A device for and a method for producing a body of a quasicrystalline high-strength aluminium alloy

Abstract

A device for producing a body of a quasicrystalline high-strength aluminium alloy, said device comprising a holding furnace (1), a die (2) that defines a die cavity (3), a shot sleeve (4), connected in one end to the die (2) and defining a first channel (5) that communicates with the die cavity (3), a piston (6), which is arranged inside said first channel (5) and arranged to force a liquid metal through the first channel (5) into the die cavity (3), a dosing funnel (7) extending from the holding furnace (1) to the shot sleeve (4) and defining a second channel (8) that communicates with the holding furnace (1) in a first end and with the first channel (5) in a second end. There are first tempering means (9) for tempering the die (2) such that a liquid aluminium alloy introduced into the die cavity (3) and filling the die cavity (3) is cooled with a cooling rate within a predetermined range down to a predetermined temperature range.

Description

TECHNICAL FIELD

[0001] The present invention relates to a device for producing a body of a quasicrystalline high-strength aluminium alloy, said device comprising a holding furnace, a die that defines a die cavity, a shot sleeve, connected in one end to the die and defining a first channel that communicates with the die cavity, a piston, which is arranged inside said first channel and arranged to force a liquid metal through the first channel into the die cavity, a dosing funnel extending from the holding furnace to the shot sleeve and defining a second channel that communicates with the holding furnace connected in a first end and with the first channel in a second end.

[0002] The invention also relates to a method of producing a body of a quasicrystalline high-strength aluminium alloy by means of a device according to the invention.BACKGROUND

[0003] Traditional die casting, also recognized as high-pressure die casting (HPDC), stands as a metal casting method with a history spanning over a century. This process usually entails the compelling or injecting of molten metal at elevated pressures into a die cavity. The die cavity is shaped through machining two or more die portions to match the desired casting form. Depending on the type of metal being utilized, one may employ either a hot or cold chamber die casting machine, alongside squeeze casting methods.

[0004] Aluminium HPDC is a thermal process which means that the entire process is dependent on the temperature and matter state of aluminium. To instantiate the process, a set of different mechanical and electro-mechanical systems needs to be integrated into a coherent production solution.

[0005] The basic physics principle is that to change the shape of the hardened aluminium alloy in the form of ingots through casting, sufficient energy in the form of heat must be put inside the solid-state aluminium, to change the state of its matter into liquid.

[0006] This means that the temperature of the aluminium atoms needs to at reach at least, but in practice exceed the liquidus temperature level.

[0007] However, due to practical reasons such as heat losses and the improvement of the aluminium castability due to reduced viscosity of the melt, the temperature of the molten material needs to exceed the liquidus state by a certain safety margin. Thus, one aims to cast standard aluminium alloys at around 630 °C + / - 10 °C in the shot-sleeve (Td). This temperature varies depending on the process specifics, alloy specifics and uniqueness of the production setup - its instantiation.

[0008] Once the material reaches the desired temperature above its liquidus state in the melting furnace, it undergoes several steps before it is high-pressure cast in the HPDC die. Every single step needs to be monitored and analysed in terms of its effect on the temperature state of the melt to reach the desired material characteristics and part quality.

[0009] The material preparation starts in a melting furnace into which the ingots are put. Once the aluminium alloy exceeds its liquidus temperature and is fully molten, it is poured inside the transport pot and transferred to the degassing station. At the degassing station, the material is mixed while cleaning agents (e.g. salts) and nitrogen or argon are injected inside the melt. This combination creates a chemical reaction with impurities and hydrogen that may be inside the melt. The result of the chemical reaction is the formation of slag on top of the molten aluminium. The slag is removed, for example with a ladle. The aluminium is now cleaned and prepared for casting.

[0010] The prepared molten aluminium is now ready to be dosed towards the HPDC die. The dosing process starts by pouring the material on to the dosing funnel by reaching a pressure difference inside the holding furnace, by using a vacuum dosing unit or by using a ladle. The material then travels down the dosing funnel towards the shot-sleeve. It enters the shot-sleeve via a top inlet hole. Once the shot-sleeve is filled between 40 - 50%, the pre-lubricated piston pushes (shoots) the material inside the HPDC die in 3 separate stages.

[0011] Once the material is shot in its liquid state inside the HPDC die, the shape-change process takes place. The molten material due to high cooling rates quickly solidifies inside the HPDC die. Once solidified, the casting is ejected from the die and the cavity surface is sprayed with a release agent that prevents the aluminium from sticking to the die's surface. Despite not being the release agent's main function, the die is during spraying also cooled down.

[0012] For the cast part quality, it is crucial to reach the correct surface temperature. For standard alloys, we aim to reach surface temperatures in the range of 160 to 220 °C, depending on cast component specifics. The cavity surface temperature is affected by several factors, such as: Thickness and material volume of the shot, Die's tempering system layout, Set tempering temperature, Spraying time with the release agent, HPDC process settings, such as the combination of different cycle lengths.

