CN109811164B

CN109811164B - Preparation method of additive manufacturing aluminum alloy

Info

Publication number: CN109811164B
Application number: CN201910154978.6A
Authority: CN
Inventors: 蔡志勇; 王日初; 马如龙; 周朝辉; 李晓庚; 曹玄扬
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2019-03-01
Filing date: 2019-03-01
Publication date: 2020-10-16
Anticipated expiration: 2039-03-01
Also published as: CN109811164A

Abstract

The invention provides a preparation method of an additive manufacturing aluminum alloy, which comprises the following steps: (1) gas atomization powder preparation: melting aluminum alloy raw materials into a melt, crushing the melt into fine liquid drops by adopting high-pressure inert gas, and forming powder after solidification and cooling; (2) preparing the powder into a blocky blank by adopting a selective laser melting technology; (3) cold deformation processing: performing plastic processing on the blank in the step (2) at room temperature to obtain a deformed blank; (4) and carrying out heat treatment on the deformed blank to obtain the aluminum alloy. According to the invention, deformation processing treatment is added on the basis of the selective laser melting technology, so that residual pores in the selective laser melting process can be removed, and the density and the tissue uniformity of the aluminum alloy are improved, thereby improving the comprehensive mechanical property of the aluminum alloy; and rolling, extruding and forging are carried out at room temperature, and fine structures in the blank can not be coarsened.

Description

Preparation method of additive manufacturing aluminum alloy

Technical Field

The invention relates to the technical field of metal material preparation, in particular to a preparation method of additive manufacturing aluminum alloy.

Background

The aluminum alloy has the advantages of small density, high specific strength, good corrosion resistance, excellent processing and forming properties, low cost and the like, and is a non-ferrous metal structural material which is most widely applied in modern industry. Particularly, the high-performance aluminum alloy is of great importance to the fields of weaponry such as aviation, aerospace, weapons and ships, for example, in the aviation field, a large number of complex integral structural members formed by processing thick aluminum plates are adopted to replace parts assembled by a plurality of parts in the past, so that the structural weight can be reduced, the load capacity and the range can be improved, the high-performance aluminum alloy can also ensure the stability of the performance of an airplane, is mainly used for landing gears, engine cabins, airplane body parts, seats, control systems and the like, and can replace aluminum die forgings in most cases.

The traditional forming process of the aluminum alloy generally needs to melt raw materials, then cast the raw materials in a mould, and then carry out deformation processing, solid solution, aging treatment and the like. In the traditional forming process, the solid solubility of certain alloy elements is limited due to the precipitation of the alloy elements in a matrix in the solution treatment process, so that the increasingly high requirements of the development of modern science and technology on materials are gradually difficult to meet.

Additive manufacturing, namely 3D printing, is a novel material molding technique, by which materials are built up layer by layer from bottom to top to make various complex structures. The selective laser melting technology is used as one of additive manufacturing, metal powder is completely melted by the heat action of laser, and then the metal powder is rapidly cooled and solidified to form. Because the selective laser melting technology can realize the rapid cooling molding of the metal melt, the problem of limited solid solubility of the alloy elements in the traditional molding process is hopeful to be solved.

The selective laser melting technology is used for manufacturing the aluminum alloy parts, and the raw materials of the aluminum alloy are melted and atomized to prepare powder; then, slicing and layering the three-dimensional digital model of the part through special software; after contour data of each section are obtained, a layer of aluminum alloy powder is laid on a powder table, laser scanning is controlled according to the contour data, and the laser scanning is stopped after the powder is rapidly heated and melted so as to be rapidly cooled and solidified; and then continuously spreading the powder layer by layer on the layer basis, and scanning, melting, solidifying and stacking the powder layer by layer to form the required structure. Because the technology is formed by melting and solidifying and accumulating aluminum alloy powder layer by layer, the lower layer is cooled and solidified, the upper layer is in a melting state in the operation process, two adjacent layers cannot be synchronously fused and cooled, and pores are generated at the joint, so that the mechanical property of the aluminum alloy is reduced.

Disclosure of Invention

Based on the method, the invention provides the preparation method of the additive manufacturing aluminum alloy, which can eliminate residual pores in the selective laser melting solidification process and improve the uniformity of the structure, so that the aluminum alloy with compact and uniform microstructure is obtained.

