EP2155920A1

EP2155920A1 - Use of an al-mn alloy for high temperature resistant products

Info

Publication number: EP2155920A1
Application number: EP08749463A
Authority: EP
Inventors: Babette Tonn; Hennadiy Zak; Carsten Reeb
Original assignee: Technische Universitaet Clausthal
Current assignee: Technische Universitaet Clausthal
Priority date: 2007-05-16
Filing date: 2008-05-15
Publication date: 2010-02-24
Also published as: DE102007023323A1; DE102007023323B4; WO2008138614A1

Abstract

The invention relates to an aluminum-manganese alloy having high temperature resistance and high thermal stability in operation, comprising aluminum as a main component, at least 2.1 weight % of manganese, 0 to 4 weight % of iron, and 0 to 4 weight % each of further alloying constituents, for producing highly thermally stable and temperature-resistant products, namely for machine elements, engine, turbine, and power plant components, pistons, cylinder heads, cylinder crankcases, cylinder liners, connecting rods, camshafts, turbine blades, and for components in foundry or high-temperature materials handling systems.

Description

Use of an Al-Mn alloy for high-temperature products

The invention relates to the use of an aluminum-manganese alloy with aluminum as the main component and at least 2.1 wt.% Manganese for thermally highly resilient and heat-resistant products, a special alloy for this purpose and the products themselves. More specifically, the invention relates to heat-resistant and Wear-resistant cast aluminum alloys, such as are needed in particular for engine, turbine and engine components, with manganese as a second alloying ingredient.

The continuous increase in engine power in conjunction with higher power densities is placing ever-increasing technical demands on engine components made of aluminum alloys such as cylinder heads, cylinder blocks, pistons, liners and connecting rods. This is especially true in terms of strength, thermo mechanical shock resistance, thermal shock and creep resistance at temperatures up to 350 ⁰ C. When piston alloys are expected to use temperatures of up to 430 ⁰ C for passenger car diesel engines in the coming years.

AI cast alloys are state of the art in engine construction, and are widely used because of their low specific gravity, ease of molding, and ease of processing. Even complicated engine parts can be produced with these alloys using various casting methods.

A proven alloy group for the production of engine components are Al-Si alloys. These materials are typically with silicon contents between 6 and 18 wt .-%, in some cases up to 24 wt .-%, and with admixtures of 1 to 1, 5 wt .-% magnesium, between 1 and 4 wt .-% copper and frequently also between 1 and 3% by weight of nickel (catalog "Aluminum Casting Alloys", VAW-IMCO), but in this case the improvement of the mechanical strength is a deterioration of the thermo-mechanical resistance to change and corrosion resistance to. The same applies to Al-Cu and Al-Mg-Si-based alloys used for cylinder heads and crankshaft housings.

In all of the abovementioned Al-casting alloys, although strength-forming Mg ₂ Si and Al ₂ Cu precipitates form via heat treatment, they are not stable above 150 ^° C. and therefore can not cope with the thermo-mechanical loads of modern motors. By contrast, the intermetallic phases, such as Al ₆ Mn, Al ₃ Fe, Al ₇ Cr, Al ₃ Ni, Al ₈ Fe ₂ Si, Al ₇ Cu ₄ Ni, Ali ₅ Mn ₃ Si ₂ , Al ₅ FeSi, Al ₃ Ti and Al ₃ Zr is not affected by thermal long-term stress and, given a favorable design (quantity, size, shape and distribution), can make a considerable contribution to increasing the mechanical properties of the Al-Si alloys for engine construction. It is of particular importance to ensure the homogeneous distribution and fine formation of the intermetallic phases in the cast structure so as not to impair the ductility of the alloy and its casting properties.

US 2003/0152478 A1 discloses Al-Ni-Mn alloys with 0.5-6 wt.% Nickel, 1-3 wt.% Manganese, less than 1 wt.% Iron, less than 1 wt. -% silicon, less than 0.3 wt .-% titanium and less than 0.06 wt .-% boron, which were developed for the production of structural parts for automobiles and aerospace engineering. These alloys have a low hot crack tendency, have very high ductility already in the cast state, but have the drawbacks of insufficient strength, heat resistance and wear resistance, and are thus useful for the production of engine components, such as e.g. Crankcase, cylinder heads, pistons, connecting rods and liners, unsuitable. In addition, the high nickel content is a non-negligible cost driver.

