JP2002544392A - Manufacturing method for painted molded products - Google Patents

Abstract

A process of producing a shaped article suitable for use as an automotive body panel intended for finishing by painting and, if necessary, baking. The process comprises obtaining a sheet article made of an aluminum alloy of the 2000 or 6000 series in a T4 or T4P temper and that exhibits an increase in hardness after painting and optionally baking, shaping the sheet article by forming to produce an intermediate shaped article, and subjecting the intermediate shaped article to a thermal spiking treatment prior to painting and optionally baking. The thermal spiking treatment involves heating the intermediate shaped article from ambient temperature to a temperature in a range of 150 to 300 DEG C with or without holding at that temperature for a period of time to enhance the increase in hardness.

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to a method for heat-treating a molded article, and more particularly to a molded article suitable for manufacturing a body panel.
shaped article). More specifically, the present invention relates to a molded article made of an aluminum alloy sheet material, which exhibits improved hardness after a paint baking treatment.

[0002] At present, aluminum alloy sheets are increasingly used as structural materials and closure materials for vehicle bodies, and automobile manufacturers are surpassing in reducing vehicle weight in order to improve fuel economy. I'm sick. According to a conventional method, an aluminum alloy is formed into a base metal by a direct cooling method or a thick alloy sheet material by a continuous casting method, and then hot-rolled to form a predetermined thickness. As a separate operation, the alloy sheet is cold rolled to form a final thickness and wound on a coil. Then the coil:
Solution strengthening is necessary for strengthening the panel molded body by painting / baking. The coating / baking process of a molded part of an automobile performed by an automobile manufacturer or the like is generally called a paint baking process or a paint curing process.

In general, several aluminum alloys of the AA (Aluminum Association) 2000 series and 6000 series are considered for automotive panel applications. The AA 6000 series alloy contains magnesium and silicon, and may or may not contain copper, but can be classified as an AA 2000 series alloy according to its copper content. These alloys are in formable T4 or T4P temper conditions and become more tough after the painting / baking process. This increased strength due to painting / baking is highly desirable,
Thinner and therefore lighter panels can be manufactured.

[0004] Aluminum alloy sheets, when supplied to a manufacturer, are stamped or formed into a desired form with relatively easy deformation, without difficulty and without excessive springback. It is highly desirable to be able to form a product.
On the other hand, it is desirable that a product made of an aluminum alloy plate has relatively high hardness, is thin, and shows good impact resistance after being subjected to a normal coating / baking treatment.

Here, in order to make it easier to understand the contents of the present invention, terms used for the temper of the alloy will be briefly described in order. A temper called T4 is well known (for example, see Aluminum Standards and Data (1984) p.11, The Aluminum Ass
ociation), according to a conventional method, without an intermediate batch annealing treatment and a pre-aging treatment. This is typically the temper applied to automotive alloy sheet panels when supplied to automotive component manufacturers for the formation of skin panels and the like. Next, an aluminum material which is subjected to an intermediate batch annealing treatment but not to a pre-aging treatment is called T4A temper. Next, the aluminum alloy that has reached the peak strength by performing only the solution treatment and the artificial aging is called T6 temper. The material that is pre-aged but not subjected to intermediate batch annealing is T4
An aluminum material that is called P temper and performs both the intermediate annealing treatment and the pre-aging treatment is called T4PA temper. T8 temper relates to alloys such as those obtained by solution treatment, cold working and then artificial aging. Artificial aging is a process in which an alloy is kept at a high temperature for a long time. T8X temper is a T8 temper material that is 2% deformed by applying tension and then artificially aged at 177 ° C. for 30 minutes. It is.

One purpose of the above process is to obtain a “paint bake response”, ie, a substantial difference between the T4 / T4P temper and the final T8X temper.

