EP3251767A1 - Method for producing a profile from a metal alloy - Google Patents

Abstract

The invention relates to a method for producing a profile (1) from a metal alloy, wherein the metal alloy is processed in the partially liquid state, wherein the present in particular in the form of chips metal alloy is extruded continuously with an extruder (E), wherein strength-increasing particles are incorporated, to produce a starting material for a metal matrix composite.

Description

The invention relates to a method for producing a profile from a metal alloy, wherein the metal alloy is processed in the partially liquid state.

For the production of semi-finished products or workpieces made of metals or alloys, various casting methods such as continuous casting or chill casting are known. In particular, components made of light metals are often also produced close to the final dimensions by die casting, wherein a melt is poured into a cavity. More recently, methods have been developed in a further context, in which the material to be processed is brought into a partially liquid state and processed in this state or poured into a cavity to form a workpiece. For this purpose, alloys are usually brought to a temperature which lies between the solidus curve and the liquidus curve, so that both the solid and the liquid phase portions are present in the processed material. The processing of semi-liquid material with the introduction of a shear results in a round-shaped structure, which usually also good material properties are achieved.

The known processes for processing material in the semi-solid or semisolid state are thixomolding processes. In this case, a granulate of a metal alloy is partially melted in a barrel with a screw and subjected to a shear stress with the screw to bring the material in a thixotropic state. Subsequently, the material is injected into a mold or cavity by an axial stroke is performed with the screw. Although components can be produced close to the final dimensions with a thixomolding process, the technology is complicated because the cavities must be sealed to the barrel after each injection process until the next injection process follows. In particular, continuous production of a strand or the like is not possible.

Metal matrix composite (MMC) composites are constructed of a metal matrix with an internal reinforcement. Several types are known from the prior art for the production of such metal matrix composite materials, which however are all expensive.

The object of the invention is to provide a method of the type mentioned, with which it is possible to process chips, granules or the like of a metal alloy in only one step to a solid or semi-solid material for a metal matrix composite material.

This object is achieved in that in a method of the type mentioned in particular in the form of chips present metal alloy is extruded continuously with an extruder, wherein strength-enhancing particles are incorporated to produce a starting material for a metal matrix composite material.

An advantage achieved by the invention is to be seen in particular in the fact that in an extrusion process in the two-phase region in the metal matrix composite, a strength-increasing effect can be achieved. Thus, the advantages of processing in the thixotropic state are combined with the advantages of continuous process control. By supplying strength-increasing particles, a strength of the profile produced by the method according to the invention is increased. The particle size and particle type is chosen to produce a strength enhancing effect in the metal matrix composite. For example, ceramic particles such as particles of silicon carbide can be incorporated. In order to achieve a strength-increasing effect, a pre-wetting of the particles by the alloy to be reinforced is necessary, which is given in the semi-liquid range.

The chips and particles are continuously processed into a profile usable as a starting material for a metal matrix composite in just one step by applying shear forces. The profile can be made solid or semi-solid or not completely solidified. A profile produced by the method according to the invention or a metal matrix composite material can also be remelted and / or reshaped without demixing of the metal alloy and of the particles. Further, by the continuous process of the present invention, it is possible to produce a large amount of metal matrix composite in a relatively short time. Consequently, a profile usable as a metal matrix composite material can be produced which can be further processed into components in industrial casting methods and forming methods. It thus follows the ability to separate a manufacturing process for a starting material and a casting process or forming process spatially and temporally from each other. The particles are either fed directly into the process or mixed with the chips from a metal alloy before the start of the process and then added as a mixture to the process. It is understood that the metal alloy may be in a different form, for example as granules or particles.

With the method according to the invention profiles can be produced with different sized solid phase fractions. In a production of a semi-solid profile z. B. solid phase fractions between 2% and 30%, in particular between 5% and 35%, particularly preferably between 8% and 50% processed. In the production of a solid profile, by contrast, solid phase fractions, for example, between 70% and 97%, in particular between 65% and 95%, particularly preferably between 60% and 90%, processed.

