CN111004948A

CN111004948A - Method for local vacuum casting of aluminum alloy

Info

Publication number: CN111004948A
Application number: CN201911196955.8A
Authority: CN
Inventors: 刘勇纯; 黄志其; 蔡知之; 刘胤伸; 杨杨; 周京辉; 周思根
Original assignee: Foshan Sanshui Fenglu Aluminium Co Ltd; Guangdong Fenglu Aluminium Co Ltd
Current assignee: Foshan Sanshui Fenglu Aluminium Co Ltd; Guangdong Fenglu Aluminium Co Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2020-04-14
Anticipated expiration: 2039-11-29
Also published as: CN111004948B

Abstract

The invention provides a method for local vacuum casting of aluminum alloy, which comprises the steps of gradually adding raw materials step by step, and combining ultrasonic vibration treatment and mechanical stirring treatment, can remarkably promote the refinement of melt tissues, reduce the dendritic crystal spacing and stabilize the dendritic crystal spacing; the alloy casting is formed under the action of vacuum and pressure formed on the upper part of the crystallizer by a local vacuum-pumping casting method, the grain diameter is smaller, the structure is compact, the hole defects are fewer, the connection among the filter chamber box, the molten aluminum inlet and the crystallizer is always kept in a vacuum state, the situations that the aluminum alloy is segregated in production, generates turbulent flow, is easy to be entrained and oxidized are reduced, the stirring amplitude of the aluminum alloy liquid level is stable, and the slag entrainment phenomenon can be obviously improved; in addition, the aluminum alloy local vacuum-pumping casting method has the advantages of simple equipment and simple operation, the prepared aluminum alloy surface has no obvious defects of cracks, pits, slag inclusion and the like, and the method has the advantages of high tensile strength, good yield strength and high extrudability.

Description

Method for local vacuum casting of aluminum alloy

Technical Field

The invention relates to the field of alloy preparation, in particular to a method for local vacuum casting of aluminum alloy.

Background

The aluminum alloy casting has good mechanical property and corrosion resistance and higher specific strength, but the dendritic crystals of the aluminum alloy casting structure are thicker and can influence the composition segregation of the aluminum alloy and the distribution of phase body micro-holes, thereby influencing the structure and the performance of the aluminum alloy casting, therefore, the obtained aluminum alloy casting with fine grains and compact structure has to control and improve the casting conditions and ensures that the liquidity of liquid metal among dendrites is good. In addition, when an aluminum alloy is cast, gases such as oxygen exist in the aluminum alloy liquid as molecular simple substances or composite gases, and as the temperature of the cast aluminum alloy liquid is lowered to a solidification temperature, the solubility of hydrogen and nitrogen is suddenly reduced, so that the gases dissolved in the alloy liquid are precipitated to form a pinhole characteristic. And turbulence is easily generated in the process of pouring and filling the aluminum alloy liquid, so that the alloy liquid is easy to curl up gas and oxidize, and the defects of pinholes, air holes, impurities and the like are easily generated in the aluminum alloy casting. The casting conditions also affect the surface quality of the casting and the metallurgical quality of the internal structure.

For example, patent No. CN201811360842.2 discloses a method for preparing an aluminum alloy, which comprises adding silicon powder, copper powder, manganese powder, carbon nanotubes, graphene, silicon carbide whiskers, and aluminum powder in balance, dispersing, ball-milling, and sintering to obtain a product with excellent tensile strength. Also, for example, patent No. cn201810955611.x discloses a method for preparing an aluminum alloy by combining strong plastic deformation of metal and heat treatment of metal, and an aluminum alloy with high corrosion resistance is prepared by preparing a rod-shaped material, performing solution treatment, quenching, deforming and the like. Further, as disclosed in PCT/CN2012/076106, an aluminum-silicon-magnesium cast aluminum alloy and a casting process thereof are disclosed, which improve the tensile strength of the aluminum alloy through cooling and aging treatment, but generally consume large energy, and cannot solve the problems of dendrite coarseness and segregation in aluminum alloy casting.

In the field of aluminum alloy preparation, many practical problems to be treated in practical application still have no specific solution.