Heretofore, attention has been focused on the steps performed on the alloy sheet before the step of forming the alloy sheet. For example, a method for producing 6000 series aluminum alloy sheets having T4 and T8X tempers is disclosed, which tempers are compatible with the production of automotive parts (U.S. Pat.No. 5,782,241, issued May 17, 1998). , Gupta et al., Alca
n International Limited). According to this manufacturing method, the aluminum alloy sheet is subjected to a solution treatment and a quenching treatment before a forming treatment, and then, before substantial age hardening occurs, the aluminum alloy sheet material is subjected to one or more aluminum alloy sheet materials. In the heat treatment, the aluminum material is heated to a peak temperature of 100 to 300 ° C., the peak temperature is maintained for less than 1 minute, and then the alloy sheet material is cooled.

Similarly, the alloy sheet product is subjected to a solution treatment (heating to 500 to 570 ° C.) after cold rolling, and then quenched or cooled. The cooling rate is carefully controlled to the extent of "pre-aging" [
U.S. Patent No.5,616,189, issued April 1, 1997, Jin et al., Alcan International
Limited). In this way, fine and stable precipitate clusters are formed,
This cluster promotes the formation of well-dispersed precipitate structures during the painting / baking process for automotive panels, resulting in a relatively high T8X temper.

Although the known methods have met with some success, they need to be modified over the conventional methods of forming strip-shaped aluminum alloys. This modification is inconvenient, and modifying existing production equipment requires high costs. Furthermore, the known methods require that the temperature be controlled very carefully, which, while difficult, requires a high cost to achieve.

[0010] It would therefore be highly advantageous to be able to process the product produced from an aluminum alloy sheet into a desired form by certain methods. At this point, the additional steps can be easily adjusted, since such products require in any case processing and production for painting / baking, which is very advantageous.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a hardening response without modification (modification) to the conventional method for producing T4 or T4P tempered aluminum alloy sheet material.
) Is to provide a method for producing a molded article with improved characteristics.

It is another object of the present invention to provide a solution treated aluminum alloy product that exhibits a good hardening reaction during the molding and finishing of the molded article.

Still another object of the present invention is to produce a molded article from an aluminum alloy sheet material having a low yield strength in a T4 temper state and a high yield strength in a T8X temper.

According to one aspect of the present invention, there is provided a method of manufacturing a coated molded article, comprising obtaining an aluminum plate shape formed from a 2000 or 6000 series aluminum alloy of T4 or T4P temper. An aluminum plate shape is formed to form a molded product, and the formed molded product is subjected to a heat spike treatment and temporarily heated to a peak temperature of 150 to 300 ° C. Applying a paint to form a painted article, and if necessary, baking the painted article at a temperature of at least about 177 ° C. to further increase the hardness of the painted article and / or And a method for curing the paint.

As used herein, “thermal spike treatment”
The term "is used to quickly raise the temperature of the product from ambient temperature (or the heating temperature of the alloy sheet material in the part processing line) to a predetermined maximum temperature, and then with or without holding at the peak temperature, It means a step of quenching or cooling.

[0016] As used herein, the term "molded article" refers to any molded article used in the manufacture of a finished product or a component and obtained from an aluminum alloy sheet material. Molded articles are also included. The term refers to a profile in a planar form that is simply cut from an alloy sheet material, but often also refers to a non-planar profile, such as an automobile manufactured by a folding or stamping process Means fender or door. The term does not include unformed or uncut sheet material of indeterminate length, such as rolled sheets made directly from metal or cast strip.

The present invention is practiced with any precipitation hardening aluminum alloy of the AA2000 or AA6000 series, ie, an alloy containing Al-Mg-Si or Al-Mg-Si-Cu that can exhibit age hardening reactions. be able to.

According to another aspect of the present invention, the present invention relates to a painted aluminum alloy sheet molded article produced by the method of the present invention.

Heretofore, the desired increase in hardness has generally been described as "paint bake res
ponse), but this term has become somewhat less relevant as manufacturing processes evolve. Importantly, the above-mentioned increase in hardness (hardening reaction) occurs during the forming process (cutting / forming / stamping) that is initially performed on the alloy sheet product, and it is reported to automobile manufacturers and the like. It can also occur during the step of finishing the molding for feeding. According to modern processing methods, there is no traditional paint baking process. This is because a coating material having a low curing temperature can be used.
Therefore, in this specification, the modern term "curing reaction" is used instead of the conventional term "paint baking response". This term refers to the change from the tensile properties of the material before molding to the tensile properties of the material at the end of the painting and finishing operations, optionally with baking. In the present invention, as will be described in more detail below, this increase may occur partly or entirely during painting and baking, or partly or completely before painting and baking, i.e. during the heat spiking itself. Can occur.

