EP2518173B1 - Method for manufacturing a sheet metal structure component and sheet metal structure component - Google Patents

Description

The present invention relates to a method for producing a sheet metal structural component for a motor vehicle according to the features in the preamble of patent claim 1.

Various Umformoperationsmöglichkeiten are known from the prior art for the production of sheet metal structural components. The achievable forming limits are given by the forming process and the material used, and can be extended by appropriate heat treatment options.

For this purpose, in turn heat treatment process, heat treatment process or else heat aftertreatment process are known, with which on the one hand the moldability of the material used is extended, on the other hand, the mechanical properties can be selectively restored or adjusted after the forming operation.

In particular, in the production of forming components made of hardenable aluminum alloys are made of " Altenpohl, Dietrich: Aluminum from the inside, Aluminiumverlag, Dusseldorf, 1994 In particular, the components can be produced very well if they are shaped directly after the solution annealing of the starting state of the aluminum alloy or else at a temperature of at least 400 ° C.

However, the good formability goes hand in hand with corresponding losses in the mechanical strength values of the component after forming.

In particular, in the bodywork of motor vehicles, however, it is desired on the one hand to achieve high shaping degrees of freedom, so that according to the function or design requirement, complex shaped components can be created, which are usually part of a self-supporting motor vehicle body. In addition, a large portion of the self-supporting automobile body forms the passenger safety cell, which in turn requires high strength requirements with respect to a potential occurring vehicle crash.

From the US 4 090 889 A or the US 6 033 499 A It is known to provide an aluminum sheet board, to heat them to a heating temperature and then transform.

The object of the present invention is therefore to provide a method for the production of sheet-metal structural components from an aluminum alloy, with which high degrees of freedom of shaping can be achieved and wherein there are no significant losses in the strength values of the sheet-metal structural component to be produced. It is a further object of the present invention to provide a corresponding sheet metal structural component.

The above object is achieved with a method for producing a sheet-metal structural component for a motor vehicle according to the features in patent claim 1.

Advantageous embodiments of the present invention are part of the dependent claims.

According to the invention, in the method for producing a sheet metal structural component for a motor vehicle, wherein the sheet metal structural component is formed from a precipitation-hardenable aluminum alloy, first an aluminum sheet board in the state T4 or T5 or T6 or T7 is provided. Subsequently, the aluminum sheet is heated to a heating temperature between 100 ° C and 450 ° C. Following this, the heated aluminum sheet is formed in a tool to the sheet metal structural component. Again, subsequently, the formed sheet metal structural component is subjected to a subsequent heat post-treatment.

The transformation can first take place directly after heating to the heating temperature. It would also be conceivable to heat the sheet metal blank in the tool itself and directly reshape it. An alternative to this is that after heating to the heating temperature, the aluminum sheet is first cooled in air or quenched with a medium and then cold worked in a mold.

The designation T4, T5, T6 or T7 are heat-treated states of an aluminum alloy in accordance with DIN EN 515. Hereinafter, state T4 means that the aluminum sheet is solution-annealed and cold-aged. State T5 means that the aluminum sheet board is quenched from the thermoforming temperature and is warm-aged. T6 means that the board is solution heat treated and warmed and T7 means that the board is solution annealed and overcured.

With the method according to the invention a production of complex moldings is possible, which would not be produced without heating the board, since the increase in temperature significantly improves the forming property of hardenable aluminum wrought alloys. The mechanical properties, in particular the strength properties at the end of the process according to the invention are approximately equal to the mechanical strength properties of Aluminum sheet blanks in the initial state. According to the invention, the heat post-treatment of the formed sheet metal structural component does not mean solution heat treatment, ie no post heat treatment above 450 ° C., which in turn means an additional energy and time saving in the production of a sheet metal structural component according to the invention. A further advantage of the method according to the invention is that, by dispensing with a solution annealing treatment with subsequent quenching, component distortion or the use of an additional holding device can be avoided.

In a preferred embodiment, the heating to heating temperature is carried out in less than 60 minutes, preferably less than 30 minutes and in particular less than 10 minutes, so that the cycle times can be made particularly short in sheet metal structural components produced according to the invention. Furthermore, there is a high energy saving, due to the short heat pre-treatment. Overall, this makes the production process significantly cheaper.

