JP6688828B2 - Aluminum alloy plate for automobile structural member, automobile structural member and method for manufacturing aluminum alloy plate for automobile structural member - Google Patents

Description

TECHNICAL FIELD The present invention relates to an Al—Mg—Si (6000 series) aluminum alloy plate produced by ordinary rolling, and particularly to an aluminum alloy plate for automobile structural members having excellent crushability.
The aluminum alloy plate referred to in the present invention is a rolled plate that has been hot-rolled or cold-rolled, and after being subjected to tempering such as solution treatment and quenching treatment, the automobile structural member used. It is a material aluminum alloy plate that has not yet been molded into an artificial age hardening treatment such as paint bake hardening treatment. Further, in the following description, aluminum is also referred to as “aluminum” or “Al”.

  In recent years, due to consideration for the global environment and the like, social demand for weight reduction of automobile bodies has been increasing more and more. In order to meet such demands, parts of automobile bodies such as panels (hoods, doors, outer panels such as roofs and inner panels), bumper reinforcements (bumper R / F), reinforcements such as door beams, etc. Aluminum alloy materials are used instead of steel materials such as steel plates.

  In order to further reduce the weight of automobile bodies, aluminum alloy materials are also applied to members such as side members, frames, and automobile structural members such as pillars, which contribute particularly to weight reduction among automobile members. Is required to do. These automobile structural members include a shock absorbing property at the time of a vehicle body collision and a crushing property (a pressure crushing property or a pressure crushing property) for the purpose of occupant safety while maintaining the strength and formability of the same material plate as the above-mentioned automobile panel material. It is necessary to use an aluminum alloy material having excellent crushing properties).

  As a test for measuring the crushability, there is, for example, "VDA238-100 Plate bending test for metallic materials" (hereinafter referred to as "VDA bending test") standardized by German Automobile Manufacturers Association (VDA). In recent years, in Europe and other countries, in order to respond to the improvement (stricter) of automobile collision safety standards, evaluation by VDA bending test has been carried out, and automobile structural members such as frames and pillars having superior crushing properties have been developed. It has been demanded.

  As a means for improving the crushability of a 6000 series aluminum alloy for automobile structural members, conventionally, a method of controlling the size and morphology of crystal grains and the area ratio of Cube orientation has been known. A 6000-series aluminum alloy plate is disclosed in which the diameter is defined and the ratio between the grain size in the plate thickness direction and the grain size in the rolling direction is controlled (see Patent Document 1).

  Further, a 6000 series aluminum alloy plate in which the average area ratio of the Cube orientation of the plate cross section is 22% or more is also proposed by adjusting the addition amounts of Mg, Si and Cu (see Patent Document 2). In addition, in the above-mentioned Patent Document 2 for the purpose of improving the crushability, it is described that the VDA bending test as an evaluation test of the crushability of the plate has a correlation with the crushability at the time of an automobile collision. The bending angle obtained by the VDA bending test can quantitatively evaluate the superiority or inferiority of the crushability.

JP, 2001-294965, A JP, 2017-88906, A

  However, the formability and crushability of the aluminum alloy sheet, and the strength and crushability are all in a trade-off relationship. To do. Further, if the strength is increased by adjusting the metal content in the aluminum alloy, there is a problem that the crushability is lowered. As described above, safety standards for automobiles and the like are becoming stricter year by year, and there is a demand for an aluminum alloy plate having characteristics such that safety becomes higher. Therefore, development of an aluminum alloy sheet having more excellent crushability without lowering strength and formability is expected.

  Further, in the structural member of automobile, in addition to strength, formability and crushability, from the viewpoint of reliability as a structural member, corrosion resistance corresponding to a corrosive environment such as salt water is also required. That is, a structural member using an aluminum alloy is required to have excellent corrosion resistance such that intergranular corrosion does not occur for a long period of time.

  In view of such a situation, an object of the present invention is a 6000 series aluminum alloy plate manufactured by ordinary rolling, and the strength, formability, crushability and corrosion resistance of the material plate are excellent in a well-balanced manner. The object is to obtain an aluminum alloy plate for a member, an automobile structural member, and a method for manufacturing an aluminum alloy plate for an automobile structural member.

  As a result of repeated studies by the present inventors to solve the above problems, the chemical composition of the aluminum alloy is appropriately adjusted, and the anisotropy of the texture of the aluminum alloy is defined by the ear ratio, and this value is set to a predetermined value. It has been found that an aluminum alloy sheet having a good balance of strength, formability, crushability and corrosion resistance can be obtained by limiting the range.

That is, the aluminum alloy plate for automobile structural members according to the present invention is, in mass%, Mg: 0.4% or more and 1.0% or less, Si: 0.6% or more and 1.2% or less, Cu: 0.5. % contained the following, the remainder Ri is Do of Al and unavoidable impurities, the plate thickness is an Al-Mg-Si based aluminum alloy sheet Ru der than 1.5 mm, the ear rate -10.0% ~ - 3.0% der is, after performing artificial aging treatment for 20 minutes at a temperature of 180 ° C., and having a bake hardenability as a 0.2% yield strength of more than 215 MPa, VDA bending test at more than 93 ° have a crush resistance of the bending angle characterized Rukoto.

