JP7316951B2 - Method for manufacturing aluminum alloy member - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an aluminum alloy member, and more particularly to a method for manufacturing an aluminum alloy member by plastic working a heat-treated aluminum alloy extruded material of T1 refining at a warm temperature.

Amid the trend of tightening fuel efficiency regulations against the background of resource and environmental problems, the weight reduction of transportation equipment such as automobiles, airplanes, construction equipment, and ships is progressing. Aluminum alloys have a density of about 2.7 gcm ⁻³ , which is about 1/3 that of steel and are light in weight. Therefore, aluminum alloys are increasingly being used for structural members of transportation machinery, particularly automobiles.
As these structural members, in addition to castings and forgings, rolled materials (plates) and extruded materials are used. Of these, the extruded material has the advantage that a long material with a hollow closed cross-section having an arbitrary thickness distribution can be obtained without additional processing, and is suitable for the manufacture of automotive frame parts and energy absorbing parts. Such automobile frame parts include rockers, side members, pillars, subframes, and the like, and energy absorbing parts include door reinforcements, bumper reinforcements, roof reinforcements, and the like.

The weight reduction effect obtained by replacing steel parts with parts manufactured from aluminum alloy extrusions greatly depends on the strength (proof stress) of aluminum alloys. Alloy development is underway.
Typical high-strength aluminum alloys include 6000 series (Al-Mg-Si-(Cu) system) and 7000 series (Al-Zn-Mg-(Cu) system), which are heat-treated (precipitation hardening) alloys. There is In general, a 6000 series aluminum alloy has a 0.2% yield strength of about 200 to 350 MPa, and a 7000 series aluminum alloy has a 0.2% yield strength of about 300 to 500 MPa with T5, T6 or T7 tempering. In particular, 7000 series aluminum alloys are expected to have high strength and high weight reduction effect.

On the other hand, high-strength 7000-series aluminum alloys have a problem of stress corrosion cracking (SCC), which occurs at locations where tensile stress is constantly generated in a corrosive environment. Since this stress corrosion cracking is sensitive, it progresses quickly and the risk of sudden breakage increases, so it is strongly avoided from the viewpoint of quality assurance.
Among 7000 series aluminum alloys, the susceptibility to stress corrosion cracking generally increases as the strength increases. In addition, it is known that the susceptibility to stress corrosion cracking varies depending on the temper even in alloys of the same composition, and stress corrosion cracking is less likely to occur in T7 temper than in T5 or T6 temper. Stress corrosion cracking is a bottleneck, and the adoption of high-strength 7000 series aluminum alloys for automobile parts is often postponed.
Stress corrosion cracking occurs when a portion where tensile stress exceeds a certain threshold is exposed to a corrosive environment. This tensile stress is often caused by tensile residual stress generated during plastic working, cutting, and heat treatment (such as quenching) during the manufacturing process.

In order to make an aluminum alloy extruded material into an automobile part, additional processing such as plastic working and cutting is generally required. Plastic working is a means of deforming a material by mechanical force and forming it into a product of a given shape and size. This includes variable cross-section processing such as widening and widening, and shearing processing such as drilling and cutting with a press machine.
Tensile residual stress in an aluminum alloy member (a member obtained by subjecting an aluminum alloy extruded material to additional working or heat treatment) is generated by additional working (plastic working or cutting) or heat treatment. A particular problem is tensile residual stress caused by plastic working. Typical examples of plastic working performed on an aluminum alloy extruded material are the above-described bending, cross-section working, and shearing, and strong tensile residual stress is generated when the above plastic working is performed in the cold. In 7000 series aluminum alloy extruded material, which has a risk of stress corrosion cracking, suppression of tensile residual stress due to plastic working is a technical issue.

By the way, the plastic working (cold working) of the heat-treated aluminum alloy extruded material is often performed not on the T5, T6, and T7 tempered materials but on the T1 tempered material. This is because the T1 tempered material is softer than the T5, T6, and T7 tempered materials, has high ductility, and is excellent in workability. However, if the T1 tempered material has high strength and lacks ductility, it may be subjected to softening heat treatment (restoration treatment) before plastic working, as shown in Patent Document 1. be. In addition, the T1 tempered material means an aluminum alloy extruded material that has not undergone any tempering treatment other than natural aging after extrusion.

Moreover, in order to improve the workability of a heat-treated aluminum alloy extruded material, it is also known to subject the extruded material to plastic working (warm working) at a temperature higher than room temperature. For example, in Patent Literature 2, plastic working of an aluminum alloy extruded material is performed using a high-temperature state immediately after extrusion. In Patent Document 3, after the aluminum alloy extruded material is solution treated, heat treatment is performed at 50 to 100 ° C. for 1 to 30 minutes, and after natural aging, it is reheated within the temperature range of 100 to 200 ° C., and within that temperature range. We are doing plastic working.

Japanese Patent No. 5671422 JP-A-5-69069 JP 2009-114514 A

As described above, warm working of an aluminum alloy extruded material is a method for improving the ductility and workability of the extruded material. In addition, since the magnitude of residual stress in aluminum alloy extruded material (after artificial aging treatment) is approximately proportional to the strength during plastic working, warm working reduces the tensile residual stress of the product (aluminum alloy member), It is also a method for improving stress corrosion cracking resistance.

