Arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts

Abstract

The present invention provides an arc additive manufacturing method for a Mg-Y-Nd-Zr rare earth magnesium alloy structural part, using Mg-Y-Nd-Zr as a wire material of the main alloying element as a raw material, using a CMT arc additive process, starting from the first layer on the substrate in an upward growth manner according to a preset program, printing layer by layer until the last layer is printed to obtain a print; wherein, when printing each layer, a double arc is adopted, and the substrate or the previous layer of deposited body is preheated in front with a TIG arc, and the CMT additive arc is processed in an additive manner on the preheated substrate or the previous layer of deposited body, thereby achieving preheating and additive simultaneously, and improving the mechanical properties and surface quality of the formed component; the print is transferred to a heat treatment furnace by heat preservation using an insulation box, and after being kept warm for a period of time, heat treatment is performed to obtain the required Mg-Y-Nd-Zr rare earth magnesium alloy structural part. The method of the present invention improves the mechanical properties and surface quality of the formed component and improves the additive efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of arc additive manufacturing, and in particular to an arc additive manufacturing method for a Mg-Y-Nd-Zr rare earth magnesium alloy structural part. Background Art

[0002] Mg-Y-Nd-Zr (WE series) rare earth magnesium alloys are characterized by high temperature resistance and high strength. The addition of rare earth elements significantly enhances the alloy's high-temperature mechanical and thermal properties. They are widely used in aerospace applications, such as in new aircraft engine gearboxes and helicopter transmission systems, and are gradually replacing medium-strength aluminum alloys in some structures. Furthermore, their high ignition point makes them widely applicable in coal mines, natural gas, and components exposed to easily combustible materials.

[0003] Currently, the main manufacturing method for rare earth magnesium alloy structural parts is casting, but the casting difficulty increases for complex structural parts. The magnesium alloy shrinks greatly during solidification, and there will be defects such as shrinkage, shrinkage cavities and oxidation inside the casting.

[0004] Arc additive manufacturing has the advantages of flexible forming process, high material utilization, low cost, and excellent mechanical properties of the deposited body. It is especially suitable for manufacturing complex structural parts. However, due to the high thermal conductivity and fast heat dissipation of magnesium alloys, when the first layer of arc additive is performed, the heat generated by the arc will be quickly conducted through the substrate and further dissipated into the air. Due to insufficient heat, the liquid metal pool formed on the substrate within the range of the arc is small in range, shallow in depth, and unstable in shape, resulting in an unstable bond between the first layer of additive metal and the substrate, which will cause pore defects. At the same time, the stress of the subsequent additive body will gradually accumulate to the bonding site, causing cracking. In severe cases, the deposited body and the substrate cannot be bonded. The most commonly used solution at present is to preheat the substrate. The current methods for preheating the substrate by arc additive are mainly contact heating, induction heating, and in-situ heating.

[0005] Contact heating requires the use of an asbestos electric blanket in contact with the substrate and the deposited body, generating heat conduction between the two for heating. However, this method has low heat conduction efficiency, takes a long time, and consumes a lot of energy. In addition, for the deposited body with a complex structure and a large area, when performing interlayer heating, the use of contact heating will require more asbestos electric blankets to ensure that the surface to be heated can be fully covered, which means that the area of the asbestos electric blanket that is not in contact with the deposited body increases rapidly, causing more heat to be dissipated into the air, resulting in energy waste.

[0006] In the induction heating method, since magnesium alloys are not ferromagnetic, the induction heating efficiency of magnesium alloys is lower than that of ferromagnetic materials, usually between 45% and 60%. Therefore, induction heating consumes a lot of energy and takes a long time.

[0007] In-situ heating uses an additive arc to add 1 to 2 layers of material on the substrate to increase the substrate temperature. Its advantage is that the additive arc is used directly for heating without the need for an external heat source. However, its disadvantages are obvious. The essence of in-situ heating is to add material on the substrate, which will change the surface shape of the substrate and affect the transition layer between the deposited body and the substrate. Defects will occur in the transition layer. At the same time, the 1 to 2 layers of metal used for in-situ heating will be wasted. In addition, in-situ heating is only suitable for heating the substrate and cannot be used to heat the deposited body. Summary of the Invention

[0008] The purpose of the present invention is to address the deficiencies in the prior art and provide an arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts. The method uses Mg-Y-Nd-Zr rare earth magnesium alloy wire as the filling material, adopts a dual arc method, and uses a TIG arc for preheating in the front and a CMT additive arc for additive processing in the back to improve the mechanical properties and surface quality of the formed components and improve the additive efficiency.

