JP5671422B2 - Method for producing high strength 7000 series aluminum alloy member and high strength 7000 series aluminum alloy member - Google Patents

Description

  The present invention relates to a method for producing a high strength 7000 series aluminum alloy member and a high strength 7000 series aluminum alloy member. The aluminum alloy member referred to in the present invention refers to a product obtained by forming a extruded shape or rolled plate as a raw material into a product shape (use shape) accompanied by generation of residual stress.

  As is well known, the 7000 series aluminum alloy member is an artificial aging treatment (artificial aging treatment) using the age hardening property by adjusting the amount of alloying elements such as Zn, Mg and Cu as main components as the composition of the extruded shape of the material. The required high strength is ensured by tempering such as age hardening. Examples of main applications include automotive reinforcement members such as bumper hose and door beam, and structural members for aircraft, etc. In order to reduce the weight by thinning, higher strength is required, 0.2% A high strength of 300 MPa or more is required in terms of yield strength.

  However, it is known that the 7000 series aluminum alloy member has a low SCC resistance (stress corrosion cracking resistance) as compared with other alloy series because of the large amount of the alloy elements.

  As is well known, the 7000 series aluminum alloy member is hardened by natural age hardening (hereinafter also referred to as natural aging or room temperature aging) after being manufactured as an extruded shape as a raw material because of its age hardening. For example, the strength which was about 150 MPa with 0.2% proof stress immediately after hot extrusion is cured to about 240 MPa with 0.2% proof strength after 20 days of natural aging (room temperature aging).

  In this way, the material extruded shape that has been naturally aged is extremely deteriorated in the formability during the forming process with respect to the member, which is selected from the bending process, the crushing process of the cross section, and the punching process. This is the same even after the manufactured material extruded profile is separately reheated and subjected to a solution treatment (solution treatment and quenching treatment). The natural aging progresses as time elapses.

  In addition, even if the molding process is possible, the strength of the extruded profiles depends on the difference in time from the production of the extruded material to the molding process, that is, the degree of natural age hardening (progress). Are different, that is, the strength of the extruded profiles varies. In addition, there is a problem that the amount of springback during molding depending on the proof stress varies depending on the extruded shapes, and there is also a problem that the molding accuracy of the members varies for each extruded shape. Furthermore, when natural aging progresses, there is a problem that the uniform elongation and local elongation of the extruded shape member are lowered, and the moldability and molding accuracy of the member are further lowered.

  Further, in the forming process to the member with plastic working, which is selected from the bending process, the crushing process of the cross section, and the punching process described above, the residual stress is easily added, and the higher the applied residual stress is, There is also a problem that the SCC resistance at the molding site is significantly lowered.

  In order to improve the formability of the naturally aged material extruded profile, a recovery process has been conventionally performed in which the naturally aged material extruded profile is heat treated to reduce the strength such as the yield strength.

  For example, Patent Document 1 describes a method for manufacturing an aircraft frame or the like. And in the molding method of the part which carries out plastic processing after the solution treatment of the material extruded profile or material plate of 7000 series aluminum alloy, immediately before molding, the heating temperature is 150 to 350 ° C., and the heating time is 30 seconds to The material cured by natural aging after solution treatment is softened by performing a restoration treatment for 5 minutes (170 to 200 ° C. × 20 seconds to 3 minutes if rapid heating is possible) to ensure moldability, Molded after eliminating variations in springback due to differences in aging progress.

  Patent Document 2 describes a spinning process and a method for producing a high-strength aluminum alloy pipe in which the spun pipe is artificially aged. And after solution treatment of the precipitation hardening type high hardness aluminum alloy pipe such as extruded 7000 series which is the material, the pipe naturally aged after the solution treatment, friction heat generation between the roller and the material pipe by spinning, Heat generation due to plastic deformation of pipes and the high thermal conductivity of aluminum materials, the temperature rises in a short time locally in the temperature range of 150 ° C to 250 ° C, cooling effect in self-cooling and spinning process Spinning processing that takes into account the recovery process of lowering the temperature.

  Patent Document 3 describes a method for producing a 7000-type high-strength aluminum alloy extruded tube suitable as a front fork outer tube material for a motorcycle having excellent tube expansion workability even after long-term natural aging. . Then, after T4 tempering the aluminum alloy extruded tube, heat treatment is performed at a temperature of 105 ° C. to 250 ° C. for 30 seconds to 180 minutes, and in this heat treatment, the temperature increase rate from at least 100 ° C. to the heat treatment temperature is less than 1 ° C./second. It is proposed to perform the restoration process. In the examples, the tensile strength, proof stress and elongation after two-stage aging are excellent, and the stress corrosion cracking life is also excellent.

  In addition, Patent Document 4 discloses that in order to improve the stress corrosion cracking resistance of a high-strength aluminum alloy extruded tube for a front fork outer tube, the 7000 series high-strength aluminum alloy extruded tube is subjected to solution treatment and quenching, and 100% at room temperature. After natural aging for at least a period of time, heat treatment is performed at a temperature of 150 to 250 ° C. for 30 seconds to 10 minutes, and in this heat treatment, a restoration treatment is performed at a rate of temperature increase from at least 100 ° C. to the heat treatment temperature of 1 ° C./second or more. A method for performing artificial aging treatment at the end is proposed.

