WO2023135189A1

WO2023135189A1 - Aluminum alloy

Info

Publication number: WO2023135189A1
Application number: PCT/EP2023/050590
Authority: WO
Inventors: Thomas Kurt Stürzel
Original assignee: Zf Friedrichshafen Ag
Priority date: 2022-01-13
Filing date: 2023-01-12
Publication date: 2023-07-20
Also published as: DE102022200303A1

Abstract

The present invention relates to an aluminium alloy consisting of 6.0 – 8.0% by weight Si, 0.25 – 0.60% by weight Mg, 0.10 – 0.40% by weight Ce, 0.10 – 0.35% by weight Mo, 0 – 1.00% by weight Fe, 0 – 0.03% by weight Sr, and as the remainder Al and unavoidable impurities, where the % by weight together total 100% by weight in the alloy, and where the unavoidable impurities make up altogether no more than 0.15% by weight and no individual impurity makes up more than 0.03% by weight. The present invention also relates to a method for producing a component from the aluminium alloy according to the invention, to a corresponding component and also to the use of the aluminium alloy according to the invention for producing a component. The invention also relates furthermore to an asynchronous machine and to an electrically driven vehicle with a drive unit formed as an asynchronous machine.

Description

aluminum alloy

The present invention relates to an aluminum alloy consisting of 6.0-8.0% by weight Si, 0.25-0.60% by weight Mg, 0.10-0.40% by weight Ce, 0. 10-0.35% by weight Mo, 0-1.00% by weight Fe, 0-0.03% by weight Sr, and the remainder Al and unavoidable impurities, the weight% being 100 wt% in the alloy, and wherein the unavoidable impurities total not more than 0.15 wt% and no single impurity accounts for more than 0.03 wt%. The present invention also relates to a method for producing a component from the aluminum alloy according to the invention, a corresponding component and the use of the aluminum alloy according to the invention for producing a component. Furthermore, the invention also relates to an asynchronous machine and an electrically driven vehicle with a drive assembly designed as an asynchronous machine.

In an electric drive, the rotor is a main component in addition to the stator. In asynchronous machines (ASM), the rotor has a squirrel-cage winding that is integrated into a rotor base body, which is usually made of aluminum or aluminum-based alloys and, in particular, in slots of the rotor base body is cast on or in. For this purpose, the squirrel-cage winding comprises a plurality of rods which run essentially axially to a rotor axis of rotation and which are mechanically and electrically connected to one another on the face side with short-circuit rings which are generally manufactured at the same time, in particular cast on.

The material requirements for the squirrel cage winding of an ASM rotor are very high. The material has to withstand the high mechanical forces that occur at the high speeds of the e-machine rotor. A failure of the material due to breakage can lead to the destruction of the motor. The material must therefore have good mechanical properties, in particular a high yield point even at high temperatures and the associated high-temperature strength. Furthermore, the material must also have good conductivity for its use in an ASM rotor. After all, the metal or metal alloy must have a good Have castability, so that a satisfactory casting quality can be achieved and more complicated rotor shapes can be cast. If there is insufficient castability, numerous defects such as porosity included in the cast can occur during the complex casting process, which reduces the quality of the cast body and thus impairs its mechanical properties and electrical conductivity.

Technical purity aluminum was originally intended as the material for ASM rotors. Aluminum in technical purity (AI99.7) has good electrical conductivity and high elongation at break. However, it has a very low 0.2% yield strength (Rpo,2) at elevated temperatures and poor castability.

Starting with AI99.7, efforts were therefore made to develop an aluminum-based alloy that has a higher yield strength and high-temperature strength compared to AI99.7 while still having good electrical conductivity. The commercially available aluminum alloy Anticorodal®-71 (also known as Ac-71 or [AISi7MgO,3] and sold by Rheinfelden) contains aluminum as well as silicon (about 7% by weight) and magnesium (about 0.4 wt%). This alloy, which is highly alloyed with regard to the Si content, shows a significant increase in yield strength and tensile strength compared to AI99.7 while still having a very high elongation at break and sufficient conductivity.

Against this background, the object of the present invention is to provide an aluminum alloy which, in comparison with conventional alloys, has a further improved yield strength, even at high temperatures, and associated high-temperature strength, high electrical conductivity and, at the same time, improved castability.