In the aluminum alloy plate for automobile structural member according to a preferred embodiment of the present invention, the content of Mg is 0.4% or more and 0.6% or less by mass%.
In the aluminum alloy plate for automobile structural member according to a preferred embodiment of the present invention, the content of Si is 0.6% or more and 0.8% or less by mass%.
The aluminum alloy plate for automobile structural members according to a preferred embodiment of the present invention has a bake hard property that the 0.2% proof stress becomes 215 MPa or more after performing the artificial aging treatment at a temperature of 180 ° C. for 20 minutes.

  The automobile structural member according to the present invention is characterized by using any one of the above-mentioned aluminum alloy plates for automobile structural members.

Moreover, the manufacturing method of the aluminum alloy plate for automobile structural members which concerns on this invention is Mg: 0.4% or more and 1.0% or less, Si: 0.6% or more and 1.2% or less, Cu: A step of casting an aluminum alloy containing 0.5% or less and the balance consisting of Al and unavoidable impurities, a step of homogenizing heat treatment, a step of hot rolling, and a final plate thickness of 1.5 mm or more Thus, in the method of manufacturing an Al-Mg-Si-based aluminum alloy sheet, which includes a step of cold rolling, an annealing step, a solution treatment step, and a quenching step, in the cold rolling step. The rolling ratio is controlled to 40% or higher, the heat treatment temperature in the annealing step is set to 275 ° C. or higher, and the ear ratio of the aluminum alloy plate is −10.0% to −3.0%, and the temperature of 180 ° C. When artificial for 20 minutes at temperature After carrying out the effect treatment, it is characterized in that the 0.2% proof stress has a bake hard property of 215 MPa or more and a crushing property of a bending angle of 93 ° or more in the VDA bending test .

According to the present invention, by appropriately adjusting the chemical composition of the aluminum alloy and imparting anisotropy of the texture of the aluminum alloy, an automobile structural member having excellent balance of strength, formability, crushability and corrosion resistance. An aluminum alloy plate for use can be provided.
Further, by adjusting the chemical composition of the aluminum alloy, and by adjusting the cold rolling rate in the manufacturing process and the heat treatment temperature during annealing, an aluminum alloy for automobile structural members excellent in strength, formability, crushability and corrosion resistance. A plate and an automobile structural member using the aluminum alloy plate can be manufactured.

It is a perspective view which shows the aspect of the VDA bending test which evaluates crushability. It is a front view of the punch in FIG. It is a side view of the punch in FIG.

Hereinafter, the reasons for limiting the chemical composition and ear ratio of the aluminum alloy plate for automobile structural members according to the embodiment of the present invention (this embodiment) and the reasons for limiting numerical values in the method for manufacturing the aluminum alloy plate for automobile structural members will be described in detail. explain.
As a premise, the Al-Mg-Si (hereinafter also referred to as "6000") aluminum alloy plate of the present invention is used for the above-mentioned automobile structural member rather than the conventional automobile panel material.
Therefore, this automobile structural member (hereinafter, also referred to as "structural member") has the same moldability as that of the conventional automobile panel material described above, and also has excellent crushability which is a characteristic peculiar to the use of automobile structural members, and It is required to have high yield strength even after artificial aging. If any of these characteristics is lacking, it will be insufficient as a structural member targeted by the present embodiment.

Therefore, the following description of the requirements of the present embodiment is made for these structural members, and is significant in order to satisfy and satisfy specific required characteristics.
In addition, in this embodiment, "-" means that it is more than the lower limit value and less than the upper limit value.

(Chemical composition of aluminum alloy plate)
In order to satisfy the required characteristics of the structural member in terms of chemical composition, the Al-Mg-Si-based aluminum alloy plate according to the present embodiment has a mass% of Mg: 0.4% or more and 1.0% or more. Hereinafter, Si: 0.6% or more and 1.2% or less, Cu: less than 0.7% are contained, and the balance is made of Al and impurities.

  The range and meaning of the content of each element in the Al-Mg-Si based aluminum alloy or the permissible amount will be described below. In addition, all percentages of the content of each element mean% by mass.

<Mg: 0.4% or more and 1.0% or less>
Mg, together with Si, forms and precipitates a compound phase such as Mg ₂ Si during artificial aging treatment such as baking coating treatment. Therefore, by appropriately adjusting the content of Mg, the strength of the aluminum alloy plate is enhanced. You can
When the content of Mg is less than 0.4%, it becomes difficult to obtain sufficient strength as a structural member.
On the other hand, when the content of Mg exceeds 1.0%, the compound phase such as Mg ₂ Si crystallizes or precipitates as coarse particles during casting and solution hardening, and these act as starting points for minute fracture. Since it works, the crushability is reduced. The content of Mg is preferably 0.8% or less, more preferably 0.6% or less.

