WO2023053845A1

WO2023053845A1 - Forming method for aluminum alloy sheet

Info

Publication number: WO2023053845A1
Application number: PCT/JP2022/033106
Authority: WO
Inventors: 渉一廣澤; 智美前野; 准模金; 欣鈴木; 光二成谷
Original assignee: 国立大学法人横浜国立大学; 株式会社ジーテクト
Priority date: 2021-09-30
Filing date: 2022-09-02
Publication date: 2023-04-06
Also published as: JP7410534B2; EP4411011A1; JPWO2023053845A1

Abstract

According to the present invention, in a first step S101, a sheet material composed of a 7000-series aluminum alloy which has been T6 treated is heated to a first temperature at which hot press forming is possible; in a second step S102, the sheet material which was heated to the first temperature is hot press formed and a formed body is produced; and in a third step S103, the formed body is heated at a second temperature for 20-30 minutes and conductivity and hardness are increased. The second temperature may be any temperature 170-200°C.

Description

Forming method of aluminum alloy plate

The present invention relates to a method for forming an aluminum alloy plate.

Currently, it is important to reduce the weight of automobiles in order to improve their fuel efficiency. Weight reduction is progressing mainly through thinning with ultra-high-tensile steel, but since it affects rigidity exponentially, it is difficult to secure the rigidity of parts and there is a limit to reducing the thickness. On the other hand, since aluminum alloy not only has high strength but also has a low specific gravity, it is possible to secure the plate thickness and reduce the weight. In particular, Al--Zn--Mg alloys or Al--Zn--Mg--Cu alloys (7000 series aluminum alloys) are effective due to their high strength.

JP 2010-159489 A

However, high-strength aluminum alloys such as 7000 series have a low ductility of about 10% at room temperature in age-hardened plate materials, making cold press forming difficult. For this reason, in the prior art, the plate material is subjected to solution heat treatment, and then pressed and molded in an annealed state (see Patent Document 1). However, with this technology, for example, at the production site of high-strength aluminum alloy sheet material such as 7000 series for automobiles, the strength of the formed sheet material cannot be set to the desired state, and stress corrosion cracking (Stress Corrosion Cracking) A problem that cracking (SCC) is likely to occur (low SCC resistance) was confirmed.

The present invention was made to solve the above problems, and aims to further improve the strength and SCC resistance of press-formed aluminum alloy plate materials.

A method for forming an aluminum alloy plate according to the present invention includes a first step of heating a plate material made of a 7000 series aluminum alloy that has undergone a T6 treatment to a first temperature that enables hot press forming, and heating to the first temperature. A second step of hot press-molding the plate to form a compact, and a third step of heating the compact at a second temperature for 20 to 30 minutes to increase the electrical conductivity and hardness.

In one configuration example of the aluminum alloy plate forming method, the first temperature is any temperature in the range of 250°C to 270°C.

In one structural example of the aluminum alloy plate forming method, the first step is to heat the plate material to the first temperature for 150 seconds at the maximum.

In one configuration example of the aluminum alloy plate forming method, the second temperature is any temperature in the range of 170°C to 200°C.

In one structural example of the aluminum alloy plate forming method, the plate material is A7075 aluminum alloy.

As described above, according to the present invention, the compact after hot pressing is heated at a second temperature in the range of 170° C. to 200° C. for 20 minutes to 30 minutes, Since the electrical conductivity and hardness are increased, the strength and SCC resistance of the press-formed aluminum alloy sheet material can be further improved.

