Aluminum Alloy, in Particular for a Casting Method, and Method for Producing a Component from Such an Aluminum Alloy

Abstract

An aluminum alloy, in particular for a casting method, where the aluminum alloy includes at least aluminum, magnesium, manganese and copper. The aluminum alloy includes 0.001 to 0.50 wt. % of molybdenum, 0.05 to 0.4.5 wt. % of magnesium, 0.05 to 0.60 wt. % of manganese, up to 1.5 wt. % of iron, 0.25 to 4.00 wt. % of copper and 0.001 to 0.25 wt. % of vanadium.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an aluminum alloy, in particular for a casting method, and to a method for producing a component from such an aluminum alloy.

An aluminum alloy of this type, in particular for a casting method, is already disclosed for example in DE 10 2011 115 345 A1. In this instance, the aluminum alloy comprises at least aluminum (Al), magnesium (Mg), manganese (Mn) and copper (Cu).

The object of the present invention is to produce an aluminum alloy and a method of the type mentioned at the outset such that particularly advantageous, in particular mechanical, properties of the component can be realized.

In order to further develop an aluminum alloy, in particular for a casting method, such that particularly advantageous, in particular mechanical, properties of a component produced from the aluminum alloy can be realized, the invention provides for the aluminum alloy to comprise between 0.001 weight percent (wt. %) and 0.50 weight percent (wt. %) molybdenum. The aluminum alloy furthermore comprises magnesium in a range of from 0.05 wt. % to 0.45 wt. %, manganese in a range of from 0.05 wt. % to 0.60 wt. %, iron up to 1.5 wt. % and copper in a range of from 0.25 wt. % to 4.00 wt. % inclusive and vanadium in a range of from 0.001 wt. % to 0.25 wt. %. Preferably, the aluminum alloy comprises at least 0.10 wt. % and less than 0.40 wt. % manganese.

It has been found that, by adjusting the magnesium concentration, in particular to less than 0.30 wt. %, the proportion of brittle π-Al8FeMg3Si6 phases can be reduced to the extent that these phases are hardly present and can therefore have no detrimental effect on the ductility of the aluminum alloy, or on a component produced from the aluminum alloy. The reduction in the manganese content to less than 0.40 wt. % is advantageous insofar that the iron/manganese-containing intermetallic phases Al15(Fe, Mn)3Si2 can be reduced such that these phases cannot occur in a morphology that is too coarse and block-like.

It has been demonstrated to be additionally particularly advantageous for the aluminum alloy to comprise molybdenum (Mo) in a range of from 0.001 wt. % to 0.50 wt. % inclusive, it being preferable for the aluminum alloy to comprise 0.10 wt. % molybdenum. By adding molybdenum in a targeted manner, for example at a proportion of 0.10 wt. %, a rounded molding, including a polygonal morphology, and a finer distribution of the above-mentioned iron/manganese phases (Fe/Mn phases) can be produced, which leads to a further increase in ductility. Overall, sufficient ductility in the form of elongation at break can be realized as a result, which is then particularly advantageous if the component produced from the aluminum alloy is used in a drivetrain of a motor vehicle. The component can for example be designed as a crankcase of an internal combustion engine, which is preferably designed as a diesel engine. Alternatively, the component can also be part of an internal combustion engine of a gasoline engine. A component of this type, produced from the aluminum alloy, has sufficient strength, in particular heat resistance, on account of the strength mechanism of the aluminum alloy. Furthermore, the aluminum alloy according to the invention can be used advantageously for producing, from the aluminum alloy, a cylinder head of the internal combustion engine, which is for example a reciprocating internal combustion engine, such that a single alloy for the crankcase and the cylinder head is conceivable. Costs, logistics, energy consumption and CO₂ emissions can thus be reduced in the foundry and in the recycling process. It is furthermore possible, by artificially ageing the aluminum alloy, to achieve an increase in strength by means of copper-containing and/or magnesium-containing precipitates in the aluminum matrix.