In the present specification, the "strength of the aluminum alloy plate" can be evaluated by the measured value (MPa) of 0.2% proof stress of the solution treated and quenched aluminum alloy plate (before artificial aging). .
Moreover, a prestrain of 2% or more is applied to this aluminum alloy plate, and the 0.2% proof stress of the aluminum alloy plate (after artificial aging) after artificial aging treatment at a temperature of 180 ° C. for 20 minutes. It can be evaluated by the measured value.
The higher the 0.2% proof stress, the higher the strength and the higher the bake hardness (BH property).

<Si: 0.6% or more and 1.2% or less>
Since Si also forms a compound phase such as Mg ₂ Si and precipitates during artificial aging treatment such as baking coating treatment together with Mg, the strength of the aluminum alloy plate should be increased by appropriately adjusting the Si content. You can
If the Si content is less than 0.6%, it becomes difficult to obtain sufficient strength as a structural member. The Si content is preferably 0.7% or more, more preferably 0.8% or more.
On the other hand, when the Si content exceeds 1.2%, the compound phase such as Mg ₂ Si crystallizes or precipitates as coarse particles during casting and solution hardening treatment, and these serve as starting points for minute fracture. Since it works, the crushability is reduced. The Si content is preferably 1.1% or less, more preferably 1.0% or less, still more preferably 0.8% or less.

<Cu: less than 0.7%>
When Cu is contained in excess of 0.7% or more, a solute-deficient layer of Cu (also referred to as a precipitation free zone or PFZ) is formed in the vicinity of the grain boundary together with aging precipitation, and in a corrosive environment, the potential is higher than in the grain The base layer is selectively dissolved and the intergranular corrosion resistance (corrosion resistance) deteriorates.
Therefore, the Cu content is less than 0.7%. The Cu content is preferably 0.5% or less, more preferably 0.3% or less. There is no lower limit of the Cu content, and the case of 0% is included.

<Other elements>
Other elements other than the above (elements shown below, etc.) are basically impurities in the present embodiment. The upper limit of the content of each of the following is the allowable amount when the material is contained in the ingot as a raw material for melting, such as scrap. It should be noted that there is no lower limit for each content, including the case of 0%.
Mn: 1.0% or less, Fe: 0.5% or less, Cr: 0.3% or less, Zr: 0.2% or less, V: 0.2% or less, Ti: 0.1% or less, Zn: 0.5% or less, Ag: 0.1% or less, Sn: 0.15% or less And, if it is within this range, not only when it is contained as an unavoidable impurity but also when it is positively added. Even if there is, it does not hinder the effect of the present invention.

(Aluminum alloy plate thickness: 1.5 mm or more)
The lower limit of the plate thickness of the Al-Mg-Si-based aluminum alloy plate of the present embodiment is not particularly limited, but the plate thickness is, for example, 1.5 mm or more in order to have strength and rigidity required as an automobile structural member. Is. Also, the upper limit of the plate thickness is not particularly limited, but considering the limit of forming such as press forming and the range of weight increase without impairing the weight reduction effect from the steel sheet as a comparative material, for example, it is 4.0 mm or less. is there. A hot rolled plate or a cold rolled plate is appropriately selected from the range of the plate thickness.

(Ear rate: -10.0% to -3.0%)
The ear rate of the aluminum alloy plate shows anisotropy of the texture, and has a strong correlation with the degree of integration of the Cube orientation. When the ear rate exceeds −3.0%, the degree of integration of the Cube orientation of the Al alloy plate is weak, and the shear band during bending deformation during crushing is not suppressed, so the crushability decreases.
On the other hand, when the ear rate is less than -10.0%, the degree of integration of the Cube orientation of the Al alloy plate is too strong and the strain is concentrated in the Cube orientation, resulting in a decrease in elongation at break, that is, a decrease in formability.

<Measurement method of ear ratio>
A disc-shaped test piece (blank) having an outer diameter of 66 mm is punched from the test plate, and the test piece is cupped using a punch having a diameter of 40 mm to produce a squeeze cup having a cup diameter of 40 mm. By measuring the ear height of this squeezing cup, the ear ratio (%) can be calculated based on the following formula (1).
In the following formula (1), hX represents the ear height of the squeeze cup. The subscript X of h indicates the measurement position of the cup height, which means the position forming an angle of X ° with the rolling direction of the Al alloy plate.
Ear rate (%) = [{(h45 + h135 + h225 + h315)-(h0 + h90 + h180 + h270)} / {1/2 (h0 + h90 + h180 + h270 + h45 + h135 + h225 + h315)}] × 100 ... (1)
In addition, as an explanation of the significance of the above equation (1), the following equation (2) can be used.
Ear ratio (%) = {(average value of heights at 45 locations in 45 ° direction based on bottom surface of cylindrical container (rolling direction) −4 locations in 0 ° and 90 ° directions based on bottom surface of cylindrical container) Height average value) / (average height value at 8 positions in 0 °, 45 °, 90 ° direction based on the bottom surface of the cylindrical container)} × 100 ... (2)