The preparation method of the additive manufacturing aluminum alloy comprises the following steps:

(1) gas atomization powder preparation: melting aluminum alloy raw materials into a melt, crushing the melt into fine liquid drops by adopting high-pressure inert gas, and forming powder after solidification and cooling;

(2) preparing the powder into a blocky blank by adopting a selective laser melting technology;

(3) cold deformation processing: performing plastic processing on the blank in the step (2) at room temperature to obtain a deformed blank;

(4) and carrying out heat treatment on the deformed blank to obtain the aluminum alloy.

Compared with the prior art, the method has the advantages that deformation processing is added on the basis of the selective laser melting technology, so that residual pores in the selective laser melting process can be removed, the density and the tissue uniformity of the aluminum alloy are improved, and the comprehensive mechanical property of the aluminum alloy is improved; and rolling, extruding and forging are carried out at room temperature, and fine structures in the blank can not be coarsened.

Further, the step (2) specifically comprises the following steps:

paving a layer of powder prepared in the step (1) on a substrate, gradually scanning the layer of powder by using high-energy laser to melt the powder, and solidifying and cooling to obtain a first layer of blank matrix;

laying a second layer of powder on the surface of the first layer, gradually scanning the layer of powder by using high-energy laser to melt the powder, and obtaining a second layer of blank matrix after solidification and cooling;

and thirdly, repeating the steps for a plurality of times until a block blank with a set size and shape is obtained.

Furthermore, the laser spot is 0.1mm in the laser scanning process, the laser power is 200-400W, and the laser scanning speed is 400-2000 mm/s.

Further, the pressure of the high-pressure inert gas in the step (1) is 0.9-1.3 MPa.

Further, the particle size of the powder in the step (1) is 15-53 μm.

Further, the heat treatment in the step (4) is heat preservation for 12-48 hours at 120-160 ℃.

Further, the cold deformation processing pressure is 120-200 MPa.

Drawings

FIG. 1 is a microstructure of an Al-10Si-Mg alloy prepared in example 1;

FIG. 2 is a tensile fracture morphology of the Al-10Si-Mg alloy prepared in example 1;

FIG. 3 is an X-ray diffraction pattern of the Al-10Si-Mg alloy prepared in example 1;

FIG. 4 is a tensile stress-strain curve of the Al-10Si-Mg alloy prepared in example 1;

FIG. 5 is a microstructure of the Al-6Mg-0.3Sc alloy prepared in example 2;

FIG. 6 is a tensile fracture morphology of the Al-6Mg-0.3Sc alloy prepared in example 2;

FIG. 7 is an X-ray diffraction pattern of the Al-6Mg-0.3Sc alloy prepared in example 2;

FIG. 8 is a tensile stress-strain curve for the Al-6Mg-0.3Sc alloy prepared in example 2.

Detailed Description

The invention eliminates the residual pores in the additive manufacturing process by combining the selective laser melting technology with the deformation processing technology, and the technical scheme of the invention is described in detail by specific embodiments below.

Example 1

In this example, an Al-10Si-Mg alloy is prepared by the following steps:

(1) gas atomization powder preparation

Pure aluminum, Al-Si intermediate alloy and pure Mg are used as raw materials, and the raw materials are mixed according to the weight percentage of 10 percent of Si, 0.4 percent of Mg and the balance of Al and then are smelted into melt. And (3) deslagging the melt, crushing the melt into fine liquid drops by using high-pressure nitrogen at 0.9-1.3 MPa, solidifying, cooling and performing grading treatment to obtain powder with the particle size of 15-53 microns.

(2) Preparing the powder into block-shaped blank by adopting selective laser melting technology

And establishing a model of the aluminum alloy blank by using software, slicing and layering, and then introducing data into selective laser melting equipment. And (2) paving a first layer of powder prepared in the step (1) on a powder table in selective laser melting equipment, and then controlling laser to selectively scan the first layer of powder according to data, wherein a laser spot is 0.1mm in the scanning process, the laser power is 200-400W, and the laser scanning speed is 400-2000 mm/s.

And after the first layer of blank matrix is obtained after the first layer of blank matrix is cooled and solidified, continuously paving a second layer of powder, and repeating the laser scanning operation. Repeating the steps for multiple times to obtain a block-shaped blank.