FIG. 1 is a flow chart illustrating a method for forming an aluminum alloy plate according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing changes in temperature of a plate material and a compact. FIG. 3A is a characteristic diagram showing the results of an experiment in which the first step, second step, and third step of the aluminum alloy plate forming method according to the embodiment of the present invention were simulated at a first temperature of 250°C. . FIG. 3B is a characteristic diagram showing the results of an experiment in which the first step, second step, and third step of the aluminum alloy plate forming method according to the embodiment of the present invention were simulated at a first temperature of 255°C. . FIG. 3C is a characteristic diagram showing the results of an experiment in which the first step, second step, and third step of the aluminum alloy plate forming method according to the embodiment of the present invention were simulated at a first temperature of 260°C. . FIG. 3D is a characteristic diagram showing the results of an experiment in which the first step, second step, and third step of the aluminum alloy plate forming method according to the embodiment of the present invention were simulated at a first temperature of 265°C. . FIG. 4A shows the results of an experiment in which the first, second, and third steps of the aluminum alloy plate forming method according to the embodiment of the present invention were simulated under the conditions of the third step at 170° C. for 20 minutes. FIG. 4 is a characteristic diagram showing differences in Vickers hardness and electrical conductivity after three steps under each condition. FIG. 4B shows the results of an experiment in which the first, second, and third steps of the aluminum alloy plate forming method according to the embodiment of the present invention were simulated under the conditions of the third step at 200° C. for 30 minutes. FIG. 4 is a characteristic diagram showing differences in Vickers hardness and electrical conductivity after three steps under each condition.

　Hereinafter, a method for forming an aluminum alloy plate according to an embodiment of the present invention will be described with reference to Figs. FIG. 2 shows changes in temperature (temperature of plate material and compact) in each process described below.

First, in the first step S101, a plate material made of a 7000 series aluminum alloy that has undergone T6 treatment is heated to a first temperature that enables hot press forming. The first temperature can be any temperature in the range of 250°C to 270°C. Also, in this step, the plate may be heated to the first temperature for up to 150 seconds.

In this step, for example, it is preferable to set the heating rate to 10°C/second or more. For example, as the heat treatment conditions in the first step, by performing rapid heating at 10 ° C./sec to 250 ° C., in addition to reducing deformation resistance (300 MPa) and improving moldability (breaking elongation 17%), room temperature after molding The hardness is 153HV, satisfying the target value (>140).

On the other hand, when low-speed heating is performed at 1 ° C./sec to 250 ° C. as the heat treatment condition in the first step, the deformation resistance can be reduced (208 MPa) and the moldability can be improved (breaking elongation 17%). The room temperature hardness is 107 HV, failing to satisfy the target value (>140). The hardness target value will be described later.

In addition, it is preferable that this heat treatment be carried out by well-known contact heating from the viewpoint of temperature increase rate. This heating enables press molding, which will be described later. The plate material is made of an Al--Zn--Mg alloy such as A7075 (JIS) or an Al--Zn--Mg--Cu alloy.

Next, in the second step S102, the plate material heated to the first temperature is hot press-molded to form a compact. In hot press forming, a sheet material that is at a moldable temperature is press-formed using a die and at the same time, is rapidly cooled by the die. Due to this rapid cooling, the plate material is cooled from the first temperature to about 20° C. to 25° C., for example. For example, the above-described hot pressing can be performed by using a mold equipped with a cooling mechanism such as water cooling. In addition, by discharging cooling water from the inner surface of the mold to the object to be pressed and passing the cooling water between the surface of the mold and the object to be pressed, the direct water cooling method directly cools the object to be pressed. An intermediate press can be performed.

Here, in order to prevent the temperature drop of the sheet material, it is transported in a heat insulating box or a heating box while being kept warm or heated from the heating furnace where heat treatment is performed to the press machine where hot press forming is performed. is desirable.

Next, in the third step S103, the compact is heated at the second temperature for 20 to 30 minutes to increase the electrical conductivity and hardness (strength). The second temperature can be any temperature in the range of 170°C to 200°C.

According to the aluminum alloy plate forming method according to the above-described embodiment, the strength and SCC resistance of the press-formed aluminum alloy plate material (formed body) can be further improved. In addition, since a plate material made of a 7000 series aluminum alloy that has undergone T6 treatment is used, handling by parts manufacturers is facilitated. According to the embodiment, since the plate material is heated to the first temperature at which hot press forming is possible, it is possible to press form a part having a cross section of a hat, such as the skeleton of an automobile body. Since this press molding can be held at 20° C. for one day, it is possible to ensure the transportation time from the parts manufacturer to the automobile manufacturer.

Heat treatment (re-aging treatment; 3rd step) at a temperature of 170°C or 200°C for 20 minutes or 30 minutes has a heat history equivalent to the paint baking treatment conditions generally adopted by automobile manufacturers in Japan, Europe and the United States. Become. Therefore, the heat treatment in the paint drying furnace after the conveyed plate material (part) is assembled to the automobile body can be carried out as the third step. It should be noted that this heat treatment (third step) does not require the use of a coating drying oven. It is also possible to attach this component to the vehicle body with a thermosetting adhesive and cure the adhesive at the same time.

