EP3370900A1

EP3370900A1 - Method for producing a light metal cast component and light metal cast component

Info

Publication number: EP3370900A1
Application number: EP16788143.2A
Authority: EP
Inventors: Josef Gartner; Werner Hubauer
Original assignee: Mubea Performance Wheels GmbH
Current assignee: Mubea Performance Wheels GmbH
Priority date: 2015-11-02
Filing date: 2016-10-31
Publication date: 2018-09-12
Anticipated expiration: 2036-10-31
Also published as: WO2017076801A1; AU2016351164A1; KR20180067565A; KR102196323B1; US10801089B2; BR112018008345A2; EP3162460A1; EP3370900B1; PL3370900T3; MX2018005246A; JP2019501777A; US20180305793A1; CN108290210B; JP6824264B2; CN108290210A

Abstract

The invention relates to a method for producing a light metal cast component from a melt comprising an aluminium casting alloy which contains, respectively by weight, 3.5 to 5.0% silicon, 0.2 to 0.7% magnesium, 0.07 to 0.12% titanium, at most 0.12 % boron, optionally less than a total of 1.5% of other alloy elements, the remainder being aluminium and unavoidable impurities. The melt is produced from a basic melt, a first grain refiner comprising an aluminium-silicon alloy and a second grain refiner comprising an aluminium titanium alloy wherein, relative to the total weight, the melt contains in total an amount of 0.1 to 5.0% of the first and second grain refiners; wherein the casting is carried out by the low-pressure method and, after casting, the melt is subjected to pressure.

Description

m producing a light metal cast component and

Alloy cast component

description

The invention relates to a light metal casting component, in particular for a motor vehicle, which is produced from a hypoeutectic aluminum casting alloy. The invention further relates to a method for producing such a light metal cast component.

The trend towards lightweight construction and occupant protection, which is particularly prevalent in the motor vehicle industry, leads to the increased development of high-strength and highest-strength components which have a lower weight than conventional components with at least the same strength properties. It is known that light-alloy wheels for motor vehicles can be produced by means of casting or forging. The requirements for the casting molds and the alloy used differ during forging and casting.

Forged alloy wheels have exceptional strength that allows for a slimmer and lighter construction than comparable steel wheels. Due to the high strengths also relatively thin walls and spokes can be constructed, resulting in a low weight. The preparation is usually done by gravity casting of a wrought alloy. The mold is usually flat and corresponds only in diameter approximately to the final product. After casting, the blank is pressed at about 500 ° C gradually with up to two thousand tons of pressure in a mold. This completes the actual rim bowl. At- closing the rim base is made by rolling and there is a machining. Forged wheels are alloyed much more with strength-enhancing alloying elements such as magnesium, silicon and titanium compared to cast wheels.

During casting, the shape of the mold is designed close to the final shape of the component to be produced. After one possibility, the casting can be done in low pressure casting with about 1 bar from bottom to top. Alternatively, a die casting method can be used in which the liquid melt is pressed under high pressure of about 10 to 200 MPa in a preheated mold, where it then solidifies. The melt displaces the air present in the mold and is kept under pressure during the solidification process. After leaving the mold, the component is machined. Cast wheels usually have only a very small proportion of foreign metals such as titanium compared to forged wheels.

In the case of components produced by means of the casting process, the casting properties of metal alloys and the mechanical properties of the finished component essentially depend on the particle size. Grain-refining melt treatment can improve the static and dynamic strength values in castings and the feedability of the melt in the mold as well as its flowability. The solidification of many metallic alloys begins with the formation of crystals that grow from seed sites on all sides until they abut the adjacent grain or wall. For a high strength of the component to be produced, it is desirable to set the size of the grains as uniformly as possible or as finely as possible. For this purpose, a so-called grain refinement is often carried out, wherein the solidifying melt as many nucleating agents (foreign nuclei) are offered. From JP H1 1 293430 A a method for producing a high-strength aluminum casting is known. The aluminum casting after casting has a composition, by weight, of 3.5 to 5.0% silicon, 0.15 to 0.4% magnesium, up to 1.0% copper, up to 0.2% Iron, treatment and the rest Aluminum. After casting, the cast component is heated at 550 ° C to 575 ° C for a period of two to four hours, then rapidly cooled and then subjected to another heat treatment at 160 ° C to 180 ° C for a period of one to three hours.

From JP H05 171327 A an aluminum casting alloy for high pressure casting is known, which has a composition, in each case by weight, of 4.0 to 6.0% silicon, 0.3 to 0.6% magnesium, up to 0, 5% iron, 0.05 to 0.2% titanium. The alloy can be used to cast vehicle wheels.

