DE102008001986B4 - Moldings of a magnesium-containing composite material and process for its preparation - Google Patents

Abstract

Molded body of a magnesium-containing composite material consisting of a matrix of particles of magnesium and / or of a magnesium alloy with 5 to 80% by volume of particles of Al60Mg40 finely distributed therein.

Description

The invention related to the field of materials science describes a molded article of a special composite material. For example, because of its relatively high strength properties, this material is often used for building components. The composite can also be used in various fields of engineering, in particular as a construction material in mechanical engineering, aircraft construction, rocket construction, shipbuilding, railway construction, motor vehicle construction as well as in the pharmaceutical industry and in medical device construction, in construction and in household technology. Furthermore, the invention relates to a method for producing such a composite material.

Magnesium and magnesium rich alloys have gained increasing economic and scientific importance.

The range of applications for light metal components is constantly expanding. Especially in the automotive industry, but also in many other areas are lightweight components - especially aluminum, but also magnesium or titanium - now standard (Venir, ATZ / MTZ - Special Edition: Materials in the automotive industry (1998-1999) 54-56; Brungs, H. and Others, ATZ / MTZ - Special Edition: Materials in Automotive Engineering (1998-1999) 50-53).

Current lightweight concepts pursue the use of higher-strength steels as well as aluminum, titanium and magnesium for weight reduction. However, special measures must be taken to achieve materials with the desired properties. For example, in the current six-cylinder gasoline engines with an aluminum-magnesium composite crankcase, BMW has partly replaced light aluminum with even lighter magnesium. This shines with a specific weight of 1.74 g / cm ³ and is also used at BMW for the steering wheel, the steering spindle and the intake system of the V8 engine. At Porsche, there are wheels made of magnesium and magnesium composites. Gearboxes, instrument or seat carriers as well as fuel caps are also made of magnesium in some of the stirrers (Materialica 2001).

It is clear that magnesium played an important role due to the possible weight reduction and the resulting reduction in fuel consumption in aviation (Material Processing, RWP GmbH, Rötgen). For this reason, magnesium has been used gradually as a material in the past. The aircraft XP56, built in 1943, was a so-called all-magnesium aircraft. A Model F-80C built later in the 1950s also had many structural components made of magnesium. Today, the proportion of magnesium among the materials used in aircraft is rather low. Magnesium alloys are currently used in aviation, especially in helicopter production (eg gearbox housing) and very rarely in aircraft.

This fact seems to result from the fact that there may not be enough and insufficiently adapted to the applications magnesium alloys that meet, for example, the requirements of aircraft manufacturers in terms of their mechanical properties, such as strength and damping properties. In fact, about 20 Mg alloys are currently known and more than 99.7% of magnesium components are cast.

The main area of application for magnesium alloys is currently the automotive sector such. For example, for gearbox (light, good noise insulation), rims, wheels, interior equipment and as load-bearing components (eg Smart "FOR2"). As early as 1937, VW used 21 kg of magnesium in every beetle engine. Until 1972, consumption at VW increased to 42,000 t Mg / year. This trend is understandable, because magnesium is 35% lighter than aluminum and 75% lighter than steel. The individual car manufacturers use different amounts of Mg, worldwide, an average value of about 2 kg per car applies.

• – Magnesium-Aluminium-Zink (AZ): – hohe Löslichkeit von Zink im System Mg-Al-Zn – homogene Mischkristalle und intermetallische Phasen, daher aushärtbar Beispiel: AZ91 (9%Al, 1%Zn), AZ60 oder AZ80, optimale Kombination von mechanischen Eigenschaften und Gießbarkeit
• – Magnesium-Aluminium-Mangan (AM): – Umwandlung metallischer Verunreinigungen in intermetallische Phasen – Mangan bildet mit Aluminium sehr harte und unlösliche Ausscheidungen: Nachteil: Verschlechterung der Zerspanbarkeit Beispiel: AM50 (5%Al, > 1%Mn) AM60 (6%Al, > 1%Mn), gute Gieß- uns Verformbarkeit, gute Energieabsorption bei hoher, sehr gute Gießbarkeit Festigkeit
• – Magnesium-Aluminium-Silizium (AS): – Silizium erhöht die Kriechbeständigkeit Beispiel: AS21 (2%Al, 1%Si), gute Kriecheigenschaften bis 150°C

Known magnesium alloy combinations are:

• - Magnesium-aluminum-zinc (AZ): - high solubility of zinc in the system Mg-Al-Zn - homogeneous mixed crystals and intermetallic phases, therefore curable Example: AZ91 (9% Al, 1% Zn), AZ60 or AZ80, optimal combination of mechanical properties and castability
• - Magnesium-Aluminum-Manganese (AM): - Conversion of metallic impurities into intermetallic phases - Manganese forms very hard and insoluble precipitates with aluminum: Disadvantage: Deterioration of machinability Example: AM50 (5% Al,> 1% Mn) AM60 (6% Al,> 1% Mn), good casting us deformability, good energy absorption at high, very good castability strength
• - Magnesium-aluminum-silicon (AS): - Silicon increases creep resistance Example: AS21 (2% Al, 1% Si), good creep properties up to 150 ° C

The magnesium-aluminum alloys are the most popular commercial alloys among the magnesium-based alloys. These can be due to diverse manufacturing methods in the resulting equilibrium phases or non-equilibrium phases are produced, such. B. AZ91, AZ60 or AZ80, AM50, AM60 or AS21 (BL Mordike, et al., Conference: Magnesium Alloys to their Applications, April 28-30, 1998, Wolfsburg, Germany, pp. 199-400).

