Study On The Mechanism And Mechanical Properties Of Selective Laser Melting Of Titanium Alloy Thin-walled Structures

Titanium alloy is a typical lightweight material,which has the characteristics of high specific strength,good corrosion resistance and excellent comprehensive mechanical properties.Thin-walled structure is a main structural feature of lightweight parts,which is difficult to form by traditional machining method.Selective laser melting(SLM)is a kind of laser additive manufacturing technology based on powder bed.It directly forms metal parts by rapidly melting and solidifying metal powder point by point and layer by layer by high-energy beam laser,which provides an effective forming method for lightweight parts with thin-walled structure.Compared with block structure,the SLM forming of thin-walled structure is more complex in performance control and defect generation mechanism.Therefore,the mechanism and mechanical properties of titanium alloy thin-walled structure fabricated by selective laser melting of were studied in this paper.The main research contents are as follows:(1)Temperature field and molten pool of thin-walled structures formed by SLM based on titanium alloy were researched.The variation law of temperature field during the forming process of titanium alloy thin-walled structure was studied,and the finite element model of thin-walled structure was established.The accuracy of the model was verified by comparing the simulation results with the geometrical dimensions of the molten pool under the corresponding process parameters of the single channel scanning experiment.The similarities and differences of the temperature field of thin-walled structures with different thicknesses were compared,and the law of the temperature field of SLM thin-walled structures with different scanning strategies was analyzed.The study found that during multi-channel scanning,because the laser scans the first current melt channel and repeatedly heats the adjacent melt channel.So scans the next layer,the previous layer will also be heated,which is conducive to the release of thermal stress.Therefore,the thicker the wall thickness of the thinwalled structure,the more favorable it is for forming.(2)Carry out research on the forming quality of thin-walled structures based on the SLM process.Study the formability of thin-walled structures with different wall thicknesses and different placement positions,explore the limit wall thickness,ultimate forming height and dimensional accuracy of the SLM thin-walled structure in the direction of wall thickness,and establish the wall thickness,placement and limit forming of thin-walled structures Highly mathematical model.The study found that the forming height of titanium alloy thin-walled structure increases gradually with the increase of wall thickness,and the absolute error in the direction of wall thickness gradually decreased.When the wall thickness reaches 1mm and above,the thin-walled structure can be formed to the design height of 100 mm.There is a nonlinear relationship between the wall thickness,placement position and the ultimate forming height of thin-walled structures.(3)Carry out research on mechanical properties of thin-walled structures based on SLM process.Study the effect of wall thickness and forming height on the mechanical properties of thin-walled structures,explore the anisotropy of mechanical properties of thin-walled structures under different wall thicknesses and different forming heights,and the anisotropy of thin-walled structures was analyzed as a function of wall thickness and sampling height.The study found that with the increase of the wall thickness,the mechanical properties of the thin-walled structure gradually improved.With the increase of the forming height under the same wall thickness,the mechanical properties of the thin-walled structure gradually decreased.The smaller the wall thickness of the thin-walled structure,the greater the anisotropy in the sampling height direction.When the wall thickness reaches 1.8 mm,the anisotropy in the sampling height direction tends to be stable.(4)Carry out research on the microstructure and defects of thin-walled structures based on the SLM process.Through metallographic microscope,scanning electron microscope and CT technology,the defects of thin-walled structures are explored,the source and difference of defects in solid and thin-walled structures are explored,and the reasons for the change of mechanical properties of solid and thin-walled structures are analyzed.The study found that the microstructure of solid and thin-walled structures is mainly acicular martensite,and the microstructure has little effect on the mechanical properties of thin-walled structures.The defects of the thin-walled structure are the inclusion of powder pores,while the solid defects are small and spherical pores.