[0009] The present invention relates to an arc additive manufacturing method for a Mg-Y-Nd-Zr rare earth magnesium alloy structural part, comprising the following steps:

[0010] Using Mg-Y-Nd-Zr as the main alloying element wire as the raw material, the CMT arc additive process is used to print layer by layer on the substrate in an upward growth manner according to the preset program until the last layer is printed to obtain the printed part;

[0011] Among them, when printing each layer, dual arcs are used, with the TIG arc in front to preheat the substrate or the previous layer of deposited body, and the CMT additive arc in the back to perform additive processing on the preheated substrate or the previous layer of deposited body, thereby achieving preheating and additive processing at the same time, improving the mechanical properties and surface quality of the formed components;

[0012] The printed parts are transferred to a heat treatment furnace in an insulation box. After a period of insulation, heat treatment is performed to obtain the required Mg-Y-Nd-Zr rare earth magnesium alloy structural parts.

[0013] As an optional embodiment, the composition of the wire includes, by mass percentage: 4.8-5.5% Y, 4.0-4.5% Nd, 0.4-0.5% Zr, Gd≤0.01%, Zn≤0.015%, Fe≤0.015%, Mn≤0.015%, and the remainder is Mg.

[0014] As an optional embodiment, an AC TIG welding arc is used to preheat the substrate or the previous deposited layer, with a tungsten electrode diameter of 2 mm, a welding current of 40 to 80 A, a welding speed of 500 to 2000 mm / min, a preheating temperature of the substrate of 135 to 150°C, and a preheating temperature of the previous deposited layer of 120 to 130°C.

[0015] As an optional embodiment, in the CMT arc additive process, the dry extension is 13 to 16 mm, and the arc additive speed, wire feeding speed and welding current are determined according to the parameters of the rare earth magnesium alloy workpiece.

[0016] As an optional implementation, the arc additive speed is 0.02-0.03 m / s, the wire feeding speed is 5.5-6.0 m / min, and the welding current is 140-150 A.

[0017] As an optional embodiment, during the arc additive process, a mixture of argon and helium is used as the shielding gas, wherein the volume proportions of the gases are: 60-70% argon and 30-40% helium.

[0018] As an optional embodiment, the temperature in the heat preservation box is 90-110°C.

[0019] As an optional embodiment, after the printed part enters the heat treatment furnace, it is kept warm at a temperature of 120 to 150° C. for 10 to 12 hours.

[0020] As an optional implementation, the printed part after the insulation is completed is subjected to heat treatment, including solution treatment and aging treatment.

[0021] As an optional embodiment, the solution treatment is: keeping the temperature at 520°C to 525°C for 6 to 8 hours; the aging treatment is: keeping the temperature at 240°C to 250°C for 16 to 20 hours.

[0022] Compared with the prior art, the present invention has the following significant beneficial effects:

[0023] The arc additive manufacturing method of the Mg-Y-Nd-Zr rare earth magnesium alloy structural component of the present invention uses Mg-Y-Nd-Zr rare earth magnesium alloy wire as the filling material, adopts a dual arc, and performs processing in a manner of preheating with a TIG arc in the front and additively manufacturing with a CMT additive arc in the back. When the TIG arc is heated, no molten pool is formed on the surface of the substrate, and the surface flatness of the substrate is not changed, thereby not affecting the transition layer between the deposited body and the substrate, avoiding defects in the transition layer. Moreover, because the TIG arc adopts the AC welding mode, it has a cathode cleaning effect, which can clean the oxide film on the surface of the magnesium alloy, reduce the intrusion of magnesium alloy oxides during the additive process, reduce the occurrence of defects in the deposited body, and improve the mechanical properties and surface quality of the formed component.

[0024] The arc additive manufacturing method of the Mg-Y-Nd-Zr rare earth magnesium alloy structural part of the present invention adopts TIG arc as a heat source for preheating, and the TIG arc performs reciprocating motion and gradually heats the part using arc heat. The arc heating has high heat transfer efficiency, which improves the additive efficiency. In addition, the TIG arc can fully act on the deposited body, and there will be no situation where the heat source outputs heat but the deposited body cannot absorb it. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a process flow chart of the arc additive manufacturing method of the Mg-Y-Nd-Zr rare earth magnesium alloy structural part of the present invention.

