KR101455606B1 - Aluminum alloy sheet for cold press forming, method of manufacturing the same, and cold press forming method for aluminum alloy sheet - Google Patents

Abstract

The Al-Mg-Si aluminum alloy sheet subjected to the aging treatment at room temperature (or under aging) is heated at a temperature within the range of 150 to 350 占 폚 for 5 minutes or less before press molding, (Partial conversion heat treatment) in which the difference in strength between the heating portion and the non-heating portion is made to be 10 MPa or more (0.2% proof stress difference). The alloy plate thus treated is subjected to cold press forming under the condition that the low-strength heating portion is brought into contact with the crease restraining mechanism of the press and the non-heated portion with low strength is brought into contact with the shoulder portion (radius) of the punch. In the partial conversion heat treatment, the cooling rate is set to 30 占 폚 / min or more at the temperature raising rate and cooling to 100 占 폚 or lower. Further, the period for allowing the alloy plate to stand at room temperature until the cooling press molding after the partial conversion heat treatment is set within 30 days.

Aluminum alloy plate for cold press forming, cold press forming method

Description

TECHNICAL FIELD [0001] The present invention relates to an aluminum alloy sheet for cold press forming, a method for producing the same, and a cold press forming method for an aluminum alloy sheet. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to an Al-Mg-Si aluminum alloy plate used after molding, particularly cold press forming and baking of a coating film thereon, a production method thereof, and a cold press molding method using the same. More specifically, the present invention is preferably used for various components and components such as automobiles, ships and aircrafts, such as automobile body plates and body panels, as building materials, structural materials, or for various devices, household appliances, Al-Mg-Si based aluminum alloy plate.

Conventionally, automobile body plates have been obtained mainly by using cold rolled steel sheets in the past. However, in recent years, in view of global warming inhibition, a rolled aluminum alloy sheet has been mainly used as a result of a wide recognition of the importance of weight reduction of the vehicle body in response to a request to reduce CO ₂ emissions. On the other hand, rolled aluminum alloy sheets are generally inferior in formability to cold rolled steel sheets and limit their wide range of applications. In order to improve the formability of the rolled aluminum alloy sheet, it is urgently required to improve the formability of the blank material itself and to research unique methods for forming the blank material.

Also, in this kind of application, the rolled steel is usually baked on it prior to its use. Therefore, the rolled steel is required to have properties to ensure high strength after baking (bake hardenability or BH performance).

JP-A 4-351229 and 2006-205244 propose the application of the warm deep drawing method to improve the formability of an aluminum alloy sheet. The warm forming method can improve the deep drawability of the aluminum alloy sheet, but applying this method to large-scale industrial production involves some problems.

Specifically, the warm deep drawing method is characterized in that it is necessary to perform deep drawing under the condition of heating the flange portion and cooling the punch-corresponding portion. This causes the following problems:

1. The press requires a longer total molding time as compared to the case of cold press forming, since the function for heating and cooling of the aluminum alloy sheet must be provided, resulting in lower production efficiency and increased molding cost.

2. Since molding is carried out under a warm condition, it is necessary to develop a new lubricant since a conventional lubricant for cold forming can not be used.

3. The press is complicated in configuration, which leads to an increase in equipment cost.

4. As presses become more complex, difficulties in quality control arise.

On the other hand, the warm deep drawing method is a method of locally heating and softening a portion of an aluminum alloy plate blank to be formed with a large working range before molding. Therefore, in consideration of the timing of molding, the warm deep drawing method can be said to be a method of studying the improved formability by locally imparting a difference in strength to an aluminum alloy plate blank. In this connection, as another method of studying the similarly improved formability by providing a difference in strength in an aluminum alloy plate blank, there is known a method of previously performing local heat treatment on the blank (see, for example, JP-A 2000-117338 Patent Document 3]). This method is particularly effective when applied to aging-hardenable alloys that can achieve large strength changes by solution-ing and precipitation in a matrix by heat treatment, such as Al-Mg-Si alloys, do.

Here, in the technique disclosed in Patent Document 3, while the Al-Mg-Si based alloy sheet transferred after the solution treatment in the aluminum rolling machine is maintained at room temperature, ultrafine precipitates composed of Mg and Si are uniformly dispersed in the matrix by room temperature aging And a strength difference is introduced into the alloy plate blank by using the fact that the strength is improved in comparison with the strength immediately after the sol-coating treatment. Specifically, in the technique according to Patent Document 3, by using the fact that the above-mentioned precipitate formed at room temperature is easily re-dissolved by heating at a relatively low temperature of 250 占 폚 or more for a short time and the strength at the heating portion is lowered, It is explained that the localized strength difference can be given to the aluminum alloy sheet by the treatment to be performed on the aluminum alloy sheet.

On the other hand, in the technique disclosed in Patent Document 3, the formability of the aluminum alloy plate blank is improved under the premise that the blank is press-molded under the condition that its periphery is completely fixed by clamping; Thus, except for the area contacted by the shoulder of the punch, the area in the blank surface which is placed underneath during press forming and is contacted by the punch is softened by heating to provide improved formability. However, in this case, a problem has been found that the deformation concentrates on the area to be laid under the punch and softened, and the plate thickness is considerably lowered locally in this area to lower the rigidity of the molded article. In addition, since the press molding is performed under the condition that the periphery of the blank is completely fixed, the inflow of the material from the peripheral restraining portion of the blank is not allowed completely, and the degree of improvement in formability is limited. Further, when considered as an automobile body plate, bending (hemming) may be performed at the peripheral portion of the molded article after press molding. In this connection, in the technique of Patent Document 3, the plate region below the punch, that is, the central portion of the plate is heated, while the peripheral portion of the plate is placed in the state at the time of age precipitation due to room temperature aging, It is very inferior and causes a crack in the bent portion.

It is difficult to satisfactorily satisfy the moldability of the automobile body plate and other required performance at present in the molding of the Al-Mg-Si alloy sheet according to the related art described above.

Concretely, in contrast to the related art in recent years, a demand for high moldability of a material, particularly a high drawability, has demanded a high design quality for an automobile panel shape. In addition, it is naturally required not only to improve the formability index such as drawing performance but also to prevent deterioration of bending property (hemming property) and strength, and at the same time, to improve drawability. High molding productivity is also required. From these viewpoints, the conventional method of forming an Al-Mg-Si alloy plate is not yet satisfactory.

The present invention is made in view of the above-described circumstances. It is therefore an object of the present invention to provide an aluminum alloy sheet which can ensure both the high moldability of the aluminum alloy sheet and the maintenance of high molding productivity and which can be suitably used without deteriorating the required properties, A Mg-Si-based aluminum alloy plate, a method of manufacturing the same, and a press molding method using the same.

Specifically, a technique of subjecting an aluminum alloy sheet blank to a partial heat treatment (conversion treatment) in advance to give a difference in strength in the surface of the plate blank is a basis of the present invention. In order to allow the inflow of the material from the restraining periphery in the cold drawing, the cold-dip drawing of the blank in which the strength distribution is optimized by appropriately adjusting the heating portion in the partial conversion heat treatment. This facilitates the inflow of the material from the periphery of the blank, thereby enabling the production of molded parts and deep drawing with a uniform sheet thickness. Further, bending applied to the peripheral portion of the molded article is facilitated. Further, the time required for the pre-heat treatment is shortened, and at the same time, the curing property of the film baking of the heating portion is maintained, and the high production efficiency of the conventional cold press forming is not deteriorated.

The present inventors have conducted various experiments and investigations to solve the above-mentioned problems. As a result of experiments and investigations, it has been found that when the partial conversion heat treatment is carried out to improve the deep drawability and the bendability of the aged-precipitated aluminum alloy sheet or the aluminum alloy sheet subjected to normal temperature aging or artificially aging after the solid solution treatment, It has been found that it is important to optimally select the part. By optimizing the heating temperature reached in the partial conversion heat treatment, the heating rate and the cooling rate after heating are increased, and the portion of the related plate can be effectively softened in a very short time by restoration and the bendability of the plate can be also improved And that a high film bake hardenability can be imparted to the plate. Based on these findings, the present invention is achieved.

The term "transition" as used herein means that the aging-hardenable aluminum alloy is rapidly cooled after solubilization to dissolve the alloying element at room temperature to a supersaturated level, and then the alloy is maintained at room temperature or slightly higher than room temperature, To improve the strength of the alloy, and then heating the alloy at a temperature exceeding the holding temperature for a short time to induce redissolution of the fine precipitates, thereby lowering the strength. Further, the treatment for causing the phenomenon by heating the material held at the above-mentioned temperature after the solution treatment (solution treatment) is referred to as "conversion heat treatment ". In addition, the term "partial" conversion heat treatment herein refers to a treatment for selectively heating only a predetermined portion (region) in the surface of an aluminum alloy plate blank for restoration to soften only a predetermined portion.

According to one embodiment of the present invention, after a partial conversion heat treatment is performed by an Al-Mg-Si-based aluminum alloy and cooled to room temperature, a cold press having a 0.2% difference in resistance between its heating portion and its non- An aluminum alloy sheet for molding is provided.

In an aluminum alloy for cold press forming, the region of the plate which is preferably suppressed by the crease restraining mechanism during cold pressing is set as the heating portion, and the region of the plate where the punch shoulder portion is pressed during cold pressing is set as the non-heating portion.

According to another embodiment of the present invention, an area of the plate, which is constituted by an Al-Mg-Si based aluminum alloy and suppressed by a wrinkle restraining mechanism during cold pressing, is set as a heating part, In which the difference between the tensile strength of the non-heated portion and the 0.2% proof stress of the heated portion is increased by 20 MPa or more through the partial conversion heat treatment under the condition that the area of the non- .

According to another embodiment of the present invention, there is provided a method of manufacturing a rolled Al-Mg-Si based aluminum alloy sheet rolled to a predetermined sheet thickness as a blank material, a rolling treatment of the rolled sheet at a temperature in the range of 480 to 590 캜, A step of leaving the back-rolled plate at room temperature for at least one day, and a step of partially heat-treating the rolled plate before cold press forming to make the 0.2% strength difference between the heating portion and the non- A method for producing an aluminum alloy sheet for cold press forming is provided.

In the above-described manufacturing method, preferably, the partial conversion heat treatment is performed by setting the region of the plate which is suppressed by the crease restraining mechanism during cold press forming to the heating portion, and the region of the plate where the punch shoulder portion is pressed during cold pressing is set to the non- .