According to a preferred embodiment of the present invention, the advantages of the present invention include at least the following. (1) Components made of alloy sheet material subjected to heat spike processing (for example, automobile panels) have higher strength than panels not subjected to heat spike processing. (2) In one embodiment of the present invention, the maximum curing reaction in the molded part can be obtained only by a thermal spike, without depending on the paint curing process (or without performing any paint curing). (3) At least in one embodiment of the present invention, the thermal spike method can be performed continuously in a furnace typically used for paint curing. Thus, the method of the present invention can be continuously integrated with conventional methods for forming / finishing part-formed articles, thus leading to convenience, efficiency and economy. (4) The method of the present invention provides an alternative that provides higher strength than that obtained from T4P material.

DESCRIPTION OF THE DRAWINGS FIG . 1 is a graph showing a typical thermal spike process according to the present invention. FIG. 2 is a graph described in the following examples, and shows a conventional product AA6111- which was subjected to (a) pre-strain (prestrain) and (b) pre-strain + 177 ° C. for 時間 hour. The change in yield strength (YS) of T4 is shown. FIG. 3 is a graph described in the following examples, wherein (a) pre-strain and (b)
FIG. 4 shows the change in yield strength (YS) for AA6111 which was subjected to treatment for 1/2 hour at a pre-strain of + 177 ° C. and heat treated according to the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION According to one preferred embodiment of the invention, a T4 / T4P temper AA2000 or AA6000.
In order to improve the hardening reaction of alloy plates for automobiles, after forming (for example, cutting / secondary forming / stamping) a profile made of an alloy plate, it is subjected to a heat spike treatment at a temperature in the range of 150 to 300 ° C. . In this processing, (1) a low temperature region portion of the above temperature range (for example, 150 to
225 ° C), depending on the curing by a subsequent paint baking step, or (2) high temperature part of the above temperature range (eg 225-300 ° C)
(A conventional coating and baking is not harmful, but if desired, baking in a conventional temperature range may be performed). Can be avoided). The latter form of the invention is of particular interest. Because, as new paints are developed,
The paint bake temperature is expected to be below 160 ° C., since the curing action occurring at temperatures below 160 ° C. is too slow to fully strengthen the part during the normal curing period.

Conventional 6XXX materials of T4 or T4P temper are composed of a large number of fine metastable clusters and zones evenly distributed throughout the metal matrix.
rs and zones). Conventionally, during paint cure, some particulate instability clusters / zones redissolve in the metal matrix, while others
Age hardening improves the strength of the material. In the method of the present invention, the alloy material can exhibit an improved aging reaction (hardening reaction). However, the exact mechanism is unknown. Without wishing to be bound by any particular theory, thermal spiking in the range of 150-225 ° C. dissolves some of the clusters and zones and increases the supersaturation of the volume in the part part matrix. it is conceivable that. As a result, the part molding softens slightly, while the curing reaction during subsequent painting / baking is improved compared to conventional materials. It should be noted that when the heat spike treatment is performed at a higher spike temperature, the molded part does not soften. This is primarily because the improved aging masks the softening caused by cluster dissolution. Surprisingly, the dislocations that occur during part molding do not hinder the precipitation process as would normally be expected. Based on this finding, the heat spiked panel was able to achieve the desired improved strength during paint cure.

To achieve the desired curing reaction, the lower part of the temperature range (eg, 150-225
° C) thermal spikes can result from relatively slow heating rates (e.g., about 1-70), especially when the molded article is not held at peak temperature at all, but is simply allowed to cool (or force cool) as soon as the peak temperature is reached. ° C / min). Relatively slow heating rates have often been found to be necessary to improve the subsequent paint bake response. That is, the desired improvement in hardness is often not realized at high heating rates. As a result, in this embodiment of the invention, heating to peak temperature may be too time consuming to incorporate this step into a continuous stamping and painting line. Therefore, batch processing is required.

