Method for producing 7055 aluminum alloy large billets using powder semi-solid hot pressing

Abstract

The present application relates to a method for preparing a 7055 aluminum alloy large blank by using powder semi-solid hot pressing. First, nano-ZnO powder and 7055 aluminum alloy powder are ball-mixed, screened and dried, then rare earth elements are added again for ball-mixing, and after ball-mixing, screening and drying are carried out. The cold-pressed block sample is sintered in a vacuum heating furnace at a semi-solid temperature, and after sintering, it is heated to a semi-solid temperature together with a mold in a vacuum heating furnace for heat preservation, and then semi-solid hot pressing is carried out on an oil press and pressure is maintained. Mixed powder is laid between the two hot-pressed samples, and the two samples are hot-pressed again on the oil press. According to the thickness of the sample, the hot-pressed sample is stacked multiple times, and finally the sample of the required size is obtained. The present application can avoid the problems of hot cracking in liquid forming and porosity in solid forming, and can prepare a 7055 aluminum alloy large-size blank with fine and uniform grains, high density and better mechanical properties.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum matrix composites, and particularly relates to a method for preparing a 7055 aluminum alloy large blank by using powder semi-solid hot pressing. BACKGROUND

[0002] 7055 aluminum alloy is one of 7xxx series aluminum alloys, and belongs to Al-Zn-Mg-Cu series alloy. The 7xxx series (Al-Zn-Mg-Cu) aluminum alloy has the characteristics of high specific strength, low density (lighter mass under the same performance conditions), good welding performance, plastic deformation capacity and processability, low-temperature resistance, and good radiation resistance, and is widely used in the field of aerospace, such as the manufacture of fuselage, wing beam, cabin of an airplane or aircraft, and high-strength structural parts of a rocket, and is an important material indispensable to the aerospace industry of the world.

[0003] In the commonly used aluminum matrix composite preparation method, the ordinary melting method needs to be operated at high temperature, and the matrix alloy is easy to oxidize in the preparation process, which causes changes in the chemical composition of the composite material and the mixing of impurities, and casting defects such as shrinkage, pores and alloy composition segregation are easy to occur in the casting process. In order to inhibit the cracking phenomenon of large-size blanks, grain refinement is the most effective method, and grain refinement is also an effective method to improve the strength of the alloy. By adding nano ceramic particles (such as Al2O3) in the matrix through in-situ method, the grain size can be obviously refined, and the growth of the grain can be effectively inhibited, and the nano particle shell is formed at the grain boundary, which prevents the diffusion of molten atoms in the liquid phase to the solid-liquid interface.

[0004] The introduction of rare earth elements (Y, Er, Ce, Sc and La, etc.) into the powder metallurgy structural material preparation process can play the roles of matrix purification, grain refinement and dispersion strengthening due to its excellent chemical activity, thermal stability and mechanical properties, and can improve the mechanical properties of the product. This will have a significant effect on uniform dispersion of particles and grain refinement. In order to obtain a certain size blank with higher density and no thermal cracking, the use of powder semi-solid hot pressing forming technology is the best method. The powder semi-solid hot pressing method, which combines semi-solid forming technology and powder hot pressing forming technology, is a new composite material preparation technology, and the preparation process is not limited by the content and size of the particle reinforced phase. At the same time, the composite material prepared has more uniform organization, smaller grain size, higher density and more excellent performance. SUMMARY

[0005] The purpose of the present application is to prepare a large-size 7055 aluminum alloy blank by using powder semi-solid hot pressing. The present application can avoid the problems of thermal cracking in liquid forming and porosity and pores in solid forming.

[0006] The principle of this invention is as follows: First, 7055 alloy powder and nano ZnO are ball-milled. As the ball-milling time increases, the oxide film on the surface of Al particles is broken, which improves the interaction between Al and nano ZnO. Using nano-sized ZnO particles can also improve the reaction activity, ultimately reducing the reaction temperature of Al-ZnO, and then nano Al2O3 particles can be generated at a semi-solid temperature.

[0007] Rare earth powders (Y, Er, Ce, Sc, or La) are added during the second ball milling process. Due to the larger atomic radii of rare earth elements, this helps prevent the alloy powders from welding together during ball milling. During the semi-solid temperature reaction, according to the relationship of interfacial energy, only when the interfacial energy γ between the solid phases is... ss Interfacial energy γ between solid and liquid sl Satisfying γ ss <γ sl Only then can the two solid particles coalesce. Because rare earth elements tend to accumulate in the liquid phase between solid particles, γ... ss The increase in size makes it more difficult for Al2O3 particles to merge, preventing them from continuing to grow and promoting their dispersion.

