ALUMINUM ALLOY, WIRE AND CONNECTING ELEMENT MADE FROM THE ALUMINUM ALLOY

Description

[0001] The invention relates to an aluminum alloy for wire production for cold forming, in particular for the production of connecting elements, according to the preamble of patent claim 1. The invention further relates to a wire produced from the aluminum alloy and a connecting element made of the aluminum alloy.

[0002] In the automotive sector, reducing the weight of components is of great importance, as the weight of a vehicle has a direct impact on fuel consumption and CO2 emissions. One focus here is on the use of light metals such as aluminum and magnesium. Aluminum screws are used as fasteners for components made of these metals, particularly for connecting housing components. The advantage of using similar fasteners lies not only in the weight savings compared to steel screws; rather, special advantages arise from the lower corrosion potential and the epitaxial expansion of the fastener and component during operation. Aluminum alloys and their chemical composition are listed in DIN EN 573-3.

[0003] As a compromise between formability, strength, and corrosion resistance, an aluminum alloy according to EN AW-6056 (Al Si1MgCuMn) is used to manufacture aluminum screws. However, a disadvantage of this aluminum alloy has proven to be its limited temperature resistance. Therefore, fasteners made from this alloy can only be used in temperature ranges up to 150°C, e.g., for screwing together oil pans or gearbox housings. Fasteners made from this alloy are not suitable for areas where higher temperatures occur, particularly in the engine area, where temperatures of 180°C and higher prevail. In addition, these alloys exhibit mechanical properties that are insufficient for numerous automotive applications.For this reason, for example, steel screws are still used to screw the cylinder head, even though the engine block is usually made of light metal.

[0004] In the aerospace sector, fasteners made of an aluminum alloy according to EN AW-2024 (Al Cu4Mg1) are used. These are high-strength alloys that, through the precipitation of the Al2Cu phases through effective precipitation hardening, enable tensile strengths of up to R m = 570 MPa. However, wire production from this alloy is very complex.

[0005] The use of a 6056 Al alloy for fasteners in the automotive sector can be seen, for example, in Isao Iwayama et al., in Sei technical review, no. 77, pp. 74-78, "6056 Aluminium Alloy wire for automotive fasteners".

[0006] Based on the prior art described above, the object of the present invention is to provide an aluminum alloy which has high strength and corrosion resistance, enables economical wire production and is suitable for the production of connecting elements for use in temperature ranges of 180°C and higher.

[0007] According to the invention, this object is achieved by an aluminum alloy having the features of claim 1. In addition to aluminum with a proportion of greater than 88% and copper with a proportion of greater than or equal to 5%, nickel and silicon are further alloying elements, with an alloying proportion of nickel greater than or equal to 0.15% and silicon less than or equal to 1.0%. All previously mentioned and subsequent proportions are given in mass %. The aluminum proportion is preferably greater than 89% or greater than 90%. For example, it is in the range from 88% to 90% or is greater than 90%.

[0008] Surprisingly, it has been shown that the addition of these amounts of nickel and silicon achieves high strength while simultaneously improving processability.

[0009] The nickel alloy content is between 0.15% and 1.0%, and the silicon alloy content is between 0.4% and 1.0%. The copper alloy content is between 5.0% and 6.1%.

[0010] According to the invention, magnesium is a further alloying component, with an alloying content of between 1.5% and 2.2%. This ensures good basic strength of the alloy, which, when added to the alloying component nickel, enables the alloy to achieve very good strength properties.

[0011] In a further embodiment of the invention, manganese and / or titanium are additional alloy components. Manganese has a positive effect on the heat resistance of the alloy, while titanium has a grain-refining effect, thereby improving formability.

[0012] The present invention further relates to a wire made of such an alloy according to patent claim 5 as well as to a connecting element made of such an alloy according to patent claim 6.