When the thermal spike treatment extends over a high temperature region (eg, a temperature exceeding 225 ° C.)
The heating rate can be very rapid (e.g., 10-280 [deg.] C / min) even when there is substantially no retention time at the peak temperature. Although the desired increase in hardness occurs regardless of whether the heating rate is in the low or high speed portion of the above range, to incorporate the method of the present invention into a continuous stamping and painting / bake line, In general, it has been found that the peak metal temperature (PMT) must be reached within about one minute. If the lowest ambient temperature that can be encountered is 15 ° C., the effective range for continuous operation appears to be 210-285 ° C./min, which is a suitable heating rate for high temperature thermal spike processing.

The time period for maintaining the temperature at the peak thermal spike temperature can range from zero to any time that is practical under the circumstances. From a metallurgical point of view, the longer the temperature is maintained, the better to achieve the desired curing reaction. In practice, this period is usually from 0 to about 5 minutes.

FIG. 1 is a graph depicting a preferred thermal spike process showing a preferred range of peak metal temperature, a range of total heating rates, and a preferred range of retention time at peak metal temperature.

The present invention will be described in the following examples, which are not intended to be limiting.

Example 1 The present invention was tested using commercially available AA6111 material.

Double-length DC ingot [600 × 160 mm, AA6111 alloy: Cu 0.72%, M
g 0.7%, Si 0.6%, Fe 0.25%, Mn 0.20% and Cr 0.06%] were cast on an industrial scale. The obtained ingot is 12.5mm per rolled surface and is completely homogenized.
Hot rolled and cold rolled to a final 0.93 mm gauge, fully solution, quenched, 48
After natural aging for more than an hour, samples were taken for laboratory evaluation.

After subjecting the resulting material to a heat treatment according to the present invention, the paint baking response of the material was evaluated. Tensile specimens were pre-strained in various amounts to simulate a typical forming operation, subjected to a heat spike in a sand bed furnace at 240 ° C, and at 177 ° C for 30 minutes. Aged. The results are summarized in Table 1 below.

[0032]

[Table 1]: Tensile properties of sample (uniaxial pre-strain treatment or untreated, 240 ° C heat spike treatment in experimental furnace)

[0033] The yield strength of the material that has been pre-strained and artificially aged (1/2 hour at 177 ° C) (YS
) Are plotted for the conventional method and the method of the present invention in FIGS. 2 and 3 of the accompanying drawings, respectively.

According to FIG. 2, the paint bake response of the AA6111-T4 material was increased by about 30 MPa by the aging treatment at 177 ° C. for 30 minutes (paint hardening simulation). A similar response is observed for pre-strained materials. However, the net yield strength (YS) for the 5 and 10% pre-strained products is slightly lower due to recovery. The yield strength (YS) of the heat spiked material is about 40 MPa lower at all levels of prestrain. However, the paint baking response is about 90 MPa, which is larger than the conventional material (compare FIGS. 2 and 3). Ten
The% prestrained material shows a slightly smaller paint bake response. This paint bake response is related to the loss of strength due to recovery. As can be seen from FIGS. 2 and 3, in general, the method of the present invention significantly improves paint bake response for both pre-strained and non-pre-strained materials. From the experimental results, it has been proved that the method of the present invention can be used for heat treatment of a molded part and can achieve improved paint curing strength.

Example 2 Three different parts were cut from a bonnet molded from a T4P temper material,
The tensile properties of these three samples were measured as they were and after artificial aging. Table 2 describes the results of tests performed under various conditions.

[0036]

Table 2: Yield strength (MPa) of bonnet outer surface at different parts before and after aging at various temperatures

It can be seen that the aging response of the bonnet is about 20 MPa lower than expected from laboratory simulations under all aging conditions. In Table 3 below, the properties of the bonnet material were compared to a bonnet material that had been subjected to a heat spike at 240 ° C. according to the method of the present invention.

[0038]

[Table 3]: Mechanical properties of bonnet outer surface and action by thermal spike

It is clear that the strength of the heat spiked material aged at 177 ° C. for 40 minutes is about 14 MPa higher than the corresponding conventional shaped aging material.