The patent specification DE 1533297 discloses aluminum alloy with a high tensile strength and hardness and a method for its heat treatment. This alloy contains 0.3-1, 2 wt .-% zirconium and 6-25 cm ^{3 of} hydrogen per 100 g alloy weight, balance aluminum. In addition, this alloy may contain one or more of the further alloying elements, namely 1-3% by weight of manganese, 0.1-1.5% by weight of silicon, 0.3-2% by weight. Magnesium, 0.5-3 wt .-% nickel and 1-4 wt .-% copper. The improvement of the mechanical properties is attributed to this patent exclusively to a high hydrogen content in combination with zirconium. The subject of the patent DE 1533297 are also two variants of the method for heat treatment of a wrought alloy and a casting alloy. For a casting alloy, hydrogen contents mentioned in this patent are not acceptable for quality reasons. In the foundry practice, it has proven to be very important to keep the hydrogen content in aluminum melts as low as possible by appropriate degassing measures in order to avoid the formation of defects such as voids and pores. The guideline for the hydrogen content in the aluminum casting alloys is less than 5 cm ³ / 100g.

The invention has for its object to provide a suitable for the production of engine components in particular alloy, which has a high heat resistance and thereby allows a measured at the melting point of the aluminum alloy high thermal load during operation. The alloy should have mechanical properties suitable for use, such as high strength, creep resistance and wear resistance, as well as sufficient ductility, with at the same time low susceptibility to corrosion and should be inexpensive to produce. In addition, the alloy should have good casting technological properties to ensure proper production of the sophisticated components.

This object is achieved by the targeted adjustment of preferred concentrations of selected alloying elements in the Al-Mn alloys. Due to the amount of manganese, the high heat resistance is ensured and good corrosion properties are achieved. For the permanent preservation of these properties it is important that a certain manganese-to-iron ratio is not undershot. The invention provides this solution for Al-Mn cast and wrought alloys.

Basically, the solution of the invention task is the use of an aluminum-manganese alloy (preferably an Al-Mn cast or wrought alloy) with aluminum as the main component, at least 2.1 wt .-% manganese and 0 to 4 wt .-% iron and other alloying constituents for thermally highly resilient and heat-resistant products, namely for machine elements, in particular engine, turbine and engine components, pistons, cylinder heads, cylinder crankcases, liners, connecting rods, camshafts, turbine blades, as well as for components in the foundry or high-temperature conveying , Preferably, the condition Mn: Fe ≥ 2 is simultaneously satisfied.

By definition, the term "hot strength" is to be understood as meaning that a product or component produced from the alloy can be subjected to a temperature of 0.6-0.8 theoretical temperature the hardness determined at elevated temperature and / or after prolonged thermal stress.

The term "thermally highly resistant" can be used to refer to an aluminum alloy component if it can be used at operating temperatures of up to 430 ^° C. for extended periods without replacement or complete failure.

Particularly preferred is the use according to the invention for machine elements, in particular engine, turbine and engine components. In general, the alloy is suitable for all products, components or machine elements that are exposed to high temperatures during operation.

Accordingly, the alloy used according to the invention contains 2.1 to 5 wt .-% manganese, optionally individually from 0 to 4 wt .-% of the following alloying constituents: iron, magnesium, silicon, chromium, cobalt, copper, zinc, nickel, vanadium, niobium , Molybdenum, tungsten, beryllium, lead, yttrium, cerium, scandium, hafnium, silver, zirconium, titanium, boron, strontium, sodium, calcium, antimony, bismuth, carbon, these total alloy minor components preferably not more than 10% by weight and aluminum and unavoidable impurities. In addition to aluminum as the main constituent and manganese as the second alloy constituent, the alloy may contain minor amounts of further alloying constituents and also unavoidable impurities.

The aluminum content will preferably not be below 80% by weight. The manganese content is preferably from 2.1 to 5% by weight and the alloying minor components preferably add up to not more than 10% by weight, more preferably not more than 6% by weight, and in particular not more than 4% by weight. % out.

Specifically, the alloying minor components may preferably comprise the following elements: iron, magnesium, silicon, chromium, cobalt, copper, zinc, nickel, vanadium, niobium, molybdenum, tungsten, beryllium, lead, yttrium, cerium, scandium, hafnium, silver, zirconium, Titanium, boron, strontium, sodium, calcium, antimony, bismuth, carbon.