In this manufacturing method, the partial conversion heat treatment is preferably performed by heating the rolled plate at a temperature raising rate of 30 DEG C / min or more to a temperature within a range of 150 to 350 DEG C, And then cooling the rolled plate to a temperature of 100 DEG C or less at a cooling rate of 30 DEG C / min or more.

In this manufacturing method, preferably, the partial conversion heat treatment is performed by heating the rolled plate at a temperature raising rate of 50 to 350 占 폚 at a temperature raising rate of 50 占 폚 / min or more, , And then cooling the rolled plate at a cooling rate of 50 DEG C / min or more to a temperature of 100 DEG C or lower, whereby the tensile strength of the non-heated portion and the tensile strength of the heated portion The difference between the 0.2% proof stress increases by more than 20 MPa.

According to another embodiment of the present invention, there is provided a method of performing cold press forming using an aluminum alloy sheet for cold press forming manufactured by the above-described manufacturing method, wherein the cold press forming is a step of heat- Before leaving for 30 days.

According to another embodiment of the present invention, an Al-Mg-Si-based aluminum alloy plate blank in an aged-precipitated state at room temperature aging is subjected to a cold press forming process by suppressing the end portion thereof by using a punch Wherein a portion of the aluminum alloy plate blank which is located on the outer side of the area contacted by the shoulder portion of the punch during press forming is smaller than the whole or all of the portion of the aluminum alloy plate blank is set as the heating portion , Setting a portion other than the heating portion as a non-heating portion; In the aluminum plate blank, the heating portion is rapidly heated to instantly dissolve the aged-precipitate to soften the heating portion, while the non-heating portion is subjected to the partial conversion heat treatment to lower the strength of the heating portion in comparison with the strength of the non- Rapidly cooling the heating part to room temperature; Then, the aluminum alloy plate blank is subjected to cold press forming before the strength of the heating portion is returned to the level before the partial conversion heat treatment by the age precipitation during the holding at room temperature.

According to another embodiment of the present invention, there is provided a process for producing an Al-Mg-Si-based aluminum alloy sheet, which comprises subjecting a solid solution to a sub-aging treatment at 140 DEG C or lower by artificial aging or a step of aging at room temperature and an artificial aging , Wherein the aluminum alloy sheet blank has a 0.2% proof strength of 90 MPa or more based on the application of the aging treatment to the outside of the area contacted by the shoulder portion of the punch during press forming The heating portion is set to a portion which is less than the entirety or the entirety of the portion of the upper surface of the heating portion, while the other portion than the heating portion is set as the non-heating portion; The aluminum plate blank is subjected to a partial conversion heat treatment in which the heating portion is rapidly heated to dissolve the aged-precipitate momentarily to soften the heating portion and not to the non-heating portion to lower the strength of the heating portion in comparison with the strength of the non- Rapidly cooling the portion to room temperature; Then, the aluminum alloy plate blank is subjected to cold press forming before the strength of the heating portion is returned to the level before the partial conversion heat treatment by the age precipitation during the holding at room temperature.

In the cold press forming method, the partial conversion heat treatment is preferably performed by heating the plate blank to a temperature within a range of 150 to 350 占 폚 at a temperature raising rate of 30 占 폚 / min or more, a period of 5 minutes or less Holding the plate blank at a temperature within this range, and thereafter cooling the plate blank to a temperature of 100 DEG C or less at a cooling rate of 30 DEG C / min or more.

In the cold press forming method, preferably, the partial conversion heat treatment is performed by heating the plate blank to a temperature within a range of 180 to 350 占 폚 at a temperature raising rate of 50 占 폚 / min or more, a period of 5 minutes or less And then cooling the plate blank to a temperature of 100 DEG C or less at a cooling rate of 50 DEG C / min or more, whereby the tensile strength of the non-heated portion and the heating The difference between the 0.2% of the negative history increases by more than 20 MPa.

In the cold press forming method, preferably, a portion of the aluminum alloy sheet blank which is subjected to bending after forming a cold press on a portion on the outer side of the region to be contacted by the punch shoulder portion during cold pressing is included in the heating portion in the partial conversion heat treatment do.

In the cold press forming method, preferably, at least one zone of the entire interior of the area of the aluminum alloy plate blank, or any shape within this area, which is contacted by the punch shoulder during cold pressing, .

According to another embodiment of the present invention, there is provided a cold press-formed aluminum alloy product obtained by the cold press forming method of the above-described aluminum alloy sheet, wherein the aluminum alloy product is heated by artificial aging treatment performed within 30 days after the partial conversion heat treatment The internal strength of the negative electrode is improved by 20 MPa or more.

In the above-described aluminum alloy sheet for cold press forming, preferably, the Al-Mg-Si aluminum alloy sheet contains 0.2 to 1.5% (mass%, the same applies hereinafter) of Mg and 0.3 to 2.0% 0.03 to 1.0% of Fe, 0.03 to 0.6% of Mn, 0.01 to 0.4% of Cr, 0.01 to 0.4% of Zr, 0.01 to 0.4% of V, 0.005 to 0.3% of Ti, 0.03 to 2.5% of Zn and 0.01 To 1.5% of Cu, and the balance of Al and unavoidable impurities.

In the above-described method for producing an aluminum alloy sheet for cold press forming, preferably, the Al-Mg-Si aluminum alloy sheet contains 0.2 to 1.5% Mg and 0.3 to 2.0% Si, and 0.03 to 1.0% Fe , 0.03 to 0.6% of Mn, 0.01 to 0.4% of Cr, 0.01 to 0.4% of Zr, 0.01 to 0.4% of V, 0.005 to 0.3% of Ti, 0.03 to 2.5% of Zn and 0.01 to 1.5% of Cu An aluminum alloy sheet containing at least one selected and the remainder being Al and unavoidable impurities.

In the cold press forming method of the above-described aluminum alloy plate, preferably, the Al-Mg-Si aluminum alloy plate contains 0.2 to 1.5% of Mg and 0.3 to 2.0% of Si, and 0.03 to 1.0% of Fe, 0.03 To 0.6% of Mn, 0.01 to 0.4% of Cr, 0.01 to 0.4% of Zr, 0.01 to 0.4% of V, 0.005 to 0.3% of Ti, 0.03 to 2.5% of Zn and 0.01 to 1.5% of Cu And the remainder being aluminum and unavoidable impurities.

According to the present invention, an Al-Mg-Si based aluminum alloy plate subjected to normal temperature aging after solution treatment (solution treatment) or an aging treatment obtained by a combination of artificial aging or room temperature aging and artificial aging is carried out, (Partial conversion treatment) of the Al-Mg-Si-based aluminum alloy sheet having the suppressed peripheral portion and the non-heating portion is performed between the punch shoulder contact portions So that the press formability of the alloy sheet can be improved. In addition, since the partial conversion heat treatment is performed before the cold press molding as other steps than the cold press molding, the press molding itself can be performed at a high speed by using a conventional cold press machine. Therefore, it is possible to prevent an increase in apparatus cost or reduction in production efficiency for a press as in the case of applying hot forming, and the necessity of a specific lubricant is eliminated.

Further, according to the present invention, the shape freezing performance of the molded article is improved by the suppressed peripheral portion whose strength is lowered. In addition, since the hardening speed at the baking of the film is high and the strength thereof is rapidly recovered, the portion with reduced strength through the conversion phenomenon can obtain a high film age-hardening property (BH-performance) Can be prevented from deteriorating. In addition, the bendability of the molded article can be improved by the optimum selection of the region where the switching heating is performed.

The aluminum alloy sheet used in the present invention is basically an aged alloy which is in an aged-precipitated state at room temperature aging after a solution treatment (solution treatment) at a high temperature, or a combination of artificial aging or room temperature aging and artificial aging Al-Mg-Si based aluminum alloy plate in an aged state obtained by the aging treatment obtained by the above-mentioned aging treatment. From this point of view, the present invention will be described in detail in accordance with its main items.

Process for producing aluminum alloy sheet for cold press forming

First, a method of producing an aluminum alloy sheet for cold press forming is basically performed by a method commonly used in the field of aluminum alloy manufacturing, in which a blank material constituting an aluminum alloy blank to be formed by the molding method according to the present invention is manufactured .

Specifically, a melt of an aluminum alloy melted and conditioned in a predetermined composition is cast by appropriately selecting among a melting and casting method in general. Examples of typical melting and casting methods include a semi-continuous casting method (DC casting method) and a thin plate continuous casting method (such as a roll casting method). Then, the thus obtained aluminum alloy ingot is homogenized at a temperature of 480 DEG C or higher. The homogenization treatment is a process in which the fine segregation of the alloying element in the solidification of the melt and the alloy melt containing various transition elements other than Mn and Cr are carried out in a homogeneous and dense manner in a matrix of dispersed particles of an intermetallic compound mainly composed of these elements This is a necessary step for precipitation. In the homogenization treatment, the heating time is usually one hour or more, and the heating is usually terminated within 48 hours for economic reasons. Note that in the homogenization treatment, the heating temperature is close to the heat treatment temperature for heating to the hot rolling start temperature before hot rolling, so that the homogenization treatment can be performed by heat treatment functioning both as heating for homogenization and pre-hot rolling heating. After properly facing before or after the homogenization treatment, hot rolling is started at a temperature in the range of 300 to 590 DEG C, and then cold rolling is performed to produce an aluminum alloy plate having a predetermined thickness. During the hot rolling between the hot rolling and the cold rolling, or during the cold rolling, the intermediate annealing can be performed as required.

Then, an aluminum alloy plate obtained by cold rolling is subjected to a solution treatment (solution treatment). The solid solution treatment is an important step for imparting bake hardenability to the alloy plate by dissolving Mg ₂ Si and element Si in the matrix and improving the strength of the alloy plate after baking the coating film. This step also contributes to an improvement in ductility and bendability by lowering the distribution density of the two-phase particles through dissolution (into a solid solution) of Mg ₂ Si, elemental Si particles and the like; This step is also important for achieving good moldability through recrystallization. In order to exhibit these effects, this treatment is carried out at 480 DEG C or higher. Incidentally, eutectic melting may occur if the solvating temperature exceeds 590 占 폚. Therefore, the sol-gel treatment is performed at 590 占 폚 or lower.