[0013] To reach the desired surface temperature, one first needs to create a thermal inspection by using an IR camera and / or a contact surface measuring method. Such inspections show the hot and cold spots of the HPDC die and what temperatures are reached at the cavity surface level. To reach the desired temperature, the before mentioned process settings need to be optimized.

[0014] If the surface temperature is too high, it can lead to: Faster die thermal cracking and thereby shorter HPDC die life, Larger shrinkage porosities inside the cast part, Leidenfrost effect of the release agent on the cavity surface, Leakage of oil inside the thermal system at locations of sealed connections, Problems with moving parts of the die due to excessive thermal expansion of different die components.

[0015] However, on the other hand, if the cavity surface is too cold, it can lead to: Increase of melt viscosity and thereby resulting filling (quality) problems, such as cold shuts and poor weld lines, Delamination of cast part surface, Black spots on cast part and air porosity due to excessive remains of release agent.

[0016] It is crucial to reach the correct surface temperature to meet the part quality requirements and material's mechanical characteristics. Once the cavity surface temperature is stable (repeatable in production cycle phases), the HPDC die is in a thermally stable state.

[0017] In connection to the high pressure die casting of quasicrystalline high-strength aluminium alloys, temperature control becomes even more important than for standard alloys.THE OBJECT OF THE INVENTION

[0018] It is an object of the present invention to present a device for and a method of producing a body of a QC (quasicrystalline) high-strength aluminium alloy that enables reaching adequate material temperature states and resulting cooling rates, which is a prerequisite for reaching the desired mechanical properties of the novel QC alloy.SUMMARY

[0019] The object of the invention is achieved by means of a device for producing a body of a quasicrystalline high-strength aluminium alloy, said device comprising a holding furnace, a die that defines a die cavity, a shot sleeve, connected in one end to the die and defining a first channel that communicates with the die cavity, a piston, which is arranged inside said first channel and arranged to force a liquid metal through the first channel into the die cavity, a dosing funnel extending from the holding furnace to the shot sleeve and defining a second channel that communicates with the holding furnace connected in a first end and with the first channel in a second end, said device being characterised in that it comprises first tempering means for tempering the die such that a liquid aluminium alloy introduced into the die cavity and filling the die cavity is cooled with a cooling rate within a predetermined range down to a predetermined temperature range.

[0020] According to some embodiments the device further comprises second tempering means for tempering the shot sleeve.

[0021] According to some embodiments, the die comprises a steel having a thermal conductivity of at least 30 W / mK, preferably at least 40 W / mK, or even more preferably at least 50 W / mK.

[0022] According to some embodiments, the dosing funnel has a thermal conductivity lower than 1 W / mK.

[0023] According to some embodiments, the piston has a thermal conductivity lower than 25 W / mK.

[0024] According to some embodiments, the dosing funnel comprises an inner coating on an inner wall defining said second channel, wherein said coating has lower tendency to stick to an aluminium alloy than has the material of said inner wall. According to some embodiments, the coating comprises boron nitride. According to some embodiments the inner wall of the dosing funnel comprises a ceramic as its main constituent.

[0025] According to some embodiments, the device comprises third tempering means for tempering the dosing funnel. According to some embodiments, the tempering means comprises an electrical heater.

[0026] According to some embodiments, the device further comprises temperature measuring means for measuring the temperature of an aluminium alloy introduced into the die cavity, a control unit for controlling the first tempering means on basis of input from the temperature measuring means.

[0027] The object of the invention is also achieved by means of a method of producing a body of a quasicrystalline high-strength aluminium alloy by means of a device according to the invention, characterised in that it comprises tempering the die by means of the first tempering means such that the cooling rate of the aluminium alloy is in the range of 100-1000 K / s.

[0028] According to some embodiments, the method comprises tempering the die by means of the first tempering means such that the cooling rate of the aluminium alloy is in the range of 500-1000 K / s.

[0029] According to some embodiments the tempering of the die comprises heating or cooling the die such that an inner surface thereof that delimits the die cavity has a temperature of at least 200 °C, preferably at least 250 °C.

[0030] According to some embodiments, the method comprises the steps of conducting molten aluminium alloy from the holding furnace to the shot sleeve via the dosing funnel and controlling the temperature of the shot sleeve by means of the second tempering means such a that the temperature of the molten aluminium alloy in the shot sleeve is more than 20 °C above the liquidus temperature of the aluminium alloy.

[0031] According to some embodiments, the tempering of the shot sleeve comprises heating the shot sleeve such that an inner surface thereof that delimits the first channel has temperature of at least 200 °C, preferably at least 250 °C.