The following contents appear particularly suitable:

Iron: 0.1 to 2.0% by weight, in particular 0.5 to 1.5% by weight; Magnesium: 0.01 to 1.5% by weight, in particular 0.2 to 1.0% by weight;

Silicon: 0.01 to 2.0 wt .-%, in particular 0.3 to 1, 6 wt .-%;

Chromium: 0.001 to 1, 0 wt .-%, in particular 0.1 to 0.6 wt .-%;

Cobalt: 0.001 to 0.5% by weight, especially 0.1 to 0.4% by weight;

Copper: 0.001 to 2.0% by weight, in particular 0.3 to 1.0% by weight; Zinc: 0.001 to 2.0 wt .-%, in particular 0.1 to 1.5 wt .-%;

Nickel: 0.001 to 0.5 wt .-%, in particular 0.3 to 0.5 wt .-%;

Vanadium: 0.001 to 0.4 wt .-%, in particular 0.05 to 0.2 wt .-%;

Niobium: 0.0001 to 0.6% by weight, especially 0.005 to 0.4% by weight;

Molybdenum: 0.0001 to 0.6% by weight, especially 0.005 to 0.4% by weight; Tungsten: 0.0001 to 0.6% by weight, especially 0.005 to 0.4% by weight;

Beryllium: 0.0001 to 0.2 wt .-%, in particular 0.005 to 0.3 wt .-%;

Lead: 0.0001 to 0.4% by weight, especially 0.005 to 0.2% by weight;

Yttrium: 0.0001 to 0.4% by weight, especially 0.05 to 0.3% by weight; Cerium: 0.0001 to 0.4% by weight, especially 0.05 to 0.3% by weight;

Scandium: 0.0001 to 0.6 wt .-%, in particular 0.05 to 0.3 wt .-%;

Hafnium: 0.0001 to 0.6% by weight, especially 0.05 to 0.3% by weight;

Silver: 0.0001 to 1, 0 wt .-%, in particular 0.4 to 1, 0 wt .-%;

Zirconium: 0.001 to 1.2% by weight, especially 0.3 to 0.9% by weight;

Titanium: 0.001 to 0.8% by weight, in particular 0.15 to 0.6% by weight;

Boron: 0.0001 to 0.08 wt .-%, in particular 0.01 to 0.06 wt .-%;

Strontium: 0.0001 to 0.08 wt .-%, in particular 0.005 to 0.04 wt .-%;

Sodium: 0.0001 to 0.2 wt .-%, in particular 0.002 to 0.02 wt .-%;

Calcium: 0.0001 to 0.006 wt .-%, in particular 0.002 to 0.004 wt .-%;

Antimony: 0.001 to 0.5% by weight, especially 0.1 to 0.3% by weight;

Bismuth: 0.001 to 1.0% by weight, especially 0.1 to 0.8% by weight;

Carbon: 0.0007 to 0.1 wt .-%, in particular 0.0015 to 0.006 wt .-%.

With the help of the elements silicon, magnesium, iron, cobalt, copper, zinc, nickel, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lead, yttrium, cerium, scandium, hafnium, antimony, silver, zirconium, titanium, boron, Strontium, sodium, calcium, carbon, it is possible to customize the properties of the alloy according to the invention to the particular manufacturing process and purpose of use. For example, the additions of transition elements give the casting a high structural strength at elevated temperature.

To improve the formability, the alloy according to the invention may contain the elements iron, cobalt, chromium, cerium individually or in combination with one another. The contents of these elements are matched to the requirements of the casting.

In order to obtain a low hot crack tendency and a good combination of mechanical properties, it is essential that the iron content be adjusted with the manganese content such that a ratio of Mn / Fe is greater than or equal to two. It has also been found that by adding the elements molybdenum, niobium, chromium, scandium, hafnium, vanadium, yttrium, cerium, tungsten, zirconium, titanium, antimony, silver, zinc, copper, nickel, magnesium and silicon, the strength properties the alloy of the invention can be significantly improved both at room temperature and at higher temperatures.

The alloy of the present invention may be additionally added with lead, carbon, strontium, sodium, calcium and beryllium singly or in combination with each other. These elements help to transform the intermetallic phases into small, spherical particles, which are distributed homogeneously in the structure and thus less impair the mechanical properties.

The elements vanadium and beryllium substantially reduce the tendency of the alloy according to the invention to oxidize, which occurs especially at maximum magnesium contents.

A certain amount of boron and / or carbon associated with titanium is required for refining, with the addition of these elements to aluminum boron, aluminum-titanium-boron and aluminum-titanium-carbon master alloys. Good refinement contributes significantly to the improvement of the mechanical properties and the castability of the alloy according to the invention.