From JP 2001 288547 A is an aluminum casting having a composition, by weight, from 2.0 to 6.0% silicon, 0.15 to 0.34% magnesium, up to 0.2% iron, 0, 0003-0.01% strontium, the remainder aluminum and unavoidable impurities known, and with optionally 0.01 to 0.25% titanium and 0.0001 to 0.001% boron. After casting, the component is solution heat treated at 540 ° C to 570 ° C for 15 to 60 minutes and quenched.

EP 0 488 670 A1 discloses a high-strength cast aluminum with, by weight, 2.4 to 4.4% silicon, 1.5 to 2.5% copper, 0.2 to 0.5% by weight. Magnesium, and the balance aluminum, wherein the matrix of aluminum casting Dendrite with a grain size of 30 microns or less includes.

From DE 10 2006 039 684 B4 an aluminum safety component for the automotive construction is known, which is made of an aluminum-silicon die-cast alloy. The die cast alloy comprises 1, 0 to 5.0 weight percent silicon, 0.05 to 1, 2 weight percent chromium and balance aluminum and unavoidable impurities. The chrome is to achieve improved castability and formability. The die cast alloy may further comprise titanium at a level of 0.01 to 0.15 weight percent, with titanium acting as a grain refiner, particularly when used with boron. From EP 0 601 972 A1 a hypoeutectic aluminum-silicon casting alloy is known, which contains a master alloy as a grain refining agent. The cast alloy includes a silicon content of 5 to 13 weight percent and may further include magnesium at a level of 0.05 to 0.6 weight percent. The master alloy contains 1.0 to 2.0 percent by weight of titanium and 1.0 to 2.0 percent by weight of boron. The aluminum-silicon casting alloy is used to make automobile rims by low pressure die casting. The addition of the master alloy takes place, in relation to the total amount of the melt, in an amount of 0.05 to 0.5 percent by weight. From DE 692 33 286 T2, for example, a method for grain refining of aluminum and aluminum alloys is known, in which a solid silicon-boron alloy is added to molten aluminum or molten aluminum alloy. The resulting melt contains about 9.6 weight percent silicon and at least 50 ppm boron. The melt-fabricated component has grain sizes in the range of 300 micrometers.

From EP 1 244 820 B1, a process for grain refining of high-strength aluminum casting alloys is known, in order to achieve a cast product having a particle size of less than 125 micrometers. Various alloys are proposed for this purpose, for example an alloy with more than 3.8% by weight of copper, at most 0.1% by weight of silicon and 0.25% to 0.55% by weight of magnesium, or an alloy with more than 4.5 and less than 6 , 5 weight percent zinc, at most 0.3 weight percent silicon and 0.2 to 0.8 weight percent magnesium. For grain refining, dissolved titanium having a grain size of less than 125 micrometers in an amount of 0.005 to 0.1 weight percent and borides is added to the melt.

WO 2001 042521 A1 discloses a process for producing a grain refining agent based on an aluminum-titanium-boron master alloy by introducing titanium- and boron-containing starting materials into an aluminum melt to form TiB2 particles and solidifying this master alloy melt. In a source cited there, a theory of the course of the processes in the grain refining of aluminum alloys by adding an Al-Ti-B master alloy, for example ΑΙΤΊ5Β1. Thereafter, the best grain refining results when the TiB2 particles insoluble in the aluminum melt are at least partially coated with a layer of Al3Ti phase at their surface. The nucleation of the alpha-aluminum phase takes place on the AI3Ti layers, the effect of which increases with decreasing layer thickness.

From EP 2 848 333 A1 a method for producing a metallic component by means of a casting and molding tool is known, comprising the steps of: pouring a melt into the casting and molding tool at a first pressure, pressurizing the solidifying melt in the tool with a larger second pressure, and compressing the melt-solidified component in the tool with a larger third pressure. The present invention has for its object to provide a light metal casting with a fine-grained structure, which has good strength properties and is easy to produce. The object is also to propose a corresponding method for producing such a Leichtmetallgussbauteils. One solution is a light metal cast component made of a hypoeutectic cast aluminum alloy, wherein the light metal cast component contains 3.5 to 5.0 weight percent silicon and 0.2 to 0.7 weight percent magnesium, and wherein the light metal cast component has a mean grain size of a maximum of 500 microns. In particular, it is envisaged that the light metal cast component in addition to silicon and magnesium with the specified proportions also titanium with 0.07 to 0.12 weight percent, boron with a maximum of 0.012 weight percent, optionally further alloying elements together less than 1, 5 weight percent, the balance aluminum and contains unavoidable impurities. An advantage of the light metal cast component is that it can be produced by low-pressure casting due to the relatively low silicon content and, due to the fine-grained microstructure, has good mechanical properties, in particular with regard to strength, ductility, elongation at break and porosity. The tensile strength (Rm) of the light metal cast component is preferably at least 270 N / mm ² , in particular at least 300 N / mm ² , or at least 320 N / mm ² .