Here, the cold-rolled sheet obtained in the form of a coil can be efficiently subjected to a solubilization treatment (solution treatment) by continuously passing a continuous annealing furnace having a heating zone and a cooling zone. In the treatment by the use of such a continuous annealing furnace, the aluminum alloy sheet is heated to a high temperature in the range of 480 to 590 캜 when passed through the heating zone, and then rapidly cooled when passed through the cooling zone. By this series of processing steps, Mg and Si which function as main alloying elements among the alloys adopted as the target material in the present invention are dissolved once into the matrix at a high temperature, and the elements are supersaturated and melted at room temperature at the subsequent rapid cooling .

Aging during the period from solute treatment to conversion heat treatment

In order to provide a difference in strength between the heated portion and the non-heated portion of the alloy sheet by partial conversion heat treatment, a certain amount of clusters or fine precipitates are removed by room temperature aging (natural aging) during the period during which the alloy sheet is left at room temperature It needs to be formed. However, for such clusters or fine precipitates, a desired transition phenomenon may not occur in the heating portion in the subsequent partial conversion heat treatment, so that the strength reduction of the heating portion intended by the partial conversion heat treatment may not be realized. Therefore, after the solid solution treatment, the alloy plate is left at room temperature for at least one day until the partial conversion heat treatment. Incidentally, the period for allowing the rolled sheet to stand at room temperature before molding in the molding machine after the solution treatment in the blank remanufacturing machine is generally 10 days or more. In addition, the room temperature aging proceeds at the beginning of the starting period, but after a lapse of about six months, the aging at room temperature is not likely to proceed further. From this viewpoint, there is no upper limit set specifically for the period during which the alloy plate is left at room temperature before the heat treatment for conversion. Here, "room temperature" means specifically a temperature within the range of 0 to 40 占 폚.

However, according to the present invention, even in the case of the artificial aging after the solid solution treatment or the combination of the room temperature agitation and the artificial aging after the solid solution treatment, the partial conversion heat treatment A difference in strength can be given to the alloy plate. In the case of performing artificial aging, the strength of the alloy plate blank can be more easily improved as a whole before the partial conversion heating as compared with the case of the normal temperature aging alone. However, it is noted that the artificial aging temperature is 140 ° C or less, and the aluminum alloy sheet after aging is in an aged state. If the artificial aging temperature exceeds 140 캜, precipitates composed of Mg and Si formed by precipitation may aggregate, and the precipitates may not be easily dissolved in the solid solution in a short time by the subsequent partial conversion heat treatment. As a result, it takes a long time to soften through restoration, which lowers the productivity of press molding. When the artificial aging temperature is 140 ° C or lower, but artificial aging is performed for such a long time to bring the alloy plate blank into the post-peak-aged state or the over-aged state, precipitates composed of Mg and Si formed by precipitation may aggregate And the precipitate may not be easily dissolved in the partial conversion heat treatment, and it takes a long time to recover. From these viewpoints, a more preferable artificial aging temperature is 100 DEG C or less.

In the present invention, with respect to the material strength immediately after aging and immediately before the subsequent partial conversion heat treatment, the proof stress of the material (0.2% proof stress) is preferably 90 MPa or more. When the strength is less than 90 MPa from the viewpoint of the proof stress, the strength reduction in the portion recovered by heating in the subsequent partial conversion heat treatment may be insufficient and it may be difficult to impart a satisfactory strength difference to the material. This can be difficult. Incidentally, the more preferable strength value is 110 MPa or more.

Partial conversion heat treatment

The most important characteristic of the present invention is that the Al-Mg-Si aluminum alloy sheet aged as described above is cooled to room temperature before cold press forming, and then heated to a temperature between the heating portion (portion heated by the partial conversion heat treatment) (This means "part" with respect to the position on the two-dimensional surface and does not mean "part" with respect to extension or grade) in such a way that the difference in strength (0.2% ).

Here, it is known that the restriction of the deep drawing is determined by the gradation relationship between the breaking strength of the punch shoulder contacting portion and the inflow resistance of the suppressing peripheral portion (flange portion). Usually, the aluminum alloy plate for an automobile body plate is left at room temperature throughout the period from the blank remelt treatment to the user (molding machine) to press molding in the manufacturer. Since the Al-Mg-Si alloy is an aging-hardening alloy, the material strength can be improved due to the room temperature aging at a room temperature when the room temperature is maintained for a long time (a period of time during which the alloy plate is left at room temperature). If the alloy plate in this state is directly subjected to cold press forming, the press formability may be lowered due to the high inflow resistance of the restraining peripheral portion of the alloy plate.

On the other hand, when the alloy plate is subjected to the partial heat treatment before cold press forming, clusters and / or fine precipitates formed through room temperature aging (or a combination of artificial aging or room temperature aging and artificial aging) are decomposed and redissolved in solid solution, A decrease in strength, that is, a switching phenomenon occurs in the heating portion of the plate. The present invention uses this phenomenon only, and the amount of the decrease in strength in this case is 10 MPa or more.

More specifically, when the cold press forming is performed, the heating portion whose strength has been lowered by 10 MPa or more is brought into contact with the wrinkle restraining mechanism of the press while the hot portion is maintained at a high strength obtained by room temperature aging (or a combination of artificial aging or room temperature aging and artificial aging) The non-heated portion comes into contact with the shoulder portion (radius) of the punch. This improves the press formability, prevents the hemming property from deteriorating, and prevents the strength of the heating portion after baking the coating film from being lowered. Incidentally, in order to further improve the press formability, it is preferable to set the difference in strength between the heating portion and the non-heating portion of the alloy plate to a value of 20 MPa or more.

As a result of further studies conducted by the present inventors, it has been found that the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature is extended to 20 MPa or more through partial conversion heating. By imparting such a large difference in strength, the resistance against the inflow of the material from the restrained peripheral portion in which the strength (resistance of the restraining peripheral portion) is lowered at the time of drawing is lowered and the material strength of the punch shoulder portion ), And as a result, a deeper drawing is possible. Therefore, a method in which the difference between the tensile strength in the non-heated portion and the proof stress in the heated portion, which is essential for enhancing the drawability, is used as an index and the index is enlarged through the partial conversion heating is effective for improving the deep drawability of the alloy sheet . Incidentally, when the increase (increment) in the difference between the tensile strength of the non-heated portion at room temperature by the partial conversion heat treatment and the proof stress of the heating portion at room temperature is less than 20 MPa, it is impossible to achieve sufficient moldability improvement.

Here, in the state before the partial conversion heat treatment, the tensile strength and the proof stress can be regarded as being substantially uniform throughout the alloy plate blank. Therefore, the tensile strength and proof stress obtained by the tensile test on the tensile test specimen sampled from any position of the alloy plate blank can be regarded as the tensile strength of the non-heated portion before the partial conversion heat treatment and the proof stress of the heating portion before the treatment. On the other hand, the tensile test is to be carried out on the tensile test specimen sampled from each part, since the heating part and the non-heated part have different strengths in the state after the partial conversion heat treatment. Here, the "non-heated portion" means a portion (region) that does not intend to lower the strength by the partial conversion heat treatment. However, depending on the performance of the partial conversion heat treatment and / or the heating temperature reached in the partial conversion heat treatment, the temperature of the non-heating portion may rise to some extent due to the heat (remaining heat) transferred from the heating portion. In the case where the partial conversion heat treatment is performed in an ideal manner in which substantially no temperature rise occurs in the non-heated portion, the tensile strength of the non-heated portion is equivalent to the tensile strength before partial conversion heat treatment. In this case, therefore, the reduction in the strength in the heating portion is an increase (increment) in which the difference between the tensile strength of the non-heating portion at room temperature and the proof stress of the heating portion at room temperature increases through the partial conversion heat treatment. On the other hand, depending on the method and conditions of the partial conversion heating, the temperature of the non-heating portion may be increased to some extent due to the partial conversion heat treatment, and as a result, some restoration may be performed to lower the tensile strength of the non- . However, even in this case, as long as the increment (increment) of the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature is 20 MPa or more through the partial conversion heat treatment as described in the present invention, Can be substantially improved. This is because the tensile strength of the non-heated portion at room temperature through the partial conversion heat treatment and the increase in the proof stress of the heating portion at room temperature are used as an index of the present invention.

Details of the portion subjected to the partial conversion heat treatment

Now, the heated portion and the non-heated portion in the partial conversion treatment will be described in detail below.

Basically, by selecting the portion to be heated, the heating portion with low strength comes into contact with the wrinkle restraining mechanism of the press while the non-heating portion with high strength comes into contact with the shoulder portion (radius) of the punch. The progress of press forming for deep drawing is schematically shown in Fig. 1, and the portion where partial conversion heating is performed will be described below with reference to Fig. 1, reference numeral 1 denotes a die, 2 denotes a punch, 3 denotes a shoulder portion (radius) of the punch 2, 4 denotes a wrinkle restraining mechanism, and 5 denotes an aluminum alloy plate blank. In the partial conversion heat treatment, in the aluminum alloy plate blank 5 shown in Fig. 1, the area A (the area on the side of the wrinkle restraining mechanism 4) on the outer side of the area B, which is contacted by the punch shoulder part 3, It is effective that the whole part smaller than the whole part is softened by setting it as a heating part. In a particular case where one or more of the more deeply drawn shapes are partially present in the area C on the inner side of the area B which is to be contacted by the punch shoulder 3 (for example, see examples 4 and 6 to be described later) In obtaining the molded article, it is effective that at least one region having an arbitrary shape optimized in correspondence with the internal shape of the region C is added as the heating portion as described in Claim 14.

According to the present invention, it is also possible to solve the problem of low bendability of a molded product which is encountered in the related art in which the improvement of moldability is studied by applying a partial heat treatment to an alloy plate blank aged at room temperature. This problem confronts panels that require bending after press forming. The bending after press forming is applied to the portion of the region A on the outer side of the region B which is in many cases contacted by the punch shoulder portion. Using this fact, the portion to be subjected to the bending process after press forming can be selectively added as the heating portion, thereby solving the above-mentioned problem; This point is specified in claim 13. Here, the conversion heat treatment functions to greatly improve the bendability which is considerably lowered due to room temperature aging. This is the reason why the above-mentioned effect can be obtained.

Detailed conditions for partial conversion heat treatment

The partial conversion heat treatment is performed by heating the rolled plate at a temperature elevation rate of 30 DEG C / min or more to a temperature within a range of 150 to 350 DEG C, and heating the rolled plate at a temperature within this range for 5 minutes Time) of cooling the rolled plate at a cooling rate of 30 DEG C / min or more, and then cooling the rolled plate to a temperature of 100 DEG C or less at a cooling rate of 30 DEG C / min or more. The basis for these specifications is as follows.

