Process for producing particle-reinforced metals

Abstract

A process for producing particle-reinforced metals, in which micro- or nanoscale reinforcing particles are introduced into the molten metal and mechanically distributed therein, characterized in that a mixture is introduced into the molten metal which consists of particles soluble in the molten metal and reinforcing particles and particles which form reinforcing particles in the molten metal.

Description

[0001] The invention relates to a process for producing particle-reinforced metals, in which micro- or nanoscale reinforcing particles are introduced into the metal melt and mechanically distributed therein.

[0002] Such a process is already known. It involves introducing nanoscale ceramic reinforcement particles into a molten aluminum alloy and dispersing them throughout the melt using a stirrer.

[0003] In addition to particle separation from the melt due to density differences, agglomerates, i.e., a clumping of particles, are frequently observed in particle-reinforced metals. The reason for the occurrence of particle agglomerates is, on the one hand, the high interfacial forces, particularly in the case of nanoparticles, which cause the particles to already exist as agglomerates prior to processing. On the other hand, the low energy exerted on the agglomerates by the mixing processes in the melt is usually insufficient to separate the agglomerates during the process. In addition, the poor wetting of the ceramic particles with the molten metal prevents effective breakup of the agglomerates.

[0004] Increasing the strength of castings through the incorporation of nanoparticles has a very high potential for increasing room-temperature strength, high-temperature strength, and creep resistance. Nanoparticles reduce ductility far less than microparticles or reinforcing fibers.

[0005] To effectively utilize the mechanisms of metal hardening with nanoparticles, the aim is to achieve the most homogeneous distribution of the nanoparticles in the metal matrix. In practice, the goal is to distribute nanoparticles with a particle size of a few nanometers so finely in the cast component that the ideal free passage distance for dislocations is achieved between the particles. This distance depends, among other things, on the respective alloy, but is generally between 20 nm and 200 nm. The reinforcing particles impede the migration of dislocations in the metal when externally applied stresses are applied, thereby increasing the resistance to plastic deformation of the component. However, an excessively high proportion of reinforcing particles leads to a brittle material.

[0006] For effective dispersion hardening in cast-processed nanoparticle-reinforced composites, the agglomerates must be separated into their individual particles.

[0007] Even in microparticle-reinforced metals, a homogeneous distribution of the particles within the metal has a positive effect on the material properties. In particular, ductility, creep behavior, and wear properties are positively influenced by a homogeneous material structure.

[0008] Document JP H08-325654 A relates to a process for producing a magnesium-based composite material. In the process of document JP H08-325654 A, SiO2 is mixed with SiC powder as a penetration aid, and 0.01 to 0.1 wt.% Ca is added to the molten metal obtained by penetrating the molten Mg alloy as a matrix into the powder mixture. The mixture is stirred to prevent the formation of aggregated SiC lumps.

[0009] Document EP 1 611 980 A1 relates to a method for producing a grain refiner for metallic materials, in particular for the casting of products made of metallic materials. In the method described in document EP 1 611 980 A1, nanoscale particles of a first agent are subjected to a joint grinding process together with a metallic powder until the nanoscale particles are wetted with the metallic powder.

[0010] The object of the invention is therefore to achieve a particularly economic and homogeneous distribution of nano- or microscale reinforcing particles in the molten metal.

[0011] This is achieved according to the invention by the method having the features of claim 1 and the method having the features of claim 2. Advantageous embodiments of the invention are recited in the subclaims.

[0012] According to the invention, a mixture of reinforcement particles and particles soluble in the molten metal is first prepared. This mixture is then introduced into the molten metal. The soluble particles are dissolved in the molten metal, thereby separating the reinforcement particles. In an agglomerate of reinforcement particles and soluble particles in the mixture, the soluble particles form placeholders, which disappear upon dissolution in the melt, leaving the separated reinforcement particles behind.

[0013] When such an agglomerate comes into contact with the molten metal, there is a strong driving force for the selective reaction of the molten metal with the soluble particles. When the soluble particles dissolve in the melt, the agglomerates are broken down at a micro- or nanoscale, and the microscale or nanoscale reinforcement particles are separated. The majority of the energy for separating the particles thus does not come from the externally supplied mechanical energy during the mixing of the particles in the molten metal; rather, the enthalpy of dissolution is extracted from the melt.

[0014] If the soluble particles dissolve, this can also be due to a chemical reaction. For example, silicon dioxide particles can be used as soluble particles in a molten magnesium alloy. The silicon dioxide can then react with the metal components of the alloy, for example, to form metal oxides and metal silicides. The energy for separating the particles can therefore also come from the chemical energy of reactions taking place in the molten metal.