Due to the relatively low silicon content of less than 5 percent by weight results in a hypoeutectic aluminum-silicon alloy. The light metal cast component produced therefrom has a high ductility and elongation at break. The elongation at break (A5) of the light metal cast component is at least 5%, in particular at least 8%. The breaking elongation can be below the breaking elongation usual for a forging part, in particular below 12%.

The light metal cast component preferably has a yield strength (Rp0.2) of at least 220 N / mm ² , in particular of at least 250 N / mm ² , or of at least 280 N / mm ² .

Preferably, the Leichtmetallgussbauteil has a maximum porosity of less than 0.5%, in particular less than 0.1%. The low porosity also contributes to good strength properties and toughness. The light metal cast component may have a surface roughness of less than 50 microns, more preferably less than 20 microns.

The low surface roughness of less than 50 micrometers contributes to particularly good mechanical characteristics of the surface quality of the component. According to a preferred embodiment, the light metal cast component in a raw cast surface area has a yield strength (Rp0.2) of at least 280 N / mm ² , an elongation at break (A5) of at least 8% and a tensile strength (Rm) of at least 320 N / mm ² . In this case, by raw-cast surface area is meant an area of the raw cast component, unprocessed after casting, having a depth of up to 1.0 mm from the component surface.

The light metal cast component can be subjected to a heat treatment after solidification, in particular solution heat treatment and subsequent aging. The heat treatment contributes to the improvement of the known material properties, in particular to increase the strength. The abovementioned material parameters relate in particular to a condition after heat treatment has taken place. Main alloying elements of the casting alloy used for the production of the light metal casting component are aluminum and silicon. In this respect, the casting alloy can also be referred to as aluminum-silicon casting alloy.

In addition to aluminum, silicon and manganese, the cast alloy can also contain other alloying elements or unavoidable impurities. The proportion of further alloying elements and unavoidable impurities is in particular less than 1.5% by weight, based on the total weight of the light metal cast component, preferably less than 1.0% by weight. Accordingly, the aluminum-silicon casting alloy in particular at least 93 weight percent, preferably at least 95 weight percent aluminum.

In principle, it is desirable for the light metal cast component to be produced to have good mechanical properties, in particular high strength. On the other hand, strength-enhancing alloying elements can lead to an increased tendency to corrosion, which in turn is undesirable.

It is therefore particularly envisaged that the proportion of strength-increasing alloying elements is as low as possible, so that the light metal casting component has a high corrosion resistance. The corrosion resistance should be so high that the relevant corrosion tests for the respective Leichtmetallgussbauteil be met. Standardized corrosion tests are described, for example, in EN ISO 9227 or ASTM B1 17. Depending on the component, corrosion tests that relate to the external stress of motor vehicles, such as the CASS test (copper accelerated salt spray test) or the filiform test for vehicle wheels, should also be fulfilled. The CASS test is carried out especially on coated or painted components. The components to be tested in a chest-like system are permanently exposed to different, highly corrosive salt mists. The examination of filiform corrosion can, for example according to DIN EN 3665 or a comparable standard.

The subcritical amount of strength-enhancing alloying elements depends on the respective alloy composition and the corrosion test used, and therefore can not be stated in an absolute or concrete way. Therefore, it is merely exemplified herein that the amount of strength enhancing alloying elements such as copper (Cu), zinc (Zn) and titanium (Ti) may be less than one weight percent, based on the total weight of the component.

In one embodiment, the aluminum casting alloy copper (Cu) having a maximum content of 1, 0 weight percent, in particular of at most 0.5 weight percent, in particular of up to 550 ppm (parts per million) have. It can also be provided that the casting alloy or the component produced therefrom contains less than 250 ppm or no copper at all.

In one embodiment, the aluminum casting alloy may include zinc (Zn) with a maximum content of 550 ppm (parts per million). It can also be provided that the casting alloy or the component produced therefrom contains less than 250 ppm or no zinc at all.

In one embodiment, the aluminum casting alloy may comprise titanium (Ti) having a maximum content of 0.12 weight percent. In particular, it can be provided that a proportion of 0.07 to 0.12 percent by weight of titanium is contained in the casting alloy or in the component produced therefrom.

In one embodiment, the aluminum casting alloy boron (B) having a maximum content of 0.12 weight percent, in particular of at most 0.012 weight percent, in particular of at most 0.06 weight percent. If titanium is also present, the proportion of boron may be less than the proportion of titanium. The titanium and the boron can be provided according to an embodiment in the form of titanium boride in the aluminum casting alloy or in the component produced therefrom. In particular, the aluminum casting alloy titanium boride (TiBor) with a share of less than 30 ppm.

