Method for manufacturing a component

Abstract

Method for manufacturing a component (11) wherein an aluminum-based alloy (20) is provided and converted into a semi-solid state and the component (11) is manufactured from it by a semi-solid process, characterized in that the alloy (20) contains less than 1.3 wt.% iron and at most 0.2 wt.% silicon.

Description

[0001] The invention relates to a method for manufacturing a component, having the features of the preamble of claim 1, and to the use of an aluminum-based alloy for manufacturing a component.

[0002] Components made of aluminum or aluminum alloys are used in various sectors, particularly in automotive engineering. Compared to steel components, their lower density, in addition to their higher corrosion resistance, is a significant advantage. The latter allows for weight reduction, even if greater material thicknesses are sometimes necessary to achieve the desired material properties. Various processes can be used to manufacture aluminum components (which in this context includes components made of aluminum alloys). Besides primary forming, this includes both hot and cold forming. While the metal is in a liquid state during primary forming processes, such as aluminum die casting, and in a solid state during conventional forming processes, so-called semi-solid processes involve setting a temperature at which the metal is partially liquid and partially solid.In the transition temperature range between solid and liquid, the thixotropic state is reached, in which finely dispersed, crystallized components are embedded in molten regions. In this thixotropic state, the viscosity of the material decreases under the influence of shear forces, allowing it to be precisely pressed into almost any shape at comparatively low pressure. In particular, very thin-walled components can be produced compared to conventional die casting. Semi-solid processes aim to create an optimal volume fraction of the liquid phase, enabling low-friction forming of the remaining, still solid alloy components through forging, casting, extrusion, flow forming, etc., of the metallic material in its thixotropic state.

[0003] Not all aluminum alloys suitable for conventional die casting are also suitable for semi-solid processes. This is particularly true for many silicon-free alloys known in the prior art, such as Castaduct®-42 (AlMg4Fe2). The latter material is suitable for die casting and, in the solid state, is characterized by advantageous mechanical properties, especially high ductility. However, in the transition temperature range required for semi-solid processes, an Al13Fe4 phase forms, while no Al phase develops. To carry out a semi-solid process, the formation of an Al phase embedded in liquid material would be necessary. This can be achieved in the prior art with aluminum alloys containing a significant proportion of silicon, for example, between 5 and 10 wt.% (where, here and in the following, the terms "wt.(The terms "%" and "mass percent" are used synonymously). However, such alloys generally exhibit significantly reduced ductility and are therefore unsuitable for certain applications.

[0004] US Patent 9,920,401 B2 discloses a high-thermal-conductivity aluminum alloy intended for die casting. In addition to aluminum, the alloy contains 0.2–2.0 wt.% magnesium, 0.1–0.3 wt.% iron, and 0.1–1.0 wt.% cobalt. It is intended, in particular, for the manufacture of LED components.

[0005] US Patent 9,715,971 B2 discloses an electrode for a secondary battery comprising a foil made of an aluminum alloy. The aluminum alloy contains 0.03–0.1 wt% iron, up to 0.1 wt% silicon, and optionally titanium and copper. The alloy is first produced as an ingot by continuous or semi-continuous casting, which is then thermally homogenized and subsequently rolled to form the foil. US Patent 2013 / 0269842 A1 relates to a similar electrode, in which the aluminum alloy contains 0.03–0.1 wt% iron, 0.01–0.1 wt% silicon, and small amounts of copper.

[0006] US patent 2018 / 0274073 A1 discloses a high-strength aluminum alloy containing, in addition to aluminum, 0.3-1.0 wt.% iron, as well as zinc, magnesium, nickel, copper, zirconium, titanium, scandium, and chromium. The alloy is designed to produce aluminides of an Al9FeNi phase comprising at least 2% by volume. Components can be cast or forged from this aluminum alloy.

[0007] From CN 108165842 A, an aluminum alloy is known which is particularly suitable for semi-solid processes. In addition to aluminum, the alloy contains 6.6–7.4 wt.% silicon, at most 0.15 wt.% iron, 0.15–0.25 wt.% magnesium, as well as titanium, chromium, ytterbium, tellurium, beryllium and possibly traces of other elements.

[0008] US patent 2003 / 0178106 A1 discloses an aluminum alloy with 6.5-8.5 wt.% silicon, 0.6-1.0 wt.% iron, as well as manganese, magnesium, zinc, titanium, copper, and up to 0.15 wt.% of other elements. The alloy is intended in particular for semi-solid processes.

[0009] US Patent 5,115,770 A pertains to an aluminum alloy containing up to 0.8 wt.% iron, up to 0.6 wt.% silicon, as well as copper, manganese, vanadium, zirconium, and optionally small amounts of zinc, manganese, and nickel. Components exhibiting exceptional tensile strength, even when exposed to elevated temperatures for extended periods, such as a piston for an internal combustion engine, can be manufactured from this alloy using die casting.