[0026] Figure 2 Schematic diagram of a dual path of preheating and deposition in an exemplary embodiment of the present invention.

[0027] Figure 3 It is a schematic structural diagram of an exemplary print transfer incubator of the present invention.

[0028] Figure 4 This is a physical picture of the rare earth magnesium alloy structural component obtained in Example 1 of the present invention.

[0029] Figure 5 3 is a cross-sectional view of the rare earth magnesium alloy structural component obtained in Example 1 of the present invention; wherein, part a is the sample in the deposited state, and part b is the sample after heat treatment.

[0030] Figure 6 This is a microstructure diagram of the rare earth magnesium alloy structural component obtained in Example 1 of the present invention; wherein, part a is the sample in the deposited state, and part b is the sample after heat treatment.

[0031] Figure 7 This is a physical picture of the sample obtained in Comparative Example 1 of the present invention.

[0032] Figure 8 This is a physical picture of the sample obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0033] In order to better understand the technical content of the present invention, specific embodiments are given and described below with reference to the accompanying drawings.

[0034] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to be comprehensive. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of a number of ways.

[0035] Combine Figure 1As shown in the flowchart, the exemplary arc additive manufacturing method of the present invention for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts includes the following steps:

[0036] Using Mg-Y-Nd-Zr as the main alloying element wire as the raw material, the CMT arc additive process is used to print layer by layer on the substrate in an upward growth manner according to the preset program until the last layer is printed to obtain the printed part;

[0037] Among them, when printing each layer, dual arcs are used, with the TIG arc in front to preheat the substrate or the previous layer of deposited body, and the CMT additive arc in the back to perform additive processing on the preheated substrate or the previous layer of deposited body, thereby achieving preheating and additive processing at the same time, improving the mechanical properties and surface quality of the formed components;

[0038] The printed parts are transferred to a heat treatment furnace in an insulation box. After a period of insulation, heat treatment is performed to obtain the required Mg-Y-Nd-Zr rare earth magnesium alloy structural parts.

[0039] As an optional embodiment, the composition of the wire includes, by mass percentage: 4.8-5.5% Y, 4.0-4.5% Nd, 0.4-0.5% Zr, Gd≤0.01%, Zn≤0.015%, Fe≤0.015%, Mn≤0.015%, and the remainder is Mg.

[0040] At present, the arc additive manufacturing of rare earth magnesium alloys mainly uses Mg-Gd-Y series magnesium alloys, whose main alloying elements are Gd and Y. They can improve the performance of rare earth magnesium alloys to a certain extent, but the cost of adding Gd elements is relatively high. The use of Mg-Y-Nd-Zr (WE series) magnesium alloys has lower costs and a wider range of applications.

[0041] As an optional embodiment, an AC TIG welding arc is used to preheat the substrate or the previous deposited layer, with a tungsten electrode diameter of 2 mm, a welding current of 40 to 80 A, a welding speed of 500 to 2000 mm / min, a preheating temperature of the substrate of 135 to 150°C, and a preheating temperature of the previous deposited layer of 120 to 130°C.

[0042] As an optional embodiment, in the CMT arc additive process, the dry extension is 13 to 16 mm, and the arc additive speed, wire feeding speed and welding current are determined according to the parameters of the rare earth magnesium alloy workpiece.

[0043] As an optional implementation, the arc additive speed is 0.02-0.03 m / s, the wire feeding speed is 5.5-6.0 m / min, and the welding current is 140-150 A.

[0044] As an optional embodiment, during the arc additive process, a mixture of argon and helium is used as the shielding gas, wherein the volume proportions of the gases are: 60-70% argon and 30-40% helium.

[0045] As an optional embodiment, the temperature in the heat preservation box is 90-110°C.

[0046] As an optional embodiment, after the printed part enters the heat treatment furnace, it is kept warm at a temperature of 120 to 150° C. for 10 to 12 hours.

[0047] As an optional implementation, the printed part after the insulation is completed is subjected to heat treatment, including solution treatment and aging treatment.