(Crushability)
Crushability is the characteristic that when an impact load such as a car collision is applied, the structural members do not crack or collapse (or even if they occur) at the initial stage or on the way of deformation, and they deform to the end. However, a member having good crushability bends and deforms into a bellows shape without (or even if) cracking or crushing.
As described above, if the Mg content and the Si content in the aluminum alloy exceed the upper limits of the ranges of the present embodiment, the crushability decreases. The crushability can be evaluated by the VDA bending test shown below, and the bending angle is preferably 93 ° or more, more preferably 100 ° or more, further preferably 105 ° or more, and 110 ° or more. Even more preferable.
In this embodiment, those having a crushing property with a bending angle of 93 ° or more are evaluated as acceptable for automobile structural members. On the other hand, the crushability of the bending angle of less than 93 ° is insufficient for automobile structural members.

The bending test for evaluating the crushability is performed according to the VDA bending test, which is a standard of the German Automobile Manufacturers Association (VDA).
This test method is shown in a perspective view in FIG. 1, and in FIGS. 2A and 2B, a front view and a side view of a punch 3 which is a plate-shaped pressing and bending jig are respectively shown.
First, as shown by a dotted line in FIG. 1, the plate-shaped test piece 1 is horizontally placed on two rolls 2 provided with a roll gap L and arranged in parallel to each other, at positions which are even with respect to the left and right sides of the roll 2. Place on.
Next, the punch 3, which is a plate-shaped pressing and bending jig, is placed above the plate-shaped test piece 1 so as to stand vertically to the test piece 1. Specifically, the punch 3 is placed such that the side of the tip thereof is located at the center of the roll gap L, and the rolling direction of the plate-shaped test piece 1 and the extending direction of the plate-shaped punch 3 are orthogonal to each other. The roll 2, the test piece 1, and the punch 3 are placed so that they are oriented in the same direction.
Then, the punch 3 is pressed against the central portion of the plate-shaped test piece 1 from above to apply a load F, and the plate-shaped test piece 1 is pushed and bent toward the narrow roll gap L (bending) to bend and deform. The central portion of the plate-shaped test piece is pushed into the narrow roll gap.

  At this time, the bending outside angle of the central portion of the plate-shaped test piece 1 when the load F from the punch 3 from above is the maximum is measured as the bending angle (°), and the bending angle is Assess crushability. That is, the larger the bending angle, the more the plate-shaped test piece continues to be bent and deformed without being crushed, and it can be determined that the crushability is high.

As the test conditions of this VDA bending test, the plate-shaped test piece 1 had a plate thickness of 2.0 mm, and had a square shape with one side length b: 60 mm × the other piece length 1: 60 mm, and two pieces. The diameter D of each roll 2 was 30 mm, and the roll gap L was 4.0 mm, which was 2.0 times the plate thickness of the plate-shaped test piece 1. S is the pushing depth into the roll gap of the central portion of the plate-shaped test piece when the load F becomes maximum.
As shown in FIG. 2B, the punch 3 has a side length of 90 mm in contact with the test piece 1, and the lower end side (pointed portion) in contact with the central portion of the plate-shaped test piece 1 is a front view thereof. As shown by, the taper is sharp so that the radius r becomes 0.2 mmφ.
On the side opposite to the apex of the punch 3, two recesses having a width of 9 mm and a depth of 12 mm are formed, and these recesses are fitted to an overload device (not shown). The punch 3 is configured to apply a load to the test piece 1.

(Strength)
The aluminum alloy plate according to the present embodiment, after applying a pre-strain of 2% or more to the solution-treated and hardened aluminum alloy plate, after artificial aging treatment for 20 minutes at a temperature of 180 ° C., The 0.2% proof stress (bake hard property or BH property) is preferably 215 MPa or more.
When the 0.2% proof stress is 215 MPa or more, the strength required as an alloy plate for automobile structural members can be secured. The 0.2% proof stress can be controlled not only by the content of the aluminum alloy described above, but also by the thermal history and the rolling reduction of each step among the steps of the manufacturing method described later.

(Moldability)
As will be described later, if the rolling ratio of the cold rolling in the method for manufacturing an aluminum alloy sheet according to this embodiment is less than the lower limit of the range of this embodiment, the formability decreases. The formability can be evaluated by the breaking elongation shown in Examples described later, and it is preferable that the breaking elongation is 25% or more.
In the present embodiment, those having a formability of 25% or more at break are evaluated as acceptable for automobile structural members. On the other hand, if the elongation at break is less than 25%, the moldability is insufficient for automobile structural members.

(Method of manufacturing aluminum alloy plate for automobile structural member)
Next, a method for manufacturing the aluminum alloy plate of this embodiment will be described below.
The method for manufacturing an aluminum alloy plate for an automobile structural member according to the present embodiment includes a step of casting an aluminum alloy having the above chemical composition, a step of homogenizing heat treatment, a step of hot rolling, and a step of cold rolling. A method of manufacturing an Al-Mg-Si-based aluminum alloy sheet having an annealing step, a solution treatment step, and a quenching step, wherein a rolling rate in the cold rolling step is controlled to 40% or more. The heat treatment temperature in the annealing step is set to 275 ° C or higher.