[0010] From DE 601 26 529 T2 a die-cast product made of an aluminium-magnesium alloy is known, which contains 2.7 to 6.0 wt.% magnesium, up to 1 wt.% iron and up to 1.4 wt.% silicon in addition to other elements.

[0011] Given the current state of the art, the production of components with increased ductility from an aluminum alloy offers room for improvement.

[0012] The invention is based on the objective of enabling the production of components with increased ductility from an aluminum alloy using a semi-solid process.

[0013] According to the invention, the problem is solved by a method with the features of claim 1, wherein the dependent claims relate to advantageous embodiments of the invention. The problem is further solved by use with the features of claim 10.

[0014] It should be noted that the features and measures listed individually in the following description can be combined in any technically feasible manner and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0015] The invention provides a method for manufacturing a component. In this context, the term "component" is to be interpreted broadly and refers not only to fully finished parts that require no further processing, but also to parts that may require further processing before use, e.g., by machining, surface treatment, surface coating, or the like. In particular, the term also includes semi-finished products.

[0016] In this process, an aluminum-based alloy is provided and converted into a semi-solid state, and the component is then manufactured from it using a semi-solid process. The aluminum-based alloy, or aluminum alloy, preferably contains at least 70 wt.%, more preferably at least 80 wt.%, and even more preferably at least 90 wt.% aluminum. In addition to aluminum, it contains at least one other element. This at least one other element can be, in particular, a metal, but optionally also a metalloid and / or nonmetal. The alloy is provided, or rather, produced, and converted into a semi-solid state. This state, which can also be described as a thixotropic state, is characterized by the fact that parts of the alloy are solid, while other parts are liquid. The semi-solid state is usually achieved by first melting the alloy.Individual components of the alloy are melted and then mixed to form the alloy, after which the alloy is cooled until it reaches a semi-solid state near its transition temperature. The alloy may be contained in a vessel equipped with cooling and / or heating elements to stabilize the alloy's temperature, and thus its semi-solid state, at least temporarily. Furthermore, mixing elements may be provided to thoroughly mix the alloy, at least in its liquid state, and possibly also in its semi-solid state. This mixing can be achieved, for example, by electromagnetic fields, ultrasound, or an enthalpy exchanger. Once the alloy has been brought into the semi-solid state, the component is manufactured from the alloy using a semi-solid process.In this context, the term "semi-solid process" generally refers to a forming process in which the shaping takes place while the alloy is in a semi-solid state. A semi-solid process is generally characterized as a primary forming process.

[0017] According to the invention, the alloy contains less than 1.3 wt.% iron and at most 0.2 wt.% silicon. Due to the low silicon content, which can also be negligible within the scope of the invention, the alloy can also be considered (virtually) silicon-free. This contrasts with aluminum alloys used in the prior art for semi-solid processes, which have significant silicon contents, for example, in the range of 5-10 wt.%. While such alloys are well suited for semi-solid processes, the components manufactured from them exhibit comparatively low ductility or low elongation at break (although these can be increased by heat treatment). By limiting the weight fraction of iron to less than 1.3% according to the invention, it is possible to prevent the formation of an Al13Fe4 phase while a pure aluminum phase is not yet present.According to the invention, a semi-solid state can be achieved in which solid aluminum particles are incorporated into or suspended within an otherwise liquid phase. The low iron content by weight according to the invention also results in a lower proportion of the Al13Fe4 phase being present after cooling and hardening of the alloy, which has a beneficial effect on the ductility and elongation at break of the finished component. It has been shown that by reducing the iron content to less than 1.3 wt.%, the temperature range in which the alloy remains in the semi-solid state can be increased. This significantly simplifies the process.

[0018] In principle, the inventive process can belong to different process types, e.g., thixoforging, in which the shaping takes place between two dies that are moved towards each other. Preferably, the component is produced by rheocasting, in which the alloy, in a semi-solid state, is introduced through at least one transfer opening into a predominantly closed mold cavity and solidifies in the mold cavity. The mold cavity is a hollow space formed within a mold. The mold can, for example, be formed by two mold halves that are joined together before the alloy is introduced to create the mold cavity. The latter is predominantly closed but has at least one transfer opening for introducing the alloy. The alloy can also be introduced into the mold cavity simultaneously or sequentially through a plurality of transfer openings.In particular, it can be pressed or injected into the mold cavity under pressure. The alloy can initially be received in a liquid state in a container, as described above, which may optionally include cooling and / or heating means. Once the semi-solid state has been reached, the alloy can be conveyed from the container into the mold cavity through at least one transfer opening, for example, by a pressure piston or a screw conveyor.