Japanese Patent Laid-Open No. 7-305151 JP 2005-194620 A JP 2007-119853 A JP-A-10-168553

  All of these conventional restoration processes are likely to be a complete O material treatment when estimated from conditions such as the heating temperature and the length of the holding time. That is, in order to avoid the O material treatment, as described later, as in the restoration treatment of the present invention, rapid heating by a specific heating rate, a specific actual temperature of a material such as a 7000 series aluminum alloy extruded shape, It is necessary to satisfy various conditions such as holding for a specific very short time and quenching at a specific cooling rate. In addition, after satisfying these processing conditions, it is necessary to satisfy the condition of 0.2% yield strength reduction due to the restoration processing and the characteristic difference of conductivity. However, these conventional restoration processes do not disclose these conditions, and the probability of inevitably becoming a complete O material process increases. For this reason, even if the tempering treatment is performed after the yield strength is once lowered by the restoration treatment, there is a great limit to the strength that can be improved by the artificial age hardening treatment. Incidentally, the description of these conventional restoration processing temperatures is an ordinary furnace atmosphere temperature, and not an actual temperature in many cases.

  On the other hand, in the restoration process using the frictional heat generation between the roller and the material pipe by spinning processing and the heat generation by plastic deformation of the pipe as in Patent Document 2, the material shape is limited to the aluminum alloy pipe, Not applicable. In addition, when the frictional heat generated between the roller and the material pipe by the spinning process and the heat generated by the plastic deformation of the pipe are used, it is difficult to control the restoration processing conditions, and the variation in the restoration processing conditions increases. For this reason, it is difficult to restore a necessary portion of the material accurately and uniformly.

  Furthermore, these conventional techniques have a problem of deterioration of formability due to natural aging after tempering such as solution treatment of 7000 series high-strength aluminum alloy extruded shapes. Therefore, although the restoration process before molding for improving the moldability is considered, in common, the residual stress applied in the molding process with the plastic processing after the restoration process is completely considered. Not. That is, even if the residual stress is removed by the restoration process, and even if the moldability is thereby improved, the member is subjected to plastic working such as the bending process, the crushing process of the cross section, and the punching process after the restoration process. In this molding process, a large residual stress is still applied.

  Moreover, this residual stress cannot be removed when the molded member is not subjected to solution treatment and quenching treatment. For this reason, these conventional techniques have not been solved in common with respect to the problem of the SCC resistance deterioration at the molding site of the member to which the residual stress is applied by the molding process. And the tendency for this SCC resistance to fall becomes so remarkable that a 7000 series aluminum alloy member becomes high intensity | strength.

  The present invention has been made in view of such a problem, and can reduce the residual stress applied by the forming process to the member accompanied by the plastic processing such as the bending process, the crushing process of the cross section, and the punching process later, and the proof stress is once increased. An object of the present invention is to provide a method for producing a high-strength 7000 series aluminum alloy member and a high-strength 7000 series aluminum alloy member, which can be subjected to a tempering treatment even after being lowered and the strength can be greatly improved by the artificial age hardening treatment.

In order to achieve the above object, the gist of the manufacturing method of the high-strength 7000 series aluminum alloy member of the present invention is mass%, Zn: 5.0-8.0%, Mg: 0.3-2.0% Cu: 0.05 to 0.5%, Mn: 0.01 to 0.3%, Cr: 0.01 to 0.3%, Zr: 0.01 to 0.3% Alternatively, after manufacturing a 7000 series aluminum alloy material containing two or more types and the balance consisting of inevitable impurities and aluminum by plastic working from an ingot, it is restored without artificial tempering except for natural aging This restoration process is rapidly heated at a heating rate of 0.5 ° C./second or more, held for a short time of less than 20 seconds in an actual temperature range exceeding 200 ° C. and 500 ° C. quenched with 0.5 ° C. / sec or more cooling rate, the With the following 120MPa 0.2% yield strength of the material immediately after cooling, and this and conductivity of the material immediately after quenching, the difference between the conductivity of the material immediately before the restoration process to less than 5% IACS, the Within one hour after the completion of the rapid cooling to the room temperature of the restoration process, there is a residual stress selected from bending, cross-section crushing, and punching without artificial conditioning except for the restoration process. A member is formed by performing a forming process, and the member is subjected to artificial aging treatment without solution treatment and quenching treatment, and the 0.2% proof stress of the member after the artificial aging treatment is set to 300 MPa or more. The residual stress at the position of the member that has been subjected to is set to 160 MPa or less.

Moreover, the summary of the high-strength 7000 series aluminum alloy member of this invention for achieving the said objective is the mass%, Zn: 5.0-8.0%, Mg: 0.3-2.0%, Cu : 0.05-0.5%, and Mn: 0.01-0.3%, Cr: 0.01-0.3%, Zr: 0.01-0.3% A 7000 series aluminum alloy extruded shape that contains two or more types and the balance is composed of inevitable impurities and aluminum is restored, and the 0.2% proof stress of the extruded shape immediately after quenching after the restoration treatment Is 120 MPa or less, and the difference between the conductivity of the extruded shape immediately after the rapid cooling and the conductivity of the extruded shape immediately before the restoration treatment is less than 5% IACS, crushing processing of the cross-section, the occurrence of residual stress is selected from stamped It is a 7000 series aluminum alloy member that is formed into a member by the accompanying forming process and is subjected to artificial aging treatment without solution treatment and quenching treatment after the forming process, and 0.2% proof stress is 300 MPa or more And it is that the residual stress in the member position which received the said shaping | molding process is 160 Mpa or less.

