EP4124668A1

EP4124668A1 - Cast alloy

Info

Publication number: EP4124668A1
Application number: EP21188809.4A
Authority: EP
Inventors: Stuart Dr.-Ing. Wiesner
Original assignee: Aluminium Rheinfelden Alloys GmbH
Current assignee: Aluminium Rheinfelden Alloys GmbH
Priority date: 2021-07-30
Filing date: 2021-07-30
Publication date: 2023-02-01
Also published as: US20230043878A1; KR20230019055A; CN115679158A; JP2023021070A

Abstract

The casting alloy according to the invention is based on aluminum-iron-nickel and consists of the following elements:

Description

FIELD OF THE INVENTION

The present invention relates to a casting alloy based on aluminum, iron and nickel with the addition of boron. Further the invention relates to the use of the alloy for high pressure die casting or gravity die casting. The alloy according to the invention is used for the production of rotors and stators for electric motors and heat exchangers, cooling and heating elements in the electronics sector or in vehicle construction.

BACKGROUND OF THE INVENTION

The use of Rotor-Aluminum (e.g. in qualities of 99.7% Al) in high pressure die casting has been known for a long time. Typically, a metallic body is placed in the die-casting mold and the aluminum rotor or stator is cast into this metallic body. In this way, difficulties that arise when casting such an alloy are avoided, above all the high tendency to stick to steel, which otherwise leads to rapid wear of the casting mold. Other typical disadvantages are high shrinkage, very high casting temperatures, poor mechanical machinability and particularly low strength (e.g. Rp0.2 of 20-40 MPa for the alloy Al99.7E).
For heat exchangers produced via high pressure die casting, alloys of the AlSi type are often used, e.g. the alloy AlSi9Sr (Castasil-21). Compared to Rotor-Aluminum, these alloy type is better castable. The tendency to stick to the casting mold, shrinkage, mold fillability and casting temperatures are more advantageous. However, the lower electric and thermal conductivity compared to Rotor-Aluminum are disadvantageous. With the help of a heat treatment, an electric conductivity of up to 28 MS / m can be achieved, the thermal conductivity is then 190 (W / K m). The yield strength of such an alloy (Rp0.2) is 80-100 MPa.
The applicant's patent EP3 235 916 B1 discloses an alloy of the AlMg4Fe2 (Castaduct-42) type, which is preferably used for crash-relevant structural components in automobile construction. The metallurgical basis of this alloy is the Al3Fe eutectic. The electric conductivity is 16-17 MS / m.
In the prior art there are aluminum alloys with high conductivity and low strength or there exist alloys with high strength and low conductivity.

SUMMARY OF THE INVENTION

One object of the invention is, that at least one disadvantage of the alloys known from the prior art is solved.
It is an object of the alloy according to the invention that the alloy has an electric conductivity, preferably of least 23 MS / m, more preferred over 30 MS / m. At the same time the alloy should provide a high strength, preferably a Rp0.2 of at least 74 MPa, more preferred over 95 MPa.
Further object is providing an alloy composition with a good castability.
Further object is, to provide an alloy composition that does not require heat treatment, while still maintaining the desired strength and conductivity.
Further object is providing an alloy composition which is suitable for mechanical machining, joining or which is corrosion resistant.

At least one of the objects, mentioned above is solved by an alloy consisting of:
The alloy according to the inventions consists of:

Iron (Fe)	0,8 to3,0 % by weight
Nickel (Ni)	0,1 to 3,5 % by weight
Boron (B)	40 to 300 ppm
Zinc (Zn)	0 - 5 % by weight
Tin (Sn)	0 - 5 % by weight
Copper (Cu)	0 - 3 % by weight
Manganese (Mn)	0 - 1 % by weight
Magnesium (Mg)	0 - 0,6 % by weight
Phosphorus (P)	0- 500 ppm
Silicon (Si)	0 - 0.4%

and 0- 0.8% by weight of an element or a group of elements selected from chromium (Cr), lithium (Li), vanadium (V), titanium (Ti), calcium(Ca), molybdenum (Mo) and zirconium (Zr) and the remainder aluminum and inevitable impurities.