On the other hand, as a method of heating an aluminum alloy extruded material for warm working, heating by an in-line heater or an oil heater described in Patent Documents 2 and 3 can be considered. Among these heaters, the in-line heater is capable of stable heating, but has the problem that the heating rate is slow, the equipment is large, and the cost is high. Oil heaters are capable of rapid heating, but have problems with safety and running costs, and are not suitable for mass production due to the need to wash off oil adhering to workpieces (aluminum alloy extruded materials).

The present invention aims to achieve low cost and high productivity in commercialization (manufacturing aluminum alloy members) by plastic working (warm working) of a heat-treated aluminum alloy extruded material with a hollow cross section. aim.

In the present invention, an aluminum alloy extruded material having a hollow cross section is heated to reach a temperature within a predetermined temperature range, then subjected to plastic working (warm working) within the temperature range, then cooled, and then artificially In the method for producing an aluminum alloy member that undergoes aging treatment, the aluminum alloy extruded material is a heat-treated aluminum alloy extruded material T1 tempered material, the temperature range is 150 to 300 ° C., and the aluminum alloy extruded material is used. , sandwiched between upper and lower heating dies heated to 200 to 350 ° C., provided with a heating mechanism, and heated by heat transfer from the heating dies to reach a temperature within the above temperature range. .

The method for manufacturing the aluminum alloy member includes the following specific forms.
(1) The aluminum alloy is a 7000 series aluminum alloy.
(2) The load applied from the mold to the extruded material when the temperature of the aluminum alloy extruded material is raised is P (unit: N), and the upper and lower contact points between the aluminum alloy extruded material and the heating mold When the projected area of is A (unit: m ² ), the relationship P/A≧0.07 MPa is satisfied.
(3) In the cross section of the aluminum alloy extruded material, the total length (unit: mm) of contact with the upper and lower molds during temperature rise and the cross-sectional area S (unit: mm ² ) satisfy the relationship S / L ≤ 8 mm. Fulfill.
(4) The heating mold is made of either steel, aluminum or copper.
(5) The aluminum alloy member is an energy absorbing part or an automobile frame part.

According to the present invention, when the T1 tempered aluminum alloy extruded material is subjected to plastic working (warm working) and commercialized, the aluminum alloy extruded material is sandwiched between heating dies heated from above and below. By raising the temperature, it is possible to achieve high productivity (high heating rate) at low cost.
By plastic working the aluminum alloy extruded material at a temperature within the above temperature range (150 to 300 ° C), the deformability of the aluminum alloy extruded material is improved, the tensile residual stress generated due to plastic working is reduced, and the product ( aluminum alloy members) can be improved in stress corrosion cracking resistance.
In addition, in the present invention, since the T1 tempered aluminum alloy extruded material is used as a material, energy absorbing parts such as door reinforcements, bumper reinforcements, roof reinforcements, etc., which require strength, rockers, side members, pillars, etc. Automobile frame parts such as subframes can be manufactured at low cost.

1 is a flow diagram of the process of the present invention; FIG. FIG. 4 is an explanatory diagram of an example of a temperature rising process; FIG. 5 is an explanatory diagram of another example of the temperature raising process; FIG. 5 is an explanatory diagram of another example of the temperature raising process; FIG. 5 is an explanatory diagram of another example of the temperature raising process; FIG. 5 is an explanatory diagram of another example of the temperature raising process; FIG. 5 is an explanatory diagram of another example of the temperature raising process; FIG. 5 is an explanatory diagram of another example of the temperature raising process; 1 is a graph showing the relationship between heat transfer coefficient and P/A (contact pressure) between steel-to-steel, aluminum-to-aluminum, and steel-to-aluminum in contact with each other. 1 is a diagram illustrating the meaning of a contact length L (L ₁ +L ₂ ) with a heating die and a cross-sectional area S in a cross section of an aluminum alloy extruded material 1. FIG. It is the temperature history of the test material obtained when the test material for temperature history measurement of Experiment 1 was inserted into the air furnace set to 500 degreeC. FIG. 3 is a diagram showing the relationship between the temperature and the occurrence of cracks during plastic working of an aluminum alloy extruded material. Cross-sectional schematic diagram (13A) of the 7000 series aluminum alloy extruded material used in Experiment 2, side schematic diagram (13B) after plastic deformation, and cross-sectional schematic diagrams of II, II-II, and III-III in FIG. 13B (13C). FIG. 4 is a diagram showing the temperature history of an aluminum alloy extruded material sandwiched between heating dies. FIG. 5 is a diagram showing the relationship between the heat transfer coefficient during temperature rise and the time required to reach the target temperature. FIG. 4 is a diagram showing the relationship between the cross-sectional area/contact length (S/L) of the aluminum alloy extruded material during temperature rise and the time required for the aluminum alloy extruded material to reach the target temperature. FIG. 4 is a diagram showing the relationship between the temperature of the aluminum alloy extruded material and the heating time when the temperature is raised.

Hereinafter, the method for manufacturing an aluminum alloy member according to the present invention will be described more specifically. As shown in FIG. 1, this manufacturing method comprises a step (P1) of producing a T1 tempered aluminum alloy extruded material, a step (P2) of cutting the extruded material to a predetermined length and correcting it, and extruding the extruded material from 150 to A step of raising the temperature to a temperature range of 300 ° C. (P3), a step of plastic working the extruded material in the temperature range (P4), a step of cooling the extruded material (P5), and a step of performing artificial aging treatment (P6). It consists of 5 steps.