Disclosure of Invention

The invention provides a method for local vacuum casting of aluminum alloy to solve the problem.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for partial vacuum casting of aluminum alloys, comprising the steps of:

(1) based on the total weight of the aluminum alloy, the aluminum alloy elements comprise 4.2-5.5% of Mg, 0.03-0.35% of Mn, 0.02-0.25% of Cr0.02, 0.35-0.65% of Fe0.07-0.12% of Ti, 0.25-0.45% of Cu, 0.25-0.35% of trace elements and the balance of Al and inevitable other impurities, wherein the content of the inevitable other impurities is less than or equal to 0.05% singly and the total amount is less than or equal to 0.15%;

(2) adding an aluminum ingot into a smelting furnace of the vacuum electromagnetic guiding device, and heating until the aluminum ingot in the smelting furnace is melted into a first melt;

(3) carrying out ultrasonic vibration treatment and mechanical stirring treatment on the first melt, continuously adding the components Mn, Cr, Fe and Ti into the smelting furnace according to the weight percentage, controlling the temperature of the melt in the smelting furnace to be 650-750 ℃ until the alloy is completely molten, and keeping the temperature to be 650-750 ℃, adding Mg 4.18-5.42% until the alloy is uniformly molten to obtain a second melt;

(4) carrying out gas removal and impurity removal treatment on the melt II by blowing and refining with high-purity nitrogen and a refining agent, and slagging off;

(5) keeping the ultrasonic vibration treatment and the mechanical stirring treatment, sequentially adding 0.02-0.08% of Mg, 0.25-0.45% of Cu, 0.35-0.65% of Fe0.25-0.35% and 0.25-0.35% of trace elements in percentage by mass into the smelting furnace, and uniformly melting to obtain a third melt;

(6) the aluminum alloy melt III sequentially flows through the filter chamber box and the aluminum liquid inlet along the central guide pipe and is conveyed to the crystallizer for casting, and the upper part in the crystallizer is provided with a vacuum pumping port, so that the connection among the filter chamber box, the aluminum liquid inlet and the crystallizer is always kept in a vacuum state, and the aluminum alloy melt III flows into the crystallizer under the action of negative pressure.

Optionally, the trace elements are Si, Ni, La and Ce, and the addition ratio of Si, Ni, La and Ce is 1-3:1-7:1-5:0-4 in percentage by mass.

Optionally, the ultrasonic vibration treatment conditions are as follows: the ultrasonic frequency is 40KHz-120KHz, the time is 1-8min, the temperature is 650-750 ℃, and the ultrasonic vibration amplitude is 0.1-2 mm.

Optionally, the conditions of the mechanical stirring treatment are as follows: the mechanical stirring speed is 800-3000r/min, and the mechanical stirring time is 50-120 seconds.

Optionally, a degasser and a porous ceramic filter plate are arranged in the filter chamber box, the rotation speed of a graphite rotor of the degasser is 300-400 rpm, the nitrogen flow is 1-2 cubic meters per hour, and the porous ceramic filter plate has a thickness of 18-22mm, a specification of 15 pores per inch and a porosity of 80-90%.

Optionally, the casting temperature is controlled at 650-780 ℃, the casting speed is 80-110mm/min, and the pressure of the cooling water in the wall of the crystallizer is 0.3-0.5 MPa.

Optionally, one end of the vacuumizing port is connected with a vacuum pump, and during production, the upper part of the aluminum liquid level is vacuumized by a vacuumizing method.

Optionally, the vacuum degree of the vacuum is 10-20 Kpa.

Compared with the prior art, the invention has the beneficial technical effects that:

1. the aluminum alloy local vacuum-pumping casting method forms an alloy casting under the action of vacuum and pressure formed on the upper part of the crystallizer, the grain diameter is smaller, the structure is compact, the hole defects are fewer, the connection among the filter chamber box, the aluminum liquid inlet and the crystallizer is always kept in a vacuum state, the segregation of aluminum alloy in production is reduced, the conditions of turbulence generation, easy air entrainment and oxidation are reduced, the stirring amplitude of the aluminum alloy liquid level is stable, and the slag entrainment phenomenon can be obviously improved.

2. According to the local vacuum casting method for the aluminum alloy, the raw materials are added step by step and are combined with ultrasonic vibration treatment and mechanical stirring treatment, so that the melt generates a cavitation effect and an ultrasonic effect of acoustic flow and a thermal effect, the refinement of the melt structure can be remarkably promoted, the dendritic crystal spacing is reduced and stable, and the method has a positive effect on obtaining a high-quality aluminum alloy section.

