A magnesium alloy powder containing bi element for laser selective melting and application thereof

Abstract

The application belongs to the field of laser selective melting (SLM) rapid forming, discloses a Bi element containing magnesium alloy powder for laser selective melting and application thereof, and the magnesium alloy powder is composed of the following components in percentage by mass: Al element: 8.5-9.0%, Zn element: 0.5-1%, Bi element: 1-2%, Mn element: 0.2-0.4%, impurities: ≤0.05%, and the rest is Mg element. Through improvement on the specific composition of the magnesium alloy powder for laser selective melting, the application introduces appropriate Bi element into the magnesium alloy, promotes alloying in cooperation with the SLM process, and the corresponding SLM magnesium alloy forming piece has better tensile strength and yield strength, and the thermal stability of the performance of the forming piece is better.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of selective laser melting (SLM) rapid prototyping, and more particularly relates to a Bi element-containing magnesium alloy powder for selective laser melting and application thereof. BACKGROUND

[0002] Magnesium alloy is an alloy formed by mixing magnesium as the main element with other various elements. Magnesium alloy has the following advantages: small density (only 1.74 g / cm 3 ), good heat dissipation, high specific strength and specific stiffness, good electrical and thermal conductivity, large elastic modulus, greater impact load bearing capacity than aluminum alloy, good corrosion resistance to organic matter and alkali, and abundant resources and easy recycling. In practical applications, magnesium and its alloys are the lightest metal structural materials. The main alloying elements are aluminum, zinc, manganese, cerium, thorium, and a small amount of zirconium or cadmium, etc. The most common magnesium alloy is magnesium-aluminum alloy, followed by magnesium-manganese alloy and magnesium-zinc-zirconium alloy. Excellent magnesium alloy materials are widely used in aerospace, new energy vehicles, new era weapons and equipment, and other advanced basic materials.

[0003] Laser additive manufacturing technology is an advanced additive manufacturing technology based on the concept of discrete-accumulation forming. Through the construction of a three-dimensional model, the technology uses a layer-by-layer manufacturing method to realize the net forming of complex parts by using the high-temperature effect of a laser beam on metal powder. Compared with the high cost and long cycle of traditional casting process, laser additive manufacturing technology can quickly process complex structural parts while ensuring high dimensional accuracy. Selective laser melting (SLM) is a main technical approach in the field of additive manufacturing technology. In the process of processing, the powder bed is scanned layer by layer according to the path planned in the three-dimensional CAD slice model, and the laser completely melts the powder, without the need for a binder for direct forming. Therefore, the precision and mechanical properties of the formed parts are excellent. Overall, selective laser melting technology is a major research focus and future development trend in the field of rapid prototyping additive manufacturing. Due to its principle and characteristics, it has four main advantages: suitable for complex structures, wide range of forming materials, high comprehensive mechanical properties, and suitable for personalized customization.

[0004] Currently, the traditional forming method of magnesium alloy parts is mainly casting, and the biggest feature is "light", but the strength performance still has room for improvement. Specifically, the tensile strength of cast AZ91D magnesium alloy parts is about 250 MPa, and the yield strength is about 150 MPa, which has limited performance and application of magnesium alloy. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present application is to provide a Bi element-containing magnesium alloy powder for laser selective melting and an application thereof, wherein the specific composition of the magnesium alloy powder for laser selective melting is improved, an appropriate amount of Bi element is introduced into the magnesium alloy, and the alloying is promoted in combination with the SLM process, and accordingly, the SLM magnesium alloy formed part has better tensile strength and yield strength, and compared with the traditional magnesium alloy, the decrease amplitude of the creep rupture life with the increase of temperature is significantly reduced, and the thermal stability of the performance of the formed part is better.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a magnesium alloy powder for laser selective melting is provided, characterized by consisting of the following mass percentage components: Al element: 8.5-9.0%, Zn element: 0.5-1%, Bi element: 1-2%, Mn element: 0.2-0.4%, impurities: ≤0.05%, and the rest is Mg element.

