DE102013018744A1 - Making component for motor vehicle involves preparing melt of aluminum alloy, continuously casting melt in casting matrix, cooling melt in matrix to form continuous casting mass with solidified outer shell, and performing annealing of mass - Google Patents

Abstract

The method comprises preparing a melt of aluminum alloy in 6xxx series, continuously casting the melt in a casting matrix, cooling the melt in the casting matrix to form a continuous casting mass with a solidified outer shell, performing first solution annealing of the casting mass, pre-compressing the casting mass through extrusion or rolling method, quenching the pre-compresses casting mass to a room temperature, separating the quenched casting mass into single pieces, performing second solution annealing of a single piece, and hot-pressing the single piece to a component. The method comprises preparing a melt of aluminum alloy in 6xxx series, continuously casting the melt in a casting matrix, cooling the melt in the casting matrix to form a continuous casting mass with a solidified outer shell, performing first solution annealing of the casting mass, pre-compressing the casting mass through extrusion or rolling method, quenching the pre-compresses casting mass to a room temperature, separating the quenched casting mass into single pieces, performing second solution annealing of a single piece, hot-pressing the single piece to a component, quenching the component, artificially aging the component at 260[deg] C, and performing precipitation hardening of the component. The first solution annealing step is carried out at a temperature of more than 540[deg] c for 1.5-2 hours. The casting mass is compressed such that a round, polygonal or planar cross section is formed. The method further comprises performing third solution annealing of the component after the ho-pressing step at temperature of 0-570[deg] C for 15-60 minutes. The component is quenched at 500 K/s, and is subjected to an intermediate portion between T6- and T7-artificial aging processes and subjected to a straightening process.

Description

The invention relates to a method for producing a component for a motor vehicle according to claim 1.

Method of the type discussed here are known. For the production of heavy-duty components made of light metals, especially aluminum, it is known to cold-form aluminum sheets, the sheets are locally heat treated to increase their formability. However, it is possible that geometrical errors occur due to delays, which are difficult to correct. Furthermore, mechanically highly stressed components must be joined with reinforcing components, which complicates the manufacturing process and increases the weight of the component. There are also aluminum castings known, but due to inclusions and voids are mechanically limited limited. Furthermore, it is known to forge particularly heavy-duty components made of light metals or light metal alloys, in particular aluminum, with aluminum wrought alloys typically being used. However, these forged components do not always have the required properties.

From the German patent application DE 10 2011 118 014 A1 For example, a method is known in which a bodywork semi-finished product made of an aluminum wrought alloy is melted by melting secondary aluminum, thereby obtaining a secondary aluminum wrought alloy. This is shed to a blank. The blank is formed into a semi-finished aluminum body component. In this case, an extruded profile can be produced as semi-finished aluminum. The bodywork aluminum semi-finished product is further processed into the bodywork component, whereby a forging process can be carried out. Also, this known method is in need of improvement in view of a reproducible mechanical strength of the resulting components.

The invention is therefore based on the object to provide a method by means of which reproducible and reliable mechanically heavy-duty aluminum components for motor vehicles can be created.

The object is achieved by providing a method with the steps of claim 1. It is preparing a melt of an aluminum alloy. The melt is continuously cast in a cast die and allowed to cool in the casting die or allowed to cool until a continuous casting mass with solidified outer shell is formed. The cooling process is therefore carried out until a continuous casting material has formed from the melt, which has a solidified outer shell, thus a solidified outer layer. Subsequently, the continuous casting material is subjected to a first solution annealing. The solution-annealed continuous casting compound is precompressed, preferably extruded, in such a way that its pre-compacted cross-sectional area decreases to at least 15% to at most 25%, preferably to 20%, of the original cross-sectional area of the continuous casting compound prior to precompression. Alternatively or additionally, it is also possible that the continuous casting material is precompressed by rolling. Preferably, the continuous casting material is precompressed into profiles with a large ratio of width to thickness. The precompressed continuous casting material is quenched to room temperature. In this case, it is preferably quenched rapidly, particularly preferably in water. Subsequently, the precompressed and quenched continuous casting material is separated into individual pieces. In fact, the continuous casting material is in the form of endless rod material which is cut into individual pieces for further processing. Subsequently, a single piece is subjected to a second solution annealing. The solution-annealed single piece is hot-forged into a component. Subsequently, the component is quenched. This is followed by a thermal aging of the component at a maximum of 260 ° C. As a result, the heat-aging component is precipitation-hardened.