In one embodiment, the aluminum casting alloy may include strontium (Sr) at a level of from 100 ppm to 150 ppm.

In one embodiment, the aluminum casting alloy may include tin (Sn) at a level of less than 250 ppm.

According to one embodiment, the aluminum casting alloy may comprise nickel (Ni) in a proportion of less than 550 ppm.

In one embodiment, the aluminum casting alloy may include manganese (Mn) at less than 0.5 weight percent. According to one embodiment, the aluminum casting alloy may comprise chromium (Cr) in a proportion of less than 500 ppm, preferably less than 200 ppm. This includes in particular the possibility that no chromium is contained in the aluminum casting alloy or in the component produced therefrom. Incidentally, this also applies to the other alloying elements mentioned above.

In one embodiment, the aluminum casting alloy may include iron (Fe) at a level of less than 0.7 weight percent.

In one embodiment, the aluminum casting alloy may include manganese (Mn) at less than 0.15 weight percent.

It is understood that all of the above alloying elements can be provided either individually or in combination with one or more other elements. The remainder of the aluminum casting alloy consists of aluminum, silicon, magnesium, and in particular titanium and boron, and unavoidable impurities. The proportion by weight of the other alloying elements, that is, the alloying elements present in addition to aluminum, silicon, magnesium, titanium and boron is preferably less than 1, 5, in particular less than 1, 0 weight percent. An advantage of the light metal cast components according to the invention is that they have a greater design freedom than conventional light metal cast components and forged light metal components. Thus, smaller cross-sections of the components can be realized, or a complex Umformtechnische post-processing can be omitted. According to one embodiment, the light metal casting component may have, in the finished manufactured state, subsections which are mechanically unworked, in particular mechanically unconsolidated after casting. The mechanically unprocessed sections may, at least in some areas, have a wall thickness of less than 3.0 millimeters.

According to a possible embodiment, the light metal cast component can be a safety or structural component, in particular a vehicle wheel or a vehicle rim for a motor vehicle or the like. It is understood that the light metal cast component can also be designed in other form or for other applications than motor vehicles, for example for the construction industry. Preferably, the security or structural member has a weight of at least 500 grams, more preferably at least 3000 grams. The solution of the above object is further in a method for producing a light metal casting component comprising the steps of providing a melt of an aluminum casting alloy, which - in addition to aluminum - at least silicon with 3.5 to 5.0 weight percent and magnesium with 0.2 contains up to 0.7% by weight and unavoidable impurities; Pouring the melt into a casting mold with a low first pressure (P1); after completely filling the casting and molding tool, pressurizing the solidifying melt in the casting and molding tool with a second pressure (P2) greater than the first pressure (P1); and when the melt is at least largely solidified to the component, compressing the at least largely solidified from the melt component in the casting and molding tool at a third pressure (P3) which is greater than the second pressure (P2). An advantage of the casting method described is that hereby components with particularly high strength and a particularly fine microstructure can be produced in a short time. In particular, the method can be used to produce light metal cast components having an average particle size of less than 500 micrometers, in particular from 200 to 500 micrometers. In this respect, the advantages of the method and the advantages of the component produced according to the method interlock here. In this context, it is understood that all the features and benefits referred to in the context of the product also apply to the procedure, and vice versa.

Another advantage of the method is that the components produced by the compression have a near-net shape, resulting in excellent material utilization. Furthermore, the products produced by said method have a high dimensional accuracy and surface quality. The tooling costs are low, since a process tool is used to carry out different process steps. The method is particularly suitable for the production of wheel rims for motor vehicles, the production of other components is of course not excluded. According to a preferred method, the casting of the melt takes place at a temperature significantly above the liquidus temperature, in particular at a casting temperature which is at least 10% above the liquidus temperature. For example, the melt consisting of cast aluminum alloy can be cast at a temperature of 620 ° C. to 800 ° C., in particular at a temperature of 650 ° C. to 780 ° C. The casting tool, which is also referred to as a casting mold or mold, may have a low temperature of, for example, less than 300 ° C.

The pressure required to pour the melt into the casting mold depends on the casting process, such as gravity casting or low pressure casting. For example, when using gravity casting, the first pressure may be the ambient pressure, that is about 0.1 MPa (1 bar). In contrast, the first pressure when using low pressure casting accordingly high, that the melt can rise through the riser into the mold cavity of the casting tool. For example, the pressure during low-pressure casting may be between 0.3 MPa and 0.8 MPa (corresponding to 3 to 8 bar). The first pressure is at most as large as needed for low pressure casting and should preferably be less than 1 MPa.