[0048] As an optional embodiment, the solution treatment is: keeping the temperature at 520°C to 525°C for 6 to 8 hours; the aging treatment is: keeping the temperature at 240°C to 250°C for 16 to 20 hours.

[0049] In a typical embodiment, an arc additive manufacturing method for a Mg-Y-Nd-Zr rare earth magnesium alloy structural part is provided, comprising the following specific steps:

[0050] S1. Select the corresponding wire material based on the structural component material composition requirements. The content of the main rare earth elements should meet the requirements. The wire diameter should be 1.2mm to 1.6mm. It must be well packaged and free of obvious oxides and impurities on the surface.

[0051] Main material components (mass fraction): Y 4.8~5.5%, Nd 4.0~4.5%, Zr0.4~0.5%, Gd≤0.01%, Zn≤0.015%, Fe≤0.015%, Mn≤0.015%, and the rest is Mg.

[0052] WE54 is preferred for deposition substrate.

[0053] S2. Preprocess the 3D model of the target structural component to generate an additive model, and slice it using additive processing software, with a layer height of 2 to 3 mm.

[0054] Plan the deposition path for each slice layer. The path is preferably a serpentine reciprocating path with a reciprocating spacing of 1.5 to 3 mm. At the same time, the paths of adjacent slices need to be staggered with a staggered distance of 1 to 1.5 mm.

[0055] In the path planning of each slice, the arc starting point and arc extinguishing point should not overlap with the previous layer, and the interval needs to be greater than 20mm, otherwise local collapse will occur. The planned path program is imported into the robot control system;

[0056] The TIG arc heating path is planned. The heating path and the additive path have the same direction but different waveforms.

[0057] Preferably, the interlayer heating path (i.e., heating the deposited body) adopts a sinusoidal waveform, which is different from the rectangular waveform of the additive deposition path. At the same time, the waveform width and spacing value of the heating path are the same as those of the deposition path, where the width of the additive sample is the waveform width, and the spacing value is the serpentine reciprocating spacing in the deposition path, such as Figure 2 As shown;

[0058] The TIG arc is in front and the additive arc is behind. The TIG arc heats the substrate or the previous layer of deposited body. When the heating temperature reaches the requirement, the CMT additive arc starts to work. The two arcs move and work at the same time, which can realize two paths in the same layer of slice and realize the front and back work of the two arcs.

[0059] S3. Fix the substrate on a workbench, clean it using ultrasonic waves, wipe it with acetone, and air-dry it.

[0060] S4. After cleaning, preheating is performed using a TIG arc to heat the substrate. Robot A controls the TIG arc to heat the substrate according to a planned heating path, controlling the preheating temperature at 135-150°C. The welding current and movement speed of the TIG arc must also be controlled to ensure that the substrate surface does not melt.

[0061] The preferred AC TIG welding arc has a tungsten electrode diameter of 2 mm, a welding current of 40 to 80 A, and a welding speed of 500 to 2000 mm / min.

[0062] S5. When the temperature reaches the target, robot B controls the additive arc to run along the deposition path to achieve metal deposition for each layer.

[0063] The protective gas used is preferably a mixed gas, with a volume ratio of argon 60-70%, helium 30-40%, and a gas flow rate of 20-24 L / min;

[0064] The CMT welding mode is adopted, the dry extension length is 13-16 mm, the arc addition speed is 0.02-0.03 m / s, the wire feeding speed is 5.5-6.0 m / min, and the welding current is 140-150 A.

[0065] S6. After each layer of additive manufacturing is completed, the interlayer temperature needs to be controlled. The TIG arc begins working according to the interlayer heating path. Robot A carries the TIG arc and moves along the deposition path. When the temperature reaches the target, Robot B begins arc additive manufacturing.

[0066] Before adding each layer, a temperature sensor is used to measure the temperature. The interlayer temperature must be kept between 120 and 130°C. The welding current and movement speed of the TIG arc must also be controlled to ensure that the substrate surface does not melt.

[0067] Preferably, an AC TIG welding arc is used, with a tungsten electrode diameter of 2 mm, a welding current of 40 to 80 A, and a welding speed of 500 to 2000 mm / min.

[0068] The TIG arc heats the previous layer of deposited material. When the heating temperature reaches the required level, the additive arc starts working. The two arcs move and work simultaneously, enabling two paths in the same slice layer, and realizing the two arcs working in front and behind.