  In the present invention, the 7000 series aluminum alloy material is subjected to a restorative treatment under a specific condition such as a relatively high temperature and an absolute short time, whereby a residual stress applied by a subsequent forming process is applied. Was found to be reduced. As described above, the conventional restoration process is performed under the same conditions as those of the restoration process of the present invention (rapid heating at a specific heating rate, a specific substance temperature of a material, a specific value) There is no recognition of satisfying short-time holding, rapid cooling at a specific cooling rate). Further, there is no recognition that it is necessary to satisfy the condition of the 0.2% yield strength reduction or the conductivity difference due to the restoration process after satisfying these processing conditions. Therefore, these conventional restoration processes inevitably increase the probability of complete O material treatment.

  Usually, a material (T4 material) stored at room temperature or lower after solution treatment and naturally aged after this solution treatment is G.S. P. It is hardened by precipitation of zones (aggregates of solute elements in the initial stage where precipitates are formed) or very fine intermediate phases. The normal restoration process described above is a process in which the fine precipitates are re-dissolved in the matrix by heating the naturally aged material after the solution treatment to a temperature of 150 to 350 ° C. It has an effect similar to that of softening treatment, and is treated with softening O material.

  However, in the present invention, unlike these conventional restoration processes, after the 7000 series aluminum alloy extruded shape material is manufactured by hot extrusion (plastic processing) from the ingot, the restoration process is performed except for hardening by natural aging. I do. This restoration process is also carried out by rapid heating (heating rate of 0.5 ° C./second or more), and the actual temperature of the 7000 series aluminum alloy extruded shape material exceeds 200 ° C. and is 500 ° C. or less. Hold for a very short time of less than 20 seconds, and then rapidly cool to room temperature (cooling rate of 0.5 ° C./second or more).

  As a result, the 0.2% proof stress immediately after the rapid cooling of the 7000 series aluminum alloy extruded shape material is reduced to 120 MPa or less, but the restoration treatment of the present invention is different from the O material treatment for softening. In the later artificial age hardening treatment, the member strength can be secured to 300 MPa or more with a 0.2% proof stress. Incidentally, if this restoration process takes a long time, it becomes an O material treatment for softening and the residual stress applied during molding is reduced, but the strength of the member is reduced to 0 by the artificial age hardening treatment after molding. .2% proof stress cannot be secured above 300 MPa.

  Moreover, in this invention, after shaping | molding to a member, an artificial age hardening process is performed without performing solution treatment and hardening process. That is, according to the restoration process of the present invention, after the residual stress applied at the time of subsequent molding is reduced, without being subjected to solution treatment and quenching process after molding into a member, only by artificial age hardening treatment, The member strength can be secured to 300 MPa or more with a 0.2% proof stress, and the residual stress at the member position subjected to the forming process can be suppressed to 160 MPa or less.

  Therefore, according to the present invention, even a high-strength 7000 series aluminum alloy extruded shape that is naturally aged is also formed with the generation of residual stress selected from bending, cross-sectional crushing, and punching. Even if it is a high-strength 7000 series aluminum alloy member made into a member by the above-mentioned method, when this member is subjected to artificial age hardening treatment without solution treatment and quenching treatment, 0. The 2% proof stress can be 300 MPa or more. Even when the molded member is not subjected to solution treatment and quenching treatment, and the residual stress imparted by molding cannot be removed by these tempering after molding, the residual stress at the member position subjected to the molding process is 160 MPa or less. Can be suppressed.

  Further, the problem that the strength varies depending on the degree of natural age hardening and the manner of progress, that is, the problem that the strength and the amount of springback vary, is solved, and the mechanical properties and the amount of springback of the extruded shape can be made uniform. In addition, the uniform elongation and local elongation of the extruded profile when natural aging progresses are also eliminated, and the uniform elongation and local elongation are improved, and the moldability and molding accuracy of the member are further improved.

  Hereinafter, embodiments of the present invention will be specifically described in order for each requirement. In addition, the following description demonstrates as an example the extrusion shape member manufactured by extruding an ingot hot as a 7000 series aluminum alloy raw material. However, the significance of each condition is the same even in the case of a rolled sheet material manufactured by hot rolling and cold rolling an ingot.

composition:
The 7000 series aluminum alloy extruded profile (raw material) in the present invention has an Al—Zn—Mg series composition or an Al—Zn—Mg—Cu series composition including JIS standards and AA standards. However, in order to satisfy the required high strength as a member, the strength of the member after this artificial aging treatment is within the range of 120 to 160 ° C. × 6 to 16 hours, which is a normal aging treatment condition of temper T5 to T7. Must be 300 MPa or more, preferably 400 MPa or more with a 0.2% proof stress.

  A preferable 7000 series aluminum alloy extruded shape (material) composition for this purpose is, by mass, Zn: 5.0 to 8.0%, Mg: 0.3 to 2.0%, Cu: 0.05 to 0. 0.5%, and further contains one or more of Mn: 0.01 to 0.3%, Cr: 0.01 to 0.3%, Zr: 0.01 to 0.3%. The balance is composed of inevitable impurities and aluminum.

  Here, in order not to deteriorate various properties as materials or members such as formability, corrosion resistance, or weldability, Fe, Si, which is inevitably mixed as a melting raw material from metal or scrap as a raw material, Each is preferably 0.25% or less, and Ti is preferably 0.05% or less.

  Zn is a main element for improving the strength, and its preferable content range is 5.0 to 8.0%. If the content is less than the lower limit, the strength becomes insufficient. If the content exceeds the upper limit, the SCC resistance (stress corrosion cracking resistance) is significantly lowered. A more preferable content range is 6.2 to 6.8%.

  Mg is also a main element for improving the strength, and its preferable content range is 0.3 to 2.0%. If it is less than the lower limit, the strength becomes insufficient, and if it exceeds the upper limit, the SCC resistance is lowered. A more preferable content range is 0.6 to 1.5%.

