state. Then, as a result of examining an Al-Mg-Si alloy-based component capable of suppressing these surface defects and obtaining high strength, T (° C) = 667-21 ×% Cu-42 ×% Si-
When the melting start temperature T defined by 38 ×% Mg was adjusted to 585 ° C. or higher, it was found that an extruded profile having good surface properties could be obtained at a high extrusion speed. The definition formulas shown here are the 12 types listed in Table 1 and the other 14 types.
The melting start temperature of a total of 26 types of aluminum alloy billets was measured with a differential scanning calorimeter, and the relationship between the obtained melting start temperature and the added elements and their contents was determined by linear regression. At this time, a regression equation having a high correlation coefficient was obtained by setting the variables to Si, Cu, and Mg, and the coefficients for each component were −21 for Cu, −42 for Si, and −38 for Mg. Note that 667 ° C. is an intercept with the Y axis, that is, the temperature axis.

[0013] The aluminum alloy according to the present invention exhibits high strength due to precipitation strengthening and structure strengthening. The strengthening of the structure is performed by adding a transition element such as Mn, Cr, or Zr, and the amount of the transition element is determined so that the fibrous structure can be stably formed in the extruded profile. Since these transition elements are precipitated from the matrix during the homogenization treatment, the added amount thereof hardly affects the purity of the matrix at the time of extrusion, and does not affect the melting start temperature. On the other hand, Mg, Si, Cu, and the like added for precipitation strengthening dissolve in the matrix, lower the purity of the matrix, and act as a factor for lowering the melting start temperature. Therefore, it becomes a negative coefficient in the equation of the melting start temperature. Note that F
Since e, Ti, and B are almost crystallized or precipitated during casting, they do not act as a factor for lowering the melting start temperature.
As a result of the test, it was found that the lower the melting start temperature, the lower the limit extrusion speed tends to be. Therefore, for alloys having high strength and excellent extrudability, attention should be paid to the melting start temperature in determining the components, and Cu, S
The calculated melting onset temperature depending on the i, Mg content is 58
Regulated to 5 ° C or higher. In the case of an alloy having a melting start temperature of less than 585 ° C., in order to obtain an extruded material having good surface properties, the extrusion speed must be remarkably reduced as compared with 6061 alloy, which is a general extrusion alloy, and the production cost is reduced. Will rise. On the other hand, Cu, Si,
When the amount of Mg is designed, the alloy has a melting start temperature of 585 ° C. or higher, and can be extruded at an extrusion speed equal to or higher than that of the 6061 alloy.

Casting: DC within 120 minutes after adding the refiner
Casting The aluminum alloy whose components have been adjusted as described above is subjected to DC casting according to a conventional method after degassing and deslagging. DC casting is performed for a period of up to 120 minutes after the addition of a refiner such as Ti, B or Ti-B to obtain a sufficient refinement action.
If casting is performed at a point in time after 120 minutes or more, a given refining effect is not sufficiently exhibited due to sedimentation or chemical change of crystal nuclei, and casting cracks are likely to occur.

Homogenization treatment: Heating rate 200 ° C./hour or less High-temperature holding 500-580 ° C. × 1-12 hours Forced cooling at 200-500 ° C./hour High-temperature holding is performed in crystal grains and grain boundaries formed during casting. This is performed in order to homogenize the concentration segregation of Mg, Si, Cu, etc., and to precipitate a compound containing a transition metal, such as Mn, Cr, Zr, in a submicron size. The temperature raising condition of the homogenization treatment is 200 ° C./hour or less in order to uniformly precipitate a compound containing a transition metal such as Mn, Cr, and Zr. The precipitate grows to a submicron size by the subsequent high-temperature holding at 500 to 580 ° C for 1 to 12 hours. on the other hand,
Mg, Si, and Cu uniformly dissolve in the matrix during high-temperature holding. Then, by performing forced air cooling in the range of 200 to 500 ° C./hour, Mg-Si system, Al-Cu system,
The Al-Mg-Cu-based compound is precipitated to a size of 1 µm or less that can be re-dissolved during extrusion. At this time, since these compounds use a compound containing a transition metal such as Mn, Cr, or Zr grown at high temperature as a precipitation site, they are uniformly and finely precipitated. This effectively works to further improve the strength of the member in the aging treatment in the subsequent step. Fine compounds such as precipitated Mn, Cr, and Zr suppress recrystallization during extrusion. In addition, Mg, Si,
By sufficiently homogenizing Cu or the like, occurrence of rough surface during extrusion is prevented. Unless the homogenization temperature reaches 500 ° C., sufficient homogenization of Mg, Si, and Cu cannot be achieved. At homogenization treatment temperatures exceeding 580 ° C., Mn, C
Compounds containing r, Zr, and the like are coarsely precipitated to reduce the recrystallization suppressing action, and it is impossible to impart sufficient strength to the extruded profile. If the holding time does not reach 1 hour, the homogenization of Mg, Si or Cu becomes insufficient even in the temperature range of 580 ° C., and if the holding time exceeds 12 hours, the productivity is hindered and a problem arises in terms of cost. Cooling condition after holding at high temperature is 200 ° C /
If less than the time, Mg-Si system, Al-Cu system, Al-Mg
-Precipitates of compounds such as the Cu system become coarse, cannot be sufficiently dissolved during extrusion, and sufficient strength cannot be obtained by subsequent aging treatment.