The heating is carried out at least for alloys in state T4 particularly advantageous to more than 250 ° C, and for alloys in state T6 at least 300 ° C, since it has been shown by comparative studies that in such an alloy otherwise no mechanical properties comparable to the initial state achieve.

The heating is preferably carried out resistively, convectively, conductively and / or inductively and / or by means of heat radiation and / or by means of heat conduction. For example, heating may be performed by a combination of convection and thermal radiation in the oven. Inductive heating can be carried out by means of induction heat generators. Depending on requirements, for example, can be heated only partially on the inductive heating or completely in an oven. Again, the type of heating depends on the size of the sheet metal blank used.

The heating is particularly preferred for less than 10 minutes, in particular less than 1 minute and most preferably within less than 15 Seconds performed. However, at least the heating is carried out for a fraction of a second, for example within 0.1 seconds, in particular 0.5 seconds and most preferably within 1 second. After the heating time, a holding time of the temperature can optionally be particularly preferred. Particularly preferably, the component is held for less than 5 minutes, in particular for less than 3 minutes at the heating temperature before it is transferred to the forming tool. With a relatively slow heating, which is carried out in a period of about 5 to 10 minutes, a holding time before transfer into the forming tool can be completely eliminated. In particular, such a heating is carried out in a continuous furnace, wherein during the passage of the continuous furnace due to the slow heating a replacement holding is already performed.

Alternatively, a heating by heat radiation can be carried out, for example, here would be an infrared heating or a Heizrahlungserwärmung, for example via hot air blower, or even to call a microwave heating. In the context of the invention, heating via heat conduction is furthermore conceivable, heating by means of heat conduction being carried out here by direct contact with a heating plate or else with a heating means, for example in a forming tool or else in a preheating tool.

More preferably, the aluminum sheet is formed without active cooling after heating. In this case, a reduction of the heating temperature is only marginally carried out by the intermediate transfer from heating station to forming tool via the cooling in air. The heat loss is in this case preferably less than 50 ° C., in particular less than 40 ° C. and particularly preferably less than 30 ° C. The associated cooling process thus saves energy and production time.

In a further preferred embodiment of the present invention, the aluminum sheet board heated to heating temperature is passively cooled at room temperature by the ambient air and / or the heated Aluminum sheet board actively cooled, the active cooling is preferably carried out by contact with a medium and the forming is carried out after cooling. In this case, the deformation in the forming tool itself is significantly carried out as cold forming. Preferably, the transformation takes place at less than 150 ° C, in particular less than 120 ° C and more preferably less than 100 ° C component temperature. Of course, it can also be provided to perform the deterrence exclusively or in addition by blowing with gas, in particular air.

More preferably, the active cooling is carried out by quenching, preferably the quenching is carried out in and / or with water. In particular, in the context of the invention, the heated aluminum sheet can be immersed in a cooling tank in whole or wetted with water and / or sprayed. In all respects, quenching means direct contact with the water or an aqueous solution.

A rapid cooling is necessary, in particular in the case of aluminum alloys with an increased copper content, in order to ensure a freezing of the (partially) supersaturated microstructure state of the preceding heat treatment. Preferably, cooling rates of more than 100 ° C / s, preferably more than 250 ° C, more preferably more than 400 ° C / s are set.

In one embodiment variant, the postheat treatment of the formed sheet metal structural component is carried out as precipitation hardening. According to Gladman, T. Precipitation hardening in metals, precipitation hardening is a heat treatment for increasing the hardness and strength of alloys. The method is based on the deposition of metastable phases in finely divided form, so that they represent an effective barrier to dislocation movements. The yield strength of metals can be raised so much. Precipitation hardening is the most important way of increasing the strength of hardenable aluminum alloys because they are not curable by martensite formation.

In the context of the invention, precipitation hardening is to be understood as meaning a combined cold aging with artificial aging. The applicant has come in the course of investigations to the surprising realization that to achieve the initial strength to a solution annealing by targeted control of the aging processes according to the characterizing part of the method claim can be dispensed with entirely without the mechanical properties in comparison to the normal process of precipitation hardening significantly worsen.