The first solution heat treatment of the continuous casting compound has the effect that, in particular when the melt is cooled, precipitates of silicon and magnesium, which are the main constituents of an aluminum alloy of the 6xxx series, are dissolved again. The rapid cooling following the first solution annealing ensures that a fine-grained microstructure is frozen. The pre-compaction, the size of which depends on the applied pressing force, which in turn depends on the material, the temperature of the material and the tool geometry, improves the properties of the continuous casting mass because pores and voids disappear due to compaction, whereby the material also has an orientation, So a fiber direction or texture is awarded.

In hot forging, the wall thickness of the component to be produced is locally different and so specifically targeted according to the expected requirements locally adjusted so that locally only as much material is available as is required for the mechanical properties of the component or where applied different degrees of deformation Need to become. Thus, a component with locally variable cross-section or locally variable strength is thus formed, which does not have to be adapted with respect to its wall thickness to the largest expected mechanical load. Much more allows the local variability of the cross section, an adaptation of highly loaded areas to the expected loads, while less stressed areas may be formed thin-walled. As a result, the component - beyond the use of a light metal - contributes to the concept of lightweight construction. Such local differences in wall thickness can be produced at least economically only by hot forging. When cold forging this is not possible, but rather results in a higher wall thickness, a lower forming depth and larger radii. Accordingly, in particular, the aspect that the component is produced by hot forging, suitable to take into account also a locally stress-oriented design of the component and the lightweight design.

When hot forging is to ensure that the temperature of the forging tool is high enough, and at the same time the handling time for the displacement of the single piece from the used for the solution annealing furnace in the forging, forging itself, and for moving the forged component of the Forging plant to a quenching station is short and preferably constant, otherwise significant precipitation processes of magnesium and silicon, as well as significant property changes are to be expected. The time scale for the handling is therefore measured according to the kinetics of the precipitation processes of magnesium and silicon and is tuned to them so that there is no significant, affecting the properties of the component excretion of magnesium and silicon or other specific alloy constituents.

It turns out that it is possible by means of the method to reproducibly produce a component for a motor vehicle based on an aluminum wrought alloy, which is at the same time lightweight and mechanically highly resilient.

The quenching of the precompressed continuous casting material, in particular a precompressed rolled profile, and / or the quenching of the component after the hot forging preferably takes place in water, immersion in water, watering and / or spraying with a water mist being possible. In an alternative embodiment of the method, it is also possible to effect the quenching with air, in particular with tempered or untempered air.

In a preferred embodiment of the method, precipitation hardening takes place in air.

As part of the process, a melt of a series 6xxx aluminum alloy is preferably prepared.

An embodiment of the method is also preferred, which is characterized in that the continuous casting compound is heated to a temperature of at least 450 ° C to at most 570 ° C during the first solution annealing. The frictional heat generated during forming must be taken into account. Preferably, the continuous casting material is heated at the first solution annealing to a temperature of at least 480 ° C to at most 540 ° C. In the temperature ranges mentioned, the precipitates of silicon and magnesium which have occurred, in particular, during cooling of the melt, go into solution again. In this case, the temperature during the first solution annealing - in particular alloy-specific and in accordance with the precipitation behavior - is preferably maintained at a value within one of the ranges for at least 30 minutes to at most 60 minutes. This ensures effective dissolution of the precipitates of silicon and magnesium.