[0019] Preferably, the alloy contains at most 0.1 wt.% or at most 0.05 wt.% silicon. Ideally, the silicon content can be reduced even further, e.g., to at most 0.01 wt.% or at most 0.001 wt.%, so that the alloy can be considered essentially silicon-free. Advantageously, the silicon content is reduced to unavoidable impurities.

[0020] According to one embodiment, the iron content can be reduced even further, so that the alloy contains at most 1.0 wt.% iron. It has been shown that the temperature range in which the semi-solid state can be stabilized increases with decreasing iron content. Under certain circumstances, the iron content can also be at most 0.7 wt.% or at most 0.5 wt.%.

[0021] Although reducing the iron content has the positive effects described above, it is unnecessary to reduce the iron content to zero. A certain non-negligible iron content can be advantageous for adjusting specific alloy properties. Furthermore, it has been shown that this results in less wear within the mold than without iron. From this perspective, it is preferable for the alloy to contain at least 0.1 wt% iron.

[0022] Furthermore, it can be advantageous for the alloy to contain at least 0.3 wt.% iron.

[0023] The alloy may contain magnesium. This can also be present in combination with iron, so that it can be referred to as an aluminum-magnesium-iron alloy. In the finished component, the magnesium may then be present within an Al3Mg2 phase.

[0024] The weight fraction of magnesium can vary, but is normally no more than 10 wt.%. Preferably, the alloy contains 3.0–4.6 wt.% magnesium. More preferably, the lower limit for the magnesium content can be 3.2 wt.%, 3.4 wt.%, or 3.6 wt.%. The upper limit for the magnesium content can more preferably be 4.5 wt.% or 4.4 wt.%.

[0025] Typically, the alloy contains at most 1.0 wt.% of other elements other than aluminum, magnesium, iron, and silicon. Preferably, the proportion of these elements is less than 0.5 wt.%. Such optionally included other elements could be, for example, metals selected from copper, manganese, zinc, molybdenum, zirconium, beryllium, and titanium. In particular, the other elements may include copper in a weight fraction of at most 0.2 wt.% and manganese in a weight fraction of at most 0.1 wt.%, with the total weight fraction of any other elements (except Al, Mg, Fe, Si, Cu, and Mn) being less than 0.05 wt.%.

[0026] In particular, the inventive method can be used to manufacture a component for a motor vehicle. This component can be intended for the chassis or the body. Suitable components include all those where the semi-solid process or rheocasting offers advantages over other processes such as die casting, for example, when particularly thin-walled components are to be produced, and where increased ductility is advantageous. These could include trim elements, support elements, suspension components, engine components, or others. Furthermore, the method is suitable for manufacturing a component that is subsequently to be joined to a second component by self-piercing riveting (SPR). The second component can, in particular, be made of steel. The increased ductility achieved according to the invention is advantageous in this joining process.Other joining methods where this ductility is advantageous include flow-drilling screwing, high-speed stud setting, friction welding, and weld riveting.

[0027] The invention also relates to the use of an aluminum-based alloy for the production of a component by a semi-solid process, in particular by rheocasting, wherein the alloy contains less than 1.3 wt.% iron and at most 0.2 wt.% silicon. The aforementioned terms have already been explained with reference to the process according to the invention and are therefore not explained again. Further embodiments of the use according to the invention correspond to those of the process according to the invention.

[0028] Further advantageous details and effects of the invention are explained in more detail below with reference to different embodiments illustrated in the figures. It shows Fig.1 a schematic representation of a first stage of a method according to the invention; Fig. 2 a schematic representation of a second stage of the method according to the invention; Fig. 3 a phase diagram showing the dependence of different phases on the iron content of an aluminum alloy; Fig. 4 a diagram illustrating the temperature-dependent formation of individual phases in an aluminium alloy suitable for die casting; Fig. 5 a diagram illustrating the temperature-dependent formation of individual phases in an aluminium alloy suitable for the process according to the invention; and Fig. 6A-6E different stages of a joining process using a component manufactured according to the invention.

[0029] In the different figures, identical parts are always provided with the same reference symbols, which is why they are usually only described once.

[0030] Fig.Figure 1 shows a highly schematic representation of a device 1 for carrying out a method according to the invention. In this method, a component is to be produced by rheocasting from an aluminum-based alloy 20. A mold 2 is visible, comprising a first mold half 2.1 and a second mold half 2.2, which together define a mold cavity 3. The mold cavity 3 is connected on one side to a transfer opening 4, which in turn is connected to a container 5. The container 5 has a filling opening 6 through which the alloy 20 can be poured in liquid form. Inside the container 5, the alloy 20 is converted into a semi-solid state, with the required temperature being set by a temperature control device 10, which may include both cooling and heating elements. Furthermore, a mixing device 9 is arranged adjacent to the container 5, which, for example,It can be designed to generate electromagnetic fields. These act on the alloy 20 and, at least in its liquid state, result in improved mixing of the individual components. Inside the container 5, a movable piston 7 and a transfer hatch 8 are arranged. The alloy 20 is initially enclosed between the piston 7 and the transfer hatch 8 (see figure). Fig. 1).