Further embodiments of the method according to the invention, in particular concretizations of the execution parameters such as temperature-time ranges are the subject of the dependent claims.

Cold aging is performed, for example, on aluminum alloys after heat treatment with final quenching. Due to the quenching itself, the precipitation of alloying elements which normally takes place during slow cooling is suppressed. The alloying elements are in a supersaturated environment.

Quenching is followed by cold aging at room temperature. The process is based on the aluminum grid attempting to segregate the alloying elements held in the solution. This leads to alloying element rich zones, which block the sliding plane of the structure stronger. Cold aging is usually completed after several weeks or even months. By a temperature increase above room temperature, preferably at 30 ° to 40 ° C, in particular 35 ° C, I can accelerate the process, with a cooling to below room temperature delays the cold aging.

Therefore, according to the present invention, after forming and quenching, cold aging is performed preferably at room temperature for less than 251 hours, followed by heat post-treatment at 70 ° C. to 120 ° C. for 5 to 15 hours.

In a further advantageous embodiment of the present invention, the combined cold aging and artificial aging is performed in several stages, in particular the two-stage thermal aging. Here, the heat treatment subsequent to the cold aging is carried out in two stages, wherein after the aforementioned first post-heat treatment for 5 to 15 hours, at 70 ° to 120 °, a second heat treatment for 12 to 24 hours, at 100 ° to 200 ° C. ,

In particular, the inventive method is used in sheets having a sheet thickness between 0.1 and 15 mm, preferably between 0.5 and 10 mm. This ensures that the various heat treatment steps completely penetrate into the material used and thus can completely set a homogeneous desired structure.

In the context of the invention, an aluminum alloy is used, the aluminum alloy having the following alloying elements, expressed in percent by weight: zinc (Zn) [%]: 2 to 8%, magnesium (Mg) [%]: 0.3 to 5.5%, chrome (Cr) [%]: 0.05 to 1%, zirconium (Zr) [%]: 0.04 to 0.5%, copper (Cu) [%]: ≤ 4.5% manganese (Mn) [%]: ≤ 1.0%, iron (Fe) [%]: ≤ 0.8%, silicon (Si) [%]: ≤ 0.7%, titanium (Ti) [%]: ≤ 0.5%, Zirconium + titanium (Zr + Ti) [%]: 0.04 to 0.5%, aluminum (Al) [%]: rest

With the method according to the invention, it is possible to produce a sheet-metal structural component for a motor vehicle which is produced from a hardenable aluminum alloy and has good degrees of freedom of shaping with simultaneously high strength values.

In the process according to the invention, components having a tensile strength of at least 300 MPa and a yield strength of at least 250 MPa can be produced at an elongation at break of at least 12%, a yield strength of more than 300 MPa with an elongation at break of more than 14% being particularly preferably achieved ,

The aforementioned properties and advantages are arbitrarily combinable within the scope of the invention and apply mutatis mutandis, without departing from the scope of the invention.

Figur 1

ein Zeit-Temperaturdiagramm des erfindungsgemäßen Verfahrens mit zweistufiger Wärmenachbehandlung;

Figur 2

ein Zeit-Temperaturdiagramm mit Wärmenachbehandlung bei Raumtemperatur;

Figur 3

ein Zeit-Temperaturdiagramm mit zweistufiger Wärmenachbehandlung ohne Kaltauslagerung;

Figur 4

ein Zeit-Temperaturdiagramm eines erfindungsgemäßen Verfahrens, wobei Raumtemperatur kaltausgelagert wird und zweistufig wärmenachbehandelt wird;

Figur 5

ein Zeit-Temperaturdiagramm gemäß Figur 4, jedoch ohne Kaltauslagerung;

Figur 6

ein Vergleichsdiagramm der Festigkeitswerte;

Figur 7

ein Zeit-Temperaturdiagramm des erfindungsgemäßen Verfahrens mit Wärmenachbehandlung und

Figur 8

ein erfindungsgemäßer Prozessablauf.

