Method for preparing 6-series aluminum alloy through metal powder injection molding

Abstract

The invention belongs to the field of powder injection molding, and relates to a method for preparing a high-strength and high-toughness 6-series aluminum alloy through metal powder injection molding, which comprises the following steps: step 1, mixing 6-series aluminum alloy powder and a binder in a mixing mill to obtain a feed; 2, the feed is subjected to injection molding to form a green body; 3, the green body is subjected to catalytic degreasing through oxalic acid, and a brown blank is obtained; step 4, sintering the palm blank by using a vacuum degreasing sintering furnace and adopting inert gas protection negative pressure; and 5, the sintered sample is subjected to heat treatment, and a 6-series aluminum alloy product is obtained. The prepared 6-series aluminum alloy contains nano MgAl2O4 particles, the nano MgAl2O4 particles are distributed in a net shape at the grain boundary, the density of the 6-series aluminum alloy is larger than 99%, and the tensile strength of the 6-series aluminum alloy is larger than 350 Mpa.

Description

Technical Field

[0001] This application belongs to the field of powder injection molding and relates to a method for preparing high-strength and high-toughness 6-series aluminum alloy by metal powder injection molding. Background Art

[0002] Metal powder injection molding (MIM) is a near-net shaping technology that combines powder metallurgy and injection molding processes and is widely used in the manufacturing of components in fields such as consumer electronics, automotive, and defense industries. Among them, steel and stainless steel are the most widely used and mature material systems in the current industrialization of MIM. In the continuous pursuit of reducing system energy consumption and improving operation efficiency in various civil and military fields such as aerospace, transportation, and national defense, selecting lightweight and high-performance materials to achieve the lightweight of equipment components has become an important solution. In this regard, various aluminum alloys with low density, outstanding mechanical, electrical conductivity, and corrosion resistance have significant advantages. At present, there is an urgent need to develop materials and methods for preparing high-strength and high-toughness aluminum alloys suitable for near-net shaping by powder injection molding process, which can not only meet the requirements of weight reduction and efficiency increase but also realize the large-scale low-cost production of small, complex, and precision components. However, due to the high activity of the aluminum matrix, the strength and plasticity of the materials used to manufacture MIM aluminum alloy products were relatively low in the past, which limited their application range.

[0003] The information in this background art section is only intended to increase the understanding of the overall background of this application and does not necessarily constitute an admission or imply in any form that this information has become the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] In some embodiments of this application, a method for preparing 6-series aluminum alloy by metal powder injection molding is provided, including the following steps:

[0005] Step 1: Mix 6-series aluminum alloy powder and a binder in a mixer to obtain a feedstock;

[0006] Step 2: Inject the feedstock into a green body;

[0007] Step 3: Catalytically debind the green body with oxalic acid to obtain a brown body;

[0008] Step 4: Debind and sinter the brown body in a vacuum debinding sintering furnace under negative pressure with inert gas protection;

[0009] Step 5: Heat-treat the sintered sample to obtain a 6-series aluminum alloy product.

[0010] Among them, in the above Step 1, the mass ratio of the binder to the 6-series aluminum alloy powder is 15 - 30:70 - 85;

[0011] In step 3, oxalic acid is used for catalytic degreasing, with an acid inlet rate of 1-5 g / min, a nitrogen inlet rate of 20-150 L / min, a degreasing temperature of 130-140 °C, and a degreasing time of 5-9 h.

[0012] In some embodiments of the present application, in step 1, the mixing parameters are: a mixing temperature of 180 °C and a mixing time of 0.5-2 h.

[0013] In some embodiments of the present application, in step 2, the injection molding parameters are: an injection temperature of 170-180 °C, an injection pressure of 20-140 MPa, and a mold temperature of 60-90 °C.

[0014] In some embodiments of the present application, before oxalic acid degreasing catalysis, the oxalic acid furnace is cleaned with an inert gas to eliminate residual oxygen, preferably nitrogen.

[0015] In some embodiments of the present application, in step 4, the sintering is negative pressure sintering, and the sintering parameters are: a sintering temperature of 600-645 °C and an inert gas partial pressure of 5-30 Pa.