[0008] The 7055 aluminum alloy powder used as raw material has a particle size of 20–50 μm, while the added ZnO powder is nanoscale, resulting in finer grains after the reaction. Al2O3 particles can hinder grain coarsening during the formation and evolution of the matrix alloy grains. The nanoscale Al2O3 reinforcing particles can act as nucleation sites for the matrix alloy grains, increasing the nucleation rate and refining the grain structure. Furthermore, the alloy powder at the semi-solid temperature exhibits high viscosity and good flowability, which facilitates the wetting and bonding of the Al2O3 reinforcing particles with the matrix alloy, reducing macroscopic agglomeration of nanoscale Al2O3 particles and resulting in more uniform Al2O3 particle dispersion. The uniformly dispersed Al2O3 particles inhibit grain growth in the matrix alloy, thereby refining the matrix alloy grains.

[0009] The sintered sample is then hot-pressed at a semi-solid temperature. As the hot-pressing temperature increases, the atoms between particles diffuse, which accelerates the bonding between particles, making the aluminothermic reaction more complete. Furthermore, as the hot-pressing temperature increases, the plastic deformation resistance of the matrix alloy decreases and the flow properties increase, so the liquid phase can more easily enter the pores, reducing the number of pores and significantly improving the density.

[0010] After hot pressing, a layer of mixed powder is laid between two identical samples, and hot pressing is continued at semi-solid temperature for a period of time, because at semi-solid temperature, the mixed powder coexists in solid-liquid phase, and under the condition of receiving a larger pressure, the oxide films of the two samples are broken, the mixed powder coexisting in solid-liquid phase enters the samples to carry out in-situ reaction again to obtain nano-sized Al2O3 particles, and the surfaces of the two samples are combined together by mutual reaction, and the multiple stacked samples will obtain the final blank with the required thickness.

[0011] After the grain of the composite material is refined, the grain boundary is increased, and the grain boundary has a strong hindering effect on the movement of dislocations, so in the deformation process of the composite material, the dislocations in the grain are accumulated at the grain boundary, thereby playing a strengthening effect. The mechanical properties of the composite material are largely dependent on the porosity of the material, and the smaller the porosity, the smaller the probability of crack initiation and propagation of the material during deformation. The increase of the density makes the probability of crack initiation and propagation of the material in the tensile process minimum, so the in-situ generation of nano Al2O3 particles and the hot pressing process can improve the mechanical properties.

[0012] The application is realized by the following technical schemes:

[0013] Step (1): the 7055 aluminum alloy powder and the nano ZnO powder are ball-mixed, screening is carried out after the ball-milling is completed, and then the screened powder is dried to obtain the mixed powder 1;

[0014] Step (2): the rare earth powder is added into the dried mixed powder 1, ball-mixing is carried out again, screening is carried out after the ball-mixing is completed, and then the screened powder is dried to obtain the mixed powder 2;

[0015] Step (3): the mixed powder 2 after the drying treatment in step (2) is cold-pressed to obtain a preform, the preform is placed into a vacuum heating furnace, semi-solid temperature sintering is carried out under an argon atmosphere, and the sample is obtained after cooling to room temperature after heat preservation;

[0016] Step (4): commercial boron nitride (BN) high-temperature release agent is sprayed on the inner surface of the mold and dried, then the sample obtained by sintering in step (3) is placed into the dried mold, and the mold and the sample are heated together to semi-solid temperature in the vacuum heating furnace, and heat preservation is carried out for a period of time;

[0017] Step (5): the heated sample is subjected to semi-solid hot pressing on an oil press;

[0018] Step (6): a layer of the mixed powder 2 after the drying treatment in step (2) is laid on the surface of a sample obtained by semi-solid hot pressing in step (5), and then another sample obtained by semi-solid hot pressing in step (5) is stacked;

[0019] Step (7): Put the superimposed samples together into the mold which has been sprayed with release agent and dried, heat to semi-solid temperature in a vacuum heating furnace, and keep for a period of time, then semi-solid hot-press the heated samples on an oil press;

[0020] Step (8): According to the thickness requirement of the final blank, lay a layer of mixed powder 2 dried in step (2) on the surface of the sample obtained in step (7), superimpose another sample obtained by semi-solid hot-pressing in step (5) again, and repeat step (7).