The pressurization provided after the filling of the casting tool is carried out at a higher second pressure, which may be, for example, greater than 5 MPa (50 bar), in particular more than 9 MPa (90 bar). The pressurization with the second pressure begins after the mold is completely filled with melt, in particular while the melt initially solidifies to the component or when the melt passes into the semi-solid state starting. The completely filled state of the casting mold can be sensed in the low-pressure process, for example by a pressure surge at the filling piston.

The pressurization of the solidifying melt can take place, for example, at a component edge shell temperature below the liquidus line and / or above the solidus line of the light metal alloy. However, it is also conceivable that the process begins even before reaching the liquidus line, for example at 3% above the liquidus line. Under component edge shell temperature is understood in this context, a temperature which has the component in an edge layer region, or a solidifying or solidified from the melt edge shell. The solidification occurs from outside to inside, so that the temperature of the solidifying component inside are higher than in the peripheral view. The pressurization is carried out at a second pressure, which is greater than the first pressure and can be exerted on the melt, for example by the weight of the upper part.

For compression, an even higher third pressure is built up and exerted on the workpiece, which may preferably be more than 15 MPa (150 bar). The compression is preferably carried out at a component edge shell temperature, which is lower than the second temperature of already partially or largely solidified light metal alloy. A lower limit of the third temperature for carrying out the compression is preferably at half the solidus temperature of the metal alloy. Subareas of the component may also be outside the temperature. During the compression, the temperature of the component or of the tool lower part and / or upper part can be monitored by means of corresponding temperature sensors. The end of the forming process can be defined by reaching an end position of the relative movement upper part to lower part or reaching a certain temperature. After a possible process control, the melt can be prepared from a base melt containing at least aluminum, and grain refining agents. The grain refining agents act as nucleating agents in crystallizing the molten metal melt. These nucleating agents have a higher melting point than the light metal melt to be cast off and therefore solidify first during cooling. The crystals formed from the melt easily accumulate on the granulating agents. As many crystals as possible form, which then hinder their growth, resulting in a fine uniform structure. The grain refining agents may comprise an aluminum-silicon alloy grain refiner containing a maximum of 12.5 weight percent silicon, and / or an aluminum-titanium alloy grain refiner containing at least titanium and boron as alloying elements. It is provided in particular that the two grain refiners are composed of different alloys. A particularly good grain refining effect is achieved when both the first grain refiner with up to 12.5 weight percent silicon and the second grain refiner with titanium and boron are used. This leads to a significant improvement in the castability and the strength of the component produced therefrom.

In concrete terms, the melt, based on the total weight of the castable melt or of the component produced therefrom, taken together may contain an amount of 0.1 to 5.0 percent by weight of the grain refiner of the aluminum-silicon alloy and the grain refiner of the aluminum-titanium alloy , It is provided in particular that the melt of the aluminum casting alloy, or the light metal cast component produced therefrom, contains silicon with 3.5 to 5.0 percent by weight, magnesium with 0.2 to 0.7 percent by weight, titanium with 0.07 to 0.12 percent by weight , Boron with a maximum of 0.012 weight percent, optionally further alloying elements together less than 1, 5 weight percent, the balance aluminum and unavoidable impurities.

As far as alloying elements such as silicon, titanium, boron or others are mentioned, it should be understood in the context of the present disclosure that not only the pure alloying elements can be used, but also compounds are included, which include the respective alloying elements. The specified proportion of silicon of not more than 12.5 percent by weight refers to the total weight of the first grain refiner. In one embodiment, the first grain fine silicon may contain from 3.0 to 7.0 weight percent, magnesium at 0.2 to 0.7 weight percent, titanium at 0.07 to 0.12 weight percent, boron at most 0.012 weight percent, optionally further alloying elements together less than 1, 5 weight percent, the balance aluminum and unavoidable impurities. The stated values relate to the total weight of the first grain refiner. The first grain refiner may have the same or different alloy composition as the base melt. According to one possible embodiment, the first grain finer is treated with ultrasound in a molten state, so that a globally molded solid solution is formed on solidification. That is, the proportion of silicon dissolved in the aluminum forms a globulitically formed mixed crystal. The grain refiner is heated in particular up to the transition temperature between solid and liquid (semi-solid) or above. A further effect of the ultrasonic treatment is that the boron contained in the grain refining melt or the borides serve as nuclei to which Al3Ti attaches. Upon cooling, the thus formed AI3Ti particles solidify in the globulitic structure. Preferably, the first grain refining melt is solidified as quickly as possible, that is, for example, within up to 10 seconds. The AI3Ti particles are later nucleated when they are stirred into the base melt. The second grain refiner based on an aluminum-titanium alloy may in particular be a commercially available grain refiner, such as Al5 ™ B. The first and second grain refiner may be introduced into the base melt individually or as a composite grain refining system, with the nucleating first grain refiner and the nucleating second grain refiner completely melted in the melt. Subsequently, the resulting melt, which is composed of the base melt with the grain fines dissolved therein, is poured into the casting or molding tool.