[0016] In some embodiments of the present application, in step 4, the specific sintering process is as follows:

[0017] (1) Heating from room temperature to 300 °C at a rate of 4 °C / min and holding for 2 hours, (2) heating from 300 °C to 450 °C at a rate of 3 °C / min and holding for 1 hour, (3) heating from 450 °C to 520 °C at a rate of 3 °C / min and holding for 0.5 hour, (4) heating from 520 °C to 630 °C at a rate of 2 °C / min and holding for 3 hours.

[0018] In some embodiments of the present application, in step 5, the sintered sample is heat treated, including solution treatment and aging treatment, specifically holding at 545 °C for 1 hour, water quenching, and then aging at 180 °C for 10 hours.

[0019] In some embodiments of the present application, in step 2, an injection molding machine is used for extrusion, and then an extrusion granulator is used for granulation to homogenize the raw materials.

[0020] In some embodiments of the present application, the binder in step 1 includes:

[0021] Polyoxymethylene POM: 70-90 parts

[0022] High-density polyethylene HDPE: 1-10 parts

[0023] Low-density polyethylene LDPE: 1-10 parts

[0024] Polypropylene PP: 1-10 parts

[0025] Stearic acid SA: 1 - 5 parts.

[0026] In some embodiments of the present application, in step 1, 0 - 2.0% by weight of Sn (excluding the left endpoint value) is further added to the 6 - series aluminum alloy powder.

[0027] In some embodiments of the present application, the composition of the 6 - series aluminum alloy powder is Si 0.4% - 0.8%, Cu 0.15% - 0.55%, Mg 0.8% - 1.2%, Cr 0.04% - 0.35%, Fe ≤ 0.7%, Mn ≤ 0.15%, Zn ≤ 0.25%, Ti ≤ 0.15%, Co ≤ 0.002%, with the balance being Al.

[0028] In still some other embodiments of the present application, a 6 - series aluminum alloy prepared by the above - mentioned preparation method is also provided, with a relative density greater than 99% and a tensile strength greater than 350 Mpa.

[0029] Compared with the prior art, the present application has at least the following beneficial effects:

[0030] 1. The present application reasonably optimizes the feed formula for 6 - series aluminum alloy. The binder is mainly polyoxymethylene (POM). During the degreasing of the brown blank, high - temperature oxalic acid vapor will degrade POM from a solid to formaldehyde gas, thereby generating interconnected micro - channel pores connecting to the surface of the aluminum alloy powder, so as to allow oxalic acid to corrode the aluminum oxide and oxidized Si elements on the surface of the aluminum alloy.

[0031] Polyethylene and polypropylene are used as the skeleton binders, and high - density polyethylene and low - density polyethylene are used in combination to ensure that the brown blank after oxalic acid degreasing will not collapse, enabling the oxalic acid vapor to fully react with the aluminum oxide; stearic acid is used as a lubricant to reduce the viscosity of the feed and is easy to mix.

[0032] 2. The present application innovatively discovers that by reasonably controlling the amount of oxalic acid and prolonging the degreasing time during the degreasing process, oxalic acid reacts with the aluminum oxide and silicon in the metal powder to generate aluminum oxalate and silicon oxide. In subsequent sintering and solution strengthening, nano - sized MgAl2O4 particles are formed and present a static network distribution at the grain boundaries, which can well improve the plasticity of the material.

[0033] 3. The preparation method of the present application has the characteristics of high production efficiency, high material utilization rate, uniform composition distribution, high material strength, and good toughness. It can realize the low - cost mass production of high - performance complex - shaped aluminum alloy parts, greatly expanding the application scope of products and having high economic value.

[0034] 4. In some embodiments of the present application, 6000 series aluminum alloy gas atomized powder is used, and Sn is additionally added in a weight percentage of 0 - 2.0%, or Sn is additionally added in a weight percentage of 0 - 2.0% during gas atomization powder making. The Sn element can reduce the melting point during the sintering process to promote sintering and slow down the generation rate of AlN, etc.

[0035] 5. The present application adopts a two-step debinding process, namely oxalic acid-based catalytic debinding and thermal debinding during the sintering process, which promotes the destruction of the oxide layer and the reaction of surface Si.

[0036] 6. The method of the present application can not only greatly improve the density of the sintered parts, but also stimulate the co-action of multiple strengthening and toughening mechanisms, thereby obtaining high-performance MIM aluminum alloy materials.