This object is achieved by the embodiments characterized in the claims. In particular, according to the invention, an aluminum alloy is provided which consists of 6.0-8.0% by weight Si, 0.25-0.60% by weight Mg, 0.10-0.40% by weight Ce, 0. 10-0.35% by weight Mo, 0-1.00% by weight Fe, 0-0.03% by weight Sr, and the remainder Al and unavoidable impurities, the weight% being 100% by weight in the alloy, and wherein the unavoidable impurities total not more than 0.15% by weight and no single impurity accounts for more than 0.03% by weight.

Quantities in the context of the present invention relate to % by weight, unless stated otherwise or is apparent from the context. In the context of the invention, the weight % in an alloy or a component add up to 100 weight %, unless otherwise indicated or apparent from the context. In the context of the present invention, the ranges of amounts given are to be understood as including the limit values of the ranges given.

The aluminum alloy according to the invention contains 6.0-8.0% by weight Si, preferably 6.5-8.0% by weight Si and particularly preferably 6.5-7.5% by weight Si. The Si content is adjusted for an optimized cast alloy in order to enable good castability or mold filling of the alloy.

The aluminum alloy according to the invention also contains 0.25-0.60% by weight Mg, preferably 0.35-0.60% by weight Mg and particularly preferably 0.35-0.45% by weight Mg proved to be particularly suitable for increasing the strength of the alloy. Furthermore, it was found that the joint use of Si and Mg enables the production of a strength-increasing precipitation of the species Mg2Si. In the cast state, these elements are still forcibly dissolved in the Al solid solution, but can be eliminated in the form of precipitates by heat treatment. As a result, the yield point and strength increase significantly and at the same time the electrical conductivity is increased. The aluminum alloy according to the invention also contains 0.10-0.40% by weight Ce, preferably 0.20-0.40% by weight Ce and particularly preferably 0.20-0.30% by weight Ce.

According to the present invention, it was surprisingly found that the use of cerium in the specified amounts significantly improves the electrical conductivity and the castability of the alloy without significantly impairing the mechanical properties of the alloy. In addition, the addition of cerium in the specified amounts also reduces the tendency of the alloy to stick to the mold during the casting process and thus further improves the processability of the alloy into a component. Also, the tendency to heat cracking is surprisingly reduced by the addition of cerium.

The amounts of silicon, magnesium and cerium used according to the invention thus provide an alloy with an optimal ratio of mechanical properties (yield point at high temperatures or tendency to hot cracking), electrical conductivity and workability (improved castability and reduced tendency to stick).

The aluminum alloy according to the invention also contains 0.10-0.35% by weight Mo, preferably 0.10-0.20% by weight Mo. The aluminum alloy according to the invention can also contain 0-1.00% by weight Fe, preferably 0 20-1.00% by weight of Fe and particularly preferably 0.30-0.50% by weight of Fe.

In a particularly preferred embodiment, the aluminum alloy according to the invention contains both molybdenum and iron. It is preferred that the alloy contains 0.10-0.35% by weight Mo and 0.20-1.00% by weight Fe, particularly preferably 0.10-0.20% by weight Mo and 0 .30 - 0.50% by weight Fe.

Molybdenum and the optional iron are used in the alloy of the present invention to further reduce the alloy's tendency to stick to the mold during the casting process as well as increase ductility. Molybdenum is included particularly suitable for spherodizing (ie rounding) intermetallic phases (for example Fe-containing intermetallic phases such as beta-AIFeSi) with regard to their morphology and thus increasing the ductility.

Furthermore, the alloy according to the invention can contain 0-0.03% by weight Sr, preferably 0.015-0.03% by weight Sr and particularly preferably 0.015-0.025% by weight Sr. The addition of strontium in small amounts of up to 300 ppm (0.03% by weight) is used to change the three-dimensional morphology of the eutectic Si phase in Al-Si cast alloys, which is also known as chemical (permanent) modification. development of the eutectic microstructure.

The remainder of the alloy is Al and unavoidable impurities, the wt% adding up to 100 wt% in the alloy. The unavoidable impurities make up a total of no more than 0.15% by weight, preferably no more than 0.10% by weight. Each individual impurity makes up no more than 0.03% by weight, preferably no more than 0.01% by weight.