[T1 tempered aluminum alloy extruded material]
In the method for manufacturing an aluminum alloy member according to the present invention, a heat-treated aluminum alloy extruded material with T1 refining is used as the raw material. Main examples of heat treatable aluminum alloys include 6000 series (Al--Mg--Si(--Cu) series) and 7000 series (Al--Mg--Zn(--Cu) series) aluminum alloys.
The composition of the heat treatable aluminum alloy to which the present invention is applied is not particularly limited. However, as a preferred composition of the 6000 series, Mg: 0.4 to 1.2 mass%, Si: 0.3 to 0.95 mass%, Cu: 0.01 to 0.65 mass%, Ti: 0.001 0.10% by mass, and further Mn: 0.01 to 0.3% by mass, Cr: 0.01 to 0.3% by mass, Zr: 0.01 to 0.3% by mass. Alternatively, a composition containing two or more kinds and the balance being Al and unavoidable impurities can be mentioned. In addition, as a preferred composition of the 7000 series, Zn: 3.0 to 8.0% by mass, Mg: 0.4 to 2.5% by mass, Cu: 0.05 to 2.0% by mass, Ti: 0.005 0.2% by mass, and further Mn: 0.01 to 0.3% by mass, Cr: 0.01 to 0.3% by mass, Zr: 0.01 to 0.3% by mass. Alternatively, a composition containing two or more kinds and the balance being Al and unavoidable impurities can be mentioned.
In the present invention, the T1 tempered material means a material that has undergone a tempering treatment of only natural aging after extrusion. In the present invention, the extruded material means an extruded material according to the definition of a shape defined in JISH4100, and an extruded material according to the definition of a pipe defined in JISH4080, and includes both hollow materials and solid materials. .
Examples of 7000 series aluminum alloy members include energy absorbing parts such as door reinforcements, bumper reinforcements and roof reinforcements, and automotive frame parts such as rockers, side members, pillars and subframes.

[Temperature rising process]
In the temperature raising step, as shown in FIG. 2, the aluminum alloy extruded material 1 is sandwiched between heated heating dies 2 and 3 from above and below, and the entire cross section is heated to a target temperature within a predetermined temperature range (150 to 300 ° C.). The temperature rises to In this example, the aluminum alloy extruded material 1 has a rectangular cross-sectional contour, and consists of a pair of flanges 4, 5 with which the heating dies 2, 3 are in contact, and three webs 6, 7, 8 connecting them. , assuming use as a bumper reinforcement. The front surfaces of the heating molds 2 and 3 are flat and are in contact with the full width of the flanges 4 and 5 .
During the temperature rising process, a temperature gradient is generated in the cross section of the aluminum alloy extruded material from a portion near the heating mold (high temperature portion a) to a portion away from the heating mold (low temperature portion b). When the target temperature is set in the range of t ₁ to t ₂ (° C.), for example, the temperature of the low temperature part b becomes equal to or higher than the lower limit t ₁ and the temperature of the high temperature part a does not exceed the upper limit t ₂ . In other words, it is necessary to heat the aluminum alloy extruded material 1 so that the entire cross section has a temperature within the range of t ₁ to t ₂ . t ₁ and t ₂ are appropriately selected within the ranges of t ₁ ≧150° C., t ₂ ≦300° C., and t ₁ ≦t ₂ . On the other hand, the temperature of the heating molds 2 and 3 is set to a temperature within the range of 200 to 350° C. and higher than the lower limit value t ₁ of the target temperature (preferably a temperature higher by 50 to 75° C.). As a result, the entire cross section of the aluminum alloy extruded material 1 can be heated to the target temperature (t ₁ to t ₂ ) at a high heating rate.

3 to 8 are cross-sectional views of aluminum alloy extruded materials having various different cross-sectional shapes, sandwiched between heating dies from above and below and heated.
In FIG. 3, an aluminum alloy extruded material 1 consists of a pair of flanges 4, 5 in contact with heating dies 2, 3 and three webs connecting them. The flange 4 with which the die 2 contacts is bent at the center and a corresponding inclined portion is formed on the front face of the die 2 so that the die 2 contacts the entire width of the flange 4 . The front surface of the mold 3 is flat and contacts the full width of the flange 5 .
In FIG. 4, the aluminum alloy extruded material 1 comprises a hollow portion 11 having a substantially pentagonal profile and a protruding flange 12 connected to the hollow portion 11. The hollow portion 11 has surfaces 11a and 11b parallel to each other. The front surfaces of the heating molds 2 and 3 are flat and are in contact with the entire width of the surfaces 11a and 11b.

5, the aluminum alloy extruded material 1 consists of a pair of flanges 4, 5, webs 6, 7, 8, 9 connecting them, and projecting flanges 12, 13, and the outer surfaces of the flanges 4 and projecting flanges 12 forms a plane. The front surfaces of the heating molds 2 and 3 are flat, the mold 2 is in contact with the entire width of the flange 4 and the projecting flange 12 , and the mold 3 is in contact with the entire width of the flange 5 .
In FIG. 6, the aluminum alloy extruded material 1 is a circular tube, and a recess having an arc-shaped cross section is formed on the front surface of the heating molds 2 and 3, and a part of the outer periphery of the aluminum alloy extruded material 1 contacts the recess. are doing.

In FIG. 7, the aluminum alloy extruded material 1 consists of a pair of flanges 4, 5 and webs 6, 7 connecting them. in contact. It is assumed that it will be used as a door beam.
8, the aluminum alloy extruded material 1 includes a hollow portion 14 having a substantially hexagonal profile, two crossing ribs 15 and 16 formed in the hollow portion 14, and a protruding flange 17 connected to the hollow portion 14. , 18. A groove-like recess is formed in the front surface of the heating molds 2 and 3, the hollow portion 14 of the aluminum alloy extruded material 1 contacts the recess, and a protruding flange 17 is formed in the flat portion of the front surface of the heating molds 2 and 3. , 18 are in contact. The heating dies 2 and 3 have a larger contact area with the aluminum alloy extruded material 1 than when a die having only a flat front surface is used.