It is advantageous if the metal alloy and particles are processed by at least one worm shaft arranged in a cylinder, with a resulting partially liquid material being transported via the at least one worm shaft to a die. In particular, chips made of a metal alloy and particles from above are fed via a funnel to the cylinder with the worm shaft, where they are brought into a thixotropic state with the application of shear forces and processed. Particularly preferably, the strength-increasing particles are fed directly to the chips in the hopper and then metered into the cylinder, where they are incorporated into the chips. The worm shaft is in particular conical and is driven by a motor with preferably low rotational speeds to a rotational movement about its longitudinal axis. In the area of the die, a sufficiently high dynamic pressure is built up, so that pressing the material through the die creates a solid profile with a homogeneous structure. If a semi-solid profile is to be produced, a die is not absolutely necessary since only a small dynamic pressure is necessary to produce a semi-solid profile.

It is advantageous if the material is pressed continuously through the die to produce the profile. The die is designed for this purpose so that it has a sufficiently high hardness for pushing through material made of a metal alloy to a To produce starting material for a metal matrix composite material. In addition, the die is releasably secured to one end of the cylinder, in particular screws from high temperature tool steel are used for fastening. A geometry, in particular a cross-section, of the profile is determined by a shape of the die. The profile is made, for example, with a rectangular, circular or annular cross-section. The profile produced is used as a starting material for a metal matrix composite material and can then be further processed, for example, this can be further processed into a component in a casting process.

It is particularly expedient if the metal alloy and particles are processed and transported with two worm shafts rotating in the cylinder, the worm shafts in particular being driven in synchronism. These rotate around their respective longitudinal axis. The use of two screw shafts ensures a thorough mixing of the material components and, in addition, a shear necessary for the production of a thixotropic state is introduced into the material. This allows mixing of different particles directly in the funnel. The conical worm shafts are driven in particular concurrently, but can also be driven in opposite directions. Conical worm shafts have a large axial distance, which is why a torque can be readily introduced. Furthermore, shearing in the direction of a discharge area is slow due to a decreasing screw peripheral speed, which is why shear-sensitive formulations can also be utilized. Synchronously driven worm shafts clean themselves, as they strip each other. In addition, the material is transported by the worm shafts in the longitudinal direction in an open system, wherein worm threads form continuous channels. Transport of the material is mainly based on drag flow, which is why throughput is strongly dependent on the counterpressure.

Co-rotating worm shafts can be used for plasticizing, mixing, homogenizing and granulating. In addition, it is possible to disperse partially wettable additives such as particles, fibers and / or pigments partly by regular means, and to homogenize products having different viscosities. The worm shafts are driven by a drive at low speeds to ensure adequate mixing and applying shear forces. If the speeds are too high, the material will not be thoroughly mixed, but only pushed further. A rotational speed of the screw shafts may be, for example, about 10 rpm to 40 rpm, in particular 12 rpm to 35 rpm, more preferably 15 rpm to 30 rpm. The rotational speed depends on a size of the extruder. A discharge mass of the profile from the cylinder or the die of the extruder can be at least about 8 kg / h, in particular about at least 10 kg / h, particularly preferably at least about 13 kg / h, and in the production of a solid profile per unit time a semi-solid profile of at least about 30 kg / h, in particular at least about 40 kg / h, particularly preferably at least about 45 kg / h.

It is advantageous if the material is heated in the cylinder and partially melted. This wets the particles and partially melted material. For heating, for example, heating sleeves or other heating elements can be arranged on the cylinder. In addition, for example, insulating mats can be placed on the cylinder, so that heating accelerates and an exiting radiant heat is minimized. In particular, the material is partially melted by the effect of temperature so that this is present in the partially liquid state. Subsequently, the material is conveyed by applying shear forces in the direction of the die and pressed continuously through the die, whereby the profile is formed. By the high shear forces and elevated temperatures occurring in the process according to the invention, a strength-increasing effect of the metal alloy is achieved, so that a profile is produced which can be used as a starting material for a metal matrix composite material. Furthermore, it is favorable if cooling is provided at the end of the cylinder, for example an air cooling, so that the material is cooled before passing through the die. With air cooling, a fire risk is kept as low as possible.