  Cu is a main element that also improves the strength, and its preferred content range is 0.05 to 0.5%. If it is less than the lower limit, the strength becomes insufficient, and if it exceeds the upper limit, the extrusion processability is lowered. A more preferable content range is 0.08 to 0.2%.

  Mn, Cr, and Zr are elements that are selectively contained, and by containing one or two or more of them, any of them makes the crystal structure of the material finer or fibrous and improves the SCC resistance. The preferable content ranges are Mn: 0.01 to 0.3%, Cr: 0.01 to 0.3%, and Zr: 0.01 to 0.3%, respectively. When both are contained exceeding the upper limit, a coarse intermetallic compound is formed, resulting in a decrease in ductility and a decrease in moldability.

  Fe and Si are elements contained as impurities, and preferable content ranges are Fe: 0.25% or less and Si: 0.25% or less. When the content exceeds the upper limit, ductility is lowered and tube expansion workability is lowered. Further preferable content ranges are Fe: 0.20% or less, Si: 0.20% or less, and most preferable content ranges are Fe: 0.15% or less, Si: 0.15% or less.

Production method:
An explanation will be given by taking an extruded profile as an example of the 7000 series aluminum alloy material. Note that all described temperatures in the heat treatment are actual temperatures, not the furnace atmosphere temperature.

(Melting, casting)
First, in the melting and casting process, a molten aluminum alloy melt-adjusted within the above-mentioned 7000 series component composition range is cast by appropriately selecting a normal melting casting method such as a semi-continuous casting method (DC casting method). And

(Homogenization heat treatment)
Prior to hot extrusion, the cast aluminum alloy billet (ingot) is subjected to homogenization heat treatment (soaking) in the range of 470 to 565 ° C. to homogenize the structure (segregation within crystal grains in the ingot structure). Etc.). The soaking temperature is selected from the range of 470 to 565 ° C., and the homogenization time is selected from the range of 2 hours or more. If the soaking temperature is too high, the dispersed particles in the shape structure become coarse, and the crystal grains cannot be refined and strengthened. On the other hand, even if the soaking temperature is too low, the billet structure cannot be homogenized.

(Hot extrusion)
This homogenized 7000 series aluminum alloy billet is hot-extruded (direct extrusion or indirect extrusion), but it is hot-extruded under conditions that suppress the recrystallized grain layer of the extruded shape and refine and homogenize the structure. It is preferable to do. The extrusion start temperature of the billet is preferably 350 to 450 ° C.

  As for the cooling immediately after the hot extrusion, it is possible to carry out rapid cooling (on-line quenching) such as air cooling and water cooling from the extrusion (extruder) outlet temperature at the temperature of the solution zone (solution temperature). This is preferable in terms of preventing recrystallization structure on the surface of the shape material structure and coarsening of crystal grains in the internal processing structure. Incidentally, such quenching or quenching process performed on-line continuously on the extrusion process immediately after extrusion (on the exit side of the extruder) is not included in the tempering referred to in the present invention. Therefore, in the present invention, except for curing by natural aging, the restoration process is performed without tempering such as a solution treatment, and the extruded shape material is reheated off-line separate from the extrusion process. The restoration process is performed without any tempering such as solution treatment and quenching process.

(Restore process)
Unlike these conventional restoration processes, the restoration process of the present invention is a solution of a 7000 series aluminum alloy extruded shape material, except for hardening by natural aging after manufacturing by hot extrusion (plastic processing) from an ingot. And restoration processing is performed without tempering such as quenching. In other words, it is only after the restoration treatment of the present invention is applied to the extruded material of the 7000 series aluminum alloy that has been naturally aged (room temperature aging), and the residual stress applied during the subsequent molding process is reduced. The effect of securing the member strength to 300 MPa or more with 0.2% proof stress can be obtained by subsequent tempering.

(Restore processing conditions)
The conditions for the restoration process are also important for the manifestation of the effect by the restoration process. That is, the actual temperature of the extruded material of the 7000 series aluminum alloy exceeds 200 ° C. to 500 ° C. or less by rapid heating (rapid heating) at a heating rate of 0.5 ° C./second or more. Hold for a very short time of less than a second. Immediately after the holding, rapid cooling (air cooling, water cooling, mist cooling) is forced to room temperature at a cooling rate of 0.5 ° C./second or more.

  When the actual temperature of the extruded material of the 7000 series aluminum alloy is less than 200 ° C., the restoration process is insufficient, and particularly, the formability is not improved and the applied residual stress is increased. Further, if the holding time is too long for 20 seconds or more, or if the heating rate is slow (less than 0.5 ° C./second) (holding time becomes longer), the processing becomes complete O material treatment (annealing treatment) and artificial aging treatment The later strength is not improved to 300 MPa or more at 0.2% proof stress.

  By the way, if you try to control the temperature control in this restoration process with the furnace ambient temperature, the holding time as the shape material entity will be long, or the temperature as the shape material entity will be low. . The heating speed of rapid heating (rapid heating) can be controlled by a furnace heater that matches the size of the shape material, and the actual temperature holding time is the removal time (removal timing) of the extruded shape material from the furnace. It can be controlled. In addition, the cooling rate control by forced rapid cooling to room temperature immediately after the removal is based on the amount of refrigerant used (air cooling, water cooling, mist cooling, etc.) The amount or the amount of immersion). In this case, the room temperature referred to in the present invention may include a temperature (cooling to room temperature) of about 18 to 20 ° C. or less, such as several degrees C., 0 ° C. or 0 ° C. or less.