It should be noted that a load may be applied to the aluminum alloy extruded material 1 from the heating dies 2 and 3 when the temperature is raised. The greater the load, the greater the heat transfer coefficient between the dies 2 and 3 and the aluminum alloy extruded material 1, and the greater the temperature rise rate of the aluminum alloy extruded material 1. As shown in Examples described later, if the average heat transfer coefficient is 1500 Wm ^-2 K ^-1 or more, the aluminum alloy extruded material 1 can be raised to a temperature within the above temperature range (150 to 300 ° C.) in a relatively short time. can be warmed. When the heating dies 2 and 3 are made of steel, in order to achieve this average heat transfer coefficient, the load applied from the heating dies 2 and 3 to the aluminum alloy extruded material 1 is defined as P (unit: N). , where A (unit: m ² ) is the projected area in the pressurizing direction of the contact points between the aluminum alloy extruded material 1 and the heating dies 2 and 3, P/A≧0. It is preferable to satisfy the relationship of 07 MPa. In addition, when the pressing direction is the vertical direction, the projected area is the horizontal projected area.

FIG. 9 shows the relationship (estimated value) between contact pressure and heat transfer coefficient when aluminum contacts, stainless steel contacts, and aluminum contacts steel. The relationship between contact pressure and heat transfer coefficient between aluminum and stainless steel is based on SolidWorks Japan Co., Ltd. online help 2012 material (URL: http://help.solidworks.com/2012/japanese/SolidWorks/cworks/ Based on data in table on page 3 of Thermal_Contact_Resistance.htm. According to the same data, the thermal resistance (reciprocal of heat transfer coefficient) when aluminum is in contact with each other is 1.5 to 5.0×10 ⁻⁴ m ² KW ⁻¹ when the contact pressure is 0.1 MPa. It is 0.2 to 0.4×10 ⁻⁴ m ² KW ⁻¹ when the pressure is 10 MPa. The geometric mean of the maximum and minimum values of thermal resistance was obtained for each contact pressure, and then its reciprocal (heat transfer coefficient) was obtained and plotted with ⋄ marks in FIG. The heat transfer coefficient when the stainless steels were in contact with each other was also determined in the same manner and plotted with □ in FIG. Furthermore, the geometric mean of the heat transfer coefficient when aluminum contacts each other and the heat transfer coefficient when stainless steel contacts each other is obtained for each contact pressure. The heat transfer coefficient between aluminum and steel in contact with the contact pressure was estimated and plotted with Δ marks in FIG. In addition, a figure (straight line) passing through two points of the same mark (◇ and ◇, □ and □, △ and △) was drawn. On the right side of the figure in FIG. 9, the equation of each figure is described when the average heat transfer coefficient is y and P/A is x.

From the graph of the heat transfer coefficient between aluminum ^and steel in FIG ^. ) should be added.
The heat transfer coefficient between the heating mold and the aluminum alloy extruded material varies greatly depending on the material of the mold. Basically, the higher the heat conductivity of the mold, the higher the heat transfer coefficient. Therefore, when using a heating mold made of copper (pure copper or copper alloy) or aluminum (pure aluminum or aluminum alloy), which are good conductors, if the P/A is the same, compared to a steel heating mold, the number of Double higher heat transfer rate and heating rate can be achieved.

During temperature rise, the larger the contact area between the aluminum alloy extruded material 1 and the heating dies 2 and 3, the higher the temperature rising rate. In the cross section of the aluminum alloy extruded material 1 (see FIG. 10), the total contact length at the upper and lower contact points between the aluminum alloy extruded material 1 and the heating molds 2 and 3 is L (=L ₁ +L ₂ ) (unit: mm), and the cross-sectional area of the aluminum alloy extruded material 1 is S (unit: mm ² ). It is preferable to satisfy the relationship. When this relationship is satisfied, the aluminum alloy extruded material 1 can be heated to a temperature within the above temperature range (150 to 300° C.) in a relatively short period of time.

[Plastic processing]
In the present invention, the aluminum alloy extruded material is heated from room temperature to a temperature within the range of 150 to 300° C., and then subjected to plastic working (warm working) within the temperature range. Plastic processing generally includes bending, cross-section processing and shearing.
The part where the temperature of the aluminum alloy extruded material is raised in the temperature raising process should include at least a part where plastic working is performed. location where it is performed and its vicinity).
If the heating die is made of steel and the plastic working is simple variable cross-section processing (e.g., uniform crushing), the aluminum alloy extruded material is heated by the heating die and then directly heated in the heating die. Plastic working can be performed. Even if the heating die is made of steel, if the plastic working is not simple cross-section processing, or if bending or shearing, the heated aluminum alloy extruded material is removed from the heating die and another It is necessary to perform plastic working with a die (die for plastic working). Also, when the heating mold is made of copper or aluminum, it is necessary to perform plastic working with another mold (plastic working mold). The mold for plastic working can also be heated as necessary (within a range of, for example, 150 to 300° C.) to prevent or suppress the temperature drop of the aluminum alloy extruded material during plastic working.