A method is also preferred which is characterized in that the continuous casting compound for the first solution annealing is heated to the temperature provided for this purpose over a period of at least 1.5 hours to at most 2 hours. The heating time to the temperature value selected for the first solution annealing is thus preferably at least 1.5 hours to at most 2 hours. There is thus a relatively homogeneous heating, by which the in-solution going of the precipitates of silicon and magnesium is supported. As already indicated, the rapid cooling after the first solution annealing causes the fine-grained microstructure set in the solution heat treatment and preferably compacted and aligned by the precompression to be frozen.

An embodiment of the method is also preferred, which is characterized in that the continuous casting compound is compressed during extrusion or rolling in such a way that a round cross-section is formed. Alternatively, it is possible that a flat or polygonal cross section is formed. The cross-sectional area of the continuous casting mass is thus not simply reduced during precompression, but also preformed in a predetermined manner, wherein the resulting, smaller cross section may be round, polygonal, or even flat.

An embodiment of the method in which the component is subjected to a third solution annealing after hot forging is also preferred. Using the third solution anneal, it is possible to clean up precipitates of silicon and magnesium which have occurred during handling of the single piece after the second solution heat treatment from the furnace to the forging tool, the forging itself, and the transfer from the forge tool to the quench station. In particular, during forging a relevant amount of heat from the single piece is in the tool, which is given by the forging high heat conduction from the single piece in the tool. It thus comes to a temperature reduction of the single piece and therefore to precipitates, in particular of silicon and magnesium. This consideration also indicates that it may be important to set the tool temperature for the forging tool to be high, and preferably uniform, to reduce heat transfer from the single piece to the forging tool.

For hot forging is - especially depending on the contour of the component or the single piece - the single piece preferably at least held for a minimum of 20 minutes to a maximum of 60 minutes at a temperature of at least 500 ° C to 570 ° C. The mold temperature during hot-rolling is preferably from at least 200 ° C to at most 350 ° C. In hot forging, a final forging temperature of more than 480 ° C is preferably achieved.

Accordingly, preferably, the entrance temperature for the quenching operation after hot forging is more than 480 ° C. As a medium for quenching come in particular depending on the alloy and / or component requirements air, water and / or a water mist in question. In this case, the medium chosen for the quenching preferably has a temperature of at least 20 ° C. to at most 40 ° C., in particular due to distortion.

Preferably, the temperature for the third solution annealing is selected at a value of at least 500 ° C to at most 570 ° C. In the third solution annealing, the component is preferably kept at this temperature for at least 15 minutes to at most 60 minutes. Alternatively, it is possible that the total time for the third solution annealing including a heating time is at least 15 minutes to at most 60 minutes.

It is also preferred an embodiment of the method, which is characterized in that the component is quenched after hot forging or optionally after the third solution annealing - in particular depending on the property requirements - with a quenching intensity of at least 20 K / s to at most 1000 K / s. The quenching intensity is preferably 500 K / s.

In a preferred embodiment of the method, the quenching process time is 5 to 10 seconds for a thin-walled member having a wall thickness of about 1 mm to about 4 mm and a thick portion having a thickness of about 40 mm for it at up to a minute.

An embodiment of the method is also preferred, which is characterized in that the component is subjected to a heat aging, which is arranged in an intermediate region between a T6 and a T7-hot aging state. In this area, the ductility curve and the strength curve form a common or adjustable optimum. This means that neither the ductility nor the strength is greatest for itself, but in the overall view the best possible strength is achieved with the best possible ductility. The hot aging is thus in particular conducted or tuned so that overall the best possible strength is achieved at the same time the best possible ductility for the component.

The thermal aging is preferably carried out in a temperature range of at least 160 ° C to at most 260 ° C. The duration of the artificial aging is preferably from at least 30 minutes to at most 120 minutes.

In one embodiment of the method, the temperature for the hot aging in the range of temperature, which is achieved in a cathodic dip painting (KTL) of a motor vehicle bodyshell structure, thus in the range of KTL coating heat. This has the advantage that there are no property changes for the component in a later cathodic dip coating.