After a possible process control, the first and second grain finer are supplied to the base melt immediately before the casting of the respective cast component. In concrete terms, it can be provided, in particular, that the melt is poured into the casting mold within a maximum of five minutes after stirring the first grain finer and / or the second grain finer into the base melt. In this way, the AI3Ti particles of the stirred grain finer are at least substantially in solid form, so that the grain refining effects are increased.

A preferred method is explained below with reference to the drawing figures. It shows:

1 shows an inventive method for producing a Leichtmetallguss- component by means of a casting and molding tool with the process steps S10 to S50;

FIG. 2 shows a state diagram (phase diagram) for a metal alloy for producing a component according to the method according to FIG. 1.

FIGS. 1 and 2 will be described together below. FIG. 1 shows a method for producing a light metal cast component by means of a casting and molding tool in a plurality of method steps S10 to S50. The material used is a light metal casting alloy containing at least the following alloy constituents: 3.5 to 5.0% by weight of silicon, 0.2 to 0.7% by weight of magnesium, 0.07 to 0.12% by weight of titanium, a measurable fraction of boron from to at 0.012 weight percent, at least 93.0 weight percent aluminum and unavoidable impurities. The alloy may also contain minor amounts of trace elements of other elements such as copper, manganese, nickel, zinc, tin, and / or strontium. In particular, an exemplary alloy may include 4.0 weight percent silicon, 0.4 weight percent magnesium, 0.08 weight percent titanium, 0.012 weight percent boron, about 400 ppm copper (Cu), about 400 ppm zinc (Zn), about 100 ppm strontium (Sr). , about 200 ppm tin (Sn), about 400 ppm nickel (Ni), about 400 ppm manganese (Mn), further unavoidable impurities and the balance aluminum (AI).

In the first method step S10, the melt is produced for producing the light metal cast component. For this purpose, a base melt is made from a base alloy. In the base alloy, at least one grain finer can be introduced, which acts as a nucleating agent during crystallization. Concretely, in one example, a first grain refiner made from an aluminum-silicon alloy containing a maximum silicon content of 12.5 percent by weight based on the total weight of the first grain refining alloy can be used. In addition, a second grain refiner of an aluminum-titanium alloy may be used, which contains aluminum as the main component and at least titanium and boron as additional alloying elements. The grain finers are introduced into the melt of the base alloy, whereby the grain finer are melted. With regard to the proportions, provision is made in particular for a total amount of from 0.1 to 5.0 percent by weight of the first and second grain refiners to be introduced based on the total weight of the component to be produced.

In the second method step S20, the melt from the light metal casting alloy is poured into a casting and molding tool at a low first pressure (P1). sen. The casting may be done by gravity casting or low pressure casting, the first pressure (P1) preferably being less than 1.0 MPa. The melt is poured at a temperature (T1) above the quenching temperature, in particular at a temperature of 650 ° C to 780 ° C. The casting tool, which is also referred to as a casting mold or mold, may have a low temperature of, for example, less than 300 ° C.

In the subsequent method step S30, the light metal alloy located in the mold cavity is pressurized. For this purpose, a pressure P2 which is greater than 5 MPa (50 bar) is established between a lower part and an upper part of the casting tool. This pressure can be generated for example by the weight of the upper part. Before applying pressure, all openings of the casting and forming tool must be closed, so that no material is undesirably pressed out of the mold. The pressurization of the melt can take place in a component edge shell temperature range T2 from around the liquidus line TL to above the solidus line TS of the metal alloy, that is TS <T2 <TL. Before the pressurization, the material is still liquid. Upon completion of the pressurization, the material is at least partially solidified, that is, it is in a semi-solid state. After the pressurization (S30), in the subsequent method step S40, a compression of the workpiece which is at least largely solidified from the melt takes place. The compression is performed by relatively moving the base to the top at a third pressure P3 that is greater than the second pressure P2 in step S30. The compression can be done by pressing the lower part in the direction of the upper part with high forces. The compression preferably begins only when the metal alloy is at least largely solidified or in the semi-solid state. The compaction can be carried out at a component edge shell temperature T3, which is lower than the temperature T2 of the metal alloy in the step pressurizing S30. The lower limit of the temperature T3 is half of the solidus temperature TS of the metal alloy, that is T2>T3> 0.5TS. The end of the forming process is defined by reaching an end position of the relative movement top part to bottom part and the achievement of a certain temperature. ned. When compacting the component undergoes only a relatively low degree of deformation of less than 1 5%, in particular less than 10%, respectively 5%. During compaction, pores are closed in the component, so that the microstructure is improved.

