EP2173916A2 - Cast aluminum alloy, and use thereof - Google Patents

Abstract

Disclosed is a novel high-strength, heat-resistant cast aluminum silicon alloy that has good heat conductivity, is particularly suitable for producing engine parts, especially for casting cylinder heads and cylinder crankcases, and has the following composition: 2.6 to 4.5 wt.% of silicon; 0.5 to 3 wt.% of copper, 0.001 to 0.3 wt.% of magnesium, 0.001 to 0.8 wt.% of zirconium; a total of 0 to 4 wt.% of one or more of the optional elements encompassing manganese, iron, cobalt, zinc, nickel, vanadium, niobium, beryllium, lithium, yttrium, cerium, scandium, hafnium, silver, titanium, strontium, sodium, potassium, calcium, antimony, sulfur, barium, boron, nitrogen, and carbon, the remainder being composed of aluminum and inevitable impurities, at a heat conductivity which is adjusted by means of the aforementioned composition and exceeds 178 W/mK at 250°C

Description

 Aluminum casting alloy and its use

The present invention relates to a new high and heat resistant aluminum-silicon casting alloy with high thermal conductivity, which is suitable for the production of engine components, in particular for casting cylinder heads and cylinder crankcases.

In recent years, the combustion pressures and combustion temperatures of the fuel engines or internal combustion engines, especially in the diesel engine, have increased to reduce emissions and fuel consumption as well as increase engine power. This led to increased demands on the thermo-mechanical loads for engine components.

In the prior art AI casting alloys are known in particular in engine construction. AI castings are widely used because of their low specific gravity, ease of molding and ease of processing. Also, through various casting methods, complicated workpieces such as e.g. Make pistons, cylinder heads, crankcases or engine blocks.

A proven alloy group for the production of engine components are Al-Si alloys. These materials are typically with silicon contents between 4.5 and 18 wt .-%, in some cases up to 24 wt .-%, and with admixtures of magnesium 0.1 to 1, 5 wt.%, Copper between 1 and 4 wt In addition, the improvement of the mechanical strength is in this case a deterioration of the thermal shock resistance and the fatigue behavior due to excessive contents on alloying elements such as silicon, copper, magnesium. In particular, the cylinder heads are subject to high thermo-mechanical loads under operating stress. Since the heat dissipation one of the essential

Functions of the cylinder head, the thermal conductivity can affect its life more than the increase in strength or ductility of the cylinder head alloy.

The patent DE 199 25 666 C1 discloses an aluminum cylinder head alloy with 6.80 to 7.20 wt .-% silicon, 0.35 to 0.45 wt .-% magnesium, 0.35 to 0.45 wt .-% Iron, 0.30 to 0.40 wt% copper, 0.45 to 0.55 wt% nickel and 0.11 to 0.15 wt% titanium. The too low copper content of this alloy can not meet the high demands on the heat resistance at temperatures above 250 ^° C. With long-term thermal stress already above 150 ^° C., strength losses of more than 30% occur.

As prior art, the aluminum-silicon alloys from the group EN AC-45000 to EN AC-45400 are known. These alloys contain from 4.5 to 7% by weight of silicon, from 1 to 5% by weight of copper, from 0.5 to 1% by weight of iron, from 0.05 to 0.65% by weight of magnesium and from 0.15 to 2% by weight of zinc. Although these alloys have good mechanical properties due to the high copper and magnesium contents, they have poor thermal conductivity.

Similarly, DE 691 10 018 T2 discloses a high-strength cast aluminum alloy with 2.5 to 4.4 wt.% Si, 1, 5 to 2.5 wt.% Cu and 0.2 to 0.5 wt.% Mg, which should improve the alloy in terms of toughness and strength. However, this alloy is not satisfactory in terms of its thermal conductivity.

From Metals Handbook (1998), page 428 are some aluminum wrought alloys with low silicon content eg 4643 with 3.6-4.6% Si, max. 0.8% Fe, max. 0.1% Cu, max. 0.3% Mg, max. 0.05% Mn, max. 0.1% Zn and max. 0.15% Ti known. Due to the low mechanical properties both at room temperature and at elevated temperatures, these alloys for cylinder heads can not be used.

