Aluminum alloy with high conductivity and high temperature strength for electric vehicle motor

Abstract

The present disclosure provides an aluminum alloy with high conductivity and high temperature strength for an electric vehicle motor. An aluminum alloy includes iron in an amount between greater than 0.9 wt% and less than or equal to 1.5 wt%, nickel in an amount between greater than or equal to 2.0 wt% and less than 4.0 wt%, titanium in an amount between 0 wt% and less than or equal to 0.1 wt%, unavoidable impurities, and the balance aluminum. The alloy has a yield strength at 150 DEG C of between about 70 to 120 MPa and an electrical conductivity of between about 45 to 53 IACS.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to aluminum alloys, and in particular to cast aluminum alloys having high electrical conductivity and high temperature strength. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and can not constitute prior art.

[0003] High temperature strength and high electrical conductivity are desirable material properties in applications such as electric motors for electric vehicles. However, certain manufacturing methods, such as conventional casting of aluminum alloys, are not capable of producing such material properties. For example, while Al-Si based die cast alloys generally have a yield strength above 100 MPa at 150°C, their electrical conductivity is relatively low. On the other hand, 100-series aluminum alloys have high electrical conductivity, but have low high temperature strength (<40 MPa) and poor castability.

[0004] The present disclosure addresses these challenges in materials and processing for alloys used in motors for electric vehicles. SUMMARY

[0005] This section provides a general summary of the present disclosure and is not a comprehensive disclosure of its full scope or all of its features.

[0006] In one form of the present disclosure, an aluminum alloy includes iron in an amount between greater than 0.9 wt% and less than or equal to 1.5 wt%, nickel in an amount between greater than or equal to 2.0 wt% and less than 4.0 wt%, titanium in an amount between 0 wt% and less than or equal to 0.1 wt%, unavoidable impurities, and a balance of aluminum. The aluminum alloy has a 150°C yield strength between about 70 to 120 MPa and an electrical conductivity between about 45 to 53 IACS.

[0007] In variations of the alloy, which can be practiced individually or in any combination: the iron is between greater than 0.9 wt% and 1.3 wt%; the iron is between greater than 0.9 wt% and 1.1 wt%; the nickel is between 2.0 wt% and 3.5 wt%; the nickel is between 2.0 wt% and 3.0 wt%; the titanium is between 0.01 wt% and 0.1 wt%; the titanium is between 0 wt% and 0.05 wt%; the 150°C yield strength is between about 70 MPa to 100 MPa; the iron is 1.1 wt% and the nickel is 2.5 wt%.

[0008] In another form of the disclosure, a rotor for use in an electric motor is cast from an aluminum alloy. The aluminum alloy consists of: iron in an amount between greater than 0.9 wt.% and less than or equal to 1.5 wt.%, nickel in an amount between greater than or equal to 2.0 wt.% and less than 4.0 wt.%, titanium in an amount between 0 wt.% and less than or equal to 0.1 wt.%, unavoidable impurities, and a balance of aluminum. The alloy has a 150°C yield strength between about 70 to 120 MPa and an electrical conductivity between about 45 to 53 IACS.

[0009] In variations of the rotor, which can be practiced individually or in any combination, the iron is between greater than 0.9 wt.% and 1.3 wt.%; the nickel is between 2.0 wt.% and 3.5 wt.%; the nickel is between 2.0 wt.% and 3.0 wt.%; the titanium is between 0.01 wt.% and 0.1 wt.%; the iron is 1.1 wt.% and the nickel content is 2.5 wt.%.

[0010] In yet another form of the disclosure, an electric motor includes: a housing; a stator mounted within the housing; a shaft extending through a center of the stator; and a rotor mounted on the shaft. The rotor is cast from an aluminum alloy. The aluminum alloy consists of: iron in an amount between greater than 0.9 wt.% and less than or equal to 1.5 wt.%, nickel in an amount between greater than or equal to 2.0 wt.% and less than 4.0 wt.%, titanium in an amount between 0 wt.% and less than or equal to 0.1 wt.%, unavoidable impurities, and a balance of aluminum. The alloy has a 150°C yield strength between about 70 to 120 MPa and an electrical conductivity between about 45 to 53 IACS.