[0032] According to some embodiments, the step of heating the dosing funnel to a temperature of at least 700 °C, preferably at least 800 °C, before introduction of molten aluminium into the dosing funnel from the holding furnace.

[0033] According to some embodiments, the method comprises the steps of providing a molten aluminium alloy in the holding furnace and filling the die cavity with molten aluminium from the holding furnace by conducting the molten aluminium alloy from the holding furnace to the die cavity via the dosing funnel and the shot sleeve, wherein the aluminium alloy has the following composition: Balance Al, Mn a Si n X c Z e TM d , where X is one or more elements selected from the group consisting of Cu, Ni, Zn, Fe and Co; Z is one or more elements selected from the group consisting of Li, Ca, Sr, Ga, REE, mischmetals, Ce, Bi, Sn, Sb and Mg; TM is one or more elements selected from the group consisting of Cr, Ti, W, Mo, Zr and V; wherein a, n, c, e and d satisfy, by weight percent: 3≤a≤10, 0.1≤n≤3, 0.1≤c≤10, 0.1≤e≤8, and 0.1≤d≤3, and wherein 5≤a+c+e≤20; the balance being Al and inevitable impurities up to 0.5 wt.%, and comprising a metastable quasicrystal phase that is dispersed in a matrix composed of aluminium.BRIEF DESCRIPTION OF THE DRAWINGS

[0034] An embodiment of the invention will now be disclosed more in detail reference to the annexed drawing, on which Fig. 1 is a cross section of a device for producing a body of a quasicrystalline high-strength aluminium alloy according to the present invention. DETAILED DESCRIPTION

[0035] Fig. 1 shows an embodiment of the device of the invention, said device comprising comprising a holding furnace 1, a die 2 that defines a die cavity 3. The die 2 comprises two parts 2a and 2b that are movable in relation to each other in order to enable ejection of a moulded body formed in the die cavity 3. The device also comprises a shot sleeve 4, connected in one end to the die 2 and defining a first channel 5 that communicates with the die cavity 3.

[0036] There is provided a piston 6, which is arranged inside said first channel 5 and arranged to force a liquid metal through the first channel 5 into the die cavity 3. There is also a dosing funnel 7 extending from the holding furnace 1 to the shot sleeve 4 and defining a second channel 8 that communicates with the holding furnace 1 in a first end and with the first channel 5 in a second end.

[0037] The device further comprises first tempering means 9 for tempering the die 2 such that a liquid aluminium alloy introduced into the die cavity 3 and filling the die cavity 3 is cooled with a cooling rate within a predetermined range down to a predetermined temperature range. The first tempering means 9 comprises a fluid source and channels for introducing a tempered fluid into channels (not shown) provided in the die 2. As an alternative, the first tempering means 9 comprises electric resistance elements (not shown) provided in the die 2 and an electric power source connected to said resistance elements.

[0038] There are provided second tempering means 10 for tempering the shot sleeve 4. The second tempering means 9 comprises electric resistance elements (not shown) provided in the shot sleeve 4 and an electric power source connected to said resistance elements.

[0039] The die 2 comprises a tool steel having a thermal conductivity of slightly above 50 W / mK.

[0040] The he dosing funnel 7 comprises a ceramic that has a thermal conductivity lower than 1 W / mK and the piston 6 has a thermal conductivity lower than 10 W / mK.

[0041] The dosing funnel 7 comprises an inner coating on an inner wall defining said second channel 8, wherein said coating has lower tendency to stick to an aluminium alloy than has the material of said inner wall. The device further comprises third tempering means 11 for tempering the dosing funnel 7. The third tempering means 11 comprises electric resistance elements (not shown) provided in the dosing funnel 7 and an electric power source connected to said resistance elements. The device also comprises temperature measuring means 12 for measuring the temperature of an aluminium alloy introduced into the die cavity 3, a control unit 13 for controlling the first tempering means 9 on basis of input from the temperature measuring means 12.

[0042] In addition to the components mentioned hereinabove, the device also comprises components such as an ejector device 14 for ejecting a moulded body formed in the die cavity 3 and for moving the die parts 2a and 2b in relation to each other.

[0043] The invention comprises a method of producing a body of a quasicrystalline high-strength aluminium alloy by means of the device disclosed hereinabove. The method comprises tempering the die 2 by means of the first tempering means 9 such that the cooling rate of the aluminium alloy is in the range of 500-1000 K / s. The tempering of the die 2 comprises heating or cooling the die 2 such that an inner surface thereof that delimits the die cavity 3 has a temperature of at least 200 °C, preferably at least 250 °C. The method also comprises the step of heating the dosing funnel 4 to a temperature of 800 °C, before introduction of molten aluminium into the dosing funnel 4 from the holding furnace 1.