In recent years, there has been great interest in alloys with metastable structures, with one aim being to meet the material's mechanical properties requirements. Commercial magnesium-aluminum alloys, such as AZ91, AM60 and AM50, where aluminum is included as an alloying ingredient on the order of 5 to 9 weight percent among other, different additives, are widely used in the industry (G. Nussbaum, P. et al. Scripta Matell., 23 (1989) 1079-1084); C.F. Chag, u. a., Light Metal Age (1989) p. 12).

The object of the present invention is to provide a molded article of a magnesium-containing composite material, which simultaneously has a high strength and ductility and in the statement of a simple and inexpensive process for its preparation.

The object is achieved by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims.

The molding of a magnesium-containing composite material according to the invention consists of a matrix of particles of magnesium and / or a magnesium alloy with 5 to 80% by volume of finely divided particles of Al ₆₀ Mg ₄₀ dispersed therein.

Advantageously, 45 to 55% by volume of β-phase particles of an AlMg alloy are contained in the matrix.

Further advantageously, the magnesium alloy contains as alloying elements Al, Mn, Si, Li or Zn.

It is furthermore advantageous if the particles of magnesium or of a magnesium alloy have an average particle size in the range from 0.1 μm to 100 μm.

And it is also advantageous if the particles of Al ₆₀ Mg _{40 have} an average particle size in the range of 0.1 .mu.m to 100 .mu.m.

In the method of producing a molded article according to the present invention, Al ₆₀ Mg _{40 is} prepared from crystalline Al and Mg powders by powder metallurgy and mixed with crystalline Mg powder and / or magnesium alloy powder as a matrix material, and then processed into a magnesium-containing compound by powder metallurgy methods and this subsequently compacted into a shaped body.

Advantageously, Al, Mn, Si, Li or Zn are added as alloying elements to the magnesium alloy.

Also advantageously Al ₆₀ Mg ₄₀ and / or the magnesium-containing compound are prepared by mechanical alloying, wherein advantageously the mechanical alloying is carried out by grinding with a grinding time of 20 to 300 hours.

Also advantageously, the mixing of the crystalline Al powder or the aluminum alloy powder as a matrix material with particles of Al ₆₀ Mg _{40 is} carried out by means of grinding.

And further advantageously, the magnesium-containing compound is processed by hot pressing, extrusion or extrusion to form a shaped body.

The solution according to the invention makes it possible for the first time to introduce metastable structures into a composite material. This is done by powder metallurgy, and this applies both to the production of the β-phase and to the magnesium-containing composite material which is processed into the shaped bodies according to the invention. Advantageously, the powder metallurgical production takes place by mechanical alloying.

By incorporating the metastable structures into the composite, the strength of the molded article is significantly increased while increasing ductility for such composites.

First, a β-phase is produced by grinding. This β-phase is a metastable intermetallic phase that is hard and brittle and has a very large unit cell with 1168 atoms and a cubic face-centered crystal structure (hdp). After grinding, the powder with the composition of the β-phase is initially present as supersaturated Al (Mg) mixed crystal with nanocrystalline grain size. The β-phase can be generated by annealing from the supersaturated mixed crystal. The powder consists of supersaturated mixed crystals and / or of β-phase. The β-phase of the AlMg compound is a compound that consists of supersaturated Al (Mg) mixed crystals and is nanocrystalline. Then, the produced powder is mixed with Mg powder and / or a Mg alloy as a matrix material and processed into a composite material by powder metallurgy methods. Due to the nanocrystallinity of the β phase, it is distributed very finely in the matrix material. And also because the β-phase of the AlMg compound has a cubic face-centered crystal structure, a very good distribution of the crystallites in the powder mixture is possible. Likewise, a very good sintering result is achieved.

From this composite material then a molded body is produced.

The solution according to the invention makes it possible to produce a shaped body of a magnesium-rich alloy which has high strength and at the same time high ductility.

It is known that the microstructure of AZ91 consists of α-magnesium mixed crystals and precipitates of the γ-phase of the Mg ₁₇ Al ₁₂ compound and also serves to form the intermetallic Mg ₁₇ Al ₁₂ phase of the degenerate eutectic of the cast structure. Aluminum as an alloying ingredient is contained at 5 to 9 wt% among other various additives. According to the phase diagram, this alloy can only be produced by casting processes that enable non-equilibrium solidification (such as, for example, centrifugal casting).