[0021] Step (9): Repeat step (8) until the final blank with the required thickness is obtained.

[0022] As an improvement of the above technical solution, the specific implementation steps of the method are as follows:

[0023] Preferably, in step (1), the mass fraction of nano-ZnO powder in mixed powder 1 is 1.0-2.5wt.%, and 2-5% of anhydrous ethanol by mass is added to the mixed powder.

[0024] Preferably, in step (1), a horizontal ball mill is used for ball milling, the rotation speed of ball milling is 250-300 rpm, the time is 8-12 h, the grinding balls are agate balls with a diameter of 5-20 mm, and the ball-to-material ratio is 8-10:1.

[0025] Preferably, in step (1), the powder after ball milling is sieved on a 200-400 mesh screen, the residue is hand ground for 1-2 h and then sieved again, and then the mixed powder with the final residue removed is dried in a vacuum drying oven at 120-200°C for 1-2 h.

[0026] Preferably, in step (2), the mass fraction of rare earth powder in mixed powder 2 is 0.15-0.4wt.%, and 2-5% of anhydrous ethanol by mass is added to the mixed powder 2.

[0027] Preferably, in step (2), the rotation speed of ball milling is 250-300 rpm, the time is 2-4 h, the grinding balls are agate balls with a diameter of 5-20 mm, and the ball-to-material ratio is 8-10:1.

[0028] Preferably, in step (2), the powder after ball milling is sieved on a 200-400 mesh screen, the residue is hand ground for 1-2 h and then sieved again, and then the mixed powder with the final residue removed is dried in a vacuum drying oven at 120-200°C for 1-2 h.

[0029] Preferably, in step (3), the cold pressing pressure of mixed powder 2 is 30-35 MPa, the pressure holding time is 1-3 min, and the block is pressed into a diameter of 25-100 mm and a height of 5-40 mm.

[0030] Preferably, the temperature of the semi-solid sintering in step (3) is 550-580℃, the holding time is 20-40min, and the vacuum degree is 1x10 -3 ~1x10 -1 Pa.

[0031] Preferably, the thickness of the release agent in step (4) is 50-500μm, the mold material is H13 steel which can be heated to 600℃, and the commercial boron nitride high-temperature release agent is sprayed and then left to stand for 3-5h at room temperature in a ventilated place.

[0032] Preferably, the sample is placed in the bottom center of the mold in step (4), the sample center is coaxial with the bottom center of the mold, and the mold and the sample are heated to 550-580℃ in a vacuum heating furnace and held for 10-30min.

[0033] Preferably, the mold and the sample are placed on the midpoint of the square platform of the oil press in step (5), the bottom center of the mold is coaxial with the midpoint of the square platform, the hot-pressing pressure is 5-30MPa, the holding time is 30-60min, and the sample is cooled to room temperature in the furnace.

[0034] Preferably, the thickness of the mixed powder 2 between the two samples in step (6) is 50-500μm.

[0035] Preferably, the two samples are placed in the bottom center of the mold in step (7), the sample center is coaxial with the bottom center of the mold, and the mold and the sample are heated to 550-580℃ and held for 30-50min.

[0036] Preferably, the mold and the sample are placed on the midpoint of the square platform of the oil press in step (7), the bottom center of the mold is coaxial with the midpoint of the square platform, the pressure is 5-30MPa, the holding time is 30-60min, and the sample is cooled to room temperature in the furnace.

[0037] Preferably, the thickness of the mixed powder 2 in step (8) is 50-500μm.

[0038] The technical advantages of the application are as follows: by adding rare earth elements, Al and ZnO react to form uniformly dispersed nano-Al2O3 particles at a semi-solid temperature, the matrix grains are refined, multiple samples are hot-pressed at a semi-solid temperature, the mixed powder coexists in solid and liquid phases, and under the action of a large pressure, the oxide film on the surface of the sample is broken, and finally a large-sized aluminum alloy blank is obtained by successful reaction and combination, which greatly solves the problems of easy thermal cracking and low density in the production of 7055 aluminum alloy large-sized blanks. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1The effect of rare earth in powder semi-solid reaction is shown in the figure. It can be seen from the figure that the grain size is smaller and the particle dispersion is more uniform after adding rare earth.

[0040] Figure 2 The microstructure of the 7055 aluminum alloy substrate without adding ZnO and rare earth in Example 2 is shown in the figure.