In the Metals Handbook (1998), page 431, the aluminum wrought 296 alloy with low silicon and increased copper content is known. This alloy contains 2- 3% Si, max. 0.8-1, 2% Fe, 4-5% Cu, 0.03-0.05% Mg, max. 0.35% Mn, max. 0.5% Zn, max. 0.25% Ti. Due to the high copper content, the thermal conductivity and elongation at break values of this alloy are very low.

The invention has for its object to provide a suitable for the production of engine components alloy having a high thermal conductivity, high strength, heat resistance, good creep strength and sufficient ductility with low susceptibility to corrosion and is also inexpensive.

This object is achieved by targeted adjustment of a silicon content of 2.6 to 4.5 wt .-% of a copper content of 0.5 to 3 wt .-% of a magnesium content of 0.001 to 0.3 wt.% Of a zirconium content of

From 0.001 to 0.8% by weight and, optionally, individually or in total from 0 to 4% by weight of one or more of the elements, manganese, iron, cobalt, zinc, nickel, vanadium,

Niobium, molybdenum, chromium, tungsten, beryllium, lead, lithium, yttrium, cerium, scandium, hafnium, silver, titanium, boron, strontium, sodium, potassium, calcium, antimony, sulfur,

Barium, nitrogen, carbon dissolved, wherein the alloy is preferably a

Thermal conductivity at 250 ⁰ C von wenigsens 178 W / mK has

Particularly preferred for achieving good thermo-mechanical properties is when the alloy contains from 0.001 to 0.19% by weight of magnesium. The silicon content is particularly preferably 3.0 to 4.5 wt .-%. For a particularly good thermo-mechanical behavior (HCF and TMF), it is also very advantageous if the thermal conductivity of the alloy at 250 ⁰ C is at least 190 W / mK, more preferably at least 198 WVmK, that is adjusted thereto.

By adjusting the silicon content according to the invention, it is possible to set the concentration limits of important strength-increasing alloying elements, such as copper, titanium, zirconium, iron, manganese, chromium, cobalt, molybdenum and depending on the application of other transition elements relatively high, without affecting the thermal conductivity noticeably. The alloy according to the invention has excellent thermal conductivity values, which represent an important life-time criterion when using the cylinder head alloys. This gives better thermal shock resistance and better fatigue behavior under thermomechanical stress for this alloy.

With the help of the elements silicon, magnesium, manganese, iron, cobalt, copper, zinc, nickel, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lead, lithium, yttrium, cerium, scandium, hafnium, silver, zirconium, titanium, Boron, strontium, sodium, potassium, calcium, antimony, sulfur, barium, nitrogen, carbon, it is possible to tailor the properties of the alloy according to the invention to the intended use. For example, the additions of transition elements give the casting a high creep strength and structural strength at elevated temperature, so that no distortion is to be expected during demoulding.

, When the alloy developed by us, in addition to Al, Si, Cu, Mg and Zr containing at least one element of the group Fe, Ni, Co, Ti _1, is particularly advantageous for a good creep resistance of the alloy of the invention.

It is furthermore particularly advantageous if the alloy contains at least 0.01, more preferably at least 0.03, more preferably at least 0.1, even more preferably at least 0.2% by weight zirconium. As a result, AI3Zr Phases of high thermal stability, by the presence of the dispersion hardening is maintained at temperatures between 150 ⁰ C and 400 ⁰ C and contributes to the thermo-mechanical stability of the casting alloy according to the invention. In addition, the addition of zirconium converts the plate-shaped intermetallic phases, which are particularly in the presence of iron, into Chinese-type forms, which also contributes to improving the elongation at break and thermal conductivity of the alloy according to the invention. The zirconium content of the alloy is preferably from 0.001 to 0.8% by weight, more preferably from 0.03 to 0.8% by weight, more preferably from 0.1 to 0.8% by weight, further preferably from 0.2 to 0.8 wt .-%, more preferably 0.3 to 0.5 wt .-%, more preferably 0.001 to 0.5 wt .-%, further preferably 0.03 to 0.5 wt .-%.

