The porosity, pore size and softening of 6063 aluminum alloy CMT MIX + Synchropulse welded joint with different welding speeds were studied. The results show that with the increase of welding speed(from 55 to 65 cm/mi...The porosity, pore size and softening of 6063 aluminum alloy CMT MIX + Synchropulse welded joint with different welding speeds were studied. The results show that with the increase of welding speed(from 55 to 65 cm/min), the porosity increases dramatically(from 0.1% to 3.9%) and large pores(341.1 μm) appear. The pore size distributions are mainly concentrated at 87.8 and 20.6 μm in the joints produced from weld speeds of 65 and 55 cm/min, respectively. The dissolution and transformation of the β′′ phase in the base metal(BM) result in a significant softening of both the fusion zone and heat-affected zone, and the latter was more serious. The effects of welding speed on the average tensile strength of the full penetration welded joints are minor, which was about 155 MPa(67.4% that of the BM).展开更多
In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure...In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time ts/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% （3 s） to 3.0% （60 s）. The fraction of martensite/austenite （M/A） constituent increased from 2.2% （3 s） to 39.0% （60 s）, its shape changed from granular to strip, and the maximum length increased from 2.4 μm （3 s） to 7.0 μm （60 s）. As cooling time increased, the prior austenite grain size increased from 34.0 μm （3 s） to 49.0 gm （60 s）, the impact absorption energy reduced from 101.8 J （5 s） to 7.2 J （60 s）, and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.展开更多
基金financially supported by the Major Program of the National Natural Science Foundation of China (No. U1864209)the “Qinglan” Project of Jiangsu Province, China。
文摘The porosity, pore size and softening of 6063 aluminum alloy CMT MIX + Synchropulse welded joint with different welding speeds were studied. The results show that with the increase of welding speed(from 55 to 65 cm/min), the porosity increases dramatically(from 0.1% to 3.9%) and large pores(341.1 μm) appear. The pore size distributions are mainly concentrated at 87.8 and 20.6 μm in the joints produced from weld speeds of 65 and 55 cm/min, respectively. The dissolution and transformation of the β′′ phase in the base metal(BM) result in a significant softening of both the fusion zone and heat-affected zone, and the latter was more serious. The effects of welding speed on the average tensile strength of the full penetration welded joints are minor, which was about 155 MPa(67.4% that of the BM).
基金This work was financially supported by the National Natural Science Foundation of China （No. 51775102）, Open Research Fund from the State Key Laboratory of Roiling and Automation, Northeastern University （No. 2016005） and Project Funded by China Postdoctoral Science Foundation （No. 2016M601877）.
文摘In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time ts/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% （3 s） to 3.0% （60 s）. The fraction of martensite/austenite （M/A） constituent increased from 2.2% （3 s） to 39.0% （60 s）, its shape changed from granular to strip, and the maximum length increased from 2.4 μm （3 s） to 7.0 μm （60 s）. As cooling time increased, the prior austenite grain size increased from 34.0 μm （3 s） to 49.0 gm （60 s）, the impact absorption energy reduced from 101.8 J （5 s） to 7.2 J （60 s）, and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.