  In these manufacturing processes, the earring ratio specified in the present embodiment can be obtained by appropriately adjusting the rolling rate of cold rolling and the temperature of annealing treatment within the above numerical range. Hereinafter, each step will be described in more detail.

<Melting and casting>
First, in the melting and casting process, an ordinary molten casting method such as a continuous casting method or a semi-continuous casting method (DC casting method) is appropriately selected for the aluminum alloy molten metal whose melting is adjusted within the range of the chemical composition of the above 6000 series. And cast.

<Homogenized heat treatment>
Next, the cast aluminum alloy ingot is subjected to a homogenizing heat treatment prior to hot rolling. This homogenization heat treatment (soaking heat treatment) is important in order to homogenize the structure (eliminate segregation in the crystal grains in the ingot structure), which is the usual purpose, and to sufficiently dissolve Si and Mg. Is. There is no particular limitation as long as it is a condition that achieves this purpose, and ordinary one-time treatment or one-stage treatment may be used.

  The homogenizing heat treatment temperature is preferably 500 ° C. or higher and 560 ° C. or lower, and the homogenizing (holding) time is preferably appropriately selected from the range of 1 hour or more. If the homogenization temperature is low, segregation in the crystal grains cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that the crushability may decrease.

<Hot rolling>
The hot rolling of the ingot subjected to the homogenizing heat treatment includes a rough rolling step of the ingot (slab) and a finish rolling step according to the plate thickness to be rolled. In these rough rolling process and finish rolling process, a reverse type or tandem type rolling mill is appropriately used.

≪Rough rolling process≫
In the hot rough rolling step, at a rolling temperature at which the hot rolling start temperature exceeds the solidus temperature, burning may occur, which makes hot rolling itself difficult. If the hot rolling start temperature is lower than 350 ° C, the load during hot rolling becomes too high for any soaking process material, and hot rolling itself may be difficult. Therefore, the hot rolling start temperature is selected from the range of 350 ° C. to the solidus temperature and hot rolled to obtain a hot rolled plate having a plate thickness of about 2 to 8 mm. Annealing (roughening) of the hot rolled sheet before cold rolling is not always necessary, but may be performed.

≪Hot finish rolling≫
After the hot rough rolling, the hot finish rolling is preferably performed with the end temperature in the range of 250 to 350 ° C. If the end temperature of this hot finish rolling is too low, that is, less than 250 ° C., the rolling load becomes high and the productivity may decrease. On the other hand, when the finish temperature of hot finish rolling is increased in order to form a recrystallized structure without leaving a large amount of processed structure, if this temperature exceeds 350 ° C, Mg ₂ Si coarsely precipitates and the crushing property decreases. There is a possibility that it will increase.
Annealing (roughening) of this hot rolled sheet before cold rolling is not necessary, but may be carried out.

<Cold rolling>
In the step of cold rolling the hot-rolled sheet to a desired sheet thickness, if the cold rolling rate is increased, uniform strain can be introduced in the sheet thickness direction, and uniform fine and equiaxed crystal grains can be obtained during solution heat treatment. can get. That is, by setting the cold rolling rate to 40% or more, it is possible to give the anisotropy of the texture capable of achieving both the crushability and the formability. This makes it possible to obtain an aluminum alloy plate having an ear ratio of -10.0% or more.
On the other hand, when the rolling ratio of cold rolling is less than 40%, almost no strain is introduced by cold rolling, the processed structure of hot rolling remains, and the earring becomes less than -10.0%. As a result, the crushability of the obtained aluminum alloy plate is improved, but the formability is significantly deteriorated. Therefore, the rolling rate of cold rolling is 40% or more.
The rolling rate of cold rolling is preferably 60% or more.

<Annealing treatment>
By performing the annealing treatment at a temperature of 275 ° C. or higher, it is possible to preferentially grow the nuclei of the Cube orientation remaining after the cold rolling without coarsening, and the aluminum alloy plate having the ear ratio of −3.0% or less. Can be obtained. As a result, it is possible to obtain high crushability in addition to excellent moldability equivalent to that in the past. When the annealing temperature is lower than 275 ° C., the temperature is lower than the recrystallization temperature, recrystallization does not occur at the time of annealing, the earing ratio exceeds −3.0%, and the moldability is good, but the crushability is remarkably lowered.
The annealing temperature is preferably 300 ° C or higher.
The temperature rising rate of the annealing treatment is preferably 1 to 500 ° C./h. If the rate of temperature increase is less than 1 ° C./h, the crystal grain size becomes coarse and the crushability tends to decrease. When the rate of temperature increase is higher than 500 ° C./h, the nuclei of Cube are small, the area ratio of the Cube orientation becomes low after the solution treatment, and the crushability is likely to decrease.