After the component has completely solidified, it is removed from the casting tool. Subsequently, the workpiece, also referred to as a raw casting component in this state, is mechanically reworked in method step S50. The mechanical reworking may be, for example, a machining operation, such as a turning or milling machining, or a reshaping machining, such as ironing.

The light metal cast component may be subjected to a heat treatment after solidification, before or after the mechanical reworking. For example, the light metal cast component can be solution annealed and then tempered. By the heat treatment in particular the strength properties of the component can be increased.

It may be followed by other usual process steps such as quality control, for example by means of X-ray, as well as painting.

With the method according to the invention, cast blanks can be produced in several stages in the same lower mold, by casting (S20), subsequent pressurization (S30) and subsequent compacting / reshaping (S40). The pressurization takes place above the solidus temperature (liquid to semi-solid state) of the alloy used in each case.

FIG. 2 shows a state diagram (phase diagram) for a light metal alloy for producing a component according to the method according to the invention. The X-axis indicates the content ratio of a metal alloy (WL) that includes XA% of a metal A and XB% of a metal B. In the present case, the metal A is aluminum and the metal B is silicon. Due to the stated proportions of aluminum and silicon, the light metal alloy formed out hypoeutectic, that is, the proportion of silicon (metal B) is in relation to aluminum (metal A) in the light metal alloy (WL) SO small that a structure is created to the left of the eutectic (WEU).

The temperature (T) is indicated on the Y axis. The casting takes place at a temperature T1 clearly above the liquidus temperature TL or the liquefaction line LL. The temperature range T1 is shown in phantom. The temperature range T2 for pressurizing, which is preferably below the liquidus temperature (TL) and above the solidus temperature TS (TL> T2> TS), is shown in FIG. 2 with hatching from bottom left to top right. Depending on the process time during pressurization (S20), a residual degree of deformation of less than 1 5% remains for a subsequent compaction. The compression (S30) takes place in particular in a temperature range T3 between the temperature T2 and the half solidus temperature 0.5TS (T2> T3> 0.5 TS). This area is hatched in Figure 2 from top left to bottom right. Optionally, a mechanical reworking (S40) takes place at a temperature T4 below the solidus temperature (T4 <TS).

The light metal cast component produced by the above method has a particularly fine-grained structure with a low porosity and good mechanical properties, in particular with regard to the strength, ductility and elongation at break. The light metal cast component has a maximum porosity of less than 0.5%, in particular less than 0.1%, and a surface roughness (Ra) of less than 50 micrometers, in particular less than 20 micrometers. The tensile strength (Rm) of the light metal cast component after heat treatment is at least 270 N / mm ² , in particular at least 320 N / mm ² . The elongation at break (A5) is at least 5%, in particular at least 8%. The yield strength (Rp0.2) is at least 220 N / mm ² , in particular at least 280 N / mm ² .

The light metal cast component can be designed in the form of a safety or structural component for a motor vehicle, in particular as a vehicle wheel or a vehicle rim. The process is particularly suitable for the production of safety or structural components having a weight of at least 500 grams, in particular of at least 3000 grams, without being limited thereto. An advantage of the described method is that a component produced therewith has a particularly fine-grained, lunkerarmes structure. Overall, this leads to an increased strength of the component. Thus, tests have shown that the tensile strength (Rm) of a component according to the invention could be increased by more than 20% over conventionally produced components. The yield strength (Rp0.2) could even be increased by more than 40%. Overall, a component with significantly higher strength can thus be produced with the same material use, or it can be made with less material use a lighter component.

Claims

claims

1 . Method for producing a light metal cast component with the steps:

Providing a melt of an aluminum casting alloy, the silicon of 3.5 to 5.0 weight percent, magnesium of 0.2 to 0.7 weight percent, titanium of 0.07 to 0.12 weight percent, boron of at most 0.012 weight percent, optional containing in total less than 1, 5 percent by weight of the balance aluminum and unavoidable impurities, the melt being produced from a base melt containing aluminum, a first grain refiner made of an aluminum-silicon alloy containing a maximum of 12 silicon, 5 wt .-% and aluminum, and a second grain refiner made of an aluminum-titanium alloy containing as alloying elements at least titanium, boron and aluminum, the melt, based on the total weight, in total an amount of 0.1 to 5.0 weight percent of Grain refiner of the aluminum-silicon alloy and the grain finer of the aluminum-titanium alloy;

Pouring the melt into a casting and forming tool in the low-pressure process at a low first pressure (P1), in particular by means of gravity casting or low-pressure casting,

after complete filling of the casting and molding tool, pressurizing the solidifying melt in the casting and molding tool with a second pressure (P2) which is greater than the first pressure (P1), and when the melt is at least largely solidified to the component, compressing the at least largely solidified from the melt component in the casting and molding tool at a third pressure (P3) which is greater than the second pressure (P2).