[0041] Figure 3 The OM image of the in-situ Al2O3 particle reinforced aluminum matrix composite prepared in Example 2 is shown in the figure. It can be seen from the figure that the grain is obviously refined.

[0042] Figure 4 The SEM image of the in-situ Al2O3 particle reinforced aluminum matrix composite prepared in Example 2 is shown in the figure. It can be seen from the figure that the Al2O3 particles are uniformly dispersed on the crystal surface.

[0043] Figure 5 The microstructure of the in-situ Al2O3 particle reinforced aluminum matrix composite after hot pressing in Example 2 is shown in the figure. It can be seen from the figure that the grain size is deformed after hot pressing, the grain is refined, and the hole is less. DETAILED DESCRIPTION

[0044] The application will be described in detail below in combination with specific examples. The following examples are implemented on the basis of the technical scheme of the application. The detailed implementation scheme and specific operation process are given below, but it should be noted that the protection scope of the application is not limited to the following examples.

[0045] Example 1:

[0046] 1.0wt.% of nano-ZnO powder based on the mass of mixed powder 1 was added to the 7055 aluminum alloy powder for ball milling. 2% of anhydrous ethanol based on the mass of the mixed powder was added to prevent cold welding. The rotation speed was set to 250 rpm, the ball-to-powder ratio was 8:1, and the ball milling was carried out for 8 h. After ball milling, the powder was sieved through a 200 mesh sieve, and the residue was hand ground for 2 h and then sieved again. The ground powder was dried in a vacuum drying oven at 180℃ for 2 h to obtain the dried mixed powder. The mixed powder was cold pressed using a tablet press at 10 MPa, and the pressure was maintained for 1 min to obtain a preform block with a diameter of 50 mm and a height of 10 mm. The preform block was placed in a vacuum heating furnace, and the vacuum degree was maintained at 1×10 -1After 2 h, sintering was started, and the temperature was raised to 450 °C in an argon atmosphere and held for 10 min. The temperature was then raised to 550 °C, and held for 30 min before furnace cooling to room temperature. Boron nitride release agent was sprayed onto the inner surface of the mold to a thickness of 50 pm, and the sintered sample was placed in the mold after the boron nitride release agent was dried for 3 h at room temperature in a well-ventilated area. The mold and sample were placed in a vacuum heating furnace, and the heating temperature was 550 °C. After the specified temperature was reached, the mold was held for 10 min, and then removed. The mold was placed in the center of an oil press, and the pressure was set to 5 MPa. The sample was removed after holding for 30 min, and the purpose of densification was achieved. The two samples after hot pressing were then stacked, with a layer of mixed powder 50 pm thick in between. The stack was placed in a mold, and then placed in a vacuum heating furnace. The temperature of the mold was raised to 550 °C, and held for 30 min. The mold and sample were removed together and placed in the center of an oil press, with the pressure set to 5 MPa. The sample was removed after holding for 30 min, and furnace cooling to room temperature. The sample was then stacked according to the thickness of the blank, and the above operations were repeated to obtain a 7055 aluminum alloy blank with a height of 43 mm.

[0047] Example 2:

[0048] The 7055 aluminum alloy powder was ball milled with 2.0 wt.% of nano-ZnO powder based on the mass of the mixed powder 1. Anhydrous ethanol was added to prevent cold welding, with an amount of 4% of the mass of the mixed powder 1. The rotation speed was set to 300 rpm, and the ball-to-powder ratio was 10:1. The ball milling was performed for 10 h. After ball milling, the powder was sieved through a 300-mesh sieve, and the residue was hand ground for 1 h before being sieved again. The ground powder was dried in a vacuum drying oven at 200 °C for 1 h to obtain dried mixed powder 1. The sieved powder was mixed with 0.3 wt.% of rare earth Y powder based on the mass of the mixed powder 2. The rotation speed was set to 300 rpm, and the ball-to-powder ratio was 10:1. The ball milling was performed for 3 h. Anhydrous ethanol was added to prevent cold welding, with an amount of 4% of the mass of the mixed powder 2. After ball milling, the powder was sieved through a 300-mesh sieve, and the residue was hand ground for 1 h before being sieved again. The ground powder was dried in a vacuum drying oven at 200 °C for 1 h to obtain dried mixed powder 2. The mixed powder was cold pressed using a tablet press at 30 MPa for 2 min to obtain a preform with a diameter of 25 mm and a height of 15 mm. The preform was placed in a vacuum heating furnace, and the vacuum degree was adjusted to 1 x 10 -2After 24 h, sintering was started, and the temperature was raised to 450 °C for 10 min, and then to 580 °C for 10 min, and then the furnace was cooled to room temperature. Boron nitride release agent was sprayed on the inner surface of the mold to a thickness of 100 pm, and the mold was placed in a well-ventilated room at room temperature for 4 h. After the boron nitride release agent was dried, the sintered sample was placed in the mold. The mold and sample were placed in a vacuum heating furnace, and the heating temperature was 580 °C. After the temperature reached the specified temperature, the mold was kept at the temperature for 20 min, and then removed. The mold was placed in the center of the oil press, the pressure was set to 15 MPa, and the pressure was kept for 30 min, and then for 50 min. The sample was removed after the furnace was cooled to room temperature, and the purpose of densification was achieved. Then, the two samples after hot pressing were stacked, and a layer of mixed powder with a thickness of 100 pm was placed in the middle. The mold was placed in a vacuum heating furnace, and the temperature inside the mold was raised to 580 °C. The mold and sample were kept at the temperature for 50 min, and then removed together and placed in an oil press with a pressure of 15 MPa. The pressure was kept for 50 min, and then the sample was removed after the furnace was cooled to room temperature. The sample was stacked according to the thickness of the blank, and the above operation was repeated to obtain a 7055 aluminum alloy blank with a height of 50 mm.