By performing plastic working on the aluminum alloy extruded material within the above temperature range, especially in the 7000 series aluminum alloy extruded material, the occurrence of cracks during plastic working is suppressed, and the tensile residual generated in the product (aluminum alloy member) due to plastic working. Stress can be reduced. However, if the temperature during plastic working is less than 150°C, the effect of preventing cracking is not sufficient, and even if cracking does not occur, the tensile residual stress generated in the product by plastic working cannot be sufficiently reduced. . On the other hand, if the temperature reached during heating and the temperature during plastic working exceed 300° C., the strength of the product (aluminum alloy member) after the artificial aging treatment is not sufficiently improved. In order to improve the product strength after the artificial aging treatment, the cooling after the plastic working is preferably performed at a cooling rate of 3° C./second or more.

(Experiment 1)
An experiment was conducted to confirm the relationship between the temperature during plastic working and the occurrence of cracks in extruded aluminum alloys.
A T1 tempered 7000 series aluminum alloy extruded material (Kobe Steel Co., Ltd. aluminum alloy standard Z6W) is heated from room temperature, the ultimate temperature is varied, and plastic working (warm working) is performed at the reached temperature. , the temperature conditions under which cracks do not occur were investigated. The aluminum alloy extruded material has a rectangular profile with a cross section of about 50 mm in height x about 150 mm in width, has two hollow portions, has a wall thickness of 2 to 4 mm, and a pair of flanges with a length of about 150 mm. , consisting of three webs approximately 50 mm in length, equidistantly connected to said pair of flanges. This aluminum alloy extruded material is used, for example, as a material for reinforcing bumpers.

The extruded material was cut perpendicularly to the extrusion direction into a fixed length to prepare a test material for temperature history measurement and a plurality of test materials for plastic working.
The temperature of the test material was raised in an air furnace set at 500°C. First, a thermocouple was attached to the web of the test material for temperature history measurement, and the web was placed in the air furnace to measure the temperature history of the test material. The results are shown in FIG. From the temperature history, the time (reaching time) from when the test material was charged into the air furnace until it reached various temperatures (reaching temperatures) was determined. Incidentally, as shown in FIG. 11, the rate of temperature increase up to 350° C. was about 5° C./s.
Next, the test material for plastic working is charged into the air furnace one by one, and after reaching a predetermined temperature (that is, immediately after a predetermined time has elapsed), the test material is removed from the air furnace, and immediately Plastic working (warm working) was performed. For the plastic working, an ordinary pressing machine was used, the upper and lower parallel dies were kept at the above-mentioned attained temperature, and the test material was crushed until the cross-sectional height reached 20 mm.

At the crushed portions, the web was greatly bent and deformed, and depending on the temperature reached, cracks parallel to the ridge line of the bend and surface roughness were observed on the outer side of the bend. FIG. 12 shows a plot (x, .DELTA., .smallcircle.) of the relationship between the attained temperature and the external appearance quality of the bent outside of the web. In FIG. 12, x means the generation of clear cracks, Δ means the generation of slight cracks, and ◯ means the generation of rough surface only.
As shown in FIG. 12, when the temperature during plastic working is 150° C. or higher, cracks do not occur in plastic working (crushing working).

(Experiment 2)
Experiments were conducted to confirm the relationship between temperature and tensile residual stress during plastic working of aluminum alloy extruded materials.
A T1 tempered 7000 series aluminum alloy extruded material was subjected to plastic working at various temperatures exceeding room temperature, and the relationship between plastic working temperature and tensile residual stress was investigated. The composition of this 7000 series aluminum alloy is the same as that of Example 1. The extruded shape is used, for example, as a material for door beams, and as shown in FIG. The flanges and webs are perpendicular to each other. One of the pair of flanges (thin side flange) has a thickness of 2.2 mm and a width of about 34 mm, and the other flange (thick side flange) has a thickness of 5.6 mm and a width of 40 mm. Both webs have a thickness of 2 mm and a length of 27.2 mm.

The extruded material was cut perpendicularly to the direction of extrusion to a given length, and the projecting portion of the thick side flange was cut off to prepare a plurality of test materials.
The test material is inserted into an air furnace set to 500 ° C. and heated, and after reaching 500 ° C., it is removed from the air furnace, cooled while controlling the temperature with a contact thermometer, and each test temperature (300 ° C., 250 °C, 200°C, 150°C, and 50°C), plastic working was immediately performed. For plastic working, a normal press was used, and vertically parallel molds were held at the test temperature, and the test material was crushed from the tip to a length of 200 mm until the cross-sectional height reached 25 mm. Two test materials were used for each test temperature, and the same crushing process was performed on each test material.
After crushing, the test material was immediately forcibly cooled to room temperature.

The web is greatly bent and deformed at the crushed portions.
Using the crushed test material (before aging treatment), the residual stress generated on the bending outer side of the web due to crushing was measured using an X-ray stress measuring device MSF-3M (manufactured by Rigaku Corporation). The measurement points are the position near the thick side flange (measurement point A) in the area between the crushed area (area with a cross-sectional height of 25 mm) and the area without crushing (area with a cross-sectional height of 35 mm), A position near the thick side flange (measurement point B) in the crushed area was used. Measurement conditions and analysis conditions are shown in Table 1, and measurement points A and B are indicated by ◯ marks in FIGS. 13B and 13C. The measurement point A is substantially flat, and the measurement point B is a recess.
Table 2 shows the plastic working temperature and the measurement results. The values of tensile residual stress shown in Table 2 are average values of two test materials. In Table 2, numerical values given with - are compressive residual stresses.