It has been found that addition of the elements molybdenum, niobium, scandium, hafnium, vanadium, cobalt, chromium, manganese, lithium, yttrium, cerium, tungsten, zirconium, titanium, silver, zinc significantly improves the strength properties of the alloy according to the invention without significantly affecting their elongation values. The preferred content for individual addition of these elements is 0.03 to 0.5 wt .-%, but should not exceed 4 wt .-% in total.

Preferably, the following proportions apply to the additionally added elements in a lesser amount:

Copper (Cu) preferably in an amount of 0.5 to 3 wt .-%, in particular 1 to

2.5% by weight;

Iron (Fe) preferably in an amount of 0 to 1, 4 wt .-%, in particular 0.2 to

0.5% by weight; Manganese (Mn) preferably in an amount of 0.001 to 0.6 wt .-%, in particular

0.001 to 0.4% by weight; Titanium (Ti) preferably in an amount of 0.001 to 0.3 wt .-%, in particular 0.1 to 0.2 wt .-%;

Cobalt (Co) preferably in an amount of 0.001 to 0.5 wt .-%, in particular 0.1 to 0.4 wt .-%;

Chromium (Cr) preferably in an amount of 0.001 to 0.5 wt .-%, in particular

0.1 to 0.4% by weight;

Beryllium (Be) preferably in an amount of 0.0001 to 0.2 wt .-%, in particular 0.005 to 0.1 wt .-%; Zinc (Zn) preferably in an amount of 0.001 to 3 wt .-%, in particular 0.3 to 2 wt .-%;

Tungsten (Wo) preferably in an amount of 0.001 to 0.6 wt .-%, in particular

0.1 to 0.2% by weight;

Nickel (Ni) preferably in an amount of 0.001 to 1, 5 wt%, in particular 0.5 to 1, 0 wt .-%;

Vanadium (V) preferably in an amount of 0.001 to 0.3 wt .-%, in particular

0.05 to 0.2% by weight;

Hafnium (Hf) preferably in an amount of 0.0001 to 0.2 wt .-%, in particular

0.005 to 0.15% by weight; Niobium (Nb) preferably in an amount of 0.0001 to 0.3 wt .-%, in particular

0.005 to 0.2% by weight;

Lead (Pb) preferably in an amount of 0.0001 to 0.2 wt .-%, in particular

0.005 0.1% by weight;

Strontium (Sr) preferably in an amount of 0.0001 to 0.06 wt .-%, in particular 0.005 to 0.04 wt .-%;

Sodium (Na) preferably in an amount of 0.0001 to 0.01, especially 0.002 to 0.005 wt .-%;

Calcium (Ca) preferably in an amount of 0.0001 to 0.006 wt .-%, in particular 0.002 to 0.004 wt .-%; Boron (B) preferably in an amount of 0.0001 to 0.08, in particular 0.01 to

0.05% by weight; Cer (Ce) preferably in an amount of 0.0001 to 0.4 wt .-%, in particular 0.05 to 0.3 wt .-%; Scandium (Sc) preferably in an amount of 0.0001 to 0.6 wt .-%, in particular 0.05 to 0.3 wt .-%; Carbon preferably in an amount of 0.0001 to 0.006 wt .-%, in particular 0.0005 to 0.003 wt .-%;

Nitrogen (N) preferably in an amount of 0.0001 to 0.006 wt .-%, in particular 0.0005 to 0.003 wt .-%.

To improve the formability, the alloy according to the invention may contain from 0.1 to 1.4% by weight of iron. In addition, the high iron content in die casting is used to reduce the adhesion tendency.

With the alloy composition according to the invention, a high strength can be achieved for castings already in the cast and heat treatment state both at room temperature and at elevated temperatures. The achieved optimum combination of mechanical properties is on a finely formed

Al-Si eutectic and the precipitation of Al ₂ Cu and Mg ₂ Si phases in the alloy according to the invention, which in turn are influenced by a suitable heat treatment.