Zirconium improves both the strength properties and the casting-technological properties of the alloy according to the invention by means of refinement. In addition, it is possible to achieve a dispersion-hardening effect in the alloy according to the invention by adding zirconium. The mechanism for the increase in high temperature strength and creep resistance can be seen in the formation of the fine zirconium aluminides, which have a high stability even at temperatures of about 300 ⁰ C. It is also advantageous that the dispersion hardening can be caused either by special heat treatment or without heat treatment by thermal stress at the use temperatures of 300 to 430 ⁰ C. The invention further comprises a special aluminum-manganese alloy (preferably an aluminum-manganese cast or wrought alloy) which is particularly suitable for the intended use within the scope of the invention. This aluminum-manganese alloy comprises aluminum as the main constituent, at least 2.1% by weight of manganese, less than 0.5% by weight of nickel, and from 0 to 4% by weight of iron and other secondary alloying constituents, all in all than 10% by weight. It is particularly preferred if the manganese-to-iron ratio satisfies the condition Mn: Fe ≥ 2. Furthermore, the alloy may be specified as described above with reference to the use according to the invention.

For the processing of the alloy according to the invention, basically all casting methods are suitable. These include u.a. Sand casting, gravity die casting, low pressure die casting, differential pressure die casting, thixocasting, squeeze casting, die casting and vacuum die casting. The greatest advantages are found in casting processes that proceed at high cooling rates, such as in the die casting process. The production of pistons, liners and connecting rods from the alloy according to the invention can take place inter alia by forging semi-finished products. In this case, the use of extruded products or cast strands of the alloy according to the invention is particularly suitable.

The liners made of the alloy according to the invention can also be produced by the extrusion process according to this invention.

In order to ensure a sufficient melt quality, the melt can be degassed by purge gas, purge gas tablets or by vacuum.

Although good mechanical values are already present in the cast state, castings produced from the alloy according to the invention can be subjected to all known heat treatments. A heat treatment is preferred which comprises the following steps:

1) annealing at a temperature between 300 and 350 ^° C. for half an hour up to five hours, 2) annealing at a temperature between 350 and 500 ^° C. for half an hour up to five hours,

3) cooling in air.

For adjusting the maximum strength properties in alloys according to the invention having zirconium contents of up to 0.3% by weight, the following heat treatment is suitable:

1st step: annealing at 300-350 ⁰ C for 0.5-5 h, 2nd step: annealing at 450-500 ⁰ C for 0.5-5 h, 3rd step: cooling in air

With zirconium contents of 0.3 to 1.2% by weight, the following heat treatment was found to be particularly advantageous:

Step 1: annealing at 300-350 ⁰ C for 0.5-5 h,

2nd step: annealing at 350-450 ⁰ C for 0.5-5 h,

3rd step: cooling in the air

The invention further includes refractory products of the alloys of this invention. These are preferably machine elements and in particular engine, turbine or engine elements.

In general, the invention is particularly suitable for the following products and components: pistons, cylinder heads, cylinder crankcases, liners, connecting rods, camshafts, turbine blades, components in foundry or high-temperature conveying technology.

With reference to the figures, the invention will be explained in more detail by means of examples, without the invention being limited to the examples.

Show it: Fig. 1: Yield point as a function of the storage temperature, determined in a hot tensile test after 100 hours of advance storage

Fig. 2: hardness as a function of the pre-storage temperature, determined at room temperature

Fig. 3: flow curves as a function of the pre-storage temperature, determined in the cylinder compression test. Test at storage temperature.

Example 1. Tensile tests at elevated temperatures

The following materials were used as reference alloys:

Alloy AISiI 7Cu4Mg. Application: Cylinder crankcases, pistons.

Alloy AICu5Ni1, 5CoSbZr. Application: highly stressed cylinder heads.

The chemical composition of the reference alloys is given in Table 1.

Table 1. Chemical composition of the reference alloys and the alloy according to the invention

Melting took place in a resistance-heated crucible furnace with a crucible capacity of 3 kg. The melt and mold temperature was set dustemperatur to 100 ⁰ C above the liquidity. For the investigations of the mechanical properties, the above alloys were poured into a mold according to DIN 29531 and test bars with the sample diameter of 6 mm according to DIN 50125 were manufactured mechanically. The alloy AISiI 7Cu4Mg was investigated in state T6 and the alloy Al-Cu5Ni1, 5CoSbZr in state T7. The alloy according to the invention AIMn3ZrO, 8CrO, 6 was annealed at 400 ⁰ C for 5 hours. Subsequently, the samples of this alloy were cooled in air and showed in this state the following mechanical properties: R _m 214 MPa, R _p o, 2 210 MPa, A ₅ 0.4%. The results of the hot tensile tests after the preliminary storage for 100 hours at the test temperature are shown in FIG.