In a preferred embodiment of the iron content lies between 1.0-2.5% by weight.
In a further preferred embodiment of the iron content lies between 1.2-2.0% by weight.
In a further preferred embodiment of the iron content lies between 1.4-1.9% by weight.
In a further preferred embodiment the nickel content lies between 0.3-3.0% by weight.
In a further preferred embodiment of the nickel content lies between 0.8-2.0% by weight.
In a further preferred embodiment the boron content lies between of 70-200 ppm.
In a further preferred embodiment the boron content lies between 100-1 60 ppm.
In a further preferred embodiment the boron content lies between 80-150 ppm.
In a further preferred embodiment of the silicon content lies between 0- 0.3% by weight silicon.
In a further preferred embodiment of the copper content lies between 0.2-3% by weight.
In a further preferred embodiment of the copper content lies between 1.0-3.0% .
In a further preferred embodiment of the zinc content lies 0-3% by weight zinc.
In a further preferred embodiment the zinc content lies between 0.5% to 4.0 by weight of zinc.
In a further preferred embodiment of the magnesium content lies between 0-0.4% by weight of magnesium.
In a further preferred embodiment the magnesium content lies between of 0.2-0.4%.
In a further preferred embodiment the manganese content lies between 0-0.1% by weight.
In a further preferred embodiment of the tin content lies between 0- 2.5% by weight.
In a further preferred embodiment of the tin content lies between 0.2-2.5% by weight.
According a further aspect of the invention the cast alloy is used for high pressure die-casting, preferably for high pressure die casting of rotors and stators for electric motors and heat exchangers, cooling and heating elements in the electronics sector or in vehicle construction.
A high pressure die casted product, preferably rotors and stators for electric motors and heat exchangers, cooling and heating elements in the electronics sector or in vehicle construction are manufactured from a cast alloy according to the invention.
The castability of the alloy according to the invention, is achieved by adding the alloying elements iron and nickel, whereby eutectic phases are formed (eutectic phases improve the castability of an alloy). In particular, an Al9FeNi phase should be achieved which is, according to the literature, created in the ideal ternary system with a composition of 1.75 wt% Fe and 1.25 wt% Ni. In the case of alloy variants, an Al3Fe or Al3Ni phase, may also exist. The Al3Ni phase occurs with a high Ni and at the same time a low Fe content.
According to the invention the Fe content should be high and promote the formation of Al9FeNi together with a smaller amount of Al3Fe eutectic. In this way the tendency of the alloy to stick is reduced and the castability is improved.
All three phases Al9FeNi, Al3Fe and Al3Ni show very fine, long fibers in the micrograph and have a similar eutectic temperature (640, 650 and 655 ° C). As a result, they are created almost at the same time and in almost the same place in the casting process, which can lead to a mixing of these phases. Industrially produced die-cast parts also show numerous structural defects. As a result, these three phases (Al9FeNi, Al3Fe and Al3Ni) are often difficult to distinguish in the micrograph.
As long as no further element is added, the alloy according to the invention hardly reacts to heat treatments. Heat treatment can have a positive effect on electric conductivity and thermal conductivity. The metallurgical background is mostly an agglomeration of additional elements and a coarsening of the phases, which leads to a better conductivity of the Alpha-AI.
It is possible to increase the strength of the alloy by adding further alloy elements.
Basically a solid solution strengthening of the alpha-AI-phase should be achieved. In general, however, such solid solution strengthening usually leads to a reduction in conductivity, which is why only certain elements are even considered.
The Si content should not exceed 0.4% in order to ensure Si-free eutectics. Up to this level, only an enrichment in the alpha-AI phase is to be expected, which can slightly increase the strength.
The addition of boron of around 40-300 ppm leads to a slight increase in conductivity. The metallurgical background is the formation of borides, which can reduce the negative effects of impurities. On one hand such borides can be put out during a degassing and the other hand they lead to an agglomeration of impurities and thus lead to higher conductivity (electric and thermal conductivity).
An element for increasing strength is Mg. It does not form phases with Fe, has a high solubility in Alpha-AI and however, has a negative effect on conductivity (electric and thermal conductivity). In addition, MgNi-containing phases can be formed, which interfere with the formation of an Al9FeNi phase. The alloy according to the invention should therefore either be Mg-free or contain only a small proportion of Mg, preferably maximum 0.6%.
If Si is present in the alloy, a Mg2Si phase (or one of its metastable variants) is formed, which increases strength. Further a heat treatment becomes possible.
It is known that, Zn increases the strength of the alloy according to the invention and its negative effect on conductivity (electric and thermal) is limited. Without the addition of Mg, however, no significant increase in strength could be achieved. If both Mg and Zn are added, the material hardens and the strength increases.
Another element in aluminum, which increase strength is the element Cu. Its negative effect on conductivity is less than that of Mg. However, a significant increase in strength could only be achieved with Cu by adding a small amount of Mg.
Further elements, which may have a strength-increasing effect are Sn, Mn, Cr, Li, V, Ti, Ca, Ga, Bi, Mo and Zr.