As shown in Table 2, when the plastic working temperature is R.M. T. At 50°C, which is close to , high tensile residual stress is generated at both measurement points A and B, but at a plastic working temperature of 150°C or higher, the tensile residual stress is reduced to 60% or less of that at 50°C. Moreover, when the plastic working temperature exceeded 150°C, the tensile residual stress decreased significantly. It has been confirmed that when the plastic working temperature is 150° C. or higher, the magnitude of the tensile residual stress generated in the web is sufficiently low, and the value does not change significantly due to the artificial aging treatment.

(Experiment 3)
An experiment was conducted to confirm the relationship between the temperature during plastic working and the 0.2% yield strength after aging treatment for aluminum alloy extruded materials.
Using the same T1 tempered 7000 series aluminum alloy extruded material as in Experiment 1, JIS 13B test pieces (No. 1 to 23) were prepared so that the longitudinal direction from the flange was parallel to the extruded direction. The thickness of this test piece is 3 mm. Of these, No. 1 to 20 test pieces were heated from room temperature, the temperature was varied, held at the temperature for a predetermined time, and then cooled to room temperature at various cooling rates. properties were measured.

No. The ultimate temperature of the test pieces 1 to 20 is set to either 150 ° C., 200 ° C., 250 ° C., or 275 ° C., and the temperature is raised to the target temperature by an oil bath (150 ° C., 200 ° C.) held at the target temperature. Alternatively, it was carried out in a saltpeter furnace (250°C, 275°C). The holding time at the attained temperature was set to 30 s, 60 s, 90 s, 150 s, or 180 s, and the cooling method was natural air cooling or water cooling. The cooling rate from the attained temperature to 140° C. was about 1° C./s for natural air cooling and about 100° C./s for water cooling. The temperature history of each test piece was measured by attaching a T thermocouple to each test piece with Kapton (registered trademark) tape.
Also, No. After the test pieces No. 21 to 23 were reheated and subjected to solution treatment (holding at 480° C. for 3600 s, cooling with a fan), no. The specimens were aged under the same conditions as the specimens Nos. 1 to 20, and the mechanical properties were measured.

A tensile test was performed in accordance with JISZ2241 (2011) using test pieces (No. 1 to 23) after aging treatment, and mechanical properties (0.2% proof stress, tensile strength, elongation at break) were measured. .
In Table 3, No. 1 to 20 test pieces reached temperature, holding time at the reached temperature, cooling method, tensile strength, 0.2% proof stress and breaking elongation values, and No. Solution treatment conditions (holding temperature, holding time), 0.2% yield strength, tensile strength and elongation at break of test pieces No. 21 to 23 are shown.
Furthermore, the solution-treated No. The average value of the 0.2% proof stress of the test pieces Nos. 21 to 23 was taken as the reference value (YS ₀ ), and the No. to the reference value. The 0.2% yield strength (YS) ratio ((YS/YS ₀ )×100) of each test piece No. 1 to 20 was determined and listed in Table 3.

As shown in Table 3, the test piece with a low reaching temperature (assuming the temperature during plastic working) and a short holding time at the reaching temperature has a level of 0 that is comparable to that of the solution-treated test piece. .2% proof stress is obtained. Among mechanical properties, 0.2% proof stress is considered to be the most important for strength members.

[Artificial aging treatment]
Artificial aging treatment is performed to improve the mechanical properties of the product (aluminum alloy member), particularly the 0.2% proof stress value. Conditions for artificial aging treatment are not particularly limited, and general aging treatment conditions for ordinary 6000 series or 7000 series aluminum alloys can be used. Alternatively, aging treatment (overaging treatment) can be performed under conditions of higher temperature and longer time than general aging treatment.

The higher the set temperature of the heating mold, the faster the rate of temperature rise of the aluminum alloy extruded material, and the more efficient temperature rise becomes possible. However, the temperature difference between the portion in contact with the heating mold and the portion away from the heating mold increases, and the entire cross section of the aluminum alloy extruded material cannot be kept within the target temperature (t ₁ to t ₂ ). becomes difficult. In this example, an experiment was conducted to evaluate the proper range of the set temperature of the heating mold.
Referring to FIG. 2, the target aluminum alloy extruded material 1 is made of a 7000 series aluminum alloy, has a rectangular cross-sectional profile, is composed of a pair of flanges and three webs, and has a width of about 150 mm and a height of about 50 mm. , with a cross-sectional area of about 1300 mm ² . The target temperatures were 200°C for _t1 (lower limit temperature) and 250°C for _t2 (upper limit temperature). The heating dies 2 and 3 are made of steel (carbon steel S50C), and sandwich the aluminum alloy extruded material 1 from above and below with an average pressure (P/A) of 0.4 MPa. As shown in FIG. 9, when the average pressure (P/A) applied to the aluminum alloy extruded material 1 from the heating dies 2 and 3 is 0.4 MPa, the average heat transfer coefficient (estimated value) is about 3000 W/ m ⁻² K ⁻¹ .

The temperature was measured at the side surface (web 8) near the heating mold 3 (high temperature part a) and at the farthest point from the heating mold 3 (low temperature part b). The temperatures (surface temperatures) of the heating molds 2 and 3 are 225°C, 250°C, 275°C, and 300°C (the lower limit of the target temperature t ₁ (200°C) to 25°C, 50°C, 75°C, and 100°C. above). FIG. 14 shows the temperature history of the high-temperature portion a and the low-temperature portion b after the aluminum alloy extruded material 1 was sandwiched between the heating dies 2 and 3 . When the temperature of the heating molds 2 and 3 is t ₁ +25° C. (FIG. 14A), the temperature rise rate is slow and the low temperature portion b does not reach t ₁ (200° C.) even after 60 seconds. On the other hand, when the temperature of the heating molds 2 and 3 is t ₁ +100° C. (FIG. 14D), the rate of temperature increase is extremely high, and the risk of exceeding the upper limit value t ₂ of the target temperature is high. Therefore, it can be said that the set temperature of the heating molds 2 and 3 is preferably about 50 to 75° C. higher than the lower limit t ₁ of the target temperature (FIGS. 14B and 14C).