Example 2. Hardness depending on the pre-storage temperature

To determine the influence of thermal load over a longer period of time on the properties of Al alloys, the drained sample rods were for all three alloys additional 500 hours at 250 ⁰ C, ahead stored 350 ⁰ C and 400 ⁰ C. The results of these experiments are given in Fig.2. It can be seen that the alloy according to the invention AIMn3ZrO, 8CrO, 6 is clearly superior to the reference alloys. While an increasing pre-storage temperature reduces the hardness values with the known alloys, it comes in the inventive LE Government in the temperature range of 250 ⁰ C to 350 ⁰ C even what explains the increase in hardness, with the Aushärtungseffekten the Al matrix by zirconium precipitates. Thus, for Al-Mn cast alloys after a long thermal stress, a significantly better wear resistance than for reference alloys is to be expected.

Example 3. Cylinder compression tests to determine the flow curve at high temperatures

In addition to good tensile strength properties in the tensile test, the Al alloys for engine construction also demand good hot compressive strength properties. An important criterion for the evaluation of the thermal behavior under compressive stress is the flow curve of the alloy at the appropriate temperature. The cylinder upsetting tests to determine the flow curve were performed with a Umformdilatometer carried out. A cylindrical sample (diameter 5 mm, length 10 mm), equipped with a thermocouple, is compressed between two flat parallel tool surfaces and can be heated inductively under an inert gas atmosphere. The servohydraulically actuated plungers are connected to two LVDTs and measure the change in length of the sample with a resolution of 0.05 μm. The flow curve determination was carried out without consideration of friction losses, since only comparative values under identical conditions are required.

From Fig. 3 it can be seen that the yield strength of the alloy according to the invention in the temperature range 350-450 ⁰ C after 100 h pre-storage at test temperature is twice as high as that of the piston and engine block alloy AISM7Cu4Mg.

ML / rü

Claims

claims:

1. Use of an aluminum-manganese alloy with aluminum as the main constituent, at least 2.1% by weight of manganese, from 0 to 4% by weight of iron and from 0 to 4 in each case

Wt .-% of other alloying constituents for thermally highly resilient and heat-resistant products, namely for machine elements, in particular engine, turbine and engine components, pistons, cylinder heads, cylinder crankcases, liners, connecting rods, camshafts, turbine blades, as well as for components in the foundry or high-temperature materials handling.

2. Use according to claim 1, wherein the condition Mn: Fe ≥ 2 is satisfied.

3. aluminum-manganese alloy with aluminum as the main component, at least 2.1 wt .-% manganese, less than 0.5 wt .-% nickel, 0 to 4 wt .-% of iron and other alloying secondary constituents, the sum not more than 10 wt .-% and additionally wherein the condition Mn: Fe ≥ 2 is satisfied, for the use according to claim 1 or 2.

4. aluminum manganese alloy according to claim 3, characterized in that the manganese content of 2.1 to 5 wt .-% is.

5. Aluminum-manganese alloy according to claim 3 or 4, characterized in that the alloying secondary constituents total not more than 6 wt .-%, preferably not more than 4 wt .-% make up.

6. Aluminum-manganese alloy according to one of claims 3 to 5, characterized in that the alloying secondary constituents comprise the following elements: iron, magnesium, silicon, chromium, cobalt, copper, zinc, nickel, vanadium, niobium, molybdenum, tungsten , Beryllium, lead, yttrium, cerium, scandium, hafnium, silver, zirconium, titanium, Boron, strontium, sodium, calcium, antimony, bismuth, carbon.

An aluminum-manganese alloy according to any one of claims 3 to 6, characterized in that it has been subjected to a heat treatment comprising the following steps:

1) annealing at a temperature between 300 and 350 ^° C. for half an hour to 5 hours, 2) annealing at a temperature between 350 and 500 ^° C. for half an hour to 5 hours, 3) cooling in air.

8. A high-temperature alloy product according to one of claims 3 to 7.

9. High-temperature product according to claim 8, characterized in that it is an engine, turbine or engine element.

10. High-temperature product according to claim 8 or 9, characterized in that it is one of the following components: piston, cylinder head, cylinder crankcase, liner, connecting rod, camshaft, turbine blade, component in the foundry or the high-temperature conveyor.

ML / rü