[0037] 7. The preparation method of the present application solves the problems of the oxide film on the surface of aluminum alloy powder hindering sintering densification and the low comprehensive performance level.

[0038] 8. Through the preparation method of the present application, it is possible to achieve a MIM 6061 aluminum alloy close to the theoretical density. During the subsequent heat treatment process, the oxide layer serves as a precursor for forming a nano-MgAl2O4 quasi-network heterostructure. This heterostructure significantly enhances the strength-ductility synergy, making the mechanical properties of the heat-treated MIM 6061 aluminum alloy reach or even exceed those of forged and additive manufactured 6061 aluminum alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the reaction process in some embodiments of the present application;

[0040] Figure 2 It is an electron microscope image and a diagram of grain changes during the reaction process in some embodiments of the present application:

[0041] (a) Schematic diagram of the formation mechanism of the static network heterostructure of nano-MgAl2O4 particles;

[0042] (b) Cross-sectional SEM image of the brown compact powder and the corresponding EDS results;

[0043] (c) SEM image of the solution-treated 6061 MIM aluminum alloy and the corresponding EDS results;

[0044] Figure 3 It is a performance comparison diagram of 6061 MIM aluminum alloy and other preparation processes in some embodiments of the present application;

[0045] Figure 4Microstructure diagrams of 6061 MIM aluminum alloy in some embodiments of this application: (a, e) SEM diagrams, (b, f) IPF diagrams, (c, g) grain size distributions, (d, h) high-magnification SEM diagrams and corresponding EDS results. (a - d) Sintered state, (e - h) aged state.

[0046] Figure 5 The stress - strain curve diagram in some embodiments of this application. Detailed implementation manners

[0047] To enable those skilled in the art to better understand the technical solutions of this disclosure, the following will provide a detailed description of this disclosure in conjunction with the accompanying drawings and specific implementation manners.

[0048] All terms used in this disclosure (including technical terms or scientific terms) have the same meaning as understood by those of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as those, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0049] For technologies, methods, and devices known to those of ordinary skill in the relevant fields, they may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the specification.

[0050] The following will be combined with the attached Figures 1-5 to illustrate the detailed technical solutions of this application.

[0051] 6xxx series aluminum alloys are a type of aluminum alloy composed of elements such as aluminum, magnesium, and silicon. They include common models such as 6061 and 6063, and are commonly used in fields such as aerospace, shipbuilding, automotive, construction, and electronics. 6xxx series aluminum alloys have excellent mechanical properties, corrosion resistance, and machinability, and are one of the most widely used aluminum alloys at present.

[0052] The inventors' research found that in the MIM production of 6xxx series aluminum alloys, through reasonable feedstock formulation and process control, the oxide film on the surface of the aluminum alloy powder is destroyed, and nano - silica is formed. After solution aging, nano - MgAl2O4 is formed, and the final product has high strength and toughness.

[0053] In some embodiments of this application, a feedstock formulation for MIM high - strength and high - toughness aluminum alloy is provided, including a binder and 6xxx series aluminum alloy powder, and the mass ratio of the binder to the 6xxx series aluminum alloy powder is 15 - 30:70 - 85;

[0054] The binder includes:

[0055] Polyoxymethylene POM: 70 - 90 parts

[0056] High-density polyethylene HDPE: 1 - 10 parts

[0057] Low-density polyethylene LDPE: 1 - 10 parts

[0058] Polypropylene PP: 1 - 10 parts

[0059] Stearic acid SA: 1 - 5 parts.

[0060] In this application, the binder is mainly polyoxymethylene POM. During the degreasing of the brown billet, high-temperature oxalic acid vapor will degrade POM from a solid to formaldehyde gas, thereby generating interconnected microchannel pores that connect to the surface of the aluminum alloy powder.

[0061] Polyethylene and polypropylene are used as the skeletal binders, and high-density polyethylene and low-density polyethylene are used in combination to ensure that the brown billet after oxalic acid degreasing does not collapse, enabling the oxalic acid vapor to fully react with alumina.

[0062] Stearic acid is used as a lubricant to reduce the viscosity of the feedstock and facilitate mixing.