[0069] TIG arc heating and additive arc deposition are carried out layer by layer to finally complete the manufacturing of rare earth magnesium alloy structural parts.

[0070] S7. After the structural part is added, use the sample transfer insulation box in time to transfer the deposited body to the heat treatment furnace for insulation. The temperature in the box is required to be 100℃.

[0071] In a preferred embodiment, Figure 3 As shown, the structure of the sample transfer insulation box is: a box body 1 and a box door 2 connected to the box body, the box body 1 is surrounded by a metal shell, the inner cavity of the box body 1 is provided with an asbestos layer 11, and the inner wall of the box body is provided with a resistance heating wire 12 and a temperature sensor 13.

[0072] The box body is powered by a built-in lithium battery 3 and is also provided with a temperature controller 4 and a temperature indicator 5 inside the box.

[0073] The working principle is: using a lithium battery power supply, the resistance heating wire heats up, the temperature inside the box rises, the asbestos layer can prevent heat from dissipating outwards, and improve the thermal insulation performance of the box. When the temperature reaches the required temperature, the heating is stopped. Because the box will dissipate heat outwards, the temperature inside the box is lower than the required temperature. The power is turned on, and the resistance heating wire continues to work, so that the temperature inside the box can reach the requirement.

[0074] Conventional arc additive manufacturing processes do not use a transfer box and directly transport samples to a heat treatment furnace. This process is time-consuming, causes the deposited sample to cool, and can lead to cracks at the junction between the substrate and the deposited body. The present invention promptly transfers the sample to an insulated box after the additive process is completed, controlling the ambient temperature of the sample. Furthermore, the insulated box carries its own lithium battery and can be moved with any transport vehicle, eliminating the need for an external power cord. This makes it quick and convenient.

[0075] S8. After the sample enters the heat treatment furnace, it is first kept warm. The temperature setting is: temperature 120-150℃, and the holding time is 10-12h;

[0076] Heat treatment shall be started within 2 hours after the end of insulation. The heat treatment plan includes solution treatment and aging treatment. Solution treatment is carried out at 520℃~525℃ for 6~8 hours, and aging treatment is carried out at 240℃~250℃ for 16h~20h. The furnace temperature is required to be controlled within ±4℃.

[0077] For better understanding, the present invention will be further described below with reference to specific examples, but the processing technology is not limited thereto, and the content of the present invention is not limited thereto.

[0078] Example 1

[0079] 1. According to the material composition requirements of the structural parts, the corresponding wire is selected. The wire composition is: 4.3% Nd, 5.0% Y, 0.41% Zr, 0.006% Gd, 0.012% Zn, 0.015% Fe, 0.015% Mn, and the rest is Mg.

[0080] The wire diameter is 1.2mm, and it is required to be well packaged, with no obvious oxides and impurities on the surface. The deposition substrate is WE54.

[0081] 2. Pre-process the 3D model of the target structural part and generate an additive model using Solidworks software.

[0082] Use R-CAM additive processing software for layered slicing, with a layer height of 2mm. The deposition path of each layer is a serpentine reciprocating path with a reciprocating spacing of 1.5mm. At the same time, the paths of adjacent layers of slices need to be staggered with a staggered distance of 1mm. In the path planning of each layer of slices, the arc starting point and arc extinction point should not overlap with the previous layer, and the interval needs to be greater than 20mm;

[0083] Plan the TIG arc heating path. The heating path adopts a sinusoidal waveform with a waveform pitch of 1.5 mm, and the TIG arc is in front and the additive arc is behind.

[0084] Import the planned path into the robot control system.

[0085] 3. Fix the substrate on the workbench, clean it with ultrasonic wave, wipe it with acetone and let it air dry.

[0086] 4. After cleaning, preheating is performed. The preheating method is to use TIG arc to heat the substrate. Robot A controls the TIG welding gun to move on the substrate, continuously heating the plate, and controlling the preheating temperature to 135-150°C. Use AC TIG welding arc, tungsten electrode diameter of 2mm, welding current of 50A, and welding speed of 1200mm / min.

[0087] 5. After the preheating temperature reaches the required level, Robot B controls the additive arc to follow the deposition path to deposit each layer of metal.