Further advantages, features, characteristics and aspects of the present invention are part of the following description. Preferred embodiments are shown in the schematic figures. These are for easy understanding of the invention. The embodiments according to the Figures 2 . 3 and 5 are merely illustrative of the inventive idea and are not covered by the scope of this patent. Show it:

FIG. 1

a time-temperature diagram of the method according to the invention with two-stage post-heat treatment;

FIG. 2

a time-temperature diagram with postheat treatment at room temperature;

FIG. 3

a time-temperature diagram with two-stage heat post-treatment without cold aging;

FIG. 4

a time-temperature diagram of a method according to the invention wherein room temperature is cold-aged and post-treated in two stages;

FIG. 5

a time-temperature diagram according to FIG. 4 but without cold aging;

FIG. 6

a comparison diagram of the strength values;

FIG. 7

a time-temperature diagram of the method according to the invention with post-heat treatment and

FIG. 8

an inventive process flow.

In the figures, the same reference numerals are used for the same or similar designations, even if a repeated description is omitted for reasons of simplification.

FIG. 1 shows a time-temperature diagram of an inventively performed forming process with cold aging and two-stage post-heat treatment. The temperature T is entered on the ordinate and the time Z on the abscissa. Thus, after the beginning of heating 1, a time t1 of a maximum of 60 minutes is recorded. Following this, the transfer into the mold 2 begins, wherein between the beginning of transfer 2 and the beginning of forming 3 only a slight drop in temperature and a short time t 2 pass. After the completion of the forming process, ie towards the forming end 3 ', the formed component is cooled. The cooling is preferably carried out actively for a period t3 ', so that a cold aging start 4 can begin at about room temperature RT. The cold aging in the component is then carried out for a period t4. If the cold aging is carried out for a specific time period t4 at room temperature RT, then in a multistage heat post-treatment, first warm-aging 5 takes place in a first stage and the temperature of the first stage is kept constant for a period t5. Following this, the temperature is increased to the second stage 6 and again kept constant for a period t6. Subsequently, it is cooled again to room temperature RT. The cooling here can be active and / or passive.

FIG. 2 shows a time-temperature diagram of another. The metal sheet is heated to a heating start 1 over a period t1 of a maximum of 60 minutes to a heating temperature. If the heating temperature is reached, this temperature is kept substantially constant over a holding time t1 'and then begins the transfer into a forming tool 2, in which case only one low temperature drop during the transfer time t2 is recorded. Thereafter, the transformation begins, wherein only at the end of the transformation 3 'in the time t3 is cooled rapidly or in the air to room temperature RT. Following this, a cold aging 4 takes place.

FIG. 3 shows a further embodiment, in which case again the sheet metal blanket is heated from a warming start 1 to a heating temperature, and is transferred from reaching the heating temperature in a mold 2. Following this, a transformation takes place, wherein between Umformbeginn 3 and forming end 3 'takes place a cooling function of the mold temperature. With the present tool, the cooling takes place almost to room temperature RT. Thereafter, there is a direct heating to a first stage for hot aging 5 instead. This is held for a period t5 and then there is a heating to a second stage for hot aging 6, which in turn is held for a period of the second stage t6. This is then subsequently cooled or quenched to room temperature RT.

FIG. 4 shows a fourth embodiment of the method according to the invention, in which case after heating to the heating temperature followed by cooling at room temperature RT, the sheet metal blank is reshaped. Thus, between the beginning of forming 3 and forming end 3 ', a marginal increase in temperature occurs, which occurs due to deformation. After the end of the forming, the cold aging 4 starts, which is held for a period t4. The cold aging is followed by heating to a first stage for hot aging 5, wherein after reaching a first temperature for hot aging for a period t5, the first stage of the aging process is kept constant. Subsequently, it is heated to a second stage for hot aging 6, wherein the second temperature of the heat aging is again kept constant for a period t6. When the second stage of aging is complete, it is cooled or quenched to RT.

FIG. 5 shows an alternative embodiment, the analog FIG. 4 is constructed, in which case the cold aging after the end of the conversion 3 'is dispensed with and is stored directly warm.