[0063] In some embodiments of this application, the 6-series aluminum alloy powder includes 0 - 2.0% by weight of Sn, excluding the left endpoint value; the addition of Sn element reduces the melting point and promotes sintering during the sintering process, and slows down the generation rate of AlN.

[0064] In some embodiments of this application, the particle size D90 of the 6-series aluminum alloy powder is < 30 um, and the oxygen content is < 1500 ppm.

[0065] In some embodiments of this application, the 6-series aluminum alloy powder is 6061 aluminum alloy gas atomized powder. By mass percentage, its composition is Si 0.4% - 0.8%, Cu 0.15% - 0.55%, Mg 0.8% - 1.2%, Cr 0.04% - 0.35%, Fe ≤ 0.7%, Mn ≤ 0.15%, Zn ≤ 0.25%, Ti ≤ 0.15%, Co ≤ 0.002%, and the balance is Al.

[0066] In some embodiments of this application, the binder and the 6-series aluminum alloy powder are put into a mixer and mixed under the protection of a nitrogen atmosphere. The mixing temperature is 180°C, and the mixing time is 0.5 - 2 h to make the feedstock.

[0067] In some embodiments of this application, the rotation speed of the mixer is 30 rpm.

[0068] In some other embodiments of this application, there is also provided an application of a feedstock formula for MIM high-strength and high-toughness aluminum alloy, which is used to prepare 6-series aluminum alloy with a density greater than 99%.

[0069] In some embodiments of the present application, the specific application is as follows:

[0070] Inject the feeding formula into a green body using an injection molding machine;

[0071] Debind the green body using a debinding furnace to obtain a brown body;

[0072] Sinter the brown body using a vacuum debinding and sintering furnace under the protection of an inert gas.

[0073] In some embodiments of the present application, oxalic acid is used for debinding, with an acid feeding rate of 1 - 5 g / min, a nitrogen feeding rate of 20 - 150 L / min, a debinding temperature of 130 - 140 °C, and a debinding time of 5 - 9 h.

[0074] In some embodiments of the present application, the debinding is carried out in three stages, specifically:

[0075] The first stage of debinding: temperature 130 °C, acid feeding rate 2 g / min, debinding time 1.5 h, nitrogen flow rate 60 L / min; the second stage of debinding: temperature 135 °C, acid feeding rate 4 g / min, debinding time 3.5 h, nitrogen flow rate 60 L / min; the third stage of debinding: temperature 135 °C, acid feeding rate 1 g / min, debinding time 2 h, nitrogen flow rate 70 L / min.

[0076] In some embodiments of the present application, the obtained brown body is put into a vacuum sintering furnace for negative pressure sintering, where the sintering temperature is 630 °C, the nitrogen partial pressure is 15 Pa, and the high-temperature sintering time is 3 h.

[0077] In some embodiments of the present application, the product of vacuum negative pressure sintering is heat-treated, specifically by maintaining at 545 °C for 1 hour, water quenching, and then aging at 180 °C for 10 hours.

[0078] In some embodiments of the present application, the prepared 6-series aluminum alloy contains nano-MgAl2O4 particles, which are statically distributed in a network shape at the grain boundaries.

[0079] In still some other embodiments of the present application, a method for preparing 6-series aluminum alloy by metal powder injection molding is provided, including the following steps:

[0080] Step 1: Mix 6-series aluminum alloy powder and a binder in a mixer to obtain a feedstock;

[0081] Step 2: Inject the feedstock into a green body;

[0082] Step 3: Debind the green body using oxalic acid catalysis to obtain a brown body;

[0083] Step 4: Sinter the brown blank using a vacuum degreasing sintering furnace with inert gas protection under negative pressure. The total sintering time is about 10 - 24 h;

[0084] Step 5: Perform heat treatment on the sintered sample to obtain a 6-series aluminum alloy product.

[0085] Among them, in the step 1, the mass ratio of the binder to the 6-series aluminum alloy powder is 15 - 30:70 - 85;

[0086] In the step 3, oxalic acid is used for catalytic degreasing, with an acid inlet amount of 1 - 5 g / min, a nitrogen inlet amount of 20 - 150 L / min, a degreasing temperature of 130 - 140 °C, and a degreasing time of 5 - 9 h.