3. The aluminum alloy local vacuum-pumping casting method has the advantages of simple equipment and simple operation, the prepared aluminum alloy surface has no obvious defects of cracks, pits, slag inclusion and the like, and the method has the advantages of high tensile strength, good yield strength and high extrudability.

Drawings

The invention will be further understood from the following description in conjunction with the accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. Like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a schematic production view of a part of a method of partial vacuum casting of an aluminum alloy in one embodiment of the present invention;

FIG. 2 is a schematic production view of a part of a method of partial vacuum casting of an aluminum alloy in one embodiment of the present invention;

FIG. 3 is a schematic view showing the microstructure of an aluminum alloy obtained by the method of the present invention in comparative example 1 in which an aluminum alloy is partially vacuum cast;

FIG. 4 is a schematic view showing the microstructure of an aluminum alloy obtained by the method of the present invention in comparative example 2 in which an aluminum alloy is partially vacuum cast;

FIG. 5 is a schematic view showing the microstructure of an aluminum alloy obtained by the method of the present invention in comparative example 3 in which an aluminum alloy is partially vacuum cast;

FIG. 6 is a schematic representation of the microstructure of an aluminum alloy according to one embodiment of the present invention in a method of partial vacuum casting of an aluminum alloy.

Description of reference numerals: 1-a vacuum pumping port; 2-aluminum liquid level; 3-aluminum liquid inlet; 4-a crystallizer; 5, ingot casting; 6-smelting furnace; 7-a filter chamber box.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to embodiments thereof; it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Other systems, methods, and/or features of the present embodiments will become apparent to those skilled in the art upon review of the following detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. Additional features of the disclosed embodiments are described in, and will be apparent from, the detailed description that follows. The present embodiment is for illustrative purposes only and is not to be construed as limiting the present patent, and a person of ordinary skill in the art can understand the specific meaning of the above terms according to specific situations.

The invention discloses a method for casting an aluminum alloy in a partial vacuum, which comprises the following steps according to the shown embodiment:

example 1:

(1) based on the total weight of the aluminum alloy, the aluminum alloy elements comprise 4.2% of Mg, 0.03% of Mn0.02%, 0.02% of Cr0.02%, 0.35% of Fe0.07% of Ti, 0.25% of Cu, 0.25% of trace elements and the balance of Al and inevitable other impurities, wherein the content of the inevitable other impurities is less than or equal to 0.05% singly and the total amount is less than or equal to 0.15%;

(3) carrying out ultrasonic vibration treatment and mechanical stirring treatment on the first melt, continuously adding the components Mn, Cr, Fe and Ti in percentage by weight into the smelting furnace, controlling the temperature of the melt in the smelting furnace to be 650-750 ℃ until the alloy is completely molten, and keeping the temperature at 650 ℃ and adding Mg 4.18% until the alloy is uniformly molten to obtain a second melt;

(5) keeping the ultrasonic vibration treatment and the mechanical stirring treatment, sequentially adding 0.02 mass percent of Mg, 0.25 mass percent of Cu, 0.35 mass percent of Fe0.25 mass percent and 0.25 mass percent of trace elements into the smelting furnace, and uniformly melting to obtain a third melt;

(6) the aluminum alloy melt III sequentially flows through the filter chamber box and the aluminum liquid inlet along the central conduit and is conveyed into the crystallizer for casting, a vacuumizing port is arranged at the upper part in the crystallizer, one end of the vacuumizing port is connected with a vacuum pump, the upper part of the aluminum liquid surface is vacuumized by a vacuumizing method during production, the vacuum degree of the vacuum is 10Kpa, the connection among the filter chamber box, the aluminum liquid inlet and the crystallizer is always kept in a vacuum state, and the aluminum alloy melt III flows into the crystallizer under the action of negative pressure; the filter chamber box is internally provided with a degasser and a porous ceramic filter plate, the rotation speed of a graphite rotor of the degasser is 300 revolutions per minute, the nitrogen flow is 1 cubic meter per hour, and the porous ceramic filter plate has the thickness of 18mm, the specification of 15 holes per inch and the porosity of 80 percent; the casting temperature is controlled at 650 ℃, the casting speed is 80mm/min, and the pressure of cooling water in the wall of the crystallizer is 0.3 Mpa.