  As a result, the 0.2% proof stress immediately after the rapid cooling of the 7000 series aluminum alloy extruded shape material is reduced to 120 MPa or less, but the restoration treatment of the present invention is different from the O material treatment for softening. By the artificial age hardening treatment in the subsequent tempering, the member strength can be secured to 300 MPa or more with a 0.2% proof stress. The 0.2% yield strength immediately after the rapid cooling of the restoration process is an important measure as to whether or not the restoration process of the present invention was effectively performed, and since natural aging starts immediately after the rapid cooling in the present invention, If the 0.2% proof stress immediately after quenching exceeds 120 MPa, various effects in the molding process cannot be obtained.

  Furthermore, according to the knowledge of the present inventors, another important measure as to whether or not the restoration process has been performed effectively is the conductivity of the extruded profile material immediately after the rapid cooling in the restoration process. There is a difference from the conductivity of the extruded shape material immediately before the restoration process. Generally, due to the restoration process, the conductivity immediately after the restoration process is higher than that before the restoration process. However, in the case of the restoration process of the present invention and the complete O material process (annealing process) in the conventional restoration process, this conductivity difference is greatly different. That is, the conductivity after the restoration process (immediately after quenching) of the present invention is always less than 5% IACS, and often higher in the range of 1 to 3% IACS than the conductivity of the T1 material (natural aging material) just before the restoration process. Thus, the conductivity difference in the restoration process of the present invention is always less than 5% IACS, preferably in the range of 1 to 3% IACS. As described above, when the conductivity difference is less than 5% IACS, preferably in the range of 1 to 3% IACS, various effects in the molding can be obtained, and the restoration process is reliably and effectively performed.

  On the other hand, the conductivity after the conventional restoration process is always 5% IACS or more higher than the conductivity before the treatment, and the conductivity difference in the case of the complete O material treatment in the conventional restoration process is always 5%. % IACS or higher. When the conductivity difference is 5% IACS or more as in the case of the complete O material processing in the conventional restoration process, the O material is close to the fully annealed O material, or becomes the O material, in the molding. Various effects cannot be obtained. Therefore, in order to reliably achieve the effect of the restoration process in the restoration process of the 7000 series aluminum alloy extruded shape material, the 0.2% proof stress immediately after the quenching after the restoration process is set to 120 MPa or less, and the conductive It is preferable that the rate difference is less than 5% IACS (both are satisfied).

  According to the restoration process of the invention performed under the above conditions, the 7000 series aluminum alloy extruded profile is made into a member by a forming process accompanied by generation of residual stress selected from bending process, crushing process of cross section, and punching process. Even if it is a strength 7000 series aluminum alloy member, the 0.2% proof stress of the tempered member when it is tempered can be set to 300 MPa or more, and the member subjected to the forming process The residual stress at the position can be suppressed to 160 MPa or less.

  However, the reason why various effects described later can be obtained by these restoration processing conditions, and the reason why various effects described later cannot be obtained when deviating from these restoration processing conditions is unknown. However, if this restoration process is longer than the above-mentioned time, or if the above-mentioned rapid heating and quenching conditions are removed, the process will be the same as the conventional O-material treatment for softening, but the moldability is improved. The residual stress applied at the time of molding is not reduced, and the member strength cannot be secured at 300 MPa or more with 0.2% proof stress by the artificial age hardening treatment in the tempering after molding.

  According to the restoration process of the present invention, even a naturally-aged and high-strength 7000 series aluminum alloy extruded shape is formed with the occurrence of residual stress selected from bending, crushing of the cross section, and punching. Even if it is a high-strength 7000 series aluminum alloy member made into a member by processing, the 0.2% proof stress of this tempered member when tempering this member can be 300 MPa or more, Residual stress at the position of the member subjected to the forming process can be suppressed to 160 MPa or less.

  Further, the problem that the strength varies depending on the degree of natural age hardening and the manner of progress, that is, the problem that the strength and the amount of springback vary, is solved, and the mechanical properties and the amount of springback of the extruded shape can be made uniform. In addition, the uniform elongation and local elongation of the extruded profile when natural aging progresses are also eliminated, and the uniform elongation and local elongation are improved, and the moldability and molding accuracy of the member are further improved.

(Molding)
However, in order to exhibit this restoration processing effect in the molding process, it is necessary to perform the molding process as soon as possible (without delay) after the restoration process. That is, the forming process of the 7000 series aluminum alloy extruded shape material into the member shape (product shape) needs to be performed before the natural aging after the restoration process has progressed, or while the natural aging has progressed and is still minute. . As a guideline, of course, it depends on the manufacturing conditions of the extruded material of the 7000 series aluminum alloy. However, if these are determined by pushing them, the (required) time from immediately after the rapid cooling of the restoration process to the start of the forming process is 1 Within time (hr). If it exceeds 1 hour, the high-strength 7000 series aluminum alloy extruded shape material has a natural aging that is excessively advanced as described above due to its composition, the formability is remarkably reduced, and the significance of the restoration treatment is lost.

  The natural aging (strength increase) of the extruded material of 7000 series aluminum alloy proceeds in a short time, in other words, the degree of aging (strength increase) greatly proceeds at the initial stage of natural aging. For this reason, even if the restoration process is performed within the restoration process conditions and the 0.2% proof stress of the extruded shape material is 120 MPa or less, the time from immediately after the restoration process is rapidly cooled to the start of the molding process is 1 hour. If this is exceeded, natural aging will progress too much. As a result, of course, the effect of the restoration process of the present invention is not sufficiently exhibited in the molding process, although it depends on the molding process time.