[0087] In some embodiments of the present application, in the step 1, the mixing parameters are: a mixing temperature of 180 °C and a mixing time of 0.5 - 2 h.

[0088] In some embodiments of the present application, in the step 2, the injection molding parameters are: an injection temperature of 170 - 180 °C, an injection pressure of 20 - 140 MPa, and a mold temperature of 60 - 90 °C.

[0089] In some embodiments of the present application, before oxalic acid degreasing catalysis, the oxalic acid furnace is purged with nitrogen to eliminate residual oxygen.

[0090] In some embodiments of the present application, in the step 4, the sintering is vacuum negative pressure sintering, and the sintering parameters are: a sintering temperature of 630 °C and a nitrogen partial pressure of 15 Pa.

[0091] In some embodiments of the present application, in the step 4, the specific sintering process is as follows:

[0092] (1) Heat from room temperature to 300 °C at a rate of 4 °C / min and hold for 2 hours, (2) Heat from 300 °C to 450 °C at a rate of 3 °C / min and hold for 1 hour, (3) Heat from 450 °C to 520 °C at a rate of 3 °C / min and hold for 0.5 hour, (4) Heat from 520 °C to 630 °C at a rate of 2 °C / min and hold for 3 hours. Thermal degreasing is carried out in steps (1) - (3).

[0093] In some embodiments of the present application, in the step 5, heat treatment of the sintered sample includes solution treatment and aging treatment, specifically holding at 545 °C for 1 hour, water quenching, and then aging at 180 °C for 10 hours.

[0094] In some embodiments of the present application, in the step 2, an injection molding machine is used for extrusion, and then an extrusion granulator is used for granulation to homogenize the raw materials.

[0095] In some embodiments of the present application, the binder in step 1 includes:

[0096] Polyoxymethylene POM: 70-90 parts

[0097] High-density polyethylene HDPE: 1-10 parts

[0098] Low-density polyethylene LDPE: 1-10 parts

[0099] Polypropylene PP: 1-10 parts

[0100] Stearic acid SA: 1-5 parts.

[0101] In some embodiments of the present application, in step 1, 0-2.0 weight % Sn is also added to the 6 series aluminum alloy powder, excluding the left endpoint value.

[0102] In some embodiments of the present application, the composition of the 6 series aluminum alloy powder is Si 0.4%-0.8%, Cu 0.15%-0.55%, Mg 0.8%-1.2%, Cr 0.04%-0.35%, Fe≤0.7%, Mn≤0.15%, Zn≤0.25%, Ti≤0.15%, Co≤0.002%, and Al balance.

[0103] In some embodiments of the present application, a method for preparing a 6 series aluminum alloy by metal powder injection molding comprises the following steps:

[0104] Step 1: placing 6 series aluminum alloy powder and a binder in a mixer to mix and obtain feed;

[0105] A 6061 aluminum alloy atomized powder was selected, and its mass percentage was: Si 0.7%, Cu 0.51%, Mg 0.96%, Cr 0.14%, Fe 0.18%, Mn 0.042%, Zn 0.015%, Ti 0.022%, Co 0.0018%, and Al balance. The powder particle size D90 was less than 30um, and the oxygen content was less than 1500ppm.

[0106] According to weight percentage, 80 parts of 6061 aluminum alloy aerosol powder containing 0.5% Sn (or 6061 aluminum ingot with additional 0.5% Sn added for aerosolization) are taken, and 20 parts of binder are taken, wherein the binder composition is POM:PP:HDPE:LDPE:SA=76:6:8:8:2.

[0107] The above ingredients were put into a mixer for mixing at a mixing temperature of 180°C for 1 hour and a nitrogen flow rate of 15 L / min. After being fully mixed, they were cooled and crushed to make feed;

[0108] Step 2: Inject and mold the feedstock into a green compact;

[0109] Put the feedstock into a metal injection molding machine for aluminum alloy to carry out injection molding to obtain a green compact. The injection temperature is 170 °C, the injection pressure is 25 MPa, and the mold temperature is 90 °C.