[0007] As a further preferred embodiment of the present application, the particle size of the powder is 15-53 μm.

[0008] According to another aspect of the present application, the present application provides a preparation method of the above-mentioned magnesium alloy powder for laser selective melting, characterized by comprising the following steps:

[0009] S1: ball milling treatment is performed on the bismuth powder so that the particle size of the bismuth powder is 15-53 μm;

[0010] S2: the raw material magnesium alloy containing Al element, Zn element and Mn element is prepared as a raw material magnesium alloy powder; the raw material magnesium alloy powder is subjected to ball milling treatment so that the particle size of the raw material magnesium alloy powder is 15-53 μm;

[0011] S3: the raw material magnesium alloy powder and the bismuth powder are respectively subjected to drying treatment so that the powders are fully dried;

[0012] S4: the raw material magnesium alloy powder and the bismuth powder after drying are proportioned and mixed according to the target mass percentage of each component in the magnesium alloy powder for laser selective melting, and the mixing is specifically performed by ball milling and physical powder mixing, so that the target magnesium alloy powder for laser selective melting is obtained.

[0013] As a further preferred embodiment of the present application, in the step S3, the drying treatment of each powder is specifically performed by drying the powder in a vacuum drying oven at 60°C for 3-4 h.

[0014] According to still another aspect of the present application, the present application provides an application of the above-mentioned magnesium alloy powder for laser selective melting in laser selective melting.

[0015] As a further preferred embodiment of the present application, the method comprises the following steps:

[0016] (1) drying the magnesium alloy powder for laser selective melting, and preheating a substrate installed in a forming cavity of the laser selective melting device;

[0017] (2) performing laser selective melting on the magnesium alloy powder in an inert atmosphere to obtain a magnesium alloy forming piece through layer-by-layer scanning.

[0018] As a further preferred embodiment of the present application, in the step (2), the process parameters of the laser selective melting are set as follows: the laser output power is 200-300 W, the layer thickness is 30-40 μm, the scanning speed is 600-1000 mm / s, the scanning interval is 100-120 μm, and the scanning strategy is strip scanning with an angle of 67°.

[0019] As a further preferred embodiment of the present application, in the step (1), the preheating temperature is 150-200 °C.

[0020] As a further preferred embodiment of the present application, in the step (2), the inert atmosphere is an argon atmosphere.

[0021] Preferably, the oxygen content of the forming cavity of the laser selective melting device is not more than 200 ppm.

[0022] More preferably, the inert atmosphere is a pure argon atmosphere.

[0023] According to another aspect of the present application, the present application provides a magnesium alloy forming piece obtained by the above method.

[0024] Compared with the prior art, the above technical scheme of the present application can achieve the following beneficial effects:

[0025] (1) The present application adds an appropriate amount of Bi element to the conventional magnesium alloy powder to obtain a new type of magnesium alloy powder, which is used as the powder raw material for laser selective melting. In the laser printing process, the tensile strength, yield strength and creep rupture life of the obtained forming piece are enhanced based on the precipitation strengthening effect. In addition, considering that the SLM process is known to have better SLM process effect when the particle size of the used powder raw material is 15-53 μm, the particle size of the new type of magnesium alloy powder obtained by the present application can also be preferably 15-53 μm.

[0026] The present application can enhance the precipitation strengthening effect in the printing process by adding an appropriate amount of Bi element in the traditional magnesium-zinc alloy, thereby improving the strength performance of the magnesium alloy material, such as tensile strength, yield and creep rupture life. Bi element is a typical precipitation strengthening element for magnesium alloy. By doping an appropriate amount of Bi element in the traditional magnesium alloy powder, based on the selective laser melting technology in the field of additive manufacturing, the precipitation strengthening effect in the printing process can be enhanced. The mass percentage of Bi element in the system is 1-2%. Due to the presence of Bi element, dense Mg3Bi2 particles can appear in the microstructure, thereby increasing the microhardness and melting point of the alloy, and further improving the comprehensive strength performance of the magnesium alloy, so that the performance of the magnesium alloy is strengthened.