Wherein the trace elements are Si, Ni, La and Ce, and the addition ratio of the Si, the Ni, the La and the Ce is 1:1:1:4 in percentage by mass; the ultrasonic vibration treatment conditions are as follows: the ultrasonic frequency is 40KHzKHz, the time is 1-8min, the temperature is 650 ℃, and the ultrasonic vibration amplitude is 0.1 mm; the mechanical stirring treatment conditions are as follows: the mechanical stirring speed is 800r/min, and the mechanical stirring time is 50 seconds.

Example 2:

(1) based on the total weight of the aluminum alloy, the aluminum alloy elements comprise Mg5.5%, Mn0.35%, Cr0.25%, Fe0.65%, Ti0.12%, Cu0.45%, trace elements 0.35%, and the balance of Al and inevitable other impurities, wherein the content of the inevitable other impurities is less than or equal to 0.05% and the total content is less than or equal to 0.15%;

(3) carrying out ultrasonic vibration treatment and mechanical stirring treatment on the first melt, continuously adding the components Mn, Cr, Fe and Ti in percentage by weight into the smelting furnace, controlling the temperature of the melt in the smelting furnace to be 650-750 ℃ until the alloy is completely molten, and keeping the temperature at 750 ℃ and adding 5.42 percent of Mg until the alloy is uniformly molten to obtain a second melt;

(5) keeping the ultrasonic vibration treatment and the mechanical stirring treatment, sequentially adding 0.08 percent of Mg, 0.45 percent of Cu0.45 percent of Fe, 0.65 percent of trace elements and 0.35 percent of trace elements into the smelting furnace, and uniformly melting to obtain a third melt;

(6) the aluminum alloy melt III sequentially flows through the filter chamber box and the aluminum liquid inlet along the central conduit and is conveyed into the crystallizer for casting, a vacuumizing port is arranged at the upper part in the crystallizer, one end of the vacuumizing port is connected with a vacuum pump, the upper part of the aluminum liquid surface is vacuumized by a vacuumizing method during production, the vacuum degree of the vacuum is 10-20Kpa, the connection among the filter chamber box, the aluminum liquid inlet and the crystallizer is always kept in a vacuum state, and the aluminum alloy melt III flows into the crystallizer under the action of negative pressure; the filter chamber box is internally provided with a degasser and a porous ceramic filter plate, the rotation speed of a graphite rotor of the degasser is 400 rpm, the nitrogen flow is 2 cubic meters per hour, and the porous ceramic filter plate has the thickness of 22mm, the specification of 15 holes per inch and the porosity of 90 percent; the casting temperature is controlled at 780 ℃, the casting speed is 110mm/min, and the pressure of cooling water in the wall of the crystallizer is 0.5 Mpa.

Wherein the trace elements are Si, Ni, La and Ce, and the addition ratio of the Si, the Ni, the La and the Ce is 3:7:5:4 in percentage by mass; the ultrasonic vibration treatment conditions are as follows: the ultrasonic frequency is 120KHz, the time is 8min, the temperature is 750 ℃, and the ultrasonic vibration amplitude is 2 mm; the mechanical stirring treatment conditions are as follows: the mechanical stirring speed is 3000r/min, and the mechanical stirring time is 120 seconds.

Example 3:

(1) based on the total weight of the aluminum alloy, the aluminum alloy elements comprise 5.0% of Mg, 0.3% of Mn0.15%, 0.15% of Cr0.15%, 0.45% of Fe0.09% of Ti, 0.32% of Cu, 0.30% of trace elements and the balance of Al and inevitable other impurities, wherein the content of the inevitable other impurities is less than or equal to 0.05% singly and the total amount is less than or equal to 0.15%;

(3) carrying out ultrasonic vibration treatment and mechanical stirring treatment on the first melt, continuously adding the components Mn, Cr, Fe and Ti into a smelting furnace according to the weight percentage, controlling the temperature of the melt in the smelting furnace to be 700 ℃ until the alloy is completely molten, and keeping the temperature at 700 ℃ to add Mg4.73% until the alloy is uniformly molten to obtain a second melt;

(5) keeping the ultrasonic vibration treatment and the mechanical stirring treatment, sequentially adding 0.27 mass percent of Mg, 0.30 mass percent of Cu, 0.45 mass percent of Fe0.45 mass percent and 0.30 mass percent of trace elements into the smelting furnace, and uniformly melting to obtain a third melt;