The heating rate of the aluminum alloy extruded material when the aluminum alloy extruded material is sandwiched between the heating molds depends on the contact area (cross-sectional contact length) between the heating mold and the aluminum alloy extruded material and the heat transfer of the contact interface. and the temperature difference between the heating mold and the aluminum alloy extruded material, and inversely proportional to the volume of the aluminum alloy extruded material (part to be heated). The time required for the extruded aluminum alloy material to reach the target temperature was estimated by numerical simulation, using the heat transfer coefficient as a parameter, discretizing the heat conduction equation by the finite difference method. The software used for the simulation is the VBA function of Excel (registered trademark).
The target aluminum alloy extruded materials are two 7000 series aluminum alloy extruded materials having different cross-sectional shapes (cross section A and cross section B). As shown in FIG. 2, the aluminum alloy extruded material of section A has a rectangular cross-sectional profile, and consists of a pair of flanges and three webs, and has a flange length of 150 mm, a cross-sectional height of 53 mm, and a cross-sectional area of 1300 mm ² . As shown in FIG. 7, the aluminum alloy extruded material of section B consists of a pair of flanges and a pair of webs connecting them, and has a flange length of 37 mm, a cross-sectional height of 53 mm, and a cross-sectional area of 410 mm ² and

Assuming that a pair of flange portions of the aluminum alloy extruded material of cross section A and cross section B are sandwiched between heating dies heated to 300 ° C. (surface temperature) as shown in FIGS. Alternatively, the time required for the lowest temperature portion (see low temperature portion b in FIG. 2) to reach the target temperature (250° C.) was calculated. The contact length L (=L ₁ +L ₂ ) (see FIG. 10) between the aluminum alloy extruded material and the heating mold is 300 mm for cross section A and 74 mm for cross section B. However, since both sections A and B of the aluminum alloy extruded material are symmetrical sections, the analysis model was a 1/2 symmetrical model for the sake of simplicity.
The initial temperature of the aluminum alloy extruded material is 10°C, and the surface not in contact with the heating die is assumed to contact air at 10°C with a heat transfer coefficient of 45 Wm ^-2 K ^-1 , and heat transfer in the extrusion direction should be considered. First (2D model), the temperature distribution in the plate thickness direction was assumed to be negligibly small. Further, the density ρ of the aluminum alloy extruded material was set at 2790 kgm ⁻³ , the specific heat c at 900 Jkg ⁻¹ K ⁻¹ , and the thermal conductivity λ at 160 Wm ⁻¹ K ⁻¹ .

FIG. 15 shows the simulation results. According to FIG. 15, when the heat transfer coefficient is lower than 1500 Wm ⁻² K ⁻¹ , the time for raising the temperature of the aluminum alloy extruded material to the target temperature (250° C.) increases suddenly. Therefore, in order to raise the temperature of the aluminum alloy extruded material to the target temperature in a short period of time (for example, within 60 seconds (= processing capacity of 60 or more per hour)), a heat transfer coefficient of approximately 1500 Wm ^-2 K ^-1 or more is required. is necessary. According to FIG. 9, when the heating mold is made of steel, a heat transfer coefficient of 1500 Wm ⁻² K ⁻¹ or more is obtained at an average pressure (P/A) of 0.07 MPa or more.

The heating rate of the aluminum alloy extruded material when the aluminum alloy extruded material is sandwiched between the heating molds depends on the contact area (cross-sectional contact length) between the heating mold and the aluminum alloy extruded material and the heat transfer of the contact interface. and the temperature difference between the heating mold and the aluminum alloy extruded material, and inversely proportional to the volume of the aluminum alloy extruded material (part to be heated). That is, the form factor for the rate of temperature increase is volume/contact area, which in turn is cross-sectional area/contact length. An experiment was conducted to measure the cross-sectional area/contact length of the aluminum alloy extruded material and the time required for the aluminum alloy extruded material to reach the target temperature.

The aluminum alloy extruded materials used in the experiment are two aluminum alloy extruded materials having different cross-sectional shapes (cross section A and cross section B), both of which are made of 7000 series aluminum alloy. The aluminum alloy extruded material of cross section A (see FIG. 10) has a cross-sectional area S of about 1300 mm ² , a cross-sectional height of about 53 mm, and contact lengths L ₁ and L ₂ (upper and lower flange widths) with the heating mold. Each is approximately 150 mm. The aluminum alloy extruded material of section B (see FIG. 7) has a cross-sectional area of about 410 mm ² , a cross-sectional height of about 35 mm, and contact lengths L ₁ and L ₂ (upper and lower flange widths) with the heating mold, respectively. It is approximately 37 mm.