FIG. 6 shows the obtained mechanical strength properties of various aluminum alloys in comparison. The yield strength is shown in the dimension on the left in Megapascal and the elongation at break A50 in the dimension on the right in percent. Comparatively, sheet metal blanks in the condition T6 (A) and T4 (B) are each shown with yield strength and elongation at break. In contrast, a board (C) after completion of the inventive method according to FIG. 1 presented as well as a 4-week only cold-discharged board (D). It can be seen that the yield strength with respect to the initial states T6 (A) or T4 (B) is approximately the same in a process used according to the invention. Compared with a 4-week cold aging process (D), the yield strength exceeds almost three times the yield strength set here. On the other hand, the elongation at break is maintained at a good level between the state T6 (A) and T4 (B) in a device manufactured by the method of the present invention.

FIG. 7 shows a time-temperature diagram of an inventively performed forming process with cold aging and two-stage post-heat treatment. The temperature T is entered on the ordinate and the time Z on the abscissa. Thus, after the beginning of heating 1, a time t1 of a maximum of 60 minutes is recorded. Following this, the transfer into the mold 2 begins, wherein between the beginning of transfer 2 and the beginning of forming 3 only a slight drop in temperature and a short time t 2 pass. In the forming tool itself, the workpiece is then cooled from the beginning of forming 3 to the forming end 3 'so that it has a temperature at forming end 3' that is substantially at room temperature RT or substantially slightly above room temperature RT. Following this, the component is kept at room temperature RT or else cooled from the temperature slightly above the room temperature RT to room temperature RT, which is carried out in the time t3 'between the forming end of the cold aging start. Following this, the cold aging 4 starts at room temperature RT, wherein the cold aging is maintained for a period t4. If the cold aging is carried out for a specific time period t4 at room temperature RT, in a multistage heat post-treatment first warm-aging is carried out in a first stage 5 and the temperature of the first stage is kept constant for a period t5. thereto Subsequently, the temperature is increased to the second stage 6 and again kept constant for a period t6. Subsequently, it is then cooled again to room temperature RT in a cooling time. The cooling here can be active and / or passive.

FIG. 8 shows the application of a method according to the invention on a forming line, wherein first a board 11 is provided as curable light metal plate in the state T4, T5, T6 or T7. This is located at the position A. Subsequently, the board is heated in a heating device 12, which according to the invention, for example, conductively, inductively or in other heating methods mentioned in the invention can be performed. The heating device 12 is in the position B. More preferably, the heating takes place in a period of less than 10 minutes, in particular less than 1 minute. The component is then transferred directly into the forming tool. If the heating temperature is maintained, this is preferably carried out for less than 3 minutes. As a particularly preferred embodiment of the method according to the invention, the board is heated for a period of less than 15 seconds and kept at the heating temperature for a period of less than 5 minutes before being transferred to the forming tool.

This is followed by a further transfer to a forming station 13, which in the FIG. 8 at the position C is shown. Preferably, the forming tool of the forming station 13 is not tempered, so that it has substantially room temperature RT. As a result, the heated board 11 is quenched during the forming. Further preferably, the forming tool can also be actively cooled, so that the heated board 11 is initially only slightly cooled during the forming and then quenched by the active cooling.

From the position C, a removal from the forming tool and a transport to position D takes place. This is a storage at room temperature RT, so that the formed sheet metal blanks can cold outsource. This is preferably carried out at room temperature RT, in particular for a period of about 80 hours. From the storage position D then takes a Transfer to position E. This is a first furnace 14 in which a hot aging process is performed, in particular in the example shown here at about 90 ° C and for a period of 10 hours. Subsequent to the first furnace 14 at position E, a transfer to a second furnace 15 in the region of position F takes place. Here, a second hot aging stage, particularly preferably about 150 ° C., takes place for a period, particularly preferably 18 hours. The first and the second furnace 14, 15 may also be a two-zone furnace, through which the component is then guided for the period of thermal aging. The illustration of the method according to the invention FIG. 8 is also applicable to the various positions for all other arbitrary process variants as well as time periods and temperature ranges according to the present invention.