<Solution treatment and quenching treatment>
After cold rolling, solution treatment and subsequent quenching treatment up to room temperature are performed. A normal continuous heat treatment line may be used for this solution hardening treatment. However, in order to obtain a sufficient solid solution amount of each element such as Mg and Si, after solution treatment at a temperature of 500 ° C. or higher and a melting temperature or lower, the average cooling rate to room temperature is set to 20 ° C./sec or higher. Preferably. At a temperature lower than 500 ° C., the re-solid solution of the compound such as the Mg—Si system which has been formed before the solution treatment becomes insufficient and the solid solution Mg amount and the solid solution Si amount decrease.

  Further, when the average cooling rate is less than 20 ° C./sec, Mg-Si based precipitates are mainly generated during cooling to reduce the amount of solid solution Mg and the amount of solid solution Si. There is a high possibility that the quantity cannot be secured. In order to secure this cooling rate, in the quenching treatment, air cooling such as a fan, water cooling means such as mist, spraying, dipping and the like are selected and used. After such solution treatment, a pre-aging treatment may be appropriately performed.

(Automotive structural member)
The present embodiment also relates to an automobile structural member using the aluminum alloy plate described above. The aluminum alloy plate according to the present embodiment has a well-balanced strength, formability, and crushing property of the material plate, and thus has a higher level of safety when used as an automobile structural member.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples as well as the present invention, and may be appropriately modified within a range compatible with the gist of the preceding and the following. It is also possible to carry out, and all of them are included in the technical scope of the present invention.

6000 series aluminum alloy ingots of each chemical composition shown in Table 1 were prepared, aluminum alloy plates for automobile structural members were manufactured under various manufacturing conditions shown in Table 2, and the ear ratio was measured.
Further, by measuring the 0.2% proof stress (MPa) before and after the artificial aging treatment, the elongation at break (%), and the VDA bending angle (°) after the artificial aging on the obtained aluminum alloy plate, respectively, The strength, formability and crushability of the aluminum alloy plate were evaluated. These results are also shown in Table 2.

<Production of aluminum alloy plate>
First, the manufacturing conditions will be described in detail. An aluminum alloy having the chemical composition shown in Table 1 was melt cast, and the obtained ingot was homogenized under the condition of holding the temperature of 540 ° C. for 4 hours. Then, hot rolling was performed so that the end temperature was 250 ° C to 350 ° C. Further, cold rolling was performed at each rolling rate shown in Table 2 so that the final plate thickness was 2.0 mm, to obtain a cold rolled plate.
The cold rolled sheet was subjected to an annealing treatment in which the temperature was raised at 30 ° C./h in an air furnace, the annealing temperature shown in Table 2 was maintained for 4 hours, and then the temperature was lowered at 40 ° C./h. However, in Comparative Example 1, the annealing treatment was not performed.
Then, under the following common conditions, a heat treatment equipment was subjected to a tempering treatment (T4 treatment). Specifically, the plate after the annealing is heated at an average heating rate up to the solution treatment temperature of 5 ° C./sec, and the solution is subjected to the solution treatment by holding it at a temperature of 525 ° C. for 28 seconds, and then average cooling. It was cooled to room temperature by performing fan air cooling at a speed of 20 ° C./sec. Immediately after this cooling, a pre-aging treatment was carried out immediately under the condition of holding at 80 ° C. for 5 hours, and after the pre-aging treatment, it was gradually cooled (cooled) to obtain an aluminum alloy plate (T4 material).

<Measurement of ear ratio>
A test plate was sampled from the obtained aluminum alloy plate, and the ear ratio was measured by the method described below. A disc-shaped test piece having an outer diameter of 66 mm was punched out from the test plate, and the test piece was cupped using a punch having a diameter of 40 mm to produce a squeeze cup having a cup diameter of 40 mm. The ear height of this squeezing cup was measured, and the ear ratio (%) was calculated by the above formula (1).

<Evaluation of strength: 0.2% proof stress measurement>
A JIS13A tensile test piece (20 mm × 80 mm GL × 2.0 mm) is taken from each of the test plates, and a tensile test is performed at room temperature under the following conditions. The 0.2% proof stress was measured. First, two sets of test materials after the preliminary aging treatment were prepared, and one of them was not subjected to the additional heat treatment and was used for the measurement of 0.2% proof stress. On the other hand, while applying a pre-strain of 2% or more and performing artificial aging treatment at a temperature of 180 ° C. for 20 minutes, 0.2% proof stress was measured.

  In the tensile test, the tensile direction of the test piece was the direction orthogonal to the rolling direction. The tensile speed was 5 mm / min up to 0.2% proof stress, and 20 mm / min after proof stress. Further, the number of measurements was set to 5 and the average value was calculated for each. If the measurement result of the 0.2% proof stress after the artificial aging treatment was 215 MPa or more, it was judged that the structure had sufficient strength for automobile structural members, and was evaluated as acceptable.