Working and Comparative Examples

In the following tables, different compositions of the alloy according to the invention and three prior art alloys, AlMg4Fe2, AlSi9Sr and Rotor Al99.7 are shown The data are in% by weight (or ppm). Values for Zn of 0.01 or 0.02 % or even below can be considered as composition free of Zn. Values for Si of 0.03 or 0.04% or even belwo can be considered as a composition fee of Si.
For the high pressure die-cast samples (C to E, I and J, P, R to T, V to Z), the mechanical parameters (Rm, Rp0.2, A5) and the electric conductivity were measured on high pressure die casted plates with a thickness of 3 mm plates The average value from at least 6 tensile tests or 5 electric conductivity measurements is shown in table 2.
As comparative samples, Variants I and J both alloys, known from the prior art named Castaduct-42 and Castasil-21 are shown. Variant T is a further known alloy named, Rotors-Al99.7.
Variant K to O refer to gravity die casting (GDC). The measuring results with respect to mechanical parameters UTS (ultimate tensile strength), YS (yield strength) and E (A5 elongation at break) have been measured by using a Diez molds with a diameter of 16 mm. The electric conductivity was measured on separately cast and machined samples. The average value from at least 5 tensile tests or 2 conductivity measurements is shown table 3.

Results achieved

High Pressure Die Casting (HPC), Status F

Gravity Die Casting (GDC), Status F

Table 3

	UTS [MPa]	YS [MPa]	E [%]	Electric Conductivity [MS/m]
Variant K	100	55	26,0	33,2
Variant L	110	57	21,5	31,7
Variant M	129	63	18,4	32,4
Variant N	129	62	21,9	30,8
Variant O	169	72	7,8	25,4

Claims

Cast alloy based on aluminum-iron-nickel, consisting of: iron 0,8 to 3,0 % by weight nickel 0,1 to 3,5 % by weight boron 40 to 300 ppm zinc 0 - 5 % by weight tin 0 - 5 % by weight copper 0 - 3 % by weight manganese 0 - 1 % by weight magnesium 0 - 0,6 % by weight phosphorus 0- 500 ppm Silicon 0-0.4%

and 0- 0.8% by weight of an element or a group of elements selected from chromium, lithium, vanadium, titanium, calcium, molybdenum and zirconium and the remainder aluminum and inevitable impurities.
Cast alloy according to claim 1, characterized by 1.0-2.5% by weight iron.
Cast alloy according to one of the preceding claims, characterized by 1.2-2.0% by weight of iron.
Cast alloy according to one of the preceding claims, characterized by 1.4-1.9% by weight of iron.
Cast alloy according to one of the preceding claims, characterized by 0.3-3.0% by weight of nickel.
Cast alloy according to one of the preceding claims, characterized by 0.8-2.0% by weight of nickel.
Cast alloy according to one of the preceding claims, characterized by 70 - 200 ppm boron.
Cast alloy according to one of the preceding claims, characterized by 100 - 160 boron.
Cast alloy according to one of the preceding claims, characterized by 0- 0.3% by weight silicon.
Cast alloy according to one of the preceding claims, characterized by 0.2-3% by weight of copper, for example 1.0 - 3.0% copper.
Cast alloy according to one of the preceding claims, characterized by 0-3% by weight zinc, for example 0.5% to 4.0 by weight of zinc..
Cast alloy according to one of the preceding claims, characterized by 0-0.4% by weight of magnesium, for example 0.2 -0.4% by weight of magnesium.
Cast alloy according to one of the preceding claims, characterized by 0-0.1 % by weight of manganese.
Cast alloy according to one of the preceding claims, characterized by a 0-2.5% by weight of tin, for example 0.2-2.5% by weight of tin.
Use of a cast alloy according to any one of the preceding claims for high pressure die-casting, preferably for high pressure die casting of rotors and stators for electric motors and heat exchangers, cooling and heating elements in the electronics sector or in vehicle construction.
A high pressure die casted product, preferably rotors and stators for electric motors and heat exchangers, cooling and heating elements in the electronics sector or in vehicle construction, manufactured from a cast alloy according to one of the preceding claims 1 to 14.