  The forming process itself is selected from 7000 series aluminum alloy extruded profile, which is the entire longitudinal direction of the profile, or a partial bending process, a partial crushing process of the profile section, and a punching process to the profile. The These are forming processes into a member shape as plastic working accompanied by generation of residual stress, and these forming processes are selected as appropriate, alone or in combination.

(refining)
In the present invention, an artificial aging treatment is performed on the molded member (7000-type aluminum alloy extruded profile member) to increase the strength. In the present invention, when quenching or quenching is performed on-line continuously on the extrusion process immediately after extrusion (on the exit side of the extruder), after the molding process and before artificial aging treatment The solution heat treatment and quenching by reheating are not performed.

  In order to improve the mechanical properties of the member, the artificial age hardening treatment is preferably performed by heating at 100 to 200 ° C., preferably for 12 to 36 hours (hr). Such an artificial aging treatment ensures a 0.2% proof stress of 300 MPa or more for the product.

  According to the preferred 7000 series aluminum alloy composition and manufacturing method described above, the extruded profile is formed into a member by a forming process accompanied by the generation of residual stress, and an artificial aging treatment is performed after the forming process. A high-strength 7000 series aluminum alloy member that is a member and has a 0.2% proof stress of 300 MPa or more and a residual stress of 160 MPa or less at the position of the member subjected to the forming process can be obtained.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not restrict | limited by the following Example from the first. For example, if the above-mentioned conditions and the following example conditions are replaced from extrusion to rolling as well as an extruded profile, it can be applied to a rolled sheet as a material, and is included in the technical scope of the present invention.

  Next, examples of the present invention will be described. A hollow extruded shape (raw material) made of each 7000 series aluminum alloy shown in Table 1 is hot-extruded, and this hollow extruded shape is subjected to Table 2 without any artificial tempering other than natural aging after the end of extrusion. Restoration processing was performed under various conditions shown. And after completion | finish of this decompression | restoration process (after completion | finish of rapid cooling to room temperature), after various time passages shown in Table 2, as a shaping | molding process with generation | occurrence | production of a residual stress, without artificially refining except this restoration | repair process. The material was made into a member by bending under common conditions. Then, the material after bending is subjected to tempering only by artificial aging treatment without solution treatment and quenching treatment under common conditions, such as 0.2% proof stress of the tempered member. The mechanical properties and the residual stress at the position of the member subjected to the bending process were measured and evaluated. These results are shown in Table 3.

  As specific manufacturing conditions, first, billets (round bar ingots) made of 7000 series aluminum alloys shown in Table 1 were cast. The billet is subjected to a homogenization heat treatment at 500 ° C. for 10 hours in the same manner as in each example, followed by direct hot extrusion that is water-cooled (rapidly cooled) from a temperature of 500 ° C. at the extrusion start temperature of 440 ° C. Thus, a hollow extruded shape (long material) having a substantially rectangular mouth-shaped cross section intended for a door beam as a member was obtained.

  As an example of a door beam, the hollow extruded shape has a rectangular cross section, the width of the flange on the outside of the bend is relatively short 40.0 mm, and the width of the flange on the inside of the bend is 50.0 mm, which is relatively long. The distance between the outer sides of these flanges parallel to each other (vertical width of the profile) was 30.0 mm. The distance between the outer sides of the right and left ribs that connect the inner and outer flanges at right angles to each other (the width of the profile) was 25.0 mm. The length (width) from the outside of each of the left and right ribs is 5.00 mm on the left and right sides of the flange that is the outer side of the bend, and the outer sides of the left and right ribs are also on the left and right sides of the flange that is the inner side of the bend. The left and right ribs were erected at positions where the flanges protruded from the left and right, each having a length (width) of 10.00 mm. Therefore, the cross section of the hollow extruded shape (door beam) is substantially pie-shaped. Further, the thicknesses of the flanges on the outside of the bends were each uniform 4.0 mm, the thicknesses of the flanges on the inside of the bends were each 4.5 mm, and the thicknesses of the left and right ribs were each 2.3 mm.

  After the hot extrusion, in common, after cutting to an appropriate length, after 20 days natural aging (room temperature aging) (without artificial tempering other than this natural aging) The restoration process was performed using various heating, holding temperature (substance temperature), holding time, and cooling conditions shown in Table 2.

  The heating speed during rapid heating in the restoration process was controlled by a heater of a glass stone furnace, and after holding at a predetermined actual temperature, the holding time was controlled by the timing of taking out the extruded shape material from the furnace. And the cooling rate was controlled to the temperature of room temperature of about 18-20 degreeC by the grade of the water cooling to an extruded shape raw material immediately after this taking out. The actual temperature of the extruded shape material is measured by bringing a commercially available contact thermometer directly into contact with the extruded shape material, but may be measured industrially by a non-contact radiation thermometer or the like.

  At this time, as a change with time of 0.2% proof stress of the extruded shape material, immediately after production (rapid cooling) by the hot extrusion, immediately after the natural aging for 20 days, immediately before the restoration process, and quenching in the restoration process The 0.2% proof stress of the extruded profile material was measured after the tensile test procedure described later.

  Further, the conductivity of the extruded shape material (T1 material = natural aging material) immediately before the restoration process and the conductivity of the extruded shape material immediately after the rapid cooling in the restoration process are measured using a commercially available digital conductivity meter (eddy current: Measurement was performed at electromagnetic induction, test frequencies 60 KHz, 500 KHz (when using a standard probe), measurement range 0.8 to 110% IACS, 0.45 to 64 MS / m resolution). The measurement result was an average value at five arbitrary locations. Then, the difference between the conductivity (average value) of the extruded shape material immediately after the rapid cooling in the restoration process and the conductivity (average value) of the extruded shape material (T1 material) immediately before the restoration process is expressed as T1. It calculated | required as a conductivity difference with material. These results are shown in Table 2.