<Evaluation of formability: measurement of elongation at break>
A JIS 13A tensile test piece (20 mm × 80 mm GL × 2.0 mm) was sampled from each of the test plates, and a tensile test was performed at room temperature under the following conditions. In the tensile test, a tensile tester was used to pull the test piece at a speed of 5 mm / min, and the elongation when the test piece was cut (broken) was measured.
The tensile direction of the test piece was 3 directions of 0 ° direction, 45 ° direction, and 90 ° direction with respect to the rolling direction, and the number of measurements was 5, and the average value of the values calculated by the following formula (3) was calculated as the breaking elongation. And In the following formula (3), Lo is the distance between the gauge points before the tensile test, and L is the distance between the gauge points at break.
Elongation at break (%) = 100 × (L−Lo) / Lo ... (3)
If the breaking elongation was 25% or more, it was determined that the material had sufficient formability for automobile structural members, and was evaluated as acceptable.

<Evaluation of crushability: measurement of VDA bending angle>
A pre-strain of 2% or more was applied to the test plate after the pretreatment, and artificial aging treatment was performed at a temperature of 180 ° C. for 20 minutes to obtain a plate thickness of 2.0 mm and a width b of 60 mm. A square test piece having a length 1 of 60 mm was collected and evaluated for crushability by a VDA bending test.
The VDA bending test was based on VDA238-100, and was a three-point bending test in which the bending line was parallel to the rolling direction. The test speed until the load reached 30 N was 10 mm / min, and the test speed thereafter was 20 mm / min. Bending was set to stop when the load decreased by 60 N from the maximum load due to cracking or reduction in plate thickness.
The bending test was carried out on three test pieces, and the average value of them was adopted as the bending angle (°).
If the bending angle was 93 ° or more, it was determined that the material had sufficient crushability for automobile structural members, and was evaluated as acceptable.

Table 2 shows the evaluation results of strength, moldability and crushability. In Table 2, the content of each component, the manufacturing conditions of the aluminum alloy plate, and the material structure that do not satisfy the scope of the present invention are indicated by underlining the numerical values.
Similarly, in the evaluation results of strength, moldability, and crushability, those that could not be evaluated as acceptable for automobile structural members are indicated by underlining the values.

As is clear from Table 2, Examples 1 to 9 are those in which the chemical composition of the aluminum alloy is within the scope of the present invention and the aluminum alloy was manufactured under the conditions specified in the present invention.
That is, in Examples 1 to 9, the chemical composition of the aluminum alloy is% by mass, Mg: 0.4% or more and 1.0% or less, Si: 0.6% or more and 1.2% or less, and the ear rate is -10. Since the content is 0.0% to −3.0%, an aluminum alloy sheet having a good balance of strength, formability, and crushability could be obtained.

In addition, comparison is made between Example 2 (Mg: 0.4%), Example 8 (Mg: 0.6%), and Example 9 (Mg: 1.0%), in which conditions other than the Mg content are common. In this case, it can be read that the crushing property is particularly excellent when the Mg content is 0.4% or more and 0.6%.
In addition, Example 5 (Si: 0.6%), Example 6 (Si: 0.8%), Example 2 (Si: 1.0%), and implementation in which conditions other than the Si content are common When compared in Example 7 (Si: 1.2%), it can be read that the crushability is particularly excellent when the Si content is 0.6% or more and 0.8%.

  On the other hand, in Comparative Examples 1 to 10, although the chemical composition of the aluminum alloy deviates from the scope of the present invention or the chemical composition is within the scope of the present invention, the rolling ratio of cold rolling or the annealing temperature is the same as that of the present invention. Out of range. As a result, either the 0.2% proof stress or the crush resistance after the artificial aging treatment was poor.

More specifically, since Comparative Example 1 was not subjected to the annealing treatment, the ear ratio was out of the range of the present invention, and the crushability was lowered. Further, in Comparative Examples 2 and 3, since the annealing temperature was less than the range specified in the present invention, the ear rate was out of the range of the present invention, and the crushability was lowered.
In Comparative Examples 4 to 6, since the rolling ratio during cold rolling was less than the range specified in the present invention, the selvage ratio was out of the range of the present invention, and the formability was lowered.
In Comparative Example 7, the Si content in the aluminum alloy was less than the range specified by the present invention, so the strength was low.
In Comparative Example 8, since the Si content in the aluminum alloy exceeds the range specified by the present invention, the crushability was low.
In Comparative Example 9, the content of Mg in the aluminum alloy was less than the range specified in the present invention, so the strength was low.
In Comparative Example 10, the Mg content in the aluminum alloy exceeded the range specified in the present invention, and thus the crushability was low.

  Subsequently, aluminum alloy ingots of alloy numbers 1 and 11 shown in Table 1 were prepared, and the rolling ratio of the cold rolling rate and the annealing temperature were the same as those shown in Table 3, and the other manufacturing conditions were as described above. Under the conditions described in <Fabrication of Aluminum Alloy Plate>, an aluminum alloy plate for automobile structural members was manufactured and the intergranular corrosion resistance (corrosion resistance) was evaluated.