The limitation of the magnesium content to a maximum of 0.3 wt .-%, preferably 0.19 wt .-%, causes the elongation values of the alloy according to the invention in the casting state does not fall below 4%. In order to achieve a significantly higher elongation, however, the magnesium content must be limited to a maximum of 0.15% by weight, more preferably to a maximum of 0.1% by weight. The setting of the lowest possible magnesium contents also ensures at the same time excellent thermal conductivity of the alloy according to the invention. A certain amount of titanium or boron and / or carbon in combination with titanium is used for grain refining, the addition of these elements with aluminum-titanium, aluminum-boron, aluminum-titanium-boron and aluminum-titanium-carbon Pre-alloys takes place. The α-aluminum mixed crystal can also be grain-refined by zirconium additions of 0.2 to 0.8 wt%. A good grain refining contributes significantly to the improvement of the mechanical properties and castability of the alloy according to the invention. The master alloys AITi6, AIB4, AITi3C0,15, AIZMO and AITiI, 8B1, 8 were particularly effective.

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

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 chill casting, Differential pressure chill casting, Die casting and Vacuum die casting.

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 heat treatments.

The invention will be explained in more detail by way of example, without the invention being limited to the example.

Exemplary embodiment: chill casting

As a concrete example of the alloy according to the invention, the following composition is given:

Alloy 1 4.0 wt% Si 0.5 wt% Cu 0.4 wt% Fe 0.1 wt% Mg 0.3 wt% Zr ad 100 wt% Al

For the investigations of the mechanical properties, the above-mentioned alloy was used in a mold according to DIN 29531 at the casting temperature of

740 ⁰ C poured off and test bars with the sample diameter of 6 mm after

DIN 50125 mechanically manufactured. For comparison, three were added

Standard alloys used. On test bars were the mechanical

Tensile strength (R _p o, ₂ ), tensile strength (R _m ) and elongation at break (A ₅ ) determined in the tensile test according to DIN 50 145. The strain rate was after the

Apply a preload of 100 N to the fracture of the sample 0.08 mm / s.

To determine the influence of thermal load over a longer period of time on the properties of Al alloys, the drained sample rods were stored ahead of an additional 100 hours at 250 ⁰ C for all alloys.

The thermal conductivity λ at 250 oC was calculated using the following formula: λ = a * Cp * p

Table 1 gives a comparison of the alloy according to the invention with conventional alloys for engine components.

λ - thermal conductivity a - thermal diffusivity

Cp - specific heat capacity p - density

The determination of the thermal diffusivity was carried out with a laser flash apparatus. The specific heat capacity was determined with a high-temperature calorimeter.

Table 1 gives a comparison of the alloy according to the invention with conventional alloys for engine components.

Table 1

ML / rü

Claims

claims: 1. aluminum casting alloy, characterized in that the alloy 2.6 to 4.5 wt .-% silicon 0.5 to 3 wt .-%, copper, 0.001 to 0.3 wt.% Magnesium, 0.001 to 0, 8 wt .-% zirconium and optionally one or more of the elements manganese, iron, cobalt, zinc, nickel, vanadium, niobium, beryllium, lithium, yttrium, cerium, scandium, hafnium, silver, titanium, strontium, sodium, potassium, calcium , Antimony, sulfur, barium, boron, nitrogen, carbon in the sum of 0 to 4% by weight and balance aluminum and unavoidable impurities and has a thermal conductivity at 250 ° C of more than 178 W / mK. 2. Cast aluminum alloy according to claim 1, characterized in that the alloy contains 0.001 to 0.19 wt .-% magnesium. 3. aluminum casting alloy according to claim 1 or 2, characterized in that in addition to Al, Si, Cu, Mg and Zr at least one element of the group Ti, B, C is present. 4. Cast aluminum alloy according to one of claims 1 to 3, characterized in that the alloy contains 3.0 to 4.5 wt .-% silicon. 5. Cast aluminum alloy according to one of claims 1 to 4, characterized in that the alloy 0.03 to 0.8 wt .-% zirconium, preferably 0.1 to 0.8 wt .-% Zr, more preferably 0, 2 to 0.8 wt .-% Zr, more preferably 0.3 to 0.5 wt.% Zr. 6. Cast aluminum alloy according to one of claims 1 to 5, characterized in that the alloy has a thermal conductivity at 250 ⁰ C of greater than 190, more preferably at least 198 W / mK. 7. Use of the aluminum casting alloy according to one of claims 1 to 6 for casting engine components. 8. Use of the aluminum casting alloy according to claim 7 for casting cylinder heads and cylinder-crankcases.