[0027] (2) The alloying between Bi element and magnesium alloy produces dense Mg3Bi2 particles, so that the creep rupture life of the formed part after printing is improved. As shown in the examples below, under certain external force and temperature conditions, the endurance life of the formed part can be enhanced.

[0028] (3) Based on the present application, the enhancement effect of the high-strength magnesium alloy formed part obtained does not decrease sharply with the increase of temperature, and the creep rupture life remains at a good level (as compared and analyzed in the examples below), that is, the performance improvement effect is still good after heating, which is better than that of the traditional cast magnesium alloy.

[0029] (4) The present application changes the composition of each element in the magnesium alloy powder, especially promotes alloying through SLM, and obtains different strength enhancement under the processing mode of selective laser melting, thereby further widening the application range of magnesium alloy on the basis of existing research. Based on the present application, the parameter conditions of SLM can be preferably: laser output power is 200-300 W, laser diameter is about 0.1 mm, layer thickness is 30-40 μm, scanning speed is 600-1000 mm / s, scanning interval is 100-120 μm, scanning strategy is strip scanning, and angle is 67°. Through such preferred setting, better forming effect can be ensured, and the formed part has no cracks, few holes and high density.

[0030] In summary, the present application adds an appropriate amount of Bi element in the traditional magnesium alloy, and enhances the comprehensive strength performance under the processing mode of selective laser melting, thereby further widening the application range of magnesium alloy on the basis of existing research. The Bi element of the present application provides a new idea for the development of SLM technology in the field of printing magnesium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a schematic diagram of the principle of the selective laser melting technology (SLM).

[0032] Figure 2 is a flow chart of the preparation method of the magnesium alloy material and the high-strength magnesium alloy material based on the SLM technology in the embodiments of the present application.

[0033] Figure 3 is a stress-strain curve of the high-strength magnesium alloy sample obtained in Embodiment 1.

[0034] Figure 4 is a stress-strain curve of the high-strength magnesium alloy sample obtained in Embodiment 2.

[0035] Figure 5 is a stress-strain curve of the high-strength magnesium alloy sample obtained in Embodiment 3. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0037] In general, the magnesium alloy powder for laser selective melting in the present application contains: Al mass fraction of 8.5-9.0%, Zn mass fraction of 0.5-1%, Bi element mass fraction of 1-2%, Mn element mass fraction of 0.2-0.4%, total mass fraction of other unavoidable impurities (such as Si, Fe, Cu, Ni, etc.) less than or equal to 0.05%, and the balance of Mg element.

[0038] Based on the component ratio of the magnesium alloy powder for laser selective melting in the present application, the magnesium alloy powder for laser selective melting can be prepared according to the following steps:

[0039] Step A, ball milling the bismuth raw material and the magnesium alloy material into powder respectively;

[0040] Step B, placing the two kinds of powders after ball milling into a vacuum oven, and vacuum drying at 60°C for 3-4h;

[0041] Step C, according to the mass percentage of the target component, adding the bismuth powder to the magnesium alloy powder, further ball milling and physical mixing of the powder, so that the particle size is 15-53μm, so as to ensure the spreading effect before printing and the fluidity during printing.

[0042] Similar to the SLM process in the prior art, the SLM process using the magnesium alloy powder for laser selective melting in the present application (the powder can be filled in the forming cavity equipped with a powder distribution filler in the SLM equipment, and the powder can be uniformly spread on the substrate) can include the following steps:

[0043] Step one, install the substrate in the forming cavity and preheat it, for example, the substrate temperature can reach 150-200℃; the substrate can be a magnesium alloy material plate with a thickness greater than or equal to 2cm;

[0044] Step two, deoxygenate the forming chamber by inert gas, for example, the oxygen content in the cavity can be controlled at 200ppm or below;

[0045] Step three, SLM forming, specifically, after falling powder, it is uniformly spread on the substrate by the powder spreading roller, the focused laser beam selectively melts the powder on the powder bed, after depositing a layer, the platform is lowered by the layer height and the powder feeder is raised by the layer height;

[0046] Step four, repeat the steps of spreading powder and laser melting in step three until the part is formed to the required thickness.