An embodiment of the method is also preferred, which is characterized in that the component is locally cooled during heat aging in at least one area. This makes it possible to selectively adjust different strengths of the component, and this tailored as needed to tailor the use and the expected mechanical stresses. The local cooling can be effected, for example, by local application of a cooling medium, in particular with water, air and / or a water mist. Alternatively or additionally, it is possible to achieve a local cooling by targeted selection of a support point of the component, where this results in an increased heat dissipation over a contact surface.

Finally, an embodiment of the method is preferred in which the component is subjected to a straightening process, in particular depending on the shrinkage behavior - preferably after hot aging. This is preferably used when warping occurs during quenching of the component. However, it is alternatively or additionally possible for delays compensate for the corresponding holding of the tool geometry during hot forging, so that a straightening process can be completely eliminated in the optimal case.

Overall, it turns out that using the method, in particular flat, thin-walled components made of wrought aluminum alloys with targeted variation of the wall thickness and functionality at the same time targeted and stress-sensitive adjustment of the component properties, in particular an elongation, strength, and / or ductility for high-strength components and / or for Impact stresses can be produced. In this case, in particular due to the process control significantly higher strengths and / or strains than cold-formed parts can be achieved. At the same time, at most minimal residual stresses occur, so that distortion-related geometric deviations are reduced. Using the method, it is readily possible to set various requirements within the component.

Using the method in particular thin-walled components with a wall thickness of at least 1.5 mm to a maximum of 6 mm, as well as components with a strong wall thickness jump between at least 1.5 mm to a maximum of 20 mm by the hot forming process with subsequent process-integrated heat treatment of light metal produced. As part of the process, there is a significantly higher freedom of design of the components compared to cold-formed parts, as well as an improvement in the quality of the component due to reduced solidification stresses resulting from the forming process. Property profiles of the components to be produced can be adjusted by process variation and not only by varying pre-material dimensions and / or the composition of the starting material.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011118014 A1 [0003]

Claims (9)

Method for producing a component for a motor vehicle, comprising the following steps: preparing a melt of an aluminum alloy, preferably of the 6xxx series; Continuous casting of the melt into a casting die; Cooling the melt in the casting die until a continuous casting mass with solidified outer shell is formed; first solution annealing the continuous casting mass; Precompressing the continuous casting mass by extrusion or rolling to at least 15% to at most 25%, preferably to 20%, of an original cross-sectional area prior to precompression; Quenching the precompressed continuous casting mass to room temperature; Separating the quenched continuous casting mass into individual pieces; second solution annealing of a single piece; Hot forging the solution-annealed single piece into a component; Quenching the component; Hot aging of the component at most 260 ° C, and precipitation hardening of the outsourced component. Method according to one of the preceding claims, characterized in that the continuous casting compound is heated in the first solution annealing to a temperature of at least 450 ° C to at most 570 ° C, preferably from at least 480 ° C to 540 ° C, the temperature preferably for at least 30 minutes to a maximum of 60 minutes. A method according to claim 2, characterized in that the continuous casting compound is heated for at least 1.5 hours to a maximum of 2 hours. Method according to one of the preceding claims, characterized in that the continuous casting material during extrusion or rolling is compressed so that a round or polygonal or flat cross-section is formed. Method according to one of the preceding claims, characterized in that the component is subjected after hot forging a third solution annealing, preferably at a temperature of at least 500 ° C to at most 570 ° C, preferably for a time of at least 15 minutes to at most 60 minutes , Method according to one of the preceding claims, characterized in that the component with at least 20 K / s to at most 1,000 K / s, preferably at 500 K / s, quenched. Method according to one of the preceding claims, characterized in that the component is subjected to a heat aging in an intermediate region between a T6 and a T7 hot aging. Method according to one of the preceding claims, characterized in that the component is cooled locally during hot aging at least in one area. Method according to one of the preceding claims, characterized in that the component is subjected to a straightening process.