Using the aluminum alloy according to the invention for producing a component, it is possible for the component, in the heat treatment state T5mod, to have a 0.2% proof stress R_p0.2 of more than 180 megapascals, a tensile strength R_m of more than 220 megapascals and an elongation at break A₅ of more than 1 percent at room temperature and, in the heat treatment state T6red to have a 0.2% proof stress R_p0.2 of more than 200 megapascals, a tensile strength R_m of more than 230 megapascals and an elongation at break A₅ of more than 1.5 percent at room temperature. In the heat treatment state T5mod, at a test temperature of 150° C., it was possible to achieve the following values: R_p0.2>170 megapascals, R_m>210 megapascals and A₅>1.5 percent.

In the heat treatment state T6red, at a test temperature of 150° C., it was possible to achieve the following values: R_p0.2>200 megapascals, R_m>220 megapascals and A₅>3 percent.

The invention is based in particular on the following findings: brittle intermetallic phases are suppressed in alloys having a high Fe content (Fe: iron) by means of the low magnesium content, or magnesium proportion, which leads to an increase in ductility. Copper leads to a significant increase in strength by means of artificial ageing and to an increased heat resistance of the aluminum alloy.

The aluminum alloy according to the invention has proven to be particularly advantageous for producing thick-walled components having a wall thickness in a range of from 4 millimeters to 30 millimeters inclusive. It is furthermore provided that the casting method used for producing the component from the aluminum alloy is a diecasting method or a laminar diecasting method or a sand/permanent mold method. The aluminum alloy according to the invention is in particular a heat-resistant aluminum alloy, in particular a heat-resistant aluminum casting alloy, which is particularly advantageously suitable for producing components for drivetrains.

The invention also includes a method for producing a component from an aluminum alloy according to the invention. Advantages and advantageous embodiments of the aluminum alloy according to the invention are to be considered advantages and advantageous embodiments of the method according to the invention, and vice versa.

Further advantages, features and details of the invention emerge from the following description of preferred embodiments and with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a backscatter electron image (BSE image) of the alloy 233 comprising copper (Cu) and molybdenum (Mo) in the heat treatment state T5mod, in which, for example, a component designed as a crankcase and made of the specified alloy is produced by means of diecasting;

FIG. 2 schematically shows a BSE image of the alloy 226D (AlSi10Cu3) in the heat treatment state T5mod, in which a crankcase for example is produced from the alloy;

FIG. 3 is a BSE image of the alloy 233 comprising Cu and Mo in the heat treatment state T6red;

FIG. 4 is a BSE image of the alloy 226D in the heat treatment state T6red;

FIG. 5 is a diagram for illustrating mechanical characteristics of the component formed from the respective alloys at room temperature; and

FIG. 6 is a diagram for illustrating mechanical characteristics of the component produced from the respective alloys at 150° C.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings, elements that are the same or functionally the same are provided with the same reference signs.

FIGS. 1 to 4 each show backscatter electron images (BSE images) of alloys from which the respective components are produced. The alloy is in each case, for example, an aluminum alloy, in particular an aluminum casting alloy and in this case preferably a heat-resistant aluminum casting alloy.

The component produced by the respective alloys is in each case, for example, a component used in a drivetrain of a motor vehicle, the component being, for example, a crankcase, in particular a diecast crankcase. This means that the component made of the respective alloys is produced by means of casting, in particular diecasting. In particular, the component can be a thick-walled component which has a wall thickness in a range of from 4 millimeters to 30 millimeters inclusive. By means of the aluminum alloy described in more detail in the following, particularly advantageous properties, in particular mechanical properties, of the component can be realized. Preferably, the aluminum alloy in each case has the following composition:

8.0 wt. % to 11.0 wt. % silicon,

0.25 wt. % to 4.00 wt. % copper,

0.10 wt. % to 0.50 wt. % magnesium,

0.05 wt. % to 0.60 wt. % manganese,

less than or equal to 0.3 wt. % titanium,

less than or equal to 0.3 wt. % zirconium,

less than or equal to 400 parts per million (ppm) strontium,

at most 1.5 wt. % iron,

at most 1.5 wt. % zinc,

0.001 wt. % to 0.25 wt. % vanadium,

additional additives of 0.01 wt. % to 0.50 wt. % molybdenum,

at most 0.25 wt. % chromium,

at most 0.20 wt. % nickel,

at most 0.15 wt. % cobalt,

and the remainder aluminum, it being possible for impurities or additional elements to be optionally provided in a proportion of less than 0.05 wt. %.

