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CN-122007630-A - High-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive manufacturing method

CN122007630ACN 122007630 ACN122007630 ACN 122007630ACN-122007630-A

Abstract

The invention belongs to the technical field of laser additive manufacturing, and discloses a high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive manufacturing method. The method comprises the steps of preprocessing in the step 1, constructing a two-module pulse hot wire system in the step 2 and setting a process window, constructing a laser coaxial fuse wire system, introducing a high-frequency pulse hot wire power supply with a parallel two-module topological structure into a wire feeding path, metallographic preparation and tissue evaluation in the step 3, mechanical property test in the step 4, and parameter optimization based on defect-tissue-performance three-level screening in the step 5. The invention utilizes the skin effect, transient thermal shock and high-frequency Lorentz force generated by the controlled high-frequency pulse current in the wire feeding process to actively break the growth of dendrites and increase the nucleation rate in a molten pool, thereby promoting the equiaxial crystal transformation (CET) of columnar crystals and obtaining the titanium alloy component with excellent isotropy.

Inventors

  • CONG BAOQIANG
  • YU KAI
  • JIANG ZIHAO
  • YANG MINGXUAN
  • WANG XUHAN
  • ZHANG RAN

Assignees

  • 北京航空航天大学

Dates

Publication Date
20260512
Application Date
20260403

Claims (8)

  1. 1. A high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive manufacturing method is characterized by comprising the following specific steps: Step 1 pretreatment: Cleaning the titanium alloy wire; step 2, constructing a two-module pulse hot wire system and setting a process window: Setting up a laser coaxial fuse wire additive manufacturing system, introducing a high-frequency pulse hot wire power supply with a parallel two-module topological structure into a wire feeding path, outputting a basic value current I b by a first module, outputting a high-frequency pulse current I p by a second module, and presetting technological parameters and hot wire parameters to obtain a printing sample; and 3, carrying out metallographic preparation of microstructure and quantitative evaluation of grain refinement effectiveness: Performing linear cutting, grading grinding, polishing and corrosion treatment on the printing sample, and performing tissue evaluation; Step 4, multi-directional mechanical property test and anisotropic evaluation: Preparing a national standard tensile sample along the X/Y direction and the Z direction of the deposition direction, performing room temperature tensile test to obtain tensile strength UTS, yield strength YS and elongation EL, and calculating an anisotropy coefficient; step 5 parameter optimization based on "defect-tissue-performance" tertiary screening: Based on the microscopic analysis of step 3 and the mechanical feedback of step 4, the following screening logic is established to determine the final parameters: primary screening, namely eliminating parameter combinations which cause serious splashing or discontinuous deposition; Secondary screening, namely, in the process of good forming, optimizing parameters with highest equiaxed crystal proportion; three-stage screening-in the fine grain group, the combination with an anisotropy coefficient% IPAs closest to 1.0 is preferred as the final manufacturing process parameter.
  2. 2. The method for manufacturing the high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse wire additive according to claim 1, wherein in the step 2, the process parameters are laser power 1200W and movement speed 15mm/s.
  3. 3. The method for manufacturing the high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse wire additive according to claim 1, wherein in the step 2, the standard and method for setting hot wire parameters are that firstly, a wire resistance heating pre-experiment is carried out, under the condition that no laser is used for only wire feeding, the instantaneous melting current value I m of the wire at a specific wire feeding speed is measured, and a process window is set by taking the I m as a reference: The average current I of the hot wire is set to be 0.3-0.8I m ; the hot wire base value current I b is set to be 0.3-0.5I; The high-frequency pulse current frequency f p of the hot wire is set to be 20-100 kHz; the duty ratio D of the hot wire high-frequency pulse is set to be 30% -60%; The hot wire high-frequency pulse current I p is set to be (I-I b )/D.
  4. 4. The method for manufacturing the high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive according to claim 1, wherein the specific wire feeding speed is 35mm/s.
  5. 5. The manufacturing method of the high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse wire additive is characterized in that in the step 3, step 3 is carried out by sequentially using 240# SiC sand paper, 600# SiC sand paper, 1000# SiC sand paper and 2000# SiC sand paper, step 3 is carried out by carrying out mechanochemical polishing by using SiO 2 suspension with the particle size of 0.05 mu m, and step 3 is carried out by immersing the titanium alloy laser coaxial fuse wire in corrosive liquid consisting of HF, HNO 3 and H 2 O for 10-15s.
  6. 6. The method for manufacturing the high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive according to claim 5, wherein the volume ratio of HF, HNO 3 and H 2 O is 1:1:18.
  7. 7. The method for manufacturing a high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse wire additive according to claim 1, wherein in the step 3, the structure evaluation criteria is that the crystal grains with the ratio AR <2.0 of the major axis to the minor axis of the crystal grains are defined to be equiaxed grains by observation with an optical microscope, the area ratio of the equiaxed grains in the field of view is counted, and if the area ratio is more than 60%, the parameter set is determined to be effective for grain refinement.
  8. 8. The method for manufacturing the high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse wire additive according to claim 1, wherein in the step 4, the anisotropic evaluation criterion is: Defining the Strength anisotropy coefficient Wherein, the method comprises the steps of, X max is the maximum value of the measured tensile strength, and X min is the minimum value of the measured tensile strength; If% IPAs is not less than 0.95 and |EL Z -EL XY | is not more than 2%, the member is judged to be isotropic.