Next, the results of experiments simulating the first, second, and third processes will be explained. As an experiment, first, a test piece (20 mm×20 mm, thickness 2 mm) of A7075 plate material subjected to T6 treatment was prepared.

Next, the test piece was heated to 250-265°C for 60-150 seconds (first step) and cooled to 20°C by water cooling (second step). The heat treatment was performed by immersing the test piece in an oil bath or salt bath at 250-265°C. The temperature of this heat treatment corresponds to the first temperature. Moreover, the water cooling process described above is likened to rapid cooling by a mold in the second step of hot pressing.

Next, after holding for one day at 20°C (natural aging), heat treatment is performed at 170°C or 200°C for a treatment time of 20 minutes or 30 minutes (re-aging treatment). This treatment corresponds to the third step described above, and has a heat history equivalent to the paint baking treatment conditions generally adopted by automobile manufacturers in Japan, Europe, and the United States. Also, the temperature in this process corresponds to the second temperature.

A Vickers hardness test and conductivity measurement were performed at each heat treatment stage. The results of the tests and measurements are shown in Figures 3A, 3B, 3C and 3D. 3A shows the result when the heat treatment condition of the first step is 250° C., FIG. 3B shows the result when the heat treatment condition of the first step is 265° C., and FIG. 3C shows the result of the first step. This is the result when the heat treatment condition is 260°C, and Fig. 3D is the result when the heat treatment condition of the first step is 255°C. In these treatments, the test piece is considered to have reached the temperature (first temperature) of each heat treatment condition. Further, the solid line indicates the second temperature of 170°C, and the dashed line indicates the second temperature of 200°C. In addition, in the dotted ellipse of the third step S103, the last plotted point is 30 minutes of processing time, and the previous plotted point is 20 minutes of processing time.

In each graph, at the stage of the second step S102, the hardness decreases from the initial state (T6 treatment is performed), and the hardness increases due to the treatment conditions of the third step S103. At any temperature (250 ° C., 255 ° C., 260 ° C., 265 ° C.) in the first step S101, compared with the value of A7075 subjected to T6 treatment (195 HV, 32 IACS%), after the second step S102 The hardness is greatly reduced and the conductivity is greatly increased. Further, the higher the temperature (≈first temperature) in the first step S101 and the longer the time of the first step S101, the larger the amount of change.

On the other hand, regarding the hardness and conductivity after the third step S103, both values increased compared to after the second step S102 under all conditions where the second temperature was 170°C. Under the condition of 200° C., the conductivity increases under many conditions in the first step S101, but the hardness remains unchanged or decreases. Among these, for example, the treatment of the third step S103 improved the SCC resistance of the T6-treated A7075 material T76 material (167HV, 38IACS%) or the hardness equivalent to T73 material (153HV, 40IACS%). Some have hardness and conductivity. As product characteristics, the hardness should be HV140 or more, the conductivity should be 38%IACS or more, and the hardness should be HV153 or more. From these results, it is considered that the present invention can provide a formed body made of a sheet material made of a 7000 series aluminum alloy, which is excellent not only in strength but also in SCC resistance.

Next, FIG. 4A and FIG. 4B show the differences in Vickers hardness and electrical conductivity after the third step in the above experiment according to each condition. In FIG. 4A, the conditions for the third step are 170° C. and 20 minutes. In FIG. 4B, the conditions for the third step are 200° C. and 30 minutes. Also, the number shown in each plot point is the processing time of the first step. Further, the temperature shown in the figure indicates the result of measuring the temperature of the test piece in the first step using a thermocouple (corresponding to the first temperature). From these results, there are conditions under which the strength (hardness) and SCC resistance can be further improved at each treatment time considering the time margin in actual work, and it can be used in actual use. I understand.