[0088] The process parameters include: the protective gas is a mixed gas of 70% argon and 30% helium, and the gas flow rate is 24L / min;

[0089] The welding mode is CMT, the dry extension is 13 mm, the arc addition speed is 0.02 m / s, the wire feeding speed is 5.6 m / min, and the welding current is 140 A.

[0090] 6. After each layer of additive manufacturing is completed, the interlayer temperature needs to be controlled. The TIG arc starts working according to the interlayer heating path. The interlayer heating path adopts a sine waveform with a waveform spacing of 1.5mm. It is adjusted according to the actual shape of each layer. Robot A carries the TIG arc and moves along the heating path. After the temperature reaches the standard, Robot B starts arc additive manufacturing. Before each layer of additive manufacturing, the temperature is measured using a temperature sensor to ensure that the interlayer temperature is 120-130℃.

[0091] The TIG arc heats the previous layer of deposited material. When the heating temperature reaches the required level, the additive arc starts working. The two arcs move simultaneously, enabling two paths in the same slice, and realizing the two arcs working in front and behind. TIG arc heating and additive arc deposition are carried out layer by layer, and finally the rare earth magnesium alloy structural parts are manufactured.

[0092] 7. After the structural parts are added, use the sample transfer insulation box in time to transfer the deposited body to the heat treatment furnace for insulation. The temperature in the box is required to be 100℃.

[0093] 8. In the heat treatment furnace, the insulation setting is: temperature 130℃, insulation time 12h; heat treatment starts within 2h after the insulation ends. The heat treatment plan includes solution treatment and aging treatment. Solution treatment is kept at 525℃ for 8h, and aging treatment is kept at 240℃ for 18h. The furnace temperature is required to be controlled within ±4℃.

[0094] Comparative Example 1

[0095] The difference from Example 1 is that the substrate and the previous layer of deposited body are not preheated, and the material addition is performed directly.

[0096] Comparative Example 2

[0097] Steps 1 to 6 in Example 1 were followed to obtain a rare earth magnesium alloy print, which was then cooled to room temperature.

[0098] Morphology

[0099] The Mg-Y-Nd-Zr rare earth magnesium alloy deposition sample obtained in this embodiment (such as Figure 4As shown in the figure, the deposited sample was removed from the substrate, and the bottom (joint with the sample) and the top 10mm part of the sample were removed. The remaining part was sampled by wire cutting. After cutting, inlaying, rough grinding, fine grinding, polishing and corrosion, the cross-section formation and microstructure of the deposited body were observed. The results are shown in the figure. Figure 5 and Figure 6 shown.

[0100] exist Figure 5 In a, it can be found that there are pores inside the deposited metal, which mainly occur near the junction line between the serpentine reciprocating lanes, and a small amount occurs in the inner area of a single lane. Using a high-power optical microscope, it is found that Figure 6 aResults show that pores mainly occur at the boundaries of metal grains.

[0101] Depend on Figure 6 As can be seen from b, after heat treatment, the eutectic structure at the grain boundary dissolves, changing from a continuous strip distribution to a short rod and point distribution, and the segregation of Cu elements is improved. At the same time, the pores disappear. After appropriate heat treatment temperature and time, it can be seen that all the pores on the cross section of the deposit disappear. Figure 5 b. At the same time Figure 5 As can be seen from Figure a, there are no pores near the bonding line between the layers. This shows that the TIG arc heating effect of the interlayer metal used in the present invention is good.

[0102] Figure 7 For the sample of comparative example 1, the substrate is not preheated. It can be seen that when the substrate is not preheated, the substrate does not melt in the first layer of arc additive. This is because the arc heat is conducted away by the substrate, and the remaining heat is not enough to melt the substrate. No liquid molten pool is generated on the substrate. As a result, the deposited body and the substrate cannot be combined. After being subjected to the stress of the deposited body, the deposited body and the substrate are completely separated.

[0103] If the sample is not kept warm in time after the arc addition is completed, but heat treatment is performed after the sample cools down, it will be found that the sample will crack before heat treatment. Figure 8 The sample from Comparative Example 2 shown here exhibits cracking. This is due to the rapid release of internal stress generated by continuous deposition during rapid cooling of the sample, which manifests itself at stress concentration points within the structure. Stress concentration near the junction of the deposited sample and the substrate causes transverse cracks to form between the first, second, and third layers of deposited metal, extending across the cross-section of the deposit.