  After this restoration process, as shown in Table 2, the time (required time) from immediately after completion of the rapid cooling to the room temperature to the start of the molding process was changed variously, and the rest of the process was not artificially tempered except for the restoration process. Bending, cross-sectional crushing, and punching were each selected as the forming process involving generation of stress and plastic working. These may be necessary in combination or independently as a forming process when forming the extruded shape material into a door beam member.

  Bending is performed using a three-point bending test die with a radius of 150 mm, and an extruded shape material with a length of 1055 mm is placed on two roller stands (φ30 mm) spaced 800 mm apart, and the bending outer flange side is on the upper side. It was placed so that the left and right sides would be of equal length. Then, the three-point bending test die was pushed by 500 mm toward the center of the bent outer flange on the upper side from the upper side to the lower side, and the member was given a permanent deformation that bent in an arc shape in the longitudinal direction. .

  Before crushing, the crushing of the cross-section is placed in the hollow space from the end of the extruded profile at the position where the mandrel is to be crushed, and the part of the extruded profile where the mandrel is installed is bent. Restrained by a die from the lower side of the inner flange, a punch having a radius of 150 mm is disposed on the upper side of the bent outer flange so as to face the mandrel. Partial crushing (press molding) was performed up to a distance of 1/3 of the flange: 10.3 mm.

  In the punching process, a hole having a diameter of 10 mm was punched out from above the bent outer flange of the extruded profile.

  And each of these moldability of each extruded shape material was evaluated. The evaluation is an example in which 5 pieces of the same material are molded under the same conditions, and 5 pieces (5 times) have no molding defects such as cracks and deformations at the time of each forming process. The case in which molding defects such as cracks and deformation occurred during processing was evaluated as x. The results are shown in Table 3.

  Moreover, the spring back property in each molding example of each of the extruded shape materials was evaluated. Evaluation was performed by the size of the deviation width from the set shape among the above five molding examples (5 times). Even if one piece (one time), the deviation from the set dimensions and shape due to the spring back is large, and those that are judged to require correction processing are ×, all are within the set dimensions and shape range, and it is determined that correction processing is unnecessary. Examples were evaluated as ○. The results are shown in Table 3.

  Each of these molded members was tempered by an artificial aging treatment at 130 ° C. for 12 hours in common with each example. In Table 2, an example of performing this tempering is marked with a circle. Then, the 0.2% proof stress of the tempered member and the residual stress at the position where the three-point bending test die was pressed (center portion) were measured.

Tensile properties:
Tensile strength, proof stress, and elongation were measured using a JIS No. 4 tensile test specimen taken from an arbitrary position in the extrusion direction of the member in accordance with a metal material test method defined in JISZ2241. In addition, these measured values were made into the average value of the measured value of three collection test pieces in each example. The results are shown in Table 3.

Residual stress:
The residual stress was measured by the following procedure using a cutting method. The respective processing positions of the member (bending processing is a mold pressing center position, cross section crushing processing is a crushing processing center position, and punching processing is a hole peripheral position) are set as measurement target positions. Then, the surface of the measurement target position is polished with sandpaper, washed with acetone, the strain gauge 2 is adhered to the polished portion with an instantaneous adhesive, and left at room temperature for 24 hours, and then the lead wire 3 of the strain gauge 2 is used as a strain gauge. Connect and set the zero point, cut the area around the strain gauge 2 with a metal saw to 10 mm square and 2 mm depth to release the stress, measure the strain amount ε after cutting, and determine the residual stress value σ by the following formula Was calculated. σ = −E × ε (E; Young's modulus), where E = 68894 N / mm ² .

The aluminum alloy of each invention example of the alloy numbers 1-4 of Table 1 is in this invention component composition range. The extruded shapes of each invention example in Table 2 using these were subjected to the restoration process within the above-described preferable condition range, and the 0.2% proof stress immediately after the quenching in the restoration process was reduced to 120 MPa or less. The conductivity difference between the extruded shapes before and after the restoration process (immediately before the restoration process and immediately after the rapid cooling) is less than 5% IACS.
As a result, as shown in Table 3, each invention example can surely exhibit the various effects of the restoration process. That is, the 0.2% proof stress of the tempered member is at least 300 MPa, and in a higher example, it is 350 MPa or more or 400 MPa or more. At the same time, the residual stress at the position of the member that has undergone the forming process is 160 MPa or less, and 120 MPa or less in the lower example even if it is high.

  As a result, according to the restoration process of the present invention, even a high-strength 7000 series aluminum alloy extruded shape after 20 days of natural aging (room temperature aging), it is also possible to form a member by forming with residual stress. Even when the high-strength 7000 series aluminum alloy member is made, the 0.2% proof stress of the member after the artificial aging treatment can be increased to 300 MPa or more, and it has undergone the above-described forming process without solution treatment. It can be seen that the residual stress at the member position can be suppressed to 160 MPa or less.

  Furthermore, as shown in Table 3, each invention example is an extruded shape when natural aging has progressed. As a result, the amount of springback is reduced, and as a result, the moldability and molding accuracy of the member can be further improved. .

  On the other hand, the aluminum alloy of each comparative example of alloy numbers 5, 6, and 7 in Table 1 has too little Zn, Mg, and Cu, respectively. For this reason, even if it is a member manufactured on the same conditions as an invention example like Comparative Examples 7, 8, and 9 of Table 2 using these alloys, 0.2% of members after artificial aging treatment Yield is less than 300 MPa.