In the case of the Al-Mg-Si based aluminum alloy, the strength reduction of 10 MPa or more in the heating part by the partial conversion heat treatment described above can be attained by heating the alloy plate at a temperature within the range of 150 to 350 占 폚 for a maximum of 5 minutes have.

In addition, rapid heat-up is required for the strength difference between the heating portion and the non-heating portion set to 10 MPa or more by the partial conversion heat treatment; Specifically, a heating rate of 30 DEG C / min or more is required. If the rate of temperature rise is less than 30 캜 / min, the percentage of strength reduction due to recovery can be reduced while the percentage of increase in strength due to aging can be improved, resulting in a difference in strength between the heated and non- Can be difficult to do. For the same reason, the temperature raising rate is preferably 50 DEG C / min or more, and more preferably 100 DEG C / min or more.

Here, when the reaching heating temperature is lower than 150 캜, the percentage of strength reduction due to recovery is low, and it is difficult to generate a difference in strength between the heating portion and the non-heating portion. On the other hand, if the heating temperature reached exceeds 350 ° C, grain boundary precipitation may occur and the ductility is lowered.

The holding time at the reached temperature is within 5 minutes (including the case where the holding time is 0, that is, when the alloy plate does not stay at the predetermined temperature but is cooled as soon as the predetermined temperature is reached). If the holding time at the reached temperature exceeds 5 minutes, the percentage of strength reduction due to recovery can be lowered, while the percentage of increase in strength due to aging can be improved, and it is difficult to lower the strength of the heating portion , Productivity may be lowered.

In addition, in the cooling step after the partial conversion heat treatment, cooling to 100 deg. C may be performed rapidly. Concretely, when the cooling rate to 100 占 폚 is less than 30 占 폚 / min, grain boundary precipitation may occur easily upon cooling, resulting in deterioration of ductility of the material. Therefore, the cooling rate is preferably 30 DEG C / min or more. For the same reason, the cooling rate is preferably 50 DEG C / min or more, and more preferably 100 DEG C / min or more. If the material temperature after cooling exceeds 100 캜, age hardening may occur, which makes it difficult to lower the strength of the heating portion. Therefore, it is specified that the alloy plate should be cooled to 100 DEG C or less after the partial conversion heat treatment.

On the other hand, the partial conversion heat treatment for the purpose of increasing the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature by 20 MPa or more through partial conversion heat treatment, Heating the rolled sheet at a temperature within the range of 180 to 350 DEG C at a heating rate, holding the rolled sheet at a temperature within the range for 5 minutes (including a time of 0 seconds), and thereafter heating the rolled sheet at 50 DEG C / lt; RTI ID = 0.0 > 100 C < / RTI > The basis for these specifications is as follows.

In order to increase the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature through the partial conversion heat treatment by 20 MPa or more, the temperature of the region (i.e., the heated portion) Is set within a range of " a " When the reached heating temperature is less than 180 占 폚, sufficient recovery is not achieved by the heat treatment performed during such a short time so as not to impair the productivity, as compared with the productivity in the cold press forming; In this case, the material strength in the heating portion is not sufficiently lowered. As a result, the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature is not increased by more than 20 MPa through the partial conversion heat treatment, and the improvement of the moldability of the alloy plate by the partial conversion heat treatment is insufficient. On the other hand, if the heating temperature reached exceeds 350 캜, fine precipitates composed of Mg and Si can be dissolved in a solid solution in a very short time, and minute precipitates composed of Mg and Si are immediately formed and aged, Can again be cured. This aging occurs continuously during subsequent cooling. Therefore, the strength drop after cooling is reduced. Further, since grain boundary precipitation occurs simultaneously with the transition phenomenon, the stretching is considerably lowered and uniformity tends to occur during press forming; Therefore, the moldability is not substantially improved. On the other hand, when the reached heating temperature is within the range of 180 to 350 占 폚, the difference in strength can be effectively imparted to the alloy plate blank with high efficiency so as not to impair the productivity of press molding.

Here, the heating temperature reached in the partial conversion heat treatment can be further divided into two temperature ranges depending on the speed of the intensity change with time in the heating section.

When the reached heating temperature is in the range of 250 to 350 占 폚, the fine precipitate composed of Mg and Si is dissolved in the solid solution, and the recovery is completed in a short time of several seconds. After cooling to room temperature at a predetermined cooling rate, The difference between the tensile strength of the non-heated portion at room temperature and the strength of the heated portion at room temperature increases by 20 MPa or more. However, when switching heating is performed in this temperature range, a large number of spaces (molecular levels) remain at room temperature after cooling. This space promotes the diffusion of Mg and Si while maintaining the room temperature at the part where the partial conversion heat treatment is performed, thereby promoting the formation of fine precipitates at room temperature. As a result, while the alloy sheet is left at room temperature for several days, the value of the strength once lowered at this portion can rapidly return to the level before the conversion heat treatment. The density of the space increases as the heating temperature reaches, and the increase of the spatial density promotes the increase of the value of the strength at room temperature. This rapid change in intensity distribution causes incompatibility with previously optimized press forming conditions, increasing the likelihood of incomplete shape or incomplete appearance of the press-molded article. Therefore, for stable production of an acceptable molded article, it is preferable that the holding time at room temperature after the partial conversion heat treatment and before the press molding is as short as possible. On the other hand, when the conversion heat treatment is performed in a temperature range of 180 ° C or more and less than 250 ° C, restoration is completed in a short time without compromising the productivity as compared with the productivity of cold press forming. Further, the density of the space at room temperature after cooling is sufficiently low, and the increase in the value of the strength against time over the holding time at room temperature after the partial conversion heat treatment is sufficiently small. Therefore, when the partial conversion heat treatment is performed in this temperature range, an acceptable molded article can be stably produced even when the alloy plate blank is kept at room temperature for several days. Thus, when a flexible plan of production is very important, the heating temperature reached in the partial conversion heat treatment is preferably set within the range of 180 to 250 DEG C, and the alloy plate blank is maintained at room temperature for several hours after the partial conversion heat treatment And then press forming can be performed. Here, in order to stably produce an acceptable molded article, the increment (increment) in which the value of the strength of the heating portion heated in the partial conversion heat treatment for 5 days after the partial conversion heat treatment is increased is set to 50 MPa or less, 30 MPa or less.

In order to ensure that the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature increases by 20 MPa or more through partial restoration heat treatment, the holding time at the reached temperature is maximum 5 minutes (holding time is 0, That is, when the alloy plate is not substantially maintained at the reached temperature, but is cooled immediately upon reaching the temperature). Similarly, in order to ensure that the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature is increased by 20 MPa or more through the partial conversion heat treatment, the rate of temperature rise in the partial conversion heat treatment is set to 50 DEG C / . When the heating rate is less than 50 캜 / min, redissolution of the fine precipitate to the solid solution by recovery at the time of temperature elevation can proceed, and restoration can be terminated at the time of heating or at the heating temperature reached, The strength can be increased. As a result, since it is difficult to effectively reduce the proof stress of the heating portion, it is difficult to ensure that the difference between the tensile strength of the non-heating portion at room temperature and the proof stress of the heating portion at room temperature increases by 20 MPa or more through partial conversion heat treatment. The cooling rate of the heating section after the partial conversion heat treatment is preferably set to 50 DEG C / min or more. If the cooling rate is 50 DEG C / min or more, the strength can be increased by aging during cooling, and it is difficult to effectively reduce the proof stress of the heating portion. As a result, it is difficult to ensure that the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature increases by 20 MPa or more through the partial conversion heat treatment.

Incidentally, the specific means for partially heating the alloy plate blank as the partial conversion heat treatment is not particularly limited. Examples of the heating means include a method of bringing a metal body heated during press forming into contact with a plate portion corresponding to the suppressing peripheral portion, and a method of heating only the plate portion with hot air.

Here, by the partial conversion heat treatment as described above, the shape freezing performance of the molded article is improved because of the strength reduction of the suppressing peripheral portion. In addition, the hardened portion due to the conversion phenomenon will have a high curing speed upon baking the coating film thereon, and its strength will rapidly recover. Therefore, a high film baking-curing property (BH performance) can be obtained and strength deterioration after baking of the coating film is prevented. This is because the baking of the coating film after the clust formed by the room temperature aging is dissolved in the solid solution once by the heating in the partial conversion heat treatment causes the formation of the high density of the large precipitate more effectively contributing to the improvement of the strength. On the other hand, when baking the coating film is performed under the condition that the clusters formed by room temperature aging remain, once the clusters are dissolved in the solid solution at the reached heating temperature, which is mainly less than 180 占 폚, Lt; / RTI > Therefore, when the coating is baked by keeping the work for a short time of about 20 minutes at the reached heating temperature, the degree of curing is so low that a high film bake-curing property can not be obtained. On the other hand, in the case of the molded article obtained through the partial conversion heat treatment according to the present invention, the proof stress of the heating portion heated in the partial conversion heat treatment is improved by 20 MPa or more by the coat-bake treatment (equivalent to artificial aging) performed within 30 days after the partial conversion heat treatment , It is possible to provide the rigidity required for use as a body panel to a molded article. This is specified in claim 15.

Leave at room temperature from partial conversion heat treatment to cold press forming

As described in claim 8, it is preferable that the alloy plate is left at room temperature until the cold press forming after the partial conversion heat treatment, and the room temperature leaving period is set to 30 days or less. If the room temperature left after the partial conversion treatment exceeds 30 days, the strength of the portion where the strength is temporarily lowered due to heating and recovery can be increased by the new aging at room temperature, and the strength difference between the heating portion and non- And it is possible to make it difficult to obtain a high press formability. In order to safely limit the new room temperature aging, it is advantageous from the standpoint of productivity to set the room temperature holding period to be preferably 72 hours or less, more preferably 24 hours or less.

The period during which the alloy plate is allowed to stand at room temperature until the cold press molding after the partial conversion heat treatment is substantially the same as the previous period when the strength of the softened portion by the partial conversion heat treatment is returned to the strength before processing. A more substantially preferred period of time is the period during which the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature after the partial conversion heat treatment is maintained. Incidentally, it is preferable that the lubricant applying step usually required for press forming is performed during a room temperature stretching period or immediately before press forming.