[0047] Next, commercially available Bi powder and commercially available gas-atomized AZ91D powder are used as raw materials for experiments.

[0048] Example 1

[0049] A magnesium alloy material based on SLM laser 3D printing technology, composed of the following mass fractions of elements:

[0050] Al: 8.9%, Zn: 0.5%, Mn: 0.4%, Bi: 1%, impurities: 0.05%, the rest is Mg.

[0051] The magnesium alloy material based on SLM laser 3D printing technology and the preparation method of high-strength magnesium alloy formed parts, the specific implementation steps are as follows:

[0052] (1) Ball mill the AZ91D magnesium alloy powder and Bi powder obtained by gas atomization respectively, then take 99:1 of the two by mass fraction, and then ball mill and mix the powder again to reach the specified particle size (i.e. 15-53μm, same below), then dry at 60℃ under vacuum conditions for 4h, to obtain the raw powder for SLM printing;

[0053] (2) Process the magnesium alloy plate to a thickness of 2cm as a substrate, and preheat it to a temperature of 180℃. On the other hand, deoxygenate the forming cavity with the substrate installed, until the internal oxygen content is 200ppm or below;

[0054] (3) The SLM forming is carried out in a pure argon inert atmosphere environment, and the specific process parameters are as follows: the laser output power is 200 W, the laser diameter is about 0.1 mm (the SLM equipment used in this embodiment and the following embodiments and comparative examples is the same, and the laser diameter is fixed at about 0.1 mm), the layer thickness is 30 μm, the scanning speed is 600 mm / s, the scanning interval is 100 μm, the scanning strategy is strip scanning, and the angle is 67°;

[0055] (4) A high-strength magnesium alloy material based on SLM laser 3D printing technology is obtained by layer-by-layer scanning and melting.

[0056] (5) At room temperature, the tensile strength of the sample of this embodiment is 296 MPa, and the yield strength is 210 MPa. Compared with the traditional cast AZ91D magnesium alloy (see Comparative Example 1 below), it is increased by 18.4% and 31.3%, respectively; the elongation at break is 7.8%; the formed piece is subjected to a constant tensile force of 70 MPa at 150°C, and the creep rupture life is 136 h, which is increased by 40.2% compared with the traditional cast AZ91D magnesium alloy (see Comparative Example 1 below).

[0057] Embodiment 2

[0058] A magnesium alloy material based on SLM laser 3D printing technology is composed of the following mass fractions of elements:

[0059] Al: 8.8%, Zn: 0.5%, Mn: 0.4%, Bi: 1.5%, impurities: 0.05%, and the rest is Mg.

[0060] The preparation method of the magnesium alloy material based on SLM laser 3D printing technology and the high-strength magnesium alloy formed piece, and the specific implementation steps are as follows:

[0061] (1) The AZ91D magnesium alloy powder and Bi powder obtained by gas atomization are respectively subjected to ball milling, and then the two are weighed according to the mass fraction percentage of 197:3, and then subjected to ball milling and powder mixing again to reach the specified particle size, and then dried at 60°C under vacuum conditions for 4 h to obtain the required printing raw powder;

[0062] (2) The magnesium alloy plate is processed to a thickness of 2 cm as a substrate, and is preheated to a temperature of 180°C. On the other hand, the forming cavity with the installed substrate is subjected to deoxidation treatment until the internal oxygen content is 200 ppm or less;

[0063] (3) SLM forming is carried out in a pure argon inert atmosphere environment, and the specific process parameters are as follows: the laser output power is 200 W, the laser diameter is about 0.1 mm, the layer thickness is 30 μm, the scanning speed is 600 mm / s, the scanning interval is 100 μm, the scanning strategy is strip scanning, and the angle is 67°;

[0064] (4) A high-strength magnesium alloy material based on SLM laser 3D printing technology is obtained by layer-by-layer scanning and melting.

