Due to poor metallurgical weldability of magnesium alloy,laser welding crack is still one of the main defects.The generations of welding crack seriously affected the weld quality and reduce the mechanical properties o...Due to poor metallurgical weldability of magnesium alloy,laser welding crack is still one of the main defects.The generations of welding crack seriously affected the weld quality and reduce the mechanical properties of welded joints which have become a bottleneck of the magnesium alloy products widely used in the structure materials.In this paper,AZ31B magnesium alloy sheet with 2mm thickness was used for this investigation.The forming reason and extending characteristics of the welding cracks were investigated during the Nd:YAG pulsed laser welding.The results show that welding cracks are mainly solidification crack which were always present in the weld centers.Few welding hot cracks appear multiple furcation phenomenons,and main and branch cracks were intercrystalline crack.The partial branch crack was mixed intercrystalline and transgranular extension.In addition,few cracks in the weld were caused due to irregular shape porosity and inclusion.The delayed crack weren't observed in the weld after deposited 48 hours.In the pre-process on the basis,the characteristics and generation mechanism of YAG pulsed laser welding cracks of magnesium alloy were analyzed further.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
文摘Due to poor metallurgical weldability of magnesium alloy,laser welding crack is still one of the main defects.The generations of welding crack seriously affected the weld quality and reduce the mechanical properties of welded joints which have become a bottleneck of the magnesium alloy products widely used in the structure materials.In this paper,AZ31B magnesium alloy sheet with 2mm thickness was used for this investigation.The forming reason and extending characteristics of the welding cracks were investigated during the Nd:YAG pulsed laser welding.The results show that welding cracks are mainly solidification crack which were always present in the weld centers.Few welding hot cracks appear multiple furcation phenomenons,and main and branch cracks were intercrystalline crack.The partial branch crack was mixed intercrystalline and transgranular extension.In addition,few cracks in the weld were caused due to irregular shape porosity and inclusion.The delayed crack weren't observed in the weld after deposited 48 hours.In the pre-process on the basis,the characteristics and generation mechanism of YAG pulsed laser welding cracks of magnesium alloy were analyzed further.
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.