According to a preferred embodiment, the alloy according to the invention consists of 6.5-7.5% by weight Si, 0.35-0.45% by weight Mg, 0.20-0.30% by weight Ce, 0. 10-0.20% by weight Mo and the remainder Al and unavoidable impurities, the weight% adding up to 100% by weight in the alloy, and the unavoidable impurities totaling no more than 0.15% by weight % and no single impurity is more than 0.03% by weight.

According to another preferred embodiment, the alloy according to the invention consists of 6.5-7.5% by weight Si, 0.35-0.45% by weight Mg, 0.20-0.30% by weight Ce, 0 10 - 0.20 wt.% Mo, 0.30 - 0.50 wt.% Fe, 0.015 - 0.025 wt.% Sr and the remainder Al and unavoidable impurities, the wt.% being 100 wt% in the alloy, and wherein the unavoidable impurities total not more than 0.10 wt% and no single impurity accounts for more than 0.03 wt%. In summary, the element contents were adjusted in such a way that the optimum ratio of strength and electrical conductivity is achieved by the aluminum alloys according to the invention and at the same time castability is improved and the tendency to hot cracking and the tendency to stick to the mold is reduced. The additional addition of molybdenum further reduces the tendency to stick and also increases the ductility.

The present invention also relates to the use of the components according to the invention for the production of a component, preferably an ASM rotor.

The present invention also relates to a method for producing a component, preferably an ASM rotor, from the aluminum alloy according to the invention, comprising the following steps:

(a) melting the aluminum alloy from at least one master alloy and/or the chemical elements in the appropriate weight ratios,

(b) pouring the molten aluminum alloy into a mold,

(c) allowing or cooling the aluminum alloy poured into the mold, and

(d) heat treating the cooled aluminum alloy at a temperature in the range of 200°C to 260°C for a period of 1 to 6 hours.

According to step (a) of the process, the aluminum alloy according to the invention is melted from at least one master alloy and/or the chemical elements in the appropriate weight ratios. The aluminum alloy can be smelted from any suitable master alloy or element. The aluminum alloy is preferably melted from the pure elements or the elements with technical purity (for example Al99.7).

An optional nitrogen impeller treatment, a salt treatment and/or a boron precipitation can be carried out after step (a) and before step (b). become. These optional measures for cleaning the melt are known to those skilled in the art.

The nitrogen impeller treatment is a common melt treatment in the area of aluminum casting. An impeller, usually made of graphite, is introduced into the melt and then rotated at speeds of around 500 rpm for 4 to 15 minutes in the Al melt. The impeller introduces nitrogen into the melt, which is finely distributed by the impeller head. The fine nitrogen bubbles in the melt collect oxides and hydrogen and bring them to the surface of the bath. There they can then be removed as scabies. This process can also be combined with a salt treatment.

During boron precipitation, boron is added to the melt in a targeted manner so that elements such as Ti or V combine to form the respective borides and can precipitate in the melt. This leads to cleaning of the alloy and a further increase in conductivity, since Ti and V, for example, are dissolved in the Al mixed crystal and would then disrupt the crystal lattice and thus impair conductivity.

According to step (b) of the method, the molten (ie, liquid) aluminum alloy is poured into a mold. For this purpose, all the mold casting processes known to those skilled in the art can be used, for example the pressure casting process, the low-pressure casting process or the centrifugal casting process. The temperature at which the pouring takes place can be selected in a suitable manner by a person skilled in the art depending on the molding process used, with the risk of insufficient filling of the mold and cold runs if the pouring temperature is too low. The die-casting process is preferably carried out at a temperature in the range from 650°C to 750°C, more preferably at a temperature from 660°C to 680°C. This particularly preferred pouring temperature of between 660°C and 680°C is particularly advantageous in comparison to Al99.7 with a higher pouring temperature of 700 to 720°C that is customary there. The pressure is usually up to 1000 bar. According to a particularly preferred embodiment of the method according to the invention, the step of casting is carried out in the form of a pressure casting process at a temperature in the range from 650° C. to 750° C. or in the form of a centrifugal casting process.

According to step (c), the aluminum alloy poured into the mold is cooled or allowed to cool. For this purpose, the aluminum alloy is cast, for example, into a temperature-controlled and/or forced or vacuum-vented mold, particularly preferably in a temperature-controlled and/or forced-vented or vacuum-vented permanent mold. The temperature control of the mold has the advantage that the aluminum alloy can be cooled in a targeted and controlled manner by the temperature control and thus the service life of the casting tool is increased by cooling it.