[0011] In variations of the electric motor, which can be practiced individually or in any combination, the iron is between greater than 0.9 wt.% and 1.3 wt.%; the nickel is between 2.0 wt.% and 3.0 wt.%; the titanium is between 0.01 wt.% and 0.1 wt.%; the iron is 1.1 wt.% and the nickel is 2.5 wt.%.

[0012] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0013] So that the disclosure can be well understood, various forms thereof will now be described by way of example with reference to the drawings in which:

[0014] Figure 1A is a ternary phase diagram of an aluminum, iron, and nickel alloy (Al-Fe-Ni) in accordance with the teachings of the present disclosure;

[0015] Figure 1B is Figure 1A an enlarged view within Detail A of the ternary phase diagram of

[0016] Figure 2A is a microstructure of an alloy of aluminum, iron, and nickel (Al-Fe-Ni) at different magnifications in accordance with the teachings of the present disclosure;

[0017] Figure 2B is a microstructure of an alloy of aluminum, iron, and nickel (Al-Fe-Ni) at different magnifications in accordance with the teachings of the present disclosure;

[0018] Figure 3 is a graph showing stress-strain curves measured at 150°C for two Al-Fe-Ni alloys in accordance with the teachings of the present disclosure;

[0019] Figure 4 is a graph showing the solid fraction as a function of temperature based on simulated thermodynamic data for two Al-Fe-Ni alloys in accordance with the teachings of the present disclosure;

[0020] Figure 5A is an image of a typical dumbbell-shaped casting mold used to test hot-tear;

[0021] Figure 5B is an image of a typical hot-tear crack;

[0022] Figure 5C is an image of a typical hot-tear fracture;

[0023] Figure 6 is a perspective view of an electric motor employing an aluminum alloy in accordance with the teachings of the present disclosure; and

[0024] Figure 7 is a cross-sectional view of an electric motor of Figure 6 in accordance with the teachings of the present disclosure.

[0025] The drawings described herein are for purposes of illustration only and are not intended to limit the scope of the present disclosure in any way. DETAILED DESCRIPTION

[0026] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

[0027] Aluminum is a material with good electrical conductivity properties that can be easily cast for numerous applications. However, in certain applications, it can lack proper strength at high temperatures. The present disclosure provides a new cast aluminum alloy with both high strength and high electrical conductivity at high temperatures.

[0028] The aluminum alloy according to the present disclosure includes iron (Fe) and nickel (Ni). In one form, the aluminum alloy also includes titanium (Ti). More specifically, the aluminum alloy consists of iron in an amount between greater than 0.9 wt% and less than or equal to 1.5 wt%, nickel in an amount between greater than or equal to 2.0 wt% and less than 4.0 wt%, and titanium in an amount between 0 wt% and less than or equal to 0.1 wt%. In a particular form, the iron is 1.1 wt% and the nickel is 2.5 wt%.

[0029] The iron in the aluminum alloy serves to enhance strength at room temperature and high temperatures. Additionally, by forming a eutectic with aluminum, hot shortness and weldability sensitivity can be reduced, which can result in better castability. However, too much iron can reduce the electrical conductivity and castability of the alloy. Thus, the amount of iron is greater than 0.9 wt% and less than or equal to 1.5 wt% to balance the desired mechanical properties, namely high electrical conductivity and high strength at high temperatures. In another form, the iron is between greater than 0.9 wt% and 1.3 wt%. In a particular form, the iron is 1.1 wt%.

[0030] The nickel is added to the aluminum alloy to enhance strength at room temperature and high temperatures. Nickel also forms a eutectic with aluminum, which can result in the alloy having better castability. However, too much nickel can reduce the electrical conductivity of the alloy. The inventors have found that an amount of nickel between greater than or equal to 2.0 wt% and less than 4.0 wt% results in a favorable combination of high strength and high electrical conductivity at high temperatures. In another form, the nickel is between 2.0 wt% and 3.0 wt%. In a particular form, the nickel is 2.5 wt%.

[0031] Optionally, the aluminum alloy also includes titanium. Titanium refines the grain boundaries of the aluminum, which has a positive effect on the strength of the aluminum alloy at high temperatures. The amount of titanium is between 0 wt% and less than or equal to 0.1 wt%. In another form, the titanium is between 0.01 wt% and 0.1 wt%.