[0049] Example 3:

[0050] The 7055 aluminum alloy powder was ball milled with 2.5 wt.% of nano-ZnO powder based on the mass of the mixed powder 1, and 5% of anhydrous ethanol based on the mass of the mixed powder 1 was added to prevent cold welding. The rotation speed was set to 280 rpm, and the ball-to-material ratio was 9:1. The ball milling was performed for 12 h. After ball milling, the powder was sieved through a 400-mesh sieve, and the residue was hand ground for 1.5 h and then sieved again to obtain the mixed powder 1. The powder was placed in a vacuum drying oven and dried at 200 °C for 1.5 h. 0.4 wt.% of rare earth Er powder based on the mass of the mixed powder 2 was added to the sieved powder, and the rotation speed was set to 280 rpm. The ball-to-material ratio was 9:1, and the ball milling was performed for 4 h. 5% of anhydrous ethanol based on the mass of the mixed powder 2 was added to prevent cold welding. After ball milling, the powder was sieved through a 400-mesh sieve, and the residue was hand ground for 1.5 h and then sieved again. The ground powder was dried in a vacuum drying oven at 200 °C for 1.5 h to obtain the dried mixed powder. The mixed powder was cold pressed using a tablet press at 20 MPa for 3 min to obtain a preform with a diameter of 100 mm and a height of 30 mm. The preform was placed in a vacuum heating furnace, and the vacuum degree was raised to 1 × 10 -3After the Pa, sintering was started, and the temperature was raised to 450°C in an argon atmosphere for 10 min, and then raised to 560°C for 40 min, and then cooled to room temperature in the furnace. A boron nitride release agent was uniformly sprayed on the inner surface of the mold, with a thickness of 500 μm, and left to stand at room temperature for 5 h. After the boron nitride release agent was dried, the sintered sample was placed in the mold. The mold and sample were placed in a vacuum heating furnace for heating, and the heating temperature was 580°C. After reaching the specified temperature, the mold was kept for 30 min, and then removed. The mold was placed in the center of an oil press, with a pressure setting of 30 MPa, and kept for 60 min. After cooling to room temperature in the furnace, the sample was removed, and densification was achieved. Subsequently, the two samples after hot pressing were stacked, with a layer of mixed powder with a thickness of 500 μm in between, placed in the mold, and then placed in a vacuum heating furnace. The temperature inside the mold was raised to 560°C, and kept for 30 min. The mold and sample were removed together and placed in the center of an oil press, with a pressure setting of 30 MPa, and kept for 60 min. After cooling to room temperature in the furnace, the sample was removed. The two samples were combined together, and the sample was stacked again according to the thickness of the blank. A 7055 aluminum alloy blank with a height of 80 mm was obtained.