[0065] (5) At room temperature, the tensile strength of the sample of the embodiment is 313 Mpa, and the yield strength is 221 Mpa. Compared with the traditional cast AZ91D magnesium alloy, it is increased by 25.2% and 38.1%, respectively; the elongation at break is 7.4%; the formed piece is subjected to a constant tensile force of 70 Mpa at 150℃, and the creep rupture life is 143h, which is increased by 47.4% compared with the traditional cast AZ91D magnesium alloy.

[0066] Example 3

[0067] A magnesium alloy material based on SLM laser 3D printing technology is composed of the following mass fractions of elements:

[0068] Al: 8.6%, Zn: 0.5%, Mn: 0.4%, Bi: 2%, impurities: 0.05%, and the rest is Mg.

[0069] The preparation method of the magnesium alloy material based on SLM laser 3D printing technology and the high-strength magnesium alloy formed piece, and the specific implementation steps are as follows:

[0070] (1) The AZ91D magnesium alloy powder and Bi powder obtained by gas atomization are respectively subjected to ball milling, and then the two are weighed according to the mass fraction percentage of 49:1, and then subjected to ball milling and powder mixing again to reach the specified particle size, and then dried at 60℃ under vacuum conditions for 4h to obtain the required printing raw powder;

[0071] (2) The magnesium alloy plate is processed to a thickness of 2cm as a substrate, and is preheated to a temperature of 180℃. On the other hand, the forming cavity with the installed substrate is subjected to deoxidation treatment until the internal oxygen content is 200ppm or less;

[0072] (3) SLM forming is carried out in a pure argon inert atmosphere environment, and the specific process parameters are as follows: the laser output power is 200 W, the laser diameter is about 0.1 mm, the layer thickness is 30 μm, the scanning speed is 600 mm / s, the scanning interval is 100 μm, the scanning strategy is strip scanning, and the angle is 67°;

[0073] (4) A high-strength magnesium alloy material based on SLM laser 3D printing technology is obtained by layer-by-layer scanning and melting to a certain thickness.

[0074] (5) At room temperature, the tensile strength of the sample of the embodiment is 340 Mpa, and the yield strength is 236 Mpa. Compared with the traditional cast AZ91D magnesium alloy, it is increased by 36% and 47.5%, respectively; the elongation at break is 7.1%; the obtained shaped part is subjected to a constant tensile force of 70 Mpa at 150℃, and the creep rupture life is 146h, which is increased by 50.5% compared with the traditional cast AZ91D magnesium alloy.

[0075] Embodiment 4

[0076] A magnesium alloy material based on SLM laser 3D printing technology is composed of the following mass fractions of elements:

[0077] Al: 8.7%, Zn: 0.5%, Mn: 0.4%, Bi: 2%, impurities: 0.05%, and the rest is Mg.

[0078] The preparation method of the magnesium alloy material based on SLM laser 3D printing technology and high-strength magnesium alloy shaped part is as follows:

[0079] (1) The AZ91D magnesium alloy powder and Bi powder obtained by gas atomization are respectively subjected to ball milling, and then the two are weighed according to the mass fraction percentage of 49:1, and then subjected to ball milling and powder mixing again to reach the specified particle size, and then dried at 60℃ under vacuum conditions for 4h to obtain the required printing raw powder;

[0080] (2) The magnesium alloy plate is processed to a thickness of 2cm as a substrate, and is preheated to a temperature of 180℃. On the other hand, the forming cavity with the installed substrate is subjected to deoxidation treatment until the internal oxygen content is 200ppm or less;

[0081] (3) SLM forming is carried out in a pure argon inert atmosphere environment, and the specific process parameters are as follows: laser output power is 250W, laser diameter is about 0.1mm, layer thickness is 30μm, scanning speed is 720mm / s, scanning interval is 100μm, scanning strategy is strip scanning, and angle is 67°;

[0082] (4) A high-strength magnesium alloy material based on SLM laser 3D printing technology is obtained by layer-by-layer scanning and melting to a certain thickness.

