| Wire Arc Additive Manufacturing(WAAM)has the advantages of flexible manufacturing,high material utilization,high forming efficiency,environmental friendliness and small size limitation of forming parts,which has great potential application value in the manufacturing of large metal components.However,the directional heat dissipation during WAAM stainless steel will cause the growth of coarse columnar grains along the build direction of the components,resulting in strong anisotropy of mechanical properties in WAAM components and reducing its strength.It limit their practical engineering applications.In this paper,304 stainless steel with good welding performance,corrosion resistance and machining performance was used as the research object.Firstly,a set of WAAM equipment was built and the forming process was studied.Then,the microstructure of WAAM-304 stainless steel components was refined by adding nano-sized modifiers(Si C,WC),and the mechanical properties such as strength and hardness were improved,and the anisotropy of mechanical properties was reduced.The research in this paper realized the more excellent mechanical properties of WAAM components,and provided research ideas and reference significance for the improvement of additive manufacturing performance of other metal materials.The main research contents and results of this paper are as follows:(1)Firstly,the WAAM equipment was built,which included hardware design and software development.It mainly included three parts: welding system based on GMAW,three-axis motion platform and control system.Through the control system,the displacement,velocity and acceleration of the gantry motion platform were controlled by using the man-machine interaction interface.The welding torch was fixed on the gantry frame by aluminum alloy buckle,and the welding torch motion path was realized by driving the three-axis motion to complete the rapid forming of the component.Printing test was carried out after the completion of the WAAM experimental platform,and the solid components(thin-walled wall components,spiral thin-walled components and multi-track and multi-layer components)were successfully printed.Through the component profile,it can be found that there was no obvious porosity and the forming was good.(2)Based on the WAAM platform,the forming process experiment of 304 stainless steel was carried out to study the influence of process parameters on the morphology and size of single-track single-layer and single-track multi-layer deposits.The results showed that when the welding current was fixed and the traveling speed was too fast(or the traveling speed was fixed and the welding current was too small),the deposition quality of the deposited layer was significantly reduced and the welding path was discontinuous.When the welding current was fixed and the traveling speed was too slow,the molten metal overflows on both sides and the weld bead was too wide.In the single-track multi-layer experiment,the optimal forming process parameters range of 304 stainless steel single-pass multi-layer was obtained by analyzing the forming process and morphology,which laid the foundation for the forming process experiment of introducing modifier.(3)The effects of nano-sized(particle diameter ≤ 1 μm)modifiers Si C and WC on the microstructure and mechanical properties of WAAM-304 stainless steel were studied by coating hard ceramic alcohol solution in WAAM process.The results showed that the dendritic structure oriented along the longitudinal direction(LD)in the component with Si C and WC was effectively transformed into fine grain structure,and with the increase of Si C and WC content in the thin-walled wall component,there were more uniform microstructure and fine grains in the component.At the same time,the hardness,yield strength and ultimate strength are significantly improved.The the yield strength of transverse direction(TD)and LD component with Si C increased from 306 MPa and 303 MPa to 351 MPa and 347 MPa,respectively,with an increase of about 15 %.However,the yield strengths in the transverse and longitudinal directions of the WC-added components increased to381 MPa and 379 MPa,an increase of about 25%,which was higher than that of the Si C-added components.The ultimate strength in the TD and LD of the Si C-added component increased from 604 MPa and 550 MPa to 727 MPa and 695 MPa,respectively,while the ultimate strength in the transverse and longitudinal directions of the WC-added component increased to 714 MPa and 707 MPa,respectively.Compared with the components without these two modifiers,the ultimate strength is significantly improved,and the anisotropy in TD and LD directions is also significantly decreased.The improvement of these mechanical properties is attributed to more uniform microstructure and finer grains. |
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