Description

High-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive manufacturing method Technical Field The invention relates to the technical field of laser additive manufacturing, in particular to an additive manufacturing method for realizing grain refinement in a laser coaxial fuse additive process by utilizing a high-frequency pulse current hot wire mode. Background Titanium alloy is widely applied to the fields of aerospace, ocean engineering and the like due to the excellent characteristics of high specific strength, strong corrosion resistance, high temperature resistance and the like. The laser coaxial fuse wire additive manufacturing technology has the advantages of high deposition efficiency, high material utilization rate, higher forming precision, suitability for manufacturing large-scale structural parts and the like. However, due to the low thermal conductivity of titanium alloys and the extremely large temperature gradient and rapid cooling characteristics that exist during laser additive manufacturing, the as-deposited structure typically exhibits coarse as-formed beta columnar crystals and is prone to epitaxial growth along the height of the deposit. The coarse columnar crystal structure causes great differences in mechanical properties of the component in different directions (namely remarkable anisotropism), and severely limits the application of the component in a main bearing structure piece. To solve the above problems, the prior art generally employs external field assistance (e.g. ultrasound, interlayer plastic deformation) or the addition of grain refiners. However, the outfield equipment is complex and difficult to integrate, and the refiner changes the material composition and is not suitable for aviation grade titanium alloy. Although a hot wire laser material-increasing process exists in the prior art, the current of the hot wire laser material-increasing process mostly adopts a constant current mode, and the main purpose is only to improve the deposition efficiency by utilizing the Joule heat, and the solidification behavior of a molten pool is not actively regulated and controlled by utilizing a current waveform. The limitation of the prior art is that the stable heat convection mode in the molten pool cannot be broken, and the columnar crystal growth is difficult to inhibit from the dynamics of the molten pool. Therefore, a method for realizing grain refinement and isotropy promotion on the premise of not changing components by actively regulating and controlling the thermodynamic behavior of a molten pool through power parameters and breaking dendrites through high-frequency electromagnetic force and transient thermal shock is needed. In order to solve the problem of coarse grains, there is a method of treating a metal material with an electric pulse in the prior art. For example, the prior art (e.g., CN113444871 a) discloses solid state heat treatment of ferritic stainless steel sheet materials with high frequency pulsed current to achieve stiffening. However, such methods mainly utilize the electro-plastic effect of current in solid metals or promote recrystallization. Such processing logic for "solid forms" cannot be directly applied to "liquid puddle" dominated additive manufacturing processes. The reason is that: 1. The physical field environment is different in that the additive manufacturing involves a rapid solidification process with extremely high temperature gradients, grain control needs to be completed within an extremely short time window (millisecond level) of the liquid-solid interface front, where the long aging mechanism of the solid state process fails. 2. If the high-current high-frequency pulse of the processed plate is directly applied to the wire with small diameter, the wire is easily fused before entering a molten pool, and the printing process is destroyed. 3. The mechanism is lacking that the existing power supply device (such as CN 117144094A) only provides current output, lacks energy control strategy for a wire-laser-molten pool coupling system, and cannot generate magnetic fluid stirring effect for liquid metal. Therefore, a process method capable of balancing wire preheating stability and molten pool dynamics disturbance is needed to be specially used for the laser fuse additive manufacturing liquid solidification process. Disclosure of Invention In view of the above, the invention provides a manufacturing method of a high-frequency pulse current hot wire assisted titanium alloy laser coaxial fuse additive. The invention utilizes the skin effect, transient thermal shock and high-frequency Lorentz force generated by the controlled high-frequency pulse current in the wire feeding process to actively break the growth of dendrites and increase the nucleation rate in a molten pool, thereby promoting the equiaxial crystal transformation (CET) of columnar crystals and obtaining the titanium alloy component with excellent isotr