[0013] Further developments and refinements of the invention are specified in the subclaims. One embodiment is described in detail below:

[0014] An alloy chosen as a preferred embodiment comprises the following composition: alloying elements Mass% Silicon (Si) 0,65 Iron (Fe) 0,09 Copper (Cu) 5,72 Manganese (Mn) 0,48 Magnesium (Mg) 1,82 Chromium (Cr) 0,11 Nickel (Ni) 0,8 Zinc (Zn) 0,18 Titanium (Ti) 0,15

[0015] Furthermore, other impurities may be present, but not exceeding 0.15% in total and preferably not exceeding 0.05% individually. (Alternatively, the specified Mg and Zn values may vary slightly, e.g., 1.83% (Mg) and 0.19% (Zn).)

[0016] A rolled cast wire rod based on an alloy according to this embodiment enables an economical wire drawing process in which the wire is drawn to the desired final diameter. This wire, in turn, enables the economical production of fasteners, particularly screws. Production takes place according to known methods. Specifically, a head with a shaft is formed from the wire through one or more (cold) forming processes, wherein the shaft is provided with a thread in at least a partial area, particularly by thread rolling. Alternatively, a threaded bolt or other connecting or fastening elements such as rivets are produced.

[0017] Due to the alloy's improved properties, cold-formed fasteners, especially screws, made from this wire exhibit high mechanical and corrosion stability while simultaneously maintaining high heat resistance. Due to their temperature resistance, such fasteners can also be used in temperature ranges of 180°C and higher.

[0018] Specifically, fasteners made from this aluminum alloy, especially screws, exhibit a tensile strength of preferably greater than 570 MPa (at room temperature). This alloy thus exhibits significantly improved tensile strength compared to the conventional aluminum alloy according to EN AW-6056.

[0019] In a preferred embodiment, the fastener, particularly a screw, made from this alloy is characterized by particularly high heat resistance. Thus, when exposed to temperatures of 200 °C for 24 hours, the fastener still exhibits a residual tensile strength that is greater than 0.8 times the tensile strength at room temperature. Additionally or alternatively, the residual tensile strength is more than 400 MPa and, in particular, more than 450 MPa. Furthermore, it can be seen that the overall tensile strength exhibits only a roughly linear decrease with a slight gradient. The tensile strength remains at a high level of approximately 500 MPa.

[0020] This makes such a fastener particularly suitable for use in areas subject to high thermal stress and is expediently used in such areas. Areas subject to high thermal stress are defined as areas that at least temporarily have a temperature of greater than 150°C, preferably greater than 180°C, and preferably greater than 200°C. These temperatures are reached repeatedly for periods of, for example, greater than 0.5 hours or even greater than 1-3 hours. Such recurring thermal loads occur, for example, in automobile engines.

[0021] The fastener is specifically used and installed within a motor vehicle, particularly in the engine area and specifically in the engine itself. The engine is, in particular, an internal combustion engine. The screw is therefore used primarily as an engine screw, for example, as a cylinder head screw.

[0022] Alternatively, the connecting element is preferably used as an electrical contact element, especially in the area of a battery connection of a motor vehicle battery. The connecting element can be, for example, a pole terminal or a screw for such a pole terminal. Especially in electric vehicles with an electric traction motor, high-capacity batteries are installed in the vehicle, which are subjected to very high charging currents for short charging times. These batteries are also designed for high power output to the electric traction motors, which often have an electrical output of more than 100 kW. Due to the correspondingly high currents, the electrical cables and especially the battery terminals are subjected to high thermal stress.

[0023] If it is stated here that the wire or the connecting element is made of the aluminum alloy, this is understood to mean a wire or a connecting element which consists entirely of the alloy and is optionally also provided with a coating, e.g. a sliding coating. In addition, however, this also includes elements in which the wire or the connecting element consists of two different materials with a core made of a first material and a sheath made of a second material. Either the core (preferred) or the sheath consists of the aluminum alloy according to the invention. A screw of this type can be found in DE 10 2014 220 337 A1. In this case, an aluminum core is surrounded by a titanium sheath. A special manufacturing process for a screw of this type can be found in DE 10 2014 220 338 A1.