<Evaluation of intergranular corrosion resistance>
The evaluation test of the intergranular corrosion resistance was based on ISO11846 Method B. The test material is each test material plate after solution treatment, and in order to remove the surface film, it is immersed in 5% NaOH (60 ° C.) for 1 minute, washed with water, and immersed in 70% HNO ₃ for 1 minute. It was washed again with water and dried at room temperature.
An aqueous solution containing HCl and NaCl (containing 30 g / L of NaCl and 10 ± 1 mL / L of 36% concentrated hydrochloric acid) was prepared as a corrosive solution, and corrosion was performed at 25 ° C. for 24 hours at 5 ml per 1 cm ² of surface area of the material. The test material was immersed in the liquid. Then, the corrosion product was removed by immersion in 70% HNO ₃ and brushing with a plastic brush, followed by washing with water and drying at room temperature.
Subsequently, by the depth of focus method, three sites (30 mm × 50 mm each) that are judged to be deeply corroded in the above-mentioned test material are arbitrarily selected, and each site is embedded in a cross section, and each cross section is observed with an optical microscope. The deepest intergranular corrosion depth was measured. In this test example, a sample having a maximum intergranular corrosion depth of 300 μm or less was evaluated as acceptable.

Table 3 shows the evaluation results of the intergranular corrosion resistance. In Table 3, the content of each component that does not satisfy the range of the present invention is indicated by underlining the numerical value.
Similarly, in the evaluation results of the intergranular corrosion resistance, those that could not be evaluated as acceptable are shown by underlining the values.

As shown in Table 3, since the Cu content in the aluminum alloy was within the range specified by the present invention, Example 1 was excellent in intergranular corrosion resistance.
On the other hand, Comparative Example 11 was inferior in intergranular corrosion resistance because the Cu content in the aluminum alloy exceeded the range specified in the present invention.

  From the results of the above Examples and Comparative Examples, it is understood that the aluminum alloy plate satisfying all the chemical compositions and structures defined in the present invention is suitable for automobile structural members.

  According to the present invention, a 6000 series aluminum alloy sheet produced by ordinary rolling can have both formability and corrosion resistance in addition to excellent crushability and strength, which are characteristics peculiar to automobile structural member applications. Therefore, the application of the 6000 series aluminum alloy plate can be expanded as an automobile structural member.

1 Plate test piece 2 Roll 3 Punch

Claims (7)

% By mass, containing Mg: 0.4% or more and 1.0% or less, Si: 0.6% or more and 1.2% or less, Cu: 0.5% or less , and the balance of Al and unavoidable impurities. Ri, thickness is a Al-Mg-Si based aluminum alloy sheet Ru der least 1.5 mm,
Ear rate Ri -10.0% - - 3.0% der,
After being subjected to artificial aging treatment at a temperature of 180 ° C. for 20 minutes, it has a bake hard property with a 0.2% proof stress of 215 MPa or more, and
Automobile structural member for an aluminum alloy sheet, wherein Rukoto at VDA bending test have a crush resistance which is a 93 ° or more bending angle. Further, in mass%, Mn: 1.0% or less, Fe: 0.5% or less, Cr: 0.3% or less, Zr: 0.2% or less, V: 0.2% or less, Ti: 0. The automobile according to claim 1, comprising at least one selected from 1% or less, Zn: 0.5% or less, Ag: 0.1% or less, and Sn: 0.15% or less. Aluminum alloy plate for structural members. The aluminum alloy plate for an automobile structural member according to claim 1 or 2 , wherein the content of Mg is 0.4% or more and 0.6% or less in mass%. Content of said Si is 0.6% or more and 0.8% or less by mass%, The aluminum alloy plate for automobile structural members of any one of Claims 1-5 characterized by the above-mentioned.   An automobile structural member using the aluminum alloy plate for an automobile structural member according to any one of claims 1 to 4. % By mass, Mg: 0.4% or more and 1.0% or less, Si: 0.6% or more and 1.2% or less, Cu: 0.5% or less , and the balance being Al and inevitable impurities. Aluminum alloy casting step, homogenizing heat treatment step, hot rolling step , cold rolling step so that the final plate thickness is 1.5 mm or more , annealing step, and solution treatment A method for manufacturing an Al-Mg-Si-based aluminum alloy sheet, which comprises a step and a quenching step,
Controlling the rolling ratio in the cold rolling step to 40% or more,
The heat treatment temperature in the annealing step is set to 275 ° C. or higher ,
The ear ratio of the aluminum alloy plate is -10.0% to -3.0%,
After performing the artificial aging treatment for 20 minutes at a temperature of 180 ° C., while obtaining the bake hard property with a 0.2% proof stress of 215 MPa or more,
A method for producing an aluminum alloy plate for an automobile structural member, which is characterized in that it has a crush resistance of 93 ° or more in a VDA bending test . Further, the aluminum alloy is, in mass%, Mn: 1.0% or less, Fe: 0.5% or less, Cr: 0.3% or less, Zr: 0.2% or less, V: 0.2% or less. At least one selected from: Ti: 0.1% or less, Zn: 0.5% or less, Ag: 0.1% or less, and Sn: 0.15% or less. 7. The method for producing an aluminum alloy plate for an automobile structural member according to item 6.

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