The aluminum alloy extruded material was sandwiched between heated upper and lower heating dies, and the time required for the lowest temperature point of the aluminum alloy extruded material to reach the target temperature was measured. The heating mold is made of steel (carbon steel S50C). In addition, No. in Table 4. In 1 and 2, the upper and lower heating dies were brought into contact with the aluminum alloy extruded material. No. In 3, only one heating die was brought into direct contact with the aluminum alloy extruded material, and a heat insulating material was sandwiched between the other heating die and the aluminum alloy extruded material to prevent heat transfer. The lowest temperature point of the aluminum alloy extruded material is No. In No. 1 and 2, the part farthest from the upper and lower heating molds (see the low temperature part b in FIG. 2); 3 is the location farthest from the one heating mold (location near the other heating mold). The average pressure applied from the heating die to the aluminum alloy extruded material was set to 0.4 MPa, the temperature (surface temperature) of the heating die was set to 250°C, and the target temperature of the aluminum alloy extruded material was set to 200°C.
Table 4 shows test conditions and test results. Also, FIG. 16 shows the test results.

As shown in Table 4 and FIG. 16, the larger the cross-sectional area to contact length ratio (S/L) of the aluminum alloy extruded material, the longer it takes to reach the target temperature. According to FIG. 16, in order to heat the aluminum alloy extruded material to the target temperature in a short time (for example, within 60 seconds (= processing capacity of 60 or more per hour)), it is necessary to make S / L ≤ 8 mm. There is

A 7000 series aluminum alloy extruded material having the same cross-sectional shape as the aluminum alloy extruded material used in Example 3 was heated by various methods, and the time required to reach the target temperature (200° C.) was measured.
The heating method was the method according to the present invention (the method of sandwiching between heating molds), an air furnace, and an oil bath. Regarding the method according to the present invention, the heating mold was made of steel (carbon steel S50C), and the time required to reach the target temperature (200°C) was the same as No. 3 in Example 3. 1 was used. The temperature of the air furnace was set at 250°C and the temperature of the oil bath was set at 220°C. In all the methods, the temperature measurement point is the position of the low temperature portion b (the center of the web) shown in FIG.
Table 5 shows the measurement results.

As shown in Table 5, the method of the present invention in which a heating mold is sandwiched can raise the temperature to the target temperature at a higher speed than other heating methods.

The influence of the material of the heating die on the heating rate of the extruded aluminum alloy was investigated.
An aluminum alloy extruded material was sandwiched between a steel (carbon steel S50C) heating mold and an aluminum alloy (A5052) heating mold, and the rate of temperature increase was measured. The aluminum alloy extrusion has a rectangular cross-sectional profile, consists of a pair of flanges and three webs (see FIG. 2), and has a width of about 150 mm, a height of about 50 mm, and a cross-sectional area of about 1200 mm ² . This aluminum alloy extruded material was sandwiched from above and below by heating dies set at a temperature of 250° C. and pressurized at an average pressure (P/A) of 0.3 MPa. The ratio S/L of the cross-sectional area S of the aluminum alloy extruded material and the sum total L (L ₁ +L ₂ ) of the contact length between the aluminum alloy extruded material and the heating mold is 4.00 mm.

The temperature of the aluminum alloy extruded material was measured with a thermoviewer at the position of the low temperature portion b (the center of the web) shown in FIG. Fig. 17 shows the relationship between the temperature of the aluminum alloy extruded material and the heating time during heating.
As shown in FIG. 17, the time required for the aluminum alloy extruded material to reach 100° C. was about 4 seconds when the heating mold was made of steel, and about 2 seconds when it was made of aluminum alloy. The time required for the aluminum alloy extruded material to reach 200° C. was about 20 seconds when the heating mold was made of steel, and about 10 seconds when it was made of aluminum alloy. The temperature rise rate when using an aluminum alloy heating mold is about twice that when using a steel heating mold, and the heating mold is made of a material with high thermal conductivity. , the time required to raise the temperature of the aluminum alloy extruded material can be greatly reduced.

1 Aluminum alloy extruded material 2, 3 Heating mold 4, 5 Flange 6, 7, 8 Web

Claims (6)

After raising the temperature of the aluminum alloy extruded material with a hollow cross section to reach a temperature within a predetermined temperature range, plastic working is performed within the temperature range, then after cooling, artificial aging treatment is performed. In the manufacturing method, the aluminum alloy extruded material is a heat-treated aluminum alloy extruded material T1 tempered material, the temperature range is 150 to 300 ° C., and the aluminum alloy extruded material is heated to 200 to 350 ° C. A method of manufacturing an aluminum alloy member, comprising: sandwiching between upper and lower heating dies; 2. The method of manufacturing an aluminum alloy member according to claim 1, wherein the aluminum alloy is a 7000 series aluminum alloy. The load applied from the heating die to the aluminum alloy extruded material when the temperature of the aluminum alloy extruded material is raised is P (unit: N), and the upper and lower contact between the aluminum alloy extruded material and the heating die 3. The method for manufacturing an aluminum alloy member according to claim 1, wherein a relationship of P/A≧0.07 MPa is satisfied, where A (unit: m ² ) is the projected area of the portion. In the cross section of the aluminum alloy extruded material, the sum of the contact lengths at the upper and lower contact points between the aluminum alloy extruded material and the heating mold is L (unit: mm), and the cross-sectional area of the aluminum alloy extruded material is 4. The method for manufacturing an aluminum alloy member according to any one of claims 1 to 3, wherein S (unit: mm ² ) satisfies the relationship S/L≦8 mm. The method for manufacturing an aluminum alloy member according to any one of claims 1 to 4, wherein the heating mold is made of steel, aluminum or copper. The method for producing an aluminum alloy member according to any one of claims 1 to 5, wherein the aluminum alloy member is an energy absorbing part or an automobile frame part.

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