[0083] (5) The tensile strength of the sample of the present example is 343 MPa and the yield strength is 235 MPa at room temperature. Compared with the conventional cast AZ91D magnesium alloy, it is increased by 37.2% and 46.9%, respectively. The formed piece is subjected to a constant tensile force of 70 MPa at 150°C to obtain a creep rupture life of 144 h, which is increased by 48.4% compared with the conventional cast AZ91D magnesium alloy.

[0084] In addition, in addition to the above-mentioned Examples 1-4, orthogonal experiments of different SLM process parameters are also carried out. The laser output power is changed in the range of 150-300 W with a step of 25 W, the layer thickness is changed in the range of 30-50 μm with a step of 10 μm, the scanning speed is changed in the range of 500-1200 mm / s with a step of 100 mm / s, and the scanning pitch is changed in the range of 100-160 μm with a step of 20 μm. The results show that when the laser output power is 200-300 W, the layer thickness is 30-40 μm, the scanning speed is 600-1000 mm / s, and the scanning pitch is 100-120 μm, all have good SLM forming effect.

[0085] Comparative Example 1

[0086] This example is used for comparison with the above four examples. The AMZ91D magnesium alloy material based on traditional casting forming is composed of the following mass fractions of elements:

[0087] Al: 9%, Zn: 0.5%, Mn: 0.4%, no Bi added, impurities: 0.05%, and the rest is Mg.

[0088] The tensile strength of the cast forming piece is 250 MPa, the yield strength is 160 MPa, the elongation at break is 8.2%, and the creep rupture life at 150°C and 70 MPa is 97 h.

[0089] Comparative Example 2

[0090] This example is used for comparison with the above four examples, i.e. the AMZ91D magnesium alloy material based on SLM laser technology is composed of the following mass fractions of elements:

[0091] Al: 9%, Zn: 0.5%, Mn: 0.4%, no Bi added, impurities: 0.05%, and the rest is Mg.

[0092] The magnesium alloy material based on SLM laser 3D printing technology and the preparation method thereof are as follows:

[0093] (1) The AZ91D magnesium alloy powder obtained by gas atomization is ball milled to reach the specified particle size, and then dried at 60°C under vacuum conditions for 4 h to obtain the required printing raw material powder;

[0094] (2) The magnesium alloy plate is processed into a thickness of 2 cm as a substrate, and is preheated to a temperature of 180°C. On the other hand, the forming cavity with the installed substrate is subjected to oxygen removal treatment until the internal oxygen content is 200 ppm or less;

[0095] (3) SLM forming is carried out in a pure argon inert atmosphere environment, and the specific process parameters are as follows: laser output power is 200 W, laser diameter is about 0.1 mm, layer thickness is 30 μm, scanning speed is 600 mm / s, scanning spacing is 100 μm, scanning strategy is strip scanning, and angle is 67°;

[0096] (4) A certain thickness of a magnesium alloy material based on SLM laser 3D printing technology is obtained by layer-by-layer scanning and melting.

[0097] (5) At room temperature, the tensile strength of the sample of the present comparative example is 276 Mpa, and the yield strength is 198 Mpa. Compared with the traditional cast AZ91D magnesium alloy, it is increased by 10.4% and 23.8%, respectively; the formed piece is subjected to a constant tensile force of 70 Mpa at 150°C, and the creep rupture life is 111 h, which is increased by 14.4% compared with the traditional cast AZ91D magnesium alloy. On the other hand, all the performances are lower than those of Examples 1-4.