[0110] Step 3: Catalytically debind the green compact with oxalic acid to obtain a brown compact;

[0111] Put the green compact into an oxalic acid catalytic debinding furnace to carry out debinding to obtain a brown compact. The debinding temperature is 135 °C, the amount of oxalic acid is 3 g / min, the nitrogen is 100 L / min, and the acid inlet time is 6 h.

[0112] Step 4: Sinter the brown compact in a vacuum debinding and sintering furnace under negative pressure with inert gas protection. The sintering temperature is 630 °C and the nitrogen partial pressure is 15 Pa. The specific sintering process is as follows: (1) Heat from room temperature to 300 °C at a rate of 4 °C / min and hold for 2 hours, (2) Heat from 300 °C to 450 °C at a rate of 3 °C / min and hold for 1 hour, (3) Heat from 450 °C to 520 °C at a rate of 3 °C / min and hold for 0.5 hour, (4) Heat from 520 °C to 630 °C at a rate of 2 °C / min and hold for 3 hours. Steps (1)-(3) are mainly for thermal debinding.

[0113] Step 5: Perform heat treatment on the sintered sample, including solution treatment and aging treatment. Specifically, hold at 545 °C for 1 hour, water quench, and then age at 180 °C for 10 hours to obtain a 6-series aluminum alloy product.

[0114] During the process of catalytic debinding with oxalic acid, generally, the complete removal of the binder is accelerated through the acidolysis of oxalic acid without causing unexpected reactions with alloy components, that is, the debinding can be completed when oxalic acid just decomposes POM. Through long-term research on 6000 series aluminum alloys by the inventor, it is found that after oxalic acid completes the decomposition of POM, the POM in the green body is gradually decomposed, forming a large number of interconnected microchannels connecting to the surface of aluminum alloy powder. By continuously extending the acid introduction time, oxalic acid reacts with the oxide layer on the surface of aluminum alloy powder along the microchannels, generating aluminum oxalate and water, thereby destroying the oxide layer on the surface of aluminum alloy powder. As the oxide layer is continuously destroyed, the surface layer of Si in the aluminum alloy powder is exposed to the oxalic acid vapor environment and reacts with the oxygen present in the oxalic acid vapor, forming nano-sized SiO2 on the surface of the aluminum alloy powder (aluminum alloy powder). This nano-sized SiO2 occupies the position on the surface of the aluminum alloy powder, preventing the aluminum below it from being oxidized and forming diffusion channels during the subsequent sintering process; during the subsequent sintering process, as the temperature rises, SiO2 continuously aggregates and grows, while Mg is redissolved into the matrix and reacts with SiO2 to form MgO. At the same time, these MgO also react with Al2O3 in the matrix to form nano-sized MgAl2O4 particles. The occupied SiO2 forms diffusion channels after reacting with Mg, and at the same time, Mg also reacts with the surface Al2O3 to form diffusion channels. At high temperatures, diffusion channels are formed between aluminum alloy powder particles, and rapid densification occurs under the drive of high surface energy, making the density of the sintered product reach more than 99%. And the nano-sized MgAl2O4 particles show a static network distribution at the grain boundaries ( Figure 1 , Figure 2 ), and the formation of this heterogeneous structure improves the plasticity of the material. In addition, the nano-sized MgAl2O4 particles can improve the strength of the matrix due to thermal mismatch strengthening and load transfer strengthening effects.

[0115] As Figure 3 and Figure 5 shown, the tensile strength of the aluminum alloy prepared by the preparation method of this patent is greater than 350 Mpa, which is superior to the aluminum alloy products prepared by other preparation processes.