In step (d) of the method according to the invention, the cooled aluminum alloy is heat-treated at a temperature in the range from 200° C. to 260° C. for a period of 1 to 6 hours, for example in a convection chamber furnace. This heat treatment can take place directly in the cooled mold, but not yet removed. Alternatively, it is possible to first remove the mold and heat-treat the component obtained by casting directly. The heat treatment step is beneficial to achieve the desired properties of the alloy. The mixed crystal can be "cleaned" by the heat treatment and the alloying elements are eliminated, so that the conductivity increases significantly in each case. Furthermore, the heat treatment increases the mechanical strength of the alloy.

The heat treatment is carried out at a temperature in the range from 200°C to 260°C, preferably at a temperature in the range from 220°C to 250°C. In order to achieve the optimal mechanical properties, it is advantageous to select the heat treatment temperature in such a way that it is about 20°C to 30°C above the later intended use temperature of the component. The heat treatment time is 1 to 6 hours, preferably 1 to 3 hours. Preferably, the heat treatment is in the form of a T5 heat treatment (ie quenched from the thermoforming temperature and artificially aged). The T5 heat treatment is advantageously carried out at a temperature of 220°C or 250°C for a period of 3 hours.

The present invention also relates to a component which comprises the alloy according to the invention or can be obtained by the method according to the invention described above. The component is preferably a component for vehicle or engine construction. The component is particularly preferably an ASM rotor. Together with a stator, the ASM rotor forms an asynchronous machine, which can be used, for example, as a drive unit for driving an electric or hybrid vehicle. In this respect, based on this, the invention also relates to an asynchronous machine and a vehicle with an asynchronous machine.

As explained above, the component according to the invention has improved mechanical properties and improved electrical conductivity.

Accordingly, the component can have an electrical conductivity of at least 30 MS/m. The electrical conductivity is particularly preferably in the range from 30 MS/m to 34 MS/m, even more preferably in the range from 30 MS/m to 32 MS/m. The electrical conductivity can be determined on the samples using the eddy current principle, for example with a FISCHER SIGMASCOPE SMP350, at a test frequency of 240 kHz. The measurement is made after heat treatment at a temperature ranging from 200°C to 260°C for a period of 1 to 6 hours, in particular after a T5 heat treatment at 250°C for 3 hours. If the component is produced using the production method according to the invention described above, it has already been heat-treated in step (d) of the production method, so that no further heat treatment needs to be carried out before measuring the electrical conductivity. If the component, which comprises the aluminum alloy according to the invention described above, was produced by means of a different production method without a corresponding heat treatment, then this is the case carry out this heat treatment before determining the electrical conductivity.

Furthermore, the component according to the invention preferably has a 0.2% proof stress R _P 0.2 of at least 100 MPa after heat treatment at a temperature in the range from 200° C. to 260° C. for a period of 1 to 6 hours. The 0.2% yield strength R _P 0.2 is particularly preferably in the range from 110 MPa to 160 MPa, even more preferably in the range from 120 MPa to 150 MPa. According to the invention, the 0.2% proof stress R _P 0.2 is to be determined at room temperature. The measurement is made after heat treatment at a temperature ranging from 200°C to 260°C for a period of 1 to 6 hours, in particular after a T5 heat treatment at 250°C for 3 hours. If the component is produced using the production method according to the invention described above, it has already been heat-treated in step (d) of the production method, so that no further heat treatment needs to be carried out before measuring the electrical conductivity. If the component, which comprises the aluminum alloy according to the invention described above, was produced by means of a different production process without a corresponding heat treatment, this heat treatment must be carried out before the electrical conductivity is determined.

The mechanical and electrical properties of the components according to the invention are also stable.

