Electron Beam Welding Procedure Of Ti40/TC4 Dissimilar Titanium Alloy Joint And Microstructure And Properties Of Welded Joints

This paper bings out research aiming at the electron beam welding(EBW)process,microstructure and properties of 3 mm thick Ti40/TC4 titanium alloy.It conducts analysis the macroscopic forming,microstructure and mechanical properties of Ti40/TC4 dissimilar titanium alloy electron beam welded Jointss by using optical microscopy,scanning electron microscopy,energy dispersive spectroscopy,X-ray diffraction phase analysis,microhardness and room temperature tensile test.It also make an inquiry of the effects of different technological parameters on the microstructure and properties of Ti40/TC4 dissimilar titanium alloy.Consequently,the optimal process parameters of Ti40 / TC4 heterogeneous titanium alloy electron beam are obtained.The results show that:The penetration width is inversely proportional to the welding speed before and after penetration welding,while proportional to the welding speed when penetrating conditions.The increased scan frequency makes the weld appearance gradually change from bell shape to funnel shape,and large scan frequency or the use of square wave scanning will make the weld surface unstable area and accoMPanied by obvious defects.The surface width of the linear type scan weld seam is larger than that of the circular arc type scan.Increasing the welding speed after maintaining the weld penetration can have a slight control effect on the defect.When scan frequency selected at 400 Hz,the use of linear type scan significantly improve the defects.No scanning electron beam welding depth is almost no pores.When the welding speed is slow,the increased amount of metal in the base metal making the number of stomata in the weld increases.When using the linear type scan waveform,the increased scan frequency makes the number of stomata to show a decreasing trend,and the stomatal size is gradually smaller as well.The number of stomata in the linear type scan is significantly smaller than that of the circular arc type scan,and the stomatal size also shows a decreasing trend.The upper part of the welds of the non-scanning electron beam welded Jointss is β-columnar crystal and a few equiaxed β grains.The β-columnar crystal have dark spots α phase precipitation inside,and the edge of the fusion line has a macro-segregation.The lower part of the weld is larger than the upper part,and the number of equiaxed grains increased with a small amount of Ti5Si3.The grain size of Ti40 heat affected zone did not change significantly,but a small amount of α phase precipitation.TC4 heat affected zone β phase coarse,grain boundary blurred and α ’needle-like martensite intertwined fine α-sheet structure.The periodic agitation of the linear type scan has improved the macro-segregation phenomenon in the weld effectively,and the grain in the weld zone is converted to equiaxed and refined obviously.It is difficult for Circular arc type scan to work to stirred pool,refine the role of grain and produces weld zone macro-segregation.The increase in scan frequency aggravates the cyclical agitation of the bath,and the precipitation of α phase in the weld zone increases.The welding speed has little effect on the hardness,when the scanning function is not added,the microhardness curve increases first and then decreases.Ti40 side heat affected zone average hardness higher than Ti40 base material 15-25 HV,TC4 side heat affected zone average hardness higher than TC4 base material 20-40 HV,the average hardness of the upper part of the weld zone is 358 HV lower than the lower part 10-15 HV,TC4 side heat affected zone hardness reached peak value 383 HV.The scan frequency increases the hardness of the weld zone.When the scan frequency is 1000 Hz,the upper part and lower part hardness of the weld zone is higher than no scanning electron beam welding for 35-52 HV and up to 408 HV.Linear type scan is higher than the average hardness of the circular arc type scan weld seam for 23-41 HV,the circular arc type scan weld seam average hardness than that of did no scanning Joints weld seam hardness for 5-10 HV.When the welding speed is too low,the plastic of the Joints decreases obviously,the tensile strength reduces slightly,and the tensile specimen is broken in the fused area.When the scan frequency is too low or too high,Joints strength and plasticity decreased.When the scan frequency is too low,the tensile specimen is broken in the fused area,When the specimen is too high,the tensile specimen is broken in the weld zone.The rest of the joints are all broken in the Ti40 base material.Linear type scan has improved performance,while circular arc type scan did not play a strengthening effect but has weakened the effect.The mixed fracture characteristic,which constituted of intergranular fracture,cleavage fracture and trans-granular fracture,can be observed in the fracture surface of Ti40 base metal.The tensile specimen is broken in the fusion zone and the weld zone,the fracture is characterized with ductile fracture and Quasi cleavage fracture,stomatal and collapse will have a negative i MPact on tensile properties.