Particularly preferably, the aluminum alloy comprises magnesium at at least 0.10 wt. % and less than 0.30 wt. %. Alternatively or additionally, the aluminum alloy preferably comprises manganese at at least 0.10 wt. % and less than 0.40 wt. %. By reducing the manganese concentration, the extensive primary formation of iron-manganese-containing intermetallic Al₁₅(Fe, Mn)₃Si₂ phases is counteracted by the aluminum mixed crystals and a rough, block-like formation of the morphology is avoided. In order to set iron (Fe), however, molybdenum is additionally added, which leads to a polygonal morphology and a finer distribution of the Fe intermetallic phases. As a result, the formation of acicular or plate-like β-Al₅FeSi phases is suppressed, which phases would occur when there is a high Fe content and a low Mn content (Mn: manganese). The magnesium content is reduced to the extent that, as far as possible, the π-Al₈FeMg₃Si₆ phase is not formed. This phase does not dissolve at a solution treatment temperature of 465° C. and would merely set on account of the increased Fe content of the additionally alloyed magnesium (Mg) and lead to skeletal Fe-containing intermetallic phases which are detrimental to ductility in the form of a decrease in the elongation at break and no longer provide for strength-increasing precipitate formation.

The copper content (Cu content) is used to adjust the required strength in a. targeted manner due to the formation of strength-increasing precipitates during artificial ageing, Nevertheless, it is important to be aware that a copper proportion that is too high during T5 heat treatment leads to embrittlement. The full strength potential of the copper in the alloy can be exploited during T6 heat treatment.

The addition of titanium (Ti) brings about grain refinement of the aluminum dendrites. A combination with zirconium (Zr) in an adjusted concentration can lead to Al₃(Ti, Zr) precipitates which can have a strength-increasing effect. Care should also be taken at this juncture that titanium and zirconium are not added by alloying in too high a concentration since this leads to an undesirable formation of Al—Ti—Zr intermetallic phases which reduce ductility. Adding strontium (Sr) brings about an improvement of the Al/Si eutectic system from coarse and plate-like to an improved, coral-like morphology, thus increasing ductility. This fine Si morphology can be molded quickly and easily by a T6 solution treatment and the ductility can thus be increased once more.

Production of a component made of an aluminum alloy of this type is described in the following. During production, the above-mentioned aluminum alloy is smelted from master alloys, pure elements or produced by alloying suitable secondary alloys, for example 223 or 226, at a sufficiently high temperature. The alloy is furthermore cast into a temperature-controlled, forced-deaerated or vacuum-deaerated permanent mold. If the casting temperature is too low, there exists a danger of inadequate mold filling and cold running and of undesirable formation of intermetallic phases, whereas casting temperatures that are too high increase the danger of porosity, cavitation and hot cracks. After removing the component produced by casting, the component in order to realize the heat treatment state T6red—is cooled in air or—in order to realize the heat treatment state T5mod—is cooled by means of water.