Thus, the electrical conductivity decreases, preferably by no more than 10%, even after a further heat treatment for 500 hours at a temperature 30° C. below the heat treatment temperature in production step (d). If F(TI) represents the electrical conductivity after the heat treatment T1 (according to step (d), for example at 250°C for 3 hours) and F<TI+T2) represents the electrical conductivity after a further heat treatment for 500 hours at a temperature 30 °C below the temperature of the first heat treatment (e.g. 220°C for 500 h), then:

(F<TI) - F(TI+T2)) / F(T1)) < 0.1 Likewise, the 0.2% yield point is preferably not reduced by more than 10% even after a further heat treatment for 500 hours at a temperature 30° C. below the heat treatment temperature according to production step (d). If R _P O,2(TI) represents the 0.2% yield strength after heat treatment T1 (according to step (d), for example at 250°C for 3 hours) and R _P O,2(TI+T2) represents the 0 .2% yield strength after a further heat treatment for 500 hours at a temperature 30°C below the temperature of the first heat treatment (e.g. 220°C for 500 hours), then:

( _RP 0.2(T1) - _RP 0.2(T1 +T2)) / _RP 0.2(T1)) < 0.1

The present invention is described in more detail below using examples. However, these do not represent any limitation of the scope of protection of the invention.

Examples:

Aluminum alloys with the following chemical composition (Example 1) are produced and cast into a component by means of a die-casting process with subsequent heat treatment at 250° C. for 3 hours. Likewise, as a comparison, an Anticorodal®-71 alloy is cast in the same way in a component.

It is found that the alloy according to the invention has improved castability and reduced sticking compared to Anticorodal®-71. The corresponding component obtained according to the invention has an electrical conductivity > 30 MS/m as well as a 0.2% yield point R _P o.2 > 100 MPa and thus shows comparable values with Anticorodal®-71 in relation to these properties.

Claims

Claims Aluminum alloy consisting of

6.0 - 8.0 wt% Si,

0.25 - 0.60 wt% Mg,

0.10 - 0.40 wt% Ce,

0.10 - 0.35 wt% Mo,

0-1.00% by weight Fe,

0-0.03% by weight Sr, and the remainder Al and unavoidable impurities, the weight% adding up to 100% by weight in the alloy, and the unavoidable impurities totaling no more than 0.15 wt% and no single impurity is more than 0.03 wt%. Aluminum alloy according to claim 1, which

6.5 - 7.5 wt% Si,

0.35 - 0.45 wt% Mg,

0.20 - 0.30 wt% Ce,

0.10 - 0.20 wt% Mo,

0-1.00% by weight Fe and

0 - 0.03 wt% Sr. Aluminum alloy according to claim 1 or 2, which has 0.20 - 1.00 wt.% Fe. Aluminum alloy according to any one of claims 1 to 3, which contains 0.01 - 0.03 wt% Sr. Aluminum alloy according to any one of claims 1 to 4, which

6.5 - 7.5 wt% Si, 0.35 - 0.45 wt% Mg,

0.20 - 0.30 wt% Ce,

0.10 - 0.20 wt% Mo,

0.30 - 0.50 wt% Fe and

0.015 - 0.025 wt% Sr. Aluminum alloy according to one of Claims 1 to 5, which has a total of not more than 0.10% by weight of unavoidable impurities. Method for producing a component, preferably an ASM rotor, from the aluminum alloy according to any one of claims 1 to 6, comprising the following steps:

(e) melting the aluminum alloy from at least one master alloy and/or the chemical elements in the appropriate weight ratios,

(f) pouring the molten aluminum alloy into a mold,

(g) allowing or cooling the aluminum alloy poured into the mold, and

(h) heat treating the cooled aluminum alloy at a temperature in the range of 200°C to 260°C for a period of 1 to 6 hours. A method according to claim 7, wherein the step of casting is carried out by a die casting process at a temperature in the range of 650°C to 750°C or by a centrifugal casting process. Component, preferably an ASM rotor, comprising the alloy according to any one of claims 1 to 6 or obtainable by the method according to claim 7 or 8. Component according to claim 9, which after heat treatment at a temperature in the range 200°C to 260°C C has an electrical conductivity of at least 30 MS/m for a period of 1 to 6 hours. Component according to Claim 9 or 10, which after heat treatment at a temperature in the range from 200°C to 260°C for a period of 1 to 6 hours has a 0.2% yield strength R _P 0.2 of at least 100 MPa. Use of an aluminum alloy according to one of Claims 1 to 6 for the production of a component, preferably an ASM rotor. Asynchronous machine (ASM) with a component according to one of Claims 9 to 11. Electrically driven vehicle with a drive unit designed as an asynchronous machine according to Claim 13.

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