It is advantageous if the profile is protected from oxidation by a protective gas curtain provided in front of a female mold. After exiting the cylinder or passing through the die, the profile is still hot. In addition, too be provided that for several components of the extruder protective fumigation is provided so that the material is protected throughout the production of the profile throughout from oxidation.

• Fig. 1 einen Extruder.

Other features, advantages and effects will become apparent from the embodiment illustrated below. In the drawing, to which reference is made, shows:

• Fig. 1 an extruder.

Fig. 1 shows an extruder E for carrying out a method according to the invention. The extruder E is designed to produce a profile 1 of a metal alloy and comprises a cylinder 2, in which at least one worm shaft 3 is arranged. At the end of the cylinder 2, a die 4 is provided, through which a material of a metal alloy and strength-increasing particles is pressed. The die 4 is releasably secured to the cylinder 2 with screws of high temperature tool steel. In addition, a heating device 5 is provided with which the material in the cylinder 2 is heated and partially melted. The worm shaft 3 is driven by a drive 6, which is designed in particular as a frequency-controlled AC motor. This drives the worm shaft 3 at low speed. Furthermore, the extruder E comprises a funnel 7 and a heat exchanger 8 or heat exchanger, wherein the heat exchanger 8 is designed in particular as an oil-air heat exchanger.

Particularly preferably, two screw shafts 3 are provided, whereby the extruder E is designed as a so-called twin-screw extruder. The worm shafts 3 are conical and are driven synchronously or counter-rotating, wherein the worm shafts 3 are arranged in the cylinder 2. For maintenance purposes, the screw shafts 3 can be removed from the cylinder 2. The use of two screw shafts 3 allows a good mixing of the material and the penetration of the necessary shear in the same.

In a method according to the invention for producing a profile 1 from a metal alloy, chips made of a metal alloy are fed to an extruder E, wherein strength-enhancing particles are incorporated. The particles are in particular mixed directly in a funnel 7 with the chips. About the hopper 7, the material is guided from chips and particles in the cylinder 2. In the cylinder 2, in particular two screw shafts 3 are arranged, which mix the material and bring in a necessary shear. The material is further transported via the screw shafts 3 to a die 4. The cylinder 2 with the screw shafts 3 is heated, so that the material is partially melted and a partially liquid state. The mixed and partially melted material is forced through the die 4 under the action of shear forces, thereby producing the profile 1 which is used as a starting material for a metal matrix composite. A cross section of the profile 1 is determined by a shape of the die 2. The worm shafts 3 rotate in particular concurrently in the cylinder 2. At the output of the die 4 or before the same a protective gas curtain is provided to protect the still hot at the exit point profile 1 from oxidation. By the method according to the invention, a solid or semi-solid profile 1 can be produced, depending on how high the solid phase fractions are. A profile 1 produced by the method according to the invention is used as a starting material for a metal matrix composite material and can be remelted and / or reshaped. For example, a magnesium alloy profile 1 is prepared for a metal matrix composite starting material that can be further processed like a conventional magnesium alloy in a die casting process.

It can also be provided that the extruder E is formed without a die 4. The dynamic pressure is built up at a different location of the extruder E. Consequently, the material can be withdrawn from the extruder E in a semi-solid state and used further.

Claims (6)

A method for producing a profile (1) from a metal alloy, wherein the metal alloy is processed in the partially liquid state, characterized in that the present in particular in the form of chips metal alloy is extruded continuously with an extruder (E), wherein strength-increasing particles are incorporated to to produce a starting material for a metal matrix composite. A method according to claim 1, characterized in that the metal alloy and particles are processed by at least one in a cylinder (2) arranged worm shaft (3), wherein a resulting partially liquid material via the at least one worm shaft (3) transported to a die (4) becomes. A method according to claim 2, characterized in that the material is pressed continuously through the die (4) to produce the profile (1). A method according to claim 2 or 3, characterized in that the metal alloy and particles with two in the cylinder (2) rotating screw shafts (3) are processed and transported, wherein the screw shafts (3) are driven in particular concurrently. Method according to one of claims 2 to 4, characterized in that the material in the cylinder (2) is heated and partially melted. Method according to one of claims 1 to 5, characterized in that the profile (1) by a front of a die (4) provided protective gas curtain is protected from oxidation.

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