[Brief description of the drawings]

FIG. 1 is a graph showing a heat spike process of the present invention.

FIG. 2 is a graph showing a change in yield strength (YS) of the conventional product AA6111-T4.

FIG. 3. Yield strength (YS) for AA6111 heat treated according to the method of the present invention.
Graph showing changes in

[Procedural Amendment] Submission of translation of Article 34 Amendment

[Submission date] June 11, 2001 (2001.6.11)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Contents of correction]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Contents of correction]

According to one aspect of the present invention, there is provided a method of manufacturing a coated molded article, comprising obtaining an aluminum plate shape formed from a 2000 or 6000 series aluminum alloy of T4 or T4P temper. An aluminum plate shape is formed by bending or stamping to form a non-planar molded product, and a paint is applied to the formed molded product to form a painted molded product. And baking the painted article at a temperature of at least 177 ° C. to further increase the hardness of the painted article and / or harden the applied paint. To 150-300 ℃
Temporarily heating to a peak temperature of

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Contents of correction]

[0016] As used herein, the term "molded article" refers to any molded article used in the manufacture of a finished product or a component and obtained from an aluminum alloy sheet material. Molded articles are also included. The term refers to a non-planar molded article produced by a folding or stamping process, such as a fender or door of an automobile. The term does not include unformed or uncut alloy sheet material of indefinite length, such as rolled sheets made directly from metal or cast strip.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 602 C22F 1/00 602 623 623 630 630 630A 682 682 686 686A 691 691A 691B 691C 1/05 1 / 05 (72) Inventor David James Lloyd Canada, K0H1G0, Ontario, Bus, Rural Route Number 3, Nicholsons Point 106 (72) Inventor Pierre Henri Marois Canada, K7M / 4J5, Ontario, Kingston, Crescent Drive 38B-number F term (reference) 4D075 BB06X BB08X BB18Y BB23X BB26Z BB93X BB93Z BB95X CA47 DA23 DB07 DC13

Claims (14)

[Claims] 1. A method for producing a coated molded article, comprising: obtaining an aluminum plate section formed from a 2000 or 6000 series aluminum alloy of T4 or T4P temper, and forming the obtained aluminum plate section. , Forming a molded article, applying a paint to the formed molded article to form a painted molded article, and, if necessary, baking the painted molded article at a temperature of at least about 177 ° C. A method for further increasing the hardness of the finished molded article and / or curing the applied paint, wherein the formed molded article is subjected to a heat spike treatment before the above-mentioned coating treatment, to a temperature of 150 to 300 ° C.
Temporarily heating to a peak temperature. 2. The method according to claim 1, wherein the peak temperature is from 150 to 225 ° C. 3. The method according to claim 2, wherein the heating rate of the formed molded article is 1 to 70 ° C./min. 4. Baking the painted part at a temperature of at least about 177 ° C.,
The method according to claim 2 or 3, wherein the hardness of the painted article is further increased. 5. The method according to claim 1, wherein the peak temperature is 225 to 300 ° C. 6. The method according to claim 5, wherein the heating rate of the formed molded article is 10 to 280 ° C./min. 7. The method according to claim 5, wherein the heating rate of the formed molded product is 210 to 285 ° C./min. 8. The method according to claim 5, wherein the baking at a temperature of at least about 177 ° C. is omitted. 9. The method according to claim 1, wherein in the heat spike treatment, the formed molded article is cooled immediately after reaching a peak temperature. 10. The method according to claim 1, wherein in the heat spike treatment, the formed article is held at a peak temperature for a predetermined period before the cooling treatment. 11. The method of claim 10, wherein the predetermined time period is up to about 5 minutes. 12. The heat spike treatment is performed in a continuous heat treatment furnace.
12. The method according to any one of 1 to 11. 13. The method of claim 12, wherein said heat spiking is performed as part of a continuous molding and painting process. 14. A molded article adapted to be used as a part of a vehicle, wherein the molded article is manufactured by the method according to any one of claims 1 to 13.