Composition of aluminum alloy plate

The aluminum alloy sheet for forming in the present invention may basically be an Al-Mg-Si alloy, and its specific composition is not particularly limited. Usually, the blank material contains an alloy having the composition as specified in claims 16 to 18, i.e., 0.2 to 1.5% of Mg and 0.3 to 2.0% of Si, 0.03 to 1.0% of Fe, 0.03 to 0.6% of Mn, At least one selected from the group consisting of 0.01 to 0.4% of Cr, 0.01 to 0.4% of Zr, 0.01 to 0.4% of V, 0.005 to 0.3% of Ti, 0.03 to 2.5% of Zn and 0.01 to 1.5% of Cu, And the remainder is Al and an aluminum alloy which is an unavoidable impurity.

The reason for the restriction on the composition of the blank alloy as specified in claims 16 to 18 will be described later.

Mg:

Mg is an alloy element based on an alloy of the system considered in the present invention, and contributes to strength improvement in cooperation with Si. When the Mg content is less than 0.2%, a sufficient strength improvement can not be obtained due to a small amount of the? "Phase leading to the improvement of the strength by precipitation hardening during baking of the coating film. On the other hand, Si-based intermetallic compound is formed and the moldability, particularly the bendability, is deteriorated. Taking these viewpoints into consideration, the Mg content is set within the range of 0.2 to 1.5%. [0030] The better formability of the final alloy plate, It is preferable that the Mg content is in the range of 0.3 to 0.9%.

Si:

Si is also a basic alloying element to alloys of the system considered in the present invention, which in combination with Mg contributes to strength improvement. In addition, Si is formed as a crystallization product of metallic Si at the time of casting, and the periphery of the metallic Si particles is deformed at the time of working to become the formation site of recrystallized nuclei in the solution treatment (solution treatment). Therefore, Si also contributes to purification of the recrystallized structure. When the Si content is less than 0.3%, the above-mentioned effect can not be sufficiently obtained. On the other hand, when the Si content exceeds 2.0%, coarse Si particles and / or coarse Mg-Si based intermetallic compounds are produced and the formability, particularly the bendability, is lowered. Taking these points into consideration, the Si content is set within 0.3 to 2.0%. In order to obtain a better balance between press formability and bendability, the Si content is preferably in the range of 0.5 to 1.4%.

Mg and Si are alloy elements based on Al-Mg-Si based aluminum alloys, and the alloy contains 0.03 to 1.0% of Fe, 0.03 to 0.6% of Mn, 0.01 to 0.4% of Cr, 0.01 to 0.4% of Zr, 0.01 To 0.4% of V, 0.005 to 0.3% of Ti, 0.03 to 2.5% of Zn and 0.01 to 1.5% of Cu. The reasons for the addition of these elements and the reasons for the limitation of the amount of the added elements are as follows.

Ti, V:

Ti is an element effective for improving strength and corrosion prevention through purification of an ingot structure, and V is an element effective for improving strength and preventing corrosion. When the Ti content is less than 0.005%, a sufficient effect can not be obtained. On the other hand, when the Ti content exceeds 0.3%, the effect of the addition of Ti to the ingot tissue refining effect and the corrosion prevention effect are saturated. When the V content is less than 0.01%, sufficient effect can not be obtained. On the other hand, when the V content exceeds 0.4%, the corrosion inhibiting effect of the V addition is saturated. Further, when the upper limit is exceeded, the amount of the coarse intermetallic compound based on Ti or V increases, resulting in lowering of moldability and / or deterioration of hemming.

Mn, Cr, Zr:

These elements are effective for improving the strength, crystal grain refinement, or improving the aging property (bake hardenability). When the Mn content is less than 0.03% or the Cr and Zr content are each less than 0.01%, the above-mentioned effect can not be satisfactorily obtained. On the other hand, when the Mn content exceeds 0.6% or the Cr and Zr content exceed 0.4%, respectively, the above-mentioned effect is saturated and many types of intermetallic compounds are formed, which adversely affects the formability, particularly the hemming property . Therefore, the Mn content is set within the range of 0.03 to 0.6%, and the Cr and Zr contents are set within the range of 0.01 to 0.4%, respectively.

Fe:

Fe is usually contained as an unavoidable impurity in a conventional aluminum alloy at a content of less than 0.03%. On the other hand, Fe is an effective element for improving the strength and crystal grain refining. In order to exhibit these effects, Fe can be positively added in an amount of 0.03% or more. However, it is noted that sufficient effect can not be obtained when the Fe content is less than 0.03%. On the other hand, an Fe content exceeding 1.0% can lower moldability, particularly bendability. Therefore, in the case of positive addition of Fe, the Fe content is set within the range of 0.03 to 1.0%.

Zn:

Zn is an element which contributes to the improvement of the strength through the improvement of the aging property and is effective for improving the surface treatment property. When the Zn content is less than 0.03%, the above-mentioned effect can not be satisfactorily obtained. On the other hand, a Zn content exceeding 2.5% causes a decrease in moldability and a decrease in corrosion resistance. Therefore, the Zn content is set within 0.03 to 2.5%.

Cu:

Cu is an element added for improving moldability and strength. For the purpose of improving moldability and strength, Cu is added in an amount of 0.01% or more. However, when the Cu content exceeds 1.5%, the corrosion resistance (grain boundary corrosion resistance, actual shape corrosion resistance) deteriorates. Therefore, the Cu content is limited to 1.5% or less. Incidentally, when the strength improvement is very important, the Cu content is preferably 0.4% or more. When the corrosion resistance is intended to be improved, the Cu content is preferably 1.0% or less. In addition, when the corrosion resistance is very important, Cu is not added positively, and the Cu content is preferably limited to 0.01% or less.

In addition, B (boron) may be added together with Ti for the purpose of refining the ingot structure in an ordinary Al alloy. The addition of B together with Ti acts more significantly in the purification and stabilization of the ingot tissues. In the present invention, up to 500 ppm of B may be added with Ti.

Example

Hereinafter, embodiments of the present invention will be described with reference to comparative examples. Incidentally, the following examples are intended to illustrate the effects of the present invention, and the processes and conditions described in the examples are not limited to the technical scope of the present invention.

Example 1

As shown in Table 1, the aluminum alloys A1 to A6 were melted and adjusted in composition, and the melts were cast by a DC casting process to produce aluminum alloy ingots. Each ingot was placed at 530 DEG C for 10 hours, and then subjected to hot rolling and cold rolling in accordance with a conventional method to obtain an alloy sheet having a thickness of 1 mm. Each alloy sheet thus obtained was subjected to a solution treatment at 530 캜 and rapidly cooled to room temperature. After the solution treatment and rapid cooling, each alloy sheet was allowed to stand at room temperature for 60 days. Subsequently, the portion of each alloy plate which became the inhibition peripheral portion at the time of drawing was subjected to the partial conversion heat treatment under the heating condition shown in Table 2. [ After the entire alloy plate was cooled to room temperature, the alloy plate was measured for strength (tensile strength and 0.2% proof stress) of the unheated portion and the heated portion, the limit drawing ratio (LDR) And used for measuring the bake strength. In addition, the hemming property of the heating section was measured in a room temperature standing period of 24 hours.

LDR (Limit Drawing Ratio) Test:

The alloy sheet was drawn under the conditions of a punch diameter (P) of 32 mm, a wrinkle restraining force of 150 kg and varying blank diameters, and the LDR value of the alloy sheet was calculated by the equation LDR = D / P, where D is the maximum drawing Blank diameter. Drawings were made by applying Johnson Wax (trademark) as a lubricant to both sides of each alloy sheet.

Application baking strength:

With respect to each alloy sheet, JIS No. 1 was used. 5 The specimens were stretched 2% and then baked at 170 占 폚 for 20 minutes and used in the tensile test. In the tensile test, 0.2% proof stress was measured as the mechanical strength.

Evaluation of Heming Castle:

Each alloy sheet was subjected to 5% stretching of the bending test piece and subjected to 180 ° contact bending. Upon bending, the presence / absence of cracks was visually confirmed. Here, symbol O indicates the presence of cracks, and symbol X indicates the presence of cracks.

All of the alloys A1 to A6 shown in Table 1 are within the composition ranges as specified in claims 16 to 18 of the present invention.

The test piece No. shown in Table 2 was used. 1 to 5 all belong to the examples of the present invention. 6 to 9 belong to Comparative Examples.

The test specimens of all examples satisfied the condition that the difference in strength between the non-heated portion and the heated portion (0.2% proof stress difference) was +12 MPa or more; In addition, they have a high LDR value of 2.09 or more, as well as a good hemming property and a high strength after baking of the coating film.

On the other hand, the test piece of the comparative example had inferior performance, particularly LDR. Among these test specimens, the specimen No. 1 was used. 6, 7 and 8 have the following problems since the heating conditions of the partial conversion heat treatment applied to them are out of the range of the present invention. These test pieces had high strength in the heating portion and low strength in the non-heating portion, as opposed to the test pieces of the examples of the present invention. Therefore, At 6 to 8, the inhibitory periphery was high in strength, while the punch shoulder contact was low in strength, resulting in a significant reduction in LDR. Further, 7 and 8 were also deteriorated in hemming ability. Test piece No. 1 belonging to the comparative example. 9 is a test piece obtained by cold pressing an alloy plate not subjected to the partial conversion heating test, so that the strength was uniform. Test piece No. 9 is an example of the present invention, Test specimen No. 1 having the same alloy composition as that of No. 9. 1, the strength after baking of the LDR and the coating film was inferior.

Example 2

In the process, the second embodiment is to prove the effect of the method as described in claims 7 and 12 of the present invention. However, it should be noted that the embodiments which are outside the conditions specified in claims 6 and 11, but which are within the scope of the conditions specified in claims 7 and 12, are also explained by reference. Here, an embodiment that satisfies the conditions specified in claims 7 and 12 is referred to as a " second embodiment " (of the present invention), while the conditions specified in claims 6 and 11 are satisfied, An unsatisfactory embodiment is referred to as a " first embodiment " (of the present invention), and an embodiment that does not satisfy either of the two conditions is referred to as a "comparative example ".

Aluminum alloys B1 to B3 as shown in Table 3 were melted and the melts were cast by a DC casting process to produce an aluminum alloy ingot having the chemical composition shown in Table 3. [ Each ingot was submerged at 530 DEG C for 10 hours, and then subjected to hot rolling and cold rolling in a usual manner to obtain an alloy sheet having a thickness of 1 mm. Each alloy sheet thus obtained was subjected to a solution treatment at 530 캜, and then rapidly cooled to room temperature.