[0044] The method further comprises the steps of conducting molten aluminium alloy from the holding furnace 1 to the shot sleeve 4 via the dosing funnel 7 and controlling the temperature of the shot sleeve 4 by means of the second tempering means 10 such that the temperature of the molten aluminium alloy in the shot sleeve 4 is more than 20 °C above the liquidus temperature of the aluminium alloy.

Claims

1. A device for producing a body of a quasicrystalline high-strength aluminium alloy, said device comprising - a holding furnace (1), - a die (2) that defines a die cavity (3), - a shot sleeve (4), connected in one end to the die (2) and defining a first channel (5) that communicates with the die cavity (3), - a piston (6), which is arranged inside said first channel (5) and arranged to force a liquid metal through the first channel (5) into the die cavity (3), - a dosing funnel (7) extending from the holding furnace (1) to the shot sleeve (4) and defining a second channel (8) that communicates with the holding furnace (1) in a first end and with the first channel (5) in a second end, said device being characterised in that it comprises - first tempering means (9) for tempering the die (2) such that a liquid aluminium alloy introduced into the die cavity (3) and filling the die cavity (3) is cooled with a cooling rate within a predetermined range down to a predetermined temperature range.

2. A device according to claim 1, further comprising second tempering means (10) for tempering the shot sleeve (4).

3. A device according to claim 1 or 2, wherein the die (2) comprises a steel having a thermal conductivity of at least 30 W / mK, preferably at least 40 W / mK, or even more preferably at least 50 W / mK.

4. A device according to any one of claims 1-3, wherein the dosing funnel (7) has a thermal conductivity lower than 1 W / mK.

5. A device according to any one of claims 1-4, wherein the piston (6) has a thermal conductivity lower than 25 W / mK.

6. A device according to any one of claims 1-5, wherein the dosing funnel comprises an inner coating on an inner wall defining said second channel (8), wherein said coating has lower tendency to stick to an aluminium alloy than has the material of said inner wall.

7. A device according to any one of claims 1-6, further comprising third tempering means (11) for tempering the dosing funnel (7).

8. A device according to any one of claims 1-7, further comprising temperature measuring means (12) for measuring the temperature of an aluminium alloy introduced into the die cavity (3), a control unit (13) for controlling the first tempering means (9) on basis of input from the temperature measuring means (12).

9. A method of producing a body of a quasicrystalline high-strength aluminium alloy by means of a device according to any one of claims 1-8, characterised in that it comprises tempering the die (2) by means of the first tempering means (9) such that the cooling rate of the aluminium alloy is in the range of 100-1000 K / s.

10. A method according to claim 9, characterised in that it comprises tempering the die (2) by means of the first tempering means (9) such that the cooling rate of the aluminium alloy is in the range of 500-1000 K / s.

11. A method according to claim 9 or 10, wherein the tempering of the die (2) comprises heating or cooling the die (2) such that an inner surface thereof that delimits the die cavity (3) has a temperature of at least 200 °C, preferably at least 250 °C.

12. A method according to any one of claims 9-11, comprising the steps of conducting molten aluminium alloy from the holding furnace (1) to the shot sleeve (4) via the dosing funnel (7) and controlling the temperature of the shot sleeve (4) by means of the second tempering means (10) such a that the temperature of the molten aluminium alloy in the shot sleeve (4) is more than 20 °C above the liquidus temperature of the aluminium alloy.

13. A method according to claim 12, wherein the tempering of the shot sleeve (4) comprises heating the shot sleeve (4) such that an inner surface thereof that delimits the first channel (5) has temperature of at least 200 °C, preferably at least 250 °C.

14. A method according to any one of claims 9-13, comprising the step of heating the dosing funnel (7) to a temperature of at least 700 °C, preferably at least 800 °C, before introduction of molten aluminium into the dosing funnel (7) from the holding furnace (1).

15. A method according to any one of claims 9-14, comprising the steps of providing a molten aluminium alloy in the holding furnace (1) and filling the die cavity (3) with molten aluminium from the holding furnace (1) by conducting the molten aluminium alloy from the holding furnace (1) to the die cavity (3) via the dosing funnel (7) and the shot sleeve (4), and wherein the aluminium alloy has the following composition: Balance Al, Mna Sin Xc Ze TMd, where X is one or more elements selected from the group consisting of Cu, Ni, Zn, Fe and Co; Z is one or more elements selected from the group consisting of Li, Ca, Sr, Ga, REE, mischmetals, Ce, Bi, Sn, Sb and Mg; TM is one or more elements selected from the group consisting of Cr, Ti, W, Mo, Zr and V; wherein a, n, c, e and d satisfy, by weight percent: 3≤a≤10, 0.1≤n≤3, 0.1≤c≤10, 0.1≤e≤8, and 0.1≤d≤3, and wherein 5≤a+c+e≤20; the balance being Al and inevitable impurities up to 0.5 wt.%, and comprising a metastable quasicrystal phase that is dispersed in a matrix composed of aluminium.

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