[0098] Comparative Example 3

[0099] This example is used for comparison with the above four examples, that is, a magnesium alloy material based on SLM laser 3D printing technology, which is composed of the following mass fractions of elements:

[0100] Al: 8%, Zn: 0.5%, Mn: 0.4%, Bi: 3%, impurities: 0.05%, and the rest is Mg.

[0101] The magnesium alloy material based on SLM laser 3D printing technology and the preparation method thereof, the specific implementation steps are as follows:

[0102] (1) The AZ91D magnesium alloy powder and Bi powder obtained by gas atomization are respectively subjected to ball milling, and then the two are weighed according to the mass fraction percentage of 97:3, and then subjected to ball milling and powder mixing again to reach the specified particle size, and then dried under vacuum conditions at 60°C for 4 h to obtain the required printing raw powder;

[0103] (2) The magnesium alloy plate is processed into a thickness of 2 cm as a substrate, and is preheated to a temperature of 180°C. On the other hand, the forming cavity with the installed substrate is subjected to oxygen removal treatment until the internal oxygen content is 200 ppm or less;

[0104] (3) The SLM forming is carried out in a pure argon inert atmosphere, and the specific process parameters are as follows: the laser output power is 200 W, the laser diameter is about 0.1 mm, the layer thickness is 30 μm, the scanning speed is 600 mm / s, the scanning interval is 100 μm, the scanning strategy is strip scanning, and the angle is 67°;

[0105] (4) A magnesium alloy material based on the SLM laser 3D printing technology is obtained by layer-by-layer scanning and melting.

[0106] (5) At room temperature, the tensile strength of the sample of the present comparison example is 311 Mpa, and the yield strength is 205 Mpa. Compared with the traditional cast AZ91D magnesium alloy, the tensile strength and the yield strength are respectively increased by 24.4% and 28.1%; the formed piece is subjected to a constant tensile force of 70 Mpa at 150℃, and the creep rupture life is 128 h, which is increased by 32% compared with the traditional cast AZ91D magnesium alloy, and the improvement effect is lower than that when the Bi element is added in an amount of 1-2%; on the other hand, the elongation at break is sharply decreased compared with the example and the comparison example 1, and is decreased to 4.4%, so the comprehensive strength performance is obviously decreased.

[0107] The above examples are only examples, for example, in addition to using the laser selective melting magnesium alloy powder in the present application and obtaining the magnesium alloy formed piece by SLM, the powder can also be combined with other different alloy powders according to actual needs, each kind of powder corresponds to a printing area, and the preparation of the formed piece with different areas and different components is realized.

[0108] It is easy for those skilled in the art to understand that the above only describes the preferred embodiments of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for forming an SLM magnesium alloy formed part with good thermal stability and high density by selective laser melting, characterized in that: The specific steps include: (1) Drying the magnesium alloy powder for selective laser melting, and at the same time, installing the substrate in the forming cavity of selective laser melting, and preheating the substrate; the magnesium alloy powder for selective laser melting is composed of the following components in percentage by mass: Composition: Al element: 8.5-9.0%, Zn element: 0.5-1%, Bi element: 1-2%, Mn element: 0.2-0.4%, impurity: ≤0.05%, and the rest is Mg element; the Bi element can enhance the precipitation strengthening effect during laser printing; (2) Using the magnesium alloy powder for laser selective melting, laser selective melting is performed in an inert atmosphere, and magnesium alloy formed parts are obtained by scanning layer by layer; The process parameters of the laser selective melting are set as follows: laser output power is 200-300 W, layer thickness is 30-40 μm, scanning speed is 600-1000 mm / s, scanning spacing is 100-120 μm, scanning strategy is strip scanning, and the angle is 67°.

2. The method according to claim 1, wherein: In the step (1), the preheating temperature used in the preheating is 150-200°C.

3. The method according to claim 1, wherein: In the step (2), the inert atmosphere is an argon atmosphere; The oxygen content of the laser selective melting molding cavity does not exceed 200 ppm.

4. The method according to claim 1, wherein: In the step (2), the inert atmosphere is a pure argon atmosphere.

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