Patent Application
20250122599
This application claims priority to European Patent Application No. 23203621.0 filed Oct. 13, 2023, the disclosure of which is hereby incorporated by reference in its entirety.
The present invention relates to a die casting alloy based on aluminium, iron, magnesium and silicon.
The aluminium casting industry plays a crucial role in various applications, from the automotive industry to electronic devices. In recent years, the demand for environmentally friendly and cost-efficient casting alloys, especially die casting alloys, has increased. One of the challenges is to enable the use of low-grade aluminium scrap resp. secondary aluminium, which is obtained from aluminium scrap of various origins, in order to reduce waste and use resources more efficiently.
According to the state of the art, wheel scrap is used for the production of AlSi9MnMg alloys with a high recycled content, especially because of the low iron content of wheel scrap. Other types of scrap with a higher iron content or other impurities are generally not usable.
A die casting alloy based on aluminium, iron and magnesium is known from EP 3235916 B1, which is used in particular in the field of vehicle structural components.
In some embodiments, there is provided an alloy composition which has a high content of secondary aluminium without having to compromise too much on properties such as strength, ductility, corrosion resistance and/or processability.
In some embodiments, the die casting alloy consists of the following elements:
0-0.8% of an element or element group selected from the group consisting of chromium (Cr), lead (Pb), lithium (Li), vanadium (V), titanium (Ti), phosphorus (P), molybdenum (Mo), zirconium (Zr), gallium (Ga), and the rest aluminium and unavoidable impurities, wherein the respective wt. % are based upon the total weight of the alloy.
In some embodiments, the die casting alloy has a silicon content of 0.4-0.9 wt. % silicon.
In some embodiments, the die casting alloy has a silicon content of 0.5-0.8 wt. % silicon.
In some embodiments, the die casting alloy has an iron content of 1.0-1.7 wt. % iron.
In some embodiments, the die casting alloy has an iron content of 1.1-1.5 wt. % iron.
In some embodiments, the die casting alloy has a magnesium content of 2.5-6.0 wt. % magnesium.
In some embodiments, the die casting alloy has a magnesium content of 3.5-5.0 wt. % magnesium.
In some embodiments, the die casting alloy has a calcium content of 0.08-1.5 wt. % calcium, or 0.1-1.0 wt. % calcium, or 0.1-0.5 wt. % calcium.
In some embodiments, the die casting alloy has a vanadium content of 0.01-0.05 wt. % vanadium.
In some embodiments, the die casting alloy has a zinc content of 0-1.0 wt. % zinc.
In some embodiments, the die casting alloy has a zinc content of 0.1-0.5 wt. % zinc.
In some embodiments, the die casting alloy has a manganese content of 0.1-1 wt. % manganese.
In some embodiments, the die casting alloy has a copper content of maximum 2.0 wt. %, or maximum 0.1 wt. % copper.
In some embodiments, the die casting alloy has a nickel content of maximum 0.1 wt. % nickel.
Unless the context clearly indicates otherwise, the singular forms of the terms used in the present disclosure may be interpreted as including the plural forms. As used herein, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly states otherwise.
For the purposes of this disclosure, unless otherwise indicated, all numbers expressing quantities of elements, components, ingredients, reaction conditions, dimensions, physical characteristics, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following disclosure are approximations that may vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include any and all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, all subranges beginning with a minimum value equal to or greater than 1 and ending with a maximum value equal to or less than 10, and all subranges in between, e.g., 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.
The alloys disclosed herein are die casting alloys or, in other words, the alloy compositions are used for die casting, in some embodiments for die casting of structural components for automotive manufacture. The term die casting alloys comprises alloy compositions which are processed into a die cast component by means of a die casting process. Die casting alloys must be clearly distinguished from wrought alloys. Die casting alloys are alloy compositions that are further processed in one step by means of a die casting process into the direct end product, the die cast component. The alloy composition can be introduced into the casting mould as a liquid melt or as a partially solidified melt.
If necessary, in some embodiments this product is subsequently heat-treated or such a heat treatment is to be deliberately avoided. The die-cast product then already exhibits the desired material properties in the casting state “state F”. Non-limiting examples of products are die-cast structural components of cars.