(3) Cold deformation working

And (3) rolling the blank prepared in the step (2) at room temperature for multiple times to obtain a deformed blank, wherein the deformation of each time is 15-16%, and the total deformation is 70-75%.

Heating the deformed blank to 160 ℃ and preserving heat for 12h to obtain the final Al-10Si-Mg alloy.

Please refer to fig. 1 and 2, wherein fig. 1 is an SEM microstructure of the Al-10Si-Mg alloy, and fig. 2 is a fracture scanning photograph of the Al-10Si-Mg alloy. FIG. 1 shows that the Al-10Si-Mg alloy has fine internal structure size and uniform distribution, and FIG. 2 shows that the Al-10Si-Mg alloy has high compactness. Meanwhile, the phase analysis of the X-ray diffraction in figure 3 reflects that the Al-10Si-Mg alloy prepared by the invention only has simple substance diffraction peaks of all alloy elements and has no obvious impurity peaks, which indicates that the alloy elements in the Al-10Si-Mg alloy are uniformly distributed and have no segregation phenomenon. Mechanical testing was performed on the Al-10Si-Mg alloy to obtain a tensile stress-strain curve as shown in fig. 4. As can be seen from FIG. 4, when the strain is within 0.55%, the tensile stress is proportional to the strain, which indicates that the Al-10Si-Mg alloy can be elastically deformed within the range and can generate the tensile stress of 450MPa at most; when the strain exceeds 0.55%, a tensile stress-strain curve has tiny yield sawteeth, the Al-10Si-Mg alloy generates elastic-plastic deformation, and the tensile stress is maintained at about 500 MPa.

Example 2

In this embodiment, an Al-6Mg-0.3Sc alloy is prepared by the following steps:

(1) gas atomization powder preparation

Pure aluminum, Al-Sc intermediate alloy and pure Mg are used as raw materials, and the raw materials are mixed according to the weight percentage of 6 percent of Mg, 0.3 percent of Sc and the balance of Al and then are smelted into melt. And (3) deslagging the melt, crushing the melt into fine liquid drops by using high-pressure nitrogen at 0.9-1.3 MPa, solidifying, cooling and performing grading treatment to obtain powder with the particle size of 15-53 microns.

And after the first layer scanning is finished, continuously paving a second layer of powder on the first layer, and repeating the above laser scanning operation. Repeating the steps for multiple times to obtain a block-shaped blank.

(3) Cold deformation working

And (3) rolling the blank prepared in the step (2) at room temperature for multiple times to obtain a deformed blank, wherein the deformation of each time is 16-18%, and the total deformation is 70-80%.

Heating the deformed blank to 120 ℃ and preserving heat for 48 hours to obtain the final Al-6Mg-0.3Sc alloy.

Please refer to fig. 5 and 6, wherein fig. 1 is the SEM microstructure of the Al-6Mg-0.3Sc alloy, and fig. 2 is the fracture scanning photograph of the Al-6Mg-0.3Sc alloy. FIG. 5 shows the internal structure size of Al-10Si-Mg alloy and its fineness and uniformity, and FIG. 6 shows that Al-6Mg-0.3Sc alloy has very high compactness. Meanwhile, the phase analysis of the X-ray diffraction of FIG. 7 reflects that the Al-6Mg-0.3Sc alloy prepared by the invention has no obvious impurity peak. According to the tensile stress-strain curve shown in FIG. 8, when the strain is within 1.0%, the tensile stress is proportional to the strain, which indicates that the Al-6Mg-0.3Sc alloy has recoverable elastic deformation and can generate the tensile stress of 550MPa at most; when the strain exceeds 1.0%, yield sawteeth and yield platforms appear on a tensile stress-strain curve, the Al-10Si-Mg alloy is subjected to elastoplastic deformation, and the tensile stress is maintained at about 600MPa, which reflects that the Al-6Mg-0.3Sc alloy has good mechanical properties.

Example 3

The selective laser melting technology is to melt aluminum alloy powder layer by layer, then rapidly cool, solidify and stack layer by layer, the inner part of each layer is uniform, and the key point is to improve the joint condition between two adjacent layers in order to improve the uniformity and compactness of the whole aluminum alloy. In addition to the improvement of the bonding between the adjacent two layers by external force, the cold deformation processing means as used in examples 1 and 2 can also be improved from the inside. Therefore, the applicant tries to change the microstructure of the joint between two adjacent layers to improve the joining strength between the two layers, so as to improve the uniformity and compactness of the aluminum alloy. In the embodiment, taking preparation of an Al-10Si-Mg alloy as an example, the preparation steps are as follows:

(1) gas atomization powder preparation

In this example, the aluminum alloy raw materials were melted together into a melt, and the melt was broken into fine droplets by high-pressure inert gas, solidified and cooled to form powder, as in example 1.