[0032] Some small amounts of impurities are inevitable in any alloying process. However, the alloy according to the present disclosure does not include intentional additions of other elements beyond those set forth above. Specifically, the aluminum alloy includes only Si, Mg, Cr, Sr, Mn, Zr, V as unintentional impurities that negatively contribute to the desired high electrical conductivity.

[0033] Turning now to Figure 1A and Figure 1B a ternary phase diagram of an alloy of aluminum, iron, and nickel (i.e., an Al-Fe-Ni alloy) is shown, where Figure 1B is shown Figure 1BAn enlarged view of the lower left portion of Figure 1, corresponding to a range of less than 10 wt% nickel and iron, with the balance being aluminum. The Al-Fe-Ni alloy forms a ternary eutectic system, where Alo.9wt%Fe4.6wt%Ni undergoes a constant eutectic reaction at 645°C. The reaction is between face-centered cubic (FCC) aluminum, Al3Ni, and Al9FeNi. Near-eutectic compositions are often good candidates for casting processes because the eutectic phase that forms after the Al dendrites form helps to reduce the susceptibility to hot tearing.

[0034] Referring to Figure 2A and Figure 2B , microstructures of two inventive Al-Fe-Ni cast alloys (i.e., Alloy A and Alloy B as shown in Table 1 below) in accordance with the teachings of the present disclosure are shown.

[0035] Alloy of the Invention Aluminum (wt%) Iron (wt%) Nickel (wt%) Alloy A Balance 1.1 2.5 Alloy B Balance 0.9 4.5

[0036] Table 1

[0037] As shown in Figure 2A , aluminum dendrites 210 and ternary eutectic 220 are present in the microstructure of Alloy A. As the composition approaches the eutectic point, the dendrites 210 decrease and more ternary eutectic 220 is present, as shown in the microstructure of Alloy B in Figure 2B , which has less iron and more nickel than Alloy A. For an alloy with 9 wt% iron and 4.6 wt% nickel, a nearly fully eutectic microstructure is obtained at 645°C. The dendrites provide mechanical properties and the presence of eutectic corresponds to increased strength at high temperatures. A microstructure containing both fine dendrites and eutectic in the microstructure yields a balanced range of properties.

[0038] Experimental testing was performed on two compositions in accordance with the present disclosure (i.e., Alloy A and Alloy B).

[0039] The test results, including mechanical and electrical properties as shown, are shown in Table 2 below.

[0040]

[0041] Table 2

[0042] As shown, the alloys of the present disclosure can achieve a yield strength greater than 70 MPa at temperatures up to 150 °C. Alloy A has a yield strength of 69.8-80.6 MPa, and Alloy B has a yield strength of 113.0-128.6 MPa. Further, Alloy A has an ultimate tensile strength of 132.0 ± 4.0 MPA and an elongation of 27.3 ± 8.4%. Alloy B has an ultimate tensile strength of 188.8 ± 14.7 MPA and an elongation of 10.0 ± 2.9%. Without being bound by any particular theory, the experimental results suggest that alloying iron and nickel into aluminum through the thermally stable eutectic phase improves strength at room temperature and high temperatures.

[0043] According to this preliminary testing, the electrical conductivity of the two aluminum alloys of the present disclosure ranged from 44 to 52.2 IACS (International Annealed Copper Standard). It can be seen that the electrical conductivity decreased as the nickel content increased from 2.5 wt% to 4.5 wt%. Without being bound by any particular theory, the experimental results suggest that alloying higher amounts of iron and nickel into aluminum decreases the electrical conductivity of the alloy. Thus, the range of iron and nickel content is critical to balancing the strength and electrical conductivity properties.

[0044] Referring to Figure 3 , stress-strain curves measured at 150 °C are shown for two alloys of the present disclosure, namely Alloy A and Alloy B. The curves represent the relationship between stress and strain under deformation. The shape of the curves indicates that Alloy B has a higher yield strength; however, Alloy A can sustain a greater strain before breaking.

[0045] In addition to having sufficient strength and electrical properties, the aluminum alloys of the present disclosure are also castable. One measure of castability is the susceptibility to hot tearing, a type of casting defect. Hot tearing defects occur in a critical temperature range when 80% to 100% of the cast material is in the solid phase, i.e., the solid fraction of the alloy is between 0.8 and 1.0 during casting. In this range, the material exhibits reduced ductility and does not retain channels within the dendritic structure to allow inward filling flow to occur. As a result, the metal can break or crack, leading to the formation of hot tearing during the casting process. As the solid fraction moves from 80% to 100%, alloys with a narrower temperature change are therefore less likely to form hot tearing defects. The hot tearing susceptibility of the near-eutectic compositions of the alloys of the present disclosure were evaluated by both computational and experimental methods.