The following die casting processes are non-limiting examples of die casting processes: HPDC (High Pressure Die Casting), Vacuum Die Casting, Rheo Die Casting (so-called Reocasting), and/or Vacural Die Casting.
In die casting processes in general, the molten alloy is shot into a mould at high speed, the so-called gate speed, for example of 20-100 m/s and solidifies there at a holding pressure of about 500-1000 bar. There are process variants in which the gate speed is only 1-10 m/s. In the case of aluminium, only cold chamber systems have been used up to now. For larger casting weights, these are usually arranged horizontally, in some cases vertically or at an oblique angle.
The alloys disclosed herein are alloy(s) in which the aluminium comes from a secondary source, for example aluminium scrap, such as AlMg profiles, lithographic material and/or can scrap. Can scrap may comprise so-called UBC material (Used Beverage Cans) according to DIN EN 13920-10.
The alloys disclosed herein can be used to prepare die-cast structural components of cars such as for example suspension strut domes, side members or even larger components such as integral supports for the front or rear of the car.
Aluminium alloys used for structural components in automobiles generally have the following material properties:
Good castability, material properties of Rm=200-270 MPa, Rp0.2=100-180 MPa, A=7-15%, good suitability for joining (riveting, welding, adhesive bonding, etc.) and corresponding corrosion resistance, where Rm is tensile strength, Rp0.2 is yield point, and A is elongation determined with a tensile test, e.g., in accordance with ISO 6892 series of standards.
The end products prepared from the alloys disclosed herein can show a slightly increased strength compared to conventional casting alloys, for example AlSi alloys, which are also used for structural components in automotive manufacture. In addition, the alloys disclosed herein already have mechanical properties in the as-cast state (state F) that make it possible to dispense with heat treatment, which reduces manufacturing costs and energy consumption.
Foundries demand good castability of the alloy. In general, this is understood to mean that the alloy has good flowability when cast in die casting, good mould filling capacity, good solidification behaviour (i.e., for example low shrinkage and/or no tendency to crack) and/or favourable behaviour when ejected from the mould (i.e., for example low tendency to stick). In practical casting tests, this could also be shown for the alloy compositions disclosed herein.
The basis for the alloy compositions disclosed herein is the AlFe eutectic, mostly in the form Al14Fe3, which ensures the castability of the alloy. It reduces the shrinkage of the aluminium in the die-casting mould and/or considerably reduces its tendency to stick in the mould (usually a steel mould). In some embodiments, the high iron content of the alloys disclosed herein leads, in addition to the formation of an Al14Fe3 eutectic, to a low chemical attack against the mould steel. The consequences are a low, necessary use of release agents, a low adhesive bonding of the component on the mould during ejection and/or a low mould wear. The formation of the eutectic causes solidification at a constant temperature. These properties of an alloy are described among experts as good castability. In addition, the alloys have no tendency to hot cracking and a high formability in the temperature range of 250-500° C. Both reduce the tendency to cold cracking during solidification, which also has a positive influence on castability.
Magnesium (Mg) serves as a solid solution strengthener to increase strength. Silicon (Si) together with magnesium (Mg) also increases the strength by forming Mg2Si. It was found that despite the presence of silicon (Si) no embrittlement occurs, and/or no brittle AlFeSi phases are formed.
Calcium (Ca) reduces the oxidation tendency of the melt. By adding vandium (V) in addition to calcium, the oxidation tendency of the melt could be reduced even further. The reduction of the oxidation tendency of the melt also reduces the magnesium melting loss and thus the magnesium loss during the production of the alloy compositions disclosed herein.
Further elements are not absolutely necessary, but can be tolerated to a greater extent than is the case with other ductile die casting alloys, such as conventional AlSi alloys, which are generally used as standard in structural components in automotive manufacture. These comprise, for example, the elements Mn, Cr, Cu and/or Zn.
Zinc leads to a slight improvement in castability in terms of mould filling capacity if between 0.2-0.5% Zn is present. A higher content (3-4%) increases the strength of the alloy considerably, but also the susceptibility to corrosion.
