Light metal cast component

Abstract

A method includes producing a light metal cast component from a melt of an aluminium casting alloy. The alloy contains, by weight, silicon with 3.5 to 5.0%, magnesium with 0.2 to 0.7%, titanium with 0.07 to 0.12%, boron with a maximum of 0.012%, and optionally further alloy elements together with less than 1.5%, the rest, aluminium as well as unavoidable impurities, wherein the melt is produced from a base melt, a first grain refiner of an aluminium-silicon alloy and a second grain refiner of an aluminium-titanium-alloy, wherein the melt, in relation to the total weight, contains in total an amount of 0.1 to 5.0% of the first and the second grain refiner; wherein the casting is carried out by a low-pressure method and the melt is acted upon by compacting after the casting.

Claims

1. A method for producing a light metal cast component, comprising: providing a melt from an aluminium casting alloy that includes silicon of 3.5 to 5.0 percent by weight, magnesium of 0.2 to 0.7 percent by weight, titanium of 0.07 to 0.12 percent by weight, boron of at most 0.012 percent by weight, wherein the melt is produced from a base melt that contains aluminium, a first grain refiner of an aluminium-silicon-alloy that contains a proportion of silicon of at most 12.5 percent by weight, and aluminium, and a second grain refiner of an aluminium-titanium-alloy that contains as alloy elements at least titanium, boron and aluminium, wherein the melt, in relation to a total weight, contains in total an amount of 0.1 to 5.0 percent by weight of the grain refiner of the aluminium-silicon-alloy and of the grain refiner of the aluminium-titanium-alloy; casting the melt into a casting- and forming tool at a low first pressure by means of gravity casting or low-pressure casting; after completely filling the casting and forming tool, applying a pressure to the solidifying melt in the casting and forming tool with a second pressure that is larger than the first pressure; and when the melt is at least mostly solidified to the component, compacting the component that is at least mostly solidified from the melt in the casting and forming tool at a third pressure that is larger than the second pressure.

2. The method of claim 1, wherein the melt contains as further alloy elements at least one of: strontium (Sr) with 100 to 150 parts per million, tin (Sn) with less than 250 parts per million, copper (Cu) with less than 1.0 percent by weight, nickel (Ni) with less than 550 parts per million, titanium boride with less than 30 parts per million, zinc (Zn) with less than 550 parts per million, chromium (Cr) with less than 500 parts per million, iron (Fe) with less than 0.7 percent by weight, and manganese (Mn) with less than 0.15 percent by weight.

3. The method of claim 1, wherein the first grain refiner is produced by producing a grain refinement melt from the aluminium-silicon-alloy and treating the grain refinement melt with ultrasonic sound, such, that after the solidification, a globule-like formed-in alpha-mixed crystal is present.

4. The method of claim 1, wherein the first grain refiner and the second grain refiner are introduced into the base melt by stirring.

5. The method of claim 1, wherein the casting of the melt takes place at most five minutes after introduction of at least one of the first grain refiner and the second grain refiner.

6. The method of claim 1, wherein the casting takes place at a first temperature of 620 C. to 800 C.

7. The method of claim 1, wherein the pressure application with the second pressure is carried out at a second temperature that is lower than the first temperature and is below the liquidus line, wherein the compacting with the third pressure is carried out at a third temperature that is lower than the second temperature and that is at least half of the solidus temperature of the aluminium casting alloy.

8. The method of claim 1, wherein the light metal cast component is subjected to a heat treatment after the solidification.

9. The method of claim 1, wherein the melt includes further alloy elements that are less than 1.5 percent by weight, the remainder being aluminium and unavoidable impurities.

10. A light metal cast component produced by: providing a melt from an aluminium casting alloy that includes silicon of 3.5 to 5.0 percent by weight, magnesium of 0.2 to 0.7 percent by weight, titanium of 0.07 to 0.12 percent by weight, boron of at most 0.012 percent by weight, wherein the melt is produced from a base melt that contains aluminium, a first grain refiner of an aluminium-silicon-alloy that contains a proportion of silicon of at most 12.5 percent by weight, and aluminium, and a second grain refiner of an aluminium-titanium-alloy that contains as alloy elements at least titanium, boron and aluminium, wherein the melt, in relation to a total weight, contains in total an amount of 0.1 to 5.0 percent by weight of the grain refiner of the aluminium-silicon-alloy and of the grain refiner of the aluminium-titanium-alloy; casting the melt into a casting and forming tool at a low first pressure by means of gravity casting or low-pressure casting; after completely filling the casting and forming tool, applying a pressure to the solidifying melt in the casting and forming tool with a second pressure that is larger than the first pressure; and when the melt is at least mostly solidified to the component, compacting the component that is at least mostly solidified from the melt in the casting and forming tool at a third pressure that is larger than the second pressure; wherein the light metal cast component contains 3.5 to 5.0 percent by weight silicon and 0.2 to 0.7 percent by weight magnesium, 0.07 to 0.12 percent by weight titanium, at most 0.012 percent by weight boron; and wherein the light metal cast component has an average grain size of at most 500 micrometers.