With the process variants previously different in the figures, but in particular with the process variant according to FIG. 7 and / or 8, it is possible in the component strength properties according to the column C in FIG. 6 adjust. These are especially in a range of tensile strength at least 280 MPa to 500 MPa, preferably from at least 300 MPa to 450 MPa. Furthermore, the components have a yield strength of at least 230 MPa to 500 MPa, preferably at least 250 MPa to 450 MPa.

Furthermore, they have an elongation at break of at least 12%. Particularly preferably, a yield strength of more than 300 MPa is achieved with an elongation at break of more than 14%. The above values are considered limited at 500 MPa and 20%.

Reference numerals:

1 -

the initiation of heating

1' -

hold time

2 -

Transfer to mold

3 -

Umformbeginn

3 '-

Forming

4 -

Cold aging start

4 '-

Cold aging end

5 -

Warm up first stage

6 -

second stage warm out

t1 -

Time warming

t1 '-

hold time

t2 -

transfer time

t3 -

forming time

t3 '-

Time forming at cold aging start

t4 -

Time cold outsourcing

t5 -

Time warm up first stage

t6 -

Time warm up second stage

t7 -

cooling

11 -

circuit board

12 -

heater

13 -

forming station

14 -

1st oven

15 -

2nd oven

A -

State T6

B -

Condition T4

C -

Variant according to FIG. 1

D -

SdT 10min KA

RT -

room temperature

Z -

Time

T -

temperature

Claims (9)

1. Method for producing a sheet-metal structural component for a motor vehicle, the sheet-metal structural component being formed from an aluminium alloy, characterised by the following method steps:

   - providing an aluminium sheet panel in state T4 or T5 or T6 or T7,

   - heating the aluminium sheet panel to a heating temperature of between 100 and 450°C,

   - shaping the aluminium sheet panel to form the sheet-metal structural component, natural ageing being carried out at room temperature for less than 251 hours after the shaping,

   - and a heat post-treatment subsequently being carried out for from 5 to 15 hours at from 70 to 120°C,

   - a precipitation-hardenable aluminium alloy being used, the aluminium alloy having the following alloy elements, expressed as percentages by weight: zinc (Zn) [%]: 2 to 8%, magnesium (Mg) [%]: 0.3 to 5.5%, chromium (Cr) [%]: 0.05 to 1%, zirconium (Zr) [%]: 0.04 to 0.5%, copper (Cu) [%]: ≤ 4.5%, manganese (Mn) [%]: ≤ 1.0%, iron (Fe) [%]: ≤ 0.8%, silicon (Si) [%]: ≤ 0.7%, titanium (Ti) [%]: ≤ 0.5%, zirconium + titanium (Zr + Ti) [%]: 0.04 to 0.5% aluminium (Al) [%]: remainder.
2. Method according to claim 1, characterised in that the heating to the heating temperature is carried out in less than 60 min., preferably less than 30 min., and in particular less than 10 min.
3. Method according to claim 1 or 2, characterised in that the heating is carried out conductively, convectively, resistively and/or inductively, and/or by means of thermal radiation and/or by means of thermal conduction.
4. Method according to any one of claims 1 to 3, characterised in that the aluminium sheet panel is shaped without active cooling after the heating.
5. Method according to any one of claims 1 to 4, characterised in that the aluminium sheet panel shaped in a heated shaping tool.
6. Method according to any one of claims 1 to 5, characterised in that the aluminium sheet panel, heated to the heating temperature, is cooled passively at room temperature RT by the ambient air, and/or in that the heated aluminium sheet panel is cooled actively, the active cooling preferably being carried out by contact with a medium, and the shaping being carried out after the cooling.
7. Method according to claim 6, characterised in that the active cooling is carried out by quenching with a cooling rate of more than 100°C/s, preferably more than 250°C, particularly preferably more than 400°C/s, in and/or with water.
8. Method according to any one of claims 1 to 7, characterised in that the heat treatment subsequent to the natural ageing is carried out in two stages, a second heat treatment of between 12 and 24 hours being carried out at from 100 to 200°C after the first heat treatment.
9. Method according to any one of claims 1 to 8, characterised in that the sheet-metal thickness is processed between 0.1 and 15 mm, preferably from 0.5 to 10 mm.

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