[0015] The reinforcing particles can also be produced in situ, for example, from particles that are oxidized in the melt, thereby forming reinforcing particles made of a high-melting oxide. This means that, according to the invention, a mixture consisting of particles soluble in the metal melt and particles that form reinforcing particles in the metal melt can also be introduced into the metal melt.

[0016] The individual reinforcement particles are mechanically distributed homogeneously in the melt. This can be achieved using a stirrer, an extruder, or other mixing device.

[0017] According to the invention, the mechanical energy that must be applied to the melt to separate the agglomerates is low.

[0018] Preferably, both as reinforcing particles and as soluble particles, microscale particles, i.e. particles with an average particle size of 1 µm to 1,000 µm, or nanoscale particles, i.e. particles with an average particle size of 1 nm to 1 µm, preferably 100 nm to less than 1 µm, are used.

[0019] The average particle size of the soluble particles and the reinforcement particles is preferably of the same order of magnitude. For example, the ratio of the average particle size of the soluble particles to the average particle size of the reinforcement particles can be between 10:1 and 1:10. If the proportion of soluble particles is too low, the agglomerates will not break down into individual reinforcement particles sufficiently; if the proportion of soluble particles is too high, an undesirable change in the properties of the metal can occur. Mixtures with a high proportion of soluble particles can facilitate the dosing of small amounts of reinforcement particles.

[0020] The volume fraction of the reinforcing particles in the metal is preferably 0.1% to 10% for nanoscale reinforcing particles, in particular 1% to 10% for microscale particles, and 2% to 30% for microscale particles, in particular 5% to 20%.

[0021] While the soluble particles dissolve, the reinforcing particles are preferably insoluble in the melt. However, partially soluble reinforcing particles can also be used, but their solubility in the melt should not exceed 50 vol%.

[0022] The reinforcement particles can therefore behave inertly in the molten metal. If they partially dissolve, this may be due to a chemical reaction at the interface. In this case, the reaction kinetics must be designed such that any reactions with the reinforcement particles proceed significantly slower than with the soluble particles.

[0023] Ceramic particles are particularly used as reinforcement particles, for example, carbides such as silicon carbide (SiC) or metal oxides such as aluminum oxide, as well as mixtures of these compounds. The soluble particles can be made of metals or ceramics. Silicon dioxide, for example, is suitable for magnesium alloys.

[0024] Mixtures of soluble particles in the molten metal and reinforcing particles and / or particles that form reinforcing particles in the molten metal are often produced as by-products in other processing processes, for example, flame spraying. Such mixtures are used particularly economically according to the invention. Thus, flame spraying often produces a particle mixture of aluminum, aluminum oxide, and silicon dioxide particles, which is used according to the invention.

[0025] The process according to the invention is particularly suitable for the production of particle-reinforced light metals, especially for the production of cast components made of aluminum or magnesium alloys. Such cast components can be used as engine components, for example, crankcases or engine support blocks, as chassis parts, and also, for example, as instrument panel supports. Example

[0026] A melt of a MgAl6Sr2 alloy is mixed with a mixture of Al2O3 particles and SiO2 particles in a volume ratio of 1:5, which is evenly distributed throughout the melt by stirring. The particle size of both particles is 20 nm to 50 nm. The amount of the mixture is 10 wt.%, based on the melt.

Claims

[1] Process for the production of particle-reinforced metals in which micro- or nanoscale reinforcing particles are introduced into the molten metal and mechanically distributed therein, characterized by that a mixture is introduced into the molten metal, which mixture consists of particles soluble in the molten metal and reinforcing particles and particles which form reinforcing particles in the molten metal. [2] Process for the production of particle-reinforced metals in which micro- or nanoscale reinforcing particles are introduced into the molten metal and mechanically distributed therein, characterized by that a mixture consisting of particles soluble in the metal melt and / or reinforcing particles and particles forming reinforcing particles in the metal melt is introduced into the metal melt, the mixture used being a by-product of another processing operation. [3] Method according to one of the preceding claims, characterized by that microscale particles with a particle size of 1 µm to 1000 µm or nanoscale particles with a particle size of 1 nm to 1000 nm are also used as soluble particles. [4] Method according to one of the preceding claims, characterized by that the volume ratio of the reinforcing particles to the soluble particles in the mixture is 1:100 to 20:

1. [5] Method according to one of the preceding claims, characterized by that the volume fraction of the reinforcing particles in the metal is 0.1% to 10% for nanoscale particles and 2% to 30% for microscale particles. [6] Method according to claim 1, characterized by that the metal is an aluminum or magnesium alloy. [7] Method according to one of the preceding claims, characterized by that ceramic particles are used as reinforcing particles. [8] Method according to one of the preceding claims, characterized by that particles which are completely soluble in the molten metal or which form compounds with components of the molten metal are used as soluble particles.