[0046] Computational Analysis / Data

[0047] The solid fraction as a function of temperature for Alloy A and Alloy B was calculated through thermodynamic simulation. The results of the simulation are shown in Figure 4 . The temperature change for both Alloy A and Alloy B is between 80% and 100% of the solid fraction Figure 4The difference between the solid fractions at 0.8 and 1.0 is negligible. Because these alloys have a small temperature change between 80% and 100% solid fraction, the alloys of the present invention resist the formation of hot tear defects during the casting process.

[0048] Experimental Data

[0049] Referring to Figure 5A , Figure 5B and Figure 5C , the evaluation of the formation of hot tear defects is typically performed using dumbbell-shaped casting molds 500. As shown in Figure 5A , each dumbbell-shaped casting mold 500 has a wider end 510 and a connecting rod 520 having a smaller diameter. A series of casting molds having connecting rods 520 of different diameters are cast from a particular alloy. During the casting process, the dumbbell shape of the two end structures creates hot spots, particularly where the connecting rod 520 meets the wider end 510. These hot spots can initiate the formation of hot tear defects, including hot tear cracks and even hot tear breaks. As the diameter 530 of the connecting rod 520 increases, the likelihood of hot tear breaks increases. Figure 5B depicts a hot tear crack, while Figure 5C shows a hot tear break.

[0050] The aluminum alloy samples listed in Table 3 below were tested for hot tearing using dumbbell-shaped casting molds.

[0051]

[0052] Table 3

[0053] The alloys tested included a prior art silicon and magnesium containing alloy (Al-7Si-2.5Mg) commonly used in cast aluminum applications, the alloys of the present invention - Alloy A and Alloy B discussed above, and a comparative alloy C. Alloy C contains 1.6 wt% iron, 2.5 wt% nickel, and the balance aluminum. For each of these alloys, a set of dumbbell-shaped casting molds 500 having connecting rods of a particular diameter (8 mm, 6 mm, and 4 mm) were cast. After casting, the total number of test molds showing cracks and breaks was counted for each alloy and for each different diameter. The results are summarized in Table 3.

[0054] As shown in Table 3, the prior art Al7Si2.5MgMn alloy exhibits poor hot tear resistance. Hot tear fractures were observed in samples having a diameter of 8 mm. For alloys A and B of the present disclosure, hot tear cracks were only observed in limited samples having a diameter of 6 mm and 4 mm, while no hot tear defects were observed for diameters greater than or equal to 8 mm. However, when the Fe content in alloy C was increased above 1.6 wt.%, hot tear fractures were observed, indicating a decrease in hot tear performance.

[0055] Reference is now made to Figure 6 and Figure 7 In accordance with one aspect of the present disclosure, the aluminum alloys of the present disclosure described herein are used in electric motor applications. It should be appreciated that the aluminum alloys of the present disclosure can be used in other applications having similar mechanical and electrical property requirements, and thus the electric motor applications should not be construed as limiting the application of the present disclosure. The illustrated electric motor 600 includes a housing 610, a stator 620 mounted within the housing 610, a shaft 630 extending through the center of the stator 620, and a rotor 640 mounted on the shaft 630. In this application, the rotor 640 is cast from one of the aluminum alloys of the present disclosure. The rotor must be electrically conductive while being strong enough to withstand operating stresses, which the alloys of the present disclosure provide.

[0056] It should also be appreciated that the elemental ranges discussed herein include all incremental values between the minimum alloying elemental composition value and the maximum alloying elemental composition value. That is, the minimum alloying elemental composition value can range from the minimum value to the maximum value. Likewise, the maximum alloying elemental composition value can range from the maximum value shown to the minimum value discussed. For example, the minimum nickel content can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, and any value between these incremental values, and the maximum nickel content can be 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, and any value between these incremental values.