[0116] As Figure 4 shown, it shows the SEM images, inverse pole figure (IPF) diagrams and grain size distributions of sintering and heat treatment of MIM 6061 aluminum alloy. As can be seen from Figure 4 (a), the ellipsoidal micron-sized particles are uniformly distributed along the grain boundaries, and no obvious pore defects are observed. This indicates that the MIM 6061 aluminum alloy has reached a high densification level. The density results further reveal that the sintered mass density and relative density are 2.684 ± 0.002 g / cm 3 and 99.9% respectively, and the change after heat treatment is negligible. Figure 4Figure (d) is a high-magnification SEM image of the sintered grain boundary. It can be found that the ellipsoidal particles are rich in Si and O elements, and these ellipsoidal particles are determined to be the SiO2 phase. In addition, a small amount of nanoparticles rich in Al, Mg, and O elements are found at some grain boundaries and are determined to be MgAl2O4. Its formation is related to the destruction of the oxide layer, which is related to magnesium. It can be found that no obvious diffraction peaks are observed during the sintering process, indicating that there is no MgAl2O4, mainly due to its low content. After heat treatment ( Figure 4 Figures (e) and (h)), the SiO2 phase disappears from the microstructure, and a large number of white nanoparticles of MgAl2O4 appear at the grain boundaries. A new MgAl2O4 phase is formed during the heat treatment, and its formation is related to the reaction of Mg, Al, and SiO2. The MgAl2O4 particles formed at the grain boundaries show a quasi-network structure distribution, enhancing the strength and ductility. Figure 4 Figures (b) and (f) clearly reveal the fine equiaxed grains in sintering and heat treatment, with average grain sizes of 13.6 μm and 14.7 μm, respectively.

[0117] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing 6 series aluminum alloy by metal powder injection molding, characterized in that: The following steps are involved: Step 1: placing 6 series aluminum alloy powder and a binder in a mixer to mix and obtain feed; Step 2: injection molding the feed material into a green body; Step 3: degreasing the green body by catalytic degreasing with oxalic acid to obtain a brown body; Step 4: Sintering the brown blank in a vacuum degreasing sintering furnace under negative pressure with inert gas protection; Step 5: heat-treating the sintered sample to obtain a 6 series aluminum alloy product; Wherein, in step 1, the mass ratio of the binder to the 6-series aluminum alloy powder is 15-30:70-85; In step 3, oxalic acid is used for catalytic degreasing, the acid feed rate is 1-5 g / min, the nitrogen feed rate is 20-150 L / min, the degreasing temperature is 130-140° C., and the degreasing time is 5-9 h.

2. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In the step 1, the mixing parameters are: mixing temperature 180° C., mixing time 0.5-2 h.

3. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In step 2, the parameters of injection molding are: injection temperature 170-180° C., injection pressure 20-140 MPa, and mold temperature 60-90° C.; preferably, before oxalic acid degreasing catalysis, the oxalic acid furnace is cleaned with inert gas to eliminate residual oxygen.

4. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In the step 4, the sintering is negative pressure sintering, and the sintering parameters are: sintering temperature 600-645° C., inert gas partial pressure 5-30 Pa.

5. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In step 4, the specific sintering process is: (1) heating from room temperature to 300°C at a rate of 4°C / min, and holding for 2 hours; (2) heating from 300°C to 450°C at a rate of 3°C / min, and holding for 1 hour; (3) heating from 450°C to 520°C at a rate of 3°C / min, and holding for 0.5 hours; (4) heating from 520°C to 630°C at a rate of 2°C / min, and holding for 3 hours.

6. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In the step 5, the sintered sample is subjected to heat treatment, including solution treatment and aging treatment, specifically, maintaining at 545° C. for 1 hour, water quenching, and then aging at 180° C. for 10 hours.

7. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: The binder in step 1 comprises: Polyoxymethylene POM: 70-90 parts High-density polyethylene HDPE: 1-10 parts Low-density polyethylene LDPE: 1-10 parts Polypropylene PP: 1-10 parts Stearic acid SA: 1-5 parts.

8. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In the step 1, Sn is further added to the 6 series aluminum alloy powder, 0<Sn≤2%, calculated in mass percentage.

9. The method for preparing 6 series aluminum alloy by metal powder injection molding according to claim 1, characterized in that: In terms of mass percentage, the composition of the 6 series aluminum alloy powder is Si0.4%-0.8%, Cu 0.15%-0.55%, Mg0.8%-1.2%, Cr 0.04%-0.35%, Fe≤0.7%, Mn≤0.15%, Zn≤0.25%, Ti≤0.15%, Co≤0.002%, and Al balance.

10. A 6 series aluminum alloy, characterized in that: The 6-series aluminum alloy is prepared by the method described in any one of claims 1 to 9, wherein the 6-series aluminum alloy contains nano-MgAl2O4 particles and is distributed in a network at the grain boundaries. The 6-series aluminum alloy has a density greater than 99% and a tensile strength greater than 350Mpa.

Images