  Further, Comparative Examples 10 to 22 in Table 2 are invention example aluminum alloys of Alloy Nos. 1, 2, and 3 in Table 1, but any condition of the restoration treatment is out of the preferable range. Therefore, the 0.2% proof stress immediately after the rapid cooling in the restoration process is not reduced to 120 MPa or less, or the conductivity of the extruded shape before and after the restoration process (immediately before the restoration process and immediately after the quenching) in the restoration process. The difference is 5% IACS or more.

  In Comparative Examples 11, 15, 19, and 22, as shown in Table 2, the conductivity difference of the extruded profile before and after the restoration process in the restoration process (immediately before the restoration process and immediately after the rapid cooling) is less than 5% IACS. The 0.2% yield strength immediately after the rapid cooling in the restoration process exceeds 120 MPa. As a result, as shown in Table 3, in Comparative Examples 11, 15, 19, and 22, even if the 0.2% proof stress of the member after the artificial aging treatment is 300 MPa or more, the residual stress at the member position subjected to the molding process Exceeds 160 MPa. In each of these comparative examples, as shown in Table 3, the amount of spring back of the extruded shape when the natural aging has progressed is not reduced. Among these, in Comparative Examples 11, 15, and 22, it takes one hour (hr) to take too long until the member is molded after the restoration process.

  In other comparative examples, as shown in Table 2, the 0.2% proof stress immediately after the rapid cooling in the restoration process is 120 MPa or less, but the conductivity difference between the extruded shapes before and after the restoration process (just before the restoration process and immediately after the quenching). Is over 5% IACS. As a result, as shown in Table 3, although the residual stress at the member position subjected to the molding process is as low as 160 MPa or less, the 0.2% proof stress of the member after the artificial aging treatment is only at a low level of less than 300 MPa, and the restoration is performed. It turns out that it has become perfect O material by processing.

  From the above examples, the 0.2% yield strength immediately after the rapid cooling in the restoration process is reduced to 120 MPa or less, the conductivity difference before and after the restoration process is less than 5% IACS, and these The significance of satisfying both is supported. Further, even after natural aging of each specified condition of the restoration process in the present invention, the formability of the 7000 series aluminum alloy extruded shape material itself to the member can be improved, and the residual stress applied by this forming process can be reduced. Further, the technical significance that can be further strengthened by tempering is supported.

  According to the present invention, a high-strength 7000 series aluminum that can improve the formability itself even after natural aging, reduce the residual stress applied by this forming process, and further increase the strength by applying a tempering treatment. An alloy member manufacturing method and a high-strength 7000 series aluminum alloy member can be provided. For this reason, the present invention can be suitably used for a bumper hose made of a lightweight high-strength 7000 series aluminum alloy, a reinforcing member for an automobile such as a door beam, or a structural member for an aircraft.

Claims (3)

In mass%, Zn: 5.0-8.0%, Mg: 0.3-2.0%, Cu: 0.05-0.5%, and Mn: 0.01-0. 7000 series aluminum alloy containing 3%, Cr: 0.01-0.3%, Zr: 0.01-0.3%, or two or more kinds, with the balance being inevitable impurities and aluminum After the material is manufactured by plastic working from the ingot, a restoration process is performed without artificially refining except natural aging, and the restoration process is rapidly heated at a heating rate of 0.5 ° C./second or more. ° C., greater 0 after holding for a short time of less than 20 seconds at 500 ° C. less substantial temperature range, quenched with room temperature to 0.5 ° C. / sec or more cooling rate, immediately after the quenching of the material. 2% yield strength with a less 120 MPa, the material immediately after the quenching Conductivity and, wherein the difference between the conductivity of the material of the restoration process just before is less than 5% IACS, after quenching completion of the room temperature of the restoration process within one hour, than the restoration process is artificially regulated The material is formed into a member by forming with residual stress selected from bending, cross-sectional crushing, and punching without being subjected to quality treatment, and this member is subjected to artificial aging treatment without solution treatment and quenching treatment. A high-strength 7000 series aluminum alloy member characterized in that the 0.2% proof stress of the member after the artificial aging treatment is set to 300 MPa or more and the residual stress at the member position subjected to the forming process is set to 160 MPa or less. Manufacturing method. The method for producing a high-strength 7000 series aluminum alloy member according to claim 1 , wherein the aluminum alloy material is an aluminum alloy extruded shape, and the plastic working is hot extrusion. In mass%, Zn: 5.0-8.0%, Mg: 0.3-2.0%, Cu: 0.05-0.5%, and Mn: 0.01-0. 7000 series aluminum alloy containing 3%, Cr: 0.01-0.3%, Zr: 0.01-0.3%, or two or more kinds, with the balance being inevitable impurities and aluminum The extruded profile is restored, and the 0.2% proof stress of the extruded profile immediately after the rapid cooling after the restored process is 120 MPa or less, and the conductivity of the extruded profile immediately after the rapid cooling and the restoration The difference from the electrical conductivity of the extruded shape material immediately before the processing is less than 5% IACS, and the material is formed into a member by forming processing accompanied by generation of residual stress selected from bending processing, cross-section crushing processing, and punching processing. In addition, after this forming process, solution treatment and quenching treatment A 7000 series aluminum alloy member that has been subjected to artificial aging treatment without being deformed, and has a 0.2% proof stress of 300 MPa or more and a residual stress at a position of the member subjected to the forming process of 160 MPa or less. A high-strength 7000 series aluminum alloy member.