11. The light metal cast component of claim 10, wherein the light metal cast component has a maximal porosity of less than 0.5%.

12. The light metal cast component of claim 10, wherein the light metal cast component has an elongation at fracture of at least 5%.

13. The light metal cast component of claim 10, wherein the light metal cast component has a yield strength of at least 220 Newton per square millimeter.

14. The light metal cast component of claim 10, wherein the light metal cast component has a tensile strength of at least 270 Newton per square millimeter.

15. The light metal cast component of claim 10, wherein the light metal cast component has a surface roughness of less than 50 micrometers.

16. The light metal cast component of claim 10, wherein the light metal cast component has a yield strength of at least 280 Newton per square millimeter, an elongation at fracture of at least 8% and a tensile strength of at least 320 Newton per square millimeter in the area of a cast blank surface.

17. The light metal cast component of claim 10, wherein the light metal cast component has partial portions in the finished state that are mechanically unmachined after the casting, wherein the mechanically unmachined partial portions have a wall thickness of less than 3.0 millimeters.

18. The light metal cast component of claim 10, wherein the light metal cast component is a safety- or structural component of a motor vehicle.

19. The light metal cast component of claim 18, wherein the safety or structural component has a weight of at least 500 grams.

20. The light metal cast component of claim 10, wherein the melt includes further alloy elements that are less than 1.5 percent by weight, the remainder being aluminium and unavoidable impurities.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An example process embodiment is described in the following using the drawings.

(2) FIG. 1 illustrates a method for producing a light metal cast component by means of a casting and forming tool with the method steps S10 to S50; and

(3) FIG. 2 illustrates a phase diagram for a metal alloy for producing a component according to the method of FIG. 1.

DESCRIPTION

(4) FIGS. 1 and 2 are described together in the following. FIG. 1 shows a method for producing a light metal cast component by using a casting and forming tool in several method steps S10 to S50.

(5) As a material a light metal cast alloy is used, which contains at least the following alloying components: 3.5 to 5.0 percent by weight silicon, 0.2 to 0.7 percent by weight magnesium, 0.07 to 0.12 percent by weight titanium, a measurable amount of boron of up to 0.012 percent by weight, at least 93.0 percent by weight aluminium as well as unavoidable impurities. Furthermore, the alloy can contain in low amounts traces of further elements like copper, manganese, nickel, zinc, tin and/or strontium.

(6) An exemplary alloy can have in particular 4.0 percent by weight silicon, 0.4 percent by weight magnesium, 0.08 percent by weight titanium, 0.012 percent by weight boron, approximately 400 ppm copper (Cu), approximately 400 ppm zinc (Zn), approximately 100 ppm strontium (Sr), approximately 200 ppm tin (Sn), approximately 400 ppm nickel (Ni), approximately 400 ppm manganese (Mn), further unavoidable impurities and the rest aluminium (Al).

(7) In the first method step S10, the melt is produced for producing the light metal cast component. For this, a base melt is made from a base alloy. At least one grain refiner can be added to the base alloy, which acts as nucleating agent during crystallisation. In concrete terms, as an example, a first grain refiner of an aluminium-silicon-alloy can be used that contains an amount of silicon of up to 12.5 percent by weight in relation to the total weight of the first grain refiner alloy. Additionally a second grain refiner of an aluminium-titanium-alloy can be used, which contains as a main component aluminium and as additional alloy elements at least titanium and boron. The grain refiners are added to the melt of the base alloy, wherein the grain refiners are melted. Concerning the proportions it is especially provided that an amount of in total 0.1 to 5.0 percent by weight of the first and second grain refiner relative to the total weight of the to be produced component are added.

(8) In the second method step S20, the melt of the light metal casting alloy is poured into a casting- and forming tool at a low first pressure (P1). The casting can be carried out by gravity casting or low pressure casting, wherein the first pressure (P1) is preferably below 1.0 MPa. The melt is poured with a temperature (T1) above the liquidus temperature, in particular at a temperature of 650 C. to 780 C. The casting tool, which can also be designated as casting mold or permanent mold, can have in contrast thereto a low temperature of for example below 300 C.

(9) In the following method step S30, an application of pressure onto the light metal alloy contained in the hollow mold space is carried out. For this, a pressure P2 is produced between a lower part and an upper part of the casting tool, which is larger than 5 MPa (50 bar). This pressure can for example be produced by the dead weight of the upper part. Before the pressure application, all openings of the casting and forming tool are to be closed, so that no material is unwantedly pressed out of the mold. The pressure application to the melt can be carried out at a component-surface-layer-temperature range T2 starting from around the liquidus line TL up to above the solidus line TS of the metal alloy, i.e., TS<T2<TL. Before the pressure application the material is still liquid. After completion of the pressure application, the material is at least partially solidified, i.e., it is in a semi-solid-state.