(6) the aluminum alloy melt III sequentially flows through the filter chamber box and the aluminum liquid inlet along the central conduit and is conveyed into the crystallizer for casting, a vacuumizing port is arranged at the upper part in the crystallizer, one end of the vacuumizing port is connected with a vacuum pump, the upper part of the aluminum liquid surface is vacuumized by a vacuumizing method during production, the vacuum degree of the vacuum is 15Kpa, the connection among the filter chamber box, the aluminum liquid inlet and the crystallizer is always kept in a vacuum state, and the aluminum alloy melt III flows into the crystallizer under the action of negative pressure; the filter chamber box is internally provided with a degasser and a porous ceramic filter plate, the rotation speed of a graphite rotor of the degasser is 350 r/min, the nitrogen flow is 2 cubic meters per hour, and the porous ceramic filter plate has the thickness of 20mm, the specification of 15 holes/inch and the porosity of 85 percent; the casting temperature is controlled at 700 ℃, the casting speed is 100mm/min, and the pressure of cooling water in the wall of the crystallizer is 0.4 MPa.

Wherein the trace elements are Si, Ni, La and Ce, and the addition ratio of the Si, the Ni, the La and the Ce is 2:4:3:2 in percentage by mass; the ultrasonic vibration treatment conditions are as follows: the ultrasonic frequency is 80KHz, the time is 5min, the temperature is 700 ℃, and the ultrasonic vibration amplitude is 1.2 mm; the mechanical stirring treatment conditions are as follows: the mechanical stirring speed is 1500r/min, and the mechanical stirring time is 80 seconds.

In addition, in this embodiment, a first air pressure detector needs to be arranged at the upper part of the crystallizer, a second air pressure detector needs to be arranged in the filter chamber box, when the deaerator is filled with nitrogen for 2 hours, the vacuumizing operation is performed, and meanwhile, the first air pressure detector and the second air pressure detector operate, if the situation that the pressure in the filter chamber or the crystallizer is large in floating is detected, an alarm prompt is sent to indicate that the production can be continued after the filter chamber or the crystallizer needs to be overhauled.

Comparative example 1:

(3) continuously adding the components Mn, Cr, Fe and Ti into the smelting furnace according to the weight percentage, controlling the temperature of the melt in the smelting furnace to be 700 ℃ until the alloy is completely melted, and keeping the temperature at 700 ℃ and adding Mg4.73% until the alloy is uniformly melted to obtain a second melt;

(5) continuously adding 0.27 mass percent of Mg, 0.30 mass percent of Cu, 0.45 mass percent of Fe0.45 mass percent and 0.30 mass percent of trace elements into the smelting furnace in sequence, and uniformly melting to obtain a third melt;

Wherein the trace elements are Si, Ni, La and Ce, and the addition ratio of the Si, the Ni, the La and the Ce is 2:4:3:2 in percentage by mass.

Comparative example 2:

(3) carrying out ultrasonic vibration treatment and mechanical stirring treatment on the first melt, continuously adding the components of Mg, Mn, Cr, Fe and Ti in percentage by weight into a smelting furnace, controlling the temperature of the melt in the smelting furnace to be 700 ℃ until the alloy is completely molten, and keeping the temperature at 700 ℃ and adding 0.30 percent of Cu, 0.45 percent of Fe0.45 percent and 0.30 percent of trace elements until the mixture is uniformly molten to obtain a second melt;

(5) the aluminum alloy melt II sequentially flows through the filter chamber box and the aluminum liquid inlet along the central conduit and is conveyed into the crystallizer for casting, a vacuumizing port is arranged at the upper part of the crystallizer, one end of the vacuumizing port is connected with a vacuum pump, the upper part of the aluminum liquid surface is vacuumized by a vacuumizing method during production, the vacuum degree of the vacuum is 15Kpa, the connection among the filter chamber box, the aluminum liquid inlet and the crystallizer is always kept in a vacuum state, and the aluminum alloy melt III flows into the crystallizer under the action of negative pressure; the filter chamber box is internally provided with a degasser and a porous ceramic filter plate, the rotation speed of a graphite rotor of the degasser is 350 r/min, the nitrogen flow is 2 cubic meters per hour, and the porous ceramic filter plate has the thickness of 20mm, the specification of 15 holes/inch and the porosity of 85 percent; the casting temperature is controlled at 700 ℃, the casting speed is 100mm/min, and the pressure of cooling water in the wall of the crystallizer is 0.4 MPa.