Next, a test piece (20 mm × 20 mm, thickness 2 mm) made of A7075 plate material treated with T6 was subjected to the first step under various conditions, held at 20 ° C. for one day, and then 170 ° C. for 20 minutes. Table 1 shows the measurement results of the Vickers hardness and conductivity when the third step was performed under the conditions of . In addition, a test piece (20 mm × 20 mm, thickness 2 mm) made of A7075 plate material treated with T6 was subjected to the first step under various conditions, held at 20 ° C. for one day, and then held at 200 ° C. for 30 minutes. Table 2 shows the measurement results of Vickers hardness and conductivity when the third step was performed under the conditions.

Note that the heat treatment was performed by immersing the test piece in an oil bath. In addition, as a treatment corresponding to the rapid cooling by the mold in the hot press in the second step, it was cooled to 20° C. by water cooling. "Temperature" in the table indicates the value (corresponding to the first temperature) of the temperature of the test piece measured using a thermocouple. From these results, it was found that the strength (hardness) and SCC resistance were further improved at each treatment time considering the time margin in the actual work, and the conditions under which it could be used in actual use were found. I know there is.

By the way, in the above description, the Vickers hardness test is used to roughly estimate the strength, and the conductivity measurement by the eddy current method is used to roughly estimate the SCC resistance.・It is clear that the electrical resistivity measurement method can be used for rough estimation. Note that if the first temperature is 270° C. or higher, the hardness is too low, which is not preferable. Moreover, if the first temperature is 250° C. or lower, it is not easy to obtain the desired conductivity within a practical processing time in consideration of mass production.

As described above, according to the present invention, the compact after hot pressing is heated at a second temperature in the range of, for example, 170° C. to 200° C. for 20 minutes to 30 minutes. , the electrical conductivity and hardness are increased, so that the strength and SCC resistance of the press-formed aluminum alloy plate material can be further improved.

Some or all of the above embodiments are also described in the following appendices, but are not limited to the following.

[Appendix 1]
A first step of heating a plate material made of a 7000 series aluminum alloy that has undergone a T6 treatment to a first temperature at which hot press forming is possible;
a second step of hot press-molding the plate material heated to the first temperature to form a compact;
A method of forming an aluminum alloy plate, comprising: a third step of heating the formed body at a second temperature for 20 to 30 minutes to increase conductivity and hardness.

[Appendix 2]
In the method for forming an aluminum alloy plate according to Supplementary Note 1,
The method of forming an aluminum alloy plate, wherein the first temperature is any temperature in the range of 250°C to 270°C.

[Appendix 3]
In the method for forming an aluminum alloy plate according to Appendix 1 or 2,
The forming method of an aluminum alloy plate, wherein the first step heats the plate material to the first temperature for 150 seconds at the maximum.

[Appendix 4]
In the method for forming an aluminum alloy plate according to any one of Appendices 1 to 3,
The method of forming an aluminum alloy plate, wherein the second temperature is any temperature in the range of 170°C to 200°C.

[Appendix 5]
In the method for forming an aluminum alloy plate according to any one of Appendices 1 to 4,
A method for forming an aluminum alloy plate, wherein the plate material is an A7075 aluminum alloy.

It should be noted that the present invention is not limited to the embodiments described above, and many modifications and combinations can be implemented by those skilled in the art within the technical concept of the present invention. It is clear.

Claims

A first step of heating a plate material made of a 7000 series aluminum alloy that has undergone a T6 treatment to a first temperature at which hot press forming is possible;
a second step of hot press-molding the plate material heated to the first temperature to form a compact;
A method of forming an aluminum alloy plate, comprising: a third step of heating the formed body at a second temperature for 20 to 30 minutes to increase conductivity and hardness.
In the method for forming an aluminum alloy plate according to claim 1,
The method of forming an aluminum alloy plate, wherein the first temperature is any temperature in the range of 250°C to 270°C.
In the method for forming an aluminum alloy plate according to claim 1,
The forming method of an aluminum alloy plate, wherein the first step heats the plate material to the first temperature for 150 seconds at the maximum.
In the method for forming an aluminum alloy plate according to claim 1,
The method of forming an aluminum alloy plate, wherein the second temperature is any temperature in the range of 170°C to 200°C.
In the method for forming an aluminum alloy plate according to any one of claims 1 to 4,
A method for forming an aluminum alloy plate, wherein the plate material is an A7075 aluminum alloy.