Thereafter, under the conditions shown in Tables 4 and 5, an aging treatment was performed by a combination of room temperature aging (NTA) or artificial aging (AA) or two kinds of aging (NTA and AA). A tensile test specimen (JIS No. 5 specimen shape) was sampled from the alloy plate thus treated to make the tensile direction perpendicular to the rolling direction. Tensile test specimens were used in the tensile test and their mechanical properties (tensile strength, proof stress and elongation) were tested and the results are shown in Tables 4 and 5. Each alloy sheet was subjected to a partial conversion heat treatment according to the method described later, and then used in the formability evaluation test.

First, a circular disk blank having a predetermined size was prepared from each alloy plate for formability evaluation. As shown in Fig. 2, the 55.7 mm? Center area (blank 5) of the disk sample is set to the unheated area (unheated area) Q while the surrounding area is set to the heated area And the partial blank heat treatment was performed on the disk blank 5 under this condition. The heating portion is the entirety of the portion on the outer side of the region which is contacted by the shoulder portion (radius) 3 of the punch 2 during press forming. For the specific method of carrying out the partial conversion heat treatment, the disk blank 5 was fixed between the upper plate 6 and the lower plate 7 of the partial conversion heat treatment system of the shape shown in Fig. 3 . 3, among the upper plate 6 and the lower plate 7, the center portion is set to the non-heating portion 8 cooled by water cooling, and the peripheral portion is heated by the heating portion 9 having the heater incorporated therein Respectively. The heating temperature, heating time (heating holding time), heating rate and cooling rate reached in the heating section in the partial conversion heat treatment are shown in Tables 4 and 5.

The disc blank subjected to the partial conversion heat treatment under these conditions was used in the moldability evaluation test described later. For each disk blank corresponding to this condition, ten small-sized tensile test pieces shown in Fig. 4 were sampled from the heating portion P and the non-heated portion Q respectively (the sampling position is shown in Fig. 5) And the proof stresses in the unheated portion Q and the heating portion P were tested, and the results are shown in Tables 6 and 7. The evaluation of the strength at the position (P, Q) after the partial conversion heat treatment was performed as soon as possible after the partial conversion heat treatment and substantially within 5 hours after the partial conversion heat treatment. Further, in order to measure the time change (time-dependent change) of the proof stress in the heating portion of each disk blank subjected to the partial conversion heat treatment under the above-described conditions, heating of the disk blank after one and five days from the end of the partial conversion heat treatment Tensile test specimens were similarly sampled, and the test specimens were used in the tensile test immediately after sampling, and the strength values were tested after each elapse of the time, and the results are shown in Tables 6 and 7. After completion of the partial conversion heat treatment, the disk blank was kept at room temperature for the same period as the period until the execution of the formability evaluation test, and then a small tensile test piece was sampled from the heating portion and the non-heated portion Lt; / RTI > These test pieces were subjected to 2% deformation as a simulation of press molding in advance, and then artificial aging was carried out at 170 캜 for 20 minutes under conditions corresponding to the film baking treatment. The thus treated specimens were used in the tensile test to measure the strength at each position and the increase in the strength at each position by the heat treatment equivalent to the film baking treatment is shown in Tables 6 and 7. After the partial conversion heat treatment was completed, the disk blank was kept at room temperature for the same period as the period of the moldability evaluation test plus 3 days, and then a small tensile test piece was sampled from the heating portion of the disk blank. After applying 5% tensile strain to these tensile test specimens, the parallel parts of each specimen were cut and used in the bendability test according to the following method. First, a line perpendicular to the tensile direction at the center of the parallel portion of each test piece was set as a line of bending, and the parallel portion was bent at a bending radius of 0.8 mm until it reached an angle of 90 deg. Further, the parallel portion was bent at an angle of 135 DEG. Then, assuming insertion of the inner panel to the inside, a strip of 1.0 mm in thickness was inserted inside the bent parallel portion, the parallel portion was bent at an angle of 180 and the strip was sandwiched, and the rigid Contact was obtained. The outside of the bent portion was visually inspected through a magnifying lens, and the tested parallel portion of the test piece was evaluated as good or bad of bendability according to the absence of the crack.

For the moldability evaluation test, the partially converted heat treated disc blank was held at room temperature for the period of time shown in Tables 6 and 7 and then used in the cylinder deep drawing test. The punch used in this test had a punch diameter of 50 mm and a punch corner radius of 5.0 mm. The die used for the test had a shape with an inside diameter of the die of 53.64 mm and a die shoulder radius of 13.0 mm. The deep drawing test was conducted using Johnson Wax (trademark) as a lubricant under conditions of a punch speed of 180 mm / min and a wrinkle restraining force of 150 kg. The partially barrel heat treated alloy sheet blank was used for the deep drawing test. When three plate blanks were able to be drawn from five plate blanks of the same kind, a new blank test piece was prepared by increasing the disc diameter by 0.5 mm, and the deep drawing test was conducted again using a new blank test piece. This process was repeated to measure the maximum disc diameter allowing the drawing, and the maximum disc diameter was divided by the punch diameter of 50 mm to obtain the limiting drawing ratio LDR. For comparison, LDR was also measured for a disk blank produced from an alloy plate not subjected to partial conversion heat treatment. Table 5 shows the results of the cylinder deep drawing test. Here, when the LDR value obtained by the partial conversion heat treatment shows an increase of 0.1 compared with the LDR value obtained without the partial conversion heat treatment, it is judged that the formability is substantially improved by the partial conversion heat treatment.

Conditions 1 to 4 are examples in which partial conversion heat treatment and / or similar treatment is performed on alloy B1 under the conditions specified in claims 7 and 12 of the present invention (second embodiment). In each of these cases, the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature increased by more than 20 MPa through partial conversion heat treatment. Also, in the formability evaluation test, the LDR value increased by more than 0.1 as compared to the LDR value obtained without partial conversion heat treatment; Thus, we recognized the moldability-enhancing effect that affects actual-use. In addition, it was confirmed that the increase in the strength of 20 MPa or more was observed in the heating part after the heat treatment equivalent to the film baking treatment, thereby proving that the required strength level of the car body plate is secured. Also, the time change (the variation with time) of the strength of the heating section after the partial conversion heat treatment was appropriate, and the increase in the internal strength for 5 days after the partial conversion heat treatment was stable to less than 50 MPa. From this fact, it has been confirmed that an acceptable molded article can be stably produced by press molding without defective shape or defective appearance. In addition, the bending property of the heating portion in the partial conversion heat treatment is good, and it has been proved that the bending can be easily performed when the bending portion of the final press-molded article is set as the heating portion.

On the other hand, condition 5 indicates that the heating temperature reached in the partial conversion heat treatment is higher than that of the present invention in order to confirm that the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased by 20 MPa or more through partial conversion heat treatment 7 and 12 (the first embodiment). In this case, sufficient softening effect of restoration could not be obtained in the heating portion, and the above-mentioned increase was 20 MPa or less. Therefore, it was found that the LDR value obtained in the formability evaluation test did not show a sufficient improvement compared to the LDR value obtained without partial conversion heat treatment.

Condition 6 is a comparative example in which the heat treatment temperature reached in the partial conversion heat treatment exceeds the temperature range according to the present invention. In this case, the precipitation of the aging proceeded immediately after completion of the restoration within a short period of time in the heating section, thereby undesirably increasing the proof stress of the heating section. As a result, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased only to less than 20 MPa through partial conversion heat treatment. Therefore, the LDR value obtained in the formability evaluation test can be compared with the LDR value obtained without the partial conversion heat treatment, indicating that the formability is not improved. Further, precipitation at the interface is induced by heating at the reached heating temperature, and bendability is greatly lowered. Thus, it has been found that bending of the molded article can not be carried out. In this case, the increase in the proof stress due to the post-molding artifact of the heating portion was less than 20 MPa. Therefore, the strength required for the body panel can not be secured.

Condition 7 shows that the difference in tensile strength between the non-heated portion at room temperature and the proof stress at room temperature increased by 20 MPa or more through the partial conversion heat treatment. In the transition heat treatment, (The first embodiment). In this case, during the process of raising the temperature of the low speed and the temperature of the heat treatment reached, the precipitation of the aging succeeded to the recovery of the heating portion. As a result, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased only to less than 20 MPa through partial conversion heat treatment. Therefore, no LDR improvement of 0.1 or more was observed, and the moldability-improving effect of sufficient partial conversion heat treatment was not recognized.

In condition 8, in order to confirm that the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased by 20 MPa or more through the partial conversion heat treatment, The cooling rate is not higher than the cooling rate specified in 12 (Example 1). In this case, even if the heating portion is once softened by restoration, it hardens again due to the progress of precipitation in the slow cooling process after the heat treatment. As a result of this shape, the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature increased only to less than 20 MPa through partial conversion heat treatment. Therefore, no improvement in the sufficient LDR of 0.1 or more was observed, and the moldability-improving effect of sufficient partial conversion heat treatment was not recognized.

Conditions 9 and 10 are examples in which the partial conversion heat treatment or the like is performed within the conditions within the ranges specified in claims 7 and 12 after aging treatment obtained by combination of room temperature aging and artificial aging (second embodiment). In each case, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased by more than 20 MPa through partial conversion heat treatment. Therefore, also in the formability evaluation test, the LDR value was increased by 0.1 or more as compared with the LDR value obtained without partial conversion heat treatment. Thus, we recognized the moldability-enhancing effect that affects actual-use. It was also confirmed that the increase in the internal stress of 20 MPa or more was present in the heating section after the heat treatment equivalent to the coating film baking treatment. Therefore, it was possible to secure the required strength level in the automobile body plate. Also, the time variation (the variation with time) of the strength of the heating section after the partial conversion heat treatment was appropriate, and the increase in the strength for 5 days after the partial conversion heat treatment was stable to less than 50 MPa. From this fact, it has been confirmed that an acceptable molded article can be stably produced by press molding without defective shape or defective appearance. Further, the bending property of the heating portion by the partial conversion heat treatment is good, and the bending can be performed when the bending portion of the final press-formed product is previously set as the heating portion.

On the other hand, condition 11 is a comparative example in which the proof strength before the partial conversion heat treatment is lower than the range according to the present invention even though the room temperature aging is performed. In this case, even if the subsequent partial conversion heat treatment or the like is performed under the conditions within the range according to the present invention, the partial conversion heat treatment does not obtain a sufficient decrease in the proof strength in the heating portion. Therefore, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature only increased to less than 20 MPa through partial conversion heat treatment. In addition, the LDR value obtained in the formability evaluation test showed only a slight increase compared to the LDR value obtained without partial conversion heat treatment. Therefore, the substantial moldability-strengthening effect of the partial conversion heat treatment could not be recognized.