After the first layer is scanned and cooled and solidified, Ar is applied to the surface of the first layer⁺And carrying out surface etching for 3-4 minutes by using an ion beam. And after the etching is finished, laying a second layer of powder on the surface of the first layer, and repeating the laser scanning operation and the ion etching operation. Repeating the steps for multiple times to obtain a block-shaped blank.

(3) Cold deformation working

Heating the deformed blank to 140 ℃ and preserving heat for 12h to obtain the final Al-10Si-Mg alloy.

Through electronic scanning observation of the Al-10Si-Mg alloy of the embodiment, the internal structure of the aluminum alloy is finer and more uniform than that of the embodiment 1, and the alloy strength is improved by 30 percent compared with that of the embodiment 1.

The change is mainly caused by that in the selective laser melting operation process, the surface of the solidified material of the first layer is subjected to ion etching, so that a nano-dot array is formed on the surface of the first layer; therefore, the second layer of aluminum alloy powder laid subsequently is melted during laser scanning, and because alloy atoms can move freely during melting, part of the alloy atoms can penetrate into the nano-dot array; after the laser is removed, the second layer is rapidly cooled and solidified, alloy atoms penetrating into the first layer of nano-dot array are instantly solidified and do not move any more, and are tightly combined with the nano-dot array on the surface of the first layer, no pore is left, so that an acting force similar to occlusion is generated between the first layer and the second layer, and the joining strength between the two layers is improved. Similarly, each subsequent layer has such interaction, and the overall compactness is finally improved.

It should be noted that the method of the present invention can be used to prepare any common aluminum alloy or modified aluminum alloy, and is not limited to the Al-10Si-Mg alloy and the Al-6Mg-0.3Sc alloy in the above-mentioned examples.

Compared with the prior art, the method has the advantages that deformation processing is added on the basis of the selective laser melting technology, and residual pores in the selective laser melting process can be removed, so that the final aluminum alloy has extremely high density, the mechanical property of the aluminum alloy is improved, and the aluminum alloy has good strain resistance. And the deformation processing is carried out at room temperature, so that fine and uniform tissues in the blank can be reserved, and segregation and impurities can not be generated. In addition, the invention also carries out ion etching on the solidified material of each layer in the selective laser melting operation process to generate a nano array on the surface of the solidified material, so that alloy atoms of the later layer penetrate into the nano array of the last layer, thereby improving the joining strength between the two adjacent layers and finally improving the density of the whole aluminum alloy; the mechanical strength of the aluminum alloy is closely related to the density, so that the integral mechanical strength of the aluminum alloy can be improved through ion etching.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims

1. A preparation method of an additive manufacturing aluminum alloy is characterized by comprising the following steps:

(2) the method for preparing the powder into the blocky blank by adopting the selective laser melting technology comprises the following steps:

ion etching the surface of the first layer of blank substrate;

thirdly, laying a second layer of powder on the surface of the first layer of blank matrix, gradually scanning the layer of powder by using high-energy laser to melt the powder, and obtaining a second layer of blank matrix after solidification and cooling;

fourthly, repeating the third step until a blocky blank with a set size and shape is obtained;

2. The method of making an additive-manufactured aluminum alloy of claim 1, wherein: in the laser scanning process, the laser spot is 0.1mm, the laser power is 200-400W, and the laser scanning speed is 400-2000 mm/s.

3. The method of making an additive-manufactured aluminum alloy of claim 2, wherein: the pressure of the high-pressure inert gas in the step (1) is 0.9-1.3 MPa.

4. The method of making an additive-manufactured aluminum alloy of claim 3, wherein: the particle size of the powder in the step (1) is 15-53 mu m.

5. The method of making an additive-manufactured aluminum alloy of claim 4, wherein: the heat treatment in the step (4) is heat preservation for 12-48 hours at 120-160 ℃.

6. The method of making an additive-manufactured aluminum alloy of claim 5, wherein: the cold deformation processing pressure is 120-200 MPa.