Extrusion processing: Billet pre-heat treatment 430-520 ° C. × 1-60 minutes Surface temperature immediately after extrusion 500-555 ° C. In the press-end quenching extrusion processing in which water is cooled from a surface temperature of 430 ° C. or more at the start of shape cooling, 430-52 before extrusion
Pre-heat treatment at 0 ° C for 1 to 60 minutes is applied to the billet,
The surface temperature of the profile immediately after extrusion is controlled in the temperature range of 500 to 555 ° C. Compounds such as Mg-Si-based, Al-Cu-based, and Al-Mg-Cu-based compounds precipitated by forced air cooling after the billet homogenization treatment form a solid solution again due to heat generation during preheating and extrusion. Subsequently, the solution treatment is completed during the extrusion by performing water cooling from a surface temperature of 430 ° C. or more at the time of cooling the profile at the press end. By the above treatment, precipitation hardening of the Mg-Si-based or Al-Cu-Mg-based compound is obtained in the subsequent aging treatment step, and the member strength can be improved.

If the billet preheating temperature does not reach 430 ° C., the deformation resistance becomes large due to the low processing temperature, and a high extrusion speed cannot be obtained. If the preheating time does not reach 1 minute, the billet temperature will not be uniform. In addition, since the surface temperature of the extruded material does not reach 500 ° C., Mg-Si
, Al-Cu-based, Al-Mg-Cu-based compounds, etc. do not sufficiently re-dissolve in solid form, and sufficient strength cannot be obtained in the subsequent aging process. Conversely, if the preheating temperature exceeds 520 ° C., the temperature of the profile increases, and surface roughness and tearing are likely to occur. Therefore, in order to obtain a product having good surface properties, the extrusion speed must be reduced. If the surface temperature of the shaped material exceeds 555 ° C., the fine compound containing Mn, Cr, Zr or the like does not have sufficient pinning action to suppress recrystallization and causes a reduction in member strength. Preheating for more than 60 minutes is not economical. Surface temperature of profiled material by press end quenching 4
Quenching from 30 ° C. or higher can be achieved by re-dissolving Mg, C
This is because u, Si and the like are not precipitated during the extrusion. If the profile surface temperature is lower than 430 ° C., precipitation of a size that does not contribute to room temperature strength occurs, and the subsequent age hardening property is reduced. In the aluminum alloy of the present invention, the melting start temperature is 5
Since the temperature is set to 85 ° C. or higher, it can be extruded at a temperature equal to or higher than that of a normal 6000 series alloy. To that extent, the hot deformation resistance is reduced, and the extrusion speed can be increased. However, according to investigations and studies by the present inventors, it has been found that unless extruded at a temperature lower than the melting start temperature by 30 ° C. or more, the surface of the extruded shape becomes rough. Therefore, the upper limit of the surface temperature of the extruded profile was set to 555 ° C.

Aging treatment: 170-200 ° C. × 1-12 hours → air cooling In the aging treatment, β′-Mg ₂ Si, S′-CuMg is obtained from a supersaturated solid solution obtained by extrusion and quenching at the press end.
By precipitating Al ₂ or the like, the strength of the member is improved. If the aging treatment temperature does not reach 170 ° C., a long treatment exceeding 12 hours is required, which is not economical. Conversely, if the aging treatment temperature exceeds 200 ° C., overaging occurs, the peak strength is low, and sufficient member strength cannot be obtained. Also, 1
If the holding time is shorter than the time, the aging becomes insufficient and stable strength cannot be obtained.

[0019]

EXAMPLE A melt having the composition shown in Table 1 was prepared by a usual dissolution method, sedated for 1 hour after the addition of a refiner, and had a diameter of 254 mm.
Cast into billets. Each billet was heated at a heating rate of 80 ° C./hour, and subjected to a homogenizing treatment at 540 ° C. × 4 hours.
Forced air cooling was performed to room temperature at a cooling rate of 300 ° C./hour. A sample was taken from the billet and the melting onset temperature was measured with a differential scanning calorimeter. According to the invention, T (° C.) = 667-21
Table 1 also shows the calculated values of the melting onset temperature calculated with x% Cu-42x% Si-38x% Mg, compared with the actually measured values. As seen in Table 1, the difference between the calculated value and the measured value is 0.
-4 ° C, and it can be seen that the calculated values in the design obtained by the regression analysis show high consistency with the actually measured values.

[0020]

Next, the billet is preheated to 450 ° C.
After holding for minutes, length 150mm, width 50mm, wall thickness 2mm
In a hollow rectangular cross section (FIG. 2). At this time, the surface temperature of the profile immediately after extrusion varied depending on the extrusion speed, but was in the range of 520 to 555 ° C. The extruded profile was water-cooled at the press end during extrusion, then subjected to an aging treatment at 180 ° C. for 6 hours, and air-cooled. A test piece JIS No. 14B was cut out from the shape material after the aging treatment, and subjected to a tensile test to measure mechanical properties such as tensile strength, 0.2% proof stress, and elongation. In addition, the extrusion speed was increased until surface roughness occurred, and the maximum speed was measured as the limit extrusion speed. Table 2 shows the survey results.