Results similar to those obtained from alloy B1 were obtained from alloy B2, which is an Al-Mg-Si-Cu alloy. Specifically, all of the conditions 12 to 15 are embodiments in which partial conversion heat treatment or the like is performed under the conditions specified in claims 7 and 12 of the present invention. In each case, the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature increased by more than 20 MPa through partial conversion heat treatment. Also, in the formability evaluation test, the LDR value increased by more than 0.1 as compared to the LDR value obtained without partial conversion heat treatment; Thus, we recognized the moldability-enhancing effect that affects actual-use. In addition, it was confirmed that the increase in the strength of 20 MPa or more was observed in the heating part after the heat treatment equivalent to the coating baking treatment, and it was proved that the required strength level was secured in the car body plate. Also, the time variation (the variation with time) of the strength of the heating part after the partial conversion heat treatment was appropriate, and the increase in the strength for 5 days after the partial conversion heat treatment was stable and less than 50 MPa. From this fact, it has been confirmed that an acceptable molded article can be stably produced by press molding without a defective shape or a defective appearance. Further, the bending property of the heating portion by the partial conversion heat treatment is favorable, and when the bending portion of the final press-molded product is previously set as the heating portion, bending can be facilitated.

On the other hand, condition 16 regarding alloy B2 is that the heat treatment temperature reached in the partial conversion heat treatment is higher than the heat treatment temperature reached in the partial conversion heat treatment in order to confirm that the difference between the tensile strength of the unheated part at room temperature and the proof stress of the heating part at room temperature increases by 20 MPa or more Which is lower than the temperature range specified in claims 7 and 12 of the present invention (first embodiment). In this case, a sufficient softening effect of restoration could not be obtained in the heating portion. Moreover, the aforementioned increase was less than 20 MPa. Therefore, it was proved that the LDR value obtained in the formability evaluation test did not show a sufficient improvement compared to the LDR value obtained without partial conversion heat treatment.

Conditions 17 and 18 relating to the alloy B2 are comparative examples in which the heat treatment temperature achieved in the partial conversion heat treatment is not lower than the temperature range according to the present invention. In this case, the precipitation of the aging proceeded immediately after completion of the restoration within a short period of time in the heating section, thereby undesirably increasing the proof stress of the heating section. As a result of this phenomenon, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased only to less than 20 MPa through partial conversion heat treatment. Therefore, the LDR value obtained in the formability evaluation test was only compared with the LDR value obtained without partial conversion heat treatment. Therefore, it was confirmed that the moldability was not substantially improved in this case. Further, it was confirmed that the precipitation at the interface at the heat treatment was induced by the induction of the grain boundary, whereby the bendability was greatly reduced, and the bending of the molded article could not be performed. In addition, the increase of the proof stress due to the artificial aging after the molding of the heating part was merely less than 20 MPa. Therefore, it was confirmed that it is impossible to secure the necessary strength to the vehicle body panel.

Condition 19 relating to the alloy B2 is a comparative example in which the heating time in the partial conversion heat treatment is longer than the range according to the present invention. In this case, since the recovery is completed at the time of heat treatment, even if the heating portion is once softened, the heating portion gradually cures due to the progress of the age precipitation. As a result of this phenomenon, the difference between the tensile strength of the non-heated portion at room temperature and the proof stress of the heated portion at room temperature increased (decreased) to a negative value through partial conversion heat treatment. Therefore, the LDR value obtained in the formability evaluation test was lower than the LDR value obtained without partial conversion heat treatment. In this case, the bending property of the heating portion after molding was low. Thus, it has been found that the molded article can not be subjected to the bending treatment.

Condition 20 relating to the alloy B2 is an embodiment in which the proof stress and the tensile strength before the partial conversion heat treatment are lower than the range according to the present invention even though the room temperature aging is carried out. In this case, even if the subsequent partial conversion heat treatment or the like is carried out under the conditions within the ranges specified in claims 7 and 12 of the present invention, the partial conversion heat treatment does not obtain a sufficient reduction in the proof strength in the heating section. Therefore, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature only increased to less than 20 MPa through partial conversion heat treatment. In addition, the LDR value obtained in the formability evaluation test showed only a slight increase compared to the LDR value obtained without partial conversion heat treatment. Therefore, it has been found that the moldability-enhancing effect of the partial conversion heat treatment is not substantially recognized.

Conditions 21 and 22 relating to alloy B3 are obtained by performing room temperature aging or artificial aging under the conditions within the relevant range according to the present invention and then performing partial conversion heat treatment or the like under conditions within the ranges specified in claims 7 and 12 of the present invention (Second embodiment). In each case, the difference between the tensile strength of the non-heated part at room temperature and the proof stress of the heated part at room temperature increased by more than 20 MPa through partial conversion heat treatment. Therefore, in the formability evaluation test, the LDR value is improved by 0.1 or more as compared with the LDR value obtained without partial conversion heat treatment. Thus, the practically-used moldability-enhancing effect was recognized. It was also confirmed that the increase in the strength of 20 MPa or more was observed in the heating portion after the heat treatment equivalent to the coating baking treatment. Therefore, it was possible to secure the required strength level in the automobile body plate. In addition, the increase of the strength for 5 days after the partial conversion heat treatment was stable and less than 50 MPa. From this fact, it has been confirmed that an acceptable molded article can be stably produced by press molding without a defective shape or a defective appearance. Further, the bending property of the heating portion heated by the partial conversion heat treatment is good, and it has been proved that bending is easy when the bending portion of the final press-molded article is set in advance by the heating portion.

Example 3

The rolled plate of the alloy B1 used in Example 2 was prepared as a test piece. The conditions such as the heat treatment temperature, the heating rate and the cooling rate reached in the aging condition after partial treatment and the partial conversion heat treatment were the same as the condition 2 shown in Table 4 , The aging treatment and the partial conversion heat treatment were performed. However, in Example 3, it should be noted that the regions of the heating portion and the non-heating portion in the partial conversion heat treatment are variously modified as shown in Table 8 in which the partial conversion heat treatment is performed. Three days after the partial conversion heat treatment, the LDR was measured by using the blank subjected to the partial conversion heat treatment under the condition of the region in the cylinder deep drawing test under the same conditions as in Example 1. The results are shown in Table 8.

Condition number In the partial conversion heat treatment, In the partial conversion heat treatment, LDR division One radish radish 2.01 Comparative Example 2 Whole department Whole department 2.02 Comparative Example 3 Ø40 mm circular
Outer region Ø40 mm circular
Inner and outer regions 2.01 Comparative Example 4 Ø 50 mm circular
Outer region Ø 50 mm circular
Inner and outer regions 2.02 Comparative Example 5 The circular shape of φ55.7 mm
Outer region The circular shape of φ55.7 mm
Inner and outer regions 2.26 Example 6 Φ60 mm circular
Outer region Φ60 mm circular
Inner and outer regions 2.25 Example 7 φ70 mm circular
Outer region φ70 mm circular
Inner and outer regions 2.23 Example

As a comparative example, Condition 1 is an embodiment in which no heated region exists; That is, the partial conversion heat treatment is not substantially performed in this embodiment. In this case, the LDR was 2.01. As a comparative example, Condition 2 is an embodiment in which the entire additional heating portion of the blank is set. In this case, the LDR slightly increased to 2.02. Therefore, sufficient moldability-strengthening effect could not be obtained in this case.

As a comparative example, Condition 3 is an embodiment in which the entire portion (region B in Fig. 1) of the portion to be brought into contact with the punch shoulder portion during molding and the entire portion (the region A in Fig. 1) . In this case, the strength of the punch shoulder contact portion was lowered, and therefore, this portion was liable to be ruptured. Therefore, the LDR was only 2.01. Therefore, it was confirmed that the moldability was not improved in this case.

As a comparative example, Condition 4 is an embodiment in which a portion of a portion (region B in FIG. 1) and an entire portion on the outside of the portion (region A in FIG. 1) contacted by a punch shoulder portion during molding are set as heating portions. In this case, the punch shoulder contact portion has a low strength and is therefore likely to rupture at this portion. Therefore, the LDR was only 2.02. Therefore, it was confirmed that the moldability was not improved in this case.

On the other hand, Condition 5 as an embodiment of the present invention is an embodiment in which the entire portion (the region A in FIG. 1) of the portion on the outer side of the portion (region B in FIG. 1) that is contacted by the punch shoulder portion during molding is set as the heating portion. In this case, the blank portions contacted by the punch shoulder portions are higher in strength than the portions on the outer sides thereof. Therefore, the LDR was 2.26, which shows an effective increase of 0.1 or more compared to the LDR value obtained without partial conversion heat treatment. Therefore, it was confirmed that the formability was improved in this case.

Conditions 6 and 7 as an embodiment of the present invention are embodiments in which a part of the portion on the outer side of the portion (region B in Fig. 1) which is brought into contact with the punch shoulder portion during molding is set as the heating portion. In this case, the blank portion contacting the punch shoulder portion has a higher strength than a portion of the portion on the outer side thereof. Therefore, the LDR was 2.25 and 2.23, respectively, which showed an effective increase of 0.1 or more compared to the LDR value obtained without partial conversion heat treatment. Therefore, it was confirmed that the formability was improved in this case.

Example 4

The rolled plate of the alloy B1 used in Example 2 was prepared as a test piece. The conditions such as the heat treatment temperature, the heating rate and the cooling rate reached in the aging condition after partial treatment and the partial conversion heat treatment were the same as the condition 2 shown in Table 4 , The aging treatment and partial conversion heat treatment were performed. However, it should be noted that, in Embodiment 4, the shape of the punch used in the press forming is different from those in the above-described embodiment. Specifically, as shown in Fig. 6, a two-stage cylindrical punch 2 having two punch shoulder portions 3A and 3B was used. The first end of the punch 2 has a punch shoulder 3A of 5 mm R and a size of 50 mm and the second end of the punch 2 has a punch shoulder 3B. Further, a die corresponding to the shape of the two-stage punch 2 was used. Press forming of the disc blank 5 was carried out by using a two-stage punch 2 and a die.