(10) After the pressure application (S30), in the following method step (S40) a compacting of the component that is at least mostly solidified from the melt is carried out. The compacting is effected by relative movement of the lower part relative to the upper part at a third pressure P3 that is larger than the second pressure P2 in method step S30. The compacting can be carried out by pressing the lower part in direction of the upper part with high forces. The compacting possibly starts only then, when the metal alloy is at least mostly solidified, i.e., is in a semi-solid-state. The compacting can take place at a component-surface-layer-temperature T3 which is lower than the temperature T2 of the metal alloy at the method step of the pressure application S30. As a lower boundary for the temperature T3, half the solidus temperature TS of the metal alloy is identified, i.e. T2>T3>0.5 TS. The end of the forming process is defined by the reaching of an end position of the relative movement of the upper part relative to the lower part and the reaching of a specific temperature. During the compacting, the component experiences only a comparable low deformation of less than 15%, in particular less than 10%, respectively 5%. During the compacting the pores in the component are closed, so that the microstructure is improved.

(11) After the component is completely solidified, it is removed from the casting tool. Following this, the component, which is also referred to as cast blank in this condition, is mechanically finished in method step S50. The mechanical finishing can for example be a machining process, such as a turning or milling process, or a forming process, like flow-forming.

(12) After the solidification, the light metal cast component can be subjected to a heat treatment before or after the mechanical processing. For example, the cast light metal component can be solution annealed and then tempered. Due to the heat treatment, in particular the strength properties of the component can be increased.

(13) Further common method steps like quality control, for example by means of x-raying, as well as varnishing can be carried out.

(14) By means of the disclosed method, cast blanks can be produced in several steps in the same lower mold, by means of casting (S20), following pressure application (S30) and following compacting/forming (S40). The pressure application takes place above the solidus temperature (liquid to semi-solid-state) of the respectively used alloy.

(15) FIG. 2 shows a condition diagram (phase diagram) for a light metal alloy for producing a component in line with the method according to the invention. On the X-axis the proportion of a metal alloy (W.sub.L) is given, which contains X.sub.A% of a metal A and X.sub.B% of a metal B. In the present case, the metal A is aluminium and the metal B is silicon. Due to the named proportions of aluminium and silicon, the light metal alloy formed therefrom is hypoeutectic, that means the proportion of silicon (metal B) in relation to aluminium (metal A) is so low in the light metal alloy (W.sub.L), that a structure is achieved left of the eutectic (W.sub.Eu).

(16) On the Y-axis the temperature (T) is given. The casting takes place at a temperature T1 clearly above the liquidus temperature TL and/or the liquidus line LL. The temperature range T1 is shown dash-dottedly. The temperature range T2 for the pressure application, which is preferably below the liquidus temperature (TL) and above the solidus temperature TS (TL>T2>TS), is shown in FIG. 2 with a hatching from left below to the right above. In dependency of the process time during the pressure application (S20), the residual deformation degree with less than 15% remains for a following compacting. The compacting (S30) takes place in particular at a temperature range T3 between the temperature T2 and half of the solidus temperature 0.5TS (T2>T3>0.5TS). This range is shown hatched in FIG. 2 from left above to the right below. Optionally, a mechanical post-processing (S40) takes place at a temperature T4 below the solidus temperature (T4<TS).

(17) The cast light metal component produced with the named method has an especially fine grained structure with a low porosity as well as good mechanical properties, in particular in view of the strength, ductility and elongation at fracture. The light metal cast component has a maximal porosity of less than 0.5%, in particular less than 0.1%, and a surface roughness (Ra) of less than 50 micrometers, in particular less than 20 micrometers. The tensile strength (Rm) of the light metal cast component is after the carried out heat treatment at least 270 N/mm.sup.2, in particular at least 320 N/mm.sup.2. The elongation at fracture (A5) is at least 5%, in particular at least 8%. The yield strength (Rp0.2) is at least 200 N/mm.sup.2, in particular at least 280 N/mm.sup.2.

(18) The light metal cast component can be configured in the form of a safety- or structural component for a motor vehicle, in particular as a vehicle wheel, respectively a vehicle rim. The method is especially suitable for producing safety- or structural components with a weight of at least 500 grams, in particular at least 3000 grams, without being limited thereto.

(19) An advantage of the described method is, that a component produced therewith has an especially fine grained structure nearly free of cavities. This leads altogether to an increased strength of the component. Thus, tests have shown, that the tensile strength (Rm) of a component produced according to the invention was increased compared to components produced in the common manner by more than 20%. The yield strength (Rp0.2) was even increased by more than 40%. Thus, overall, a component with higher strength can be produced with the same material consumption, or a lighter component can be produced with a lower material consumption.