[0024] There are numerous possibilities for designing and developing the aluminum alloy according to the invention. The range of alloy compositions according to the invention is shown in Table 1 below: alloying elements Value of (in mass%) Value up to (in mass %) Silicon (Si) 0,4 1,0 Iron (Fe) 0 0,2 Copper (Cu) 5,0 6,1 Manganese (Mn) 0 0,5 Magnesium (Mg) 1,5 2,2 Chromium (Cr) 0 0,2 Nickel (Ni) 0,15 1,0 Zinc (Zn) 0 0,3 Titanium (Ti) 0 0,25

[0025] Other admixtures must not exceed 0.15% in total, and preferably 0.05% individually. The remaining portion is aluminum, which should be greater than 88% and preferably greater than 90%. The aluminum content should also preferably be less than 93%.

[0026] Embodiments of the invention are explained in more detail below with reference to the figures. The figures show Fig.1 a simplified comparison diagram for the heat strength of various aluminum alloys and Fig. 2 a screw in side view.

[0027] In the Fig. 1 The tensile strength (expressed in MPa) versus time (aging time) for elements (screws) made of various alloys is given. The elements were heated to 200 °C and held at this temperature for a total of 24 hours.

[0028] The different alloys are two reference alloys, V1 and V2, and the inventive alloy L (dashed line). Reference alloy V1 is the alloy according to EN AW-6056 (solid line), and reference alloy V2 is a so-called 7xxx alloy (dotted line).

[0029] The diagram clearly shows that the inventive alloy L exhibits a significantly higher tensile strength compared to the reference alloy V1. This is more than 100 MPa higher than the tensile strength of the reference alloy V1 over the entire aging period.

[0030] Compared to the comparative alloy V2, the alloy L according to the invention has a lower tensile strength at the beginning of the aging period, but is characterized by a significantly better high-temperature strength, so that the tensile strength remains high even with longer aging periods and already has a higher tensile strength than the comparative alloy V2 after just a few hours.

[0031] Due to these properties, the inventive alloy L is particularly suitable for applications in areas subject to high thermal stress and is also used there. The alloy is used specifically for the production of fasteners such as screws.

[0032] Fig. 2shows an example of such a screw 2 in a side view. The screw 2 extends along a central longitudinal axis from a head 4, to which a shaft 6 is connected. A portion of the shaft 6 is provided with a thread 8. The screw 2 shown is an engine screw, specifically a cylinder head screw. These typically have a length of several centimeters up to ten or 15 cm and are designed, for example, as M8, M10, M11, or M12 screws.

Claims

1. Aluminium alloy for wire production for cold forming, in particular for the production of connecting elements, having an alloy content of aluminium greater than 88% and copper greater than or equal to 5% as main alloy elements, characterized in that the aluminium alloy consists of: - 5.0% to 6.1% copper - 0.15% to 1.0% nickel, - 0.4% to 1.0% silicon, - 0% to 0.2% iron, - 0% to 0.2% manganese, - 1.5% to 2.2% magnesium, - 0% to 0.2% chromium, - 0% to 0.3% zinc, - 0% to 0.25% titanium, - 0% to 0.15% addition and - aluminium as the balance.

2. Aluminium alloy according to Claim 1, characterized in that the alloy content of aluminium is between 88% and 90% or greater than 90%.

3. Aluminium alloy according to either of the preceding claims, characterized in that manganese is a further alloy constituent.

4. Aluminium alloy according to any of the preceding claims, characterized in that titanium is a further alloy constituent.

5. Wire for production of connecting elements, in particular screws, characterized in that it is made of an aluminium alloy according to any of the preceding claims.

6. Connecting element, in particular screw, characterized in that it is made of an aluminium alloy according to any of the preceding claims.

7. Connecting element according to the preceding claim, having a tensile strength of greater than 570 MPa at room temperature.

8. Connecting element according to one of the two preceding claims having high hot strength, wherein the connecting element after thermal stress at 200°C over 24 h has residual tensile strength of greater than 0.8 times the tensile strength at room temperature and / or residual tensile strength of greater than 400 MPa, in particular greater than 450 MPa.

9. Connecting element according to any of Claims 6 to 8, used in a region subject to thermal stress, in particular in a motor vehicle, in which the temperature is at least intermittently above 180°C.

10. Connecting element according to any of Claims 6 to 9, used as an engine screw in an internal combustion engine.

11. Connecting element according to any of Claims 6 to 10, used as a contact element, in particular as pole clamp or screw for a pole clamp of an accumulator.