In this research, pulverization plate and base of a fuel injector in an automobile electronic-controlled engine was joined by pulsed laser welding. The different welding parameters were evaluated and effect of process...In this research, pulverization plate and base of a fuel injector in an automobile electronic-controlled engine was joined by pulsed laser welding. The different welding parameters were evaluated and effect of process parameters on joint characteristics was analyzed. The optimal process parameters were obtained as follows： welding current 120 A, welding speed 600 ram/rain, pulse duration 1.80 ms and pulse frequency 60 Hz. The microstructure of weld metal was investigated. Results show that the fusion zone is austenitic dendrite, the weld center is equiaxed grain, while the transition zone between fusion zone and weld center is mixed crystal with austenitic dendrite and equiaxed grain. The weld layered phenomenon was observed, and eddy caused by keyhole effect is the main reason for the formation of layered structure in molten pool.展开更多
The experiment of Nd： YAG pulsed laser self-fluxing welding for 304 stainless steel/Ti6Al4V titanium alloy dissimilar metal was carried out. The microstructure properties of welded joint were analyzed by SEM, EDS and...The experiment of Nd： YAG pulsed laser self-fluxing welding for 304 stainless steel/Ti6Al4V titanium alloy dissimilar metal was carried out. The microstructure properties of welded joint were analyzed by SEM, EDS and XRD. The equilibrium lattice constants, enthalpies of formation, cohesive energies, mechanical properties, Debye temperatures and valence electron structures of Ti-Fe intermetallic compounds （IMCs） were calculated by the first principle pseudopotential plane wave method based on density functional theory （DFT）. According to the thermodynamic data of Ti-Fe-Cr compounds, the Gibbs free energy per mole of compound at different temperatures was calculated and their thermal stability was compared. The results show that there are no macroscopic cracks in the welded joints, and the IMCs distributed evenly along the welding interface exhibits 3 distinct layers of microstructure with different colors. The welds interface generates IMCs of TiFe, TiFe 2 and a small amount of Ti 5Cr 7Fe 17 IMCs. Ti-Fe IMCs with high thermodynamic stability and easy alloying formation. The results of Gibbs free energies show that the sequence of precipitates in the interface is Ti 5Cr 7Fe 17 , TiFe 2 and TiFe in high temperature during the metallurgical reaction. The G/B values of Ti-Fe IMCs are greater than the critical value of 0.5, indicating that it is an intrinsic brittleness.展开更多
Laser welding of dissimilar titanium/aluminum alloys has been employed at an increasing rate,particularly in the aerospace industry,owing to its advantages in terms of current design flexibility and fuel/cost savings....Laser welding of dissimilar titanium/aluminum alloys has been employed at an increasing rate,particularly in the aerospace industry,owing to its advantages in terms of current design flexibility and fuel/cost savings.The major problem with dissimilar Ti/Al welds arises from the difference in the thermal expansion and contraction of the two metals,which leads to hot-cracking susceptibility and the mitigation of the mechanical property after welding.In the present study,pulsed Nd:YAG laser welding of Ti6 Al4 V and AA6060 has been addressed.Hot-cracking susceptibility in the heat affected zone and the shear fracture behavior of the lap joints were investigated through microstructural characterization and mechanical tests.The results indicate that the hot cracking tendency can be reduced by increasing the pulse peak power(7.5–8.5 kW)and the laser point diameter(0.8–1.0 mm)with specific pulse duration and overlap.An alternative control strategy for less hot cracks in the Ti/Al lap joint can be to increase the weld width and decrease the cooling rate during solidification.The shear fracture of the Ti/Al lap joint is likely to occur along the lower side path of the weld interface with decreasing weld surface collapsed amount and increasing aluminum base metal melt depth.展开更多
文摘In this research, pulverization plate and base of a fuel injector in an automobile electronic-controlled engine was joined by pulsed laser welding. The different welding parameters were evaluated and effect of process parameters on joint characteristics was analyzed. The optimal process parameters were obtained as follows： welding current 120 A, welding speed 600 ram/rain, pulse duration 1.80 ms and pulse frequency 60 Hz. The microstructure of weld metal was investigated. Results show that the fusion zone is austenitic dendrite, the weld center is equiaxed grain, while the transition zone between fusion zone and weld center is mixed crystal with austenitic dendrite and equiaxed grain. The weld layered phenomenon was observed, and eddy caused by keyhole effect is the main reason for the formation of layered structure in molten pool.
基金supported by the National High Technology Research and Development Program of China(Grant No.2013AA041003)the National Natural Science Foundation of China(Grant No.51365039)
文摘The experiment of Nd： YAG pulsed laser self-fluxing welding for 304 stainless steel/Ti6Al4V titanium alloy dissimilar metal was carried out. The microstructure properties of welded joint were analyzed by SEM, EDS and XRD. The equilibrium lattice constants, enthalpies of formation, cohesive energies, mechanical properties, Debye temperatures and valence electron structures of Ti-Fe intermetallic compounds （IMCs） were calculated by the first principle pseudopotential plane wave method based on density functional theory （DFT）. According to the thermodynamic data of Ti-Fe-Cr compounds, the Gibbs free energy per mole of compound at different temperatures was calculated and their thermal stability was compared. The results show that there are no macroscopic cracks in the welded joints, and the IMCs distributed evenly along the welding interface exhibits 3 distinct layers of microstructure with different colors. The welds interface generates IMCs of TiFe, TiFe 2 and a small amount of Ti 5Cr 7Fe 17 IMCs. Ti-Fe IMCs with high thermodynamic stability and easy alloying formation. The results of Gibbs free energies show that the sequence of precipitates in the interface is Ti 5Cr 7Fe 17 , TiFe 2 and TiFe in high temperature during the metallurgical reaction. The G/B values of Ti-Fe IMCs are greater than the critical value of 0.5, indicating that it is an intrinsic brittleness.
基金The supports from the National Natural Science Foundation of China(No.51705080,No.51805087)the Natural Science Foundation of Fujian Province(No.2018J01761,No.2018J01764)。
文摘Laser welding of dissimilar titanium/aluminum alloys has been employed at an increasing rate,particularly in the aerospace industry,owing to its advantages in terms of current design flexibility and fuel/cost savings.The major problem with dissimilar Ti/Al welds arises from the difference in the thermal expansion and contraction of the two metals,which leads to hot-cracking susceptibility and the mitigation of the mechanical property after welding.In the present study,pulsed Nd:YAG laser welding of Ti6 Al4 V and AA6060 has been addressed.Hot-cracking susceptibility in the heat affected zone and the shear fracture behavior of the lap joints were investigated through microstructural characterization and mechanical tests.The results indicate that the hot cracking tendency can be reduced by increasing the pulse peak power(7.5–8.5 kW)and the laser point diameter(0.8–1.0 mm)with specific pulse duration and overlap.An alternative control strategy for less hot cracks in the Ti/Al lap joint can be to increase the weld width and decrease the cooling rate during solidification.The shear fracture of the Ti/Al lap joint is likely to occur along the lower side path of the weld interface with decreasing weld surface collapsed amount and increasing aluminum base metal melt depth.