2. The method according to claim 1,

characterized,

that the melt contains, as further alloying elements, at least one of: strontium (Sr) with 100 to 150 ppm,

Tin (Sn) less than 250 ppm,

Copper (Cu) less than 1.0% by weight, in particular less than 550 ppm,

Nickel (Ni) less than 550 ppm,

Titanium boride (TiBor) less than 30 ppm,

Zinc (Zn) less than 550 ppm,

Chromium (Cr) less than 500 ppm,

Iron (Fe) less than 0.7 weight percent and

Manganese (Mn) less than 0.15 weight percent

contains.

3. The method according to claim 1 or 2,

characterized,

in that the first grain refiner is produced by producing a grain refining melt from the aluminum-silicon alloy and treating the grain refining melt with ultrasound, such that after solidification there is a globularly shaped alpha mixed crystal.

4. The method according to any one of claims 1 to 3,

characterized,

that the first grain finer and the second grain finer are introduced by stirring into the base melt, in particular with at least partial temporal overlap.

Method according to one of claims 1 to 4,

characterized,

that the casting of the melt takes place no later than five minutes after the introduction of the first grain refiner and / or the second grain refiner.

Method according to one of claims 1 to 5,

characterized,

the casting takes place at a first temperature (T1) of 620 ° C to 800 ° C, in particular at a first temperature of 650 ° C to 780 ° C.

Method according to one of claims 1 to 6,

characterized,

the pressurization with the second pressure (P2) is performed at a second temperature (T2) which is lower than the first temperature and below the liquidus line,

wherein the compression at the third pressure (P3) is performed at a third temperature (T3) that is less than the second temperature (T2) and that is at least one-half the solidus temperature of the aluminum casting alloy.

Method according to one of claims 1 to 7,

characterized,

that the light metal cast component is subjected after heat treatment to a solidification, in particular a solution annealing and subsequent aging.

Light metal cast component, in particular for a motor vehicle,

manufactured by the method according to one of claims 1 to 8,

wherein the light metal cast component comprises 3.5 to 5.0 percent by weight silicon and 0.2 to 0.7 percent by weight magnesium, 0.07 to 0.12 percent by weight titanium, maximum 0.012 percent by weight boron, optionally further alloying elements with together less than 1, 5 weight percent, the balance contains aluminum and unavoidable impurities, and

wherein the Leichtmetallgussbauteil has a mean grain size of a maximum of 500 micrometers.

10. Light metal cast component according to claim 9,

characterized,

in that the light metal cast component has a maximum porosity of less than 0.5%, in particular less than 0.1%.

1 1. Light metal cast component according to claim 9 or 10,

characterized,

in that the light metal cast component has an elongation at break (As) of at least 5%, in particular at least 8%.

12. Light metal cast component according to one of claims 9 to 1 1,

characterized,

in that the light metal cast component has a yield strength (Rpo, 2) of at least 220 N / mm ² , preferably of at least 250 N / mm ² , in particular of at least 280 N / mm ² .

13. Light metal cast component according to one of claims 9 to 12,

characterized,

in that the light metal cast component has a tensile strength (Rm) of at least 270 N / mm ² , preferably of at least 300 N / mm ^2, in particular of at least 320 N / mm ² .

14. Light metal cast component according to one of claims 9 to 13,

characterized,

in that the light metal cast component has a surface roughness [Ra] of less than 50 micrometers, in particular less than 20 micrometers.

15. Light metal cast component according to one of claims 9 to 14,

characterized,

in the region of a raw casting surface, the light metal cast component has a yield strength (Rpo, 2) of at least 280 N / mm ² , an elongation at break (As) of at least 8% and a tensile strength (Rm) of at least 320 N / mm ² .

16. Light metal cast component according to one of claims 9 to 15,

characterized,

that the light metal cast component in finished manufactured state has partial sections which are mechanically unworked after casting, in particular mechanically unconsolidated, wherein the mechanically unprocessed sections have a wall thickness of less than 3.0 millimeters.

17. Light metal casting component according to one of claims 9 to 16,

characterized,

the light metal cast component is a safety or structural component, in particular a vehicle wheel of a motor vehicle.

18. Light metal cast component according to one of claims 9 to 17,

characterized,

the safety or structural component has a weight of at least 500 grams, in particular of at least 3000 grams.