[0031] Once the alloy 20 has been brought into the semi-solid state, the actual forming process begins, for which the transfer hatch 8 is opened (see Fig. 2) while the piston 7 is moved towards the mold 2. This moves the alloy 20 through the container 5 and further into the mold cavity 3 via the transfer opening 4, while it remains in a semi-solid state. Inside the mold cavity 3, the alloy 20 hardens and forms the desired component.

[0032] In particular, the manufactured component could be a body panel part that is later joined to another component, e.g., made of steel, by self-piercing riveting (SPR). The increased ductility achieved according to the invention is advantageous in this process.

[0033] The alloy 20 used in this example has the following components: Magnesium: 4.3 wt.% Iron: 1.0 wt.% Silicon: 0.1 wt.% Copper: 0.1 wt.% Manganese: 0.075 wt.% Aluminum: rest

[0034] The significance of limiting the iron content to less than 1.3 wt.% (in this case 1.0 wt.%) is shown in the phase diagram in Fig.Figure 3 clearly illustrates the formation of different phases depending on the iron content. It is evident that a mixed phase with solid aluminum in a liquid phase can only be achieved if the iron content is limited as described and thus remains below 1.3 wt.% for the eutectic. Otherwise, solid Al13Fe4 forms first, before the pure aluminum phase develops. This would be the case, for example, with prior art alloys suitable for die casting, which typically have an iron content between 1.5 wt.% and 1.7 wt.%. An example of this would be Castaduct®-42, which differs from the alloy used according to the invention, in particular, by its iron content of 1.6 wt.%.

[0035] The facts are further clarified by the diagrams in Fig. 4 and Fig. 5, each illustrating the temperature-dependent formation of individual phases. Fig. Figure 4 shows a corresponding diagram for an alloy not usable according to the invention, comprising the following components: Magnesium: 4.3 wt.% Iron: 1.3 wt.% Silicon: 0.1 wt.% Copper: 0.1 wt.% Manganese: 0.075 wt.% Aluminum: rest

[0036] It is evident that the formation of Al13Fe4 begins at approximately 655°C, while the formation of the Al phase only begins below approximately 633°C. Fig. Figure 5 shows a diagram for the alloy described above, which can be used according to the invention. By reducing the iron content to 1.0 wt.%, the formation of the Al13Fe4 phase is suppressed, so that it only begins below approximately 631°C, while the formation of the Al phase begins below approximately 633°C.

[0037] In the alloy used here according to the invention, the silicon content is 0.1 wt.%. This content can be further reduced without impairing the advantageous properties described above, e.g. to 0.05 wt.%, 0.01 wt.% or 0.001 wt.%.

[0038] Fig.Figures 6A-6E show various phases of a process in which a component manufactured according to the invention, hereinafter referred to as the aluminum part 11, is joined to a steel part 12 by self-piercing riveting. Both parts 11 and 12 are shown here as flat sheets, which, however, is not to be understood as a limitation. The aluminum part 11 is placed on a die 13, with the steel part 12 resting on the component 11. A semi-tubular rivet 14 is held in a setting unit 15 (see Figure 6A-6E). Fig. 6A). The setting unit 15 is placed onto the steel part 12, thereby fixing the intended joining point. At the same time, the semi-tubular rivet 14 is advanced and positioned ( Fig. 6B). Further feeding initially causes plastic deformation of the steel part 12 and the aluminum part 11 into the die 13, while the semi-tubular rivet 14 retains its original shape ( Fig.6C). Furthermore, the semi-tubular rivet 14 only punches through the upper steel part 12 and plastically forms the lower aluminum part 11 into a locking head 11.1 ( Fig. 6D and Fig. 6E). Simultaneously, the shank of the semi-tubular rivet 14 expands, thereby completing the positive-locking connection. It is understood that a high degree of deformation takes place in the area of ​​the rivet head 11.1, requiring particularly high ductility to prevent cracks or fractures. It has been shown that components manufactured according to the invention exhibit a particularly low tendency to cracking using this method.

[0039] Apart from the punch riveting shown here as an example, the aluminium part 11 can also be used advantageously in other joining processes, which include in particular flow hole forming screwing, high speed stud setting, friction welding and weld riveting. Reference symbol list: 1 Device 2 Form 2.2 Mold half 3 Mold cavity 2.1, 4 Transfer opening 5 containers 6 Filling opening 7 pistons 8 Transfer hatch 9 Mixing device 10 Temperature control device 11 Component 11.1 Locking head 12 steel parts 13 die 14 semi-tubular rivets 15 setting units 20 alloy

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