[0104] From the above tests, it can be seen that the surface of the rare earth magnesium alloy structural parts obtained by the method of the present invention is well formed. After preheating with TIG arc, the interlayer bonding of the deposited body is good, especially the bonding between the deposited body and the substrate is good, and no crack defects are found. The molten pool on the substrate is deep, forming a good bond with the first layer of deposited metal. At the same time, timely insulation measures are adopted after the arc addition is completed, so that the internal stress of the deposited body will not be suddenly released and cracks will not occur. Its stress will be gradually released during the heat treatment stage without affecting the deposited body. In addition, there will be tiny pores in the deposited body. If they are not treated, it will affect the mechanical properties. The use of a reasonable heat treatment process can eliminate the internal pores and improve the performance of the sample.

[0105] Mechanical properties testing

[0106] According to GB / T 228.1-2010, Tensile tests on metallic materials — Part 1: Room temperature test methods, tensile specimens were taken from the deposited specimens and tensile tests were performed at room temperature. The tensile test results were compared with the mechanical property requirements for materials of similar composition specified in ISO 3116:2007(E).

[0107]

[0108] It can be seen from the test results that the tensile strength and yield strength of the Mg-Y-Nd-Zr rare earth magnesium alloy deposition sample after heat treatment are higher than the requirements of ISO3116, among which the tensile strength is increased by about 12% and the yield strength is increased by about 30%. The main reasons for the strength increase are the dissolution of the supersaturated solid solution and the precipitation of the strengthening phase. Solid solution strengthening and precipitation strengthening are the main strengthening methods for improving strength. The mechanical performance structure meets the design requirements of Mg-Y-Nd-Zr rare earth magnesium alloy castings, so it can be used to replace rare earth magnesium alloy castings.

[0109] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. An arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts, characterized in that: The following steps are involved: Using Mg-Y-Nd-Zr as the main alloying element wire as the raw material, the CMT arc additive process is used to print layer by layer on the substrate in an upward growth manner according to the preset program until the last layer is printed to obtain the printed part; When printing each layer, dual arcs are used. The TIG arc is used in the front to preheat the substrate or the previous layer of deposited body, and the CMT arc is used in the back to perform additive processing on the preheated substrate or the previous layer of deposited body. The heating path of the TIG arc is consistent with the additive path direction of the CMT arc additive, so that preheating and additive processing can be carried out simultaneously, improving the mechanical properties and surface quality of the formed components. The printed parts are transferred to a heat treatment furnace in an insulation box. After a period of insulation, heat treatment is performed to obtain the required Mg-Y-Nd-Zr rare earth magnesium alloy structural parts.

2. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: The composition of the wire material includes, by mass percentage, 4.8-5.5% Y, 4.0-4.5% Nd, 0.4-0.5% Zr, Gd≤0.01%, Zn≤0.015%, Fe≤0.015%, Mn≤0.015%, and the remainder is Mg.

3. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: AC TIG welding arc is used to preheat the substrate or the previous deposited layer. The tungsten electrode diameter is 2 mm, the welding current is 40~80 A, the welding speed is 500~2000 mm / min, the preheating temperature of the substrate is 135~150℃, and the preheating temperature of the previous deposited layer is 120~130℃.

4. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: In the CMT arc additive process, the dry extension is 13-16 mm, and the arc additive speed, wire feed speed and welding current are determined according to the parameters of the rare earth magnesium alloy workpiece.

5. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: The arc additive speed is 0.02~0.03m / s, the wire feeding speed is 5.5~6.0m / min, and the welding current is 140~150A.

6. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: During the arc additive process, a mixture of argon and helium is used as the shielding gas, with the volume proportions of the gases being: 60-70% argon and 30-40% helium.

7. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: The temperature inside the insulated box is 90~110℃.

8. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: After the printed part enters the heat treatment furnace, it is kept at a temperature of 120~150℃ for 10~12 hours.

9. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 1, characterized in that: After the insulation is completed, the printed parts are subjected to heat treatment, including solution treatment and aging treatment.

10. The arc additive manufacturing method for Mg-Y-Nd-Zr rare earth magnesium alloy structural parts according to claim 9, characterized in that: The solution treatment is: keeping warm at 520℃~525℃ for 6~8h; the aging treatment is: keeping warm at 240℃~250℃ for 16h~20h.

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