With the method according to the invention a complicated centrifugal casting is not necessary or even possible, since the new composite material of a Mg matrix or magnesium alloy matrix with the β-phase can be produced only by means of powder metallurgical methods and in particular by means of mechanical alloying.

The alloy according to the invention can find application in various fields of technology. It has high operating characteristics and has high parameters of mechanical properties at normal temperature.

The invention will be explained in more detail using an exemplary embodiment.

example 1

The preparation of the β-phase of the compound Al ₃ Mg _{2 was} carried out by mechanical alloying. For this purpose, a powder mixture of 60 wt .-% crystalline aluminum powder and 40 wt .-% of crystalline magnesium powder, each having a particle size of 1-5 microns and having a purity of 99.95%. The powder mixture is mixed under a high purity argon atmosphere (less than 1 ppm O ₂ and H ₂ O) in a grinding bowl and ground in a planetary ball mill (Retsch PM400). The grinding process is carried out using steel balls (∅ = 10 mm) and the mass ratio between balls and powder corresponds to 10: 1 ie in the case of 300 g of steel grinding balls, 30 g of powder mixture are used. The speed of the planetary ball mill is 150 rpm. The mechanical alloying takes place at room temperature for a period of 300 h. At the end of the grinding process, a secondary powder consisting entirely of supersaturated Al (Mg) mixed crystals is present. This secondary powder is nanocrystalline, which is advantageous for the later high strength.

Subsequently, the secondary powder is heated to 430 ° C. At this temperature, a phase transformation takes place, whereby the metastable β-phase of the compound Al ₃ Mg _{2 forms} in powder form.

50% by weight of these metastable β-phase powders of the compound Al ₃ Mg ₂ are subsequently mixed again with 50% by weight of pure magnesium powder under a high-purity argon atmosphere in a grinding bowl and ground in a planetary ball mill under the abovementioned conditions. After 1 h grinding time, the powder is well mixed and the nanocrystalline metastable β phase of the compound Al ₃ Mg ₂ is finely dispersed in the matrix of aluminum. Thereafter, the powder is hot pressed at 100 ° C and compressed under 50 MPa pressure, and extruded by means of extruding with 4 mm diameter.

The porosity of the obtained sample is relatively high, the density is 98.5%. It was found that during extrusion the metastable β-phase of the compound Al ₃ Mg ₂ diffuses into the magnesium matrix and spreads well.

The β phase serves as reinforcement of the Mg matrix, which can be clearly demonstrated by the following results.

The sample, made from the material produced, has shown the following properties:
Room temperature strength of 300 MPa (compared to the strength of AZ91 (9 wt% Al and 1 wt% Zn) at 255 MPa, relative elongation (measure of ductility) of 2% (compared to the relative elongation of AZ91 with 3%), hardness according to Vickers 250 HV and density at 98.5% (values of AZ91 from ASM Manual Vol2 and Material Science and Technology Vol8 / 9.p.140).

Claims (11)

Shaped body of a magnesium-containing composite material, consisting of a matrix of particles of magnesium and / or of a magnesium alloy with 5 to 80 vol .-% finely dispersed particles of Al ₆₀ Mg ₄₀ therein. Shaped body according to Claim 1, in which 45 to 55% by volume of particles of Al ₆₀ Mg _{40 are} contained in the matrix. Shaped body according to claim 1, wherein the magnesium alloy contains as alloying elements Al, Mn, Si, Li or Zn. Shaped body according to claim 1, wherein the particles of magnesium or of a magnesium alloy have an average particle size in the range of 0.1 .mu.m to 100 .mu.m. Shaped body according to claim 1, wherein the particles of Al ₆₀ Mg _{40 have} an average particle size in the range of 0.1 .mu.m to 100 .mu.m. A process for producing a shaped article according to any of Claims 1 to 5, wherein Al ₆₀ Mg _{40 is} prepared from crystalline Al and Mg powder by powder metallurgy and mixed with crystalline Mg powder and / or magnesium alloy powder as matrix material and again through processed powder metallurgical process to a magnesium-containing compound and this is subsequently compacted into a shaped body. A method according to claim 6, wherein Al, Mn, Si, Li or Zn are added as alloying elements to the magnesium alloy. The method of claim 6, wherein Al ₆₀ Mg ₄₀ and / or the magnesium containing compound are prepared by mechanical alloying. A method according to claim 8, wherein the mechanical alloying is carried out by grinding with a grinding time of 20 to 300 hours. The method of claim 6, wherein the mixing of the crystalline Al powder or the aluminum alloy powder as a matrix material with particles of Al ₆₀ Mg _{40 is} carried out by means of grinding. The method of claim 6, wherein the magnesium-containing compound is processed by hot pressing, extrusion or extrusion to form a shaped body.