The effect of impurities on the corrosion tendency of the alloy according to the invention turned out to be less than that of conventional AlSi alloys. The compositions are listed in Table 4. Alloy named M1 is an example for a conventional AlSi alloy in comparison to the compositions A1, J2 according to the present disclosure. A PH neutral salt spray test (e.g., in accordance with ASTM B117) was carried out over 720 h at normal conditions (about 25° C.) on die pressure cast, non-surface treated, 3×60×60 mm plates. Table 1 shows the weight losses before and after the test.
As expected, the corrosion resistance of alloy A1 was higher than that of alloy J2. J2 contains relatively high contents of Mn, Cu and Zn compared to alloy A1.
Surprisingly, it was found that compared to a conventional AlSi alloy (see alloy composition M1), the corrosion resistance of the alloy according to the invention is better than that of the AlSi alloy, despite similar contents of Mn, Cu and Zn (see Table 4, M1, J2). In the alloy according to the present disclosure, there is an insular structure of brittle, corrosion-prone intermetallic phases caused by impurities (for example, the elements Fe, Mn, Cr and Cu form such phases). The aluminium phase between these phases prevents a too strong reduction of ductility and a too fast progress of the corrosion attack.
In the alloy M1 (state F), intermetallic phases contaminated by impurities are often found within an AlSi eutectic connected in a net-like manner through the entire material. Such a structure is more brittle and clearly more susceptible to corrosion.
The following table shows a composition of a can scrap used for an example of an alloy according to the present disclosure (so-called UBC material, see line “Recycled material”). An example of the composition according to the invention is listed in the line “Alloy composition J1”. Depending on the composition of the recycled material, it is necessary to adapt the addition of the required alloying elements to the impurities found (see line “Addition of elements”). In this example, the addition of just under 3.2% Mg already leads to a yield tensile strength of over 160 MPa. Without the content of 0.23% Cu and 0.80% Mn, among others, in the starting alloy, this strength would not have been achieved; the addition of a larger quantity of Mg would have been necessary.
For the composition according to present disclosure listed in Table 2, the melting interval (solidus-liquidus) was calculated to be 571-660° C. with the aid of a phase simulation, and the heat of fusion was calculated to be 485 KJ/kg. Despite the high content of impurities, these values indicate good castability in die casting. The heat of fusion is comparable to that of conventional AlSi alloys, which are considered by experts to have good castability. The heat of fusion of rotor alloys rated as poor castability is, as an example, approx. 80 KJ/kg lower.
Table 3 discloses a further embodiment of an alloy composition (V2) according to the present disclosure. As an example, the effect of addition of Ca and V and the magnesium burn-off will be explained here. Table 3A shows the composition of the alloy V2 and comparative example V1 (without Ca) at the start of the experiment and Table 3B the composition 7 days later.
Table 3A, 3B shows the effect on magnesium burn-off. Already an addition of 0.082 Ca and 0.023 V led to a no longer measurable loss of magnesium. In addition, a significantly lower oxide layer on the melt was visually determined.
It was found that Ca in combination with V (see V2) reduced the loss of Mg.
The addition of V without Ca did not improve the oxidation tendency, i.e., the thickness of the oxide layer was not reduced. After the end of the test, a measurable loss of Mg resulted (see V1).
Table 4 compares compositions of examples of alloys according to the invention. The figures are in wt. %.
For the cast samples in Tables 4, the mechanical properties (Rm, Rp0.2, A5) were measured on die-casted 3 mm plates. The mean value from at least 6 tensile tests is shown in each case.
The results of the tests in the as-cast state (state F) yielded remarkable mechanical properties despite a high recycling rate and high contamination with different elements (see Table 5).
The cast samples from test B1 and B3 were subjected to a T5 heat treatment (1 h, 200° C.). Table 6 below shows the results:
The results of the tests with a heat treatment T5 (1 h 200° C.) show a hardly changed tensile strength, a slight increase of the yield tensile strength by 10-13 MPa and a decrease of the elongation at fracture by 0.5-1.5% compared to the state F. The alloy according to the invention can thus be used without heat treatment for structural components for automotive manufacture.
The recycling content indicates the approximate secondary aluminium content obtained from consumer scrap, so-called post consumer recycling (PCR). Industrial waste (pre-consumer recycling) was not used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23203621.0 | Oct 2023 | EP | regional |