The special characteristic of the microstructure of the component produced from the aluminum alloy can be seen with reference to FIGS. 1 to 4. FIG. 1 shows a backscatter electron image of the specified secondary alloy 233 comprising copper and molybdenum. Rounded to polygonal molybdenum-containing AlFeMnSi intermetallic phases can be seen. These phases can be found distributed relatively evenly among the Al dendrites in the Al/Si eutectic system since they set concurrently with the system. Due to the small size and rounded morphology of these phases, these increase the ductility of the secondary alloy. The π phase Al₈FeMg₃Si₆ can be found sporadically and cannot be dissolved by a solution treatment at 465° C. (cf. FIG. 3). By reducing the Mg content, the formation of this brittle phase can be suppressed and the ductility thus further increased. Potential phases Φ-Al₂Cu and Q-Al₅Cu₂Mg₈Si₆ resulting during solidification should be dissolved by a solution treatment for three hours at 450° C. (cf. FIG. 3) such that the alloy elements Mg and Cu, which are set into these phases, are provided in the Al mixed crystal for precipitate formation.

FIG. 2 shows a backscatter electron image of the specified secondary alloy 226D (AlSi10Cu3). On account of the high Fe and Mn content, coarse, block-like intermetallic Al₁₅(Fe, Mn, Cr, Cu)₃Si₂ phases are present which, on account of the size thereof, have formed primarily in the casting chamber of the diecasting machine. This accumulation of brittle phases inhibits ductility. Additionally, smaller, polygonal Fe-containing intermetallic phases are present which occur only in the actual diecasting mold. In addition to said Fe-containing intermetallic phases, β-Al₅FeSi phases are also present on account of the high Fe content, which phases appear as needles in the two-dimensional microsection surface and in reality are present as three-dimensional plates and therefore as extensive, sharp-edged microstructure divisions between the ductile Al dendrites. These phases reduce ductility significantly. On account of the relatively high content of Ni impurities in this secondary alloy, Al₇Cu₂(Fe, Ni) phases are also formed which cannot be dissolved by a solution treatment at 465° C. and are therefore furthermore present as brittle phases and additionally set Cu (cf. FIG. 4).

While the alloy is setting, formed Al₂Cu, which is not pronounced in eutectic form Al—Al₂Cu—Al₅Cu₂Mg₈Si₆—Si, can be completely dissolved by a solution treatment at 465° C. (cf. FIG. 4), such that, by means of water quenching, the Al mixed crystal is subsequently saturated in Cu. The eutectic pockets Al—Al₂Cu—Al₅Cu₂Mg₈Si₆—Si, however, cannot be completely dissolved at 465° C. for three hours. FIGS. 5 and 6 are diagrams for illustrating mechanical properties of components produced from the specified aluminum alloy. Bars 10 illustrate the 0.2% proof stress R_p0.2, whereas bars 12 illustrate the yield point R_m. Triangles 14 illustrate the elongation at break A₅.

Claims

1.-7. (canceled)

8. All aluminum alloy, comprising:

aluminum;

0.001 wt. % to 0.50 wt. % molybdenum;

0.05 wt. % to 0.45 wt. % magnesium;

0.05 wt. % to 0.60 wt. % manganese;

up to 1.5 wt. % iron;

0.25 wt. % to 4.00 wt. % copper; and

0.001 wt. % to 0.25 wt. % vanadium.

9. The aluminum alloy according to claim 8, wherein the manganese is at least 0.10 wt. % and less than 0.40 wt. %.

10. The aluminum alloy according to claim 8 further comprising 8.0 wt. % to 11.0 wt. % silicon.

11. The aluminum alloy according to claim 8 further comprising:

at most 0.3 wt. % titanium;

at most 0.3 wt.% zirconium;

at most 400 parts per million strontium;

at most 1.5 wt. % zinc;

at most 0.25 wt. % chromium;

at most 0.20 wt. % nickel; and

at most 0.15 wt. % cobalt.

12. A method, comprising the steps of:

producing a component from an aluminum alloy according to claim 8 by casting, without pressure or pressurized at an effective pressure of between 0 bar and 1,000 bar.

13. The method according to claim 12, wherein the aluminum alloy is cast into a mold at a temperature of 650° C. to 730° C.

14. The method according to claim 12, wherein the aluminum alloy is cast at a temperature of 580° C. to 650° C. thixotropically, without pressure or pressurized at an effective pressure of between 0 bar and 1,000 bar.