| As the lightest structural material,magnesium alloy has a great application prospect in the fields of aerospace,automobile,and medical treatment.However,the processing and manufacturing of magnesium alloy faced many difficulties due to its thermal sensitivity.Wire arc additive manufacturing(WAAM)based on low heat input cold metal transition technology(CMT)is a new research hotspot in magnesium alloy processing.In this study,based on the existing studies on the deposition trajectory of linear type,three types of other new deposition trajectories with the same deposition efficiency―namely triangular trajectory,trapezoidal trajectory,and circular trajectory―were designed to improve the property of the CMT-WAAM processing.The microstructural characteristics of CMT single-pass deposition welds and CMT-WAAM thin-walled components of magnesium alloy were studied and analyzed under these three types of deposition trajectories.The results of CMT single-pass deposited welds with three trajectories show that the deposition process’ s energy input and molten pool morphology are periodic changes with different characteristics,and the weld’s formation characteristics are significantly different from the traditional linear deposition trajectory.The alternating grain orientation of the weld is significantly enhanced.Among the three deposition trajectories,the arc energy of triangular trajectory diverges from the weld axis to both sides,the arc concentrated heat action on substrate is weak and the heat affected zone is the smallest;the heat accumulation of trapezoidal trajectory on weld axis area is the strongest,the weld depth of fusion is the largest,and the weld grain is the coarsest;the circular trajectory’s inhibition effect on columnar crystal is the strongest because the deposition path of circular trajectory is the longest,the pool oscillation is intense,and the weld metal remelting ratio is the highest.Compared with the traditional linear deposition trajectory for Mg alloy wire arc additive manufacturing,applying the three new deposition trajectories can significantly reduce the heat accumulation effect on the component and achieve the modulation of the microstructure characteristics.The microstructural characteristics analysis of the three trajectories CMT-WAAM formed thin-walled components shows that the microstructural characteristics are composed of columnar crystal region,equiaxed crystal region,and local fine crystal region,which does not find heat affected zone.There are different degrees of inhomogeneity in the microstructural characteristics of the three components,the grain morphology and dimensional characteristics vary in different positions of the trajectory and different regions of the component.Compared with the linear trajectory,the three new trajectories have a significant grain refinement effect on the components.The grain size of both the triangular and trapezoidal trajectories is reduced by more than 40 %.Among the three deposition trajectories,the circular trajectory has the strongest inhibitory effect on columnar crystals,which the percentage of columnar crystals ranging from 31.1 % to 43.1 % in different regions of the component.Due to the continuous deviation along the axis of the weld,the three trajectories break the columnar growth pattern of the traditional linear trajectory component,which grow concentratedly along the weld superposition direction.It is helpful to improve the significant anisotropy characteristics of the linear trajectory component.The change of deposition trajectory can effectively improve the microstructure characteristics of the CMT-WAAM magnesium alloy component without affecting the deposition efficiency,which has good effects on the inhibition of heat affected zone,grain size refinement,grain morphology,and growth orientation control of the component.Based on the optimization of deposition trajectory,further studies of the CMT-WAAM magnesium alloy would be helpful to improve the quality of manufactured components. |
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