In the embodiment of the present invention, the region A on the outer side of the region B contacted by the first-stage punch shoulder 3A at the time of molding is set as the heating portion in the partial conversion heat treatment, and the punch shoulder portion And the region A 'on the outer side of the region B' contacted by the contact portion 3B is additionally set as the heating portion. On the other hand, in the comparative example, the partial conversion heat treatment was performed by a method in which only the region A outside the region B which is contacted by the punch shoulder portion 3A at the time of molding was set as the heating portion in the partial conversion heat treatment. For each of the blanks subjected to the two types of partial conversion heat treatment according to the examples and the comparative examples of the present invention, press molding was performed using the punch (2) and the die three days after the partial conversion heat treatment. As a result, a two-stage cylindrical molded article could be produced from the blank according to the embodiment of the present invention without rupture of the blank during molding. On the other hand, the blank according to the comparative example ruptured at a portion corresponding to the punch shoulder portion 3B of the molded article.

The present invention may be embodied or embodied in other ways without departing from the spirit or essential characteristics of the present invention. The preferred embodiments described herein are therefore intended to be illustrative and not restrictive, and are intended to cover all modifications that come within the meaning and range of equivalency of the claimed invention as indicated by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing a process of press forming an aluminum alloy plate in order to explain a heating section and a non-heating section during a partial conversion heat treatment according to the present invention;

FIG. 2 is a schematic view showing a heating unit and a non-heating unit in the partial conversion heat treatment in Embodiment 2; FIG.

3 shows a schematic perspective view of the partial conversion heat treatment system used in Example 2;

4 is a plan view showing the shape and dimensions of the tensile test specimen sampled in Example 2;

5 is a front view showing a position where a tension test piece is sampled from a heating portion and a non-heating portion of a blank subjected to partial conversion heat treatment in Embodiment 2; And

Fig. 6 is a schematic cross-sectional view showing the positions of the heating section and the non-heating section during the two-stage punch of the press used in the fourth embodiment and the partial conversion heat treatment applied to the blank in the fourth embodiment.

Claims (18)

Preparing a rolled Al-Mg-Si based aluminum alloy sheet rolled to a predetermined sheet thickness as a blank material, subjecting the rolled sheet to a solution treatment at a temperature within a range of 480 to 590 DEG C, And allowing the rolled plate to undergo a partial conversion heat treatment before cold press forming so that the difference in 0.2% strength between the heating portion and the non-heating portion is at least 10 MPa after cooling to room temperature, The partial conversion heat treatment is performed under the condition that the region of the plate to be suppressed by the crease restraining mechanism during the cold press forming is set to the heating portion and the region of the plate on which the punch shoulder portion is pressed during the cold press forming is set to the non- Wherein the partial conversion heat treatment comprises heating the rolled plate at a temperature elevation rate of 30 DEG C / min or more to a temperature within a range of 150 to 350 DEG C, heating the rolled plate at a temperature within the range of 5 minutes or less (including a time of 0 seconds) And then cooling the rolled plate at a cooling rate of 30 占 폚 / min or more to a temperature of 100 占 폚 or less. Preparing a rolled Al-Mg-Si based aluminum alloy sheet rolled to a predetermined sheet thickness as a blank material, subjecting the rolled sheet to a solution treatment at a temperature within a range of 480 to 590 DEG C, And allowing the rolled plate to undergo a partial conversion heat treatment before cold press forming so that the difference in 0.2% strength between the heating portion and the non-heating portion is at least 10 MPa after cooling to room temperature, The partial conversion heat treatment is performed under the condition that the region of the plate to be suppressed by the crease restraining mechanism during the cold press forming is set to the heating portion and the region of the plate on which the punch shoulder portion is pressed during the cold press forming is set to the non- Wherein the partial conversion heat treatment is performed by heating the rolled plate at a heating rate of 50 DEG C / min or more to a temperature within a range of 180 to 350 DEG C, heating the rolled plate at a temperature within this range for 5 minutes or less (including 0 second) And then cooling the rolled plate to a temperature of 100 DEG C or less at a cooling rate of 50 DEG C / min or more, whereby the tensile strength of the non-heated portion and the 0.2% And the difference between the strengths is increased by 20 MPa or more. A method for cold pressing, which comprises cold press forming an aluminum alloy plate for cold press forming manufactured by the method described in claim 1, wherein the plate is subjected to cold press forming before allowing the plate to stand at room temperature for 30 days after the partial conversion heat treatment. There is provided a cold press forming method of an aluminum alloy plate based on application of a process of cold press forming by suppressing the end portions of an Al-Mg-Si based aluminum alloy plate blank in an aged-precipitated state at room temperature aging by using a punch , A portion of the aluminum alloy plate blank which is smaller than the whole or an entire portion of the portion on the outer side of the region to be contacted by the punch shoulder portion during press forming is set as the heating portion and the portion other than the heating portion is set as the non- Set; The heating portion is quickly heated to the aluminum plate blank to instantaneously dissolve the aged-precipitate to soften the heating portion while performing the partial conversion heat treatment in which the non-heating portion is not heated, so that the strength of the heating portion is higher than the strength of the non- After lowering, the heating portion is rapidly cooled to room temperature; Then, the aluminum alloy plate blank is subjected to cold press forming before the strength of the heating portion is returned to the level before the partial conversion heat treatment by the aging precipitation during the holding at room temperature, Wherein the partial conversion heat treatment comprises heating the plate blank to a temperature within a range of 150 to 350 占 폚 at a heating rate of 30 占 폚 / min or more, heating the plate at a temperature within this range for 5 minutes or less (including 0 seconds) Holding the blank, and thereafter cooling the plate blank at a cooling rate of 30 DEG C / min or more to a temperature of 100 DEG C or less. After the solid solution treatment, an Al-Mg-Si-based aluminum having a 0.2% proof stress of 90 MPa or more, which has been aged by artificial aging at a temperature of 140 占 폚 or below and aging treatment at a temperature of not more than 140 占 폚 A cold press forming method of an aluminum alloy plate on the basis of application of a cold press forming process in which an alloy plate is used to suppress the end portion thereof by using a punch, wherein the aluminum alloy plate blank is brought into contact with the shoulder portion of the punch Setting a portion of the portion on the outer side of the region that is less than the entire portion or the entire portion to the heating portion and setting the other portion than the heating portion as the non-heating portion; The heating portion is quickly heated to the aluminum plate blank to instantaneously dissolve the aged-precipitate to soften the heating portion while performing the partial conversion heat treatment in which the non-heating portion is not heated, so that the strength of the heating portion is higher than the strength of the non- After lowering, the heating portion is rapidly cooled to room temperature; Then, the aluminum alloy plate blank is subjected to cold press-molding before the strength of the heating portion is returned to the level before the partial conversion heat treatment by the age precipitation during the holding at room temperature, Wherein the partial conversion heat treatment comprises heating the plate blank to a temperature within a range of 150 to 350 占 폚 at a heating rate of 30 占 폚 / min or more, heating the plate at a temperature within this range for 5 minutes or less (including 0 seconds) Holding the blank, and thereafter cooling the plate blank at a cooling rate of 30 DEG C / min or more to a temperature of 100 DEG C or less. There is provided a cold press forming method of an aluminum alloy plate based on application of a process of cold press forming by suppressing the end portions of an Al-Mg-Si based aluminum alloy plate blank in an aged-precipitated state at room temperature aging by using a punch , A portion of the aluminum alloy plate blank which is smaller than the whole or an entire portion of the portion on the outer side of the region to be contacted by the punch shoulder portion during press forming is set as the heating portion and the portion other than the heating portion is set as the non- Set; The heating portion is quickly heated to the aluminum plate blank to instantaneously dissolve the aged-precipitate to soften the heating portion while performing the partial conversion heat treatment in which the non-heating portion is not heated, so that the strength of the heating portion is higher than the strength of the non- After lowering, the heating portion is rapidly cooled to room temperature; Then, the aluminum alloy plate blank is subjected to cold press forming before the strength of the heating portion is returned to the level before the partial conversion heat treatment by the aging precipitation during the holding at room temperature, Wherein the partial conversion heat treatment comprises heating the plate blank to a temperature within a range of 180 to 350 占 폚 at a heating rate of 50 占 폚 / min or more, heating the plate blank at a temperature within this range for 5 minutes or less (including 0 seconds) And then cooling the plate blank to a temperature of 100 DEG C or less at a cooling rate of 50 DEG C / min or more, whereby the tensile strength of the non-heated portion and the tensile strength of the heating portion And the difference between the 0.2% proof stress is increased by 20 MPa or more. The method according to claim 4 or 5, wherein a portion of the portion on the outer side of the area of the aluminum alloy plate blank which is contacted by the punch shoulder portion during the cold press forming is subjected to bending after forming the cold press, Wherein the aluminum alloy sheet is included in the cold press forming method. 6. The method according to claim 4 or 5, wherein at least one zone of the entire interior of the area contacted by the punch shoulder portion during cold press forming of the aluminum alloy plate blank, or at least one zone of any shape within the area, Wherein the heating portion is provided with a plurality of through holes. A cold press-formed aluminum alloy obtained by a cold press forming method of an aluminum alloy plate described in claim 4 or 5 and having an internal force of 20 MPa or more improved by an artificial aging treatment performed within 30 days after the partial conversion heat treatment product. The Al-Mg-Si-based aluminum alloy sheet according to claim 1, wherein the Al-Mg-Si-based aluminum alloy sheet contains 0.2 to 1.5% of Mg and 0.3 to 2.0% of Si and contains 0.03 to 1.0% Fe, 0.03 to 0.6% At least one selected from the group consisting of Cr of 0.4%, Zr of 0.01 to 0.4%, V of 0.01 to 0.4%, Ti of 0.005 to 0.3%, Zn of 0.03 to 2.5%, and Cu of 0.01 to 1.5% Al and an aluminum alloy plate which is an unavoidable impurity. The aluminum alloy sheet according to claim 4 or 5, wherein the Al-Mg-Si-based aluminum alloy sheet contains 0.2 to 1.5% of Mg and 0.3 to 2.0% of Si, 0.03 to 1.0% of Fe, 0.03 to 0.6% At least one selected from Mn, 0.01 to 0.4% Cr, 0.01 to 0.4% Zr, 0.01 to 0.4% V, 0.005 to 0.3% Ti, 0.03 to 2.5% Zn, and 0.01 to 1.5% And the remainder is aluminum and an aluminum alloy plate which is inevitable impurities. delete delete delete delete delete delete delete

Images