[0022]

As shown in Table 2, in Test Nos. 1 to 5 according to the present invention, the tensile strength was 350 N / mm ² or more,
High mechanical strength of 0.2 N proof stress of 330 N / mm ² or more and high-speed extrusion at a limit extrusion speed of 8 m / min or more were possible. One factor in high-speed extrusion is that the melting start temperatures of Test Nos. 1 to 5 are as high as 585 ° C. or higher. On the other hand, in Test Nos. 6 to 8, the melting start temperature was 58
When the extrusion speed was increased below 5 ° C., the surface became rough, and the limit extrusion speed did not reach the target value of 8 m / min. In Test No. 9, since the Mg content was small, the amount of Mg ₂ Si precipitated was small, and the 0.2% proof stress was low. Test number 10 is M
Although the contents of g and Si were appropriate, the tensile strength and proof stress were insufficient due to the low Cu content. In addition, since the structure is designed to strengthen the structure only by adding Mn,
Although the content was increased, the effect of suppressing recrystallization was weaker than that of the composite addition with Cr or Zr, and it did not lead to an improvement in strength. Test No. 11 shows that the Si content was slightly lower than the Mg content, and only Cr was added, and the Cr content was low, leading to an increase in strength as compared to the composite addition with Mn or Cr. Did not. Sample number 1
In No. 2, sufficient strength was not obtained because the Cu content was small and the added amount of Mn + Cr was small.

[0024]

As described above, according to the present invention, the Al-
For the Mg-Si alloy, the composition of each alloy component is adjusted, and T (° C.) = 667-21 ×% Cu-42 ×% Si—
The alloy is designed so that the melting start temperature T defined by 38 ×% Mg is 585 ° C. or more, and the tensile strength is adjusted by appropriately adjusting the casting conditions, billet homogenization treatment conditions, extrusion conditions and aging conditions. 350 N / mm ² or more, 0.2%
A proof strength of 330 N / mm ² or more and a material strength comparable to that of steel SS400 can be obtained. Therefore, aluminum can be used in place of steel, and various devices and structures can be significantly reduced in weight.
In addition, since extrusion can be performed with a productivity of 6061 alloy or more, an extruded member having excellent characteristics can be provided at low cost.

[Brief description of the drawings]

FIG. 1 Range of Si content and Mg content defined in the present invention

FIG. 2 is an extruded profile obtained in an example of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Tsuchida 1-34-1, Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Inside the Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor: Kazuto Kamio 1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture (34) Inventor Masaharu Morohashi 2-7-23 Kiba, Koto-ku, Tokyo Nippon Light Metal Co., Ltd.

Claims (5)

[Claims] 1. Cu: 0.2-0.9% by weight, Si:
0.6 to 1.1% by weight, Mg: 0.4 to 1.0% by weight,
Fe: 0.1 to 0.3% by weight, Mn: 0.2 to 0.5% by weight, Cr: 0.1 to 0.3% by weight, Ti: 0.005
-0.05% by weight, B: 0.001-0.01% by weight, T (° C.) = 667-21 ×% Cu-42 ×% Si
Melting start temperature T defined by −38 ×% Mg is 585 ° C.
A high-strength Al-Mg-Si alloy for structural materials having a composition designed to be as described above and having excellent extrudability. 2. The composition according to claim 1, further comprising Zr: 0.0.
High strength Al-Mg- for structural materials containing 5 to 0.2% by weight
Si-based alloy. 3. Point A (0.8, 1.0), point B (0.6, 0.4), point C (1.1, 0.4) in a coordinate system of Si content-Mg content. 3) and a high-strength Al— material for a structural material according to claim 1 or 2, wherein the area ABCD defined by the point D (1.1, 0.8) has a Si content and a Mg content.
Mg-Si based alloy. 4. The total content of Mn, Cr and Zr is 0.4.
4. The composition according to claim 1, wherein the content is adjusted in a range of 3 to 0.8% by weight.
High-strength Al-M for structural materials having the composition described in any one of the above.
g-Si alloy. 5. An Al—Mg—Si alloy having a composition according to claim 1 which is DC-cast within 120 minutes after the addition of the refining agent, and has a heating rate of 200 ° C./hour or less. High temperature holding 500-580 ° C x 1-12 hours, cooling rate 200-
A homogenization treatment of 500 ° C./hour is performed, and preheating is performed at 430 to 520.
℃ x 1 to 60 minutes, surface temperature of the profile immediately after extrusion 500 to 5
Extruded at 55 ° C, water-cooled from the surface temperature of 430 ° C or higher, and then subjected to press end quenching.
A method for producing a high-strength Al-Mg-Si-based alloy extruded section for a structural material, which is subjected to an aging treatment of holding at 200C for 1 to 12 hours and then air cooling.