Comparative example 3:

(6) the aluminum alloy melt III sequentially flows through a filter chamber box and an aluminum liquid inlet along a central guide pipe and is conveyed to a crystallizer for casting, a degassing machine and a porous ceramic filter plate are arranged in the filter chamber box, the rotation speed of a graphite rotor of the degassing machine is 350 revolutions per minute, the nitrogen flow is 2 cubic meters per hour, and the porous ceramic filter plate is 20mm in thickness, 15 holes per inch in specification and 85% in porosity; the casting temperature is controlled at 700 ℃, the casting speed is 100mm/min, and the pressure of cooling water in the wall of the crystallizer is 0.4 MPa.

Performance tests were performed on the aluminum alloys prepared in examples 1-3 and comparative examples 1-3 and reported as follows:

(remarks: A-excellent, B-good, C-medium, D-poor divisions)

The data show that the aluminum alloy prepared by the invention has good mechanical property and casting property, the yield strength is more than 390Mpa, the breaking strength is more than 410Mpa, the elongation is more than 9.1%, and the prepared aluminum alloy has excellent cutting property and corrosion property. And the alloy casting is formed by combining with a microscopic structure schematic diagram, the grain diameter is small, the structure is compact, the hole defects are few, and the dendrite spacing is small.

Although the invention has been described above with reference to various embodiments, it should be understood that many changes and modifications may be made without departing from the scope of the invention. That is, the methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For example, in alternative configurations, the methods may be performed in an order different than that described, and/or various components may be added, omitted, and/or combined. Moreover, features described with respect to certain configurations may be combined in various other configurations, as different aspects and elements of the configurations may be combined in a similar manner. Furthermore, elements therein may be updated as technology evolves, i.e., many elements are examples and do not limit the scope of the invention or the claims.

Specific details are given in the description to provide a thorough understanding of the exemplary configurations including implementations. However, configurations may be practiced without these specific details, e.g., well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configuration of the claims. Rather, the foregoing description of the configurations will provide those skilled in the art with an enabling description for implementing the described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.

It is intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention. The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.

Claims

1. The method for the partial vacuum casting of the aluminum alloy is characterized by comprising the following steps of:

(5) keeping the ultrasonic vibration treatment and the mechanical stirring treatment, sequentially adding 0.02-0.08% of Mg0.02-0.08%, 0.25-0.45% of Cu, 0.35-0.65% of Fe0.25-0.35% and 0.25-0.35% of trace elements in percentage by mass into the smelting furnace, and uniformly melting to obtain a third melt;

2. The method for partial vacuum casting of aluminum alloy according to claim 1, wherein the trace elements are Si, Ni, La and Ce, and the addition ratio of Si, Ni, La and Ce is 1-3:1-7:1-5:0-4 in mass percent.

3. The method of partial vacuum casting of aluminum alloy according to claim 1, wherein the ultrasonic vibration treatment is performed under the following conditions: the ultrasonic frequency is 40KHz-120KHz, the time is 1-8min, the temperature is 650-750 ℃, and the ultrasonic vibration amplitude is 0.1-2 mm.

4. The method of partial vacuum casting of aluminum alloys according to claim 1, characterized in that the conditions of the mechanical stirring treatment are: the mechanical stirring speed is 800-3000r/min, and the mechanical stirring time is 50-120 seconds.

5. The method for aluminum alloy partial vacuum casting according to claim 1, wherein a degasser and a porous ceramic filter plate are arranged in the filter chamber box, the rotation speed of a graphite rotor of the degasser is 300-400 rpm, the nitrogen flow is 1-2 cubic meters/hour, and the porous ceramic filter plate has a thickness of 18-22mm, a specification of 15 holes/inch and a porosity of 80-90%.

6. The method of aluminum alloy partial vacuum casting as claimed in claim 1, wherein the casting temperature is controlled at 650-780 ℃, the casting speed is 80-110mm/min, and the pressure of the cooling water in the crystallizer wall is 0.3-0.5 Mpa.

7. The method for partial vacuum casting of aluminum alloy according to claim 1, wherein a vacuum pump is connected to one end of the vacuum port, and the vacuum is formed in the upper part of the aluminum liquid surface by the vacuum pumping method during production.

8. The method of partial vacuum casting of aluminum alloys according to claim 7, wherein the vacuum is 10-20 Kpa.