[0057] Unless otherwise specifically indicated herein, all numerical values indicating mechanical / thermal properties, composition percentages, dimensions and / or tolerances or other properties are to be understood as modified by the word "about". Such modifications are to be understood as encompassing variations that can exist

[0058] As used herein, the phrase at least one of A, B, and C should be interpreted to use the non-exclusive logical OR as denoted by the following logical representation (A or B or C), and should not be interpreted to denote "at least one of A, and at least one of B, and at least one of C."

[0059] The description of the present disclosure is merely exemplary in nature and, thus, variations that do not depart from the essence of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.

[0060] According to the present invention, there is provided a rotor for use in an electric motor, the rotor being cast from an aluminum alloy, the aluminum alloy being provided to have: iron in an amount between greater than 0.9 wt% and less than or equal to 1.5 wt%; nickel in an amount between greater than or equal to 2.0 wt% and less than 4.0 wt%; titanium in an amount between 0 wt% and less than or equal to 0.1 wt%; unavoidable impurities; and a balance of aluminum, the alloy having a 150°C yield strength between about 70 to 120 MPa and an electrical conductivity between about 45 to 53 IACS.

[0061] According to an embodiment, the iron is between greater than 0.9 wt% and 1.3 wt%.

[0062] According to an embodiment, the nickel is between 2.0 wt% and 3.5 wt%.

[0063] According to an embodiment, the nickel is between 2.0 wt% and 3.0 wt%.

[0064] According to an embodiment, the titanium is between 0.01 wt% and 0.1 wt%.

[0065] According to an embodiment, the iron is 1.1 wt% and the nickel content is 2.5 wt%.

[0066] According to the present invention, there is provided an electric motor having: a housing; a stator mounted within the housing; a shaft extending through a center of the stator; and a rotor mounted on the shaft, the rotor being cast from an aluminum alloy, the aluminum alloy consisting of: iron in an amount between greater than 0.9 wt% and less than or equal to 1.5 wt%; nickel in an amount between greater than or equal to 2.0 wt% and less than 4.0 wt%; titanium in an amount between 0 wt% and less than or equal to 0.1 wt%; unavoidable impurities; and a balance of aluminum, the alloy having a 150°C yield strength between about 70 to 120 MPa and an electrical conductivity between about 45 to 53 IACS.

[0067] According to an embodiment, the iron is between greater than 0.9 wt% and 1.3 wt%.

[0068] According to an embodiment, the nickel is between 2.0 wt% and 3.0 wt%.

[0069] According to an embodiment, the titanium is between 0.01 wt% and 0.1 wt%.

[0070] According to an embodiment, the iron is 1.1 wt% and the nickel is 2.5 wt%.

Claims

1. An aluminum alloy consisting of: iron in an amount between greater than 0.9 wt.% and less than or equal to 1.5 wt.%; nickel in an amount between greater than or equal to 2.0 wt.% and less than 4.0 wt.%; titanium in an amount between 0 wt.% and less than or equal to 0.1 wt.%; inevitable impurities; and aluminum in the balance, the alloy having a 150°C yield strength between about 70 to 120 MPa and an electrical conductivity between about 45 to 53 IACS.

2. The aluminum alloy of claim 1, wherein the iron is between greater than 0.9 wt.% and 1.3 wt.%.

3. The aluminum alloy of claim 1, wherein the iron is between greater than 0.9 wt.% and 1.1 wt.%.

4. The aluminum alloy of claim 1, wherein the nickel is between 2.0 wt.% and 3.5 wt.%.

5. The aluminum alloy of claim 1, wherein the nickel is between 2.0 wt.% and 3.0 wt.%.

6. The aluminum alloy of claim 1, wherein the titanium is between 0.01 wt.% and 0.1 wt.%.

7. The aluminum alloy of claim 1, wherein the titanium is between 0 wt.% and 0.05 wt.%.

8. The aluminum alloy of claim 1, wherein the 150°C yield strength is between about 70 MPa to 100 MPa.

9. The aluminum alloy of claim 1, wherein the iron is 1.1 wt.% and the nickel is 2.5 wt.%.

10. A rotor for use in an electric motor, the rotor cast from the aluminum alloy of claim 1.

11. An electric motor comprising: a housing; a stator mounted within the housing; a shaft extending through the center of the stator; and a rotor mounted on the shaft, the rotor cast from the aluminum alloy of claim 1. ​ ​

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