Claims

1. A method for producing a 7055 aluminium alloy billet by powder semi-solid hot pressing, characterized in that, The specific steps are as follows: Step (1): 7055 aluminum alloy powder and nano-ZnO powder are ball-mixed, after ball-milling, sieving is performed, and then the sieved powder is dried to obtain mixed powder 1; Step (2): rare earth powder is added to the dried mixed powder 1, ball-mixing is performed again, after ball-milling, sieving is performed, and then the sieved powder is dried to obtain mixed powder 2; Step (3): the mixed powder 2 after drying in step (2) is cold-pressed to obtain a preform, the preform is placed in a vacuum heating furnace, semi-solid temperature sintering is performed under an argon atmosphere, and after heat preservation, cooling to room temperature obtains a sample; Step (4): commercial boron nitride (BN) high-temperature release agent is sprayed on the inner surface of the mold and dried, then the sample obtained by sintering in step (3) is placed in the dried mold, the mold and the sample are heated together in a vacuum heating furnace to a semi-solid temperature, and heat preservation is performed for a period of time; Step (5): semi-solid hot pressing is performed on the heated sample on an oil press; Step (6): a layer of mixed powder 2 after drying in step (2) is laid on the surface of a sample obtained by semi-solid hot pressing in step (5), and then another sample obtained by semi-solid hot pressing in step (5) is stacked; Step (7): the stacked samples are placed together in a mold that has been sprayed with release agent and dried, heated to a semi-solid temperature in a vacuum heating furnace, and heat preservation is performed for a period of time, and semi-solid hot pressing is performed on the heated sample on an oil press; Step (8): according to the required thickness of the final blank, a layer of mixed powder 2 after drying in step (2) is laid on the surface of the sample obtained in step (7), and then another sample obtained by semi-solid hot pressing in step (5) is stacked, and step (7) is repeated; Step (9): repeat step (8) until the final blank of the required thickness is obtained.

2. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (1), the mass fraction of nano-ZnO powder in mixed powder 1 is 1.0-2.5wt.%, and 2-5% of anhydrous ethanol by mass is added to the mixed powder; a horizontal ball mill is used for ball-mixing, the rotation speed of ball-mixing is 250-300 rpm, the time is 8-12 h, the grinding balls are 5-20 mm in diameter, and the ball-to-material ratio is 8-10:

1.

3. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (1), the powder after ball-milling is sieved on a 200-400 mesh screen, the residue is hand-ground for 1-2 h and then sieved again, and then the mixed powder after removing the final residue is dried in a vacuum drying oven at 120-200℃ for 1-2 h.

4. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (2), the mass fraction of rare earth powder in mixed powder 2 is 0.15-0.4wt.%, and 2-5% of anhydrous ethanol by mass is added to the mixed powder 2; the rotation speed of ball-mixing is 250-300 rpm, the time is 2-4 h, the grinding balls are 5-20 mm in diameter, and the ball-to-material ratio is 8-10:1; the powder after ball-milling is sieved on a 200-400 mesh screen, the residue is hand-ground for 1-2 h and then sieved again, and then the mixed powder after removing the final residue is dried in a vacuum drying oven at 120-200℃ for 1-2 h.

5. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (3), the cold-pressing pressure of the mixed powder 2 is 30-35 MPa, the pressure holding time is 1-3 min, and the block with a diameter of 25-100 mm and a height of 5-40 mm is formed; the semi-solid sintering temperature is 550-580°C, the holding time is 20-40 min, and the vacuum degree is 1 x 10 -3 -1 x 10 -1 Pa.

6. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (4), the release agent thickness is 50-500 μm, the mold material is H13 steel which can be heated to 600 °C, and the sample is placed in the center of the bottom of the mold after spraying a commercial boron nitride high-temperature release agent and standing for 3-5 h at room temperature in a ventilated place; the mold and the sample are heated to 550-580 °C in a vacuum heating furnace, and kept for 10-30 min.

7. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (5), the mold and the sample are placed on the midpoint of the square platform of the oil press, the bottom center of the mold is coaxial with the midpoint of the square platform, the hot-pressing pressure is 5-30 MPa, the pressure is kept for 30-60 min, and the furnace is cooled to room temperature.

8. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (6), the mixed powder 2 between the two samples is 50-500 μm thick.

9. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (7), the two samples are placed in the center of the bottom of the mold, the sample center is coaxial with the bottom center of the mold, the mold and the sample are heated to 550-580 °C and kept for 30-50 min; the mold and the sample are placed on the midpoint of the square platform of the oil press, the bottom center of the mold is coaxial with the midpoint of the square platform, the pressure is 5-30 MPa, the pressure is kept for 30-60 min, and the furnace is cooled to room temperature.

10. The method of making a 7055 aluminum alloy billet by powder semi-solid hot pressing of claim 1, wherein, In step (8), the mixed powder 2 is 50-500 μm thick.

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